Wei Mao, Ziqi Jiang, Thomas Ulrich, Hong Zhong, Linbo Shang
Under conditions typically found in the Earth’s crust, there is a large pressure-temperature-composition range in the H2O-NaCl system where fluids may separate into a low-salinity vapor end member and a high-salinity liquid end member. However, heterogeneous trapping is common during the formation of fluid inclusions in an immiscible fluid system, violating the fundamental assumption of homogeneous entrapment for fluid inclusion microthermometry. This has profound consequences on the composition of these fluid phases and consequently on the formation of ore deposits from hydrothermal systems. At the same time, minor mixture of the high-salinity liquid phase with the low-salinity vapor phase cannot be distinguished from the end-member vapor-rich fluid inclusions by their bubble sizes. Precise determination of the salinities of vapor-rich fluid inclusions using microthermometry is deterred by the very small proportion of the liquid phase and the limitation of the analytical precision. All this will lead to erroneous compositional data from fluid inclusion analysis. We have quantitively calculated the variations of fluid inclusion properties caused by heterogeneous entrapment during phase separation in the H2O-NaCl system and showed that the salinity, and thereby the element contents and element/Na ratios of the vapor-rich fluid inclusions, is significantly changed in heterogeneously trapped fluid inclusions. The addition of 1 vol % of the high-salinity end member to the low-salinity end member results in a salinity change from 0.99 to 4.4 wt % NaCl equiv at the phase separation condition of 800 bar and 750°C. This will have a significant impact when it comes to determining the concentration of elements transported as chlorine complexes and typically leads to an overestimation of the mass transport capability by the vapor phase. Therefore, every effort should be taken during microthermometry to find and measure the least affected vapor-rich fluid inclusions. Our numerical calculations and synthetic fluid inclusions reveal that there is a linear relationship between the salinity and element contents for fluid inclusions at different extents of heterogeneous entrapment. Therefore, linear correction to the measured lowest vapor salinity can obtain a good approximation of the element contents in the end-member vapor phase.
{"title":"Improvements in the Quantification of End-Member Vapor Compositions in Fluid Inclusion Boiling Assemblages and Implications for Metal Transport by Low-Density Fluids","authors":"Wei Mao, Ziqi Jiang, Thomas Ulrich, Hong Zhong, Linbo Shang","doi":"10.5382/econgeo.5059","DOIUrl":"https://doi.org/10.5382/econgeo.5059","url":null,"abstract":"\u0000 Under conditions typically found in the Earth’s crust, there is a large pressure-temperature-composition range in the H2O-NaCl system where fluids may separate into a low-salinity vapor end member and a high-salinity liquid end member. However, heterogeneous trapping is common during the formation of fluid inclusions in an immiscible fluid system, violating the fundamental assumption of homogeneous entrapment for fluid inclusion microthermometry. This has profound consequences on the composition of these fluid phases and consequently on the formation of ore deposits from hydrothermal systems. At the same time, minor mixture of the high-salinity liquid phase with the low-salinity vapor phase cannot be distinguished from the end-member vapor-rich fluid inclusions by their bubble sizes. Precise determination of the salinities of vapor-rich fluid inclusions using microthermometry is deterred by the very small proportion of the liquid phase and the limitation of the analytical precision. All this will lead to erroneous compositional data from fluid inclusion analysis.\u0000 We have quantitively calculated the variations of fluid inclusion properties caused by heterogeneous entrapment during phase separation in the H2O-NaCl system and showed that the salinity, and thereby the element contents and element/Na ratios of the vapor-rich fluid inclusions, is significantly changed in heterogeneously trapped fluid inclusions. The addition of 1 vol % of the high-salinity end member to the low-salinity end member results in a salinity change from 0.99 to 4.4 wt % NaCl equiv at the phase separation condition of 800 bar and 750°C. This will have a significant impact when it comes to determining the concentration of elements transported as chlorine complexes and typically leads to an overestimation of the mass transport capability by the vapor phase. Therefore, every effort should be taken during microthermometry to find and measure the least affected vapor-rich fluid inclusions. Our numerical calculations and synthetic fluid inclusions reveal that there is a linear relationship between the salinity and element contents for fluid inclusions at different extents of heterogeneous entrapment. Therefore, linear correction to the measured lowest vapor salinity can obtain a good approximation of the element contents in the end-member vapor phase.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":null,"pages":null},"PeriodicalIF":5.8,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141046608","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}
Hidaya Hassan, Jacob Kaavera, Akira Imai, Kotaro Yonezu, Thomas Tindell, Kenzo Sanematsu, Koichiro Watanabe
High-grade Cu mineralization was recently discovered in the Mbesa prospect in southern Tanzania, but its origin is poorly constrained. Herein, we present new major element, trace element, rare earth element (REE), and platinum group element (PGE) geochemistry and petrographic data to constrain the origin of the mineralization. The sulfide mineralization is dominated by chalcopyrite and bornite and characterized by high Cu/Ni over 100 in the massive and disseminated ores. The mineralization lacks pyrrhotite and pentlandite, which are found commonly in magmatic Ni-Cu-PGE sulfide deposits. Platinum group minerals present are michenerite (PdBiTe) and sudburyite (PdSb). PGE concentrations expressed as Pd + Pt + Au are up to 1.31 and 1.04 ppm in the massive and disseminated ores, respectively. The δ34S of chalcopyrite separates range from –3.9 to –0.6‰, bornite separates vary from –1.8 to 1.1‰, and bornite-chalcopyrite mixtures yield –1.3 and 0.6‰, mostly consistent with a magmatic sulfur origin. The sulfides are hosted by coarse-grained plagioclase amphibolite and hornblende gneiss with recrystallization textures suggestive of metamorphism. Both rocks are characterized by enrichment in large ion lithophile elements (LILEs), with negative anomalies of Zr and Nb, consistent with crustal contamination of magmas derived from partial melting of subcontinental lithospheric mantle (SCLM). An SCLM origin is further suggested by the close association of Cu sulfides with carbonates and apatite. It is suggested that the sulfides crystallized from the fractionated Cu-rich sulfide melt enriched in intermediate solid solution (iss) at shallow crustal levels. Sulfide were likely mobilized as droplets attached to CO2 vapor phase as expressed by close association between carbonates and apatite with the Cu-rich sulfides. Nickel-rich sulfides may remain undiscovered at deeper portions around the Mbesa prospect.
