GMPV5.2

The timing and degree of immiscible sulfide precipitation in a magma effectively controls the formation of magmatic sulfide deposits and the budget of degassing sulfur species in volcanic systems. Besides the absolute sulfur (S) content, sulfide precipitation is strongly affected by the sulfur content at sulfide saturation (SCSS) in the host silicate melt. Assimilation of S-rich wall-rocks, such as black shales, effectively increases the S content in the magma, while simultaneously lowering the SCSS. Accordingly, assimilation has been identified as the most important process in the formation of many economically significant magmatic base metal sulfide deposit, especially in continental tectonic settings. Detailed understanding of the relation between wall-rock assimilation and sulfide saturation requires accurate thermodynamic models for open magmatic systems experiencing assimilation-fractional crystallization (AFC).

The Magma Chamber Simulator (MCS) is currently the only geochemical modeling software that considers the thermodynamic phase equilibria in open magmatic systems involving magma and wall-rock (and recharge) subsystems. We utilized the MCS to explore how assimilation affects the SCSS and S content of the magma. With the current lack of thermodynamic data for sulfides, we tentatively modeled S as a trace element and varied its compatibility to wall-rock in the different models. For a case study, we chose the mafic layered intrusions of Duluth Complex, Minnesota, which host some of the largest Cu-Ni sulfide deposits in the world. Assimilation of the adjacent black shale has been established as the main source for S in the deposits.

Our MCS models show in detail how continuous assimilation of the black shale lowers the SCSS of the melt. Partial melt from the black shale enriches the magma in SiO₂, Al₂O₃, K₂O, and H₂O, while depleting FeO, MgO, CaO, and Na₂O, which causes a first order decrease in the SCSS. The compositional change also replaces troctolitic cumulates (plagioclase, olivine ± clinopyroxene) with norite (plagioclase and orthopyroxene), which leads to more pronounced FeO depletion in the melt, further lowering the SCSS. On the other hand, the assimilated partial melt also increases the melt mass in the magma subsystem, which counteracts the S enrichment. Accordingly, in the model where S is compatible to the wall-rock residual, the degree of sulfide saturation only slightly increases relative to the same magma experiencing FC without assimilation.

More than half of the wall-rock S must partition to the assimilated partial melt in order to meet the S isotopic criteria of the modeled Cu-Ni-deposits. The main stage of sulfide precipitation is associated with ~30 wt.% crystallization of the assimilating host magma. The proportion of sulfides relative to silicates in these models is smaller than observed in the Duluth Complex deposits, which underlines the role of dynamic processes in concentrating sulfides from the silicate magma.

How to cite: Virtanen, V., Heinonen, J., Barber, N., and Molnár, F.: Modeling the sulfide saturation in continuously assimilating magmatic systems with the Magma Chamber Simulator, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7903, https://doi.org/10.5194/egusphere-egu21-7903, 2021.

Iron oxide-apatite (IOA) deposits are an important source of iron ore based on the modal abundance of magnetite > 90 vol.%. Further interest is generated due to the high variability of apatite and hematite in some of these ores. The origin of the so-called Kiruna-type deposits has been subject to controversy for more than a century. Models range from a purely magmatic origin to ore-forming processes that involve variable stages of hydrothermal fluid involvement to a not widely accepted sedimentary-exhalative origin. In contribution of understanding ore-forming processes of this deposit type, we performed mineral chemistry and trace element analyses on samples from the Per Geijer deposits. They account for the lesser studied deposits in the Kiruna district of northern Sweden. A comprehensive mineral-chemical dataset of magnetite and hematite obtained by electron microprobe analysis (EPMA) and LA-ICP-MS from representative drill core samples is presented. Magnetite and four different types of hematite constitute the massive orebodies: Primary and pristine magnetite with moderate to high concentrations of Ti (∼61–2180 ppm), Ni (∼11–480 ppm), Co (∼5–300 ppm) and V (∼553–1831 ppm) indicate a magmatic origin for magnetite. Hematite type I appears as a replacement of magnetite with high Ti (∼15,700–42,300 ppm), relatively constant V (∼1460–2160 ppm) and moderate Sn (∼29–105 ppm) concentrations. Moderate and variable Ti (∼369–12,490 ppm) and low Sn (∼1.4–19 ppm) concentrations are representative for hematite type II. Hematite type III has lowest Ti (∼99–1250 ppm) concentrations. Significantly high Ti concentrations (∼12,100–78,700 ppm), low V (∼132–381 ppm) and high Sn (∼129–456 ppm) concentrations account for type IV. The presence of fluorapatite and disseminated pyrite with high Co:Ni ratios (> 1–10) in massive magnetite ores are consistent with a high temperature (∼ 800°C) genesis for the deposit. The different and abundant types of hematite state subsequent hydrothermal events.

