BEHAVIOUR OF GOLD IN EARLY-STAGE MELT OF THE GREAT TOLBACHIK FISSURE ERUPTION

Abstract

The authors investigated the gold distribution in rocks formed by the first, earliest melt out flow of the Great Tolbachik fissure eruption (GTFE). That melt was equivalent in composition to basalt. The petrologic model derived for this eruption shows that it created two dominant rock types, magnesian basalt moderately high in alkalies and subalkalic basalt high in alumina, as well as a variety that was intermediate in composition between them. The first basalt variety of a crystallization product of magma generated within the upper mantle at depths of 100 to 120 km and melted out from an ultramafic substrate. The second originated in magma chambers at depths of 20 to 40 km near the base of the Earth's crust. Finally, the melt of intermediate composition resulted from mixing of parent melts of these two basalt varieties. The petrography of the first portion of melt erupted at the Earth's surface and the transport of gold by that flow were studied. Statistical methods were used to evaluate the samples collected.