Ore-bearing Horizons Research Articles

Origin of the Filizchay ore field (the southern slope of the Greater Caucasus)


 
 
 he article deals with the origin of the Filizchay ore field, which is a valuable object for the extraction of zinc, lead, copper, silver as well as for the extraction of the associated com- ponents. The data and types (VMS, SEDEX, VMT) of the pyrite deposits in the world have been briefly presented. Their comparative analysis has been carried out and it has been revealed that the Filizchay ore field is very different from the VMS-type pyrite deposits and it belongs to the SEDEX type. A direct relationship with vol- canism has not been observed in this deposit. Unlike the containing rocks related to volcanism in the Filizchay field , there are fine-rhyth- mic flyschoids with packages of sandstones, clay shales and silt-clay shales . The ratio of the natural ore types composed of the different mineral associations, with stages of the folded and disjunctive dislocations, allows us to divide the process of the deposit formation into the following three stages of the ore formation: 1. deposits of the massive hydrothermal-sedimentary essentially pyrite ores; 2. formation of the hydrothermal-metasomatic ores of the pyrite-copper-polymetallic composition; 3. deposition of the hydrothermal-meta- morphogenic ores of the copper-pyrrhotite composition. The available data indicate a favorable environment for sedimentary pyrite ore formation subject to a significant role of Corg. and sulfate-reducing bacteria. Moreover, the hydrothermal-sedimentary processes played the main role in the accumulation of the main volume of the sulfide masses. On the basis of the sulfur isotopic composition (according to Zairi, 1992) of the main minerals (pyrite, galena, sphalerite, pyrrhotite, chalcopyrite) from various types of the Filizchay ore field ores it was concluded that the deposit formation occurred from several portions of the entered hydrothermal solutions. It was found that by the period of accumulation of sediments of the ore-bearing horizon in the northern block – there occurred outpouring of the spilites and basalts in the narrow trough-like depression. The iron sulfides supplying the more southern basin with stagnant waters can be associated with their post-volcanic exhalations (as primary sources). The Filizchay ore field being connected with basaltic volcanism is combined according to formation method. It has been formed due to components which have been carried out by hydrothermal flows and due to basalts, which are associated with underwater alteration. The temperatures of the primary pyrite-polymetallic ores formation are relatively low (200-100 0С).
 
 

Mineralogy of the Vovchansk Zircon-Rutile-Ilmenite Deposit (Ukrainian Shield)

The article provides generalized data on the geological structure, the results of laboratory analyzes of the heavy fraction of the main placer-forming minerals of the Vovchansk zircon-rutile-ilmenite deposit, which was being developed by Demurinsky Mining and Processing Plant LLC in 2002. The geological structure of the Vovchansk deposit includes a complex of Precambrian rocks of the crystalline basement, the Paleozoic-Cenozoic weathered crust, the Paleozoic-Cenozoic sediments, and Quaternary deposits. The industrial concentration of heavy minerals is confined to the middle and upper parts of the Middle Sarmatian subsuite of the Neogene, composed of fine-grained, essentially quartz sands, with a total thickness of 0.4 to 63 m. The content of heavy minerals in the ore-bearing horizon of the deposit ranges from 93.8 to 485 kg/m3 (ilmenite from 37.6 to 242.6 kg/m3, rutile from 15.9 to 64.6 kg/m3, zircon from 2.9 to 9.4 kg/m3, sillimanite and disthene from 20.4 to 117.5 kg/m3). The content of major and minor elements-impurities in individual minerals of the ore-bearing horizon (178 grains) was determined: ilmenite (18 samples), rutile (40 samples), zircon (35 samples), sillimanite (30 samples), staurolite (25 samples), tourmaline (12 samples), ganite (8 samples), monazite (10 samples). The conducted research clarified the typomorphic features of minerals from the sands of the Vovchansk deposit, established their absolute age and probable original sources.

