Gallium concentration in natural melts and fluids

Resumo

We generalize, for the first time, published and original data on the gallium concentrations in natural magmatic melts and fluids obtained by studying quenched glasses in volcanic rocks and inclusions in minerals. Based on 2688 determinations, gallium concentrations in magmatic melts vary between 0.47 and 495 ppm at average content of 18.0 ppm (+4.2/–3.4). Gallium concentrations in magmatic melts generated in different geodynamic settings show different distribution. Minimum concentrations (on average, 16.0 ppm, +3.6/–2.9) are typical of the island-arc melts, while maximum contents were determined in melts of oceanic islands (on average, 29.1 ppm, +13.4/–9.2) and intracontinental rifts and hot spots (26.5 ppm, +25.4/–13.0). Published and new 339 determinations of gallium concentrations in natural fluids indicate the wider range of their variations as compared to those of melts: from 0.02 to 11260 ppm, at average 1.6 ppm (+10.8–1.4). The possible gallium fractionation in fluid—magmatic systems is discussed.