quakes99 wrote: If you'd like to understand how large deep underground deposits like Arrow have been explored and developed in the past, you should read the history of the McArthur River mine as described in a really interesting paper written by B.W. Jamieson of Cameco. It takes the reader on a walk through the exploratory drilling at McArthur River and the underground delineation drilling that they undertook to fully define that resource, and the mining program that followed.
Back in the 1990's the technology for doing surface-based delineation of deep deposits was not as advanced as it is today. Using improving directional drilling methods, NexGen is trying to accomplish something that has never been effectively done before... define Indicated & Measured resouce solely from surface drilling. But that comes at a cost, because the first 400-500m of every drill hole is wasted expense given the high-grade is not found in that region. Re-using a single hole for the upper portion, then multiple directional holes at depth, cuts a lot of that expense, but also reduces the chances of discovering shallower high-grade that would come with a fresh hole each time you drill down. Also very hard to get closely spaced holes at all the necessary angles when working from half a kilometre above. So, it's a compromise.
It would be far more effective to do as was done at McArthur River, which was to sink a shaft down to depth then do short horizontal holes from subsurface drilling bays. I suspect NexGen will have to go that route eventually, as it is just so time consuming to spend 2 weeks to drill a single hole from surface, when a large number of short delineation holes could be drilled at depth in the same time frame.
I'll put an excerpt of the Jamieson paper here but you really need to read the whole report to see the diagrams of the shafts and subsurface drilling bays that were used to drill out in fan-shaped patterns in order to intersect the ore body sufficiently to determine its overall size, shape, and average grade from over 500m underground.. You can pick up a copy of the paper at the link below:
https://www.iaea.org/inis/collection/NCLCollectionStore/_Public/33/032/33032922.pdf Here's an excerpt:
In 1988 the ore body was discovered following eight years of systematic exploration in the area. Improvements to large-loop time-domain electromagnetic methods allowed the definition of graphite conductors in the basement fault structure which controls the location of the ore. Drilling confirmed this structure and discovered sub-economic mineralization five kilometres to the southwest of the McArthur River ore body. The recognition of favourable alteration patterns in drill holes helped guide the exploration drilling to the ore body.
Several years of core drilling from surface followed and resulted in the outlining of high-grade mineralization over 1.7 kilometres of strike length. By 1991, 60 holes were completed of which 37 holes intersected uranium mineralization at a depth of 500 to 600 metres. Based on this information a resource of 260 million pounds at an average grade of 5% U3O8 was estimated. Seventy per cent of the estimated resource was based on only seven drill holes, and 18% was based on a single hole which graded 43% U3O8 over 25 metres [1]. Following completion of the surface drilling it was decided to undertake an underground exploration programme which would provide the detailed information about the shape of the individual ore bodies.
The project was referred to the Joint Federal-Provincial Panel on Uranium Mining Developments in Northern Saskatchewan, in February, 1991. Scoping meetings were held in nine northern and three southern communities in early 1992 to get public input into the guidelines for the environmental impact statement (EIS). The guidelines were issued later that year, after a public review of the draft. Environmental studies had already been started to develop the information necessaiy for the EIS. An EIS for underground development was developed and the Panel conducted hearings on this subject at five northern and two southern communities in December, 1992. After a favourable report from the Panel and licensing by both the federal Atomic Energy Control Board (AECB)1 and the Province of Saskatchewan, shaft sinking commenced in the spring of 1993 [2].
Under that excavation license, horizontal development on the 530 metre level was undertaken to permit diamond drilling along a 300 metre strike length of the mineralized zone. This definition drilling increased the reserves and resources to 416 000 000 pounds U3O8 at an average grade of 15% [3]. A second EIS to proceed to underground production was submitted in late 1995, and the public hearings were conducted in the fall of 1996. A favourable Panel report was issued in February, 1997. Both provincial and federal government approvals were received in May, 1997.
In August 1997 all licenses and permits had been received by both federal and provincial agencies to allow the two years construction of the project to proceed. The main license issued being the 'License to Construct' by the AECB. Construction was completed within the feasibility cost estimate and on schedule. Operating licenses were received in October, 1999 for McArthur River, and in November, 1999 for Key Lake to receive and process the high grade McArthur River ore. Production commenced, as scheduled, in early December, 1999 following the commissioning of process equipment with waste rock and low grade ore.
3. UNDERGROUND EXPLORATION PROGRAMME
In July of 1994 underground development commenced to allow the detailed diamond drilling of the ore zones identified by surface drilling. This program was aimed at determining the shape, grade and continuity of the central part of the ore body, on a strike length of 300 metres.
Once essential services were established for power, and the collection and pumping of mine water, development was extended to within 3 5 metres of the ore zone. Development then progressed southwards and parallel to the strike of the ore zone for approximately 300 metres. A total of 998 metres of development was completed by June 1996.
Diamond drill bays were created every 30 metres along strike. Diamond drilling commenced once development had adequately advanced, and holes were drilled on sections and fanned above and below the mineralized areas. Infill drilling was conducted, as encouraging results and time permitted, to define the ore zones every 10 metres along strike.
During the 1995/1996 underground drilling programme 115 holes were completed. The drilling of these holes provided both the ore geometry and grade as well as geotechnical and hydrogeological information necessary to select mining methods and design material handling systems [4].
As the high-grade ore was encountered, extremely high levels of radon (up to 8.869 billion2 Bq/m3) were found associated with the ground water. The higher levels of radon were usually associated with low water flows, however the water pressures were normally hydrostatic at a pressure of 51 Bars.
Things to note, of course, are that in order to sink the shaft to conduct the underground surveys they had to do an Environmental Impact Study and get buy-in and engagement/approval from local communities and government. That alone took over 2 years before shaft sinking could commence prior to the underground drill program.
The history of Uranium mining in the Athabasca Basin is a fascinating story.
Good luck with your own research and due diligence!
Cheers!