Uranium Vanadium mineralisation in the Yilgarn and its correlation with Barrambie giant ring structure.
Location and size.
Barrambie giant ring structure (GRS) centre is near the Barrambie mining centre at coordinates 27˚28’S and 119˚15’E. It is 450 km in diameter to the outer ring.
Genesis
It is suggested Barrambie was formed during the late Heavy Bombardment LHB when the upper crust was formed by massive lava extrusions. This implies an undeformed underlying older Greater Yilgarn Cratonic plate of at least 3.8 Ga in age at the time of the GRS formation.
Uranium vanadium deposits, What determines their location in Western Australia?
Nearly all of the largest uranium projects in the Yilgarn are associated with Barrambie GRS centre (Geology Survey map, www.dmp.wa.gov.au ). This suggests more than just a spatial relationship to the widespread granitic intrusive events that occurred near the finalisation of Yilgarn cratonisation. It suggests that the granites in the centre of the Barrambie GRS have a high uranium content relative to the other granites in the Yilgarn and a deep-seated mechanism for remobilisation of uranium.
The 30˚S seismic tomography section studied by Watchorn in paper YW #6, in 2018 https://geotreks.com.au/work/giant-ring-structures/watchorn-grs-craton-tomography/ , suggests the giant ring (phi Ø) structures extend to at least 250 km depth as steep arcuate and bowl structures. These are the prime structures up which earth-scale stress would be relieved and up which mineralising intrusive rocks and fluids will travel. Thus, the granites may pick up uranium rich minerals from the original impact derived metallogeny
All of the major, and most of the minor uranium deposits lie in palaeochannels within the central ring of the Barrambie GRS. The largest deposits lie in granite dominated geology and are associated with the inner margins of the Wiluna ring and lie beside the largest greenstone areas many of which are vanadium rich.
The Palaeochannel system formed during the Permian by glacial over-deepening of the fracture systems following GRS rings. The largest calcrete hosted uranium deposits form in those palaeochannels that are inside the median Wiluna ring. The best deposits form a circle halfway between the GRS centre and Wiluna ring.
The morphology of the region (including the Gascoyne and southern Pilbara) at the commencement of palaeochannel formation is also important. At the end of the build-up of the Yilgarn craton at approximately 2.63 Ga the craton was the most elevated land in Western Australia. The later lithologies in the Gascoyne to the NW and the Fraser Orogen to the SE would have been derived from the Archaean Yilgarn Craton and would include uranium and vanadium rich sediments from the granites.
Uranium deposits formation in Yilgarn craton
Carnotite is a uranium-bearing vanadium oxide of potassium (K[U+6O2][V+5O4].xH2O). It’s formation in calcrete is determined by geochemical processes that control the concentration of potassium, uranium and vanadium in groundwater and in playa lakes. The key to the uranium concentration in the Barrambie GRS is the abundance of Vanadium rich rocks at Barrambie, Windimurra, Gabanintha and other locations.
What determines the location of Western Australia’s Vanadium deposits? The vanadium deposits are related to large late (2.7 – 2.8 Ga) layered igneous intrusions similar to Windimurra. They are located in the central area of the Barrambie GRS which is suggested to be an older than 3.8 Ga impact. This implies continuing volcanic activity over a >1 Ga duration.
The source rocks for the largest Yilgarn uranium deposits are uranium rich granites spatially associated with the rings of the Barrambie GRS. The weathered granites form sediments in the Permian palaeochannels which follow the rings of the various Yilgarn GRS. The calcrete hosted Palaeochannel related deposits, while differing in mode of deposition from metasomatic deposits, are primary reconcentration of the granite derived uranium even though they may be recent in origin
The calcrete hosted uranium deposits nearly always lie down palaeochannel from the vanadium deposits.
The secondary roll front sandstone hosted deposits may have been formed by upward penetrating solutions dissolving and remobilising the uranium in these buried basement sediments and redepositing it in the younger overlying strata both in the NW of the Gascoyne and SE in the Fraser Orogen. These uranium reconcentrations may then have been again upgraded by meteoric waters associated with Cainozoic downward weathering.
The largest roll front sandstone hosted deposits form at the termination of these palaeochannels into younger basins.
Are radiometrics defining a metallogenic province?
Why is uranium only associated with the Barrambie GRS and not the other GRS? The Yilgarn GRS all have similar morphology and structure. It is suggested that the Barrambie GRS impact area, or the impacting bolide itself, was initially more uranium and vanadium rich.
The area inside the Wiluna ring of the Barrambie GRS is a more intense green than the surrounding area. A green radiometric signature is composed of yellow (thorium) and blue (uranium). It has been suggested by recent external research that impacts can be classified by their different original meteorite/bolide composition.
Can Yilgarn impacts may be classified by metallogeny on this radiometric basis? The Yilgarn GRS have conspicuous, individual, radiometric signatures. It is suggested that this observation may form the basis for using the GRS as a basis for separating metallogenic provinces and that this may lead to targeting for the specific associated minerals within these areas.
A brief investigation of the mines in each area suggest that the radiometric signature is defining the main mineral exploited in each GRS. Radiometric characteristics are already used extensively for local targeting. It is suggested that they can also be used for regional targeting.
Uranium vanadium deposits, exploration targeting for calcrete and roll front uranium deposits.
The palaeochannels are target areas for calcrete uranium deposits. The target areas for roll front uranium deposits are where the palaeochannels flow into deeper, more recent, basins. There are quite a few palaeochannels where there are Vanadium rich source rocks with no discovered uranium deposits in the downstream palaeochannels. These are good target areas.
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| YB#2 Barrambie GRS uranium vanadium Exploration Targets.pdf | 1 MB |