Abdul Latheef Thathrampally, Rajarshi Chakravarti, Crystal Laflamme, Paul Olin
The Neoproterozoic carbonaceous metapelites of the Mandhali Formation in the inner Lesser Himalaya contain diagenetic pyrite with above-background levels of Au (>200 ppb) when analyzed by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). These metapelites exhibit progressively metamorphosed zones (from south to north), ranging from the chlorite-muscovite zone (~372°C), to the muscovite ± biotite (~520°C) zone, to the greenschist-amphibolite transition (~570°C, >5 kbar). Within this regional framework, we document a hitherto unknown paragenesis of pyrite growth from diagenesis to peak metamorphism along with a localized phase of contact metamorphism, which predates regional metamorphism. A comparative assessment of pyrite trace element concentrations from the progressive metamorphic zones reveals that >80% of Au and ~65% of As is released from diagenetic pyrite during early chlorite dehydration at ~372°C, that is, in the chlorite-muscovite zone. Further into the muscovite ± biotite zone, at the terminal chlorite breakdown stage (480°–520°C), pyrite still occurs as the major sulfide with subordinate pyrrhotite. However, by this stage, ~93% of Au; ~75% of As; and ≥90% of Mo, Cd, Pb, Sb, W, Cu, Bi, Te, and Tl are released from pyrite. With the transition of pyrite to pyrrhotite (500°–550°C), almost all trace elements are released from pyrite into metamorphic fluids, except Co that is incorporated into the metamorphic pyrrhotite. This documented grain-scale elemental mobility is also reflected in bulk-rock Au assays; that is, mean Au of 9.8 ppb in the chlorite-muscovite zone and 1.1 ppb in the muscovite ± biotite zone. Our results suggest that pyrite recrystallization during chlorite dehydration is relatively more significant than pyrite-pyrrhotite transition in terms of Au and As release, and by extension, orogenic gold formation.
{"title":"Gold and Trace Element Release From Pyrite During Prograde Metamorphism of Carbonaceous Metapelites: Implications for Orogenic Gold Formation","authors":"Abdul Latheef Thathrampally, Rajarshi Chakravarti, Crystal Laflamme, Paul Olin","doi":"10.5382/econgeo.5168","DOIUrl":"https://doi.org/10.5382/econgeo.5168","url":null,"abstract":"The Neoproterozoic carbonaceous metapelites of the Mandhali Formation in the inner Lesser Himalaya contain diagenetic pyrite with above-background levels of Au (>200 ppb) when analyzed by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). These metapelites exhibit progressively metamorphosed zones (from south to north), ranging from the chlorite-muscovite zone (~372°C), to the muscovite ± biotite (~520°C) zone, to the greenschist-amphibolite transition (~570°C, >5 kbar). Within this regional framework, we document a hitherto unknown paragenesis of pyrite growth from diagenesis to peak metamorphism along with a localized phase of contact metamorphism, which predates regional metamorphism. A comparative assessment of pyrite trace element concentrations from the progressive metamorphic zones reveals that >80% of Au and ~65% of As is released from diagenetic pyrite during early chlorite dehydration at ~372°C, that is, in the chlorite-muscovite zone. Further into the muscovite ± biotite zone, at the terminal chlorite breakdown stage (480°–520°C), pyrite still occurs as the major sulfide with subordinate pyrrhotite. However, by this stage, ~93% of Au; ~75% of As; and ≥90% of Mo, Cd, Pb, Sb, W, Cu, Bi, Te, and Tl are released from pyrite. With the transition of pyrite to pyrrhotite (500°–550°C), almost all trace elements are released from pyrite into metamorphic fluids, except Co that is incorporated into the metamorphic pyrrhotite. This documented grain-scale elemental mobility is also reflected in bulk-rock Au assays; that is, mean Au of 9.8 ppb in the chlorite-muscovite zone and 1.1 ppb in the muscovite ± biotite zone. Our results suggest that pyrite recrystallization during chlorite dehydration is relatively more significant than pyrite-pyrrhotite transition in terms of Au and As release, and by extension, orogenic gold formation.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"35 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145674286","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The depth level at which porphyry Cu–forming magmas fractionated and exsolved mineralizing fluids is actively debated. In the classic model, extensive magma fractionation occurs in large, upper crustal magma chambers, and concomitant fluid exsolution leads to forceful expulsion of residual magmas in the form of porphyry dikes, stocks, and breccia pipes, which subsequently serve as pathways for the mineralizing fluids. In contrast, some recent studies highlighting the role of deep crustal magma fractionation in the production of fertile magmas essentially deny the existence of upper crustal magma chambers at the time of mineralization. To address this, we conducted a detailed thermobarometric investigation of 13 intermediate to felsic, porphyritic intrusive rocks related to porphyry-skarn Cu mineralization at Santa Rita and Hanover-Fierro, New Mexico, United States, representing two premineralization magmas (61–60 Ma), seven synmineralization magmas (60–58 Ma), and four late- to postmineralization magmas (58–57 Ma). For each sample, the pressure of last magma crystallization before final magma ascent to the current exposure level was reconstructed based on Al-in-hornblende barometry of small hornblende inclusions trapped within quartz phenocrysts and through titanium-in-quartz (TitaniQ) thermobarometry of the host quartz phenocrysts themselves. Since quartz is one of the last crystallizing magmatic minerals, and no significant phenocryst growth could have occurred in small dikes and stocks after final magma emplacement, quartz phenocrysts and their contained hornblende inclusions record the depth of last magma crystallization before final magma ascent. When present, hornblende phenocrysts and hornblende inclusions within other major phenocrysts were also analyzed. Both quartz and hornblende barometers return consistent average pressures of 3.2 ± 0.4 kbar for the entire suite of pre- to postmineralization magmas, corresponding to depths of 11 to 14 km. The synmineralization magmas return even more consistent average pressures of 3.1 ± 0.2 kbar, corresponding to a depth of 12 ± 1 km. The volume of the mineralizing porphyry dikes and stocks at the emplacement level is far too small to have provided all the fluids and metals required to form the observed ore deposits. Therefore, the majority of the ore-forming fluids must have originated from the magmas that crystallized at 12 ± 1 km depth. The ore deposits, conversely, formed at ~5-km paleodepth. This implies that most of the mineralizing fluids traveled an average vertical distance of ~7 km from their magmatic source to the eventual site of ore precipitation. The relatively unaltered nature and low veining degree of deeper parts of mineralized porphyry dikes and stocks suggest that the fluid transport through these intrusive bodies occurred mostly at near-solidus conditions by means of fluid percolation along grain boundaries. In summary, our results suggest that (1) a large, upper crustal pluton ex
