NUCLEAR FUELS 



461 



Blind River-Elliot Lake district, Canada, deposits 

 containing uraninite and brannerite are 7-15 feet 

 thick and from hundreds of feet to 2 miles across, 

 and contain more than 5 million tons of ore. Min- 

 able grade averages 0.12-0.16 percent UsOs; gold 

 values are 0.02-0.03 ounce per ton. The thorium- 

 uranium ratio is 1:4 to 1:3 and some thorium has 

 been recovered as a byproduct. In the Witwaters- 

 rand, South Africa, the deposits are larger and more 

 extensive than at Blind River-Elliot Lake, but their 

 uranium content is lower, generally 0.03-0.07 per- 

 cent UaOg. Uranium is produced mainly as a byprod- 

 uct of gold mining and locally as a coproduct. Ore 

 minerals are uraninite with minor amounts of bran- 

 nerite. Thorium is not recovered because of the 

 small amount in the ore. Possibly similar deposits of 

 undetermined magnitude have recently been identi- 

 fied in Precambrian rocks near Belo Horizonte, Bra- 

 zil (L. A. Moura, Commissao Nacional de Energia 

 Nuclear, Brazil, oral commun., 1972). 



VEIN DEPOSITS 



Uranium-bearing veins are fissure fillings in faults, 

 joints, and fracture zones ; they occur in many kinds 

 of rocks ranging from Precambrian to Tertiary in 

 age, and in diverse geologic settings. Ore occurs as 

 tabular bodies, irregular stockworks, pipelike masses 

 at fracture intersections, and in mineralized gouge 

 and breccia. Chief types of alteration associated with 

 uranium veins are sericitic, argillic, chloritic, and 

 hematitic. Individual veins are a few inches to sev- 

 eral feet wide and extend along strike and downdip 

 as much as several hundred feet; these combine to 

 form vein systems which extend as much as 1,300 

 feet below the surface in the United States and 

 5,000 feet in Canada and which contain 10 tons to 

 millions of tons of ore. Average mined grade ranges 

 from 0.10 to 1.0 percent UgOs. Deposits in which 

 base-metal sulfides constitute appreciable to major 

 amounts of the ore include the large deposits at 

 Shinkolobwe, Zaire (formerly Belgian Congo) and 

 at Port Radium, Northwest Territories, Canada, both 

 now depleted; and the moderate-sized deposits at 

 Joachymov, Czechoslovakia, and at the Schwartz- 

 walder mine, Colorado (Walker and others, 1963). 

 Pyrite is the only abundant sulfide in the very large 

 deposits at Beaverlodge Saskatchewan, Canada. 

 Fluorite is a characteristic component of the mod- 

 erate-sized deposits at Marysvale, Utah. 



At Bancroft, Ontario, Canada, uraninite-thorite 

 veins and irregular pods cut and replace bodies of 

 unzoned granitic pegmatite and form fairly large 

 deposits (Robinson and Hewitt, 1958). They contain 

 an average of about 0.1 percent UaOg and 0.025-0.2 



percent ThOa. 



Veins are thought to have been deposited from 

 hydrothermal solutions derived by differentiation of 

 magmas. Uranium-bearing veins in the United States 

 formed mainly during Late Cretaceous to late Ter- 

 tiary time. 



OTHER EPIGENETIC DEPOSITS 



A few major epigenetic deposits do not fit into the 

 preceding groups. The Midnite mine, Washington, is 

 in Precambrian metasedimentary rocks along their 

 contacts with Cretaceous granite. Individual ore 

 bodies are as much as 200 feet wide, 700 feet long, 

 and more than 150 feet thick. The average mined 

 grade is about 0.23 percent UaOg. The deposit proba- 

 bly was formed shortly after granitic intrusion, by 

 hydrothermal solutions directed along favorable 

 zones adjacent to the intrusive contact (Becraft and 

 Weis, 1963). At the Ross Adams mine in south- 

 eastern Alaska, numerous uraninite- and thorium- 

 bearing veinlets cut peralkaline granite in which 

 abundant uranothorite and uranoan thorianite occur 

 as late crystallizing accessory minerals (MacKevett, 

 1963). This deposit has yielded about 70,000 tons of 

 ore that averaged more than 0.60 percent UsOg. Al- 

 though the uranium-thorium ratio is about 1:1, 

 thorium has not been recovered. 



Deposits in this miscellaneous group in foreign 

 areas include: (1) A several-million-ton irregular 

 pipelike body of uraninite and uranophane dissemi- 

 nated in brecciated syenitic rock at the Gunnar mine, 

 Beaverlodge area, Saskatchewan, Canada, (2) a sub- 

 horizontal, irregular, tabular body of mineralized 

 metamorphic rock at Rabbit Lake, Saskatchewan 

 (H. W. Little, Geol. Survey of Canada, oral commun., 

 1972), and (3) probably the Nabarlek, Jim Jim, and 

 Ranger deposits in older Precambrian rocks discov- 

 ered recently in the Northern Territory, Australia. 



URANIFEROUS IGNEOUS ROCKS 



In the United States, only small amounts of urani- 

 um have been mined from pegmatites, most of which 

 are the zoned type. 



Aside from pegmatites, a few igneous rock bodies 

 contain anomalous concentrations of uranium as an 

 indigenous constituent. The biotite phase of the Con- 

 way Granite of Triassic or Jurassic age in central 

 New Hampshire contains an average of 0.0015 per- 

 cent UsOg over a 300-square-mile area. It also con- 

 tains about 0.0064 percent ThOj. (See under Thori- 

 um in this chapter. ) 



Bodies of a variety of uraniferous igneous rocks 

 in other countries are mostly smaller but richer in 

 uranium than the Conway granite. They include 



