Economic Geology最新文献

{"title":"Geology of the Nautanen North Cu-Au-Ag-(Mo) Deposit, Norrbotten, Sweden","authors":"David Drejing-Carroll, Murray W. Hitzman, David Coller","doi":"10.5382/econgeo.5019","DOIUrl":"https://doi.org/10.5382/econgeo.5019","url":null,"abstract":"Abstract The Nautanen North deposit in the Gällivare-Malmberget area of Norrbotten, Sweden, currently contains a resource of 21 Mt at 1.46% Cu, 0.78 g/t Au, 6 g/t Ag, and 99 g/t Mo and remains open at depth and along strike. This study, based on extensive examination of drill core, geochemical data, and petrographic analyses, represents the first comprehensive description of the structural controls, hydrothermal alteration facies and paragenetic sequence of mineral precipitation, and styles and relative timing of iron oxide and sulfide mineralization at the deposit. The deposit is localized between bounding shear zones within the Nautanen deformation zone. High grades of Cu occur within discrete zones of brecciation and veining and as mineralized shear bands. Breccias in the northern portion of the deposit developed within a vertically stacked, relay-like zone in response to late deformation. Hydrothermal alteration of the host rocks was initially dominated by Na facies alteration, which was subsequently overprinted by Na-Ca-Fe, HT (high-temperature) Ca-Fe, HT Ca-K-Fe, HT K-Fe, and LT (low-temperature) K-Fe facies alteration. Magnetite mineralization occurred in at least two phases: an early phase during Na and Na-Ca-Fe facies alteration accompanied by apatite that is interpreted to reflect a distal signature of formation of the proximal Malmberget magnetite-apatite deposit and a later phase coincident with HT Ca-Fe to K-Fe alteration, which overlapped with the onset of Cu and Fe sulfide mineralization under HT Ca-K-Fe and K-Fe and LT K-Fe conditions. The Nautanen North deposit is shown to meet key criteria to be classified as an iron oxide-copper-gold deposit.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"6 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":"134971369","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":"Trace Element Composition of Chalcopyrite from Volcanogenic Massive Sulfide Deposits: Variation and Implications for Provenance Recognition","authors":"Enzo Caraballo, Georges Beaudoin, Sarah Dare, Dominique Genna, Sven Petersen, Jorge M.R.S. Relvas, Stephen J. Piercey","doi":"10.5382/econgeo.5020","DOIUrl":"https://doi.org/10.5382/econgeo.5020","url":null,"abstract":"Chalcopyrite from 51 volcanogenic massive sulfide (VMS) and sea-floor massive sulfide (SMS) deposits from six lithostratigraphic settings was analyzed for trace elements by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to evaluate its potential as an indicator mineral for exploration. Partial least squares discriminant analysis (PLS-DA) results reveal that chalcopyrite from different lithostratigraphic settings has different compositions reflecting host rock assemblages and fluid composition. Three random forest (RF) classifiers were developed to distinguish chalcopyrite from the six lithostratigraphic settings with a divisive approach. This method, which primarily classifies according to the major host-rock affinity and subsequently according to VMS settings, yielded an overall accuracy higher than 0.96 on test data. The model validation with literature data having the same elements required by the models yielded the highest accuracies (>0.90). In validation using published data with missing elements, the accuracy is moderate to high (0.60–1); however, the performances decrease significantly (<0.50) when the most important elements are missing. Similarly, RF regression models developed using all sets of analyzed elements to determine ccp/(ccp + sp) ratio (ccp = chalcopyrite; sp = sphalerite) in chalcopyrite within a single VMS setting reported high performances, thus showing a potential to predict the Cu/Zn ratio (Cu-rich vs. Zn-rich) of the mineralization based on chalcopyrite composition. This study demonstrates that trace element concentrations in chalcopyrite are primarily controlled by lithotectonic setting and can be used as predictors in an RF classifier to distinguish the different VMS subtypes.