Three-Dimensional Geological–Geophysical Modeling and Prospecting Indications of the Ashele Ore Concentration Area in Xinjiang Based on Irregular Sections

The Ashele ore concentration area is an important area for polymetallic ore concentration in Xinjiang, China. Scholars have made progress in understanding the ore-controlling structures, ore-bearing horizons, and metallogenic age of this area. However, there are still uncertainties about the 3D distributions of plutons, fault structures, and ore-bearing strata, which restrict the development of deep and peripheral ore prospecting and the discovery of new ore bodies in the area. This study proposes a geological–geophysical modeling method based on irregular sections and uses this method to establish a 3D geological–geophysical model based on physical property data, boreholes, surface geological maps, and geophysical data. The model shows that the study area has many hidden rock masses with various depths and shapes and fracture structures with complex shapes. The fault structure in the area is complex, and the ore bodies are controlled by the faults. The ore-bearing geological units (Ashele Formation) exhibit an obvious east–west-trending W-shaped fold structure. The deep part of the northern Ashele Formation extends northward slightly, and the southern Ashele Formation has thick strata, with depths generally greater than 2 km. Based on the information on deep structures provided by the model, three metallogenic prospective areas are predicted, which points out the direction for further prospecting work in the ore concentration area and shows that the adopted modeling method and process have good applicability for constructing 3D models of ore concentration areas with sparse data, large area, and complex geological structures. The proposed modeling method provides technical support for ore prospecting, particularly in the overburden area or ore concentration area with sparse data.

Coupling and decoupling of Au and As in pyrite from Carlin-type Au deposits, southwest China

The low-temperature geochemistry of gold (Au) and arsenic (As) in pyrite from Carlin-type Au deposits is significant for understanding the enrichment mechanisms of Au in pyrite, but remains poorly understood due to the complex processes that lead to the precipitation of micron-scale pyrite grains. This paper concerns the geochemical behaviors of Au and As during the precipitation of pyrite from six Carlin-type Au deposits (the Nibao, Shuiyindong, Banqi, Jinya, Yata, and Zimudang deposits), southwest China. These deposits are located in different locations and ore-bearing horizons of the Youjiang Basin. Arsenian pyrite and/or arsenopyrite are the dominant Au-bearing minerals. Gold-bearing pyrite grains are typically zoned (core, intermediate, and rim), with multiple, oscillatory banded sub-zones. In situ analysis demonstrates that invisible Au exists mainly as cationic Au+ in the growth zones of pyrite. Gold and As are positively correlated (i.e., coupled) in the Nibao and Shuiyindong deposits, negatively correlated in the Banqi, Jinya, and Yata deposits, and poorly correlated in the Zimudang deposit. Arsenic and S substitution in pyrite and the presence of a reduced fluid promoted the incorporation of Au, resulting in the coupling of Au and As. The Au precipitation was affected by changes in the physicochemical conditions of the hydrothermal systems, independent of the As concentration, resulting in decoupling of Au and As. As such, invisible Au precipitation is controlled by the extrinsic physicochemical conditions of the ore-forming fluids and microscopic reactions at the fluid–mineral interface, and also the episodic incursion of Au-rich hydrothermal fluids. High As contents in pyrite favor Au incorporation, but are not solely responsible for Au enrichment. Gold and As contents in pyrite in Carlin-type Au deposits may be coupled or decoupled.

Three-dimensional reflection seismic imaging of the iron oxide deposits in the Ludvika mining area, Sweden, using Fresnel volume migration

Abstract. We present pre-stack depth-imaging results for a case study of 3D reflection seismic exploration at the Blötberget iron oxide mining site belonging to the Bergslagen mineral district in central Sweden. The goal of the study is to directly image the ore-bearing horizons and to delineate their possible depth extension below depths known from existing boreholes. For this purpose, we applied a tailored pre-processing workflow and two different seismic imaging approaches, Kirchhoff pre-stack depth migration (KPSDM) and Fresnel volume migration (FVM). Both imaging techniques deliver a well-resolved 3D image of the deposit and its host rock, where the FVM image yields a significantly better image quality compared to the KPSDM image. We were able to unravel distinct horizons, which are linked to known mineralization and provide insights on their possible lateral and depth extent. Comparison of the known mineralization with the final FVM reflection volume suggests a good agreement of the position and the shape of the imaged reflectors caused by the mineralization. Furthermore, the images show additional reflectors below the mineralization and reflectors with opposite dips. One of these reflectors is interpreted to be a fault intersecting the mineralization, which can be traced to the surface and linked to a fault trace in the geological map. The depth-imaging results can serve as the basis for further investigations, drilling, and follow-up mine planning at the Blötberget mining site..

