Porphyry and skarn Cu prospectivity of Sumatra with GIS spatial modelling techniques

Abstract

Decades of mineral exploration on Sumatra Island, situated along the Sunda magmatic arc in Indonesia, have only resulted in the discovery of one mid-sized, economically viable porphyry Cu deposit and a few exploited Cu-rich polymetallic skarns. Nevertheless, studies indicate that more Cu resources remain to be discovered. This contribution integrated geochemical, structural and relief evidential layers with the fuzzy logic- and weights-of-evidence (WoE) methods to produce mineral prospectivity maps that show not only a strong correlation between the generated favourable areas and known porphyry and skarn Cu prospects or lithologic units commonly associated with such deposits, but also other potentially new exploration districts throughout Sumatra. A local singularity fractal map of Cu-enriched zones helped define exploration priorities within the large fuzzy logic or WoE prospective areas, as well as cross-validated the results of the fuzzy models. The Cu potential maps can thus be used as base maps for porphyry and skarn Cu exploration. While the inclusion of relief data in the modelling proved useful for filtering out signal noise arising from other evidential layers and for overcoming the over-fitting issue encountered in the model that excluded this evidential layer, it could marginalise or even omit potential prospective areas lying outside the applied parameters. Although Sumatra Island hosts only one mid-sized, economically viable porphyry Cu deposit and a few exploited Cu-rich polymetallic skarns, studies indicate that more Cu resources remain to be discovered. This contribution integrated geochemical, structural, and relief evidential layers with the fuzzy logic- and weights-of-evidence (WoE) methods to produce mineral prospectivity maps that show a strong correlation between the generated favourable areas and the existing porphyry and skarn Cu prospects, as well as potentially new exploration districts throughout Sumatra. Moreover, a local singularity fractal map of Cu-enriched zones reduces the proposed target areas and cross-validates the results of the fuzzy model. The inclusion of relief data in the modelling filters out signal noise arising from other evidential layers and overcomes the over-fitting issue encountered in the model that excluded a relief map. The resulting Cu potential maps can thus be used as base maps for regional porphyry and skarn Cu exploration.