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"43 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":"134971467","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.118.6.ip01","DOIUrl":"https://doi.org/10.5382/econgeo.118.6.ip01","url":null,"abstract":"","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135200620","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":"Depositing >1.5 Mt of Tin Within <1 m.y. of Initial Granitic Intrusion in the San Rafael Tin (-Copper) Deposit, Southeastern Peru","authors":"M. Harlaux, D. Kontak, Alan H. Clark, K. Kouzmanov, Christopher S. Holm-Denoma, Stefano Gialli, Oscar Laurent, R. Spikings, A. Chauvet, Andrea Dini, Miroslav Kalinaj, L. Fontboté","doi":"10.5382/econgeo.5021","DOIUrl":"https://doi.org/10.5382/econgeo.5021","url":null,"abstract":"\u0000 The San Rafael Sn (-Cu) deposit, located in the Eastern Cordillera of southeast Peru, is one of the world’s largest cassiterite-bearing vein systems (>1 Mt Sn produced since 1969). The deposit consists of a quartz-cassiterite-chlorite-sulfide lode system spatially associated with an upper Oligocene (ca. 24 Ma) S-type granitic pluton. Based on a revised paragenetic sequence for the deposit, we interpret the temporal setting of both magmatic (biotite, K-feldspar) and hydrothermal (muscovite, adularia, cassiterite) minerals analyzed by 40Ar/39Ar step-heating and U-Pb laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) geochronology. The least-disturbed biotite sample from the megacrystic monzogranite yielded a 40Ar/39Ar plateau age of 24.10 ± 0.26 Ma (2σ), which constrains the time of cooling of the upper part of the pluton to below 300°C. Greisen developed on top of the granitic cupola and its immediate metamorphic aureole dated at 24.24 ± 0.24 Ma (2σ; 40Ar/39Ar muscovite average plateau age) is interpreted to be contemporaneous with the emplacement of pre-ore quartz-tourmaline veins and breccias. In situ U-Pb dating of cassiterite, including both botryoidal cassiterite (“wood tin”) and coarse-grained cassiterite in quartz-chlorite veins and breccias, constrains the timing of the main Sn ore stage to between 24.10 ± 0.37 and 23.47 ± 0.53 Ma (2σ). Botryoidal and coarse-grained cassiterite are characterized by similar trace element compositions with fluctuating metal concentrations across growth banding, suggesting significant changes of physicochemical conditions of the hydrothermal system during cassiterite precipitation, likely caused by rapid and repeated mixing between magmatic fluids and meteoric groundwaters. Polymetallic sulfide-rich veins and quartz-carbonate veins are constrained to have formed between 22.72 ± 0.11 and 22.29 ± 0.24 Ma (2σ), based on adularia 40Ar/39Ar plateau ages. The latter overlap partially reset 40Ar/39Ar age spectra for K-feldspar megacrysts in the host granite and thus reflect pervasive alteration by hydrothermal fluids. Collectively, the results show the magmatic-hydrothermal system spanned at least 2 m.y. with the main Sn ore stage representing <1 m.y. in the lifetime of the deposit. The latest polymetallic stages postdate the main Sn ore stage by ca. 1 m.y. and reflect the waning of the hydrothermal system, accompanied by additional incursion of meteoric groundwaters. This study provides further evidence that the present-day exposed level of the San Rafael granite was a passive host for the Sn mineralization and only provided the structural focusing for the mineralizing fluids derived from a deeper part of the magmatic system.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"12 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86557421","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.118.7.ip01","DOIUrl":"https://doi.org/10.5382/econgeo.118.7.ip01","url":null,"abstract":"","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135782176","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":"The Roles of Various Types of Crustal Contamination in the Genesis of the Jinchuan Magmatic Ni-Cu-PGE Deposit: New Mineralogical and C-S-Sr-Nd Isotope Constraints","authors":"Shengchao Xue, Qingfei Wang, Ya-lei Wang, Wenlei Song, Jun Deng","doi":"10.5382/econgeo.5017","DOIUrl":"https://doi.org/10.5382/econgeo.5017","url":null,"abstract":"\u0000 Addition of crustal sulfur to the Jinchuan magma or oxidation of the magma associated with carbonate assimilation has been considered to be the main cause of sulfide saturation in the magma by two opposing groups of researchers. To address this controversy, we have carried out an integrated mineralogical and C-S-Sr-Nd isotope study of the Jinchuan magmatic Ni-Cu-platinum group element (PGE) sulfide ore deposit. Pure marble, olivine marble, serpentine marble, and hybrid rocks occur in the contact zone. The δ13Ccarb values of the Jinchuan sulfide-bearing ultramafic rocks containing calcite xenocryst are from –4.7 to –2.9‰, which are similar to or slightly lower than those of the marbles and associated hybrid rocks (–3.9 to 0.8‰) but significantly higher than those of the calcite-barren intrusive rocks (–9.3 to –8.0‰). This, together with the calcite xenocryst and calcium-silicate minerals in hybrid rocks and some intrusive rocks, indicates that carbonate assimilation took place during magma-carbonate interaction. Only less than several hundred ppm of