Femtosecond laser ablation-ICP-mass spectrometry and CHNS elemental analyzer reveal trace element characteristics of Danburite from Mexico, Tanzania, and Vietnam

Danburite is a calcium borosilicate that forms within the transition zones of metacarbonates and pegmatites as a late magmatic accessory mineral. We present here trace element contents obtained by femtosecond laser ablation-inductively coupled plasma (ICP)-mass spectrometry for danburite from Mexico, Tanzania, and Vietnam. The Tanzanian and Vietnamese samples show high concentrations of rare earth elements (∑REEs 1900 µg∙g−1 and 1100 µg∙g−1, respectively), whereas Mexican samples are depleted in REEs (<1.1 µg∙g−1). Other traces include Al, Sr, and Be, with Al and Sr dominating in Mexican samples (325 and 1611 µg∙g−1, respectively). Volatile elements, analyzed using a CHNS elemental analyzer, reach <3000 µg∙g−1. Sr and Al are incorporated following Ca2+ = Sr2+ and 2 B3+ + 3 O2− = Al3+ + 3 OH− + □ (vacancy). REEs replace Ca2+ with a coupled substitution of B3+ by Be2+. Cerium is assumed to be present as Ce4+ in Tanzanian samples based on the observed Be/REE molar ratio of 1.5:1 following 2 Ca2+ + 3 B3+ = Ce4+ + REE3+ + 3 Be2+. In Vietnamese samples, Ce is present as Ce3+ seen in a Be/REE molar ratio of 1:1, indicating a substitution of Ca2+ + B3+ = REE3+ + Be2+. Our results imply that the trace elements of danburite reflect different involvement of metacarbonates and pegmatites among the different locations.