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Chapter 17 Geochemistry and geochronology of granites hosting the Mawchi Sn–W deposit, Myanmar: implications for tectonic setting and emplacement

AUNG ZAW MYINT1,2*, KHIN ZAW3, YE MYINT SWE4, KOTARO YONEZU1, YUE CAI5, TAKAYUKI MANAKA3 & KOICHIRO WATANABE1 Department of Earth Resources Engineering, Kyushu University, Fukuoka 819-0395, Japan Department of Geology, University of Yangon, Yangon, Kamayut 11041, Myanmar CODES ARC Centre of Excellence in Ore Deposits, University of Tasmania, Hobart TAS7001, Tasmania, Australia Department of Geological Survey and Mineral Exploration, Naypyitaw 100604, Myanmar Lamont-Doherty Earth Observatory of Columbia University, 61 Rt. 9W, Palisades, NY 10964, USAThe Mawchi Mine in Myanmar is a historic world-class Sn–W deposit within the tin province of Southeast Asia, extending from Yunnan in SW China through Myanmar and Thailand, via Malaysia, to the Tin Islands of Indonesia, over a distance of 2700 km (Cobbing et al. 1992; Schwartz et al. 1995). The Mawchi Mine (Fig. 17.1) is located about 219 km SE of Nawpyitaw, the capital city of Myanmar. It was the worlds largest tin–tungsten quartz vein system exploited before World War II, and between 1980 and 1990 the Mawchi Mine produced 17 000 tons of ore (unpublished Mawchi Mine data). Fig. 17.1. Granitoid belts of Myanmar and adjacent countries (modified after Cobbing et al. 1992 and Sone & Metcalfe 2008). Bender (1983) gave a summary of the geology of the Mawchi Mine described by Hobson (1940, 1941); the petrology of the rock types and mineralization were described by Dunn (1938). Subsequently Khin Zaw & Khin Myo Thet (1983) discussed fluid inclusion studies, but no new data have been published on the geology of the Sn–W granites of the Mawchi Mine in recent years. In this contribution we discuss the petrogenesis and tectonic setting of granites associated with the Mawchi Sn–W deposit based on our recent investigations of its petrology, geochemistry and its timing through U–Pb zircon dating. Cobbing et al. (1986, 1992) distinguished Granitic Provinces in the Southeast Asian Tin Belt; this concept has formed a widely accepted basis for the discussion of the granites in Southeast Asia. In Myanmar the Central Valley Granite Province (Cobbing et al. 1992) extends from Wuntho southwards into Salingyi and Popa. Most of the granitoids in this belt are metaluminous, calc-alkaline I-type granites; their composition ranges from diorite to granodiorite and their ages from Cretaceous to Cenozoic (Khin Zaw 1990; …