Orals: Tue, 29 Apr | Room 0.16
Wheeler, J.1, Henley, R. W.2, Gardner, J.1, Mernagh, T.2, Leys, C.3, Troitzsch, U.2, Bevitt, J.4, Brink, F.2, Knuefing, L.2, Limaye, A.2 Turner, M.2 & Zhang, Y.2
1 Department of Earth, Ocean, and Ecological Sciences, University of Liverpool, Liverpool, UK
2 Australian National University, Canberra
3 P.T. Freeport Indonesia, Papua
4 Australian Nuclear Science and Technology Organisation, NSW 2234, Australia
Porphyry copper deposits are not formed just by crystallisation of ores from Cu-bearing hydrothermal fluids; metasomatism can be involved. We present a metamorphic point of view of the Grasberg porphyry deposit in Papua, which is hosted by intensely altered calc-alkaline plutonic rocks characterised by albite and anhydrite. We propose that plagioclase reacts with magmatic SO2 to form anhydrite and albite, and this releases H2S that plays a major role in Cu ore formation [1]. We split a complex set of reactions into conceptual “building blocks”: these did not happen in a particular order but help to explain our observations.
- SO2 (in the volcanic gas) reacts with water to becomes H2S and H2SO4.
- H2SO4 reacts with Ca from plagioclase to form anhydrite (in veins) c.f. [2].
- Albite is left over.
- H2S reacts with Cu (in the volcanic gas) to form Cu minerals.
- Fe from biotite similarly reacts to form CuFe minerals.
- K-feldspar is left over.
Partly because of these reactions the potassic zone contain more K-feldspar than the protoliths. This is not due to the introduction of magma-derived K by metasomatism; a large chemical dataset shows that unaltered and altered rocks have similar major element bulk compositions. The “HSC Chemistry” package which includes thermodynamics of gases with varied chemistry has been used for preliminary models of reaction.
Electron Backscatter Diffraction work on the new albite shows it is replacing plagioclase inheriting the crystallographic orientation. This resembles microstructures in “coupled dissolution precipitation” reactions [3] though we are not implying the reaction mechanisms are necessarily the same. The thermodynamics and kinetics of the plagioclase breakdown will affect the overall amount of copper ore formed.
[1] Henley et al. JVGR (2022) 432: 107710.
[2] Henley et al. Nat Geosci (2015) 8: 210.
[3] Gardner et al. Lithos (2021) 396-397.
How to cite: Wheeler, J., Gardner, J., and Henley, R.: Genesis of porphyry copper deposits: key roles for plagioclase and anhydrite in metasomatism, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15902, https://doi.org/10.5194/egusphere-egu25-15902, 2025.
Earth’s enriched lithospheric mantle is postulated to be a natural repository of gold and rare earth element (REE) concentrations. We reviewed evidence for gold and REE enriched mantle from the Jiaobei and Luxi terranes in the North China Craton (NCC), which are the world’s third largest gold province and the China’s third largest REE deposit, respectively. In both terranes, extensive Archean tonalite–trondhjemite–granodiorite (TTG) suites are exposed, but whether their mantle source and partial melting pressure are different that caused diverse metallogeny remains ambiguous. Based on a comprehensive analysis of geochemical data, zircon U–Pb, and Hf isotopic compositions from the TTGs, we evaluate the petrogenesis, crustal–mantle evolution, and the role of source magma composition in the formation of crust as well as gold and REE mineralization. Zircon U–Pb–Hf isotope systematics reveal that magma emplacement occurred during three major pulses at ca. 2.9 Ga, 2.7 Ga, and 2.5 Ga in the Jiaobei Terrane, whereas magmatism in the Luxi Terrane was largely concentrated from ca. 2.7 to 2.5 Ga. Geochemical and isotopic data show that the ca. 2.9 Ga and ca. 2.7 Ga TTGs in the Jiaobei Terrane are inferred to have been generated by high- and low-pressure partial melting of an enriched mantle wedge and mafic crust of a thickened arc. The ca. 2.6 Ga and ca. 2.5 Ga TTGs in the Jiaobei Terrane were generated from low- to medium-pressure partial melting the crust of a continental arc. The mantle was gradually metasomatized by slab–derived fluids in the Jiaobei Terrane during ca. 2.7–2.5 Ga, and by additional melts from sedimentary protoliths in the Luxi Terrane during ca. 2.6–2.5 Ga. The spatial distribution of isotopic and geochemical patterns of TTGs reveals the presence of a heterogeneous enriched lithospheric mantle beneath the Jiaobei and Luxi terranes, formed by variable degrees of metasomatism and experienced variable degrees of partial melting. We propose that mantle metasomatism induced by melts derived from sedimentary precursors and low-pressure partial melting played an important role in the formation of the REE deposits and gold fertility within the SCLM.
How to cite: Li, S., Qiu, K.-F., Kusky, T., Wang, L., Yu, H.-C., Wu, M.-Q., Frimmel, H., Gao, Y.-X., Zhou, T., Yang, Z.-Y., Xi, Z.-C., and Deng*, J.: Mantle metasomatism facilitates the formation of continental crust and metal enrichment, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8010, https://doi.org/10.5194/egusphere-egu25-8010, 2025.
