Alteration Alteration, Mineralization and Geochemistry of Metamorphic Rocks Hosted Hydrothermal Gold Deposit at Rumbia Mountains, Bombana Regency, Southeast Sulawesi, Indonesia

Abstract

In Indonesia, gold is commonly mined from porphyry, epithermal and skarn type deposits that are commonly found in volcanic/magmatic belts. However, were recently numerous gold prospects discovered in association with metamorphic rocks. This paper is intended to describe an alteration and ore mineralogy hosted by metamorphic rocks at Rumbia mountains, Bombana regency, Southeast Sulawesi province, Indonesia. The study area is found the placer and primary gold hosted by metamorphic rocks. The placer gold is evidently derived from gold-bearing quartz veins hosted by Pompangeo Metamorphic Complex (PMC). This study is conducted in three stages, three stages including desk study, field work and laboratory analysis. Desk study mainly covers literature reviews. Field work includes mapping of surface geology, alteration and ore mineralization as well as sampling of representative rocks types, altered rocks and gold-bearing veins. Laboratory analysis includes the petrologic observation of handspecimen samples, petrographic analysis of the thin section and ore microscopy for polished section, XRD (X-ray diffraction), ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy), ICP-MS (Inductively Coupled Plasma Emission Mass Spectrometry and FA/AAS (Fire Assay/Atomic Absorbtion Spectophotometry) analysis. The results shows that the alteration characteristics of hydrothermal gold deposits in Mendoke and Rumbia mountain consist of 3 (three) alterations namely sericitic, argillic dan propylitic. Characteristics of mineralization hydrothermal gold deposits in the research area are generally p related to gold-bearing quartz veins/veinlets consist of chalcopyrite, pyrite, chrysocolla, covellite, cinnabar, magnetite, hematite and goetite in rocks categorized into greenschist facies. There are three generations of veins identified including the first is parallel to the foliations, the second crosscut the first generation of veins/foliations, and the third is of laminated deformed quartz+calcite veins at the late stage. The quartz veins commonly deformed, segmented, massive, laminated, irregular, brecciated, and occasionally sigmoidal. The veins contain erratic gold in various grades from below detection limit <0.0002 ppm to 18,4000 at found in third generation veins which are laminated quartz±calcite in argillic alteration. ppm. The protoliths of metamorphic rocks in Rumbia Mountain, which comes from sedimentary rocks, spesifically pelitic rocks and graywacke. Based on those characteristics, it obviously indicates that the primary gold deposit present in the study area is of orogenic gold deposits type. The orogenic gold deposit is one of the new targets for exploration in Indonesia.

The Quartz Veins, Hydrothermal Alteration and Ore Mineralization of Orogenic Gold Deposit at Mendoke Mountains, Southeast Sulawesi, Indonesia

“…The appearance of Hg and Sb in samples genetically show that the orogenic gold deposits at study area similar with orogenic gold deposits at Golden Mile, Lancefield, Racetrack, Mt. Charlotte in Western Australia; Dome, Kircland Lake, Ross Mine and wiluna in Canada; and Bombana Mountains, Southeast Sulawesi, Indonesia (Groves, 1993;Gebre-Mariam et al, 1995;Groves et al, 1998;Idrus et al, 2011;Hasria et al, 2019). Generally, the presence of ore minerals in the Mendoke Mountains is similar to ore minerals associated with orogenic gold deposits found around the world (Groves, 1993;Idrus et al, 2012;Hasria et al, 2019).…”

“…Based on the results of field observations, it shows that the quartz veins in metamorphic rocks found in mica schist, actinolite schist, and chlorite schist and graphite schist are petrologically included in the greenschist facies. The type and texture of quartz veins at Mondoke Mountains similar with quartz veins at Rumbia mountains (Idrus et al, 2012;Hasria et al, 2019). Commonly quartz veins of various minerals at Mendoke Mountains are be related with hydrothermal mineralization/ore deposits (Best, 2003).…”

“…Charlotte in Western Australia; Dome, Kircland Lake, Ross Mine and wiluna in Canada; and Bombana Mountains, Southeast Sulawesi, Indonesia (Groves, 1993;Gebre-Mariam et al, 1995;Groves et al, 1998;Idrus et al, 2011;Hasria et al, 2019). Generally, the presence of ore minerals in the Mendoke Mountains is similar to ore minerals associated with orogenic gold deposits found around the world (Groves, 1993;Idrus et al, 2012;Hasria et al, 2019). The presence of ore minerals in the Mendoke Mountains is controlled by the geological structure trending southeast-northwest and east-west.The presence of ore minerals at Mendoke Mountains in accordance with the orogenic gold deposits at worldwide (Groves, 1993;Gebre-Mariam et al, 1995;Groves et al, 1998;Idrus et al, 2012;Goldfarb & Groves, 2015;Hasria et al, 2019).…”

“…The Southeast Sulawesi Province is part of the Sulawesi Island which is located in the center of Indonesian region crotching the equator which is also affected by the interactions of these plates (Hamilton, 1979). Therefore, Southeast Sulawesi Province has a complex morphology, lithology and geological structure as well as a diversity of types of mineral deposits such as laterite nickel, laterite Fe, chromite and gold deposits (Van Leeuwen and Pieters, 2012;Surono, 2013;Hasria et al, 2019;Hasria et al, 2021a;2021b). The Mendoke Mountains are located in the central part of Southeast Sulawesi Province (Fig.…”

“…Gold in Indonesia is not only explored in volcanic and magmatic arcs, but also in sedimentary and metamorphic belts (Hasria et al, 2019). Many current discoveries of gold deposits with hosted metamorphic rocks such as Buru and Seram Islands orogenic gold deposits, in Mollucas (Idrus et al, 2014;Samalehu et al, 2021); LS-epithermal at Poboya, Central Sulawesi (Syafrizal et al, 2017); mesothermal at Awak Mas, South Sulawesi (Querubin and Walters, 2011) and orogenic gold deposits at Rumbia Mountains, Southeast Sulawesi (Idrus et al, 2012;Hasria et al, 2019). One of the most important types of gold resources in metamorphic belts that are formed by orogenic processes and contain more than half of the world's gold production ore is orogenic gold deposits (Goldfarb et al, 2019).…”