Quartz-pebble Conglomerates Research Articles

Audio-magnetotelluric investigation of sulfide mineralization in Proterozoic–Archean greenstone belts of Eastern Indian Craton

Greenstone belts are well known for gold occurrences at different regions of the world. The Dhanjori basin in the eastern Singhbhum region shows major characteristics of a rifted greenstone belt. Initially, we conducted 14 audio-magnetotelluric (AMT) measurements for a profile of $$\sim $$ 20 km in the frequency range of 1 kHz to 10 Hz over this rather complex geologic environment covering Dhanjori Volcanics (DhV) and Kolhan Group (KG). Subsequently, gravity and magnetic surveys were also conducted over this AMT profile. The purpose of the survey was to identify and map conductive features and to relate them to metallogeny of the area along with the mapping of the basement of Dhanjori basin. The strike analysis showed $$\hbox {N30}^{\circ }\hbox {W}$$ strike for DhV for all the frequencies and for sites over KG domain in the frequency range of 100–10 Hz, but for KG domain, the obtained strike in 1 kHz to 100 Hz is $$\hbox {N45}^{\circ }\hbox {E}$$ . As the combination of transverse electric (TE), transverse magnetic (TM) and tipper (Tzy) can recover the electrical signature in complex geological environment, we discuss the conductivity model obtained from TE+TM+Tzy only. The inversion was carried for the regional profile with 14 sites and for 7 sites over KG domain. Conductivity model shows two well resolved conductors, one each in KG and Quartz Pebble Conglomerate Dhanjori (QPCD) domains respectively showing common linked concordant features between these regional and KG profiles. The conductors are interpreted as sulfide mineralization linked with QPCD group of rocks which may host gold. These conductors are also horizontally disposed due to the intrusive younger Mayurbhanj Granite. These intrusives correlate well with the gravity modeling as well. The thickness of the Dhanjori basin at the central is about 3.0 km, similar to that from gravity modeling. The conductivity model also indicates the presence of shallow conductors, but could not be resolved due to lack of high frequency data. However, the results from the close-by drill site indicate the presence of shallow sulfide mineralization hosting gold. The deep level conductors delineated from AMT studies are associated with gravity high and low magnetic. ICP-AES results of Dhanjori samples show significant concentration of gold $$\sim $$ 5.0 g/t, which is of economic consideration. Thus, it can be inferred that the conductors have evidences of sulfide mineralization which host gold.

Retention of rare earth elements in authigenic phases following biogeochemical dissolution of ore from Elliot Lake, Ontario

The aim of this pilot study is to investigate the retention of uranium (U) and rare earth elements (REEs) by secondary phases following the biogeochemical mineral dissolution of quartz-pebble conglomerate originating from Elliot Lake, Ontario. An understanding of the geochemical controls of U and REE dissolution and subsequent retention in authigenic secondary phases following biogeochemical ore dissolution could provide information relevant to the environmental management of mine waste materials and economic element recovery. The retention of U, thorium (Th), REE, and base metals in secondary phases following biogeochemical ore dissolution formed on mineral surfaces, both in terms of their concentration and association with other elements present in the ore, is characterized in this study. The loss of mass of U (87%) from the quartz conglomerate ore is significantly higher than for the associated REE's, reflecting the mobile character of UO22+. A small but significant portion of the uranyl ions (13%) is retained in the ore sample, either as residual uraninite or as uranyl-phosphate complexes and minerals within Fe- and Al-rich surface coatings. The preliminary adsorption of phosphate (PO43−) ions on the surfaces of Al-Fe-(hydr)oxide mineral surface coatings forms negatively-charged surface sites within the porous media of the leached mineral material, providing adsorption sites for positively-charged metal species on the phosphate-bearing surface sites, allowing the formation of either ternary metal-phosphate-Al-Fe-(hydr)oxides complexes or nucleation of metal-phosphates, thus leading to the retention of U, REE, Th, Zn and Pb. Similarly, the observed retention of Pb, Zn, Cu and Ni is explained by the neoformation of authigenic minerals of the jarosite group within the pore spaces of Fe-, Al- and Si-rich coatings.

