Most of Australia's uranium resources are in two kinds of orebodies,
unconformity-related and breccia complex, while sedimentary deposits are
less significant than overseas.
Uranium deposits world-wide can be grouped into 14 major categories of
deposit types based on the geological setting of the deposits (OECD/NEA
& IAEA, 1996).
Australian uranium deposits can be grouped into 6 of these categories,
with some mineralisation in two further ones
Unconformity-related deposits arise from geological changes occurring
close to major unconformities. Below the unconformity, the metasedimentary
rocks which host the mineralisation are usually faulted and brecciated.
The overlying younger Proterozoic sandstones are usually undeformed.
Unconformity-related deposits constitute approximately 33% of the World
Outside Centrally Planned Economies Area (WOCA)'s uranium resources and
they include some of the largest and richest deposits. Minerals are
uraninite and pitchblende. The main deposits occur in Canada (the
Athabasca Basin, Saskatchewan and Thelon Basin, Northwest Territories);
and Australia (the Alligator Rivers region in the Pine Creek Geosyncline,
NT and Rudall River area, WA). Unconformity-related deposits-
constitute a major proportion (22%) of Australia's total uranium resources
and more than 80% of Australia's total production since 1980 has been
mined from two of these deposits - Ranger #1 and Nabarlek (now mined out).
Other major deposits in the Alligator Rivers region are Ranger # 3,
Jabiluka (North Ranger), Koongarra and Ranger 68.
In 1996, more than 95% of Canada's total uranium production was from
unconformity-related deposits - Key Lake, Cluff Lake, and Rabbit Lake
deposits. Other large, exceptionally high grade unconformity-related
deposits which are being developed for future mining include Cigar Lake
(averaging 9.1% U3O8, some zones over 50% U3O8); McArthur River (averaging
5.0% U3O8, some zones average 42% U3O8); Eagle Point, Collins Bay A and D
orebodies and McClean Lake.
The deposits in the Athabasca Basin occur below, across and immediately
above the unconformity, with the highest grade deposits situated above (eg
Cigar Lake) and across the unconformity (eg Key Lake).
In the Alligator Rivers region, the known deposits are below the
unconformity and are generally much lower grade than the Canadian
deposits. Uranium exploration in the Alligator Rivers region and Arnhem
Land has been restricted since the late 1970s because of political and
environmental factors. Much of the Alligator Rivers region and Arnhem Land
have only been subjected to first pass exploration designed to detect
outcropping deposits and extensions of known deposits, eg Jabiluka 2 was
found by drilling along strike from Jabiluka 1. There has been very little
exploration to locate deeply concealed deposits lying above the
unconformity similar to those in Canada. It is possible that very high
grade deposits occur in the sandstones above the unconformity in the
Alligator Rivers/Arnhem Land area.
The Kintyre deposit in the Rudall River area is similar to the
deposits in the Alligator Rivers region. Metallurgical tests have shown
that Kintyre ore can be radiometrically sorted and upgraded prior to
milling and processing.
The Olympic Dam deposit is one of the world's largest deposits ofuranium,
and accounts for about 66% of Australiaís reserves plus resources. The
deposit occurs in a hematite-rich granite breccia complex in the Gawler
Craton. It is overlain by approximately 300 metres of flat-lying
sedimentary rocks of the Stuart Shelf geological province.
The central core of the complex is barren hematite-quartz breccia, with
several localised diatreme structures, flanked to the east and west by
zones of intermingled hematite-rich breccias and granitic breccias. These
zones are approximately one kilometre wide and extend almost 5 km in a
northwest-southeast direction. Virtually all the economic copper-uranium
mineralisation is hosted by these hematite-rich breccias. This broad zone
is surrounded by granitic breccias extending up to 3 km beyond the outer
limits of the hematite-rich breccias.
