Coupled substitutions in goldfieldite–tetrahedrite minerals from the Iriki mine, Japan

Abstract Chemical compositions of goldfieldite-tetrahedrite series minerals from the Iriki mine in Japan are reported for the frst time. The compositional variations of coexisting goldfieldite [atomic proportion Te > (Sb + As + Bi)], tellurian tetrahedrite [Sb > (Te + As + Bi)], and Te-free tetrahedrite from this locality are considered alongside data from the literature. These show that the substitution of (Sb, As) 3+ for Te 4+ in natural goldfieldite-tetrahedrite series minerals occurs by the following two mechanisms: (i) tetrahedrite, and goldfieldite, form a continuous solid-solution according to the coupled substitution of Cu + Te 4+ for (Cu,Fe,Zn) 2+ (Sb,As) 3+ , and (ii) goldfieldite, and the ideal end-member, might also form a continuous solid-solution by the coupled substitution of ☐(vacancy)Te 4+ for Cu + (Sb,As) 3+ . According to this work, the general formulae of tellurian tetrahedrite and goldfieldite are, therefore, respectively, , with x = 0 to 2 and , with y = 0 to 2.