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Formation of polymetallic ores in the metasedimentary rocks of Rangpo area, Sikkim Lesser Himalaya, India: Mineralogical and geochemical attributes
Geological Journal ( IF 1.4 ) Pub Date : 2022-09-19 , DOI: 10.1002/gj.4592 Vandana Jha 1 , Rajesh Sharma 1
Geological Journal ( IF 1.4 ) Pub Date : 2022-09-19 , DOI: 10.1002/gj.4592 Vandana Jha 1 , Rajesh Sharma 1
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Present work investigates the ore mineralogy, geochemistry of host metasedimentary rocks, and the mineral chemistry of the main sulphide minerals, namely, sphalerite, chalcopyrite, galena, and pyrite from the Rangpo sulphide mineralization, Sikkim. Based on the textural relationships of the oxide and sulphide minerals such as mutual boundary, exsolution blebs, and replacement features, three stages including two stages of primary ore mineral formation, and an alteration stage of secondary mineral development is established. Oxide and sulphide minerals predominantly magnetite, chalcopyrite, sphalerite, galena, pyrrhotite, and cobaltite occur as stage-I ore minerals, and the sulphide minerals namely galena, pyrrhotite chalcopyrite, arsenopyrite, sphalerite, and pyrite are identified as stage-II minerals. The alteration minerals malachite and azurite represent stage-III. The geochemistry of host metasedimentary rocks is characterized by SiO2 in the range of 53.28 to 85.62 wt%, Mg# values between 25.48 and 49.60, MgO and K2O having a strong negative correlation with SiO2, high values of Zr/Sc (32.5) versus Th/Sc (3.44), and enrichment of trace elements like Cr (30–87 ppm), V (27–81 ppm), Ni (13–49 ppm), and Sc (3–12 ppm). The Th/Sc versus Zr/Sc, K2O/Na2O versus SiO2, and Th/Co versus La/Sc plots attribute that the host metasedimentary rocks are recycled sediments largely of passive continental margin with a felsic source. However, the Mg# versus SiO2 and K2O/Na2O versus SiO2 point to the incorporation of mantle material from the orogenic margin, possibly arc-related and mafic in nature. The features such as the mineral assemblage, the simultaneous crystallization shown by mutual boundaries and exsolution blebs, and the mineral chemical data of ore minerals favour a high-temperature hydrothermal environment of ore deposition. This inference is substantiated by general high Fe concentration in sphalerite and other ore minerals, 800 to 2,400 ppm Cd in sphalerite, Ag and Sb in galena from 1,000 to 2,500 ppm and 400 to 800 ppm respectively, and noticeable Ag in chalcopyrite. The inferred depositional and tectonic environment of host metasedimentary rocks, the petrographic features of ores, and their mineral chemical data altogether invoke that the Rangpo ore mineralization in metasedimentary rocks was formed at high temperature in an environment where mafic mantle material from the active arc was amalgamated with the passive margin sediments derived from the felsic source rocks.
