Thunderbird Resources (ASX: THB) is homing in on evidence of uranium mineralisation after drilling significant hydrothermal alteration and detecting radioactivity at its Hidden Bay project in Canada’s Athabasca Basin.
The maiden four-hole drilling campaign was designed primarily to test possible basement-hosted uranium targets close to the Athabasca Basin unconformity and the company now believes it may be close to unveiling a “uranium mineralising system”. The drilling intersected intense alteration and rock-fabric destruction, which is believed to be the cause of deep-seated basement geophysical anomalism and the origin of locally-elevated radioactivity.
Three holes were completed out of the four proposed for the original program. The second and third holes were put in to test two other gravity low targets.
Then, an additional follow-up hole was collared 270m west of the first and it has already been completed to 264m depth. A total of 1320m have been drilled in the four holes.
The second hole was terminated at 176m before attaining its intended 430m-deep gravity low target. The third hole was completed to 440m depth and also intersected significant alteration.
The key object of the first hole was to test a priority gravity low identified close to the unconformity and where one of two major north-to-south-trending transcurrent Tabbernor faults cut through the project tenement. The hole initially intersected the relatively shallow unconformity at 19.5m, which along with other geophysical data locates the project at the eastern margin of the basin.
Below the unconformity, the first hole bored through metasediments to 44.5m and was then dominated by various felsic intrusives ranging between granitic and granodioritic composition, with scattered intervals of pegmatite and minor amphibolites.
It pierced pervasive deformation and alteration between 405.4m and end-of-hole (EOH) at 440m. The most significant deformation was recorded between 405m and 409m, accompanied by intense clay, hematite and chlorite alteration that continued to EOH.
The alteration is interpreted to be the probable cause of the gravity low and is potentially indicative of an unconformity-related uranium mineralising system. The drill rig has now moved to test a fifth gravity target in the eastern part of the company’s tenement area.
We’re very encouraged to have intersected a strong zone of alteration in our first drill hole at Hidden Bay. This alteration may indicate that we are proximal to a uranium mineralising system and follow-up work is now being planned, which will hopefully enable us to vector towards uranium mineralisation.
Thunderbird Resources Executive Chairman George Bauk
The Hidden Bay project sits on the eastern margins of the Athabasca Basin, which spans the Canadian provinces of Alberta and Saskatchewan and is known for its many world-class, high-grade uranium mines and exploration projects.
The basin measures about 400km east-to-west by about 200km north-to-south. Its crystalline basin rocks have historically produced around 20 per cent of the world’s primary uranium supply.
A series of major uranium deposits are developed at the basin-wide unconformity between the underlying crystalline metamorphic Palaeoproterozoic rocks that form the floor of the basin and the overlying Athabasca sandstones that fill it. It is thought that the uranium mineralisation originates in, or near the unconformity.
Some of the more significant plays in the area include the advanced Triple R, Arrow, Midwest, Rough Rider, Phoenix, Gryphon, Millenium, Shea Creek and Centennial deposits, while operating projects or those on hold include Cigar Lake and McArthur River.
Other projects that have reported past production include Eagle Point, Cluff Lake, Key Lake and McClean Lake and other unassigned operations include the Dawn Lake Amok/Carswell and Rabbit Lake operations.
Hidden Bay sits about 345km east of Cluff Lake and NexGen Energy’s massive Arrow deposit that was discovered in 2014.
Cluff Lake reported past production of 62.5 million pounds of uranium oxide at 0.92 per cent. NexGen Energy’s 100 per cent-owned Rook I project – the host of its Arrow deposit – is the biggest development-stage uranium project in Canada and one of the world’s leading resources.
The Arrow deposit comprises a measured reserve of 209.6 million pounds of uranium oxide at a grade of 4.35 per cent, in addition to other resources in indicated and inferred categories. The project boasts outstanding economics based on US$50 ($AU74.40) per pound of uranium oxide, with a post-tax net present value (NPV) at 8 per cent of C$3.47 billion (AU$3.8 billion) and an internal rate of return of 52.4 per cent.
The average annual production rate for the first five years is 28.8 million pounds of uranium oxide and the projected mine life is 10.7 years. The estimated average annual operating cost is projected to be C$7.58 (AU$8.30) per pound of uranium oxide.
A further positive aspect for the Hidden Bay project is that the unconformity margin arcs through more than two thirds of Thunderbird’s project tenement. The company believes the project is manifestly underexplored, with previous drilling confined to depths of 30m or less and it is understood only a single drillhole has been put into the property since 1987.
Exploration history of the ground includes work undertaken – mostly in the in 1970s and 80s – by Gulf Minerals, while 26 historical drillholes have tested EM conductors on the western edge of Thunderbird’s ground to depths between 89m and 292m. More recently, Thunderbird has undertaken airborne gravity and magnetic surveys and respective reinterpretative work in 2022, along with reconnaissance geological mapping, soil-radon sampling and soil-gas hydrocarbon (SGH) sampling for uranium in selected target areas this year and results are pending.
The company has identified six priority gravity low anomalies coinciding with an east/north-east structural corridor aligned with the unconformity margins and a significant thrust fault paralleling the same margin that runs diagonally through the property.
That thrust fault also links the major Tabbernor Dragon Lake and Ahenakew Lake faults and Thunderbird’s ground is sandwiched between them. It suggests that potential could exist for various conduits for mineralisation at Hidden Bay, which could have transported uranium mineralisation downwards from the unconformity into various points of concentration.
The company is now awaiting analytical results from its current drilling campaign and is planning more geophysical exploration around the first gravity anomaly to test the extent of the alteration zone and the geology of the granite and metasedimentary contact zone.
With plenty of strong provenance and examples to draw upon and with enough active local exploration and geographical, geological, spatial and mineral analogues to keep a whole crop of explorers occupied, Thunderbird’s maiden drilling can be hailed an initial success. Now, it remains for the company to home in on the origins and extent of the radioactivity it has identified in its first drillhole.
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