矿床地质2023，Vol.42Issue(6)：1081-1100,20.DOI:10.16111/j.0258-7106.2023.06.
还原性围岩在斑岩钼矿成矿中的作用
Role of reductive surrounding rocks in formation of porphyry Mo deposits
摘要
Abstract
Porphyry Mo deposits are the most important type of Mo resource.They result from a high oxygen fugacity of the parent magma,which acts as an effective indicator for evaluating the mineralization.In the ore-forming sys-tem of porphyry Mo deposits,sulfur exists mainly as sulfate in highly oxidized magma but as sulfide in ores.What triggers the reduction in the mineralization system that leads to sulfide precipitation has not yet been deter-mined.Most of the previous studies have focused on the origin and evolution of the ore-forming parent magma,and the effects of reductive surrounding rocks on porphyry mineralization have been ignored.In this study,a com-prehensive geological-geochemical investigation and review have been performed on the typical porphyry Mo de-posits,the Nannihu-Sandaozhuang-Shapingou,and Caosiyao deposits in China,and the Mt.Emmons deposits in America.Black carbonaceous sedimentary layers commonly surround porphyry Mo ores,which are widely al-tered and discolored during mineralization.CH4 is commonly present in fluid inclusions in the main mineraliza-tion stage,and the δ13C values of calcite and fluid inclusions from the altered surrounding rocks and ore deposits are generally low and significantly different from those of marine sedimentary carbonate rocks,indicating that the involvement of reductive components from carbonaceous surrounding rocks might be key to the redox state trans-formation leading to mineral precipitation.On the other hand,the CH4 produced by the thermal decomposition of organic matter or carbonaceous reaction with H2O can diffuse into the ore-forming system along the structural fractures and reduce the SO2-4 in the ore-forming hydrothermal fluids to form sulfide precipitation without direct contact between the intrusion and the carbonaceous surrounding rocks.Moreover,the CH4 content controls the lo-cation of the orebody formation with the high content producing orebodies mainly in the porphyry intrusion and complexes in the early stage,while the low CH4 content results in the orebodies mainly occurring at the contact zone between the porphyry and carbonaceous surrounding rocks.Compared with the magmatic stage of mineral-ization,the involvement of reductive components in the carbonaceous surrounding rocks during the hydrothermal stage is more favorable for forming giant/large Mo deposits.The intermediate-basic volcanic rock are another im-portant surrounding rock type of porphyry Mo ores.They provide Fe2+to reduce SO2-4 with widely magnetite altera-tion during mineralization,and orebodies mainly occur at the contact zone between the porphyry and Fe-rich vol-canic rocks.The highly oxidized porphyry with reductive carbonaceous surrounding rocks or Fe-rich volcanic rocks offers a new indicator for efficiently evaluating porphyry Mo mineralization.关键词
高氧逸度/还原性围岩/甲烷还原剂/斑岩钼(铜)矿Key words
high oxygen fugacity/carbonaceous surrounding rocks/reductive agent CH4/porphyry Mo deposits分类
天文与地球科学引用本文复制引用
郭东伟,李延河,段超,范昌福,万秋,孙鹏程..还原性围岩在斑岩钼矿成矿中的作用[J].矿床地质,2023,42(6):1081-1100,20.基金项目
本文得到国家自然科学基金项目(编号:41973022、41627802、42172102)资助 （编号:41973022、41627802、42172102）
