2- Sandstone deposits Definition - PowerPoint Presentation

1. 2- Sandstone depositsDefinitionSandstone uranium deposits occur in carbon and/or pyrite-bearing fluvial (less commonly marine), arkosic, medium to coarse-grained sandstones that contain, are interbedded with, and are bounded by less permeable horizons.Primary uranium minerals are predominantly pitchblende, coffinite, and to a lesser extent vanadates and phosphates . Uranium is precipitated under reducing conditions caused by a variety of reducing agents within the sandstones (for example, carbonaceous material, sulphides, hydrocarbons and ironmagnesium minerals as chlorite).Sandstone uranium deposits can be divided into four main types :-

2. 1- Roll front type—Moinkum, Inkai and Mynkuduk (Kazakhstan), Crow Butte and Smith Ranch (USA) and Bukinay, Sugraly and Uchkuduk (Uzbekistan).2- Tectonic-lithologic type — Mikouloungou (Gabon) and Mas Lavayre, Lodève district (France).3- Basal channel type — Dalmatovskoye, Transural region and Khiagdinskoye, Vitim district (Russian Federation) and Beverley (South Australia).• Tabular type — Ambrosia Lake, Grants Mineral Belt, New Mexico (USA): Westmoreland (Australia), Akouta, Imouraren and Arlit (Niger), Coutras (France) and Colorado Plateau (USA).

3. 3-Hematite Breccia Complex deposits DefinitionDeposits of this group occur in hematite-rich breccias and contain uranium in association with copper, gold, silver and rare earths. The main representative of this deposit type, Olympic Dam.The Olympic Dam deposit occurs in a hematite-rich granite breccia complex in South Australia. It is overlain by approximately 300m of flat-lying sedimentary rocks . The breccia complex is associated with a plutonic intrusion and co-magmatic continental felsic volcanics. The intrusion,volcanics and breccia complex developed in a post-orogenic tectonic setting.The Olympic Dam copper–uranium–gold deposit has the world’s largest known resource of low-cost uranium. Initial resources were more than 1.552 Mt U with average grade 0.34 kg/t U (0.034% U). Exploration drilling has discovered major extensions of the deposit to the south-east, which will increase the size of the resources. As at June 2006, the total resources at Olympic Dam were estimated to be 4430 Mt averaging 1.1% Cu, 0.4 kg/t U3O8, 0.5 g/t Au and 2.2 g/t Ag which represents 1.503 Mt contained U. The operation is a major producer of uranium, copper, gold and silver. The deposit has significant amounts of rare earth elements(lanthanum and cerium), and has an iron content of about 26% Fe.

4. 4-Quartz-pebble conglomerate depositsDefinitionQuartz-pebble conglomerate uranium deposits are restricted to early Proterozoic basins (older than 2.3–2.4 Ga) downwarped into Archean basement assemblages that include granites. Host rocks for this deposit type typically consist of cross-bedded, quartz-pebble conglomerate beds with a pyritic matrix interbedded with quartzite and argillite beds. This suite of lithologies typically occurs as basal units in fluvial to deltaic braided stream systems.Two economic subtypes of quartz-pebble conglomerate uranium deposits have been identified: polymetallic (Au+U, Witwatersrand Basin, South Africa andmonometallic (Blind River-Elliot Lake area, Canada). Detrital minerals (dominated by uraninite and REE minerals) and later formed authigenic phases occur as disseminated matrix components in pyritic (5 to 20 wt.%). Uraninite, uranothorite, uranothorianite, monazite, and xenotime are the prevailing detritalminerals. Authigenic minerals include U-Ti-oxide phases (brannerite), coffinite, thucholite, and locally gummite. (Resources+production: >400 000 t U, 0.05 to 0.12 % U; U was the primary commodity produced with occasional recovery ofTh and some REE, particularly Y).

