Abstract The thick laterite developed over platinum group element (PGE)-bearing ultramafic rocks of the Owendale Alaskan-Uralian Complex in New South Wales, Australia, provides an ideal environment in which to address the question of whether Pt-Fe nuggets are formed during lateritization. This is an important issue to settle because Pt-Fe nuggets in alluvial placers and eluvial deposits associated with the Alaskan-Uralian complexes were the world’s major source of Pt prior to the commencement of Pt production from the Bushveld Complex and continue to produce a significant amount of Pt. Some of the Owendale laterites have high Pt but low Cu contents, while others have both high Pt and high Cu contents. Heavy mineral concentrates were prepared from about 1 kg of drill chips from both types of laterites. Only five of the 61 samples processed contained any platinum group minerals (PGMs) greater than 5 μm in size, even though many of the samples contained more than 1 g/t Pt. The largest PGM found was about 100 μm long, and the majority were <20 μm. The bulk of the PGMs recovered were zoned PGMs consisting of a core of isoferroplatinum mantled by tetraferroplatinum with an outer rim of tulameenite; many of these zoned PGMs are encased in hematite grains that often have high Pt contents and appear to be pseudomorphs after the PGMs. The textural evidence indicates that at least half of the primary PGMs in the ultramafic protoliths to the laterites were destroyed during weathering and that the liberated PGEs could have been available for the formation of PGM nuggets. However, despite the large amount of PGEs liberated during the destruction of the primary PGMs, no evidence was found for the neogenic growth of PGE nuggets. Rather, the Pt liberated during the destruction of the PGMs appears to have only traveled distances of micrometers to tens of centimeters to form Pt nanoparticles or Pt oxides or to be absorbed/adsorbed by the Fe oxide hosts.
{"title":"Are Placer Platinum Nuggets Formed During Lateritization? The Verdict from the Owendale Alaskan-Uralian Complex in Australia Is an Emphatic No!","authors":"Bocheng Ma, Reid R. Keays","doi":"10.5382/econgeo.5027","DOIUrl":"https://doi.org/10.5382/econgeo.5027","url":null,"abstract":"Abstract The thick laterite developed over platinum group element (PGE)-bearing ultramafic rocks of the Owendale Alaskan-Uralian Complex in New South Wales, Australia, provides an ideal environment in which to address the question of whether Pt-Fe nuggets are formed during lateritization. This is an important issue to settle because Pt-Fe nuggets in alluvial placers and eluvial deposits associated with the Alaskan-Uralian complexes were the world’s major source of Pt prior to the commencement of Pt production from the Bushveld Complex and continue to produce a significant amount of Pt. Some of the Owendale laterites have high Pt but low Cu contents, while others have both high Pt and high Cu contents. Heavy mineral concentrates were prepared from about 1 kg of drill chips from both types of laterites. Only five of the 61 samples processed contained any platinum group minerals (PGMs) greater than 5 μm in size, even though many of the samples contained more than 1 g/t Pt. The largest PGM found was about 100 μm long, and the majority were &lt;20 μm. The bulk of the PGMs recovered were zoned PGMs consisting of a core of isoferroplatinum mantled by tetraferroplatinum with an outer rim of tulameenite; many of these zoned PGMs are encased in hematite grains that often have high Pt contents and appear to be pseudomorphs after the PGMs. The textural evidence indicates that at least half of the primary PGMs in the ultramafic protoliths to the laterites were destroyed during weathering and that the liberated PGEs could have been available for the formation of PGM nuggets. However, despite the large amount of PGEs liberated during the destruction of the primary PGMs, no evidence was found for the neogenic growth of PGE nuggets. Rather, the Pt liberated during the destruction of the PGMs appears to have only traveled distances of micrometers to tens of centimeters to form Pt nanoparticles or Pt oxides or to be absorbed/adsorbed by the Fe oxide hosts.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"145 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135723562","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}
Sandra C. Wind, Mark D. Hannington, David A. Schneider, Jan Fietzke, Stephanos P. Kilias, J. Bruce Gemmell
Abstract Polymetallic veins and breccias and carbonate-replacement ore deposits in the Cyclades continental back arc, Greece, formed from a range of fluid and metal sources strongly influenced by the dynamics of the late Mesozoic-Cenozoic Hellenic subduction system. These complexities are recorded in the isotopic signatures of hydrothermal barite. We investigated 17 mineral occurrences on four Cycladic islands and from Lavrion on the mainland. Here, barite occurs in almost all deposit types of Miocene to Quaternary age. We used a multiple isotope and geochemical approach to characterize the barite in each deposit, including mineral separate analysis of δ34S and δ18O and laser ablation-inductively coupled plasma-mass spectrometry of 87Sr/86Sr and δ34S. Barite from carbonate-hosted vein and breccia Pb-Zn-Ag mineralization on Lavrion has a wide range of δ34S (2–20‰) and δ18O (10–15‰) values, reflecting a mix of magmatic and surface-derived fluids that have exchanged with isotopically heavy oxygen in the carbonate host rock. Sulfur (δ34S = 10–13‰) and oxygen (δ18O = 9–13‰) values of barite from the carbonate-hosted vein iron and barite mineralization on Serifos are permissive of a magmatic sulfate component. Barite from epithermal base and/or precious metal deposits on Milos has δ34S (17–28‰) and δ18O (9–11‰) values that are similar to modern seawater. In contrast, barite from vein-type deposits on Antiparos and Mykonos has a wide range of δ34S (16–37‰) and δ18O (4–12‰) values, indicating a seawater sulfate source modified by mixing or equilibration of the hydrothermal fluids with the host rocks. Strontium isotope ratios of barite vary regionally, with 87Sr/86Sr ≥ 0.711 in the central Cyclades and 87Sr/86Sr ≤ 0.711 in the west Cyclades, confirming the strong influence of upper crustal rocks on the sources of fluids, Sr, and Ba in the formation of ore.
