Tracing metal sources in orogenic gold deposits of the Timburu Goldfield, Meratus, Indonesia: A geochemical and statistical approach

Abstract

Orogenic gold deposits at the Timburu Goldfield, Indonesia, are primarily hosted by metamorphosed ultramafic and volcanic rocks, as well as quartz lodes formed along shear zones. Gold mineralisation developed along the lithological contacts between serpentinites, porphyritic intrusions, and granitoids. The mineralization is represented by electrum and hessite, with trace amounts of chalcopyrite, galena, tetrahedrite, and Co-Ni-As-S phases. The alteration mineralogy of mafic rocks in Timburu includes magnesite, dolomite, sericite, albite, calcite, and chlorite. This study integrates a multi-statistical evaluation of in-situ trace-element data, geological relationships, and detailed mineralogical characterisation to better understand the evolution of geochemical reservoirs responsible for metal accumulation during orogenic events. Principal component analysis (PCA) produced three significant components that explained 80% of the cumulative variance. We divide the pyrite data into three groups based on trace element correlations, which are likely linked to pyrite texture and paragetic sequences. The results show that the Ni-Co and other metals were leached from metamorphosed ultramafic rocks and mobilised during alteration. Metals, including Au have been released during greenschist- to amphibolite-facies metamorphism in the context of a continent–continent collision. The rare earth element (REE) patterns of metavolcanic and serpentinised ultramafic rocks may be similar to other accretionary complexes formed during continent–continent collision. The transformation of serpentinite to listvenite is controlled by the addition of carbon dioxide and the mobilisation of SiO₂, MgO, and CaO. Chemical changes during alteration are primarily dominated by the incorporation of trace elements into pyrite.