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

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℃.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.