Jolan Acke, Stijn Dewaele, Renata Barros, Christian Burlet, Simon Nachtergaele, Justin Uwiringiyimana, Tobias Fußwinkel, Anouk Borst
Pegmatites in the Mesoproterozoic Karagwe-Ankole belt of Central Africa are associated with large granitic complexes that were emplaced around 1 Ga. This study analyzes drill core samples of fresh albite-spodumene pegmatites from the Musha-Ntunga area (East Rwanda), spatially associated with the Lake Muhazi granitic pluton. We combine petrographic and cathodoluminescence microscopy with Raman spectroscopy and elemental geochemistry to study the paragenetic sequence, microtextural variations, and lithium distribution, from the magmatic and magmatic-hydrothermal stages to the hydrothermal stage and during deformation processes. Five textural types of spodumene are distinguished. Coarse-grained spodumene type 1 and symplectitic type 2 are interpreted to have formed during primary magmatic crystallization, whereas spodumene types 3 and 4 formed during magmatic-hydrothermal alteration. Deformation locally affected the pegmatite intrusions. Spodumene type 1 crystals deformed in a brittle and ductile manner, displaying sigma-clast-shaped porphyroclasts (“spodumene fish”) and boudinage textures. The large strained spodumene crystals were also partially recrystallized to fine-grained elongated crystals (type 5), which occur in bands along with mica, quartz, and apatite and define the main orientation of foliation. Montebrasite occurs both as a late primary magmatic phase with spodumene and as a secondary phase that recrystallized during magmatic-hydrothermal alteration and deformation. Eucryptite, lithiophilite, and cookeite occur as late-stage hydrothermal phases, replacing primary lithium assemblages. Associated phases muscovite, apatite, microcline, albite, quartz, and columbite-tantalite further demonstrate the transition from a magmatic to a (magmatic-)hydrothermal and deformational regime. Elevated lithium contents in tourmaline within the metasedimentary host rock indicate dispersion of lithium into the host rock during pegmatite emplacement, subsequent crystallization, and alteration. The results of this multimethod approach demonstrate that different generations of lithium-bearing minerals and associated textures not only record the full transition from a magmatic to hydrothermal regime but also document deformation-related processes that can impact the distribution of metals within pegmatites.
{"title":"Magmatic, Magmatic-Hydrothermal, and Deformational Mineral Evolution of Spodumene Pegmatites from the Musha-Ntunga Area (Rwanda)","authors":"Jolan Acke, Stijn Dewaele, Renata Barros, Christian Burlet, Simon Nachtergaele, Justin Uwiringiyimana, Tobias Fußwinkel, Anouk Borst","doi":"10.5382/econgeo.5173","DOIUrl":"https://doi.org/10.5382/econgeo.5173","url":null,"abstract":"Pegmatites in the Mesoproterozoic Karagwe-Ankole belt of Central Africa are associated with large granitic complexes that were emplaced around 1 Ga. This study analyzes drill core samples of fresh albite-spodumene pegmatites from the Musha-Ntunga area (East Rwanda), spatially associated with the Lake Muhazi granitic pluton. We combine petrographic and cathodoluminescence microscopy with Raman spectroscopy and elemental geochemistry to study the paragenetic sequence, microtextural variations, and lithium distribution, from the magmatic and magmatic-hydrothermal stages to the hydrothermal stage and during deformation processes. Five textural types of spodumene are distinguished. Coarse-grained spodumene type 1 and symplectitic type 2 are interpreted to have formed during primary magmatic crystallization, whereas spodumene types 3 and 4 formed during magmatic-hydrothermal alteration. Deformation locally affected the pegmatite intrusions. Spodumene type 1 crystals deformed in a brittle and ductile manner, displaying sigma-clast-shaped porphyroclasts (“spodumene fish”) and boudinage textures. The large strained spodumene crystals were also partially recrystallized to fine-grained elongated crystals (type 5), which occur in bands along with mica, quartz, and apatite and define the main orientation of foliation. Montebrasite occurs both as a late primary magmatic phase with spodumene and as a secondary phase that recrystallized during magmatic-hydrothermal alteration and deformation. Eucryptite, lithiophilite, and cookeite occur as late-stage hydrothermal phases, replacing primary lithium assemblages. Associated phases muscovite, apatite, microcline, albite, quartz, and columbite-tantalite further demonstrate the transition from a magmatic to a (magmatic-)hydrothermal and deformational regime. Elevated lithium contents in tourmaline within the metasedimentary host rock indicate dispersion of lithium into the host rock during pegmatite emplacement, subsequent crystallization, and alteration. The results of this multimethod approach demonstrate that different generations of lithium-bearing minerals and associated textures not only record the full transition from a magmatic to hydrothermal regime but also document deformation-related processes that can impact the distribution of metals within pegmatites.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"54 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144900784","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. Humphreys, M. Brounce, M. A. McKibben, P. Dobson, N. Planavsky, B. Kalderon-Asael
The behavior of lithium during geothermal brine and host-rock interactions in the Salton Sea geothermal field is underconstrained. The lithium brine reservoir inventory is between 4 and 18 million metric tons of lithium carbonate equivalent, with an even larger amount present within the reservoir rock mineral phases. Here, we present bulk-rock and brine Li concentration and δ7Li, and in situ Li concentrations of minerals from the California State 2-14 scientific drill core and commercial wells in the Salton Sea geothermal field to identify the mineral hosts of Li and constrain Li behavior during brine-rock interactions. Lithium contents are highest in chlorite (270–580 ppm, ~2,358 m), which encases pyrite, indicating that Li is fixed from the brine into the host rocks during hydrothermal alteration. Lithium abundances in chlorite decrease with depth (70–100 ppm, ~2,882 m), as does whole-rock Li content, whereas whole-rock δ7Li increases (δ7Li = 2.0–4.3‰, ~2,485-m depth; δ7Li = 4.3–7.9‰ from ~2,819 to ~2,882 m). This change in behavior of Li at ~2,500 m suggests temperature dependent partitioning of Li in chlorite; Li becomes more incompatible in chlorite at depths >~2,500 m, corresponding to ~325°C in the reservoir. The brines have δ7Li = 3.7 to 4.7‰ and calculated isotopic fractionation factors between the brine and the host rock agree with a change in Li behavior at ~325°C. Simple closed-system batch modeling does not describe the geothermal system, suggesting open-system behavior of Li within the Salton Sea geothermal field.
