Mantle and deep crustal xenoliths in basalts from the Bo Rai ruby deposit, eastern Thailand: Original source of basaltic ruby

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

“…Anorthoclase and sanidine crystals are intergrown with sapphire in xenoliths from alkali basalt that suggest crystallization from intermediate magmas in the lower crust/upper mantle (Upton et al, 1983;Aspen et al, 1990;Coenraads et al, 1990). The compositions of the pyroxene, garnet, plagioclase, and spinel inclusions support mafic granulites as the possible source of ruby and purple sapphire, as reported by Sutthirat et al (2018) and Promprated et al (2003). Nepheline, the most common of the feldspathoid minerals, occurs in alkaline rocks (Deer et al, 2013).…”

Geographic Origin Determination of Ruby

“…Rubies in this group have much more diverse geological origins, ranging from basaltrelated rubies such as those found in Thailand and Cambodia to more metamorphic or metasomatic rubies found in Mozambique and Madagascar. The common thread, geologically speaking, seems to be that rubies in this group probably were derived from similar geological formations, which was most likely (ultra)mafic or basic intrusive igneous rocks (Mercier et al, 1999;Smith et al, 2016;Fanka and Sutthirat, 2018;Sutthirat et al, 2018;Palke et al, 2018). It was these iron-rich rocks that imparted their characteristic trace element profiles on the rubies (see Giuliani and Groat, 2019, pp.…”

Mineralogy and Geochemistry of Ruby

“…The pyrope + ruby assemblages formed at depths greater than 60 km and the source rock proposed was a mafic ruby-pyrope-pyroclasite or ruby-pyrope-clinopyroxenite. Sutthirat et al [145] rejected a magmatic crystallization for the ruby and this was confirmed by later studies of Thai ruby [148,149,154].…”

“…We will now examine the main ruby deposits worldwide using the above classification. During recent decades, studies of sapphire and ruby xenocrysts in alkali basalts focused on the nature of solid and fluid inclusions [11,75,85,[145][146][147][148][149][150], trace element chemistry [70,[72][73][74]81,150], oxygen isotopes [40,144,[151][152][153], and the nature of their parental xenoliths [75,77,81,145,154] to show that gem corundum may have different magmatic and metamorphic origins. Whatever their origin, these rubies are classified in the Type I category because the classification is based on their geological environment and not on their genetic origin.…”

“…Mineral inclusions are also key features in the debate about metamorphic versus magmatic origin of rubies. The most common solids are clinopyroxene (Al-rich diopside), plagioclase (bytownite to andesine), K-feldspar-spinel association [148,149], garnet (pyrope, ± almandine), sapphirine, scapolite, Cr-spinel, meionite, phlogopite, anatase, apatite, sillimanite, and sulphides [5,68,77,105,145,146,154,156]. All of these minerals are described in rubies found in metamorphic environment, although some of them are also found in magmatic assemblages.…”