Economic Geology最新文献

{"title":"Tourmaline Breccias from the Río Blanco-Los Bronces Porphyry Copper District, Chile: Constraints on the Fluid Source and the Utility of Tourmaline Composition for Exploration","authors":"Michael Hohf, R. Trumbull, Patricio Cuadra, M. Solé","doi":"10.5382/econgeo.4991","DOIUrl":"https://doi.org/10.5382/econgeo.4991","url":null,"abstract":"\u0000 Tourmaline-cemented breccia bodies host much of the ore in the Río Blanco-Los Bronces porphyry Cu-Mo deposits. We determined the chemical and B isotope composition of tourmaline as well as S isotope ratios of anhydrite and sulfide minerals to shed light on the composition and origin of mineralizing fluids. Also, the utility of tourmaline as an indicator mineral was tested by comparing mineralized and barren breccias. Tourmaline in mineralized samples has a narrow Mg range (1.5–2 apfu) and variable, generally low Al contents (4–6.5 apfu). A strong negative correlation of Al with Fe indicates monovalent substitution of Al and Fe3+, implying relatively oxidizing fluids. In contrast, tourmaline from barren breccias has a narrower Al range (6–7 apfu), lower and more variable Mg (0.2–2.5 apfu), and a strong negative Mg-Fe correlation, suggesting more reduced fluids with a dominance of Fe2+. These features and the implications of redox contrast may have exploration significance. Tourmaline from all breccia samples yielded δ11B values from 1.8 to 7.9‰. A magmatic source of boron is concluded from the identical B isotope values of granite-hosted tourmaline in the district (1.2–7.7‰) and from the similar range of regional volcanic and porphyry rocks in the Central Andes. The δ34S values of coexisting anhydrite (11.6–14.5‰) and chalcopyrite (–1.5 to –0.2‰) in mineralized breccia give S isotope exchange temperatures of 377° to 437°C, consistent with fluid inclusion temperatures. Total sulfur δ34Sfluid estimates between 1.4 ± 3.9 and 8.8 ± 1.3‰ are broadly consistent with a magmatic source but not well constrained. However, published O and H isotope ratios of quartz and tourmaline from the Río Blanco-Los Bronces breccias have a clear magmatic signature, so this is the preferred scenario. Mass balance simulations of the boron budget show that typical magma flux rates, water contents, and boron concentration for the Central Andes can produce the estimated 107 tons of boron in the Río Blanco-Los Bronces breccias within the 4-m.y. duration of porphyry intrusions if (1) magma accumulated and evolved at midcrustal levels before emplacement and (2) boron partitioned strongly to the fluid phase (DBfluid/melt> 3).","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"51 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78634139","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}

{"title":"APATITE VOLATILE CONTENTS OF PORPHYRY Cu DEPOSITS CONTROLLED BY DEPTH-RELATED FLUID EXSOLUTION PROCESSES","authors":"Ming‐Liang Huang, Jing-jing Zhu, M. Chiaradia, R. Hu, Leiluo Xu, X. Bi","doi":"10.5382/econgeo.5000","DOIUrl":"https://doi.org/10.5382/econgeo.5000","url":null,"abstract":"\u0000 Porphyry Cu deposits are formed by Cu- and volatile (e.g., Cl, S)-rich fluids exsolved from underlying magma reservoirs. Intuitively, higher magmatic Cl and S contents likely correspond to higher magma fertility. However, the Cl contents of syn-ore magmatic apatite, one of the major Cl-bearing mineral phases in magmas, are highly variable among deposits (from <0.1 to >2 wt %). These variations may be controlled by different timing of apatite crystallization relative to fluid saturation among deposits, but the causes of these different relative timings remain obscure. Here we compile existing chemical data of magmatic apatite and amphibole phenocrysts from 25 porphyry Cu deposits worldwide and use these data to calculate magmatic physical-chemical conditions, such as water contents and magma reservoir depths. We find that the porphyry Cu deposits associated with deeper magma reservoirs are characterized by systematically higher magmatic H2O contents and apatite Cl, but lower apatite F contents and F/Cl ratios compared to shallower deposits. These correlations are best explained by early fluid exsolution and Cl loss that predate apatite crystallization in shallower porphyry Cu systems, which leads to elevated apatite F/Cl ratios. This is supported by the common occurrence of primary fluid inclusions in apatite from shallower systems. Postsubduction porphyry Cu deposits are normally associated with lower apatite Cl contents and shallower magma reservoirs, which is attributed to their formation under relatively extensional tectonic regimes. Our results demonstrate that the magma reservoir depth exerts an important control on the timing of fluid exsolution and accompanying Cl loss. In contrast, relatively high and constant apatite S content among deposits is minimally affected by fluid exsolution, possibly due to buffering of early-saturated sulfate in oxidized and S-rich magmas, and therefore might be used as a better potential fertility indicator than Cl.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"516 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77124328","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}

