Fluid inclusion study of the Penjom, Tersang, and selinsing orogenic gold deposits, peninsular Malaysia

Abstract

Ore‐forming fluids in the auriferous district of the Central gold belt in Peninsular Malaysia were studied for their temperature, salinity, and relationship to the surrounding geology. Microthermometric analysis carried out showed homogenisation temperatures range from 210 to 348 °C (Tersang), between 194 and 348 °C (Selinsing), and from 221 to 346 °C (Penjom). Salinities range from 2.41 to 8.95 wt % NaCl equiv (Tersang), between 1.23 and 9.98 wt % NaCl equiv (Selinsing), and from 4.34 to 9.34 wt % NaCl equiv (Penjom). Laser Raman studies indicated that at the Tersang gold deposit, most inclusions are either pure or nearly pure CO2‐rich (87–100 mol %), except for one inclusion, which contains CH4 gas (13 mol %). In addition, at Selinsing, most inclusions are CO2‐rich (100 mol %). However, an inclusion was found containing CO2 (90 mol %), with minor N2 and CH4. Additionally, at the Penjom gold deposit, most fluid inclusions are CO2‐ rich (91–100 mol %), whereas one fluid inclusion is N2‐rich (100 mol %) and another one has minor N2 and CH4. At a basin scale, homogenisation temperatures against salinity suggests an isothermal mixing of fluids. Most fluids are CO2‐rich and are interpreted to be of metamorphic origin. The evidence further indicates involvement of magmatic fluids that is supported by the association of sandstone and carbonaceous black shales with magmatic rocks, such as rhyolite, rhyolite‐dacite, and trachyte‐andesite at the Tersang and Penjom orogenic gold deposits.