青海牛苦头矿区锰质黑柱石成因及其地质意义  

Genesis and geological significance of manganilvaite in the Niukutou deposit, Qinghai Province

作　　者：王新雨 祝新友[1] 李加多 王玉往[1] 龙灵利[1] 李顺庭[1] 吴锦荣 程细音[1] 蒋斌斌[1] WANG Xinyu;ZHU Xinyou;LI Jiaduo;WANG Yuwang;LONG Lingli;LI Shunting;WU Jinrong;CHENG Xiyin;JIANG Binbin(Beijing Institute of Geology for Mineral Resources,Beijing Deep Exploration Technic Center for Non-ferrous Mines,Beijing,100012;The Qinghai Hongxin Mining Co.,Ltd,Golmud,Qinghai,816099)

机构地区：[1]北京矿产地质研究院,有色金属矿山深部资源勘查工程技术研究中心,北京100012 [2]青海鸿鑫矿业有限公司,青海格尔木816099

出　　处：《地质学报》2020年第8期2279-2290,共12页Acta Geologica Sinica

基　　金：中国铜业科技型项目(编号QHHXKCZYB-007);国家重点研发计划项目(编号2017YFC0602403)资助的成果。

摘　　要：锰质黑柱石是矽卡岩型铅锌矿床中一种常见的脉石矿物,其与铅锌矿体关系密切。本文对东昆仑祁漫塔格地区牛苦头铅锌多金属矿床中黑柱石的产状、矿物共生组合、化学成分等进行了研究。牛苦头矿区锰质黑柱石主要产于3种矿物组合:黑柱石+石榴子石+磁铁矿组合;黑柱石+锰钙(铁)辉石+方铅矿+磁铁矿组合;黑柱石+方解石+石英+硫化物(黄铁矿+磁黄铁矿+其他硫化物)组合,并形成自内向外石榴子石-磁铁矿—黑柱石—锰钙辉石的矽卡岩分带。上述3种组合分别对应矿床的3个蚀变矿化阶段:进变质阶段(阶段I),石榴子石被交代分解,形成黑柱石;退变质阶段(阶段Ⅱ),锰钙(铁)辉石分解形成黑柱石;石英硫化物阶段(阶段Ⅲ),黑柱石进一步分解,形成磁铁矿、方解石和石英。电子探针结果,牛苦头矿床黑柱石的化学分子式为Ca0.94-0.98(Fe1.22-1.92Mn0.10-0.75Mg0.01-0.03)■(Fe0.83-0.93Al0.01-0.07)■[Si2.00-2.07O7]O(OH);LA-ICP-MS原位分析显示,牛苦头矿区黑柱石的稀土配分曲线与矿区进变质阶段形成的石榴子石、锰钙(铁)辉石近乎一致。综合研究认为,矿区黑柱石为进变质阶段的石榴子石和辉石蚀变分解的产物;矿床自内向外的矽卡岩分带反映了矽卡岩被逐渐交代的过程,并伴随了成矿流体从主矽卡岩阶段的"还原(Fe2+、Mn2+)"环境向退变质阶段偏氧化(先是Fe2+-Mn2++Fe3+,后是Fe3+)环境的转变。Ilvaite, a common calcium silicate mineral in skarn-type deposit, which is associated with the Pb-Zn mineralization closely. In this study, the optical property, mineral association and chemical composition of ilvaite in Niukutou deposit are discussed. There are three ilvaite-bearing association in the Niukutou deposit:(1) Ilvaite+garnet+magnetite mineral assemblage;(2) Ilvaite+mangan-hedenbergite(Mn-Hd)+johannsenite(Jo)+galena+magnetite mineral assemblage;(3) Ilvaite+calcite+quartz+sulfide(pyrite, pyrrhotite and other sulfide) mineral assemblage, and formed a garnet-magnetite+ilvaite+johannsenite skarn zonation outward from the skarn-related pluton. These three mineral associations are corresponding to three mineralization phases, respectively. Stage Ⅰ, the prograde garnet was replaced by the ilvaite. Stage Ⅱ, the mangan-hedenbergite(Mn-Hd) or johannsenite(Jo) were replaced by the manganilvaite. Stage Ⅲ,similar to quartz sulfide stage, the further breakdown of ilvaite produced magnetite, calcite and quartz. The mineral chemical composition by EPMA showed that the molecular formula of the Niukutou ilvaiteis Ca0.94-0.98(Fe1.22-1.92Mn0.10-0.75Mg0.01-0.03)■(Fe0.83-0.93Al0.01-0.07)■[Si2.00-2.07O7]O(OH). The in situ LA-ICP-MS trace element analysis showed that the REE patterns of ilvaites are similar to the prograde garnet-pyroxene, which is an evidence for their inheritance in the hydrothermal process. Together with the mineral assemblage, we suggest that ilvaite originated from the continuous alteration and replacement of the early skarn silicates. The skarn zonation in Niukutou deposit is indicative of evolution of the hydrothermal process from reducing(Fe2+, Mn2+) during the formation of the primary skarns, to hydrated and more oxidizing(with Fe2+, Mn2++Fe3+, and then Fe3+) during the overlapping retrograde alterations and deposition of the ore minerals.

关 键 词：电子探针 锰质黑柱石 LA-ICP-MS原位微区 铅锌矿 牛苦头 祁漫塔格 

分 类 号：P618.32[天文地球—矿床学]