New discoveries of ore deposits are essential to secure our future demand on raw materials. Exploration for major hidden ore deposits at depth requires novel exploration concepts based on mineral system analyses beyond the deposit scale. Such approaches seek to develop a fundamental understanding of the process chain of coupled physical and chemical interactions between magmas, fluids and rocks that lead to the formation of large ore deposits. Numerical models will play a key role in bridging spatial and temporal scales varying by orders of magnitude. In this contribution, we present new numerical constraints on the formation of porphyry Cu-Mo and epithermal Au-Ag deposits. The model can simultaneously resolve both magma (Navier‐Stokes) and hydrothermal (Darcy) flow. It further uses realistic non-linear properties of crystallizing magmas and saline fluids, dynamic permeability feedbacks including fault structures, and proxies for metal transport. The simulations describe the interplay of episodic sill emplacements, magma convection, focused volatile degassing, hydraulic fracturing, fluid phase separation and mixing. The model further simulates the fate of chemical components like salts and metals, considering fluid-melt and vapor-brine partitioning, as well as precipitation and remobilization. The simulation results show that the coupled physicochemical interactions of all of these processes can self-organize into the accumulation of voluminous hydrous magma reservoirs, distinct stages of degassing and ore precipitation by interaction with groundwater convection in typical porphyry ore shells (e.g. Gruzdeva et al., 2024). The modelled temporal and spatial evolution of the magmatic-hydrothermal system successfully reproduces and explains many observations at porphyry and epithermal deposits worldwide. Combining these first-order constraints from simplified numerical models with geochemical and geophysical data provides a promising avenue for the development of multi-method approaches to develop robust exploration criteria for future discoveries of critical mineral deposits.
Gruzdeva, Y., Weis, P., Andersen, C. (2024): Journal of Geophysical Research: Solid Earth, 129, 7, e2023JB028433. https://doi.org/10.1029/2023JB028433
How to cite: Weis, P. and Gruzdeva, Y.: Numerical Modelling of Coupled Interactions of Magmas, Fluids and Rocks in the Formation of Porphyry Copper Deposits, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5671, https://doi.org/10.5194/egusphere-egu25-5671, 2025.
Reported Paleoproterozoic rare earth element (REE) deposits worldwide are quite limited. Here, we present the first detailed studies on a volcanic-sedimentary metamorphic type REE deposit, namely the Shengtieling REE deposit in NE China, to give a further case. The Shengtieling REE deposit (central Liaoning) occurs in the Lieryu Formation of the South Liaohe Group and is located in the Paleoproterozoic Jiao-Liao-Ji tectonic belt. The BSE images, combined with the monazite LA-ICP-MS in-situ trace elements, show that the main REE minerals are monazite, xenotime, and apatite from the magnetite leptynite. According to zircon and monazite U-Pb geochronological results, the maximum depositional age for magmatic clastic zircon is 1.95Ga, but both metamorphic zircons and monazites give similar ages of 1.90~1.87Ga. Whole-rock trace elements data suggest a continental island arc origin for the magnetite leptynite samples, thus indicating that the protolith may be arc-related sedimentary rocks. Notably, the 1.90~1.87Ga metamorphism is consistent with the timing of regional metamorphism, confirming the existence of arc-continent collision during the formation of the Jiao-Liao-Ji tectonic belt. Thus, based on the above new results, the Shengtieling REE deposit should be a typical Paleoproterozoic volcanic-sedimentary metamorphic type REE deposit. More attention should be paid to exploring similar REE deposit types in NE China and elsewhere.
How to cite: Liu, B., Ju, N., and Liu, X.: Zircon and monazite U-Pb geochronology and trace elements unravel a Paleoproterozoic volcanic-sedimentary metamorphic type rare earth element deposit in NE China, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3683, https://doi.org/10.5194/egusphere-egu25-3683, 2025.
Despite their close temporal and spatial relationships, the effects of tectono-thermal events on ore formation remain obscure. To better understand this process, a comprehensive geochemical investigation was conducted on syn-tectonic pegmatite and quartz veins associated with the Devonian subduction and Permian collision of the Chinese Altai. We found that the Devonian fluids were organic alkanes-CO2-S-Ca-Mg-rich saline fluids with variable CO2/CH4, lower F−/SO42− and Al3+/Mg2+ ratios, whereas the Permian fluids are immiscible fluids including CO2-C4H10-CO-rich oxidized gas bubbles and CH4-C3H8-C2H6-Ca-Na-K-Al-S-Cl-F-rich reduced saline fluids with lower CO2/CH4 (mostly <1), higher F−/SO42− and Al3+/Mg2+ ratios. The Devonian and Permian fluids also have similar δ13C-CO2 values of −3.5~−23.8‰ and −3.7~−16.5‰, repressively. These data suggest that both fluids derived mainly from devolatilization and dehydration melting of metasediments but the Permian fluids likely involve more muscovite dehydration and biotite melting in the shallower and deeper crust, respectively. Besides, the Devonian fluids contain more meteoric components whereas the Permian fluids contain more mantle-derived components. Base metal-dominated Devonian mineralization occurred as the deep-sourced organic matter-S-rich fluids promote base metal migration whereas the relatively oxidized fluid conditions inhibited mineralization of many other metals. By contrast, the more reduced and F-rich Permian fluids with more mantle contributions facilitated the extraction of Au and uptakes of rare metals from reworked metasediments and promoted their mineralization. These findings provide more complete pictures of how tectono-thermal events fertilize the crusts and demonstrate that syn-tectonic fluids can serve as proxies for metallogenic processes during orogenic cycles in general.
