Petrochemistry of igneous rocks in the southern parts of the Chatree, Changwat Pichit

Abstract

The studied N and V prospects in the southern parts of Chatree Gold Mine, Changwat Pichit is located in the central part of the north-trending Permo-Triassic Loei-Petchabun-Nakhon Nayok Volcanic Belts. Two main types of igneous rocks are recognized petrographically, namely porphyritic granodiorite and andesite. The former show lines of evidence of intrusion into the latter. The porphyritic granodiorite is characterized by phenocrysts of plagioclase (An [subscript 30]), k-feldspar, quartz, hornblende and biotite set in fine-grained quartz-rich groundmass. Associated alterations are predominant potassic alteration with minority of phyllic alteration. Pyrite is principal ore in veins and veinlets whereas chalcopyrite and molybdenite are present in small amount. The andesite host is unvariably porphyritic and largely composed of altered plagioclase and hornblende phenocrysts set in glassy-microlite groundmass. The alteration of vocalnic rocks are widespread and is peripheral with propylitic alteration. Twenty-two least-altered and least-weathered samples of both plutonic and volcanic rocks were selected for mobile-and immobile-elemental analyses using XRF, ICP-OES and ICP-MS methods. Both petrographically and chemically, these studied igneous rocks can be classified as granodiorite to tonalite and basaltic andesite. Geochemically, the studied rocks belong to the calc-alkaline affinity occurring as volcanic arc granite and island arc tholeiite to volcanic arc basalt. Spider diagrams of trace and rare-earth elements reveal that granodiorite shows a pattern consistent with those of the Tertiary intrusive igneous rocks of Azerbaijan, Iran. Principal mineralization at the studies N and V prospects is believed to belong to porphyry-copper type occurring in the shallow intrusive environment and was formed as a result of oceanic subduction during Permo-Triassic Period between Lumpang-Chiang Rai and Nakhon Thai plates.