Geochemical Characteristics and Information Extraction in GASH Ore Concentration Area, Eritrea
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摘要:
GASH金矿集区位于厄立特里亚西部的碧沙Au多金属成矿带，具有良好的区域成矿背景。区内1∶10万水系沉积物测量数据的地球化学特征表明，Au、Hg、As、W、Bi等元素呈强分异的分布特征，Au、As、Sb、W具有强富集的分布特征，显示优异的Au找矿前景。通过元素相关性分析，筛选出能够有效指导Au矿勘查的F5因子（Au-Hg元素组合）、指示区域断裂构造分布的F2因子(Ag-Bi-Mo-W元素组合)及F3因子（As-Sb-Pb元素组合），指示基性–超基性地质体分布的F1、F4特征因子。对F5因子得分开展异常信息提取，并结合矿产地质特征，圈定出可开展进一步原生岩金矿勘查工作的异常区8处，基于指示成矿热液活动的F2、F3、F5特征因子推断出NE、N–NE向的规模较大的断裂12条，为研究区的找矿预测及勘查工作部署提供了有利的地球化学依据。
Abstract:GASH Au ore concentration area belongs to Bisha gold metallogenic belt in West Eritrea, with a good regional metallogenic setting. The geochemistry of stream sediment mapping at scale of 1∶100,000 indicate: Au, Hg, As, W, Bi are characteristic of strong-differentiated distribution, Au, As, Sb, W are characteristic of strong-rich distribution, showing a good prospecting for Au exploration. Through the correlation analysis, F5 factor (Au-Hg association) is confined to guide the Au exploration, F2 factor (Ag-Bi-Mo-W association) and F3 factor (As-Sb-Pb association) which are confined to guide the distribution of fault structures, F1 and F4 factor are confined to guide the distribution of basic and ultrabasic geological unit. with the anomaly information extract from F5 factor combined with the geological characteristic, 8 anomaly area with good Au metallogenic prospecting were determined, base on the characteristic of F2, F3, F5 factors, which are useful in indicating the metallogenic hydrothermal activity, 12 regional fault with NE, N-NE attitude were deduced. All the information extracted are useful geochemical evidence to the following gold exploration and the work deployment.
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Key words:
- Africa /
- Eritrea /
- gold /
- geochemical /
- anomaly extract /
- fault structure
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图 1 研究区地质构造简图（图a据赵凯，2018；图b据Greig，2004）
Figure 1.
表 1 各元素地球化学特征参数
Table 1. Statistical characteristics of elements geochemical values
元素 平均值 中值 最大值 均方差 克拉克值 变异系数 富集系数 Au 3.88 1.40 71.00 8.63 0.90 2.22 4.32 Ag 0.04 0.04 0.42 0.03 0.06 0.63 0.70 As 3.21 2.19 43.50 3.73 2.40 1.16 1.34 Sb 0.24 0.21 0.94 0.12 0.18 0.50 1.34 Hg 0.0049 0.004 0.05 0.01 0.01 2.24 0.49 W 0.85 0.62 17.30 1.18 0.60 1.40 1.41 Mo 0.64 0.54 9.10 0.57 0.50 0.88 1.29 Bi 0.09 0.06 4.37 0.21 0.14 2.22 0.67 Sn 1.26 1.21 3.73 0.40 1.40 0.32 0.90 Cu 37.04 30.60 169.00 23.66 26.00 0.64 1.42 Pb 8.05 7.60 34.30 3.02 15.00 0.37 0.54 Zn 51.67 46.80 187.00 25.36 76.00 0.49 0.68 Co 19.41 15.60 207.00 17.12 19.00 0.88 1.02 Cr 65.24 48.60 879.00 74.63 76.00 1.14 0.86 Ni 27.29 20.50 256.00 24.27 31.00 0.89 0.88 Ti 4422.00 4114.00 26651.00 2550.00 4000.00 0.58 1.11 V 129.22 117.00 804.00 72.53 112.00 0.56 1.15 Fe2O3 5.78 5.35 29.18 2.88 2.45 0.50 2.36 MgO 1.56 1.39 10.50 1.02 3.16 0.65 0.49 注：粗体标注元素变异系数大于1.3，富集系数大于1.2，在特征参数分析工作中需重点关注。Au含量为10–9；Fe2O3、MgO含量为%；其余元素含量为10–6。 
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表 2 研究区主要岩石单元Au含量特征
Table 2. The Au content of main rock unit in study area
岩石单元 Au含量均值（10–9） 岩性特征 元古宙火山岩 0.95 岩性以蚀变安山岩为主，在研究区广泛分布，整体呈NE向展布 元古宙变沉积岩 0.82 岩石的片理化特征明显，多与火元古宙山岩相邻分布，呈NE向展布 花岗岩区 1.74 颜色较闪长岩浅，常见构造变形特征，整体呈NE向展布，分布面积较大 闪长岩区 1.73 岩石具有明显的片理化特征，颜色较花岗岩深，区内分布面积相对较小 辉长-辉石岩区 0.61 岩石颜色较深，矿物颗粒较大，在区内呈零星分布
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表 3 因子分析特征参数统计
Table 3. Characteristic parameters of factor analysis
因子 因子特征值及方差贡献率 元素 正交旋转载荷矩阵 特征值 方差贡献率（%） 累积贡献率（%） F1 F2 F3 F4 F5 F1 6.66 35.03 35.03 Ag 0.09 0.68 0.32 0.18 0.12 F2 2.86 15.08 50.11 As 0.10 0.02 0.84 0.14 0.04 F3 1.61 8.47 58.58 Bi −0.06 0.90 −0.07 −0.05 0.11 F4 1.54 8.13 66.70 Co 0.14 0.08 0.52 0.61 0.06 F5 1.02 5.36 72.06 Cr 0.31 −0.02 −0.08 0.82 0.01 F6 0.91 4.81 76.87 Cu 0.65 0.32 0.43 0.14 0.13 F7 0.72 3.81 80.69 Hg 0.09 0.12 0.15 0.02 0.75 F8 0.54 2.86 83.55 Mo 0.06 0.81 0.18 0.03 0.10 F9 0.53 2.78 86.33 Ni 0.15 −0.01 0.20 0.89 0.01 F10 0.48 2.55 88.88 Pb 0.12 0.21 0.61 −0.04 0.08 F11 0.42 2.20 91.08 Sb 0.11 0.15 0.88 0.11 0.08 F12 0.35 1.83 92.91 Sn 0.52 0.30 0.28 −0.13 0.11 F13 0.30 1.59 94.51 Ti 0.88 0.05 0.17 0.01 0.07 F14 0.27 1.41 95.91 V 0.79 0.13 0.22 0.28 0.08 F15 0.22 1.14 97.06 W −0.04 0.80 0.03 −0.03 0.10 F16 0.21 1.11 98.16 Zn 0.82 0.13 0.24 0.22 0.09 F17 0.20 1.06 99.22 Fe2O3 0.85 0.16 0.26 0.31 0.10 F18 0.08 0.44 99.67 MgO 0.52 0.05 −0.005 0.71 0.05 F19 0.06 0.33 100.00 Au −0.001 0.17 0.03 0.04 0.79 注：表中左侧粗体为特征值大于1的因子项，反映数据主要信息的主因子；右侧粗体反映5个主因子分别代表的元素载荷。
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