Origin and deep prospecting implications of the 1665~1700 m copper orebody discovered by the scientific drilling in south Hunan
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摘要:
湘南科学钻(ZK16508)位于宝山铜-铅-锌多金属矿田北西，旨在通过深部探测完善铜矿深部成矿模式和找矿标志。该科学钻在1664.82~1699.84 m处的石磴子组含炭质灰岩中揭露视厚度35.02 m的铜矿体，其中Cu达到工业品位，同时伴生Ag、Au、Ga和Se。为揭示深部铜矿体的成矿机理，对铜矿石开展了Re-Os同位素测年和硫同位素分析。铜矿体全岩Re-Os年龄为159.1±1.1 Ma，与成矿花岗闪长岩侵位年龄和浅部铜钼矿体成矿时代一致，说明它们是同一成矿系统的产物。铜矿石中的硫化物可分为2个世代，早阶段形成粗粒黄铁矿，晚阶段形成细粒共生的黄铁矿、黄铜矿、毒砂、菱铁矿等集合体。早阶段粗粒黄铁矿δ34S值(平均5.97‰)略高于花岗闪长岩值，说明早阶段热液流体在演化过程中萃取了少量的地层硫，晚阶段细粒黄铁矿δ34S值(平均3.79‰)大致与花岗闪长岩相当，说明形成黄铜矿的成矿流体为岩浆期后热液，演化过程中未受到地层的影响。研究表明，宝山矿田1.5 km以深铜矿找矿潜力大，其产出分布受成矿母岩花岗闪长岩和碳酸盐中的构造破碎带控制，磁异常是重要的找矿标志，而矽卡岩化则是指示铜多金属矿体分布的充分但不必要条件。
Abstract:The 3000-meter scientific drilling in south Hunan is located in the northwest of the Baoshan Cu-Pb-Zn ore field, and aims to improve the deep metallogenic model and prospecting clues of copper deposits through deep exploration.A 35.02-meter copper orebody was discovered by this scientific drilling at the depth interval of 1664.82~1699.84 m, with the mineralized element Cu reached the industrial grade, and Ag-Au-Ga-Se met the standard of comprehensive utilization.In order to reveal ore genesis of the deep Cu orebody, this study conducted Re-Os isotopic dating and sulfur isotopic analyses.The whole-rock Re-Os age of the copper ores was dated at 159.1±1.1 Ma, which is consistent with the emplacement age of the ore-associated granodiorite and the ore-forming age of the Cu-Mo orebody at shallow depths, indicating that they represent products of the same metallogenic system.The sulfides of the copper ore can be divided into two generations, with the coarse-grained pyrite at the early stage, while the fine-grained aggregates of pyrite, chalcopyrite, arsenopyrite and siderite at the late stage.The δ34S value of the early-stage coarse-grained pyrite(5.97‰ in average)is slightly higher than that of the granodiorite, indicating that the early-stage hydrothermal fluid extracted a small amount of sulfur from the carbonate formation.However, the δ34S value of the late-stage fine-grained pyrite(3.79‰ in average)is approximately similar to the granodiorite, indicating that the ore-forming fluid that responsible for chalcopyrite deposition is a post-magmatic hydrothermal fluid, which was not affected by the carbonate formation.Our results show that the prospecting potential of deep copper deposits below 1.5-kilometer depth of the Baoshan ore field is of great importance, with the distribution of orebodies controlled by the structural fracture zone in carbonate formation and associated with granodiorite.Magnetic anomalies are important prospecting clues, while skarnization is a sufficient but unnecessary clue that signals the distribution of copper orebodies.
