Textural and petrographic features of ultramafic rocks within area of "Deposit #33", eastern part of Sredniy Kraka massif (South Urals)

This article presents the results of a petrographic and X-ray tomographic structural study of the chrome bearing ultramafic rocks. It is shown that formation of the ore-grade chromite concentration is controlled by the solid-phase (rheomorphic) re-distribution of the mantle material under a visco-plastic flow. The structures developed at early stages of dunite formation are investigated on example of the fine veinlets within peridotite. It is shown that new grains of chrome spinellids in dunite form under deformation induced segregation of chrome from the olivine grains. At first, the ultrafine particles of chrome spinellids and their thready aggregates appears on the surface of deformed olivine grains. Then, the coalescence and spheroidation of these aggregates continue the transformation process. The analogy of observed structures with those developed under plastic deformation of metals and alloys is noted.