{"title":"Origin of Hydrothermal Barite in Polymetallic Veins and Carbonate-Hosted Deposits of the Cyclades Continental Back Arc","authors":"Sandra C. Wind, Mark D. Hannington, David A. Schneider, Jan Fietzke, Stephanos P. Kilias, J. Bruce Gemmell","doi":"10.5382/econgeo.5028","DOIUrl":"https://doi.org/10.5382/econgeo.5028","url":null,"abstract":"Abstract Polymetallic veins and breccias and carbonate-replacement ore deposits in the Cyclades continental back arc, Greece, formed from a range of fluid and metal sources strongly influenced by the dynamics of the late Mesozoic-Cenozoic Hellenic subduction system. These complexities are recorded in the isotopic signatures of hydrothermal barite. We investigated 17 mineral occurrences on four Cycladic islands and from Lavrion on the mainland. Here, barite occurs in almost all deposit types of Miocene to Quaternary age. We used a multiple isotope and geochemical approach to characterize the barite in each deposit, including mineral separate analysis of δ34S and δ18O and laser ablation-inductively coupled plasma-mass spectrometry of 87Sr/86Sr and δ34S. Barite from carbonate-hosted vein and breccia Pb-Zn-Ag mineralization on Lavrion has a wide range of δ34S (2–20‰) and δ18O (10–15‰) values, reflecting a mix of magmatic and surface-derived fluids that have exchanged with isotopically heavy oxygen in the carbonate host rock. Sulfur (δ34S = 10–13‰) and oxygen (δ18O = 9–13‰) values of barite from the carbonate-hosted vein iron and barite mineralization on Serifos are permissive of a magmatic sulfate component. Barite from epithermal base and/or precious metal deposits on Milos has δ34S (17–28‰) and δ18O (9–11‰) values that are similar to modern seawater. In contrast, barite from vein-type deposits on Antiparos and Mykonos has a wide range of δ34S (16–37‰) and δ18O (4–12‰) values, indicating a seawater sulfate source modified by mixing or equilibration of the hydrothermal fluids with the host rocks. Strontium isotope ratios of barite vary regionally, with 87Sr/86Sr ≥ 0.711 in the central Cyclades and 87Sr/86Sr ≤ 0.711 in the west Cyclades, confirming the strong influence of upper crustal rocks on the sources of fluids, Sr, and Ba in the formation of ore.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"27 3","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135513607","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}
Jie Yu, Laura J. Morrissey, Martin Hand, Justin L. Payne, Yan-Jing Chen
Abstract The northern Olympic Cu-Au province, Gawler craton, Australia, includes a series of magnetite-dominated deposits/prospects associated with minor Cu-Au mineralization such as the 8.37 million tonne Cairn Hill deposit. Cairn Hill has long been considered a deep, magnetite end member of the iron oxide copper-gold (IOCG) family that is largely represented in the southern Olympic province by the 1590 Ma hematite-dominated Olympic Dam, Carrapeteena, and Prominent Hill deposits. In contrast to the southern district, the deposits in the northern Olympic Cu-Au province are hosted in rocks that experienced multiple phases of high-temperature metamorphism and deformation. New U-Pb zircon geochronology shows the magnetite-hornblende lodes at Cairn Hill were formed at ca. 1580 Ma at amphibolite facies conditions. The magnetite lodes are crosscut by ca. 1515 Ma granitic dikes. A second high-temperature event is recorded by U-Pb monazite geochronology at ca. 1490 Ma and involved deformation and metamorphism along the Cairn Hill shear zone at conditions of 4.6 to 5.3 kbar and 740° to 770°C. The 1490 Ma event reworked the iron lodes and 1515 Ma granitic dikes. However, Cu mineralization at Cairn Hill occurs in brittle fractures and quartz-biotite veins, overprinting the 1490 Ma deformation and metamorphism. Despite a spatial association between magnetite and Cu, the long thermal history that affected magnetite mineralization and the clear petrographic links between magnetite and high-temperature granulite facies minerals contrast with the late, low-temperature hydrothermal Cu mineralization and indicate the two are not paragenetically related. Therefore, the spatial but not temporal association between magnetite and Cu has effectively overlain two distinct episodes of mineralization to create the Fe-Cu deposit observed today. Although this fits within the broad IOCG deposit family, exploration strategies for Cairn Hill-style composite deposits should be distinct from IOCG deposits with cogenetic Fe and Cu.