Geochemistry of Archean Radioactive Quartz Pebble Conglomerates and Quartzites from western margin of Singhbhum-Orissa Craton, eastern India: Implications on Paleo-weathering, provenance and tectonic setting

Lenses of radioactive Quartz Pebble Conglomerates (QPC) and associated quartzites are exposed along western margin of Archean Bonai Granite in Singhbhum-Orissa Craton, eastern India intermittently spreading over a strike length of 8–10km. QPCs are radioactive while quartzites are mostly non-radioactive in nature. The purpose of the research is to investigate and characterize the radioactive QPC and quartzites geochemically to decipher their paleo-weathering conditions, provenance characteristics and possible tectonic setting of deposition. Geochemical data suggest moderate to high chemical weathering conditions in the provenance areas of QPC and quartzites. Major, trace and REE data indicate predominantly felsic to partly mafic-ultramafic sources for the deposition of radioactive Quartz Pebble Conglomerates from the surrounding Archean terrain.Elevated values of Th, U, Pb, La, Ce, Y and low Sc with high critical trace elemental ratios of Th/Sc, La/Sc, Th/Cr and Zr/Sc in radioactive QPC indicate their derivation from felsic igneous source. Low concentration of Th and Sc in quartzites compared to QPC and their variable Th/Sc ratios indicate both felsic and mafic sources for quartzites, albeit their preferential felsic affiliation. Higher Cr/Th ratios in quartzites (18.4), moderate Cr/Th in QPC (5.42), low to moderate Y/Ni in QPC (0.36–12.4) and quartzite (0.29–1.88), along with Au ranging from 30 to 1527ppb, Pt up to 188ppb and 682ppb in QPC and quartzites respectively point towards some contribution from mafic-ultramafic source as well. REE patterns and in particular negative Eu anomalies for both QPC and quartzites further support their derivation from felsic rocks and could possibly linked to some of the phases of Archean Singhbhum Granite and Bonai Granite. Granitic to pegmatitic source for QPC is also revealed by the presence of rounded to sub-rounded monazite, zircon and thorian-uraninite grains in their matrix. Study indicates that QPC and quartzites were deposited in a passive margin tectonic setting developed during Archean between a span of 3.3 and 3.16Ga along the western margin of Bonai Granite when the reducing condition was prevalent as indicated by their low Th/U ratios (<4.0) and presence of detrital grains of uraninite and pyrite in QPC. Radioactive QPC from western margin of Archean Singhbhum-Orissa Craton bears broad resemblance with QPC from Witwatersrand basin of South Africa and Elliot Lake, Canada and thus appears to be ideal sites for exploring QPC hosted U (+Au-PGE) mineralization in the analogous areas.

The Wajid Sandstone around Abha/Khamis Mushayt and in its type area: lithostratigraphic architecture and correlations

The Wajid Sandstone of southeastern Saudi Arabia is a prolific aquifer and a recent target for hydrocarbon exploration, but a sedimentologic model and the stratigraphic architecture of the sediments have only recently been presented for the type area of the Wajid Group around Wadi Dawasir. Farther to the west, the Wajid Sandstone was also recognized, but stratigraphic architecture and sedimentology are poorly known. This paper presents the preliminary results of investigations targeted at the outcrops west and south of the type area, covering the area between Wadi Dawasir, Najran in the south, and Abha in the west. Two successions are recognized, a lower red one and an upper beige one. Although the lower one sedimentologically shares several features with the lowermost unit in the type area, the marine Dibsiyah Formation, a correlation remains doubtful. The red succession lacks the Skolithos fauna of the Dibsiyah Formation, and its facies associations point to a fluvial depositional environment. From its stratigraphic position and from its lithology, the red succession is similar to the Siq Formation of the northern Kingdom and it will be discussed whether the red succession might be a yet unrecognized equivalent of the Siq Formation. The lower red unit is bounded by a major unconformity, separating it from the underlying basement. This pan-African unconformity developed during a latest Neoproterozoic–Cambrian episode of intensive weathering and peneplanation. It is characterized by a thick weathering zone and an overlying coarse but thin quartz pebble breccia to conglomerate, which together represent a regolith. The beige succession is definitely correlated to the Khusayyayn Formation. Both successions are characterized by macro-scale to giant 2D and 3D submarine dunes and share many other phenomena. The basal unconformity also shows regolith development with a quartz pebble conglomerate, whose clasts seem to have been reworked from the pan-African regolith.