{"title":"Characterization of Li in the Salton Sea Geothermal Field","authors":"J. Humphreys, M. Brounce, M. A. McKibben, P. Dobson, N. Planavsky, B. Kalderon-Asael","doi":"10.5382/econgeo.5161","DOIUrl":"https://doi.org/10.5382/econgeo.5161","url":null,"abstract":"The behavior of lithium during geothermal brine and host-rock interactions in the Salton Sea geothermal field is underconstrained. The lithium brine reservoir inventory is between 4 and 18 million metric tons of lithium carbonate equivalent, with an even larger amount present within the reservoir rock mineral phases. Here, we present bulk-rock and brine Li concentration and δ7Li, and in situ Li concentrations of minerals from the California State 2-14 scientific drill core and commercial wells in the Salton Sea geothermal field to identify the mineral hosts of Li and constrain Li behavior during brine-rock interactions. Lithium contents are highest in chlorite (270–580 ppm, ~2,358 m), which encases pyrite, indicating that Li is fixed from the brine into the host rocks during hydrothermal alteration. Lithium abundances in chlorite decrease with depth (70–100 ppm, ~2,882 m), as does whole-rock Li content, whereas whole-rock δ7Li increases (δ7Li = 2.0–4.3‰, ~2,485-m depth; δ7Li = 4.3–7.9‰ from ~2,819 to ~2,882 m). This change in behavior of Li at ~2,500 m suggests temperature dependent partitioning of Li in chlorite; Li becomes more incompatible in chlorite at depths >~2,500 m, corresponding to ~325°C in the reservoir. The brines have δ7Li = 3.7 to 4.7‰ and calculated isotopic fractionation factors between the brine and the host rock agree with a change in Li behavior at ~325°C. Simple closed-system batch modeling does not describe the geothermal system, suggesting open-system behavior of Li within the Salton Sea geothermal field.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"47 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144900785","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Madison Myers, Roberta Spallanzani, Darin M. Schwartz, Celestine Mercer, Behnaz Hosseini
The partitioning behavior of Li in magmatic systems is increasingly being investigated due to the economic importance of Li in the transition to sustainable energy resources (e.g., batteries). However, at upper crustal pressures, it remains uncertain whether Li preferentially partitions into the vapor or liquid (brine) phase or remains in the silicate melt. This complicates our ability to determine where Li resides—silicate melt, minerals, or fluid phase—upon eruption, a crucial factor for understanding its postdepositional movement and concentration into a brine or volcano-sedimentary deposit. Here, we present a novel investigation into the behavior of Li within natural evolved melts during continuous magma decompression and ascent using melt embayments (open melt inclusions). Mineral-hosted melt embayments preserve records of the evolving composition of the exterior melt, including degassing pathways and ascent timescales, when paired with appropriate diffusion coefficients. Lithium concentration profiles were measured in quartz-hosted melt embayments from the rapidly quenched eruptive phases of five rhyolitic, caldera-forming eruptions to investigate the behavior of Li during magma decompression and ascent, where vapor partitioning and ascent dynamics were previously established by investigating H2O and CO2 profiles. We find that in four systems, embayments contain lower interior Li concentrations than the coerupted melt inclusions; the fifth system contains the same Li concentrations in embayments and melt inclusions. However, many of these embayments contain gradients, with 84% preserving Li enrichment near the melt-bubble interface, as compared to their interior concentration. We interpret these characteristics to represent two distinct stages of Li partitioning during magma decompression and ascent, in contrast to existing literature that proposes only one type of partitioning behavior. The first stage is interpreted as melt depletion of Li, likely driven by partitioning into an exsolved supercritical fluid phase, supported by the strong correlation between the extent of Li depletion and Cl concentration in the melt, as well as the decompression rate. This behavior then fundamentally shifts, where Li reenriches in the melt, postulated to be driven by the unmixing of the supercritical fluid phase at shallow pressures. For the one system that did not develop Li gradients through decompression, we attribute this to the lower values of Na and Cl in the melt, potentially inhibiting the partitioning of Li into a fluid phase. Importantly, the behavior of Li during decompression is not consistent within or between volcanic centers, highlighting the need for systematic experimental investigation in variable composition melts at pressures relevant to conduit dynamics. This knowledge would improve our ability to model Li profiles to understand magma decompression, and predict where Li resides (e.g., stored in volcanic glass, gas, or crystals) upon er
{"title":"Variable Partitioning of Lithium in Rhyolitic Melt During Decompression and Ascent","authors":"Madison Myers, Roberta Spallanzani, Darin M. Schwartz, Celestine Mercer, Behnaz Hosseini","doi":"10.5382/econgeo.5171","DOIUrl":"https://doi.org/10.5382/econgeo.5171","url":null,"abstract":"The partitioning behavior of Li in magmatic systems is increasingly being investigated due to the economic importance of Li in the transition to sustainable energy resources (e.g., batteries). However, at upper crustal pressures, it remains uncertain whether Li preferentially partitions into the vapor or liquid (brine) phase or remains in the silicate melt. This complicates our ability to determine where Li resides—silicate melt, minerals, or fluid phase—upon eruption, a crucial factor for understanding its postdepositional movement and concentration into a brine or volcano-sedimentary deposit. Here, we present a novel investigation into the behavior of Li within natural evolved melts during continuous magma decompression and ascent using melt embayments (open melt inclusions). Mineral-hosted melt embayments preserve records of the evolving composition of the exterior melt, including degassing pathways and ascent timescales, when paired with appropriate diffusion coefficients. Lithium concentration profiles were measured in quartz-hosted melt embayments from the rapidly quenched eruptive phases of five rhyolitic, caldera-forming eruptions to investigate the behavior of Li during magma decompression and ascent, where vapor partitioning and ascent dynamics were previously established by investigating H2O and CO2 profiles. We find that in four systems, embayments contain lower interior Li concentrations than the coerupted melt inclusions; the fifth system contains the same Li concentrations in embayments and melt inclusions. However, many of these embayments contain gradients, with 84% preserving Li enrichment near the melt-bubble interface, as