Typomorphism and geochemical features of gold-quartz mineralization of the Upryamoye ore field, Western Chukotka

The composition and typomorphic properties of native gold and gold-bearing sulfides of the Upryamoye gold field (Western Chukotka) were studied in detail using optical, scanning electron microscopy, electron probe microanalysis (EPMA), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Gold occurs in three identified forms: a) gold in the form of fine and finely dispersed inclusions in pyrite and arsenopyrite; b) free gold cementing fragments of sulfide minerals; c) structurally bound «invisible» gold in pyrite and arsenopyrite. Pyrite-III and arsenopyrite-II, formed at the early hydrothermal stage, are the most enriched in the «invisible» gold (up to 55 ppm and 204 ppm, respectively). Distinctions in the geochemical features of different sulfide generations were revealed. Based on the Se content of pyrite, its crystallization temperatures were determined (173–376 °C). The calculated temperature range of the arsenopyrite formation was 348–400 °C. The new data on the macro- and microelement composition of the sulfides indicate the formation of gold-quartz mineralization from solutions of mixed genesis at medium and low temperatures. The established distribution pattern of gold is of critical importance for the development of integrated ore beneficiation schemes.