How to cite: Krolop, P., Niiranen, K., Gilbricht, S., Schulz, B., Oelze, M., and Seifert, T.: Trace element geochemistry of iron oxides from the Per Geijer apatite iron ores in the Kiruna district, northern Sweden: Implications for ore genesis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1987, https://doi.org/10.5194/egusphere-egu21-1987, 2021.

Voia deposit belongs to the Săcărâmb-Cetraș-Cordurea Miocene volcano-tectonic alignment of the South Apuseni Mountains, Romania. This large volcanic complex represents a Sarmatian-Pannonian magmatic-hydrothemal mega-system of around 5 km² with an estimated 3–4 Ma time-space evolution, consisting of seven andesitic volcanic structures grouped in a circle, three subvolcanic andesite-quartz porphyry microdiorite and associated porphyry Cu-Au(Mo), pyrite Ca-Mg skarns and epithermal Au-Ag-Pb-Zn-Cu mineralizations.

The mineral assemblages of alteration and mineralization processes belong to several mineralized zones on a vertical scale, according to sampling evidence and laboratory studies. HS products are found in the upper part of the structure (300-500 m), with dominant advanced and intermediate argillic alterations and sulfide-sulfate gold-poor veins (pyrite, marcasite, base metal sulfides, Fe-Ti oxides, vuggy quartz, alunite, gypsum, anhydrite). Within the 500-1200 m depth, the HS mineral assemblages gradually decrease in favor of IS and LS products. It is characterized by the coexistence of gold-rich LS assemblage (native gold, base metal sulfide, adularia, sericite-illite, chlorite, carbonates ± anhydrite veins), with the IS assemblage (iron oxides, chalcopyrite, pyrite, quartz, anhydrite). These assemblages overprint the HS mineral associations, resulting in a transition zone characterized by gold - pyrite - chalcopyrite - iron oxides - quartz - anhydrite mineral assemblage characteristic for HS and native gold - pyrite - base metal sulfides - carbonates - quartz mineral assemblage corresponding to IS+LS type.

Gold is present in all of the identified mineralization forms: porphyry-epithermal Cu-Au, epi-mesothermal carbonate veins with gold - base metal sulfides, quartz veins with pyrite - chalcopyrite - magnetite ± hematite ± anhydrite, anhydrite veins with base metal sulfides and sulfosalts, anhydrite veins with pyrite - anhydrite ± quartz, vuggy quartz (silica residue) with gold-poor pyrite veins and impregnations in porphyry systems.

Drilling core samples revealed that in Voia deposit, gold is concentrated in chalcopyrite (drills no. 7, 19, 37) along with pyrite - magnetite - hematite - quartz assemblage from the late potassic stage. The major amount of gold associated with chalcopyrite tends to be mainly submicroscopic. Pyrite from anhydrite veins of the early potassic stage ± phyllic alteration is relatively poor in gold (drills no. 1-6, 8-14). However, the highest gold contents are present in pentagonal dodecahedron pyrites (drills no. 33, 38, 39) of pyrite-chalcopyrite-magnetite ± hematite-quartz assemblage from late potassic stage ± phyllic alteration. Pyrite associated with magnetite from anhydrite veins tends to be poor in gold (drills no. 8, 11, 15, 28, 29). A carbonate vein containing gold-bearing base metal sulfides that was intercepted at 960,00-960,30m depth by drill no. 17 is one of the richest in gold.

