Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original Paper

Johan, Mantienne

Thallium-rich mineralization at Jas Roux, Hautes-Alpes, France: A complex epithermal, sediment-hosted, ore-forming system

Journal of the Czech Geological Society, volume 45 (2000), issue 1-2, 63 - 77

The Jas Roux deposit, which is hosted by strongly silicified Triassic sedimentary rocks, is characterized by a complex mineralization of pyrite, sphalerite, twinnite, zinckenite, andorite, stibnite, chabourneite, parapierrotite, pierrotite, smithite, laffittite, routhierite, aktashite, wakabayashilite, realgar and barite, plus four new mineral phases: (i) a phase Pb₉Ag(Sb,As)₁₃S₂₉ with optical properties similar to jamesonite, VHN₂₅ = 165 kg/mm², a composition close to the ideal formula, and a monoclinic unit-cell with a = 17.640, b = 18.464, c = 3.967 Å, ß = 90°48', V = 1292 Å ³, Z = 1, D_calc = 5.51; (ii) a phase Tl(As, Sb)₁₀S₁₆ that is X-ray amorphous; (iii) a phase Tl(Sb,As)₇S₁₁ that is weakly anisotropic with reflectivity close to chabourneite; and (iv) a phase Ag₂SbAsS₄, representing a reaction product between smithite and chabourneite. Hypotheses on the genesis of the deposit, based on the determined crystallization sequence, reveal similarities between the Jas Roux ore-forming system and low-temperature active geothermal brines.