Sai Pyae Sone, K. Yonezu, A. Imai, Koichiro Watanabe, T. Tindell, K. Sanematsu
The Tagun‐Khin‐Dan gold deposit in the Mogok‐Mandalay‐Mergui Belt, Central Myanmar, is characterized by an array of quartz‐veins hosted in mudstone of the Kogwe Formation of the Carboniferous Mergui Group. Two major deformational stages were recorded in the area; (1) N‐S shortening and (2) uplifting and emplacement of various dykes and quartz veinlets. The N‐S shortening within the area lead the development of km‐scale faults, determined largely by the presence of a zone of major WNW‐ESE trending dextral strike‐slip faulting. Quartz veins in the deposit include: (1) type‐A quartz veins, parallel to the dextral NW‐SE trending major fault; and (2) type‐B quartz veins which occur as isolated parallel veins. Gold in the type‐A quartz vein is present as native gold and electrum locked within pyrite and associated with pyrite and galena and in the type‐B quartz veins as electrum associated with sulfide minerals such as pyrite, chalcopyrite, galena and sphalerite. The mineralization stages can be classified into the type‐A quartz vein stage and the type‐B quartz vein stage. Two type of fluid inclusions; liquid‐rich aqueous inclusions (L‐type) and vapor‐rich aqueous inclusions (V‐type) are identified in the type‐A quartz veins. The homogenization temperature of L‐type fluid inclusions of the type‐A quartz veins ranges from 203 to 321°C and salinity of the fluid inclusions varies from 0.4 to 1.6 wt% NaCl equiv. The homogenization temperature of V‐type fluid inclusions of type‐A quartz veins ranges from 290 to 340°C with a salinity ranging from 0.4 to 1.9 wt% NaCl equivalent. In the type‐B quartz veins, only liquid‐rich aqueous inclusions (L‐type) are identified. The type‐B quartz veins yielded low homogenization temperatures from 160 to 220°C, with low salinities from 0.2 to 1.9 wt% NaCl equiv. compared with those of the type‐A veins. The depth range of ore formation is estimated to be a shallow depth of less than 0.2 km based on fluid inclusion microthermometry. Fluid boiling is evident during the type‐A quartz vein stage, and fluid cooling and mixing in the later type‐B quartz vein stage. Precipitation of pyrite in the ore zone occurred as four recognized types: arsenic‐rich pyrite‐1, 2, 3 in the type‐A quartz veins and pyrite‐4 in the type‐B quartz veins. A positive relation between Au and As contents of pyrites suggests that the gold is present together with arsenic in the structure of pyrites of the type‐A quartz veins as solid solution in addition to as nanoparticle inclusions. The high Co and Ni contents of pyrites of both the type‐A and the type‐B quartz veins, with no evidence of CO2 in the system indicate that the ore‐forming fluids were epizonal magmatic‐hydrothermal fluids rather than metamorphic fluid. The hydrothermal fluids of the Tagun‐Khin‐Dan deposit were driven by faulting to form the mudstone‐hosted epithermal gold mineralization and related to continuing northwards movement of the Indian Plate that initiated the displacement on the st
{"title":"Geological, mineralogical and ore fluid characteristics of the Tagun‐Khin‐Dan gold mineralization in Mogok‐Mandalay‐Mergui Belt, Central Myanmar","authors":"Sai Pyae Sone, K. Yonezu, A. Imai, Koichiro Watanabe, T. Tindell, K. Sanematsu","doi":"10.1111/rge.12298","DOIUrl":"https://doi.org/10.1111/rge.12298","url":null,"abstract":"The Tagun‐Khin‐Dan gold deposit in the Mogok‐Mandalay‐Mergui Belt, Central Myanmar, is characterized by an array of quartz‐veins hosted in mudstone of the Kogwe Formation of the Carboniferous Mergui Group. Two major deformational stages were recorded in the area; (1) N‐S shortening and (2) uplifting and emplacement of various dykes and quartz veinlets. The N‐S shortening within the area lead the development of km‐scale faults, determined largely by the presence of a zone of major WNW‐ESE trending dextral strike‐slip faulting. Quartz veins in the deposit include: (1) type‐A quartz veins, parallel to the dextral NW‐SE trending major fault; and (2) type‐B quartz veins which occur as isolated parallel veins. Gold in the type‐A quartz vein is present as native gold and electrum locked within pyrite and associated with pyrite and galena and in the type‐B quartz veins as electrum associated with sulfide minerals such as pyrite, chalcopyrite, galena and sphalerite. The mineralization stages can be classified into the type‐A quartz vein stage and the type‐B quartz vein stage. Two type of fluid inclusions; liquid‐rich aqueous inclusions (L‐type) and vapor‐rich aqueous inclusions (V‐type) are identified in the type‐A quartz veins. The homogenization temperature of L‐type fluid inclusions of the type‐A quartz veins ranges from 203 to 321°C and salinity of the fluid inclusions varies from 0.4 to 1.6 wt% NaCl equiv. The homogenization temperature of V‐type fluid inclusions of type‐A quartz veins ranges from 290 to 340°C with a salinity ranging from 0.4 to 1.9 wt% NaCl equivalent. In the type‐B quartz veins, only liquid‐rich aqueous inclusions (L‐type) are identified. The type‐B quartz veins yielded low homogenization temperatures from 160 to 220°C, with low salinities from 0.2 to 1.9 wt% NaCl equiv. compared with those of the type‐A veins. The depth range of ore formation is estimated to be a shallow depth of less than 0.2 km based on fluid inclusion microthermometry. Fluid boiling is evident during the type‐A quartz vein stage, and fluid cooling and mixing in the later type‐B quartz vein stage. Precipitation of pyrite in the ore zone occurred as four recognized types: arsenic‐rich pyrite‐1, 2, 3 in the type‐A quartz veins and pyrite‐4 in the type‐B quartz veins. A positive relation between Au and As contents of pyrites suggests that the gold is present together with arsenic in the structure of pyrites of the type‐A quartz veins as solid solution in addition to as nanoparticle inclusions. The high Co and Ni contents of pyrites of both the type‐A and the type‐B quartz veins, with no evidence of CO2 in the system indicate that the ore‐forming fluids were epizonal magmatic‐hydrothermal fluids rather than metamorphic fluid. The hydrothermal fluids of the Tagun‐Khin‐Dan deposit were driven by faulting to form the mudstone‐hosted epithermal gold mineralization and related to continuing northwards movement of the Indian Plate that initiated the displacement on the st","PeriodicalId":21089,"journal":{"name":"Resource Geology","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84295592","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Tungsten (W) deposits are commonly related to the exsolution of magmatic‐hydrothermal fluids from high‐Si granites (SiO2 > 70%). However, whether the W‐related high‐Si granitic magma is produced via partial melting of metasedimentary source rocks or by high degree of fractional crystallization remains controversial. Here we present new geochronological and geochemical data on the intrusions associated with the Lyangar W‐Mo skarn deposit in the Southern Tianshan Orogenic Belt, Uzbekistan. Our new U–Pb zircon age data show that the major intrusion exposed in the region are ca. 280 Ma biotite gabbroic diorite and biotite granite and about 260 Ma porphyritic granite and muscovite porphyritic granite. The molybdenite grains in the skarn rocks and orebodies show weighted Re‐Os ages of 261.4 ± 7.8 Ma and 261.1 ± 3.8 Ma, respectively. In combination with the field contact, we confirm that the muscovite porphyritic granite is genetically related to the W mineralization. The gradual transition from the porphyritic granite to muscovite porphyritic granite, similar mineral assemblages and geochemical variations indicate that they are co‐magmatic, and that the porphyritic granite represents less evolved member. Rhyolite‐MELTS modeling further reinforces that the muscovite porphyritic granites can be produced by high degree of fractional crystallization (~33%, including ~1.2% biotite, ~27% plagioclase, ~2% alkali‐feldspar, ~0.21% Fe‐Ti oxides, and ~2.7% amphibole) of the porphyritic granite magma. On the basis of the positive ƐHf(t) values (+3.03 to +6.02), high‐SiO2 contents and CIPW characters, the porphyritic granite is considered to have formed from dehydration melting at low pH2O of juvenile basaltic source rocks around 16 kbar and 850–1000°C. Our study demonstrates that extreme fractional crystallization of granitic magma plays a significant role in W enrichment in the granitic melt.
{"title":"Extremely fractionated magmas linked with W mineralization: Evidence from the Lyangar W‐Mo deposit, South Tianshan Orogenic Belt","authors":"Xia Fei, Zhaochong Zhang, Zhiguo Cheng, Mamta Santosh, Zhenzhen Gao, B. Nurtaev","doi":"10.1111/rge.12301","DOIUrl":"https://doi.org/10.1111/rge.12301","url":null,"abstract":"Tungsten (W) deposits are commonly related to the exsolution of magmatic‐hydrothermal fluids from high‐Si granites (SiO2 > 70%). However, whether the W‐related high‐Si granitic magma is produced via partial melting of metasedimentary source rocks or by high degree of fractional crystallization remains controversial. Here we present new geochronological and geochemical data on the intrusions associated with the Lyangar W‐Mo skarn deposit in the Southern Tianshan Orogenic Belt, Uzbekistan. Our new U–Pb zircon age data show that the major intrusion exposed in the region are ca. 280 Ma biotite gabbroic diorite and biotite granite and about 260 Ma porphyritic granite and muscovite porphyritic granite. The molybdenite grains in the skarn rocks and orebodies show weighted Re‐Os ages of 261.4 ± 7.8 Ma and 261.1 ± 3.8 Ma, respectively. In combination with the field contact, we confirm that the muscovite porphyritic granite is genetically related to the W mineralization. The gradual transition from the porphyritic granite to muscovite porphyritic granite, similar mineral assemblages and geochemical variations indicate that they are co‐magmatic, and that the porphyritic granite represents less evolved member. Rhyolite‐MELTS modeling further reinforces that the muscovite porphyritic granites can be produced by high degree of fractional crystallization (~33%, including ~1.2% biotite, ~27% plagioclase, ~2% alkali‐feldspar, ~0.21% Fe‐Ti oxides, and ~2.7% amphibole) of the porphyritic granite magma. On the basis of the positive ƐHf(t) values (+3.03 to +6.02), high‐SiO2 contents and CIPW characters, the porphyritic granite is considered to have formed from dehydration melting at low pH2O of juvenile basaltic source rocks around 16 kbar and 850–1000°C. Our study demonstrates that extreme fractional crystallization of granitic magma plays a significant role in W enrichment in the granitic melt.","PeriodicalId":21089,"journal":{"name":"Resource Geology","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88847933","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
R. Abidi, N. Slim-Shimi, Christan Marignac, A. Somarin, C. Renac, E. Deloule, N. Hatira, D. Gasquet
The Ain Allega, Mjar Hannech and Sidi Driss Pb‐Zn‐Ba‐Sr‐As‐(Hg) deposits in northern Tunisia are hosted in a post‐nappe anticline with a core of a Triassic evaporite diapir affected by the NE–SW‐trending Ghardimaou‐Cap Serrat and E‐W lineament. The ore minerals show different styles; particularly, impregnation in dolomite, cement of breccias, replacement ore and open space filling in the dissolution cavities and fractures. Ore minerals include sphalerite, galena, marcasite, pyrite and cinnabar. Principal gangue minerals are composed of barite, celestine, calcite, dolomite and quartz. The orebodies are hosted by Triassic carbonate rocks (Ain Allega ore deposits), Cretaceous carbonate rocks (Mjar Hannech ore deposits) and by the volcanoclastic layers (Sidi Driss ore deposits). These host rocks show hydrothermal alteration, dissolution and brecciation. Sphalerite in the carbonate‐hosted Zn‐Pb deposits in Tunisia occurs as nano‐size microglobular blebs and peloids and forms finely‐laminated bands with wavy and even ripped up features. Peloids are present in collapse breccias of karst cavities. Peloids (5–100 μm) and bacterial filaments (1 μm long) locally form the common micro‐texture of the sulfide mineralization. The core and the shell of peloids are composed of different minerals; there are 1–3 shells and each shell is 1–1.5 μm thick, commonly with coarse crystals. These textures probably represent fossil microbial mats as in‐situ sulfate‐reducing bacteria products and are similar to nano‐textures observed in bacterial biofilms. Electron microscopy, combined with major element changes (Zn, Pb, As, Fe, and Cd) and sulfur isotope values suggest that sphalerite nano‐textures and nano‐spheres are associated with fossilized bacterial‐mat. The δ34S values of sphalerite (−43.9 to +22.38‰) show that the microbial production of H2S controlled sphalerite precipitation. The biogenic nano‐ to macro‐textured sphalerite and sulfur isotope data suggest that microbes had an important role in the genesis of carbonate‐hosted Zn‐Pb deposits in Tunisia during the Miocene.
