Displays

High field strength elements (HFSE) such as Zr and Hf are relatively insoluble in most natural hydrothermal solutions and consequently immobile in most geological systems. However, fluoride forms stable aqueous complexes with many HFSE ions, including Zr⁴⁺ and Hf⁴⁺, and is thus a potent mobilizer of these elements. Due to their identical charge and similar ionic radius (590 pm and 580 pm, respectively), Zr and Hf behave almost identically in geological system and are therefore referred to as geochemical twins. Fluoride complexation in hydrothermal environments is one of few processes in the Earth's crust that can effectively fractionate them from one another. This fact can be used to trace past fluoride activity in fossil hydrothermal systems by investigating Zr/Hf ratios, if fluoride complexation of Zr and Hf is sufficiently well understood. Mobility of metals as complexes is controlled by two distinct but related mechanisms: Formation of the complex itself and solvation of that complex in the solvent. Poly(hydrogen-fluoride) bridging of fluoride complexes to the surrounding aqueous solvent is crucial to the understanding of the solvation and therefore the mobility of fluoride complexes.

We report geometries of Zr and Hf fluoride complexes up to 400°C, determined by extended X-Ray absorption fine structure (EXAFS) in a hydrothermal autoclave. Existing data sets on the stability of those complexes at lower temperatures are extended to 400°C. Our data show strong temperature dependence of the complex stability for both metals. However, the effect of temperature is not equally strong for Zr and Hf. Fractionation of the twin pair is thus a function of temperature as well as fluoride activity.

How to cite: Loges, A., Louvel, M., Wilke, M., Klemme, S., John, T., and Hasenstab-Riedel, S.: Unraveling Zr/Hf fractionation: Hydrothermal zirconium and hafnium fluoride complexation up to 400°C, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20323, https://doi.org/10.5194/egusphere-egu2020-20323, 2020.

Global phosphate demand is rising due to growing population and associated food demand. World consumption of P₂O₅ is forecasted to increase to 46 million tonnes in 2020. Phosphate deposits and occurrences are widely distributed in Europe. However, very little phosphorus is produced in the EU to satisfy the growing demand for fertilizers. As a consequence, the European countries are net importers of phosphate, with an average of 4 M tonnes of natural phosphate-rich material imported per year. The European Commission has listed phosphates among critical raw materials with a significant supply risk. Other elements pertaining to this list can also be recovered from the phosphate deposits, as the rare earth elements (REE) and fluorspar (Goodenough et al., 2016). Estonia holds, the largest in Europe, unused sedimentary phosphate rock reserves, about 3 Billion metric tons (ca 819 Million metric tons of P₂O₅; Bauert & Soesoo, 2015). The Estonian shelly phosphate rocks are friable or weakly cemented bioclastic quartz sandstones deposited in shallow marine shoreface environment with a variable content of phosphatic brachiopod shells detritus. These sediments formed approximately 488 million years ago. The content of fossil shells ranges from 5–10% to 80–90 vol%. Brachiopod shells and enriched detritus contain up to 35–37% P₂O₅. Recent studies have revealed relatively enriched but variable content of REEs in these phosphate shells. For example, La in single shells ranges 50 to 550 ppm, Ce – 40–1200 ppm, Pr - 4–170 ppm, Nd – 20–800 ppm, Sm – 3–180 ppm, Gd – 4–135 ppm. The total REEs can reach 3000 ppm, however, in average they are ranging between 1000 and 2000 ppm.  At the moment the Estonian phosphorites cannot regarded as an economic REE source, but considering REEs as a co-product of phosphorous production, it may economically be feasible. Large variability in REE concentrations results probably from post-depositional diagenetic processes but its geological controls need further study. Although the raw ore enrichment (separating shells from sandstone) and phosphorous extraction are technologically easy, the technology for REE extraction in parallel with the phosphorous acid production needs further developments. Relying on the vast phosphorite reserves in Estonia, the critical nature of both the phosphorus and REEs for the European economy and security, it may be a worthwhile opportunity to develop these resources into production at the European scale. 

REFERENCES

1. Goodenough, J. Schilling, E. Jonsson, P. Kalvig, N. Charle, F. Tuduri, E. Deady, M. Sadeghi, H. Schiellerup, A. Müller, B. Bertrand, N. Arvanitidis, D. Eliopoulos, R. Shaw, K. Thrane, N. Keulen. Europe's rare earth element resource potential: An overview of REE metallogenetic provinces and their geodynamic setting. Ore Geology Reviews, 72, 838-856 (2016).
2. Bauert, A. Soesoo. Shelly phosphate rocks of Estonia, in Strategic raw materials of Estonia, Rakvere Conference, Rakvere, Estonia, (2015).

How to cite: Soesoo, A. and Kirsimäe, K.: Estonian Paleozoic shelly phosphorites: a continent-scale resource for phosphorus and potential for rare earth elements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6062, https://doi.org/10.5194/egusphere-egu2020-6062, 2020.

Geochemistry of the manganese ore and black shale in the Datangpo Formation: Implications for the ore genesis and oceanic redox during the interglaciation of Neoprozeotoic Snowball Earth  

Jia W.L.¹, Tan Z.Z.^1,2, Li J.¹, Peng P.A.^1,2

¹ Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China; ² University of Chinese Academy of Sciences, Beijing, China

Introduction: The Cryogenian are critical period for the evolution of ocean system and biosphere, and black shales have been frequently found during the interglaciation. The Datangpo Formation from South China is a typical interglacial stratum with black shale in lower section, and unique by the development of manganese (Mn) carbonate underlying the black shale. Details about the hydrothermal fluids and the enrichment of OM for ores need further investigation, and the geochemsitry of global black shales in the interglaciation should be summarized for elucidating the oceanic oxygenation.

Samples and Methods: One typical section, composed of both Mn carbonate and overlying black shale, was selected for detailed sampling. Pulverized samples were analysed for the content and carbon isotopes of both organic carbon and inorganic carbon, the abundance of major and trace elements as well as the molybdenum (Mo) isotopes.

Results: (1). The samples with Mn content greater than 5% have an average TOC value of 2.4%, which is lower than that (~3.06%) of the samples with less Mn. (2). The abundance of redox-sensitive element (Mo, U, V) and TOC/P ratio are very low for Mn carbonate, indicating suboxic to oxic condition. (3). A hydrothermal source for the Mn carbonate is indicated by clear positive Eu anomaly, relatively large Fe/Ti ratios but low Al/(Al+Fe+Mn) ratios. In addition, more mafic material could have contributed to the Mn carbonate, as suggested by overall larger La/Th ratios but lower abundance of high field strength elements (Nb, Ta, Zr and Hf) relative to the overlying balck shale. (4) The nutrient elements, such as redox-sensitive Fe, Ba and P and OM-related Cu, Zn and Ni, all show much higher level for Mn carbonate relative to overly black shale. This is consistent with reported statistical results for overall larger abundance of P for mafic magmatic rocks relative to felsic ones, which is called as “mafic nutrient pump”.  (5) A compiling of elemental and Mo isotopic data for interglacial shale worldwide in the Cryogenian has been performed, which shows the maximal Mo content, Mo/TOC ratio and δ⁹⁸Mo value mostly less than 50 ppm, 20 and 1.5‰.

Conclusion: Relatively abundant residual OM in Mn carbonate may be due to abundant nutrients associated with the hydrothermal fluid that has contributed to a high productivity level. The hydrothermal fluid may be from continental origin as previously reported Sr and Nd isotopes, however, elemental data supported large contribution from mafic material which can give more nutrient than felsic one.  The interglacial ocean for the Snow Ball Earth was generally anoxic, and episodic bottom water oxygenation may be arose by the influx of high-density ice melting water.  

How to cite: Jia, W.: Geochemistry of the manganese ore and black shale in the Datangpo Formation: Implications for the ore genesis and oceanic redox during the interglaciation of Neoprozeotoic Snowball Earth, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9766, https://doi.org/10.5194/egusphere-egu2020-9766, 2020.

The Tomtor carbonatite complex, with an area of 250 km², is confined to the eastern framing of the Anabar Anteclise; it is located withtin the Ujinsky province of ultrabasic alkaline rocks and carbonatites (Northeast of Siberian Platform) (Erlich, 1964). The complex has a concentric zonal structure: the outer ring is composed of alkaline and nepheline syenites, the inner incomplete ring is nepheline-pyroxene rocks of the foidolite family, the core is represented by carbonatites. All rocks of the massif are intersected by dikes and explosion tubes of picrites and alneites. Onkuchakh apatite-magnetite deposit is located on the northeastern border of the carbonatite core. Apatite-magnetite ores (camaforites, phoscorites, nelsonites) form a series of ore steeply dipping (75-80^o) lenticular bodies of north-western strike. The resources of the apatite-magnetite ores of the Tomtor massif are about 1 billion tons of iron (Tolstov, 1994). Primary and pseudo-secondary fluid inclusions were studied in apatite, calcite and potassium feldspar of camaforites. Inclusions have isometric or elongated shapes up to 50 microns. Most of the studied inclusions have a negative crystal form located in the central parts and zones of apatite growth.

Apatite contains a multiphase (crystal-fluid) inclusions with gas, liquid and 1-5 visible crystalline phases. The gas phase is represented by CO₂, contains subordinate amounts of H₂O, H₂S and SO₂. The liquid phase is represented by H₂O with SO₄^2-, HSO^4- and HCO^3- ions. The solid phases in the inclusions are represented by mainly halite (NaCl) and sylvite (KCl), with strontianite (SrCO₃), barite (BaSO₄) and Ca-Sr-REE F-carbonate crystals. Complete homogenization occurs in the temperature range from 290 to 350 °C, the concentration is 30-45 wt. % of NaCl-eq. Calcite has the similar in composition fluid inclusions. The solid phases are mainly represented by halite (NaCl) and sylvite (KCl), as well as the dolomite (CaMg(CO₃)₂), strontianite (SrCO₃), REE phosphates and sulfates of Sr and Ba. Complete homogenization occurs at 250-300 °C, the concentration is 35-55 wt. % of NaCl-eq. The gas phase of the fluid inclusions in K-feldspar is predominantly CO₂; the liquid phase is H₂O. The solid phases are represented by witherite (BaCO₃) and calcite (CaCO₃). The homogenization temperature of fluid inclusions occurs at 350-375 °C.

The results show that the hydrothermal fluids of camaforites of the Tomtor massif are represented by the concentrated high-medium temperature sulfate-carbonate-chloride solutions of complex composition . The fluid composition is explained by the evolution of the carbonatite melt.

The work was supported by the Russian Science Foundation (RSF), project # 19-17-00013.

References

1. Erlich, E.N., 1964. The new province of alkali rocks on the north of Siberian platform and its geological aspects. Proc. All-Soviet Mineral.Soc.93,682–693.
2. Tolstov, A.V., 1994.Mineralogy and geochemistry of apatite-magnetite ores of the Tomtor Massif (NorthwesternYakutia). Russ.Geol. Geophys.35,76–84.

How to cite: Baranov, L., Tolstov, A., and Prokopyev, I.: Hydrothermal fluids of apatite-magnetite ores of the Tomtor carbonatite massif (NE, Russia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7414, https://doi.org/10.5194/egusphere-egu2020-7414, 2020.

Kiruna in northern Sweden is one of the most productive mining areas in Europe. The area hosts the largest underground iron mine in the world and numerous exploration targets for iron and copper-gold are to be found in the area. Kiruna has a long tradition of geological research and the Kiirunavaara iron deposit forms the archetypal example for iron oxide-apatite (IOA) deposits, however, many fundamental questions remain unanswered. In this project, we focus on the structural setting and evolution in Kiruna and the relation to iron oxide-apatite, Fe-Cu-sulphides and their associated hydrothermal alteration footprint. Petrological and geochronological data from earlier studies together with our new stratigraphical and structural data and interpretations are in accordance with Orosirian basin development in an overall extensional (back-arc) setting synchronously with the emplacement of iron oxide-apatite bodies. The basin was inverted during subsequent compression (D₁-D₂) including movements along lithostructural boundaries and shear zones developed in sedimentary and volcanosedimentary rocks. D₁ is dominantly ductile in character and the strain is distributed regionally, whereas D₂ is associated to strong strain partitioning, brittle-ductile reactivations, and folding of D₁ structures. Microstructures of shear zones indicate east-block-up kinematics in the central Kiruna area, whereas the areas east and west of central Kiruna indicate reverse kinematics (west-block-up). This causes juxtaposition of  different crustal levels outcropping on either side of central Kiruna.

Regionally, D₁ is associated to scapolite ± albite ± sulphide alteration formed coeval with magnetite ± amphibole alteration. The alteration styles associated to D₂ are more diverse and potassic in character and associated to Fe-Cu-sulphides. A distinct D₂ brittle Fe-Cu-sulphide overprint is recognized in the region. Primarily chalcopyrite, bornite, and pyrite are hosted by a wide range of D₂-structures including fractures and brittle veins in competent volcanic units, and fold hinges and ductile shear bands in rheologically weak rocks. Competence contrast is assumed to be the most critical parameter controlling how and where Fe-Cu-sulphides were concentrated during D₂ and are linked to the basin inversion phase of the geological evolution. This implies that IOA emplacement happened during a dominantly extensional setting whereas the Fe-Cu-sulphides were concentrated in an overall late compressive setting and the mineralized systems can be linked to different phases of the structural evolution. 

Tectonic models presented by earlier workers contradict each other and the conclusions vary depending on the geological discipline of the researchers. In general, models based on petrology/geochemistry include an extensional pre-tectonic phase whereas models focusing on geological structures include the development of a fold-thrust belt during D₁. In this project, we show that the structural configuration in Kiruna can be explained by basin inversion and we hope that our contribution will bridge geological disciplines by providing a structural framework in agreement with petrological results.

How to cite: Andersson, J., Logan, L., Bauer, T., and Martinsson, O.: Structural setting of iron oxide-apatite and Fe-Cu-sulphide occurrences in Kiruna, northern Sweden, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-280, https://doi.org/10.5194/egusphere-egu2020-280, 2020.

Kiruna-type apatite-iron-oxide ores are key iron sources for modern industry. The origin of the Kiruna-type apatite-iron-oxide ores remains ambiguous, however, despite a long history of study and a concurrently intense scientific debate. Diverse ore-forming processes have been discussed, comprising low-temperature hydrothermal processes versus a high-temperature origin from magma or magmatic fluids. We present an extensive set of new and combined iron and oxygen isotope data from magnetite of Kiruna-type ores from Sweden, Chile and Iran, and compare them with new global reference data from layered intrusions, active volcanic provinces, and established low-temperature and hydrothermal iron ores. We show that approximately 80% of the magnetite from the investigated Kiruna-type ores exhibit δ⁵⁶Fe and δ¹⁸O ratios that overlap with the volcanic and plutonic reference materials (> 800 °C), whereas ~20%, mainly vein-hosted and disseminated magnetite, match the low-temperature reference samples (≤400 °C). Thus, Kiruna-type ores are dominantly magmatic in origin, but may contain late-stage hydrothermal magnetite populations that can locally overprint primary high-temperature magmatic signatures [1] .

