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":null,"pages":null},"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}
Min Wang, Martin Yan Hei Li, Mei-fu Zhou, Jia-xi Zhou, Guotao Sun, Ye Zhou, Yin Li
Regolith-hosted rare earth element (REE) deposits have been the focus of recent studies. Most studies concern deposits formed over granites and felsic volcanic rocks, but little is known about those deposits developed over silica-undersaturated alkaline igneous rocks. The recently discovered Puxiong REE deposit in Southwest China formed through the weathering of nepheline syenite that has REE concentrations ranging from 177 to 9,336 ppm. Hydrothermal processes partially enriched the parent nepheline syenite in REEs. About 60% of the REEs in the bedrock are hosted in britholite-(Ce), tritomite-(Ce), and cerite-(Ce) and ~21% in REE minerals that occur as inclusions in K-feldspar, with the rest in titanite, hiortdahlite, apatite, fluorite, and calcite. These minerals all can be easily decomposed to release REEs into soil solutions during weathering. The released REEs are adsorbed on clay minerals or precipitate as supergene rhabdophane and an Fe-Mn-REE oxyhydroxide phase. Nepheline syenite-derived regolith-hosted REE deposits are enriched in illite and halloysite, which have a higher ion exchange capacity than the parent granites. Illite formed through the weathering of primary alkali minerals in the nepheline syenite. In the strongly eroded midslope and valley, the regolith has the lowest total REE concentration (997 and 1,001 ppm on average, respectively) across the ore-bearing catchment, whereas the regolith in the hilltop and footslope has REE concentrations of up to 1,564 and 1,677 ppm, respectively. Moreover, regolith at the footslope has the highest heavy REE (HREE) concentration of 110 ppm on average. The light REEs (LREEs) tend to be concentrated in the B horizon and laterally across the hilltops, whereas the HREEs are mobilized by groundwater and soil solutions and accumulated in the upper C horizon vertically and the footslope profiles laterally. In conclusion, nepheline syenite was hydrothermally enriched in the REEs, and these elements were released to the weathering solution and then adsorbed onto clay minerals in sufficient concentrations to form economic regolith-hosted REE deposits. This process, which was controlled at Puxiong by the nature of clay minerals, pH, the redox conditions, the mobility of the REEs, and topography, led to maximum enrichment of the LREEs in the lower B horizon at the hilltop, and HREE enrichment in the upper C horizons vertically and in the footslope laterally.
{"title":"Enrichment of Rare Earth Elements During the Weathering of Alkaline Igneous Systems: Insights from the Puxiong Regolith-Hosted Rare Earth Element Deposit, SW China","authors":"Min Wang, Martin Yan Hei Li, Mei-fu Zhou, Jia-xi Zhou, Guotao Sun, Ye Zhou, Yin Li","doi":"10.5382/econgeo.5024","DOIUrl":"https://doi.org/10.5382/econgeo.5024","url":null,"abstract":"\u0000 Regolith-hosted rare earth element (REE) deposits have been the focus of recent studies. Most studies concern deposits formed over granites and felsic volcanic rocks, but little is known about those deposits developed over silica-undersaturated alkaline igneous rocks. The recently discovered Puxiong REE deposit in Southwest China formed through the weathering of nepheline syenite that has REE concentrations ranging from 177 to 9,336 ppm. Hydrothermal processes partially enriched the parent nepheline syenite in REEs. About 60% of the REEs in the bedrock are hosted in britholite-(Ce), tritomite-(Ce), and cerite-(Ce) and ~21% in REE minerals that occur as inclusions in K-feldspar, with the rest in titanite, hiortdahlite, apatite, fluorite, and calcite. These minerals all can be easily decomposed to release REEs into soil solutions during weathering. The released REEs are adsorbed on clay minerals or precipitate as supergene rhabdophane and an Fe-Mn-REE oxyhydroxide phase. Nepheline syenite-derived regolith-hosted REE deposits are enriched in illite and halloysite, which have a higher ion exchange capacity than the parent granites. Illite formed through the weathering of primary alkali minerals in the nepheline syenite.