Zonal tennantite-tetrahedrites from the Chelopech deposit: a SEM-EDS study

The composition and structure of tennantite-tetrahedrites from blocks 17 and 18 of the copper-gold high to intermediate sulphidation Chelopech deposit were determined by SEM-EDS. Based on 31 analyses is determined that the tennantites are mostly ferrous, while the tetrahedrites are zinc-rich. In zonal tennantite-tetrahedrite aggregates, sharp saw-shape chalcopyrite bands are evidence of coupled dissolution-precipitation reactions, during the replacement of the former. The fine oscillatory zoning in other tennantite crystals also is related predominantly to internal “self-organization” processes rather than external. In some cases, however, the irregular boundaries between tennantite matrix and tetrahedrite rims and strips and their variable thickness could be due to uneven penetration of fluid into the crystal along the weak zones as a result of replacement rather than overgrowth.