Application of multifractal and local singularity analysis method to the identification of deep-level geochemical anomalies in the Duolong mineral district, Tibet, China
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摘要:
勘查地球化学数据作为成矿地质体预测最重要的信息载体之一,在识别提取成矿异常以及挖掘深层次成矿信息中具有重要作用。基于地球化学元素空间分布的尺度不变性和广义自相似性,以多龙矿集区1∶5万勘查地球化学数据中的Cu、Au元素为例,运用分形/多重分形和奇异性理论开展分析研究,进行成矿元素空间分布模式的识别和异常提取。针对研究区全区、断裂缓冲区和地层分区分别运用矩方法计算多重分形谱,用于描述局部地区元素的相对富集及亏损程度,并对区内Cu、Au成矿元素进行局部奇异性分析,以识别提取成矿元素的弱、缓异常信息,圈定成矿潜力区。研究表明,多龙矿集区内Cu、Au元素均表现为成矿有利模式。其中,Cu元素存在区域的弱富集,Au元素存在局部范围的超富集,近EW向与NE向断裂的交汇区域以及侏罗系为区内最有利成矿位置。通过绘制局部奇异性指数空间分布图,表征了Cu、Au元素地球化学异常空间分布特征,进而圈定了矿集区的中部和北部为成矿潜力区。
Abstract:Objective As one of the most crucial information carriers for predicting mineralized geological bodies, exploration geochemical data play a significant role in the identifying and extracting mineralization-associated anomalies as well as in analyzing deep-level mineralization information.
Methods Based on the scale invariance and generalized self-similarity characteristics of the spatial distribution of geochemical elements, this paper uses Cu and Au in the 1:50 000 exploratory geochemical data of the Duolong mineral district as an example and conducts a study using fractal/multifractal and singularity theories to identify the spatial distribution patterns of ore-forming elements and extract anomalies. The multifractal spectrum which is derived by the exploratory moment method for the whole study area, the fault buffer zone and the stratigraphic zone, is used to describe the relative enrichment and depletion of elements in the local area and to analyze the local singularity of Cu and Au mineralized elements, so as to identify and extract weak and low anomalies of mineralized elements and delineate potential mineralization zones.
Results Both Cu and Au exhibit mineralization-favoured patterns in the Duolong mineral district, with the Cu showing weak enrichment in the region and Au being over-enriched on a local scale. The intersections of the east-west and northeast-trending faults, as well as the Jurassic strata, are identified as the most promising locations for mineralization in this region.
Conclusion The spatial distribution of the local singularity index is mapped to characterize the distribution features of Cu and Au geochemical anomalies, therefore, the central and northern regions of the ore district are subsequently identified as potential areas for mineralization.
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图 1 多龙矿集区区域位置图(a)及地质简图(b)[37]
Figure 1. Regional geological map(a) and simplified geological map(b) of the Duolong mineral district
图 8 多龙矿集区地层分区图(地层代号含义同图 1)
Figure 8. Stratigraphic zoning map of the Duolong mineral district
表 1 多龙矿集区勘查地球化学数据分析精确度、精密度及检测方法[25]
Table 1. Analytical accuracy, precision and detection methods for exploration geochemical data in the Duolong mineral district