An innovative seismic and statistical approach to understand 3D magmatic structures and ore deposits in the western Bushveld Complex, South Africa

In this paper, we demonstrate the effectiveness of a novel approach to identify and quantify structural features that disrupt ore-bearing horizons using 3D seismic attributes and a horizon-surface processing technique (difference-of-two-surfaces) on high-resolution 3D reflection seismic data from the Lonmin Platinum Mine in the Bushveld Complex, South Africa. We demonstrate that seismic attribute analysis is an effective tool to enhance the intelligibility of the UG-2, a PGE-enriched chromitite layer, as well as potholes (slump structures), faults, iron-rich ultramafic pegmatite bodies (IRUPs) and other subtle geological features. Furthermore, the horizon-surface processing technique is able to quantify the dimensions and geometry of potholes. In total, we identify 66 potholes and show that they are probably randomly distributed in 2D on the UG-2 horizon with some extent of clustering. Roughly two classes of potholes are identifiable by size. The larger potholes are clustered around a major normal fault (the Marikana Fault) and its branches in the area. Using a first-order pothole structure/geometry statistical analysis, we demonstrate that: (1) the diameters and surface areas of the potholes are strongly related to their depths; and (2) the volume of the potholes is substantially log-normally distributed. We interpret these findings to implicate a coherent and pervasive pothole formation mechanism. Furthermore, we show that statistically-derived pothole structure/geometry knowledge can be used to constrain the validity of several hypotheses. Our findings indicate the most probable pothole formation hypothesis is a widespread extensional regime in the Bushveld Complex magma chamber. Therefore, our study provides important, large-scaled and highly data-driven insights with an approach that can be applied to a wide range of magmatic structures. Furthermore, relationships identified between various pothole characteristics, in addition to their academic value, also allows for predictive modelling that can guide mine planning and resource extraction.

Stable isotope and fluid inclusion studies of early Zn-Cu-(Ni-Co)-rich ores, lower ore zone of Brushy Creek mine, Viburnum Trend MVT district, Missouri, U.S.A.: Products of multiple sulfur sources and metal-specific fluids

Mississippi Valley-type (MVT) deposits of the Viburnum Trend are typically lead-dominant and occur in the upper portion of the Cambrian Bonneterre Dolomite. Unusual zinc- and copper-rich ores, with notable enrichments in Ni, Co, and Ag, have been discovered within the lower Bonneterre Dolomite, >30 m below the district’s main ore-bearing horizon. These ores appear to be localized along fault/fracture zones within the Lamotte Sandstone, which promoted extreme dissolution of the base of the overlying Bonneterre Dolomite and resulted in pronounced vertical zoning of early Ni-Co, Cu, Zn and Pb ores above the sandstone/dolomite contact.Stable isotope and fluid inclusion studies were undertaken to assess whether the deep ores resulted from a single fluid reservoir that evolved from Cu-Ni-Co-rich to Zn-rich to Pb-rich or are instead products of distinct fluids unrelated to the stratigraphically higher, main Pb-rich ores of the district. Sphalerite-hosted fluid inclusions from the lower orebody appear to be geochemically distinct from those that formed the upper orebodies. They record the highest K/Na and Mg/Na ratios in the southeast Missouri MVT district, suggesting dominance of siliceous lithologies (arkose and/or felsic igneous rocks) over limestones along their ore-fluid pathways. Paragenetic trends indicate that distinct fluid compositions are associated with specific generations of sphalerite, which likely reflects the presence of multiple fluids.The δ34S values of ore minerals (early pyrite and chalcopyrite, −7 to +5‰; early sphalerite, +6 to +15‰; main sphalerite, +7 to +17‰ V-CDT) indicate deposition from fluids that utilized isotopically distinct sulfide reservoirs. Low-δ34S sulfur sources for early ores likely included sulfide in local brines within the Lamotte Sandstone and diagenetic sulfide minerals within the basal units of the Bonneterre Dolomite. A trend of increasing δ34S values of ore sulfides (from −5 toward +17‰) with vertical distance above the Lamotte Sandstone-Bonneterre Dolomite contact indicates that as the deep ore fluid system worked its way upward, it breached less permeable units in the lower Bonneterre Dolomite, allowing incorporation of high-δ34S sulfide from brines present higher in the stratigraphic section. A concomitant up-section pattern of decreasing δ18O values of dolomite cement and recrystallized remnant host rock (from −3 toward −9‰ V-PDB) is also consistent with a localized, deep mineralizing fluid system, which interacted progressively with the stratigraphically higher, regional-scale, Pb-rich fluid system.The episodic nature of metal sulfide deposition in the lower ore zone points to a system in which fluid mixing would have been highly variable, both temporally and spatially. Reaction path models require mixing of multiple, ore metal-specific and sulfide-bearing fluids in order to form the orebody. The sequence and concentrations of metal sulfides are inconsistent with ore formation from a single, evolving metal-bearing fluid.This study indicates that faults localized early metal- and sulfide-bearing fluids, facilitating mixing of fluids that resulted in the accumulation of high-grade ores near the Bonneterre Dolomite-Lamotte Sandstone contact. Recognition of fault/fracture patterns beneath more typical Pb-rich orebodies in the Viburnum Trend may be a viable exploration strategy for similar Zn-Cu-Co-Ni-rich deposits.

