Petrology of ultramafic rocks from Pt. Sebuku iron lateritic ore (SILO) concession area, Sebuku Island, South Kalimantan, Indonesia

Serpentinized ultramafic rocks are widely distributed in Sebuku Island, South Kalimantan, especially in the concession area of PT. Sebuku Iron Lateritic Ore (SILO). Nine representative samples were taken from field sites and subject to detail petrographic analyses to determine the rock type and characteristics. The ultramafic rocks in the study area consist of peridotite which has been low to highly serpentinized and serpentinite. The ultramafic rocks show pseudomorphic texture consists of mesh, bastite, blades/flaky, hourglass, vein and veinlet texture. Olivine, pyroxene occur as major minerals and partly to fully replaced by serpentine minerals and also spinel and magnetite occur as accessory minerals. Secondary minerals are serpentine, chlorite and talc. Serpentine occurs as lizardite, chrysotile, and antigorite. In terms of petrological characteristics, the ultramafic rocks from the studied area share the similarity with ultramafic rocks from South Arm Sulawesi.