| 还原性含碳质围岩在斑岩铜矿成矿中的作用 |
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| 引用本文：李延河,段超,曾普胜,简伟,万秋,胡古月,赵晓燕,武晓珮.2020.还原性含碳质围岩在斑岩铜矿成矿中的作用[J].地球学报,41(5):637-650. |
| DOI：10.3975/cagsb.2020.071403 |
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| 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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| 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) |
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| 中文摘要:斑岩铜矿是最重要的铜矿资源类型, 高氧逸度岩浆是公认的评价斑岩成矿的有效指标。硫在成矿岩浆中主要以硫酸盐形式存在, 在矿石中则以硫化物为主。什么触发了高氧化性成矿岩浆热液的还原与成矿？这是关系斑岩铜矿形成机制和高效评价的重大科学谜题。前人关注的焦点是成矿母岩浆的起源与演化, 还原性围岩在成矿中作用长期被忽视。还原性围岩主要有两种: 富碳质围岩和富亚铁围岩。本文在前人工作基础上, 以甲玛、德兴、普朗等大型-超大型斑岩铜矿为例, 研究了斑岩铜矿的空间分布与含碳质围岩之间的关系, 发现斑岩铜矿围岩中普遍发育黑色含碳质地层, 并在成矿过程中普遍发生褪色蚀变; 发现蚀变围岩和矿床中方解石和矿石矿物流体包裹体的δ13CV-PDB值普遍较低, 与沉积碳酸盐围岩的值显著不同。首次提出并论证了含碳质围岩中甲烷等还原性气体组分的加入可能是引发斑岩成矿系统氧化-还原转换和矿质沉淀的关键。CH4沿构造裂隙扩散进入斑岩成矿系统, 无需成矿斑岩与围岩直接接触即可将成矿溶液中SO2– 4还原, 解决了困扰矿床学家多年的一道难题。围岩中碳质含量高, 产生的甲烷数量大, 可将成矿热液中SO2– 4在斑岩体内全部还原, 形成金属硫化物沉淀, 则矿体主要产在斑岩体之内; 围岩中碳质含量低, 产生的甲烷数量不足, 则矿体主要赋存于斑岩体与围岩的内外接触带。含碳质围岩中还原组分即可在岩浆阶段加入, 也可在热液阶段加入。在岩浆阶段加入将造成岩浆还原, 形成“还原型斑岩”, 易导致成矿物质分散, 不利于形成大矿富矿; 在热液阶段加入, 对成矿更有利。“高氧化性斑岩+还原性富碳质地层/富铁火山岩”是高效评价斑岩成矿的新指标。 |
| 中文关键词:斑岩铜矿 高氧逸度 含碳质围岩 甲烷还原剂 |
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| The Role of Reductive Carbonaceous Strata in the Formation of Porphyry Copper Ores |
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| Abstract: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. |
| keywords:porphyry copper deposit high oxygen fugacity carbonaceous surrounding rock methane reducing agent |
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