How to cite: Xiao, M., Zhao, G., and Jiang, Y.: Syn-tectonic fluids decoding effects of tectono-metamorphic cycles on regional metallogenic evolution of the Chinese Altai, central Asia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15366, https://doi.org/10.5194/egusphere-egu25-15366, 2025.
Thermodynamic modelling of H2O, HCl and NaCl ionization at magmatic-hydrothermal conditions provides essential basis for understanding speciation, acidity changes, metal complexation and ore-deposit formation. We critically evaluate modelling of H2O, HCl and NaCl ionization using pre-existing approaches in literature, that include: (i) electrostatic models [1,2]; (ii) models based on semi-empirical logarithmic correlations with water density [3]; (iii) models based on virial expansion [4]; (iv) approaches based on stepwise hydration of solute [5], and (v) various statistical-mechanics-based theories [6]. Simulations of H2O, HCl and NaCl ionization from individual models are consistent up to 400 °C and pressures above 3 kbar. However, significant discrepancies emerge with increasing temperatures and decreasing pressures. Electrostatic and virial models at low pressures (below 300 bar) and at high fluid density poorly perform partly because loose physical significance. Hydration models and approaches based on mean spherical approximation inaccurately describe pressure-temperature dependence. Density models emerge as the most accurate in ionization predictions and therefore, as promising approach for constructing new equations of state for ionic species. We develop a new low-parametric density model to depict the thermodynamic properties of aqueous species in low-density hydrothermal fluids with a more rigorous theoretical framework that incorporates intrinsic properties of aqueous solute (entropy, enthalpy, heat capacity and hardcore volume) and accounts for solute-solvent interactions (via volume compression). Our new density model offers improved accuracy and performance in the temperature-pressure space requiring fewer equation parameters in comparison to existing models in literature. The new density model is applied for the prediction of H2O, HCl and NaCl speciation along four fluid-flow paths representing distinct crustal settings, specifically: transcrustal metamorphic devolatilization, intrusion-related lateral, vertical and adiabatic flow. Simulations reveal that metamorphic fluids have ionization capability by four orders of magnitude greater than the upper-crustal magmatic fluids. This demonstrates the superior effectiveness of high-pressure fluids in the transport of ionic species and acidity generation. Fluids exsolved from upper-crustal magmatic sources during lateral or vertical flow exhibit mutually comparable behavior upon cooling and progressively ionize species and produce significant acidity from 400 °C. By contrast, speciation occurring during adiabatic flow is mainly controlled by decreasing fluid density, and as the fluid cools and expands solute species remain completely associated. Overall, the simulation of the four thermal gradients highlights the major impacts that pressure and fluid density have on H2O, HCl and NaCl ionization and the various efficiency for acidic alteration and mineralization of hydrothermal fluids along their specific pathways and hydrodynamic conditions.
References:
[1] Tanger IV J C, Helgeson H C (1988) Am J Sci 288: 19-98
[2] Shock E L et al. (1992) J Chem Soc Faraday Trans 88: 803-826
[3] Marshall W L and Franck E U (1981) J Phys Chem Ref Data 10: 295-304
[4] Akinfiev N N and Diamond L W (2003) Geochim Cosmochim Acta 67: 613-627
[5] Djamali E and Cobble J W (2009) J Phys Chem 113: 2398-2403
[6] Lvov S N et al. (2018) J Molecul Liq 270: 62-73
How to cite: Salomone, F. and Dolejs, D.: Ionization of H2O, HCl, and NaCl in low-density crustal fluids: thermodynamic modeling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11313, https://doi.org/10.5194/egusphere-egu25-11313, 2025.
Vein-type gold orebodies in hydrothermal gold deposits normally develop vein-type orebodies normally composed of quartz and metal sulfides. Calcite, as one of the common minerals in vein-type gold deposits, commonly formed in the late mineralization stage. The Phapon gold deposit, located in northern Laos, is a unique deposit that is characterized by calcite as the main gangue mineral, free gold coexist with iron oxide, very low content of quartz and metal sulfides, and no spatial correlation with intrusive rock. The auriferous veins are hosted in lower Permian carbonate rocks and controlled by subparallel, NNW-trending brittle faults. The gold orebody is composed of a 0.3–2.0 m wide auriferous calcite vein that fills the fault zone, and the surrounding siderite and hematite alteration zones, with sparsely disseminated silification and sulfidation. The auriferous calcite vein consists of calcite (~90 vol%), subsequent siderite (~5 vol%) and hematite (~3 vol%), and a small amount of quartz, realgar, magnetite, orpiment, and traces of pyrite. In the siderite and hematite alteration zones, the hydrothermal mineral assemblage is similar to the veins, with less quartz, realgar, and orpiment and lacking pyrite.
