Economic Geology最新文献

{"title":"Tin Mineralization in the Triassic Chacaltaya District (Cordillera Real, Bolivia) Traced by In Situ Chemical and δ18O-δ11B Compositions of Tourmaline","authors":"L. Torró, Matthieu Harlaux, Angela Castro-Morante, Jean Vallance, Lorenzo Tavazzani, A. Bouvier, T. Bovay, Cyril Chelle-Michou, Thierry P. A. Sempere, Joan Carles Melgarejo","doi":"10.5382/econgeo.5051","DOIUrl":"https://doi.org/10.5382/econgeo.5051","url":null,"abstract":"\u0000 We present a petrographic and geochemical study of tourmaline from the Triassic Chacaltaya Sn-polymetallic district in the Cordillera Real of Bolivia. Tourmaline is associated with greisens, breccias, and veins, which occur around the Triassic Chacaltaya peraluminous granitic stock hosted by Silurian metasedimentary rocks. Three main petrographic types of hydrothermal tourmaline have been identified: pre-ore greisen-related (Tur-1), syn-ore breccia-related (Tur-2), and syn-ore vein-related (Tur-3). The three types of tourmaline belong to the alkali group and have Fe-rich compositions mostly close to the schorl end member. Overlapping Fe/(Fe + Mg) ratios suggest broadly similar compositions of the hydrothermal fluids during the deposition of tourmaline. The most notable differences in minor and trace element contents include relative enrichment in Zn and Li in Tur-1 and relative enrichment in Ca, Sc, V, Cr, Sr, Sn, Y, Cs, Be, and Zr in Tur-3, with Tur-2 showing intermediate compositions between those of Tur-1 and Tur-3. The progressive enrichment in Sn from Tur-1 (avg = 14 ppm) through Tur-2 (avg = 311 ppm) and Tur-3 (avg = 476 ppm) indicates an increase of Sn concentrations in the hydrothermal system coinciding with cassiterite deposition in breccias and veins. The transition from high Li and Zn contents in Tur-1 to elevated Ca, Sr, V, and Cr contents in Tur-3 is interpreted as reflecting interaction between a hydrothermal fluid of magmatic origin and the metasedimentary country rocks. Strong and relatively steady positive Eu anomalies in all tourmaline types suggest dominantly reduced hydrothermal conditions. In situ δ18O and δ11B analyses of greisen-related Tur-1 reveal crystallization in isotopic equilibrium with magmatic water derived from a peraluminous S-type granite. In contrast, higher δ18O values of breccia-related Tur-2 and vein-related Tur-3 indicate crystallization in isotopic equilibrium with a fluid of metamorphic origin or a magmatic fluid that variably interacted with the metasedimentary host rocks. Geochemical modeling reproduces interactions between a fluid of magmatic origin and the host metasedimentary rocks at moderate water/rock ratios between 0.1 and 0.5. We conclude that cassiterite mineralization in the Chacaltaya district was formed primarily through interaction between B-Sn–rich magmatic fluids and the metasedimentary country rocks.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":" 28","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138963442","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":"Nature and Origin of a Massive Sulfide Occurrence in the Karrat Group: Evidence for Paleoproterozoic VMS Mineralization in Central West Greenland","authors":"Y. M. DeWolfe, J. Kolb, E. Sørensen, D. Rosa, P. Guarnieri","doi":"10.5382/econgeo.5036","DOIUrl":"https://doi.org/10.5382/econgeo.5036","url":null,"abstract":"\u0000 Mafic volcanic rocks of the Kangilleq Formation of the Paleoproterozoic Karrat Group host volcanogenic massive sulfide (VMS) mineralization in the area of central Kangiusap Kuua, central West Greenland. The mafic volcanic rocks display evidence of subaqueous, effusive eruption and redeposition by mass debris flows generated along fault scarps on the sea floor. A zone of semiconformable quartz alteration and disconformable chlorite alteration within hydrothermal breccias and mafic tuff breccias near the top of the volcanic sequence is interpreted to reflect a synvolcanic hydrothermal system. Conformable, massive to semimassive, and discordant, stringer-style sulfide mineralization is hosted within the quartz- and chlorite-altered volcanic rocks. The massive to semimassive sulfide mineralization is ~10 m thick and crops out along strike for ~2,000 m. The stringer zone is ≤10 m thick with individual sulfide stringers ranging in width from 5 to 90 cm. All sulfide zones are dominated by coarse pyrrhotite and pyrite, with trace amounts of sphalerite and chalcopyrite.