Hydrothermal Alteration, Ore Mineralization, and Fluid Inclusions Study of the Mount Muro Low Sulphidation Epithermal Deposit, Murung Raya Regency, Central Kalimantan Province, Indonesia

Abstract

Mount Muro is a part of the ‘Central Kalimantan Gold Belt’, which is found in Murung Raya Regency, Central Kalimantan Province, Indonesia. The study area is part of the Mount Muro mineralized district which includes Serujan Project, Bantian Project, and Kerikil Project. In order to optimize the production yield of the Mount Muro mine, it is important to understand the update data and analyses about the ores characteristics along with their mineral associations and the paleo-fluids involved in it. This research aims to elucidate the mineralization model based on their alteration mineral assemblages, ore minerals formation, and their hydrothermal fluids characteristics. This research is dealing with characteristics of wallrock hydrothermal alteration using X-Ray Diffraction (XRD) and thin section to identify the associations of hydrothermal alteration minerals, ore microscopy to identify the type, associations, and paragenesis of the ore minerals, and fluid inclusions studies which include fluid inclusions petrography and microthermometry measurements to identify paleo-fluid characteristics in the research location. Four alteration types based on their mineral assemblages are identified, namely argillic, silicification, propylitic, and sericitization alterations. Silicification is marked by abundant quartz ± illite ± smectite. Propylitic alteration is typified by chlorite + smectite + calcite + quartz ± epidote ± illite ± adularia. Argillic alteration is presence by clay minerals such as illite + smectite + kaolinite + palygorskite. Sericite + chlorite + illite + smectite assemblage is key minerals of sericitization alteration. Metalliferous and ore minerals are found as native gold, acanthite-argentite, native silver, electrum, pyrite, sphalerite, galena, chalcopyrite, tetrahedrite, tennantite, chalcosite, covellite, goethite, and hematite. Based on fluid inclusion studies on the quartz veins, four fluid inclusion types are identified, namely type I (monophase, liquid rich) where L = 100%, type II (liquid rich, L+V) where L>50%, type III (vapor rich, V+L) where V>50%, type IV (vapor rich, V) where V = 100%. Homogenization temperature (Th) mean of banded vein ranged from 279°C - 284°C, with salinity mean 4.2 - 2.6 wt% eq. NaCl and formed around 806 - 711 meters depth under paleosurface. Homogenization temperature (Th) mean of cockade vein 278°C, with salinity mean 2.3 - 2.4 wt% eq. NaCl and formed around 728 - 726 meters depth under paleosurface. Homogenization temperature (Th) mean of massive barren vein is 267°C, with salinity 2.2 wt% eq. NaCl and formed around 607 meters depth under paleosurface. Binary plot between Th and salinity result and coexisting liquid-rich and vapor-rich fluid inclusions confirm that boiling processes took major place during the ore mineralization. Based on ore mineralogy, hydrothermal alteration mineral assemblage, and fluid inclusions characteristics, deposit is categorized into a deep low sulphidation epithermal deposits type, specifically in transition of precious metal to basemetal zone.