Based on detailed field investigation, and microscopic and CL studies, three ore-forming stages were recognized as the pre-ore calcite(Cal-1)±quartz±pyrite veins, main-ore calcite(Cal-2)-siderite-hematite-realgar±orpiment-gold veins, and post-ore calcite(Cal-3) veins. The primary metal sulfides are mostly replaced by goethite during secondary oxidation. Gold normally formed as free gold that occurs in microcracks or along grain boundaries of Cal-2, or coexisted with goethite and fibrous hematite aggregates.Fluid inclusion petrography and microthermometry study suggested that the ore-forming fluids belong to a median-low temperature (180–240°C) and low salinity (3–10 wt% NaCl eq.) NaCl-H2O-CO2 system. Gold precipitation was mainly related to fluid immiscibility caused by pressure drop. Considering the coexistence of pyrite and iron-oxides in gold ores, gold deposition may be also related to changes of Eh and pH during the hydrothermal processes. Calcite LA-ICP-MS trace element analysis suggests inheritance between hydrothermal calcite and carbonate wall rock. Cal-2 shows higher REE, Mn, and Fe concentrations and the most obvious LREE-enrichment patterns compare to Cal-1 and Cal-3, indicating the ore-forming fluids in the main-stage are more acidic and have more intense fluid-rock interaction at the deposit trap. Vein calcite was dated by LA-SF-ICP-MS and obtained a lower intercept U-Pb age of 221.6 ± 7.6 Ma, which is interpreted as the Au mineralization age for the Phapon deposit. This age indicates that the epizonal orogenic gold mineralization event continued in the Late Triassic along the northwestern margin of the Indochina Block, postdating the late Permian–middle Triassic low-sulfidation epithermal and porphyry-skarn Au mineralization events and corresponds to the collision between the Sibumasu Terrane and the Indochina Block.
No similar deposit has been described until now, further study on the P-T-Eh-pH controlling factors during gold enrichment and precipitation process of Phapon will probably help to establish the metallogenic model of this kind of calcite-iron oxide vein-type gold deposits that spatially unrelated to intrusive rock mass, and further enriches the metallogenic theory of hydrothermal gold deposits.
How to cite: Guo, L.-N., Kolb, J., and Tang, Y.-W.: Gold enrichment and precipitation in the unique calcite-iron oxide vein-type Phapon gold deposit, Laos, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7713, https://doi.org/10.5194/egusphere-egu25-7713, 2025.
Calcite is one of the primary host for rare earth elements (REE) in carbonatites. The Kamthai carbonatite complex contains the largest REE budget among Indian carbonatite complexes. This study reports new 87Sr/86Sr isotope ratios of six textural types of calcite in carbonatite and calcite-quartz veins in phonolite of Kamthai along with their major and trace element composition to constrain the magmatic and hydrothermal evolution of carbonatite. Four textural types of calcite (magmatic: CalM and CalPR; and secondary: CalSK and CalS) in carbonatite show consistent mantle-like 87Sr/86Sr ratios. The CalM has restricted 87Sr/86Sr (0.70437±0.00005) and contains high concentrations of ƩREE, Sr, Ba, and Mn without any Ce anomaly. It probably crystallized from the late-stage brine-melt with primary carbocernaite. The CalM is partially re-equilibrated into CalPR (0.70425±0.00024) during interaction with syn-magmatic fluid, resulting in the loss of a significant amount of REE and Sr. The two secondary varieties of calcite show overlapping and marginally higher 87Sr/86Sr (CalSK: 0.70469±0.00041; CalS: 0.70478±0.00025; δCe*: <0.7 for both) than CalM, indicating that they were altered by syn– to para– magmatic fluids with partial contribution from external hydrothermal fluid. The fluid-induced re-equilibration led to the expulsion of most of its original Sr and REE content. Two types of secondary calcite (CalS1 and CalS2) are identified in three veins within phonolite. These contain the lowest abundance of ΣREE+Y, Sr, Ba, and Mn. One type of calcite (CalS1) defines two clusters of 87Sr/86Sr ratios: 1) one cluster (0.70443±0.00035) is identical to CalM and crystallized from late-stage syn– to para–magmatic fluids. 2) Calcite defining the second cluster has significantly more radiogenic 87Sr/86Sr (0.70768±0.00063) compared to the other varieties of calcite. Calcite of both clusters is characterized by prominent negative Ce (δCe*: <<0.034) anomalies, indicating their crystallization from oxidized fluids that removed Ce as Ce(IV). Mixing calculations indicate that mixing of 40–70% post-magmatic fluid with syn-magmatic fluid can account for the higher 87Sr/86Sr composition. The other type of calcite (CalS2) is characterized by LREE-depleted REE patterns without any anomaly and mantle-like 87Sr/86Sr (0.70434±0.00073). It possibly crystallized from late-stage para-magmatic fluids exsolved from the carbonatite melt after primary LREE mineralization.
