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Mineral Inclusions in Ruby and Sapphire from the Bo Welu Gem Deposit in Chanthaburi, Thailand

2019; Gemological Institute of America; Volume: 55; Issue: 3 Linguagem: Inglês

10.5741/gems.55.3.354

2376-4473

Supparat Promwongnan, Chakkaphan Sutthirat,

Geochemistry and Geologic Mapping

ccurrences of gem ruby and sapphire in Thailand are located in the provinces of Chanthaburi-Trat, Kanchanaburi, Phrae-Sukhothai, Ubon Ratchathani, Si Sa Ket, and Phetchabun (figure 1).However, a few main areas have been economically mined and supplied gems to the world market.Sapphire mines were once extensively operated in Kanchanaburi, but most have recently closed down.The Chanthaburi-Trat area has been the most significant source of Thai corundum, and a few small mines are still in operation there.The most famous source of Thai rubies is located in the Bo Rai deposit in the eastern part of Trat Province, close to the Cambodian province of Pailin (figure 1).What became known as "Siamese ruby" was first named from here and adjacent areas.Meanwhile, the main gem mining area for sapphire (yellow, green, and blue, along with golden star and black star sapphires) is the Bang Ka Cha deposit in western Chanthaburi (again, see figure 1).Most gem mines in the central deposits, around Khlung District within Chanthaburi Province, have supplied more sapphire than ruby (Vichit, 1992;Pattamalai, 2015).The focus of this study, the Bo Welu gem field located in the central gem deposits, has been mined for both ruby and sapphire.Corundum from this area is generally heat-treated to enhance its color, especially the red (or purplish red) ruby and the blue sapphire (figure 2), which are in high demand, particularly within Thailand.Although gem mines in this area are not currently in operation, a few artisanal miners can be found working along streams during the rainy season.The rarity of Thai ruby ensures strong demand in the local and international markets and high value.The sapphires, meanwhile, possess a natural greenish blue color that becomes an intense blue after heating.In this study, ruby and sapphire from Bo Welu were investigated to determine their mineral inclu-