Gold and Uranium Occurrences in Quartz-Pebble Conglomerate of Iron Ore Group, Bagiyabahal-Baratangra Area, Sundargarh District, Odisha, India

India is deficient in both gold and uranium resources. Almost one-third of the annual global mine production of ~2500 tonnes of gold is imported into India to fulfil the high gold consumption. Uranium is important for production of nuclear energy, more specifically to execute the country's ambitious programme to generate 20 GW of electricity by 2020.

Mineral chemistry of tourmaline from Mashak Pahar, South Purulia Shear Zone (SPSZ), eastern Indian Shield

The area of investigation at and around Mashak Pahar, Bankura district, West Bengal, India comprises a number of rock types namely: granite gneiss, migmatized quartz tourmaline gneiss, quartz pebble conglomerate, ferruginous quartzite, quartz tourmaline veins (as veins) and graphite schists. Interestingly, the study area lies in the region extending South Purulia Shear Zone (∼Tamar–Porapahar Shear Zone) which marks the boundary between two contrasting tectonic blocks of eastern India, namely, the Chhotanagpur Gneissic Terrane (CGC) to the north and Singhbhum Group of rocks to the south. The rocks of the study area are poly-phasedly deformed by three phases of folding, namely, F1, F2 and F3. All the tourmalines are classified to be of ‘Alkali Group’. Chemistry of tourmalines from migmatized quartz tourmaline gneiss and those from quartz tourmaline veins are in conformity with their relation to (earthquake induced) shear system evolution in this terrain. In general, the compositional evolution of tourmaline during prograde metamorphism (∼400°–730°C) has been supported by both petrographic and chemical evidences. Assessment of mineral–chemical data of constituent tourmaline grains clearly suggests compositional variations across zonal boundaries within tourmaline that was controlled by changing metamorphic milieu in this terrane. Field and petrographic evidences clearly indicate activation of earlier and later shears in this region accompanied by infiltration of boron and formation of zoned tourmaline crystals.

Two Types of Archaean Supracrustal Belts in the Bundelkhand Craton, India: Geology, Geochemistry, Age and Implication for Craton Crustal Evolution

Abstract: Two Archaean supracrustal complexes are documented in the Bundelkhand craton viz. 1) the Central Bundelkhand greenstone complex (formed the Babina and Mauranipur belts), and 2) the Southern Bundelkhand metasedimentary (paragneisses, schists) complex (formed the Girar belt). The Central Bundelkhand greenstone complex consists of (i) an early assemblage composed of basic-ultrabasic, felsic volcanics, banded iron formation (BIF), and (ii) a late assemblage which contains felsic volcanics. The U-Pb zircon ages of felsic volcanics from the early assemblage, formed in an arc-type subduction setting, are 2813 Ma (Mesoarchaean). The U-Pb zircon ages of felsic volcanics from the late assemblage, which also occur in subduction settings as an active continental marginal type, are 2542 Ma (Neoarchaean). The Girar belt, located in the southern part of the craton, consists generally of metasedimentary rocks namely quartzites and BIFs. Quartzites are represented by fuchsite- and hematite-bearing quartz arenite and lesser quartz pebble conglomerates that have been subjected to low-grade metamorphism. BIF is represented by thinly-bedded quartz–hematite (±magnetite) rocks. Some lenses of marble and chlorite schist are present at the contact between the two formations. BIF is fairly rich in Cr and Ni, poor in Zr, Hf, Ba, Th, Sr, Yb and Lu, and displays a distinct positive Euanomaly (Eu/Eu* = 1.14-2.46). Zircons from quartzites give two U-Pb ages: 3432±9.7 Ma and 3252±6.4 Ma. The Sm-Nd isotope study of quartzite from the Girar belt shows that the TDM is 3.29 Ga. This TDM correlates well with the U-Pb ages of zircon and indicates that the continental crust in the Girar area began to form in the Paleoarchaean (3.4-3.2 Ga). The Central Bundelkhand greenstone complex was thus formed in a subduction-accretion setting in Mesoarchaean (ca 2.8 Ga) and Neoarchaean (2.54 Ga) time, and the Southern Bundelkhand metasedimentary complex originated in a sedimentary basin on the old continental crust apparently at ca ~ 2.7 Ga.

