Muaramaderas District is one of PT Aneka Tambang, Tbk. property area that explored for gold commodity. The area lies on Neogen magmatic-arc of Sumatera Island emplaced in the vicinity of major Sumatera Strike Slip trend. Hence, Sako structural setting was controlled by the fault system, which is formed strike-slip fault complex as the dilatation of the major fault on the district.
The lithology of the area is a part of Late Oligocene-Early Miocene of Hulusimpang Formation. Mineralization was hosted on Sako volcaniclastic rocks consisted of altered andesit lava and tuffaceous rocks. On the surface clays alteration was dominated by halloysite, illite and kaolinite which were present with montmorillonite as well as quartz, and accompanied by the oxidation mineral of hematite and gibbsite. The alteration assemblages are a typical of epithermal alteration that marked by the haloes of propilit, sub-argillic, argillic and silicification.
The precious metal occurrences were identified by the presence of native gold, electrum and argentite associated with galena, sphalerite and chalcopyrite. The geology activity that related to the mineral deposition were started by the magmatic activity then, soon after the activityaccomplished, deformation tectonic took place. This event gave way to the existence of hydrothermal process divided in fourth stages. The accumulation of those events influenced the precipitation of Au with strong correlation with Ag deposit associated with quartz as primary gangue mineral. The quartz growth showed by the formation of colloform, crustiform, cockade and chalcedony banded textures classified as colloform-crustiform superzone.
Fluid inclusion analysis from drill core reveals that quartz was formed on homogenization temperature of 210-258 oC, Tm (-0,5) – (-1) oC and salinity 0,9 – 1,2 % weight NaCl eq. which are represented the precipitation of solution in epithermal environment.
Those characteristic evidences concluded that mineralization in the area is a typically epithermal lowsulphidation deposit and the discovered mineralization zone is in the precious metal leve