How to cite: Chandra, J., Upadhyay, D., Patel, A. K., and Mishra, B.: Calcite trace element chemistry and in-situ measured 87Sr/86Sr composition as a recorder of hydrothermal interaction of carbonatite: a case study from the Kamthai complex (western India) , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-199, https://doi.org/10.5194/egusphere-egu25-199, 2025.
The development of high-grade Cl brines is linked to some of the major mineral deposits, such as IOCG and skarns, that are often characterized by wide aureoles of scapolitization. In terranes of enhanced metallogenesis, the prograde track scapolitization can be obscured by the later intense hydrothermal reworking, making it difficult to reconstruct the prograde fluid development. For these reasons, studying the unmineralized country rocks in a deposit vicinity could provide otherwise erased information on deposit formation. The augen orthogneisses from scapolitization aureoles, located beneath the Varena Iron Ore Deposit (VIOD), in the East European Craton (Lithuania) were chosen for this study. The rocks are composed of Cpx-Amf-Bt-Pl-Kf-Scp-Qtz-Ilm-Mag-Ttn. They range from domain-structured gneiss with Pl phenocryst remains (partly or entirely replaced by Scp) in distal parts (samples D8 and D9), to almost pure scapolite rock at contact with the iron ore (sample V987), suggesting re-equilibration at different temperature and varying fluid composition and fluid/rock ratios.
Scapolite replacing Pl phenocrysts (D8 and D9) from the prograde metamorphic assemblage of Cpx+Pl+Kf+Bt+Qtz+Ilm in the mafic domains has a Cl content increasing from 0.44 apfu in the core to 0.87 apfu in the rim. The matrix scapolite forming channel-like patchwork in the felsic matrix has Cl content up to 1 apfu and is in equilibrium with the peak-temperature Mg-Hst (750 °C, sample D9). Similar Ap-Bt temperatures of 694-766 °C were obtained in the sample D8. Biotite is thinning out towards the mafic domain centre, where it completely disappears, suggesting a partial melting of the biotite and formation of the Pl+Kf+Qtz+Scp felsic matrix around the mafic domains.
An inverse relationship in scapolite chlorinity was observed in samples with high fluid/rock ratios (V987). Here, the Cl content of 0.64-0.89 apfu is recorded in the blocky scapolite, surrounded by an analcime-scapolite (Cl content of 0.32-0.76) matrix with minor calcite and anhydrite. The Cl content in matrix scapolite is decreasing towards the contact with the ore. This indicates a change in fluid regime and its chemistry during the retrogression, with decreasing chlorinity and increased oxygen fugacity.
High Cl content in scapolite at the estimated peak conditions suggests the presence of a fluid with high aCl and low aH2O. Domain structure, dehydrated biotite and dark-CL metamorphic zircon rims are in favour of partial melting at the peak temperatures. Water is highly partitioned into the silicate melt, whereas chlorine solubility in silicic melts is very limited and is usually retained in the fluid phase. Thus, in a rock-buffered fluid, partial melting could shift fluid composition in the ternary system H2O-CO2-NaCl towards or into the “halite” stability field, producing molten salts, capable of mobilizing elements such as Fe, REE, U and Th.
How to cite: Šiliauskas, L. and Skridlaite, G.: Effect of a partial melting on the development of ore-forming fluid: a case study from the Varena Iron Ore Deposit, SE Lithuania, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-523, https://doi.org/10.5194/egusphere-egu25-523, 2025.
Mineral dendrites are tree-like, branched patterns commonly found on or within rocks, typically formed by the deposition of minerals like manganese or iron oxides. In natural systems these patterns exhibit diverse morphologies and shapes, varying in thickness or degree of branching. This study focuses on quasi-planar dendritic patterns growing along fractures and bedding planes. In these dendrites, abrupt morphological transitions, where their thickness changes suddenly, are often observed. Understanding the mechanisms behind this phenomenon is the aim of this work.
Dendrites form through the infiltration of fractured rocks by manganese- or –iron-bearing fluids. When these fluids mix with oxygenated solutions, metal oxides precipitate, creating the dendritic patterns. The exact deposition mechanism remains debated. One model suggests that as the fluids mix, nanoscale particles of manganese or iron oxide are first formed. These nanoparticles then aggregate, resulting in the formation of mineral dendrites.
In such a scenario, the final dendrite morphology turns out to be highly sensitive to the initial concentrations of manganese (or iron) in the system. We show that morphological transitions can be triggered by subsequent infiltrations of metal-bearing fluids, characterized by different concentrations of manganese/iron ions. However, we also point to another factor that can induce morphological transitions in dendrites, this time related to the change in the aperture of the fracture or bedding plane along which they grow. We show that larger fracture apertures correlate with the formation of thicker dendritic structures. We analyze the characteristics of both transitions, focusing on the features that allow them to be distinguished from one another.
The ultimate goal would be to establish a link between the morphology of the dendrites and the physicochemical conditions in which they grew. This connection would allow for the decoding of the hydrogeochemical history of the dendrite-bearing rock strata.
How to cite: Woś, D., Szymczak, P., and Hou, Z.: Morphological transitions in mineral dendrites, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-695, https://doi.org/10.5194/egusphere-egu25-695, 2025.
