Porphyry-type ore deposits are the most important source of Cu and Mo for our society, while also providing significant amounts of Au and Ag, making the understanding of their formation crucial to the targeted exploration of these metals. Recent studies emphasize the importance of the timing and depth of fluid exsolution for controlling magmatic sulphide saturation and fluid-assisted ore metal and sulphur extraction from the magma, and thus the overall ore fertility of arc magmas. As emplacement depth is related to the pressure (P) and temperature (T) of the magmatic system, accurate constraints on the influence of P and T on the fluid/melt partition coefficients (Df/m) of Cu, Ag, Au and Mo are vital in understanding the genesis of porphyry deposits. To this end, experiments were conducted by equilibrating a synthetic rhyolite starting glass with S-free fluids containing 5.5 and 37 wt.% NaClEq chlorides at pressures of 150–700 MPa (corresponding to ~5–25 km depth) and temperatures of 750–950 °C. Experiments were performed using Au-Ag-Cu alloy capsules as a source of metals and the equilibrium fluid was entrapped as synthetic fluid inclusions in natural quartz fractured in-situ during experimental runs. Externally heated molybdenum-hafnium carbide pressure vessels were used for experiments up to P = 300 MPa, above which a piston cylinder apparatus was used. Results indicate a moderate decrease in Df/mCl with increasing T and a partitioning maximum at a P of about 400 MPa. Considering the ore metals, Cu, Ag, and Au partition coefficients decrease with increasing temperature, with the effect being greater at higher fluid salinity. Pressure has a weak effect on the partitioning of these metals at constant Cl concentration in the fluid phase and Df/m may display a maximum at ~400 MPa. As for Mo, temperature has a negligible effect on Df/mMo while increasing pressure increases Mo partitioning into the fluid, but only at low salinities. The results suggest that lower temperatures and moderate pressures (~400 MPa or ~12 km depth) are the most conducive to the generation of magmatic fluids with a high potential for porphyry ore generation. The new results serve as an important building block of semi-empirical models currently in development to predict the fluid/melt partition coefficients of porphyry ore metals in P-T-compositional space.
How to cite: Gennaro, I., Tsay, A., and Zajacz, Z.: Magma emplacement depth and magmatic-hydrothermal ore fertility: The effects of pressure and temperature on the fluid/melt partitioning of porphyry ore metals, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16557, https://doi.org/10.5194/egusphere-egu25-16557, 2025.
Hydrothermal minerals intimately associated with mineralization processes are pivotal in deciphering the genesis of porphyry deposits. A meticulous examination of these hydrothermal minerals serves to quantitatively delineate the progression of ore-forming hydrothermal fluids and to scrutinize the myriad factors influencing porphyry Cu-Mo mineralization. In this study, we employed a multifaceted approach encompassing mineral geochemistry, geochronology, and diffusion chronology to probe into the time scales of mineralization, as well as to characterize and trace the evolution of ore-forming fluids within the Yulong porphyry Cu-Mo deposits located in eastern Tibet.
Quartz extracted from hydrothermal veins displays cathodoluminescence (CL) images characterized by diverse brightness and textures. Trace element analyses reveal a robust correlation between the intensity of CL and the titanium (Ti) content within the quartz. This study takes advantage of diffusion chronology to determine time scales of multistage magma-related hydrothermal events. The pronounced Ti concentration gradients observed in CL images, in conjunction with Ti diffusion modeling for distinct quartz generations, suggest that the majority of mineralization at the Yulong deposit occurred within a relatively brief interval ranging from 880,000 to 16,000 years. The complex, multi-stage hydrothermal stockwork veins and the relatively short time scales indicate that fluid pulses at Yulong developed rapidly, within spans of tens of thousands of years. These research outcomes underscore that delineating the time scale of a singular mineralization pulse is instrumental in constructing a more precise chronological framework for porphyry deposits, thus facilitating the quantification of extensive metal enrichment processes. In comparison with other globally recognized giant porphyry deposits, this study identifies the mineralization rate, magma injection rate, and fluid flux as critical determinants influencing the magnitude of porphyry mineralization.
Hydrothermal rutile (TiO2), a common accessory mineral found in hydrothermal veins and alteration assemblages of porphyry deposits, offers significant insights into the characteristics of hydrothermal fluids. In the Yulong deposit, TiO2 polymorphs have been identified through Raman spectroscopy, textural analysis, and chemical characterization. Brookite and anatase pseudomorphs are indicative of low-temperature hydrothermal fluids that destabilize primary Ti-bearing minerals during argillic alteration processes. Rutile intergrown with sulfides in veins exhibits well-defined patchy and sector zoning, with notable tungsten enrichment in the backscattered bright patches and sector zones. The enrichment of tungsten is effectively facilitated by halogen-rich (F, Cl) aqueous fluids during the hydrothermal mineralization. Consequently, the chemical and isotopic compositions preserved in rutile provide comprehensive information that enhances our understanding of the hydrothermal fluids active during the formation of porphyry deposits. This enhanced understanding may potentially aid in delineating vectors that lead to the localization of porphyry deposits. Moreover, precise identification of TiO2 polymorphs is crucial for a deeper comprehension of hydrothermal processes, especially when employing rutile geochemistry as an indicator for mineralization.
How to cite: Chen, Q.: Mineralization and time scales of the Yulong porphyry Cu-Mo deposit in eastern Tibet, China: Insights derived from hydrothermal quartz and tungsten-bearing rutile, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2240, https://doi.org/10.5194/egusphere-egu25-2240, 2025.
The Kuh-e Janja porphyry Cu-Au deposit is located 60 km southeast of Nehbandan in southern Iran, within the northern part of the Sistan Suture Zone. Several distinct stockwork vein types are recognized, differing in morphology, vein mineralogy, and associated alteration type. Early biotite (EB) veins containing biotite and minor amounts of quartz, magnetite, and anhydrite form the earliest veins. They are crosscut by A veins that are typically several millimeters in thickness and associated with potassic alteration envelopes. The abundant A veins at Kuh-e Janja consist of Q1 quartz that shows textural evidence for extensive recrystallization. Primary oscillatory growth zoning is rarely preserved in Q1 grains. Fluid inclusions in the quartz have been affected by post-entrapment modification. The A veins are interpreted to have formed at high (≳500°C) temperatures at lithostatic pressures. AB veins contain euhedral Q2 quartz crystals that have grown perpendicular to the vein walls within vugs. Molybdenite occurs as ribbons in recrystallized Q1 and Q2 quartz or as an infill in open spaces between the euhedral Q2 quartz crystals. The euhedral Q2 quartz crystals show well-developed sector and oscillatory growth zoning and are characterized by hypersaline liquid-rich and coexisting vapor-rich fluid inclusions that were entrapped at temperatures below ~500°C at the transition from lithostatic to hydrostatic pressure conditions. The AB veins formed at conditions of K-feldspar stability. Zones of high Cu grades at Kuh-e Janja are typified by the presence of abundant hairline fractures coated by chalcopyrite, pyrite, and minor molybdenite. These C veins are surrounded by minor chlorite alteration of the host rocks and crosscut all earlier vein types. The contacts between the early Q1 and Q2 quartz grains and chalcopyrite are irregular in shape. Chalcopyrite crosscuts the primary oscillatory zoning of the Q2 quartz grains suggesting that sulfide deposition occurred under conditions of retrograde quartz solubility. Wallrock or hydrothermal biotite in contact with chalcopyrite is frequently chloritized. Vapor-like single-phase fluid inclusions occur along healed microfractures hosted by euhedral Q2 crystals that are in contact with chalcopyrite in C vein. As many of the fluid inclusions host small triangular opaque phases interpreted to be chalcopyrite, the vapor-like, near-critical density, single-phase fluid likely was the ore-forming fluid. Late D veins containing variable proportions of pyrite and quartz are surrounded by texturally destructive sericite alteration envelopes of the host rocks. Q3 quartz contains primary and secondary liquid-rich fluid inclusions entrapped at hydrostatic pressure conditions. Rare polymetallic E veins at Kuh-e Janja contain Q4 quartz, sphalerite, galena, and minor chalcopyrite. The study of the different vein types suggests that hypogene Cu mineralization at Kuh-e Janja occurred after potassic alteration of the host porphyry at temperatures close to the ductile-brittle transition. The mineralization formed from vapor-like, near-critical density, single-phase fluids along hairline fractures during their escape from lithostatic to hydrostatic conditions.
How to cite: Soleymani, M., Niroomand, S., Monecke, T., Reynolds, T. J., Rajabi, A., and Rajabpour, S.: Magmatic-Hydrothermal Evolution at the Kuh-e Janja Porphyry Cu-Au Deposit, Southeastern Iran: Relative Timing of Hypogene Cu Mineralization from Vapor-Like, Near-Critical Density, Single-Phase Fluids, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-141, https://doi.org/10.5194/egusphere-egu25-141, 2025.
