A preliminary sedimentological and geochemical approach to appraise gold occurrences in Gin Ganga Sediments at Neluwa, Sri Lanka.

Abstract

As a precious metal, gold can occur naturally as a native form since its least reactivity. It commonly exists as dendritic formations, nuggets, and grains in rocks, whereas cumulates, fragments, and flakes in alluvial deposits. Since known economic-grade gold deposits have been emplaced extensively during the Precambrian era, there is a very high potential to exist such gold formations associated with the Precambrian crystalline terrain of Sri Lanka. Considering this high potentiality and Gondwana linkages to Pan-African tectonic events, several investigations have been conducted by some researchers and reported the existence of alluvial gold cumulates among some streams bed loads. Although some clues on gold occurrences in the Gin Ganga river have been reported in newspapers, there is not reported scientific investigation to appraise the gold occurrences in the Gin Ganga river basin. Therefore, this study aims to appraise gold occurrences in Gin Ganga at the Neluwa area. Collected bed load sediments samples were dried in an oven under 110 °C and then sieved using 2.36mm, 600µm, 300µm, and 75µm sieves. The Pan fraction of each sieved sample passed through a 75µm sieve, was analyzed using an X-Ray Fluorescence spectrometer for its gold content. Retain fractions on 2.36mm, 600µm, 300µm, and 75µm sieves were carefully analyzed under a metallurgical zoom microscope. The microscopic observations and geochemical results indicated that the studied samples are enriched with gold contents. During microscopic observations, small fragments of gold were observed within the 600µm, 300µm, and 75µm size black color sand fractions in bed load sediments. Also, a 7.72 ± 0.01 ppm level of average gold concentration was detected associated with fine-size bed load sediments. These laboratory investigation results were further proved by an illicit gold prospector accidentally found in the field. Therefore, there is a possibility to extract approximately one sovereign pound of gold fragments as secondary alluvial gold fragments by washing one tonne of black sands in bed load sediments of Gin River close to the Neluwa area. Since this gold concentration is quite comparable with the current cut-off grade of globally operating gold mines, further studies are required to assess the economic feasibility and model the formation conditions of this gold occurrence.