Economic Geology最新文献

{"title":"Niobium, Critical Metal, and Progeny of the Mantle","authors":"A. Williams-Jones, O. Vasyukova","doi":"10.5382/econgeo.4994","DOIUrl":"https://doi.org/10.5382/econgeo.4994","url":null,"abstract":"\u0000 Niobium is a critical metal in high demand because of technological advances and the supply risk created by the fact that over 90% of its production is by a single country (Brazil). In this paper, we review the geology of the deposits that are currently being mined and other potentially economic deposits as well as develop models for their genesis. With the exception of the Lovozero deposit (Russia), which is hosted by a layered silica-undersaturated alkaline igneous complex, all the deposits that are currently being mined for niobium are hosted by carbonatites, and most of the deposits with economic potential are also hosted by these rocks. Niobium owes its concentration in carbonatites and alkaline silicate rocks to its highly incompatible nature and the small degree of partial melting of the mantle required to generate the corresponding magmas. The primary control on the concentration of niobium to economic levels in alkaline silicate magmas is fractional crystallization, partly prior to but mainly after emplacement. In the case of silica-undersaturated magmas, the final residue saturates in minerals like eudialyte and loparite to form niobium-rich horizons in the layered complexes that crystallize from these magmas. The final residue, in the case of silica-saturated magmas, crystallizes the pegmatites that are the hosts to the economic niobium mineralization, which commonly takes the form of pyrochlore. In contrast, carbonatitic magmas undergo little to no fractional crystallization prior to emplacement. Moreover, fractional crystallization on emplacement has minimal impact on the concentration of niobium to economic levels. Instead, we propose that the metasomatic interaction of the carbonatitic magmas with their hosts to form rocks like phlogopitite (glimmerite) consumes much of the magma, leaving behind a phoscoritic residue from which pyrochlore crystallizes in amounts sufficient to form economic deposits. Although many niobium deposits display evidence of intense hydrothermal alteration, during which there can be major changes in the niobium mineralogy, the extremely low solubility of niobium in aqueous fluids at elevated temperature precludes significant mobilization and, thus, enrichment of the metal by hydrothermal fluids. However, weathering of carbonatite-hosted niobium deposits leads to supergene enrichment (due largely to the dissolution of the carbonate minerals) that can double the niobium grade and make subeconomic deposits economic. Pyrochlore is the principal niobium mineral in these laterite-hosted deposits, although its composition differs considerably from that in the primary mineralization. This paper evaluates the processes that appear to be responsible for the genesis of niobium ores and provides a framework that we hope will guide future in-depth studies of niobium deposits and lead to more effective strategies for their successful exploration and exploitation.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"26 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2022-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78139677","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":"UNDERSTANDING Cu DEFICIENCY AND Mo ENRICHMENT IN THE JURASSIC ZHANGGUANGCAI-LESSER XING’AN CONTINENTAL ARC (NE CHINA): INSIGHTS FROM THE LUMING PORPHYRY MO DEPOSIT","authors":"Hegen Ouyang, John T. Caulfield","doi":"10.5382/econgeo.4989","DOIUrl":"https://doi.org/10.5382/econgeo.4989","url":null,"abstract":"\u0000 Continental arcs are favorable sites for porphyry Cu ± Mo deposits. In contrast, the Jurassic Zhangguangcai-Lesser Xing’an continental arc, northeastern China, hosts numerous porphyry Mo deposits with only minor total Cu endowment. The reasons for this remain elusive. Here, we address the issue by tracking the origin and evolution of a long-lived (ca. 12 m.y.) magmatic suite associated with one of the largest Mo deposits in the Zhangguangcai-Lesser Xing’an range continental arc—the Luming porphyry Mo deposit. In combination with previous geochronological data, our results indicate that the pre- (187.5–186.5 Ma) and syn-ore (178.6–175.6 Ma) intrusions at Luming represent separate magma batches from isotopically similar parental magmas with the signature of subduction-metasomatized mantle-derived magmas mixed with crustal melts. The Sr/Y, La/YbN, Dy/YbN, and Eu/Eu* values, together with fO2 and apatite S and Cl concentrations of the syn-ore intrusions, however, are systematically higher than pre-ore intrusions. These data indicate that there is a distinct change in magma chemistry during the period of