{"title":"Ultramafic-Hosted Ni-Cu-Co-(As) Mineralization from an Ancient Oceanic Transform Fault Zone in the Troodos Ophiolite, Cyprus: An Analogue for Ultramafic Sea Floor Massive Sulfide Mineralization?","authors":"Andrew J. Martin, C. MacLeod, K. McFall, I. McDonald, J. Jamieson, S. Cox","doi":"10.5382/econgeo.4996","DOIUrl":"https://doi.org/10.5382/econgeo.4996","url":null,"abstract":"\u0000 Accumulations of sulfide minerals that are enriched in Ni-Cu-Co-(As) occur as sea floor massive sulfide (SMS) deposits associated with ultramafic rock types on the sea floor and in ophiolite terranes as Outokumpu-type mineralization. In this study we focus on similar mineralization at Lakxia tou Mavrou in the Limassol Forest Complex of Cyprus, which represents the on-land exposure of an oceanic transform fault zone preserved within the Troodos ophiolite. Mineralization here consists of massive lenses of pyrrhotite associated with veins of isocubanite, chalcopyrite, Co pentlandite, and chrome spinel hosted in serpentinized mantle peridotite. We reexamine the field context of mineral occurrences and use in situ mineral chemistry, element mapping, and sulfur isotope ratios (δ34S) to constrain metal sources and provide an updated paragenetic model for Lakxia tou Mavrou. Highly variable S/Se ratios (304–108,571), a depletion in platinum group elements relative to mantle values, and an average δ34S value of –3.7 ± 2.4‰ (1σ, n = 17) in sulfide minerals support a hybrid hydrothermal and magmatic origin for the mineralization. Metals at Lakxia tou Mavrou were sourced from both the serpentinization of peridotites and from crosscutting intrusions, with later intrusions into the already serpentinized mantle lithosphere host providing a heat source to drive prolonged hydrothermal circulation. The reexamination of the field context of mineralization shows that the Ni-Cu-Co-(As) mineralization at Lakxia tou Mavrou originally formed because of the fault-guided intrusion of hot primitive magma bodies into serpentinized shallow mantle lithosphere in the active domain of an ocean-floor transform fault zone. The mineralization was subsequently partially disrupted by structures related to emplacement of the Troodos ophiolite. We show that the relationship between serpentinization, magmatism, and hydrothermal circulation at Lakxia tou Mavrou can be used to understand the formation of ultramafic-hosted SMS deposits in transform fault and other ultramaficdominated slow- and ultraslow-spreading mid-ocean ridge settings.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"30 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90431516","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}

{"title":"Pyrite as a Microtextural and Geochemical Tracer of Ore-Forming Processes, Central Zone Orogenic Gold Deposit, Gabgaba District, Sudan","authors":"Célestine Berthier, Julien Perret, A. Eglinger, A. André-Mayer, J. Feneyrol, A. Voinot, Y. Teitler, Rémi Bosc","doi":"10.5382/econgeo.5001","DOIUrl":"https://doi.org/10.5382/econgeo.5001","url":null,"abstract":"\u0000 Gold deposition in structurally controlled deposits is triggered by changes in the mineralizing fluid conditions. Recent research has demonstrated that in deposits with a well-established paragenesis, the processes that control the ore-forming fluid conditions, and thus the gold timing and deposition, can be inferred from the study of both textural and chemical characteristics of ore-bearing minerals such as sulfides, which are ubiquitous in almost every gold deposit type. In this contribution, we carried out a coupled investigation of (1) microscopic-scale expression of regional deformation, (2) textures of mineralized veins and pyrite generations, and (3) laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) trace element concentrations in pyrite from the Neoproterozoic Central Zone gold deposit, located in the poorly studied Gabgaba gold district, central Keraf suture, Sudanese Nubian shield.\u0000 The Central Zone gold mineralization is associated with late-collisional Keraf strike-slip shearing. It is expressed by visible gold-bearing quartz-ankerite-(albite) conjugate veins hosted by metagranitoids surrounded by metasediments. Some structurally lattice-bound gold occurs in proximal As-Au-Ni–enriched pyrite associated with sericite-albite-ankerite alteration. Vein textures and proximal pyrite oscillatory zoning and geochemical signatures indicate that vein infilling occurred as a response to sudden pressure drops and boiling of the mineralizing fluid. We therefore interpret the Central Zone deposit as a typical orogenic gold deposit, with microtextural evidence and geochemical data supporting the existence of earthquake-induced fault-valve processes.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"1 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78365777","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}

