PARAGENESIS ALTERASI DAN MINERALISASI ENDAPAN PORFIRI-SKARN Cu-Au GRASBERG BLOCK CAVE (GBC) SECTION GRS34, DISTRIK ERTSBERG, PAPUA, INDONESIA

• Main Author: Apriliani, Vini
• Format: Final Project
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/34359
• Institution: Institut Teknologi Bandung

The research area is administratively located in Ertsberg District, Tembagapura Sub-District, Mimika Regency, Papua, at coordinate 734600 E ? 735100 E dan 9550900 N ? 9551600 N. Grasberg Block Cave is an underground mining area which is located exactly under the open mining Grasberg at an elevation of 3300-2600 m and included to the contract area of The Freeport Indonesia Company. This study uses core data from five wells, those are GCZ-241-01, GCZ-243-02, GRD35-03, GRD34-21, and GRD34-12. Macroscopic observation with microscopic analysis (such as petrography and mineragraphy), NIR (Near Infrared) analysis, and also geochemical assay analysis were made on each core samples to determine litology, the zonation of alteration , and zonation of mineralization. Based on these analyzes, the study area is composed of six rock units, from old to young, namely: Limestone Unit, Andesite Intrusion Unit, Andesite Porphyr Intrusion Unit, Microdiorite Plagioclase Porphyr Intrusion Unit, Microdiorite Hornblende Porphyr Intrusion Unit, and Microdiorite Biotite Porphyr Intrusion Unit. In the study area, there are seven alteration zones, from beginning to end processes, those are (1) Anhydrite-Almandine-Diopsid Zone, (2) Actinolite-Tremolite-Epidote Zone, (3) Quartz-Biotite±K-feldspar-Magnetite Zone, (4) Magnetite Zone, (5) Quart-Sericite-Pyrophyllite-Pyrite Zone, (6) Sulphide Zone, and (7) Montmorilonite Zone. Mineralization processes that occur in the study area includes two types: porphyry skarn and supergene enrichment. The mineralization process formed five zones, from beginning to end processes, those are 1) Pyrite Zone, 2) Chalcopyrite-Magnetite-Bornite Zone, 3) Magnetite Zone, 4) Pyrite-Chalcopyrite-Pyrrhotite Zone, and 5) Bornite-Chalcocite-Covelite Zone. Medium?high grade of Cu (0,5?1% and >1%) and medium?high grade of Au (0,5-1 ppm and >1 ppm) associated with Chalcopyrite-Bornite-Magnetite Mineralization Zone which is associated with Quartz-Biotite±K-feldspar-Magnetite Alteration Zone and Bornite-Chalcocite-Covelite Mineralization Zone. This area is an economic zone which could be a Cu-Au mining target.