magmatism quiescence between the pre- and syn-ore magmatism. The marked change in magma chemistry is coincident with an episode of major compression and crustal thickening in the Zhangguangcai-Lesser Xing’an range. We, therefore, interpret that the chemical changes most likely reflect a deepening of the locus of lower crustal magma evolution, linked to increased crustal thickness and/or melt H2O contents accompanying an increase in orogenic stress. Considering the tectonic setting, magmatic evolution in the deep crust, emplacement depth, fractionation degree, and oxygen fugacity of the porphyry-Mo related intrusions at Luming, they are very similar to porphyry Cu deposits worldwide. Accordingly, we propose that the deficiency in Cu and enrichment in Mo of the porphyry deposits in the Zhangguangcai-Lesser Xing’an range most likely formed due to mantle-derived magmas interacting with reduced crustal materials or melts in the deep crust. This resulted in substantial sequestration of Cu and S, decreasing porphyry Cu potential. Such an inference is supported by the distinctly lower S and Cl concentrations of the Mo-related intrusions in the Zhangguangcai-Lesser Xing’an range compared to those associated with porphyry Cu deposits. Our results confirm the fundamental role of increasing compressive stress, crustal thickening, and transcrustal petrologic processes in the formation of porphyry deposits and highlight the role of crustal components in modulating the Mo/Cu ratio of porphyry deposits in a continental arc setting. In addition, we tentatively propose that magmatic apatite SO3 and/or Cl contents can be used to discriminate porphyry Mo-related intrusions from those associated with porphyry Cu deposits in continental arcs.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"7 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2022-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82491457","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 RECENTLY DISCOVERED TRACHYTE-HOSTED RARE EARTH ELEMENT-NIOBIUM-ZIRCONIUM OCCURRENCE IN NORTHERN MAINE, USA","authors":"Chunzeng Wang, J. Slack, A. Shah, M. Yates, D. Lentz, A. Whittaker, R. Marvinney","doi":"10.5382/econgeo.4993","DOIUrl":"https://doi.org/10.5382/econgeo.4993","url":null,"abstract":"\u0000 Reported here are geological, geophysical, mineralogical, and geochemical data on a previously unknown trachyte-hosted rare earth element (REE)-Nb-Zr occurrence at Pennington Mountain in northern Maine, USA. This occurrence was newly discovered by a regional multiparameter, airborne radiometric survey that revealed anomalously high equivalent Th (eTh) and U (eU), confirmed by a detailed ground radiometric survey and by portable X-Ray fluorescence (pXRF) and whole-rock analyses of representative rock samples. The mineralized area occurs within an elongate trachyte body (~1.2 km2) that intrudes Ordovician volcanic rocks. Geologic constraints suggest that the trachyte is also Ordovician in age. The eastern lobe (~900 × ~400 m) of the trachyte is pervasively brecciated with a matrix containing seams, lenses, and veinlets composed mainly of potassium feldspar, albite, and fine-grained zircon and monazite. Barite is locally abundant. Minor minerals within the matrix include columbite, bastnäsite, euxenite, chlorite, pyrite, sphalerite, and magnetite. The pXRF analyses of 22 samples (App. Table A1) collected from the eastern lobe demonstrate that this entire part of the trachyte is highly mineralized. Whole-rock geochemical analyses for samples from the eastern lobe document high average contents of Zr (1.17 wt %), Nb (1,656 ppm), Ba (3,132 ppm), Y (1,140 ppm), Hf (324 ppm), Ta (122 ppm), Th (124 ppm), U (36.5 ppm), Zn (689 ppm), and Sn (106 ppm). Among light REE, the highest average concentrations are shown by La (763 ppm) and Ce (1,479 ppm). For heavy REE (HREE), Dy and Er are the most abundant on average (167 and 114 ppm, respectively). No HREE-rich minerals such as xenotime have been identified; the HREE may reside chiefly in monazite and bastnäsite, and within the fine-grained zircon. Very strong positive correlations (R2) of 0.92 to 0.98 exist between Th and Zr, Nb, Y, Ce, Yb, and Sn, indicating that the radiometric data for eTh are valid proxies for concentrations of these metals in the mineralized rocks.\u0000 Trachyte-hosted REE-Nb-Zr deposits like the occurrence at Pennington Mountain also are known in eastern Australia and in the south Qinling belt of Central China. Based on comparisons with these deposits, and the lack of detailed geologic mapping in the Pennington Mountain region, we suggest that other rare-metal occurrences contained in trachyte may exist elsewhere in northern Maine, and more widely in the Appalachian-Caledonian orogen where volcanic and subvolcanic trachytes have been recognized.