Arc magmatic systems are thought to attain fluid saturation already at mid to lower crustal depths, and magmatic fluids may play an important role in transporting ore metals and sulfur within the magma reservoir system and from the magma to the site of ore deposition. Therefore, tracking the migration of magmatic fluids within such systems is important for understanding magmatic-hydrothermal ore genesis and volcanic degassing.
We developed new geochemical tools to track magma degassing at crustal depths, by experimentally determining the partition coefficients of chlorine, bromine and iodine between aqueous fluids and silicate melts. We investigated a large range of pressures (P=150–835 MPa), temperatures (T=800–1000 oC), fluid salinities (from ~3 to ~62 wt% NaCl equivalent) and silicate melt composition (basalt to rhyolite following the calc-alkaline and alkaline magmatic trends) using a vector approach (i.e. changing only one variable at the time). The experimental phase assemblages were contained in Au capsules and run in externally heated René 41 or Molybdenum-Hafnium Carbide pressure vessels and a piston cylinder apparatus depending on the experimental P and T. The composition of the run product glasses was determined by Electron Probe Microanalysis (major elements + Cl), and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (major elements + Cl, Br, I). The equilibrium fluid compositions were derived by mass balance calculation.
The results highlight that the fluid/melt partition coefficients (Df/m) of Cl, Br and I increase with increasing halide ion radius and increasing fluid salinity leading to a drop in the Br/Cl and I/Cl ratios in the silicate melt during progressive degassing. Therefore, halogen ratios such as Br/Cl and I/Cl are good tracers for magma degassing and fluid fluxing in relatively evolved magmas, where traditional proxies such as CO2/H2O ratios have limited usefulness. Moreover, these ratios can be used as a proxy to quantify the fraction of the initial Cl budget degassed from a magmatic system, which closely relates to the extraction of ore metals. Importantly, pressure has a strong effect on the Df/m of the three studied halogens, the extent of which depends on the fluid salinity. At low fluid salinities, all halogens increasingly partition into the fluid with increasing P up to 400-500 MPa and decreasing T; however, above 500 MPa their Df/m decreases over the entire fluid salinity range. This has important implications for ore metal transport in deep crustal magmatic fluids. Finally, the Df/mof all halogensrapidly drops as the silicate melt becomes more mafic. Model equations capable to predict Df/mhalogens in P-T-melt and fluid compositional space were constructed.
How to cite: Miranda, M., Tsay, A., and Zoltan, Z.: Halogens as a proxy for magma degassing at crustal depths, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9740, https://doi.org/10.5194/egusphere-egu25-9740, 2025.
Long-lived accretionary orogens like the Tasmanides of eastern Australia have typically undergone a series of compressional and extensional episodes with multiple magmatic and hydrothermal events that shape its rheological, compositional and metallogenic character. In the state of Victoria, the Western Lachlan Orogen (WLO) of the Tasmanides is home to one of the world’s largest gold provinces. Multi-million-ounce orogenic gold deposits of Ordovician age occur in the Bendigo and Stawell zones, whilst the oldest known gold mineralisation in the Melbourne Zone is Devonian with the largest deposits associated with a mafic to intermediate dyke swarm. Widespread Devonian magmatism in the WLO resulted in goldfields spatially associated with granites with some older orogenic gold deposits overprinted by Devonian magmatism (e.g. Maldon). This study, driven by the underexplored Tabberabbera Zone (potential long-strike extension of the Bendigo Zone according to the Lachlan Orocline model), addresses those challenges.
Eight gold deposits in the WLO of Victoria are revisited. Five are spatially associated with, and in the hornfels surrounding, the Devonian Beechworth and Yackandandah I-type granites in the northern Tabberabbera Zone (Barambogie, Twist Creek, Bon Accord, Homeward Bound and Happy Valley). Others include Haunted Stream near the Dead Bird Suite in the southern Tabberabbera Zone, Golden Mountain in the hornfels of the Devonian S-type Strathbogie Granite in the central Melbourne Zone and the classic orogenic style at Gill Reef in the world-class Bendigo Goldfield in the north central Bendigo Zone. A macro- to micro-scale approach is used, integrating micro-XRF MAIA mapping, automated mineralogy, EPMA-CL mapping, and apatite U-Pb geochronology.
At Golden Mountain, gold is disseminated in the cordierite-bearing Strathbogie Granite and hosted in fault structures in the surrounding hornfels with no Bi and Te identified. Gold mineralisation is hosted as free gold in quartz veins at Barambogie, Twist Creek and Bon Accord. These veins host apatite with U-Pb ages that are coeval with the Devonian intrusions. Occurrences of Bi and Te, lollingite, Ti in quartz and the thermal U-Pb reset of the detrital apatite suggest this gold mineralisation is intrusion-related. In contrast, at Haunted Stream, the abundance of sulfides, gold locked in pyrite and a lack of Bi and Te indicate an orogenic style. Apatite in quartz veins at Haunted Stream yield a Jurassic age suggesting reactivation of the nearby Haunted Stream Fault during the breakup of Gondwana. Apatite in low-temperature Al-rich quartz veins at Happy Valley and Gill Reef yield Triassic and Carboniferous ages respectively. Gold mineralisation at Happy Valley is not associated with the Yackandandah Granite. Instead, rare Triassic magmatism in eastern Victoria and the occurrence of weak Bi suggest a likely distal magmatic signature. At Gill Reef, the Carboniferous hydrothermal apatite may result from late stage magmatic-related activity of the Upper Devonian Harcourt Granodiorite. Apatite located in arsenopyrite-bearing stylolitic veinlets suggest a potential gold remobilisation/enrichment event during the emplacement of the intrusion, like the Maldon deposit. New U-Pb geochronology of apatite in quartz veins and the hornfels integrated with mineralogical observations have been crucial in unravelling the cryptic gold metallogeny of the WLO.
How to cite: Siégel, C., Kohan Pour, F., Cairns, C., McFarlane, H., Cayley, R., Pintér, Z., Verrall, M., MacRae, C., and Lewis, J.: Intrusion-related versus orogenic gold, Western Lachlan Orogen, Tasmanides, Australia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14565, https://doi.org/10.5194/egusphere-egu25-14565, 2025.
The Cu-Zn mineralization in the Kuzuluk (Sakarya) region has hosted within the tuffaceous rocks of the Eocene Yığılca formation along the fault zones in the Western Pontides. The study area is made up of the Permian-Triassic Sultaniye Metamorphites, Upper Cretaceous Abant formation, Early-Middle Eocene Çaycuma and Yığılca formations, and Pliocene Örencik formation. It is characterized by significant tectonic activity represented by dip-slip fault zones, particularly within the tuffaceous rocks of the Yığılca formation. The ore zone occurred within the fracture zone in the tuffaceous rocks of the Yığılca formation represented by an epigenetic mineralized vein-type structure including pyrite, chalcopyrite, sphalerite, bornite, quartz, and calcite. The geochemical studies indicated that this ore zone contains approximately 2620 ppm Cu and 1440 ppm Zn concentrated within the fracture zone. Carbonatization is the main hydrothermal alteration in the study area. To assess the sulfur origin in the mineralization, ten sulfide samples from pyrite and chalcopyrite minerals were analyzed for sulfur isotopes. Their δ34S data vary from +28.56 to +29.52 ‰, which shows that the enrichment is due to the vigorous interaction between hydrothermal fluids and sedimentary sulfate reserves. Additionally, this reflects the impact of hydrothermal fluid and organic matter dissolution in the area, in contrast to magmatic sulfur sources. Therefore, circulation of the hydrothermal fluids along fault zones played a crucial role in the formation of the ore zone, facilitating the precipitation of Cu-Zn minerals and gangue minerals (quartz and calcite). These findings suggest that the geological processes that lead to the formation of the Cu-Zn Kuzuluk mineralization contribute to clarifying hydrothermal mineralization within Western Pontides fault zones.
How to cite: Kaya, M.: Epigenetic Cu-Zn Mineralization in the Yığılca Formation Tuffs of Kuzuluk (Sakarya), Western Pontides, Turkey: Insights from Sulfur Isotope Analysis and Hydrothermal Processes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13609, https://doi.org/10.5194/egusphere-egu25-13609, 2025.
