The investigation of ore mineral composition from the Abyz gold-pyrite-copper-zinc deposit has detected silver sulfate salts are constituents of late gold- silver association developed in quartz-carbonate veins crossing sulphite ore.
Among them proustite and detected intermediate variety of proustite-pyrargyrite united under common name "red silver ore" are of interest. They both close growing and odd isolation of invalid form, the size of which fluctuates from 0.005-0.02 mm to 0.3-0.6 mm.
Chemical composition of "red silver ore" determined with microprobe showed non-homogeneity of mineral. Considerable fluctuations have been detected content of As and Sb-bearing proustite - Ag$_{3.31}$ (As$_{0.83}$ Sb$_{0.17}$)S$_{2.87}$ and intermediate proustite-pyrargyrite variety - Ag$_{3.15}$ (As$_{0.54}$ Sb$_{0.46}$) S$_{3}$.
The possibility of isomorphism between As and Sb in the proustite-pyrargyrite is not well studied and previously the mineral composition intermediate was not known. XRPD analysis confirmed the presence of intermediate proustite-pyrargyrite variety with the unit cell parameters: a= 10.96(1) Å c= 8.73(1) Å V= 908(2) Å$^{3}$.