Geology, metallogenic features and genesis of the El Teniente porphyry copper-molybdnum deposit in Central Chile
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摘要:
智利中部埃尔特尼恩特矿床是世界级超大型铜钼矿床之一，其铜矿石（含铜0.62%）储量达12.4×108t，钼矿石（含钼0.018%）储量达7.8×108t。矿床位于智利中部安第斯山脉晚中新世-早上新世铜-钼成矿省。该成矿省赋存于晚中新世火山活动带。埃尔特尼恩斑岩型铜-钼矿床赋存于中-晚中新世代伐尔隆斯建造，后者伏于科亚-玛查理建造之下，两者之间呈构造不整合或局部不整合接触关系。矿床产于伐尔隆斯的组成部分晚中新世火山深成杂岩中，该杂岩由厚层的玄武质至流纹质喷出岩及侵入岩组成。矿床围岩为安山岩、长英质-中性侵入岩和布莱登岩筒角砾岩。该矿床流体包裹体组合特征表明，岩浆热液演化及成矿作用经历了4个阶段。流体包裹体成分研究表明，该矿床的形成是富含Cu和可能还富含S的深源流体向不断脱挥发分的巨型次火山岩浆房发生贯入作用的结果。
Abstract:The El Teniente deposit, one of the world's largest known copper-molybdenum deposits, contains 12.4 billion metric tons copper ore at 0.62 percent Cu and 7.8 billion metric tons molybdenum ore at 0.018 percent Mo. It is located in the Late Miocene to Early Pliocene copper-molybdenum metallogenic province of Central Chile Andean Cordillera. The deposit occurs in a Late Miocene volcanic active belt. The mid-Late Miocene Farellones Formation hosts the El Teniente copper-molybdenum deposit. The Farellones Formation is underlain by the Coya-Machali Formation. The contact between the two formations is structural or locally unconformable. The El Teniente deposit occurs in a late Miocene volcano-plutonic complex, which is part of the Farellones Formation, consisting of a thick sequence of eruptive and intrusive rocks of basaltic to rhyolitic compositions. The main host rocks of the deposit are andesites, felsic-intermediate intrusive rocks and the Braden pipe breccia that intruded into andesites. The characteristics of the fluid inclusion assemblages suggest that the hydrothermal activity and mineralization at El Teniente can be divided into four stages. The fluid inclusion component research shows that the ore-forming process of the El Teniente deposit resulted from injection of a deep-sourced Cu-rich and probably S-rich fluid into a more continuously devolatilizing subvolcanic large magma chamber.
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表 1 埃尔特尼恩特矿床长英质至中性侵入岩岩石学和地质年代学特征
Table 1. Petrology and geochronology of the felsic to intermediate intrusive rocks at the El Teniente deposit
侵入岩名称 产出位置 矿物成分 岩石结构 年龄 苏埃尔石英闪长岩 矿床东南部 斜长石、角闪石、黑云母、钾长石、石英、绢云母、绿泥石和绿帘石 等粒结构 7.4±1.0~7.1±1.5Ma（K/Ar年龄） 外层到内部 斜长石、黑云母、钾长石、石英、绢云母、绿泥石和硬石膏 斑状结构，含30%~50%斑晶，基质为细晶状 6.15±0.16Ma，5.59±0.17Ma（锆石U-Pb年龄） 灰色斑岩 侵入苏埃尔英安岩，产于与矿区安山岩的接触带附近 斜长石、黑云母、钾长石（条纹长石）和硬石膏 斑状结构， 不等粒状基质 6.46±0.11Ma（锆石U-Pb年龄）和5.67±0.19Ma（黑云母K/Ar年龄） 英安岩岩筒 产于英安斑岩以东的若干岩筒，也沿接触带侵入苏埃尔英安岩 基质为石英-斜长石-钾长石质，斑晶为斜长石、石英和黑云母 斑状结构，含30%~50%斑晶，基质为细晶（< 0.12mm）到粗粒（达0.5mm）状 6.28±0.16Ma和5.50±0.24Ma，6.11±0.13Ma和5.48±0.19Ma（锆石U-Pb年龄） 英安斑岩 产于面积为1500m×200m的英安岩岩墙的北端 基质为石英-斜长石-钾长石质，斑晶为斜长石、石英和黑云母 自形斑状结构，基质细晶状 5.28±0.1Ma（锆石U-Pb年龄），4.7~4.5Ma（黑云母K/Ar年龄） 产于英安岩岩墙的中部 半自形斑状结构，基质粗晶状 未测年龄 产于上述所有侵入岩单元的接触带 基质为石英-长石-黑云母质，斑晶为斜长石、钾长石、黑云母和石英 含围岩捕虏体 < 20% 未测年龄 安粗岩岩墙 与布莱登岩筒及北东走向力岩墙呈同心状产出 基质为石英-斜长石-钾长石质，斑晶为斜长石、石英和黑云母，岩石已绢云母化 斑状结构，含30%~50%的显晶体，非常细粒的细晶状基质（< 0.02mm） 4.82±0.09Ma 煌斑岩岩墙 北东走向细脉中 角闪石、辉石、橄榄石和斜长石 细粒状、斑状结构 3.85±0.18Ma 
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表 2 埃尔特尼恩特矿床不同热液矿化阶段流体包裹体类型、鉴别标志及归属[24]
Table 2. Fluid inclusion types, identification signs and attribution of different hydrothermal mineralization stages of the El Teniente deposit
矿化阶段 流体包裹体类型 气泡体积/% 子矿物 鉴别标志 蚀变产物 阶段2 ID2-0 40~50 不透明矿物 岩石学特征与ID2-1和V2-2十分相似，但盐度和均一温度略高 ID2-1 40~50 不透明矿物 与V2-2十分相似，均一化作用达到液相 V2-1 80~>90 不透明矿物 偶尔与B2-1和B2-2共存 V2-2 60~80 不透明矿物 包泡占比小于V2-1，与ID2-0和ID2-1相似，但均一化作用达到气相 B2-1 10~20 石盐、不透明矿物 被B2-2的包裹体痕迹横切 B2-2 10~20 石盐、钾石盐、赤铁矿、不透明矿物及其他盐类矿物 多种子矿物 B2-3 10~20 石盐、不透明矿物 被B2-1和B2-2的包裹体痕迹横切 阶段3 ID3 40~50 不透明矿物 岩石学特征与ID2-1相同但出现于3的矿脉中 绢云母 B3 10~20 赤铁矿、不透明矿物 岩石学特征与B2-1相同但出现于3的矿脉中 阶段4 L4 10~20 无 在矿化阶段2的石英晶体上生成最晚期的生长带 绢云母 注：B—低溶性卤水；ID—超溶性液态流体；L—水状流体； V—低溶性气体
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