Lithofacies zoning and titanium-zirconium potential of the Mansi and North Sos’va areas,Transural placer region

The lithofacies and morphostructural analyses of the Mansi and North Sos’va areas of the Transural placer region allowed us to establish factors of the spatial and lithostratigraphic control of titanium-zirconium placer potential. It was established that the placers are localized in sediments of the upper stage of the Oligocene-Miocene complex and rocks of Oligocene basin shows facies zoning. The most promising are the paleolittoral and shoal facies formed under moderate hydrodynamic activity. In tectonic aspect, the position of promising areas and their lithofacies composition are controlled by flank zones of local domes that experienced epeirogenic movements. Regressive regime in the Oligocene basin suggests the highest probability for the discovery of titanium-zirconium placers of the littoral type in inner zones of neotectonic domes.     

Specific features of the mineral composition of titanium-zirconium placers in Russia

Specific features of the mineral composition of economically promising titanium-zirconium placers in Russia are analyzed. Generalization of the data made it possible to classify titanium-zirconium deposits with respect to different parameters of mineral composition, which can govern technological properties, and to identify specific characteristics with insignificant differences. Ore sands of titanium-zirconium placers are characterized by the following qualitative characteristics: TiO₂ content; mineral form of this dioxide (zircon); mineral-carriers of elements that degrade the quality of sands (primarily, Cr and P); physical properties of minerals; grain size composition of sands; and mass and composition of clayey fraction in the sands. Characteristics of the currently exploited Malyshev deposit are given.     

Zirconium-titanium placers of the Voronezh Anteclise: Types,epochs and factors of formation,and forecast

The early and late Frasnian, Barremian-Aptian, Cenomanian, early Santonian, early Campanian, and Oligocene-Miocene epochs of the formation of various types of zirconium-titanium placers are distinguished in the Voronezh Anteclise. The factors of their formation are considered, and a forecast of prospecting has been made. Lower Frasnian sedimentary rocks occur in the southeast, where the placers are related to the ilmenite-bearing volcanosedimentary rocks of the Yastrebovo Sequence. The upper Frasnian productive quartz sand of the Petino Sequence occurs in the central part of the Voronezh Anteclise. The Barremian-Aptian productive quartz sand and kaolinite clay occur in the northern and northeastern parts of the anteclise (Ryazan and Lipetsk oblasts). The placers formed in the Cenomanian are known in the Tambov oblast in the northeast of the Voronezh Anteclise and are related to phosphate-bearing glauconite-quartz sand. The early Campanian phosphorite-glauconite-quartz formation is widespread in the northwest of the Voronezh Anteclise at the junction with the northeastern wall of the Dnieper-Donets Basin (Bryansk oblast). The Oligocene-Miocene epoch was characterized by quartz sands abundant in the northwestern and south-western areas. The formation of zirconium-titanium placers is controlled by structural-tectonic, facies, volcanic, paleogeographic, stratigraphic, and evolutional factors. The indispensable condition for heavy mineral concentration is existence of positive forms of underwater topography. These are mostly structural elements of the third and fourth orders on the slopes of the Voronezh Anteclise at the boundaries of the adjacent negative structures. As concerns the facies factor, the occurrence of coastal and shallow-water marine facies with alternating and medium hydrodynamic activity and predominance of sand fractions 0.25–0.05 mm are criteria of elevated concentration of heavy minerals in sand. One of the conditions providing concentration of heavy minerals is a multiple rewashing of sands close to a relatively stable shoreline. The volcanic factor is determinant for the lower Frasnian marine placers fed by volcanic sources. The Cretaceous and Paleogene zirconium-titanium placers were formed owing to scouring of the older Paleozoic and Mesozoic sedimentary rocks of the Voronezh Anteclise, as well as the Baltic Shield, Moscow Syneclise, and the Volga-Ural Anteclise. The age of placers was estimated with accuracy up to substages (lower Aptian, lower Santonian, lower Campanian). The evolution factor is expressed in variation of localization and composition of placers in time and space. The forecast of potentially ore-bearing areas is based on optimal combinations of favorable factors.     