突尼斯北部的Ain Allega、Mjar Hannech和Sidi Driss Pb - Zn - Ba - Sr - As - (Hg)矿床赋存于后推覆背斜中，其核心为三叠纪蒸发岩底喷岩，受NE-SW -走向的Ghardimaou - Cap Serrat和E - W构造的影响。矿石矿物表现出不同的风格;主要表现为白云岩浸渍、角砾岩胶结、补矿、溶蚀孔洞和溶蚀裂隙的空隙充填。矿石矿物有闪锌矿、方铅矿、黄铁矿、朱砂等。脉石矿物主要有重晶石、天青石、方解石、白云石和石英。矿体赋存于三叠系碳酸盐岩(Ain allea矿床)、白垩系碳酸盐岩(Mjar Hannech矿床)和火山碎屑层(Sidi Driss矿床)。这些寄主岩石表现为热液蚀变、溶蚀和角化作用。在突尼斯的碳酸盐型锌铅矿床中，闪锌矿以纳米级微球状泡和球状体的形式出现，并形成具有波浪状甚至撕裂特征的精细层状带。似球粒存在于溶洞的塌陷角砾岩中。球状体(5-100 μm)和细菌细丝(1 μm长)在局部形成了硫化物矿化的共同微观结构。球状体的核和壳由不同的矿物组成;有1-3个外壳，每个外壳厚1-1.5 μm，通常有粗晶。这些结构可能代表化石微生物垫作为原位硫酸盐还原细菌产物，与细菌生物膜中观察到的纳米结构相似。电子显微镜、主要元素变化(Zn、Pb、As、Fe和Cd)和硫同位素值表明闪锌矿纳米结构和纳米球与细菌垫化石有关。闪锌矿的δ34S值(−43.9 ~ +22.38‰)表明微生物生产H2S控制了闪锌矿的沉淀。生物成因的纳米-宏观结构闪锌矿和硫同位素数据表明，微生物在突尼斯中新世碳酸盐型锌- Pb矿床的成因中发挥了重要作用。
{"title":"The microbial controls on the deposition of Pb‐Zn minerals in carbonate‐hosted Tunisian ore deposits","authors":"R. Abidi, N. Slim-Shimi, Christan Marignac, A. Somarin, C. Renac, E. Deloule, N. Hatira, D. Gasquet","doi":"10.1111/rge.12287","DOIUrl":"https://doi.org/10.1111/rge.12287","url":null,"abstract":"The Ain Allega, Mjar Hannech and Sidi Driss Pb‐Zn‐Ba‐Sr‐As‐(Hg) deposits in northern Tunisia are hosted in a post‐nappe anticline with a core of a Triassic evaporite diapir affected by the NE–SW‐trending Ghardimaou‐Cap Serrat and E‐W lineament. The ore minerals show different styles; particularly, impregnation in dolomite, cement of breccias, replacement ore and open space filling in the dissolution cavities and fractures. Ore minerals include sphalerite, galena, marcasite, pyrite and cinnabar. Principal gangue minerals are composed of barite, celestine, calcite, dolomite and quartz. The orebodies are hosted by Triassic carbonate rocks (Ain Allega ore deposits), Cretaceous carbonate rocks (Mjar Hannech ore deposits) and by the volcanoclastic layers (Sidi Driss ore deposits). These host rocks show hydrothermal alteration, dissolution and brecciation. Sphalerite in the carbonate‐hosted Zn‐Pb deposits in Tunisia occurs as nano‐size microglobular blebs and peloids and forms finely‐laminated bands with wavy and even ripped up features. Peloids are present in collapse breccias of karst cavities. Peloids (5–100 μm) and bacterial filaments (1 μm long) locally form the common micro‐texture of the sulfide mineralization. The core and the shell of peloids are composed of different minerals; there are 1–3 shells and each shell is 1–1.5 μm thick, commonly with coarse crystals. These textures probably represent fossil microbial mats as in‐situ sulfate‐reducing bacteria products and are similar to nano‐textures observed in bacterial biofilms. Electron microscopy, combined with major element changes (Zn, Pb, As, Fe, and Cd) and sulfur isotope values suggest that sphalerite nano‐textures and nano‐spheres are associated with fossilized bacterial‐mat. The δ34S values of sphalerite (−43.9 to +22.38‰) show that the microbial production of H2S controlled sphalerite precipitation. The biogenic nano‐ to macro‐textured sphalerite and sulfur isotope data suggest that microbes had an important role in the genesis of carbonate‐hosted Zn‐Pb deposits in Tunisia during the Miocene.","PeriodicalId":21089,"journal":{"name":"Resource Geology","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79436554","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Reza Al Furqan, Yasushi Watanabe, A. Arribas, C. Leys, T. Echigo, Rici Anggun Putri, Renanda Sevirajati
The Grasberg Cu—Au—(Mo) deposit comprises the shallower Main Grasberg porphyry Cu—Au and the deeper Gajah Tidur (GT) porphyry Cu—Mo—(Au) systems. The GT porphyry preserves various types of white mica whose geochemical variations provide insights into the white mica‐dominated alteration of porphyry systems. The white mica assemblages within the GT porphyry system comprise: (1) muscovite‐anhydrite‐chlorite (MAC), (2) muscovite‐chlorite‐anhydrite (MCA), and (3) muscovite‐quartz ± pyrophyllite (MQP). These assemblages display zonation from central and deep parts of the system to its shallower and peripheral parts. The MAC alteration white micas are characterized by high Na, Fe, Ti, and V concentrations, and with short‐wave infrared Al—OH absorption wavelengths of 2203–2208 nm. The MCA white micas have higher Mg content than the other two GT white mica assemblages but similar Al—OH absorption wavelengths to the MAC white micas. The MQP alteration white micas have low Na, Fe, Mg, and Ti, but relatively high Si, Al, and F, and Al—OH absorption wavelengths are largely shorter than 2202 nm. We interpret that the high Fe and Ti content of the MAC white micas is due to inheritance of these elements from mafic minerals they replaced. The higher Fe content of these white micas explain their longer wavelength Al—OH absorption positions relative to the MQP white micas. In contrast, lower Fe content and shorter Al—OH wavelengths of the MQP white micas are caused by their higher Si and Al content, which reduces iron occupancy in the white mica crystal structure. White micas in this assemblage formed at lower temperature and probable lower pH condition that may have led to a replacement of Fe by Al. The short‐wave infrared Al—OH position of white mica together with the associated hydrothermal assemblage can be used as a proximitor for porphyry Cu hydrothermal centres. White mica associated with chlorite, anhydrite, and chalcopyrite, which commonly occur overprinting or adjacent to the potassic alteration center, are characterized by Al—OH absorption positions at 2200–2215 nm. By contrast, white mica associated with quartz‐pyrite are characterized by Al—OH wavelengths shorter than 2202 nm. In the distal part of porphyry Cu system, white micas may be associated with chlorite and have Al—OH absorption positions longer than 2204 nm.