{"title":"Cu-Au-Platinum Group Element Mineralization in the Mbesa Prospect, Southern Tanzania: Unconventional Magmatic Sulfides","authors":"Hidaya Hassan, Jacob Kaavera, Akira Imai, Kotaro Yonezu, Thomas Tindell, Kenzo Sanematsu, Koichiro Watanabe","doi":"10.5382/econgeo.5068","DOIUrl":"https://doi.org/10.5382/econgeo.5068","url":null,"abstract":"High-grade Cu mineralization was recently discovered in the Mbesa prospect in southern Tanzania, but its origin is poorly constrained. Herein, we present new major element, trace element, rare earth element (REE), and platinum group element (PGE) geochemistry and petrographic data to constrain the origin of the mineralization. The sulfide mineralization is dominated by chalcopyrite and bornite and characterized by high Cu/Ni over 100 in the massive and disseminated ores. The mineralization lacks pyrrhotite and pentlandite, which are found commonly in magmatic Ni-Cu-PGE sulfide deposits. Platinum group minerals present are michenerite (PdBiTe) and sudburyite (PdSb). PGE concentrations expressed as Pd + Pt + Au are up to 1.31 and 1.04 ppm in the massive and disseminated ores, respectively. The δ<sup>34</sup>S of chalcopyrite separates range from –3.9 to –0.6‰, bornite separates vary from –1.8 to 1.1‰, and bornite-chalcopyrite mixtures yield –1.3 and 0.6‰, mostly consistent with a magmatic sulfur origin. The sulfides are hosted by coarse-grained plagioclase amphibolite and hornblende gneiss with recrystallization textures suggestive of metamorphism. Both rocks are characterized by enrichment in large ion lithophile elements (LILEs), with negative anomalies of Zr and Nb, consistent with crustal contamination of magmas derived from partial melting of subcontinental lithospheric mantle (SCLM). An SCLM origin is further suggested by the close association of Cu sulfides with carbonates and apatite. It is suggested that the sulfides crystallized from the fractionated Cu-rich sulfide melt enriched in intermediate solid solution (iss) at shallow crustal levels. Sulfide were likely mobilized as droplets attached to CO<sub>2</sub> vapor phase as expressed by close association between carbonates and apatite with the Cu-rich sulfides. Nickel-rich sulfides may remain undiscovered at deeper portions around the Mbesa prospect.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":null,"pages":null},"PeriodicalIF":5.8,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140817772","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}
Pub Date : 2024-05-01DOI: 10.5382/econgeo.119.3.507
{"title":"Letter Introducing the New Editor, David Cooke","authors":"","doi":"10.5382/econgeo.119.3.507","DOIUrl":"https://doi.org/10.5382/econgeo.119.3.507","url":null,"abstract":"","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":null,"pages":null},"PeriodicalIF":5.8,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141024603","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}
Marina D. Schofield, Bruno Lafrance, Harold L. Gibson, K. Howard Poulsen, Christophe Scheffer, Benoît Quesnel, Georges Beaudoin, Michael A. Hamilton
The Rouyn-Noranda mining district of Quebec contains 20 Cu-Zn (±Au ±Ag) volcanogenic massive sulfide (VMS) deposits, including the giant and gold-rich Quemont and Horne deposits. Mineralized epigenetic veins are also present, but their origin and relative timing remain enigmatic. The nature and extent of their alteration signatures and the effect of their superposition on district-scale alteration patterns is unknown. The VMS-related quartz-sulfide Cu-Zn-Ag veins have δ18Oquartz values of 8.5 ± 0.8‰, reflecting δ18Ofluid compositions of –0.4 to 3.1‰ (250°–350°C) that are typical of Archean seawater. They are associated with a proximal Fe-rich chlorite alteration and marginal spotted sericite-chlorite alteration with whole-rock δ18O values of 2.9 to 5.9‰ and are interpreted to have formed within the structurally controlled discordant upflow zones of a VMS hydrothermal system. Younger gold-bearing quartz-carbonate veins were emplaced along mechanical anisotropies created by mafic dikes during north-south compression and the formation of regional E-trending faults, folds, and cleavage. They are characterized by δ18Oquartz values of 11.3 ± 0.8‰, reflecting δ18Ofluid compositions of 2.4 to 5.9‰ (250°–350°C), typical of a metamorphic fluid, possibly mixed with a lower δ18O upper crustal fluid. They are associated with ankerite, calcite, muscovite, chlorite, albite, and quartz ± hematite alteration with whole-rock δ18O values of 5.8 to 10.3‰. Chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb zircon ages for two tonalite intrusions constrain the maximum age of the Cu-Zn-Ag veins to 2697.6 ± 0.7 Ma and the minimum age to 2695.3 ± 1.0 Ma, which is also the maximum age of the gold quartz-carbonate veins. Superposition of alteration related to the gold quartz-carbonate veins on previously chlorite- and sericite-altered rocks has resulted in mixed alteration signals with whole-rock δ18O values of ~6 to 8‰ that have perturbed and masked regional alteration patterns related to older VMS mineralization, such as those found in the Quemont and Horne deposits. These results indicate that defining alteration vectors in camps that have superimposed hydrothermal systems requires full consideration of the hydrothermal history of the camp, and if such constraints are lacking, whole-rock δ18O values should not be used as a stand-alone exploration method.
