PETROLOGY, ALTERATION AND MINERALISATION OF MULTIPHASE INTRUSION ROCKS IN THE BABAK RIVER AND SIGUNTU RIVER, PALOPO, SOUTH SULAWESI, INDONESIA

Abstract

The research was conducted along the Siguntu River and Babak River in the Latuppa area, Palopo, South Sulawesi.This study aims to investigate the petrogenesis of granitoid rocks and their implications for hydrothermal mineralisation processes.Methods included detailed field observations combined with microscopic laboratory analyses, comprising petrography, mineragraphy and X-ray fluorescence geochemistry of major rock oxides.The study area is dominated by plutonic rocks classified as granitoids, including quartz diorite, granodiorite, and porphyry quartz monzonite, as well as sub-volcanic rocks represented by porphyry andesite.Geochemical data from hydrothermally altered granitoids, particularly granodiorite and porphyry quartz monzonite, indicate derivation from acidic magmas with granodiorite to granite compositions.These rocks are classified as I-type granitoids with high-K calc-alkaline affinity, metaluminous to weakly peraluminous character, and magnesian composition.The presence of three granitoid types suggests multiphase intrusive activity within the study area.This activity generated potassic alteration assemblages characterised by secondary biotite, secondary K-feldspar, anhydrite, and magnetite; inner propylitic alteration with actinolite, epidote and diaspore; and phyllic alteration composed of sericite, quartz, chlorite and pyrite.Associated mineralisation of bornite, chalcopyrite and covellite is typical of porphyry-type deposits.In contrast, sub-volcanic intrusions produced adularia alteration assemblages consisting of adularia, sericite, quartz and pyrite, accompanied by sphalerite and chalcopyrite mineralisation characteristic of epithermal deposits.Overall, hydrothermal alteration and mineralisation indicate an overprinting of porphyry systems by epithermal systems formed in a syn-collisional setting evolving toward crustal extension, associated with granitoid exhumation to shallow crustal levels.

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