{"title":"Two Decades of Monitoring Hydrothermal Plumes at the Brothers Submarine Volcano, Kermadec Arc, New Zealand","authors":"S. Walker, C. D. de Ronde","doi":"10.5382/econgeo.4998","DOIUrl":"https://doi.org/10.5382/econgeo.4998","url":null,"abstract":"\u0000 Brothers volcano is arguably the most well-studied submarine arc volcano on Earth. Between 1996, when massive sulfides were first recovered by dredging, and 2018, when International Ocean Discovery Program (IODP) Expedition 376 recovered cores from as deep as 453 m below the sea floor at two chemically distinct hydrothermal upflow zones, over 60 conductivity-temperature-depth (CTD) vertical casts and tow-yo operations mapped hydrothermal plumes over and around the edifice by employing hydrothermal tracer-specific sensors. These surveys started in 1999 and were completed during nine separate expeditions at one- to three-year intervals, except for a six-year gap between 2011 and 2017. Hydrothermal plume distributions over this two-decade period show variability in the intensity and vertical rise height of plumes from the four main vent fields (Upper Cone, Lower Cone, NW Caldera, and Upper Caldera, with the latter not discovered until 2017). Upper Cone plumes were more intense than all other sites in 1999, 2002, 2007, and 2009, then significantly diminished from 2011 to 2018. The Lower Cone plume was the most intense in 2004, then the NW Caldera site became the dominant source of hydrothermal particles from 2011 to 2018. Despite the gap of six years between 2011 and 2017, hydrothermal output appears to have increased within the caldera sometime after the 2009 survey while simultaneously decreasing in intensity at the cone sites. This supports other evidence of linkages between the cone and caldera sites in the deep hydrothermal circulation system, and may be related to the predicted deepening of hydrothermal circulation, infiltration of seawater to facilitate “mining” of magmatic brines, and modulation of subseafloor mineralization processes associated with a modeled, pulsed injection of magmatic gasses. The surveys also revealed ways in which the highly variable regional hydrographic environment impacts the flux of hydrothermal products to the surrounding ocean. Plumes from sources located above the caldera rim disperse hydrothermal components without hindrance, but particles and heat from sources within the caldera become trapped and are dispersed episodically by caldera-flushing events. While on site for 18 days in 2018, repeat CTD casts into the deepest part of the caldera, which was isolated from the surrounding ocean, showed a progressive increase in temperature, representing a net heat flux of 79 MW from conductive and advective sources deeper than 1,570 m.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"68 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-03-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87634418","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}

