Mineralogical and Technological Features of the Titanium-Bearing Sandstones of the Pizhemskoye Deposit

Abstract

The material composition of pseudorutile-leucoxene sandstones of the Pizhemskoye deposit is investigated. It is shown that the formation of minerals of this deposit occurred as a result of metamorphism of primary ilmenite under oxidative hydrothermal conditions with the participation of carbon dioxide, which proceeded with the removal of iron in the form of iron bicarbonate, followed by its transformation into siderite. The main titanium-containing phases formed during the weathering of ilmenite are pseudorutile (Fe2+,Fe3+)2 – nTi3O9 (modified ilmenite) and leucoxene. As the iron was removed, the voids formed in the ore grains of ilmenite were filled with ultrafine quartz, which crystallized from the silica brought by hydrothermal solutions. The products of ilmenite alteration (siderite and iron oxides), as well as clay minerals, could be filtered by meteoric waters through quartz sand (or sandstone) into the lower layers, as a result of which the Pizhemskoye deposit acquired a layered structure. The upper layer is represented by gray-colored sandstones, characterized by a low content of ferrous minerals. The lower layer is red-colored ferruginous sandstones, and the intermediate layer is red-colored siltstones with a high content of clay and ferruginous minerals. Siderite, crystallizing from hydrothermal solutions in the form of a cementing bond, densely filled all the space and pores between the grains of mineral phases, as a result of which it is very difficult to open the ore phases even with fine grinding (<0.2 mm) of sandstones. In addition, siderite has magnetic properties. Therefore, its presence in the form of inclusions or growths on the surface of mineral phase grains affects their magnetic susceptibility and other physical properties. The combination of these factors complicates the application of physical methods for the enrichment of pseudorutile-leucoxene sandstones of the Pizhemskoye deposit.