compared to their interior concentration. We interpret these characteristics to represent two distinct stages of Li partitioning during magma decompression and ascent, in contrast to existing literature that proposes only one type of partitioning behavior. The first stage is interpreted as melt depletion of Li, likely driven by partitioning into an exsolved supercritical fluid phase, supported by the strong correlation between the extent of Li depletion and Cl concentration in the melt, as well as the decompression rate. This behavior then fundamentally shifts, where Li reenriches in the melt, postulated to be driven by the unmixing of the supercritical fluid phase at shallow pressures. For the one system that did not develop Li gradients through decompression, we attribute this to the lower values of Na and Cl in the melt, potentially inhibiting the partitioning of Li into a fluid phase. Importantly, the behavior of Li during decompression is not consistent within or between volcanic centers, highlighting the need for systematic experimental investigation in variable composition melts at pressures relevant to conduit dynamics. This knowledge would improve our ability to model Li profiles to understand magma decompression, and predict where Li resides (e.g., stored in volcanic glass, gas, or crystals) upon er","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"13 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-08-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144900636","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Qinghai-Xizang Plateau is globally acknowledged as the second-largest concentration area of lithium brine deposits, with the Qaidam basin standing out as the largest endorheic basin in this region, boasting numerous salt lakes and abundant lithium brine resources. Lithium brine deposits within the Qaidam basin are predominantly categorized into modern salt lake brines and deep brines. The former are the principal raw materials for the production of lithium salt products in China, whereas the latter are considered vital lithium reserve resources. The origin of lithium in modern salt lake brines is intricately linked to lithium-rich hot springs surfacing from deep, extensive fault zones surrounding the basin. The distribution of lithium-rich salt lakes is mainly governed by the evolution of ancient lake basins, induced by the Neotectonic activities. The formation of deep lithium-rich brines is subject to multiple factors, with water-rock interactions playing a crucial role. An important scientific endeavor for future studies on modern salt lakes in the Qaidam basin and the whole Qinghai-Xizang Plateau region involves a thorough analysis of the geochemical behavior of lithium throughout its migration and enrichment processes to clarify the genetic connections between hard-rock lithium mines and lithium-rich salt lakes.
{"title":"Genesis and Resource of Lithium Brines in the Qaidam Basin of North Qinghai-Xizang Plateau: An Overview","authors":"Xiying Zhang, Weiliang Miao, Guang Han, Wenxia Li, Yulong Li, Wenxia Han, Wenhu Yuan","doi":"10.5382/econgeo.5164","DOIUrl":"https://doi.org/10.5382/econgeo.5164","url":null,"abstract":"The Qinghai-Xizang Plateau is globally acknowledged as the second-largest concentration area of lithium brine deposits, with the Qaidam basin standing out as the largest endorheic basin in this region, boasting numerous salt lakes and abundant lithium brine resources. Lithium brine deposits within the Qaidam basin are predominantly categorized into modern salt lake brines and deep brines. The former are the principal raw materials for the production of lithium salt products in China, whereas the latter are considered vital lithium reserve resources. The origin of lithium in modern salt lake brines is intricately linked to lithium-rich hot springs surfacing from deep, extensive fault zones surrounding the basin. The distribution of lithium-rich salt lakes is mainly governed by the evolution of ancient lake basins, induced by the Neotectonic activities. The formation of deep lithium-rich brines is subject to multiple factors, with water-rock interactions playing a crucial role. An important scientific endeavor for future studies on modern salt lakes in the Qaidam basin and the whole Qinghai-Xizang Plateau region involves a thorough analysis of the geochemical behavior of lithium throughout its migration and enrichment processes to clarify the genetic connections between hard-rock lithium mines and lithium-rich salt lakes.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"25 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144737038","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Kate R. Canham, David A. Holwell, Lara Du Preez, Paul AM. Nex, Allan H. Wilson, Katie McFall, Erin S. Thompson, Hannah SR. Hughes, Andy Lloyd
The Base Metal zone at Sandsloot in the Northern limb of the Bushveld Complex, South Africa, is a highly unusual and high-grade Os-Ir-Ru-Rh, Fe-Ni sulfide-rich horizon hosted within the deep Platreef, below the main platinum group element (PGE) horizon. The Base Metal zone ranges from 5 to 100 meters in thickness and is located up to 150 meters beneath the PGE reef. Base metal sulfide mineralization occurs as disseminated/blebby to semimassive/massive sulfides, with a typical assemblage of ~60/25/15 pyrrhotite/pentlandite/chalcopyrite modal %. The Base Metal zone is characterized by high (Os + Ir + Ru + Rh)/(Pt + Pd) ratios that reflect monosulfide solid solution, primitive mantle-normalized PGE profiles. The PGM assemblage is dominated by laurite (RuS2) (62% by area) and iridium-group platinum group element (IPGE) + Pt arsenosulfides (21% by area). The PGE tenors of the sulfides vary between different textural styles, either reflecting R-factor variations or dilution of tenors by addition of crustal S. Disseminated/blebby sulfides have the highest tenors (up to 153 ppm Pd, 249 ppm Rh, 818 ppm Ru), whereas semimassive/massive sulfides have lower tenors (up to 2.8 ppm Pd, 1.8 ppm Pt, 11 ppm Rh, 17 ppm Ru, 2.2 ppm Os, 3.5 ppm Ir). The PGE geochemistry, IPGE-dominant platinum group metal (PGM) assemblage, abundance of Fe sulfides, and high Ni/Cu ratios are consistent with the Base Metal zone representing the monsulfide solid solution portion of a sulfide liquid formed by fractional crystallization. Furthermore, the Cu + Pt + Pd + Au-poor nature of the Base Metal zone suggests that these metals were removed from the Base Metal zone, and some Cu-rich veins and sections are present around the margins of Ni-Fe sulfide to support this. Increasing Pd/Ir and decreasing Rh/Cu ratios downhole indicate the sulfide liquid fractionated downward. Therefore, a residual Cu-rich liquid, with associated Pt + Pd + Au, likely separated from monosulfide solid solution and was mobilized downward and away from the Base Metal zone. Significantly, the mobilization of a Cu-rich liquid leaves the possibility that an undiscovered Cu + Pt + Pd + Au orebody may exist at depth.
