西藏多龙矿集区水系沉积物地球化学数据定量分析与解释

位于西藏改则县的多龙矿集区是班公湖—怒江结合带最重要的斑岩型铜-金产地,具有较大的找矿潜力。本文利用MML-EM算法(Minimum Message Length-Expectation Maximization Algorithm)和ILR变换(Isometric Log-Ratio Transformation)为基础的主成分分析定量研究多龙矿集区水系沉积物化探数据的统计分布规律。混合分布筛分结果表明,Cu、Pb、Zn、Cr、Ni、Mn、Ag、Sn、W、Mo、As、Sb、Bi、Hg和Au的元素含量都服从包含两个对数正态分布的混合分布。大部分元素的高均值子分布反映了该地区多期次岩浆或热液活动。通过作ILR变换(Isometric Log-Ratio Transformation),消除了多龙地区化探数据的闭合效应,第一主成分的元素组合指示该地区的铜-金成矿潜力。多龙地区大部分铜-金矿床(点)和地表蚀变落在第一主成分得分较高的区域。根据第一主成分的得分,本文圈定了若干个成矿潜力较大的靶区。

QUANTITATIVE ANALYSIS AND INTERPRETATION OF THE GEOCHEMICAL DATA OF THE STREAM SEDIMENT IN DUOLONG MINERAL DISTRICT, TIBET, CHINA

Geochemical data are typical compositional data and their closure effect exists in the rock major elements as well as in all trace elements and their arbitrary subsets. However, the closure effect is often ignored in many cases. Ten porphyry and epithermal Cu-Au deposits were recently found in Duolong mineral district, northwest Tibet, China. There are still great prospecting potential of copper resources in Duolong. The geochemical data of the stream sediment in Duolong were analyzed using Minimum Message Length-Expectation Maximization Algorithm (MML-EM) and Isometric Logratio Transformation (ILR) based on principal component analysis. It is found that all the fifteen elements data contain two log-normal populations. The high-average population of most elements reflects the multiple magmatic activities or hydrothermal processes in Duolong. The closure effect was overcome after ILR transformation and the element associations in the first principal component were interpreted to be indicators for the Cu-Au mineralization potential in Duolong. The areas with high scores of the first component are consistent with most of the found Cu-Au deposits and the alteration zones exposed at surface. Four zones with high scores are suggested for further investigation on their mineral potential.