[1] Troll, V.R., Weis, F.A., Jonsson, E. et al. Global Fe–O isotope correlation reveals magmatic origin of Kiruna-type apatite-iron-oxide ores. Nature Communications 10, 1712 (2019) doi:10.1038/s41467-019-09244-4

How to cite: Troll, V. R., Weis, F., Jonsson, E., Andersson, U. B., Madjidi, S. A., Högdahl, K., Harris, C., Millet, M.-A., Chinnasamy, S. S., Kooijman, E., and Nilsson, K.: Global Fe–O isotope correlation reveals magmatic origin of Kiruna-type apatite-iron-oxide ores, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8676, https://doi.org/10.5194/egusphere-egu2020-8676, 2020.

IOCG deposits are economically important providing amongst other resources, around 12% of global copper production and 47% of Australian copper production. A number of different genetic models have been proposed for the formation of IOCG deposits including ore systems for which fluids and metals are sourced from igneous bodies (Hauck, 1990; Groves and Vielreicher, 2001; Pollard, 2001) and others where mineralising fluids are non-magmatic. There are two main non-magmatic models. The first suggests that the key heat source is igneous and contact metamorphism drives thermal convection and development of metal rich brines with possible input of metals from the igneous bodies themselves (Haynes et al., 1995; Barton and Johnson, 1996, 2000; Haynes, 2000). The second non-magmatic model suggests that hypersaline brines are produced by metamorphic reactions at depth and the resulting metamorphic brines become metal rich through wall rock interaction as they migrate and possibly mixing with other aqueous phase to form a deposit (Williams, 1994; de Jong et al., 1997; Hitzman, 2000).

A number of alteration type occurrs in IOCG systems including albitization, scapolitization, “red-rock” alteration (calc-sodic), carbonate alteration, potassic alteration, chlorite alteration as described by Barton (2013). Yet the fundamental relationship between the alteration, the mobility of chemical elements and the formation of the deposits is not well known.
We assess metal mobility during different styles of alteration using a mass balance approach comparing suites of well characterised altered rocks of different types to their least altered parent rocks. We aim to identify which styles of alteration can be shown to mobilise metals and therefore constrain potential sources of metals for IOCG ore deposits in metamorphic terranes, with a focus on Olympic and Mt Isa Provinces in Australia.

Preliminary results of mass balance calculations from the Olympic Province show that potential altered source rocks are significantly depleted in Cu relative to their least altered protoliths. The median Cu and Au mass variation values of rocks albitised at variable degrees (Na alteration) are respectively -87% (range -93% to +258%, n=7) and -27% (range -76% to +69%, n = 7) Similarly rocks with variable potassic alteration (K) have a median Cu mass variation of -52% (range -52% to +186%, n=6) and rocks affected by calc-sodic alteration have Au mass change median of -36% (range -36% to +1656%, n = 10). Mass change in the altered rocks is highly variable with both enrichment and depletion occurring within the same alteration styles. Samples affected by carbonate and potassic alteration are enriched in Au, and calc-sodic and carbonate altered rocks are enriched in Cu. Availability of the particular element in the source rock and lithology play presumably a role in these changes of behaviour in element mobility. 

How to cite: Hamisi, J., Pitcairn, I., Tomkins, A., Brugger, J., and Micklethwaite, S.: Element mobility and alteration types in Iron Oxide Copper and Gold (IOCG) systems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18783, https://doi.org/10.5194/egusphere-egu2020-18783, 2020.

Porphyry copper deposits are predominantly mined for the major commodities Cu, Mo and Au. From some of these deposits, minor (trace) elements are also recovered as by-products (e.g. Ag, Pd, Te, Se, Bi, Zn, Pb). This list will potentially expand with the increasing demand for critical raw materials in modern energy-related technologies. Key components for such technologies are energy-critical elements (ECEs), many of which are classified as credit elements (e.g. Co, Ga, Ge and In). However, even if currently recovered as by-products, their deportment in copper ores and their overall distribution at the deposit scale have received little research attention. This gap in knowledge is limiting more effective recovery of ECEs. The same applies to elements that might incur refining penalties (e.g. As, Cd, Sb and Sn). Characterizing the trace element inventory of host mineral phases contributes to an improved understanding of the distribution of trace metals. By informing geometallurgy, element deportment studies can thus potentially promote economic and ecologic benefits in the form of improving recovery, adding value to ore resources and helping to reduce the dispersion of deleterious metals into the environment.

This study focused on the deportment of ECEs and precious metals in the northwestern high-grade section of the Bingham Canyon Cu-Mo-Au porphyry deposit. Contained Cu-(Fe-) sulphides were characterised with scanning electron microscopy and analysed by laser ablation (LA) ICP-MS for their metal endowment and for their potential use as discriminators of magmatic-hydrothermal processes. The availability of copper (iron) sulfides was found to exert principal control over the chalcophile trace element budget. The abundance of bornite and digenite primarily controls the Bi and Ag- budgets of the overall system and significantly affects variations in Te and Se. Chalcopyrite predominantly controls the Co, Ga and In budgets. By contrast, Ge, As, Cd, Sn, Sb and Au are not significantly controlled by the major sulfides indicating their residence in accessory phases. The presence of electrum and Ag-(Au) tellurides governs the distribution of Au, and most likely also the Te budget.
At the small scale relevant to mineral processing, the Bingham ore shows a particularly interesting phenomenon. Digenite (Cu₉S₅) is invariably present within bornite likely as the exsolution product of a copper-rich bornite solid solution. LA-ICP-MS analyses revealed that the exsolution process has resulted in a redistribution of trace elements, including some ECEs. Trace element partitioning between bornite and digenite is evident in element maps of the complex intergrowths. Silver, Te and Au strongly partition into digenite, while Se seems to retain its primary homogenous distribution, unaffected by exsolution. Elements that are preferentially retained in bornite (Sn and Bi), or at similar levels between the two sulphide species (In) show more complex zoning patterns in bornite. Zones of lowest concentration in bornite, peripheral around exsolved digenite grains, indicate stress-induced diffusion due to accumulating lattice distortions in bornite during digenite growth. The findings from digenite exsolution in bornite at Bingham show that relatively late, solid-state processes can result in complex deportment of precious metals and ECEs within copper-iron sulphides.

How to cite: Brodbeck, M., McClenaghan, S., Kamber, B. S., and Redmond, P.: Energy Critical Element and Precious Metal Deportment in Cu-(Fe-) Sulphides from the Bingham Canyon Porphyry Cu-Mo-Au Deposit, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22017, https://doi.org/10.5194/egusphere-egu2020-22017, 2020.

Porphyry deposits are the major natural source of copper and a significant natural source of gold, which are essential metals for our society. Porphyry deposits form at convergent margins both during subduction (syn-subduction, Andean-type deposits) and in post-subduction to post-collision and extensional geodynamic settings (post-subduction deposits). Syn-subduction porphyry deposits are typically associated with calc-alkaline magmas often characterized by high Sr/Y values (~50-150). In contrast, post-subduction deposits are mostly associated with variably alkaline magmas having lower Sr/Y values (~25-75). The reasons of the association of porphyry deposits with magmas having different geochemical affinities and of their widely variable Cu and Au endowments (from <1 to >100 Mt for Cu and from few tens to >2500 tons for gold) remain unconstrained.

Porphyry Cu-Au deposits define two distinct trends in plots of Au versus Cu endowments and Au endowment versus duration of the ore process (Chiaradia, 2020): one trend (Cu-rich) is characterized by steep Cu/Au endowment values (Cu/Au~250000) and an average low rate of Au deposition (~100 tons Au/Ma); the other trend (Au-rich) is characterized by low Cu/Au endowment values (Cu/Au~12500) and an average high rate of gold deposition (~4500 tons Au/Ma). The Au-rich trend is defined to the greatest extent by seven, alkaline magma-related, porphyry gold systems (>1100 tons Au) and subordinately by numerous calc-alkaline systems (<1300 tons Au). The Cu-rich trend is defined only by calc-alkaline magma-related porphyry systems.

Modelling of petrological and metal precipitation processes using a Monte Carlo approach suggests that, whereas Cu-rich porphyries are formed by large volumes of magma, Au-rich porphyries result from a better precipitation efficiency of Au. The specific association of the largest Au-rich porphyry deposits with variably alkaline magmas also points out that alkaline magma chemistry favours an upgrade of Au endowments.

References

Chiaradia, M. (2020) Gold endowments of porphyry deposits controlled by precipitation efficiency. Nature Communications 11, 248, https://doi.org/10.1038/s41467-019-14113-1.

How to cite: Chiaradia, M.: Controls on copper and gold endowments of porphyry deposits, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7918, https://doi.org/10.5194/egusphere-egu2020-7918, 2020.

The Yerington batholith is located in western Nevada (USA) within a volcanic-arc area. This pluton is approximately 15 km in diameter, extends to 7-8 km in vertical dimension and consists of 3 granitic units: the McLeod Hill quartz monzodiorite (1,000km³), the Bear quartz monzonite (256 km³) and the Luhr Hill granite (70 km³), together with three mineralized porphyry centres: Yerington, Bear, MacArthur and Ann-Mason porphyry copper deposits. It is overlain by coeval the Artesia Lake and Fulstone Spring volcanic rocks. The batholith was emplaced into Triassic and Jurassic volcanic and sedimentary rocks at ca. 168 Ma. This event was related to the subduction of the Pacific plate, west of California. It was a part of a belt of Andean-type arc magmatism that developed on the continental margin in both North and South Americas. The complex was then cut by three sets of normal faults, which caused the batholith to drop ca. 2.5 km deep along the faults that tilted the area, so that it is now exposed in cross-section.  This event now allows sampling of volcanic and plutonic rocks from each unit, which were originally emplaced at depths of 1 to 8 km.

It is widely accepted that porphyry deposits are genetically related to subduction zones but what is not understood is why some porphyry systems are ore-bearing while others, apparently similar systems, are barren. The key question remains unanswered: what controls magma fertility? Understanding the processes involved in the creation of metal deposits is a crucial aspect for the exploration industry. A bottom line in determining the fertility of a porphyry suite is likely to be the relative timing of sulfide and volatile saturation. If sulfide saturation occurs early, the chalcophile elements may be locked in an underlying magma chamber at depth and unavailable to enter the hydrothermal fluid when magma eventually becomes volatile saturate.

Plots of whole-rock concentrations of SiO₂, total FeO, CaO and V against MgO show that all samples, from all three units, cumulate and volcanic rocks, follow the same trend line, and are therefore likely to be related by fractional crystallization. Attempts to determine the timing of sulfide saturation using Cu were unsuccessful. A plot of whole-rock Cu against MgO showed that the Cu concentrations are scattered, with no clear correlation, which is attributed to overprinting by hydrothermal mineralization. For this reason, the behaviours of Cu during magma processes cannot be deducted. As a consequence, we have turned to the platinum group elements (PGE) to determine the timing of sulfide saturation. The PGE have the advantage of having much higher partition coefficient into immiscible sulfide melts than Cu, and lower solubilities into hydrothermal fluids, so that they are less affected by secondary processes. We will address the problem of identifying sulfide saturation by reporting the concentration of PGE, Re and Au, measured by fire-assay isotope dilution method, for 20 samples from the Yerington batholith. Detection limits are ca. 15 ppt of Pd and less than 1 ppt for the other PGE.

How to cite: Misztela, M. and Campbell, I.: Platinum-group element geochemistry to track magmatic evolution of the Yerington porphyry copper district (Nevada, USA), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-131, https://doi.org/10.5194/egusphere-egu2020-131, 2020.

How to cite: Gopon, P., Douglas, J. O., Auger, M. A., Hansen, L., Wade, J., Cline, J. S., Robb, L. J., and Moody, M. P.: Insights from atom probe tomography into Carlin type gold mineralization, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22303, https://doi.org/10.5194/egusphere-egu2020-22303, 2020.

Northern Sweden is dominated by supracrustal and related intrusive rocks formed and deformed during the Svecofennian orogeny (1.90-1.78 Ga). The orogeny comprises several phases of crustal extension and shortening, resulting from subduction and repeated arc-accretion events. An early-Svecofennian extensional phase (c. 1.90-1.88) Ga results in the formation of iron oxide-apatite deposits (IOA, e.g. Kiruna and Malmberget) in the back-arc region and volcanogenic massive sulfide deposits (VMS, e.g. Kristineberg) in the arc. These deposits have been subjected to deformation and regional metamorphism resulting in transposition and re-mobilisation of ore bodies. The latest phase of the Svecofennian orogeny (1.80-1.78 Ga) is characterized by a distinct E-W-directed crustal shortening at high crustal levels representing the last continental assembly resulting from late arc-accretion and followed by a post-orogenic collapse. This leads to folding of early metamorphic fabrics and mainly brittle to brittle-ductile shear zone re-activation. A general N-S gradient from deeper-crustal conditions in Northern Norrbotten (north) to higher-crustal conditions in Västerbotten (south) is observable. The emplacement of syn-tectonic, felsic and mafic intrusive bodies causes high temperature conditions while pressures remain low. Such conditions are favorable for driving fluids and leading to the formation of structurally controlled, Au-bearing deposits in 3^rd and 4^th order structures of large, crustal-scale, re-activated shear zone complexes. Deposits in Northern Norrbotten that are related to this late-Svecofennian phase show both ductile and brittle features and host Cu and Au, hence often assigned to the IOCG group of deposits. Deposits that formed during the same phase in Västerbotten are typically characterized by Au-bearing quartz veins that formed as lower-order structures, hence often classified as orogenic Au-deposits. Weather these deposits are entirely newly formed or just represent various grades of re-mobilization of older mineralization remains an open question. Looking at these deposits on a crustal-scale, they represent structurally-controlled deposits, hosted by lower-order structures in re-activated shear zone complexes whereas differences in mineralogy and hydrothermal alteration assemblages are an effect of different crustal levels during formation and differences in host rock compositions.

How to cite: Bauer, T.: A continuum between structurally controlled Cu-Au and Au-only systems in northern Sweden, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7030, https://doi.org/10.5194/egusphere-egu2020-7030, 2020.

