Unconformities

Unconformity-Related Deposits. Deposits of the unconformity-related type occur spatially close to significant unconformities. These deposits usually developed during the period about 1800—800 million years ago in intracratonic basins. Deposits also developed during Phanerozoic time. Examples of unconformity-related deposits include the ore bodies at Cluff Lake, Key Lake, and Rabbit Lake in northern Saskatchewan, Canada, and those in the Alligator Rivers area in northern AustraHa (12). 

Quartz-Pebble Conglomerate Deposits. Known quartz-pebble conglomerate ores are restricted to a specific period of geologic time. These ore types occur in basal Lower Proterozoic beds unconformably situated above Archaean basement rocks composed of granitic and metamorphic strata. A number of commercial deposits are located in Canada and South Africa. Some subeconomic occurrences have been reported in Brazil and India... 

The younger formations (Ittori, and Tobe formations) of late Miocene to Pliocene overlie the Shishigamori, Shigenai and Harukizawa formations and are comprised mostly of mudstones, interbedded felsic tuffs, and tuffaceous sandstones. The total thickness of these formations is ca. 500 m. The formations of Pleistocene unconformably overlie the... 

Quaternary volcanic rocks unconformably overlie the Shimanto Supergroup. Quaternary volcanic rocks consist of Hishikari Lower Andesites (0.98-1.62 Ma), Hishikari Middle Andesites (0.78-0.79 Ma), Kurozonsan Dacites (0.95-1.56 Ma), Shishimano Dacites (0.66-1.6 Ma), and Hannyaji Welded Tuff (0.56-0.731 Ma) (Izawa et ah, 1990, 1993). 

The Nigorikawa (Mori) geothermal system is located in southwest Hokkaido (Fig. 2.15). The area is composed of basement rocks (sedimentary rocks such as limestone), and Tertiary andesitic rocks (Yoshida, 1991). The area is characterized by a Krakatoan-type caldera which was formed by volcanic activity about 12,000 to 20,000 years ago (Sato, 1988). The caldera is filled with sediments consisting of clays, conglomerate, and fall back materials (tuff and tuff breccia). The rock formations surrounding the caldera consist of pre-Tertiary rock which are unconformably overlain by the Neogene Tertiary formation in thicknesses of 300-700 m. 

Unconformity-related The ore bodies at Cluff Lake, Key Lake, and Rabbit Lake in northern Saskatchewan, Canada, and those in the Alligator rivers area in northern Australia... 

J Unconformity related-type (both contact and subconformity-type)... 

Treasure Lake Group, overlain by felsic ignimbrite sheets of the Faber Group (Goad et al. 2000). Ore minerals mainly consists of Fe-, As-, Co- and Cu-sulphides, native Au and Bi. Intense, pervasive, polyphase iron-oxide (magnetite-dominant)-hornblende-biotite-tourmaline-K-feldspar-carbonate replacive alteration occurs in the upper metasedimentary sequence below the volcanic-sedimentary unconformity... 

The basement is made up of crystalline schists of the meso-metamorphic Somes Series. Sedimentation started during Permian with detritic deposits interbedded with rhyolites. The overlying Triassic deposits are unconformable and include detritic formations (Lower Triassic) and massive layers of carbonate rocks (Middle Triassic). The absence of the Upper Triassic is due to the uplift of the region during the Kimmeric tectonic phase. 

KEYWORDS Unconformity Hosted Uranium Deposit, Nunavut, Geochemistry, Uranium Exploration, Oxygen Stable Isotopes... 

The Lac Cinquante unconformity associated uranium deposit is located in the Kivalliq district of Nunavut approximately 350 km west of Rankin Inlet, and is centered on approximately Latitude 62° 34 33 N, Longitude... 

Fig.1. Geology of the Lac Cinquante region shows Archean (green rocks) and ProterozOc rocks (yellow, grey, brown, and pink) separated by an unconformity (dashed line). The location of the two major zones of mineralization, the main zone and south zone, documented by Miller et al. (1987) are noted on the map.

Figure 6. Stratigraphic section above economic basement for the central portion of the North Slope of Alaska. The Brookian and Ellesmerian sequences are separated at the major Lower Cretaceous unconformity. Both commercial and noncommercial oil gas fields are shown at right (from Engel and Macko, 1993).

The mineralized district is restricted by two main strike-slip faults of Kubanan to the east and Posht e Bdam to the west (Fig. la). The host rocks are a thick sequence of Upper Precambrian-Cambrian rhyolite, tuff, alkali granite, syenite, mafic dykes, magnetitite, dolomite, gypsum, limestone, black shale, and sandstone. The Upper Percambrian-Cambrian sequence is overlain unconformably by Mesozoic and... 

Abstract uranium isotopes fractionate as a result of nuclear volume effects such that ratios vary as a funotion of uranium oxidation state, being highest in reduced species such as U"" in uraninite. The values of uranium minerals from volcanic-, metasomatic-, unconformity-,... 

Unconformity-type uranium deposits, as well as sandstone-hosted deposits, should be zoned in their 238y 5y pg jgg gg g result of two processes. In the first process, the 238y 235y... 

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