Experimental brackets (300-450 degrees C) on Sb-Bi partitioning between stibnite-bismuthinites (Sb,Bi) 2 S 3 and sulfosalts in the AgSbS 2 -AgBiS 2 binary subsystem (alpha -Ag(Sb,Bi)S 2 , beta -Ag 5 (Sb,Bi) I4 (Sb,Bi) II S 10 ) and extant constraints are used to define mixing properties and standard state Gibbs energies of Sb-Bi exchange reactions. They are also used to construct a phase diagram for Ag(Sb,Bi)S 2 sulfosalts. We infer that the non-ideality associated with Sb-Bi mixing is largest in minerals of the beta -Ag 5 (Sb,Bi) I4 (Sb,Bi) II S 10 series, and is sufficient to produce miscibility gaps between an ordered intermediate species Ag 5 (Sb) I4 (Bi) II S 10 and Sb- and Bi-end-members at T<240 degrees C (measured in terms of symmetric regular-solution-type parameters 1/4W (super Ibeta ) (sub Bi-Sb) = W (super IIbeta ) (sub Bi-Sb) approximately 8.5 kJ/gfw). The non-ideality associated with the Sb-Bi substitution in stibnite-bismuthinite and alpha -Ag(Sb,Bi)S 2 is nearly equal 70% that in the Ag 5 (Sb,Bi) I4 (Sb,Bi) II S 10 series (W BS (sub Bi-Sb) nearly equal 12.0 kJ/gfw; W (super alpha ) (sub Bi-Sb) nearly equal 6.0 kJ/gfw). It is insufficient to produce exsolution at temperatures of ore deposition (T>T c nearly equal 88 degrees C), but most likely is responsible for a preponderance in molar Sb/Bi ratios towards end-member compositions. Finally, positive Gibbs energies of the Sb-Bi exchange reactions 1/2Bi 2 S 3 + AgSbS 2 = AgBiS 2 + 1/2Sb 2 S 3 (Delta G (super BS-alpha ) (sub Bi-Sb) nearly equal 2.70 kJ/gfw) and 1/2Bi 2 S 3 + 1/5Ag 5 Sb 5 S 10 = 1/5Ag 5 Bi 5 S 10 + 1/2Sb 2 S 3 (Delta G (super 0BS-beta ) (sub Bi-Sb) nearly equal 4.89 kJ/gfw) indicate that Bi is more compatible in stibnite-bismuthinite sulfides than in Ag(Sb,Bi)S 2 sulfosalts.

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