Tennantite-(Cu) after enargite

anglesite (?); chalcocite (?); enargite; sphalerite; undetermined (?)

A matrix of vuggy sulphide, giving way to free-standing but highly corroded pseudomorphs of tennantite after enargite (to 30 mm). The crystal surfaces are heavily altered with a thin layer rich in undetermined blue-green secondary copper species.

Reflected light microscopy and quantitative WDS analysis on a transverse polished section of one of the pseudomorphs reveals a core of residual enargite inside a sheath of tennantite-(Cu). The minor presence of sphalerite and chalcocite (?) (or a species of very similar stoichiometry) are also WDS verified, as is the minor presence of a transparent phase with the composition of anglesite (WDS indicated). Further analytical work is required to characterise the copper secondaries.

The specimen is significant in that it appears to be the first analytically confirmed occurrence of tennantite-(Cu) from Tsumeb; the mean composition indicated from 32 WDS analyses is presented in Exhibit 2.

The specimen was purchased from Ian Bruce in 2016 but without earlier provenance and with no record of location in the mine.