Paragenesis of upper cretaceous titanium-zirconium placers and phosphate mineralization in the southern East European Platform

Association of titanium-zirconium placers and phosphate mineralization in Upper Cretaceous rocks of the East European Platform is shown with the Tsentral’noe (Central) and Unecha deposits as example. This paragenesis is caused by interaction between the multicomponent placer ore (phosphate-rare metal) concentrations and mechanical-chemical differentiation that shows up periodically during the sub-aerial migration of sedimentary material. Clastic ore components were mainly derived from intermediate collectors, while the phosphate material was delivered by the phosphate-containing solutions and particulates in the chemical weathering crust. Such phosphorite-titanium-zirconium occurrences can also be detected in other regions, including areas with rare metal placers.     

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.     

Provenances of late Pliocene rare-metal-titanium placers in the Tamansky Peninsula

The comprehensive mineralogical analysis of the Taman nearshore Ti-Zr placers and their provenances in the adjoining late Pliocene sedimentation basin is presented. Taking into account paleogeographic reconstructions and contemporary mineral potential of sediments in the Sea of Azov, a contribution of specific feeding sources of terrigenous minerals to the formation of the late Pliocene placers have been estimated. These sources are crystalline and sedimentary rocks of the Caucasus, the southern Russian Plate, and the southeastern Ukrainian Shield (listed in the order of their contribution). The Miocene placers of the Stavropol Arch and Adygea Prominence, as well as the Cretaceous and younger placers of the Ukrainian Shield and the Voronezh Anteclise are suggested to be transitional reservoirs. Economic deposits are forecasted in the zone of paleostraits.     

自然重砂成因矿物学特征及找矿指示作用

自然重砂是地质体经自然风化、剥蚀、搬运、沉积等地质作用而分离出的单矿物(或矿物组合)。自然重砂矿物晶体由于仍然保留有许多矿物成因信息,包括颜色、形态、化学成分、物理性质和矿物组合等特征,因此常用于追溯源区地质体或者找矿勘查。这种方法被认为是一种经济实用的找矿方法——自然重砂测量。本文基于全国自然重砂找矿的数据资料,系统梳理了自然重砂的矿物类型、出现频率及其分布等特点,分析了自然重砂的矿物组合和成因矿物学特征,研究了自然重砂矿物的源区烙印、搬运距离及标型指示矿物组合特征,探讨了自然重砂成因矿物学研究意义及其找矿应用前景。自然重砂矿物的颜色、形态及内部结构依然保留着明确的成因矿物学信息:其颜色和晶体形态具有继承性而与其源区母体联系起来,体现源区母体的特性;其矿物组成可分出残余原生重矿物(包括造岩矿物、副矿物、矿石矿物等)和新生重砂矿物两个部分,如赤铜矿、孔雀石等反映着源区岩性体的成分或者赋存状态特征,其矿物组合也在很大程度上继承原生共生矿物而体现诸如有无矿化等意义;重砂颗粒的磨圆度、边界光滑性等表面特征反映搬运距离,有利于明确响应源区母体或者物源,而具有良好的找矿指示意义。     

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.     