\u0000 In the strongly eroded midslope and valley, the regolith has the lowest total REE concentration (997 and 1,001 ppm on average, respectively) across the ore-bearing catchment, whereas the regolith in the hilltop and footslope has REE concentrations of up to 1,564 and 1,677 ppm, respectively. Moreover, regolith at the footslope has the highest heavy REE (HREE) concentration of 110 ppm on average. The light REEs (LREEs) tend to be concentrated in the B horizon and laterally across the hilltops, whereas the HREEs are mobilized by groundwater and soil solutions and accumulated in the upper C horizon vertically and the footslope profiles laterally. In conclusion, nepheline syenite was hydrothermally enriched in the REEs, and these elements were released to the weathering solution and then adsorbed onto clay minerals in sufficient concentrations to form economic regolith-hosted REE deposits. This process, which was controlled at Puxiong by the nature of clay minerals, pH, the redox conditions, the mobility of the REEs, and topography, led to maximum enrichment of the LREEs in the lower B horizon at the hilltop, and HREE enrichment in the upper C horizons vertically and in the footslope laterally.","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":null,"pages":null},"PeriodicalIF":5.8,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139638576","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}
Pub Date : 2024-01-01DOI: 10.5382/econgeo.119.1.ip01
{"title":"INTERESTING PAPERS IN OTHER JOURNALS","authors":"","doi":"10.5382/econgeo.119.1.ip01","DOIUrl":"https://doi.org/10.5382/econgeo.119.1.ip01","url":null,"abstract":"","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":null,"pages":null},"PeriodicalIF":5.8,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139635496","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}
Jean Vallance, Renzo Galdos, Macneill Balboa, B. Berna, Omar Cabrera, Freddy Huisa, Camille Baya, Caroline Van De Vyver, Willem Viveen, D. Béziat, Stefano Salvi, S. Brusset, Patrice Baby, G. Pokrovski
Sediment-hosted gold deposits represent a significant portion of the world’s gold resources. They are characterized by the ubiquitous presence of organic carbon (Corg; or its metamorphosed product, graphite) and the systematic occurrence of invisible gold-bearing arsenian pyrite. Yet the role played by these features on ore formation and the distribution of gold remains a long-standing debate. Here, we attempt to clarify this question via an integrated structural, mineralogical, geochemical, and modeling study of the Shahuindo deposit in northern Peru, representative of an epithermal gold deposit contained in a sedimentary basin. The Shahuindo deposit is hosted within Lower Cretaceous fluvio-deltaic carbon-bearing sandstone, siltstone, and black shale of the Marañón fold-and-thrust belt, where intrusions of Miocene age are also exposed. The emplacement of the auriferous orebodies is constrained by structural (thrust faults, transverse faults) as well as lithological (intrusion contacts, permeable layers, anticlinal hinge in sandstone) features. The defined gold reserves (59 tons; t) are located in the supergene zone in the form of native gold grains. However, a primary mineralization, underneath the oxidized zone, occurs in the form of invisible gold in arsenian pyrite and arsenopyrite. Here, four subsequent pyrite generations were identified—namely, pyI, pyII, pyIII, and pyIV. PyI has mean Au concentrations of 0.3 ppm, contains arsenic that is not detectable, and is enriched in V, Co, Ni, Zn, Ag, and Pb compared to the other pyrite generations. This trace element distribution suggests a diagenetic origin in an anoxic to euxinic sedimentary basin for pyI. Pyrite II and pyIV have comparable mean Au (1.1 and 0.7 ppm, respectively) and As (2.4 and 2.9 wt %, respectively) concentrations and precipitated under conditions evolving from lower (pyrrhotite, chalcopyrite, sphalerite) to higher (enargite, digenite, chalcocite) sulfidation, respectively. The pyIII generation is the major gold event in the primary mineralization, with pyrite reaching 110 ppm Au (mean ~7 ppm) and 5.6 wt % As (mean ~1.8 wt %), while coeval arsenopyrite attains 460 ppm