Two new occurrences of benleonardite, a rare silver-tellurium sulphosalt, and a possible new occurrence of cervelleite

Abstract

Benleonardite, ideally Agg(Sb,As)Te253, occurs in ore specimens from the Mayflower and Gies epithermal gold-silver telluride deposits in Montana commonly spatially associated with hessite and tetrahedrite. In these deposits, it is Cu-bearing (up to 2.7 wt.%) and exhibits a slight deficiency in Ag+Cu coupled with a slight excess in S. A cervelleite-like mineral coexists with benleonardite at Mayflower and is unusual in composition in that it is Se-bearing suggesting the possibility of solid solution with aguilarite (Ag4SeS).

New structural data reveal benleonardite to be a member of the pearceite-polybasite group

“…3-4 a.p.f.u.) when normalized on the basis of 14 atoms, thus reinforcing the suggestion by Spry and Thieben (1996) that the formula proposed by Stanley et al (1986) needs to be modified.…”

“…n.i.not indexed. Stanley et al (1986); analyses 7-8: Spry and Thieben (1996); analyses 9-10: Zhang and Spry (1994); analyses 11-12: Spry and Thieben (1996); analysis 13: Karup-Møller and Pauly (1979); analysis 14: Pals and Spry (2003); analyses 15-17: Pals and Spry (2003).…”

“…By means of powder X-ray diffraction investigations, benleonardite was originally given as tetragonal with a = 6.603(5) and c = 12.726(6) Å, but the crystal structure remained unknown. Although benleonardite-like minerals have been found in several occurrences [Zyranov gold deposit, Russia (Aksenov et al, 1969), Ivigtut cryolite deposit, Greenland (Karup-Møller and Pauly, 1979), Gies gold-silver telluride deposit, Montana (Zhang and Spry, 1994;Spry and Thieben, 1996), Mayflower gold-silver telluride deposit, Montana (Spry and Thieben, 1996), Um Samiuki Zn-Pb-Cu-Ag volcanogenic massive sulfide deposit, Egypt (Helmy et al, 1999;Pals and Spry, 2003), black smoker chimney fragments from the Yaman Kasy massive sulfide deposit, southern Urals (Herrington et al, 1998)], no additional structural investigations have been reported in the literature to date.…”

Cervelleite, Ag4TeS: solution and description of the crystal structure

“…Cervelleite, along with other cervelleite-like minerals, has been reported from various ore types including the intrusion-hosted San Martin deposit, Argentina (Paar and De Brodtkorb 1996), the epithermal Mayflower Au-Ag deposit, Montana (Spry and Thieben 1996), the Um Samiuki volcanogeneic massive sulfide deposit, Egypt (Helmy 1999), epithermal (Larga, Roşia Montană) and skarn (Băiţa Bihor and Ocna de Fier) occurrences in Romania (Cook and Ciobanu 2003;Ciobanu et al 2004), the Eniovche epithermal deposit, Bulgaria (Dobrev et al 2002), the intrusion-hosted Funan Au deposit, China (Gu et al 2003), and several volcanic-hosted massive sulfide deposits in the southern Urals (Novoselov et al 2006). Unnamed Agsulfotellurides [(Ag,Cu) 6 TeS 2 -(Ag,Cu) 4 TeS] were described from the Funan deposit (Gu et al 2003), and a phase with the composition Ag 2 Cu 2 TeS was reported by Cook and Ciobanu (2003) from the Băiţa Bihor and Ocna de Fier skarns in Romania.…”