The deposit contains iron, copper, uranium, gold, silver, rare earth
elements (mainly lanthanum and cerium) and fluorine. Only copper, uranium,
gold, and silver are recovered. Uranium grades average from 0.08 to 0.04%
U3O8, the higher-grade mineralisation being pitchblende. Copper grades
average 2.7% for proved reserves, 2.0% for probable reserves, and 1.1% for
indicated resources. Gold grades vary between 0.3-1.0 g/t.
Details of the origin of the deposit are still uncertain. However
the principal mechanisms whichformed the breccia complex are considered to
have been hydraulic fracturing, tectonic faulting, chemical corrosion, and
gravity collapse. Much of the brecciation occurred in near surface
eruptive environment of a crater complex during eruptions caused by
boiling and explosive interaction of water (from lake, sea or groundwater)
Sandstone uranium deposits occur in medium to coarse-grained sandstones
deposited in a continental fluvial or marginal marine sedimentary
environment. Impermeable shale/mudstone units are interbedded in the
sedimentary sequence and often occur immediately above and below the
mineralised sandstone. Uranium precipitated under reducing conditions
caused by a variety of reducing agents within the sandstone including:
carbonaceous material (detrital plant debris, amorphous humate, marine
algae), sulphides (pyrite, H2S), hydrocarbons (petroleum), and interbedded
basic volcanics with abundant ferro-magnesian minerals (eg chlorite).
Three main types of sandstone deposits: rollfront deposits - arcuate
bodies of mineralisation that crosscut sandstone bedding;
tabular deposits - irregular, elongate lenticular bodies parallel to the
depositional trend, deposits commonly occur in palaeochannels incised into
underlying basement rocks;
tectonic/lithologic deposits - occur in sandstones adjacent to a permeable
Sandstone deposits constitute about 18% of world uranium resources.
Orebodies of this type arecommonly low to medium grade (0.05 - 0.4% U3O8)
and individual orebodies are small to medium in size (ranging up to a
maximum of 50 000 t U3O8). The main primary uranium minerals are uraninite
and coffinite. Conventional mining/milling operations of sandstone
deposits have been progressively undercut by cheaper in situ leach mining
The United States has large resources in sandstone deposits in the
Western Cordillera region, and most of its uranium productionin has been
from these deposits. Uranium is being recovered from in situ leach mining
of sandstone deposits in the South Texas area (Texas Gulf Coast).
Large uranium resources within sandstone deposits also occur in
Niger, Kazakstan, Uzbekistan, Gabon (Franceville Basin), and South Africa
(Karoo Basin). Kazakstan has reported substantial reserves in sandstone
deposits with average grades ranging from 0.02 to 0.07% U. In 1994,
approximately 75% of Uzbekistan's uranium production and 70% of
Kazakstan's production was from in situ leach mining of sandstone
Sandstone deposits represent only about 6% of Australia's total
reserves plus resources of uranium .In the Westmoreland area, northwest
Queensland, the bulk of the resources are within five ore lenses in
sandstones along the flanks of the Redtree joint zone. The mineralised
sandstone is overlain by basic volcanics.
Within the Frome Embayment, six uranium deposits are known, the
largest being Beverley and Honeymoon. Tests have shown that these two
deposits are amenable to in situ leach mining methods. At the Mulga Rock
deposit, 230 km east-northeast of Kalgoorlie, uranium mineralisation is in
peat layers interbedded with sand and clay within a buried palaeochannel.
these deposits make up approximately 13% of theworld's uranium resources.
Where uranium is recovered as a by-product of gold mining, the grade may
be as low as 0.01% U3O8. In deposits mined exclusively for uranium,
average grades range as high as 0.15% U3O8. Individual deposits range in
size from 6000-170 000 t contained U3O8.
Major examples are the Elliot Lake deposits in Canada and the
Witwatersrand gold-uranium deposits in South Africa. Mining operations in
the Elliot Lake area have closed in recent years because these deposits
are uneconomic under current uranium market conditions.
No such economic deposits are known in Australia, although
quartz-pebble conglomerate containing low-grade uraninite mineralisation
exists in several Archaean-Palaeoproterozoic basins in Western Australia.
