Mineralogical and Geochemical Characteristics of the Volcanogenic Massive Sulphide Deposits in Sangkaropi District, North Toraja, Indonesia

This paper describes an update study of the Kuroko-type volcanogenic massive sulphide deposits in Sangkaropi mineralization district, North Toraja, South Sulawesi Province, Indonesia, which focused on their associated hydrothermal alteration, ore and gangue mineralogy, as well as ore grades. Rock and mineralization samples were collected from field work to be studied using petrography, ore microscopy, X-ray diffraction, and chemical analyses of Instrumental Neutron Activation Analysis and Total Digestion Inductively Coupled Plasma methods. The study resulted that host rocks of the mineralizations were altered tuff and dacitic volcanic breccia. The mineralizations mainly occurred as massive closely-spaced disseminated sulphides, with veins, vein stockworks, and sulphide stringers. Quartz and barite were identifed as the main gangues. Ore mineral assemblages include chalcopyrite, galena, sphalerite, pyrite, bornite, pyrrhotite, and covellite, with azurite and malachite as supergene minerals. Hydrothermal alteration minerals identified in clay, silicification, and altered host rocks include quartz, muscovite, halloysite, anorthite, chlorite, paragonite, and calcite, which generally consistent to the inner zones of Kuroko-type volcanogenic massive sulphide deposits alteration zones. Chemical analysis of two selected mineralization samples resulted highest ore grades of 3.5 ppm Au, 159 ppm Ag, >1% Cu, 0.49% Pb, and >1% Zn. From three localities of Kuroko-type deposits in the district, based on their ore grade characteristics, Rumanga deposit is the most promising to be detailly investigated in the future.

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