{"title":"Discriminating Superimposed Alteration Associated with Epigenetic Base and Precious Metal Vein Systems in the Rouyn-Noranda Mining District, Quebec; Implications for Exploration in Ancient Volcanic Districts","authors":"Marina D. Schofield, Bruno Lafrance, Harold L. Gibson, K. Howard Poulsen, Christophe Scheffer, Benoît Quesnel, Georges Beaudoin, Michael A. Hamilton","doi":"10.5382/econgeo.5063","DOIUrl":"https://doi.org/10.5382/econgeo.5063","url":null,"abstract":"The Rouyn-Noranda mining district of Quebec contains 20 Cu-Zn (±Au ±Ag) volcanogenic massive sulfide (VMS) deposits, including the giant and gold-rich Quemont and Horne deposits. Mineralized epigenetic veins are also present, but their origin and relative timing remain enigmatic. The nature and extent of their alteration signatures and the effect of their superposition on district-scale alteration patterns is unknown. The VMS-related quartz-sulfide Cu-Zn-Ag veins have δ<sup>18</sup>O<sub>quartz</sub> values of 8.5 ± 0.8‰, reflecting δ<sup>18</sup>O<sub>fluid</sub> compositions of –0.4 to 3.1‰ (250°–350°C) that are typical of Archean seawater. They are associated with a proximal Fe-rich chlorite alteration and marginal spotted sericite-chlorite alteration with whole-rock δ<sup>18</sup>O values of 2.9 to 5.9‰ and are interpreted to have formed within the structurally controlled discordant upflow zones of a VMS hydrothermal system. Younger gold-bearing quartz-carbonate veins were emplaced along mechanical anisotropies created by mafic dikes during north-south compression and the formation of regional E-trending faults, folds, and cleavage. They are characterized by δ<sup>18</sup>O<sub>quartz</sub> values of 11.3 ± 0.8‰, reflecting δ<sup>18</sup>O<sub>fluid</sub> compositions of 2.4 to 5.9‰ (250°–350°C), typical of a metamorphic fluid, possibly mixed with a lower δ<sup>18</sup>O upper crustal fluid. They are associated with ankerite, calcite, muscovite, chlorite, albite, and quartz ± hematite alteration with whole-rock δ<sup>18</sup>O values of 5.8 to 10.3‰. Chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb zircon ages for two tonalite intrusions constrain the maximum age of the Cu-Zn-Ag veins to 2697.6 ± 0.7 Ma and the minimum age to 2695.3 ± 1.0 Ma, which is also the maximum age of the gold quartz-carbonate veins. Superposition of alteration related to the gold quartz-carbonate veins on previously chlorite- and sericite-altered rocks has resulted in mixed alteration signals with whole-rock δ<sup>18</sup>O values of ~6 to 8‰ that have perturbed and masked regional alteration patterns related to older VMS mineralization, such as those found in the Quemont and Horne deposits. These results indicate that defining alteration vectors in camps that have superimposed hydrothermal systems requires full consideration of the hydrothermal history of the camp, and if such constraints are lacking, whole-rock δ<sup>18</sup>O values should not be used as a stand-alone exploration method.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":null,"pages":null},"PeriodicalIF":5.8,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140817838","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}
Robert R. Loucks, Gonzalo J. Henríquez, Marco L. Fiorentini
To meet surging requirements of copper for the green energy revolution, minable resources subequal to all copper production in history must be found in the next two decades. We show that trace elements in zircon and whole-rock samples that are diagnostic of unusually high-pressure magmatic differentiation and high hydration state and oxidation state of their parent silicate melt are effective for discriminating copper sulfide-ore-productive arc magmas from infertile arc magmas. Tests on our database of 5,777 zircons from 80 igneous complexes, including 2,220 zircons from ore-generative intrusions in 37 major porphyry and high-sulfidation epithermal Cu(-Au-Mo) deposits worldwide, demonstrate that our magmatic copper fertility discriminants apparently perform equally well in intraoceanic arcs, continental margin arcs, and continental collision orogens of Ordovician to Quaternary age. That performance consistency means that the tectono-magmatic controls on development of magmatic-hydrothermal copper ore-forming fertility are essentially the same in all those plate-convergence settings. The ratio Ce/√(U × Ti) in zircon is a quantitative indicator of the relative oxygen fugacity of the silicate melt and its sulfur-carrying capacity. The ratio of the europium anomaly to ytterbium in granitoid melts and zircon is an uncalibrated but empirically useful indicator of the melt’s hydration state and ability to provide chloride-complexed metals to exsolving hydrothermal fluids. Plots of (EuN/Eu*)/YbN vs. Ce/√(U × Ti) in zircon are remarkably effective for discriminating igneous complexes, arc segments, and time intervals within them that can generate and are likely to host magmatic-hydrothermal Cu(-Au-Mo) ore deposits. Arrays of cognate zircons on such plots have slopes that vary with pressure-dependent chlorinity of exsolving fluid and its efficacy in scavenging CuCl from the melt. Our zircon indicators of Cu metallogenic fertility are applicable to detrital as well as in situ zircons and can assist with ore discovery in watersheds upstream from a sediment sampling site. We formulated a composite zircon copper fertility index (ZCFI) that can be applied to each microbeam spot analysis—ZCFI = 104 (EuN/EuN*)/YbN + 5 Ce/√(Ui × Ti)—and substantially decreases the number of zircon analyses needed for reliable prospectivity assessment in a detrital grain population, thereby making this watershed-scale exploration tool cost-competitive with other methods of geochemical exploration.