The trace-element geochemistry of sphalerite is commonly used as a proxy for the sulfur fugacity and temperature evolution of ore-forming fluids. In this study, in-situ laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of paragenetically well-constrained sphalerite crystals spanning the sequence of mineral deposition in the Aouli polymetallic Pb-Zn-Cu (Ag, Ni, Co, As) deposit, with indicated resources of 10 Mt of ore at an average grade of 5% Pb, 150–600 g/t Ag and 200–700 g/t Bi, were performed to track back the physico-chemical characteristics of the ore-forming fluids responsible for the deposition of Cu-Ag-Ni-Co-As-rich and Pb-Zn-rich ores. The sulfide/sulfosalt Pb-dominant mineralization consists of an array of open-space fillings of transtensional veins, veinlets, stockwork, and breccia veins. The host rocks of presumed Cambrian–Ordovician age comprise a variably deformed and weakly metamorphosed succession of interlayered low- to very-low-grade siliciclastic and volcaniclastic rocks with interbedded tuffs, and amphibolites. Several syntectonic to late tectonic granitoid batholiths and stocks (ca. 340–330 Ma), ranging from calc-alkaline to alkaline and metaluminous to peraluminous, as well as mafic rocks (gabbro-diorite) and cordierite-garnet anatectic granites, intrude the host rocks. The idealized paragenetic sequence includes an early pre-ore iron-sulfide-rich stage, followed by the main stage of Zn-Pb ore and the later Cu-Ag-Ni-Co-As-rich stage. Gangue minerals comprising quartz, fluorite, and barite were formed during the main ore mineralization stages. The trace element composition of sphalerite is used to compare the mineralization conditions between Pb-Zn-rich and Cu-Ag-Ni-Co-As-rich ores. Sphalerite typically occurs as greenish to brownish-colored, closely packed patches of anhedral to euhedral sphalerite crystals ranging from 100 μm to up to 5 cm in size, embedded in quartz ± fluorite ± barite. Based on paragenetic position, mineral color, textural features, and luminescence in CL alongside chemical compositions, three distinct generations of sphalerite referred to as Sp-1, Sp-2, and Sp-3 are recognized. Statistical analyses of the compositional data show systematic differences between the three generations of sphalerite. Compared to Sp-2 and Sp-3, Sp-1 shows high Co, Ga, and In concentrations, while Sb, As, Cu, Hg, Pb, Mn, and Ag concentrations are lower. Cu, Ga, Sb, and Mn concentrations of Sp-2 and Sp-3 display similar distribution trends. Conversely, Sp-3 relative to Sp-2 is enriched in As, Ag, and Hg but more depleted in Fe. Formation temperatures and sulfur fugacity estimated from the GGIMFis (Ga, Ge, In, Mn, and Fe in sphalerite) geothermometer and Fe contents in sphalerite indicate similar T and fS2 conditions for the Cu-Ag-rich and Pb-Zn-rich ores, with temperatures < 250 °C. More importantly, the evolutionary trend shown by the three generations of sphalerite which plot within the intermediate-sulfidation field along the “rock buffer” line, argues for a common origin for the Cu-rich and Zn-rich ores, and that the hydrothermal ore fluids interacted extensively with the enclosing host rocks.
How to cite: zaid, K., Bouabdellah, M., Frenzel, M., van Schijndel, V., Yans, J., and Belkacim, S.: LA-ICP-MS trace element geochemistry of sphalerite as a proxy to the origin of the polymetallic Aouli sulfide Pb-Zn-Cu (Ag, Ni, Co, As) deposit (Eastern Meseta, Morocco), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10562, https://doi.org/10.5194/egusphere-egu25-10562, 2025.
Volcanic arcs host complex marine magmatic-hydrothermal systems where polymetallic Au-rich seafloor massive sulfides (SMS) may form. In such geological setting, reconstructing the mineral system leading to ore formation is challenging due to the diversity of potential metal sources, mobilizing mechanisms (i.e. hydrothermal leaching of country rocks, magmatic degassing), fluids (magmatic or seawater-derived hydrothermal fluids) and precipitation mechanisms on and below the seafloor. A case-study of the Au-rich SMS at Kolumbo volcano (Greece) provides new insights on the source to sink processes leading to epithermal metals enrichment in volcanic arcs. The favorable geological setting of Kolumbo allows for a representative sampling of the different potential metal sources of the magmatic-hydrothermal system. The country rocks forming the stratigraphy below Kolumbo were sampled on the neighboring islands of Ios, Anafi and Thera, while volcanic rocks of Kolumbo allowed to reconstruct its magmatic evolution and associated metal mobilizing processes. Whole rock geochemistry coupled with petrography and numerical modelling reveals that despite early sulfide saturation, the magma remains fertile until reaching magmatic degassing. Metals are transferred from the magma to the hydrothermal system as exsolving fluids leach metals, either from the melt or by oxidizing magmatic sulfides, as indicated by occurrence of sulfide-volatile compounds in the volcanic rocks. By comparing the Pb isotope signature of the SMS minerals with the potential source rocks, we show that hydrothermal leaching of rhyolite is associated with pyrite formation in hydrothermal chimneys while transient input of magmatic fluids provides Ag, As, Au, Cu, Hg, Pb, Sb and Sn, leading to formation of galena and Sb-Pb sulfosalts. A major outcome of this holistic study of the Kolumbo volcano relates to metal mobilization mechanisms in magmatic-hydrothermal system. We show that formation and oxidation of sulfide-volatile compounds is leading to an efficient transfer of S and chalcophile metals from the magma to shallow hydrothermal systems. While this mechanism contributes to the formation of Au-rich SMS, it is likely also implicated in porphyry and epithermal deposits formation.
How to cite: Hector, S., Patten, C., Nomikou, P., Kilias, S., Peillod, A., and Kolb, J.: Source to sink overview of Au-rich SMS formation at Kolumbo volcano, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12222, https://doi.org/10.5194/egusphere-egu25-12222, 2025.
Water-rich magmatic systems are important for the formation of many magmatic hydrothermal ore deposits because degassing intrusions can provide both the heat and the chemical compounds needed for their formation. However, for different types of ore deposits, the processes and their complex interplay leading to mineral precipitation vary. Here, we use numerical simulations to investigate the thermal evolution of silicic magmatic systems similar to those hosting some of the largest Sn deposits. Detailed field and oxygen isotope studies suggest that these deposits can form due to convective mixing of hot magmatic fluids and meteoric water (e.g., Fekete et al., 2016). The timing and location of this fluid mixing as well as the long-term thermal evolution of large magmatic hydrothermal systems, however, has attracted surprisingly little attention (e.g., Large et al., 2021) and has mostly been investigated by either using purely conductive heat transfer approaches or by neglecting magmatic fluid production and degassing during crystallisation.
Here, we present 2D fluid-flow simulations for laccolith-shaped intrusions emplaced at 3 and 5 km depth to (1) explore the long-term hydrothermal evolution related to silicic magmatic systems, and (2) identify preferred conditions to form tin deposits (i.e., mixing of meteoric and magmatic water). The intrusion has dimensions of 20 km width and 1 km thickness and releases aqueous fluids during crystallisation.
We observe a significant temporal delay between the crystallisation of the magma chamber and the emergence of the hydrothermal system. While the intrusion solidifies completely within a few 103 to 104 years, the hydrothermal convection reaches its maximum extent after full solidification of the magma chamber. Importantly, the temporal delay is larger for intrusions emplaced at 5 km depth. This is because the lower rock permeability at greater depths limits fluid flow velocities and thus prevents significant advection. Fluid convection starts to establish once heat conduction provides sufficient heat to higher-permeability rocks at shallower depths. Due to the low rock permeability, a considerable amount of the magmatic fluids remains trapped in the crystallised intrusion.
For an emplacement depth of 3 km, significant mixing of magmatic and meteoric fluids can occur already during the early stages of degassing (< 10,000 years). Here, higher rock permeability allows for mixing of hot ascending magmatic fluids into meteoric water. In the case of deeper intrusions, the most significant mixing occurs at later stages of the convecting hydrothermal system (> 60,000 years), when downwards-flowing meteoric fluid slowly infiltrates into the crystallised intrusion and mixes with the trapped magmatic fluid.
Overall, we suggest that emplacement depth is a critical parameter controlling the location and timing of fluid mixing around laccolith-like intrusions and therefore potential tin precipitation mechanisms.
REFERENCES
Fekete, Sz. et al. 2016: Contrasting hydrological processes of meteoric water incursion during magmatic–hydrothermal ore deposition: An oxygen isotope study by ion microprobe, EPSL, 451, 263‒271.
Large, S. et al. 2021: Copper-mineralised porphyries sample the evolution of a large-volume silicic magma reservoir from rapid assembly to solidification, EPSL, 563, 116877.