the CO2 gas produced in the reaction zone could be added to the Jinchuan magma. Such a trace amount of additional CO2 was rapidly swamped by the much greater mass of FeO in the magma, resulting in little change in the FeO/Fe2O3 of the magma, and thereby negligible change of magma redox state. This is evident from similar calculated fO2 values for the calcite-bearing (~QFM+0.7) and calcite-barren (~QFM+0.6) intrusive rocks. The new results rule out the possibility that sulfide saturation in the Jinchuan magma resulted from in situ carbonate assimilation. The Sr-Nd isotope data from this study and previous studies are consistent with up to 20% bulk contamination with siliceous crustal materials at depth, followed by minor amounts of in situ carbonate assimilation by the Jinchuan magma. Our new sulfur isotope data expand the range of δ34S for the Jinchuan deposit significantly. The new range is from −7.6 to 3.0‰, with an average of −1.8‰, which is generally lower than the mantle value (0 ± 2‰). The new result supports the premise that crustal sulfur was involved in the genesis of the Jinchuan deposit. Very high, crustal-like S/Se ratios (as high as 8080) for some of the samples from the deposit provide additional support for the interpretation. The country rocks in the vicinity of the Jinchuan deposit analyzed to date have δ34S values varying from −4.0 to 11.3‰, with an average of 2.9‰, which is higher than both the mantle value and the average value of the Jinchuan deposit, suggesting that the Jinchuan magma acquired some crustal sulfur at depth, likely concurrent with the siliceous assimilation. Numerical modeling of δ34S-S/Se of sulfide ores and country rocks further illustrates that the observed variations of δ34S and S/Se ratios are related to the assimilation of S-rich rocks located at depth, followed by progressive dilution of the contaminated δ34S-S/Se signature. Based on the new results, we con","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"47 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83966383","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":"A Fluid Chemical Study of the World-Class, Intrusion-Related Archean Windfall Gold Deposit, Quebec, Canada","authors":"Brandon Choquette, D. Kontak, Édouard Côté-Lavoie, M. Fayek","doi":"10.5382/econgeo.5033","DOIUrl":"https://doi.org/10.5382/econgeo.5033","url":null,"abstract":"\u0000 Windfall is a world-class Archean intrusion-related Au deposit (7.4+ Moz of Au) located in the underexplored Urban-Barry greenstone belt (Quebec, Canada). The deposit remains an enigmatic Au setting—its intrusion-related features contrast with the more common orogenic deposit type in the Au-endowed Abitibi greenstone belt. Mineralization consists of quartz-pyrite-carbonate ± tourmaline veins and stockworks that cut sericite-pyrite ± silica ± tourmaline ± fuchsite replacement zones, all of which overprint a swarm of 2697.6 ± 2.6 Ma quartz-feldspar porphyry dikes. That the ore zones and quartz-feldspar porphyry dikes are cut by a later set of 2697.6 ± 0.4 Ma quartz-feldspar porphyry dikes constrains mineralization temporally and spatially to intrusive activity. To further address the deposit genesis, ore petrology integrated with scanning electron microscopy-energy dispersive spectrometry analysis and cathodoluminescence imaging, laser ablation-inductively coupled plasma-mass spectrometry mapping of pyrite, fluid inclusion studies, and in situ secondary ion mass spectrometry isotopic studies (O, S) were completed. Ore-related sulfides are dominated by pyrite with lesser arsenopyrite, sphalerite, chalcopyrite, tennantite-tetrahedrite, galena, gold, electrum, and minor Sb-rich and telluride alloys. Four pyrite generations (Py1-Py4) occur, with elemental maps indicating primary Au is related to As-rich Py2 that is also enriched in Ag-Sb-Hg-Cu-Zn-Pb-Bi-Te. The δ34Spyrite values are similar for Py1 to Py3, with an inferred δ34Sfluid of ~5‰ consistent with a magmatic reservoir, whereas δ18Oquartz for both igneous (avg = 8.4‰, n = 28) and vein (5.7–14.6‰, n = 53) material suggests mixing of a magmatic fluid with an 18O-poor reservoir. Fluid inclusion studies from pre- to postmineralization veins indicate the predominance of a carbonic (±CH4) fluid, with rare aqueous-carbonic (CO2 = 5–98 mol %) and variably saline aqueous types. Whereas the data are considered to best reflect an intrusion-related deposit model, we note that some data, such as the carbonic-rich nature of fluid inclusions and large range in δ18Oquartz, are equivocal in regard to their meaning, and thus further studies are needed to resolve some aspects of this ore system.