{"title":"THE Fe-Cu DISCONNECT: UNRAVELING A COMPOSITE IRON OXIDE COPPER-GOLD DEPOSIT IN THE OLYMPIC Fe-Cu-Au PROVINCE, GAWLER CRATON","authors":"Jie Yu, Laura J. Morrissey, Martin Hand, Justin L. Payne, Yan-Jing Chen","doi":"10.5382/econgeo.5037","DOIUrl":"https://doi.org/10.5382/econgeo.5037","url":null,"abstract":"Abstract The northern Olympic Cu-Au province, Gawler craton, Australia, includes a series of magnetite-dominated deposits/prospects associated with minor Cu-Au mineralization such as the 8.37 million tonne Cairn Hill deposit. Cairn Hill has long been considered a deep, magnetite end member of the iron oxide copper-gold (IOCG) family that is largely represented in the southern Olympic province by the 1590 Ma hematite-dominated Olympic Dam, Carrapeteena, and Prominent Hill deposits. In contrast to the southern district, the deposits in the northern Olympic Cu-Au province are hosted in rocks that experienced multiple phases of high-temperature metamorphism and deformation. New U-Pb zircon geochronology shows the magnetite-hornblende lodes at Cairn Hill were formed at ca. 1580 Ma at amphibolite facies conditions. The magnetite lodes are crosscut by ca. 1515 Ma granitic dikes. A second high-temperature event is recorded by U-Pb monazite geochronology at ca. 1490 Ma and involved deformation and metamorphism along the Cairn Hill shear zone at conditions of 4.6 to 5.3 kbar and 740° to 770°C. The 1490 Ma event reworked the iron lodes and 1515 Ma granitic dikes. However, Cu mineralization at Cairn Hill occurs in brittle fractures and quartz-biotite veins, overprinting the 1490 Ma deformation and metamorphism. Despite a spatial association between magnetite and Cu, the long thermal history that affected magnetite mineralization and the clear petrographic links between magnetite and high-temperature granulite facies minerals contrast with the late, low-temperature hydrothermal Cu mineralization and indicate the two are not paragenetically related. Therefore, the spatial but not temporal association between magnetite and Cu has effectively overlain two distinct episodes of mineralization to create the Fe-Cu deposit observed today. Although this fits within the broad IOCG deposit family, exploration strategies for Cairn Hill-style composite deposits should be distinct from IOCG deposits with cogenetic Fe and Cu.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"36 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136057852","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}
Anne B. Virnes, Marco L. Fiorentini, Stephen J. Barnes, Stefano Caruso, Laure A.J. Martin, Matvei Aleshin, Louise E. Schoneveld, Malcolm P. Roberts, Quentin Masurel, Nicolas Thebaud
Abstract Komatiites require external sulfur from country rocks to generate immiscible sulfide liquid, which concentrates metals to form economic nickel sulfide deposits. Although signatures related to mass-independent fractionation of S isotopes (MIF-S, denoted as Δ33S) may identify external S sources, their values may not be directly indicative of the S reservoirs that were tapped during the ore-forming process, because of dilution by S exchange between assimilated sulfide xenomelt and komatiite silicate melt. To quantify this process and be confident that MIF-S can be effectively used to track S sources in magmatic systems, we investigated the effect of silicate melt-sulfide liquid batch equilibration, using the proxy of silicate/sulfide mass ratio, or R factor, on the resulting MIF-S signatures of pentlandite-rich ore from the Mount Keith MKD5 nickel sulfide deposit, Agnew-Wiluna greenstone belt, Western Australia. We carried out in situ multiple S isotope and platinum group element (PGE) analyses on pentlandite from a well-characterized drill core through the deposit. The variability in Pd tenor and MIF-S signature suggests that these are decoupled during batch equilibration and that the latter is not controlled by metal-derived R factor. Rather, the observed spread of MIF-S signatures implies that the sulfide xenomelt was initially heterogeneous and that chemical equilibration of S isotopes is incomplete as opposed to that of PGEs in a komatiite melt. Consequently, magmatic sulfides, which formed in the hottest, most dynamic, and likely fastest equilibrating magmatic systems on Earth, may still preserve their initial MIF-S isotope compositions, reflecting the range of crustal S reservoirs that were available upon komatiite emplacement.