Native gold occurs as fine inclusions in ore minerals (5-20 μm). Large irregular grains of native gold (>50 μm) appear at mineral boundaries and along the fissures. The gold color is bright yellow and has a measured Au:Ag ratio of 5:1, suggesting that native gold has been formed at a relatively high temperature.

Acknowledgments: This work was supported by two Romanian Ministry of Research and Innovation grants: PN-III-P4-ID-PCCF-2016-4-0014 and PN-III-P1-1.2-PCCDI-2017-0346/29.

How to cite: Iatan, E.-L.: The occurrence of gold in Voia deposit, South Apuseni Mountains, Romania, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4813, https://doi.org/10.5194/egusphere-egu21-4813, 2021.

Magmatic-hydrothermal gold deposits form clusters in the Earth’s crust and are heterogeneously distributed within lithospheric blocks. A global assessment of whole-rock gold abundances in mantle lithologies worldwide indicates that Au concentrations increase with increasing fertility of mantle peridotites, with median Au contents ranging from 0.50 ppb in dunites, 1.00 ppb in harzburgites, and up to 1.26 ppb in lherzolites. Of particular interest are those volumes of fertile Subcontinental Lithospheric Mantle (SCLM) veined by pyroxenites and wehrlites, usually the Au-richest lithologies in the mantle as they have 2.05 ppb median Au concentrations. Partial melting of SCLM domains endowed in gold seems to play a key role in the genesis of gold-enriched magmas parental to magmatic-hydrothermal gold deposits in continental arc settings. The mineralogical expressions of gold inventory in such fertile mantle rocks are accessory Ni-Fe-Cu sulfides and discrete micron-to-nano-sized Au mineral particles that control the extraction and transport of gold in the mantle. Mantle xenoliths from the Neogene Volcanic Province (NVP) of southeast Spain represent an excellent example of SCLM refertilized by gold-sulfide-rich silicate melts underlying a gold metallogenic province. Here we present mineralogical and compositional data of sulfides in mantle xenoliths from this area (Tallante volcanic center), which are anomalously rich in gold (up to 46 ppm) compared to sulfides from SCLM not associated with Au-metallogenic provinces. We propose that these gold-rich, fertile mantle sources may have melted during the Cenozoic evolution of the westernmost Mediterranean subduction system and fed the ore-productive volcanic activity in southeast Spain.

How to cite: Schettino, E., Marchesi, C., González-Jiménez, J. M., Saunders, E., Hidas, K., Gervilla, F., and Garrido, C. J.: Gold fingerprint of the SCLM beneath a metallogenic province, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11150, https://doi.org/10.5194/egusphere-egu21-11150, 2021.

Vladimirskoe gold-rare metal deposits are located in the Urik-Kitoiskaya gold zone, at the edges of the Neoarchean age Gargan microcontinent, in the southeastern part of the Eastern Sayan. Gold mineralization is localized in sheared, beresitised mineralized zones among granite gneiss of the Gargan Group (NARg). The width of the zones is 3-10 m and the length is up to 800 m. The material composition of the ores is sulfide-carbonate-quartz. The main ore minerals are pyrite, chalcopyrite, pyrrhotite, galena, sphalerite, as well as tellurides and sulfosalts of silver, lead, and bismuth. The main minerals at the deposit are gold, associated - silver, and bismuth, associated with sulfide mineralization. Average gold grades in ores are 7-12 g / t.

Mineralized ore zones are associated with faults, and are often localized at their intersection with dike complexes. Several fault systems are identified in the deposit. The first-order fault system is a right-lateral dip-slip with a submeridional strike. The second-order system has a northwest strike and represents zones of viscous faults, expressed by zones of cleavage, beresitisation, silicification, and sulfidization, which are associated with gold mineralization.

There are two types of dike complexes within the region. The first dike complex of the barun-holba subvolcanic complex (O-S) has basic composition. Dikes are widespread throughout the entire area and are characterized by diabase porphyrites, metabasalts, and more rarely, basaltic andesite porphyrites. The rocks have a porphyry structure with phenocrysts (1-3 cm) characterized by plagioclase, altered to form epidote and muscovite. Large porphyry segregations up to 10 cm, bearing traces of deformation processes are observed in some cases. The groundmass has a fine-grained, microlepidogranoblastic structure and is composed of a secondary epidote-chlorite-albite aggregate.