{"title":"Zircon and Whole-Rock Trace Element Indicators of Magmatic Hydration State and Oxidation State Discriminate Copper Ore-Forming from Barren Arc Magmas","authors":"Robert R. Loucks, Gonzalo J. Henríquez, Marco L. Fiorentini","doi":"10.5382/econgeo.5071","DOIUrl":"https://doi.org/10.5382/econgeo.5071","url":null,"abstract":"To meet surging requirements of copper for the green energy revolution, minable resources subequal to all copper production in history must be found in the next two decades. We show that trace elements in zircon and whole-rock samples that are diagnostic of unusually high-pressure magmatic differentiation and high hydration state and oxidation state of their parent silicate melt are effective for discriminating copper sulfide-ore-productive arc magmas from infertile arc magmas. Tests on our database of 5,777 zircons from 80 igneous complexes, including 2,220 zircons from ore-generative intrusions in 37 major porphyry and high-sulfidation epithermal Cu(-Au-Mo) deposits worldwide, demonstrate that our magmatic copper fertility discriminants apparently perform equally well in intraoceanic arcs, continental margin arcs, and continental collision orogens of Ordovician to Quaternary age. That performance consistency means that the tectono-magmatic controls on development of magmatic-hydrothermal copper ore-forming fertility are essentially the same in all those plate-convergence settings. The ratio Ce/√(U × Ti) in zircon is a quantitative indicator of the relative oxygen fugacity of the silicate melt and its sulfur-carrying capacity. The ratio of the europium anomaly to ytterbium in granitoid melts and zircon is an uncalibrated but empirically useful indicator of the melt’s hydration state and ability to provide chloride-complexed metals to exsolving hydrothermal fluids. Plots of (Eu<sub>N</sub>/Eu*)/Yb<sub>N</sub> vs. Ce/√(U × Ti) in zircon are remarkably effective for discriminating igneous complexes, arc segments, and time intervals within them that can generate and are likely to host magmatic-hydrothermal Cu(-Au-Mo) ore deposits. Arrays of cognate zircons on such plots have slopes that vary with pressure-dependent chlorinity of exsolving fluid and its efficacy in scavenging CuCl from the melt. Our zircon indicators of Cu metallogenic fertility are applicable to detrital as well as in situ zircons and can assist with ore discovery in watersheds upstream from a sediment sampling site. We formulated a composite zircon copper fertility index (ZCFI) that can be applied to each microbeam spot analysis—ZCFI = 10<sup>4</sup> (Eu<sub>N</sub>/Eu<sub>N</sub>*)/Yb<sub>N</sub> + 5 Ce/√(U<sub>i</sub> × Ti)—and substantially decreases the number of zircon analyses needed for reliable prospectivity assessment in a detrital grain population, thereby making this watershed-scale exploration tool cost-competitive with other methods of geochemical exploration.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":null,"pages":null},"PeriodicalIF":5.8,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140817872","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}
Yan Liu, A. Chakhmouradian, E. Reguir, Zengqian Hou, Xu Zheng, Haobang Fu, Jian Sun
Carbonatite complexes are globally significant sources of rare earth elements (REEs); however, mechanisms governing REE deposition in various tectono-lithologic settings, encompassing host rocks, wall rocks, ore-controlling structures, and metasomatism, remain inadequately understood. The Zhengjialiangzi mining camp, situated within the extensive Muluozhai deposit (containing 0.45 million metric tons [Mt] at 4.0 wt % REE2O3) in the northern segment of the Mianning-Dechang belt, Sichuan (southwestern China), is characterized by a complex vein system that evolved within metamorphosed supracrustal rocks of the Yangxin and Mount Emei Formations. The mineralization is coeval with Oligocene intrusions of carbonatite and nordmarkite at ~27 Ma. The major gangue minerals include fluorite, barite (transitional to celestine), and calcite, with bastnäsite serving as the primary host for REEs in all analyzed orebodies. Several other accessory to minor minerals were identified in the ore veins, including some that had not previously been known to occur in the Muluozhai deposits (e.g., thorite and pyrochlore). The stable isotopic (C-O-Ca) and trace element compositions of calcite, along with whole-rock data, suggest that carbonate material was derived from the mantle and subsequently reequilibrated with the Yangxin marbles. The radiogenic isotope (Sr-Nd-Pb) compositions of vein material remained unaffected by wall-rock contamination and suggest a mantle source influenced by crustal recycling, consistent with other REE deposits hosted by carbonatite and nordmarkite in the region. The combined petrographic and geochemical evidence suggests derivation of Muluozhai mineralization from a carbonatitic source and interaction of carbonatite-derived fluids with wall rocks, xenoliths, and early-crystallizing mineral phases, particularly barite.
