Mineral assemblages of titanium-zirconium sands at the Central deposit,the east European platform

The study of mineral assemblages at the Central deposit allowed us to substantially refine the evolutionary model of the deposit and reveal the two main factors that control the variability of its mineralic space: (1) heterogeneity of the ore layer, consisting of a sublittoral bottom placer (the lower part) and a subaerial dune complex partly reworked in the course of a new transgression (the upper part), and (2) postore epigenetic alteration of the ore constituent of sands, which affected the quality of ore concentrates. The results obtained will be used in geological and technological mapping and development of the production program.     

History of the Formation of the Tsentral'noe Titanium–Zirconium Sand Deposit in the European Part of Russia

Based on the study of the Tsentral'noe deposit, specific features of the formation of mineral assemblages of complex titanium–zirconium placers are considered. The placers formed during the multiple redeposition of clastogenic minerals from source rocks and younger sedimentary rocks (intermediate collectors of titanium–zirconium minerals). The location of erosion and sedimentation zones significantly varied in the Phanerozoic in the adjacent region, resulting in the development of intricate relationships between different-aged terrigenous rocks (possible intermediate collectors) that provided the formation of new mineral assemblages of clastogenic ore minerals. In addition, erosional processes during the continental evolution of the study region could promote the exposure of more ancient rock complexes, the local washout of crystalline basement rocks, and the delivery of ore minerals from the latter rocks to the coastal zone of sedimentary basins. The aim of this communication is to attract the attention of researchers to the issue of the formation of mineral assemblages of complex placers of heavy minerals with similar hydraulic grain dimension and migration capacity for concentration in a rather narrow grain size range. Such mineral assemblages only slightly inherit the primary compositional features of provenances and primarily reflect changes in the sedimentation environment.     

Evolution of Placer Formation in Shelf Regions of Russia

Paleogeographic comparative analysis of placer deposits at shelves of Russia shows that all placer provinces and megaprovinces of this region are characterized by complex polymineral profiles. They reflect combinations of various rocks and native sources in feeding areas and intricate transformations of placer mineral assemblages in the course of transport and multifold redeposition of material during alternating stages of continental and coastal-marine lithogenesis. It has been established that Cenozoic placers in shelf zones of Russia are asynchronous formations. The number and timing of major epochs of both proved and inferred placer formation markedly vary depending on the tectonic setting of shelf zones and evolution of the adjacent oceanic basins.     

Prerequisites for the formation of titanium-zirconium deposits in the transural placer region: A regional geological-evolutionary model

In the Transural placer region of the western Khanty-Mansi autonomous district (KHMAD), Oligocene-Miocene rocks with titanium-zirconium potential are represented by mineralogically mature coastalmarine sediments. Source of placers are represented by both the Uralian weathering crust and placers of older sedimentary rocks. Sedimentation pattern of this period was governed by tectonic activation of the Uralian mountain system and sequential regressive dislocation of coastal lines from west to east. Location of perspective sectors was controlled by peripheral segments of local domes of the third order. Study of the mineral composition of sediments confirms the presence of two diverse (in mineralogy) Cenozoic terrigenous associations—(i) mature oligomictic association mainly composed of quartzose silty-sandy sediments with minerals of the titanium-zirconium assemblage (Oligocene-Miocene Complex) and (ii) polymictic (Neopleistocene) association dominated by unstable minerals and rock fragments. In terms of the set of lithofacies criteria, Oligocene-Miocene rocks are most perspective for the discovery of coastal-marine titanium-zirconium placers.     

Supraore Haloes of Buried Submarine Placers: Formation Conditions and Implications for Prospecting

The structure and formation conditions of secondary geochemical haloes above the buried and flooded placers and their submarine sources in the nearshore shelf zone are considered with a special emphasis on the geochemical processes in placers. It is shown that these processes are most contrasting during periodical emergence and submergence of the shelf. They are of crucial importance in the prospecting for buried mineralization. Submarine tin placers on the Eterikan Strait shelf in the northern framework of Bol'shoi Lyakhovskii Island (New Siberian Islands) were investigated. It was established that ore placers buried below the sealevel are accompanied by contrasting supraore anomalies that penetrate the entire overlying sedimentary sequence and reach the seafloor. The most contrasting anomalies of ore element assemblages are typical of the modern active layer of bottom sediments. It plays the role of an efficient complex geochemical barrier that can accumulate the geochemical information on underlying sediments. Facts demonstrating the efficiency of prospecting works within contours of these anomalies and discovery of buried submarine placers are presented.     

Inhomogeneity of the mineral field of complex polymineral placers

The mineral field structure of a complex placer is a set of features reflecting the distribution and correlation of useful and accompanying placer-forming minerals, their variation trends, the ordering degree of mineral assemblages, inhomogeneity levels, etc. The mineral field structure is one of the most important characteristics of polymineral placers. Along with other properties, it allows one to judge the regional and local formation condition of a placer and to assign it to a certain dynamic class. The informativeness of this parameter increases if the mineral field inhomogeneity of complex placers is estimated using various statistical models, in particular, the method of major components, which is one of the modifications of the factor analysis. This method allows one to restore the structure of such a multifactor system as mineral assemblages of complex heavy-mineral placers. This analysis yields particularly interesting results in the reconstruction of formation environments of fossil placers that have lost connection with the recent topography (Devonian gold-diamond-rare metal placers in the middle Timan region and Mesozoic-Cenozoic titanium-zirconium placers in northern Kazakhstan). It is demonstrated that the mineral field of a proximal polymineral placer is extremely disordered; its mineral assemblages primarily reflect the provenance rock composition and only insignificantly the formation environment of the placer itself. The mineral field of a complex coastal-marine placer of heavy minerals (CMP), in contrast, reflects practically exclusively the lithodynamic situation within the shoreline zone, including an influence of local factors. Only in exceptional cases, the inhomogeneity of the mineral field of a certain CMP reflects an additional influence of rocks of the source area.