Comparison of Heavy Mineral Composition along Mahaweli River with Placer Deposits at North East Coast of Sri Lanka

Abstract

Pulmoddai and Verugal are two economically important heavy mineral beach placer deposits located on the northeast coast of Sri Lanka. Pulmoddai deposit is situated northward from the Mahaweli River mouth while the Verugal deposit is situated southward from the river mouth. At present, Pulmoddai is exploited for Ti and Zr raw material, whereas Verugal deposit is still in exploration stage. In the present study, we investigate and compare heavy mineral composition of selected locations along Mahaweli River and Pulmoddai and Verugal deposits to understand the river contribution of sediments towards these placer deposits. Sediment samples were collected from representative places along the Mahaweli River and both placer deposits. Sieve analysis was carried out to identify the textural significance. Panning was done to separate heavy minerals from the samples. Accuracy and reliability of panning process was tested using bromoform test. Grain counting method through a petrological microscope was used to analyze the mineral types in the panned heavy mineral fraction and to calculate their volumetric percentages. Data were analyzed using Gradistat™ 4.0 software. Results revealed that llmenite, Rutile, Zircon and the Garnet were the dominant heavy minerals in the northeast coast and the Mahaweli River sediments. Further, results revealed that heavy mineral assemblage of Mahaweli River sediments and Verugal deposit are more or less similar in heavy mineral composition in contrast to Pulmoddai deposit. These results support Mahaweli River sediments, mainly transport its sentiments towards the Verugal deposit.