Origin of the silica sand deposits in western Sri Lanka with special emphasis to the Ekala deposit

Abstract

Among the sources for the quartz (silica) which are found in Sri Lanka, including vein quartz, quartz sand and quartzite, more attention is paid on quartz (silica) sand because silica sand is the major raw material used in manufacturing glass owing to its specific features being fine graded, white in colour and high purity making its commercially viable. Few commercially extracted silica sand deposits are known to occur in western Sri Lanka at Nattandiya, Marawila, Madampe, which extend towards south of Colombo as sporadically distributed deposits. The deposit intercalated with the marshy and lagoonal deposits, which has considerably acidic peaty soils and underlies the Precambrian metamorphic rocks. Relatively undisturbed deposit of silica sand has been recognized at Ekala, the territory of the Sri Lanka Air Force premises, which appeared to be of aeolian origin, has been unconfirmed until the present study (Fig.1). The objectives of the study were to (i) establish procedures for interpreting the provenance of silica sand deposits located at the west coast referring to the undisturbed deposit at Ekala and (ii) to study the effect of peaty layers to change the colour of silica sands from usual brown to white colour. Here we present mineralogical, sedimentological and geochemical evidence to prove the origin of silica sand deposits in the west of Sri Lanka. These results infer that the silica sand deposits located at the Sri Lanka Air Force Premises in Ekala are aeolian in origin and later was subjected to reworking in the lagoonal environment and its typical white colour is resulted by the continuous washout if the iron coatings of the grain with the acidic water created due to the presence of peat beneath silica deposits. Finally, it can be satisfied with the purity of the deposits which meet the necessary requirement to be utilized commercially.