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"26 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88268288","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":"Metallogenic Setting and Temporal Evolution of Porphyry Cu-Mo Mineralization and Alteration in the Delamerian Orogen, South Australia: Insights From Zircon U-Pb, Molybdenite Re-Os, and In Situ White Mica Rb-Sr Geochronology","authors":"Wei Hong, A. Fabris, T. Wise, A. Collins, Sarah E. Gilbert, D. Selby, S. Curtis, A. Reid","doi":"10.5382/econgeo.5012","DOIUrl":"https://doi.org/10.5382/econgeo.5012","url":null,"abstract":"\u0000 Paleozoic porphyry-style hydrothermal alteration and mineralization has previously been recognized within the Delamerian orogen, South Australia, where porphyry prospects include Anabama Hill, Netley Hill, and Bendigo. However, limited exploration due in part to thick postmineralization cover hinders the understanding of the temporal context, metallogenic setting, and mineral potential of the porphyry systems along the Proterozoic continental margin of Australia. In this study, we have characterized the hydrothermal alteration and mineralization of these porphyry occurrences. Zircon U-Pb, molybdenite Re-Os, and white mica Rb-Sr ages have been determined to constrain the timing for emplacement of magmatic intrusions, precipitation of metal-bearing sulfides, and duration of hydrothermal alteration in the Delamerian orogenic belt. Zircon U-Pb laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of nine granitoids reveal that the intrusive rocks were emplaced mostly between 485 and 465 Ma, whereas three intrusions at Bendigo have zircon U-Pb ages of 490 to 480 Ma. Molybdenite isotope dilution-negative thermal ion mass spectrometry (ID-NTIMS) Re-Os dating of the four prospects identifies two porphyry Cu-Mo mineralization events at 480 and 470 to 460 Ma, respectively. Nineteen white mica Rb-Sr LA-ICP-MS/MS (tandem mass spectrometers) analyses return an age range between 455 and 435 Ma for phyllic alteration at the Anabama Hill and Netley Hill prospects, whereas intense white mica-quartz-pyrite alteration at Bendigo prospect appears to have developed between 470 and 460 Ma. These geochronologic results indicate that the Delamerian porphyry systems postdated subduction-related magmatism in the region (514–490 Ma) but instead formed within an inverted back-arc regime, where mineralized magmas and fluids ascended along favorable lithospheric-scale structures, probably due to asthenospheric upwelling triggered by mafic delamination. Porphyritic stocks, dikes, and aplites with ages of 470 to 460 Ma are the most likely hosts to porphyry-style mineralization in the Delamerian orogen that appears to have formed simultaneously with the oldest known porphyry systems in the intraoceanic Macquarie arc (e.g., Marsden, E43, and Milly Milly; 467–455 Ma). These results emphasize the significance and potential of Early-Middle Ordovician intrusive systems to host such a type of magmatic-hydrothermal mineralization in the Delamerian orogen.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"54 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76886304","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":"A Model for the Lithospheric Architecture of the Central Andes and the Localization of Giant Porphyry Copper Deposit Clusters","authors":"Alexander D. Farrar, D. Cooke, J. Hronsky, D. G. Wood, Sebastian B. Benavides, M. Cracknell, James F. Banyard, Santiago Gigola, T. Ireland, Simon M. Jones, J. Piquer","doi":"10.5382/econgeo.5010","DOIUrl":"https://doi.org/10.5382/econgeo.5010","url":null,"abstract":"\u0000 In the central Andes, giant porphyry copper deposits of similar ages group into discrete geographic clusters that are regularly spaced and aligned within orogen-parallel belts. This clustering highlights how exceptional geologic processes affected localized regions of the lithosphere during mineralization and that the spatial and temporal distribution of giant porphyry deposits is nonrandom. Development of favorable regions of lithosphere for significant metal concentration are linked to the overlap of structural pathways that focus fluid and magma flow from the mantle to upper crust during high-horizontal-compressive-strain events. These structural pathways are notoriously difficult to identify in the field due to their often-subtle surficial manifestations and continental scale. Field mapping at multiple scales in northwest Argentina and southern Peru, as well as regional structural traverses throughout the central Andes, indicates the presence of regional-scale structural corridors 5 to 25 km wide and hundreds of km long that consist of myriad fault planes. The variable width and diffuse surface expression of these corridors is interpreted to reflect the upward propagation of underlying zones of basement weakness through younger supracrustal