科马地岩需要外部岩石中的硫才能生成不混溶的硫化物液体，这种硫化物液体将金属富集，形成经济的硫化镍矿床。虽然与S同位素的质量无关分馏(MIF-S，表示为Δ33S)相关的特征可以识别外部S源，但它们的值可能不能直接指示成矿过程中开采的S储层，因为同化的硫化物xenommelt和komatiite硅酸盐熔体之间的S交换稀释了S。为了量化这一过程，并确信MIF-S可以有效地用于跟踪岩浆系统中的S源，我们研究了硅酸盐熔融-硫化物液体间歇平衡的影响，使用硅酸盐/硫化物质量比(R因子)作为代理，对来自西澳大利亚Agnew-Wiluna绿岩带Mount Keith MKD5硫化镍矿床的富镍褐铁矿矿石的MIF-S特征进行了研究。我们对该矿床特征良好的钻取岩心中的镍黄铁矿进行了原位多S同位素和铂族元素(PGE)分析。Pd音调和MIF-S特征的可变性表明，它们在批平衡过程中解耦，而后者不受金属衍生R因子的控制。相反，观察到的MIF-S特征的分布表明，硫化物xenommelt最初是异质的，并且S同位素的化学平衡是不完整的，而不是科马铁矿熔体中的PGEs。因此，岩浆硫化物，形成于地球上最热、最活跃、可能最快平衡的岩浆系统中，可能仍然保留了它们最初的MIF-S同位素组成，反映了在科马铁矿就位后可用的地壳S储集层的范围。
{"title":"Decoupling of Sulfur Isotope Signatures from Platinum Group Elements in Komatiite-Hosted Ore Systems: Evidence from the Mount Keith MKD5 Ni-(Co-Cu) Deposit, Western Australia","authors":"Anne B. Virnes, Marco L. Fiorentini, Stephen J. Barnes, Stefano Caruso, Laure A.J. Martin, Matvei Aleshin, Louise E. Schoneveld, Malcolm P. Roberts, Quentin Masurel, Nicolas Thebaud","doi":"10.5382/econgeo.5030","DOIUrl":"https://doi.org/10.5382/econgeo.5030","url":null,"abstract":"Abstract Komatiites require external sulfur from country rocks to generate immiscible sulfide liquid, which concentrates metals to form economic nickel sulfide deposits. Although signatures related to mass-independent fractionation of S isotopes (MIF-S, denoted as Δ33S) may identify external S sources, their values may not be directly indicative of the S reservoirs that were tapped during the ore-forming process, because of dilution by S exchange between assimilated sulfide xenomelt and komatiite silicate melt. To quantify this process and be confident that MIF-S can be effectively used to track S sources in magmatic systems, we investigated the effect of silicate melt-sulfide liquid batch equilibration, using the proxy of silicate/sulfide mass ratio, or R factor, on the resulting MIF-S signatures of pentlandite-rich ore from the Mount Keith MKD5 nickel sulfide deposit, Agnew-Wiluna greenstone belt, Western Australia. We carried out in situ multiple S isotope and platinum group element (PGE) analyses on pentlandite from a well-characterized drill core through the deposit. The variability in Pd tenor and MIF-S signature suggests that these are decoupled during batch equilibration and that the latter is not controlled by metal-derived R factor. Rather, the observed spread of MIF-S signatures implies that the sulfide xenomelt was initially heterogeneous and that chemical equilibration of S isotopes is incomplete as opposed to that of PGEs in a komatiite melt. Consequently, magmatic sulfides, which formed in the hottest, most dynamic, and likely fastest equilibrating magmatic systems on Earth, may still preserve their initial MIF-S isotope compositions, reflecting the range of crustal S reservoirs that were available upon komatiite emplacement.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"87 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135044016","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}
Jiaxin Wang, A. E. Williams-Jones, A. Timofeev, Xueni Zhang, Jiajun Liu, Shunda Yuan
Abstract Although scandium is commonly concentrated to economic levels by magmatic processes, hydrothermal fluids also play an important role in its concentration. Indeed, the most important source of scandium is currently the Bayan Obo deposit in China, where scandium is extracted from hydrothermally produced aegirine. To know how and why scandium is concentrated by hydrothermal fluids, it is necessary to understand the speciation of scandium in hydrothermal fluids. In a recently published study, we showed that scandium forms stable species with fluoride ions and proposed that such species may have been responsible for the hydrothermal transport of scandium in deposits like Bayan Obo. Chloride ions, which have been shown to form stable complexes with the other rare earth elements (REE), however, are much more abundant in most hydrothermal fluids than fluoride ions, as are hydroxide ions, particularly at high pH. We, therefore, conducted solubility experiments designed to investigate the stability of scandium chloride and hydroxide complexes in hydrothermal fluids. The experiments investigating the role of chloride species considered the solubility of Sc2O3(s) in the H2O-NaCl-HCl system at 100°, 150°, 300°, and 350°C and saturated water vapor pressure. These experiments showed that scandium concentration is independent of chloride concentration over the range of chlorinity investigated, i.e., up to 3.6 mol Cl– and that scandium, therefore, does not form stable complexes with chloride ions. To evaluate the role of hydroxide species in scandium transport and avoid the effect of chloride ions in the complexation, a second set of experiments was conducted that determined the solubility of Sc2O3(s) in H2O-NaClO4-HClO4 solutions at 100°, 150°, 200°, and 250°C, and saturated water vapor pressure. The results of these experiments showed that the solubility of Sc2O3(s) depends on pH and temperature. Based on the former dependence, two scandium hydroxide complexes, Sc(OH)2+ and Sc(OH)3°, were identified at low and higher pH, respectively. The formation constant (log β) determined for Sc(OH)2+ is 10.29 ± 0.07, 10.32 ± 0.07, 10.35 ± 0.19, and 10.91 ± 0.20 at 100°, 150°, 200°, and 250°C, respectively. That of Sc(OH)3° is 27.22 ± 0.68, 26.66 ± 1.35, 27.04 ± 0.13, and 28.02 ± 0.14 at the same temperatures, respectively. These results demonstrate that, unlike the case for the other rare earth elements, chloride plays a negligible role in transporting scandium in hydrothermal fluids. Instead, they show that scandium hydroxide complexes can be important in the transport of scandium and could have contributed significantly to the formation of deposits like those at Bayan Obo.
