CGG Aviation (Australia) Pty Ltd. of West Perth, Australia completed a FALCON® airborne gravity gradiometer gravity survey which included magnetic and laser scanning digital elevation components: 987 line-km flown at 200-metre line spacing covering a grid area of approximately 10 x 14 km (see Alpha news release dated March 12, 2015).
The survey showed the magnetic signature is relatively smooth indicating deep sources, and a generally increasing depth to source going northward. This is consistent with non‐magnetic sediments overlying magnetic basement rocks within a basin which is generally deepening to the north. Drill hole data collected in the area is consistent with this observation. Image processing of the magnetic data helps bring out some less obvious details in the data. An obvious feature is the somewhat sinuous low seen trending southwest-northeast through the centre of the entire block. This is roughly coincident with a mapped fault on Government of Saskatchewan 1:250 000 maps and also with the Derkson corridor. This magnetic signature will allow more precise definition of the location of the corridor and fault. In addition, some of the direction changes in the corridor appear to be related to breaks in the magnetic material to the southeast, which may represent crosscutting faults or shears. In other areas, the magnetics can similarly be used to refine locations of inferred corridors. The western edge of the block shows a higher magnetic intensity in general than the rest of the block, perhaps suggesting a lithology change in the basement.
The FALCON® gravity gradiometry gD response is seen to be highest in the southern portion of the Hook Lake area, and lowest to the northwest. There is a marked boundary between low and high across the location of the Derkson corridor, particularly in the north end of the block. Overall the response appears to reflect the varying depth of the unconformity and thickness of the sedimentary package. A thicker low density sediment package on top of higher density basement rocks results in a gD low. The change in gD suggests vertical motion along the Derkson corridor, with the basin being deeper on the northwest side of the corridor. Drill hole information is consistent with this interpretation.
Historical Exploration Uranium exploration in the vicinity of the Hook Lake property has been reported since 1969. The region surrounding and including the current property has had a myriad of companies and surveys completed and reported since 1969. There have been several major conductive trends found on the property, including the Carter, Derkson and Patterson Lake conductors. Details of exploration with significant results in the area that cover a portion of the current property are as follows:
In 1996, Uranerz Exploration and Mining discovered, through boulder sampling, that the area north of Derkson Lake to Carter Lake and along the Williams River was geochemically anomalous with elevated boron (dravite), kaolinite and chlorite content.
An east-flanking zone of strong illitization was also observed. In 1997, UEM and Cameco completed Fixed Loop Time-Domain Electromagnetic (FLTEM) discovering several conductive trends, and follow up boulder sampling was carried out. In 1998, the same companies completed additional ground EM surveys and a larger airborne GEOTEM survey.
The current property was drill tested in 1999 with four drill holes, again in 2001 with one drill hole and in 2003 with one drill hole.
Several holes displayed criteria favourable to unconformity uranium deposits with anomalous clay alteration, quartz dissolution, Athabasca Group and basement structure and/or anomalous geochemical enrichment. Between 2005 and 2007, ALX Uranium predecessor, ESO Uranium, conducted exploration including Airborne EM surveys, ground resistivity and diamond drilling. The PIMA analyses performed on drill core in 2007 were re-evaluated in 2013. This work identified clay alteration minerals including sudoite (chlorite), dravite, smectite/illite, sericite, and probable carbonate. In addition, anomalous values of pathfinder elements including nickel, copper, silver, tungsten, and mercury were found in certain samples in Athabasca sandstone, which along with the dissolution and silicification noted in drill logs provide evidence of hydrothermal alteration along the northern end of the Derkson corridor. Follow-up drilling along the corridor is warranted.
The northern portion of the property was explored by the Nexgen Energy Corp. predecessor, Dejour Enterprises Ltd. and Titan Uranium Inc., between 2005 and 2010 with airborne EM, ground Fixed Loop EM, Moving Loop EM and DC Resistivity surveys.
Two drill holes in 2006 tested historic conductors. The recent ground EM and resistivity surveys have not yet been drill tested.