{"title":"Depth of Magma Crystallization and Fluid Exsolution Beneath the Porphyry-Skarn Cu Deposits at Santa Rita and Hanover-Fierro, New Mexico, USA","authors":"Andreas Audétat, Jia Chang, Sean P. Gaynor","doi":"10.5382/econgeo.5197","DOIUrl":"https://doi.org/10.5382/econgeo.5197","url":null,"abstract":"The depth level at which porphyry Cu–forming magmas fractionated and exsolved mineralizing fluids is actively debated. In the classic model, extensive magma fractionation occurs in large, upper crustal magma chambers, and concomitant fluid exsolution leads to forceful expulsion of residual magmas in the form of porphyry dikes, stocks, and breccia pipes, which subsequently serve as pathways for the mineralizing fluids. In contrast, some recent studies highlighting the role of deep crustal magma fractionation in the production of fertile magmas essentially deny the existence of upper crustal magma chambers at the time of mineralization. To address this, we conducted a detailed thermobarometric investigation of 13 intermediate to felsic, porphyritic intrusive rocks related to porphyry-skarn Cu mineralization at Santa Rita and Hanover-Fierro, New Mexico, United States, representing two premineralization magmas (61–60 Ma), seven synmineralization magmas (60–58 Ma), and four late- to postmineralization magmas (58–57 Ma). For each sample, the pressure of last magma crystallization before final magma ascent to the current exposure level was reconstructed based on Al-in-hornblende barometry of small hornblende inclusions trapped within quartz phenocrysts and through titanium-in-quartz (TitaniQ) thermobarometry of the host quartz phenocrysts themselves. Since quartz is one of the last crystallizing magmatic minerals, and no significant phenocryst growth could have occurred in small dikes and stocks after final magma emplacement, quartz phenocrysts and their contained hornblende inclusions record the depth of last magma crystallization before final magma ascent. When present, hornblende phenocrysts and hornblende inclusions within other major phenocrysts were also analyzed. Both quartz and hornblende barometers return consistent average pressures of 3.2 ± 0.4 kbar for the entire suite of pre- to postmineralization magmas, corresponding to depths of 11 to 14 km. The synmineralization magmas return even more consistent average pressures of 3.1 ± 0.2 kbar, corresponding to a depth of 12 ± 1 km. The volume of the mineralizing porphyry dikes and stocks at the emplacement level is far too small to have provided all the fluids and metals required to form the observed ore deposits. Therefore, the majority of the ore-forming fluids must have originated from the magmas that crystallized at 12 ± 1 km depth. The ore deposits, conversely, formed at ~5-km paleodepth. This implies that most of the mineralizing fluids traveled an average vertical distance of ~7 km from their magmatic source to the eventual site of ore precipitation. The relatively unaltered nature and low veining degree of deeper parts of mineralized porphyry dikes and stocks suggest that the fluid transport through these intrusive bodies occurred mostly at near-solidus conditions by means of fluid percolation along grain boundaries. In summary, our results suggest that (1) a large, upper crustal pluton ex","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"198200 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145651157","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}
Eduardo Mansur, Alf Andre Orvik, Nolwenn Coint, Magdalena H. Huyskens, Trond Slagstad, Henrik Schiellerup, Sarah Dare
The Storgangen deposit is located in the Rogaland anorthosite province, Norway, and forms an E-W–trending, 4-km-long, and up to 60-m-thick sheetlike intrusion. We have combined field and petrographic observations, whole-rock and mineral compositional variations, and Sr isotope composition through a profile across the deposit. The predominant lithology is a medium-grained, magnetite-ilmenite–rich norite, which is massif at the base and becomes gradually more fine layered upward in the stratigraphy. Although ilmenite is the predominant oxide, there is a decrease in ilmenite proportions relative to magnetite upward in the stratigraphy, which leads to lower whole-rock Ti/Fe ratios in the sampled profile. Mineral compositional variations display a decrease of compatible elements in ilmenite and magnetite (e.g., Co, Cr, V) and in Mg# in orthopyroxene upward in the stratigraphy. These compositional trends support a progressive upward fractionation during the formation of the deposit. Based on the composition of oxides, we estimate that the orebody developed following only about 40% crystallization of the parental magma and preferential accumulation of Fe-Ti oxides at the bottom of the magmatic system due to gravitational segregation. The Storgangen deposit represents a staging chamber within the Rogaland anorthosite province that was part of a larger system. In situ Sr isotope ratios in plagioclase display a slight stratigraphic variation, with 87/86Srinitial varying from 0.70558 to 0.70602, which is greater than values from the host anorthosite in the vicinity of the deposit of 0.70540 to 0.70554. Thus, if contamination occurred, it may have taken place within a deeper staging chamber prior to emplacement. Alternatively, the Sr isotope signature may be inherited from variably contaminated parental primitive jotunites previously described in the Rogaland anorthosite province. Our results support that Fe-Ti-P deposits from the Rogaland anorthosite province likely define a compositional trend from high- to low-Ti/Fe systems, with the Storgangen deposit displaying relatively intermediate Ti/Fe ratios. Such a trend has been proposed for the Central Grenville province and may thus be a global feature of Fe-Ti-P deposits associated with massif-type anorthosites.