{"title":"Enigmatic High-Tenor Rh-, Ru-, Ir-, and Os-Rich Base Metal Sulfide Mineralization Within the Northern Limb of the Bushveld Complex: A Product of Fractionation of a Sulfide Liquid?","authors":"Kate R. Canham, David A. Holwell, Lara Du Preez, Paul AM. Nex, Allan H. Wilson, Katie McFall, Erin S. Thompson, Hannah SR. Hughes, Andy Lloyd","doi":"10.5382/econgeo.5159","DOIUrl":"https://doi.org/10.5382/econgeo.5159","url":null,"abstract":"The Base Metal zone at Sandsloot in the Northern limb of the Bushveld Complex, South Africa, is a highly unusual and high-grade Os-Ir-Ru-Rh, Fe-Ni sulfide-rich horizon hosted within the deep Platreef, below the main platinum group element (PGE) horizon. The Base Metal zone ranges from 5 to 100 meters in thickness and is located up to 150 meters beneath the PGE reef. Base metal sulfide mineralization occurs as disseminated/blebby to semimassive/massive sulfides, with a typical assemblage of ~60/25/15 pyrrhotite/pentlandite/chalcopyrite modal %. The Base Metal zone is characterized by high (Os + Ir + Ru + Rh)/(Pt + Pd) ratios that reflect monosulfide solid solution, primitive mantle-normalized PGE profiles. The PGM assemblage is dominated by laurite (RuS2) (62% by area) and iridium-group platinum group element (IPGE) + Pt arsenosulfides (21% by area). The PGE tenors of the sulfides vary between different textural styles, either reflecting R-factor variations or dilution of tenors by addition of crustal S. Disseminated/blebby sulfides have the highest tenors (up to 153 ppm Pd, 249 ppm Rh, 818 ppm Ru), whereas semimassive/massive sulfides have lower tenors (up to 2.8 ppm Pd, 1.8 ppm Pt, 11 ppm Rh, 17 ppm Ru, 2.2 ppm Os, 3.5 ppm Ir). The PGE geochemistry, IPGE-dominant platinum group metal (PGM) assemblage, abundance of Fe sulfides, and high Ni/Cu ratios are consistent with the Base Metal zone representing the monsulfide solid solution portion of a sulfide liquid formed by fractional crystallization. Furthermore, the Cu + Pt + Pd + Au-poor nature of the Base Metal zone suggests that these metals were removed from the Base Metal zone, and some Cu-rich veins and sections are present around the margins of Ni-Fe sulfide to support this. Increasing Pd/Ir and decreasing Rh/Cu ratios downhole indicate the sulfide liquid fractionated downward. Therefore, a residual Cu-rich liquid, with associated Pt + Pd + Au, likely separated from monosulfide solid solution and was mobilized downward and away from the Base Metal zone. Significantly, the mobilization of a Cu-rich liquid leaves the possibility that an undiscovered Cu + Pt + Pd + Au orebody may exist at depth.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"57 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144712302","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Markus Staubmann, David R. Cooke, Scott Halley, Tilen Milojkovic, Ben Reid, Matthew Green, Ned Howard, Mathew Clifford
The 2.74 Moz structurally controlled epithermal GRE46 gold deposit is located on the western margin of the Cowal Igneous Complex in central New South Wales, Australia. At the regional scale, the Cowal Igneous Complex is located toward the southern end of the poorly exposed Junee-Narromine volcanic belt, the westernmost of four remnant volcanic belts that together constitute the Ordovician to early Silurian Macquarie arc. The GRE46 deposit is located at the northern end of a 4.5-km-long structural corridor that is defined by several prominent arc-parallel structures. This structural corridor also contains the E40, E41, and E42 gold deposits, and has a collective pre-mining gold endowment of over 14 Moz. The GRE46 deposit is hosted in a sequence of calc-alkalic to shoshonitic subaqueous volcanic and volcaniclastic rocks, interpreted to have formed in an intra-oceanic magmatic arc environment. The host stratigraphy is dominated by reworked volcanic deposits and nonvolcanic sedimentary deposits that include mud- to sandstones, pebble to cobble conglomerates and polymictic volcanic breccias and debris flows. Lesser primary volcanic rocks consist of coherent andesite to dacite flows with common hyaloclastite and peperite textures, and diorite to granodiorite dikes and sills. Gold mineralization at GRE46 occurs primarily in association with millimeter- to centimeter-scale quartz-carbonate-pyrite veins, with minor chalcopyrite, galena, sphalerite, and rare telluride minerals. Multiple styles of mineralized veins are present, including composite and banded dilatant veins, shear veins, stringer veins, and high-grade quartz-sulfide breccia veins. The host rocks were variably hydrothermally altered, with the style and intensity of alteration influenced by proximity to fluid-flow controlling structures and protolith compositions. The highest gold grades are closely associated with pervasive quartz + white mica + ankerite + pyrite alteration that overprinted chlorite + albite + calcite ± magnetite alteration. At the deposit scale, gold mineralization was strongly influenced by the pre-existing structural architecture, leading to heterogeneous hydrothermal fluid flow in zones of enhanced permeability that were created due to competency contrasts in the volcano-sedimentary stratigraphic package. GRE46 can be classified as an intrusion-related epithermal style of gold mineralization. The deposit has several characteristics, including the ore and gangue mineralogy, style and textures of associated veining, and the alteration assemblage, which are broadly consistent with both the intermediate sulfidation and the carbonate-base metal epithermal models.
