Zeolite Minerals from Wat Ocheng, Ta Ang, Ratanakiri Province, Cambodia – Occurrence, Composition, and Paragenesis

ABSTRACT Located in the southwest corner of Ratanakiri Volcanic Province, Wat Ocheng basalt is first known zeolite locality Cambodia. The a fine-grained, vesicular to amygdaloidal, subalkaline transitional alkaline intraplate tholeiite comprised 30% lath-like plagioclase (average: Ab51An45Or4), 35% interstitial augite Wo44En35Fs21), 25–30% zeolites after and volcanic glass, minor skeletal ulvöspinel. It contains mineralized amygdales ranging size from 0.5 × cm 5 9 cm. Nine species occur at Ocheng, including analcime, chabazite-Ca, gonnardite, natrolite, phillipsite-Ca, thomsonite-Ca, along with clays, aragonite, calcite, pyrite. All are being described Cambodia for time. secondary mineral assemblages observed similar those reported other localities, neighboring Vietnam, product alteration primary Ca-Na minerals glass as result burial metamorphism infiltration heated meteoric waters. assemblage not homogeneous across within exposed lava flow, suggesting localized closed systems, likely early precipitation clay fine-grained zeolites. Decreased porosity differences fluid geochemistry would account diversity assemblages. Four stages hydrothermal zeolitization have been defined based on textures chemistry. Zeolite formation began Ca- (chabazite-Ca phillipsite-Ca) Na- (analcime) dominant, high TSi (Si/Si+Al) Stage II following deposition I. III characterized by increasing Na+K contents decreasing TSi. Crystallization coarse-grained chabazite-Ca phillipsite-Ca rims crystals followed development natrolite later-stage epitaxial overgrowth thomsonite-Ca. final stage mineralization (Stage IV) included late-stage pyrite, termination growth acicular sprays Post-magmatic cooling circulation water fluids derived alluvial sediments overlying basalts were involved zeolitization. Thermal sources include an underlying basaltic andesite flow well regional deep-seated, extensional pull-apart structures, thinned lithosphere injection fertile mantle collision Eurasian Indochina plates during Himalayan Orogeny.