{"title":"Formation of an Fe-Ti Deposit Within an Open-System Magmatic Chamber: Insights from the Storgangen Deposit, Rogaland Anorthosite Province, Southwest Norway","authors":"Eduardo Mansur, Alf Andre Orvik, Nolwenn Coint, Magdalena H. Huyskens, Trond Slagstad, Henrik Schiellerup, Sarah Dare","doi":"10.5382/econgeo.5185","DOIUrl":"https://doi.org/10.5382/econgeo.5185","url":null,"abstract":"The Storgangen deposit is located in the Rogaland anorthosite province, Norway, and forms an E-W–trending, 4-km-long, and up to 60-m-thick sheetlike intrusion. We have combined field and petrographic observations, whole-rock and mineral compositional variations, and Sr isotope composition through a profile across the deposit. The predominant lithology is a medium-grained, magnetite-ilmenite–rich norite, which is massif at the base and becomes gradually more fine layered upward in the stratigraphy. Although ilmenite is the predominant oxide, there is a decrease in ilmenite proportions relative to magnetite upward in the stratigraphy, which leads to lower whole-rock Ti/Fe ratios in the sampled profile. Mineral compositional variations display a decrease of compatible elements in ilmenite and magnetite (e.g., Co, Cr, V) and in Mg# in orthopyroxene upward in the stratigraphy. These compositional trends support a progressive upward fractionation during the formation of the deposit. Based on the composition of oxides, we estimate that the orebody developed following only about 40% crystallization of the parental magma and preferential accumulation of Fe-Ti oxides at the bottom of the magmatic system due to gravitational segregation. The Storgangen deposit represents a staging chamber within the Rogaland anorthosite province that was part of a larger system. In situ Sr isotope ratios in plagioclase display a slight stratigraphic variation, with 87/86Srinitial varying from 0.70558 to 0.70602, which is greater than values from the host anorthosite in the vicinity of the deposit of 0.70540 to 0.70554. Thus, if contamination occurred, it may have taken place within a deeper staging chamber prior to emplacement. Alternatively, the Sr isotope signature may be inherited from variably contaminated parental primitive jotunites previously described in the Rogaland anorthosite province. Our results support that Fe-Ti-P deposits from the Rogaland anorthosite province likely define a compositional trend from high- to low-Ti/Fe systems, with the Storgangen deposit displaying relatively intermediate Ti/Fe ratios. Such a trend has been proposed for the Central Grenville province and may thus be a global feature of Fe-Ti-P deposits associated with massif-type anorthosites.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"54 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145509096","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}
Juliana de Araújo Carvalho, Adalene Moreira Silva, Catarina Labouré Bemfica Toledo, Fernando Martins Vieira Matos, Carlos Augusto de Medeiros Filho
Located in the northern sector of the Carajás mineral province, the Salobo Cu-Au deposit is the largest copper deposit in Brazil. “Salobo Profundo” (Deep Salobo) refers to the portion of the orebody beneath the final proposed pit, where deep exploration drill holes have investigated a panel approximately 700 m deep and 1,800 m long. The alteration footprint of this portion of the deposit has been documented through the integration of petrographic, hyperspectral, and geochemical data from three boreholes, totaling approximately 3,000 m. Hydrothermal zoning is characterized by albitization (Na (I)) and silicification in the distal halo, transitioning to calcic-potassic iron zones proximal to mineralization. Intense Fe metasomatism, along with potassic iron and iron alteration is most closely associated with copper and gold mineralization. Late-stage alteration is characterized by Na-Ca (II) alteration and a later type of a more intense albitic alteration (Na (II)). Hyperspectral scanning, encompassing visible-near infrared (VNIR, 380–1,000 nm), short-wave infrared (SWIR, 1,000–2,500 nm), and long-wave infrared (LWIR, 7,700–12,300 nm) wavelength ranges, has mapped the main minerals involved in the alteration processes at a centimeter-scale resolution. Minerals such as amphiboles, biotite, garnet, chlorite, quartz, and albite were identified, with garnet abundance showing a close association with copper-rich zones. The geochemical data are consistent with the characteristics of many iron oxide copper-gold (IOCG) systems, exhibiting the classic association of Fe, Cu, ± Au, along with enrichment in Ag, Bi, Co, Cs, F, Mo, Ce, La, and U. These results indicate that hyperspectral core scanning, combined with geochemical data analysis, is an effective approach for defining alteration zonation around IOCG deposits. This method enhances the characterization and refined modeling of hydrothermal zoning, providing a powerful tool for exploring for similar deposits, not only in Carajás but also in other metallogenic provinces worldwide.