中文翻译：
印度锡金小喜马拉雅地区让波地区变质沉积岩中多金属矿的形成：矿物学和地球化学属性
目前的工作调查了矿石矿物学、宿主变质沉积岩的地球化学，以及主要硫化物矿物的矿物化学，即来自锡金 Rangpo 硫化物矿化区的闪锌矿、黄铜矿、方铅矿和黄铁矿。根据氧化物和硫化物矿物的相互边界、溶出气泡、交代特征等结构关系，建立了原生矿成矿两个阶段和次生矿产蚀变阶段三个阶段。以磁铁矿、黄铜矿、闪锌矿、方铅矿、磁黄铁矿和钴矿为主的氧化物和硫化物矿物作为 I 级矿石矿物出现，硫化物矿物即方铅矿、磁黄铁矿黄铜矿、毒砂、闪锌矿和黄铁矿被确定为 II 级矿物。蚀变矿物孔雀石和蓝铜矿代表第三阶段。主变质沉积岩的地球化学特征为 SiO2在 53.28 到 85.62 wt% 的范围内，Mg# 值在 25.48 和 49.60 之间，MgO 和 K 2 O 与 SiO 2具有很强的负相关性，Zr/Sc (32.5) 与 Th/Sc (3.44) 的高值， Cr (30–87 ppm)、V (27–81 ppm)、Ni (13–49 ppm) 和 Sc (3–12 ppm) 等微量元素的富集。Th/Sc 对比 Zr/Sc、K 2 O/Na 2 O 对比 SiO 2和 Th/Co 对比 La/Sc 图表明，主体变质沉积岩是主要来自具有长英质源的被动大陆边缘的再循环沉积物。然而，Mg# 对比 SiO 2和 K 2 O/Na 2 O 对比 SiO 2指向来自造山带边缘的地幔物质的结合，可能与弧相关并且本质上是镁铁质。矿物组合、相互边界和溶出气泡的同时结晶以及矿石矿物的矿物化学数据等特征有利于成矿的高温热液环境。这一推论得到了闪锌矿和其他矿石矿物中 Fe 浓度普遍较高、闪锌矿中 800 至 2,400 ppm Cd、方铅矿中 Ag 和 Sb 分别为 1,000 至 2,500 ppm 和 400 至 800 ppm 以及黄铜矿中明显的 Ag 的证实。宿主变质沉积岩的推断沉积和构造环境，矿石的岩相特征，
更新日期：2022-09-19
中文翻译：
印度锡金小喜马拉雅地区让波地区变质沉积岩中多金属矿的形成：矿物学和地球化学属性
目前的工作调查了矿石矿物学、宿主变质沉积岩的地球化学，以及主要硫化物矿物的矿物化学，即来自锡金 Rangpo 硫化物矿化区的闪锌矿、黄铜矿、方铅矿和黄铁矿。根据氧化物和硫化物矿物的相互边界、溶出气泡、交代特征等结构关系，建立了原生矿成矿两个阶段和次生矿产蚀变阶段三个阶段。以磁铁矿、黄铜矿、闪锌矿、方铅矿、磁黄铁矿和钴矿为主的氧化物和硫化物矿物作为 I 级矿石矿物出现，硫化物矿物即方铅矿、磁黄铁矿黄铜矿、毒砂、闪锌矿和黄铁矿被确定为 II 级矿物。蚀变矿物孔雀石和蓝铜矿代表第三阶段。主变质沉积岩的地球化学特征为 SiO2在 53.28 到 85.62 wt% 的范围内，Mg# 值在 25.48 和 49.60 之间，MgO 和 K 2 O 与 SiO 2具有很强的负相关性，Zr/Sc (32.5) 与 Th/Sc (3.44) 的高值， Cr (30–87 ppm)、V (27–81 ppm)、Ni (13–49 ppm) 和 Sc (3–12 ppm) 等微量元素的富集。Th/Sc 对比 Zr/Sc、K 2 O/Na 2 O 对比 SiO 2和 Th/Co 对比 La/Sc 图表明，主体变质沉积岩是主要来自具有长英质源的被动大陆边缘的再循环沉积物。然而，Mg# 对比 SiO 2和 K 2 O/Na 2 O 对比 SiO 2指向来自造山带边缘的地幔物质的结合，可能与弧相关并且本质上是镁铁质。矿物组合、相互边界和溶出气泡的同时结晶以及矿石矿物的矿物化学数据等特征有利于成矿的高温热液环境。这一推论得到了闪锌矿和其他矿石矿物中 Fe 浓度普遍较高、闪锌矿中 800 至 2,400 ppm Cd、方铅矿中 Ag 和 Sb 分别为 1,000 至 2,500 ppm 和 400 至 800 ppm 以及黄铜矿中明显的 Ag 的证实。宿主变质沉积岩的推断沉积和构造环境，矿石的岩相特征，
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