Application of integrated geophysical method in prospecting: A case study of the magnetite-type IOCG deposits in the Moon Mountain exploration area, Copiapo, Chile
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摘要: 智利科皮亚波地区地处海岸山带东侧的智利铁带北段，已发现多个中—大型磁铁矿型IOCG矿床，该类矿床的形成与大洋俯冲背景下陆缘弧中性—铁镁质火山岩和火山-沉积建造中早白垩世中酸性岩浆岩的侵入中心密切相关。该成矿带大面积被第四系砂砾层覆盖，在成矿地质特征研究基础上，采用综合地球物理方法对覆盖层下隐伏矿床（体）进行定位预测成为技术关键并具有现实需求。通过深入研究科皮亚波地区磁铁矿型IOCG矿床的成矿地质特征，并采用航磁深部地质解译初选勘查靶区，结合磁铁矿型IOCG矿床成矿地质-物性参数统计分析，建立了勘查区磁铁矿型IOCG矿床成矿地质-地球物理异常模式，采用综合地球物理方法在月亮山勘查区第四系覆盖区圈定的深部靶位经钻孔验证，发现了大型隐伏磁铁矿型IOCG矿床。Abstract: Many medium to large magnetite-type IOCG deposits have been found in the Copiapo area of Chile, which is located in the north fragment of the Chilean iron belt on the east side of the coastal mountain belt. The formation of these deposits is closely related to the neutral mafic volcanic rocks in the continental margin arc under the background of ocean subduction and the intrusion center of Early Cretaceous intermediate-acid magmatic rocks intruded in the volcanic sedimentary formation. The metallogenic belt is largely covered by Quaternary gravel layer. Using integrated geophysical methods with metallogenic geological characteristics to locate the concealed deposits (ore-bodies) under the overburden has become a key technology and a practical demand. We conducted an in-depth study of the metallogenic geological characteristics of magnetite-type IOCG deposits in the Copiabo area, and interpreted the preliminary exploration target by aeromagnetic deep-geological interpretation. Combining the interpretation results with the statistical analysis of metallogenic geological-physical parameters of magnetite-type IOCG deposits, a metallogenic geological-geophysical anomaly model of magnetite-type IOCG deposits in the Copiabo area is established. A large concealed magnetite-type IOCG deposit was found and verified by drilling in the deep target area delineated in the Quaternary coverage area of the Moon Mountain exploration area by using the integrated geophysical method.
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图 1 智利中北部阿塔卡玛断裂带和IOCG矿床
Figure 1. Atacama fault zone and IOCG deposits in north central Chile
图 2 智利科皮亚波区域地质-航磁异常综合图(据Arévalo, 1995修改)
Figure 2. Integrated map of regional geology and aeromagnetic anomalies in Copiapo, Chile(modified after Arévalo, 1995)
图 3 智利科皮亚波地区航磁△T异常和系列上延异常图
a—△T异常; b—上延高度1000 m; c—上延高度2000 m; d—上延高度5000 m
Figure 3. Maps showing aeromagnetic anomaly and anomalies upward in Copiapo, Chile
(a) △T anomaly; (b) Upward continue to 1000 m; (c) Upward continue to 2000 m; (d) Upward continue to 5000 m
图 4 勘查区(月亮山7号点)及外围地质简图
Figure 4. Geological sketch of the exploration area (Spot 7 in the Moon Mountain area) and the periphery
图 5 勘查区(月亮山7号点)IOCG型铁铜矿区磁异常平面图
a—原始磁异常; b—剩余磁异常
Figure 5. Plan of magnetic anomaly of IOCG iron-copper deposits in the exploration area (Spot 7 in the Moon Mountain area)
(a) Original magnetic anomaly; (b) Remnant magnetic anomaly
图 6 反演三维磁化率模型图
图中灰度体为反演磁化率≥0.65SI的磁性体, 灰度由浅至深表示反演磁化率由0.65→0.90SI
Figure 6. Model of three-dimensional magnetic susceptibility inversion (coordinate unit: m)
The gray volumns are the magnetic volumns with inverse magnetic susceptibility ≥0.65SI, and the grayscale from light to dark indicates that the inverse magnetic susceptibility changes from 0.65 to 0.90SI
图 7 月亮山IOCG型铁铜矿区P2剖面综合断面图
Figure 7. Integrated section of Profile P2 of the IOCG iron-copper deposits in the Moon Mountain area
表 1 勘查区岩(矿)石磁化率参数测试统计表
Table 1. Statistical table of magnetic susceptibility parameters of rocks (ores) in the exploration area
岩矿石名称 标本数/块 SI/×10-3(国际单位制) ucgs(高斯单位制) 极值 平均值 极值 平均值 安山岩 34 9.47~25.50 14.81 754~2029 1179 安山质角砾岩 37 1.06~16.80 6.88 84~1337 547 构造角砾岩 33 0.13~8.27 3.70 10~658 294 硅化构造角砾岩 51 0.002~9.710 3.15 0~773 251 蚀变安山岩 31 0.22~6.84 2.62 18~544 241 闪长岩 162 14.70~68.50 39.10 1170~5451 3111 赤铁矿 65 0.14~21.70 6.95 11~1727 553 赤铁矿化硅化安山角砾岩 114 0.66~27.00 8.60 53~2149 688 磁铁矿化安山岩 28 24.80~124.00 55.30 1974~9868 4400 磁铁矿化硅化安山角砾岩 18 28.60~117.00 63.20 2276~9311 5032 磁赤铁矿 22 37.80~88.00 51.20 3008~7003 4074 磁铁矿 30 317~(>1000) 693.00 25226~(>80000) 55147 含铁铜安山质角砾岩 15 0.93~27.20 12.42 74~2165 988 含铜磁铁矿 9 77.10~526.00 195.80 6135~41858 15581 黄铁矿化硅化安山角砾岩 14 1.34~28.10 12.21 107~2236 971 表中">"表示大于 
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表 2 勘查区岩(矿)石电阻率、极化率参数测试统计表
Table 2. Statistical table of resistivity and polarizability parameters of rocks (ores) in the exploration area
岩矿石名称 标本数/块 极化率/% 电阻率/(Ω·m) 最小 最大 平均值 最小 最大 平均值 赤铁矿 10 1.04 2.71 1.65 895.14 1835.30 1117.20 蚀变安山岩 6 0.69 1.89 1.20 147.09 813.03 529.80 安山岩 13 0.67 1.65 1.13 800.00 1350.96 1023.20 闪长岩 10 0.69 1.67 1.11 811.59 1822.71 1117.75 含铜磁铁矿 6 3.45 14.75 6.29 45.85 1430.97 330.58 磁铁矿 11 3.94 14.34 5.78 15.93 170.45 55.12 辉绿岩 2 0.76 1.00 0.88 160.84 485.56 323.20 构造角砾岩 13 0.45 2.11 1.19 853.03 1440.00 1116.29 黄铁矿化角砾岩 6 2.96 5.03 3.71 254.52 938.89 511.76
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