{"title":"Hydrothermal Footprint of the Salobo Profundo Cu-Au Orebody, Carajás Mineral Province, Brazil","authors":"Juliana de Araújo Carvalho, Adalene Moreira Silva, Catarina Labouré Bemfica Toledo, Fernando Martins Vieira Matos, Carlos Augusto de Medeiros Filho","doi":"10.5382/econgeo.5189","DOIUrl":"https://doi.org/10.5382/econgeo.5189","url":null,"abstract":"Located in the northern sector of the Carajás mineral province, the Salobo Cu-Au deposit is the largest copper deposit in Brazil. “Salobo Profundo” (Deep Salobo) refers to the portion of the orebody beneath the final proposed pit, where deep exploration drill holes have investigated a panel approximately 700 m deep and 1,800 m long. The alteration footprint of this portion of the deposit has been documented through the integration of petrographic, hyperspectral, and geochemical data from three boreholes, totaling approximately 3,000 m. Hydrothermal zoning is characterized by albitization (Na (I)) and silicification in the distal halo, transitioning to calcic-potassic iron zones proximal to mineralization. Intense Fe metasomatism, along with potassic iron and iron alteration is most closely associated with copper and gold mineralization. Late-stage alteration is characterized by Na-Ca (II) alteration and a later type of a more intense albitic alteration (Na (II)). Hyperspectral scanning, encompassing visible-near infrared (VNIR, 380–1,000 nm), short-wave infrared (SWIR, 1,000–2,500 nm), and long-wave infrared (LWIR, 7,700–12,300 nm) wavelength ranges, has mapped the main minerals involved in the alteration processes at a centimeter-scale resolution. Minerals such as amphiboles, biotite, garnet, chlorite, quartz, and albite were identified, with garnet abundance showing a close association with copper-rich zones. The geochemical data are consistent with the characteristics of many iron oxide copper-gold (IOCG) systems, exhibiting the classic association of Fe, Cu, ± Au, along with enrichment in Ag, Bi, Co, Cs, F, Mo, Ce, La, and U. These results indicate that hyperspectral core scanning, combined with geochemical data analysis, is an effective approach for defining alteration zonation around IOCG deposits. This method enhances the characterization and refined modeling of hydrothermal zoning, providing a powerful tool for exploring for similar deposits, not only in Carajás but also in other metallogenic provinces worldwide.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"31 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145509127","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}
Zarshuran is the largest gold deposit in the Middle East. However, the structural controls and ore-forming processes at Zarshuran remain poorly understood. This study presents new geologic mapping results, detailed descriptions of ore textures, and calcite in situ U-Pb dating and thermochronological data to propose a new genetic model addressing the knowledge gap. New field mapping results demonstrate that the Zarshuran deposit is hosted in the Iman Khan Complex, which exhibits abundant ductile fabrics, and gold mineralization is spatially associated with the Zarshuran fault separating the Neoproterozoic Iman Khan and Cambrian Chaldagh units in its footwall from the Cambrian Zarshuran unit and Oligocene-Miocene Qom Formation in its hanging wall. Ore textures include syntectonic gold-bearing pyrite veins around felsic porphyroclasts, syntectonic cata-clastic flow around lenses, syntaxial euhedral calcite, and pyrite veins filled in brittle fracture and stratabound within the Qom Formation. Muscovite-quartz schist of the Iman Khan Complex underwent peak metamorphism of greenschist facies at pressure-temperature (P-T) conditions of 0.20 to 0.44 GPa and 372° to 446°C as constrained by chemical compositions of muscovite. The 40Ar/39Ar dating of syntectonic muscovite yielded a plateau age of 20.59 ± 0.32 Ma. In situ U-Pb dating of calcite associated with gold-bearing pyrite yields 14.5 ± 2.0 Ma. Apatite (U-Th)/He ages range from 12.73 ± 0.77 to 5.55 ± 0.46 Ma. These ages, combined with HeFTy thermal modeling, suggest that the Zarshuran deposit underwent a slow cooling stage from 20.6 to 14.5 Ma, a rapid cooling stage from 14.5 to 9 Ma, and an extremely slow cooling stage at <9 Ma. We propose that the Iman Khan Complex is an incipient metamorphic core complex (MCC), and gold mineralization occurred in the ductile and brittle deformation stages (20.6–14.5 Ma) associated with exhumation of the Iman Khan MCC. Other MCCs in the Tethyan metallogenic belt may be potential gold exploration targets.
{"title":"Generation of the Zarshuran Gold Deposit in Northwest Iran Triggered by Exhumation of the Iman Khan Metamorphic Core Complex","authors":"Hongrui Zhang, Zhiming Yang, Pinghua Liu, Shu Yang, Mehraj Aghazadeh, Zengqian Hou, Tiannan Yang, Zahra Badrzadeh","doi":"10.5382/econgeo.5192","DOIUrl":"https://doi.org/10.5382/econgeo.5192","url":null,"abstract":"Zarshuran is the largest gold deposit in the Middle East. However, the structural controls and ore-forming processes at Zarshuran remain poorly understood. This study presents new geologic mapping results, detailed descriptions of ore textures, and calcite in situ U-Pb dating and thermochronological data to propose a new genetic model addressing the knowledge gap. New field mapping results demonstrate that the Zarshuran deposit is hosted in the Iman Khan Complex, which exhibits abundant ductile fabrics, and gold mineralization is spatially associated with the Zarshuran fault separating the Neoproterozoic Iman Khan and Cambrian Chaldagh units in its footwall from the Cambrian Zarshuran unit and Oligocene-Miocene Qom Formation in its hanging wall. Ore textures include syntectonic gold-bearing pyrite veins around felsic porphyroclasts, syntectonic cata-clastic flow around lenses, syntaxial euhedral calcite, and pyrite veins filled in brittle fracture and stratabound within the Qom Formation. Muscovite-quartz schist of the Iman Khan Complex underwent peak metamorphism of greenschist facies at pressure-temperature (P-T) conditions of 0.20 to 0.44 GPa and 372° to 446°C as constrained by chemical compositions of muscovite. The 40Ar/39Ar dating of syntectonic muscovite yielded a plateau age of 20.59 ± 0.32 Ma. In situ U-Pb dating of calcite associated with gold-bearing pyrite yields 14.5 ± 2.0 Ma. Apatite (U-Th)/He ages range from 12.73 ± 0.77 to 5.55 ± 0.46 Ma. These ages, combined with HeFTy thermal modeling, suggest that the Zarshuran deposit underwent a slow cooling stage from 20.6 to 14.5 Ma, a rapid cooling stage from 14.5 to 9 Ma, and an extremely slow cooling stage at &lt;9 Ma. We propose that the Iman Khan Complex is an incipient metamorphic core complex (MCC), and gold mineralization occurred in the ductile and brittle deformation stages (20.6–14.5 Ma) associated with exhumation of the Iman Khan MCC. Other MCCs in the Tethyan metallogenic belt may be potential gold exploration targets.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"183 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145509094","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}