How to cite: Krattiger, N., Köpping, J., and Driesner, T.: The long-term (hydro-)thermal evolution around laccolith-like intrusions with implications for tin deposit formation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13149, https://doi.org/10.5194/egusphere-egu25-13149, 2025.
The Variscides of Europe and northwestern Africa formed during the collision of the vast Peri-Gondwana shelf of Africa / Arabia with Laurussia eventually leading to the assembly of western Pangea. Late- to post-orogenic granites with Li and W mineralization were emplaced throughout the entire belt, but only complexes of the former Armorican spur (Kroner et al., 2013), i.e., Cornwall, the Erzgebirge and N-Iberia, host primary Sn mineralization of economic value. These deposits are related to late-orogenic high temperature metamorphism (N-Iberia, Erzgebirge) and to post-orogenic advective heat transfer from the mantle (Cornwall, Erzgebirge), respectively. Thus, it is not the tectonic setting of magmatism that controls the distribution of Sn deposits, but the protoliths (which formed long before supercontinent assembly) and the accretionary development before collision (Romer and Kroner, 2022). Common to all Gondwana-derived crustal fragments in the Variscan belt is the presence of voluminous, early Ordovician siliciclastic sedimentary units deposited on the Peri-Gondwana shelf during the breakup of Pannotia. These sediments represent deeply weathered continental sediments that have been redeposited from the interior of Gondwana to its margins (Romer and Kroner, 2016) and are slightly metal enriched (residual enrichment). The weathering is important as it affects the later melting behavior of these sedimentary rocks. The change from a passive to an active continental margin setting of the hyperextended Gondwana shelf results in the accretion and stacking of shelf sediments during the prolonged formation of Pangea. This tectonic accumulation locally resulted in metal redistribution within the former shelf sediments, leading to domains that are depleted or enriched. Such redistribution may lead to extreme Sn enrichments as in local metasedimentary sequences of the Erzgebirge (Bohemian Massif) that contain Sn-rich and cassiterite bearing peak metamorphic minerals, clearly showing prograde Sn enrichment. The distinctive feature of the Armorican spur of the Gondwana plate is its prolonged subduction accretion tectonics lasting from the early Devonian to the early Carboniferous. As the Armorican spur hosts the most important Variscan Sn deposits, we argue that metal enrichment in continental accretionary complexes is an essential step in the formation of tin specialized granitic melts.
Kroner, U. and R. L. Romer: Two plates - Many subduction zones: The Variscan orogeny reconsidered, Gondwana Research, 24/1, 298-329, https://doi.org/10.1016/j.gr.2013.03.001, 2013.
Romer, R. L. and U. Kroner: Phanerozoic tin and tungsten mineralization—Tectonic controls on the distribution of enriched protoliths and heat sources for crustal melting, Gondwana Research, 31, 60-95, https://doi.org/10.1016/j.gr.2015.11.002, 2016.
Romer, R. L. and U. Kroner: Provenance control on the distribution of endogenic Sn-W, Au, and U mineralization within the Gondwana-Laurussia plate boundary zone, New Developments in the Appalachian-Caledonian-Variscan Orogen, 25-46, https://doi.org/10.1130/2021.2554(02), 2022.
How to cite: Kroner, U. and Romer, R.: Continental accretionary tectonics of western Pangea and the formation of Sn, W and Li deposits, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12785, https://doi.org/10.5194/egusphere-egu25-12785, 2025.
Northern Sardinia, Italy, shows substantial potential for W-Sn-Mo-Bi and F-REE granite-related ore deposits. In the Oschiri area, mineralized greisen and hydrothermal veins occur at intrusive contacts between late-Variscan granites and high-grade metamorphic rocks [1].
The greisen consists of K-feldspar, plagioclase, rutile, biotite, and zoned muscovite rimmed by quartz, sericite, chlorite, and ore minerals such as molybdenite, rare interstitial Bi-Te alloy, scheelite, columbite, partially hematitized pyrite, LREE phosphates and fluorocarbonates (monazite, synchysite-Ce), and pyrochlore-(Y). Hydrothermal veins are primarily composed of fluorite and quartz, with rare barite, galena and apatite. Together, these ore bodies form an "F-rich open system" [2] where greisenization occurred at ~400–300°C, introducing an early phase of ore minerals. Subsequent HF-rich hydrothermal fluids circulation below 300°C produced brecciated and argillitic bands in granite and greisen. The Nb-Y-F signature suggests a metallogenic affinity with NYF (Niobium-Yttrium-Fluorine) pegmatites.
Electron microprobe analyses of muscovite zonation were performed on five greisen samples, with 146 core analyses and 163 rim analyses for F, Na, Mg, Si, Al, Ba, K, Cl, Ca, Mn, Ti, Ni, Fe, and Cr. These analyses revealed an average increase in Si (3.08–3.13 apfu), Fe (0.06–0.15 apfu), Mg (0.01–0.02 apfu), Mn (0.003–0.007 apfu), and Ti (0.002–0.005 apfu), and a decrease in Al (2.75–2.56 apfu) toward the rims, consistent with a Tschermak-type substitution. Additionally, an increase in OH (1.82–1.84 apfu) and a decrease in F (0.18–0.15 apfu) suggest more hydrous conditions at the rims. This chemical zonation, combined with the textural relationships between muscovite and ore minerals, indicates alteration driven by the mineralizing fluid circulating during greisenization [3]. Dating these altered rims will enhance the genetic model by constraining the timing of the mineralization [4], providing a valuable interpretative framework for similar geological settings and offering a novel approach to dating granite-related ores.
The identification of economically significant elements such as W, Mo, LREE, and F within the greisen and hydrothermal system, coupled with the possible potential for NYF pegmatite occurrences, underlines the area's untapped resource potential. This study highlights Northern Sardinia as a promising region for future exploration and resource development, offering critical guidance for targeted exploration strategies.
References
[1] Cossu, D., Attardi, A., Deidda, M. L., Naitza, S. (2024). Studio giacimentologico sulle mineralizzazioni legate ai granitoidi dell’area di Oschiri-Alà dei Sardi (Sardegna Nord-orientale). [Master’s Thesis], University of Cagliari, 121.
[2] Pirajno, F. (2009). Hydrothermal processes and mineral systems. Springer, 1250.
[3] Attardi, A., Cossu, D., Naitza, S., Majka, J., 2024. The role of micas in modelling ore-bearing greisen in Sardinia, Italy. Mineralogia – Special Papers, 52, 33.
[4] Rösel, D., Zack, T. (2021). LA-ICP-MS/MS single-spot Rb-Sr dating. Geostandards and Geoanalytical Research, 46(2), 143–168. https:// doi. org/ 10. 1111/ ggr.12414
How to cite: Attardi, A., Cossu, D., Deidda, M. L., Majka, J., and Naitza, S.: Modelling and Exploration of CRMs-bearing greisen systems of Northern Sardinia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11979, https://doi.org/10.5194/egusphere-egu25-11979, 2025.
The basic-ultrabasic bodies of Mohammad Abad, with an outcropped area of 28 km2, are located 7 km southwest of Horand city, NW of Iran. This area is part of the Central Iranian Domain (Agha Nabati, 2004) and Urumieh-Dokhtar Magmatic Arc (UDMA) of Cenozoic. Rock units in the area include Upper Cretaceous-Paleocene flyschoid sandstone, shale, pelagic carbonate rocks and volcanic-volcanoclastic rocks, including andesitic lavas, dacitic breccias and acidic tuffs. The ultrabasic pyroxenite body is intruded by Oligocene gabbroic body and dikes, in which large pyroxenite xenoliths are present. Moreover, several syenitic and nepheline syenitic dikes cross-cut the ultrabasic-basic complex. Considering their mineralogic similarities with the neighboring well-studied nepheline-syenites of Kaleybar, these dikes can be attributed to Oligocene. The occurrence of gabbro and syenite bodies and dikes at the margins of an ultrabasic complex may refer to an alkaline ring complex formation in the area. According to petrographic studies, ultrabasic rocks are composed of clinopyroxene (diopside), olivine, phlogopite and opaque minerals such as magnetite and pyrite, while gabbros comprise plagioclase, clinopyroxene (diopside), amphibole (pargasite to tschermakite) and lesser phlogopite, biotite and magnetite. Gabbros have shoshonitic affinity, with metaluminous nature and post-collisional volcanic arc setting, produced by low-degree partial melting of an enriched spinel-garnet lherzolite mantle, while garnet remained as residual phase within the source area.