The second dike complex is less pronounced and is characterized by felsic dikes belonging to the Early Paleozoic Holba complex. It is located in the southeastern part of the region and is characterized by granite-porphyries, leucocratic pegmatoid granites, and dacites. Dikes of felsic composition have a felsic structure caused by microliths of albitised plagioclase, biotite, and secondary minerals (chlorite, epidote, amphibole, calcite).

Dikes and dike belts are the ore-controlling structures of gold mineralization. In intersecting zones of a northwestern strike, gold mineralization is concentrated near dikes and gradually fades away as we move from them. The greatest development of mineralized zones and the associated quartz-vein ore mineralization can be observed at the intersection of fault zones with dikes. In this case, ore columns with a thickness of 20-50 m formed, extending to a depth of 3 km. Vladimirskoe deposits belong to vein-dike ore-magmatic systems, their source of ore matter is of deep origin.

This work is supported by RFBR grants: No. 19-05-00764 and the Russian Ministry of Education and Science. 

References:

Gordienko I.V. et al., // Geology Ore Deposits. 2016. V. 58, № 5, P. 405-429.

Seminsky Zh. V. et al. // Proceedings of the Siberian Branch of the Section of Earth Sciences of the Russian Academy of Sciences. T. 45, N. 2. 2014. P. 19-34.

How to cite: Nharara, B., Airiyants, E., Kiseleva, O., Belyanin, D., Roshchektaev, P., and Zhmodik, S.: Ore-controlling dike complexes of the gold-rare metal deposit Vladimirskoe (Eastern Sayan), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14847, https://doi.org/10.5194/egusphere-egu21-14847, 2021.

Europe´s major Sn and W resources are hosted by magmatic-hydrothermal ore deposits of the Variscan Belt: e.g. in Cornwall, the Erzgebirge, the Iberian Massif, and the French Massif Central. In the Erzgebirge, several major skarn bodies are located in the Schwarzenberg district (12 x 15 km). Although recent geochronological data relates (skarn) ore-formation to late- and post-orogenic magmatic-hydrothermal activity, details on the nature and duration of mineralization events remain insufficiently understood.

In this study we present innovative in-situ LA-ICP-MS U-Pb geochronology of garnet from several skarn prospects in the Schwarzenberg district, which is complemented with available geochronological data on intrusions and mineralization in order to constrain the timing of skarn formation within the Variscan orogenic cycle.

Eighteen garnet dates range from 338.2 ± 2.5 to 294 ± 8.3 Ma. Associated errors are in the range of 2.5 to 8.4 Ma, but generally tend to be <7 Ma. The oldest ages (338-331 Ma, stage I) are related to metasomatic garnets of the Globenstein skarn (n=5) – a skarn that is exceptionally enriched in W compared to the other skarn prospects in the same district. Conversely, the other skarns (Antonsthal, Breitenbrunn, Hämmerlein) are younger and range from 327 to 313 Ma (stage II) and 304 to 294 Ma (stage III), respectively. Stage I and II garnets lie within the range of available zircon ages of major intrusive bodies in this area (Aue-Schwarzenberg granite suite: 334-322 Ma; Eibenstock granite: 326-311 Ma). The third stage, in contrast, does not overlap with the age of any known granite intrusions in the Schwarzenberg district. However, it coincides with widespread early Permian volcanic rocks, which presumably have intrusive roots that are not yet exposed in the Erzgebirge region.

The distribution of garnet ages implies that skarn formation occurred episodically during the ~45 Ma life-time of the Variscan orogen, with the onset of magmatic-hydrothermal activity occurring significantly earlier than previously assumed – at 338 Ma, immediately after the peak of regional metamorphism. Tin and W deposits (skarn, greisen and vein-type) seem to have formed episodically over the entire 45 Ma orogenic cycle of the Erzgebirge – this is consistent with the age range of available geochronological data related to magmatic-hydrothermal ore deposits from other internal parts of the European Variscan Belt.