Neal E. Mankins, John L. Muntean, Matthieu Harlaux, Matthew Mann, Robert A. Creaser
The Robertson deposit, formerly known as Tenabo, is an Eocene reduced intrusion-related gold deposit located 5 km north of Pipeline, a world-class 20+ Moz Carlin-type gold deposit in the northern Shoshone Range, Nevada. This study is the first in-depth examination of Robertson describing gold mineralization, hydrothermal alteration, petrology of the intrusive rocks, and geochronology of the magmatic and hydrothermal events. We present six new U/Pb zircon ages of intrusive phases, one vein-hosted molybdenite Re/Os age, and one hydrothermal orthoclase 40Ar/39Ar age. Gold mineralization is spatially and temporally related to an intrusive complex referred to as the Tenabo stock, which is composed of successive intrusive phases including an early ilmenite-bearing diorite, andesite dikes, hypabyssal dacitic porphyry dikes, composite ilmenite-bearing granodiorite, granitic porphyry dikes, and hypabyssal rhyolitic dikes. Emplacement of the Tenabo stock resulted in contact metamorphism of the host siliciclastic rocks, yielding quartz, biotite, and calc-silicate hornfels that formed an aureole up to 1 km from the stock. Through petrographic observations and geochemical analyses, distinct alteration assemblages are identified, encompassing sodic-calcic, potassic, calcic, sericitic, and chloritic alteration. Petrographic observations of veins at Robertson indicate the succession of three main stages referred to as (1) pregold, (2) syngold, and (3) postgold. The pregold stage consists of barren quartz veins, potassic alteration veins comprising biotite veinlets and quartz-K-feldspar, quartz-arsenopyrite, quartz-chalcopyrite, and quartz-molybdenite veins. The syngold stage is composed of quartz-gold ± Bi-Te-Se-Pb-Ag–bearing sulfosalt veins containing native visible gold observed as single grains in quartz and/or rimming pyrrhotite, arsenopyrite, chalcopyrite, and loellingite (FeAs2) grains. The postgold veins encompass pyrite ± quartz, quartz-calcite-polymetallic sulfide veins with Pb-Zn-Sb-Ag-Sn base metal sulfides, bull quartz veins, and calcite veins. Crosscutting relationships, along with U/Pb zircon dating of intrusive phases, Re/Os molybdenite dating, and 40Ar/39Ar orthoclase dating, indicate two distinct magmatic phases at Robertson. Phase one is an early phase associated with hydrothermal activity, and phase two is a late phase associated with hypabyssal rhyolitic dikes. The period of gold mineralization at Robertson is linked with the initial phase of magmatism and subsequent hydrothermal activity, which was found to occur between 39.6 and 39.0 Ma. This study demonstrates that gold mineralization is spatially and temporally related to the emplacement of an upper Eocene 39.6 Ma reduced ilmenite-bearing intrusive complex into Paleozoic siliciclastic sedimentary rocks. This produced a high-tonnage, low-grade gold deposit characterized by an Au-As-Bi-Te-Cu metal association. Mineral assemblages observed at Robertson, comprising native bismuth, Bi sulfosal
Robertson矿床，以前称为Tenabo，是一个始新世减少侵入体相关的金矿床，位于内华达州肖肖尼山脉北部的世界级的20moz卡林型金矿床Pipeline以北5公里处。本研究首次深入考察了Robertson对金矿化、热液蚀变、侵入岩岩石学以及岩浆和热液事件年代学的描述。我们获得了6个新的侵入相U/Pb锆石年龄、1个脉状辉钼矿Re/Os年龄和1个热液正长石40Ar/39Ar年龄。金矿成矿在空间和时间上与Tenabo杂岩有关，该杂岩由早期含钛闪长岩、安山岩脉、浅成英质斑岩脉、复合含钛花岗闪长岩、花岗斑岩脉和浅成流纹岩脉等连续侵入期组成。Tenabo岩石的侵位导致了寄主硅质岩石的接触变质作用，产生了石英、黑云母和钙硅酸盐角砾岩，这些角砾岩形成了距离岩石1公里的光圈。通过岩石学观察和地球化学分析，确定了不同的蚀变组合，包括钠钙、钾、钙、绢云母和绿泥石蚀变。罗伯逊岩脉的岩石学观察表明，三个主要阶段依次为(1)前金阶段、(2)同金阶段和(3)后金阶段。前金期由光秃秃的石英脉、由黑云母脉和石英钾长石、石英毒砂、石英黄铜矿和石英辉钼矿脉组成的钾蚀变脉组成。同金阶段由石英-金±bi - te - se - pb - ag -含亚硫酸盐脉体组成，其中含有可见的天然金，在石英和/或边缘磁黄铁矿、毒砂、黄铜矿和辉绿石（FeAs2）颗粒中以单粒形式存在。后金脉包括黄铁矿±石英脉、含Pb-Zn-Sb-Ag-Sn贱金属硫化物的石英-方解石-多金属硫化物脉、牛石英脉和方解石脉。通过对侵入相U/Pb锆石定年、Re/Os辉钼矿定年和40Ar/39Ar正长石定年的分析，表明Robertson地区存在两个不同的岩浆相。第一阶段为早期热液活动阶段，第二阶段为晚期浅成流纹岩岩脉阶段。罗伯逊金矿成矿期与岩浆活动初始阶段及随后的热液活动有关，成矿期在39.6 ~ 39.0 Ma之间。研究表明，上始新统39.6 Ma含钛铁矿的还原侵入杂岩侵位于古生代硅屑沉积岩中，与金矿成矿具有时空关系。形成了以Au-As-Bi-Te-Cu金属组合为特征的高吨位、低品位金矿床。在Robertson观测到的矿物组合，包括天然铋、铋磺酸盐、毒砂、磁黄铁矿和钙辉石（FeAs2），具有低硫化和氧化状态的特征，类似于全球描述的与侵入体相关的减少的金矿床和金夕卡岩。
{"title":"Paragenetic Evolution of the Robertson Deposit: Eocene Reduced Intrusion-Related Gold Deposit in the Northern Shoshone Range, Nevada","authors":"Neal E. Mankins, John L. Muntean, Matthieu Harlaux, Matthew Mann, Robert A. Creaser","doi":"10.5382/econgeo.5191","DOIUrl":"https://doi.org/10.5382/econgeo.5191","url":null,"abstract":"The Robertson deposit, formerly known as Tenabo, is an Eocene reduced intrusion-related gold deposit located 5 km north of Pipeline, a world-class 20+ Moz Carlin-type gold deposit in the northern Shoshone Range, Nevada. This study is the first in-depth examination of Robertson describing gold mineralization, hydrothermal alteration, petrology of the intrusive rocks, and geochronology of the magmatic and hydrothermal events. We present six new U/Pb zircon ages of intrusive phases, one vein-hosted molybdenite Re/Os age, and one hydrothermal orthoclase 40Ar/39Ar age. Gold mineralization is spatially and temporally related to an intrusive complex referred to as the Tenabo stock, which is composed of successive intrusive phases including an early ilmenite-bearing diorite, andesite dikes, hypabyssal dacitic porphyry dikes, composite ilmenite-bearing granodiorite, granitic porphyry dikes, and hypabyssal rhyolitic dikes. Emplacement of the Tenabo stock resulted in contact metamorphism of the host siliciclastic rocks, yielding quartz, biotite, and calc-silicate hornfels that formed an aureole up to 1 km from the stock. Through petrographic observations and geochemical analyses, distinct alteration assemblages are identified, encompassing sodic-calcic, potassic, calcic, sericitic, and chloritic alteration. Petrographic observations of veins at Robertson indicate the succession of three main stages referred to as (1) pregold, (2) syngold, and (3) postgold. The pregold stage consists of barren quartz veins, potassic alteration veins comprising biotite veinlets and quartz-K-feldspar, quartz-arsenopyrite, quartz-chalcopyrite, and quartz-molybdenite veins. The syngold stage is composed of quartz-gold ± Bi-Te-Se-Pb-Ag–bearing sulfosalt veins containing native visible gold observed as single grains in quartz and/or rimming pyrrhotite, arsenopyrite, chalcopyrite, and loellingite (FeAs2) grains. The postgold veins encompass pyrite ± quartz, quartz-calcite-polymetallic sulfide veins with Pb-Zn-Sb-Ag-Sn base metal sulfides, bull quartz veins, and calcite veins. Crosscutting relationships, along with U/Pb