Portfolio summary: Gascoyne complex, Western Australia
In the Gascoyne Complex of central Western Australia, known uranium deposits in Tertiary calcrete overlying Proterozoic granite and metamorphics include Minindi Creek, 250 km east of Carnarvon, and Jailor Bore, 200 km northeast of Carnarvon. The location map attached gives a broad overview of the distribution of known uranium occurrences in the Gascoyne Complex.
Desert Energy has a large ground position in the Gascoyne Complex including areas of uranium radiogenic granites, potential sources for uranium to be released into streams and deposited in sediments and drainage channels. Despite the numerous uranium occurrences in the area, previous uranium exploration within the tenements appears to have been localized.
Desert Energy Calcrete Uranium Projects in the Gascoyne Complex
Desert Energy's Yannarie Project is located over calcrete deposits along parts of the Yannarie River and its tributaries. These drain a large area of Proterozoic uranium-rich granites which host several uranium occurrences.
Within the Minnie Creek Project area, uranium mineralization has been identified at Middle Well, and nearby Poorinoo Well. The project covers the junction of the Alma and Edmund tributaries to the Lyons River which drain broad areas of radiogenic granite.
The Minnie Creek and Yannarie exploration licence applications cover 125 km of interpreted uranium-channel airborne radiometric anomalies and more than 165 km strike length of near-surface calcrete.
A government report records grades of 0.03% to a maximum of 0.15% U3O8 from surface grab samples by previous explorers in a small area at Minnie Creek. Follow up drilling of this area, over 150m by 50m, produced maximum grades between 0.03% and 0.07% U3O8. Previous exploration records up to 0.09% U3O8 in shallow drilling in the northern part of the Yannarie project. Follow up drilling of this area, over 10km by 3km grid produced samples up to 0.03% U3O8. The results demonstrate that the conditions in the area were potentially favourable for the formation of uranium, as the mineral carnotite, in calcrete.
Yannarie and Minnie Creek Projects lie north of the Paddy Well uranium prospect of U3O8 Limited, and south of the Manyingee uranium deposit of Paladin Resources (resource of 12,000t of contained U308 )
Uranium in calcrete has been identified in tributaries to the Gascoyne River, and the Company’s tenement holding at the Glenburgh Project along the Gascoyne River and its tributaries holds potential for secondary uranium mineralisation, including areas covered by more recent river sediments potentially covering earlier-formed calcrete.
The re-processed airborne radiometric database at the Company’s Limejuice property has defined radiometric responses over targets with no or limited previous exploration and where potential for uranium mineralization is believed to exist.
Project summary: Yilgarn block, Western Australia
The Company’s Yilgarn Block Uranium project areas include Tertiary to Recent drainage channels where calcrete and/or other valley fill sediments have accumulated. The Yilgarn Block is host to the Yeerlirrie deposit and a number of other known Calcrete Uranium deposits, and a large number of uranium occurrences where mineralizing processes have been at work in the arid surface environment. The location of these occurrences is shown on the Yilgarn Block location map attached to this report.
Due to the large number of Aurora Minerals tenements, they have been grouped into North Murchison and South Murchison Project areas.
Desert Energy's Calcrete Uranium Projects on the Yilgarn Block
North Murchison Projects
The Berringarra and Chesterfield tenements cover large sections of the soil and sand covered plain alongside the Murchison River and its main tributaries. Calcrete is exposed along the main present-day river channels and is inferred to exist beneath the recent soil and sand cover flanking the rivers
Downs and Charlie prospects cover uranium-channel radiometric responses over sections of various drainages along the northern edge of the Yilgarn Craton.
South Murchison Project
There is potential for calcrete-hosted uranium mineralization on tenements at Dawson and Old Station prospects. Airborne radiometric coverage shows uranium-channel anomalies coincident with mapped drainage and valley-fill sediments.
Selection process
Desert Energy has a portfolio of tenement applications prospective for calcrete hosted uranium deposits in the Gascoyne and Yilgarn Provinces of Western Australia. Uranium deposits in calcrete are the largest of the near surface (surficial) deposits of which the Yeelirrie deposit in Western Australia is the best known example.
In Western Australia, Calcrete Uranium deposits and occurrences are believed to have been formed where uranium has been leached from granites in a semi-arid to arid climate, and transported along the creeks or rivers, to be redeposited in or near calcrete, at suitable “trap” sites within the drainage system.
In Western Australia calcrete tends to occur in valley fill sediments along Tertiary drainage channels and in playa lake sediments. The drainage channels can be up to several kilometres wide, and can be very long, with calcrete developed variably along the length. Uranium mineralization may, if geological and mineralizing conditions are favourable, be deposited in small portions of these channels.
Uranium mineralization is generally detected by measuring the response of its natural radioactive decay. Airborne radiometric surveys have been and continue to be used extensively in the exploration for uranium mineralization. These surveys can be followed up by closer spaced surveys in order to highlight the best anomalies for drilling.
In 2006 Desert Energy commissioned a specialist geophysical consultant group to compile a GIS database of available uranium channel airborne radiometric surveys over Western Australia.
Using this database, together with Geological Survey of Western Australia published mapping, the Company then proceeded to apply a series of selection criteria to identify acquisition opportunities in the Archean Yilgarn Block in the southern part of Western Australia, and the Proterozoic Gascoyne province in central Western Australia.
The preferred selection criteria included:
presence of a uranium channel radiometric anomaly(ies),
suitable drainage system (i.e. creeks and arid river systems),
presence of calcrete in or on the flanks of the drainage,
presence of known uranium mineralization or uranium-radiogenic granites in the catchment area.
It is estimated that less than 50 centimetres of sand or other non-radioactive cover could mask, partially or completely, a radiometric reading at surface. Therefore in areas of extensive recent sand or other cover, there is a possibility that even subtle uranium-channel radiometric anomalies may relate to buried mineralisation.
The uranium-channel radiometric anomalies identified by Desert Energy range from prominent through moderate to subtle. Where exploration licences have been applied for over subtle anomalies, Aurora believes the prospect has potential to host buried or concealed uranium mineralization, which could be tested for by more detailed radiometric surveys and shallow drilling.