USE OF INDICATOR MINERALS IN SEDIMENTARY GEM EXPLORATION: A CASE STUDY FROM THE KUKULE GANGA BASIN, SRI LANKA

Abstract

The presence and the distribution of heavy minerals such as ilmanite, garnet, sillimanite, monazite, rutile, zircon, magnetite, tourmaline, spinel, corundum, allanite, fluorite and topaz in the heavy mineral fraction of the stream sediments samples of the Kukule Ganga basin were studied. Panning, sieving, heavy mineral separation and magnetic separation methods were used to concentrate the heavy minerals from the stream sediments. Grain mounting on glass slides was done for the purpose of microscopic identification of the very fine heavy mineral concentration of +125-150 pm and +150-180 pm mesh sizes. Though the presence of corundum recorded in parts per thousand range in only a few samples, it indicates that the provenance of gem minerals. Spinel, garnet, zircon were recorded in high range of weight percentages while tourmaline, fluorite, topaz, monazite and allanite recorded rather low weight percentages of total heavy minerals. But the presence of such minerals act as indicators of rare earth elements bearing minerals and pathfinders of gem minerals. Some samples show higher concentrations of sillimanite and other transparent and translucent heavy minerals rather than ilmanite that indicates higher quantity of indicator minerals.