Petrography of Volcanic Rocks at Q-prospect, Akara Gold Mine, Pichit Province, North Central Thailand
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Abstract
Permo-Triassic volcanic rocks at Q-prospect, northern Akara gold mining area in Phichit Province, north central Thailand, can be subdivided into porphyritic andesite, andesitic tuff and rhyolitic tuff which are mostly cross cut by late stage andesite dike. All of these volcanic rocks and dike were sampled for this study. Porphyritic andesite samples usually show hypocrystalline with microporphyritic to porphyritic textures. Their groundmass usually contains plagioclase microlite and glass. In addition, adularias are rarely present as fine-grained crystals and as rhombic forms in some veinlets. Andesitic tuff contains up to 20 % volcanic fragments (ranging in size from 0.05-2 mm) embedded in volcanic ash and glassy materials. Rhyolitic tuff usually present 0.5-2 mm quartz grains and wedge-shaped rock fragments, mainly replaced by chlorites; these crystals and rock fragments are set in microcrystalline quartz and glass. Andesite dike samples normally show subophitic texture, small plagioclase enclosed partly by pyroxene crystals. Based on whole-rock geochemistry, Zr/TiO2 versus SiO2 diagram indicates that volcanic hosts are equivalent to andesite/sub-alkaline basalt to rhyodacite/dacite and rhyolite. They appear to have derived from cogenesis calc-alkaline magma. Zr-Ti tectono diagram suggest that these rocks may have originated in vicinities of island arc tholeiite and/or volcanic arc.
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Copyright © 2008 Department of Geology, Faculty of Science, Chulalongkorn University. Parts of an article can be photocopied or reproduced without prior written permission from the author(s), but due acknowledgments should be stated or cited accordingly.
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