Geology, geochemistry, and copper occurrences of the Mid Proterozoic Gateway Formation (member A of Kintla formation), Purcell Supergroup, SW. Alberta and SE. British Columbia, Canada

The lower 650 to 2000 feet of the Gateway Formation of the Mid Proterozoic Purcell Supergroup in SW Alberta and SE British Columbia consists of oxidized, alluvial, red, fine to medium-grained sandstones. A 4 to 35 foot thick gray-green bed located in the upper middle part of the redbed sequence is the focus of this study. The gray-green unit may be subdivided into three subunits based on mineralogy, geochemistry and, therefore, rock type. Subunit A, the lower part of the unit, is 0 to 4 feet thick and marks the beginning of a reducing environment. This subunit consists of slightly metamorphosed, calcarous siltstone and argillites. Subunit B consists of 2 to 8 feet of argillaceous dolomite, siltstone and micrite. Subunit C represents the upper part of the reduced unit and is composed mostly of argillaceous, micritic dolomite and some siltstone. Sedimentary structures such as ripple marks, intraclasts, peloids, desiccation cracks, and possibly stromatolites indicate a sedimentary regime that comprised a tidal flat environment fringing an arid shoreline. Other common sedimentary features such as water escape structures, load casts, and heavy minerals sagging are the result of late stage sediment deformation. Cu mineralization ranges from background ($\u3c$100 ppm) to about 0.5% and is hosted by the gray-green unit, particularly subunit B, where Ba and Mo concentrations are high. Within the unit P\sb2O\sb5 increases upward, but Zr, Fe, Hg, Zn, and V decrease. Se show no significant variation. Geochemical study shows that TiO\sb2, Hg, Zn and B are concentrated in the mica fraction of the rock. Ore petrography reveals veinlets and disseminated chalcocite (Cu\sb2S) and/or digenite (Cu\sb{1.8}S); bornite (Cu\sb5FeS\sb4), covellite (CuS) and blue-remaining covellite (Cu\sb{1.28}S). Electron microprobe analysis shows that chalcocite is intergrown with djurleite (Cu\sb{1.96}S) and anilite (Cu\sb{1.75}S). Commonly, chalcocite replaces bornite and covellite and sulfides replace primary quartz and carbonate minerals. Sulfide distribution, replacement textures, and relationship of sulfides to the host rocks support a diagenetic model for the origin of copper sulfides in the Gateway Formation

Mobilization and Redistribution of Elements in Laterites of Semail Ophiolite, Oman: A Mass Balance Study

Several samples of laterites were collected from four paleosol profiles, Ibra, East Ibra, Al-Russayl, and Tiwi representing the vertical lithological variation within each profile. The mineralogical and geochemical composition of laterites in every section revealed differences in thickness and redistribution of elements reflecting different conditions of weathering processes. Elemental mass balance was calculated for every profile relative to the parent rock. The results indicated redistribution of elements from the surface to deeper zones with an enrichment of elements in the saprolite and oxide zones. Among the different sections, the profile of East Ibra composite 1 and 2 is characterized by high concentration of all elements compared to the other profiles. Sc/Fe ratio in different zones indicates low values for the profile of Tiwi profile 1, Ibra profile and Al-Russayl composite 2 and 3 profile due to the significant enrichment of Fe in these zones independently of redox conditions. Large fluctuations characterize Th/U ratios and reflect redox condition more reduced in Tiwi area than in East Ibra and Al-Russayl areas

Radiometric Surveys for Detection of Uranium in Dhofar Region, Sultanate of Oman

The Proterozoic basement of the Dhofar region of the Sultanate of Oman might be considered as a potential source of Uranium mineralization like other Proterozoic basins of the world, which collectively contribute 30%-40% to the global production.  Uranium exploration assumes great importance in this part of the world and therefore geochemical and geophysical exploration for Uranium was initiated.  Initial, random sampling of the study area with Gamma ray spectrometry as well as in situ XRF (Xray Florescence) analysis indicated the presence of   around 30-40 ppm of Uranium. Since Gamma ray spectrometry results in the calculation of the heat produced during radioactive decay of Potassium (K), Uranium (U) and Thorium (Th) within the rocks in the study area, measurements were acquired along eleven traverses of varying length from 100-250 m at a traverse interval of 20 m and sampling interval of 10 m. Individual plots of the concentrations  of radioelements such as U, K and Th have shown favorable anomalous radioactive sources. Besides this, Uranium to Thorium (eU/eTh) and Uranium to Potassium (eU/K) ratio plots have been presented and the alteration zones associated with Uranium mineralization through all traverses have been identified. Further, the generated composite ternary image based on the combination of K, Th and U from Gamma ray spectrometry determines different relative amounts of radioelements and paves the way for deciphering the level of radioactivity in the study area. However, there seems to be no presence of strong Uranium anomalies in the near surface of the limited study area. As the study area is heavily faulted, the depth to concealed  subsurface fault structures  is  estimated to be around  64 m based on Hartley spectral analysis of total magnetic anomaly (line-6).

Aspects of U-Th fractionation in Tertiary limestones and calcretes of Dhofar, southern Oman

This paper presentsfindings from a comprehensive geochemical and geophysical re-examination of knownradiogenic anomalies in Tertiary limestones and (sub-)recent calcretes of southwestern Dhofar in the Sultanate ofOman. U-Th-enrichments seem to be associated with deep-rooted fault systems that cross-cut Corg-rich shales atdepths of some 800–1000 m, which generally show elevated gamma-ray levels in southern Oman and act as theinitial geochemical trap. Metals and radiogenic elements, such as K (max 1945 ppm), U (max 44 ppm), and Th(max 26 ppm) mobilised from these rocks and emplaced higher up in the faults must have constituted radiogeniclineaments at and near the surface (observed in a different but difficult to access location). However, successiveweathering partially obscured such anomalies through further re-mobilisation/-mineralisation processes withinthe calcretes that also enriched Sr and V. In these carbonates, uranium correlates positively with Sr but not verywell with V, while thorium shows moderate positive correlations with Sr and V. Both U and Th are also notpresent (i.e., below the detection limits of a few ppm) in a second sample group that represents backgroundconditions. Being much more immobile than U, Th remained closer to the original western fault positions of theexamined site (outlined by magnetics and VLF-EM during the surveys), while uranium moved down-dip over theplateau and through underlying sub-horizontal strata towards the eastern fault system. Here, supergene Sr-enriched calcite preferentially incorporated U, thus reflecting the observed U-Th fractionation

Precambrian basement character of Yemen and correlations with Saudi Arabia and Somalia

Abstract The Precambrian basement of Yemen occupies a key location in the Pan-African orogen of Gondwana. This paper reviews geological, isotopic and geochronological data and presents new Pb-and Nd-isotope data which help define distinct gneiss terranes within this basement, constraining correlations of these terranes with neighbouring regions of Saudi Arabia and Somalia. Existing whole-rock Pb-and Nd-isotopic data are also summarised. These data should facilitate a more objective assessment of the contribution of the Yemen Precambrian to Cenozoic magmatism associated with the opening of the Red Sea and the Gulf of Aden