{"title":"The GRE46 Epithermal Gold Deposit, Cowal, New South Wales: Geology, Mineralization, Alteration, and Ore Genesis","authors":"Markus Staubmann, David R. Cooke, Scott Halley, Tilen Milojkovic, Ben Reid, Matthew Green, Ned Howard, Mathew Clifford","doi":"10.5382/econgeo.5160","DOIUrl":"https://doi.org/10.5382/econgeo.5160","url":null,"abstract":"The 2.74 Moz structurally controlled epithermal GRE46 gold deposit is located on the western margin of the Cowal Igneous Complex in central New South Wales, Australia. At the regional scale, the Cowal Igneous Complex is located toward the southern end of the poorly exposed Junee-Narromine volcanic belt, the westernmost of four remnant volcanic belts that together constitute the Ordovician to early Silurian Macquarie arc. The GRE46 deposit is located at the northern end of a 4.5-km-long structural corridor that is defined by several prominent arc-parallel structures. This structural corridor also contains the E40, E41, and E42 gold deposits, and has a collective pre-mining gold endowment of over 14 Moz. The GRE46 deposit is hosted in a sequence of calc-alkalic to shoshonitic subaqueous volcanic and volcaniclastic rocks, interpreted to have formed in an intra-oceanic magmatic arc environment. The host stratigraphy is dominated by reworked volcanic deposits and nonvolcanic sedimentary deposits that include mud- to sandstones, pebble to cobble conglomerates and polymictic volcanic breccias and debris flows. Lesser primary volcanic rocks consist of coherent andesite to dacite flows with common hyaloclastite and peperite textures, and diorite to granodiorite dikes and sills. Gold mineralization at GRE46 occurs primarily in association with millimeter- to centimeter-scale quartz-carbonate-pyrite veins, with minor chalcopyrite, galena, sphalerite, and rare telluride minerals. Multiple styles of mineralized veins are present, including composite and banded dilatant veins, shear veins, stringer veins, and high-grade quartz-sulfide breccia veins. The host rocks were variably hydrothermally altered, with the style and intensity of alteration influenced by proximity to fluid-flow controlling structures and protolith compositions. The highest gold grades are closely associated with pervasive quartz + white mica + ankerite + pyrite alteration that overprinted chlorite + albite + calcite ± magnetite alteration. At the deposit scale, gold mineralization was strongly influenced by the pre-existing structural architecture, leading to heterogeneous hydrothermal fluid flow in zones of enhanced permeability that were created due to competency contrasts in the volcano-sedimentary stratigraphic package. GRE46 can be classified as an intrusion-related epithermal style of gold mineralization. The deposit has several characteristics, including the ore and gangue mineralogy, style and textures of associated veining, and the alteration assemblage, which are broadly consistent with both the intermediate sulfidation and the carbonate-base metal epithermal models.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"12 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144712271","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Madeleine A. Ince, Steffen G. Hagemann, Nora A. Rubinstein, Marco L. Fiorentini, Anthony I.S. Kemp, Christopher M. Fisher, Tim Ireland, Santiago Gigola
The magmatic processes that lead to porphyry Cu ore formation in continental retro-arc environments are not well understood. As a result, the uncertainty of predictive exploration in these tectonic settings is elevated, and new case studies are needed to enhance the probability of success in target identification. The Taca Taca Bajo porphyry Cu-Mo-Au deposit is a well-mineralized (11.7 Mt contained Cu), retro-arc expression of the Middle Eocene to Early Oligocene metallogenic belt in the central Andes and represents a key location for investigating continental retro-arc magmatic processes that culminate in the formation of porphyry Cu deposits. Mineralization at Taca Taca Bajo is spatially and temporally correlated with a NE-SW–trending rhyodacitic porphyry dike swarm. Six samples of the mineralized Taca Taca Bajo rhyodacite porphyry and one of the barren west rhyodacite porphyry were analyzed for whole-rock geochemistry and zircon petrochronology (U-Pb geochronology, O isotopes, Lu-Hf isotopes, trace element geochemistry). The U-Pb SHRIMP analyses of zircons from the Taca Taca rhyodacite porphyry intrusions reveal ages ranging from 30.3 ± 0.5 Ma to 29.1 ± 0.3 Ma (95% confidence interval). The barren west rhyodacite porphyry sample yields an overlapping zircon crystallization age of 30.4 ± 0.4 Ma (U-Pb SHRIMP; 95% confidence interval) with mineralized samples. Whole-rock geochemistry reveals a subducted slab component to the magma, with enrichments in Ba and Th as well as a marked negative Nb and Ta anomaly. The mean zircon δ18O of both the barren and mineralized Oligocene intrusions ranges from 5.6 ± 0.5 to 5.8 ± 0.2‰ (2 standard deviations [SD]), and zircon εHf from 5.3 ± 2.4 to 7.6 ± 0.7 (2 SD). These similarities suggest that the mineralized and barren intrusions may have a relatively juvenile mantle-derived source with minor assimilation of older crust. Inherited zircons yield U-Pb ages of 48 to 1063 Ma, with a cluster at 230 to 280 Ma, indicative of interaction with older arc magmatic rocks of the lower Choiyoi Igneous Complex. The Taca Taca Oligocene intrusions are moderately hydrous (mean zircon Eu/Eu* = 0.25–0.34) and oxidized (mean ΔFMQ = 0.2–1.0 [FMQ = fayalite-magnetite-quartz]) as estimated from zircon-based proxies. However, they also have lower inferred H2O contents and fO2 than other Cu-porphyry deposits of the Eocene to Early Oligocene metallogenic belt (e.g., Escondida, Chuquicamata, El Salvador). Based on these data, it is possible to conclude that the Taca Taca Bajo deposit, despite being a large porphyry Cu deposit, may have failed to reach the scale of some others in the metallogenic belt because it experienced a relatively isolated, short (1–1.5 m.y.) magmatic pulse, and did not undergo the multimillion year build-up of magmatism characteristic of these major deposits.