长江水系沉积物碎屑矿物组成及其示踪意义

长江碎屑矿物组成研究表明,轻矿物以石英、长石和岩屑为主,不同支流轻矿物组成特征不同,成熟度指数平均是2.0,一般干流高于支流,成熟度随沉积物搬运距离增加而增大。QFL及QtFL三角图解显示长江沉积物主要来自再旋回造山带物源区,流域风化剥蚀速度较快,不同支流物质汇入干流,使得干流轻矿物组成复杂多变而难以和支流区别。重矿物含量从长江上游至下游呈递减趋势,其主要组合是磁铁矿-普通角闪石-普通辉石-石榴子石-绿帘石-褐铁矿-钛铁矿。红柱石和磷灰石是金沙江沉积物的特征矿物组合;蓝晶石是岷江流域的特征矿物;涪江的特征矿物是榍石;汉江的特征矿物组合是磷灰石、紫苏辉石和硅镁石;锆石是湘江的特征矿物。不同流域的特征矿物指示其源岩性质。上游的雅砻江、大渡河以及岷江等支流沉积物对中、下游干流沉积物的贡献较弱。涪陵以上长江流域风化作用强烈,母岩主要是沉积岩类(碎屑岩、泥岩);其下流域沉积物中近源弱风化物质明显增加,其源岩类型体现为岩浆岩和变质岩类;而金沙江攀枝花地区及湘江、沅江沉积物则更多来自流域内广泛分布的大片变质岩类。     

Geostatistical approach for elucidating the potential titanium-zirconium placer areas: Evidence from the Transural placer district

Geostatistical analysis of the composition of mineral assemblages of Oligocene sediments in the Mansi and Severnaya Sosva areas of the Transural titanium-zirconium placer district was accomplished by the method of the principal components. High significance of the first principal component and its composition revealed by this analysis suggest the existence of an efficient placer-forming process that can produce commercial concentrations of ore minerals. Interpretation of statistical indicators is given. The results confirm the facies zoning of sediments revealed previously in the Oligocene basin. They show that the paleolittoral and shallow-water zones with a moderate hydrodynamic activity in the depositional environment have the highest potential of titanium-zirconium raw material. Analysis of the mineral potential revealed that the Mansi and Severnaya Sosva areas can accommodate a medium-scale placer deposit.     

Influence of nearshore sediment dynamics on the distribution of heavy mineral placer deposits in Sri Lanka

Beach sediments in Sri Lanka contain industrial-grade heavy mineral occurrences. Samples of both offshore and onshore sediments were collected to examine the provenance, mineralogy and geochemical compositions of the heavy mineral occurrences. Coastal morphodynamic changes along the coastline of Sri Lanka were analyzed using the time-series satellite images. These coastal morphodynamic changes were used to identify the prominent directions of monsoon-influenced longshore currents, coastal sediment accretion and depositional trends and their relationships to the provenance of the heavy minerals. Results show the concentrations of detrital ilmenite, zircon, garnet, monazite, and rutile vary in the onshore and offshore sediments. The heavy mineral potential of the northeastern coast is high (average contents of about 45–50% in the Verugal deposit, 70–85% in the Pulmoddai deposit, and 3.5–5.0% in offshore samples stretching from Nilaveli to Kokkilai), compared to sediments in southwest (average content about 10% in onshore sediments and 2% in offshore sediments from the mouth of the Gin River). Therefore, no economic-grade heavy mineral placers were identified in the offshore environments. The high concentrations of heavy minerals in beach sediments and low concentrations in offshore sediments suggest operation of a panning system in the surf zone to form enriched placer deposits. Major and trace element compositions of beach sediments show marked enrichments of TiO₂, Fe₂O₃, La, Ce, Zr, Cr, Nb, Th and V compared to average Upper Continental Crust (UCC) values. Analysis of prominent coastal longshore transport patterns identifies bidirectional sediment transport in the northeast coast of Sri Lanka. In the southwestern coast, two transport directions occur with anti-clockwise transport from Galle to Hambantota, and clockwise transport from Hikkaduwa to Wadduwa. The heavy minerals in the placers were mainly derived from Precambrian metamorphic rocks, and transported to the coast through the river systems of Sri Lanka.     

