西秦岭常家山地区水系沉积物地球化学特征及其地质意义

西秦岭成矿带北亚带是重要的多金属成矿单元。为缩小找矿靶区,在常家山地区开展了1:2.5万水系沉积物测量工作,对采集到的1 141件样品中的Au、Ag、As、Sb、Bi、Cu、Pb、Zn、W、Mo 10种元素进行核密度估算等数理统计分析,结果显示它们的浓度高于全国水系和区域水系沉积物的平均值,表明研究区成矿潜力大。通过因子分析得到F1(Bi、Cu、Zn)、F2(Au、As、Sb)、F3(Ag、Pb)、F4(W、Mo)4个主因子。使用浓度-面积(C-A)分形模型得到各元素和因子的异常阈值,并利用克里金插值法得到相应的地球化学空间分布图;结合区域控矿因素和异常分布特征圈定出Hz1、Hz2、Hz3 3处综合异常,前缘晕、近矿晕和尾晕显示出自西北向东南分布的趋势。水系沉积物地球化学异常分析结果表明,区内构造控矿特征明显,北西方向的礼县—闾井断裂是常家山地区有利的找矿部位。

Geochemical Characteristics and Geological Significance of Stream Sediments in Changjiashan Region,Western Qinling Orogen

The northern sub-belt of Western Qinling Orogen is endowed with abundant polymetallic resource. To delineate mineral exploration targets, a 1:25,000 stream sediment geological survey was carried out in the Changjiashan district. Statistical analysis was performed from 1,141 samples for Kernal Density Estimation elements (Au, Ag, As, Sb, Bi, Cu, Pb, Zn, W, and Mo). Element concentrations are higher than the national and regional average, indicating metallogenic potential in the area. Element combinations of the four factors were obtained based on factor analysis, i.e., F1(Bi-Cu-Zn), F2(Au-As-Sb), F3(Ag-Pb), and F4(W-Mo). We obtained thresholds of geochemical elements and factor scores, and geochemical mapping via Concentration-Area (C-A) fractal modeling and Kriging interpolation, respectively. Combined with regional ore-controlling factors and anomaly spatial distributions, three polymetallic anomaly areas, i.e., Hz1, Hz2, and Hz3, were delineated. Geochemical halos comprise the supra-ore halo, near-ore hole, and sub-ore halo from northwest to southeast. Distribution of stream sediment geochemical anomalies indicates that all mineralization was fault-controlled, and the area close to the NW-trending Lixian-Lüjing fault at Changjiashan represents a favorable prospecting target.