Au. Pyrite III is also enriched in other trace elements such as Se, Ge, Mo, In, Ga, and Bi compared to the other pyrite generations, which is indicative of a magmatic source. Bulk analyses of the surrounding unmineralized rocks show only parts per billion levels of Au and less than 25 ppm As. These data, combined with mass balance considerations, demonstrate that the sedimentary rocks could not be the sole source of gold, as they could only contribute a minor portion of arsenic and sulfur (and iron) to the deposit. Conversely, fluids exsolved from a pluton crystallizing at depth likely provided the great part of the gold endowment. Equilibrium thermodynamics simulations, using geochemical constraints established in this study, demonstrate that interaction between Au-As-S-Fe–bearing fluids and organic carbon-bear
沉积型金矿床占世界黄金资源的很大一部分。它们的特点是无处不在的有机碳（Corg；或其变质产物石墨）和系统存在的隐形含金砷黄铁矿。然而，这些特征对矿石形成和金的分布所起的作用仍是一个长期争论的问题。在此，我们试图通过对秘鲁北部 Shahuindo 矿床的结构、矿物学、地球化学和建模综合研究来澄清这一问题，该矿床是沉积盆地中热液型金矿床的代表。Shahuindo 矿床位于马拉尼翁褶皱推覆带的下白垩统荧光-三角洲含碳砂岩、粉砂岩和黑色页岩中，这里还出露了中新世时期的侵入体。含金矿体的形成受到构造（推断断层、横断断层）和岩性（侵入接触、渗透层、砂岩的反斜面铰链）特征的制约。已确定的黄金储量（59 吨）以原生金粒的形式位于超生带。然而，氧化带下方的原生矿化物以隐形金的形式存在于砷黄铁矿和砷黄铁矿中。在这里，确定了四个黄铁矿后代，即 pyI、pyII、pyIII 和 pyIV。PyI 的平均金浓度为 0.3 ppm，所含砷无法检测到，与其他黄铁矿代相比，富含 V、Co、Ni、Zn、Ag 和 Pb。这种微量元素分布表明，黄铁矿 I 的成岩起源于缺氧至缺氧沉积盆地。黄铁矿 II 和黄铁矿 IV 的平均金（分别为 1.1 和 0.7 ppm）和砷（分别为 2.4 和 2.9 wt %）浓度相当，分别是在硫化程度从较低（黄铁矿、黄铜矿、闪锌矿）到较高（鹅绿泥石、地开石、黄铜矿）的条件下沉淀的。黄铁矿 III 代是原生矿化中主要的金事件，黄铁矿的金含量达到百万分之 110（平均约为百万分之 7），砷含量为百万分之 5.6（平均约为百万分之 1.8），而共生黄砷矿的金含量则达到百万分之 460。与其他黄铁矿代相比，黄铁矿 III 还富含其他微量元素，如硒、锗、钼、铟、镓和铋，这表明黄铁矿来源于岩浆。对周围未矿化岩石的大量分析表明，金含量仅为十亿分之一，砷含量低于 25 ppm。这些数据结合质量平衡的考虑，表明沉积岩不可能是金的唯一来源，因为它们只能为矿床提供少量的砷和硫（以及铁）。相反，从深部结晶的深成岩中流出的流体可能提供了大部分的金禀赋。利用本研究建立的地球化学约束条件进行的平衡热力学模拟证明，含金-砷-硫-铁流体与含有机碳岩石之间的相互作用，通过综合提高 pH 值和水体硫化物浓度，最大限度地提高流体作为 AuI 硫氢化物复合物的溶解度，从而有力地增强了流体搬运金的能力。这一发现对传统的定性观点提出了挑战，即有机物只充当 AuI 的还原剂，应促进金以原生状态（Au0）沉积，而不是提高其在流体中的溶解度。我们的研究结果对碳质沉积环境的勘探具有重要意义。这种环境可能为金的集中迁移提供了一种非常有效的机制。与石油系统中的情况类似，在渗透性较强的结构和岩性陷阱中，砷黄铁矿的沉淀会促进金以化学结合的形式从溶液中清除。我们的综合研究强调了沉积含粟特岩在金及相关金属资源的形成和分布方面的重要潜力。
{"title":"Combined Effect of Organic Carbon and Arsenic on the Formation of Sediment-Hosted Gold Deposits: A Case Study of the Shahuindo Epithermal Deposit, Peru","authors":"Jean Vallance, Renzo Galdos, Macneill Balboa, B. Berna, Omar Cabrera, Freddy Huisa, Camille Baya, Caroline Van De Vyver, Willem Viveen, D. Béziat, Stefano Salvi, S. Brusset, Patrice Baby, G. Pokrovski","doi":"10.5382/econgeo.5040","DOIUrl":"https://doi.org/10.5382/econgeo.5040","url":null,"abstract":"\u0000 Sediment-hosted gold deposits represent a significant portion of the world’s gold resources. They are characterized by the ubiquitous presence of organic carbon (Corg; or its metamorphosed product, graphite) and the systematic occurrence of invisible gold-bearing arsenian pyrite. Yet the role played by these features on ore formation and the distribution of gold remains a long-standing debate. Here, we attempt to clarify this question via an integrated structural, mineralogical, geochemical, and modeling study of the Shahuindo deposit in northern Peru, representative of an epithermal gold deposit contained in a sedimentary basin. The Shahuindo deposit is hosted within Lower Cretaceous fluvio-deltaic carbon-bearing sandstone, siltstone, and black shale of the Marañón fold-and-thrust belt, where intrusions of Miocene age are also exposed. The emplacement of the auriferous orebodies is constrained by structural (thrust faults, transverse faults) as well as lithological (intrusion contacts, permeable layers, anticlinal hinge in sandstone) features. The defined gold reserves (59 tons; t) are located in the supergene zone in the form of native gold grains. However, a primary mineralization, underneath the oxidized zone, occurs in the form of invisible gold in arsenian pyrite and arsenopyrite. Here, four subsequent pyrite generations were identified—namely, pyI, pyII, pyIII, and pyIV. PyI has mean Au concentrations of 0.3 ppm, contains arsenic that is not detectable, and is enriched in V, Co, Ni, Zn, Ag, and Pb compared to the other pyrite generations. This trace element distribution suggests a diagenetic origin in an anoxic to euxinic sedimentary basin for pyI. Pyrite II and pyIV have comparable mean Au (1.1 and 0.7 