Rhaetian diamond placers in Siberia

Large diamond placers have been discovered in a Rhaetian basal horizon (Upper Triassic) in the north of the Sakha Republic (Yakutia) in the drainage areas of the Eekit, Nikabyt, Kelimyar, and Bur Rivers. In typomorphic features the found diamonds and indicator minerals of kimberlites are completely similar to those from Carnian basal horizons but, in contrast to them, are well sorted, and pyropes show features of mechanical wear. Analysis of the geologic evolution of the study area, morphology of diamonds and indicator minerals, and composition of the latter showed that the Rhaetian productive sediments resulted from the erosion of Carnian placers.     

Problem of the Formation of Eolian Gold Placers on the East European Platform

The distribution of eolian gold in various Proterozoic–Cenozoic sediments on the East European Platform is considered. Eolian placers of the Timan Ridge are characterized by specific features: significant areal distribution and consistent strike of the thin (0–30 cm) productive bed. Prospecting criteria of eolian gold placer in the study territory can be the presence of gold flakes and other minerals with signs of eolian reworking, specific structure of productive bed, deflation structure of relief, and characteristic lithological composition of sediments. It is concluded that since gold flakes with eolian reworking make up high metal concentrations, such as placer deposits in the Timan Ridge, eolian placers of different age may be found on the East European Platform.     

Structure,composition, and depositional environments of the lower cretaceous rocks of the Zhuravlevka terrane,Central Sikhote Alin

The structure, mineralogical-petrographic composition, and formation settings of the Berriasian-Albian terrigenous rocks of the Zhuravlevka terrane (Central Sikhote Alin) are considered. The rocks are interpreted as sediments accumulated in a virtually nonvolcanic basin along the transform plate boundary. Judging from the composition of terrigenous rocks, the main sources of clastic material were represented by the eroded granitic-metamorphic rocks of a mature continental crust, and, possibly, granitoid intrusions of ancient arc roots. Genetic features of the sediments suggest their accumulation on the shelf, underwater slope, foothill, and the adjacent basin plains of an oceanward-open marginal sea.     

Geological setting and mineral composition of Famennian manganese ores in the Lemva zone of Pai-Khoi: Evidence from ore occurrences of the Nizhny Silov group

The results of geological-mineralogical study of stratificated manganese ores in Famennian rocks of the Lemva facies in Pai-Khoi are presented. Carbonate manganese ores make up conformable stratified and lenticular bodies (up to 0.6 m thick) in the interval between the Gromashor and Silovayakha formations that are composed of jasperoids and carbonate-siliceous rocks. Ores are characterized by fine wavy bedding and development of transverse quartz veinlets. The ores are mainly composed of kutnahorite. Secondary minerals are represented by dolomite, calcite, pyrite, ransayite, and cryptomelane (?). Mn-muscovite, micro-cline, pyrophanite, galena, barite, apatite, and monazite are accessory minerals. The average MnO content is 23.81 wt %. The interval also includes a long (up to 40 m) lens of rhodonite rocks (Silovayakha occurrence) that replace carbonate ores along the strike. The major minerals in these rocks are represented by rhodochrosite, rhodonite, pyroxmangite, and quartz. Secondary minerals are observed as tephroite, alleghanyite, friedelite, caryopilite, neotocite, sussexite, pyrite, and supergene manganese oxides. Spessartine, albandine, barite, and apatite are accessory minerals. Based on the analysis of factual material, we suggest that ore material was derived from hydrothermal paleoceanic systems associated with Devonian volcanism. Ore concentration in the sedimentation zone was related to the stagnant reduced setting of bottom water. Ore deposition was promoted by the delivery of fresh portions of ocean water. Ore matter was accumulated mainly by chemogenic mechanism and partly with the’ participation of bacteria. It is suggested that boundary between the Gromashor and Silovayakha formations should be corrected to unite rocks of the Famennian manganiferous association into a single formation.     

