| 还原性含碳质围岩在斑岩铜矿成矿中的作用 |
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| 关键词:porphyry copper deposit high oxygen fugacity carbonaceous surrounding rock methane reducing agent |
| 基金项目:基本科研业务费项目(编号: YYWF201710);国家自然科学基金项目(编号: 41973022; 41627802) |
| 作者 | 单位 | E-mail | | 李延河 | 中国地质科学院矿产资源研究所, 自然资源部成矿作用与资源评价重点实验室,自然资源部同位素地质重点实验室 | lyh@cei.cn | | 段超 | 中国地质科学院矿产资源研究所, 自然资源部成矿作用与资源评价重点实验室,自然资源部同位素地质重点实验室 | | | 曾普胜 | 国家地质实验测试中心 | | | 简伟 | 中国地质科学院矿产资源研究所, 自然资源部成矿作用与资源评价重点实验室,自然资源部同位素地质重点实验室 | | | 万秋 | 安徽省地质调查院(安徽省地质科学研究所) | | | 胡古月 | 中国地质科学院矿产资源研究所, 自然资源部成矿作用与资源评价重点实验室,自然资源部同位素地质重点实验室 | | | 赵晓燕 | 中国地质科学院矿产资源研究所, 自然资源部成矿作用与资源评价重点实验室,自然资源部同位素地质重点实验室 | | | 武晓珮 | 中国地质科学院矿产资源研究所, 自然资源部成矿作用与资源评价重点实验室,自然资源部同位素地质重点实验室 | |
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| The Role of Reductive Carbonaceous Strata in the Formation of Porphyry Copper Ores |
| The porphyry copper deposit is the most important type of copper resources, and high oxygen fugacity of magma is generally recognized as an effective indicator to evaluate its mineralization. In the porphyry copper deposit, sulfur mainly exists as sulfate in the ore-forming magma and sulfide in ores. What triggered the reduction of the high oxidizing ore-forming magmatic-hydrothermal fluid that led to the mineralization? It is a major scientific puzzlement related to the formation mechanism and efficient assessment of porphyry copper deposits. Most of previous studies have focused on the origin and evolution of the ore-forming parent magma for a long time, while the reductive surrounding rock has been neglected. The carbonaceous strata and Fe rich volcanic rocks are two primary reductive surrounding rocks in the porphyry copper deposits. Based on the results obtained by previous researchers, the authors studied the relationship between the spatial distribution of porphyry copper deposits and the surrounding carbonaceous rocks, taking Jiama, Dexing, and Pulang large or superlarge porphyry copper deposits as examples. It is found that black carbonaceous strata commonly occur in the surrounding rocks of these deposits, and they were altered and discolored in the process of mineralization. δ13CV-PDB values of calcite and fluid inclusions from altered wall rocks and ore minerals are generally low, which is significantly different from the values of the sedimentary carbonate surrounding rocks. It is proposed for the first time that the involvement of methane and other reducing gas components from surrounding carbonaceous rocks may be the key to the oxidation-reduction transformation and mineral precipitation of the ore-forming system. CH4 could diffuse into the ore-forming system along the structural fracture without the direct contact between the intrusion and the carbonaceous strata. The high carbon content in the surrounding rocks could produce a large amount of methane and reduce the SO2– 4 in the ore-forming hydrothermal solution in the porphyry intrusion, forming metal sulfide precipitation and making the orebody mainly occur in the porphyry intrusion. If the carbon content in the surrounding rock is low and the amount of methane produced is insufficient, the orebody would mainly occur in the contact zone between the porphyry and the surrounding rock. The reducing components from surrounding carbonaceous rocks can be involved in the magmatic stage or hydrothermal stage. The addition of reducing components in the magmatic stage would lead to the reduction of magma, forming a reductive system, which would lead to the dispersion of ore-forming materials. The addition of reductive components in the hydrothermal stage would be more favorable for mineralization and the formation of large or superlarge deposits. High oxidation porphyry with the reductive carbonaceous strata or the Fe rich volcanic rocks would be a new indicator to evaluating porphyry mineralization efficiently. |
| LI Yan-he,DUAN Chao,ZENG Pu-sheng,JIAN Wei,WAN Qiu,HU Gu-yue,ZHAO Xiao-yan,WU Xiao-pei.2020.The Role of Reductive Carbonaceous Strata in the Formation of Porphyry Copper Ores[J].Acta Geoscientica Sinica,41(5):637-650. |
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