Geochemical anomaly characteristics and mineral potential mapping in Milashan area of Tibet
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摘要:
水系沉积物地球化学异常分析在勘查找矿方面一直发挥着重要作用。采用中位数+2倍绝对中位差和C-A分形法，对米拉山地区1：5万水系沉积物Cu元素及由R型因子分析确定的Cu+Au+Ag组合元素进行了异常分析，确定了阈值。结果显示C-A分形法能更好地识别异常下限，且C-A分形模型确定的Cu元素异常比Cu+Au+Ag组合元素能更有效地反映米拉山地区与铜矿相关的化学异常特征。进而对Cu元素进行了S-A多重分形滤波处理，筛选出背景场和异常场，为圈定异常区提供更精准的依据。借助S-A分形模型和中位数方法划分了甲类异常2处（驱龙、甲玛）、乙类异常3处（达布、拉抗俄、程巴）、丙类异常2处（普雄、甲布纳）。甲类异常区包含冈底斯最大的2个斑岩铜矿，异常强，具有四级浓度分带，异常面积最大，外围找矿潜力巨大。乙类异常区包含3个大中型铜矿，都具有四级浓度分带，具有很好的找矿潜力。丙类异常区目前尚未发现铜矿，但值得进一步开展地质工作，查明成矿潜力。
Abstract:The analysis of geochemical anomalies derived from stream sediment geochemical data is a fundamental task in mineral prospecting.In this study, median+2 median absolute deviations(median+2MAD)and concentration-area(C-A)were applied to analyze geochemical anomaly delineation of Cu and Cu+Au+Ag association from factor analysis of stream sediment geochemical data in Milashan area of Tibet.The results show that the C-A fractal method is a favorable means for identifying the anomaly.Cu anomaly provides more information than Cu+Au+Ag associated anomaly.Furthermore, the S-A analysis was used to decompose the Cu element and distinguish the background from anomaly components, which provides a more accurate basis for delineating the anomalous area.Six anomalous areas have been classified into classes A(Qulong and Jiama), B(Dabu, Lakange and Chengba)and C(Puxiong and Jiabuna).Class A anomalous areas containing two largest porphyry copper deposits in the Gangdise belt are characterized by great anomalous intensity and largest anomalous area, and have great potential for periphery prospecting.Class B prospective areas contain three large and medium-sized copper deposits.Particularly, the Chengba anomalous area has similar anomalous intensity to Qulong and Jiama anomalous areas and thus has good prospecting potential.Copper deposits have not been discovered in Class C anomalous areas, but it deserves exploration work for identifying the mineral potential.
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Keywords:
- stream sediment data /
- anomaly /
- factor analysis /
- ore prospecting /
- Milashan area
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图 3 米拉山地区Cu元素(A)、Cu+Au+Ag元素组合直方图(B)及Q-Q(C、D)图解
Figure 3. Histograms of Cu(A), Cu+Au+Ag(B), and Q-Q plots of Cu(C), Cu+Au+Ag(D)in Milashan area
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图 4 Cu元素(A)和Cu+Au+Ag(B)元素组合C-A模型双对数图
Figure 4. Log-log plots showing the relationship between area and Cu(A)and Cu+Au+Ag(B)generated using the C-A fractal model
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图 5 C-A模型下米拉山地区Cu元素地球化学异常图
Figure 5. Spatial distributions of Cu anomaly based on C-A fractal model in Milashan area
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图 6 C-A模型下米拉山地区Cu+Au+Ag组合元素地球化学异常图
Figure 6. Anomaly diagram of Cu+Au+Ag association based on C-A fractal model in Milashan area
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图 7 Cu元素S-A模型双对数图
Figure 7. Log-log plots showing the relationship between area and Cu, generated using the S-A fractal model
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图 8 S-A模型下米拉山地区Cu元素背景场
Figure 8. Background component of Cu determined by S-A fractal model in Milashan area
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图 9 S-A模型下米拉山地区Cu元素异常场及异常区分布
Figure 9. Spatial distributions of Cu anomaly and anomaly area determined by S-A fractal model in Milashan area
表 1 米拉山水系沉积物数据特征统计
Table 1 Statistics of stream sediment geochemical data from Milashan area
参数 Au Ag Cu Pb Zn Ba Mo Sn Sb Bi W 采样点个数 15622 15622 15622 15622 15622 15622 15622 15622 15622 15622 15622 平均值 3.29 0.14 47.57 54.58 94.2 435.96 1.71 3.22 2.13 1.1 4.19 中位数 1.86 0.09 22.5 30 71.8 431 0.78 3.04 1.18 0.48 3.37 标准偏差 17 0.49 277 1391 972 94 14 3 27 10 9 方差 278 0.25 77133 193526 944468 8831 188 8 741 103 74 偏度 58 31 35 93 75 2 60 19 71 31 33 峰度 3887 1267 1779 9658 6109 10 4523 487 5439 1182 1584 最小值 0.01 0.01 2.10 4.90 10.40 3.00 0.10 0.44 0.04 0.04 0.23 最大值 1236 26 18600 153000 89200 1852 1206 103 2384 501 528 25%累计频率 1.24 0.07 18.30 25.90 61.00 398.00 0.59 2.39 0.90 0.35 2.61 50%累积频率 1.86 0.09 22.50 30.00 71.80 431.00 0.78 3.04 1.18 0.48 3.37 75%累积频率 2.82 0.13 28.10 34.40 83.40 467.00 1.10 3.71 1.52 0.61 4.10 95%累积频率 7.4 0.25 62.1 53.79 119 577 3.16 4.77 3.75 1.18 7.84 98%累积频率 16.2 0.45 266.54 88.35 184.54 658 9.08 5.32 7.01 2.69 15.5 注：元素含量Au的单位为10-9，其他元素均为10-6 
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表 2 米拉山地区正交旋转因子(F1-F3)载荷矩阵
Table 2 Orthometric rotating factor(F1-F3)loading matrix in Milashan area
因子 F1 F2 F3 Au 0.007 0.856 -0.035 Ag 0.259 0.739 0.403 Cu 0.480 0.686 0.186 Pb 0.960 0.041 0.001 Zn 0.975 0.079 0.020 Ba -0.078 0.052 -0.39 Mo 0.929 0.230 0.033 Sn -0.017 0.203 0.807 Sb 0.957 0.192 0.015 Bi -0.02 0.204 0.839 W 0.794 0.121 0.174 累计方差贡献率/% 46 66 75
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表 3 Cu元素及Cu+Au+Ag组合元素异常下限值确定
Table 3 Anomaly threshold values calculated for Cu and Cu+Au+Ag
元素 异常下
限方法异常
下限总矿
床数覆盖
矿床
个数异常面积
出现矿床
概率(n)/%异常面积
占比(s)
/%n/s Cu C-A分形法 70 16 7 43.8 5.2 8.4 中位数方法 32 16 10 62.5 15.4 4.1 Cu+Au+Ag C-A分形法 72 16 8 50.0 7.8 6.4 中位数方法 59 16 9 56.3 13.7 4.1
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