{"title":"Chemical and short‐wave infrared characteristics of white mica associated with the Gajah Tidur porphyry copper system at the deep Grasberg Cu—Au—(Mo) deposit, Indonesia","authors":"Reza Al Furqan, Yasushi Watanabe, A. Arribas, C. Leys, T. Echigo, Rici Anggun Putri, Renanda Sevirajati","doi":"10.1111/rge.12296","DOIUrl":"https://doi.org/10.1111/rge.12296","url":null,"abstract":"The Grasberg Cu—Au—(Mo) deposit comprises the shallower Main Grasberg porphyry Cu—Au and the deeper Gajah Tidur (GT) porphyry Cu—Mo—(Au) systems. The GT porphyry preserves various types of white mica whose geochemical variations provide insights into the white mica‐dominated alteration of porphyry systems. The white mica assemblages within the GT porphyry system comprise: (1) muscovite‐anhydrite‐chlorite (MAC), (2) muscovite‐chlorite‐anhydrite (MCA), and (3) muscovite‐quartz ± pyrophyllite (MQP). These assemblages display zonation from central and deep parts of the system to its shallower and peripheral parts. The MAC alteration white micas are characterized by high Na, Fe, Ti, and V concentrations, and with short‐wave infrared Al—OH absorption wavelengths of 2203–2208 nm. The MCA white micas have higher Mg content than the other two GT white mica assemblages but similar Al—OH absorption wavelengths to the MAC white micas. The MQP alteration white micas have low Na, Fe, Mg, and Ti, but relatively high Si, Al, and F, and Al—OH absorption wavelengths are largely shorter than 2202 nm. We interpret that the high Fe and Ti content of the MAC white micas is due to inheritance of these elements from mafic minerals they replaced. The higher Fe content of these white micas explain their longer wavelength Al—OH absorption positions relative to the MQP white micas. In contrast, lower Fe content and shorter Al—OH wavelengths of the MQP white micas are caused by their higher Si and Al content, which reduces iron occupancy in the white mica crystal structure. White micas in this assemblage formed at lower temperature and probable lower pH condition that may have led to a replacement of Fe by Al. The short‐wave infrared Al—OH position of white mica together with the associated hydrothermal assemblage can be used as a proximitor for porphyry Cu hydrothermal centres. White mica associated with chlorite, anhydrite, and chalcopyrite, which commonly occur overprinting or adjacent to the potassic alteration center, are characterized by Al—OH absorption positions at 2200–2215 nm. By contrast, white mica associated with quartz‐pyrite are characterized by Al—OH wavelengths shorter than 2202 nm. In the distal part of porphyry Cu system, white micas may be associated with chlorite and have Al—OH absorption positions longer than 2204 nm.","PeriodicalId":21089,"journal":{"name":"Resource Geology","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84887947","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
To determine local deposit features in the vein‐type gold–silver ore deposit of the historical Togi mine, Noto Peninsula, central Japan, we investigated the occurrence and chemical compositions of ore minerals, especially silver‐ and/or gold‐bearing minerals, and wall‐rock alteration in the Togo No. 3 tunnel, a major tunnel of the Urukami mining area of the Togi mine. In the tunnel, the stockwork veins which are generally 0.1–1.5 m wide runs in Neogene pyroxene andesite. In the ore‐bearing quartz vein, in addition to the sulfides such as sphalerite, pyrite and chalcopyrite, the following Au and/or Ag ore minerals were identified: electrum with <49.3 mol% Ag, uytenbogaardtite, fischesserite, silver‐rich minerals of the Ag2S–Ag2Se solid solution series, and Se‐rich pearceite. Gangue minerals in the quartz veins are quartz and adularia. The wall rock is silicified, chloritized, and sericitized pyroxene andesite. Multiple generations of adularia grown on quartz suggest that adularia has grown by repeatedly passing the hydrothermal solution through the vein. Based on the characteristic occurrence of the Ag and/or silver‐rich ore minerals such as electrum, fischesserite, and Se‐rich pearceite and a gangue mineral, adularia, and on the wall‐rock alteration characterized by chlorite, sericite, and calcite, the Togi deposit is classified as a Se‐type and low‐sulfidation epithermal gold vein deposit. The K‐Ar ages of illite/smectite mixed‐layer minerals from the altered outcrop and plagioclase from a fresh andesite sample are 17.68 ± 0.41 and 17.52 ± 0.43 Ma, respectively, in agreement with published data of the Besshodake andesite. These results indicate that the hydrothermal fluids generated by the Miocene andesitic magma activity infiltrated the fissures relating to the formation of the Togi‐gawa Nangan Fault at the northern boundary of the Togi mining area, and Au and/or Ag‐rich ore minerals were formed from the hydrothermal fluid with decreasing temperature at the shallow level.