{"title":"THE ROLE OF SCANDIUM CHLORIDE AND HYDROXIDE COMPLEXES IN THE FORMATION OF SCANDIUM DEPOSITS: INSIGHTS FROM EXPERIMENTS AND MODELING","authors":"Jiaxin Wang, A. E. Williams-Jones, A. Timofeev, Xueni Zhang, Jiajun Liu, Shunda Yuan","doi":"10.5382/econgeo.5026","DOIUrl":"https://doi.org/10.5382/econgeo.5026","url":null,"abstract":"Abstract Although scandium is commonly concentrated to economic levels by magmatic processes, hydrothermal fluids also play an important role in its concentration. Indeed, the most important source of scandium is currently the Bayan Obo deposit in China, where scandium is extracted from hydrothermally produced aegirine. To know how and why scandium is concentrated by hydrothermal fluids, it is necessary to understand the speciation of scandium in hydrothermal fluids. In a recently published study, we showed that scandium forms stable species with fluoride ions and proposed that such species may have been responsible for the hydrothermal transport of scandium in deposits like Bayan Obo. Chloride ions, which have been shown to form stable complexes with the other rare earth elements (REE), however, are much more abundant in most hydrothermal fluids than fluoride ions, as are hydroxide ions, particularly at high pH. We, therefore, conducted solubility experiments designed to investigate the stability of scandium chloride and hydroxide complexes in hydrothermal fluids. The experiments investigating the role of chloride species considered the solubility of Sc2O3(s) in the H2O-NaCl-HCl system at 100°, 150°, 300°, and 350°C and saturated water vapor pressure. These experiments showed that scandium concentration is independent of chloride concentration over the range of chlorinity investigated, i.e., up to 3.6 mol Cl– and that scandium, therefore, does not form stable complexes with chloride ions. To evaluate the role of hydroxide species in scandium transport and avoid the effect of chloride ions in the complexation, a second set of experiments was conducted that determined the solubility of Sc2O3(s) in H2O-NaClO4-HClO4 solutions at 100°, 150°, 200°, and 250°C, and saturated water vapor pressure. The results of these experiments showed that the solubility of Sc2O3(s) depends on pH and temperature. Based on the former dependence, two scandium hydroxide complexes, Sc(OH)2+ and Sc(OH)3°, were identified at low and higher pH, respectively. The formation constant (log β) determined for Sc(OH)2+ is 10.29 ± 0.07, 10.32 ± 0.07, 10.35 ± 0.19, and 10.91 ± 0.20 at 100°, 150°, 200°, and 250°C, respectively. That of Sc(OH)3° is 27.22 ± 0.68, 26.66 ± 1.35, 27.04 ± 0.13, and 28.02 ± 0.14 at the same temperatures, respectively. These results demonstrate that, unlike the case for the other rare earth elements, chloride plays a negligible role in transporting scandium in hydrothermal fluids. Instead, they show that scandium hydroxide complexes can be important in the transport of scandium and could have contributed significantly to the formation of deposits like those at Bayan Obo.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"37 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135146937","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}
Abstract The genetic relationship between organic-rich source rocks and Hg deposits remains the subject of debate. This paper evaluates the role of organic-rich source rocks in cinnabar ore formation in the Terlingua mining district, Texas, which was deposited at relatively shallow depths in Cretaceous sedimentary rocks spatially related to intrusive alkali igneous rocks. The mineralization formed at ~45 bar and ~200°C. The aqueous ore-forming fluid had a pH of ~5 to 7 and was H2S saturated. Cinnabar was deposited as a result of H2S oxidation through mixing and cooling with local meteoric water. Both Hg0(org) and Hg0(aq) species were likely important in cinnabar ore formation. However, recent studies on the solubility of Hg0 in hydrocarbons show that at cinnabar saturation, Hg0 is more than an order of magnitude more soluble in hydrocarbons (Hg0(org) = 163 mg/kg) than Hg0 in water (Hg0(aq) = 10.8 mg/kg). Despite their proximity in some deposits, conditions of ore formation of the rare Hg oxychloride and sulfate minerals are not compatible with conditions under which most cinnabar ores formed, requiring fO2 conditions orders of magnitude more oxidizing, a relatively high chloride ion activity (>10–1), and alkaline conditions, with pH > 10. Mass dependent fractionation versus mass independent fractionation of Hg isotope data from Hg-bearing minerals in Terlingua support a genetic link to the source of Hg being the organic-rich marls and tuffaceous black shales of the Lower Eagle Ford Formation. This source rock is chronostratigraphically equivalent to the Lower Cretaceous oceanic anoxic event (OAE-2), which defines the Cenomanian-Turonian boundary. OAE-2 represents the culmination of a global anoxic ocean event at ~94.1 Ma, believed to be a consequence of volcanic activity associated with a large igneous province. Mercury was sequestered by the organic-rich source rocks of the Lower Eagle Ford Formation and associated coeval ash and tuffs. Tabular igneous bodies that intruded and uplifted the local stratigraphy formed the Terlingua monocline and provided a source of heat for hydrothermal activity and maturation of organic matter. The subsequent generation and migration of liquid hydrocarbons and formation brines from the Lower Eagle Ford Formation transported Hg0(org) updip toward the hinge line of the Terlingua monocline where mixing with oxygenated meteoric water and subsequent oxidation of H2S produced the cinnabar-rich ores.