{"title":"Insights Into the Magma Source and Evolution of the Taca Taca Bajo Porphyry Deposit: Implications for the Metallogeny and Cu Fertility of the Central Andean Retro Arc","authors":"Madeleine A. Ince, Steffen G. Hagemann, Nora A. Rubinstein, Marco L. Fiorentini, Anthony I.S. Kemp, Christopher M. Fisher, Tim Ireland, Santiago Gigola","doi":"10.5382/econgeo.5169","DOIUrl":"https://doi.org/10.5382/econgeo.5169","url":null,"abstract":"The magmatic processes that lead to porphyry Cu ore formation in continental retro-arc environments are not well understood. As a result, the uncertainty of predictive exploration in these tectonic settings is elevated, and new case studies are needed to enhance the probability of success in target identification. The Taca Taca Bajo porphyry Cu-Mo-Au deposit is a well-mineralized (11.7 Mt contained Cu), retro-arc expression of the Middle Eocene to Early Oligocene metallogenic belt in the central Andes and represents a key location for investigating continental retro-arc magmatic processes that culminate in the formation of porphyry Cu deposits. Mineralization at Taca Taca Bajo is spatially and temporally correlated with a NE-SW–trending rhyodacitic porphyry dike swarm. Six samples of the mineralized Taca Taca Bajo rhyodacite porphyry and one of the barren west rhyodacite porphyry were analyzed for whole-rock geochemistry and zircon petrochronology (U-Pb geochronology, O isotopes, Lu-Hf isotopes, trace element geochemistry). The U-Pb SHRIMP analyses of zircons from the Taca Taca rhyodacite porphyry intrusions reveal ages ranging from 30.3 ± 0.5 Ma to 29.1 ± 0.3 Ma (95% confidence interval). The barren west rhyodacite porphyry sample yields an overlapping zircon crystallization age of 30.4 ± 0.4 Ma (U-Pb SHRIMP; 95% confidence interval) with mineralized samples. Whole-rock geochemistry reveals a subducted slab component to the magma, with enrichments in Ba and Th as well as a marked negative Nb and Ta anomaly. The mean zircon δ18O of both the barren and mineralized Oligocene intrusions ranges from 5.6 ± 0.5 to 5.8 ± 0.2‰ (2 standard deviations [SD]), and zircon εHf from 5.3 ± 2.4 to 7.6 ± 0.7 (2 SD). These similarities suggest that the mineralized and barren intrusions may have a relatively juvenile mantle-derived source with minor assimilation of older crust. Inherited zircons yield U-Pb ages of 48 to 1063 Ma, with a cluster at 230 to 280 Ma, indicative of interaction with older arc magmatic rocks of the lower Choiyoi Igneous Complex. The Taca Taca Oligocene intrusions are moderately hydrous (mean zircon Eu/Eu* = 0.25–0.34) and oxidized (mean ΔFMQ = 0.2–1.0 [FMQ = fayalite-magnetite-quartz]) as estimated from zircon-based proxies. However, they also have lower inferred H2O contents and fO2 than other Cu-porphyry deposits of the Eocene to Early Oligocene metallogenic belt (e.g., Escondida, Chuquicamata, El Salvador). Based on these data, it is possible to conclude that the Taca Taca Bajo deposit, despite being a large porphyry Cu deposit, may have failed to reach the scale of some others in the metallogenic belt because it experienced a relatively isolated, short (1–1.5 m.y.) magmatic pulse, and did not undergo the multimillion year build-up of magmatism characteristic of these major deposits.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"26 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144712299","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Erin S. Thompson, David A. Holwell, Iain McDonald, Kate R. Canham, Marc Reichow, Thomas G. Blenkinsop, Katie McFall, Hannah S.R. Hughes, Matthew A. Loader, Lara Du Preez, Kofi Acheampong, Andy Lloyd
The Platreef, northern limb of the Bushveld Complex, South Africa, is widely regarded as one of the world’s largest resources of platinum group elements (PGEs), critical metals that are essential for the growth of many sustainable technologies. In this study, the petrology, bulk geochemistry, and mineral chemistry of drill holes from the deep Platreef at Sandsloot, downdip from the established Sandsloot open pit, are examined, with the aim of establishing the magmatic stratigraphy. This newly described sequence is composed of up to six discrete pyroxenitic packages, with significant PGE and base metal mineralization observed in two consistent units: the PGE reef and the Base Metal zone. Varying CaO/Al2O3 ratios and mineral and alteration assemblages are associated with different units, alluding to varying degrees of carbonate contamination and hydrothermal alteration. Variations in parental magma compositions for the identified units are equivocal. The PGE reef and Ni-rich Base Metal zone are strongly associated with contamination from the underlying Malmani subgroup dolomites (indicated by CaO/Al2O3 ratios ≥ 2), and although this is not exclusive to the mineralized horizons, the highest PGE grades all show this signature. The stratigraphy of the deep Platreef at Sandsloot is difficult to correlate with other sections of deep Platreef/Critical zone in the northern Bushveld, which is likely a function of complex and localized contamination, and an emplacement history of discrete sills/fingers of barren and PGE-rich magmas. Notwithstanding the localized contamination, it is apparent that only some of the magmatic pulses that formed the Critical zone succession in the northern limb were PGE rich.
