Mineralogy and Hydrothermal Fluids Characteristics of the Mekarbakti Low Sulfidation Epithermal Gold Prospect at Garut Regency, West Java, Indonesia

Abstract

Abstract Mekarbakti prospect is situated in the western sector of Java Island which tectonically lies within the W-E trending Sunda-Banda magmatic arc. This arc hosts numerous prospects for ore mineralization with various types of mineral deposits, one of which is epithermal that found in the study area. The Mekarbakti prospect is located close to the Arinem prospect, about 8 km to the east, which is confirmed as a low sulfidation epithermal deposit type. Arinem is proven to be economical to mine, thus it becomes interesting to conduct study on the Mekarbakti prospect, to elucidate its mineralization model. This paper is dealing with the characteristics of hydrothermal alteration using petrographic and X-Ray Diffraction (XRD) to identify the alteration minerals, using ore microscopy analysis to identify the type of ore minerals, and fluid inclusion to reveal the hydrothermal fluid characteristics. The geological condition of the study area is composed of andesite lava, andesite breccia, tuff, lapilli, and andesite intrusion. The distribution of silicification alteration is controlled by geological structures with an NW-SE pattern, while argillic and propylitic alterations tend to have a gradient trend towards silicification alteration. Propylitic alteration is characterized by chlorite+illite+smectite±epidote. Argilic alteration is marked by the presence of clay minerals such as kaolinite+illite+smectite+quartz. Silicification alteration typified by quartz+kaolinite+diaspore+illite. Ore mineralization in the study area is associated with massive, brecciated, comb, cockade and, stockwork vein textures. Ore and metalliferous minerals are found as pyrite, hematite, goethite, chalcopyrite, sphalerite, galena, pyrrhotite, covellite, chalcocite, acanthite, native gold, and native silver. Generally, the mean homogenization temperature in the research area ranged from 248.05 – 266.12 °C, with salinity ranged from 1.01 – 1.68 wt.% NaCl eq. The epithermal deposit in the study area is classified as deep low sulfidation epithermal deposit specifically in transition between base metal and precious metal interval.