Uranium in South Africa: Exploration and Supply Capacity

The major uranium deposits types are quartz-pebble conglomerate of the Central Rand Group (Witwatersrand Supergroup) and the Dominion Group, sandstone of the Karoo Uranium Province, surficial deposits of the Namaqualand region, as well as coal of the Springbok Flats Basin. Recent exploration activities (both greenfields and near-mine) have increased the resource potentials of these deposits. South Africa's Council for Geoscience has conducted high resolution magnetic and radiometric surveys in the Namaqualand region. Witwatersrand Basin is the only deposit where uranium mining is active at present in South Africa. Total uranium production in 2015 was 448 t. However, with production expected to increase in the Witwatersrand Basin, production is expected to reach 700 t U by the end of 2018. Furthermore, with uranium production envisaged to begin in the Karoo Uranium Province, uranium production may exceed 1000 t U by the year 2020.

Gold nugget morphology and geochemical environments of nugget formation, southern New Zealand

Gold nuggets (centimetre scale) have formed in a supergene alteration zone on hydrothermal gold deposits, and occur intergrown with quartz and iron oxyhydroxide pseudomorphs after sulphide minerals, and along fractures in quartz and host rocks. The supergene alteration was driven by groundwater-driven water-rock interaction near to a regional unconformity beneath fluvial sediments, and involved clay alteration and oxidation that extended up to 50m below the unconformity. Oxidation of pyrite and arsenopyrite produced temporary thiosulphate ligands that mobilised microparticulate gold encapsulated in the sulphide minerals. The nuggets have some crystalline form, and internally they consist of anhedral grains, elongated gold plates, and intimate intergrowths of gold and iron oxyhydroxide. Nugget surfaces have further micron scale overgrowths of microparticulate gold, gold plates, and gold crystals. Nuggets were eroded and recycled into nearby proximal Miocene quartz pebble conglomerates, where they concentrated in placers near the basal unconformity. Later recycling transferred gold into Pleistocene fluvial channels. Gold dissolution and redeposition as plates and crystals occurred on the exterior surfaces of placer gold particles, with little change in mass. All groundwater maintained high pH throughout the geological history because there was sufficient calcite in the basement rocks to neutralise any acid generated by pyrite oxidation. Hence, gold mobility in sediments was driven by thiosulphate complexes as for the in situ nuggets, albeit with lower dissolved sulphur concentrations. Despite aridification of the climate in the late Cenozoic, with resulting localised high dissolved chloride concentrations, chloride complexation did not contribute to gold mobility.

Seismic exploration of the world’s deepest gold and platinum orebodies in South Africa - Overview of the past, present and a look into the future Minerals keynote paper

Without doubt, the geologically complex Witwatersrand Basin in South Africa is by far the most important known gold-producing province. It has produced about one-third of the gold ever mined, worldwide. Gold mining in the goldfields takes place at depths ranging from 500 to 4200 m below surface. Many call the underground workings the 'devil's workplace'. This means that there are an increasing number of technical challenges in exploration and optimizing new resources, with rising costs and reduced effective mine designs. There are about 20 or more gold ore bodies (quartz pebble conglomerates) that have been mined, or are currently in production. Furthermore, the Bushveld Complex of South Africa is estimated to contain about 70% of the world's reserves of platinum group elements. The most important platinum ore bodies are the Merensky Reef and the UG2. This paper presents the past and current research activities on the use and implementations of seismic methods for gold and platinum exploration and deep mine planning and designs. It, particularly, presents a state-of-the-art in seismic design and acquisition, processing, interpretation of the seismic data as well as modelling of strato-structural complexies of the basin using advance techniques. The current challenges and possible future solutions are further discussed with special emphasis on the reflection seismic imaging limitations. For example, reflection seismic data acquired on the surface in the Witwatersrand Basin and Bushveld Complex have wavelengths of approximately 60-100 m, providing vertical seismic resolution of approx. 20 m. Consequently, it is difficult to resolve the top and bottom of thin reefs (~ 1m in thickness) due to seismic wave interference as well as to detect faults with throws less than 20 m. However, gold reefs as thin as 20 cm to 1m are currently the main targets for deep mining and faults that crosscut these reefs with throws as small two meters may present difficulties to deep future mining operations. Recent research work has further demonstrated that some of these minor faults may act as conduits for ingress of water and flammable gas into underground workings. There has been more of hard-rock reflection seismics undertaken in South Africa than anywhere else in the world. Therefore, this paper attempts to answer the following trickier question: Will seismic application in the mining industry in South Africa accelerate or decline in the coming years?