{"title":"Geology of Winu-Ngapakarra, Great Sandy Desert of Western Australia, a Recently Discovered Intrusion-Related Cu-Au Deposit","authors":"H. Dalstra, A. Black, I. Mudrovska","doi":"10.5382/econgeo.5005","DOIUrl":"https://doi.org/10.5382/econgeo.5005","url":null,"abstract":"\u0000 The Winu-Ngapakarra Cu-Au deposit (Winu) was discovered in late 2017. Winu is hosted in metamorphosed massive sandstones, siltstones, and lesser mafic rocks that are possible distal and deep-water correlatives of the Malu Formation of the Yeneena basin, also host to the large Telfer Au-Cu deposit. Structure at Winu is dominated by an inclined dome formed through interference between NNW- and WNW-trending folds. Copper-gold mineralization occurs in en echelon left-stepping lodes with strike lengths between 350 and 750 m and vertical depths exceeding 750 m, northerly trends, and moderate easterly dips. These higher-grade lodes are surrounded by an extensive halo of low-grade mineralization. Two gold-rich lodes in the southeast part of the Winu deposit strike roughly easterly, toward a gold-rich satellite deposit (Ngapakarra) approximately 2 km east of Winu.\u0000 Mineralization at Winu is hosted by numerous thin, brittle veins and breccias. At least four distinct vein sets associated with Cu-Au mineralization are recognized: V1 – early, weakly mineralized K-feldspar-white mica stockworks; V2 – transitional magmatic-hydrothermal K-feldspar–rich veins; V3 – quartz-sulfide–rich veins, breccias, and fractures and quartz-bismuth-gold veins with similar timing; and V4 – poorly mineralized quartz veins. Barren carbonate-, chlorite-, white mica-, and pyrite-rich fractures (V5), breccias, and faults as well as thin dolerite dikes cut mineralization at Winu. Re-Os dating of molybdenite intergrown with chalcopyrite yielded ages of 658 to 655 Ma for the mineralized veins at Winu, and Ar-Ar dating of biotite yielded 619 Ma for an unmineralized post-ore quartz-biotite vein. A well-developed supergene chalcocite blanket overlies the primary mineralization.\u0000 Element associations and vein and alteration textures and mineralogy classify Winu as an intrusion-related Cu-Au deposit of Neoproterozoic age. Although it shares features with the reduced porphyry copper-gold group, other features, such as the dominance of pyrite over pyrrhotite and the presence of trace amounts of sulfate minerals in the mineralization, are more in accordance with oxidized intrusion-related systems. Mineralization at Winu was most likely triggered by rapidly changing stress fields during the Paterson orogeny and cooling of multiple fluid pulses above an intruding granite pluton that progressively decreased in temperature over time.\u0000 Winu is unique in this region in that it preserves evidence for an early, reduced intrusion-related gold system overprinted by a more oxidized intrusion-related copper system.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"67 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89177107","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}

{"title":"Late-Stage Low-Temperature Hydrothermal Alteration Overprint at the East Zone in the Red Chris Porphyry Cu-Au Deposit, Northwestern British Columbia, Canada","authors":"Jessica R. Norris, R. Tosdal, Joanna L. Lipske, Alan J. Wilson","doi":"10.5382/econgeo.4997","DOIUrl":"https://doi.org/10.5382/econgeo.4997","url":null,"abstract":"\u0000 High- and intermediate-temperature alteration assemblages at the East zone in the Red Chris porphyry Cu-Au deposit, northwestern British Columbia, Canada, are varyingly overprinted by a lower-temperature intermediate argillic alteration assemblage composed of illite-kaolinite-hematite-carbonate. The intermediate argillic assemblage extensively overprinted the upper 600 m of the porphyry deposit and is present discontinuously to depths of 1,500 m below the premining surface. Kaolinite is dominant in shallow levels and gradually diminishes with depth, replaced by illite as the dominant clay mineral. Hematite replaced hydrothermal and igneous magnetite, but the intensity diminishes with depth. Mixtures of ankerite, dolomite, siderite, and calcite replaced mafic silicates and formed veins. Oxygen and hydrogen isotopes confirm a magmatic fluid source for the potassic assemblages preserved at depth as well as for the overprinted phyllic assemblage in the upper part and flanks of the East zone. In contrast, the superposed intermediate argillic assemblages formed by a mixture of magmatic and meteoric fluids. Sulfide minerals and sulfur isotopes retain zonal patterns for porphyry Cu deposits and appear largely unaffected by the overprinted intermediate argillic assemblage. Carbon and oxygen isotopes in carbonate vary with depth that may reflect a thermal gradient as a rising fluid cooled. The intermediate argillic assemblage is spatially associated with and overprinted on as yet undated late monzodioritic dikes—the youngest phase in the host Late Triassic Red stock. The relative age relationships and stable isotopic geochemistry indicate the intermediate argillic alteration assemblage represents the flux of magmatic-derived hydrothermal fluid that mixed with external fluid and thus represents either the last fluid pulse in the porphyry Cu deposit or a younger, temporally distinct hydrothermal fluid.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"16 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72619771","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}

{"title":"Interesting Papers in Other Journals","authors":"","doi":"10.5382/econgeo.118.2.ip01","DOIUrl":"https://doi.org/10.5382/econgeo.118.2.ip01","url":null,"abstract":"","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136173716","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}