ppm, respectively) and As (2.4 and 2.9 wt %, respectively) concentrations and precipitated under conditions evolving from lower (pyrrhotite, chalcopyrite, sphalerite) to higher (enargite, digenite, chalcocite) sulfidation, respectively. The pyIII generation is the major gold event in the primary mineralization, with pyrite reaching 110 ppm Au (mean ~7 ppm) and 5.6 wt % As (mean ~1.8 wt %), while coeval arsenopyrite attains 460 ppm Au. Pyrite III is also enriched in other trace elements such as Se, Ge, Mo, In, Ga, and Bi compared to the other pyrite generations, which is indicative of a magmatic source. Bulk analyses of the surrounding unmineralized rocks show only parts per billion levels of Au and less than 25 ppm As. These data, combined with mass balance considerations, demonstrate that the sedimentary rocks could not be the sole source of gold, as they could only contribute a minor portion of arsenic and sulfur (and iron) to the deposit. Conversely, fluids exsolved from a pluton crystallizing at depth likely provided the great part of the gold endowment. Equilibrium thermodynamics simulations, using geochemical constraints established in this study, demonstrate that interaction between Au-As-S-Fe–bearing fluids and organic carbon-bear","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":null,"pages":null},"PeriodicalIF":5.8,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139634107","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}
Qihai Shu, Jun Deng, Zhaoshan Chang, Qingfei Wang, Xudong Niu, Kai Xing, Xiang Sun, Zhongkun Zhang, Qingwen Zeng, Hesen Zhao, Fan Yu
Jiama is a giant skarn-porphyry deposit in southern Tibet, southwestern China. It is the largest Cu (~7.4 Mt), second largest Au (~208 t), and fourth largest Mo (~0.62 Mt) skarn deposit in China. In addition, Jiama also contains considerable amounts of Zn, Pb, and Ag. The mineralization is related to a Miocene (~15 Ma) monzogranite porphyry that intruded the Upper Jurassic Duodigou Formation limestone (now mainly marble) and the overlying Lower Cretaceous Linbuzong Formation sandstone, siltstone, and shale (now mainly hornfels with minor slate). Porphyry-type orebodies occur in the intrusion and in the surrounding hornfels, whereas ~50- to 100-m-wide skarn-type orebodies wrap around the intrusion along the intrusion-marble contact, and as a ~50- to 150-m-thick stratabound blanket along the hornfels-marble boundary away from the contact. The stratabound skarns extend continuously for up to ~2 km on one side of the intrusion until the hornfels-marble boundary is exposed at the surface. Jiama is well zoned with respect to skarn minerals, metals, and stable isotope compositions, both laterally and vertically. Laterally, the proximal skarn is dominated by garnet, whereas the stratabound skarn contains progressively more wollastonite away from the intrusion center. The garnet composition changes from mixed Al and Fe rich (Ad21-79Gr20-77) in the endoskarn, to Fe rich in the proximal exoskarn (Ad70 to pure andradite), and Al rich (Gr69-88) in the stratabound skarn distal to the intrusion. Pyroxene is Mg rich (mostly Di66-97) in the deposit and is slightly more Fe rich in the distal zones. The garnet/pyroxene ratio remains high throughout the skarn. Vertically in the stratabound skarn, garnet is the dominant skarn mineral closer to the hornfels at shallower positions, whereas closer to the marble at deeper positions, there is more wollastonite, up to a wollastonite-dominant zone at the skarn-marble contact. The color of the garnet near the upper hornfels is dark red-brown, and gradually turns yellowish green downward. In terms of metals, the Mo-rich domains are dominantly within the intrusion, the Cu-Au-rich domains are in exoskarns near the intrusion, and the Zn-Pb-Ag mineralization occurs mostly in the distal zones. The Cu ore mineralogy changes vertically in the stratabound skarns, from chalcopyrite rich in the upper garnet zone, to bornite rich in the lower wollastonite zone. Values of δ34SV-CDT for chalcopyrite generally decrease from >–1‰ within the intrusion to –6‰ ~2 km away from the intrusion. The C and O isotope compositions of the marble samples show generally increasing trends downward in the stratabound part of the skarn, indicating that the fluid channel was closer to the hornfels. The lowest marble δ18OV-SMOW values (mostly <14%) occur close to the intrusion, consistent with the fluids being derived from the magmas. The organic carbon content decreases at shallower parts of the stratabound skarns and closer to the intrusion (from 0.412 t