\u0000 The pillow lavas are subalkaline with geochemical characteristics typical of modern transitional to tholeiitic mid-ocean ridge or back-arc basin basalt. Trace element and Nd isotope data suggest that these lavas erupted in an epicratonic, back-arc basin. Characteristics of the host rocks indicate a period of localized rifting, volcanism, and VMS formation during genesis of the Karrat Group, which is dominated by siliciclastic rocks.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":" 8","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138963669","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 and Structure of the Río Blanco Cu-Mo Porphyry Deposit, Central Chile","authors":"J. Skarmeta, Fernando Ortiz, Marco Solé","doi":"10.5382/econgeo.5043","DOIUrl":"https://doi.org/10.5382/econgeo.5043","url":null,"abstract":"The Río Blanco-Los Bronces deposit is the largest Cu-Mo porphyry deposit in the world in terms of contained Cu metal. It is the product of protracted superposed magmatic and hydrothermal activity associated with multiple intrusive and brecciation events, with simultaneous regional uplift, erosion and unroofing, and decompression. Magmatism resulted in three major mineralization-alteration stages. The premineralization stage occurred during the emplacement of the San Francisco batholith, resulting in late magmatic and early hydrothermal events. The synmineralization stage corresponds to the main hydrothermal events associated with the Río Blanco-Los Bronces porphyry and breccia complexes, which were related to three intrusion phases, widespread brecciation, and an epithermal-style advanced argillic alteration. Late-stage magmatism, followed by hydrothermal activity, was associated with the emplacement of subvolcanic rhyolite complexes and late-stage porphyry intrusions. The synmineralization intrusions are associated with high-grade breccia bodies that have well-defined alteration-zonation patterns. Compilation and analysis of the historical Río Blanco structural data sets from the different mines, tunnels, and pits have allowed the assignment of all mapped structures to four hierarchical orders based on their continuity, crosscutting relationships, and infill compositions. The larger structures (orders 0 and 1) have along-strike continuity, correlate between drifts and/or mine levels, whereas smaller structures (orders 2 and 3) were grouped according to their dimensions and distributions within the larger-order structure-defined panels. All orders 0 and 1 structures were modeled in three dimensions, while orders 2 and 3 were in two dimensions. The structures mapped at Río Blanco have an intimate relationship with the pre- to the late-stage geologic evolution of magmatism and mineralization. The regional- and to a lesser extent district-scale structural evolution was related to premineralization basin-opening and subsequent tectonic inversion, whereas at the camp scale, syn- to late mineralization intrusions and related hydrothermal features were superimposed on this inherited structural architecture.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"38 ","pages":""},"PeriodicalIF":5.8,"publicationDate":"2023-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139176234","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":"Superimposed Gold Mineralization Events in the Tuanshanbei Orogenic Gold Deposit, Central Jiangnan Orogen, South China","authors":"Cheng Wang, Yong-Jun Shao, Richard Goldfarb, Shi-Min Tan, Ji Sun, Chao Zhou, Han Zheng, Qing-Quan Liu, Yi-Qu Xiong","doi":"10.5382/econgeo.5034","DOIUrl":"https://doi.org/10.5382/econgeo.5034","url":null,"abstract":"Abstract The Jiangnan orogen, one of the largest gold-producing areas in China, has experienced multiple orogenic events with complex structural overprinting that is marked by multiple stages of magmatism, deformation, metamorphism, and orogenic gold mineralization. Different orogenic events have been recognized in the Neoproterozoic, mid-Paleozoic, Triassic, and Early Cretaceous, reflecting collisions and intracontinental orogenic episodes. The age of gold deposition in the Jiangnan orogen, however, has been poorly constrained owing to the absence of suitable dating minerals. Field studies in the orogen indicate the Tuanshanbei gold deposit includes two generations of auriferous quartz-ankerite-pyrite-arsenopyrite veins (Q2 and Q3), with the latter of the two notable for containing more abundant ankerite and base metal sulfides. The Q2 veins were formed throughout the near S-N–directed shortening associated with D1 deformation and along resulting subhorizontal to low-angle-dipping EW- to WNW-striking transpressive