Extraction and Assessment of Cu-Au Anomalies of the East Tianshan Ore-Forming Belt, Northwestern China
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摘要: 东天山成矿带是我国重要的铜金矿集区之一.复杂的地质演化历史导致了成矿地质背景的复杂性、成矿作用的多期性和多样性.本文分别应用地质统计学和多重分形滤波法(S-A法)对Cu、Au含量数据进行分析，获取了不同层次的致矿异常信息.结果表明：(1)东天山地区Cu、Au含量最大变程分别为80 km和47 km，最大变程方向与深大断裂走向一致，表明Cu、Au异常受深大断裂控制；Cu含量分布比Au具有更好的连续性，Cu的含量变化表现出较强的结构性特征，而Au的含量变化表现出更强的随机性特征.(2)泛克立格法和多重滤波分形分析中的低通滤波获取致矿异常信息具有相似性，均反映Cu、Au区域上的分布趋势和浓集特征.(3)多重分形滤波法能够提取不同层次的致矿异常信息，包括区域异常信息和局部异常信息，S-A法揭示的局部Cu异常突出了某些低背景中的隐蔽异常；而呈北东向串珠状分布的局部Au异常，可能暗示区内NE向次级断裂系统控制了金矿床的发育.Abstract: The east Tianshan ore-belt is one of the most important ore concentrated districts of Cu-Au in China. Long and complicated geological evolution created a complex geological background, multi-periods and diversity of mineralization. In this study, stream sediment survey data of Cu-Au are used for spatial distribution analysis, and then Geostatistical method and Spectrum-Area (S-A) method are implemented to obtain ore-forming information at different scale. The research results are as follows: (1) the modeling semivirograms show the max range of Cu and Au are 80 km and 47 km, the direction of max range is along the trend of regional deep faults, which are the major factors controlling the distribution of Cu, Au concentration. Cu concentration exhibits more strong structure character than Au in region. (2) Both low pass filtering in S-A and universal Kringing can obtain the similar ore forming information which reflect the regularity of enrichment of ore-forming elements caused by regional mineralization. (3) Multi-fractal filtering can effectively decompose the concentration data from stream sediment survey in complicated geological setting into different hierarchy, including local anomalies and regional anomalies. Different anomaly filters defined in ln(Spectrum)-ln(Area) plot can be constructed to obtain Cu and Au anomalies at different scale. The local Cu anomalies obtained by S-A method are spatially associated with known Cu deposits, which reveal some conceal ore-forming information in low background. The local anomalies of Au in pinch-and-swell and oriented in North-East trend obtained by S-A method may imply that the gold mineralization is controlled by sub-fault system in NE trend.
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图 1 东天山地质矿产简图
1.新生界；2.中晚元古代结晶基底；3.泥盆纪大南湖-头苏泉岛弧；4.三叠-白垩纪盆地沉积；5.二叠纪盆地沉积；6.中石炭世低坎儿组伸展间歇期浅水盆地沉积；7.早石炭世雅满苏裂谷；8.早石炭世干墩-苦水裂陷槽边缘相带；9.早石炭世小热泉子-梧桐窝子裂陷槽；10.震旦-泥盆纪塔北缘沉积盖层；11.中晚元古代基底；12.早元古代结晶基底；13.华力西期花岗岩；14.晋宁期花岗岩；15.华力西期斜长花岗岩；16.华力西期超基性杂岩；17.基性-超基性杂岩；18.华力西期闪长岩；19.深大断裂；20.一般断裂；21.金矿；22.铜矿；23.镍矿；24.铜镍矿；F1.大草滩断裂；F2.康古尔塔格断裂；F3.雅满苏-苦水断裂；F4.阿奇库都克断裂；F5.星星峡断裂
Fig. 1. The simplified geological map of the east Tianshan ore-forming belt
图 3 lnA(≥S)-lnS图，表明元素能谱密度与其面积的数量关系
Fig. 3. ln-ln plot showing the relationships between the element spectrum energy density and its "area" of A (≥S) : for Cu and Au
图 4 (a) 低通滤波器提取的Cu区域异常: (b)低通滤波器提取的Au区域异常; (c)带通滤波器提取的Cu局部异常: (d)高通滤波器提取的Au局部异常
Fig. 4. (a) Regional anomaly component (low frequency) of Cu; (b) Regional anomaly component (low frequency) of Au; (c)Localanomaly component of Cu (intermediate frequency); (d) Local anomaly component of Au decomposed (high frequency)
表 1 东天山地区Cu-Au含量统计参数
Table 1. Statistical parameters of Cu and Au concentration
统计参数 Cu(10-6) Au(10-9) 原始值 原始值取自然对数 剔除特异值后 剔除特异值后取自然对数 原始值 原始值取自然对数 剔除特异值后 剔除特异值后取自然对数 统计数 14 695 14 695 14 689 14 689 14 695 14 695 14 673 14 673 最小值 0.3 -1.2 0.3 -1.2 0.1 -2.3 0.1 -2.3 最大值 2 940 7.99 88.60 4.48 700 6.55 30 3.4 均值 19.21 2.81 18.97 2.80 1.70 0.06 1.45 0.05 中位数 17.00 2.83 17.00 2.83 1.10 0.10 1.10 0.10 标准差 26.24 0.55 10.14 0.05 9.69 0.81 1.62 0.79 偏度 93.95 -0.39 1.42 -0.47 55.9 0.26 6.41 -0.02 峰度 10 443 4.47 6.48 3.93 3 667.4 5.34 72.66 3.77 X+3S 97.94 / / / 30.77 / / / 
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表 2 东天山地区Cu-Au含量数据变差函数拟合参数
Table 2. Fitting semi-variogram parameters of Cu and Au concentration
元素 Cu Au 参与计算数据点 14 689 14 673 数据变换法 对数变换 对数变换 拟合模型 球型 球型 最大变程方向 79° 76° 最大变程(km) 80 47 最小变程(km) 26 34 块金常数 0.125 7 0.320 4 基台值 0.273 8 0.670 4 块金常数/基台值×100 46 48
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表 3 预测精度参数
Table 3. Precision parameter of prediction
元素 平均误差 均方根误差 平均标准误差 标准化平均误差 标准化均方根误差 Cu 0.173 2 6.171 7.893 0.115 5 0.896 1 Au -0.012 55 1.39 1.354 -0.030 16 1.221
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