{"title":"Magmatic Stratigraphy of the Deep Platreef at Sandsloot, Northern Bushveld Complex: Carbonate Contamination and Controls on Ni-Cu-Platinum Group Element Mineralization","authors":"Erin S. Thompson, David A. Holwell, Iain McDonald, Kate R. Canham, Marc Reichow, Thomas G. Blenkinsop, Katie McFall, Hannah S.R. Hughes, Matthew A. Loader, Lara Du Preez, Kofi Acheampong, Andy Lloyd","doi":"10.5382/econgeo.5163","DOIUrl":"https://doi.org/10.5382/econgeo.5163","url":null,"abstract":"The Platreef, northern limb of the Bushveld Complex, South Africa, is widely regarded as one of the world’s largest resources of platinum group elements (PGEs), critical metals that are essential for the growth of many sustainable technologies. In this study, the petrology, bulk geochemistry, and mineral chemistry of drill holes from the deep Platreef at Sandsloot, downdip from the established Sandsloot open pit, are examined, with the aim of establishing the magmatic stratigraphy. This newly described sequence is composed of up to six discrete pyroxenitic packages, with significant PGE and base metal mineralization observed in two consistent units: the PGE reef and the Base Metal zone. Varying CaO/Al2O3 ratios and mineral and alteration assemblages are associated with different units, alluding to varying degrees of carbonate contamination and hydrothermal alteration. Variations in parental magma compositions for the identified units are equivocal. The PGE reef and Ni-rich Base Metal zone are strongly associated with contamination from the underlying Malmani subgroup dolomites (indicated by CaO/Al2O3 ratios ≥ 2), and although this is not exclusive to the mineralized horizons, the highest PGE grades all show this signature. The stratigraphy of the deep Platreef at Sandsloot is difficult to correlate with other sections of deep Platreef/Critical zone in the northern Bushveld, which is likely a function of complex and localized contamination, and an emplacement history of discrete sills/fingers of barren and PGE-rich magmas. Notwithstanding the localized contamination, it is apparent that only some of the magmatic pulses that formed the Critical zone succession in the northern limb were PGE rich.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"22 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144712296","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Kolwezi area of the Democratic Republic of the Congo hosts world-class stratabound Cu-(Co) and U-(± Cu-Ni-Co-Pb-Zn) mineralization within large fragments (écaille) of Lower Roan Group units that are hosted in the regional Roan breccia. Long-debated genetic models for the development of these types of deposits include the development of tectonic mélanges, friction breccias, sedimentary mélanges, olistostromes, and halokinesis or salt tectonics. Compiled historical data and new data at K.O.V. mine, which is an amalgamation of the Kamoto-East, Oliveira, and Virgule mines, situated in the Kolwezi “klippe” or subbasin, has been reanalyzed and used in the construction of a new, fully constrained, implicit 3-D model of lithologies and major structures. This data, which spans approximately 80 years, includes diamond and reverse-circulation drilling, new structural and lithological mapping data, downhole televiewer data, and macrostructural logging. In-pit observations, combined with these new, fully constrained, implicit 3-D models, provide new insights into the geometry and genesis of these deposits and their encompassing volume. The Kolwezi subbasin, characterized by K.O.V. mine, resulted from gravity-driven mass transport processes, concomitant with sedimentary deposition within a progressively folded foreland basin during orogenesis. The final geometry of fragments is due to (1) features that were inherited from the fold-and-thrust belt in the hinterland; (2) features caused by incorporation and dismemberment of fragments throughout a regional Roan breccia, as they were shed into the foreland basin; and (3) large-scale juxtaposition and impingement of fragments, complicated by late-kinematic tightening of the Kolwezi subbasin, further dewatering of the pile, and possibly further remobilization of fluids and metals. Collectively, these features, typified by K.O.V. mine, indicate that the Kolwezi subbasin, the Tombolo subbasin, and book similar regions in the foreland constitute the localized, preserved remnants of an olistostrome that was deposited within a previously much larger foreland basin, ahead of an advancing, thin-skinned fold-and-thrust system, and against the Nzilo block on the western margin of the Lufilian arc.
刚果民主共和国的Kolwezi地区拥有世界级的层控铜（Co）和U-（±Cu- ni -Co- pb - zn）矿化，这些矿化位于Roan角砾岩的下Roan群单元的大块（samcaille）内。对于这类矿床的发育，长期争论的成因模式包括构造岩、摩擦角砾岩、沉积岩、浮岩和盐构造的发育。K.O.V.矿是位于Kolwezi“klippe”或次盆地的Kamoto-East、Oliveira和Virgule矿的合并，已对K.O.V.矿的汇编历史数据和新数据进行了重新分析，并用于构建新的、完全受限的、隐式的岩性和主要构造三维模型。这些数据跨度约为80年，包括金刚石和反循环钻井、新的构造和岩性测绘数据、井下电视观测数据以及宏观构造测井。与这些新的、完全受限的隐式三维模型相结合的井下观测，为这些矿床的几何形状、成因及其包裹体积提供了新的见解。以K.O.V.矿为特征的Kolwezi次盆地，是在造山过程中，由重力驱动的物质搬运过程和逐渐褶皱的前陆盆地内的沉积作用共同形成的。碎屑体的最终几何形状是由于(1)从腹地的褶皱冲断带继承下来的特征；(2)区域罗安角砾岩碎屑在进入前陆盆地过程中被整合和肢解形成的特征；(3)碎片的大规模并置和撞击，加之Kolwezi次盆地后期的运动收紧、桩的进一步脱水以及可能的流体和金属的进一步再活化。总的来说，以K.O.V.矿为代表的这些特征表明，Kolwezi次盆地、Tombolo次盆地以及前陆地区的其他类似地区构成了一个局部保存下来的橄榄断层的残余物，该橄榄断层沉积在以前更大的前陆盆地内，在一个向前推进的薄皮褶皱-冲断体系之前，并在陆菲连弧西缘的Nzilo地块上。
