'Paraiba'-type copper-bearing tourmaline from Brazil, Nigeria, and Mozambique: Chemical fingerprinting by LA-ICP-MS

摘要

Gem-quality bright blue to green "Paraiba"-type Cu-bearing tourmaline is now known from deposits in Africa (Nigeria and Mozambique), in addition to three commercial localities in Brazil (in Paraiba and Rio Grande do Norte States). Stones from these new localities have been mixed into parcels from the original Brazilian Paraiba occurrence. The Nigerian and Mozambique tourmalines that show saturated blue-to-green colors cannot be distinguished from the Brazilian material by standard gemological testing or on the basis of semi-quantitative chemical data (obtained by EDXRF analysis). However, quantitative chemical data obtained by LA-ICP-MS show that tourmalines from the three countries can be differentiated by plotting (Ga+Pb) versus (Cu+Mn), (Cu+Mn) versus the Pb/Be ratio, and Mg-Zn-Pb. In general, the Nigerian tourmalines contained greater amounts of Ga, Ge, and Pb, whereas the Brazilian stones had more Mg, Zn, and Sb. The new Cu-bearing tourmalines from Mozambique showed enriched contents of Be, Sc, Ga, Pb, and Bi, but lacked Mg.