FORT À LA CORNE AREA
In the FALC area, a northwest-trending kimberlite province some 50 km long by 30 km wide has been identified. The kimberlites have clearly defined magnetic anomaly signatures within a quiet background. Approximately 69 kimberlitic bodies have been drilled to date, with the majority of the kimberlite bodies discovered occurring in the extensive central zone.
The kimberlite bodies of the FALC kimberlite province occur as stacked, subhorizontal lenses or shallow zones of crater facies kimberlite of large lateral extent. While both hypabyssal and volcaniclastic kimberlitic facies have been intersected by drilling, their inter-relationship is not well known. It is possible that the former represent either late stage pulses or even xenolithic blocks. By far, the more important occurrences discovered to date comprise crater facies volcaniclastic kimberlites emplaced into Cretaceous marine, lacustrine and subaerial volcanic rocks laid down in, or along, a shallow, epicontinental sea.
The main volcaniclastic kimberlite deposits were preceded by smaller kimberlite bodies comprising conformable, graded beds of pyroclastic debris as much as 40 metres thick, indicative of subaerial eruption onto Albian (Middle Cretaceous) floodplains, intertidal zones, or lakes. Subsequently, larger, shallow craters were excavated in poorly-consolidated marine to marginal-marine shale under subaerial to shallow marine conditions and backfilled with pyroclastic sediments forming multiple-graded kimberlitic beds. Kimberlitic pyroclastic flows, erupted at the time of crater excavation, produced stacked kimberlite deposits and are preserved as aprons around the craters that can extend several hundred metres from the craters. Contact angles of the kimberlite with the surrounding country rock can range from 90 degrees to zero degrees depending on whether the contact is in the pipe or in the outflow pyroclastic deposits.
The “classical champagne-glass” shaped morphologies typically associated with FALC kimberlite bodies represent the explosive emplacement of kimberlite material within sequences of poorly consolidated sediments (Scott Smith et al., 1994). Geophysical modelling suggests that the areal extent of the individual kimberlitic bodies in the FALC kimberlite province range from 2.7 hectares to over 350 hectares.
Continued sedimentation during the Late Cretaceous buried the kimberlites. These cover rocks were largely removed by glaciation, essentially to the level of kimberlite emplacement. FALC kimberlites explored, to date, show limited to no glacial erosion. The majority of bodies drilled to date by both the FALC-JV and Shore lie just below the till/bedrock interface. Kimberlites discovered by De Beers in 1988, and later by Corona Corporation at Sturgeon Lake, 30 km northwest of Prince Albert, have no recognisable aeromagnetic signature and are regarded to be rootless, ice-thrust rafts or erratics of kimberlite, indicating erosion of a possibly later suite of kimberlites.
PROPERTY GEOLOGICAL SETTING
The Star Kimberlite was deposited within the Cretaceous-aged sediments of the Lower Colorado and Mannville groups (see Figure 6.2), which unconformably overlie Palaeozoic age limestone and dolomitic rocks. The glacial overburden thickness ranges from 90 to 130 metres. Parts of the Star Kimberlite have been emplaced contemporaneously with the deposition of the Mannville and Lower Colorado sediments. However, the major portion of the Star Kimberlite is interpreted to have erupted through the Mannville and into early parts of the Lower Colorado Group sediments (Joli Fou Formation time). The local Lower Colorado and Mannville interface is
P&E Mining Consultants Inc. NI 43-101 Technical Report No 159 Shore Gold Inc. - Star Diamond Project Resource Estimate Update
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