{"title":"Mineralogy, chronology and formation process of the epithermal gold–silver vein deposits in the historical Togi mine, Noto Peninsula, Japan","authors":"M. Hamada, W. Kobayashi, Y. Hiramatsu, N. Hasebe","doi":"10.1111/rge.12294","DOIUrl":"https://doi.org/10.1111/rge.12294","url":null,"abstract":"To determine local deposit features in the vein‐type gold–silver ore deposit of the historical Togi mine, Noto Peninsula, central Japan, we investigated the occurrence and chemical compositions of ore minerals, especially silver‐ and/or gold‐bearing minerals, and wall‐rock alteration in the Togo No. 3 tunnel, a major tunnel of the Urukami mining area of the Togi mine. In the tunnel, the stockwork veins which are generally 0.1–1.5 m wide runs in Neogene pyroxene andesite. In the ore‐bearing quartz vein, in addition to the sulfides such as sphalerite, pyrite and chalcopyrite, the following Au and/or Ag ore minerals were identified: electrum with <49.3 mol% Ag, uytenbogaardtite, fischesserite, silver‐rich minerals of the Ag2S–Ag2Se solid solution series, and Se‐rich pearceite. Gangue minerals in the quartz veins are quartz and adularia. The wall rock is silicified, chloritized, and sericitized pyroxene andesite. Multiple generations of adularia grown on quartz suggest that adularia has grown by repeatedly passing the hydrothermal solution through the vein. Based on the characteristic occurrence of the Ag and/or silver‐rich ore minerals such as electrum, fischesserite, and Se‐rich pearceite and a gangue mineral, adularia, and on the wall‐rock alteration characterized by chlorite, sericite, and calcite, the Togi deposit is classified as a Se‐type and low‐sulfidation epithermal gold vein deposit. The K‐Ar ages of illite/smectite mixed‐layer minerals from the altered outcrop and plagioclase from a fresh andesite sample are 17.68 ± 0.41 and 17.52 ± 0.43 Ma, respectively, in agreement with published data of the Besshodake andesite. These results indicate that the hydrothermal fluids generated by the Miocene andesitic magma activity infiltrated the fissures relating to the formation of the Togi‐gawa Nangan Fault at the northern boundary of the Togi mining area, and Au and/or Ag‐rich ore minerals were formed from the hydrothermal fluid with decreasing temperature at the shallow level.","PeriodicalId":21089,"journal":{"name":"Resource Geology","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85961916","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Maanijou, Mohammad Mostaghimi, Mehdi Abdollahy Riseh, D. Lentz, Ali A. Sepahi Gerow
The Sarcheshmeh porphyry copper deposit (PCD) is located in the southeast part of the arc‐related Urumieh‐Dokhtar volcano‐plutonic belt. This PCD was formed by intrusion of a Middle Miocene granodiorite to tonalite stock into the volcano‐sedimentary rocks that are mainly andesite exhibiting Early Tertiary thrusting and faulting. On the basis of geochemistry of intrusive rocks, they are calc‐alkalic and alkali‐calcic suites that are consistent with oxidized I‐type magmas. The Fe2O3/FeO ratio in the Sarcheshmeh PCD is 1 to 3, consistent with a high oxygen fugacity. The igneous rocks of Sarcheshmeh PCD belong to a mature arc, but related to a post‐collision arc setting. Considerable evidence supports adakitic affinities of the Sarcheshmeh rocks, including geochemical values of Sr > 300 ppm (ave., 594 ppm), high ratios of Sr/Y > 20 (ave., 75), La/Yb > 20 (ave., 30), and enrichment of LREE and LILE relative to HREE and HFSE. The adakites of Sarcheshmeh belong to high‐silica adakites (HSA) that can be formed by melting of subducting seawater‐altered oceanic plate, which interact with the mantle wedge then followed by slab break‐off with local transtension in the middle part of the Dehaj‐Sarduieh belt. In rocks of the region, the ratios of Th/Ce > 0.12 and Nb/Zr > 0.05 suggest that the subducting crust has a role in forming different groups of these rocks. Geotectonic discrimination diagrams are used to distinguish between normal arc and slab failure magmatic systems, including Nb versus Y, La/Sm versus Sm/Yb, La/Yb versus Gd/Yb, and Rb versus Nb + Y diagrams. The plutonic rocks of the Sarcheshmeh PCD have characteristics consistent with adakites derived via slab failure, which are obviously metallogenically favorable magmatic systems. Adakitic melts generated rapidly during sinking of a broken slab (into higher temperature mantle), buoyantly migrate through the subcontinental lithospheric mantle (SCLM), which is related to structural evolution of that SCLM with local extension or transpression.
{"title":"Petrology and geochemistry of adakitic intrusions and dykes at Sarcheshmeh porphyry Cu‐Mo ± Au deposit, Iran: Insights into their source","authors":"M. Maanijou, Mohammad Mostaghimi, Mehdi Abdollahy Riseh, D. Lentz, Ali A. Sepahi Gerow","doi":"10.1111/rge.12297","DOIUrl":"https://doi.org/10.1111/rge.12297","url":null,"abstract":"The Sarcheshmeh porphyry copper deposit (PCD) is located in the southeast part of the arc‐related Urumieh‐Dokhtar volcano‐plutonic belt. This PCD was formed by intrusion of a Middle Miocene granodiorite to tonalite stock into the volcano‐sedimentary rocks that are mainly andesite exhibiting Early Tertiary thrusting and faulting. On the basis of geochemistry of intrusive rocks, they are calc‐alkalic and alkali‐calcic suites that are consistent with oxidized I‐type magmas. The Fe2O3/FeO ratio in the Sarcheshmeh PCD is 1 to 3, consistent with a high oxygen fugacity. The igneous rocks of Sarcheshmeh PCD belong to a mature arc, but related to a post‐collision arc setting. Considerable evidence supports adakitic affinities of the Sarcheshmeh rocks, including geochemical values of Sr > 300 ppm (ave., 594 ppm), high ratios of Sr/Y > 20 (ave., 75), La/Yb > 20 (ave., 30), and enrichment of LREE and LILE relative to HREE and HFSE. The adakites of Sarcheshmeh belong to high‐silica adakites (HSA) that can be formed by melting of subducting seawater‐altered oceanic plate, which interact with the mantle wedge then followed by slab break‐off with local transtension in the middle part of the Dehaj‐Sarduieh belt. In rocks of the region, the ratios of Th/Ce > 0.12 and Nb/Zr > 0.05 suggest that the subducting crust has a role in forming different groups of these rocks. Geotectonic discrimination diagrams are used to distinguish between normal arc and slab failure magmatic systems, including Nb versus Y, La/Sm versus Sm/Yb, La/Yb versus Gd/Yb, and Rb versus Nb + Y diagrams. The plutonic rocks of the Sarcheshmeh PCD have characteristics consistent with adakites derived via slab failure, which are obviously metallogenically favorable magmatic systems. Adakitic melts generated rapidly during sinking