faults. The Q3 veins, containing about 70% of the total gold resource, were primarily localized in moderately to steeply dipping NW-striking tensional/tensional shear faults and moderately dipping NE- to NNE-striking transpressive faults that were products of NW-SE–directed shortening during D2 deformation. Both vein generations are temporally younger than the 437.2 ± 4.2 Ma Tuanshanbei granodiorite host, and both are crosscut by postgold ca. 225 Ma diabase dikes. Hydrothermal monazite coexists with native gold and gold-bearing metal sulfides in the Q2 and Q3 veins. The Q2 monazite yielded a Tera-Wasserburg lower intercept age of 415.1 ± 2.1 Ma, consistent within error with an ankerite Sm-Nd isochron age of 410 ± 15 Ma and a laser ablation-inductively coupled plasma-mass spectrometry hydrothermal zircon 206Pb/238U age of 411.2 ± 4.0 Ma. The Q3 monazite yielded a Tera-Wasserburg lower intercept age of 234.3 ± 1.1 Ma. These new ages suggest that the Early Devonian gold event was overprinted by hydrothermal activity along the same structural system almost 200 m.y. later such that the gold resource must be a product of two temporally distinct events. Geologic and structural evidence, coupled with existing published geochemical data, suggests both ore-forming events were related to crustal metamorphism typical of most orogenic gold deposits. Fluids would have been derived from Neoproterozoic metasedimentary basement rocks, most likely from metamorphic devolatilization of the Neoproterozoic Cangxiyan Group greenschist-amphibolite facies metasediments. There is no evidence suggesting any type of magmatic contribution to the ore-forming process at either time. The data are best interpreted to suggest that various parts of the basement were metamorphosed near the greenschist-amphibolite boundary at different times, but during both times, the gold-bearing metamorphic fluids eventually migrated into the same structural conduits.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"233 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135685058","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":"Are Placer Platinum Nuggets Formed During Lateritization? The Verdict from the Owendale Alaskan-Uralian Complex in Australia Is an Emphatic No!","authors":"Bocheng Ma, Reid R. Keays","doi":"10.5382/econgeo.5027","DOIUrl":"https://doi.org/10.5382/econgeo.5027","url":null,"abstract":"Abstract The thick laterite developed over platinum group element (PGE)-bearing ultramafic rocks of the Owendale Alaskan-Uralian Complex in New South Wales, Australia, provides an ideal environment in which to address the question of whether Pt-Fe nuggets are formed during lateritization. This is an important issue to settle because Pt-Fe nuggets in alluvial placers and eluvial deposits associated with the Alaskan-Uralian complexes were the world’s major source of Pt prior to the commencement of Pt production from the Bushveld Complex and continue to produce a significant amount of Pt. Some of the Owendale laterites have high Pt but low Cu contents, while others have both high Pt and high Cu contents. Heavy mineral concentrates were prepared from about 1 kg of drill chips from both types of laterites. Only five of the 61 samples processed contained any platinum group minerals (PGMs) greater than 5 μm in size, even though many of the samples contained more than 1 g/t Pt. The largest PGM found was about 100 μm long, and the majority were <20 μm. The bulk of the PGMs recovered were zoned PGMs consisting of a core of isoferroplatinum mantled by tetraferroplatinum with an outer rim of tulameenite; many of these zoned PGMs are encased in hematite grains that often have high Pt contents and appear to be pseudomorphs after the PGMs. The textural evidence indicates that at least half of the primary PGMs in the ultramafic protoliths to the laterites were destroyed during weathering and that the liberated PGEs could have been available for the formation of PGM nuggets. However, despite the large amount of PGEs liberated during the destruction of the primary PGMs, no evidence was found for the neogenic growth of PGE nuggets. Rather, the Pt liberated during the destruction of the PGMs appears to have only traveled distances of micrometers to tens of centimeters to form Pt nanoparticles or Pt oxides or to be absorbed/adsorbed by the Fe oxide hosts.