Gold geochemistry and mineralogy of till fines: a new approach for data integration

Abstract

A new method of heavy mineral (HM) separation and assessment of gold grade was compared with the results of conventional AAS analysis. Sixteen gold micronuggets and a number of particles of native metal and metal alloys (brass, tin, bismuth, lead) were extracted from 100 g of till fines (< 50 µm). From the size, number, and composition of micronuggets, the total gold grade (58 ppb) of till fines was evaluated. The assessments agree well with the results of AAS analysis (57 ppb). A slightly lower value (44 ppb) was obtained by Flame Atomic Absorption Analysis with Fire Assay (FAAS FA) method of the extracted HM. Mineralogical investigations allow identification of two types of gold micronuggets thus revealing a complex origin for the geochemical anomaly. The association of brass-pyroxene (Mg# = 80-82) with complex gold-brass-lead-tin intergrowths indicates that some gold in till is derived from ultramafic rocks.