of a broken slab (into higher temperature mantle), buoyantly migrate through the subcontinental lithospheric mantle (SCLM), which is related to structural evolution of that SCLM with local extension or transpression.","PeriodicalId":21089,"journal":{"name":"Resource Geology","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88642660","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Youjiang Basin in SW China is the second‐largest Carlin‐like goldfield in the world after Nevada, USA. However, the age and the hydrothermal origin of the gold mineralization are still in controversy, which leads to ambiguities in understanding the geodynamic setting and genetic mechanism of the gold deposition. Nibao is a large, stratabound, and fault‐controlled Carlin‐type gold deposit in the north of the Youjiang Basin. Three ore stages have been recognized in the evolution of the mineralizing hydrothermal fluid, with the stages being characterized by assemblages of the early quartz–porous pyrite, the main quartz–calcite‐apatite–sericite–pyrite–arsenopyrite‐gold, and the late quartz–calcite–fluorite–realgar–orpiment–stibnite. Calcite veins from the main and late ore stage at Nibao are enriched in middle rare earth elements, which is a distinctive characteristic of hydrothermal calcite veins associated with low‐temperature hydrothermal Au‐Sb deposits in the Youjiang Basin, and yield a Sm‐Nd isochron age of 138 ± 1 Ma. The vast majority of the ore stage calcite samples have narrow 87Sr/86Sr ratios and εNd(t) values ranging from 0.708119 to 0.708423 and − 1.1–−3.3, respectively, indicating that the gold‐bearing hydrothermal fluid could be derived from the mixing of mantle and crustal materials. Therefore, we proposed that the gold mineralization during the Early Cretaceous in the Youjiang Basin was triggered by the large‐scale lithosphere extension following the retreat of the subducted Paleo‐Pacific oceanic crust, and the hydrothermal fluid could be originated from the mantle and underwent the contamination of Yangtze upper continental crust.
{"title":"Sm‐Nd isochron age and Sr‐Nd isotopes of the calcite from the Nibao gold deposit in the Youjiang Basin, SW China","authors":"Xingzhong Ji, L. Bagas, Zhonghua Han, Wengang Liu","doi":"10.1111/rge.12292","DOIUrl":"https://doi.org/10.1111/rge.12292","url":null,"abstract":"The Youjiang Basin in SW China is the second‐largest Carlin‐like goldfield in the world after Nevada, USA. However, the age and the hydrothermal origin of the gold mineralization are still in controversy, which leads to ambiguities in understanding the geodynamic setting and genetic mechanism of the gold deposition. Nibao is a large, stratabound, and fault‐controlled Carlin‐type gold deposit in the north of the Youjiang Basin. Three ore stages have been recognized in the evolution of the mineralizing hydrothermal fluid, with the stages being characterized by assemblages of the early quartz–porous pyrite, the main quartz–calcite‐apatite–sericite–pyrite–arsenopyrite‐gold, and the late quartz–calcite–fluorite–realgar–orpiment–stibnite. Calcite veins from the main and late ore stage at Nibao are enriched in middle rare earth elements, which is a distinctive characteristic of hydrothermal calcite veins associated with low‐temperature hydrothermal Au‐Sb deposits in the Youjiang Basin, and yield a Sm‐Nd isochron age of 138 ± 1 Ma. The vast majority of the ore stage calcite samples have narrow 87Sr/86Sr ratios and εNd(t) values ranging from 0.708119 to 0.708423 and − 1.1–−3.3, respectively, indicating that the gold‐bearing hydrothermal fluid could be derived from the mixing of mantle and crustal materials. Therefore, we proposed that the gold mineralization during the Early Cretaceous in the Youjiang Basin was triggered by the large‐scale lithosphere extension following the retreat of the subducted Paleo‐Pacific oceanic crust, and the hydrothermal fluid could be originated from the mantle and underwent the contamination of Yangtze upper continental crust.","PeriodicalId":21089,"journal":{"name":"Resource Geology","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82059895","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Biao Yang, Yi-ke Li, Tao Rong, Xuan Yang, Gao‐zhen Jiang
With more than 11,000 t of gold resources, the Central Asian orogenic belt is the most significant gold deposit belt in the world. The majority of the orogenic belt's gold resources are found in a layer of carbon‐rich black shale. However, there is disagreement regarding the origin and metallogenic process of such a significant quantity of gold. The Haoyaoerhudong gold deposit is located where the northern margin of the North China Craton and the southern margin of the Central Asian orogenic belt converge. It is the most significant black shale gold deposit in the northern margin of North China Craton gold province. The pyrite that typically develops in the Haoyaoerhudong gold deposit has been categorized into five varieties through comprehensive field investigation and mineralogical research, which correspond to five metallogenic stages: Stage 1, sedimentary diagenesis; Stage 2, tectonic deformation; Stage 3, hydrothermal; Stage 4, hydrothermal transformation; Stage 5, late metallogenic. For pyrite in the previous four metallogenic stages, in situ LA‐ICP‐MS trace element analysis and pyrite sulfide isotope analyses were performed. The results suggest that: The average Au contents in the pyrite of sedimentary diagenesis stage is 0.098 ppm; the average Au contents in the pyrite of the tectonic deformation stage and hydrothermal stage, is below the detection limit mostly; the average Au contents in the pyrite of hydrothermal transformation stage is 0.12 ppm. The results indicate that only 22.4% more gold is present in hydrothermal transformation stage than in sedimentary diagenetic stage overall. It may be inferred that the gold enrichment of Haoyaoerhudong gold deposit mostly took place during the sedimentary diagenetic stage; subsequent brittle‐ductile shear and hydrothermal fluid activity did not result in a further enrichment of gold. The sulfur isotope test results of various metallogenic stages in the deposit can be analyzed, and they are generally consistent. The δ34S values range from +10.15% to +16.47%, with an average value of +13.02%. It suggests that there might be a single source of sulfur. According to extensive analysis, the Haoyaoerhudong gold deposit formed a relatively low‐grade ore body during the sedimentary diagenesis stage, and the subsequent tectonic deformation stage and hydrothermal stage provided physical conditions for further activation of gold metal but did not bring corresponding material sources for mineralization.
