Summary:
Fort À La Corne Kimberlite Model
Unlike the idealized South African kimberlite model (Hawthorne, 1975), the majority of the Fort À La Corne (FalC) kimberlites are mainly shallow bowl-shaped kimberlites which have kimberlite footprints ranging up to 2,000 m wide and extending to depths ranging from approximately 100 m to greater than 700 m.
The limited deep drilling, however, precludes any interpretation of the shape of the kimberlites below about 450 m. Therefore, at depth, the FalC kimberlites may, in fact, resemble the idealized South African model.
FalC kimberlites were emplaced into poorly consolidated Cretaceous-aged clastic and marine sedimentary rocks. They are generally interpreted to be in the form of stacked, sub-horizontal lenses or shallow zones of crater facies material with associated pyroclastic flow and fall deposits of large lateral extent. The kimberlite phases are classified entirely as crater-facies pyroclastic kimberlite, although a number of kimberlite units may be distinguished according to their grain size, style of emplacement, primary and chemical alteration and the abundance and presence of olivine macrocrysts.
PROPERTY GEOLOGY - Fort À La Corne (FalC) area
A northwest-trending kimberlite province covering a 50 km by 30 km area has been identified in the FalC area. These kimberlites have clearly defined airborne and ground magnetic anomaly signatures within a quiet background.
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 ha to over 400 ha. The kimberlite bodies themselves typically occur as stacked, sub horizontal lenses or shallow zones of crater facies kimberlite with footprints ranging up to 2,000 m wide and occur at depths ranging from 100 m to greater than 700 m. Limited deep drilling precludes interpretation of the shape of the kimberlites below about 350 m. At depth, FalC kimberlites may resemble the idealized South African kimberlite model. 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.
Star Kimberlite Geology And Mineralization
The Star Kimberlite was deposited within the Cretaceous sedimentary rocks of the lower Colorado and Mannville groups, which unconformably overlie Paleozoic limestones and dolomites. The glacial overburden thickness ranges from 90 to 130 m with an average of 92 m. Portions of the Star Kimberlite have been emplaced contemporaneously with the deposition of the Mannville and lower Colorado sediments. However, the majority of the Star Kimberlite is interpreted to have erupted through the Mannville and into the early parts of the lower Colorado Group sediments (Joli Fou Formation time). The local lower Colorado and Mannville interface is situated approximately 170 m. The Mannville Group and Paleozoic interface lies approximately 340 m, as interpreted from the Company’s core drill holes.
The Star Kimberlite consists of two distinct types of kimberlite: dominant eruptive kimberlite and subordinate kimberlitic sediments. The eruptive kimberlite deposits at the Star Kimberlite are sub- divided into five main kimberlite phases emanating from a single vent, each with distinctive physical and chemical properties (Harvey et al., 2006 and Harvey, 2009a):
1. Cantuar Kimberlite;
2. Pense Kimberlite;
3. Early Joli Fou Kimberlite (“EJF”);
4. Mid Joli Fou Kimberlite (“MJF”);
5. Late Joli Fou Kimberlite (“LJF”).
All the major kimberlite phases of the Star Kimberlite have been proven to contain macrodiamonds.
Orion South Kimberlite Geology And Mineralization
Like the Star Kimberlite, the Orion South Kimberlite was deposited within the Cretaceous sedimentary rocks of the lower Colorado and Mannville groups, which unconformably overlie Paleozoic limestones and dolomites. The glacial overburden thickness ranges from 97 to 121 m with an average of 105 m. Portions of the Orion South Kimberlite have been emplaced contemporaneously with the deposition of the Mannville and lower Colorado sediments. However, the majority of the Orion South Kimberlite is interpreted to have erupted through the Mannville and into the early parts of the lower Colorado Group sediments (Joli Fou Formation time). The local lower Colorado and Mannville interface is situated approximately 191 m below surface. The Mannville Group and Paleozoic interface lies approximately 347 m, as interpreted from drill holes. The Orion South Kimberlite is comprised of multiple eruptive units (or phases), each of which is texturally, mineralogically, physically and chemically distinct. Within the kimberlite, the units have cross-cutting relationships near conduits, but are stacked vertically within the volcanic edifice and crater / extra-crater deposits. Several conduits, feeding different units, have been identified on Orion South.
During Cantuar (Mannville Group) deposition, thought to be a time of continental fluvial-deltaic deposition (Zonneveld et al., 2004), kimberlite was deposited and reworked. Drilling indicates that the Cantuar-aged kimberlite deposits are generally thin (< 30 m thick) sheets occurring at multiple horizons within the Cantuar sediments. The bulk of the kimberlite deposits are confined within the marginal marine to marine sedimentary strata (Zonneveld et al., 2004) of the Upper Mannville Group (Pense Formation) and the lower Colorado Group (Joli Fou Formation). These kimberlite deposits are associated with the main crater excavation and crater fill. Proximal to the conduits and in close proximity to the base of the Mannville Group sandstone, the conduits flare (ScottSmith et al., 1994) at a steep angle giving way to shallow angles near the margin of the craters.
The Orion South Kimberlite consists of two distinct types of kimberlite: dominant eruptive kimberlite and subordinate kimberlitic sediments. The eruptive kimberlite deposits at the Orion South Kimberlite are sub-divided into six main kimberlite phases, each with distinctive physical and chemical properties: which enable mapping and stratigraphic correlation of units as seen in Figure (Harvey et al., 2009a & b):
1. Cantuar Kimberlite (“CPK”);
2. Early Pense (“P3”);
3. Pense Kimberlite (“Pense”);
4. Early Joli Fou Kimberlite (“EJF”);
5. Late Joli Fou Kimberlite (“LJF”);
6. Viking Pyroclastic Kimberlite (“VPK”).