Fundamental Study on the Quantitative Analysis of Sulfide Minerals by Electron Probe Microanalyser (III) : On the Chemical Composition of Natural Minerals in the Bi-Sb-S System

The natural bismuth-antimony sulfide minerals such as horobetsuite and stibiobismuthinite were analysed by the electron probe microanalyser by means of calibration curve method. Horobetsuite from the Horobetsu mine, Hokkaido shows a typical zonal structure as shown in Fig. 1 and 2. The result of the line scanning analysis of Sb and Bi (Fig.3) along a-b line in Fig. 2 suggests that the molecular ratio of Bi_2S_3 to Sb_2S_3 varies considerably in the single crystal. Themical composition of horobetsuite shown in Table 2 and 3,extends from (Bi_<0.74>, Sb<0.26>)_<2.07>S_<2.93> to (Bi_<0.24>, Sb_<0.76>)_<1.98>S_<3.02>. The later value was more antimony rich than the composition of (Bi_<0.45>, Sb_<0.55>)_2S_3 obtained by Hayase (1955). The analytical data of bismuth-antimony sulfide minerals from the Abuta and the Teine mines were corresponded to stibiobismuthinite with the composition of the range from (Bi_<0.95>, Sb_<0.05>)_<1.99>S_<3.01> to (Bi_<0.91>, Sb_<0.09>)_<1.99>S_<3.09>, and from (Bi_<0,98>, Sb_<0.02>)_<1.99>S_<3.01> to (Bi_<0.95>, Sb_<0.05>)_<2.00> S_<3.00> respectively as shown in Table 4 and 5.