Search Results (6)

Expanding anthropogenic activities, globally and in Egypt, have increased concentrations of heavy metals in surface and ground waters. Contamination of drinking water may threaten public health. In the present study, the concentrations of 10 heavy metals were analyzed from natural springs (6) and drilled wells (10) in the Nubian Sandstone Aquifer of the El-Farafra Oasis and the White Desert National Park, Egypt. The average concentrations of heavy metals were in most cases below critical values of the WHO drinking water standard, except for Fe and Mn (average values were 495 and 107 µg·L⁻¹, respectively). There is a surface circulation that develops within limestone (Post-Nubian Aquifer System—PNAS) and feeds the springs, while the water present in the wells (at least for the deeper ones) comes from the ferruginous sandstone (Nubian Sandstone Aquifer System—NSAS). This double circulation could account for the differences in the EC and TDS values (typical of a circulation in limestone-type aquifers for springs) and the Fe and Mn enrichment coming from the ferruginous sandstone of the NSAS. The average chronic daily intake (CDI) values for heavy metals in the study area are listed in decreasing order in the following: Fe > Mn > Zn > Co > Ni > Cr > As > Pb > Co > Cd. The total hazard quotient (HQ_total = HQ_oral + HQ_dermal) and Hazard Index (HI) values calculated for different heavy metals were well below the acceptable limit, indicating no significant non-carcinogenic health risks to the residents of both areas via oral and dermal absorption of drinking water. Furthermore, the results obtained for the total risk to human health showed that oral ingestion is the major pathway. Carcinogenic risk analysis indicated that the Incremental Lifetime Cancer Risk (ILCR) values for Pb, Cd, Ni, and Cr were well below the acceptable limits. Full article

Uranium anomalies were discovered in ferruginous sandstone in the Khusayyayn Formation of the Wajid Group in southern Saudi Arabia. Based on field surveys, ground radiometric surveys, and chemical analysis, this paper summarizes the characteristics of the lithology and lithofacies of the ferruginous sandstone and analyzes the genetic mechanism of uranium concentration in ferruginous sandstone. Ferric iron basically exists in the form of Fe₂O₃ in ferruginous sandstone, with an average content of 28.95 wt.%. The formation period of the ferruginous sandstone occurred during the early synsedimentary and later diagenesis stages from the Carboniferous to the Devonian. The uranium anomaly is hosted in thin-bedded and lenticular ferruginous sandstone, with a uranium content ranging from 50 to 766 ppm. The average U-Ra equilibrium coefficient of ferruginous sandstone was 1.00, indicating that the uranium was weakly reformed after the uranium concentration. Ferric ions are closely related to uranium mineralization. The initial concentration of the uranium occurred during the deposition of the ferruginous sandstone. Most of the uranium was adsorbed by a ferric colloidal solution, and part of it was reduced by Fe²⁺, organic carbon, and sulfur in the uranium preconcentrated stage during the deposition of ferruginous sandstone. The uranium ore was superimposed, transformed, and concentrated due to the change in the pH environment in the early Neogene. Full article

Generalization of the results of the study of placer gold and the mechanisms of its distribution in the east of the Siberian Platform made it possible for the first time to reveal that the ore sources of gold-bearing placers were mainly mineralization of the gold-sulfide formation formed under the influence of hydrothermal metasomatic processes occurred in deep fault zones. It is determined that the gold-bearing hydrothermal-metasomatic formations of the gold-sulfide rock formation are amagmatic, near-surface, low-temperature and spatially confined to deep faults. These formations are widespread in terrigenous-carbonate strata and sand deposits of PZ-MZ age and are observed in the zones of brecciation, silicification, and ferruginization. The analysis of the mechanisms of distribution of hydrothermal-metasomatic gold-bearing formations in the east of the Siberian Platform, based on previously conducted research of predecessors and our field observations, allowed us to establish the following. In the northeast, hydrothermal-metasomatic formations occur in the field of development of the Zhigansky fault, the Molodo-Popigai and Anabar-Eekite fault system, in the central part of the east of the Siberian Platform, the Vilyui paleorift (Kempendyai dislocations), and in the southeast in the Baikal-Patom thrust belt in ancient faults (Bappagai, Khorinsky, etc.). Metasomatites of hydrothermal origin form extended narrow formations along ancient faults activated in the Mesozoic, as well as conformable deposits in the Vendian, Cambrian carbonate strata, Jurassic and Cretaceous sandstones. It is proved that these formations are amagmatic and are not related to the widespread magmatism of the basic composition, which is confirmed by the homogenous mineral composition of metasomatites, independent of the composition of magmatic bodies spatially located with them. Zones of metasomatites with gold mineralization contain Au from 0.5 to 3.0 g/t, and in isolated cases up to 24–32 g/t. Gold is represented from finely-dispersed to visible fine, with a size from 0.01 to 0.5 mm or more. It is known that hydrothermal-metasomatic processes on the territory of Central Aldan contributed to the formation of large deposits such as Kuranakh, Tabornoye and others. It is possible that the identified gold-ore metasomatites, developed along the zones of regional faults and not confined to magmatic formations, widely occurred both in the northeast and in the southeast of the Siberian Platform, represent a huge metallogenic potential. Full article