sequences in the overriding plate. Such structural corridors are (1) apparent at multiple scales of investigation, (2) long-lived, (3) preferentially reactivated though time, and (4) evident in geophysical data sets. This structural architecture formed in response to the interplay of pre-Cenozoic tectonics and the orientation of inherited structural weaknesses. These fault systems persist in the upper crust as steep zones of enhanced permeability that can preferentially reactivate as pathways for ascending hydrous magmas and fluids during major deformation events. Linear orogen-parallel structural belts cogenetic with the magmatic arc provide the first-order control to giant porphyry copper deposit distribution. The second-order control is the intersection of orogen-oblique structural corridors with the orogen-parallel belts, localizing deposit clusters at these intersections. Such regions are inferred to have been zones of deep permeability, with vertical translithospheric pathways activated during high-strain tectonic events that affected the intra-arc stress field.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"12 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86575122","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":"Fluid Flow, Alteration, and Timing of Cu-Ag Mineralization at the White Pine Sediment-Hosted Copper Deposit, Michigan, USA","authors":"Simon M. Jones, Jonathan Cloutier, A. Prave, T. Raub, E. Stüeken, H. Stein, Gang Yang, A. Boyce","doi":"10.5382/econgeo.5013","DOIUrl":"https://doi.org/10.5382/econgeo.5013","url":null,"abstract":"\u0000 White Pine, located in Michigan’s Upper Peninsula, is an archetypal sediment-hosted stratiform copper deposit. The Midcontinent rift system is one of only seven basins globally that host a giant sediment-hosted stratiform copper deposit. Despite many similarities with other deposits of this type, White Pine displays some important differences, including the late Mesoproterozoic age, a thick basalt sequence, an apparent lack of evaporites, and a lacustrine depositional setting. This study analyzes paleofluid flow related to the formation of White Pine and places a particular emphasis on structural and diagenetic fluid pathways.\u0000 Most of the ore is located in a 30-m-wide zone spanning the Copper Harbor Formation red beds and the overlying Nonesuch Formation shales. Sedimentation of these units was accompanied by subtle synsedimentary faulting. Premineralization phases include calcite concretions and nodules, illite and hematite grain coatings, isopachous chlorite rims, emplacement of liquid petroleum (now pyrobitumen), and bleaching. Mineralization introduced native copper into the footwall sandstones and a zoned suite of native copper and sulfur-poor copper sulfide minerals across a migrating redox front in the overlying shales where copper minerals nucleated on authigenic and detrital chlorite grains. Postmineralization phases include quartz cement, calcite cement, and calcite veins that partially overlapped inversion of synsedimentary faults. Contrary to previous studies, we identified evidence for only one phase of mineralization. An Re-Os chalcocite age of 1067 ± 11 Ma places mineralization 11 to 17 m.y. after host-rock deposition. Sulfide δ34S values of –14.0 to 29.9‰ suggest an important contribution from sour gas and thermochemical sulfate reduction of seawater. Carbon (δ13C) and oxygen (δ18O) isotope compositions of five calcite generations range from –15.1 to –1.3‰ and 10.4 to 41.3‰, respectively, and record early meteoric pore water displaced by later seawater.\u0000 White Pine is both a sediment-hosted stratiform copper deposit and a paleo-oil field. Synsedimentary faults controlled the sedimentological character of the upper Copper Harbor Formation, and together these imparted a strong control on fluid flow and later diagenetic processes. Early oxidized meteoric fluids were displaced by liquid petroleum and sour gas, which were in turn succeeded by metal-rich but sulfate-poor oxidized seawater. Burial compaction during deposition of the overlying Freda Formation drove fluids through White Pine due to its situation on a paleotopographic high near the basin margin. Mineralization occurred at ~125°C at depths of ~2.0 km and spanned incipient basin inversion related to the distal effects of Grenvillian orogenesis. The hightenor copper mineral assemblage is the product of an abundant supply of metal from basaltic volcanic detritus in the Copper Harbor Formation and low seawater sulfate concentrations in late Mesoproterozoic oceans. This demons","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"47 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73019662","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}