Multivariate analysis of regolith sediment geochemical data from the Jinwozi gold field, north-western China

Abstract

The study of deep-penetrating geochemistry of arid desert terrains in the Jinwozi gold field, north-western China has generated a data set of multi-element geochemistry, characterised by high complexity and variability leading to difficulties in integration and interpretation. Three multivariate statistical methods, i.e., factor analysis (FA), hierarchical cluster analysis (HCA) and discriminant analysis (DA) were applied to a subgroup of the data set in order to define the element associations, to identify the anomalies and to classify the regolith samples. The geochemical patterns of arid desert terrains were thus interpreted with the aid of statistical techniques. The subgroup consists of Au, Ag, As, Hg, Cu, Mo, Sb and Zn concentrations of regolith samples collected from two traverse lines and five overburden boreholes. Two factors with eigenvalues greater than 1 extracted by FA account for approximately 81% of the total variance. Specifically, factor 1 explains 52% of the total variance and is highly loaded by a combination of Au–As–Hg–Ag. This combination could represent the major mineralisation and three anomalous sites have been determined. Two of which are located over the known deposit. Factor 2 explains 29% of the total variance and has positive loadings on Cu and Zn denoting the minor mineralisation and diagenesis. High positive scores of both factors could be considered as an indication of the mineralisation. Silver, As, Cu and Zn are the most effective indirect indicator elements in the Jinwozi. The HCA was then applied to the classification of samples taken from the five boreholes at the three anomalous sites. Three geochemically distinct clusters, named A1, A2 and A3, resulted from the HCA. Samples from cluster A1 with high concentrations of Au, Ag, As, Hg, Cu and Zn are highly-mineralised. In addition, samples from cluster A2 and A3 can be generally treated as non-mineralised. The DA confirmed the results obtained from the HCA. The spatial distribution of the clusters shows vertical symmetric distribution of highly-mineralised samples over the deposit. This confirms the effectiveness of the FA in delineation of the anomalies in the Jinwozi. The integration of the FA, HCA and DA proved to be an effective tool in the field of deep-penetrating geochemistry.