These are similar in lithology and age to the Witwatersrand conglomerates.
Surficial uranium deposits are broadly defined as young (Tertiary to
Recent)near-surface uranium concentrations in sediments or soils. These
deposits usually have secondary
cementing minerals including calcite, gypsum, dolomite, ferric oxide, and
halite. Uranium deposits in calcrete are the largest of the surficial
deposits. Uranium mineralisation is in fine-grained surficial sand and
clay, cemented by calcium and magnesium carbonates. Surficial uranium
deposits also occur in peat, bog, karst caverns and soils.
Surficial deposits comprise approximately 4% of world uranium
resources. Calcrete depositsrepresent 4% of Australia's total reserves and
resources of uranium. The Yeelirrie deposit in WA is by far the world's
largest surficial deposit. Other significant deposits in WA include Lake
Way, Centipede, Thatcher Soak, and Lake Maitland.
In WA, the calcrete uranium deposits occur in valley-fill sediments
along Tertiary drainage channels, and in playa lake sediments. These
deposits overlie Archaean granite and greenstone basement of the northern
portion of the Yilgarn Craton. The uranium mineralisation is carnotite
(hydrated potassium uranium vanadium oxide).
Calcrete uranium deposits also occur in the Central Namib Desert of
uranium deposits of this type occur in acid volcanic rocks and are related
tofaults and shear zones within the volcanics. Uranium is commonly
associated with molybdenum and fluorine. These deposits make up only a
small proportion of the world's uranium resources. Significant resources
of this type occur in China, Kazakstan, Russian Federation and Mexico. In
Australia, volcanic deposits are quantitatively very minor - Ben Lomond
and Maureen are the most significant deposits.
included in this type are those associated with intrusive rocks
includingalaskite, granite, pegmatite, and monzonites. Major world
deposits include Rossing (Namibia), Ilimaussaq (Greenland) and Palabora
(South Africa). In Australia, the only significant deposits are the large
bodies of low grade mineralisation at Crocker Well and Mount Victoria in
the Olary Province, SA.
- these occur in structurally-deformed rocks that were already altered
bymetasomatic processes, usually associated with the introduction of
sodium, potassium or calcium into these rocks. Major examples of this type
include Espinharas deposit (Brazil) and the Zheltye Vody deposit
In Australia the largest of this type was Mary Kathleen uranium/rare
earth deposit, 60km east of Mount Isa, Qld, which was mined 1958-63 and
1976-82. The orebody occurs in a zone of calcium-rich alteration within
Proterozoic metamorphic rocks.
- Vein deposits constitute about 9% of world uranium resources. Major
deposits include Jachymov (Czech Republic) and Shinkolobwe (Zaire). The
largest vein deposit in Australia was Radium Hill (SA) which was mined
from 1954-62. Mineralisation was mostly davidite.
The major primary ore mineral is uraninite or pitchblende (UO2 + UO3,
nominally U3O8), though a range of other uranium minerals is found in
particular deposits. These include carnotite (uranium potassium vanadate),
the davidite-brannerite-absite type uranium titanates, and the
euxenite-fergusonite-samarskite group (niobates of uranium and rare
A large variety of secondary uranium minerals is known, many are
brilliantly coloured and fluorescent. The commonest are gummite (a general
term like limonite for mixtures of various secondary hydrated uraniuim
oxides with impurities); hydrated uranium phosphates of the
phosphuranylite type, including autunite (with calcium), saleeite
(magnesian) and torbernite (with copper); and hydrated uranium silicates
such as coffinite, uranophane (with calcium) and sklodowskite (magnesian).
Mostly condensed from:
Lambert,I., McKay, A., and Miezitis, Y. (1996) Australia's uranium
resources: trends, global comparisons and new developments, Bureau of
Resource Sciences, Canberra, with their earlier paper: Overview of
Australian and World Uranium Resources, ANA Conference Nov 1995.
Minerals from: Aust IMM, Field Geologist's Manual, 1989.