Pink and Red Spinels In Marble: Trace Elements, Oxygen Isotopes, and Sources

Abstract

The oxygen isotopic composition of pink to red and other colored spinels hosted by marbles worldwide have been combined with trace elements investigated by electron microprobe analysis (EMPA). For the first time, this database enables the characterization of the geographic origin of the main productive and historical sources of gem spinel. Three consistent sets of δ18O values were found for primary and placer deposits: (1) between 5.6 and 8.6‰ for the historical Kuh-i-Lal spinels from Tajikistan; (2) from 12.1 to 18.5‰ for spinels from An Phu and Cong Troi in Vietnam, and Namya from Myanmar; and (3) between 19.0 and 24.2‰ for spinels from Paigutan in Nepal, Kiswila and Ipanko in Tanzania, Pamreso in Kenya, Mogok in Myanmar, and An Phu in Vietnam. The variation in the δ18O values for most of the deposits can be related to the buffering of the metamorphic fluids by the oxygen isotope composition of the impure marbles. The δ18O values of Kuh-i-Lal spinels result from a metasomatic skarn process between granitic intrusives and marble. Trace elements, such as Fe-Zn-Cr-V-Ti, presented in various new chemical discrimination diagrams allow for the differentiation of all the pink to red spinels. The slight overlaps observed for some chemical domains can be resolved by combination with the O-isotope composition of spinel. The present study shows that it is possible to discriminate gem spinels hosted by marbles from different geographic regions of the world and provides new insights into the traceability of historical spinels such as those from Kuh-i-Lal.