Reactions of seawater and fresh basalts below the seafloor are crucial for the formation of black-smoker type volcanogenic massive sulphide (VMS) deposits. Improved understanding of hydrothermal alteration processes can therefore help to improve the genetic model of VMS deposits, facilitating targeting in mineral exploration. Reactions of downwelling seawater with fresh basalts creates Ca-depleted, Mg- and Na- enriched “spilite” alteration (albite+chlorite+hematite+titanite±augite±epidote±quartz±calcite). The fluid in turn becomes enriched in Ca and depleted in Mg and Na. This chemically evolved, upwelling fluid can create Ca-enriched, Mg- and Na-depleted “epidosite” alteration (epidote+quartz+titanite+hematite). Epidosites have often been proposed as being the source-rocks for metals in VMS deposits. The more rarely described “pumpellyosite” alteration (pumpellyite+quartz+titanite) exhibits a very similar metasomatism to epidosite alteration and is assumed to represent the low-T equivalent of epidosite alteration.

            We recently discovered large, km²-sized areas of pumpellyosite alteration in the Semail ophiolite (Oman), allowing us to study the transition from epidosite to pumpellyosite alteration. We use reactive-transport modelling to investigate the mechanism responsible for the change from epidosite to pumpellyosite alteration. Pumpellyosite alteration was observed up to few meters below the palaeo-seafloor, indicating that evolved fluids discharged directly onto the seafloor. However, no sulphide mineralisation was observed on or below the palaeo-seafloor. This observation makes the involvement of pumpellyosite alteration in the VMS-forming system questionable. The metasomatic fingerprint of pumpellyosite alteration also strongly contrasts with the chlorite-quartz alteration typically found below VMS deposits. Since epidosite and pumpellyosite alteration appear to be genetically linked, epidosites may likewise be unrelated to the genesis of VMS deposits.

How to cite: Weber, S. and Diamond, L. W.: Pumpellyosite alteration in the oceanic crust as marker of chemically evolved hydrothermal discharge and its relation to volcanogenic massive-sulphide (VMS) deposits, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6713, https://doi.org/10.5194/egusphere-egu2020-6713, 2020.

Oxide- and silicate-dominated, stratiform iron formations are abundant in the northern part of the Sala inlier, Bergslagen, Sweden. The iron formations are commonly laminated and are associated with fine-grained siliciclastic and felsic volcaniclastic rocks in a 1.91-1.89 Ga succession dominated by pumiceous and lithic-bearing rhyolitic volcaniclastic rocks. Depositional features are consistent with a volcanically active, submarine environment, in which the iron formations and fine-grained host strata to sulphide mineralization accumulated during pauses in volcanism. At c. 1.87-1.81 Ga, the succession underwent polyphase folding and shearing under lower amphibolite facies conditions, followed by polyphase faulting under more brittle conditions.

The iron formations are locally directly stratigraphically overlain by  stratiform Zn-Pb-Ag sulphide mineralization. Detailed geological mapping has demonstrated that sulphide-bearing (proximal) iron formation is gradational into sulphide-poor (distal) iron formation along a strike extent of more than 7 km. Proximal iron formation is dominated by magnetite, grunerite, tremolite, quartz, almandine-rich garnet (Alm₅₄Sps₃₅Grs₈), muscovite, and chlorite, whereas distal iron formation is characterized by hematite, magnetite, epidote, actinolite, spessartine-rich garnet (Sps₅₃Adr₂₉Grs₁₅) and locally calcite. 

Elevated contents of Mn, Zn and Co are observed in both distal and proximal iron formation, whereby these elements help pinpoint the favorable horizon, but are of less use for vectoring along strike. Whole-rock lithogeochemistry samples of proximal iron formation differ from distal iron formation in: (1) Eu/Eu*>1, (2) Ce/Ce*<1, (3) suprachondritic Y/Ho, (4) elevated Tl, Cs, Cd, Sn, S, Cu, Pb, Sb and Au (5) lower volcaniclastic/siliciclastic content based on lower Al, Ti and Zr. Collectively, these features are indicative of Fe mineralization following interaction of a hot, acid and reduced hydrothermal fluid with oxidized seawater in a vent proximal position which was deprived of clastic or volcaniclastic input.

Sulphide mineralization, ranging from banded, to disseminated and fracture-hosted, is associated with chlorite-rich, locally graphitic mudstone immediately overlying proximal iron formation. Multi-grain δ³⁴S_V-CDT of sphalerite, pyrite and pyrrhotite are exclusively negative, ranging from -10.6 to -0.25 with no clear mode. The δ³⁴S_V-CDT distribution is unusual for Bergslagen deposits, and is indicative of a significant contribution of sulphur via bacteriogenic or thermochemical reduction of seawater SO₄^2-.

Stratigraphic analysis suggest that proximally, the mineralizing event followed a sudden deepening of the basin, and progressed from Fe oxide to polymetallic sulphide mineralization. The temporal zonation probably reflect a decrease in the redox potential of the basin, possibly due to venting and ponding of reduced hydrothermal fluids. Ore textures and host facies are consistent with of an exhalative mode of formation for both deposit types, albeit an importance of subseafloor mineralization processes is implied by lateral variability in both sulphide and chlorite content. In relation to the local stratigraphic evolution in the area, the mineralizing event can be directly linked to an event of basin deepening following a caldera-forming volcanic eruption. The results from stratigraphic analysis along with aforementioned proxies for redox and vent-proximity present first order vectors to stratiform Zn-Pb-Ag mineralization in the Jugansbo area, Bergslagen.

How to cite: Jansson, N. and Allen, R.: Using iron formations during exploration for c. 1.9 Ga Zn-Pb-Ag sulphide deposits, Jugansbo area, Bergslagen, Sweden, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8482, https://doi.org/10.5194/egusphere-egu2020-8482, 2020.

Harzburgite are the rocks that make up the mantle and consist of olivine, orthopyroxene, and clinopyroxene (<5 %). Clinopyroxene contain Ca, Al, and Ti, while orthopyroxene contain Al. On the other hand, olivine contains almost zero contents of Ca, Al and Ti. When the rising melt from the lower mantle passes through the mantle harzburgite, the clinopyroxene and orthopyroxene with lower melting points compared with olivine are fused into the melt, and the olivine is crystallized from the melt. In this genetic process, harzburgite gradually change into dunite consisting of only olivine, and Ca, Al and Ti of pyroxene in harzburgite will escape into the melt. And, as the melting point of clinopyroxene is lower than that of orhopyroxene, the Ca, Al, and Ti in clinopyroxene are escaped into the melt earlier than those in orthopyroxene. The melt with changed composition formed by melting the pyroxene are mixed with the newly rising melt with pyroxene, so that the chromian spinel in the melt becomes saturated and the chromitite are formed. By the above-mentioned mechanism, chromitite occurs with dunite and pyroxene-deficient harzburgite formed by the reaction result between melt and harzburgite. In other words, in the genetic process of high Cr chromitite, the presence of melt that fused the pyroxene within harzburgite is essential. And, in order to make high Cr chromitite, the melt must have been fused more pyroxene in harzburgite. As a result, the Ti, Ca, and Al content of harzburgite will be decreased. Therefore, considering the representative chemical composition of podiform chromitite(Robinson et al., 1997), we assumed that as we approached into harzburgite bearing high Cr chromitite(probably hidden ore body), the Ti, Ca and Al content within harzburgite will be likely to converge toward the specific contents(Ti<180ppm, Ca<0.9%, Al<0.7%). In case of Bophivum chromitite in northwestern Myanmar, it corresponds well with the representative chemical composition of high Cr chromitite in terms of the above-mentioned data. Therefore, we monitored to see whether Ti, Ca, and Al contents systematically change by the distance from the center with chromitite outcrop or high Cr anomaly zone confirmed through soil and rock geochemical exploration toward the surrounding harzburgite outcrop or not and tried to select the target element for geochemical vectoring using portable XRF. Conclusively, Ca is considered to be a more meaningful geochemical vectoring indicator than Al in terms of portable XRF measurements in the survey area.

How to cite: Heo, C., Oh, I., Yang, S., Lee, J., Park, S., and Cho, S.: Targeting the hidden chromitite using geochemical vectoring for Bophivum area, northwestern Myanmar, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4325, https://doi.org/10.5194/egusphere-egu2020-4325, 2020.

The Häme belt in southwestern Finland hosts several types of ore formations. Among others, Cu, Au, W, Li and La mineralizations have been identified. These mineralizations are linked with various types of granitoid rocks within the Paleoproterozoic Svecofennian bedrock. We have studied the granitoids and equivalent hypabyssal rocks by whole-rock geochemistry, U-Pb zircon geochronology and Sm-Nd isotope analysis. Geochemically, the granitoids show a wide range from adakitic to arc-type, implying that they had different source environments. New age data show that different types of granitoids (tonalitic, leucogranitic, granodioritic etc.) were emplaced simultaneously: the samples have ages from 1888 Ma to 1883 Ma and are coeval within the error limits. Nd isotopic results show slightly depleted compositions with initial epsilon values around +1, in line with most of the previously published data. An exception is the Cu-Au bearing Arolanmäki granite, which indicates a juvenile origin with an initial epsilon value of +3.2.

Overall the sources of granitoid magmatism vary considerably, and the overlapping ages indicate either a very rapid sequence or a simultaneous existence of varying types of magmatism. The ages coincide with the main stage of the Svecofenniean orogeny in the area. Later tectonic and hydrothermal activity is demonstrated by <1.80 Ga monazite and titanite ages as well as pegmatites. The granitoid magmatism of the Häme belt is related to several types of ore forming processes. The 1.88 Ga granitoids are hosting Cu-Au and W-Au-deposits, some of them interpreted as porphyric type deposits. The 1.80 Ga pegmatites include several LCT pegmatites hosting Li-deposits. The orogenic gold deposist of the Jokisivu-type in Häme belt have been interpreted to be controlled by the shear zones related to the 1.80 Ga granitoid magmatism. 

How to cite: Kurhila, M., Tiainen, M., Huhma, H., and Mäkitie, H.: Isotopic studies on ore potential granitoid rocks in the Häme belt, Finland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13259, https://doi.org/10.5194/egusphere-egu2020-13259, 2020.

In the Chungju area, Korea, highly enriched Zr-Nb-Y-REE deposits occur in subhorizontal layered Paleozoic granitic rocks (331±1.5 Ma), which can be divided into layered alkali granite, alkali aplite, and pegmatite. The rocks are mainly composed of alkali feldspar, quartz, and microcrystalline zircon. The ubiquitous zircon is the distinctive feature of the alkaline rocks, which plot with within plate granite, anorogenic granite, and ultrapotassic rocks, and show very similar REE patterns. Alkali aplite has especially high total rare earth elements and negative europium anomalies compared to the layered alkali granite. The Zr-Nb-Y-REE mineralization occurs as zircon-magnetite bands that are associated with several REE minerals. Repeated graded textures of layered alkali granites with interlayered Zr-Nb-Y-REE mineralization can be explained by gravity accumulation in the late magmatic stage. The compositions of zircons plot between the late magmatic and hydrothermal fields. The REE patterns of zircon-rich mineralization shows slightly negative slopes, whereas zircons show positive slopes. This can be explained by the HREE being strongly partitioned into zircon grains from the melt. Zircons with low total REE contents show high positive Ce anomalies. Although zircon analyses were conducted on one sample from a small area, it shows variable Ce anomalies and TREE, which indicates the zircons crystallized under conditions of rapidly changing oxygen fugacity, as the REE contents of zircon are related to the oxygen fugacity of the melt. The limited Th/U ratios of zircons indicate that they crystallized during a simple magmatic event, and were not affected by hydrothermal alteration and metamorphism. Here we suggest a flotation, aggregation, and gravity accumulation model can explain settle down of microcrystalline zircon and magnetite grains in fluid rich alkaline melt. This is the first report on highly evolved alkali granite that associated with Zr-Nb-Y-REE mineralization. The features displayed in these deposits have important implications for the evolution of alkali magmas.

How to cite: No, S.-G., Park, M.-E., and White, N. C.: Geochemistry and origin of a new-type of Zr-Nb-Y-REE deposit in highly-evolved alkali granite, Chungju area, South Korea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2554, https://doi.org/10.5194/egusphere-egu2020-2554, 2020.

A change in the Ta/Nb ratio in acid igneous rocks is related to crystallization differentiation processes. The genesis of rock-forming and accessory minerals, the formation of an aqueous fluid at the magmatic stage, or the separation of another liquid phase from a silicate melt through liquation can lead to a change in the Ta/Nb ratio and an increase in the contents of Ta and Nb in the residual melt. A calculation of the possible change in the Ta/Nb indicator ratio in the residual deeply differentiated granite melt is performed.

We used experimental data from various literature sources (T = 650–800 ºC, P = 1–2 kbar) on the solubility of columbite and tantalite in a silicate melt and on the distribution of Ta and Nb among a coexisting silicate melt, aqueous liquid, and aluminum fluoride melt. The Clarke values of these metals in acid rocks of the Earth’s crust were taken as the initial contents of Ta and Nb in the melt. The calculations were made using the mass balance method. It is shown that the separation of fluid in a closed magmatic system rock-forming minerals–silicate melt–water can lead to an approximately twice increase in Ta/Nb in the residual melt as compared to the initial Clarke value. In the system rock-forming minerals–silicate melt–alumino fluoride melt with the initial content of fluorine close to that in biotite granites, the Ta/Nb ratio in the residual melt can increase to ~1. Successive crystallization of minerals of the isomorphic columbite–tantalite series can lead to Ta/Nb > 2 in the residual melt. Crystallization of biotite causes a significant increase in Ta/Nb but significantly prevents the accumulation of these metals in the residual silicate melt.

How to cite: Alferyeva, Y. and Gramenitskiy, E.: Calculation of changes in the Ta/Nb ratio in differentiates of granite melt based on experimental data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7509, https://doi.org/10.5194/egusphere-egu2020-7509, 2020.

The Lijiagou spodumene deposit in the central Songpan-Garze Fold Belt (SGFB), West Sichuan, is a spodumene pegmatite-hosted deposit within the giant Songpan-Garze polymetallic belt. Systematic zircon, cassiterite and coltan U-Pb dating, Hf isotope and whole-rock geochemical analysis were undertaken. Two-mica granite and muscovite albite granite have S-type granite affinities and chemical compositions suggesting a post-orogenic setting, and the spodumene pegmatites belong to the LCT (Li-Cs-Ta) group of pegmatites. Zircon LA-MC-ICP-MS U-Pb dating of the two-mica granite, muscovite albite granite, barren albite pegmatite and albite spodumene pegmatite give crystallization ages of 219.2 ± 2.3 Ma (MSWD = 0.55), 217 ± 2.8 Ma (MSWD = 0.47), 202.8 ± 4.9 Ma (MSWD = 3.9), 200.1 ± 4.6 Ma (MSWD = 3.1), respectively. Zircons from the same units yield εHf(t) values of  −39.17 to 13.84, −22.73 to −2.83, −11.17 to 8.14, and −4.92 to −2.4, respectively, consistent with mixed crustal sources for the pegmatite and granite magmas. Cassiterite from spodumene pegmatite yields a concordia intercept age of 211.4 ± 3.3 Ma (MSWD = 2.9), while coltan yields a weighted mean age of 211.6 ± 0.5 Ma (MSWD = 0.61). The U-Pb zircon ages of the two-mica granite and muscovite albite granite are interpreted as ages of magmatic crystallization. Metamictization of zircon in both barren and spodumene pegmatites makes their U-Pb zircon ages liable to inaccuracy due to Pb loss. The coltan U-Pb age is regarded as an accurate measure of the magmatic crystallization age of the spodumene pegmatite. Given the differences in magmatic ages and εHf(t) ranges between spodumene pegmatite and both the two-mica granite and the muscovite albite granite, the spodumene pegmatite probably represents an anatectic melt and not a fractionation product of either of the granitic magmas. U-Pb coltan and U-Pb cassiterite dating are more likely to provide accurate crystallization ages of spodumene pegmatites than U-Pb zircon ages. Spodumene mineral exploration in such geological environments requires consideration both of the mineralogy and geochemistry of potential metasedimentary source rocks, and of the effects of granite intrusion in creating fertile mineral assemblages.