{"title":"In situ trace element and sulfur isotope of pyrite constraints the mineralization process of haoyaoerhudong gold deposit in Inner Mongolia, China","authors":"Biao Yang, Yi-ke Li, Tao Rong, Xuan Yang, Gao‐zhen Jiang","doi":"10.1111/rge.12302","DOIUrl":"https://doi.org/10.1111/rge.12302","url":null,"abstract":"With more than 11,000 t of gold resources, the Central Asian orogenic belt is the most significant gold deposit belt in the world. The majority of the orogenic belt's gold resources are found in a layer of carbon‐rich black shale. However, there is disagreement regarding the origin and metallogenic process of such a significant quantity of gold. The Haoyaoerhudong gold deposit is located where the northern margin of the North China Craton and the southern margin of the Central Asian orogenic belt converge. It is the most significant black shale gold deposit in the northern margin of North China Craton gold province. The pyrite that typically develops in the Haoyaoerhudong gold deposit has been categorized into five varieties through comprehensive field investigation and mineralogical research, which correspond to five metallogenic stages: Stage 1, sedimentary diagenesis; Stage 2, tectonic deformation; Stage 3, hydrothermal; Stage 4, hydrothermal transformation; Stage 5, late metallogenic. For pyrite in the previous four metallogenic stages, in situ LA‐ICP‐MS trace element analysis and pyrite sulfide isotope analyses were performed. The results suggest that: The average Au contents in the pyrite of sedimentary diagenesis stage is 0.098 ppm; the average Au contents in the pyrite of the tectonic deformation stage and hydrothermal stage, is below the detection limit mostly; the average Au contents in the pyrite of hydrothermal transformation stage is 0.12 ppm. The results indicate that only 22.4% more gold is present in hydrothermal transformation stage than in sedimentary diagenetic stage overall. It may be inferred that the gold enrichment of Haoyaoerhudong gold deposit mostly took place during the sedimentary diagenetic stage; subsequent brittle‐ductile shear and hydrothermal fluid activity did not result in a further enrichment of gold. The sulfur isotope test results of various metallogenic stages in the deposit can be analyzed, and they are generally consistent. The δ34S values range from +10.15% to +16.47%, with an average value of +13.02%. It suggests that there might be a single source of sulfur. According to extensive analysis, the Haoyaoerhudong gold deposit formed a relatively low‐grade ore body during the sedimentary diagenesis stage, and the subsequent tectonic deformation stage and hydrothermal stage provided physical conditions for further activation of gold metal but did not bring corresponding material sources for mineralization.","PeriodicalId":21089,"journal":{"name":"Resource Geology","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81796562","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Zakaria Endut, T. Ng, Jasmi Hafiz Abdul Aziz, C. Makoundi, Haslikhalijah Dauad, K. Ariffin
Penjom deposit is an orogenic gold deposit located in the Central Belt of Peninsular Malaysia. Gold mineralization is associated with various styles and textures of quartz‐carbonate veins hosted within the metasedimentary as the main host rock and felsic igneous rock including minor volcanic rock. Vein textural features and morphologies have been investigated based on macroscopic and microscopic characteristics to understand the process of veins formation, and the relationship with gold mineralization. At the hand specimen scale, veins show a variety of textures that are either primary or superimposed. Primary textures are comb, massive anhedral buck quartz veins, and laminae veins or vein septa representing early vein introduction without vein modification. Extension veins that are normally concordant to maximum compressive stress direction show either a common comb texture within these veins or buck texture inside thick veins. Secondary textures are ribbon, stylolites, breccias, and late spider veinlets that overprint early veins formed during repeated structural episodes. Later stage deformation events superimposed on the existing veins texture results in intensely deformed veins. The interrelationship of structure, vein‐type and texture, gold and sulfide mineralogy have been correlated to constrain the episodes of gold mineralization in the Penjom deposit. Characteristics of vein textures indicate physio‐environment under confining lithostatic pressure where fluids filled the space through crack and sealing mechanism. Vein systems and gold mineralization events that have been correlated with the D2D3 (fold‐fault) deformation events and inferred to be temporally related to the late‐stage regional orogenic event dated Late Triassic‐Early Jurassic that affected Peninsular Malaysia.
{"title":"Texture and morphology of veins and their relationship to gold mineralization in the Penjom deposit, Malaysia","authors":"Zakaria Endut, T. Ng, Jasmi Hafiz Abdul Aziz, C. Makoundi, Haslikhalijah Dauad, K. Ariffin","doi":"10.1111/rge.12288","DOIUrl":"https://doi.org/10.1111/rge.12288","url":null,"abstract":"Penjom deposit is an orogenic gold deposit located in the Central Belt of Peninsular Malaysia. Gold mineralization is associated with various styles and textures of quartz‐carbonate veins hosted within the metasedimentary as the main host rock and felsic igneous rock including minor volcanic rock. Vein textural features and morphologies have been investigated based on macroscopic and microscopic characteristics to understand the process of veins formation, and the relationship with gold mineralization. At the hand specimen scale, veins show a variety of textures that are either primary or superimposed. Primary textures are comb, massive anhedral buck quartz veins, and laminae veins or vein septa representing early vein introduction without vein modification. Extension veins that are normally concordant to maximum compressive stress direction show either a common comb texture within these veins or buck texture inside thick veins. Secondary textures are ribbon, stylolites, breccias, and late spider veinlets that overprint early veins formed during repeated structural episodes. Later stage deformation events superimposed on the existing veins texture results in intensely deformed veins. The interrelationship of structure, vein‐type and texture, gold and sulfide mineralogy have been correlated to constrain the episodes of gold mineralization in the Penjom deposit. Characteristics of vein textures indicate physio‐environment under confining lithostatic pressure where fluids filled the space through crack and sealing mechanism. Vein systems and gold mineralization events that have been correlated with the D2D3 (fold‐fault) deformation events and inferred to be temporally related to the late‐stage regional orogenic event dated Late Triassic‐Early Jurassic that affected Peninsular Malaysia.","PeriodicalId":21089,"journal":{"name":"Resource Geology","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76352847","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Renaldi Suhendra, R. Takahashi, A. Imai, Hinako Sato, N. Setiawan, A. Agangi