Vermiculite mineralization in the Hashtsar area occurred within the ultrabasic-basic bodies, comparable with Palabora (south Africa) and Libby (Montana, USA) deposits. Hypogene and supergene process were incorporated in its genesis. Hypogene hydrothermal fluids have altered pyroxene and amphibole minerals of the host rocks to biotite, which was later converted to hydrobiotite. Hypogene fluids may have provided by the intrusion of syenitic dikes within pyroxenites and gabbros, as vermiculite formation is more evident at the margins of these dikes. Both hypogene and supergene fluids have caused the conversion of hydrobiotite and phlogopite to vermiculite, among which the role of weathering is more prominent for the study area, considering the major occurrence of vermiculite in shallow depths (~5 m) of the ultrabasic-basic rocks and the decreasing ratio of vermiculite/phlogopite with depth. Conversion of phlogopite and biotite to vermiculite requires the removal of K and Si and addition of Mg, Fe and H2O. Mg and Fe may have provided by alteration of pyroxene and amphibole minerals from ultrabasic-basic rocks. Geochemical analysis data show that both the ultrabasic-basic bodies, and the vermiculite samples have a strong enrichment of LILE and a negative anomaly of HFSE. Moreover, the ultrabasic-basic rocks of the study area show depletion of Mg. It can be concluded that most of the magnesium from the parental rocks entered the mineral structure of vermiculite as a result of ion exchange with potassium.
Key words: Vermiculite, Pyroxenite, Gabbro, Supergene alteration, Mohammad Abad.
How to cite: Simmonds, V., Sabbaghi, S., and Hosseinzadeh, M. R.: Vermiculite mineralization associated with ultrabasic-basic rocks of the Mohammad Abad area, NW Iran, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4737, https://doi.org/10.5194/egusphere-egu25-4737, 2025.
The Junggar Basin, located in northwestern China, has garnered significant global attention due to its substantial reserves of sandstone-type uranium deposits. The sandstone type uranium deposits (spots) within the Junggar Basin are predominantly concentrated in the surrounding regions of the basin, with the primary ore-hosting strata identified as Jurassic and Cretaceous. However, there exists ongoing debate regarding the understanding of sediment sources, which is of pivotal importance for guiding uranium exploration. In this study, U-Pb dating, whole rock geochemical analysis, heavy mineral analysis, and in-situ Hf isotope composition were employed, in conjunction with sedimentology and tectonic setting, to trace the provenance of sandstone type uranium deposits in the Toutunhe Formation of the Middle Jurassic in the central-southern part of Junggar Basin. The research indicates that the sandstone debris is characterized by high concentration of feldspar and rock fragments, with volcanic rock debris being the dominant constituent. Geochronological analysis of detrital zircons reveals that the age spectrum of detrital zircons in the Toutunhe Formation exhibits a primary peak ranging from 335 to 370 Ma, with a notable peak at 355 Ma, and two secondary peaks at 395 to 475 Ma and 262 to 316 Ma, respectively. The heavy mineral assemblage, comprising zircon, garnet, apatite, and magnetite, suggests that the source area is primarily composed of acidic magmatic or metamorphic rocks. By systematically comparing the U-Pb age and Hf isotope results with previously reported data from adjacent geological units in the southern Junggar Basin, and integrating the ZTR index and paleocurrent direction, the analysis demonstrates that the principal source area for the sandstone of the Toutunhe Formation is Bogda Mountain, particularly the uranium-rich felsic rocks, and the secondary area is Tianshan Mountain.Overall, this study provides essential and incisive insights into inferring the source supply areas and transportation pathways, thereby holding considerable significance for uranium exploration endeavors within sedimentary basins on a global scale.
How to cite: Wang, T., Zhou, Y., Li, S., and Shi, X.: Source analysis of sandstone type uranium minerals in Louzhuangzi area, southern margin of the Junggar Basin, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1949, https://doi.org/10.5194/egusphere-egu25-1949, 2025.
Apatite is a ubiquitous accessory phase in igneous rocks and a prevalent phase in carbonatites, where it is commonly present throughout their entire evolutionary history. It is typically enriched in light rare earth elements (REE) and can attain high modal proportions, especially in carbonatite-derived lateritic deposits. This study investigates the textural features and apatite geochemistry in a Paleoproterozoic complex in the peri-cratonic terrains of the Reguibat Shield to elucidate the crystallization environment, petrogenetic evolution and potential REE redistribution and phosphate ore grade enhancement. Three distinct apatite populations were identified within the regolith and underlying carbonatite protolith. A primary large group of apatite consists of ovoid to pill-like crystals, reflecting the primary igneous carbonatite system with typical light REE enrichment and high Sr and Ba concentrations. A secondary generation of apatite shows evidence of hydrothermal overprinting and occurs in two distinct mineral associations. Apatites accompanied by carbonates, clinohumite, and serpentine minerals exhibit low Sr, REE, and Th contents with a negative Eu anomaly, indicating early hydrothermal reworking in a reduced environment. Whereas, light REE-depleted apatites associated with monazite, barite, and siderite point to a subsequent hydrothermal stage under more oxidizing conditions. The intimate association between monazite and apatite grains highlights fluid-mediated apatite alteration and subsequent monazite nucleation. The composition of apatite and monazite grains in the regolith mantle mirrors their composition in the underlying carbonatite, reflecting their strong genetic link. Besides, the third apatite group consists of secondary carbonate-bearing apatites cementing primary ovoid grains in the regolith horizons. The secondary apatites are depleted in REE, Sr, and Na with CO32- uptake in the PO43- site, along with F enrichment, which acts as a balancing element. Despite abnormal levels of certain deleterious elements, such as Zn and Cd, these apatites display very low concentrations of As and Th, enhancing their potential for industrial applications. The secondary apatite formation reflects the late-stage supergene processes, which triggered the leaching, recrystallization and lithification of various mineral phases, resulting in the formation of variably sized apatite-rich horizons reaching locally mineable grades.
How to cite: Malainine, C. E., Ouabid, M., Raji, O., Parat, F., and Bodinier, J. L.: Apatite as record of multi-stage evolution and ore-forming processes in carbonatites and derived regoliths, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20422, https://doi.org/10.5194/egusphere-egu25-20422, 2025.
Critical metals (CM) such as rare-earth elements (REE), platinum group elements (PGE), cobalt (Co), germanium (Ge), gallium (Ga), and indium (In) are commonly mined as by-products of base metals (i.e., Zn, Fe, Cu) with similar chemical affinities. Metamorphism can significantly influence the distribution of critical metals in base metal deposits, either upgrading or decreasing their economic importance. Critical metals deposits are frequently hosted in orogenic setting, but may be pre-, syn- or post-orogenesis. In this contribution, we will focus on the primary deposits that might have suffered metamorphism and fluid-assisted deformation during orogenesis, evaluating the role of deformation and metamorphic recrystallization on critical metals. This contribution sheds a novel light on the role of metamorphism, deformation, static or dynamic recrystallization and associated fluid flow in modifying the distribution of CM concentrations from primary into secondary-metamorphosed deposits, in a systematic manner from the large plate tectonic scale to the small mineral scale. Orogenic critical metals (OCM) can be broadly defined as the large-scale remobilization or sample-scale redistribution product of pre-existing CM concentrations, present in the primary ore, that have been triggered by metamorphism and/or tectonic processes (e.g., deformation, static or dynamic recrystallization, fluid and thermodynamic conditions). These processes may have positive or negative impacts on the endowment of the deposit. In either case, metamorphic processes may potentially create favorable conditions for redistributing CM in ore minerals (containing several wt% of CM) that may make them more accessible for industry if exploration/recovery strategies are adapted. In this contribution, the mineralogy and ore textures of ca. 200 deposits reported in the literature have been extracted in a systematic manner and in three regions of the world (Australia, China, and Europe). Based on quantitative estimations from the literature in these three districts, base metal resources, potentially hosting CM, are often found in orogens, and many show features of superimposed deformation and metamorphism. A general model is proposed, representing metamorphic and structural conditions enhancing the formation of orogenic critical metals (OCM).
How to cite: Cenki-Tok, B. and Cugerone, A.: Assessing the role of deformation and metamorphic recrystallization in the remobilization of critical metals in orogens, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1633, https://doi.org/10.5194/egusphere-egu25-1633, 2025.
The Valozoro deposit is located in the rural commune of Fiadanana, within the Ambohimasoa district in the Haute Matsiatra region, in the central-southern part of Madagascar. It lies within the extension of the Ambositra and Fianarantsoa geological series, specifically in the Faliandra sector. Dating back to the Mesoproterozoic era, this formation belongs to the Ambatolampy group, part of the Antananarivo tectono-metamorphic Domain.
