Thermochemistry of minerals in the system silver sulfide-copper(I)sulfide-antimony trisulfide-arsenic trisulfide

Daniel Eric Anders Harlov, Purdue University

Abstract

In this study phase relations in the Ag$\sb2$S-Cu$\sb2$S-Sb$\sb2$S$\sb3$-As$\sb2$S$\sb3$ system are investigated via a series of Ag-Cu exchange experiments (evacuated silica tubes; variable mass ratio) at temperatures ranging from 75 to 350$\sp\circ$C. Phases investigated include polybasite-pearceite (Ag,Cu)$\sb{16}$(Sb,AS)$\sb2$S$\sb{11}$, pyrargyrite-proustite (Ag,Cu)$\sb3$(Sb,As)S$\sb3$, miargyrite-smithite (Ag,Cu)(Sb,As)S$\sb2$, skinnerite (Cu,Ag)$\sb3$SbS$\sb3$, chalcostibite CuSbS$\sb2$, sinnerite Cu $\sb6$As$\sb4$S$\sb9$ and Ag$\sb2$S-Cu$\sb2$S sulfide phases stable above 120$\sp\circ$C. As-Sb unmixing in polybasite-pearceite is experimentally documented at 75$\sp\circ$C. Utilizing this Ag-Cu exchange data, As-Sb unmixing data, relevant crystallographic data (both actual and inferred), and calorimetric data for Ag$\sb2$S and Cu$\sb2$S, internally consistent Ag-Cu and As-Sb solution models are calibrated for polybasite-pearceite, pyrargyrite, proustite, skinnerite, miargyrite, body centered cubic-(Ag,Cu)$\sb2$S, face centered cubic-(Ag,Cu)$\sb2$S, and hexagonal close packed-(Cu,Ag)$\sb2$S. All ordering is assumed to be nonconvergent. The Gibbs energy of formation for Cu$\sb{16}$Sb$\sb2$S$\sb{11}$ polybasite (5.3 $\pm$ 1.14 kJ/gfw) and for Ag$\sb{16}$Sb$\sb2$S$\sb{11}$ polybasite ($-$31.1 $\pm$ 0.7 kJ/gfw) from the simple sulfides is estimated using these solution models and previously estimated Gibbs energies of formation for skinnerite and pyrargyrite.

Degree

Ph.D.

Advisors

Sack, Purdue University.

Subject Area

Geochemistry|Mineralogy

COinS