Kotaro Yonezu

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vein system exploited before World War II, and between 1980 and 1990 the Mawchi Mine produced 17 000 tons of ore (unpublished Mawchi Mine data).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; …

Geochemistry of rare earth elements (REE) in the weathered crusts from the granitic rocks in Sulawesi Island, Indonesia

We report for the first time the geochemistry of rare earth elements (REE) in the weathered crusts of I-type and calc-alkaline to high-K (shoshonitic) granitic rocks at Mamasa and Palu region, Sulawesi Island, Indonesia. The weathered crusts can be divided into horizon A (lateritic profile) and B (weathered horizon). Quartz, albite, kaolinite, halloysite and montmorrilonite prevail in the weathered crust. Both weathered profiles show that the total REE increased from the parent rocks to the horizon B but significantly decrease toward the upper part (horizon A). LREE are enriched toward the upper part of the profile as shown by La/YbN value. However, HREE concentrations are high in horizon B1 in Palu profile. The total REE content of the weathered crust are relatively elevated compared to the parent rocks, particularly in the lower part of horizon B in Mamasa profile and in horizon B2 in Palu profile. This suggests that REE-bearing accessory minerals may be resistant against weathering and may remain as residual phase in the weathered crusts. The normalized isocon diagram shows that the mass balance of major and REE components between each horizon in Mamasa and Palu weathering profile are different. The positive Ce anomaly in the horizon A of Mamasa profile indicated that Ce is rapidly precipitated during weathering and retain at the upper soil horizon.

Sorption behavior of the Pt(II) complex anion on manganese dioxide (δ-MnO2): a model reaction to elucidate the mechanism by which Pt is concentrated into a marine ferromanganese crust

It is difficult to directly investigate the chemical state of Pt in marine ferromanganese crusts (a mixture of hydrous iron(III) oxide and manganese dioxide (δ-MnO2)) because it is present at extremely low concentration levels. This paper attempts to elucidate the mechanism by which Pt is concentrated into marine ferromanganese crust from the Earth’s continental crust through ocean water. In this investigation, the sorption behavior of the Pt(II) complex ions on the surface of the δ-MnO2 that is a host of Pt was examined as a model reaction. The δ-MnO2 sorbing Pt was characterized by X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) to determine the chemical state of the Pt. Hydrolytic Pt(II) complex ions were specifically sorbed above pH 6 by the formation of a Mn-O-Pt bond. XPS spectra and XANES spectra for δ-MnO2 sorbing Pt showed that the sorbed Pt(II) was oxidized to Pt(IV) on δ-MnO2. The extended X-ray absorption fine structure (EXAFS) analysis showed that the coordination structure of Pt sorbed on δ-MnO2 is almost the same as that of the [Pt(OH)6]2− complex ion used as a standard. Therefore, the mechanism for the concentration of Pt in marine ferromanganese crust may be an oxidative substitution (penetration of Pt(IV) into structure of δ-MnO2) by a reduction-oxidation reaction between Pt(II) in [PtCl4-n(OH)n]2− and Mn(IV) in δ-MnO2 through a Mn-O-Pt bond.

Interaction of Au(III) and Pt(IV) complex ions with Fe(II) ions as a scavenging and a reducing agent: a basic study on the recovery of Au and Pt by a chemical method.

In order to develop a chemical technique for the recovery of gold (Au) and platinum (Pt) in the metallic state from spent catalysts, e.g., catalysts for environmental protection and automobile and petroleum catalysts, the coprecipitation behaviors of Au(III) and Pt(IV) complex ions with Fe(OH)(2) as a scavenging and reducing agent were investigated. The Au(III) complex ions were found to be stoichiometrically and rapidly reduced to metallic Au due to electron transfer in acidic aqueous solution prior to coprecipitation with Fe(OH)(2). Conversely, Pt(IV) complex ions were reduced only after coprecipitation with Fe(OH)(2) due to electron transfer through a Pt(IV)-O-Fe(II) bond on the solid Fe(OH)(2). Using this chemical technique, Au and Pt can be selectively and effectively recovered in the metallic state.

Investigating Structural and Tectonic Evolution of Central Afghanistan Using Remote Sensing and Gravity Data

This study used an integrated approach to investigate geological structure and tectonic evolution in Central Afghanistan. Several image processing techniques have been separately and simultaneously applied to data obtained from Landsat Enhanced Thematic Mapper Plus (ETM+) and Digital Elevation Models (DEM) to constrain the geological structure of the study area. Satellite images were combined with Gravity data to better understand 3D geology in the area. Analysis and interpretation of the extracted lineaments indicate that the Central Afghanistan area is controlled by two main fault systems, trending NE and EW. The two trends represent the remnants of reactivated structures that formed under the stress regimes generated during the tectonic evolution of Central Afghanistan. Gravity data indicate a NE trending basin. A two- dimensional (2D) schematic model shows that the basin deepens in the central area and gradually shallows towards the edges. The integration of the results gave insight into the tectonic evolution of the Central Afghanistan area and the adjacent areas.

Multi-Stage Mineralization of the Early Yanshanian Granites from the Central Nanling Region, South China: Implications from REE Geochemistry

Granitic rocks are widespread in the Nanling region of South China. Among them, the Early Yanshanian (ca. 190– 140 Ma) granitoids are predominant, and closely associated with numerous non-ferrous and rare metal mineral deposits (Li et al., 2007). Magmatic evolution in this region is characterized by multi-stage intrusions, which formed most of the composite granite bodies and mineralization series. Therefore, the Nanling region in the central part of South China is a unique and very important W, Sn, Mo, Bi, Pb, Zn, Cu, REE, and U metallogenic belt (Chen et al., 2002). 2 REE Geochemistry