Lei Liu, Chuntao Yin, Yasir Shaheen Khalil, Jun Hong, Jilu Feng, Huishan Zhang
The Chagai porphyry Cu belt in Pakistan is an important metallogenic terrain extending approximately 400 km in an east-west direction. Most of the known porphyry Cu deposits, such as the world-class Reko Diq deposit and Saindak deposit, are located in the western Chagai belt. In this study, the ZY1-02D hyperspectral data acquired by a recently launched spaceborne imaging spectrometer with 166 bands within a 0.4- to 2.5-μm spectral region were used to map mineral information over 8,000 km2 for exploring potential targets of porphyry Cu mineralization in the western Chagai belt. False color composite, spectral angle mapper, and wavelength position mapping methods were used in this research leading to the identification of a series of alteration minerals (including muscovite [sericite], kaolinite, alunite, epidote, chlorite, and calcite) from ZY1-02D data. The alteration mineral maps derived from ZY1-02D data match well with the known deposits and field inspections. Twenty-three new targets were identified as potential porphyry Cu mineralization targets for further exploration in the study area. Three targets, north of Saindak, Koh-i-Sultan, and Durban Chah, and six alteration sites in the southwest of Durban Chah, were inspected in the field, and Cu-Au mineralization was confirmed in all these inspected areas. As the ZY1-02D hyperspectral data covers most of the land area of the earth, this study provides new insights for mineral exploration and lithologic mapping in remote regions.
{"title":"Alteration Mapping for Porphyry Cu Targeting in the Western Chagai Belt, Pakistan, Using ZY1-02D Spaceborne Hyperspectral Data","authors":"Lei Liu, Chuntao Yin, Yasir Shaheen Khalil, Jun Hong, Jilu Feng, Huishan Zhang","doi":"10.5382/econgeo.5045","DOIUrl":"https://doi.org/10.5382/econgeo.5045","url":null,"abstract":"The Chagai porphyry Cu belt in Pakistan is an important metallogenic terrain extending approximately 400 km in an east-west direction. Most of the known porphyry Cu deposits, such as the world-class Reko Diq deposit and Saindak deposit, are located in the western Chagai belt. In this study, the ZY1-02D hyperspectral data acquired by a recently launched spaceborne imaging spectrometer with 166 bands within a 0.4- to 2.5-μm spectral region were used to map mineral information over 8,000 km<sup>2</sup> for exploring potential targets of porphyry Cu mineralization in the western Chagai belt. False color composite, spectral angle mapper, and wavelength position mapping methods were used in this research leading to the identification of a series of alteration minerals (including muscovite [sericite], kaolinite, alunite, epidote, chlorite, and calcite) from ZY1-02D data. The alteration mineral maps derived from ZY1-02D data match well with the known deposits and field inspections. Twenty-three new targets were identified as potential porphyry Cu mineralization targets for further exploration in the study area. Three targets, north of Saindak, Koh-i-Sultan, and Durban Chah, and six alteration sites in the southwest of Durban Chah, were inspected in the field, and Cu-Au mineralization was confirmed in all these inspected areas. As the ZY1-02D hyperspectral data covers most of the land area of the earth, this study provides new insights for mineral exploration and lithologic mapping in remote regions.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"26 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140096855","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}
Porphyry deposits in magmatic arcs form coincident with changes to steady-state oceanic subduction conditions, such as changes in plate convergence rate and vector or angle of subduction. However, it remains unclear whether such processes also operated during formation of postsubduction porphyry deposits. The Yulong magmatic belt in the eastern Tibetan Plateau consists of middle to late Eocene igneous rocks (~51–35 Ma) that formed during the India-Asia collision, whereas all known porphyry deposits are associated with late Eocene rocks (43–35 Ma). A synthesis of new and published geochemical data shows marked variations from the middle to late Eocene, including increasing whole-rock La/Yb, Sr/Y, and EuN/EuN* values, as well as zircon EuN/EuN* values. These geochemical variations, together with petrographic observations, indicate a transition from plagioclase-dominated to amphibole-dominated fractionation from the middle to late Eocene.Coupled changes of magma compositions and porphyry Cu metallogeny from the middle to late Eocene coincided with, or were slightly preceded by, the onset of regional uplift and crustal thickening, triggered by the India-Asia hard collision and rapid deceleration of the India-Asia convergence rate at ca. 50 to 44 Ma. Crustal thickening may have caused prolonged magma differentiation at greater depths and accumulation of dissolved H2O, both of which contributed to amphibole-dominated fractionation and generation of hydrous melt that are prospective for porphyry Cu mineralization. Our study highlights the importance of tectonic changes in the formation of the Yulong and other postsubduction porphyry Cu belts—a scenario similar to that operated in subduction-related settings such as the Andes.