Микротопохимия конкреций пирита в кремнистых алевропелитах Юбилейного медноколчеданного месторождения (Южный Урал) по данным LA-IСP-MS

Object . The zonal pyrite nodules and metacrystals from siliceous siltstones of ore-bearing horizon of the Second ore body from the Yubileynoe massive sulfide deposit are studied. Materials and methods . We used 9 samples and 15 polished sections of siliceous siltstones with pyrite mineralization. Analysis of chemical composition minerals was determined by Tescan Vega 3 with an energy dispersive microprobe Oxford Instruments X-act (Institute of Mineralogy UB RAS, Miass). Quantitave LA-ICP-MS analysis of pyrite for major and trace elements was carried out using New Wave Research UP-213 laser microprobe coupled to an Agilent 7500 quadrupole ICP-MS housed (University of Tasmania, Australia). Results. Microtopochemistry was established that the diagenetic core of the nodule is characterized by trace elements of typical poikilites of quartz (Si) and alumosilicates (Si, Al, Mg, V, Cr, K, Na, Ca), rutile and titanite (Ti), inclusions of chalcopyrite (Cu), sphalerite (Zn), galena (Pb, Sb, Bi), tetrahedrite-tennantite (As, Sb), native gold, petzite, hessite (Au, Ag, Te), tellurobismuthite, altaite, and coloradoite (Te, Bi, Pb). Cobalt and Ni substitute for Fe 2+ . The rim of subhedral pyrite is depleted in most trace elements except for Ni and As. Subhedral pyrite became rich in chalcophile (Au, Ag, Sb, Bi, Cu, Zn, Hg) and lithophile (Ca, K, Na, Cr) elements at the final stage of growth of the nodule. Similar mineralogical and geochemical zonation is typical of the pyrite metacrystals, where a micro-grained core concentrates Pb, Bi and Te, and a rim of subhedral pyrite is depleted in most trace elements. Similarly to the nodules, the outer rim of pyrite metacrystals is enriched in most trace elements (Pb, Au, Ag, Sb, Cu, As, Mo, Cr, etc.). The nodules and metacrystals were formed from diagenetic micronodule of poikilite pyrite. Conclusions. It is suggested that mineralogical and geochemical differences in pyrite metacrystals and nodules are caused by the greater degree of development of rims of subhedral pyrite.

Non-cylindrical parasitic folding and strain partitioning during the Pan-African Lufilian orogeny in the Chambishi–Nkana Basin, Central African Copperbelt

Abstract. A structural analysis has been carried out along the south-east margin of the Chambishi–Nkana Basin in the Central African Copperbelt, hosting the world-class copper and cobalt (Cu–Co) Nkana orebody. The geometrically complex structural architecture is interpreted to have been generated during a single NE–SW-oriented compressional event, clearly linked to the Pan-African Lufilian orogeny. This progressive deformation resulted primarily in asymmetric multiscale parasitic fold assemblages, characterised by non-cylindrical NW–SE-oriented periclinal folds that strongly interfere laterally, leading to fold linkage and bifurcation. The vergence and amplitude of these folds consistently reflect their position along an inclined limb of a NW-plunging megascale first-order fold. A clear relation is observed between the intensity of parasitic folding and the degree of shale content in the Copperbelt Orebody Member (COM), which hosts most of the ore. Differences in fold amplitude, wavelength and shape are explained by changes in mechanical stratigraphy caused by lateral lithofacies variation in ore-bearing horizons. In addition, strong differences in strain partitioning occur within the deforming basin, which is interpreted to be in part controlled by changes in mechanical anisotropy in the layered rock package. This work provides an essential backdrop to understand the influence of the Lufilian orogeny on metal mineralisation and (re-)mobilisation in the Copperbelt.