How to cite: Reinhardt, N., Gerdes, A., Beranoaguirre, A., Frenzel, M., Meinert, L. D., Gutzmer, J., and Burisch, M.: Constraining the time-span of magmatic-hydrothermal activity in the Variscan Orogenic Belt – U-Pb geochronology of skarn-related garnet from the Schwarzenberg district, Erzgebirge, Germany, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1584, https://doi.org/10.5194/egusphere-egu21-1584, 2021.

Hydrothermal Ag-Bi-Co-Ni-As±U (five-element) veins are particularly prevalent across Central Europe, where this type of mineralization has been mined throughout the ages for its high-grade resources of Ag, Co, Ni, and U. The timing and the detailed geodynamic setting in which this style of mineralization formed remains, however, insufficiently understood due to the limited amount of geochronological data. In this contribution, we report the results of innovative LA-ICP-MS U-Pb geochronology on the carbonate gangue of Ag-Bi-Co-Ni-As±U mineralization from six districts in the Erzgebirge/Krušné Hory metallogenic province of Germany and the Czech Republic, with the goal to constrain the timing of ore formation in the context of Central Europe's geodynamic framework.

In-situ U-Pb ages of twelve samples, including dolomite-ankerite, calcite, and siderite cogenetic with Co-Ni-Fe-arsenides, range from 129.4 ± 8.2 to 85.93 ± 3.4 Ma. The ages of Ag-Bi-Co-Ni-As±U and fluorite-barite-Pb-Zn veins from the same occurrence (Annaberg-Buchholz district) overlap each other, suggesting that these two styles of mineralization are genetically related and may form coevally. The compilation of geochronological data from other Ag-Bi-Co-Ni-As±U occurrences in Europe suggests that the origin of this style of mineralization in Central Europe can be related to continental rifting associated with the Mesozoic opening of the Atlantic and/or the Alpine Tethys (200-100 Ma). This provides for the first time evidence for the formation of Ag-Bi-Co-Ni-As±U vein mineralization across Central Europe in response to continental rifting.

How to cite: Guilcher, M., Albert, R., Gerdes, A., Gutzmer, J., and Burisch, M.: LA-ICP-MS U-Pb geochronology of carbonates from Ag-Bi-Co-Ni-As±U veins in the Erzgebirge (Germany and Czech Republic): New insights into the timing of mineralization, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3156, https://doi.org/10.5194/egusphere-egu21-3156, 2021.

The origin of gold nuggets (Au‐Ag alloys) is not completely understood. They crop out in placer deposits, potentially derived from a primary source (hydrothermal/magmatic). Meteorization, erosion and transport of primary gold deposits result in the liberation of a variety of particle size. Recent investigations suggest that both primary and secondary microstructural features may be preserved and could be related to deformation during transport, recrystallization and primary formation. Besides, the contribution of biological mechanisms (biomineralization) may have played an important role during secondary growth in some nuggets. In many cases, there is no clear evidence to distinguish between supergenic and hypogenic gold, so texture information could be excellent information to constrain the origin. Besides, it has been demonstrated that crystallography controls the de‐alloying processes in gold nuggets. This mechanism, that transforms the primary Au–Ag alloys into pure gold by preferential dissolution of Ag along crystal boundaries, could be determined by variations on texture, a factor never explored before, which may explain the dispersion in de‐alloying values in the same deposit.

In this case we have explored a selection of gold nuggets collected in the W sector of the Iberian Massif (Spain), representing the principal morphological types. As a non-destructive technique neutron diffraction appears as the technique of choice in this case. Beside, neutrons absorption is very low so that large samples could be investigated. Samples were analyzed in transmission at ILL (Grenoble) for texture. Quantitative texture and gold crystallinity was calculated using Rietveld method as implemented in Maud software (EWIMV). Mono- and polycrystalline nuggets and alloy composition were clearly identified in each particle with this technique. Our results show a close correlation between the morphology (i.e. transport length) of the particle and the crystallographic results, particularly for fibrous and discoid shapes (i.e. Zingg, Corey shape factor), what could be used to develop better transport models (distance-to-bedrock sources) and understand multisource gold placer assemblages. 

