GPR mapping as a method for placer mineral exploration: A case study in Akurala, Sri Lanka

Placer mineral exploration includes mapping underlying strata extensively. There are numerous exploration techniques, including electric and gamma logging, shallow vertical drill holes, exploratory trenches, and pits. Due to limitations of these conventional methods, geophysical methods such as Ground Penetrating Radar (GPR), are widely being used. The purpose of this study is to map placer deposits using GPR as an exploratory approach. GPR is a modern, rapid, no-contact, high-resolution technique which transmit, reflect and receipt of high frequency electromagnetic (radar) wave. This study was carried out at Akurala, Galle, Southern Sri Lanka using 300MHz antenna. Based on the GPR data, sand layers were identified in clay beds, of an old riverbed, and the sand layer is deposited as a fluvial deposit, which are the sediments deposited by paleo river channel. Average thickness of the sand bed could be interpreted as 0.94m, extending perpendicular to shoreline, and situated at approximately 1.25m depth below surface level. GPR data profile indicate that the sand layer may enrich with valuable minerals and heavy minerals, and it was validated using thin sections prepared from test pit sampling.