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"145 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135723562","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Time Series Studies and Drilling Results from IODP Expedition 376 to Brothers Volcano, New Zealand: Insights into Petrology, Hydrothermal Processes, and Mineralization—Introduction","authors":"C.E.J. de Ronde, S. E. Humphris, T. W. Höfig","doi":"10.5382/econgeo.5035","DOIUrl":"https://doi.org/10.5382/econgeo.5035","url":null,"abstract":"Research Article| November 01, 2023 Time Series Studies and Drilling Results from IODP Expedition 376 to Brothers Volcano, New Zealand: Insights into Petrology, Hydrothermal Processes, and Mineralization—Introduction C.E.J. de Ronde; C.E.J. de Ronde 1Department of Earth Resources & Materials, GNS Science, 1 Fairway Drive, Avalon, Lower Hutt 5010, New Zealand †Corresponding author: e-mail, Cornel.deRonde@gns.cri.nz Search for other works by this author on: GSW Google Scholar S. E. Humphris; S. E. Humphris 2Department of Geology & Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA Search for other works by this author on: GSW Google Scholar T. W. Höfig T. W. Höfig 3International Ocean Discovery Program, Texas A&M University, 1000 Discovery Drive, College Station, Texas 77845, USA *Present address: Project Management Jülich (PtJ), Coastal, Marine, and Polar Research, Jülich Research Centre (FZJ), Schweriner Strasse 44, Rostock 18069, Germany. Search for other works by this author on: GSW Google Scholar Author and Article Information C.E.J. de Ronde 1Department of Earth Resources & Materials, GNS Science, 1 Fairway Drive, Avalon, Lower Hutt 5010, New Zealand S. E. Humphris 2Department of Geology & Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA T. W. Höfig 3International Ocean Discovery Program, Texas A&M University, 1000 Discovery Drive, College Station, Texas 77845, USA †Corresponding author: e-mail, Cornel.deRonde@gns.cri.nz *Present address: Project Management Jülich (PtJ), Coastal, Marine, and Polar Research, Jülich Research Centre (FZJ), Schweriner Strasse 44, Rostock 18069, Germany. Publisher: Society of Economic Geologists Accepted: 31 May 2023 First Online: 14 Nov 2023 Online ISSN: 1554-0774 Print ISSN: 0361-0128 © 2023 Society of Economic GeologistsSociety of Economic Geologists Economic Geology (2023) 118 (7): 1537–1547. https://doi.org/10.5382/econgeo.5035 Article history Accepted: 31 May 2023 First Online: 14 Nov 2023 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation C.E.J. de Ronde, S. E. Humphris, T. W. Höfig; Time Series Studies and Drilling Results from IODP Expedition 376 to Brothers Volcano, New Zealand: Insights into Petrology, Hydrothermal Processes, and Mineralization—Introduction. Economic Geology 2023;; 118 (7): 1537–1547. doi: https://doi.org/10.5382/econgeo.5035 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEconomic Geology Search Advanced Search Submarine volcanoes associated with intraoceanic arcs occur at convergent plate boundaries throughout the world, but are predominantly found in the southern and western regions of the Pacific Ocean. These volcanoes are constructed on top of the ","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"13 4","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135763727","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":"Origin of Hydrothermal Barite in Polymetallic Veins and Carbonate-Hosted Deposits of the Cyclades Continental Back Arc","authors":"Sandra C. Wind, Mark D. Hannington, David A. Schneider, Jan Fietzke, Stephanos P. Kilias, J. Bruce Gemmell","doi":"10.5382/econgeo.5028","DOIUrl":"https://doi.org/10.5382/econgeo.5028","url":null,"abstract":"Abstract Polymetallic veins and breccias and carbonate-replacement ore deposits in the Cyclades continental back arc, Greece, formed from a range of fluid and metal sources strongly influenced by the dynamics of the late Mesozoic-Cenozoic Hellenic subduction system. These complexities are recorded in the isotopic signatures of hydrothermal barite. We investigated 17 mineral occurrences on four Cycladic islands and from Lavrion on the mainland. Here, barite occurs in almost all deposit types of Miocene to Quaternary age. We used a multiple isotope and geochemical approach to characterize the barite in each deposit, including mineral separate analysis of δ34S and δ18O and laser ablation-inductively coupled plasma-mass spectrometry of 87Sr/86Sr and δ34S. Barite from carbonate-hosted vein and breccia Pb-Zn-Ag mineralization on Lavrion has a wide range of δ34S (2–20‰) and δ18O (10–15‰) values, reflecting a mix of magmatic and surface-derived fluids that have exchanged with isotopically heavy oxygen in the carbonate host rock. Sulfur (δ34S = 10–13‰) and oxygen (δ18O = 9–13‰) values of barite from the carbonate-hosted vein iron and barite mineralization on Serifos are permissive of a magmatic sulfate component. Barite from epithermal base and/or precious metal deposits on Milos has δ34S (17–28‰) and δ18O (9–11‰) values that are similar to modern seawater. In contrast, barite from vein-type deposits on Antiparos and Mykonos has a wide range of δ34S (16–37‰) and δ18O (4–12‰) values, indicating a seawater sulfate source modified by mixing or equilibration of the hydrothermal fluids with the host rocks. Strontium isotope ratios of barite vary regionally, with 87Sr/86Sr ≥ 0.711 in the central Cyclades and 87Sr/86Sr ≤ 0.711 in the west Cyclades, confirming the strong influence of upper crustal rocks on the sources of fluids, Sr, and Ba in the formation of ore.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"27 3","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135513607","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"THE Fe-Cu DISCONNECT: UNRAVELING A COMPOSITE IRON OXIDE COPPER-GOLD DEPOSIT IN THE OLYMPIC Fe-Cu-Au PROVINCE, GAWLER CRATON","authors":"Jie Yu, Laura J. Morrissey, Martin Hand, Justin L. Payne, Yan-Jing Chen","doi":"10.5382/econgeo.5037","DOIUrl":"https://doi.org/10.5382/econgeo.5037","url":null,"abstract":"Abstract The northern Olympic Cu-Au province, Gawler craton, Australia, includes a series of magnetite-dominated deposits/prospects associated with minor Cu-Au mineralization such as the 8.37 million tonne Cairn Hill deposit. Cairn Hill has long been considered a deep, magnetite end member of the iron oxide copper-gold (IOCG) family that is largely represented in the southern Olympic province by the 1590 Ma hematite-dominated Olympic Dam, Carrapeteena, and Prominent Hill deposits. In contrast to the southern district, the deposits in the northern Olympic Cu-Au province are hosted in rocks that experienced multiple phases of high-temperature metamorphism and deformation. New U-Pb zircon geochronology shows the magnetite-hornblende lodes at Cairn Hill were formed at ca. 1580 Ma at amphibolite facies conditions. The magnetite lodes are crosscut by ca. 1515 Ma granitic dikes. A second high-temperature event is recorded by U-Pb monazite geochronology at ca. 1490 Ma and involved deformation and metamorphism along the Cairn Hill shear zone at conditions of 4.6 to 5.3 kbar and 740° to 770°C. The 1490 Ma event reworked the iron lodes and 1515 Ma granitic dikes. However, Cu mineralization at Cairn Hill occurs in brittle fractures and quartz-biotite veins, overprinting the 1490 Ma deformation and metamorphism. Despite a spatial association between magnetite and Cu, the long thermal history that affected magnetite mineralization and the clear petrographic links between magnetite and high-temperature granulite facies minerals contrast with the late, low-temperature hydrothermal Cu mineralization and indicate the two are not paragenetically related. Therefore, the spatial but not temporal association between magnetite and Cu has effectively overlain two distinct episodes of mineralization to create the Fe-Cu deposit observed today. Although this fits within the broad IOCG deposit family, exploration strategies for Cairn Hill-style composite deposits should be distinct from IOCG deposits with cogenetic Fe and Cu.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"36 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136057852","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Decoupling of Sulfur Isotope Signatures from Platinum Group Elements in Komatiite-Hosted Ore Systems: Evidence from the Mount Keith MKD5 Ni-(Co-Cu) Deposit, Western Australia","authors":"Anne B. Virnes, Marco L. Fiorentini, Stephen J. Barnes, Stefano Caruso, Laure A.J. Martin, Matvei Aleshin, Louise E. Schoneveld, Malcolm P. Roberts, Quentin Masurel, Nicolas Thebaud","doi":"10.5382/econgeo.5030","DOIUrl":"https://doi.org/10.5382/econgeo.5030","url":null,"abstract":"Abstract Komatiites require external sulfur from country rocks to generate immiscible sulfide liquid, which concentrates metals to form economic nickel sulfide deposits. Although signatures related to mass-independent fractionation of S isotopes (MIF-S, denoted as Δ33S) may identify external S sources, their values may not be directly indicative of the S reservoirs that were tapped during the ore-forming process, because of dilution by S exchange between assimilated sulfide xenomelt and komatiite silicate melt. To quantify this process and be confident that MIF-S can be