zircon dating of intrusive phases, Re/Os molybdenite dating, and 40Ar/39Ar orthoclase dating, indicate two distinct magmatic phases at Robertson. Phase one is an early phase associated with hydrothermal activity, and phase two is a late phase associated with hypabyssal rhyolitic dikes. The period of gold mineralization at Robertson is linked with the initial phase of magmatism and subsequent hydrothermal activity, which was found to occur between 39.6 and 39.0 Ma. This study demonstrates that gold mineralization is spatially and temporally related to the emplacement of an upper Eocene 39.6 Ma reduced ilmenite-bearing intrusive complex into Paleozoic siliciclastic sedimentary rocks. This produced a high-tonnage, low-grade gold deposit characterized by an Au-As-Bi-Te-Cu metal association. Mineral assemblages observed at Robertson, comprising native bismuth, Bi sulfosal","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"19 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145509126","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}
Hojat Shirmard, Ehsan Farahbakhsh, Karol Czarnota, R. Dietmar Müller
Internal structures and discontinuities within cratons are economically significant due to their history of tectonic reactivation from varying intraplate stress fields, which open pathways for fluid flow and facilitate mineral deposition. However, the complex overprinting tectonic processes that make cratons prospective can also lead to uncertainty regarding their internal geometries. To address this, we take a fresh perspective on these systems by using a data-driven approach to better delineate their structures and mineral potential, focusing on the Gawler craton in South Australia. We generate over 400 magnetic and gravity anomaly features and use them as input for clustering algorithms to map clusters that represent crustal structures. We compare the efficiency of two clustering methods—self-organizing map and K-means—in outlining internal craton structures at shallow (<5 km) and deep (5–30 km) crustal depths. The results are evaluated using three performance metrics alongside geologic maps. We focus on all metallic mineral systems, including mafic-ultramafic intrusions, for Co, Cr, and Ni and intrusion-related and sediment-hosted systems for Au, Cu, Fe, and Mn. Our findings indicate that most metallic mineral occurrences, particularly significant deposits, form along the boundaries of these clusters. Approximately 80% of mineral occurrences are within 7 km of deep craton structures, and almost all follow shallow and deep structures occupying less than one-third of the study area. Our approach can be easily applied to any craton at any scale and supplemented with other geophysical data, such as magnetotelluric and regional seismic tomography data, to generate more comprehensive and reliable results.
{"title":"Automated Detection of Mineralization-Related Craton Structures Using Geophysical Data and Unsupervised Machine Learning","authors":"Hojat Shirmard, Ehsan Farahbakhsh, Karol Czarnota, R. Dietmar Müller","doi":"10.5382/econgeo.5188","DOIUrl":"https://doi.org/10.5382/econgeo.5188","url":null,"abstract":"Internal structures and discontinuities within cratons are economically significant due to their history of tectonic reactivation from varying intraplate stress fields, which open pathways for fluid flow and facilitate mineral deposition. However, the complex overprinting tectonic processes that make cratons prospective can also lead to uncertainty regarding their internal geometries. To address this, we take a fresh perspective on these systems by using a data-driven approach to better delineate their structures and mineral potential, focusing on the Gawler craton in South Australia. We generate over 400 magnetic and gravity anomaly features and use them as input for clustering algorithms to map clusters that represent crustal structures. We compare the efficiency of two clustering methods—self-organizing map and K-means—in outlining internal craton structures at shallow (&lt;5 km) and deep (5–30 km) crustal depths. The results are evaluated using three performance metrics alongside geologic maps. We focus on all metallic mineral systems, including mafic-ultramafic intrusions, for Co, Cr, and Ni and intrusion-related and sediment-hosted systems for Au, Cu, Fe, and Mn. Our findings indicate that most metallic mineral occurrences, particularly significant deposits, form along the boundaries of these clusters. Approximately 80% of mineral occurrences are within 7 km of deep craton structures, and almost all follow shallow and deep structures occupying less than one-third of the study area. Our approach can be easily applied to any craton at any scale and supplemented with other geophysical data, such as magnetotelluric and regional seismic tomography data, to generate more comprehensive and reliable results.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"28 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145383550","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Zhangmajing U-Mo deposit, located in the northern margin of the North China Craton, is unusual because both U (ca. 5,000 tonnes at 0.1–0.3% U) and Mo (0.11 million tonnes at 0.339% Mo) in this deposit are of economic interest, and Mo is mainly hosted in jordisite. In this study, thallium enrichment is recognized for the first time at Zhangmajing. This deposit is hosted within rhyolite porphyry and volcanic rocks of the Zhangjiakou Formation and surrounded by the Paleoproterozoic basement. Zircon U-Pb dating indicates that the volcanic-subvolcanic rocks were emplaced during the Early Cretaceous (141–139 Ma). Zircon Hf isotopic results show negative εHf(t) values of –20.6 to –10.9, with two-stage model ages of 1.9 to 2.5 Ga, suggesting that these rocks were dominantly derived from partial melt of Paleoproterozoic crustal materials. Whole-rock geochemical analyses indicate that the ores have highly anomalous Tl concentrations (avg 151 ppm), which are positively correlated with Mo concentrations. Ore minerals at Zhangmajing consist mostly of jordisite, pitchblende, pyrite, sphalerite, and galena. Jordisite has the highest Tl concentrations (3,307–9,921 ppm), whereas those in pyrite and sphalerite are below 2,000 ppm. Pyrite, jordisite, and sphalerite have δ34S values ranging from –16.5 to 0.3‰, suggesting that the sulfur was probably derived from a mixing of sources from the Paleoproterozoic basement and volcanic-subvolcanic rocks. This study suggests that the unusual element association of U, Mo, and Tl in Zhangmajing is the result of source rocks that are enriched in these elements, and that the metals were mainly sourced from the rocks during fluid-rock interaction and subsequently precipitated at moderate temperatures (~200°C).