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"44 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2022-11-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87720707","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":"Fluids and Melts at the Magmatic-Hydrothermal Transition, Recorded by Unidirectional Solidification Textures at Saginaw Hill, Arizona, USA","authors":"W. Bain, P. Lecumberri-Sanchez, E. Marsh, M. Steele‐MacInnis","doi":"10.5382/econgeo.4952","DOIUrl":"https://doi.org/10.5382/econgeo.4952","url":null,"abstract":"\u0000 Fluid exsolution and melt evolution at the magmatic-hydrothermal transition are critical processes driving the metal enrichment of porphyry systems. Coeval fluid and melt inclusion assemblages in unidirectional solidification textures (USTs) at Saginaw Hill—a small, porphyry Cu system in southwestern Arizona—record a dynamic and repetitious process of fluid accumulation and release. The cores of quartz crystals throughout the UST bands host coeval silicate melt and brine inclusions but lack vapor-rich inclusions. This could indicate preferential expulsion of vapor and trapping of high-density brine during episodes of fracturing or the direct exsolution of single-phase high-salinity brine from the silicate melt. In contrast, the rims of UST quartz host abundant coeval brine and vapor inclusions, consistent with liquid-vapor immiscibility at lower pressures compared to the corresponding quartz cores. This transition from dominantly coeval silicate melt inclusions and brine in phenocryst cores to coeval brine and vapor in the rims suggests that the Saginaw Hill system underwent cyclic processes of fluid exsolution, accumulation, overpressure, and decompression at relatively stable temperatures (consistently ~650°C) during UST formation. Melt inclusion data indicate that the melt at this stage was highly fractionated and tended toward muscovite saturation. Metal concentrations in the brine were comparable to or higher than those in fluids reported in world-class porphyry Cu systems and were likely the result of both igneous fractionation and the high chloride content of the exsolved fluids. While limited in scale, Saginaw Hill provides evidence for processes that are predicted to occur at the magmatic-hydrothermal transition during the formation of large, well-mineralized porphyry systems.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"3 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2022-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81619473","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":"Historia, Exploración y Geología de los Yacimientos Metalíferos de Chile 900-2021. (Francisco Camus I. and Juan Carlos Castelli S.)","authors":"Marcos Zentilli","doi":"10.5382/econgeo.117.7.br01","DOIUrl":"https://doi.org/10.5382/econgeo.117.7.br01","url":null,"abstract":"","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"71 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2022-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84170599","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 Elements in Chromite as Indicators of the Origin of the Giant Podiform Chromite Deposit at Kempirsai, Kazakhstan","authors":"Wenxuan Hu, Mei‐Fu Zhou, M. Yudovskaya, I. Vikentyev, J. Malpas, Peng‐Fei Zhang","doi":"10.5382/econgeo.4955","DOIUrl":"https://doi.org/10.5382/econgeo.4955","url":null,"abstract":"\u0000 This study presents a complete trace element data set of chromite from the world’s largest podiform chromite deposit at Kempirsai, Kazakhstan, together with platinum group element (PGE) and Re-Os isotope compositions, to explore the potential of trace elements in the study of podiform chromite deposits.\u0000 Chromite orebodies in the Karaagash area of the Kempirsai Main ore field are hosted by dunites in the mantle sequence of the ophiolite. Dunites slightly distal to the orebodies are composed of olivine (forsterite content = 91.5–93.4) and minor euhedral chromite with variable Cr# (0.73–0.83). These dunites have primitive mantle-normalized Pt-Pd–poor PGE patterns and subchondritic 187Os/188Os ratios (0.12174–0.12220). Negative correlations between Cr# and incompatible trace elements (Sc and Ti) of the chromite are consistent with melt-rock reaction, whereas positive correlations between Cr# and compatible trace elements (V and Ga) reflect the role of fractional crystallization. It is therefore proposed that chromite in the distal dunites was crystallized from magmas after reaction with mantle peridotites. In comparison, chromite grains in the ores and adjacent dunites exhibit relatively uniform Cr# numbers (0.81–0.86) and higher 187Os/188Os values (0.12319–0.12414). Both compatible and incompatible trace elements of chromite exhibit negative correlations with Cr#, which are best explained by mixing between the modified magma after melt-rock reaction and a later injected magma from a more depleted source.