Granite-hosted gold deposits, a major component of global gold resources, exhibit complex geochemical evolution and diverse mineralization types. Understanding the mechanisms of gold precipitation and enrichment in these systems is crucial for mineral resources exploration and extraction. Alteration processes such as potassic alteration, sericitization and pyritization significantly influence gold mobility and concentration. However, their roles in fluid-rock interactions and coupled physical-chemical dynamics remain insufficiently understood due to the complexity of mineralogical and environmental factors, as well as limited experimental and modeling data.
This study employs PFLOTRAN-based reactive transport modeling to explore the geochemical mechanisms of gold precipitation and enrichment, using the Sanshandao gold deposit in Jiaodong Peninsula, China, as a case study. Integrating geological data, hydrothermal fluid dynamics, and thermodynamic of chemical reaction networks, the model explores the influence of alteration minerals, including K-feldspar, sericite and pyrite, on fluid composition, gold solubility and precipitation. It evaluates the effects of critical parameters such as temperature, pressure and PH on the stability and solubility of gold-bearing complexes, revealing the advantageous conditions for gold precipitation.
Alteration minerals affect hydrothermal fluid properties, such as PH and redox potential, which govern gold precipitation. For example, sericitization decreases fluid PH and enhances gold solubility, while pyritization facilitates adsorption, promoting localized gold enrichment. This underscores the importance of fluid-rock interactions and geochemical conditions in controlling gold transport and enrichment.
This study offers a framework for understanding the physical-chemical mechanisms of gold mineralization in granite-hosted gold deposits. The use of reactive transport modeling provides insights how alteration processes and fluid-rock interactions shape ore-forming mechanism similar to geological settings.
Keywords: Granite-hosted gold deposits; Reactive transport modeling; Fluid-rock interaction; Gold precipitation and enrichment; Ore-forming mechanism
How to cite: Cai, Y., Qiu, K.-F., Szymczak, P., Ladd, A. J. C., He, D.-Y., Yu, H.-C., and Cui, T.: Reactive Transport Numerical Modeling of Gold Precipitation and Enrichment of Granite-Hosted Gold Deposit, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-822, https://doi.org/10.5194/egusphere-egu25-822, 2025.
The resource demands for the ongoing energy transition require increased exploration for metal deposits. Clastic dominated (CD-type) deposits are an important target in this search because of their size and high grade. To narrow down the search for CD-type deposits, it is important to understand how they formed. One proposed formation mechanism for these deposits is sedimentary exhalative (SEDEX), in which fluid discharge from vents resulting in stratiform sulfide precipitation on the seafloor. Alternatively, it has been suggested that CD-type deposits can form beneath the seafloor, when hydrothermal fluids dissolve specific minerals (e.g., carbonate, barite) and precipitate ore in the host rock. In his study we simulate several ways in which subseafloor replacement can create stratiform mineralization that occur along laminae or single beds.
We ran a series of models using the software X2t (part of GWB) to investigate scenarios where hydrothermal fluids formed stratiform mineralization through carbonate replacement of a mixed carbonate carbonaceous mudstone unit. The models were based on the mineralogy of the Teena deposit (Australia). In the simulations, which used organic material and/or pyrite as redox buffers, a slightly acidic hydrothermal fluid replaced dolomite with sphalerite.
One scenario that resulted in stratiform mineralization was in a system with high rates of flow. The Péclet number is the ratio of advective to diffusive transport. When the Péclet number was high, advection dominated over diffusion and mineralization concentrated along preferential flow paths. The dissolution and replacement of carbonate during alteration created a feedback mechanism that enhanced flow along already permeable zones. When there were existing stratigraphic based differences in permeability, the required Péclet number for stratiform mineralization was lower.
Another set of models that produced stratiform mineralization had reducing beds that acted as a reductant for metals flowing through adjacent units. Reduced compounds flowed out of the reducing beds and caused pyrite or sphalerite precipitation in adjacent cells. This redox gradient could be created by the presence of organic matter or a simple permeability difference. Finally, a model containing mineralogic heterogeneities resulted in stratiform mineralization by creating beds with lower pH. Acid formed in areas with low initial concentrations of carbonate minerals. The acidic fluid then seeped into the adjacent beds with higher carbonate mineral concentrations. The dissolution of carbonate in the adjacent beds led to the creation preferential flow paths and stratiform mineralization.
The models simulated ways in which heterogeneities and preferential flow paths in a mixed carbonate carbonaceous mudstone unit could create stratiform mineralization during hydrothermal alteration. High flow rates and variations in permeability or mineralogy can result in not only the stratiform mineralization of the ore minerals, but also of pyrite as a reaction front preceding the ore deposition forming a distal halo.
How to cite: Berger, P. M., Magnall, J. M., Kühn, M., and Gleeson, S. A.: Mechanisms to create stratiform mineralization in sedimentary rocks through hydrothermal processes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3647, https://doi.org/10.5194/egusphere-egu25-3647, 2025.
