Intergrowth texture in Au-Ag-Te minerals from Sandaowanzi gold deposit, Heilongjiang Province: Implications for ore-forming environment

Abstract

Sandaowanzi gold deposit, Heilongjiang Province, is the only single telluride type gold deposit so far documented in the world, in which 90% of gold is hosted in gold-silver telluride minerals. Optical microscope observation, scanning electron microscope, electron probe and X-ray diffraction analysis identified abundant intergrowth textures in the Au-Ag-Te minerals, typified by sylvanite-hosting hessite crystals and hessite-hosting petzite crystals. The intergrown minerals and their chemistry are consistent, and the hosted minerals are mostly worm-like or as oriented stripes, evenly distributed in the hosting minerals, with clear and smooth interfaces. These suggest an exsolution origin for the intergrowth texture. With reference to the phase-transformation temperature derived from synthesis experiments of tellurides, the exsolution texture of Au-Ag-Te minerals implies that the veined tellurides formed at 150-220°C. The early stage disseminated tellurides formed at log f(Te 2) from -13.6 to -7.8, log f(S 2) from -11.7 to -7.6, whereas the late stage veined tellurides formed at log f(Te 2) ranging from -11.2 to -9.7 and log f(S 2) from -16.8 to -12.2. © 2012 The Author(s).