The EJF consists of pyroclastic crater fill as well as pyroclastic flow and fall deposits lying outside of the crater. The Star Kimberlite is somewhat unique in that pyroclastic kimberlite outside the crater can be confidently correlated to crater-filling kimberlite. The crater fill, near the center of the crater, consists of two kimberlite facies: PK, which is typical pyroclastic EJF, and KB, which is coarse kimberlite breccia.
A younger cross-cutting kimberlite eruptive phase, referred to as the Mid-Joli Fou Kimberlite (“MJF”) is aerially restricted to the western portion of the Star Kimberlite (see Figures 6.3 and 6.4). This eruptive phase has erupted through the older EJF Kimberlite, as evidenced by rarely preserved autoliths of EJF kimberlite. The kimberlite has some similarities to the EJF, but has a distinct matrix-supported texture, fewer indicator minerals, appears to be very poorly sorted and is generally massive to weakly bedded.
The youngest kimberlite eruptive event, referred to as the Late Joli Fou Kimberlite (“LJF”), is confined to the northern and northeastern portion of the Star Kimberlite and generally forms a thin veneer, deposited on older EJF and MJF. The LJF has many similarities to the MJF but is generally finer-grained, more massive and has the ubiquitous presence of small (0.5-50 mm) shale clasts. The relationship between the MJF and LJF remains ambiguous; however, the LJF may represent a finer-grained remobilized version of the MJF, which slumped or flowed into the marginal marine sedimentary environment incorporating poorly consolidated mudstone material. A sub-unit of the LJF, known as LJF Slump, is identified based on the distinct increase in the shale clast content and the weak development of sub-horizontal bedding planes.
Upper Kimberlitic Sediments
Sitting directly on the Late Joli Fou-aged kimberlite, or locally within the overlying shale sequence, are two main kimberlitic sedimentary units (see Figure 6.4). Directly above the LJF there is the typical development of kimberlitic sandstone, with common to abundant shale blocks ranging between 0.1 m and 5 m in size known as KDF. In general, the shale blocks appear to be massive and in sharp contact with the host kimberlitic sandstone. A distinct fining-up sequence of kimberlitic sandstone that grades into a kimberlitic siltstone and finally a calcareous light grey to white siltstone rests directly on the KDF and is more rarely separated by thick 2–10 m beds of shale. Ubiquitously situated 6-8 m above the fining-up unit is another fine-grained kimberlite sandstone horizon which acts as a distinct marker horizon over most of the kimberlite. This surface is a close approximation to the Viking-Westgate contact. Two to four metres below this bed a 1-3 cm heavy mineral lag is present in many of the core holes. This lag may represent a transgressive surface of erosion (Zonneveld et al., 2004).
6.3.2 GEOLOGICAL DESCRIPTION – STAR KIMBERLITE STRATIGRAPHY
Prior to the start of the Phase 2 and 3 bulk sampling work programs, the geological nomenclature utilized for the various kimberlitic phases found within the Star Kimberlite were simply classified as crater-facies pyroclastic kimberlite. This lithofacies was then sub-divided into two broad groups: the first described as in-situ pyroclastic kimberlite, and the second as reworked volcaniclastic kimberlite.
Shore developed a new geological nomenclature and core logging system prior to the commencement of the advanced exploration program. Under this revised scheme, the major kimberlitic stratigraphic units, sub-units and major rock types were defined based on the descriptive nature and quantitative data capture of size classification of various megacrystic,
P&E Mining Consultants Inc. NI 43-101 Technical Report No 159 Shore Gold Inc. - Star Diamond Project Resource Estimate Update
Page 32 of 109