Mineral Species
Arsenopyrite
Type Locality
No
Composition
FeAsS
Crystal System
Monoclinic
Status at Tsumeb
Questionable
Entry Number
Species; TSNB29
General Notes
The occurrence of arsenopyrite at Tsumeb is considered questionable. Given the importance of arsenates and arsenites in the supergene assemblage at Tsumeb, the scarcity / absence of arsenopyrite in the hypogene assemblage is surprising. As an accessory mineral in the sulphide ore its presence would be readily detected by reflected light microscopy, yet arsenopyrite has not been recorded in any published studies of the sulphide paragenesis. Indeed, Hughes (1987) states very clearly that "… arsenopyrite is absent from the arsenic-rich ore body."
Arsenopyrite is not included in the lists of minerals published by Lombaard et al. (1986) or by Gebhard (1991, 1999). The mineral is listed on Mindat, apparently on the basis of a specimen in the collection of Paul De Bondt in which the arsenopyrite (associated with mimetite) has been verified by EDS and XRD (http://www.mindat.org/gallery.php?loc=2428&min=305; accessed November 2015). However, there is no record of arsenopyrite from Tsumeb in the peer-reviewed literature and, in the absence of any similar material for which an unequivocal Tsumeb provenance can be demonstrated, questionable status is retained for arsenopyrite at Tsumeb.
It is notable that Otteman (1978) recorded arsenic concentrations of up to 7 wt % in colloform pyrite of supergene origin at Tsumeb.
Associated Minerals
mimetite (?)