{"title":"The Origin and Evolution of Rare Earth Element Mineralization in the Muluozhai Deposit (Sichuan, China): Insights from Mineralogical, Trace Element, and Sr-Nd-Pb-C-O-Ca Isotope Data","authors":"Yan Liu, A. Chakhmouradian, E. Reguir, Zengqian Hou, Xu Zheng, Haobang Fu, Jian Sun","doi":"10.5382/econgeo.5066","DOIUrl":"https://doi.org/10.5382/econgeo.5066","url":null,"abstract":"\u0000 Carbonatite complexes are globally significant sources of rare earth elements (REEs); however, mechanisms governing REE deposition in various tectono-lithologic settings, encompassing host rocks, wall rocks, ore-controlling structures, and metasomatism, remain inadequately understood. The Zhengjialiangzi mining camp, situated within the extensive Muluozhai deposit (containing 0.45 million metric tons [Mt] at 4.0 wt % REE2O3) in the northern segment of the Mianning-Dechang belt, Sichuan (southwestern China), is characterized by a complex vein system that evolved within metamorphosed supracrustal rocks of the Yangxin and Mount Emei Formations. The mineralization is coeval with Oligocene intrusions of carbonatite and nordmarkite at ~27 Ma. The major gangue minerals include fluorite, barite (transitional to celestine), and calcite, with bastnäsite serving as the primary host for REEs in all analyzed orebodies. Several other accessory to minor minerals were identified in the ore veins, including some that had not previously been known to occur in the Muluozhai deposits (e.g., thorite and pyrochlore). The stable isotopic (C-O-Ca) and trace element compositions of calcite, along with whole-rock data, suggest that carbonate material was derived from the mantle and subsequently reequilibrated with the Yangxin marbles. The radiogenic isotope (Sr-Nd-Pb) compositions of vein material remained unaffected by wall-rock contamination and suggest a mantle source influenced by crustal recycling, consistent with other REE deposits hosted by carbonatite and nordmarkite in the region. The combined petrographic and geochemical evidence suggests derivation of Muluozhai mineralization from a carbonatitic source and interaction of carbonatite-derived fluids with wall rocks, xenoliths, and early-crystallizing mineral phases, particularly barite.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":null,"pages":null},"PeriodicalIF":5.8,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141026693","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}
Mitchell M. Bennett, T. Monecke, T. James Reynolds, Nigel M. Kelly
Regional stream sediment surveys are an important exploration tool used in the search for concealed or partially concealed porphyry deposits. It is shown here that quartz contained in the coarse fraction of stream sediments can be used as an indicator mineral to supplement geochemical analyses conducted on the fine fraction, such as the measurement of the bulk cyanide leach extractable gold content. A method is proposed that allows separation of quartz grains from the coarse rejects of stream sediment samples to prepare grain mounts for petrographic analysis. Based on optical cathodoluminescence microscopy and fluid inclusion petrography, the number of porphyry quartz grains in each grain mount is then identified. Case studies conducted at Vert de Gris in Haiti and Hides Creek in Papua New Guinea show that porphyry quartz grains could be confidently identified in sediments in the catchment areas of both porphyries. Because the cost of microscopic analysis of quartz is small compared to the expense of sampling and geochemical analysis, the developed technique could be routinely used in large greenfield exploration programs. It is envisaged here that petrographic analysis of quartz grains can contribute valuable information for prioritization of targets defined based on their geochemical signatures.