The origin of the gold and uranium ores of the Black Reef Formation, Transvaal Supergroup, South Africa

The Black Reef Formation is a laterally extensive sedimentary succession at the base of the Transvaal Supergroup. The quartz-pebble conglomerates host erratic concentrations of gold and uranium; however, in areas that are located spatially above the gold and uranium-bearing reefs of the Witwatersrand Supergroup, the concentrations can reach ore-grade. Although the depositional environment was similar to that of the Witwatersrand Supergroup, the processes that lead to the high gold and uranium concentrations in the Black Reef were quite different. The Black Reef experienced intense, post-depositional hydrothermal alteration by circulating aqueous and hydrocarbon fluids (oils) that deposited large volumes of native gold, uranium minerals and pyrobitumen. The gold, which is filamentous, is concentrated along As–Ni-rich surfaces of pyrite, and with uraninite in pyrobitumen. In both environments, the gold is interpreted to be the product of chemically-triggered precipitation from hydrothermal fluid(s). The uraninite occurs either as precipitates in pyrobitumen or is “invisible” in the pyrite, occurring as nanoparticles in this mineral. This indicates that conditions were sufficiently oxidizing for the hydrothermal transport of uranium, and contrasts with the case for the Witwatersrand reefs where much of the uranium is detrital. Luminescent radiation damage associated with vein quartz and pyrobitumen, as well as the diffuse distribution pattern of uranium in the pyrobitumen may indicate that some uranium was transported by liquid hydrocarbons. Pyrite in the Black Reef (sedimentary, detrital and hydrothermal pyrite) is highly enriched in gold, uranium and other redox-sensitive trace elements. Provenance analyses using the trace element compositions of the pyrite show that it was not the result of erosional reworking of the underlying Witwatersrand Reefs. However, the close spatial association of high gold and uranium concentrations in the Black Reef with ore-bearing Witwatersrand reefs suggests strongly that gold and uranium, whether in pyrite or occurring as native gold and uraninite, were hydrothermally recycled (uranium may have been recycled by hydrocarbon fluids) from the Witwatersrand Reefs.

Uraniferous paleoplacers of the Mesoarchean Mahagiri Quartzite, Singhbhum craton, India: Depositional controls, nature and source of > 3.0 Ga detrital uraninites

The quartz-pebble conglomerate (QPC)-hosted detrital uranium mineralization is unique in character in terms of their restricted distribution before 2.2Ga atmosphere during pre-Great Oxidation Event (pre-GOE). Such QPC paleoplacer deposits over the world are good targets for moderate to high tonnage and low grade uranium deposits and more importantly for their gold content. The Mahagiri Quartzite, dated c. 3.02Ga for their youngest detrital zircon population, is developed unconformably over the Mesoarchean Singhbhum Granite (3.44Ga to 3.1Ga). The Mahagiri Quartzite includes a conglomerate-pebbly sandstone dominated subaerial alluvial fan to coastal braided plain sequence in the lower parts and shallow marine mature quartz arenite in the upper parts. The alluvial fan-braided plain deposits in the lower parts host a number of pyritiferous and uraniferous conglomerate and pebbly sandstone beds. The uraninite grains are rounded to subrounded in outline suggesting mechanical transport and detrital origin. Together with detrital pyrite and uraninite constitute the example of >3.0Ga paleoplacer closely comparable to the Witwatersrand Au–U deposits. EPMA and SEM-EDS studies suggest that the uraninite grains are rich in Th (>4wt.%), S and REE-Y. Chemical formula calculations from EPMA analyses suggest uraninite grains belong to two populations with different oxidation states as revealed from Y/REE and cation U4+: U6+ [apfu] ratios. The U contents of the detrital uraninite grains from Mahagiri are significantly lower than that of the ideal stoichiometric composition of UO2. This is mainly due to higher amount of heterovalent cationic substitution by Th, REE, Y, Pb, and Ca in Mahagiri QPC uraninite structures, and partial alteration and metamictization of uraninites. Alteration due to metamictization resulted in elevated concentration of Si, Al, P, and Ca in more altered and metamict uraninite grains. The REE pattern is typically flat with comparable LREE–HREE concentration. The high Th content flat REE-pattern suggests that the uraninitere presents high temperature phases (>350°C) and are magmatic in origin. The Mahagiri detrital uraninite grains suggest existence of highly felsic and K-rich (richer than TTG) granodiorite–granite–monzogranite suites (GGM) of rocks older than 3.1Ga in the Singhbhum craton.