Genesis of copper-lead mineralization in the regionally zoned Agnigundala Sulfide Belt, Cuddapah Basin, Andhra Pradesh, India

Shallow marine sandstone-shale-carbonate sedimentary rocks of the Paleoproterozoic northern Cuddapah basin host copper (Nallakonda deposit), copper-lead (Dhukonda deposit), and lead mineralization (Bandalamottu deposit) which together constitute the Agnigundala Sulfide Belt. The Cu sulfide mineralization in sandstone is both stratabound and disseminated, and Pb sulfide mineralization occurs as stratabound fracture filling veins and/or replacement veins within dolomite. Systematic mineralogical and sulfur, carbon, and oxygen isotope studies of the three deposits indicate a common ore-fluid that deposited copper at Nallakonda, copper-lead at Dhukonda, and lead at Bandalamottu under progressive cooling during migration through sediments. The ore-fluid was of low temperature (< 200 °C) and oxidized. Thermochemical reduction of basinal water sulfate produced sulfide for ore deposition. It is envisaged that basal red-bed and evaporite-bearing rift-related continental to shallow marine sediments might have acted as the source for the metals. Rift-related faults developed during sedimentation in the basin might have punctured the ore-fluid pool in the lower sedimentary succession and also acted as conduits for their upward migration. The ore-bearing horizons have participated in deformations during basin inversion without any recognizable remobilization.

Geological structure and prospects of noble metal ore mineralization of the Khayrkhan gabbroid massif (Western Mongolia)

An analysis of the distribution of noble metals in zones of sulfide mineralization makes it possible to justify the isolation of four ore-bearing horizons with a specific geochemical zonation. A rise in the gold content relative to palladium and platinum is observed from the bottom upwards along the section of the stratified series of gabbroids. The study of the mineral phases of sulphides and the noble minerals itself indicates the evolution of hydrothermal solutions, which determines the different activity and mobility of the fluid (mercury, tellurium, sulfur) and ore (copper, nickel, iron, platinum, gold and silver) components.

VOLCANIC – SEDIMENTARY METAL DEPOSITION IN PALEOMARGIN ENVIRONMENT: A “ PROTORE ” OCCURRENCE IN CENTRAL SARDINIA (ITALY)

Several metallogenic periods took place at different moments of the geological evolution of Sardinia, but at places they interacted: the close correlation between the metal parageneses in the Ordovician – Silurian sequences, outcropping in the central part of the island, and the veins and masses associated with the Hercynian magmatism is depicted. The volcanic-sedimentary mixed-sulphide lenses contained in Silurian occurrences show clear sedimentary structures, and the connection with coeval volcanics seems evident. These mineralizations are thought to be the protores for the subsequent metallogenic cycle related with the Hercynian orogenesis which had a strong effect as a promoter of the remoulding of preexisting mineral concentrations to give new ore- and industrial minerals deposits. Several geochemical campaigns have covered the entire island, and wide areas of the Paleozoic basement, mostly localised in the internal zones, showed high base- and heavymetals contents. A new prospecting programme has been started in Central Sardinia; it follows the ore-bearing horizon along the Ordovician-Silurian boundary with the purpose to better understand these primary metal depositions, their relationships with geodynamic structures, and ore mobilisation caused by the Hercynian granites. The geochemical anomalies along this horizon detected in the area of “Castello Medusa” support detailed prospecting works.

