Ore textures and chemical constraints in the Serantak goldfield, northwest Borneo, Indonesia: implications for retrograde skarn occurrences

The ore characteristics and geochemistry at the Serantak goldfield are pivotal for understanding the genetic model of the gold mineralisation. This study focuses on identifying textures, compositions and their elemental associations, which are key parameters for ore-forming processes. Research involved fieldwork, sampling, petro-mineragraphy, rock geochemistry analyses and modelling. The results demonstrate a distinct ore genesis and sequence, classified into retrograde skarn and epithermal vein styles. Syngenetic gold skarn types dominate in the proximal zone, exhibiting minerals like pyroxene ± garnet ± wollastonite–epidote–calcite, alongside disseminated sulfides such as pyrite–pyrrhotite–chalcopyrite, are confined within meta-sedimentary units in the northeast-trending intercalated bedding. Gold is associated with arsenic ± silver ± copper. In later stages, within the peripheral zone, epithermal veins develop along fractures within major reactivated northwest structures and dilatational jogs, marked by quartz–feldspar ± sericite ± chlorite hosted in volcaniclastic rocks and associated with pyrite ± arsenopyrite ± realgar. At this stage, gold shows a strong correlation with silver ± arsenopyrite. Meteoric water re-equilibration triggers a supergene enrichment process linked with manganese-jarosite ± hematite minerals. Exploration efforts in the vicinity of intrusive body and delineation of continuity vein-style mineralisation are also critical for upside potential, while additional studies on mineral chemistry and gold deportment are needed. Distinct ore genesis occurs through retrograde skarn and epithermal veins, followed by subsequent surficial supergene enrichment. Main mineralisation at Serantak is categorised as gold skarn, demonstrating a moderate positive relationship between gold and arsenic, silver and copper. The findings from genetic model and paragenetic sequence enhance the reliability of exploring overprinted deposits across the prospect area.