The widespread Early Joli Fou Kimberlite (“EJF”) is volumetrically the most important eruptive phase, with the thickest intersections occurring towards the western portion of the Star Kimberlite (see Figure 6.3 and 6.4). Distal deposits of the kimberlite sit directly on lower Joli Fou shale (Spinney Hill Member) and are interpreted as Joli Fou-age equivalent. The EJF is also observed to sit directly on older Pense and Cantuar kimberlite phases. The kimberlite is in contact with the Cantuar Formation (and at depth with the Devonian Carbonate) in the vicinity of the vent area to the west (see Figures 6.3 and 6.4).
The kimberlite is clast-supported and dominated by olivine crystals with rare juvenile lapilli. Mantle-derived xenocrysts and xenoliths are relatively common in this unit. Fining-up beds dominate and commonly occur as 1-5 m (rarely up to 15 m) thick, lithic-rich breccia basal units overlain by a xenolith-poor tuffaceous kimberlite. Contacts are represented by an abrupt change in grain-size with rare planar sharp varieties.
The upper surface of the EJF at the Star Kimberlite is shown in Figure 6.5. There are three main areas: a west-central low, a circular high surrounding the central low, and an outer zone at moderate to low level. The thickest deposits are below the west-central low. These areas are correlative with: a central vent/crater, a positive relief tephra ring (cinder cone), and an extra- crater (tephra-ring distal) zone. Kimberlite deposits largely confined to the inner crater/vent area and the positive relief tephra ring are referred to as EJF “Inner” area deposits and those confined to the distal, extra-crater areas are referred to as EJF “Outer” area deposits.
Figure 6-5: Elevation map of the EJF Kimberlite surface (lows are blue; highs are magenta).
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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