AN ATYPICAL OREBODY IN THE BRUSHY CREEK MINE, VIBURNUM TREND, MVT DISTRICT, MISSOURI: EARLY Cu-(Ni-Co)-Zn-RICH ORES AT THE LAMOTTE SANDSTONE/BONNETERRE DOLOMITE CONTACT

Mississippi Valley-type (MVT) deposits of the Viburnum Trend are typically lead dominant (Pb/Zn >5) and occur mainly in the reef-grainstone facies of the upper Bonneterre Dolomite (Cambrian). Recent drilling has encountered economic mineralization within the lower Bonneterre Dolomite of the Brushy Creek mine, more than 30 m below the main ore-bearing horizon of the district. These ores are more zinc and copper rich than typical deposits (Zn/Pb commonly >2 and Cu up to 8 wt %), with notable enrichments in Ni, Co, and Ag. There is pronounced zoning of Ni-Co, Cu, Zn, and Pb with increasing distance above the Lamotte Sandstone. Observations of drill cores and samples from active mine faces, and mineral textural relationships in thin section indicate that the lower ore mineralization contains dominantly early Zn- and Cu-bearing sulfides, which are overprinted by main-stage Pb-Zn mineralization. The lower ores contain multiple generations of chalcopyrite and sphalerite that display frequent breccia textures at the meso- and microscale. This style of breccia is uncommon for the Viburnum Trend and is composed dominantly of sulfides supported by clay (insoluble residue), which are cemented by subsequent generations of sulfides and carbonates, resulting in massive, high-grade ore. Cathodoluminescence microscopy reveals that ore is associated with two generations of dolomite cement that appear to predate the regional dolomite cement associated with main-stage Pb-Zn mineralization in the Viburnum Trend. The stratigraphic position, massive character, metal contents, mineral zoning and textures, and gangue dolomite cements of the orebody are unusual for the Viburnum Trend. Mineralogically and stratigraphically, these ores are more similar to the historically mined ores of the Indian Creek and Fredericktown-Mine La Motte districts to the north and east of the Viburnum Trend. In the Brushy Creek mine, the lower ores are not related to obvious stratigraphic controls, such as pinch-outs of the Lamotte Sandstone against Precambrian knobs, but appear to be localized along early zones of fracture-enhanced porosity and permeability within the Lamotte Sandstone, which promoted extreme dissolution of host rocks at the base of the Bonneterre Dolomite and development of high-grade Cu-(Ni-Co)-Zn-rich ore. The presence of distinct Ni- and Ni-Co-rich areas and the spatial variability of sphalerite types across the orebody indicate that there were likely multiple sites of ore fluid introduction whose influence varied with time during development of the ores.

A combined chemical, isotopic and microstructural study of pyrite from roll-front uranium deposits, Lake Eyre Basin, South Australia

The common sulfide mineral pyrite is abundant throughout sedimentary uranium systems at Pepegoona, Pepegoona West and Pannikan, Lake Eyre Basin, South Australia. Combined chemical, isotopic and microstructural analysis of pyrite indicates variation in fluid composition, sulfur source and precipitation conditions during a protracted mineralization event. The results show the significant role played by pyrite as a metal scavenger and monitor of fluid changes in low-temperature hydrothermal systems.In-situ micrometer-scale sulfur isotope analyses of pyrite demonstrated broad-scale isotopic heterogeneity (δ34S=−43.9 to +32.4‰VCDT), indicative of complex, multi-faceted pyrite evolution, and sulfur derived from more than a single source. Preserved textures support this assertion and indicate a genetic model involving more than one phase of pyrite formation. Authigenic pyrite underwent prolonged evolution and recrystallization, evidenced by a genetic relationship between archetypal framboidal aggregates and pyrite euhedra. Secondary hydrothermal pyrite commonly displays hyper-enrichment of several trace elements (Mn, Co, Ni, As, Se, Mo, Sb, W and Tl) in ore-bearing horizons. Hydrothermal fluids of magmatic and meteoric origins supplied metals to the system but the geochemical signature of pyrite suggests a dominantly granitic source and also the influence of mafic rock types. Irregular variation in δ34S, coupled with oscillatory trace element zonation in secondary pyrite, is interpreted in terms of continuous variations in fluid composition and cycles of diagenetic recrystallization. A late-stage oxidizing fluid may have mobilized selenium from pre-existing pyrite. Subsequent restoration of reduced conditions within the aquifer caused ongoing pyrite re-crystallization and precipitation of selenium as native selenium.These results provide the first qualitative constraints on the formation mechanisms of the uranium deposits at Beverley North. Insights into depositional conditions and sources of both sulfide and uranium mineralization and an improved understanding of pyrite geochemistry can also underpin an effective vector for uranium exploration at Beverley North and other sedimentary systems of the Lake Eyre Basin, as well as in comparable geological environments elsewhere.