A Preliminary Biogeochemical Study over the Uraniferous Quartz-Pebble—Conglomerate Zone near Kalasapura, Chickmagalur District, Karnataka, Southern India

Quartz-pebble-conglomerate (QPC) bearing unconformable zone at the base of Bababudan Group of rocks in Dharwar Craton in southern India is well known for its stratigraphic significance and uraniferous nature. Over this QPC zone, soil cover is very thin which is almost devoid of vegetation. A cursory biogeochemical study here indicated poor (170 to 520 ppb) uranium content in the scantily occurring herbs and shrub species as well as in the soil substratum (1.8 - 3.1 ppm). The values in plant species are much below the background values. Almost barren nature of soil surface and stunted growth of herb and shrub species suggested that geobotanical rather than biogeochemical study is more serviceable as a clue for the hidden QPC-type horizons, which quite often bear signatures of uranium mineralization.

Variations in the uranium isotopic compositions of uranium ores from different types of uranium deposits

Variations in 238U/235U and 234U/238U ratios were measured in uranium minerals from a spectrum of uranium deposit types, as well as diagenetic phosphates in uranium-rich basins and peraluminous rhyolites and associated autunite mineralisation from Macusani Meseta, Peru. Mean δ238U values of uranium minerals relative to NBL CRM 112-A are 0.02‰ for metasomatic deposits, 0.16‰ for intrusive, 0.18‰ for calcrete, 0.18‰ for volcanic, 0.29‰ for quartz-pebble conglomerate, 0.29‰ for sandstone-hosted, 0.44‰ for unconformity-type, and 0.56‰ for vein, with a total range in δ238U values from −0.30‰ to 1.52‰. Uranium mineralisation associated with igneous systems, including low-temperature calcretes that are sourced from U-rich minerals in igneous systems, have low δ238U values of ca. 0.1‰, near those of their igneous sources, whereas uranium minerals in basin-hosted deposits have higher and more variable values. High-grade unconformity-related deposits have δ238U values around 0.2‰, whereas lower grade unconformity-type deposits in the Athabasca, Kombolgie and Otish basins have higher δ238U values. The δ234U values for most samples are around 0‰, in secular equilibrium, but some samples have δ234U values much lower or higher than 0‰ associated with addition or removal of 234U during the past 2.5Ma.These δ238U and δ234U values suggest that there are at least two different mechanisms responsible for 238U/235U and 234U/238U variations. The 234U/238U disequilibria ratios indicate recent fluid interaction with the uranium minerals and preferential migration of 234U. Fractionation between 235U and 238U is a result of nuclear-field effects with enrichment of 238U in the reduced insoluble species (mostly UO2) and 235U in oxidised mobile species as uranyl ion, UO22+, and its complexes. Therefore, isotopic fractionation effects should be reflected in 238U/235U ratios in uranium ore minerals formed either by reduction of uranium to UO2 or chemical precipitation in the form of U6+ minerals. The δ238U values of uranium ore minerals from a variety of deposits are controlled by the isotopic signature of the uranium source, the efficiency of uranium reduction in the case of UO2 systems, and the degree to which uranium was previously removed from the fluid, with less influence from temperature of ore formation and later alteration of the ore. Uranium isotopes are potentially superb tracers of redox in natural systems.

