GEOLOGY, ALTERATION, AND MINERALIZATION OF THE MAIN RISKA GOLD DEPOSIT, LANUT, NORTH SULAWESI

• Main Author: BENITA NARESWARI , RATIKA
• Format: Final Project
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/30248
• Institution: Institut Teknologi Bandung

<p align="justify"> Research on the geology, alteration, and mineralization was held towards the diamond drill <br /> core of 8 holes in the Main Riska open pit, Lanut Village, Modayag District, East Bolaang Mongondow Regency, North Sulawesi Province. Riska is a high sulfidation epithermal <br /> gold mine of the North Sulawesi arc with geographical coordinate of 74,800-75,250 mN and 662,400-662,750 mE (UTM WGS 1984 zone 51). Riska Mine is located inside of PT. <br /> J Resources Contract of Work in North Lanut Mineralization District. This mine was already stopped producing since early of 2016. This study aims to obtain information on the geological setting, the distribution of alteration zone and stages, the mineralization, and the relationship between Au-Cu-Ag content with the alteration and mineralization. The methods used in this study consist of <br /> core rock logging, petrographic analysis of 26 samples, mineragraphy analysis on 7 samples, mineragraphy secondary data analysis on 3 samples, SWIR-ASD spectroscopy analysis for clays, oxides, and sulfates mineral on 23 samples, and analysis on Au, Cu, and Ag assay value on each hole. Result of analyses shows that the stratigraphy of the study area is consist of Miocene pyroclastic rocks of the Bilungala Volcanics, including the Tuf Lapilli Unit and the Tuff Unit. The study area stands in a fault zone that at least has been active since the Late Miocene. All of rock units in the research area were altered and mineralized at least until the Early Pleistocene concurrently with the uplift process. Analyses are also shows that the developed alteration zones in the research area include Quartz-Alunite Zone, Pyrophyllite-Quartz Zone, Quartz-Dickite-Kaolinite Zone, Illite/Smectite-Calcite-Quartz Zone, and Calcite-Quartz-Albite-Epidote Zone. The high sulfidation epithermal mineralization was characterized by the advance of intense vuggy quartz texture accompanied by abundant presence of pyrite, enargite, and covellite on Quartz-Alunite Zone. Pyrite is present in all of alteration zones, but has the highest <br /> percentage and associated with enargite only in the Quartz-Alunite Zone. The supergene mineralization is also indicated by the precipitation of goethite, hematite, and <br /> chalcocite/tenorite, distributed locally in fractures of the Quartz-Alunite Zone rocks. The highest value of Au, Cu, and Ag were found within high alteration intensity of Quartz- Alunite Zone, vuggy quartz texture, increased percentages of pyrite and enargite, and the presence of oxide minerals due to the supergene process. <p align="justify">