{"title":"Stream Sediment Indicator Mineral Signatures of the Casino Porphyry Cu-Au-Mo Deposit, Yukon, Canada","authors":"M. McClenaghan, C. Beckett-Brown, M. McCurdy, S. Casselman","doi":"10.5382/econgeo.4970","DOIUrl":"https://doi.org/10.5382/econgeo.4970","url":null,"abstract":"\u0000 Case studies around porphyry Cu deposits in the glaciated regions of the Canadian Cordillera have identified the indicator mineral signatures of these deposits in till samples and demonstrated that these are useful methods for porphyry Cu exploration. This study applies the same indicator methods to stream sediment samples around the Casino calc-alkaline porphyry Cu-Au-Mo deposit in the unglaciated terrain of west-central Yukon, Canada. It is one of the largest porphyry Cu-Au-Mo deposits in Canada and is hosted in Late Cretaceous quartz monzonite and associated breccias. Bulk (8–16 kg) coarse-grained stream sediment samples were collected in creeks around the deposit, nearby porphyry Cu occurrences and background areas. The Casino deposit has an obvious indicator mineral signature in the <2-mm heavy (>3.2-specific gravity [SG]) and mid-density (2.8- to 3.2-SG) fractions of stream sediments that is detectable at least 18 km downstream and includes gold, chalcopyrite, tourmaline, molybdenite, sphalerite, jarosite, goethite, and pyrite. In contrast, not all of these mineralogically anomalous samples have corresponding anomalous geochemical signatures in the fine fraction. The porphyry indicator minerals identified in this study are similar to those reported for glaciated terrain with the addition of molybdenite and secondary minerals. Indicator mineral methods provide physical evidence of nearby mineralization and can be chemically analyzed to provide insights about the nature of the mineralizing system. Government and exploration surveys could benefit from the addition of indicator mineral methods to routine stream sediment sampling protocols in unglaciated regions of the Yukon and elsewhere globally where porphyry Cu exploration is conducted.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"72 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88230871","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}

{"title":"MINERAL ASSEMBLAGES, FLUID INCLUSIONS, PYRITE TRACE ELEMENTS, AND S-O ISOTOPES OF GOLD ORES FROM THE CENOZOIC DAPING DEPOSIT, SW CHINA: IMPLICATIONS FOR THE GENESIS OF COMPLEX OROGENIC LODE GOLD SYSTEMS","authors":"Lin Yang, Qingfei Wang, D. Groves, Huajian Li, D. Zhai, Xuan Wang, Jun Deng","doi":"10.5382/econgeo.4995","DOIUrl":"https://doi.org/10.5382/econgeo.4995","url":null,"abstract":"\u0000 The Cenozoic Daping orogenic gold deposit, on the southeastern margin of the Tibetan Plateau, China, contains four lode types that contain a total of 55 t gold. Pyrite-chalcopyrite–dominated (VA) and galena-dominated polymetallic sulfide veins (VB) hosted by Neoproterozoic diorite are associated with quartz-sericite-chlorite ± epidote (± barite in VB veins) alteration. Pyrite-dominated (VC) and pyrite-pyrrhotite–dominated veins (VD) hosted by Silurian dolostone (intercalated with carbon-bearing argillaceous limestone in VD veins) are related to ankerite-siderite-quartz ± sericite alteration. All have free gold spatially and temporally associated with pyrite, chalcopyrite, galena, pyrrhotite, or quartz. Most VA and VB veins are controlled by steeply SW-dipping ductile-brittle shear zones with jigsaw wall-rock breccias in VB veins, whereas gently SW-dipping faults host VC and VD veins.\u0000 There are some significant differences between different veins: (1) there were more acidic mineralization conditions for VA and VB veins relative to VC and VD veins, and more oxidized conditions for VB veins relative to other veins; (2) pyrite is rich in Co-Ni in VA and VB veins, compared to enrichment in As-Au for VC and VD veins; (3) sulfide δ34S values of 3.2 to 11.8‰ (median 8.2‰) for VA, VC, and VD veins contrast with −4.6 to +0.9‰ (median 0‰) for VB veins. The contrasting mineral parageneses, pH values, and pyrite geochemistry can be attributed to fluid-rock interaction as evidenced by replacements of amphibole by sericite in diorite and dolomite by ankerite and siderite in dolostone. The lower (~8‰) VB sulfide δ34S values and interpreted fluid oxidation relative to other veins, together with the presence of breccias and barite, can be explained by phase separation due to flash vaporization triggered by extreme hydrofracturing. The consistent NW-trending vein sets, similar median S-O isotope ratios of original ore fluids, and lack of multistage overlap of gold mineralization and alteration zones support a single-source fluid for gold mineralization at Daping. This study is diagnostic rather than just indicative in that it systematically and quantitatively portrays the mineralization diversity in an orogenic gold system formed by a single-source fluid regulated by the external fluid-rock interactions and internal hydrofracturing.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"43 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81352022","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}