{"title":"Linking Porphyry Cu Formation to Tectonic Change in Postsubduction Settings: A Case Study from the Giant Yulong Belt, Eastern Tibet","authors":"Ming-Liang Huang, Xian-Wu Bi, Rui-Zhong Hu, Massimo Chiaradia, Jing-Jing Zhu, Lei-Luo Xu, Zong-Yong Yang","doi":"10.5382/econgeo.5052","DOIUrl":"https://doi.org/10.5382/econgeo.5052","url":null,"abstract":"Porphyry deposits in magmatic arcs form coincident with changes to steady-state oceanic subduction conditions, such as changes in plate convergence rate and vector or angle of subduction. However, it remains unclear whether such processes also operated during formation of postsubduction porphyry deposits. The Yulong magmatic belt in the eastern Tibetan Plateau consists of middle to late Eocene igneous rocks (~51–35 Ma) that formed during the India-Asia collision, whereas all known porphyry deposits are associated with late Eocene rocks (43–35 Ma). A synthesis of new and published geochemical data shows marked variations from the middle to late Eocene, including increasing whole-rock La/Yb, Sr/Y, and Eu<sub>N</sub>/Eu<sub>N</sub>* values, as well as zircon Eu<sub>N</sub>/Eu<sub>N</sub>* values. These geochemical variations, together with petrographic observations, indicate a transition from plagioclase-dominated to amphibole-dominated fractionation from the middle to late Eocene.Coupled changes of magma compositions and porphyry Cu metallogeny from the middle to late Eocene coincided with, or were slightly preceded by, the onset of regional uplift and crustal thickening, triggered by the India-Asia hard collision and rapid deceleration of the India-Asia convergence rate at ca. 50 to 44 Ma. Crustal thickening may have caused prolonged magma differentiation at greater depths and accumulation of dissolved H<sub>2</sub>O, both of which contributed to amphibole-dominated fractionation and generation of hydrous melt that are prospective for porphyry Cu mineralization. Our study highlights the importance of tectonic changes in the formation of the Yulong and other postsubduction porphyry Cu belts—a scenario similar to that operated in subduction-related settings such as the Andes.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"20 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140096930","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}
R.E. Ernst, H. El Bilali, K. L. Buchan, S.M. Jowitt
A 90° change in stress orientation has been previously proposed as the trigger for the final emplacement of the world-class Norilsk-Talnakh magmatic sulfide mineralization via the migration of accumulated sulfide melts from elsewhere within the plumbing system of the Siberian Traps large igneous province (LIP). We propose that this stress change does not require and was not triggered by a distal change in plate boundary stresses, but instead can be explained both temporally and spatially by stress changes recorded in the dike swarm patterns of the Siberian Traps LIP, namely the transition from a giant radiating dike swarm (associated with mantle plume uplift) to a giant circumferential swarm (linked to flattening of the plume head). The mantle plume stress-related changes recorded by these dike swarms, rather than distal plate boundary stress changes, were therefore most likely the trigger for the emplacement of the Norilsk-Talnakh mineralization. Other LIPs that have both giant radiating and circumferential dike swarms most likely reflect similar major and rapid changes in stress orientation, indicating that mantle plume-induced stress changes revealed by dike swarms should be considered an additional tool in magmatic sulfide exploration.
