CRIDDLEITE, TLAG2AU3SB10S10, A NEW GOLD-BEARING MINERAL FROM HEMLO, ONTARIO, CANADA

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 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 1/2. 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 color values for both natural and synthetic criddleite are given. X-ray study showed that synthetic criddleite is monoclinic (pseudotetragonal).