Felsic magmatism and uranium deposits

Abstract The strongly incompatible behaviour of uranium in silicate magmas results in its concentration in the most felsic melts and a prevalence of granites and rhyolites as primary U sources for the formation of U deposits. Despite its incompatible behavior, U deposits resulting directly from magmatic processes are quite rare. In most deposits, U is mobilized by hydrothermal fluids or ground water well after the emplacement of the igneous rocks. Of the broad range of granite types, only a few have U contents and physico-chemical properties that permit the crystallization of accessory minerals from which uranium can be leached for the formation of U deposits. The first granites on Earth, which crystallized uraninite, dated at 3.1 Ga, are the potassic granites from the Kaapval craton (South Africa) which were also the source of the detrital uraninite for the Dominion Reef and Witwatersrand quartz pebble conglomerate deposits. Four types of granites or rhyolites can be sufficiently enriched in U to represent a significant source for the genesis of U deposits: peralkaline, high-K metaluminous calc-alkaline, L-type peraluminous and anatectic pegmatoids. L-type peraluminous plutonic rocks in which U is dominantly hosted in uraninite or in the glass of their volcanic equivalents represent the best U source. Peralkaline granites or syenites are associated with the only magmatic U-deposits formed by extreme fractional crystallization. The refractory character of the U-bearing minerals does not permit their extraction under the present economic conditions and make them unfavorable U sources for other deposit types. By contrast, felsic peralkaline volcanic rocks, in which U is dominantly hosted in the glassy matrix, represent an excellent source for many deposit types. High-K calc-alkaline plutonic rocks only represent a significant U source when the U-bearing accessory minerals (U-thorite, allanite, Nb oxides) become metamict. The volcanic rocks of the same geochemistry may be also a favorable uranium source if a large part of the U is hosted in the glassy matrix. The largest U deposit in the world, Olympic Dam in South Australia is hosted by highly fractionated high-K plutonic and volcanic rocks, but the origin of the U mineralization is still unclear. Anatectic pegmatoids containing disseminated uraninite which results from the partial melting of uranium-rich metasediments and/or metavolcanic felsic rocks, host large low grade U deposits such as the Rössing and Husab deposits in Namibia. The evaluation of the potentiality for igneous rocks to represent an efficient U source represents a critical step to consider during the early stages of exploration for most U deposit types. In particular a wider use of the magmatic inclusions to determine the parent magma chemistry and its U content is of utmost interest to evaluate the U source potential of sedimentary basins that contain felsic volcanic acidic tuffs.

English

&nbsp; The present study has dealt with the field and microscopic description of different building, industrial and ornamental stones of the Tertiary sedimentary succession of Haddat Ash Sham area, Saudi Arabia. The described building and ornamental stones includes: quartz pebble conglomerates, sandstones, limestones, dolostones and clays. The stratigraphic setting, mega and microscopic description of the different types of building and ornamental stones revealed the predominance of the quartz-pebble conglomerates in the lower and upper members of the Tertiary succession of the study area while the clays and carbonates are present in the middle member of this succession. The quartz pebble conglomerates represents the most important building material which is mostly suitable for concrete industry while the sandstones are present as very thick hard ferruginous cliffs suitable for dimensional blocks for facing and decoration. The carbonates are represented by relatively thin horizons of limestone and dolostones which is easily extracted and used for concrete industry. The clay deposits are present in many levels within the sedimentary succession of Haddat Ash Sham area and represent the same extensions of the clay quarries used for brick industry in Ash Shamiyah area west of Haddat Ash Sham area. The studied building and ornamental stones need further engineering tests and measurements for the accurate evaluations from the engineering points of views. The reserves of the clay deposits must be evaluated from the economic points of views for cement and ceramic industries. &nbsp; Key words:&nbsp;Saudi Arabia, Haddat Ash Sham area, building and ornamental stones, quartz pebble conglomerates and concrete materials.

River drainage reorientation during placer gold accumulation, southern New Zealand

Many alluvial placer deposits around the world occur in river systems that have been affected by tectonic events, causing drainage reorientation and severance of links between placers and their sources. This study documents tectonic rejuvenation of topography in the Otago giant placer goldfield, New Zealand, which has resulted in numerous river capture and drainage reorientation events. These events have induced changes to gold transport directions and numerous stages of separation of detrital gold from primary sources. Goldfield-wide reconstructions of drainage patterns through time are as yet only possible for Miocene–Recent, and numerous earlier drainage changes back to Cretaceous primary orogenic mineralisation are probable. Variations in basement lithologies permit auriferous gravel provenance determinations, facilitating paleodrainage pattern reconstruction and documentation of river capture events. River capture events and timing of these events for gold-bearing paleodrainages have also been documented using genetic divergences of populations of freshwater galaxiid fish that were isolated by drainage reorientation. Gold-bearing quartz pebble conglomerates had a southeastward drainage in the Miocene. This was disrupted in the Pliocene by mountain range uplift and gold placer recycling, with deposition of lithic conglomerates containing only minor gold placers. The most dramatic changes in gold transport directions occurred through the Quaternary, as antiformal ranges grew across the pre-existing drainages. Miocene and Pliocene placers were recycled with numerous local (1–10 km scale) changes in river directions and numerous capture events. Large axial rivers were segmented into a more complex drainage pattern, and on-going river capture resulted in growth of the main Clutha River catchment at the expense of neighbouring catchments. The most productive placers developed in the Clutha River in late Quaternary when increased discharge from captured mountain catchments enhanced gold transport and concentration. Similar river drainage reorientation has occurred in other placer fields around the world, but the lack of preserved evidence inhibits documentation of most such changes.

