Summary:
Deposit Types
Uranium occurs in several different igneous, metamorphic, and sedimentary environments. The primary deposit types that are currently being exploited for uranium are sandstone-hosted deposits, unconformity-related deposits, and metamorphic vein deposits. Uranium is also produced as a byproduct from hematite breccia deposits at Olympic Dam in Australia and from quartz-pebble gold deposits in the Witwatersrand Basin in South Africa.
Geological studies on the uranium-gold deposits in the Witwatersrand Basin in South Africa and the uranium deposits in the Blind River-Elliot Lake region of Canada have resulted in the definition of the uranium-gold bearing quartz-pebble conglomerate class of mineral deposit (Robertson 1986). Uranium is produced from the Witwatersrand deposits as a by-product and the conglomerate bands are commonly referred to as “reefs”. This terminology was used at Elliot Lake to designate the uranium-bearing conglomerate beds. The Quartz-Pebble Conglomerate Deposit types also occur at other localities, such as the Jacobina District in Brazil, and at certain locations in Australia, however, most of these deposits have not yet been exploited.
The Elliot Lake deposits are interpreted to be modified paleoplacer (detrital) deposits and the source rocks are believed to be pegmatitic granite (Robertson, 1986) located to the north. The uranium and rare earthbearing heavy minerals were released from the granites as a result of weathering and transported to the site of deposition in channel systems in Early Proterozoic sedimentary basins. Heavy mineral grains along with quartz pebbles and pyrite were deposited from fast-flowing streams in topographic lows in the Archean bedrock. With the current oxygen content of the atmosphere, the uranium minerals would oxidize and dissolve in the ground water and be transported in solution. It is suggested that the erosion and sedimentation took place in the early Proterozoic in a reducing environment as a result of the low oxygen content of the atmosphere prior to 2,200 Ma.
The quartz pebbles and the uranium and associated heavy minerals were deposited in areas where the velocity of the streams was reduced, forming conglomerate beds in deltaic piles. Peripheral to the conglomerate beds, poorly sorted feldspathic sand and silt were deposited. Subsequent diagenesis resulted in the formation of the conglomerate beds intercalated within coarse sandstone with scattered pebbles and siltstone. At the Denison Mine, the highest grade uranium mineralization occurred to the lee of basement highs where the flow was more abruptly reduced (A. MacEachern, personal communication, in RPA, 2007b).
There has been post-depositional alteration of the uranium as evidenced by the formation of brannerite, secondary pyrite and the formation of secondary quartz and sericite (Robinson and Spooner, 1984). Robinson and Spooner suggest that this post-depositional modification was caused by low Eh near-neutral ground water.
The mineralogical examination of the Pardee deposit supports this suggestion and demonstrates that the uranium is now primarily contained within secondary uranium minerals as a result of the interaction of the detrital uraninite with groundwater. Within the MCB, the deposition of the secondary minerals appears to have been limited causing local upgrading of the uranium content in some areas and leaching in others. For the heavy REE there is a predominant contribution from secondary mineral phases, while the light REE are predominantly found in detrital minerals.
Mineralization
General Description
The quartzite beds in the Ryan Member in the Pardee Channel have a background grade of approximately 0.01% U3O8, rising to 0.02% within coarser grained “gritty” beds. The higher grade uranium mineralization is contained within three conglomerate beds, the Basal Conglomerate Bed (BCB), the Main Conglomerate Bed (MCB), which is equivalent to the Pardee Reef, and the Floater Reefs.
Limited rare earth assay data are available outside of the MCB intercepts drilled and assayed by Pele Mountain from 2006 to 2012. The available data show that rare earths mineralization continues above and below the MCB. The Pele Mountain sampling protocol targeted the conglomerate and pebble beds occurrences, as well as concentrations of heavy mineral bands within the Ryan Member to determine the extent of the mineralization.
The BCB is located directly above the Archean basement rocks. This unit consists of poorly sorted, angular, and rounded pebbles that are granitic, volcanic and quartzitic and are commonly 2 in. (5 cm) in diameter. It may contain up to 5% pyrite in the matrix. This bed is discontinuous and, in drill holes where it is intersected, is generally thin, averaging approximately 0.5 m in thickness. However, historically, the sampling of the BCB has not been consistent and thicker sections have been intersected at Eco Ridge. The matrix is a grey or grey-green quartzite with up to 10% medium to coarse grained pyrite, and locally some pyrrhotite. The BCB is discontinuous, but, where intersected in the historic drilling, the average thickness is approximately 0.5 m, although widths up to four metres have been intersected in recent drilling and an intersection of 11 m was returned in drill hole CB-1, approximately 20 m below the MCB.
Sprague (1965) indicated that the basal reef was interpreted as being too narrow and too local to be of primary interest in Rio Algom’s program, however, he did note that two holes, PA-26 and S-18, cut basal reef averaging 0.07% U3O8 / 1.7 m and 0.126% U3O8 / 1.4 m, respectively. Sprague suggested that detailed drilling of this reef may prove up small tonnages of interest.
The MCB is located approximately 10 m to 15 m above the BCB. It is intercalated within the quartzite beds. The MCB and the first few metres immediately above it host the Mineral Resource on the Eco Ridge property. The conglomerate contains quartz, quartzite, and dark cherty pebbles in a fine grained, pyriterich matrix. The pebbles make up to 60% of the rock and are most abundant in the lower metre. The pebbles are well rounded and 0.64 cm to 3.8 cm thick. This bed fines upwards with narrow intercalated beds of quartzite. Pyrite occurs in the matrix generally as small grains comprising 4% to 15% of the rock. Sprague reported that the bed varies from 1.3 m to 4.4 m in thickness. The highest grade uranium mineralization within the bed is located in the conglomerate band on the footwall contact with the underlying quartzite. The footwall contact is well-defined and provides a marker for geological assessment. The hanging wall contact is not as distinct due to the increased occurrences of intercalated bands of quartzite within the conglomerate.
The MCB contains the higher grade rare earths and uranium mineralization and outcrops on the Eco Ridge property and extends over a strike length of 6,000 m. The uranium and REE mineralization has been intersected in holes at a depth of 1,000 m and over a dip length of approximately 3,800 m.
A series of thin conglomerate beds are present within the quartzite overlying the hanging wall contact of the MCB. These thin conglomerate beds represent the Floater Reefs. The Floater Reefs generally extend from 6 m to 15 m above the MCB. The Floater Reefs average from 0.1 m to 2.0 m in thickness and the uranium content is generally less than 0.04%. These beds are not well developed on the Eco Ridge property and it is not possible to correlate individual beds between the drill holes. In many cases, quartzite beds logged as “grit” or “pebble conglomerate” contain low-grade mineralization and these pebble conglomerates are probably equivalent to the Floater Reefs. The quartzite with Floater Reefs above the MCB is referred to in this Technical Report as the Hanging Wall Zone (HWZ).