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表 1 湘南科学钻铜矿化层样品化学分析结果
Table 1. Geochemical results of the samples in the copper orebody discovered by the scientific drilling
样品编号 采样位置/m Cu/% Pb/% Zn/% Ag /(g·t-1) Au /(g·t-1) Ga/% Se/% MFe/% WO3/% Sn/% Mo/% ZK16508-38 1664.82~1665.82 0.41 0.02 0.01 4.32 0.06 0.000883 0.00291 0.16 0.006 0.011 0.006 ZK16508-39 1665.82~1666.82 0.57 0.02 0.01 4.88 0.06 0.000609 0.00290 0.28 0.003 0.015 0.003 ZK16508-40 1666.82~1667.82 0.54 0.09 0.06 7.97 0.04 0.000572 0.00329 0.24 0.006 0.009 0.004 ZK16508-41 1667.82~1668.82 0.38 0.02 0.01 4.72 0.05 0.000883 0.00220 0.07 0.051 0.026 0.003 ZK16508-42 1668.82~1670.23 0.32 0.02 0.01 4.81 0.08 0.00109 0.00156 0.12 0.017 0.031 0.002 ZK16508-43 1670.23~1671.99 0.01 0.02 0.07 4.7 0.01 0.000231 0.0000234 0.02 0.002 0.004 0.001 ZK16508-44 1671.99~1672.99 0.31 0.02 0.01 5.04 0.04 0.00102 0.00208 0.18 0.027 0.022 0.007 ZK16508-45 1672.99~1673.99 0.19 0.02 0.01 3.83 0.03 0.000809 0.000974 0.23 0.038 0.018 0.041 ZK16508-46 1673.99~1674.99 0.14 0.01 0.01 4.36 0.01 0.000646 0.000762 0.23 0.037 0.017 0.043 ZK16508-47 1674.99~1675.99 0.33 0.02 0.01 3.51 0.05 0.00239 0.00151 0.13 0.035 0.008 0.002 ZK16508-48 1675.99~1676.99 0.51 0.02 0.01 3.89 0.05 0.00188 0.00153 0.26 0.016 0.019 0.001 ZK16508-49 1676.99~1677.99 0.47 0.02 0.03 4.79 0.12 0.00154 0.00136 0.07 0.015 0.017 0.011 ZK16508-50 1677.99~1678.99 0.37 0.01 0.01 4.16 0.03 0.00119 0.00170 1.54 0.001 0.019 0.002 ZK16508-51 1678.99~1679.99 0.34 0.02 0.02 6.50 0.05 0.000759 0.00170 0.03 0.006 0.010 0.002 ZK16508-52 1679.99~1680.99 0.28 0.02 0.01 4.68 0.02 0.00121 0.00130 0.05 0.002 0.025 0.006 ZK16508-53 1680.99~1681.99 0.71 0.06 0.04 6.13 0.09 0.000886 0.00194 0.13 0.01 0.016 0.002 ZK16508-54 1681.99~1682.99 0.79 0.02 0.01 5.14 0.13 0.00139 0.00190 0.13 0.02 0.017 0.008 ZK16508-55 1682.99~1683.99 0.46 0.02 0.01 2.99 0.02 0.00116 0.00207 3.17 0.01 0.021 0.001 ZK16508-56 1683.99~1684.99 0.76 0.02 0.01 4.38 0.03 0.000987 0.00325 9.95 0.00 0.033 0.002 ZK16508-57 1684.99~1685.99 0.85 0.02 0.02 4.11 0.05 0.000993 0.00358 15.83 0.01 0.038 0.003 ZK16508-58 1685.99~1686.99 0.47 0.02 0.01 3.64 0.04 0.000702 0.00184 4.15 0.03 0.012 0.004 ZK16508-59 1686.99~1687.99 0.49 0.02 0.03 4.63 0.05 0.00224 0.00100 34.71 0.00 0.013 0.003 ZK16508-60 1687.99~1688.99 0.66 0.02 0.03 2.85 0.05 0.00123 0.00116 19.58 0.01 0.020 0.002 ZK16508-61 1688.99~1689.99 0.24 0.01 0.01 2.57 0.09 0.00147 0.000836 16.11 0.003 0.024 0.007 ZK16508-62 1689.99~1690.99 0.03 0.03 0.01 1.84 0.06 0.00129 0.000172 0.27 0.003 0.022 0.011 ZK16508-63 1690.99~1691.99 0.02 0.03 0.01 1.23 0.09 0.00142 0.0000942 0.13 0.001 0.014 0.004 ZK16508-64 1691.99~1692.99 0.05 0.03 0.01 1.99 0.03 0.00155 0.000282 0.26 0.001 0.032 0.007 ZK16508-65 1692.99~1693.99 0.95 0.03 0.01 5.46 0.06 0.000388 0.00266 0.07 0.001 0.016 0.001 ZK16508-66 