{"title":"Skarn Zonation of the Giant Jiama Cu-Mo-Au Deposit in Southern Tibet, SW China","authors":"Qihai Shu, Jun Deng, Zhaoshan Chang, Qingfei Wang, Xudong Niu, Kai Xing, Xiang Sun, Zhongkun Zhang, Qingwen Zeng, Hesen Zhao, Fan Yu","doi":"10.5382/econgeo.5038","DOIUrl":"https://doi.org/10.5382/econgeo.5038","url":null,"abstract":"\u0000 Jiama is a giant skarn-porphyry deposit in southern Tibet, southwestern China. It is the largest Cu (~7.4 Mt), second largest Au (~208 t), and fourth largest Mo (~0.62 Mt) skarn deposit in China. In addition, Jiama also contains considerable amounts of Zn, Pb, and Ag. The mineralization is related to a Miocene (~15 Ma) monzogranite porphyry that intruded the Upper Jurassic Duodigou Formation limestone (now mainly marble) and the overlying Lower Cretaceous Linbuzong Formation sandstone, siltstone, and shale (now mainly hornfels with minor slate). Porphyry-type orebodies occur in the intrusion and in the surrounding hornfels, whereas ~50- to 100-m-wide skarn-type orebodies wrap around the intrusion along the intrusion-marble contact, and as a ~50- to 150-m-thick stratabound blanket along the hornfels-marble boundary away from the contact. The stratabound skarns extend continuously for up to ~2 km on one side of the intrusion until the hornfels-marble boundary is exposed at the surface.\u0000 Jiama is well zoned with respect to skarn minerals, metals, and stable isotope compositions, both laterally and vertically. Laterally, the proximal skarn is dominated by garnet, whereas the stratabound skarn contains progressively more wollastonite away from the intrusion center. The garnet composition changes from mixed Al and Fe rich (Ad21-79Gr20-77) in the endoskarn, to Fe rich in the proximal exoskarn (Ad70 to pure andradite), and Al rich (Gr69-88) in the stratabound skarn distal to the intrusion. Pyroxene is Mg rich (mostly Di66-97) in the deposit and is slightly more Fe rich in the distal zones. The garnet/pyroxene ratio remains high throughout the skarn. Vertically in the stratabound skarn, garnet is the dominant skarn mineral closer to the hornfels at shallower positions, whereas closer to the marble at deeper positions, there is more wollastonite, up to a wollastonite-dominant zone at the skarn-marble contact. The color of the garnet near the upper hornfels is dark red-brown, and gradually turns yellowish green downward. In terms of metals, the Mo-rich domains are dominantly within the intrusion, the Cu-Au-rich domains are in exoskarns near the intrusion, and the Zn-Pb-Ag mineralization occurs mostly in the distal zones. The Cu ore mineralogy changes vertically in the stratabound skarns, from chalcopyrite rich in the upper garnet zone, to bornite rich in the lower wollastonite zone. Values of δ34SV-CDT for chalcopyrite generally decrease from >–1‰ within the intrusion to –6‰ ~2 km away from the intrusion. The C and O isotope compositions of the marble samples show generally increasing trends downward in the stratabound part of the skarn, indicating that the fluid channel was closer to the hornfels. The lowest marble δ18OV-SMOW values (mostly <14%) occur close to the intrusion, consistent with the fluids being derived from the magmas. The organic carbon content decreases at shallower parts of the stratabound skarns and closer to the intrusion (from 0.412 t","PeriodicalId":11469,"journal":{"name":"Economic Geology","volume":null,"pages":null},"PeriodicalIF":5.8,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139636138","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":null,"pages":null},"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":null,"pages":null},"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":null,"pages":null},"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":null,"pages":null},"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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