The deposit is defined by intrusions of harzburgites embedded in formations of pyroxene- and amphibole-bearing gneiss, micaschists, and migmatites. The nickel-rich harzburgites form a distinctive subcircular hill at Valozoro. These holomelanocratic rocks, with a granular texture, are primarily composed of olivine, orthopyroxene, and plagioclase. Due to prolonged meteoric weathering, the harzburgites have undergone supergene alteration, leading to the serpentinization of olivine and orthopyroxene.
The alteration process occurs in two key stages: (1) Early hydrolysis of olivine, resulting in the accumulation of residual iron enriched with nickel. (2) Progressive epigenization of serpentine ribbons by iron hydroxides, leading to intensified nickel enrichment. Serpentine exhibits an average nickel content of 2.5% and further alters into residual lateritic clay with nickel content ranging from 0.2% to 2.5%, averaging 1.2%. The harzburgites are intersected by significant veins of graphic pegmatite containing schorlite and milky quartz. They also feature fissures filled with centimeter-scale veinlets of garnierite, recognized by its dark green color. The primary exploitable ores at Valozoro include nickel laterites, garnierite, and serpentines.
How to cite: Rarivoarison, H. N., Andriamamonjy, A. S., Miha, T., Razafimahatratra, D., Rakotoarisoa, D., and Nisi, R. M.: Geological characteristics and Nickel mineralization of the Valozoro deposit, Central-Southern Madagascar, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15137, https://doi.org/10.5194/egusphere-egu25-15137, 2025.
The Maniitsoq nickel-copper deposit is located about 160 km north of Nuuk, Greenland. The deposit is a very large high-grade deposit with 19.5 million tons nickel @1.08%, and copper @ 0.54%, reached the world class scale. The authors comprehensively collected and analyzed the relevant data of the deposit, and compared it with China's Jinchuan nickel ore deposit. They occurred in same tectonic environment, with same rock characteristics, and mineralization features between the Maniitsoq nickel copper deposit in Greenland and the Jinchuan nickel copper deposit in China. Although the Maniitsoq and Jinchuan intrusive bodies are not large in scale, but the Jinchuan nickel copper deposit produces world-class ultra large copper nickel platinum group metal deposits, which is in line with the theory of "small rock mass forming large ore". Maniitsoq is likely to be the next world-class nickel copper sulfide deposit. By comparison, the Maniitsoq nickel copper deposit and the Jinchuan copper nickel deposit have similarities in diagenetic and deposit characteristics, and both belong to fissure penetrating magmatic deposits, i.e. "deep liquation-injection mineralization" ore-forming mechanism.
Mineralization occurs during the upwelling process in a dynamic magmatic environment, where magma melts are rich in volatile components and the upwelling activity is intense. During the migration process, magma interacts with surrounding rocks, undergoes component exchange, and accumulates ore-forming materials. Early sulfur saturation mechanisms such as crustal contamination or magma temperature reduction are necessary conditions for magma mineralization during channel migration or intrusion. In the process of deep melting penetration mineralization, the upwelling of ore bearing magma and subsequent magma recharge and mixing are important mechanisms for the accumulation of sulfides in the channels of Mg-Fe ultramafic rocks to form super large copper nickel platinum group metal deposits. We suggest that the exposed Maniitsoq intrusions represent the Ni-rich upper portions of magma conduits implying that there is potential for Cu-rich sulfides in unexposed deeper portions of the belt.
How to cite: Yang, Y. and Wang, L.: Geological comparative study of two Ni-Cu sulfide deposits of Maniitsoq and Jinchuan, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7805, https://doi.org/10.5194/egusphere-egu25-7805, 2025.
Gravity study of the Giraúl pegmatitic field (Namibe province, SW Angola)
José Luis García-Lobón1*, Carmen Rey-Moral1, Enrique Merino-Martínez2, Ezequiel Ferreira1, Félix Rubio1
1 IGME-CSIC. c/ La Calera 1. 28760 Tres Cantos. Madrid. *Corresponding author: jl.garcia@igme.es
2 IGME-CSIC. c/ Ríos Rosas, 23. 08003. Madrid.
Abstract
The Giraúl Pegmatitic Field (Namibe province, Angola) contains hundreds of pegmatite bodies, including several enriched in Li, Be, B, Cs, Rb, Sn and Ta, occurring in a corridor oriented in a WNW-ESE direction and covering an area of more than 150 km2. The pegmatites intruded into the Palaeoproterozoic Namibe Group metasediments and diverse basic to ultrabasic intrusions (gabbros, diorites, and sparse pyroxenites) scattered throughout the area. This study focuses on the gravity survey of the Muvero and Lepamby prospects of the Giraúl field, which contain Li-enriched pegmatites and are currently being explored by private companies. Between 2023-2024, 346 gravimetric stations were measured at the prospects along N-S and E-W profiles using the CG-6 Autograv™ gravimeter and the Pentax G-7 GPS system. Standard gravity data corrections were applied and an adequate reduction density was used, estimated by correlation between Bouguer anomalies and topography. The results obtained are consistent with the presence of interstratified amphibolites in the Namibe Group, along with some intrusions of dense basic to ultrabasic bodies, which create a clear density contrast with respect to the lighter pegmatites. Relative gravity minima are observed in the Bouguer anomaly map, related to pegmatitic structures. The integrated geointerpretation of surface geological information and in-depth 2.5D gravity models indicate the presence of pegmatitic bodies at depths up to 250 m. Furthermore, a number of unsuspected pegmatitic zones have been revealed. These results are very promising for future exploration of pegmatites and associated minerals in the Giraúl pegmatitic field.
How to cite: García-Lobón, J. L., Rey-Moral, C., Merino-Martínez, E., Ferreira, E., and Rubio, F.: Gravity study of the Giraúl pegmatitic field (Namibe province, SW Angola), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7907, https://doi.org/10.5194/egusphere-egu25-7907, 2025.
The Erzgebirge, a major tin (Sn) province in the Variscan orogenic belt, hosts substantial Sn deposits associated with post-kinematic granites, alongside the minor stratabound Sn deposits found in the metamorphic schists of the western Erzgebirge. These schists are derived from Early Ordovician siliciclastic sediments, which were metamorphosed during the Variscan orogeny and subsequently intruded by post-Variscan granites between 325 and 314 Ma. Cassiterite (SnO₂) inclusions and elevated Sn concentrations in metamorphic minerals indicate that Sn was already present in the rocks prior to the intrusion of granites. Early Ordovician sediments preserved in Thuringia typically contain approximately 20 ppm Sn, implying that Sn (reaching locally up to 5000 ppm) was added during prograde metamorphism that started at c. 400 Ma, as confirmed by U-Pb cassiterite dating [2]. Retrogression of the schists also resulted in the formation of a second generation of cassiterite. To differentiate the two phases of Sn mobilization and to estimate elements introduced during prograde metamorphism from those mobilized during retrogression, we compare the compositions of the protoliths [1]with non-retrogressed schists and of non-retrogressed with retrogressed schists, respectively. During prograde metamorphism there was a marked increase in Si, Fe, and Sn. During retrogression, which involved the formation of chlorite at the expense of biotite, K, Rb and Ba were lost and Sn released from biotite formed a second generation of metamorphic cassiterite. The light elements Li and B were also mobile, with preferential incorporation of Li into biotite during prograde metamorphism and B into chlorite during retrogression. Such enrichment of Sn during metamorphism is important to form source rocks whose partial melting can produce Sn-rich granites.
[1]Romer, R.L., and Hahne, K., 2010. Life of the Rheic Ocean: scrolling through the shale record. Gondwana Research, 17(2-3), pp. 236–253.
[2]Romer, R.L., Kroner, U., Schmidt, C. and Legler, C., 2022. Mobilization of tin during continental subduction-accretion processes. Geology, 50(12), pp. 1361–1365.
How to cite: Sarkar, O., Romer, R. L., Kroner, U., and Legler, C.: Mobilization of tin during metamorphism in the Variscan Orogeny, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6784, https://doi.org/10.5194/egusphere-egu25-6784, 2025.
The Samoeng (Bo Kaeo) mine, the largest primary Sn-W deposit in northern Thailand, is part of the Southeast Asian Tin Belt, which extends 2,800 km from Myanmar and Thailand to Peninsular Malaysia and Sumatra Island. In Thailand, Sn-W deposits are found in the western and central granitoid belts, but their origins are not well constrained as there are only few studies about their petrology, geochemistry and dating of the mineralization. The Sn-W ore bodies at Samoeng are associated with skarn formation between a granite and the calcareous host rock. The magmatic intrusion is a medium to coarse-grained biotite granite with pegmatite and aplite veins intruding the country rock. The biotite granite is enriched in alkalis, Rb, Th and Pb. They display S-type peraluminous characteristics (A/CNK =1.07-1.14), low FeOT/MgO ratio (0.24-0.44), and belong to the high-K calc-alkaline to shoshonitic series. The granites have elevated LREEs, a negative Eu anomaly, and a flat HREE profile. Tectonic discrimination plots (Pearce et al., 1984) classify most samples as syn-collisional granites (syn-COLG), while the Batchelor and Bowden (1985) diagram categorizes them as syn-, late, and post-collisional. Zircon U-Pb geochronology dates the biotite granite to 214±2 Ma. Monazite U-Pb geochronology yields besides the Late Triassic intrusion age (~215 Ma) a younger Cretaceous age of ~80 Ma.