Peraluminous rare-metal granites from South China constitute the largest, minable hard-rock lithium resources in the world. An ongoing debate is whether the Li in these granites was concentrated to economic grades via igneous processes alone, or whether metasomatic processes played an indispensable role in achieving economic grades. The Yichun deposit is a suitable locality to study lithium mineralization processes; here, a zoned petalite (LiAlSi4O10)-bearing pegmatite sheet was intruded by underlying Li-rich granites, where both the pegmatite and granites have previously been interpreted to have originated from the same magma. Two types of sequentially crystallized quartz are present in the core zone of the pegmatite. An early quartz yields similar δ18O values to magmatic graphic quartz. This early quartz is fractured, free of mineral inclusions, and was crosscut or partially replaced by an inclusion-rich, late quartz, which exhibits comparable δ18O values to magmatic quartz, as opposed to the higher δ18O values of hydrothermal quartz at Yichun. Titanium-in-quartz thermobarometry constrains that both quartz generations were formed at comparable temperatures to the magmatic graphic quartz and share a magmatic origin. The inclusions in the late quartz are a vermicular variety, composed of abundant petalite and lesser orthoclase. Image analysis-based mass balance calculations yield an average of 2,300 ppm Li in the original melt that formed the mineral assemblage in the late quartz. Such a Li abundance is lower than the minimum Li (~5,000 ppm) required for direct crystallization of petalite from a peraluminous melt. The petalite inclusions are, therefore, interpreted as exsolution from a transient, magmatic quartz-petalite solid solution containing ~2,300 ppm Li and ~8,000 ppm Al that chemically resembled the stuffed quartz synthesized from crystallization experiments. To attain ~2,300 ppm Li in the core zone, 90% fractionation of an initial pegmatite melt containing ca. 300 ppm Li is sufficient, and formation of a boundary layer to concentrate Li is not required. The current evidence suggests that up to 1.2 wt% Li in the Yichun granite-pegmatite system resulted from metasomatism that further added Li. Such metasomatic enrichment likely applies to analogous systems in South China.
How to cite: Wu, M., Samson, I., Borst, A., Diao, X., Beard, C., and Hou, Z.: Vermicular petalite-orthoclase intergrowths in quartz: A natural occurrence of stuffed quartz and its implications for economic lithium mineralization , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5354, https://doi.org/10.5194/egusphere-egu25-5354, 2025.
Orogenic gold deposits are among the most important sources of gold globally. Ore occurs either in veins or disseminated within the host rock. While the dynamic permeability enhancement and fluid flow processes associated with vein-type ores have been extensively studied, the specific physical and chemical processes associated with fluid flux in disseminated ores have been largely overlooked. Here, we combine structural analysis, microstructural observation, and thermodynamic modeling of disseminated mineralized dacite to investigate the permeability evolution and the associated fluid flow characteristics in the Zaozigou orogenic gold deposit. The mineralized dacite is bordering an extensional quartz-stibnite vein that formed in response to rock implosion triggered by fluid pressure drops associated with co-seismic dilation on a nearby fault segment. The subsequent lateral alteration zonation on either side of the vein can be divided into four distinct zones (Z1-Z4) based on local geochemical and mineralogical variations:: Z1 is characterized by the enrichment of invisible gold, pyrite, arsenopyrite, sericite, albite, and dolomite; Z2 shows the occurrence of siderite, sericite, albite, and dolomite; Z3 can be defined by the concentration of chlorite and sericite; Z4 represents the least-altered dacite composed of quartz, biotite, and feldspar. Interconnected cracks observed in weakly altered dacite (Z3) reflect fluid pressure-induced grain-scale microcracking. In addition, the grain size reduction associated with fully altered minerals (Z1-Z2) results in the development of numerous new fluid pathways (grain boundaries) and a gradual increase in permeability. Pyrite, arsenopyrite, sericite, siderite, and chlorite are primarily distributed along the cleavage planes of biotite, while sericite and albite align with newly formed pores in feldspar. Additionally, dolomite is also observed around feldspar grains in Z1 and Z2. The spatial distribution of these hydrothermal minerals indicates that fluid flow predominantly occurred along pre-existing cleavage planes and newly formed microcracks and pores. The precipitation of hydrothermal minerals observed in altered dacite (Z1-Z3) indicates that the early increased permeability was eventually destroyed. Thermodynamic models based on our microstructural and geochemical investigations suggest that sulfidation reactions led to gold precipitation in the altered dacite and the subsequent compositional changes in reactive fluid flow are the predominant driver for the formation of the lateral alteration zoning.
How to cite: Zhang, P.-C., Qiu, K.-F., Rogowitz, A., Yu, H.-C., and Hou, Z.: Evolution of transient permeability and fluid flow in disseminated ores of Zaozigou orogenic gold deposit, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8749, https://doi.org/10.5194/egusphere-egu25-8749, 2025.
Geochemical evidence suggests that arsenic is a key accelerator reinforcing gold mineralization in pyrite. The systematic presence of Au-bearing arsenian pyrite in hydrothermal systems highlights the coupled Au-As geochemical behaviors in various physio-chemical conditions. However, there is a lack of understanding of elemental interactions at the atomic scale during gold mineralization.