How to cite: Gómez-Barreiro, J., Barrios-Sánchez, S., Compaña Prieto, J. M., Morales Sánchez-Migallón, J., dos Santos Alves, K., Tettamanti, M., and Puente Orench, I.: Quantitative texture analysis of alluvial gold: primary and secondary signatures, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15930, https://doi.org/10.5194/egusphere-egu21-15930, 2021.

In this contribution we have investigated the Fresnedoso Quaternary gold placer (Western Spain), analyzing the morphotextural and microchemical evolution of gold particles. The statistical analysis has revealed the presence of two populations of particles being consistent with primary sources situated at a distal [20 - 50 km] and a proximal [2.5 - 10 km] range. The gold morphology and chemistry point to a recycling (and potentially undiscovered) Tertiary paleoplacers. The discovery of primary laminar morphologies points to lode deposits in small-flat veins hosted in Precambrian metasediments (Schist Greywacke Complex). All these findings suggest that the Fresnedoso gold deposit is formed by mono and polycyclic particles. We have tested previous transport distance vs Flattening indexes (CFI, Shilo) models resulting in useful framework for exploration of undiscovered ores, even with a small sample dimension. Chemical analysis of the different gold morphologies depicted that the Fresnedoso gold is a AuAg bimetallic alloy. Three groups were identified based on the texture and composition of the gold particles: Type 1 (Au1= Au89-94Ag11-6), Type 2 (Au2= Au99 Ag1) and Type 3 (Au3~ Au >99). Particle's cores (gold Type 1) show a compositional range that could be interpreted as differences in primary sources, spatial dispersion of sources or the actuation of secondary processes, probably in an orogenic gold context. Microchemical heterogeneity in the particles is probably due to secondary processes. A conceptual model has been elaborated to explain particle's microchemical domains represented by gold Type 2 (rim) and Type 3 (micro-aggregates) as the result of two different de-alloying stages: A) initial Ag-leaching at the rim and/or through microcracks and grainboundaries (Type 2), B) Total reset of the primary chemical fingerprint, with porous microtexture and the precipitation of gold with iron oxyhydroxides and clays (Type 3). This model suggests a silver de-alloying mechanism favored in a chlorine-iron-rich environment as in the case of laterites. Deformation and eventually recrystallization mechanisms associated with the fluvial transport (mechanical cold-work), cooperated in the evolution of the particles (Dos Santos et al. 2020).

References 

Dos Santos Alves, K., Barrios Sánchez, S., Gómez Barreiro, J., Merinero Palomares,R. and Compaña Prieto, J.M. (2020). "Morphological and compositional analysis of alluvial gold: The Fresnedoso gold placer (Spain)." Ore Geology Reviews : 103489.

How to cite: Dos Santos Alves, K., Barrios Sánchez, S., Gómez Barreiro, J., Merinero Palomares, R., Pablo Lozano Fernández, R., and Manuel Compaña Prieto, J.: Primary and Secondary Gold Sources of Quaternary Placers of Western Spain: a Morphotextural and Compositional Analysis of the Fresnedoso Deposit., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12077, https://doi.org/10.5194/egusphere-egu21-12077, 2021.

Gold placers are abundant and intensively surveyed in western Iberia since antiquity. Three Cenozoic gold placers covering Neoproterozoic-Lower Paleozoic basement rocks have recently been revealed, which stand out for the number and size of the samples recovered: Salvatierra de Tormes (ST), Santibáñez el Alto (SA) and Casas de Don Pedro-Talarrubias (CSDP). To date, primary sources remain undiscovered. We have combined microchemical, inclusion analysis and morphology of gold nuggets to define the placer gold signature and its relationship with bedrock primary sources and infer mineralization styles. Coarse gold particles prevent secondary resetting of source signature and increase the chances to investigate mineral assemblages. Nuggets morphology analysis have reveled that ST and SA deposit are fluvial "trunk" placers, while CSDP represents an autochthon or colluvial placer type. Four different types of gold have been defined in nuggets: core gold (T1), rim gold (T2) fine grained gold in Fe-oxyhydroxides aggregates (T3) and "mustard" gold (Au+Sb-Pb-Fe-oxides) (T4).

