A nearshore geophysical survey for offshore minerals, southwestern Sri Lanka

Abstract

In 1997, the Geological Survey of Canada (Atlantic) conducted a high-resolution marine geophysical survey in the nearshore off southwestern Sri Lanka to determine the distribution, depositional environment and estimated volumes of granular sediment. The survey was the first step to identifying economic concentrations of heavy minerals. Geophysical equipment included a Simrad sidescan sonar system, an IKB Seistec subbottom profiler, and a Knudsen Engineering Ltd., 320M echo sounder. Sixty-eight grab samples provided selective ground truth of the interpreted seabed units. Analysis of the geophysical data quantified the thickness and volume of recoverable granular sediments. Eleven potential granular resource sites were identified. Estimated sediment volumes ranged from 2/spl times/10/sup 6/ m/sup 3/ to more than 120/spl times/10/sup 6/ m/sup 3/. Monazite concentrations as high as 1.1% were estimated based on gamma ray spectrometry analysis. No information exists on the subsurface concentration of heavy minerals. The 1997 marine geophysical results enabled development of a generalized model of the geomorphology and sediment distribution. Understanding the mechanisms of modern concentration of heavy mineral sands were used to develop hypotheses of emplacement during the geological evolution of the inner shelf. The model assists in identifying resource areas with the highest prospects for economic heavy mineral reserves.