Criddleite, TlAg2Au3Sb10S10, a New Gold-Bearing Mineral from Hemlo, Ontario, Canada1

Donald C. Harris, Andrew C. Roberts, J. H. Gilles Laflamme and Chris J. Stanley
Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, Canada K1A 0E8
CANMET, 555 Booth Street, Ottawa, Ontario, Canada K1A 0G1
Department of Mineralogy, British Museum (Natural History), Cromwell Road, London, England SW7 5BD
1Geological Survey of Canada Contribution Number 10288.

Abstract: Criddleite, ideally TlAg2Au3Sb10S10, is a rare constituent within the Hemlo gold deposit, Hemlo, Ontario, Canada. The mineral occurs as 20 to 50 µm-sized lath-like, tabular or anhedral grains usually surrounding or penetrating aurostibite, or associated with native antimony, native gold and stibnite. Criddleite is opaque with a metallic lustre and a black streak. It has been synthesized by reacting TlSbS2 and high purity Ag, Au, Sb and S in an evacuated silica glass tube at 400 °C. The measured density of the synthetic material is 6.86; the calculated density is 6.57 g/cm3. The difference is due to minor admixed aurostibite, native antimony and a dyscrasite-like phase within the charge. VHN25 is 94–129. Mohs hardness (calc.) = 3–3 ½. In reflected plane-polarized light in air, natural criddleite is weakly bireflectant with a discernible reflectance pleochroism from grey-blue to slightly greenish grey-blue. The mineral has a distinct to moderate anisotropy with rotation tints in shades of buff to slate grey. Reflectance spectra and colour values for both natural and synthetic criddleite are given. X-ray study showed that synthetic criddleite is monoclinic (pseudotetragonal) with refined unit-cell parameters a = 20.015(2), b = 8.075(2), c = 7.831(2) Å, β = 92.01(2)°, V = 1264.9 ± 1.0 Å3 and a:b:c = 2.4786: 1:0.9698. The space group choices are A2/m(12), A2(5) or Am(8), diffraction aspect A*/*. The seven strongest lines in the X-ray powder diffraction pattern [d in Å (I) (hkl)] are: 5.63(90) (011), 3.91(50) (002), 3.456(50) (320), 2.860(70) (700), 2.813(100) (022), 2.018(60) (040) and 1.959(70) (004). Electron microprobe analyses are reported of natural criddleite in five polished sections of drill core from four holes. The averaged empirical formulae, based on 26 atoms, are Tl0.92Ag1.99Au2.93Sb9.87S10.28 (natural) and Tl0.94Ag2.03Au2.89Sb9.76S10.38 (synthetic).

Keywords: criddleite • new mineral • Hemlo gold deposit • Hemlo • Ontario • Canada • reflectance data • X-ray data • electron microprobe analyses • synthesis

Mineralogical Magazine; December 1988 v. 52; no. 368; p. 691-697; DOI: 10.1180/minmag.1988.052.368.13
© 1988, The Mineralogical Society
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