Two key conclusions for spodumene pegmatite mineral exploration follow: 1) prior intrusion of granite may be required to generate a metasedimentary mineral assemblage that may later yield albite-spodumene pegmatite magma, and 2) a focus on the mineralogy and Li concentration of potential metasedimentary source rocks is required to identify geological environments in which albite-spodumene pegmatite magmas may have been generated.

How to cite: Fei, G., Li, Y., and Menuge, J. F.: The origin of the super-large Lijiagou spodumene pegmatite deposit in Songpan-Garze Fold Belt, West Sichuan, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17877, https://doi.org/10.5194/egusphere-egu2020-17877, 2020.

Magmatic-hydrothermal transition in highly differentiated silicic igneous systems is responsible for several mineralization styles including pegmatite-, porphyry- or greisen-related ore deposits. The Krušné hory/Erzgebirge province in central Europe is characterized by late Variscan, Sn-W greisen mineralization that is spatially and temporally associated with W-Mo pegmatite-greisen mineralization in its eastern part. In the Knöttel district at Krupka, a complete sequence of highly differentiated Li- and F-rich granites, aplites, pegmatites, breccias, greisens, hydrothermal quartzites and late quartz veins is exposed and the nature of magmatic-hydrothermal transition has been investigated and interpreted by trace element composition of quartz. Abundance of the siliceous rocks points to sharp chemical gradients, controlling the precipitation and/or mineralization processes that may have been facilitated by involvement of hydrosilicate (silicothermal) fluids. The trace element concentrations of quartz and their correlations suggest that Si⁴⁺ = Li⁺Al³⁺ and Si⁴⁺ = H⁺Al³⁺ are the most important substitution mechanisms. Ratios in Ti vs. Li, Be and Al define several distinct genetic trends: (1) magmatic, high-Li/Ti or Al/Ti trend which involves granites, aplites and K-feldspar pegmatites; (2) late-magmatic or hydrosilicate, medium-Li/Ti trend recorded by quartz megacrysts and pegmatite-textured aggregates in granites and quartz-protolithionite pegmatite; (3) hydrothermal, low-Li/Ti or Al/Ti trend represented by a stockwork of coarse-grained hydrothermal quartzites and quartz veins, and quartz replacement in greisens. The medium-Li/Ti trend plausibly represents a hydrosilicate liquid, an H₂O- and SiO₂-rich medium that was probably formed by disequilibrium crystallization in front of rapidly propagating solidification front of highly evolved granitic melt. Thermal evolution of the magmatic-hydrothermal system was monitored by Ti-in-quartz thermometry. The calculated rutile activity in the granitic melts was very low (0.3–0.05) but it increased (up to 1), that is, rutile saturation in the pegmatites and the hydrothermal quartz veins. Magmatic crystallization of the granites and aplites occurred from 700 to 580 °C, the pegmatite formation between 600 and 500 °C. The greisenization stage coincided thermally with the pegmatite crystallization, and it was followed by a late hydrothermal stage precipitating distal quartz veins at 500–390 °C. The concentrations of Ti, Al, Ge, Li and Rb in quartz reveal that the granite and pegmatite magmas at Knöttel – and in the Erzgebirge in general – have reached extremely high Al, Li, Rb and Ge enrichment in comparison with igneous rocks worldwide and their composition approaches that of pegmatites. In addition, the Knöttel system exhibits Be enrichment in quartz, apparently linked to F enrichment, and this feature marks the Mo-W-mineralized systems globally.

How to cite: Peterková, T. and Dolejš, D.: Magmatic-hydrothermal transition in Mo-W granite-pegmatite-greisen systems: trace element chemistry of quartz, Krupka district, eastern Erzgebirge (Czech Republic), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20113, https://doi.org/10.5194/egusphere-egu2020-20113, 2020.

Coupled dissolution – reprecipitation processes in apatite during metasomatism can occur both in nature as well as experimentally [1, 2, 3]. Various fluids can affect the growth of monazite and/or xenotime as well as element redistribution in apatite. We have conducted a series of hydrothermal experiments on the dissolution of fluorapatite in reactions with sulfate-bearing and saline fluids at post-magmatic P-T conditions. The fluorapatite used in these experiments are inclusion-free grains (size 0.5 - 1 mm) extracted from magnetite-apatite rocks of the Mushgai-Khudag complex (South Mongolia). The fluids used include aqueous solutions of H₂SO₄ + La₂(SO₄)₃, FeCl₃ and H₂SO₄ + Fe₂O₃ ( La₂SO₄ or FeCl₃/H₂O = 50/50, La₂SO₄ or Fe₂O₃/1N H₂SO₄ = 50/50). The solids + fluids were placed in 1 cm long/3mm wide Pt capsules and arc-welded shut.  They were then placed in a cold-seal autoclave on a hydrothermal line at 200 MPa and 600 ^oC for a duration of about 3 weeks. The experiments were quenched using compressed air and the products were analyzed by SEM and EMP.

In the La₂(SO₄)₃/H₂O experiments, the fluorapatite did not show any changes in composition compared to the original fluorapatite. Monazite and anhydrite did not form.  In the La₂(SO₄)₃/H₂SO₄ experiments, monazite and cubic crystals of anhydrite were formed along the cracks and rims of the fluorapatite grains. A single grain of fluorite was found associated with anhydrite and monazite. Fluorapatite metasomatized in a FeCl₃/H₂O saline solution developed light trails across the grain surface. These trails are moderately depleted in Ca, P, Sr, and enriched in Si, S, and LREE as compared with the darker areas, which represent the original fluorapatite. Monazite and anhydrite did not form. In the Fe₂O₃/1N H₂SO₄ experiments, the fluorapatite developed a zonal structure where light zones are enriched in Si and LREE. Cubic crystals of anhydrite formed along the cracks and rims of the fluorapatite grains. Monazite did not form. A Fe-Ca-P phase was found as rounded or elongated grains within the fluorapatite.

Our results indicate that H₂SO₄ in the fluid promotes the highest reactivity allowing for the formation of new mineral phases in the fluorapatite during the dissolution-reprecipitation process.

This work was supported by the Russian Science Foundation, grant No 19-17-00013.

[1] Harlov, D. E., Förster, H. J., 2003. Fluid-induced nucleation of (Y+ REE)-phosphate minerals within apatite: Nature and experiment. Part II. Fluorapatite. Am. Miner., 88(8-9), 1209-1229.

[2] Harlov, D. E., Wirth, R., Förster, H. J., 2005. An experimental study of dissolution–reprecipitation in fluorapatite: fluid infiltration and the formation of monazite. Contr.to Min. and Petrol., 150(3), 268-286.

[3] Harlov, D.E., Förster, H.J., Schmidt, C., 2003. High PT experimental metasomatism of a fluorapatite with significant britholite and fluorellestadite components: implications for LREE mobility during granulite-facies metamorphism. Min. Mag., 67 (1), 61-72.

How to cite: Nikolenko, A., Harlov, D., and Veksler, I.: An experimental study of apatite metasomatized by S-bearing fluid: the element redistribution and the formation of monazite and anhydrite , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12442, https://doi.org/10.5194/egusphere-egu2020-12442, 2020.

The study of magmatic enclaves can provide a vertical understanding of the variable levels at which magmatic differentiation occurs, allowing us to quantify the conditions under which processes like sulfide saturation take place. Recent studies have confirmed the importance of lower crustal hornblende-rich enclaves (Chang and Audétat, 2018) and deep pyroxene-rich cumulates, as fertile sources in post-subduction and collisional settings, by sequestrating most of the Cu extracted from the mantle (Chen et al., 2019). Moreover, studies of sulfides in the host rock (Keith et al., 2017, Georgatou et al., 2018, 2020) and in enclaves (Du et al., 2014; Georgatou et al., 2018) have shown that sulfide saturation appears to be a multi-stage process starting with Fe,Ni-rich sulfides, switching to Ni-poor, Cu-rich sulfides and finally to only Cu-rich sulfides. Bracketing the P-T range in which sulfide saturation occurs relative to the sulfide occurrence and composition for diverse geodynamic settings in both mineralised and barren systems would permit us to assess the effect of sulfide saturation on the mineralization potential of the ascending residual melt.

Here, we investigate sulfide-bearing magmatic enclaves from: (i) the Miocene volcano-plutonic complexes of Konya (hosting the Doganbey Cu-Mo-W porphyry and Inlice Au-epithermal) and Usak (hosting the Kisladag giant Au-porphyry), in Western Turkey (post-subduction settings), (ii) the Kula Plio-Quaternary volcano, in the Usak basin, also in Turkey (intraplate OIB-like signature volcano in post-subduction setting). We compare results from the above areas with those of previously studied enclaves (Georgatou et al., 2018) and of new enclaves of the Quaternary Ecuadorian volcanic arc, hosting, among others, the Cascabel Cu-Au Miocene porphyry deposits (subduction setting).

Our results confirm previous conclusions (Georgatou et al., 2018) that mafic enclaves and cumulates carry a greater amount of sulfides compared to the more felsic host rock and that sulfides are generally Cu-poorer compared to the ones found in the host rock. Preliminary thermobarometry data on sulfide bearing amphibole cores found in the host rock yield P(GPa)/T(^oC) (Ridolfi et al., 2010) of 0.39-0.53/1060-1093 for Kula, 0.46-0.11/1015-819 for Konya, 0.20-0.33/917-969 for Usak and 0.2-0.38/902-987 for Ecuador. Estimates on amphibole occuring in hornblende-rich enclaves of Kula and Ecuador indicate P/T values of 0.22-0.57/988-1097 and 0.24-0.4/900-1013, respectively. Crossrefencing with Mutch et al., 2016 shows similar temperatures but significantly higher pressures, indicating for the case of Kula 0.69-0.83 GPa in the host rock and 0.53-0.86 GPa in the enclaves. These data suggest widespread sulfide saturation occurring at mid- to upper crustal depths with the highest P-T values corresponding to the onset of early Fe,Ni-rich sulfide saturation. Future investigation of sulfide-rich enclaves found in other areas and crossreferencing with multiple thermobarometers will further constrain the P-T conditions for later stages of sulfide saturation.

Chang and Audétat 2018, J.Petrol. 59(10):1869-1898

Chen et al., 2019, Earth Planet.Sci.Lett. 531, 115971

Du et al., 2014, Geosci.Front. 5,237-248

Georgatou et al., 2019, Lithos 296-299,580-599

Georgatou and Chiaradia, 2020, Solid Earth 11(1):1-21

Keith et al., 2017, Chem.Geol. 451:67–77

Ridolfi et al., 2010, Contrib.Mineral.Petrol. 160,45-66

Mutch et al., 2016, Contrib.Mineral.Petrol. 171,85

How to cite: Georgatou, A. A. and Chiaradia, M.: The sulfide enclave cargo: Insights into magmatic-hydrothermal ore systems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8942, https://doi.org/10.5194/egusphere-egu2020-8942, 2020.

The Niaz porphyry Cu-Mo deposit in the Arasbaran metallogenic belt of NW Iran exhibits extensive hydrothermal alteration developed in three temporally and spatially overlapping zones:   early potassic, transitional phyllic and intermediate argillic, and late advanced argillic. The early and transitional zones contain biotite, either of magmatic (re-equilibrated) or hydrothermal (replacement and/or neoformed) origin. This study aims to understand the petrography and chemistry of the hydrothermal biotite for evaluating the fluid compositional changes during alteration processes. Selected samples from the different alteration zones were studied for petrography crossing from inner to outer parts of the Niaz deposit. Electron microprobe analyses (Cameca SX100) including halogens (F and Cl) were performed on the hydrothermal micas at the Centre CAMPARIS, Institut des Sciences de la Terre de Paris (ISTeP), Sorbonne University, France. The biotite composition displays an increase in Al₂O₃, FeO and Cl, but a decrease in TiO₂, MgO and F, from the potassic to the transitional phyllic and intermediate argillic alteration zones. The hydrothermal biotite with high Mg (X_Mg = 0.61-0.72) inside potassic zone tends to incorporate more F and less Cl compared to the biotite with lower Mg; a crystal-chemical effect referred to as “Fe-F and Mg-Cl avoidance rules”. The biotite from the potassic zone possesses  a moderate range of F content (0.24 to 0.91wt. %) that is significantly higher than in the phyllic (0.45 to 0.62 wt. %) and argillic (0.19 to 0.37 wt. %) zones, exhibiting a positive correlation with X_Mg and a negative correlation with Cl. However, the biotite from transitional phyllic as well as intermediate argillic alteration zones shows a scattered relationship.

The biotite from the central potassic to transitional phyllic and intermediate argillic alteration zones have average log (X_F/X_OH) values of ‑1.16, ‑1.19, and ‑1.44, respectively. The log (X_Cl/X_OH) values are ‑2.10, ‑1.97, and ‑1.98, whereas log (X_Cl/X_F) val­ues vary from 0.95, 0.78 to 0.54. The systematic variation of the logarithmic ratios reflects a sys­tematic variation of the F content in biotite associated with these alteration zones.

Microthermometric data of fluid inclusions show a decrease in temperature from potassic through phyllic to intermediate argillic zones (420, 360 and 280 °C, respectively). The log (fH₂O/fHF) and log (fH₂O/fHCl) values calculated for fluids equilibrated with biotite increase progressively outward in these alteration zones (6.04, 6.42 and 7.39, respectively). The decrease in halogen content of hydrothermal fluids toward outer parts of the deposits reflects an increase in the degree of mixing between magmatic fluid and meteoric water.

The F content of biotite decreases systematically toward the outer part of the deposit, while the Cl content shows unsystematic variations crossing the alteration zones. This finding suggests that the Cl content cannot be used as exploration tool for vectoring the mineralization. However, the positive correlation between the F content in biotite and bulk concentration of Cu in the different alteration zones may provide a possible geochemical tool to vectoring the Cu mineralization in porphyry deposits.

