Unconformity Related Deposits
Unconformity related deposits occur immediately below and above major unconformities that separate crystalline basement from overlying clastic sedimentary rocks of either Proterozoic or, less commonly, Phanerozoic age. The deposits are formed relating to geological and geochemical changes at the unconformity boundary. Some of the world’s largest and highest grade uranium deposits are unconformity-related with the Athabasca Basin in Canada being of particular note. Currently all Canadian uranium production is from the Athabasca Basin.
Large high-grade uranium or polymetallic deposits are known to occur directly at or slightly above the unconformity (Cigar Lake and McArthur River in Canada). Large but medium to high-grade uranium deposits are found below the unconformity (Rabbit Lake in Canada and Jabiluka 2 in Australia) and low-grade small deposits may be up to 200 m above the unconformity (e.g. Maurice Bay in Canada). Approximately 20% of Australia’s and 33% of the world’s known ‘Identified Resources’ or uranium is contained in unconformity-related deposits.
Australia has two main known uranium provinces that contain Proterozoic unconformity-related deposits:
- the Alligator Rivers uranium field in the Northern Territory, including Ranger 1, Nabarlek, Jabiluka, Koongarra and Ranger 68 deposits; and
- the Rudall Complex in Western Australia, which hosts the Kintyre deposit.
A large proportion of Australia’s uranium production since 1980 has been from two of these deposits Ranger (No. 1 and No. 3 orebodies) and Nabarlek. Snowden understands that uranium exploration in the Alligator Rivers uranium field and Arnhem Land has been largely restricted since the late 1970s due to political and environmental factors.
Regalpoint’s Rum Jungle project belongs to this class of deposit.