The Luk Ulo Metamorphic Complex, Central Java is a product of the Cretaceous subduction and accretion, and includes diverse types of protoliths. Two‐types of primary mineralization have been recognized in this area, namely, (1) seafloor basalt‐hosted massive sulfide mineralization and (2) low‐grade metamorphic rocks‐hosted vein type mineralization. Later erosion of these types of primary mineralization formed placer gold deposits along rivers. However, the source has never been identified. Thus, this study aims at understanding the source of placer gold, the characteristics of the primary mineralization, and the tectonic evolution of the study area on the basis of mineralogy, mineral chemistry, whole‐rock geochemistry, and sulfur isotope analyses. Volcanogenic massive sulfide (VMS)‐type mineralization was identified in the seafloor basalt and few deep‐sea sedimentary rocks, and both the ores and host rocks preserved pre‐metamorphic textures and minerals. The characteristics of this VMS‐type mineralization include (1) crustiform quartz veins with pyrite cutting the host rocks, (2) zonation of local silicification to interlayered chlorite/smectite‐chlorite‐laumontite‐calcite‐epidote alteration from central to outer zone, (3) pyrite‐dominated ores with minor amounts of arsenian pyrite, chalcopyrite, and marcasite, (4) unmetamorphosed host rocks and ores, and (5) sulfur isotope signature with a median δ34S of +3.1‰ suggesting sulfur derived from magmatic source and/or sulfur extracted from basaltic rocks with a small contribution of biogenic sulfur. On the other hand, low‐grade metamorphic rocks‐hosted vein type mineralization was identified as orogenic‐type gold mineralization, and the mineralized veins formed after the peak of metamorphism. It is characterized by (1) pyrite‐arsenian pyrite ores with minor amounts of arsenopyrite, galena, tetrahedrite, chalcopyrite, and sphalerite, (2) quartz‐illite‐graphite alteration assemblage, (3) mineralized veins cross‐cutting the foliation of metamorphic host rocks, (4) high antimony contents of pyrite (up to 1.7 wt%) and rutile (up to 160 ppm), (5) relatively high ore‐forming temperature (423 ± 9°C, calculated from arsenopyrite and graphite geothermometers), and (6) remobilized‐sedimentary sulfur signature of the ores with a median δ34S of −9.8‰. Several lines of evidence suggest that placer gold was likely derived from the erosion of orogenic‐type gold ores in the surrounding areas. This evidence includes the presence of gold‐bearing ores hosted by low‐grade metapelites and metagranitoid with characteristics of orogenic‐type gold mineralization, whereas the VMS‐type ores are barren in gold. The occurrence of the mid‐oceanic ridge‐ and accretion zone‐related mineralization in this area reflects the subduction and amalgamation of oceanic and continental crustal blocks during the Cretaceous period. Discovery of gold mineralization hosted in the Cretaceous basement rocks of the Sunda arc indicates the importanc
{"title":"Primary source of placer gold in the Luk Ulo Metamorphic Complex, Central Java, Indonesia","authors":"Renaldi Suhendra, R. Takahashi, A. Imai, Hinako Sato, N. Setiawan, A. Agangi","doi":"10.1111/rge.12300","DOIUrl":"https://doi.org/10.1111/rge.12300","url":null,"abstract":"The Luk Ulo Metamorphic Complex, Central Java is a product of the Cretaceous subduction and accretion, and includes diverse types of protoliths. Two‐types of primary mineralization have been recognized in this area, namely, (1) seafloor basalt‐hosted massive sulfide mineralization and (2) low‐grade metamorphic rocks‐hosted vein type mineralization. Later erosion of these types of primary mineralization formed placer gold deposits along rivers. However, the source has never been identified. Thus, this study aims at understanding the source of placer gold, the characteristics of the primary mineralization, and the tectonic evolution of the study area on the basis of mineralogy, mineral chemistry, whole‐rock geochemistry, and sulfur isotope analyses. Volcanogenic massive sulfide (VMS)‐type mineralization was identified in the seafloor basalt and few deep‐sea sedimentary rocks, and both the ores and host rocks preserved pre‐metamorphic textures and minerals. The characteristics of this VMS‐type mineralization include (1) crustiform quartz veins with pyrite cutting the host rocks, (2) zonation of local silicification to interlayered chlorite/smectite‐chlorite‐laumontite‐calcite‐epidote alteration from central to outer zone, (3) pyrite‐dominated ores with minor amounts of arsenian pyrite, chalcopyrite, and marcasite, (4) unmetamorphosed host rocks and ores, and (5) sulfur isotope signature with a median δ34S of +3.1‰ suggesting sulfur derived from magmatic source and/or sulfur extracted from basaltic rocks with a small contribution of biogenic sulfur. On the other hand, low‐grade metamorphic rocks‐hosted vein type mineralization was identified as orogenic‐type gold mineralization, and the mineralized veins formed after the peak of metamorphism. It is characterized by (1) pyrite‐arsenian pyrite ores with minor amounts of arsenopyrite, galena, tetrahedrite, chalcopyrite, and sphalerite, (2) quartz‐illite‐graphite alteration assemblage, (3) mineralized veins cross‐cutting the foliation of metamorphic host rocks, (4) high antimony contents of pyrite (up to 1.7 wt%) and rutile (up to 160 ppm), (5) relatively high ore‐forming temperature (423 ± 9°C, calculated from arsenopyrite and graphite geothermometers), and (6) remobilized‐sedimentary sulfur signature of the ores with a median δ34S of −9.8‰. Several lines of evidence suggest that placer gold was likely derived from the erosion of orogenic‐type gold ores in the surrounding areas. This evidence includes the presence of gold‐bearing ores hosted by low‐grade metapelites and metagranitoid with characteristics of orogenic‐type gold mineralization, whereas the VMS‐type ores are barren in gold. The occurrence of the mid‐oceanic ridge‐ and accretion zone‐related mineralization in this area reflects the subduction and amalgamation of oceanic and continental crustal blocks during the Cretaceous period. Discovery of gold mineralization hosted in the Cretaceous basement rocks of the Sunda arc indicates the importanc","PeriodicalId":21089,"journal":{"name":"Resource Geology","volume":null,"pages":null},"PeriodicalIF":1.4,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77032988","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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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