{"title":"PLUME-GENERATED 90° STRESS CHANGE LINKED TO TRANSITION FROM RADIATING TO CIRCUMFERENTIAL DOLERITE DIKE SWARMS OF THE SIBERIAN TRAPS LARGE IGNEOUS PROVINCE AND TO EMPLACEMENT OF THE NORILSK-TALNAKH ORE DEPOSITS","authors":"R.E. Ernst, H. El Bilali, K. L. Buchan, S.M. Jowitt","doi":"10.5382/econgeo.5065","DOIUrl":"https://doi.org/10.5382/econgeo.5065","url":null,"abstract":"A 90° change in stress orientation has been previously proposed as the trigger for the final emplacement of the world-class Norilsk-Talnakh magmatic sulfide mineralization via the migration of accumulated sulfide melts from elsewhere within the plumbing system of the Siberian Traps large igneous province (LIP). We propose that this stress change does not require and was not triggered by a distal change in plate boundary stresses, but instead can be explained both temporally and spatially by stress changes recorded in the dike swarm patterns of the Siberian Traps LIP, namely the transition from a giant radiating dike swarm (associated with mantle plume uplift) to a giant circumferential swarm (linked to flattening of the plume head). The mantle plume stress-related changes recorded by these dike swarms, rather than distal plate boundary stress changes, were therefore most likely the trigger for the emplacement of the Norilsk-Talnakh mineralization. Other LIPs that have both giant radiating and circumferential dike swarms most likely reflect similar major and rapid changes in stress orientation, indicating that mantle plume-induced stress changes revealed by dike swarms should be considered an additional tool in magmatic sulfide exploration.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"20 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140096852","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}
Xiao-Chun Li, Hong-Rui Fan, Jian-Hui Su, David I. Groves, Kui-Feng Yang, Xin-Fu Zhao
The giant Bayan Obo deposit in China represents the largest rare earth element (REE) resource in the world, but the mechanisms for its highly anomalous REE enrichment have long been controversial. The central debate concerns the nature and origin of the ore-hosting dolomite. In this study, a texturally constrained microanalytical study of carbonate minerals from the Bayan Obo ore-hosting dolomite is presented to resolve this controversy.The dolomite rocks contain two major components: the early-stage coarse-grained dolomite (CD) and the late-stage fine-grained dolomite (FD). The CD dolomite grains have C-O isotope ratios (δ13CVienna-PeeDee Belemnite (V-PDB): –4.8 to –3.3‰; δ18OVienna-standard mean ocean water (V-SMOW): 7.1 to 11.9‰) plotting in or adjacent to the primary igneous carbonatite field, with a narrow range of low 87Sr/86Sr ratios (0.70262–0.70327). The mantle-like C-O and Sr isotopes indicate that the coarse-grained dolomite rocks are magmatic in origin. Dolomite grains from the FD have experienced extensive hydrothermal alteration related to both REE mineralization and post-ore metamorphism of the Bayan Obo deposit. The domains of primary unaltered dolomite have high SrO and MnO contents that clearly distinguish them from sedimentary carbonates. The 87Sr/86Sr ratios of unaltered dolomite domains range from 0.70271 to 0.70473, with the majority lower than 0.7035, contrasting with higher 87Sr/86Sr ratios of Mesoproterozoic sedimentary carbonates globally. Thus, the primary unaltered fine-grained dolomite, the precursor to the FD, is also proposed to be a carbonatite.Compared with dolomite grains from the CD, most of the unaltered dolomite domains within the FD are more enriched in FeO and MnO and have higher δ13CV-PDB (-4.9 to 0.3 ‰) and δ18OV-SMOW (9.4 to 17.1 ‰) values. In addition, the FD contains abundant REE- and volatile-rich hydrothermal minerals and Fe-Mg carbonates, which are rare in the CD. The geochemical and mineralogical data in conjunction indicate that the melts forming the late-stage FD were much more evolved than