{"title":"New Recognition of Thallium Enrichment in the Zhangmajing Deposit, Northeast China, with Implications for the Genesis of Volcanic-Related U-Mo-Tl Mineralization","authors":"Long Zhang, Fangyue Wang, Taofa Zhou, Zhenyu Chen","doi":"10.5382/econgeo.5190","DOIUrl":"https://doi.org/10.5382/econgeo.5190","url":null,"abstract":"The Zhangmajing U-Mo deposit, located in the northern margin of the North China Craton, is unusual because both U (ca. 5,000 tonnes at 0.1–0.3% U) and Mo (0.11 million tonnes at 0.339% Mo) in this deposit are of economic interest, and Mo is mainly hosted in jordisite. In this study, thallium enrichment is recognized for the first time at Zhangmajing. This deposit is hosted within rhyolite porphyry and volcanic rocks of the Zhangjiakou Formation and surrounded by the Paleoproterozoic basement. Zircon U-Pb dating indicates that the volcanic-subvolcanic rocks were emplaced during the Early Cretaceous (141–139 Ma). Zircon Hf isotopic results show negative εHf(t) values of –20.6 to –10.9, with two-stage model ages of 1.9 to 2.5 Ga, suggesting that these rocks were dominantly derived from partial melt of Paleoproterozoic crustal materials. Whole-rock geochemical analyses indicate that the ores have highly anomalous Tl concentrations (avg 151 ppm), which are positively correlated with Mo concentrations. Ore minerals at Zhangmajing consist mostly of jordisite, pitchblende, pyrite, sphalerite, and galena. Jordisite has the highest Tl concentrations (3,307–9,921 ppm), whereas those in pyrite and sphalerite are below 2,000 ppm. Pyrite, jordisite, and sphalerite have δ34S values ranging from –16.5 to 0.3‰, suggesting that the sulfur was probably derived from a mixing of sources from the Paleoproterozoic basement and volcanic-subvolcanic rocks. This study suggests that the unusual element association of U, Mo, and Tl in Zhangmajing is the result of source rocks that are enriched in these elements, and that the metals were mainly sourced from the rocks during fluid-rock interaction and subsequently precipitated at moderate temperatures (~200°C).","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"114 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145383549","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}
Jie Yu, Martin Hand, Dylan Gully, Dillon Brown, Laura J. Morrissey, Wei Hong, Chris Clark
Breccia-hosted and magnetite-dominated Cu mineralization has been recently discovered in the Peake and Denison Domain, northeastern Gawler craton, Australia. The iron oxide copper-gold (IOCG)-style alteration and mineralization and proximity to the world-class Olympic and Cloncurry IOCG provinces highlight the prospectivity potential for IOCG and affiliated deposits in the Peake and Denison Domain. New zircon-titanite-apatite U-Pb and apatite Lu-Hf age data from the Wills and Mawson prospects in the Peake and Denison region are presented to construct a geochronological framework for the new Cu district in southern Australia. Zircons from the host quartzofeldspathic gneiss define a major peak at ca. 1780 Ma, two shoulder peaks at ca. 1740 and ca. 1710 Ma, and minor peaks at ca. 1850 and ca. 1900 Ma. Titanite U-Pb and apatite Lu-Hf geochronology reveals an early-stage magnetite-actinolite-titanite-apatite alteration at ca. 1530 Ma for the Wills prospect, coincident with the coeval mineralization in the Cloncurry and Mary Kathleen IOCG districts of the Mount Isa inlier. The Wills prospect subsequently underwent ca. 1500 Ma ductile deformation. Apatite Lu-Hf and U-Pb geochronology from both prospects constrain vein-type and breccia-type Cu mineralization at ca. 1465 Ma, broadly coeval with regional barren Na-Ca alteration in the Peake and Denison Domain and barren potassic alteration in the Cloncurry IOCG District. The ca. 1465 Ma Cu mineralization is equivalent to the recently discovered later-stage Cu mineralization in the northern Olympic Cu-Au Province and potentially coincided with the rifting of Proto-Australia and the supercontinent Nuna in the early Mesoproterozoic.
