Characteristics of sapphire from quy chau deposit Vietnam

Abstract

Vietnam is one of the high quality sapphire production supplying to the global market. Gem depositions appear to have occurred in both metamorphic and basaltic environments. The significant metamorphism was related to Himalayan orogeny which has been related to the collision between India and Eurasia plates. Consequently, sapphire deposits occurred extensively along the mountain range and extended to the Red River in Vietnam. The Red River Fault Zone was reactivated and influenced metamorphism and led to large deposition of sapphire in this country including Quy Chau, this study area. Quy Chau mine is located in the south of Red River Fault Zone. High quality sapphire and ruby are being produced mostly from the secondary placer deposit. However, due to lacking of database, origin determination of sapphire from this deposit is rather difficult. Sapphire samples collected from the Quy Chau mine can be categorized into 3 groups, blue samples, orangey pink samples and reddish pink samples. Samples of all groups are inert under ultraviolet light. Tubular- and irregular -shaped black inclusions are observed inside these samples. They may be spinel or amphibole. In addition, various types of inclusions such as color zone, fracture and fingerprint are also found. Based on advanced analyses, 3 distinctive spectra are discovered. Blue samples show strong absorption caused by iron whereas reddish pink sapphires display high chromium absorption. Orangey pink samples contain combination between iron and chromium absorptions. Proportional plotting between chromium and iron reveals that these samples are related to metamorphic origin. Mineral inclusions identified by Raman spectroscopy is calcite which appears to be associated with carbonate protolith. The carbonate rocks might be metamorphosed into marble which has hosted these sapphires before weathering and transportation were taken place leading to alluvial deposits.