those forming the early-stage CD. It is noteworthy that the unaltered dolomite domains within the FD have a wider range of 87Sr/86Sr ratios than those within the CD, which implies that the CD and FD, at least a proportion of them, are unlikely to have crystallized from the same progenitor magmas. Some FD was possibly the product of fractionation of less-evolved carbonatitic magma that generated the CD, whereas other FD crystallized from new pulses of magmas that were highly fractionated at depth.When compared with other carbonatite complexes, the Bayan Obo carbonatite suite is notable for having a large surface area (~48 km2 in outcrop) and containing an anomalously large proportion of highly evolved components. The voluminous
中国的巴彦鄂博巨型矿床是世界上最大的稀土元素（REE）资源，但其稀土元素高度异常富集的机制长期以来一直存在争议。争论的焦点是矿床白云岩的性质和来源。本研究对巴彦奥博矿床白云岩中的碳酸盐矿物进行了纹理约束显微分析研究，以解决这一争议。白云岩包含两个主要成分：早期粗粒白云岩（CD）和晚期细粒白云岩（FD）。CD白云岩颗粒的C-O同位素比值（δ13C维也纳-皮迪白云岩（V-PDB）：-4.8至-3.3‰；δ18OV维也纳-标准平均海水（V-SMOW）：7.1至11.9‰）：7.1至11.9‰），分布在原生火成碳酸盐岩场内或附近，87Sr/86Sr比值范围较窄（0.70262-0.70327）。类似地幔的 C-O 和 Sr 同位素表明，粗粒白云岩源于岩浆。来自 FD 的白云岩颗粒经历了广泛的热液蚀变，这与 REE 矿化和巴彦奥博矿床的矿后变质作用有关。原生未蚀变白云岩域的氧化硅和氧化锰含量较高，明显有别于沉积碳酸盐岩。未变质白云岩岩域的 87Sr/86Sr 比率在 0.70271 至 0.70473 之间，大部分低于 0.7035，与全球中新生代沉积碳酸盐岩较高的 87Sr/86Sr 比率形成鲜明对比。与CD中的白云岩颗粒相比，FD中的大部分未变质白云岩域富含更多的FeO和MnO，具有更高的δ13CV-PDB（-4.9至0.3‰）和δ18OV-SMOW（9.4至17.1‰）值。此外，FD 含有大量富含 REE 和挥发性的热液矿物和铁镁碳酸盐，这在 CD 中是罕见的。地球化学和矿物学数据共同表明，形成晚期FD的熔体要比形成早期CD的熔体进化得多。值得注意的是，FD 中未发生变化的白云岩域的 87Sr/86Sr 比值范围比 CD 中的更宽，这意味着 CD 和 FD（至少其中一部分）不太可能是由相同的原生岩浆结晶而成。一些FD可能是生成CD的低演化碳酸盐岩浆分馏的产物，而其他FD则是从深部高度分馏的新岩浆脉冲中结晶出来的。与其他碳酸盐岩群相比，巴彦奥博碳酸盐岩群的显著特点是表面积大（露头面积约48平方公里），而且含有异常大比例的高度演化成分。大量的演化碳酸盐岩显然为大量矿石金属的积累提供了基础。因此，建议巴彦奥博的巨型 REE 矿床与大体积、高演化碳酸盐岩有关。
{"title":"Giant Rare Earth Element Accumulation Related to Voluminous, Highly Evolved Carbonatite: A Microanalytical Study of Carbonate Minerals From the Bayan Obo Deposit, China","authors":"Xiao-Chun Li, Hong-Rui Fan, Jian-Hui Su, David I. Groves, Kui-Feng Yang, Xin-Fu Zhao","doi":"10.5382/econgeo.5060","DOIUrl":"https://doi.org/10.5382/econgeo.5060","url":null,"abstract":"The giant Bayan Obo deposit in China represents the largest rare earth element (REE) resource in the world, but the mechanisms for its highly anomalous REE enrichment have long been controversial. The central debate concerns the nature and origin of the ore-hosting dolomite. In this study, a texturally constrained microanalytical study of carbonate minerals from the Bayan Obo ore-hosting dolomite is presented to resolve this controversy.The dolomite rocks contain two major components: the early-stage coarse-grained dolomite (CD) and the late-stage fine-grained dolomite (FD). The CD dolomite grains have C-O isotope ratios (δ<sup>13</sup>C<sub>Vienna-PeeDee Belemnite (V-PDB)</sub>: –4.8 to –3.3‰; δ<sup>18</sup>O<sub>Vienna-standard mean ocean water (V-SMOW)</sub>: 7.1 to 11.9‰) plotting in or adjacent to the primary igneous carbonatite field, with a narrow range of low <sup>87</sup>Sr/<sup>86</sup>Sr ratios (0.70262–0.70327). The mantle-like C-O and Sr isotopes indicate that the coarse-grained dolomite rocks are magmatic in origin. Dolomite grains from the FD have experienced extensive hydrothermal alteration related to both REE mineralization and post-ore metamorphism of the Bayan Obo deposit. The domains of primary unaltered dolomite have high SrO and MnO contents that clearly distinguish them from sedimentary carbonates. The <sup>87</sup>Sr/<sup>86</sup>Sr ratios of unaltered dolomite domains range from 0.70271 to 0.70473, with the majority lower than 0.7035, contrasting with higher <sup>87</sup>Sr/<sup>86</sup>Sr ratios of Mesoproterozoic sedimentary carbonates globally. Thus, the primary unaltered fine-grained dolomite, the precursor to the FD, is also proposed to be a carbonatite.Compared with dolomite grains from the CD, most of the unaltered dolomite domains within the FD are more enriched in FeO and MnO and have higher δ<sup>13</sup>C<sub>V-PDB</sub> (-4.9 to 0.3 ‰) and δ<sup>18</sup>O<sub>V-SMOW</sub> (9.4 