PETROGRAPHIC STUDY ON THE TERTIARY SUBVOLCANIC AND INTRUSIVE ROCKS RELATED TO RINGAS GOLD MINERALIZATION, WEST KALIMANTAN, INDONESIA

• Main Author: Girmay Nega, Dagnew
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/1492
• Institution: Institut Teknologi Bandung

The Ringas epithermal-mesothermal gold deposit is situated in the western part of the Central Kalimantan Magmatic Arc about 419 km east of Pontianak, the capital city of West Kalimantan province, Indonesia. The mineralization and alteration at the Ringas area are genetically related to the subsequent post-subduction magmatism of the Tertiary dacitic and dioritic emplacement due to local uplifting during Oligocene-Miocene, and brecciation. The subsequent magma events have caused three overprinted mineralization stages and alteration assemblages. The sequence of mineralization includes: • Early syn-breccia pyrite dissemination with prophylitic (chlorite-epidote-carbonate ±quartz) alterations, poor in gold. • Late syn-breccia pyrite, sphalerite, galena, gold +chalcopyrite with phyllic (sericite-illite-chlorite-quartzcarbonate) alteration. Gold is found as inclusion with sphalerite, galena and intergrown with pyrite, rich in gold. Post-breccia pyrite-chacopyrite with argillic (kaolinillitemontomorillonite) alteration, poor in gold. The gold deposits are hosted by fluidized breccia and crackled or highly fractured porphyritic dacites and andesites; which constitutes two main high grade gold anomaly bodies (average 1.08-3.02 tilt Au), namely the Discovery Breccia and Jelimpau areas. These two anomalous areas have an elongated lateral shape trending north-south and east-west respectively, with depth continuity at least up to 200 m below the present surface. Based on this study, it is recommended that a detailed exploration may be continued at south of Ringas in order to know the extension of the anomalous areas. More attention should be focused within the highly fractured dacite and andesite rocks for their depth continuity.