Here, we employ ab initio simulations to detect the atomic-scale mechanisms governing gold incorporation in arsenian pyrite. By computing crystal unit cell volume, incorporation energy, and detailed electronic properties, we demonstrate the fundamental role of arsenic in gold occurrence, which effectively leads us to revisit the Au-As coupling.
We obtain that the Au-As substitution is one of the most favorable double substitutions into pyrite. The incorporation of As induces the expansion of the unit cell, which facilitates the substitution of the Au atom to the Fe-site. Lattice distortions of pyrite caused by other elements (including the common trace elements in pyrites) promote this process on a smaller scale. Among several calculated double substitutions, the valence shell of As and the volume of the [FeAsxS6-x] polyhedra provide a unique preferential environment that can easily accommodate incompatible elements, such as Au.
Our study provides a novel insight of the co-evolutionary process between Au-As coupling in pyrite during gold mineralization, and propose a fresh approach to detect the dynamic evolution between varying trace elements occurring in different mineralization system.
How to cite: Gao, Z.-Y., Deng*, J., Caracas, R., Long, Z.-Y., He, D.-Y., Yu, H.-C., and Qiu, K.-F.: Reappraisal of arsenic-gold interaction in pyrite: insights from ab initio simulations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13949, https://doi.org/10.5194/egusphere-egu25-13949, 2025.
Posters virtual: Thu, 1 May, 14:00–15:45 | vPoster spot 1
EGU25-2404 | Posters virtual | VPS23
Rare-metal and rare earth element mineralizations in the eastern Liaoning-southern Jilin tectonic zone in Northeast China: A reviewThu, 01 May, 14:00–15:45 (CEST) vPoster spot 1 | vP1.5
The eastern Liaoning-southern Jilin tectonic zone (also referred to as the Liao-Ji tectonic zone), a potential zone for rare-metal and REE mineralizations in China, hosts over 10 rare-metal and REE deposits and ore occurrences with varying scales and mineralization characteristics, which establish this zone as an ideal target for research on the metallogenic regularities of rare-metal and REE mineralizations.The study area resides in the northern part of the East Asian continental margin, lying on the overlapping part of the North China and the Western Pacific Plates, is located in the northeastern North China Plate, consisting of the North China Craton and the north margin orogen of the North China Plate. This area serves as a critical large-scale copper-gold and polymetallic mineral resource base in China, also providing favorable geologic conditions for the enrichment and mineralization of rare metals and REEs. So far, many rare-metal and REE deposits and ore occurrences have been discovered in the Liao-Ji tectonic zone, including two large Nb-Be-Zr-REE deposits (i.e., Lijiapuzi and Pianshishan), two medium-sized Rb-Be-Nb-Ta-REE deposits (i.e., Saima and Gangshan), one small Nb-Ta-REE deposit (i.e., Shijia), and over 10 rare metal-REE ore occurrences (e.g., Xiaolizi, and Baiqi), suggesting considerable mineralization potential. Most of the deposits in the Liao-Ji tectonic zone are closely associated with alkaline rocks.
Extensive field surveys and geochemical studies of the above deposits reveal that the ore-forming rock masses of the Pianshishan, Gangshan, and Lijiapuzi deposits include alkaline granites and pegmatites and those of the Shijia and Saima deposits are quartz syenites and aegirine nepheline syenites, respectively. The Pianshishan (67±2.2 Ma) and Gangshan (110±1.2 Ma) deposits were formed during the Yanshanian, the Shijia (226.3±2.4 Ma) and Saima (224.4±6.1 Ma) deposits originated from the Late Indosinian magmatism, while the formation of the Lijiapuzi deposit (2501±11 Ma) was associated with the Lvliang Movement. Therefore, the study area underwent three stages of regional rare-metal and REE mineralizations: the Late Yanshanian (Mesozoic), Late Indosinian (Mesozoic), and Proterozoic Lvliangian mineralizations. The petrogeochemical analysis indicates that the ore-forming rock masses of several typical deposits all belong to the metaluminous, alkaline - calc-alkaline, and tholeiitic basalt series, sharing similarities with the elemental geochemical characteristics of intraplate rift rock series and rocks in an extensional environment under plate subduction. The rare-metal and REE mineralizations in the study area were primarily governed by the evolution and crystallization differentiation of alkaline magmas. Given that the alkaline magmatic rocks were all formed by crust-mantle contamination, this study posits that the enrichment and mineralization processes of rare metals and REEs in the Liao-Ji tectonic zone are intimately associated with the highly evolved alkaline magmas. Under the action of water and volatile constituents, magmas underwent intense fractional crystallization, leading to the migration and accumulation of ore-forming elements. With changes in ore-forming conditions such as temperature and pressure, ore-bearing fluids became enriched and mineralized in the late stage of magmatism with the crystallization of primary rock-forming minerals.
How to cite: Ju, N., Yang, G., Zhang, P., Li, J., Wu, Y., Lu, S., Liu, B., Yang, X., Liu, X., and Feng, Y.: Rare-metal and rare earth element mineralizations in the eastern Liaoning-southern Jilin tectonic zone in Northeast China: A review, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2404, https://doi.org/10.5194/egusphere-egu25-2404, 2025.