Petrography and geochronology of the Pele Mountain quartz-pebble conglomerate uranium deposit, Elliot Lake District, Canada

Uranium deposits older than about 2200 Ma are generally hosted within quartz-pebble conglomerates and are a source of economic uranium. The genesis of these deposits is controversial and genetic models include hydrothermal, detrital/placer, and modified placer. Petrography of the uranium mineralogy from the Pele Mountain quartz-pebble conglomerate uranium deposit of the Elliot Lake district, Canada, shows that the dominant uranium minerals are thorite [(Th,U)SiO4] and brannerite [(U,Ca,Ce)(Ti,Fe)2O6]. Uranium-lead (U-Pb) and lead-lead (Pb-Pb) isotopic analyses of thorite, brannerite, and galena were obtained using secondary ion mass spectrometry. Thorite has U-Pb age of 2489 ± 24 in the quartzose conglomerate and 280 ± 67 Ma in the quartz arenite. Brannerite has a U-Pb age of 2403 ± 120 Ma. Thorite Pb-Pb ages range from 521 ± 19 to 248 ± 8 Ma in the arenite and from 2453 ± 12 to 935 ± 27 Ma in the conglomerate, whereas brannerite Pb-Pb ages are between 1335 ± 0.11 and 848 ± 13 Ma. Galena has a Pb-Pb age of 2659 ± 8 Ma, which likely represents the age of the source formation that produced detrital galena. The rounded texture and U-Pb age of the conglomerate thorite corresponds to the depositional age of the host conglomerate bed of the Matinenda Formation, suggesting a detrital origin. The young U-Pb age of the thorite in the arenite represents the age of a resetting event. The brannerite, which replaces rutile, has a U-Pb consistent with fluid events associated with the Blezardian or Penokean Orogenic events, and is likely of hydrothermal origin. Therefore, based on the textures and variable ages of the uranium and sulfide minerals, the Pele Mountain quartz-pebble conglomerate uranium deposit is interpreted to be a modified placer-type deposit.

Attribution of uranium ore concentrates using elemental and anionic data

Abstract The capability to correctly identify the geological or geographical source of unknown uranium ore concentrates (UOCs) has obvious nuclear security benefits. This paper reports on a scoping study where the trace elemental and anionic compositions of 24 UOC samples, sourced mainly from mines in Australia and Canada, were examined for their ability to allow attribution of the sample to a particular geological U deposit type or to a particular geographical source. Results of statistical analysis using canonical analysis of principal coordinates (CAP) showed that samples originating from certain U ore deposit types, especially phosphorite and quartz-pebble conglomerate, contained a distinct impurity composition. Samples grouped according to their geographical region of origin appeared to contain distinctive impurities in certain cases (Elliot Lake and Bancroft, Ontario). The key impurities responsible for differentiating groups of samples from a particular geological deposit type were identified and the use of certain impurities as signatures of processing history is discussed. The methodology described in this scoping study provides a promising approach for more comprehensive databases.

Genetic implications of rare uraninite and pyrite in quartz-pebble conglomerates from Sundargarh district of Orissa, Eastern India

Petrographic and EPMA studies reveal the presence of discrete grains of uraninite and pyrite are being reported for the first time in quartz-pebble conglomerates from western margin of Bonai granite pluton, Sundargarh district, Orissa. Uraninite grains (2–3 μ in size) are subrounded to muffin shaped which show variation in UO2 (63.86 to 71.73 wt %), ThO2 (5.48 to 6.42 wt %) and RE2O3 (1.57 to 2.23 wt %). Pegmatitic source of uraninite is revealed by comparing UO2, ThO2, PbO, CaO content and ratios of UO2/ThO2 and CaO/ThO2 in uraninites from pegmatite and other environments and areas. Subrounded to muffin shape of uraninite, their association with subrounded pyrite and heavies like zircon, tourmaline, chromite, monazite, magnetite and their comparable chemistry with well established quartzpebble conglomerates of India and world are indicative of their detrital origin. Pyrite, minor chalcopyrite and rare galena are observed as sulphide phases in conglomerate. Variable shapes of pyrite, their low Co (up to 0.16 wt %) and Ni contents (up to 0.09 wt %) and Co/Ni ratio less than 1.0 (mean= 0.63) favours sedimentary/diagenetic origin.