区域溪流沉积物调查是用于寻找隐蔽或部分隐蔽斑岩矿床的重要勘探工具。本文表明，溪流沉积物粗粒中所含的石英可用作指示矿物，以补充对细粒进行的地球化学分析，如测量大量氰化物浸出可提取金的含量。本文提出了一种方法，可将石英颗粒从溪流沉积物样本的粗渣中分离出来，以制备用于岩相分析的颗粒装片。然后，根据光学阴极发光显微镜和流体包裹体岩相学，确定每个颗粒镶嵌物中斑岩石英颗粒的数量。在海地 Vert de Gris 和巴布亚新几内亚 Hides Creek 进行的案例研究表明，可以在这两个斑岩集水区的沉积物中确定斑岩石英颗粒。由于与取样和地球化学分析的费用相比，对石英进行显微分析的成本较低，因此所开发的技术可在大型绿地勘探项目中常规使用。根据设想，石英颗粒的岩相分析可以为根据地球化学特征确定目标的优先次序提供有价值的信息。
{"title":"RECOGNITION OF PORPHYRY QUARTZ IN STREAM SEDIMENTS BY FLUID INCLUSION PETROGRAPHY AND CATHODOLUMINESCENCE MICROSCOPY: RESULTS OF SYSTEMATIC DISPERSION STUDIES AND POTENTIAL APPLICATIONS IN PORPHYRY EXPLORATION","authors":"Mitchell M. Bennett, T. Monecke, T. James Reynolds, Nigel M. Kelly","doi":"10.5382/econgeo.5062","DOIUrl":"https://doi.org/10.5382/econgeo.5062","url":null,"abstract":"\u0000 Regional stream sediment surveys are an important exploration tool used in the search for concealed or partially concealed porphyry deposits. It is shown here that quartz contained in the coarse fraction of stream sediments can be used as an indicator mineral to supplement geochemical analyses conducted on the fine fraction, such as the measurement of the bulk cyanide leach extractable gold content. A method is proposed that allows separation of quartz grains from the coarse rejects of stream sediment samples to prepare grain mounts for petrographic analysis. Based on optical cathodoluminescence microscopy and fluid inclusion petrography, the number of porphyry quartz grains in each grain mount is then identified. Case studies conducted at Vert de Gris in Haiti and Hides Creek in Papua New Guinea show that porphyry quartz grains could be confidently identified in sediments in the catchment areas of both porphyries. Because the cost of microscopic analysis of quartz is small compared to the expense of sampling and geochemical analysis, the developed technique could be routinely used in large greenfield exploration programs. It is envisaged here that petrographic analysis of quartz grains can contribute valuable information for prioritization of targets defined based on their geochemical signatures.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":null,"pages":null},"PeriodicalIF":5.8,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141024068","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}
Pub Date : 2024-05-01DOI: 10.5382/econgeo.119.3.509
{"title":"Letter About the Outgoing Editor, Lawrence Meinert","authors":"","doi":"10.5382/econgeo.119.3.509","DOIUrl":"https://doi.org/10.5382/econgeo.119.3.509","url":null,"abstract":"","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":null,"pages":null},"PeriodicalIF":5.8,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141051094","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 timing and mechanism of ore precipitation in porphyry copper systems are hot topics and remain controversial. The large Miocene collision-related Zhunuo porphyry Cu deposit in the Gangdese belt of southern Tibet, China, was produced by multistage quartz veining and hydrothermal alteration, accompanied by Cu sulfide precipitation. In this study, we have combined cathodoluminescence (CL) petrography with in situ oxygen isotope analysis and fluid inclusion microthermometry and laser ablation-inductively coupled plasma-mass spectrometer microanalysis to constrain the growth history of individual quartz veins, the source and evolution of the hydrothermal fluids, and the timing and mechanism of ore precipitation at Zhunuo. Early quartz A veins associated with potassic alteration are composed of quartz, K-feldspar, biotite, Cu-Fe sulfides, and pyrite. Quartz B veins are composed of quartz, Cu-Fe sulfides, molybdenite, and pyrite. CL imaging shows that quartz grains in the A and B veins consist of abundant early generation of bright-luminescent quartz (QA and QB) with volumetrically minor later generation of dull-luminescent quartz (QA-crack and QB-crack) occurring in the voids or at the margins of the QA and QB veins with embayed contacts. Cu-Fe sulfides are generally in contact with the dull-luminescent quartz and locally in contact with the bright-luminescent quartz and K-feldspar in the A and B veins or occur as disseminations in the potassic-altered porphyries that have been overprinted by chlorite ± muscovite alteration. QA and QB contain single-phase intermediate-density inclusions and abundant brine and vapor-rich inclusions. A boiling assemblage in QA has a homogenization temperature of ~560°C and trapping pressure of ~530 bar. Two boiling assemblages in QB have homogenization temperatures of ~440°C with trapping pressures of ~230 and ~250 bar, indicating a transition from lithostatic to hydrostatic conditions at a paleodepth of ~2.0 to 2.5 km. QA-crack and QB-crack contain aqueous inclusions with lower homogenization temperatures of 340° to 400°C and salinities of 6 to 12 wt % NaCl equiv. In situ oxygen isotopes indicate that QA and QB have δ18O values of 7.6 to 11.4‰, whereas QA-crack and QB-crack have δ18O values of –7.2 to 6.7‰. Combined with fluid inclusion compositions, we propose that condensation of vapors into brines and mixing with 25 to 60% meteoric water can produce the salinity and oxygen isotopes of fluids that caused the dissolution of the early bright-luminescent quartz and the precipitation of the later dull-luminescent quartz. Zhunuo Cu-Fe sulfides are in contact with the bright-luminescent quartz and cut the growth bands. The dull-luminescent quartz in contact with the Cu-Fe sulfides has oscillatory growth banding. In addition, Cu-Fe sulfides in the A and B veins or in the potassic-altered rocks coexist with chlorite ± muscovite alteration minerals. These geologic observations, together with evidence that there is an a
斑岩铜系统中矿石沉淀的时间和机制是热门话题，目前仍存在争议。中国西藏南部冈底斯带与中新世碰撞有关的卓诺大型斑岩铜矿床是由多级石英脉和热液蚀变作用产生的，并伴有硫化铜沉淀。在这项研究中，我们将阴极发光（CL）岩相学与原位氧同位素分析、流体包裹体微测温和激光烧蚀-电感耦合等离子体-质谱仪显微分析相结合，以确定卓诺矿床各个石英脉的生长历史、热液的来源和演化以及矿石沉淀的时间和机制。与钾盐蚀变有关的早期石英A矿脉由石英、K长石、斜长石、铜铁硫化物和黄铁矿组成。石英 B 矿脉由石英、铜铁硫化物、辉钼矿和黄铁矿组成。CL 成像显示，A 和 B 矿脉中的石英颗粒由大量早期生成的亮荧光石英（QA 和 QB）组成，后期生成的暗荧光石英（QA 裂缝和 QB 裂缝）在体积上较小，出现在 QA 和 QB 矿脉的空隙或边缘，并有凹凸接触。在 A 和 B 矿脉中，铜铁硫化物一般与钝荧光石英接触，局部与亮荧光石英和 K 长石接触，或者在被绿泥石±黝帘石蚀变覆盖的钾盐蚀变斑岩中呈浸染状出现。QA 和 QB 含有单相中等密度包裹体以及大量富含盐水和蒸汽的包裹体。QA 中的一个沸腾集合体的均质化温度约为 560°C，捕获压力约为 530 巴。QB 中的两个沸腾集合体的均质化温度约为 440°C，捕集压力约为 230 和 250 巴，表明在古深度约为 2.0 至 2.5 千米处出现了从岩石静力条件向流体静力条件的过渡。原位氧同位素显示，QA 和 QB 的 δ18O 值为 7.6 至 11.4‰，而 QA 裂缝和 QB 裂缝的 δ18O 值为 -7.2 至 6.7‰。结合流体包裹体成分，我们认为蒸汽凝结成盐水并与25%至60%的陨水混合，可以产生流体的盐度和氧同位素，从而导致早期亮光石英的溶解和后期暗光石英的沉淀。朱诺铜铁硫化物与发光石英接触，并切割了生长带。与铜铁硫化物接触的钝发光石英具有振荡生长带。此外，A 和 B 矿脉或钾盐蚀变岩中的铜铁硫化物与绿泥石和褐铁矿蚀变矿物共存。这些地质观察结果，以及钝荧光石英中的水流与亮荧光石英中的盐水相比，铜/（Na + K）比值骤降一个数量级以上的证据表明，铜铁硫化物的沉淀发生在钾长石蚀变阶段之后和绿泥石±麝香石蚀变阶段期间。矿石的析出与岩浆流体（盐水+蒸汽）与陨石水的混合有关，伴随着流体冷却、盐度降低，以及岩石从岩浆状态过渡到静水状态时石英的逆向溶解。在最新阶段的持续冷却过程中，热液析出了含有大量黄铁矿和少量石英的 D 矿脉。D 矿脉（QD）中的石英含有水包裹体，其温度和铜/（Na + K）比值要低得多，表明大部分铜铁硫化物已在这一阶段沉淀。
{"title":"Timing and Mechanism of Ore Precipitation in Porphyry Cu Systems: Insight from LA-ICP-MS Analysis of Fluid Inclusions and In Situ Oxygen Isotope Analysis of Hydrothermal Quartz at Zhunuo Porphyry Cu Deposit, China","authors":"Xiang Sun, Ruyue Li, Xiaobo Si, Ke Xiao, Jun Deng","doi":"10.5382/econgeo.5064","DOIUrl":"https://doi.org/10.5382/econgeo.5064","url":null,"abstract":"\u0000 The timing and mechanism of ore precipitation in porphyry copper systems are hot topics and remain controversial. The large Miocene collision-related Zhunuo porphyry Cu deposit in the Gangdese belt of southern Tibet, China, was produced by multistage quartz veining and hydrothermal alteration, accompanied by Cu sulfide precipitation. In this study, we have combined cathodoluminescence (CL) petrography with in situ oxygen isotope analysis and fluid inclusion microthermometry and laser ablation-inductively coupled plasma-mass spectrometer microanalysis to constrain the growth history of individual quartz veins, the source and evolution of the hydrothermal fluids, and the timing and mechanism of ore precipitation at Zhunuo. Early quartz A veins associated with potassic alteration are composed of quartz, K-feldspar, biotite, Cu-Fe sulfides, and pyrite. Quartz B veins are composed of quartz, Cu-Fe sulfides, molybdenite, and pyrite. CL imaging shows that quartz grains in the A and B veins consist of abundant early generation of bright-luminescent quartz (QA and QB) with volumetrically minor later generation of dull-luminescent quartz (QA-crack and QB-crack) occurring in the voids or at the margins of the QA and QB veins with embayed contacts. Cu-Fe sulfides are generally in contact with the dull-luminescent quartz and locally in contact with the bright-luminescent quartz and K-feldspar in the A and B veins or occur as disseminations in the potassic-altered porphyries that have been overprinted by chlorite ± muscovite alteration.\u0000 QA and QB contain single-phase intermediate-density inclusions and abundant brine and vapor-rich inclusions. A boiling assemblage in QA has a homogenization temperature of ~560°C and trapping pressure of ~530 bar. Two boiling assemblages in QB have homogenization temperatures of ~440°C with trapping pressures of ~230 and ~250 bar, indicating a transition from lithostatic to hydrostatic conditions at a paleodepth of ~2.0 to 2.5 km. QA-crack and QB-crack contain aqueous inclusions with lower homogenization temperatures of 340° to 400°C and salinities of 6 to 12 wt % NaCl equiv. In situ oxygen isotopes indicate that QA and QB have δ18O values of 7.6 to 11.4‰, whereas QA-crack and QB-crack have δ18O values of –7.2 to 6.7‰. Combined with fluid inclusion compositions, we propose that condensation of vapors into brines and mixing with 25 to 60% meteoric water can produce the salinity and oxygen isotopes of fluids that caused the dissolution of the early bright-luminescent quartz and the precipitation of the later dull-luminescent quartz.