to 17.1 ‰) values. In addition, the FD contains abundant REE- and volatile-rich hydrothermal minerals and Fe-Mg carbonates, which are rare in the CD. The geochemical and mineralogical data in conjunction indicate that the melts forming the late-stage FD were much more evolved than those forming the early-stage CD. It is noteworthy that the unaltered dolomite domains within the FD have a wider range of <sup>87</sup>Sr/<sup>86</sup>Sr ratios than those within the CD, which implies that the CD and FD, at least a proportion of them, are unlikely to have crystallized from the same progenitor magmas. Some FD was possibly the product of fractionation of less-evolved carbonatitic magma that generated the CD, whereas other FD crystallized from new pulses of magmas that were highly fractionated at depth.When compared with other carbonatite complexes, the Bayan Obo carbonatite suite is notable for having a large surface area (~48 km<sup>2</sup> in outcrop) and containing an anomalously large proportion of highly evolved components. The voluminous ","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"22 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140096921","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}
Rael D. Lipson, Richard J. Goldfarb, Ben M. Frieman, John Payne
The San Albino deposit is an orogenic gold occurrence hosted by a low-angle thrust that is the site of a new open-pit mine in northern Nicaragua. The deposit is hosted in greenschist facies rocks of the Jurassic metasedimentary Neuvo Segovia Formation. The schist was uplifted and exposed during arc accretion and Cretaceous thin-skin deformation, forming the NE-striking Colon fold-and-thrust belt. Deformation included emplacement of the 119 to 113 Ma NE-trending Dipilto batholith into the regionally metamorphosed clastic rocks about 5 km northwest of the San Albino deposit. Mineralization is dominated by three laminated quartz vein systems (i.e., San Albino, Naranjo, Arras) that broadly follow shallowly dipping (approx. 30°) carbonaceous shears roughly concordant to schistosity along the limbs of a doubly plunging antiform. The three main parallel shears are each separated by about 90 m and individually reach a maximum thickness of about 8 m. Maximum thickness of ore zones is where post-ore local folding and reverse motion along the shallow shears has duplicated the laminated low-angle gold-bearing veins (D2 and early D3). Additional gold was added to the veins, with abundant sulfides, during a subsequent brecciation event of the early formed quartz veins that accompanied progressive thrusting (late D3). This predated boudinage of the veins during continued compression and thrust loading (D4); high gold grades are particularly notable along pyrite- and arsenopyrite-bearing stylolites formed during D4 pressure solution. The D2 to D3 gold event is likely coeval with Albian uplift of the Dipilto batholith and with back thrusting in the schist aided by the stress inhomogeneities provided by the igneous complex.Low-angle thrust-controlled orogenic gold deposits may represent world-class exploration targets because of their large linear footprints, although they are traditionally looked at as less favorable exploration targets relative to gold systems developed more commonly along high-angle reverse faults. Our case study of the San Albino deposit shows that although low-angle deposits are not inherently misoriented for failure like the more common subvertical reverse fault-related deposits, they may be sites of significant pressure buildup due to hydrothermal mineral precipitation during initial water-rock interaction or slight temperature decreases along the low-angle flow path. Resulting fluid cycling may lead to thick laminated vein development, such as seen at San Albino, where especially high-grade zones may be associated with local steepening and/or dilational zones within the broader, low-angle vein-hosting shear system.