Ferruginous nodules and pisoliths that cap deeply weathered profiles and transported cover are characteristic of the Yilgarn Craton, Western Australia. Here we show how ferruginous nodules and pisoliths formed in the paleochannel sediments during Miocene can be used to locate buried Au mineralization. Three types of ferruginous nodules and pisoliths were identified in paleochannel sediments and saprolite, representing different parent materials and environments covering the Garden Well Au deposit: (i) ferruginous nodules formed in saprolite on the flanks of the paleochannel (NSP), (ii) ferruginous pisoliths formed in the Perkolilli Shale in the middle of the paleochannel (PPS) and (iii) ferruginous nodules formed in the Wollubar Sandstone at the bottom of the paleochannel (NWS). The appearance, mineralogy and geochemistry of ferruginous nodules and pisoliths vary according to their origin. The PPS and NWS are goethite-rich whereas NSP is a mixture of goethite and hematite which make them all suitable for (U–Th)/He dating. The average age of goethite in the NSP is 14.8 Ma, in the NWS is 11.2 Ma and in the PPS is 18.6 and 14 Ma. The goethite ages in ferruginous nodules and pisoliths are thought to be younger than the underlying saprolite (Paleocene-Eocene) and were formed in different environmental conditions than the underlying saprolite. Anomalous concentrations of Au, As, Cu, Sb, In, Se, Bi, and S in the cores and cortices of the NWS and the PPS reflect the underlying Au mineralization, and thus these nodules and pisoliths are useful sample media for geochemical exploration in this area. These elements originating in mineralized saprolite have migrated both upwards and laterally into the NWS and the PPS, to form spatially large targets for mineral exploration. Full article

The sandstones with a laminated structure are common building materials. Lamination is macroscopically expressed as colour and grain size variations observed both in the deposit and within individual beds; therefore, the properties of such sandstones are diverse depending on the spatial distribution of the binding mass and framework components. For the terrestrial sandstones of different genesis, four types of laminae have been distinguished based on petrographic studies. They have a siliceous binder or a mixed ferruginous–siliceous–argillaceous binder with different proportions of these components. In laminae of types I–III, the grain framework is built mainly of quartz grains, and in type IV, it is accompanied by numerous lithoclasts and feldspars. Knoop hardness and CERCHAR abrasivity were tested in each lamina variety, and the results were correlated with the equivalent quartz content and the longitudinal ultrasonic wave velocity measured perpendicular and parallel to the lamination. The proposed research methodology was not used in previous studies on terrestrial laminated sandstones. The results explain a strong dependence between mineral composition, structure of laminae, and technical parameters of rocks. The knowledge of this relationship facilitates the selection of rocks that meet the relevant technical requirements and helps to optimally manage the resources of sandstone deposits. Full article

A sandstone outcrop exposed to freshwater seepage supports a diverse assemblage of photosynthetic microbes. Dominant taxa are two cyanophytes (Oscillatoria sp., Rivularia sp.) and a unicellular green alga (Palmellococcus sp.). Less abundant taxa include a filamentous green alga, Microspora, and the desmid Cosmarium. Biologic activity is evidenced by measured levels of chlorophyll and lipids. Bioassay methods confirm the ability of these microbes to dissolve and metabolize Fe from ferruginous minerals. Chromatographic analysis reveals citric acid as the likely chelating agent; this low molecular weight organic acid is detectable in interstitial fluid in the sandstone, measured as 0.0756 mg/mL. Bioassays using a model organism, Synechoccus elongates strain UTEX 650, show that Fe availability varies among different ferruginous minerals. In decreasing order of Fe availability: magnetite > limonite > biotite > siderite > hematite. Biotite was selected for detailed study because it is the most abundant iron-bearing mineral in the sandstone. SEM images support the microbiologic evidence, showing weathering of biotite compared to relatively undamaged grains of other silicate minerals. Full article