元素 检测下限/wB 平均精度 检测方法 Ag 0.03×10-6 0.004 ES As 1×10-6 0.004 AFS Au 0.3×10-9 0.002 GFAAS Bi 0.1×10-6 0.007 AFS Cr 10×10-6 0.002 XRF Cu 2×10-6 0.010 XRF Hg 0.01×10-6 0.013 AFS Mn 30×10-6 0.001 XRF Mo 0.5×10-6 0.004 CP Ni 5×10-6 0.004 XRF Pb 5×10-6 0.012 XRF Sb 0.3×10-6 0.002 AFS Sn 1×10-6 0.000 ES W 0.5×10-6 0.010 CP Zn 20×10-6 0.001 XRF 注:XRF为X射线荧光光谱法;CP为催化极谱法;AFS为原子荧光光谱法;ES为发射光谱法;GFAAS为石墨炉原子吸收光谱法 表 2 盒子大小及对应数目
Table 2. Box size and corresponding number
盒子尺寸ε 1 2 4 8 盒子数目N(ε) 340 155 52 20 表 3 多龙矿集区勘查地球化学元素统计参数
Table 3. Statistical parameters of geochemical elements for exploration in the Duolong mineral district
元素 统计量 最小值 最大值 均值 标准差 变异系数 中值 偏度 w(Cu)/10-6 3 358 6.2 854.0 38.5 52.0 1.4 26.8 8.7 w(Au)/10-9 3 358 0.4 1 058.5 4.8 25.0 5.3 2.2 29.6 表 4 多龙矿集区Cu、Au元素多重分形谱参数(-10≤q≤10)
Table 4. Multifractal spectrum parameters of Cu and Au in Duolongite mineral district (-10≤q≤10)
元素 αmin α(0) αmax Δα f(αmin) f(αmax) Δf R Cu 1.385 2.017 2.184 0.799 0.243 0.868 -0.625 3.752 Au 0.962 2.015 2.682 1.720 0.072 -1.221 1.293 1.580 表 5 多龙矿集区断裂缓冲区内Cu元素多重分形谱参数(-10≤q≤10)
Table 5. Multifractal spectrum parameter table of Cu in fault buffer zone of the Duolong mineral district(-10≤q≤10)
方向 αmin α(0) αmax Δα f(αmin) f(αmax) Δf R 全区断裂 1.396 2.017 2.112 0.716 0.389 0.811 -0.422 6.508 NW向断裂 1.498 2.000 2.152 0.654 0.736 1.192 -0.456 3.303 NE向断裂 1.405 2.000 2.146 0.741 0.473 1.432 -0.959 4.075 EW向断裂 1.442 2.000 2.052 0.610 0.631 1.900 -1.269 10.731 注:表中各物理量的含义见正文,下同 表 6 多龙矿集区断裂缓冲区内Au元素多重分形谱参数(-10≤q≤10)
Table 6. Multifractal spectrum parameter table of Au in fault buffer zone of the Duolong mineral district(-10≤q≤10)
方向 αmin α(0) αmax Δα f(αmin) f(αmax) Δf R 全区断裂 0.962 2.015 2.671 1.709 0.075 -0.768 0.843 1.606 NW向断裂 0.792 1.972 2.096 1.304 0.033 1.637 -1.604 9.467 NE向断裂 0.895 1.972 2.699 1.804 0.029 -0.446 0.475 1.479 EW向断裂 0.962 2.014 2.087 1.125 0.075 1.596 -1.522 14.385 表 7 多龙矿集区主要地层Cu元素多重分形谱参数(-10≤q≤10)
Table 7. Multifractal spectrum parameter table of Cu in the main strata in the Duolong mineral district(-10≤q≤10)
地层代号 αmin α(0) αmax Δα f(αmin) f(αmax) Δf R T3r 1.606 2.036 2.164 0.558 0.716 0.942 -0.226 3.369 JM 1.403 2.009 2.062 0.659 0.440 1.862 -1.422 11.364 J1q 1.514 1.994 2.034 0.520 0.908 2.010 -1.102 12.098 J2s 1.408 2.007 2.054 0.646 -0.111 1.968 -2.079 12.658 K1m 1.445 1.999 2.084 0.639 0.666 1.847 -1.181 6.580 K2a 1.472 1.978 2.079 0.607 0.736 1.639 -0.903 4.980 注:表中地层代号同图 1, 下同 表 8 多龙矿集区主要地层Au元素多重分形谱参数(-10≤q≤10)
Table 8. Multifractal spectrum parameter table of Au in the main strata in the Duolongmineral district(-10≤q≤10)
地层代号 αmin α(0) αmax Δα f(αmin) f(αmax) Δf R T3r 1.784 2.091 2.186 0.402 0.924 1.629 -0.705 3.223 JM 1.072 2.010 2.215 1.143 0.004 0.440 -0.436 4.583 J1q 0.995 1.963 2.663 1.668 0.028 0.440 -0.412 1.383 J2s 0.962 2.038 2.225 1.263 0.075 0.601 -0.526 5.771 K1m 1.210 2.034 2.449 1.239 -0.065 -0.369 0.304 1.988 K2a 0.967 1.913 2.417 1.450 0.017 -0.467 0.484 1.877 -
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