Study on Uranium Occurrences of Sandstone-Type Uranium Deposit in Bayanwula Area, Erlian Basin, Inner Mongolia

It is a breakthrough exploratory area about sandstone-type uranium deposit of Bayanwula area in Erlian basin, Inner Mongolia, a detailed study of the form of occurrences . Ore-bearing horizon is the down cretaceous Saihan formation in Bayanwula area. Study on uranium occurrences which is significance for Uranium mining smelting.The host rocks are gray silt - fine sandstone, gray medium - fine sandstone, yellow medium - fine sandstone . The EPMA(electron probe microanalysis) results show that the uranium minerals are mainly pitchblende, coffinite, uranyl-carbonate, uranothorite, isomorphous uranium and uranium bearing phosphate. among which, the uranothorite and isomorphous uranium are of no industrial significance, uranium mineralization closely occurs with pyrite, ilmenite, quartz, feldspar, rare earth and organic matter.

The Proterozoic Strata Division and the Research of Ore Bearing Horizon in Mid-Inner Mongolia

This article introduces the contrast of the Proterozoic strata division and the ore-bearing horizon of the polymetallic deposits like iron and copper by taking advantage of the field geological investigation and the geological characteristic of mineralization to further analyze the ore-prospecting prospects in the area.

Association between catastrophic paleovegetation changes during Devonian–Carboniferous boundary and the formation of giant massive sulfide deposits

The Iberian Pyrite Belt (SW Iberia) is one of the largest sulfur anomalies in the Earth's crust. In the southern Iberian Pyrite Belt, more than 820 Mt of exhalative massive sulfides were deposited in less than one million years at the Devonian–Carboniferous boundary. The shale of the ore-bearing horizon contains biomarkers indicating major biogenic activity in a methanogenic setting, including a five-fold increase in typical vascular plant biomarkers and a significant anomaly in those probably indicating the presence of thermophilic Archaea. This contrasts with signatures in the average sedimentary rocks of the basin that indicate the sediments settled in oxic to sub-oxic environments, and that they have only minor biomarkers derived from continental paleoflora. These data show that the formation of the mineralization was not only related to major hydrothermal activity synchronous with volcanism but may also have been controlled by the input of large amounts of organic matter, mostly derived from the degradation of woodland detritus sourced in the nearby continent. This massive influx of organic matter could have accelerated extremophilic microbial activity that used short-chain hydrocarbons as electron donors for seawater sulfate reduction, resulting in concomitant massive sulfide precipitation. We propose that the giant massive sulfide deposits resulted from overlapping of geological and biological processes that occurred at the Devonian to Carboniferous transition, including: (1) continent collision during the onset of the Variscan orogeny leading to major paleogeographic changes and volcanism; (2) dramatic stress of continental ecosystems due to the combination of climatic change, volcanism, variations in the sea level and erosion on a regional scale; (3) major biomass destruction and increase of organic supply to marine environments; and, (4) generation of anoxic conditions and the thriving of sulfate reducing microorganisms. Under these conditions, massive sulfide deposits formed where venting sulfur-poor but metal-rich hydrothermal brines flowed into a hydrogen sulfide-rich anoxic water column. The data presented strongly suggest that there was a temporal and causal relationship between the Devonian–Carboniferous geotectonic, climatic and biological crises and the formation of the giant volcano-sedimentary massive sulfide deposits of the southern Iberian Pyrite Belt.

Characteristics and dynamic settings of the Central-east Asia multi-energy minerals metallogenetic domain

