Title: Microthermometric study of fluid inclusions from 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 investigated for their temperature, salinity, and relationship to the surrounding geology. Field work conducted at mine sites allowed sampling quartz vein specimens which were mounted and polished to make fluid inclusion sections prior to petrography and microthermometry. Cooling and heating experiments were carried out using the Linkam TH600 heating-freezing stage at the Centre for Ore Deposit, University of Tasmania, Australia. Homogenisation temperatures of quartz-hosted fluid inclusions 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 (Tersang), between 1.23 and 9.98 wt % NaCl (Selinsing), and from 4.34 to 9.34 wt % NaCl (Penjom). Laser Raman Spectroscopy 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 (90-100 mol %). However, an inclusion was found containing minor N2 (5 mol %) and CH4 (5 mol %). 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 (5 mol %) and CH4 (5 mol %). Microthermometric data shows an isothermal mixing of hydrothermal fluids. The three deposits have CO2‐rich fluids indicative of metamorphic origin. Field relationship shows a spatial distribution 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 indicative of involvement of magmatic fluids in the system.