{"title":"Insights from 3-D Structural and Lithological Geomodeling of K.O.V. Mine, Kolwezi Region, Democratic Republic of the Congo: Olistostromes in an Evolving Lufilian Arc Foreland Basin","authors":"M-J McCall, I. J. Basson","doi":"10.5382/econgeo.5157","DOIUrl":"https://doi.org/10.5382/econgeo.5157","url":null,"abstract":"The Kolwezi area of the Democratic Republic of the Congo hosts world-class stratabound Cu-(Co) and U-(± Cu-Ni-Co-Pb-Zn) mineralization within large fragments (écaille) of Lower Roan Group units that are hosted in the regional Roan breccia. Long-debated genetic models for the development of these types of deposits include the development of tectonic mélanges, friction breccias, sedimentary mélanges, olistostromes, and halokinesis or salt tectonics. Compiled historical data and new data at K.O.V. mine, which is an amalgamation of the Kamoto-East, Oliveira, and Virgule mines, situated in the Kolwezi “klippe” or subbasin, has been reanalyzed and used in the construction of a new, fully constrained, implicit 3-D model of lithologies and major structures. This data, which spans approximately 80 years, includes diamond and reverse-circulation drilling, new structural and lithological mapping data, downhole televiewer data, and macrostructural logging. In-pit observations, combined with these new, fully constrained, implicit 3-D models, provide new insights into the geometry and genesis of these deposits and their encompassing volume. The Kolwezi subbasin, characterized by K.O.V. mine, resulted from gravity-driven mass transport processes, concomitant with sedimentary deposition within a progressively folded foreland basin during orogenesis. The final geometry of fragments is due to (1) features that were inherited from the fold-and-thrust belt in the hinterland; (2) features caused by incorporation and dismemberment of fragments throughout a regional Roan breccia, as they were shed into the foreland basin; and (3) large-scale juxtaposition and impingement of fragments, complicated by late-kinematic tightening of the Kolwezi subbasin, further dewatering of the pile, and possibly further remobilization of fluids and metals. Collectively, these features, typified by K.O.V. mine, indicate that the Kolwezi subbasin, the Tombolo subbasin, and book similar regions in the foreland constitute the localized, preserved remnants of an olistostrome that was deposited within a previously much larger foreland basin, ahead of an advancing, thin-skinned fold-and-thrust system, and against the Nzilo block on the western margin of the Lufilian arc.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"708 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144712270","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Christopher Emproto, Thomas R. Benson, Catherine A. Gagnon, Woohyeon Baek, Daniel Ibarra, Adam C. Simon
Volcano-sedimentary lithium (Li) deposits are a potential source of battery-grade Li, although the important factors controlling Li enrichment in these systems remain unclear. At Thacker Pass in Nevada, high-grade mineralization overprinted intracaldera lacustrine claystone made of authigenic Li-rich smectite with bulk grades of ~3,000 ppm Li, converting it to illitic claystone with grades of ~6,000 ppm Li. Some attribute this enrichment to burial diagenesis, whereas others propose lacustrine Li enrichment through leaching and climate-driven evapoconcentration enhanced by postdepositional hydrothermal alteration. To better understand Li enrichment in volcano-sedimentary systems, claystones from throughout Thacker Pass were analyzed using powder X-ray diffraction (PXRD), electron microprobe (EPMA), laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), and stable isotope (clay δ18O, δ17O, and δ2H and carbonate δ13C and δ18O) methods. Compositional data suggest that illitization is required to achieve clay Li grades above ~0.9 wt % in Mg silicate clays because of a charge-coupled substitution that requires filling interlayer vacancies with K. Clay chemical trends and computational modeling exercises also suggest that F may be important in the formation of Li-rich clays by lowering kinetic barriers to clay precursor growth and illitization. The results are incompatible with diagenetic smectite/illite formation but are consistent with a model wherein authigenic smectite was subjected to hydrothermal alteration in the presence of a K-, Li-, and F-rich fluid that permeated the stratigraphy through a network of normal faults associated with caldera resurgence. These results also enhance our understanding of Li clay formation in other volcano-sedimentary systems.
{"title":"Clay Chemistry of the Thacker Pass Deposit, Nevada: Implications for the Formation of High-Grade Volcano-Sedimentary Lithium Resources","authors":"Christopher Emproto, Thomas R. Benson, Catherine A. Gagnon, Woohyeon Baek, Daniel Ibarra, Adam C. Simon","doi":"10.5382/econgeo.5155","DOIUrl":"https://doi.org/10.5382/econgeo.5155","url":null,"abstract":"Volcano-sedimentary lithium (Li) deposits are a potential source of battery-grade Li, although the important factors controlling Li enrichment in these systems remain unclear. At Thacker Pass in Nevada, high-grade mineralization overprinted intracaldera lacustrine claystone made of authigenic Li-rich smectite with bulk grades of ~3,000 ppm Li, converting it to illitic claystone with grades of ~6,000 ppm Li. Some attribute this enrichment to burial diagenesis, whereas others propose lacustrine Li enrichment through leaching and climate-driven evapoconcentration enhanced by postdepositional hydrothermal alteration. To better understand Li enrichment in volcano-sedimentary systems, claystones from throughout Thacker Pass were analyzed using powder X-ray diffraction (PXRD), electron microprobe (EPMA), laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), and stable isotope (clay δ18O, δ17O, and δ2H and carbonate δ13C and δ18O) methods. Compositional data suggest that illitization is required to achieve clay Li grades above ~0.9 wt % in Mg silicate clays because of a charge-coupled substitution that requires filling interlayer vacancies with K. Clay chemical trends and computational modeling exercises also suggest that F may be important in the formation of Li-rich clays by lowering kinetic barriers to clay precursor growth and illitization. The results are incompatible with diagenetic smectite/illite formation but are consistent with a model wherein authigenic smectite was subjected to hydrothermal alteration in the presence of a K-, Li-, and F-rich fluid that permeated the stratigraphy through a network of normal faults associated with caldera resurgence. These results also enhance our understanding of Li clay formation in other volcano-sedimentary systems.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"648 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144533192","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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