That more than 82 percent of proved sandstone-type uranium deposits coexist with proved oil-gas or coalfields in the world reflects the fact of coexistence and accumulation of multi-energy minerals including oil, gas, coal and uranium in the same basin. Especially, this phenomenon is most typical in the Central-east Asia energy basins. Across China, Mongolia and some central Asian countries, the giant Central-east Asia metallogenetic domain (CEAMD) stretches more than 6,000 km from Songliao Basin of China in the east to the Caspian Sea in the west. The multi-energy minerals distribution characteristics of the domain include: their spatial distribution is complicated and ordered; the ore-bearing horizon relates closely to the geographical region; the accumulation/mineralization and localization time is the same or close; the occurrence setting and accumulation/mineralization have close correlation; and they have rich provenance for all the minerals. All of these imply that they have close relations between each other under a unified geodynamic background. The exogenetic uranium mineralization process in CEAMD can be divided into five phases using time limits of 100 Ma, (50±2) Ma, 20±(2–4) Ma, 8–5 Ma. The major mineralization periods and their differences in each primary uranium-bearing basin are identical to the oil-gas accumulation and localization periods and phases in the same basin, and are also in response to regional tectonics and controlled in general by the regional geodynamic environment. For industrial application and commercial exploitation, it is suggested that an important period for coexistence, accumulation and localization of oil, gas, coal and uranium and their interaction mainly occur in the late/last and post basin evolution. Through generalized analysis and comparison of accumulation/mineralization environment of the energy basins in CEAMD, the authors propose that the relatively stable regional tectonic background and moderate (weaker) structural deformation probably are necessary for formation, coexistence and preservation of large and medium-scaled sandstone-type uranium ore deposits, oil-gas fields and coalfields, while basins in favor of coexistence and accumulation are those intracratonal, intermediary massif basins and corresponding reformed basins.

A Physical Volcanological, Chemostratigraphic, and Petrogenetic Analysis of the Little Falls Member, Tetagouche Group, Bathurst Mining Camp, New Brunswick

The Little Falls member of the Nepisiguit Falls Formation is situated in the northern part of the Brunswick Belt of the Bathurst Mining Camp and has been interpreted as the distal equivalent of proximal tuffaceous rocks that host the stratiform Brunswick No. 12 and No. 6 Pb-Zn massive sulfide deposits. It comprises fine-grained, greenish-gray tuffaceous sandstone in the lower part, and coarse-grained, crystal-rich tuffaceous sandstone in the upper part. Petrographic evidence suggests that these rocks have a turbiditic origin. The Little Falls member is underlain by the Vallee Lourdes member, mainly composed of relatively shallow-water calcareous rocks, and is conformably overlain by Mn-rich sedimentary rocks, mainly red argillites that host the Tetagouche Falls Mn-(Fe) deposit. All these rocks are considered to belong to the Nepisiguit Falls Formation, part of the Ordovician Tetagouche Group. Whole-rock geochemical data from the fine-grained tuffaceous sandstone and coarse-grained tuffaceous sandstone indicate that the two units of the Little Falls member are distinct. Zr and TiO 2 contents, and total rare earth element (REE) values are higher in the coarse-grained unit (average Zr/TiO 2 = 0.040, average ∑REE = 247 ppm, n = 6) than in the fine-grained unit (average Zr/TiO 2 = 0.048, average ∑REE = 158 ppm, n = 17), which can be attributed to the variation in crystal content between the two units. Both units are HREE-enriched and have elevated La/Yb relative to the typical Nepisiguit Falls Formation. Overall, the geochemical data combined with evidence from the bounding units suggest that the Little Falls member was deposited in relatively shallow water, possibly in a near-arc environment. The relationship of volcanic facies within the Nepisiguit Falls Formation and the geochemistry of these facies indicate strongly that fine grained, reworked tuffaceous rocks, regardless of whether they are the distal equivalents of proximal tuffaceous rocks, are not associated with the major ore-bearing horizons of the Bathurst Mining Camp.

U-Pb zircon dating of rocks of the platiniferous Fedorova-Pana Layered Massif, Kola Peninsula

The Fedorova–Pana Massif (~400 km 2 in area) located in the central Kola Peninsula belongs to the Northern belt of pyroxenite–gabbronorite PGE-bearing intrusions. The massif is confined to the junction of the Archean Keivy and Kola–Norwegian blocks in the north and Early Proterozoic Imandra–Varzuga structure in the south [3]. The Fedorova–Pana Massif (Fig. 1) incorporates the Fedorova, Lastjavr, Western Pana, and Eastern Pana blocks. The three latter blocks include “stratigraphic” (taxitic gabbronorite, norite, gabbronorite–gabbro) zones [4] with the ore-bearing Upper (ULH) and Lower (LLH) layered horizons. Unlike other blocks, the Fedorova block lacks the orebearing horizons.