Mercury-arsenic sulfosalts from Apuan Alps (Tuscany, Italy). I. Routhierite, (Cu0.8Ag0.2)Hg2Tl(As1.4Sb0.6)Σ=2S6, from Monte Arsiccio mine: occurrence and crystal structure

Abstract

Routhierite, ~ (Cu 0.8 Ag 0.2 )Hg 2 Tl(As 1.4 Sb 0.6 ) ∑=2 S 6 , was identified in the baryte + pyrite + iron oxide ore from Monte Arsiccio mine, Apuan Alps, Tuscany, Italy. Routhierite occurs as anhedral grains up to 0.5 mm in size forming veinlets embedded in pyrite-rich dolostones, in association with aktashite, baryte, boscardinite, cymrite, protochabourneite, pyrite, realgar, Hg-rich sphalerite, and stibnite. Rarely, euhedral crystals of routhierite were also observed in quartz+baryte+dolomite veins, with boscardinite, Hg-rich oversubstituted andorite, realgar, sphalerite, and Hg-rich tetrahedrite. Electron-microprobe data give (in wt%): Cu 4.79(7), Ag 2.00(5), Fe 0.12(1), Hg 37.31(23), Zn 0.98(1), Cd 0.11(7), Tl 19.19(16), As 9.96(31), Sb 7.16(35), S 18.86(7), Cl 0.05(1), total 100.53(18). The structural formula, based on (S + Cl) = 6 at., is (Cu 0.77 Ag 0.19 Fe 0.02 ) ∑=0.98 (Hg 1.89 Zn 0.15 Cd 0.01 ) ∑=2.05 Tl 0.96 (As 1.35 Sb 0.60 ) ∑=1.95 (S 5.99 Cl 0.01 ) ∑=6.00 . The crystal structure of routhierite from Monte Arsiccio mine was refined to R 1 = 0.030 in the I -42 m space group, with unit-cell parameters a 9.9780(5), c 11.3764(7) A, V 1132.6(1) A 3 . In the crystal structure of routhierite, (Cu,Ag)S 4 and (Hg,Zn)S 4 tetrahedra share corners to form a framework with channels parallel to [001] hosting TlS 6 and (As,Sb)S 3 polyhedra. The relatively short Tl–Tl distance (3.33 A) could indicate Tl–Tl interaction. Chemical and crystallographic data indicate the Sb-rich nature of routhierite from Monte Arsiccio mine. The Sb/(Sb + As) atomic ratio is 0.31, to be compared with 0.11–0.12 for routhierite from the type locality of Jas Roux, France. The Sb enrichment of this new occurrence is in agreement with the usual predominance of antimony in sulfosalts from hydrothermal ores of Apuan Alps.