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.