Based on those categories we have explored primary and secondary signatures in the deposits. Lode signature is observed in the core of nuggets (T1) with a fineness between 800 and 1000. Alloy composition ranges from binary (Au:Ag) in SA to ternary (Au:Ag:Cu) in ST and CSDP. Sulphides and sulfarsenides dominates inclusions association in ST, while Sb- and Sb-Pb-Fe phases appear in ST and CSDP respectively. CSDP primary gold shows a distinct Hg content. The identification of mineral phases non-compatible with supergene conditions in gold and textural remnants of annealing microstructures, point to an hypogenic origin of T1 in all deposits and coul be compatible with a mesothermal system (<400ºC) in which, CSDP represents the higher T and SA the lower T end. A hybrid hydrothermal-magmatic system is proposed.

Secondary signature is complex and reveals several stages. Older evidence of in-situ modification of primary gold was found in CSDP gold-bearing quart fragments, with pervasive alteration under oxidizing and alkaline conditions. This process liberated gold from T1 and primary phases (e.g., aurostibite), leading to the formation of auroatimonades and "mustard" gold (T4), showing a complex textural pattern. Gold particles were subsequently modified during fluvial transport and deposition through the interaction with fluids, which activated Ag-leaching processes, resulting in the development of gold-rich rims (T2). Partial dissolution and re-precipitation of gold in reduction conditions formed very fineness gold particles embedded in Fe oxy-hydroxides (T3).

How to cite: Barrios, S., Gómez Barreiro, J., Lozano Fernández, R. P., Merinero Palomares, R., Suárez Barrios, M., dos Santos Alves, K., Morales Sánchez-Migallón, J., and Malecki, J.: Tracing gold nuggets back to the source: a microchemical analysis of tertiary gold placers in Central Spain., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13358, https://doi.org/10.5194/egusphere-egu21-13358, 2021.

Mediterranean type karstic bauxite deposits are considered as the primary source for aluminum (Al) production in Europe. During the Al production, Gallium (Ga) is extracted from the so called Bayer-liquor during the processing of bauxite to alumina. Ga, a rare metal, is widely used in modern chemistry and electronic industry. During the past decades, the worldwide demand for Ga has been continuously increasing. In Turkey, karstic bauxite deposits are generally found with shallow marine carbonate rocks which were deposited during Mesozoic period and located in Tauride Carbonate platform. Most of these karstic bauxite deposits can be hosted considerable Ga enrichments, with other immobile elements such as rare earth elements (REE), titanium (Ti), lithium (Li), and iron (Fe). This work focuses on the revealing of the potential Ga enrichments in bauxides from different deposits of Turkey (Mortaş-Doğankuzu, Konya; Küçükkoraş, Karaman; Acıelma-Yoğunoluk, Kahramanmaraş bauxite deposits). Geochemical data of major and trace elements of studied bauxite deposits show that these deposits have significant Ga enrichments (up to 72.6 ppm), as well as the REE (up to 580 ppm), Ti (up to 1.8%), and Li (up to 428 ppm) enrichments. In addition, the Ga enrichments show strong positive correlation with heavy rare earth elements (HREE) and moderate positive correlation with Al, Fe, Ti, Li and Sn elements. In this context, it can be concluded that the most probable source for Ga is rock forming aluminosilicates of the source rock due to the substitution with Al³⁺ and Fe³⁺. During weathering process Ga exhibiting immobile behavior much like Al and Fe. Gallium is than incorporated into Al-bearing phases and thus enriched in the bauxite. Presence of Li content can be also interpreted as a contribution from micaceous source such as meta-carbonate rocks of Tauride platform. Moreover, geochemical association between Ga, Ti, Li, tin (Sn) and HREE can be explained by the redox and pH conditions causing other ions seperated from shallow environments.

How to cite: Bayram, H. N., Bakkalbasi, A. E., Doner, Z., Unluer, A. T., Kocaturk, H., Yıldırım, D., and Budakoğlu, M.: Tauride Carbonate Platform Bauxite Deposits (Turkey) as an Alternative Source for Gallium, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11122, https://doi.org/10.5194/egusphere-egu21-11122, 2021.