Ti–Zr placers and weathering crusts of the Karaotkel and Satpaev deposits, Kazakhstan

Abstract

The Ust-Kamenogorsk titanium and magnesium plant is one of the world’s largest titanium producers, has a production capacity of more than 20% of the total world production, and is located in East Kazakhstan (Akylbekov et al. 1999) The raw mineral base of its titanium production comprises the Satpaev and Karaotkel titanium-zirconium (Ti–Zr) placers and weathering crusts, which are located in the Kokpekty district of East Kazakhstan Kravchenko et al. (2015). The low ore grades and limited reserves means that the development of the mineral resource base in the region is strategically important. The Karaotkel and Satpaev deposits are located in the SW part of the Maytyube trough at the border of the west Kalba and Zharma-Saur metallogenic zones of the Greater Altai Kravchenko et al. (2016). The Karaotkel Ti–Zr placer and weathering crust deposit is confined to river valleys embedded in Mesozoic weathering crusts and Miocene-Pliocene alluvial gravelsandy-argillaceous sediments. The medium-size Satpaev Ti–Zr placer deposit is located 16 km to the west of the Karaotkel deposit and represents an alluvial Neogene placer Abdulin et al. (2014). Ore placers are associated with the Karaotkel and Preobrazhensk intrusive massifs, which consist of the three independent Maksut, Saikan, and Delbegei complexes, each of which have different ages. The following zones are identified in the weathering crust profiles in the study area (from the top down): (1) a kaolin clay zone represented by bleached clay eluvium that does not retain any protolith structure; (2) a hydro-mica to clay eluvium zone consisting of clay products of generated during chemical decomposition while retaining the structure of the parent rocks; (3) zone of disintegration – a zone of tectonised eluvium consisting of weathered, highly fissured rocks bleached as a result of the partial removal of alkalis and the hydration of micas. The ore-bearing units are clays of the Aral Formation that are divided into lower and upper members separated by a boundary in the form of an inter-formation break in the deposition of clay units and the erosion associated with the development of weathering crusts. Geological and genetic relationships were established to reconstruct the formation of the placers: (a) alluvial mineralisation is associated with covering porphyritic andesite units that representing the lower member of the Maityube suite (C2–3mt), the destruction of which formed the upper member of the same formation; (b) the intrusion of late Paleozoic granitoids of the Preobrazhensk and Karaotkel massifs was associated with extensive hornfels development and the contact metamorphism of volcanogenic and sedimentary formations of the Maytyube suite (C2–3mt), both of which are enriched in metamorphogenic ilmenite; (c) the localisation of ore minerals occurred during strong chemical weathering associated with a significant marine transgression that began in the Mesozoic to Cenozoic during the subsidence of the Zaisan depression. After the Oligocene the regression of the sea resulted in formation of the Miocene clays of the Aral Formation. All these factors contributed to the release of (Ti, Zr) minerals and their subsequent redeposition, establishing exploration criteria for new discoveries.