effectively used to track S sources in magmatic systems, we investigated the effect of silicate melt-sulfide liquid batch equilibration, using the proxy of silicate/sulfide mass ratio, or R factor, on the resulting MIF-S signatures of pentlandite-rich ore from the Mount Keith MKD5 nickel sulfide deposit, Agnew-Wiluna greenstone belt, Western Australia. We carried out in situ multiple S isotope and platinum group element (PGE) analyses on pentlandite from a well-characterized drill core through the deposit. The variability in Pd tenor and MIF-S signature suggests that these are decoupled during batch equilibration and that the latter is not controlled by metal-derived R factor. Rather, the observed spread of MIF-S signatures implies that the sulfide xenomelt was initially heterogeneous and that chemical equilibration of S isotopes is incomplete as opposed to that of PGEs in a komatiite melt. Consequently, magmatic sulfides, which formed in the hottest, most dynamic, and likely fastest equilibrating magmatic systems on Earth, may still preserve their initial MIF-S isotope compositions, reflecting the range of crustal S reservoirs that were available upon komatiite emplacement.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"87 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135044016","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"THE ROLE OF SCANDIUM CHLORIDE AND HYDROXIDE COMPLEXES IN THE FORMATION OF SCANDIUM DEPOSITS: INSIGHTS FROM EXPERIMENTS AND MODELING","authors":"Jiaxin Wang, A. E. Williams-Jones, A. Timofeev, Xueni Zhang, Jiajun Liu, Shunda Yuan","doi":"10.5382/econgeo.5026","DOIUrl":"https://doi.org/10.5382/econgeo.5026","url":null,"abstract":"Abstract Although scandium is commonly concentrated to economic levels by magmatic processes, hydrothermal fluids also play an important role in its concentration. Indeed, the most important source of scandium is currently the Bayan Obo deposit in China, where scandium is extracted from hydrothermally produced aegirine. To know how and why scandium is concentrated by hydrothermal fluids, it is necessary to understand the speciation of scandium in hydrothermal fluids. In a recently published study, we showed that scandium forms stable species with fluoride ions and proposed that such species may have been responsible for the hydrothermal transport of scandium in deposits like Bayan Obo. Chloride ions, which have been shown to form stable complexes with the other rare earth elements (REE), however, are much more abundant in most hydrothermal fluids than fluoride ions, as are hydroxide ions, particularly at high pH. We, therefore, conducted solubility experiments designed to investigate the stability of scandium chloride and hydroxide complexes in hydrothermal fluids. The experiments investigating the role of chloride species considered the solubility of Sc2O3(s) in the H2O-NaCl-HCl system at 100°, 150°, 300°, and 350°C and saturated water vapor pressure. These experiments showed that scandium concentration is independent of chloride concentration over the range of chlorinity investigated, i.e., up to 3.6 mol Cl– and that scandium, therefore, does not form stable complexes with chloride ions. To evaluate the role of hydroxide species in scandium transport and avoid the effect of chloride ions in the complexation, a second set of experiments was conducted that determined the solubility of Sc2O3(s) in H2O-NaClO4-HClO4 solutions at 100°, 150°, 200°, and 250°C, and saturated water vapor pressure. The results of these experiments showed that the solubility of Sc2O3(s) depends on pH and temperature. Based on the former dependence, two scandium hydroxide complexes, Sc(OH)2+ and Sc(OH)3°, were identified at low and higher pH, respectively. The formation constant (log β) determined for Sc(OH)2+ is 10.29 ± 0.07, 10.32 ± 0.07, 10.35 ± 0.19, and 10.91 ± 0.20 at 100°, 150°, 200°, and 250°C, respectively. That of Sc(OH)3° is 27.22 ± 0.68, 26.66 ± 1.35, 27.04 ± 0.13, and 28.02 ± 0.14 at the same temperatures, respectively. These results demonstrate that, unlike the case for the other rare earth elements, chloride plays a negligible role in transporting scandium in hydrothermal fluids. Instead, they show that scandium hydroxide complexes can be important in the transport of scandium and could have contributed significantly to the formation of deposits like those at Bayan Obo.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"37 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135146937","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}