Geomorphological-sedimentological studies of landform types and modern placer deposits in the savanna (Southern Malawi)

Semi-arid climatic conditions were responsible for the evolution of the vast savanna that stretches across central Africa and for the evolution of placers in this area that carry gemstones, rare earth element minerals and zircon- and titanium-bearing minerals. In combination with a polystage peneplanation, chemical weathering contributed to the emplacement of four different types of placer deposits during the Cenozoic in Malawi. Eight landform types have been defined by their geomorphological form, geometry, grain size parameters, stratification, fabric and rock contacts. Each type describes the landscape of the savanna and can be related to the emplacement of placer types within this morphoclimatic zone. Residual to eluvial placers, represented geomorphologically by landform type V, came into existence under strong chemical weathering during a period of alternating peneplanation and valley incision into soil and saprolite. Gentle valley-side slopes or elongated interfluves have a low gradient favorable for the formation and preservation of eluvial to colluvial placers (landform type Ic). Fluvial placers become economic only on outwash plains of tributaries near the confluence with their trunk rivers, beyond the point of inflection (landform types III, II). In the lower reaches of fluvial drainage systems around shallow lakes, fluvio-deltaic placers evolved during periods of rapid uplift and regression of the lake (landform type IV). Other landform types established throughout this study are cast in the role of ‘ore guides’ or, alternatively, have a negative impact on the likelihood of placer formation. The key associations of landforms discussed in this paper may be used as a geomorphological-sedimentological tool in search of modern continental placer deposits in areas where semi-arid climatic conditions occur(red) during the Cenozoic.     

Granitoids of the Ufalei block (South Urals): Sr-Nd isotope systematics, geodynamic position and genetic reconstructions

Petrogeochemical and isotopic-geochronological signatures in granitoids developed in structures with complex geological history represent an important feature for reconstructing paleogeodynamic settings. Granitoids are widespread in the western slope of the Urals, where the Uralian Orogen contacts via a collage of different-age blocks of the east European Platform. The Ufalei block located in the Central Urals megazone at the junction between the South and Middle Urals’ segments represents one such boundary structure with multistage geological evolution. The isotopic ages obtained by different methods for acid igneous rocks range from 1290 to 245 Ma. We determined close Rb-Sr and Sm-Nd ages (317 Ma) for granites of the Nizhnii Ufalei Massif. By their petrochemical parameters, granitoids and host granite-gneisses differ principally from each other: the former are close to subduction-related, while the latter, to continental-riftogenic varieties. The primary ratio (⁸⁷Sr/8⁶Sr)₀ = 0.70428 and ?_Nd ≈ +4 values indicate significant contribution of oceanic (island-arc?) material to the substrate, which served as a source for granites of the Nizhnii Ufalei Massif. Model Nd ages of granites vary from 641 to 550 Ma. Distinct oceanic rocks and varieties with such ages are missing from the surrounding structures. New isotopic dates obtained for ultramafic and mafic rocks from different zones of the Urals related to the Cadomian cycle imply development of unexposed Upper Riphean-Vendian “oceanic” rocks in the central part of the Ufalei block, which played a substantial role in the formation of the Nizhnii Ufalei granitoids. Such rocks could be represented, for example, by fragments of the Precambrian Timanide-type ophiolite association. The analysis of original materials combined with published data point to the heterogeneous composition and structure of the Ufalei block and a significant part of the western segment of the Central Uralian Uplift and extremely complex geological history of the region coupling the Uralian Orogen with the East European Platform in the present-day structure.     

Placer diamond potential of the siberian craton: possible sources and ages

Many diamond placers in the Siberian craton are heterogeneous consisting of several components that differ in origin and ages of the source. The diamonds are either kimberlite-hosted or are exotic varieties which occur mostly in the northeastern craton periphery and come from primary deposits of unknown types and ages. The two groups of diamond placers in the area represent two evolution trends: those found in Middle Paleozoic kimberlites originated in the Famennian and the exotic diamond groups became involved in sedimentation in the Carnian. The trends have been associated with successive weathering of older diamond hosts and redeposition of the minerals into younger sediments. Having joined since the Late Triassic, the two trends eventually produced a polygenetic and multistage mixture of diamond groups in placers.