The bournonite-seligmannite solid solution

Electron microprobe analyses of bournonite-seligmannite samples from the Casapalca nd Guignol Mines of central Peru reveal extensive solid solution between bournonite and seligmannite, The analyses indicated that As substitutes for Sb in bournonite to at least an As/(As * Sb) value (atomic) = 0.54. We suspect a complete solid solution exists between bournonite and seligmannite. Analyses of both bournonite-seligmannite and tennan-tite-tetrahedrite from the Casapalca Mine suggest that the distribution coefficient of Sb/As between the two solid-solution series is close to unity. The Sb/As ratios of bournon-ite-seligmannite and geocronite in the Guignol Mine suggest hat Sb favors bournon-ite-selismannite while As favors geocronite. The bournonite-seligmannite solid solution The solid solution between bournonite (PbCuSbSs) and seligmannite (PbCuAsSr) is much more extensive than previously postulated. The extent of As sub-stitution for Sb in bournonite has been estimated not to exceed es/(As + Sb) : 0.20 (Ramdohr, 1969; Schaber, 1965; Palache et al., 1944). ln this paper, elemental ratios in solid solutions are reported in atom number ratios. Seligmannite had been reported to contain 0.64 percent Sb substituting for As, giving an As/(As f Sb) value:0.98 (Palache t al., 1944). Eleclron microprobe analyses of bournon-ite-seligmannite samples from the Casapalca and Guignol Mines of central Peru reveal a more exten-sive solid solution than previously reported. Some of the analyses are reported in Table 1, and they indicate that As substitutes for Sb in bournonite to at least an Rs/(As * Sb) value: 0.54. In addition to the analy-ses tabulated in Table l, 56 other analyses of bournon-ite-seligmannite had As/(As + Sb) values in the same range. All analyses are plotted in Figure 1. The authors suspect a complete solid solution exists be-tween bournonite and selismannite. 1 Present address: Exxon Company, U.S.A., 2425 N Huachuca