Pells Range Project
Summary | Location and tenure | Geology | Exploration | Geophysics | Uranium Mineralisation
Summary
Pells Range is located near Gascoyne Junction on the Gascoyne River, 170km east of Carnarvon in WA. Initially discovered in the uranium boom of the late 1970’s following some good detective geology searching for roll front deposits in the Carnarvon Basin, the leases host significant identified uranium mineralisation, particularly near Pells Range Well where limited and very broadly spaced drilling has defined an irregular mineralised zone. There are several excellent results from widely spaced reconnaissance drilling (including 2.95kg/t U3O8 from 54m and 2.24kg/t U3O8 from 47m) that were simply never followed up due to the collapse of the boom.
The project comprises EL09/1193 which is granted, and EL09/1386 which in application.
Recent geophysical work by Newera has highlighted an excellent target co-incident with most of the best grades in the historical drilling and a drilling program is in the permitting stages.
Location and Tenure
Figure 1: Pells Range regional location diagram
The Pells Range project is situated in WA’s Gascoyne Province, some 36 km east on the Meekatharra road from Gascoyne Junction, Western Australia, and 170 km east of Carnarvon. The project area largely straddles the Gascoyne River; much of the area is covered by river channel deposits.
Newera is operating an option agreement with Cazaly Iron Pty Ltd to manage uranium exploration on the granted lease EL09/1193, and has applied for EL09/1386 in it’s own name. EL09/1193 is in it’s second year of operation.
Figure 2: Pells Range location diagram, Glenburgh 1:250,000 topographical map sheet. EL09/1193 is granted, EL09/1386 is in application. Grid is MGA.
Geology
The prospective unit is the Lower Permian Moogooloo Sandstone, which has a fluvial distributory deltaic character in the Pells Range region. The sandstone contains abundant pyritic carbonaceous matter and zones of strong sandstone channelling. Carbonaceous matter is important in that it acts on the groundwaters as a reducing agent and becomes a host for the deposition of uranium mineralisation.
The sandstone has been derived from granitic/metamorphic basement of the Pre-Cambrian Gascoyne Province exposed 25 km east of Pells Range. Superficial uranium occurrences (calcrete), minor uranium-base metal vein-type occurrences and granitic rocks relatively high in uranium are present in this basement.
Figure 3: GSWA 1:250K geology of the Pells Range project area.
The main target within the project is a sandstone hosted “tabular” uranium deposit located within the Moogooloo Sandstone. Several similar deposits have been located along the eastern margin of the Carnarvon Basin adjacent to the Gascoyne Complex including the Manyingee Deposit, 85 km south of Onslow W.A.
Exploration History
Pells Range was discovered by Afmeco Australia Ltd (Afmeco) in the late 1970’s when they were prospecting for sandstone hosted roll front type uranium deposits in the Carnarvon Basin. A mineralised zone of at least twice background radiation along a strike length of in excess of 25km was delineated in the Moogooloo Sandstone with imperial mile (approximately 1600m) spaced rotary mud percussion holes. Some infill to 400m centres was carried out by Occidental Minerals (Occidental) in JV with Afmeco from 1980.
Occidental drilled an additional 4 diamond holes to twin previous rotary mud holes containing high grade intersections. They selectively assayed the anomalous zones, with XRF results including 2.5kg/t U (2.95kg/t U3O8) from carbonaceous material at 54m depth in MOG 60 and 1.9kg/t U (2.24kg/t U3O8) from 47m in a carbonaceous silty sandstone in MOG23.
Surface rock chip samples from the margins of channels in the sandstone grade up to 1.95kg/t U (2.30kg/t U3O8).
These results were not followed up due to the collapse of uranium exploration in the early 1980’s. This was in part political and was later compounded as the former Soviet Union flooded the market with material sourced from de-commissioned weapons.
At Pells Range a demonstrated correlation of uranium mineralisation with carbonaceous content of the host sandstone exists. Sulphides are also related.
The most prospective area for a deposit within the project is to the northeast of Pells Range Well, near the projected northern extensions of two north-west trending faults along the Gascoyne River channel. Sandstone channelling trends combined with unit offsets along these faults provide proven conditions for uranium deposition.
Geophysics
As carbonaceous sediments are easily located with electromagnetic geophysical techniques, Newera initiated an aerial EM survey in March of 2007. This is a much more effective exploration tool than simply pattern drilling an area and can be used to cheaply and effectively determine the location of the most prospective ground.
Results from the survey are highly encouraging, with a zone of conductivity co-incident with the depths of mineralisation in the historic drilling being outlined beginning in the southeast and dipping shallowly to the north-northwest (fig 4). The target zone extends over an area of approximately 3km x 1.5km striking west of north, has not been closed off even in the geophysics and possibly extends further north.
Figure 4: Results of the aerial EM survey at the Pells Range project area.
A dual phase drilling program totalling over 7,200m of RC drilling has been planned, with 3250m in phase 1. This program is in the process of being permitted through the relevant government agencies and Native Title Applicant bodies.
Uranium mineralisation
Mineralisation is associated with the zones of sediment deposited in an oxygen poor environment – “reduced” conditions & hence low pH – as opposed to those with an oxidising environment. The reducing conditions are brought about by the reduction of vegetation material to carbon in the sediments, usually a fine sandy silt. Pyrite (FeS2) is also present and is associated with high uranium grades.
Because the sandstones are largely derived from fluvial river-type sands, the carbonaceous material is found in elongate channels in the sediments, which have thicknesses of anything up to about 2 metres over areas roughly 1km x 3km. There can be several such horizons in any one channel, and all are mineralised to some degree.
There is a clear relationship between radioactivity and the proportion of carbonaceous matter present. The peak radiometric anomaly of 1326 cps (counts per second) from 54 – 55m in RC hole MOG 60 returned assays in the diamond core twin of the hole of 2500 ppm Uranium from carbonaceous shale and 25 ppm Uranium from adjacent sandstone material.
The radiometric anomaly of 40 times background from the twin of Rotary-mud hole MOG 23 assayed 1900 ppm Uranium over 10cm and was contained within a 40 cm mineralized width averaging 830 ppm (0.83 kg/t) U.
The model of a “roll front” type deposit being worked with in the past is now not seen as strictly applicable. This depositional model relies on a drop in pH when waters move from an oxidised environment to a reducing one within one homogenous unit with a change in the weathering profile.
Instead the deposition appears to be far more closely related to the drop in pH when U rich solutions strike these sediments that are reduced due to the nature of the material in the unit, rather than a change in the overall weathering profile.
The mechanism of precipitation remains the same, in that the change in pH still precipitates the uranium from solution, but the disposition is not in a broad “front”, rather the distribution is related to the distribution of the host sediment.
The precipitate at Pells Range is made up of the minerals Weeksite and Autunite, hydrated potassium uranium -silica and -calcium oxides. These minerals are soft and easily treated, meaning processing costs would be comparatively low.