\u0000 Zhunuo Cu-Fe sulfides are in contact with the bright-luminescent quartz and cut the growth bands. The dull-luminescent quartz in contact with the Cu-Fe sulfides has oscillatory growth banding. In addition, Cu-Fe sulfides in the A and B veins or in the potassic-altered rocks coexist with chlorite ± muscovite alteration minerals. These geologic observations, together with evidence that there is an a","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":null,"pages":null},"PeriodicalIF":5.8,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140270945","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}
Lei Liu, Chuntao Yin, Yasir Shaheen Khalil, Jun Hong, Jilu Feng, Huishan Zhang
The Chagai porphyry Cu belt in Pakistan is an important metallogenic terrain extending approximately 400 km in an east-west direction. Most of the known porphyry Cu deposits, such as the world-class Reko Diq deposit and Saindak deposit, are located in the western Chagai belt. In this study, the ZY1-02D hyperspectral data acquired by a recently launched spaceborne imaging spectrometer with 166 bands within a 0.4- to 2.5-μm spectral region were used to map mineral information over 8,000 km2 for exploring potential targets of porphyry Cu mineralization in the western Chagai belt. False color composite, spectral angle mapper, and wavelength position mapping methods were used in this research leading to the identification of a series of alteration minerals (including muscovite [sericite], kaolinite, alunite, epidote, chlorite, and calcite) from ZY1-02D data. The alteration mineral maps derived from ZY1-02D data match well with the known deposits and field inspections. Twenty-three new targets were identified as potential porphyry Cu mineralization targets for further exploration in the study area. Three targets, north of Saindak, Koh-i-Sultan, and Durban Chah, and six alteration sites in the southwest of Durban Chah, were inspected in the field, and Cu-Au mineralization was confirmed in all these inspected areas. As the ZY1-02D hyperspectral data covers most of the land area of the earth, this study provides new insights for mineral exploration and lithologic mapping in remote regions.
{"title":"Alteration Mapping for Porphyry Cu Targeting in the Western Chagai Belt, Pakistan, Using ZY1-02D Spaceborne Hyperspectral Data","authors":"Lei Liu, Chuntao Yin, Yasir Shaheen Khalil, Jun Hong, Jilu Feng, Huishan Zhang","doi":"10.5382/econgeo.5045","DOIUrl":"https://doi.org/10.5382/econgeo.5045","url":null,"abstract":"The Chagai porphyry Cu belt in Pakistan is an important metallogenic terrain extending approximately 400 km in an east-west direction. Most of the known porphyry Cu deposits, such as the world-class Reko Diq deposit and Saindak deposit, are located in the western Chagai belt. In this study, the ZY1-02D hyperspectral data acquired by a recently launched spaceborne imaging spectrometer with 166 bands within a 0.4- to 2.5-μm spectral region were used to map mineral information over 8,000 km<sup>2</sup> for exploring potential targets of porphyry Cu mineralization in the western Chagai belt. False color composite, spectral angle mapper, and wavelength position mapping methods were used in this research leading to the identification of a series of alteration minerals (including muscovite [sericite], kaolinite, alunite, epidote, chlorite, and calcite) from ZY1-02D data. The alteration mineral maps derived from ZY1-02D data match well with the known deposits and field inspections. Twenty-three new targets were identified as potential porphyry Cu mineralization targets for further exploration in the study area. Three targets, north of Saindak, Koh-i-Sultan, and Durban Chah, and six alteration sites in the southwest of Durban Chah, were inspected in the field, and Cu-Au mineralization was confirmed in all these inspected areas. As the ZY1-02D hyperspectral data covers most of the land area of the earth, this study provides new insights for mineral exploration and lithologic mapping in remote regions.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":null,"pages":null},"PeriodicalIF":5.8,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140096855","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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