How to cite: Siahcheshm, K., Wagner, C., Orberger, B., Fialin, M., and Rividi, N.: F, Cl content of Hydrothermal Biotite as a Geochemical Indicator Vectoring to Ore: Constrain on Niaz Cu-Mo porphyry Deposit, NW Iran, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3513, https://doi.org/10.5194/egusphere-egu2020-3513, 2020.

The Rodu-Frasin Neogene volcanic structure and associated Au-Ag mineralization are located in the north-eastern part of the Metaliferi Mountains, being part of the Baia de Aries - Rosia - Bucium metallogenetic district of the "Golden Quadrilateral".

The Rodu-Frasin region's geology consists mainly of Frasin dacite dyke and dome, polymictic volcanic and phreatomagmatic breccias and related volcano-sedimentary deposits, Badenian volcanic and sedimentary rocks, and Cretaceous sedimentary rocks.

Hydrothermal alteration in the region is pervasive and widespread throughout the volcanic structure and surrounding Cretaceous formation. Five main types of hydrothermal alterations have been described: potassic, propylitic, phyllic, silicic and carbonate. Argillic alteration is present only locally.

In the area of Rodu-Frasin deposit, the ore occurs in a structurally complex environment, influenced by faults and fractures oriented in two or more directions. Au-Ag-base metals mineralization is genetically associated with hydrothermal breccias and phreatomagmatic fractures.

Ore minerals consist of sulfides, gold, carbonates, adularia and quartz. They have been prevalently emplaced as veins, breccia bodies and disseminations in open fractures and breccias in the Rodu diatreme, and as stockworks, veins and disseminations in relationship to the Frasin dome structure.

The mineralized veins contain carbonates, quartz, pyrite, sphalerite, galena, chalcopyrite, tetrahedrite and gold. Magnetite and hematite, probably formed under mesothermal conditions, have been identified only as metasomatic substitutions of possible deep-breaking Cretaceous limestone clasts.

The deposition of the ore seemed to have a pulsating nature with the evolution taking place, possibly, in three stages to which the following mineral assemblages were described: 1. magnetite, hematite - pyrite, marcasite - quartz and pyrite - quartz ± base metal sulfides, in the first stage (mesothermal?); 2. arsenopyrite, Au - base metal sulfides - quartz - adularia, “chinga”, pyrite, Au - quartz - adularia and base metal sulfides - calcite, aragonite, dolomite, ankerite, ± rhodochrosite ± kutnahorite - quartz - adularia, in the second stage (epithermal low sulfidation) and 3. quartz - pyrite - marcasite - carbonates dominant rhodochrosite - Au and alabandite - rhodochrosite - quartz in the third stage (epithermal low sulfidation).

Gold is present in various proportions, either as small grains or as sub-microscopic occurrences and has been petrographically identified as electrum. The individual grains in native state have been observed as thin sheets on pyrite, sphalerite, rhodochrosite, calcite and quartz or as short wires and sheets in geodes. Local gold concentrations are common at the intersection of the locally-called “chairs” with “crosses” veins.

Acknowledgments

This work was supported by two Romanian Ministry of Research and Innovation grants, CCCDI – UEFISCDI, project number PN-III-P4-ID-PCCF-2016-4-0014 and PN-III-P1-1.2-PCCDI-2017-0346/29, within PNCDI III.

How to cite: Elena-Luisa, I.: Ore mineralogy of the Rodu-Frasin Au-Ag deposit, Metaliferi Mountains, Romania, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2888, https://doi.org/10.5194/egusphere-egu2020-2888, 2020.

Porphyries, closely associated with the copper ore deposits in orogenic belts, are usually considered to have high oxygen fugacity and display high Sr/Y ratios. However, it is still ambiguous whether the high oxygen fugacity and the enrichment of copper are inherited from magma source or obtained by magmatic processes, and the linkage between the high Sr/Y magmas and the formation of porphyry Cu deposits remains unclear. To address these issues, an integrated study of zircon geochronology and oxygen fugacity, petrography, geochemical and Sr-Nd-Hf isotopic compositions for was carried our for the Shanyang porphyry groups from the South Qinling Orogen, Central China. The crystallization ages for the Shanyang porphyries range from ca. 152 to 140 Ma. Our results suggest that the Shanyang porphyry groups are high Ba-Sr granitoids, rather than adakitic rocks, and there is no inevitable connection between high Sr/Y magma and the formation of PCDs. Their parental magmas were derived from partial melting of enriched heterogeneous lithospheric mantle that had been metasomatized by fluid or melt released from the previous subducting slab. Through magma differentiation, the Shanyang porphyry magmas changed from the oxidation state (ΔFMQ +1 to +2) to the reduced state (ΔFMQ +1 to -0.5). The redox condition of magma may be very different from its source and can be shifted remarkably during magmatic evolution that caused by fractional crystallization of garnet in the deep crust and magma degassing in the shallow upper crust. Remelting of the early formed sulfides and gas-brine reactions could enrich copper in the exsolved volatile fluid. Furthermore, the periodic and long-lived magmatic-hydrothermal systems in the shallower magma reservoirs play a critical role in the formation of porphyry Cu deposits.

How to cite: Luo, B., Zhang, H., Zhang, L., Zhang, C., Pan, F., and Yang, H.: Evolution of oxygen fugacity and copper in the Mesozoic Shanyang porphyry groups, South Qinling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20630, https://doi.org/10.5194/egusphere-egu2020-20630, 2020.

Supergene copper mineralization (SCM) are nowadays the economic viability of many porphyry copper deposits worldwide. These mineralization are derived from supergene processes, defined by Ransome (1912) as sulfide oxidation and leaching of ore deposits in the weathering environment, and any attendant secondary sulfide enrichment. For supergene copper mineralization to form, favorable tectonics, climate and geomorphologic conditions are required. Tectonics control the uplift needed to induce groundwater lowering and leaching of sulphides from a porphyry copper deposit. Climate controls copper leaching in the supergene environment and groundwater circulation towards the locus where supergene copper-bearing minerals precipitate. Two types of SCM have been recognized: 1) in-situ SCM, which are products of descending aqueous solutions and 2) exotic SCM,  which are the products of lateral migration of supergene copper solutions from a parental porphyry copper deposit (Sillitoe, 2005).

In the Atacama Desert, such deposits seem to take place during specific Tertiary climatic periods and relief formation. But many uncertainties remain regarding the genesis and the exact timing for their formation. In this study, a coupled approach combining a petro-geochemical study and LA-ICP-MS U-Pb dating were applied to four mining copper deposits (e.g. Mina Sur, Damiana, El Cobre, Zaldivar) from hyperarid Atacama Desert of Northern Chile. Textural features are the same in all the deposits with chrysocolla as the abundant mineral, followed by black chrysocolla, pseudomalachite and minor atacamite and copper wad. Their geochemical compositions (i.e. major, traces and rare Earth elements) also show homogeneous results suggesting similar process in their genesis. U-Pb dating were performed on black chrysocolla, chrysocolla and pseudomalachite from all the deposits. Apart from Mina Sur deposit, all the mines mentioned above showed high common lead content. To try to extract in these deposit an U-Pb age, complementary analyses to quantify accurately common lead concentration are ongoing, using MC-ICPMS. At Mina Sur, U-Pb dating performed on pseudomalachite bands yields a crystallisation age of 18.4 ± 1.0 Ma. For the black chrysocolla clasts, the ²⁰⁶Pb/²³⁸U apparent ages are ranging from 19.7 ± 5.0 Ma down to 6.1 ± 0.3 Ma, a spreading that we interpret as the result of uranium and lead mobility linked to fluid circulation following crystallization. Isotopic analyses, i.e. Cu and O isotopes, are in progress to better constrain the source and nature of these fluids. This study demonstrates, for the first time, that supergene copper mineralization presents a chronological potential and can be dated, at least in some case, by the U-Th-Pb method. Furthermore, the age obtained on pseudomalachite indicates that Mina Sur deposition took place as early as 19 Ma, a result that is in agreement with geological constraints in the mining district and the supergene ages already known in the Atacama Desert. These promising results represent a new tool to understand the physico-chemical, climatic and geological conditions that prevailed during the formation of supergene copper deposits and a proxy for their prospection around the world and maybe date climatic variation.

How to cite: Kahou, Z. S., Brichau, S., Duchêne, S., Poujol, M., Campos, E., Leisen, M., d'Abzac, F.-X., Riquelme, R., Carretier, S., Choy, S., and De Parseval, P.: Integrated study of supergene copper deposits from Atacama Desert, Northern Chile: coupled petro-geochemical approach and U-Pb LA-ICP-MS in situ dating, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18257, https://doi.org/10.5194/egusphere-egu2020-18257, 2020.

Porphyry magmatic systems emplaced within carbonate host rocks constitute a major source of the world’s Cu, Mo, Pb, Zn and Au [1]. Mineralisation is generally either porphyry-style or endoskarn-style within, or porphyry-, exoskarn- or manto-style outside the porphyry intrusion(s) [1,2]. Genetic models for porphyry and skarn mineralisation are well established, however questions remain as to why endoskarn- rather than porphyry-style mineralisation predominates within certain systems and regions. This is the case in Japan, for example, where there are very few signs of porphyry mineralisation despite generally favourable geological conditions, but there are large endoskarn and exoskarn deposits [3]. Recent studies show that magmas can assimilate large volumes of crustal carbonates, potentially providing a significant amount of CO₂ to late and post-magmatic hydrothermal fluids [4]. High levels of CO₂ in magmatic-hydrothermal systems may favour endoskarn formation and affect metal fractionation and solubility of ore minerals [5]. In this contribution, we test the hypothesis that endoskarn alteration may eliminate porphyry-style Cu mineralisation and mobilise Cu into other parts of the pluton and surrounding carbonate wall-rocks (exoskarns).  

To address this hypothesis, the Daye ore district in the Middle-Lower Yangtze River metallogenic belt was selected for study as it hosts porphyry-, exoskarn- and endoskarn-styles of mineralisation [6]. The porphyry and skarn deposits lie within Late Mesozoic intrusions or along their contacts with Late Triassic carbonates. From among the many porphyry-related systems, the Tonglushan Fe-Cu-(Au) endoskarn-bearing system was selected for detailed field-, light microscopy-, cathodoluminescence-, SEM- and QEMSCAN®-based genetic studies. The current study is mainly based on a comparison of samples from a single core through altered granite, endoskarn and exoskarn. From preliminary data for the Tonglushan system, the granites distal to the endoskarn were affected by Na-Ca alteration (replacement of intermediate composition plagioclase with albite, calcite and chlorite, and hornblende with calcite and chlorite), potassic alteration (replacement of plagioclase with K-feldspar), and later quartz-calcite veining. The endoskarn, which shows relict minerals and textures from the granite, underwent: 1) sericitic alteration, 2) prograde endoskarn formation, 3) retrograde endoskarn formation, 4) potassic alteration and 5) late carbonate veining stage. The textural relationships of oxide minerals in exoskarn and endoskarn indicate that magnetite and hematite likely formed during Stage 3, whereas Cu-(Au) mineralisation in the exoskarn is considered to be genetically associated with the potassic alteration phase, with precipitation of sulphides caused by acid neutralisation within the carbonates.

References:

[1] Sillitoe R (2010) Econ Geol 105:3-41

[2] Meinert L D et al. (2005) Econ Geol 100:299-336

[3] Ishihara S (1980) Mining Geol 30:59-62

[4] Carter L B and Dasgupta R (2016) Geochem Geophys Geosyst 17:3893-3916

[5] Lowenstern J B (2001) Mineral Deposita 36:490-502

[6] Zhai Y S et al. (1996) Ore Geol Rev 11:229-248

How to cite: Zhang, F., J. Williamson, B., S.R. Hughes, H., and Rollinson, G.: Discriminating porphyry and endoskarn-forming magmatic-hydrothermal systems: a case study from the Tonglushan Fe-Cu-(Au) deposit, Daye district, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-317, https://doi.org/10.5194/egusphere-egu2020-317, 2020.

The Keban Pb-Zn-(Cu) skarn deposit in the Elazığ region, Turkey, was formed at the contact zone of the Permo-Triassic metamorphics and the Late Cretaceous plutonic rocks in the Eastern Taurus orogenic belt. The mineralization is hosted by skarn and meta-clastic/carbonate rocks of the Keban Metamorphics intruded by alkali syenite porphyry, which is associated with the Pb-Zn-(Cu) mineralization. The rock units in the region are partly hydrothermally altered graphite calc-schist containing crystallized limestone interlayers and lenses, meta-pellitic rocks (phylitte/calc-phyllite), dolomitic limestone, calc-silicate hornfels, marble and plutonic rocks. Calc-silicate hornfels is an initial metamorphic product occurred in contact zone of the intrusive unit. Results of mineralogical studies indicate that garnet and pyroxene-rich skarn formed in early (prograde) stage of skarnization whereas epidote, chlorite, tremolite, phlogopite, muscovite, calcite, quartz and fluorite are typical minerals of the retrograde stage. Using the Raman spectroscopy investigations, garnets in alteration zone are subdivided into two groups. Garnets in andradite composition are zoned and occur close to the intrusion reflecting high-temperature conditions and those of grossular composition represent low-temperature conditions. The sill/dykes and stock-like Keban plutonic rocks hosting foid syenite porphyry and nepheline syenite are of holocrystalline hipidiomorph porphyritic texture including large nepheline and plagioclase phenocrysts. Metallic minerals comprise sphalerite, galena, chalcopyrite, magnetite, bornite, pyrite, fahlore and hematite, which mainly occur as dissemination, vein and massive forms and crosscut by late-stage quartz, fluorite and calcite veinlets. Sphalerite is medium-coarse grained, semi-euhedral and contain chalcopyrite inclusions. Blebs of chalcopyrite are widely recognized in sphalerite (chalcopyrite disease). Galena replaces sphalerite and in some cases, it hosts several sulfo-salt minerals. Magnetite partly or completely transforms to limonite and chalcopyrite inclusions in sphalerite occur among the magnetite grains.

Key words: Keban, Pb-Zn-(Cu) skarn deposits, Mineralogy, Petrography, Ore Microscopy, Raman Spectroscopy

How to cite: Kirat, E. and Mutlu, H.: Mineralogy and petrography of the Keban Pb-Zn-(Cu) skarn deposit, Elaziğ, eastern Turkey, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4435, https://doi.org/10.5194/egusphere-egu2020-4435, 2020.

Calcic garnets from grossular-andradite (grandite) series have proven their ability to record the conditions and timing of their formation processes. Typically these minerals occur in skarn systems, together with other calc-silicates (diopside, epidote) and commonly host economic Cu, Zn-Pb-Ag, Au, Sn, W or Mo mineralization. Based on the U-content in the garnet structure, we used in-situ LA-ICP-MS U-Pb geochronology to determine the age record in more than 15 skarn deposits from different tectonic zones in Bulgaria. The data is partly complemented with ID-TIMS dating. The mineralogical, geochemical and petrological characteristics of the materials were described additionally. Both contact and infiltration skarns were studied.