{"title":"Elucidating the Role of Hydrocarbons in Cinnabar (HgS) Ore Formation: A Model for Hg Mineralization in the Terlingua Mining District, Big Bend National Park, SW Texas","authors":"L. Taras Bryndzia","doi":"10.5382/econgeo.5022","DOIUrl":"https://doi.org/10.5382/econgeo.5022","url":null,"abstract":"Abstract The genetic relationship between organic-rich source rocks and Hg deposits remains the subject of debate. This paper evaluates the role of organic-rich source rocks in cinnabar ore formation in the Terlingua mining district, Texas, which was deposited at relatively shallow depths in Cretaceous sedimentary rocks spatially related to intrusive alkali igneous rocks. The mineralization formed at ~45 bar and ~200°C. The aqueous ore-forming fluid had a pH of ~5 to 7 and was H2S saturated. Cinnabar was deposited as a result of H2S oxidation through mixing and cooling with local meteoric water. Both Hg0(org) and Hg0(aq) species were likely important in cinnabar ore formation. However, recent studies on the solubility of Hg0 in hydrocarbons show that at cinnabar saturation, Hg0 is more than an order of magnitude more soluble in hydrocarbons (Hg0(org) = 163 mg/kg) than Hg0 in water (Hg0(aq) = 10.8 mg/kg). Despite their proximity in some deposits, conditions of ore formation of the rare Hg oxychloride and sulfate minerals are not compatible with conditions under which most cinnabar ores formed, requiring fO2 conditions orders of magnitude more oxidizing, a relatively high chloride ion activity (&gt;10–1), and alkaline conditions, with pH &gt; 10. Mass dependent fractionation versus mass independent fractionation of Hg isotope data from Hg-bearing minerals in Terlingua support a genetic link to the source of Hg being the organic-rich marls and tuffaceous black shales of the Lower Eagle Ford Formation. This source rock is chronostratigraphically equivalent to the Lower Cretaceous oceanic anoxic event (OAE-2), which defines the Cenomanian-Turonian boundary. OAE-2 represents the culmination of a global anoxic ocean event at ~94.1 Ma, believed to be a consequence of volcanic activity associated with a large igneous province. Mercury was sequestered by the organic-rich source rocks of the Lower Eagle Ford Formation and associated coeval ash and tuffs. Tabular igneous bodies that intruded and uplifted the local stratigraphy formed the Terlingua monocline and provided a source of heat for hydrothermal activity and maturation of organic matter. The subsequent generation and migration of liquid hydrocarbons and formation brines from the Lower Eagle Ford Formation transported Hg0(org) updip toward the hinge line of the Terlingua monocline where mixing with oxygenated meteoric water and subsequent oxidation of H2S produced the cinnabar-rich ores.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"332 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135966233","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}
Abstract Carbonaceous materials are a key factor controlling mineralization processes in many world-class gold deposits. Haoyaoerhudong is the largest carbonaceous metasediment-hosted gold deposit on the north margin of the North China craton. Gold-bearing orebodies are hosted in carbonaceous slates and schists belonging to Mesoproterozoic rift-related successions. Typical hydrothermal minerals are pyrrhotite, quartz, biotite, graphite, apatite, titanite, and native gold. The ore mineralogy, combined with microthermometry and Raman spectra on fluid inclusions, has demonstrated three stages of hydrothermal activity: (I) quartz-biotite ± sulfide stage associated with gold mineralization (315°–510°C; ~4.8 wt % NaCl equiv; H2O-NaCl-CO2 ± CH4 ± N2 system); (II) quartz-sulfide stage, including quartz-sulfide stringers (IIa, 250°–334°C; ~5.4 wt % NaCl equiv; H2O-NaCl-CH4 ± CO2 ± N2 system) and fractured quartz-sulfide ores (IIb, 234°–308°C; ~4.1 wt % NaCl equiv; H2O-NaCl-N2 ± CH4 system); and (III) post-ore quartz-calcite stage (70°–219°C; ~4.8 wt % NaCl equiv; H2O-NaCl system). The molar ratios of CO2 and CH4 progressively decreased from stage I to II, consistent with the occurrence of graphite in alteration zones. Microscopic observation and Raman spectra suggest that the fine-grained graphite from altered schist (Gr-1/2) and coarse-sized graphite from gold-bearing veins (Gr-3/4) are of high crystallinity and exhibit characteristics indicating a hydrothermal origin. The δ13C values of graphite, varying from −27.1 to −26.0‰ Vienna-Pee Dee Belemnite (V-PDB), suggest that the carbon was of biogenetic origin. Apatite Sr isotopes (87Sr/86Sr: 0.708293–0.708842) and titanite Nd isotopes (εNd(t): –11.76 to –14.84) also indicate contributions from carbonaceous rocks during mineralization. Thermodynamic modeling demonstrates that graphite may have precipitated at Haoyaoerhudong due to cooling and reduction of the H2O-CO2-CH4 fluids at high temperatures. Graphite precipitation would significantly consume CO2 and effectively destabilize Au bisulfide complexes, facilitating the codeposition of pyrrhotite, graphite, and native gold at high temperatures (≥379°C). We infer that deposition of hydrothermal graphite is a crucial process for mesothermal-hypothermal mineralization in sediment-hosted orogenic gold deposits.