\u0000 After the ore formation, subsolidus reequilibration between olivine and chromite reduced Mg# and modified divalent trace elements of chromite in the order of Zn > Co = Mn > Ni but did not affect distribution of nondivalent trace elements, except V and Fe3+. The decoupling of redox-sensitive and redox-insensitive trace elements suggests that the redox states have been modified during subsolidus reequilibration. The existing iron equilibrium between olivine and chromite records high fO2 values (quartz-fayalite-magnetite buffer [∆QFM] 0.8–2.4), whereas correction of subsolidus reequilibration results in a decrease of the fO2 values toward the QFM buffer (∆QFM 0.1–0.6), indicating that increase in fO2 was not a critical factor in the ore formation.\u0000 Principal component analysis and factor analysis were further carried out to identify differences in trace elements between high-Cr and high-Al podiform chromite deposits worldwide. High-Cr chromite deposits have variable divalent trace element compositions and show complex distributions of nondivalent trace elements. The former reflects longer and slower cooling histories of the high-Cr chromite deposits with respect to the high-Al chromite deposits, whereas the latter indicates more variable magma compositions and complex processes during the formation of the high-Cr chromite deposits.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"13 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2022-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80460122","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":"High-Grade Copper and Gold Deposited During Postpotassic Chlorite-White Mica-Albite Stage in the Far Southeast Porphyry Deposit, Philippines","authors":"M. F. Calder, Z. Chang, A. Arribas, A. Gaibor, P. Dunkley, Jeffrey Pastoral, K. Kouzmanov, C. Spandler, J. W. Hedenquist","doi":"10.5382/econgeo.4940","DOIUrl":"https://doi.org/10.5382/econgeo.4940","url":null,"abstract":"\u0000 Ninety-eight underground diamond holes (~102 km) drilled by Far Southeast Gold Resources Inc. at the Far Southeast porphyry Cu-Au deposit, Philippines, from 2011 to mid-2013, provide a three-dimensional exposure of the deposit between 700- and –750-m elevation, with surface at ~1,400-m elevation. Far Southeast contains an inferred resource of 891.7 million tonnes (Mt) averaging 0.7 g/t Au and 0.5 wt % Cu, equivalent to 19.8 Moz Au and 4.5 Mt Cu. This contribution reports the spatial and temporal distribution of alteration and mineralization at Far Southeast, notably a white-mica–chlorite-albite assemblage that formed after early secondary biotite and before late quartz–white-mica–pyrite alteration and that is associated with the highest copper and gold grades.\u0000 Alteration assemblages were determined by drill core logging, short-wavelength infrared (SWIR) spectral analysis, petrographic examination, and a quantitative evaluation of materials by scanning electron microscopy (QEMSCAN) study. Alteration is limited around sparse veins or pervasive where vein density is high and the alteration halos coalesce. The alteration and mineralization zones with increasing depth are as follows: (1) the lithocap of quartz-alunite–dominated advanced argillic-silicic alteration that hosts part of the Lepanto high-sulfidation Cu-Au epithermal deposit (mostly above ~700-m elevation), (2) an aluminosilicate-dominated zone with coexisting pyrophyllite-diaspore ± kandite ± alunite and white mica (~700- to ~100-m elevation), (3) porphyry-style assemblages characterized by stockwork veins (below ~500-m elevation), (4) the 1 wt % Cu equivalent ore shell (~400- to –300-m elevation), and (5) an underlying subeconomic zone (about –300- to –750-m elevation, the base of drilling). The ore shells have a typical bell shape centered on a dioritic intrusive complex.\u0000 The paragenetic sequence of the porphyry deposit includes stage 1 granular gray to white quartz-rich (± anhydrite ± magnetite ± biotite) veins with biotite-magnetite alteration. These were cut by stage 2 lavender-colored euhedral quartz-rich (± anhydrite ± sulfides) veins, with halos of greenish white-mica–chlorite-albite alteration. The white mica is largely illite, with an average 2,203-nm Al-OH wavelength position. The albite may reflect the mafic nature of the diorite magmatism. The quartz veins of this stage are associated with the bulk of copper deposited as chalcopyrite and bornite, as well as gold. Thin Cu sulfide (chalcopyrite, minor bornite) veins with minor quartz and/or anhydrite (paint veins), with or without a white-mica halo, also occur. These veins were followed by stage 3 anhydrite-rich pyrite-quartz veins with white-mica (avg 2,197 nm, illite)–pyrite alteration halos.