Exploratory studies on substitutions in the tetrahedrite-tennantite solid solution series Part III. The solubility of bismuth in tetrahedrite-tennantite containing iron and zinc

Bismuth-bearing tetrahedrite and termanite were synthesized from dry runs in evacuated silica glass tubes at 350 degreesC, 450 degreesC and 520 degreesC, and studied by means of microprobe analyses on polished sections and X-ray powder diffraction. Charges were prepared with two Zn or Fe atoms p.f.u., with pure As, resp.

Sb, or with As: Sb = 1: 1. They were prepared with one and two atoms of Bi p.f.u., respectively, at all three temperatures. Separate sets of non-stoichiometric compositions were prepared in order to examine the influence of high- and low sulfur fugacity, respectively, on the solubility of Bi in tetrahedrite/termantite.

Our studies suggest that the solubility of Bi in tetrahedrite-termanite is 0.8 atom p.f.u. at 350 degreesC and I atom p.f.u. at 450 degreesC and 520 degreesC, independent of the Sb/As ratio. It increases with the increase in S fugacity and vice versa. The average increment of the cubic lattice parameter a is 0.011 Angstrom/l Bi atom p.f.u. for tetrahedrite, that for termantite is 0.036 Angstrom/l Bi atom p.f.u. in the range investigated.

The most prominent associated phases studied were Bi-bearing bornite, cuprobismutite, Phase Z, and wittichenite.