{"title":"Hydrothermal Graphite as a Trigger for High-Temperature Orogenic Gold Mineralization at Haoyaoerhudong, Northern China","authors":"Wenbo Li, Fanghua Zhang, Xueyuan Qiao, Tianyao Fu","doi":"10.5382/econgeo.5018","DOIUrl":"https://doi.org/10.5382/econgeo.5018","url":null,"abstract":"Abstract Carbonaceous materials are a key factor controlling mineralization processes in many world-class gold deposits. Haoyaoerhudong is the largest carbonaceous metasediment-hosted gold deposit on the north margin of the North China craton. Gold-bearing orebodies are hosted in carbonaceous slates and schists belonging to Mesoproterozoic rift-related successions. Typical hydrothermal minerals are pyrrhotite, quartz, biotite, graphite, apatite, titanite, and native gold. The ore mineralogy, combined with microthermometry and Raman spectra on fluid inclusions, has demonstrated three stages of hydrothermal activity: (I) quartz-biotite ± sulfide stage associated with gold mineralization (315°–510°C; ~4.8 wt % NaCl equiv; H2O-NaCl-CO2 ± CH4 ± N2 system); (II) quartz-sulfide stage, including quartz-sulfide stringers (IIa, 250°–334°C; ~5.4 wt % NaCl equiv; H2O-NaCl-CH4 ± CO2 ± N2 system) and fractured quartz-sulfide ores (IIb, 234°–308°C; ~4.1 wt % NaCl equiv; H2O-NaCl-N2 ± CH4 system); and (III) post-ore quartz-calcite stage (70°–219°C; ~4.8 wt % NaCl equiv; H2O-NaCl system). The molar ratios of CO2 and CH4 progressively decreased from stage I to II, consistent with the occurrence of graphite in alteration zones. Microscopic observation and Raman spectra suggest that the fine-grained graphite from altered schist (Gr-1/2) and coarse-sized graphite from gold-bearing veins (Gr-3/4) are of high crystallinity and exhibit characteristics indicating a hydrothermal origin. The δ13C values of graphite, varying from −27.1 to −26.0‰ Vienna-Pee Dee Belemnite (V-PDB), suggest that the carbon was of biogenetic origin. Apatite Sr isotopes (87Sr/86Sr: 0.708293–0.708842) and titanite Nd isotopes (εNd(t): –11.76 to –14.84) also indicate contributions from carbonaceous rocks during mineralization. Thermodynamic modeling demonstrates that graphite may have precipitated at Haoyaoerhudong due to cooling and reduction of the H2O-CO2-CH4 fluids at high temperatures. Graphite precipitation would significantly consume CO2 and effectively destabilize Au bisulfide complexes, facilitating the codeposition of pyrrhotite, graphite, and native gold at high temperatures (≥379°C). We infer that deposition of hydrothermal graphite is a crucial process for mesothermal-hypothermal mineralization in sediment-hosted orogenic gold deposits.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"22 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136011451","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}
Saeid Asadzadeh, Sabine Chabrillat, Thomas Cudahy, Bahman Rashidi, Carlos Roberto de Souza Filho
Abstract Porphyry copper deposits are associated with large alteration footprints, and alteration mapping plays a key role in the exploration of these deposits. Imaging spectroscopy is commonly deployed for exploration targeting, yet it has rarely been used to map deposit-scale alteration patterns before initiating drilling. To close this gap, the Shadan porphyry Cu-Au deposit was thoroughly studied using the HyMap hyperspectral data (visible near-infrared–short-wave infrared) at 5-m resolution corroborated by rock geochemistry, magnetometry, and laboratory spectroscopy. Shadan is a well-exposed deposit with near-perfect zonation located in the volcanic belts of eastern Iran containing >135 Mt of ore at 0.3% Cu and 0.4 g/t Au. Thirteen minerals, including white mica, Al smectite, kaolinite, ferric/ferrous minerals, biotite, actinolite, epidote, chlorite, tourmaline, and jarosite, were mapped by applying the multifeature extraction methodology. The propylitic zone was partitioned into actinolite, epidote, and chlorite subfacies. The compositions of biotite and white mica were observed to become Fe and Al rich, respectively, toward the mineralized zones. The chemistry of actinolite was observed to change from Fe to Mg rich inward, providing a new vectoring tool for porphyry copper exploration. The study provided significant information about fluid-rock interactions and the chemistry of the circulating fluids including the oxidation-reduction states and acidity. By integrating the mineral maps with other data sets using the fuzzy logic method, the promising (ore) zones were identified and used to plan the next-stage drilling. This work demonstrated that imaging spectroscopy can be effectively used to better understand porphyry systems and provide deposit-scale vectors toward the mineralized centers, facilitating drilling.