The calcareous rocks include calc-silicate rocks and marble. The calc-silicates are fine to medium-grained with interlocking crystals, primarily composed of diopside and subordinate wollastonite, phlogopite, quartz, plagioclase, clinohumite, grossular, calcite, Sn-bearing rutile or titanite, spinel, apatite, and minor cassiterite. The calcite marble is medium grained and contains quartz and diopside as accessory minerals.
The Sn-W mineralization in this area is primarily found in breccia dykes, which manifest as narrow, tabular structures intersecting the biotite granite and calc-silicate rock. These dykes, generally ranging from 2 to 5 meters in thickness, are highly weathered (kaolinitized). The breccia fragments are composed of biotite, quartz, K-feldspar and tourmaline, with lesser quantities of magnetite, spinel, cassiterite, and scheelite. The heavy mineral fraction from the Samoeng mine primarily include cassiterite and scheelite, with smaller amounts of magnetite, ilmenite, spinel, zircon, apatite, rutile, titanite, xenotime, allanite, thorianite, and monazite. Monazite U-Pb geochronology indicates several age populations of ~230, ~205 and ~75 Ma, suggesting recrystallization and re-precipitation during multiple thermal events.
Based on our data we conclude that the Sn-W mineralization occurred in the Late Triassic during the emplacement of the granitoid body which led to skarn formation and an associated contact aureole. This event is related to the Sukhothai-Sibumasu collision (closure of the Paleo-Tethys, Indosinian Orogeny). During Cratacous times a thermal overprint is recorded in monazite from the granite body but also from the mineralized skarn zone. This event in the Late Cretaceous is associated with the collision between the Sibumasu and West Burma blocks.
Batchelor, R.A. and Bowden, P. (1985) Petrogenetic Interpretation of Granitoid Rock Series Using Multicationic Parameters. Chemical Geology, 48, 43-55.
Julian A Pearce, Nigel BW Harris, Andrew G Tindle (1984). Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. Journal of Petrology, 25, 956-983.
How to cite: Santitharangkun, S., Hauzenberger, C. A., Gallhofer, D., and Skrzypek, E.: Skarn Hosted Sn-W Mineralization, Samoeng Mine, Northern Thailand: Petrology, Geochemistry and Geochronology, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10749, https://doi.org/10.5194/egusphere-egu25-10749, 2025.
The Citronen Fjord lead-zinc deposit, in reserve expansion and feasibility study stage by now, is a world-class protogenesis lead-zinc deposit. It is also known as the most northern lead-zinc deposit in the world. Both folds and thrust faults are well developed in the Citronen Fjord area and the lead-zinc ore de- posit is generally a NW-SE striking trend，mineralization zone is mainly located in Discovery Zone, Beach Zone and Esrum Zone. The ore body is hosted by Upper Ordovician-Lower Silurian mudstone and shale, and the main sulphides include pyrite, sphalerite and galena. The δS values of sulphide minerals from the Citronen Fjord ore deposit range from + 7% to + 35%(CDT)，with the bulk of analyses in the range from + 10 % to + 25 %， while the lead isotope has radiogenic characteristic. The ore-forming fluid tem- perature are in epithermal, ranging from 80℃ to 160℃. The Citronen Fjord lead-zinc deposit is genetically a SEDEX deposit. Lead-zinc resources are abundant in Greenland,and in particular,abundant in the Pa- laeozoic Franklinian Basin of North Greenland which extends for more than 2,500 km E-W. This under-ex- plored basin is believed to be an excellent target area for lead-zinc exploration in future.
How to cite: Wang, L. and Yang, Y.: Character of the Citronen Fjord Lead-Zinc Deposit，North Greenland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7787, https://doi.org/10.5194/egusphere-egu25-7787, 2025.
Cobalt and nickel are technologically critical metals used in rechargeable battery electrodes, superalloys for gas turbines and jet engines, catalysts, and resistant alloys. Numerous studies have demonstrated that cobalt and nickel often accumulate in ferromanganese nodules on the seafloor, but their enrichment behaviors in Mn-oxide nodules from terrestrial surface environments are poorly constrained. Large amounts of ferromanganese nodules occur in laterite profiles of the supergene Mn-oxide deposits that are widely distributed in South China. These nodules contain significant amounts of cobalt (10-1280 ppm, mean 308.58 ppm) and nickel (66-5000 ppm, mean 997.02 ppm) that can be potentially produced as a by-product.
52 ferromanganese nodules from three supergene Mn-oxide deposits in South China have been studied by optical microscope, scan electron microscope, bulk chemical analysis, electron probe analysis, and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to determine the minerals, textures, mineral association, and distribution of the cobalt-nickel in Mn-oxides. Petrographic observations demonstrate that Mn-oxides in the collected ferromanganese nodules consist mainly of hollandite-cryptomelane, pyrolusite and lithiophorite. All pyrolusite generally contain minor Co (10.96-526.68 ppm) and Ni (27.43-1253.56 ppm). The early lithiophorite grains occur as fine-grained to cryptocrystalline and contain high Co (560.11-3010.57 ppm) and Ni (3182.77-20135.47 ppm), while the late lithiophorite crystals are often coarse-grained and have relatively high Co (29.52-2302.38 ppm) and Ni (518.78-10906.86 ppm). The mixed hollandite-cryptomelane minerals contain relatively high Co (23.43-1311.12 ppm) and Ni (27.66-2294.98 ppm).
In lithiophorite, Co and Ni primarily incorporation into a manganese layer sheet. They are also predominantly enriched in the octahedral of hollandite-cryptomelane structure, whereas Ni is probably incorporated in hollandite-cryptomelane to a lesser extent by forming outer-sphere complexes within the tunnels. Sharp chemical gradients across different Mn-oxide species, along with irregular reaction fronts, indicate that repeated leaching and reprecipitation are the main mechanisms for the incorporation of Co and Ni. The fractionation of these elements may be attributed to low fO2 and high pH, which favor higher Co/Ni ratios in hollandite-cryptomelane. The lithiophorite with lower Co/Ni ratios precipitated which reflected an increase in Ni concentrations in fluids under conditions of high fO2 and low pH. Differences in weathering intensity in South China likely contributed to the development of diverse Mn-oxide varieties, while local physicochemical changes influenced the partitioning of elements within individual deposits.
How to cite: Li, X. and Deng, X.: Cobalt and nickel enrichment in ferromanganese nodules: insights from supergene Mn-oxides deposits in South China, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4647, https://doi.org/10.5194/egusphere-egu25-4647, 2025.
Posters virtual: Thu, 1 May, 14:00–15:45 | vPoster spot 1
EGU25-5245 | Posters virtual | VPS23
W-Sn Ore-Mineral Geochronology: New Ages Improve Genesis ModelsThu, 01 May, 14:00–15:45 (CEST) | vP1.1
Direct ore-mineral U-Pb geochronology of scheelite (CaWO4), cassiterite (SnO2), and wolframite ([Fe,Mn]WO4) using recently-developed reference materials led to new ore-genesis insights for multiple worldwide W-Sn/rare metal deposits. Scheelite from the Yellow Pine epithermal Au-W-Sb deposit in Idaho, USA was age dated using U-Pb via isotope dilution thermal ionization mass spectrometry (TIMS) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). These analyses provided both the first age constraints on the tungsten mineralization (ca. 57 Ma) and a scheelite U-Pb reference material (NMNH-107667; 57.52 ± 0.22 Ma). The data reveal ore mineralization occurred in numerous discrete pulses during crustal uplift, which contrasts with the previous two-mineralization-event model.
The Yellow Pine scheelite reference material enabled U-Pb scheelite geochronology via LA-ICP-MS for multiple other deposits worldwide; namely, the polyphase stratabound scheelite-ferberite mineralization hosted within Fe-rich magnesite zones and marbles in two locations around Mount Mallnock, Austria. Two unexpected but geologically meaningful age dates (294 ± 8 Ma) for Mallnock West and (239 ± 3 Ma) for Mallnock North revealed for the first time that ore mineralization occurred during an extensional geodynamic setting as part of the breakup of Pangea, as opposed to the previous model invoking the older compressional tectonics of the Variscan orogeny.