The obtained data revealed that the garnet composition in terms of major elements does not affect the precision of age determination. Both andradite and grossular members yield age data with very high accuracy. The dating results, however, depend on the geochemical signature of the garnets and especially on the U-content and U/Pb ratio. Our data shows that skarn samples from the vicinities of magmatic bodies or along contacts of causative pegmatite veins usually have increased U-incorporation from several to more than 70 ppm, as suggested by their proximal position to the source. The contact skarn garnets formed by intrusion of silicate melts (or pegmatites) onto carbonate-rich hosts mostly produce precise ages, which are in good agreement with the geochronological zircon data about the magmatism in the studied regions (e.g. Central Pirin, Teshevo, Plana, Gutsal, Rila-West Rhodope, Sv. Nikola etc. plutons). The infiltration skarns, though, generally reveal ages with low accuracy and significant errors, mainly due to U-content below 1 ppm. The reason for the low U-concentration and U/Pb ratio is either connected with a primary U-deficit and its depletion in the garnet-precipitating fluids with time and space but might be also related to garnet retrograde hydrothermal alteration.

The time span of the Bulgarian skarn garnets is closely connected with the causative magmatic bodies. The studied skarns reveal Paleogene (~30-42 Ma - Central Pirin and Teshevo plutons and pegmatites from Rila-West Rhodope batholith; Djurkovo, Murzian and Zvezdel Pb-Zn deposits; ~ 58 Ma - skarns from Western Rila Mts., ~ 68 Ma – Babyak Mo-Ag-Au-W-Bi-Cu-Pb-Zn deposit), Cretaceous (~ 76 Ma- Gutsal pluton, 81 Ma - scheelite bearing skarns from the Plana pluton, 86 Ma – Iglika skarn deposit) and Paleozoic (~ 303 Ma – Martinovo Fe-skarn deposit) ages. Given the occurrence of Ca-garnet in contact rocks and hydrothermal ore deposits, our results highlight the potential of grandite as a powerful U-Pb geochronometer for dating magmatism and skarn-related mineralizations.

Acknowledgements. The study is partly supported by the DNTS 02/15 bilateral project between Bulgaria and the Russian Federation, financed by the Bulgarian National Science Fund.

How to cite: Vassileva, R., Grozdev, V., Peytcheva, I., von Quadt, A., and Stifeeva, M.: U-Pb dating of skarn garnets from Bulgarian deposits, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7392, https://doi.org/10.5194/egusphere-egu2020-7392, 2020.

Remobilisation of sulphides in metamorphosed volcanic-hosted massive sulphide deposits has been investigated in many VMS districts with regards to scale, mineral assemblages, texture and relative competence of minerals under certain p-t conditions (Gilligan & Marshall, 1987; Marshall & Gilligan, 1987). Examples of syn-tectonic remobilisation can be found at the Rävliden Norra (RVN) volcanic-hosted massive sulphide in the Skellefte district. At Rävliden, polymetallic sulphide mineralization occurs at the transition from meta-volcanic rocks of the Skellefte group rocks to the overlying Vargfors group, comprising volcaniclastic metasedimentary rocks and graphitic shales. This contribution details features of mesoscale (0.1-50 cm) remobilisation of sulphides, such as sulphide-rich veins, tension gashes, ball-ore, massive sulphides with cataclastic texture, and micro-scale features such as infilling of pressure shadows, displaying evidences of brittle and ductile deformation. Sulphide-rich veins containing sphalerite, galena, and a relative high content of Ag-sulphosalts (e.g. freibergite, pyrargyrite, pyrostilpnite) are hosted in the hanging wall (HW) of the RVN mineralization. Brittle deformation is shown in accessory quartz and calcite as bulging recrystallization, grain boundary migration and deformation lamellae or twinning. Ductile expressions include ball-ore (i.e. “durchbewegung”) textures, typically made up of two components, one composed of clasts of graphite shale or tremolite-, actinolite-, talc-altered meta-volcanic rocks and the other comprising a matrix of massive sulphide mineralization. In the massive sulphide matrix of sphalerite, chalcopyrite or pyrrhotite, micro-scale tension gashes and/or pressure shadows occur around clasts infilled by pyrrhotite, chalcopyrite, galena, freibergite, boulangerite, or gudmundite. A similar mineralogy is observed in ore lenses in the ore zone, comprising sphalerite, galena and Ag-Sb-As sulphosalts, hosted structurally above chalcopyrite + pyrrhotite stringer zones in the footwall (FW). Sulphosalts and galena present a high silver content relative to other VMS deposits in the district. This is evidenced by SEM and EMPA analysis in both HW and FW ore lenses. Argentopyrite, sternbergite and stephanite are also locally present in the HW as minor silver species hosted in veins. Inclusions of freibergite in galena contain Ag with average values of 18.4 wt. % in the HW (n=5), 18 wt. % in the massive sphalerite and ball-ore (n= 15), and 20.2 wt. % in the chalcopyrite + pyrrhotite stringer zone (n= 5). Similarly, Pb is 0.2 wt. %, 0.3 wt. %, and 0.4 wt. %, respectively. For sphalerite, Fe is on average 8.0 wt. % (n=3), 7.4 wt. % (n = 11), and 8.3 wt. % (n=3), respectively. Our preliminary results suggest that mineralization in the HW is remobilized from the main ore and textural relationships support a hypothesis that remobilisation involved a relative silver-enrichment in paragenetically later assemblages. At least two stages of deformation in the deposit can be recognized. In the first stage, sphalerite- and chalcopyrite-rich mineralization was deformed along with tremolite and talc to form a S1 foliation. The second stage involved folding of S1, and remobilisation of galena, chalcopyrite and Ag-Sb-As sulphosalts as veins or breccia infill in the HW or filling tension gaps or ball-ore, in the FW. These are often parallel to S2 crenulation or axial planes.

How to cite: Rincon, J., Johansson, S., Jansson, N., Thomas, H., Kaiser, M. C., Persson, M. F., Nordfeldt, E., and Wanhainen, C.: Mineralogy, textural characteristics and mineral chemistry of remobilised sulphides and sulphosalts in the Rävliden Norra VMS deposit, Skellefte district, northern Sweden, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-485, https://doi.org/10.5194/egusphere-egu2020-485, 2020.

In this contribution, we present integrated hyperspectral and photogrammetric models from three abandoned open pit mines in the Iberian Pyrite Belt: Corta Atalaya, Tharsis, and Peña de Hierro. On those three examples, we showcase the usefulness of these data for the characterization of volcanogenic massive sulphide (VMS) mineral deposits. The digital outcrop models are generated by co-registering Structure-from-Motion photogrammetric point clouds of the mine faces with radiometrically corrected hyperspectral images in the visible–near and short-wave infrared range. We then use advanced unmixing and supervised classification techniques to distinguish and map the massive sulphide and stockwork mineralization, their sedimentary, volcanic and volcaniclastic host rocks, and domains of hydrothermal and supergene alteration. The enhanced outcrop models also enable a semi-automatic delineation of discontinuities on the point clouds guided by changes in the hyperspectral attributes, and an estimation of structure orientations from their intersection with the surface to derive simple 3D geological models.

How to cite: Kirsch, M., Lorenz, S., Thiele, S., Zimmermann, R., Khodadadzadeh, M., Tusa, L., and Gloaguen, R.: Mineralogical and structural characterization of massive sulphide deposits in the Iberian Pyrite Belt using hyperspectral digital outcrops, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13141, https://doi.org/10.5194/egusphere-egu2020-13141, 2020.

The Troodos ophiolite is widely accepted to be a fragment of Mesozoic oceanic crust, which uplifted during Alpine orogeny, due to the collision of Eurasia and Africa (Gass and Masson-Smith, 1963; Vibetti, 1993; Adamides, 2011; Antivachis, 2015). It belongs to supra-subduction ophiolites, which probably set up during subduction initiation associated with back-arc spreading (Pearce, 1975; Rautenschlein et al., 1985; Pearce and Robinson, 2010; Martin et al., 2019). The Troodos ophiolite is mentioned to be one of the most well studied and well-preserved ophiolitic sequences (Moores and Vine, 1971; Benn and Laurent, 1987; Patten et al., 2017), presenting significant Cyprus-type sulphide deposits (Constantinou and Govett, 1973; Adamides, 2014).

Cyprus-type deposits are generally, considered as mafic type volcanogenic massive sulfide deposits (VMS), mainly rich in copper and subsidiary zinc, with average grade of 1.3 ± 1.1% Cu and 0.8 ± 0.4% Zn (Hannington et al., 1998; Barie and Hannington, 1999; Patten et al., 2016). VMS deposits are formed in the sea floor, along mid-ocean ridges, by the circulation of high temperature hydrothermal fluids, which their source is seawater (Gillis and Robinson, 1988; Richards et al., 1989; Patten et al., 2017; Martin et al., 2019). In many different regions along the Troodos ophiolite, the VMS deposits are covered by thick, Fe oxides enriched gossans (Bear, 1960; Herzig et al., 1991). In general, those can be formed, when the VMS deposits are exposed to weathering and oxidizing conditions (Herzig et al., 1991), but still the conditions for their formation are debated. The studied gossans from Troodos ophiolite are variegated due to the presence of white silica, red hematite and yellow jarosite. Gossans are always a very interesting part of the ophiolitic sequence from an economic point of view, as they present not only significant amount of extractible copper and zinc, but also, gold and silver (Bear, 1960; Herzig et al., 1991).

We aim to examine the major and trace elements of gossans, which have been collected from different mines (West Apliki, Skouriotissa and Agrokipia mines) of Troodos ophiolite, and define their enrichment or depletion in copper and zinc, by coupling copper and zinc stable non-traditional isotopes. We combined copper with zinc isotopes in a very novel and original approach in order to give information about the conditions prevailing in the system of interest. As many authors mentioned before, supergene enriched environments are the best places to examine the behavior of Cu isotope fractionation under the weathering conditions of ore deposits (Mathur et al., 2008). On the other hand, Zn isotopes are not redox sensitive, but pH-sensitive (Pons, 2016). By coupling them, it can bring light in understanding the way, the nature of fluids that led to gossans formation and their enrichment in copper and zinc in different locations of Troodos ophiolite.

How to cite: Zaronikola, N., Debaille, V., Decree, S., Mathur, R., Hadjigeorgiou, C., and Georgiadou Gavrilovic, I.: An isotopic and trace element investigation of gossans from Troodos ophiolite, Cyprus, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7018, https://doi.org/10.5194/egusphere-egu2020-7018, 2020.

  The Gubong gold deposit is located in the Cheonan metallogenic province which records a highest gold production areas in the Republic of Korea. The Gubong deposit is the richest gold deposit in the province and consists of five stages of massive quartz veins that fill fractures along fault shear zones orienting NE and NW hosted in Precambrian metasedimentary rocks (Gyeonggi massif).

  Ores and alteration minerals of Gubong deposit are sericite, chlorite, epidote, illite, K-feldspar, plagioclase, biotite, quartz, calcite, magnetite, ilmenite, rutile, zircon, monazite, apatite, pyrite, gersdorffite, arsenopyrite, pyrrhotite, sphalerite, marcasite, chalcopyrite, galena, and electrum. Fluid inclusion microthermometry and textural relationships in veins indicate that early sulfide deposition is associated with H₂O-CO₂-CH₄-NaCl±N₂ bearing hotter hydrothermal fluids (203~432^oC, ≤ 13.4 wt % NaCl) and late sulfide deposition is associated with H₂O-NaCl bearing fluids (202~399^oC, 3.9~17.3 wt % NaCl) cooled and diluted possibly by mixing with meteoric water.

  Trace element analyses in quartz from veins were performed by using LA-ICP-MS (193-nm ArF Excimer laser combined with an Elan 6100 quadrupole mass spectrometer) at ETH Zürich. Concentration of trace elements in quartz including Li (<0.01~3.55 ppm), B (3.03~27.17 ppm), Na (3.23~72.79 ppm), Al (4.0~149.9 ppm), P (14.4~68.9 ppm), Sc (3.3~8.7 ppm), Ti (<0.10~1.43 ppm), Cr (<3.34~65.6 ppm), Ga (0.50~1.30ppm), Ge (0.57~2.15 ppm), Rb (<0.01~0.50 ppm), Sr (0.01~3.13 ppm), Sn (<0.29~7.24 ppm), Sb (<0.05~0.42 ppm), and Bi (<0.01~8.30 ppm) are reported. Some trace elements (Al, Na, Ga, P, Li) tend to correlate positively. Titanium versus aluminum concentrations in quartz from Gubong deposit are plotted in the field of orogenic Au deposit suggested by Rusk (2012). We analyzed quartz from other numerous Korean Au-Ag and W-Mo deposits to compare hydrothermal fluid conditions and to provide a geochemical tool for mineral exploration.

Reference

Rusk, B.G., 2012, Cathodoluminescent textures and trace elements in hydrothermal quartz: Quartz: Deposits, Mineralogy and Analytics, Jens Götze and Robert Möckel, Springer, p. 307-329.

How to cite: Yoo, B. C., Seo, J. H., Heinrich, C. A., and Lee, B. H.: Trace elements in quartz vein of Gubong gold deposit, Republic of Korea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1475, https://doi.org/10.5194/egusphere-egu2020-1475, 2020.

      The Yanbian area in northeast (NE) China is located in the eastern segment of the Central Asian Orogenic Belt. Due to its special tectonic location and complicated geologic evolution history, this area has been taken as a crucial region for studying late Paleozoic and Mesozoic tectonics, magmatism and metallogeny. There are a series of late Paleozoic volcanic-sedimentary formations in Yanbian area which host several copper polymetallic deposits including Hongtaiping in Wangqing area and Dongfengnanshan in Tianbaoshan ore district.

1. Rock assembles of ore-hosting volcanic-sedimentary formations

     Filed survey and petrography researches indicate rock types in the late Paleozoic ore-hosting volcanic-sedimentary formations within and around the Hongtaiping and Dongfengnanshan deposit, Miaoling Formation, are mainly composed of tuffaceous sandstone, andesitic tuff, rhyolite, andesite, basalt, dacite, sandstone, carbonate, as well as minor silicolite and fluorite. These rock assembles imply the ore-hosting rocks belong to shallow-marine terrigenous sedimentary-volcanic-pyroclastic rock formation.