\u0000 Combined with previous studies, we conclude that this porphyry system, including the Far Southeast porphyry and Lepanto high-sulfidation Cu-Au deposits, evolved over a period of 0.1–0.2 m.y. Three diorite porphyry stocks were emplace","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"18 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2022-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73670708","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 TRIASSIC OROGENIC GOLD MINERALIZATION EVENT IN THE PALEOPROTEROZOIC METAMORPHIC ROCKS: EVIDENCE FROM TWO TYPES OF RUTILE IN THE BAIYUN GOLD DEPOSIT, LIAODONG PENINSULA, NORTH CHINA CRATON","authors":"Jiahao Zheng, Bin Chen, Shuaijie Liu, Chuang Bao","doi":"10.5382/econgeo.4945","DOIUrl":"https://doi.org/10.5382/econgeo.4945","url":null,"abstract":"\u0000 Rutile grains often occur in different types of gold deposits, and their U-Pb ages have been widely used to determine the formation time of gold mineralization. However, the origin of rutile grains in the gold deposits remains controversial. In this paper, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of U-Pb ages and trace elements on rutile grains were applied to investigate the metamorphic and hydrothermal processes of the Baiyun gold deposit (70 t Au, avg grade: 3 g/t) in the Liaodong Peninsula in the northeastern part of the North China craton. Rutile grains in the hydrothermal altered gold schist from the Baiyun deposit yielded two group ages of 1924 ± 18 and 237.0 ± 1.8 Ma, respectively. Combined with our systematic U-Pb zircon geochronological results of the ore-hosting schists and post-ore dikes, we suggest these rutile ages record a Paleoproterozoic metamorphic event and a Triassic hydrothermal gold mineralization event, respectively. The metamorphic and hydrothermal rutile grains have no obvious textural differences, but they show distinct trace element contents of Zr, W, Nb, and Ta. Combined with previous published data, we propose that high W (>1,000 ppm) and low Zr (<200 ppm) contents in rutile can be used to distinguish hydrothermal rutile from metamorphic and magmatic rutile. The newly identified ca. 237 Ma hydrothermal event is much older than the ca. 227 to 210 Ma Triassic magmatic rocks in the region, which precludes a temporal and genetic link between the Baiyun gold mineralization and the regional Mesozoic magmatism. Rather, the ca. 237 Ma gold mineralization may be associated with the Triassic orogenic metamorphism, and Baiyun is an orogenic gold deposit. The Triassic gold deposits in the northern margin of the North China craton formed by orogenesis between the Siberian craton and the North China craton. After a hiatus, the large-scale gold deposits formed during the Early Cretaceous in the North China craton due to a westward subduction of the paleo-Pacific plate beneath the craton since the Early Jurassic. Our study highlights that rutile in gold deposits may be inherited from the host rocks and/or formed by hydrothermal fluids. Distinguishing between these two different rutile generations requires a combination of in situ age dating and trace element geochemistry in petrogenetic context.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"13 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2022-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75271981","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":"Discriminating Between Primary and Secondary Au Events in a Paragenetically Complex Archean Lode-Gold Deposit, Wawa Gold Corridor, Ontario, Canada","authors":"E. Wehrle, J. Montreuil, I. Samson, D. Kontak, Mingqian Wu","doi":"10.5382/econgeo.4972","DOIUrl":"https://doi.org/10.5382/econgeo.4972","url":null,"abstract":"\u0000 The Wawa gold corridor, located in the Michipicoten greenstone belt of the Superior province, Canada, comprises Au-bearing shear zones that crosscut the 2745 Ma Jubilee stock and that evolved during protracted deformation (D1-D3). Numerous generations of sulfide minerals crystallized before, during, and after these deformation events, and gold is associated with D1 arsenopyrite, D2 pyrite, and Bi-Te phases and chalcopyrite in assemblages that crosscut D3 veins. Observations of porosity and inclusions in D1 arsenopyrite and D2 pyrite suggest these sulfides underwent coupled dissolution-reprecipitation reactions. By coupling these textural observations with trace element analysis by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), it is evident that such replacement reactions generated gold from Au previously in solid solution. Conversely, textural relationships among paragenetically late gold and Bi-Te minerals are consistent with the precipitation of these phases from Bi-rich polymetallic melts. Mass balance calculations involving comparisons of the mass