{"title":"Alteration Mineral Mapping of the Shadan Porphyry Cu-Au Deposit (Iran) Using Airborne Imaging Spectroscopic Data: Implications for Exploration Drilling","authors":"Saeid Asadzadeh, Sabine Chabrillat, Thomas Cudahy, Bahman Rashidi, Carlos Roberto de Souza Filho","doi":"10.5382/econgeo.5041","DOIUrl":"https://doi.org/10.5382/econgeo.5041","url":null,"abstract":"Abstract Porphyry copper deposits are associated with large alteration footprints, and alteration mapping plays a key role in the exploration of these deposits. Imaging spectroscopy is commonly deployed for exploration targeting, yet it has rarely been used to map deposit-scale alteration patterns before initiating drilling. To close this gap, the Shadan porphyry Cu-Au deposit was thoroughly studied using the HyMap hyperspectral data (visible near-infrared–short-wave infrared) at 5-m resolution corroborated by rock geochemistry, magnetometry, and laboratory spectroscopy. Shadan is a well-exposed deposit with near-perfect zonation located in the volcanic belts of eastern Iran containing &gt;135 Mt of ore at 0.3% Cu and 0.4 g/t Au. Thirteen minerals, including white mica, Al smectite, kaolinite, ferric/ferrous minerals, biotite, actinolite, epidote, chlorite, tourmaline, and jarosite, were mapped by applying the multifeature extraction methodology. The propylitic zone was partitioned into actinolite, epidote, and chlorite subfacies. The compositions of biotite and white mica were observed to become Fe and Al rich, respectively, toward the mineralized zones. The chemistry of actinolite was observed to change from Fe to Mg rich inward, providing a new vectoring tool for porphyry copper exploration. The study provided significant information about fluid-rock interactions and the chemistry of the circulating fluids including the oxidation-reduction states and acidity. By integrating the mineral maps with other data sets using the fuzzy logic method, the promising (ore) zones were identified and used to plan the next-stage drilling. This work demonstrated that imaging spectroscopy can be effectively used to better understand porphyry systems and provide deposit-scale vectors toward the mineralized centers, facilitating drilling.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135487702","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}
Reed S. Lewis, David E. Stewart, Vincent H. Isakson, Niki E. Wintzer, Eric D. Stewart, Jeffrey D. Vervoort
Abstract Geologic mapping and associated U-Pb geochronologic work in the Stibnite-Edwardsburg area of central Idaho have provided regional geologic context for the gold-antimony-tungsten-mercury mineralization in this area. Roughly 6,000 m of strata that postdate the Mesoproterozoic Belt-Purcell Supergroup are preserved; overall, the strata young to the southwest and are found as roof pendants or septa within the Idaho batholith. Rocks suspected to be lower Paleozoic in age by early workers in the area contain detrital zircons as young as 500 Ma, confirming that age assignment. We recognized four mappable phases of Cretaceous intrusive rocks, ranging in age from about 95 to 85 Ma, but suspect additional dating and detailed mapping would better show the complexity of the intrusive history. Regional metamorphism ranges from greenschist to amphibolite facies and contact metamorphism is conspicuous near Cretaceous plutonic rocks. Lu-Hf garnet geochronology shows that regional metamorphism of the strata northwest of Stibnite occurred at about 113 Ma and thus prior to batholith intrusion. Contact metamorphism likely occurred some 15 to 30 m.y. later, depending on the specific pluton age. Four large-volume Eocene ash-flow deposits (and their hypothesized eruptive centers) were recognized. Important structures in the Stibnite area include a SW-directed thrust fault, now overturned, that repeats part of the section, and N- to NE-striking faults that have localized mineralization.
{"title":"Regional Geologic Framework of Mineral Deposits in the Stibnite-Edwardsburg Area, Central Idaho","authors":"Reed S. Lewis, David E. Stewart, Vincent H. Isakson, Niki E. Wintzer, Eric D. Stewart, Jeffrey D. Vervoort","doi":"10.5382/econgeo.5025","DOIUrl":"https://doi.org/10.5382/econgeo.5025","url":null,"abstract":"Abstract Geologic mapping and associated U-Pb geochronologic work in the Stibnite-Edwardsburg area of central Idaho have provided regional geologic context for the gold-antimony-tungsten-mercury mineralization in this area. Roughly 6,000 m of strata that postdate the Mesoproterozoic Belt-Purcell Supergroup are preserved; overall, the strata young to the southwest and are found as roof pendants or septa within the Idaho batholith. Rocks suspected to be lower Paleozoic in age by early workers in the area contain detrital zircons as young as 500 Ma, confirming that age assignment. We recognized four mappable phases of Cretaceous intrusive rocks, ranging in age from about 95 to 85 Ma, but suspect additional dating and detailed mapping would better show the complexity of the intrusive history. Regional metamorphism ranges from greenschist to amphibolite facies and contact metamorphism is conspicuous near Cretaceous plutonic rocks. Lu-Hf garnet geochronology shows that regional metamorphism of the strata northwest of Stibnite occurred at about 113 Ma and thus prior to batholith intrusion. Contact metamorphism likely occurred some 15 to 30 m.y. later, depending on the specific pluton age. Four large-volume Eocene ash-flow deposits (and their hypothesized eruptive centers) were recognized. Important structures in the Stibnite area include a SW-directed thrust fault, now overturned, that repeats part of the section, and N- to NE-striking faults that have localized mineralization.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134971821","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：