Tellurides associated with gold mineralization




Arsenopyrite, native gold and tetradymite. Portugal


Click hereArsenopyrite (white-yellow, right) is extensively altered to scorodite light grey, centre left). Native gold (golden-yellow, centre) is approximately 960 fine and is intergrown with tetradymite (white, centre bottom), which shows strong cleavage along (0001) and alteration to a low reflectance undetermined phase. Quartz (bottom centre) is dark grey and encloses a gold grain.



Polished block, plane polarized light, x 80, air


Tetradymite, tellurobismutite, chalcopyrite, galena and sphalerite. Clogau Mine, Wales, Britain


Click hereTetradymite (green-blue, top) is intergrown with tellurobismutite (white, centre). Galena (blue-grey, centre) occurs close to the junction between the two tellurium-bearing phases. Chalcopyrite (yellow, bottom centre) has a galena rim (bottom centre) accompanied by sphalerite (dark grey, bottom right) next to quartz (black). Galena looks grey and has a low reflectance when compared with tellurides. Chalcopyrite also appears to have a lower reflectance.



Polished block, plane polarized light, x 160, oil


Galena, cobaltite, tetradymite and pyrrhotite. Clogau Mine, Wales, Britain


Click hereCobaltite (cream-white, hard, left) is intergrown with, and included within, galena (blue-white, centre). A lath-shaped crystal of pyrrhotite (brown, top centre) and a lath of tetradymite (green-white, higher reflectance than galena, oriented north-south, centre) are also enclosed within galena. Black area is quartz.



Polished block, plane polarized light, x 160. oil


Tellurobismutite, tetradymite and galena. Clogau Mine, Wales, Britain


Click hereTellurobismutite (white, right) has higher reflectance than tetradymite (green-blue, left). Galena (blue-grey, centre) inclusions occur at the junction of the two tellurium-bearing minerals. Black areas are quartz.



Polished block, plane polarized light, x 160, oil


Tellurobismutite and hessite. Clogau Mine, Wales, Britain


Click hereTwo tellurobismutite grains show strong anisotropy. Hessite inclusions (blue, centre and red-brown, top centre) also have very strong anisotropy and lie close to the grain boundary between the tellurobismutite grains. Black areas are quartz.



Polished block, partially crossed polars, x 160, oil