1693.99~1694.99 1.26 0.17 0.11 11.64 0.11 0.000261 0.00340 0.24 0.002 0.009 0.001 ZK16508-67 1694.99~1695.99 0.61 0.38 0.19 13.66 0.11 0.000993 0.00248 0.22 0.011 0.019 0.001 ZK16508-68 1695.99~1696.99 0.65 0.06 0.01 4.10 0.03 0.000853 0.00179 0.29 0.027 0.035 0.008 ZK16508-69 1696.99~1697.99 0.37 0.01 0.01 2.68 0.06 0.00118 0.00157 0.13 0.013 0.046 0.005 ZK16508-70 1697.99~1698.99 0.16 0.01 0.01 3.86 0.03 0.00109 0.000533 11.40 0.004 0.029 0.002 ZK16508-71 1698.99~1699.84 0.36 0.01 0.01 4.15 0.09 0.00108 0.00136 12.20 0.001 0.020 0.001 
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表 2 湘南科学钻铜矿化层Re-Os同位素测试结果
Table 2. Re-Os isotopic results of the samples in the copper orebody discovered by the scientific drilling
样品编号 Re/10-9 普Os/10-9 187Re/10-9 187Os/10-9 模式年龄/Ma 测定值 不确定度 测定值 不确定度 测定值 不确定度 测定值 不确定度 测定值 不确定度 ZK16508-44 477.7 4.0 0.1230 0.0027 300.2 2.5 0.8053 0.0049 160.8 2.3 ZK16508-45 1455 12 0.0512 0.0007 914.2 7.4 2.424 0.016 158.9 2.3 ZK16508-46 1621 14 0.0404 0.0007 1019 9 2.679 0.016 157.6 2.3 ZK16508-54 362.4 2.9 0.0197 0.0004 227.8 1.8 0.5999 0.0035 157.9 2.2 ZK16508-62 463.1 3.6 0.0074 0.0005 291.0 2.2 0.7664 0.0049 157.9 2.2 ZK16508-67 365.7 2.7 0.0688 0.0007 229.8 1.7 0.6148 0.0036 160.3 2.2 ZK16508-68 941.9 8.0 0.0699 0.0010 592.0 5.0 1.584 0.009 160.3 2.3 ZK16508-69 316.4 2.1 0.0954 0.0012 198.8 1.3 0.5282 0.0033 159.2 2.1
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表 3 湘南科学钻铜矿石中黄铁矿原位硫同位素测试结果
Table 3. In situ sulfur isotopic results of pyrite in the copper ores discovered by the scientific drilling
样品编号 类型 δ34S/‰ 样品编号 类型 δ34S/‰ 样品编号 类型 δ34S/‰ ZK16508-38-1 Py1 4.69 ZK16508-38-10 Py2 2.50 ZK16508-44-18 Py2 3.78 ZK16508-38-2 Py1 4.68 ZK16508-38-11 Py2 4.44 ZK16508-44-19 Py2 3.94 ZK16508-38-3 Py1 5.33 ZK16508-38-12 Py2 5.92 ZK16508-38-20 Cp2 3.34 ZK16508-38-4 Py1 4.76 ZK16508-38-13 Py2 3.68 ZK16508-38-21 Cp2 1.83 ZK16508-38-5 Py1 5.01 ZK16508-38-14 Py2 2.38 ZK16508-38-22 Cp2 1.40 ZK16508-38-6 Py1 4.82 ZK16508-38-15 Py2 4.44 ZK16508-38-23 Cp2 3.95 ZK16508-38-7 Py1 4.57 ZK16508-38-16 Py2 3.70 ZK16508-38-24 Cp2 3.36 ZK16508-44-1 Py1 6.61 ZK16508-38-17 Py2 4.21 ZK16508-38-25 Cp2 3.83 ZK16508-44-2 Py1 7.22 ZK16508-38-18 Py2 3.29 ZK16508-44-20 Cp2 3.86 ZK16508-44-3 Py1 7.37 ZK16508-38-19 Py2 4.32 ZK16508-44-21 Cp2 1.83 ZK16508-44-4 Py1 6.70 ZK16508-44-10 Py2 3.46 ZK16508-44-22 Cp2 1.97 ZK16508-44-5 Py1 7.24 ZK16508-44-11 Py2 1.76 ZK16508-44-23 Cp2 2.21 ZK16508-44-6 Py1 6.66 ZK16508-44-12 Py2 6.45 ZK16508-44-24 Cp2 2.47 ZK16508-44-7 Py1 6.58 ZK16508-44-13 Py2 3.02 ZK16508-44-25 Cp2 2.31 ZK16508-44-8 Py1 6.53 ZK16508-44-14 Py2 3.54 ZK16508-44-26 Cp2 2.07 ZK16508-44-9 Py1 6.78 ZK16508-44-15 Py2 3.63 ZK16508-44-27 Cp2 2.76 ZK16508-38-8 Py2 4.02 ZK16508-44-16 Py2 3.55 ZK16508-44-28 Cp2 2.18 ZK16508-38-9 Py2 3.61 ZK16508-44-17 Py2 3.85
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