Paragenetic Sequence Of Ore Formation In Intermediate Sulphidation Epithermal Deposit: New Insights On Mineralizing Processes At Kotabunan, East Bolaang Mongondow, North Sulawesi
DOI:
https://doi.org/10.51835/ijeg.2025.1.2.496Abstract
The northern arm of Sulawesi is comparatively well mineralized with various types of deposits. One of the prospective areas of mineralization can be found in Kotabunan, East Bolaang Mongondow Regency, North Sulawesi. This study aims to determine the geological conditions, hydrothermal alteration, mineralization style, and the sequence of ore mineral formation through paragenesis studies. The methods used are geological field mapping, thin sections, polished sections, XRF, and reflectance spectroscopy analysis. Based on the geological mapping, stratigraphy of the research area can be divided into 11 lithostratigraphy units and eleven faults that can be identified in the research area dominated by normal right slip fault trending northwest-southeast and normal left slip fault trending northeast-southwest. The alteration zones consist of quartz + chlorite + illite ± calcite alteration zones and quartz + illite + kaolinite ± sericite alteration zones. Mineralization in the research area is present as a vein and disseminated within rocks. The presence of mineralization in the form of veins is marked by the emergence of base metal veins controlled by northwest-southeast trending faults and indicates mineralization of the intermediate sulfidation epithermal (ISE) system. The results of polished section analysis show that the presence of disseminated mineralization is dominated by pyrite. In base metal vein mineralization, pyrite is present throughout the hypogene phase and then replaced by galena. Then, galena is overprinted by intergrowth sphalerite. Tennantite occurs as an inclusion within sphalerite. Chalcopyrite is also present in veins as a replacement for sphalerite, galena, and pyrite in the form of disease texture. The presence of gold is also observed in veins that occur together with galena, as evidenced by the presence of gold in the same groundmass as galena and sphalerite. Then the covellite replaces the pyrite which indicates the supergene process, and then hematite is formed which ends the mineralization process. The results of this study have significant impacts on the understanding of ore formation of ISE deposits in Kotabunan District, East Bolaang Mongondow Regency, North Sulawesi.
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