Combining direct-ore geochronology methods for several ore minerals was particularly powerful for Sn- and W-bearing deposits in southeast Australia. A U-Pb cassiterite age date (435 ± 2 Ma) revealed the tin-bearing lithium pegmatites of the Dorchap Dyke Swarm are ca. 15 Ma older than some previous estimates suggesting mineralization was related to the earliest magmatic activity recorded in the Wagga-Omeo Metamorphic Belt. Additionally, a new U-Pb wolframite age date (395 ± 5 Ma) for the Womobi polymetallic (W-Mo-Bi) deposit is ca. 21 million years younger than the host Thologolong granite, suggesting the granite was a passive host that was mineralized by a concealed intrusion. Both instances revealed mineralization ages that were significantly different than previously accepted. More widespread application of these increasingly diverse, direct-ore geochronology methods stand to replace uncertain spatial or textural associations, thereby providing an opportunity to significantly improve ore genesis models.
How to cite: Wintzer, N., Holm-Denoma, C., Altenberger, F., and Waugh, S.: W-Sn Ore-Mineral Geochronology: New Ages Improve Genesis Models, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5245, https://doi.org/10.5194/egusphere-egu25-5245, 2025.
EGU25-4666 | ECS | Posters virtual | VPS23
Insight into the genesis of barite deposit in Vempalle Formation, Cuddapah basin, IndiaThu, 01 May, 14:00–15:45 (CEST) | vP1.3
The Vemula-Velpula hydrothermal barite deposit is hosted by mafic dykes (ca. 1850 Ma. [1]) intruding into the uppermost part of about 1900 m thick carbonate strata of the Vempalle Formation (ca. 2000 Ma. [2]) in Cuddapah basin and occurs as fracture-fill and breccia-fill veins. The veins dominantly consist of barite with minor quartz. The host mafic rock has undergone various extents of hydrothermal alteration, due to which the primary calcic plagioclase-clinopyroxene assemblage is altered to albite and clinochlore, along with the introduction of secondary epidote, quartz, and calcite. The wide range in Ba concentration of mafic rock (68 to 3012 ppm) associated with the barite mineralization indicates that Ba was mobilized and subsequently leached from the mafic rock by the hydrothermal fluid during this alteration event. The δ34S values of barite range from +16.19 to +23.24‰ which falls within the range of δ34S value of +10 to +30‰ estimated for Proterozoic seawater [3]. At shallow crustal depth where this deposit was formed, direct participation of seawater is unlikely and therefore basinal brine is inferred to be the source of sulphate ion required for barite mineralization. Primary aqueous biphase fluid inclusions in barite have homogenization temperatures ranging from 180 to 300 °C, with most of them clustering in the range 220-250°C, and salinities ranging from 2.4 to 25.8 wt.% NaCl equivalent. The first ice melting temperature of these inclusions was measured between -55 and -37°C, broadly pointing towards an H2O-NaCl-CaCl2 fluid system. Petrography and microthermometric data of fluid inclusions indicate the involvement of two fluids of different salinities, which, upon mixing and cooling, led to barite precipitation.
This research work was funded by SERB, New Delhi (Scheme No. CRG/2019/001015).
References
[1] Chakraborty K. et al. (2016), Journal of the Geological Society of India 87, 631–660.
[2] Rai A.K. et al., (2015), Journal of the Geological Society of India 86, 131–136.
[3] Strauss H (1993) Precambrian Research 63(3–4), 225–246.
How to cite: Devanand Sreekala, D. and Muthusamy, S. P.: Insight into the genesis of barite deposit in Vempalle Formation, Cuddapah basin, India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4666, https://doi.org/10.5194/egusphere-egu25-4666, 2025.
EGU25-13796 | ECS | Posters virtual | VPS23
Geology of the Isiro-Ngayu gold-bearing region, western belts of the Kibali granite-greenstone superterrane in the northeastern Congolese craton, Democratic Republic of CongoThu, 01 May, 14:00–15:45 (CEST) | vP1.4
Abstract.
The Isiro and Ngayu belts in northeastern Democratic Republic of Congo (DRC) are part of the Congo Craton and among the most poorly known Archean terrains worldwide. These belts consist of metavolcanic and metasedimentary rocks surrounded or intruded by granitoid rocks. minimum age of deposition for the supracrustal formations is defined at ca 2633 Ma (e.g. Allibone et al., 2020), whereas the granitoids were dated between 3200 Ma and 2530 Ma (Allibone et al., 2020; Turnbull et al., 2021) and are strongly deformed with variable proportions of mafic enclaves at outcrop scale (Turnbull et al., 2021). Both Isiros and Ngayu belts host important gold deposits, but the genetic relationships between gold mineralization, deformation and the diverse host rocks remain ambiguous. In this context, the work we present here is part of a multidisciplinary approach, combining the processing of satellite images and field observations using GIS to map the structural lineament that may control gold mineralization in the region. The results show that the strains are large, marked by NW-SE lineaments at low angle to the belt strikes and combined with a secondary ENE-WSW brittle structure. The overall structural pattern, together with the existence of artisanal gold mining in the area, emphasizes that gold mineralization is largely controlled by structures localization along the greenstone belts.
Key words: Congo craton, gold mineralization, field observations, satellites images, structural lineaments.
Reference
Allibone, A., Vargas, C., Mwandale, E., Kwibisa, J., Jongens, R., Quick, S., Komarnisky, N., Fanning, M., Bird, P., MacKenzie, D., Turnbull, R., Holliday, J., 2020. Chapter 9: Orogenic Gold Deposits of the Kibali District, Neoarchean Moto Belt, Northeastern Democratic Republic of Congo, in: Sillitoe, R.H., Goldfarb, R.J., Robert, F., Simmons, S.F. (Eds.), Geology of the World’s Major Gold Deposits and Provinces. Society of Economic Geologists, p. 0. https://doi.org/10.5382/SP.23.09
Turnbull, R.E., Allibone, A.H., Matheys, F., Fanning, C.M., Kasereka, E., Kabete, J., McNaughton, N.J., Mwandale, E., Holliday, J., 2021. Geology and geochronology of the Archean plutonic rocks in the northeast Democratic Republic of Congo. Precambrian Research 358, 106133. https://doi.org/10.1016/j.precamres.2021.106133
How to cite: Birimwiragi Namogo, D., Martial Akame, J., Mbuluyo, M., Debaille, V., Mango Itulamya, A. L., and Hubert-Ferrari, A.: Geology of the Isiro-Ngayu gold-bearing region, western belts of the Kibali granite-greenstone superterrane in the northeastern Congolese craton, Democratic Republic of Congo, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13796, https://doi.org/10.5194/egusphere-egu25-13796, 2025.
EGU25-3874 | ECS | Posters virtual | VPS23
Petrographic and Geochemical Characterization of Mayedo and Kinzoki Ranges (Sumbi Bauxite Region, Kongo Central/DR Congo)Thu, 01 May, 14:00–15:45 (CEST) | vP1.2
The bauxitic region of Sumbi and its surroundings in Kongo Central (DR Congo) is located in an area corresponding to “bands” of basic rocks made up of microdolerites, basalts and andesites. The problem of this study is linked to the similarity of the phenomena that generated the depositional process of these ferruginous and aluminous formations. The aim of this article is to carry out a chemical and petrographic study of samples of bauxitic materials from the Mayedo and Kinzoki regions, with a view to their possible recovery. To this end, the chemical and petrographic analysis of the weathering formations outcropping in the study area was carried out using X-ray fluorescence and thin section methods. The latter revealed that two lithologies were detected in the healthy rocks: basalts with a mineralogical assemblage of plagioclase crystals, pyroxene microcrystals and oxide opaques; and dolerites represented by plagioclase crystals, pyroxenes and a few quartz crystals. X-ray fluorescence revealed high levels of Al2O3 (32.69%) in the Mayedo zone (MHb1). This visibly gibbsite-rich level corresponds to the zone of friable, homogeneous bauxite with a massive, blood-red texture, with an estimated gibbsite percentage of 55.50. The percentage of Fe2O3 is high in these zones at 42.77%, hence the dark red colour, reflecting a strong zone of ferruginasation. This horizon contains a high concentration of hematite and goethite minerals. Highly variable SiO2 contents ranging from 13.48% to 40.82%. These variations are essentially due to the dissolution of silica by leaching and resilification.
How to cite: Mwanakangu, E. and Ungu, D.: Petrographic and Geochemical Characterization of Mayedo and Kinzoki Ranges (Sumbi Bauxite Region, Kongo Central/DR Congo), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3874, https://doi.org/10.5194/egusphere-egu25-3874, 2025.
