Ga/Mg ratio as a new geochemical tool to differentiate magmatic from metamorphic blue sapphires

Sapphires related to alkali basalts from the Cerová Highlands, Western Carpathians (southern Slovakia): composition and origin

“…5b) to assure a Ga/Mg ratio typical of a magmatic origin. The blue sapphires from Bo Phloi in Thailand have shown a similar trend, namely both metamorphic and magmatic domains (Peucat et al 2007) despite their magmatic origin. The Fe-Mg*100-Ti*10 triangular diagram defined by Peucat et al (2007) indicates a metamorphic affinity for the whole sapphires (Fig.…”

“…The Fe/Ti ratio is generally higher in magmatic than metamorphic sapphires. The Fe/Mg ratio is significantly higher for magmatic sapphires (Fe/Mg >> 100) and lower for metamorphic and metasomatic ones (Fe/Mg < 100; Peucat et al 2007). …”

“…Sutherland et al 2002Sutherland et al , 2009Garnier et al 2005;Zaw et al 2006;Peucat et al 2007). Generally, Fe and Ga reveal higher concentrations in magmatic sapphires (~1800 to 13,000 ppm Fe and ~70 to 570 ppm Ga), than in metamorphic ones which have Fe and Ga contents less than 3000 and 75 ppm, respectively.…”

“…The Ga/Mg vs. Fe diagram (Peucat et al 2007;Sutherland et al 2009) shows both magmatic and metamorphic origins for the Hajnáčka and Gortva sapphires (Fig. 5a).…”

Spectroscopic study of inclusions in gem corundum from Mercaderes, Cauca, Colombia

“…There exist three different models, including (1) deep (i.e. lower crust or even mantle) magmatic corundum formation and subsequent uplift as xenocrysts in alkali basalts, (2) formation in metamorphic rocks that were then ejected as volcanic bombs, or (3) a combination of the two formations above, which would imply coexistence of two different genetic types of corundum (Romero and Rodríguez-Vargas 2002;Duroc-Danner 2002;Peucat et al 2007). The presence of paragenetic minerals such as kyanite and hercynite seems to favour corundum formation in old metamorphic rocks (Romero and Rodríguez-Vargas 2002).…”