{"title":"A New Cu Province in Southern Australia? Geochronological Framework of Potential Iron Oxide Copper-Gold Systems in Northeastern Gawler Craton","authors":"Jie Yu, Martin Hand, Dylan Gully, Dillon Brown, Laura J. Morrissey, Wei Hong, Chris Clark","doi":"10.5382/econgeo.5184","DOIUrl":"https://doi.org/10.5382/econgeo.5184","url":null,"abstract":"Breccia-hosted and magnetite-dominated Cu mineralization has been recently discovered in the Peake and Denison Domain, northeastern Gawler craton, Australia. The iron oxide copper-gold (IOCG)-style alteration and mineralization and proximity to the world-class Olympic and Cloncurry IOCG provinces highlight the prospectivity potential for IOCG and affiliated deposits in the Peake and Denison Domain. New zircon-titanite-apatite U-Pb and apatite Lu-Hf age data from the Wills and Mawson prospects in the Peake and Denison region are presented to construct a geochronological framework for the new Cu district in southern Australia. Zircons from the host quartzofeldspathic gneiss define a major peak at ca. 1780 Ma, two shoulder peaks at ca. 1740 and ca. 1710 Ma, and minor peaks at ca. 1850 and ca. 1900 Ma. Titanite U-Pb and apatite Lu-Hf geochronology reveals an early-stage magnetite-actinolite-titanite-apatite alteration at ca. 1530 Ma for the Wills prospect, coincident with the coeval mineralization in the Cloncurry and Mary Kathleen IOCG districts of the Mount Isa inlier. The Wills prospect subsequently underwent ca. 1500 Ma ductile deformation. Apatite Lu-Hf and U-Pb geochronology from both prospects constrain vein-type and breccia-type Cu mineralization at ca. 1465 Ma, broadly coeval with regional barren Na-Ca alteration in the Peake and Denison Domain and barren potassic alteration in the Cloncurry IOCG District. The ca. 1465 Ma Cu mineralization is equivalent to the recently discovered later-stage Cu mineralization in the northern Olympic Cu-Au Province and potentially coincided with the rifting of Proto-Australia and the supercontinent Nuna in the early Mesoproterozoic.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"45 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145314690","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}
Eric D. Anderson, Brian D. Rodriguez, Karen Lund, Christopher Dail, Bill Breen
Aeromagnetic and magnetotelluric (MT) data are used to better understand the geology and mineral resources near the Stibnite-Yellow Pine mining district in central Idaho. The reduced-to-pole (RTP) transformation of regional-scale aeromagnetic data shows that allochthonous island-arc rocks west of the Salmon River suture are significantly more magnetic than the Laurentian continental rocks east of the suture and that the granitoids of the Idaho batholith have moderate to low magnetization in both early, metaluminous, and late, peraluminous phases. Application of tilt derivative to aeromagnetic data highlights major crustal-scale structures. The 5-km upward continued magnetic data indicate island-arc rocks have deep magnetic sources. The 110-km-long MT profile images resistivity structure to depths around 30 km. At shallow depths, resistivity corresponds to mapped geologic units, with moderate resistivities underlying volcanic and roof-pendant metasedimentary rocks and moderate to high resistivities occurring beneath the Idaho batholith. Crustal-scale moderate resistivities beneath the suture image the results of tectonomagmatic processes that accompanied suturing and translating allochthonous terranes. Low resistivity values beneath and fringing the batholith are derived from metasedimentary rocks that may have served as a melt source and reductant during melt generation and provided metals during later ore formation. In the Stibnite-Yellow Pine mining district, a high-resolution aeromagnetic compilation is shown to correlate with mapped lithologies and mineral deposit-related structures. The RTP transform distinguishes magnetic and nonmagnetic granitoid phases of the Idaho batholith. The tilt derivative highlights metasedimentary rocks, some of which are favorable ore hosts. The Meadow Creek fault hosts the Stibnite and Hangar Flats deposits and is imaged as a magnetic low due to hydrothermal alteration. Reconstructions of magnetic anomaly offsets and orebodies indicate around 3 km of post-95 Ma dextral separation, with some or all of the offset inferred to postdate the main Au mineralization episode (61–66 Ma).
{"title":"Aeromagnetic and Magnetotelluric Imaging of West-Central Idaho and the Stibnite-Yellow Pine Mining District: A Regional to District Perspective","authors":"Eric D. Anderson, Brian D. Rodriguez, Karen Lund, Christopher Dail, Bill Breen","doi":"10.5382/econgeo.5182","DOIUrl":"https://doi.org/10.5382/econgeo.5182","url":null,"abstract":"Aeromagnetic and magnetotelluric (MT) data are used to better understand the geology and mineral resources near the Stibnite-Yellow Pine mining district in central Idaho. The reduced-to-pole (RTP) transformation of regional-scale aeromagnetic data shows that allochthonous island-arc rocks west of the Salmon River suture are significantly more magnetic than the Laurentian continental rocks east of the suture and that the granitoids of the Idaho batholith have moderate to low magnetization in both early, metaluminous, and late, peraluminous phases. Application of tilt derivative to aeromagnetic data highlights major crustal-scale structures. The 5-km upward continued magnetic data indicate island-arc rocks have deep magnetic sources. The 110-km-long MT profile images resistivity structure to depths around 30 km. At shallow depths, resistivity corresponds to mapped geologic units, with moderate resistivities underlying volcanic and roof-pendant metasedimentary rocks and moderate to high resistivities occurring beneath the Idaho batholith. Crustal-scale moderate resistivities beneath the suture image the results of tectonomagmatic processes that accompanied suturing and translating allochthonous terranes. Low resistivity values beneath and fringing the batholith are derived from metasedimentary rocks that may have served as a melt source and reductant during melt generation and provided metals during later ore formation. In the Stibnite-Yellow Pine mining district, a high-resolution aeromagnetic compilation is shown to correlate with mapped lithologies and mineral deposit-related structures. The RTP transform distinguishes magnetic and nonmagnetic granitoid phases of the Idaho batholith. The tilt derivative highlights metasedimentary rocks, some of which are favorable ore hosts. The Meadow Creek fault hosts the Stibnite and Hangar Flats deposits and is imaged as a magnetic low due to hydrothermal alteration. Reconstructions of magnetic anomaly offsets and orebodies indicate around 3 km of post-95 Ma dextral separation, with some or all of the offset inferred to postdate the main Au mineralization episode (61–66 Ma).","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"10 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-10-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145289096","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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