The article reports the results of mineralogical studies of the Stoilensky processing plant products taken during in-process tests of the spiral separation method for obtaining highgrade iron ore concentrate. The geological structure of the deposit, types of ferruginous quartzite, and the material composition of ore strata are briefly described. The study of the concentration products by optical microscopy revealed their mineral composition, types of ore mineral intergrowth, and the size distribution patterns of magnetite and hematite. As a result of the tests, high-quality specification-grade magnetite-hematite concentrate with a total iron mass fraction of 69.96 % was obtained.