Molybdenum Mineralization of the Hannivka Deposit, Kryvyi Rih Structure

Abstract

The Hannivka molybdenum deposit is located in the northeastern side of the Kryvyi Rih structure, within the East Hannivka monocline. Molybdenum mineralization is confined to the contact zone of granitoids of the Demuryne complex with metabasites of the Novokryvorizka suite. The main volume of molybdenum mineralization is concentrated in the exocontact, in metabasites, and only 10-15% in endocontact granitoids. The molybdenum-bearing zone is represented by schistose, moderately quartzized and biotitized fine-grained metabasalts, which contain quartz, epidote-quartz, epidote, sometimes feldspar-quartz veins and veinlets and moderate (0.5-3%) sulfide mineralization. The volume of vein material ranges from 0.5% to 3-5%. The geological-morphological type of mineralization is defined as linear stockwork. Leading processes responsible for the development of molybdenite are quartzization and biotitization, namely silicic-alkaline metasomatism. Using JSM-6700F і JXСА-733 electron microscopes, the following ore minerals have been diagnosed and studied: magnetite, ilmenite, molybdenite, loellingite, arsenopyrite, pyrrhotite, pyrite, chalcopyrite, sphalerite. Based on their structural positions and relationships, several successive ore stages have been identified: early oxide (ilmenite-magnetite), main sulfide with molybdenite, potentially gold-bearing arsenide-sulfoarsenide-sulfide and late sulfide. Molybdenite is localized in zalbands of thin (1-3 mm, occasionally up to 2 cm) quartz veinlets, sometimes in the form of boudinaged structures, lenses and pockets reaching sizes up to 4 cm, as well as in host metabasalts and plagiogranites. Conditionally, three morphological types of molybdenite can be distinguished: a) medium-sized elongated tabular, platy, and foliated crystals ranging in size from 0.1 mm to 1.5-2 mm, which are oriented subparallel to the vein structures and rock foliation; b) fine-grained (from 10-20 µm to 0.1 mm) elongated flakes uniformly or randomly oriented; с) isometric crystals of hexagonal-tabular habitus with sizes ranging from 0.1 to 0.7 mm. Outlined are several areas that require further investigation: epitaxial growths of molybdenite and silicates and the conditions of their formation, the time of formation of molybdenite and ore-generating granitoids.