1. Mineralization characteristics and genetic type of stratiform ore bodies in Hongtaiping copper polymetallic deposit

      Sixteen ore bodies in Hongtaiping deposit can be classified into two types, the stratiform and vein-type. The major stratiform ore bodies are flat and nearly horizontal, consistent with the Miaoling Formation in occurrence. The largest ore body is 570m long, 50 to 150m wide. The ore in the stratiform ore body is mainly characterized by the banded, lamellar and massive structure. The metal minerals mainly include pyrrhotite, pyrite, chalcopyrite and sphalerite, and most of the metal minerals show allotriomorphic granular and weak metasomatic texture. The microscopic characteristics of the ore show that the boundary between sphalerite and pyrite is relatively flat. According to the ore-hosting rock assembles, some typical alternation and mineralization characteristics, including exhalite in ore-hosting rock series, banded and layered ore bodies, as well as comparisons between the Hongtaiping and some typical VMS-type (e.g. the Laochang in Yunnan Province and the Dabaoshan in Guangdong Province), the Hongtaiping deposit can be classified into the VMS-type.

1. Metallogenic time of Hongtaiping copper polymetallic deposit

      LA-ICP-MS zircon U-Pb dating of 69 igneous zircon grains in four volcanic clastic rock samples from the ore-hosting Miaoling Formation in the Hongtaiping deposit yields ²⁰⁶Pb/²³⁸U ages from 258±8 Ma to 293±10 Ma, and weighted mean age of 268.2±3.3Ma (MSWD=0.42), 273.8±4.7Ma (MSWD=1.3), 268.0±3.2Ma (MSWD=0.66) and 272.4±3.2Ma (MSWD=1.04), respectively. Rb-Sr isotope dating of seven sulfides (one pyrite, one sphalerite, two pyrrhotite and three chalcopyrite) yields the isochron age of 268.3±2.6Ma, which nearly consistent with LA-ICP-MS zircon U-Pb dating results of four ore-hosting volcanic rock samples. Isotope dating results demonstrate the VMS-type stratiform copper polymetallic mineralization in Hongtaiping deposit formed in the early-middle Permian period instead of late Triassic or early Jurassic period.

Acknowledgments: This work was supported by the National Natural Science Foundation of China (NSFC) (No.41772062)

How to cite: Ren, Y., Lu, S., Hou, H., and Yang, Q.: Mineralization characteristics, genetic type and metallogenic time of stratiform ore bodies in Hongtaiping copper polymetallic deposit in Yanbian area, NE China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6289, https://doi.org/10.5194/egusphere-egu2020-6289, 2020.

The Central African Copper Belt of southern Democratic Republic of Congo (DRC) and northern Zambia is one of the world’s major sources of metals and currently accounts for world ~48% of cobalt reserves which will be critical for the shift to a low-carbon economy. The Cu-Co deposits are hosted in the Neoproterozoic Katangan Supergroup. The Fishtie Cu-Co deposit is located in the Lusale basin, to the southeast of the Zambian Copperbelt. At Fishtie, the Grand Conglomerate, which is interpreted as a Sturtian-age glacial diamictite, directly overlies basement schist and quartzite. Cu-Co sulphides are hosted in both the Grand Conglomerate and overlying Kakontwe Dolomite. The current study aims to refine the geological and genetic model of the deposit and is based on detailed logging of 41 cores totalling 8,040m including newly collared exploration drill holes.

The Grand Conglomerate (Mwale Formation) is comprised of several lithofacies but can be broadly classified into two lithofacies including diamictite and siltstone. The upper contact of the Grand Conglomerate is commonly gradational with increasing dolomite contents from bedded siltstone to bedded dolomitic siltstone into the lowermost bedded silty dolomite of the overlying Kakontwe Dolomite. Kakontwe Dolomite at Fishtie is subdivided into four lithofacies: bedded silty dolostone, massive dolostone, bedded dolomitic siltstone and laminated dolostone. Inidividual lithofacies display significant thickness variations that appear to be related to syn-sedimentary fault movement.

Hypogene chalcopyrite and bornite occur as disseminations in siltstones within both the Grand Conglomerate and Kakontwe Dolomite. Sulphides are most abundant in coarser-grained beds. The bedded dolomitic siltstone of Kakotwe Dolomite was also locally significantly mineralized. The bedded silty dolostone, massive dolostone and laminated dolostone facies of the Kakontwe Dolomite were poorly mineralized. Up to several percent hypogene cobalt mineralization is recognized in the eastern part of the deposit. Current data suggests that cobalt content was not controlled by either lithology. Hypogene Cu-Co sulphides are related to the location of syn-sedimentary faults. Work is ongoing regarding the deportment and paragenesis of cobalt in the deposit.

How to cite: Tsuruoka, S. and Hitzman, M.: Stratigraphic and mineralogical characteristics of the Fishtie Cu-Co deposit in Zambia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9946, https://doi.org/10.5194/egusphere-egu2020-9946, 2020.

The Mississippian Waulsortian Formation of the Irish Midlands hosts a number of significant Zn-Pb mines including Lisheen, Galmoy and Silvermines. Consisting predominantly of sphalerite, galena and pyrite, the deposits are intimately associated with hydrothermal dolomite and dolomitic breccias, commonly referred to as “Black Matrix Breccia” (BMB). The hydrothermal dolomite and associated breccias form a predominantly tabular body that largely envelops the zone of sulphide mineralisation. A wide variety of mineralisation styles and textures are recognized, however the majority of the mineralisation resulted through replacement of this hydrothermal dolomite. Recent geochemical evidence indicates that the hydrothermal dolomite contains distinct geochemical signatures that may be useful in sulphide exploration within the Irish Midlands. To date, little work has been conducted on the spatial distribution and variability of this significant hydrothermal dolomite and the role it plays in ore genesis within the Irish Midlands. Through detailed petrographic characterisation, this study documents the distribution of the hydrothermal dolomite. This distribution helps constrain the origin of the massive Zn-Pb deposits and forms an important tool for future mineral exploration in the Irish Orefield.

How to cite: Vafeas, N., Hitzman, M., Johnson, S., and Güven, J.: Spatial Distribution of the Hydrothermal Black Matrix Breccia and its Impact on the Irish-type Zn-Pb Mineralisation , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19286, https://doi.org/10.5194/egusphere-egu2020-19286, 2020.

Geochemical significance and Formation of  Suçatı Pb-Zn Deposits – Eastern Taurides

Hatice Nur Bayram^(1)*, Ali Erdem Bakkalbaşı ^(1)*, Mustafa Kumral⁽¹⁾, Ali Tuğcan Ünlüer⁽¹⁾

⁽¹⁾Istanbul Technical University, Department of Geological Engineering, Istanbul/Turkey

(*E-mail: hnnurbayram@gmail.com)

The Middle Tauride Orogenic Belt is a productive enviroment in terms of Pb-Zn ore deposits, mostly associated with Permian aged dolomitized, shallow marine platform type carbonate rocks. There have been many studies on the origin of the ore deposits in the region, there are two important approaches that stand out for the formation of the ore deposits: the first theory is hydrothermal deposits with magmatic origin, and the other theory is Missisippi Valley-type (MVT) deposits related with the carbonate rocks commonly found in the region. Field studies at the Suçatı (Kayseri – Yahyalı, Central Anatolia, Turkey, East of Aladağlar extension of the Taurides) ore district in the Aladağ geologic unit indicate that the deposits in the region are associated with Paleo-Tethys limestones, fossiliferous limestones and dolomitic limestones. Mineralization is related to Lower Permian aged carbonate rocks include primary mineralization ore minerals as galena, sphalerite, smithsonite and goethite and as a product of hydrothermal activity, calcite mineral filled within fractures and cracks represents gangue minerals. As a result of geochemical analysis of the samples collected from the ore zones, PbO values range between 25.93% - 0.012%, ZnO values range between 51.01% - 0.042%, Fe₂O₃ values range between 42.81% - 10.21%. In conclusion hydrothermal activities closely related with compressional and extentional tectonic regimes took place in multiphase mineralization.

Keywords: Pb-Zn Deposits, MVT, Taurides, Yahyalı

How to cite: Bakkalbasi, A. E., Bayram, H. N., Kumral, M., and Unluer, A. T.: Geochemical significance and Formation of Suçatı Pb-Zn Deposits – Eastern Taurides, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8317, https://doi.org/10.5194/egusphere-egu2020-8317, 2020.

Diz alteration area is situated in the southern part of Ardabil province in the northwest of Iran. This alteration area is a limited part of Tarom-Hashtjin volcanic zone. The hydrothermal alteration process has been mostly taken place in pyroclastic and volcanic units such as tuff, ignimbrite, and trachyandesites. The alterations of this area are related to Eocene volcanism which has considerably developed in the northwest of Iran. The argillic alterations in Diz area are mainly seen in ignimbrite unit and the precursor rock has been intensely altered such that many parts of the parent rock has been fully leached and all of the mobile elements have been removed from the parent rock while the resistant elements such as Al, Si, and some other immobile elements have remained in the context. Considering to the special behavior of REEs in the weathering and alteration profiles, depending on the REE bearing mineral’s resistivity against weathering and alteration processes, REEs can be removed or fixed in the environment. In the studied samples different concentrations of REEs are observable.            

The drawn REE diagrams show unique patterns for the studied samples where Ce group elements (LREEs) show a slight enrichment comparing to Y group (HREEs). The comparison of LREEs with HREEs represents that LREEs have been enriched 4 times more than HREEs.

The positive correlation coefficient between ΣREE and TiO₂ (R²=0.70) represents the role of Ti bearing minerals such as ilmenite, pyroxene, rutile, and anatase in the fixation of REEs. On the other side the presence of considerable amounts of P₂O₅ in the studied samples and also the positive correlation coefficients between P₂O₅ and LREEs (R²=0.90), and P₂O₅ and ΣREE (R²=0.74) suggest that some minor minerals such as monazite (Ce,La,Nd,Th)(PO₄,SiO₄) must be considered. The positive correlation coefficient between Al₂O₃ and ΣREE shows the influence of clay minerals in the adsorption of REEs.         

The evaluation of REE patterns normalized to chondrite show a remarkable peak for Gd. Geochemically, Gd shows similarities with Ca²⁺. The Gd complexes may decompose in the presence of some elements such as Cu, Y, and REEs and Gd^{3+ ­­}can be released. Hence, CaO is a main component in the parent rock of the studied altered samples, the positive Gd anomaly is most likely related to the primary composition of the parent rock. Furthermore, the decomposition of Gd complexes in the presence of competitor elements and also the high Gd content of altering fluids can be thought as the main reasons of Gd positive anomaly in the studied samples.

How to cite: Bakhshandeh, B., Masoumi, R., and Parvaneh, A.: Geochemistry of REEs and trace elements in Diz alteration area, NW Iran, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4111, https://doi.org/10.5194/egusphere-egu2020-4111, 2020.

Antimony (Sb) is a critical metal for Europe. Indeed, Sb is widely used in a variety of industrial operations, especially in the European aircraft industry, such as production of flame retardants, plastics, paint pigments, glassware and ceramics, alloys in ammunition and battery manufacturing plants.

Despite its strategic importance, the knowledge on Sb and its ore deposits remains poorly constrained. Moreover, Europe remains under the threat of an essentially Chinese supply despite a proven potential for European deposits that contain also strategic and precious co-products (W, Au). In parallel, Sb and associated metalloids (As, Hg, etc) are more and more recognised as a global threat for human health and it has been demonstrated that most of elevated concentrations of Sb on earth surface originate from natural, geogenic sources. Then, a first large-scale identification of these areas where primaries resources occur and metalloids can contaminate humans should be a priority.

To achieve its objectives, the overall approach of the ERA-MIN2 AUREOLE project (2019-2022 - https://aureole.brgm.fr) is based on disruptive concepts: i) development of a 3D large-scale metallogenic model integrating deep-seated processes to determine the spatial distribution of ore deposits; ii) the use of mineral prospectivity data weighted by surface data to determine the probability of environmental risk over large areas.

The work package (WP) 1 is dedicated to produce the new 3D deep-seated metallogenic model for antimony mineralisations and contribute to the global 3D understanding of the Sb mineralising processes. The WP2 is designed to the understanding of processes - such as geomorphology, weathering, climate - that control the mobilisation and transport of metalloids at the earth surface. The WP3 will use results from WPs 1 & 2 to produce large-scale mineral prospectivity and a large-scale environmental risk assessment by weighting mineral prospectivity with earth surface properties, such as DTM, rainfall, weathering cartographic maps, etc.

The AUREOLE project will bring new scientific knowledge on Sb and Sb deposits, for a better mineral exploration targeting.

The expected outcomes will be several high-impact deliverables devoted to the targeting of new Sb deposits and a new large-scale environmental assessment maps for decision-making dealing with humans health. Long term expected impacts would be an increase of EU Sb resources and EU Sb sustainable supply. Because of its implications for European critical metals, the AUREOLE project will provide new findings and results to the SCRREEN project (Solutions for Critical Raw Materials – a European Expert Network) and to the IMP@CT project (Integrated Mobile Modularised Plant and Containerised Tools for sustainable, selective, low-impact mining of small, high-grade or complex deposits). It will also interact with the Geo-ERA FRAME project (Forecasting and assessing Europe’s strategic raw materials needs).

How to cite: Gloaguen, E., Higueras, P., Iacono-Marziano, G., Lima, A., Pierre, D., Augier, R., Aurouet, A., Battaglia-Brunet, F., Garcia, F. J., Guillou-Frottier, L., Gumiaux, C., Lorenzo, S., Sant'Ovaia, H., Sizaret, S., Thibault, A., and Wissocq, A.: ERA-MIN2 AUREOLE project : tArgeting eU cRitical mEtals (Sb, W) and predictibility of Sb-As-Hg envirOnmentaL issuEs, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17873, https://doi.org/10.5194/egusphere-egu2020-17873, 2020.

Emerald is a high-value gemstone and a variety of the Beryl group that contains traces of Chromium and Vanadium which give them their characteristic green color.  Colombian emerald deposits have been found within two main narrow belts both of them located in the Eastern Cordillera, one of the three main ranges that constitute the Colombian Andes along with the Central and Western Cordilleras.

Several authors (Kozlowski et al. 1998; Ottaway et al. 1994; Giuliani et al. 1993b) have established that the interaction between hydrothermal fluids and the emerald hosted black shales, leading into an intense albitization and carbonation of the host rocks with the depletion of many major and trace elements, resulting into the emerald mineralization along with the deposition of calcite, dolomite, pyrite, albite, quartz and rarely parasite (Giuliani et al.1995). However, the fluid-rock interaction has not been clearly explained and stablished for both productive and non-productive areas in order to provide a more useful guide for further emerald exploration.   

Inductively Coupled Plasma Atomic Mass Spectroscopy (ICP-AMS) along with X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM) data were obtained from unaltered and altered host rocks including siliceous black shales, carbonated black shales, limestones, and dolomitic limestones. The results were analyzed to establish the geochemical relationships between different lithologies and the occurrence or absence of emerald mineralization for the different emerald belts.

