Iron-titanium mineralization of the Oshurkovsky Massif (Transbaikalia)

The results of studying the composition and structure of ore minerals present in the rocks of the Oshurkovsky apatite deposit, determining their quantitative contents and distribution patterns are presented. The work is based on the materials of detailed petrographic studies, which made it possible to clarify the features of its geological structure and formation. The materials obtained indicate that the main process that determined the placement of apatite and associated ore minerals is the process of crystallization differentiation. It has been established that the nature of ore mineralization is significantly influenced by postmagmatic processes. In unchanged and slightly altered varieties, the main typomorphic mineral is hemoilmenite, while ilmenite and magnetite are minor ones. Ore minerals of unaltered varieties of alkaline gabbroids are found in close spatial association with apatite. The nature of the distribution of these minerals in the massif, a clear dependence on the content of mafic minerals in the rocks, the relationship with each other, the presence of a direct correlation between them indicate that their formation is associated with the late magmatic stage of formation of rocks of phase 1. The established regularities exclude the connection between the increased concentrations of these minerals and the redistribution of their initially dispersed dissemination due to the impact of younger granitoids. In rocks with signs of metasomatic and hydrothermal transformations, hemoilmenite is replaced by secondary magnetite, rutile, titanite. The latter develops along hemoilmenite, usually in the form of edges, less often replaces them completely. It is also one of the most abundant minerals in hydrothermally altered rocks. In association with titanite, which replaces iron-titanium ore minerals, they usually contain “leucoxene,” represented by a mixture of rutile and anatase, chlorite and iron hydroxides. Recrystallization and redeposition of magmatic apatite with the formation of its increased concentrations is also observed. There is no direct correlation between the contents of apatite and ore minerals in the rocks that have undergone changes. In the alkaline-feldspar syenites of the second phase, magnetite is the main ore mineral. ТИс presence of hemoilmenite mineralization in the Oshurkovo ores indicates that the crystallization of the rocks composing the massif occurred under conditions of an increased partial pressure of oxygen at relatively shallow depths. The increased content of iron-titanium minerals in them, comparable to the content of apatite, allows them to be considered as a potential associated component. Conclusions about the prospects for the possible practical use of ore minerals can be made only after conducting technological research aimed at obtaining iron-titanium concentrates and their qualitative assessment.

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