Characteristics of a Low-Sulfidation Epithermal Deposit in the River Reef Zone and the Watuputih Hill, the Poboya Gold Prospect, Central Sulawesi, Indonesia: Host Rocks and Hydrothermal Alteration

Abstract

Systematic exploration has delineated significant gold mineralization in the River Reef Zone and the presence of a siliceous body at Watuputih Hill, which is a Poboya gold prospect in Central Sulawesi, Indonesia. The mineralization is hosted within the Palu Metamorphic Complex. The host rocks consist of granite, biotite gneiss, and biotite schist, which is intercalated by feldspar porphyroblastic biotite schist and amphibolitic schist. The X-ray fluorescence (XRF) analysis of the granite and biotite gneiss suggests that the granitic rocks can be characterized as magnesian arc calc-alkaline rocks, with a weakly peraluminous composition. Alteration minerals were analyzed by a combination of petrographic and X-ray diffraction (XRD). In the River Reef Zone, the hydrothermal alteration zones can be sorted by their proximity to the primary fluid conduit and divided into inner, high-T, and low-T propylitic zones. In Watuputih Hill, the hydrothermal alteration can be divided into advanced argillic and argillic zones. The hydrothermal alteration assemblages indicated that the fluid was at a near-neutral pH in the River Reef Zone, whereas the fluid was acidic within Watuputih Hill. Because the hill is relatively distant from the River Reef Zone, the presence of these zones at Watuputih Hill may be indicative of another mineralization system beneath the hill.

The Alteration Mechanism of Copper-bearing Biotite and Leachable Property of Copper-bearing Minerals in Mulyashy Copper Mine, Zambia

“…Then, in the presence of CO 2 and H 2 O under natural conditions, the products of copper-bearing chlorite (EDS2) and carbonate were generated, showing in Eq. (2) 36 . Further, under the severe differentiation condition, more copper which completely replaced magnesium and iron was absorbed by carbonate of (Fe, Mg, Cu)CO 3 , leading to the generation of unstable copper carbonate (CuCO 3 ).…”

A Low‐Sulfidation Epithermal Mineralization in the River Reef Zone, the Poboya Prospect, Central Sulawesi, Indonesia: Vein Textures, Ore Mineralogy, and Fluid Inclusions

“…Syafrizal et al . () reclassified the lithology in the RRZ based on petrographic and geochemical studies. The monzonite was assessed as a magnesian arc granite that lies on the trend of calcic and calc‐alkaline borderline.…”

“…Hydrothermal alteration in the RRZ (Syafrizal et al, ) is zoned outward from the chlorite‐illite‐interstratified chlorite/smectite‐interstratified illite/smectite‐calcite zone through the chlorite‐epidote‐calcite‐interstratified illite/smectite‐smectite zone to the chlorite‐interstratified illite/smectite‐smectite zone (Fig. ).…”

“…Hydrothermal alteration zoning in the River Reef Zone (Syafrizal et al, ). From the vein zone outward, hydrothermal alteration assemblages are chlorite‐illite‐chlorite/smectite‐illite/smectite‐calcite, chlorite‐epidote‐calcite‐illite/smectite‐smectite, and chlorite‐illite/smectite‐smectite.…”

“…Gold deposits in Sulawesi are distributed in the West and North Sulawesi Arcs (modified after Garwin et al, 2005) dominated by metamorphic and volcanic terranes, respectively. (b) Geological map of the Poboya Prospect (modified from Wajdi et al, ; Syafrizal et al, ). River Reef Zone, Hill Reef Zone 1, and Hill Reef Zone 2 extend in a NW‐SE strike, along with the occurrences of schist unit, biotite gneiss, granite, molasse, and alluvium sediments.…”