{"title":"San Albino, Nicaragua: A Low-Angle, Thrust-Controlled Orogenic Gold Deposit","authors":"Rael D. Lipson, Richard J. Goldfarb, Ben M. Frieman, John Payne","doi":"10.5382/econgeo.5042","DOIUrl":"https://doi.org/10.5382/econgeo.5042","url":null,"abstract":"The San Albino deposit is an orogenic gold occurrence hosted by a low-angle thrust that is the site of a new open-pit mine in northern Nicaragua. The deposit is hosted in greenschist facies rocks of the Jurassic metasedimentary Neuvo Segovia Formation. The schist was uplifted and exposed during arc accretion and Cretaceous thin-skin deformation, forming the NE-striking Colon fold-and-thrust belt. Deformation included emplacement of the 119 to 113 Ma NE-trending Dipilto batholith into the regionally metamorphosed clastic rocks about 5 km northwest of the San Albino deposit. Mineralization is dominated by three laminated quartz vein systems (i.e., San Albino, Naranjo, Arras) that broadly follow shallowly dipping (approx. 30°) carbonaceous shears roughly concordant to schistosity along the limbs of a doubly plunging antiform. The three main parallel shears are each separated by about 90 m and individually reach a maximum thickness of about 8 m. Maximum thickness of ore zones is where post-ore local folding and reverse motion along the shallow shears has duplicated the laminated low-angle gold-bearing veins (D<sub>2</sub> and early D<sub>3</sub>). Additional gold was added to the veins, with abundant sulfides, during a subsequent brecciation event of the early formed quartz veins that accompanied progressive thrusting (late D<sub>3</sub>). This predated boudinage of the veins during continued compression and thrust loading (D<sub>4</sub>); high gold grades are particularly notable along pyrite- and arsenopyrite-bearing stylolites formed during D<sub>4</sub> pressure solution. The D<sub>2</sub> to D<sub>3</sub> gold event is likely coeval with Albian uplift of the Dipilto batholith and with back thrusting in the schist aided by the stress inhomogeneities provided by the igneous complex.Low-angle thrust-controlled orogenic gold deposits may represent world-class exploration targets because of their large linear footprints, although they are traditionally looked at as less favorable exploration targets relative to gold systems developed more commonly along high-angle reverse faults. Our case study of the San Albino deposit shows that although low-angle deposits are not inherently misoriented for failure like the more common subvertical reverse fault-related deposits, they may be sites of significant pressure buildup due to hydrothermal mineral precipitation during initial water-rock interaction or slight temperature decreases along the low-angle flow path. Resulting fluid cycling may lead to thick laminated vein development, such as seen at San Albino, where especially high-grade zones may be associated with local steepening and/or dilational zones within the broader, low-angle vein-hosting shear system.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"71 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140135939","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}
Kaixuan Hui, Bertrand Rottier, Kezhang Qin, Zoltan Zajacz, Alexandra Tsay, Junxing Zhao, Shen Gao, Ruizhe Shi
Magmatic-related epithermal silver-rich polymetallic deposits are among the most important sources of Ag in the world, and they are found associated with magmatic systems with striking differences. Most of the time, they are associated either with I-type oxidized (magnetite-series granite) intermediate to evolved intrusions or with S-type/A-type reduced (ilmenite-series granite) highly evolved intrusions. To better understand these associations, the Ag evolution has been tracked during the magmatic differentiation and the magmatic-hydrothermal transition stage of A-type highly evolved porphyritic granites associated with the giant Shuangjianzishan Ag-Pb-Zn-(Sn) epithermal deposit, the largest known Ag deposit of Asia (145 million tonnes at 128.5 g/t Ag and 2.2 wt % Pb + Zn) located in the largest known metallogenic province for Ag in China (the southern Great Xing’an Range). At the Shuangjianzishan deposit, the porphyritic granite complex consists of three temporally distinct intrusions—a coarse-grained monzogranite porphyry, a fine-grained syenogranite porphyry, and a fine-grained syenogranite—having crystallized at ~2 kbar and ~750°C and recording a continuous magmatic differentiation trend. The silicate melt that generated the last highly differentiated intrusion (fine-grained syenogranite) is interpreted as the source of the mineralizing fluids forming the Shuangjianzishan Ag-Pb-Zn-(Sn) epithermal deposit, as it is the only intrusive unit that reached fluid saturation, as indicated by cotrapped fluid and melt inclusions in quartz phenocrysts and by the occurrences of unidirectional solidification textures (USTs). Silver evolution in the different porphyritic granite facies was reconstructed with laser ablation-inductively coupled plasma-mass spectrometry analyses of quartz-hosted silicate melt inclusions, amphibole-hosted magmatic sulfide inclusions, and chemical modeling. The silicate melt forming the porphyritic granite complex was sulfide saturated during the first crystallization stage, as shown by the occurrence of Ag-rich monosulfide solid solution (MSS) inclusions hosted in amphibole phenocrysts from the coarse-grained monzogranite porphyry and from mafic microgranular enclaves hosted in the coarse-grained monzogranite porphyry. However, these Ag-rich MSSs had only a minimal impact on the Ag budget of the magmatic system, as shown by the increase of the Ag concentration (~100–1,000 ppb) in quartz-hosted silicate melt inclusions during the further evolution of the system until fluid exsolution was reached. These results combined with mass balance modeling suggest that Ag and Sn are efficiently transferred to the evolving residual melt during crystallization and crystal-melt segregation. The results of this study indicate that highly Ag endowed epithermal polymetallic deposits can be formed from the exsolution of Ag-rich mineralizing fluids from relatively low volume, highly evolved, reduced melts, similar to those responsible for the fo
与岩浆有关的表生富银多金属矿床是世界上最重要的银矿来源之一，这些矿床与岩浆系统伴生，差异显著。大多数情况下，它们要么与 I 型氧化（磁铁矿系列花岗岩）中进化侵入体有关，要么与 S 型/A 型还原（钛铁矿系列花岗岩）高度进化侵入体有关。为了更好地理解这些关联，我们对与巨大的双剑子山银-铅-锌-（锡）热液矿床相关的 A 型高度演化斑状花岗岩的岩浆分异和岩浆-热液转换阶段的银演化进行了追踪，该矿床是亚洲已知最大的银矿床（1.45 亿吨，银品位 128.5 克/吨，铅锌品位 2.2 重量%），位于中国已知最大的银成矿省（大兴安岭南部）。在双剑子山矿床，斑状花岗岩复合体由三个时间上截然不同的侵入体组成--粗粒单斜斑岩、细粒正长斑岩和细粒正长斑岩--它们在大约2千巴和大约750摄氏度的温度下结晶，并记录了连续的岩浆分异趋势。生成最后一个高度分异侵入体（细粒正长花岗岩）的硅酸盐熔体被解释为形成双剑子山银-铅-锌-（锡）热液矿床的成矿流体的来源，因为它是唯一达到流体饱和的侵入体单元，石英表晶中的共包裹体和熔体包裹体以及出现的单向凝固纹理（UST）都表明了这一点。通过对石英寄生硅酸盐熔体包裹体、闪石寄生岩浆硫化物包裹体的激光烧蚀-电感耦合等离子体-质谱分析以及化学建模，重建了不同斑状花岗岩岩相中银的演化过程。形成斑状花岗岩复合体的硅酸盐熔体在第一结晶阶段硫化物饱和，这表现在粗粒单斜斑岩中的闪石表晶和粗粒单斜斑岩中的黑云母微晶包体中都有富含Ag的单硫化物固溶体（MSS）包裹体。然而，这些富含Ag的MSS对岩浆系统Ag预算的影响微乎其微，这表现在系统进一步演化直至流体外溶解过程中，石英寄存硅酸盐熔体包裹体中Ag浓度的增加（约100-1000ppb）。这些结果与质量平衡模型相结合表明，在结晶和晶体-熔体偏析过程中，银和锡被有效地转移到不断演化的残余熔体中。这项研究结果表明，富含银的表生多金属矿床可以通过富含银的成矿流体从体积相对较小、高度演化的还原熔体中溶出而形成，这与富含锡的绿森矿床的形成过程类似。
{"title":"Silver Behavior During Magmatic and Magmatic-Hydrothermal Evolution of a Highly Evolved Reduced Granitic System Related to the Giant Shuangjianzishan Ag-Pb-Zn-(Sn) Epithermal Deposit, Northeast China","authors":"Kaixuan Hui, Bertrand Rottier, Kezhang Qin, Zoltan Zajacz, Alexandra Tsay, Junxing Zhao, Shen Gao, Ruizhe Shi","doi":"10.5382/econgeo.5031","DOIUrl":"https://doi.org/10.5382/econgeo.5031","url":null,"abstract":"Magmatic-related epithermal silver-rich polymetallic deposits are among the most important sources of Ag in the world, and they are found associated with magmatic systems with striking differences. Most of the time, they are associated either with I-type oxidized (magnetite-series granite) intermediate to evolved intrusions or with S-type/A-type reduced (ilmenite-series granite) highly evolved intrusions. To better understand these associations, the Ag evolution has been tracked during the magmatic differentiation and the magmatic-hydrothermal transition