A speculation on the existence of a mantle plume structure was raised when alluval diamonds were first found in Kalimantan about a century ago. The upward rising bouyant flow of mantle plumes has been recognised as one of the mechanism on the genesis of diamonds. Following the discovery however, the search for diamonds has been limited to placer deposits only, carried out on small-scale and traditional mining practices. The information on the primary source of diamonds, up to the present moment, was unavailable. The study presented in this paper made use of gravity data in the attempt to reveal the structure of the mantle plume. The work comprised of processing of gravity data for the spatial analysis and modelling to produce maps of images as well as sections of mantle plume models at a lithospheric scale. Result of the study demonstrates the presence of a mantle plume structure beneath Kalimantan Island. The structure is elliptical in shape, with the long axis oriented SW-NE, approximately 600 km long, 300 km wide and about 40 km thick. The depth to the top of the plume structure is about 160 km below sea level.
