EPMA characterisation and geochemistry of gold deposits of Peninsular Malaysia- genetic implications

Abstract

The highly automated electronprobe microanalyzer (EPMA) was used as a tool to characterise gold from the Raub-Tersang-Selinsing-Penjom, Rusila-Lubuk Mandi, and Jeli-Sokor areas in Peninsular Malaysia with the aim of characterising the various primary and alluvial gold deposits and tracing the alluvial gold grains to their primary sources. Gold from quartz-veins and their associated country rocks were sampled and studied in terms of . their morphology, size, inclusions, associated minerals and geochemistry. Alluvial gold and tailings in the surrounding areas were also sampled to study their association with the primary occurrences. The common mineral associated with gold in the quartz veins in all the areas sampled is pyrite. At Bukit Koman monazite was also found together with arsenopyrite and a Cu-Sb-S mineral in the gold veins. At TRA Mining, Selinsing, arsenopyrite together with a Pb-Fe-As-S mineral are associated with gold. At Specific Resources, Penjom, there is galena, chalcopyrite, sphalerite together with silver in the gold veins. At the limestone quarry at Kechau, galena is associated with chalcocite (Cu 2 S), and Cu-Sb- S and Cu-Zn-Sb-S minerals. - In Terengganu, at Rusila it was demonstrated that alluvial gold grain sizes nearest to the primary gold veins average 3.05 mm long and 2.5 mm wide while those furthest away tend to average to about 0.81 mm long and 0.7 mm wide. On the whole grains which are longer than 1 mm tend to be prismoidal in shape while those less than 1 mm are generally spherical. In the Raub-Tersang-Selinsing-Penjom area in P ahang, the alluvial samples from Sg. Ulu Tersang, a river in SE Selinsing and Sg. Terenggun and tailings samples from Kg. Pulai (Tersang) and NW Penjom generally show a bimodal distribution with dominant lengths averaging 0.4 mm for the major distribution and 1.0 mm for the minor. In Kelantan the-dominating sphericity of the alluvial samples collected in the Jeli area is prismoidal, and this differs from the samples in the Sokor area which have sphericity that ranges from subdiscoidal to discoidal. Gold grain size studies show that the samples from Sokor are fine grained which range from 0.1-0.3 mm for the lengths and the widths of the samples collected from Sg. Tui and Sg. Sokor, whereas the grain size of the samples from Jeli are bigger with an average length of 0.7 mm for samples from Sg. Pergau and an average particle size of 0.8 mm long and 0.4 mm wide for samples from Sg. Tadoh. In Terengganu, at Rusila the average Au content is 90.30% and silver is 10.46% for the gold from the veins (a fineness of 896.1889) while the alluvial gold average 88.52% Au and 10.32% Ag (a fineness of 895.5889). In Pahang, Primary gold at Bukit Koman, Raub has a fineness of 956.679, at TRA Mining, Selinsing the fineness is 881.7301, at Specific Resources, Penjom the fineness is 903.7245 and at the limestone quarry at Kechau, the fineness is 951.1200. The alluvial gold at Bukit Koman has a fineness of 982.8318, at a river in SE Selinsing the fineness is 930.9519 at Sg. Ulu Tersang the fineness is 944.0056 and at Sg. Terenggun (NW of Penjom) the fineness is 924.4767. The tailings at Kg. Pulai, Tersang show fineness of 976.5234 and those at NW Specific Resources have fineness of 891.8836. In Kelantan, EPMA studies show that the geochemistry ofthe gold grains are different for the 2 main areas. In the Jeli area, the 3 areas sampled in Sg. Pergau show average fineness of 922.9157, while the 2 areas in Sg. Tadoh average 923.7250. In the Sokor area, the fineness values are less than 900.000 and the average fineness values show a larger spread, the 2 areas in Sg. Tui average 845.1322, whereas the 2 areas in Sg. Sokor average 894.0914. Geochemical EPMA analysis of the gold grains revealed that silver is present in the gold in different amounts from different areas. It can be demonstrated that fineness is a useful character for tracing the primary sources of gold from the panned alluvial gold samples further downstream_ Preliminary results