Identification and mapping of geochemical patterns and their significance for regional metallogeny in the southern Sanjiang, China

Abstract

The southern Sanjiang region, southwestern China, comprises various continental blocks, tectonic sutures and arcs. This complex structural area is a proper place for the recognition of geochemical patterns and understanding of regional metallogenesis. Considering each individual tectonic unit (i.e., western South China block, Ailaoshan suture, Simao block, Changning–Menglian suture, Baoshan block and Tengchong block) as a statistical unit, this study identifies the distribution patterns of geochemical elements, distinguishes elemental associations for different geological backgrounds (controlled by the regional lithology) and diverse mineralizations, and thereby delineates the mineralized anomalies. To achieve the goals, the kriging interpolation, staged factor analysis and local singularity technology were utilized after the centered logratio (clr) transformation of stream sediment geochemical data. The spatial distributions of metallogenic elements (Au, Ag, Cu, Pb, Zn and Sn) show that not all the areas with high concentrations of elements contain ore deposits. It means that the formation of ore deposits is an independent anomalous geological event, not necessarily related to the original regional abundance of geochemical elements. The different element associations obtained by staged factor analysis of 28 elements are able to reveal the geological backgrounds and metallogenic signatures for different tectonic units. For example, the element associations for the first, second and third factors (Fs) in the western South China block are groups of Ti–Co–V, Sb–Ag–As and Th–U–Be (see text for the detailed element associations), which represent the Emeishan flood basalts, Ag–Pb mineralization and felsic rocks, respectively. Similarly, the element associations Co–V–Cu, Be–U–Th and Sb–Ag–Au for F1, F2 and F3 in the Ailaoshan suture respectively represent the ophiolite complex and mafic rocks, felsic rocks and Au mineralization. The associations from F1 to F4 in the Simao block are Th–U–Sn, V–Co–Cr, Cd–Ag–Pb and Au–Sb, which represent the Linchang batholith, mafic rocks, Ag–Pb–Zn mineralization and Au mineralization, respectively. The distribution patterns of their factor scores can roughly distinguish the anomalies caused by regional backgrounds and mineralizations. The local singularity of factor scores for mineralization can further identify mineralized areas in most of the tectonic units. Nevertheless, an exception occurs in the western South China block where the background element association, Ti–Co–V–Cu–Ni–Cr–P–Mn–Nb–Zn (F1), obscures the Au signature. Therefore, we substituted the single element Au for mineralized element association (F1) to perform singularity mapping, and obtained better result. It was concluded that the combination of staged factor analysis, local singularity and tectonic setting is effective in regional metallogenic potential analysis.