Petrography of chromite-bearing ultramafites of the Agardag massif (South-Eastern Tyva)

The object of the study is the ultramafites of the Agardag chromite-bearing massif, which is part of the South Tuva ophiolite belt. The work presents a petrographic characteristic of rocks and ores, and features of the mineralogical composition of ultramafites. Harzburgites with the subordinate role of dunites, and their serpentinized varieties, are widely developed in the massif. Among dunites and, more rarely, harzburgites, small bodies of chromitites with various types of structures were found: interspersed, densely interspersed and drain. Chrome spinelides in harzburgites and dunites have a homogeneous chemical composition and are represented by chromites and rarely subferrichromites. Analysis of variations in the composition of chrome spinelides in chromitites allows us to distinguish two trends in their evolution. The first trend reflects the deep mantle conditions of intense depletion of the substance of the upper mantle in the process of intense plastic deformations. The second trend in the evolution of chrome spinelides in chromitites is conditioned by the metamorphogenic transformations of chromitites, which took place in the process of moving ultramafites to the upper parts of the earth's crust.