5. 5-Vein type (granite related U deposits)DefinitionThe deposit type ‘granite related deposits’, as used in this publication copies ‘vein deposits’, a designation which referred to granite related and undifferentiated deposits. Uranium-bearing veins occur in a broad range of lithologies and geologic environments including acidic intrusives (granite, etc.) volcanics, metasediments and sedimentary rocks.Two broad subtypes of granite related deposits have been recognized based on their spatial relationship with granitic plutons and surrounding (intruded) host rocks: (1) Endo (or intra-) granitic deposits and related contact-granitic deposits (Limousin-Vendée type); and (2) perigranitic deposits in meta-sediments (monometallic Bohemian and polymetallic Erzgebirge types) and in contactmetamorphic rocks (Iberian type).

6. 6-Intrusive depositsDefinitionUranium deposits in intrusive rocks consist of disseminated primary, nonrefractory uranium minerals dominantly uraninite, uranothorianite and/or uranothorite. These deposits are generally low-grade (20–500 ppm), but may contain substantial resources (more than 100 kt U). Five subtypes of intrusive deposits are based on host rock petrology.1-Alaskite type: disseminated uranium occurs in medium- to very coarsegrained alaskite bodies (leucocratic, quartz and alkali feldspar-rich granites) that are discordant to concordant with surrounding folded and highly metamorphosed and migmatized sedimentary rocks . The alaskite bodies range in size from small lenses and tabular dikes to large stocks and domes several hundred metres across. No alteration is associated with the uranium mineralization. The main example is Rössing, in Namibia. Other examplesinclude Goanikontes, Ida Dome, Valencia/Trekkopje and SJ Claims (Namibia) and Johan Beetz (Canada).

7. 2- Granite, monzonite type (Bingham Canyon, Utah, USA): very low-grade uranium disseminations occur in highly differentiated granitic to (cupriferous) quartz-monzonitic (copper porphyries) complexes. Because of their very low U content, uranium is recovered only as a by-product of copper heap leaching. Other examples are Twin Buttes (Arizona, USA) and Yerington (Nevada, USA).3-Peralkaline syenite type (Kvanefjeld, Greenland): low-grade uranium disseminations occur in peralkaline syenitic domes or stocks. Uranium phases are commonly of a more refractory nature. Other examples are Motzfeld (Greenland), Pilanesberg (South Africa), Lolodorf (Cameroon) and Catalao (Brazil).

8. 4-Carbonatite type (Phalaborwa, South Africa): disseminated uranothorianite occurs in cupriferous carbonatite complexes. Up until 2002, uranium was recovered as a by-product from copper production. Other typical examples are Araxa (Brazil), Sokli (Finland) and Sevathur (India).5-Pegmatite type (Bancroft area, Ontario, Canada): uraninite and other uraniumthorium minerals occur in un-zoned granitic and syenitic pegmatitic dykes in sedimentary and igneous rocks, metamorphosed to the amphibolite facies.Deformation and metasomatism commonly follow metamorphism. Hematite is a characteristic alteration product. Pegmatite deposits may average up to 0.08 % U but resources are generally low (a few t U to a few hundred t U). Another example is the Campbell Island Mine (Ontario, Canada).

9. 7-Caldera related volcanic depositsDefinitionMineralization in volcanic deposits is largely structure bound, occurring in intrusive veins or stockworks in volcanic intrusions, diatremes, and flow or bedded pyroclastic units.Smaller ore accumulations occur in strata bound mineralized zones as disseminations and impregnations in permeable and/or reactive flows, flow breccias, tuffs and intercalated pyroclastic and clastic sediments. Uranium mineralization also extends into underlying and adjoining basement rock, where it is concentrated in fracturedgranite and metamorphic rocks.The main uranium minerals, pitchblende and coffinite, are commonly associated with molybdenum-sulfides and pyrite. Other metallic minerals/elements include minor traces of As, Bi, Hg, Li, Pb, Sb, Sn and W. Associated gangue minerals include fluorite, quartz, carbonates, and barite.