stage of A-type highly evolved porphyritic granites associated with the giant Shuangjianzishan Ag-Pb-Zn-(Sn) epithermal deposit, the largest known Ag deposit of Asia (145 million tonnes at 128.5 g/t Ag and 2.2 wt % Pb + Zn) located in the largest known metallogenic province for Ag in China (the southern Great Xing’an Range). At the Shuangjianzishan deposit, the porphyritic granite complex consists of three temporally distinct intrusions—a coarse-grained monzogranite porphyry, a fine-grained syenogranite porphyry, and a fine-grained syenogranite—having crystallized at ~2 kbar and ~750°C and recording a continuous magmatic differentiation trend. The silicate melt that generated the last highly differentiated intrusion (fine-grained syenogranite) is interpreted as the source of the mineralizing fluids forming the Shuangjianzishan Ag-Pb-Zn-(Sn) epithermal deposit, as it is the only intrusive unit that reached fluid saturation, as indicated by cotrapped fluid and melt inclusions in quartz phenocrysts and by the occurrences of unidirectional solidification textures (USTs). Silver evolution in the different porphyritic granite facies was reconstructed with laser ablation-inductively coupled plasma-mass spectrometry analyses of quartz-hosted silicate melt inclusions, amphibole-hosted magmatic sulfide inclusions, and chemical modeling. The silicate melt forming the porphyritic granite complex was sulfide saturated during the first crystallization stage, as shown by the occurrence of Ag-rich monosulfide solid solution (MSS) inclusions hosted in amphibole phenocrysts from the coarse-grained monzogranite porphyry and from mafic microgranular enclaves hosted in the coarse-grained monzogranite porphyry. However, these Ag-rich MSSs had only a minimal impact on the Ag budget of the magmatic system, as shown by the increase of the Ag concentration (~100–1,000 ppb) in quartz-hosted silicate melt inclusions during the further evolution of the system until fluid exsolution was reached. These results combined with mass balance modeling suggest that Ag and Sn are efficiently transferred to the evolving residual melt during crystallization and crystal-melt segregation. The results of this study indicate that highly Ag endowed epithermal polymetallic deposits can be formed from the exsolution of Ag-rich mineralizing fluids from relatively low volume, highly evolved, reduced melts, similar to those responsible for the fo","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":"20 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139752511","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}
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
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.
{"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}
Y. M. DeWolfe, J. Kolb, E. Sørensen, D. Rosa, P. Guarnieri
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. 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.
{"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}
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.
Río Blanco-Los Bronces 矿床是世界上含铜金属量最大的铜-钼斑岩矿床。它是岩浆活动和热液活动长期叠加的产物，与多次侵入和角砾岩事件有关，并同时伴有区域隆升、侵蚀和解顶以及减压。岩浆活动导致了三个主要的矿化-蜕变阶段。前矿化阶段发生在旧金山浴成岩的形成过程中，导致了晚期岩浆活动和早期热液活动。同步矿化阶段与 Río Blanco-Los Bronces 斑岩和砾岩复合体相关的主要热液事件相对应，这些热液事件与三个侵入阶段、广泛的砾岩和表生型高级箭石蚀变有关。晚期岩浆活动之后的热液活动与次火山流纹岩复合体和晚期斑岩侵入体的形成有关。同步矿化侵入体与高品位角砾岩体有关，这些角砾岩体具有明确的蚀变-分带模式。 通过对来自不同矿山、隧道和矿坑的历史 Río Blanco 构造数据集进行汇编和分析，可以根据其连续性、横切关系和填充成分将所有绘制的构造划分为四个等级。较大的结构（阶次 0 和 1）具有沿矿脉的连续性，在掘进巷道和/或矿层之间具有相关性，而较小的结构（阶次 2 和 3）则根据其尺寸和在较大阶次结构定义的板块内的分布情况进行分组。所有 0 级和 1 级构造均为三维建模，2 级和 3 级构造为二维建模。在 Río Blanco 绘制的结构与岩浆作用和矿化的前期到后期地质演变有着密切的关系。区域尺度的构造演化与成矿前的盆地开辟和随后的构造反转有关，其次是地区尺度的构造演化与成矿前的盆地开辟和随后的构造反转有关，而在营地尺度上，成矿同期至后期的侵入体和相关的热液特征叠加在这一继承的构造结构上。
{"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}
Cheng Wang, Yong-Jun Shao, Richard Goldfarb, Shi-Min Tan, Ji Sun, Chao Zhou, Han Zheng, Qing-Quan Liu, Yi-Qu Xiong
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.
{"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}
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