Black Lake is staked over the Platt Creek Fault, a major NNE trending fault parallel to the Black Lake Fault. Shear zones and faults of this style are frequently host to unconformity-type uranium deposits in the Athabasca Basin. The Black Lake property is underlain by 250 to 600 metres of Proterozoic sandstone of the Athabasca Group that dips shallowly to the south. The sandstone unconformably overlies Archean-aged basement rocks of the Tantato Domain, which comprise metavolcanic units, graphite-bearing metasedimentary gneiss, mafic sills and granites that have been affected by amphibolite to granulite facies metamorphism. Basement rocks trend mainly northeast, and are affected by tight, megascopic folds. Post-Athabasca faults also strike mainly to the northeast, and include the Platt Creek Fault, which extends through the project area northward into older syn-metamorphic shear zones.
Exploration to date has been principally directed towards the testing of a southeast-dipping reverse fault, termed the "Eastern Fault", a subparallel strand of the Platt Creek Fault system, and associated graphitic gneiss units which are defined by electromagnetic ("EM") conductors. Competency contrast between soft chloritized amphibolites or graphitic pelites and the siliceous leucocratic granitic gneiss favours the development of ductile to brittle shear zones. Reactivation of these shears may result in post-sandstone faulting. Locally multiple stages of post-sandstone faulting or branching of the same fault have resulted in more widespread fracturing and desilicification of sandstone and clay alteration of basement rocks along the fault in the vicinity of the unconformity, conditions prospective for uranium deposits. Dravite (Mg-tourmaline), siderite and less commonly pyrite veining are present in the sandstone column particularly in the northern Black Lake property, which are alteration assemblages that are often spatially associated with uranium mineralization.
The Black Lake property was initially explored in the 1970s following the discovery of radioactive boulders identified in till. EM surveys carried out initially by Eldorado Nuclear Ltd. during 1979 to 1980, and then subsequently by Cameco Corporation in 2000, identified well-defined north-northeast trending conductors now known to be associated with the Platt Creek Fault and its principal eastern strand along the east side of the conductive package, the Eastern Fault Zone.
After evaluating drill core from previous operators which intersected above background, low-grade mineralization near the unconformity, and on the basis of the strength of the Platt Creek Fault conductors, UEX commenced systematic testing for uranium mineralization on the Black Lake property in 2003.
During the 2004 summer program, hole BL-18 encountered unconformity-type uranium mineralization at a vertical depth of 310.5 metres grading 0.69% U3
over 4.4 metres between 310.5 and 314.9 metres, including 0.85% U3
over 3.3 metres between 311.0 and 314.3 metres. The mineralization occurs at the base of the Athabasca sandstone column straddling the unconformity. Also associated with the BL-18 intercept are highly anomalous concentrations of arsenic, copper, lead and nickel, which are typically associated with unconformity-style mineralization in other parts of the Athabasca Basin. On the basis of the BL-18 intersection, UEX increased its exploration activities in the project area, testing the Eastern Fault Zone and associated graphitic package primarily in the northern portion of the Black Lake property.
Subsequent drilling in 2005 and 2006 intersected additional uranium mineralization adjacent to the BL-18 intercepts, defining a small, flat-lying pod of mineralization which is developed along the unconformity several tens of metres in the footwall of the Eastern Fault Zone. In addition, significant uranium mineralization was encountered in two holes along the Eastern Fault Zone at, or immediately below, the Athabasca unconformity. In hole BL-56, located approximately 200 metres south of hole BL-18, mineralization was intersected from 319.9 to 322.5 metres, grading 0.22% U3
over 2.9 metres. Hole BL-64, located approximately 600 metres south of BL-18, intersected unconformity-style uranium mineralization, similar to that found in hole BL-18, from 338.75 to 340.75 metres, grading 0.45% U3
over 2.0 metres.
Several holes drilled in 2006 and 2007 along the Eastern Fault Zone, between sections 128+00 N and 129+00 N, intersected a small overthrust wedge of graphitic gneiss on Athabasca sandstone associated with a major reverse fault where uranium mineralization is developed. In the Athabasca Basin, the presence of such a basement "wedge" is considered an important geological feature for potential uranium deposition, having formed a structural trap for mineralizing hydrothermal fluids. The uranium mineralization in these drill holes occurs along and immediately beneath the wedge where the Eastern Fault Zone intersects the Athabasca unconformity. Drilling intercepts in this area include 0.50% U3
over 3.3 metres from 273.45 to 276.75 metres, including 1.60% U3
over 0.7 metres in drill hole BL-082, 0.24% U3
over 3.0 metres from 275.4 to 278.4 metres, including 0.56% U3
over 1.0 metres in drill hole BL-137, and 0.67% U3
over 3.0 metres from 274.1 to 277.1 metres, including 1.58% U3
over 1.0 metre in drill hole BL-140.
In summary, drilling by UEX at Black Lake to date has intersected unconformity-style mineralization in the northern Black Lake property along a strike length of more than 1.7 kilometres along and adjacent to the Eastern Fault Zone of the Platt Creek Fault system. Mineralization comprises (i) unconformity-style mineralization straddling the unconformity in the footwall of the Eastern Fault Zone, and (ii) mineralization directly along the fault where it intersects the unconformity, with best intercepts developed where a small basement wedge is present. Principal intercepts are as follows:
- BL-018: 0.69% U3O8 over 4.40 metres from 310.5 to 314.9 metres, including 1.96% U3O8 over 0.50 metres (BL-18 pod);
- BL-023: 0.28% U3O8 over 0.10 metres from 307.90 to 308.00 metres (Eastern Fault Zone);
- BL-032: 0.16% U3O8 over 1.40 metres from 313.90 to 315.30 metres (BL-18 pod);
- BL-056: 0.22% U3O8 over 2.90 metres from 319.90 to 322.50 metres (Eastern Fault Zone);
- BL-064: 0.45% U3O8 over 2.00 metres from 338.75 to 340.75 metres (Eastern Fault Zone);
- BL-082: 0.50% U3O8 over 3.30 metres from 273.45 to 276.75 metres, including 1.60% U3O8 over 0.70 (Eastern Fault Zone, fault wedge);
- BL-109: 0.10% U3O8 over 1.90 metres, from 311.70 to 313.60 metres (BL-18 pod);
- BL-110: 0.79% U3O8 over 2.82 metres, from 309.73 to 312.55 metres (BL-18 pod);
- BL-111: 0.11% U3O8 over 2.90 metres, from 312.50 to 315.40 metres (BL-18 pod);
- BL-137: 0.24% U3O8 over 3.00 metres from 275.40 to 278.40 metres, including 0.56% U3O8 over 1.00 metres (Eastern Fault Zone, fault wedge); and
- BL-140: 0.67% U3O8 over 3.00 metres from 274.1 to 277.1 metres, including 1.58% U3O8 over 1.00 metre (Eastern Fault Zone, fault wedge).