The concentration of major, trace and REE elements and particularly the of  Cr, V and Be in the host rocks and the distribution over the studied areas will provide a better understanding of whether those contents are sufficient not only for the formation of emeralds besides of the different minerals in paragenesis. The results of the ongoing results are expected to be used as a possible exploration tool in favor to identify the areas with low potential for emerald mineralization.

How to cite: Moreno Boada, G. D. and Song, S.-R.: Characterization of the fluid-rock interaction in the Colombian emerald deposits, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16525, https://doi.org/10.5194/egusphere-egu2020-16525, 2020.

Classification systems for corundum deposits have evolved over time and are based on different mineralogical and geological features. An enhanced classification for ruby deposits based on the geological environment, degree of metamorphism, styles of mineralization and the pressure-temperature conditions of formation is proposed :

Primary ruby deposits are subdivided into two types based on their geological environment of formation: (Type I) Tectonic magmatic-related, and (Type II) Tectonic metamorphic-related.

Type I is characterized by two sub-types: Type IA where xenocrysts or xenoliths of gem ruby of metamorphic origin are hosted by alkali basalts (Madagascar and others); and Type IB corresponding to xenocrysts of ruby in kimberlite (Democratic Republic of Congo).

Type II has two sub-types hosted either in metamorphic deposits sensu stricto (Type IIA) formed in the amphibolite to granulite facies, or metamorphic-metasomatic deposits (Type IIB) formed via high fluid-rock interaction and metasomatism:

- Sub-Type IIA₁ includes ruby in metamorphosed mafic and ultramafic rocks (M-UMR) as found at Montepuez (Mozambique) and Aappaluttoq (Greenland);

- Sub-Type IIA₂ concerns rubies in marble such those from the Mogok Stone Track (Myanmar), and from central and eastern Asia;

- Sub-Type IIB₁ corresponds to desilicated pegmatites i.e., plumasite in M-UMR as in the Rockland mine (Kenya) or Polar Urals (Russia);

- Sub-Type IIB₂ is characterized by ruby in shear zone-related or fold hinge-controlled deposits in different substrata, mainly ruby-bearing Mg-Cr-biotite schist (metamorphosed M-UMR) and marble. It includes the ruby occurrences of Zazafotsy (Madagascar), Kerala (southern India), Mahenge (Tanzania), and the Hokitika deposit (New-Zealand).

Secondary ruby deposits i.e., placers, are termed Tectonic sedimentary-related (Type III). These placers are hosted in sedimentary rocks (soil, rudite, arenite, silt) that formed due to   erosion, gravity, mechanical transport and sedimentation along slopes or basins related to neotectonic movements. These are divided in two main sub-types:

- Sub-Type IIIA i.e., gem placers in alkali basalt or kimberlite environments as in eastern Australia, central Madagascar, and the Democratic Republic of Congo;

- Sub-Type IIIB i.e., gem placers in metamorphic environments such as at Montepuez in Mozambique or the Mogok Stone Track in Myanmar.

- Sub-Type IIIC i.e., gem placers with ruby originating from multiple and unknown sources such as at Ilakaka (Madagascar), Tunduru and Songea (Tanzania).

How to cite: Gaston, G., Lee, G., Anthony, F., and Isabella, P.: Ruby deposits: origin and geological classification, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2547, https://doi.org/10.5194/egusphere-egu2020-2547, 2020.

Volcanoes in island arcs can undergo edifice evolution that includes submarine and subaerial volcanism. This provides a dynamic environment of magmatic heat and volatiles that drives hydrothermal fluid flow with potential inputs from sea and/or meteoric waters. This, in turn, can generate significant hydrothermal alteration that can result in economic deposits of industrial minerals such as bentonite and kaolinite. The island of Milos is Europe’s largest and actively mined calcium bentonite resource, with production capacities exceeding 400,000 tons per year. Here, we use the Milos island example to understand how magmatism, volcanic edifice evolution and hydrothermal activity interact to generate important bentonite mineralisation. We integrate field relationships of volcanic stratigraphy and alteration zones, with clay mineralogy (XRD), stable (S, O and H) isotope analysis and high precision geochronology (CA-ID-TIMS zircon U-Pb, and alunite Ar-Ar) to elucidate the timescales, thermal drivers and fluid components that lead to the development of a globally important bentonite resource.

A vertical transect through bentonite-altered volcanic stratigraphy indicates multiple magmatic pulses initiated at ca. 2.8 Ma with a submarine andesitic cryptodome and accompanying hyaloclastite carapace that display quenched and peperitic contacts. Cumulative volcanic and sub-volcanic processes occurred over ca. 170 kyrs, resulting in a volcanic pile exceeding 80 m. This period included an episode of magmatic quiescence and diatomite formation in a shallow submarine environment and is overlain by a silicic pyroclastic flow. In this upper unit, a pervasive alunite-kaolinite alteration assemblage was developed. Stable isotopic analyses of bentonite (> 85% montmorillonite) indicate a hydrothermal origin at around 125°C with the fluid being sourced from sea and meteoric waters. The timing of formation is defined by a maximum duration of ca. 170 kyrs, with clear geological evidence that a significant period of alteration occurred within <20 kyrs at ca. 2.64 Ma. Sulfur isotope analysis on alunite indicates a steaming ground origin that could be interpreted as the oxidised, shallower level counterpart to a boiling geothermal system linked to development of extensive bentonite. However, the timing of alunite can be clearly resolved to > 1 Ma after bentonite formation to 1.2 Ma, supporting a later overprint origin due to relatively recent steam heating of groundwater after emergence.

This study identifies new key parameters that have resulted in the formation of an economic-scale bentonite resource on the emergent island of Milos. In addition to the requisite appropriate protolith, we conclude that in an emergent volcanic arc setting the hydrology needed to form a bentonite deposit is not constrained to the marine environment and can be connected to emergent parts of the volcanic edifice. High precision geochronology indicates bentonite development happens on volcanic timescales (10 to 100 kyrs). A cumulative volcanic and sub-volcanic pile coeval with the formation of bentonite suggests multiple magmatic episodes over narrow timeframes provide and sustain the thermal driver for significant bentonite development. Once the volcanic edifice has completely emerged and developed a groundwater system, the steam heating of groundwater is deleterious to grade and results in the development of alunite-kaolinite overburden.

How to cite: Miles, A. J., Tapster, S. R., Naden, J., Kemp, S. J., Barfod, D. N., and Boyce, A. J.: Forming an economic industrial mineral resource in a volcanic arc environment: timescales, fluids and thermal drivers of Europe’s largest bentonite resource, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10002, https://doi.org/10.5194/egusphere-egu2020-10002, 2020.

Geochemical and mineralogical characteristics of beach sand sediments in southwestern Black Sea: An approach to heavy mineral placers  

 Hatice Nur Bayram (1*), Aslı Nur Uslu (1), Ali Erdem Bakkalbaşı (1), Demet Kiran Yildirim (1), Zeynep Doner (1), Ali Tugcan Unluer (1)

 (1) Istanbul Technical University, Faculty of Mines, Department of Geological Engineering, Istanbul, Turkey (*hnnurbayram@gmail.com)

Abstract:  

Coastal or beach placer deposits are enrichments of heavy minerals with significant metal content that have been mechanically formed. This work studies the geochemical and mineralogical characteristics of beach sand sediments of southwestern Black Sea, Turkey which cover approximately 20 km² area. The study area has 4 main geological units: Upper Cretaceous moderately-K kalkalkaline Istanbul volcanics, Oligocene Danismen Formation which is dominated by flood plain, marshy and lake environments, Upper Miocene-Pliocene Belgrad Formation which is dominated by terrestrial deposits, mostly gravel, sand and clay dominated and Quaternary formations which include sandy beaches, sand dunes and river alluvials.

A total of 8 beach sand samples were analyzed by X-ray Diffraction (XRD) and X-ray Fluorecance (XRF). Mineralogical compositions are mainly dominated by quartz, siderite, albite, calcite and minor amount of magnetite. Siderite-rich beach sands are observed in western part of the study area and mostly derived from Danismen Formation. Fe₂O₃ contents of this area are determined up to 40%.  On the other hand, in eastern part of the study area REE-Th-U content of beach sands are relatively higher than source rocks which is defined as a high-Al moderately-K kalkalkaline felsic rocks. The highest HFSE concentration were determined in -250+125µm fraction which consists of 16.5% of eastern beach sand. In this fraction LREE-Zr-U content rise drastically. It can be considered that REE-LREE contents is related with monazite minerals and U contents is related with zircon minerals, considering the monazite and zircon minerals are resistant to weathering and likely to occur in the orthomagmatic phase in the source volcanics.

Key words: Beach sand sediments; REE-Th-U; heavy minerals; southwestern of Black Sea; Turkey

How to cite: Bayram, H. N., Uslu, A. N., Bakkalbasi, A. E., Kiran Yildirim, D., Doner, Z., and Unluer, A. T.: Geochemical and mineralogical characteristics of beach sand sediments in southwestern Black Sea: An approach to heavy mineral placers , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9452, https://doi.org/10.5194/egusphere-egu2020-9452, 2020.

Organic matters, such as oil, kerogen, fossil resins have different chemical functional groups. The complexity of chemical functional groups derives from the many sources of original contributing organic matter and long-term chemical and physical changes over geologic time. Fourier transform infrared spectrometer attenuated total reflectance (FTIR-ATR) can quantify the abundance of chemical functional groups and is a sensitive, high resolution and non-destructive analytical technique. The aim of this study was to characterize the spectral behavior and chemical structure of organic matters. In order to correlate organic matters of different types with its infrared spectra. The results show that FTIR-ATR spectra of oil contain intense aliphatic C-H stretching vibration in 2960 cm^-1,2925 cm^-1,2850 cm^-1 region relative to the C–H (CH₃) scissoring vibration at 1470 cm^-1 and C=C aromatic ring stretching vibration at 1640 cm^-1. We apply FTIR-ATR analyses for evaluating oil potential of kerogens. The longest aliphatic chains having the least amount of branching testifying to the highest oil generating potential. The similar locality of fossil resins has a similar chemical vibration ratio of C-H stretching (2925 cm^-1,2850 cm^-1) and C-H scissoring (1470 cm^-1). In consequence, the analysis providing a rapid means of assessing organic matters and oil potential, and it can also rapidly identification the botanical origin of fossil resins.

How to cite: Chen, Y. Y. and Chang, Y. J.: Application of ATR-FTIR spectroscopy for the identification of chemical functional groups in kerogens and fossil resins., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9981, https://doi.org/10.5194/egusphere-egu2020-9981, 2020.

With the development of QEM*SEM, the first automated scanning electron microscopy (ASEM) system, by CSIRO in the 1970s, mineral and texture quantification in the extraction industries was revolutionised. Since then, several systems have emerged (QEMSCAN, MLA, Mineralogic, TIMA, AMICS, INCA-mineral) that now find widespread application not only in the industry but also in science. The popularity of these systems is owed to their ability to rapidly and reliably quantify the mineralogy and textures in a variety of sample types including polished rock samples, thin sections and epoxy mounts of both whole and particulate samples. However, despite their apparent automatization, to guarantee high quality data and reliable results, a key role falls to the operator. It is through a mineral database that the raw data collected by EDS-detectors is converted into quantitative mineralogical data, and the database is adjusted by the operator on a case by case basis.

In this study we qualitatively compare analyses of the same sample at two different QEMSCAN labs, Camborne School of Mines (CSM) in the UK and Boliden AB in Sweden, to highlight differences in their approach towards analysis and set-up of the database, and the consequences this has for the results. Furthermore, through modification of the database used at Boliden AB, several methods of how the results can be influenced are demonstrated.

The selected sample is a polished thin section of mineralised vein from a drill core from the Liikavaara East Cu-(W-Au) deposit in northern Sweden. The sample contains massive pyrite and pyrrhotite associated with quartz, silicates, and fine-grained clusters of carbonates and Fe-oxides. Chalcopyrite fills cracks in pyrite. Some sphalerite and scheelite are observed as well as traces of cassiterite, molybdenite, and Au-, Ag-, Bi-, and Te-minerals.

Compared to the analysis at CSM, the analysis at Boliden AB showed an overestimation of the chalcopyrite content, limited differentiation of gangue phases, and problems with identification of phases at scan resolution (~5 µm). These differences could subsequently be reduced through editing of the database.

Application of a software-tool called the ‘boundary-phase processor’  was used to correct erroneous mineral classifications resulting from mixed signals at grain boundaries, which had caused pyrite grains to show a false coating of chalcopyrite. Gangue phases were differentiated through subdivision of phase-categories, although for higher accuracy comparison with standards and fine-tuning of mineral-entries in the database would be necessary. Element-filters in the database allowed identification of phases of specific elements, e.g. Au, at or below scan resolution despite mixed signals with the surrounding phases.

While data from both analyses was generally similar, the inter-lab comparison clearly demonstrated that more detailed information could be attained with ASEM systems through optimisation of the database. In the mining industry, a loss in the level of detail is often accepted in favour of time spent on data processing. However, particularly the characterisation and quantification of complex ores and critical metals, which often occur only in traces and fine grain sizes in ore deposits, require a high level of detail to allow efficient processing of the ore.

How to cite: Warlo, M., Wanhainen, C., Bark, G., Butcher, A. R., McElroy, I., Brising, D., and Rollinson, G. K.: Emphasizing the importance of the expert user and a case-specific mineral database in automated quantitative mineralogy techniques – An inter-lab comparative study using QEMSCAN, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6392, https://doi.org/10.5194/egusphere-egu2020-6392, 2020.

Every mining operations is followed by a beneficiation process aimed to deliver quality material to the transformation industry. Mainly, in mineral processing comminution and grinding of extracted ore, are crucial operations for the following separation steps in order to obtain valuable minerals from gangue.

Comminution is the most energy consuming phase and the quality of the results is strictly related to the characteristic of the material under treatment.

A preliminary study has been performed in order to understand the crushing behaviour of a mixed sulphide ore, containing galena and sphalerite, and the distribution of the two target minerals among the different sized products of the process.

Ore samples have been examined and characterized by means of thin sections observation and SEM analyses for the determination of the free grain size, while XRD quantitative analyses have been performed for the definition of the grades.

The selected crushing circuit comprises lab-scale impact crusher, jaw crusher, disk mill and rod mill. For each stage of the process products below the free grain size threshold have been collected and particle size analyses have been carried out.

Comminution products were divided in dimensional classes suitable for flotation separation, ranging between 0.250 and 0.075mm and XRD analyses showed a variable mineral grade distribution varying with the reduction in dimension of the products.

This important trend should be considered for further investigation related to an efficient froth flotation separation.

How to cite: Baldassarre, G. and Baietto, O.: Comminution effects on mineral grade distribution, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8624, https://doi.org/10.5194/egusphere-egu2020-8624, 2020.