of Au in sulfides and the total mass of Au in their associated host rocks indicate that only D1 arsenopyrite contained enough Au to account for whole-rock Au content and overall deposit grade. Although D1 arsenopyrite is less volumetrically abundant than the various pyrite generations present in the deposit, it is often replaced by the later pyrite types, which is compatible with higher initial volumes of arsenopyrite than what is presently observed. It is concluded that the D1 Au + arsenopyrite event was the principal Au-mineralizing event in the Wawa gold corridor and that the other gold-bearing assemblages (i.e., gold + D2 pyrite, gold + Bi-Te phases + chalcopyrite) largely represent secondary mobilization of this primary enrichment. Given that LA-ICP-MS sulfide chemistry is regularly used in orogenic Au research, the approach outlined herein to assess the relative impact of distinct Au- and sulfide-mineralizing events could easily be applied to the study of other Au deposits in which complex hydrothermal parageneses are recognized.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"99 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2022-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79268267","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":"Timing of Rhyolite Intrusion and Carlin-Type Gold Mineralization at the Cortez Hills Carlin-Type Deposit, Nevada, USA","authors":"C. Henry, D. John, R. Leonardson, W. Mcintosh, M. Heizler, J. Colgan, K. Watts","doi":"10.5382/econgeo.4976","DOIUrl":"https://doi.org/10.5382/econgeo.4976","url":null,"abstract":"\u0000 Carlin-type gold deposits (CTDs) of Nevada are the largest producers of gold in the United States, a leader in world gold production. Although much has been resolved about the characteristics and origin of CTDs in Nevada, major questions remain, especially about (1) the role of magmatism, whether only a source of heat or also metals, (2) whether CTDs only formed in the Eocene, and (3) whether pre-Eocene metal concentrations contributed to Eocene deposits. These issues are exemplified by the CTDs of the Cortez region, the second largest concentration of these deposits after the Carlin trend.\u0000 Carlin-type deposits are notoriously difficult to date because they rarely generate dateable minerals. An age can be inferred from crosscutting relationships with dated dikes and other intrusions, which we have done for the giant Cortez Hills CTD. What we term “Cortez rhyolites” consist of two petrographic-geochemical groups of siliceous dikes: (1) quartz-sanidine-plagioclase-biotite-phyric, high-SiO2 rhyolites emplaced at 35.7 Ma based on numerous 40Ar/39Ar dates and (2) plagioclase-biotite-quartz ± hornblende-phyric, low-SiO2 rhyolites, which probably were emplaced at the same time but possibly as early as ~36.2 Ma. The dikes form a NNW-trending belt that is ~6–10 km wide × 40 km long and centered on the Cortez Hills deposit, and they require an underlying felsic pluton that fed the dikes. Whether these dikes pre- or postdated mineralization has been long debated. We show that dike emplacement spanned the time of mineralization. Many of both high- and low-SiO2 dikes are altered and mineralized, although none constitute ore. In altered-mineralized dikes, plagioclase has been replaced by kaolinite and calcite, and biotite by smectite, calcite, and marcasite. Sanidine is unaltered except in a few samples that are completely altered to quartz and kaolinite. Sulfides present in mineralized dikes are marcasite, pyrite, arsenopyrite, and As-Sb–bearing pyrite. Mineralized dikes are moderately enriched in characteristic Carlin-type elements (Au, Hg, Sb, Tl, As, and S), as well as elements found in some CTDs (Ag, Bi, Cu, Mo), and variably depleted in MgO, CaO, Na2O, K2O, MnO, Rb, Sr, and Ba. In contrast, some high-SiO2 rhyolites are unaltered and cut high-grade ore, which shows that they are post-ore. Both mineralized and post-ore dikes have indistinguishable sanidine 40Ar/39Ar dates. These characteristics, along with published interpretations that other giant CTDs formed in a few tens of thousands of years, indicate the Cortez Hills CTD formed at 35.7 Ma. All Cortez-area CTDs are in or adjacent to the Cortez rhyolite dike swarm, which suggests that the felsic pluton that fed the dikes was the hydrothermal heat source. Minor differences in alteration and geochemistry between dikes and typical Paleozoic sedimentary rock-hosted ore probably reflect low permeability and low reactivity of the predominantly quartzofeldspathic dikes.\u0000 Despite widespread pre-35.7 Ma miner","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"5 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2022-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86612984","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}