Petrogenesis and geochronology of Cenozoic intrusions in the Poboya and Sassak gold and copper districts in Western Sulawesi, Indonesia: Implications for the mineralization processes and magma sources

Abstract

This paper presents petrographic, geochemical and geochronological data for intrusions that area spatially related to gold and copper mineralization in the Poboya and Sassak areas in western Sulawesi. These data coupled with previous studies are then used to discuss the implications for the mineralization processes and magma sources. In the Poboya area, gold-bearing quartz veins are related to high-K calc-alkaline granitoids that display a reduced nature, whereas in Sassak area porphyry Cu-Au mineralization is associated with monzonitic intrusions intruded by gabbroic and syeno-dioritic intrusions. Granitoids from Poboya have a metaluminous to mildly peraluminous character (mol. Al2O3/mol. CaO + Na2O + K2O = 1.0–1.04) and include both I-type and S-type varieties. The Poboya and Sassak intrusions have Rb-Sr isotopic ages of 3.94 ± 0.03 Ma, 2.97 ± 0.05 Ma and 10.7 Ma ± 0.11 Ma, respectively, which are interpreted to closely approximate the time of emplacement into their country rocks. Zircon U-Pb dating of gabbro and diorite from the Sassak area yielded crystallization ages of 10.8 ± 0.16 Ma and 10.6 ± 0.19 Ma, respectively. New Sr isotopic data (87Sr/86Sr ratios >0.709) are consistent with previous data obtained from the central and northern parts of western Sulawesi, Gondwana-derived Mesozoic granitoids and enriched-mantle or lower crustal equivalents are the most likely magma sources for the Poboya and Sassak igneous rock suites, respectively. The Poboya deposit is interpreted to represent the distal part of a reduced intrusion-related gold system.