Shear recovers its largest diamond to date from Churchill

While results remain pending for a 19.5-tonne mini-bulk sample collected from a network of four new kimberlite dyke discoveries on the Churchill joint-venture project in eastern Nunavut, further microdiamond results from samples taken from the same mini-bulk surface sites illustrate the significant diamond-bearing nature of these bodies.

Shear Minerals (SRM-V, SRMUF-O) has recovered its largest diamond to date, a rough stone measuring an impressive 3.55 by 2.95 by 2.9 mm, from a surface showing of the Kahuna kimberlite dyke. A 146.2-kg surface sample returned 710 microdiamonds using a bottom stone cutoff of 0.15 mm. Sixty of the stones exceed 0.5 mm in at least two directions. The microdiamond parcel also included larger-sized stones measuring 2.14 by 1.8 by 1.4 mm and 2.64 by 1.4 by 1.36 mm.

This past summer, Shear discovered four distinct kimberlite dyke systems in different areas of the Churchill holdings — PST003, Notch and Jigsaw in the Sedna corridor and Kahuna in the Josephine River corridor. The kimberlite dykes range from 0.5 to 4 metres wide and are highly diamondiferous.

“The partners remain encouraged about the potential for recovering commercial-sized diamonds from these bodies and economic prospects of the project, which is well-located close to tidewater in a mining-friendly jurisdiction,” said Shear president Pamela Strand in a statement.

The Churchill project covers a 2-million-acre package of mineral rights nestled between the communities of Rankin Inlet and Chesterfield Inlet in the Kivalliq region of Nunavut. Shear is the operator and owns a 51% interest in the Churchill joint venture. The remainder is divided between Stornoway Diamond (SWY-T, SWYDF-O), with a 35% position, and BHP Billiton (BHP-N), at 14%.

BHP elected not to participate in last year’s exploration program and will dilute its interest to roughly 11.3%. Shear will increase its interest to 52.6% and Stornoway will hold 36.1%.

Shear discovered the Kahuna kimberlite while drilling a linear magnetic feature that extends for more than 5.5 km. A composite drill-core sample weighing 57.6 kg delivered a previously reported 199 microdiamonds in excess of 0.15 mm. In total, the Churchill joint-venture partners have 909 microdiamonds down to a sieve size fraction of 0.15 mm from the caustic fusion analysis of 203.8 kg of surface and drill core material from Kahuna. A detailed look at the microdiamond counts is provided in the accompanying table.

A 3.6-tonne sample collected from the surface showing of Kahuna is currently being analyzed for its potential for commercial-sized stone. Results for the Kahuna mini-bulk sample, as well as the mini-bulk samples from the three other kimberlite dykes, are expected in February.

The PST003 kimberlite was hit in seven shallow holes across a strike length of 150 metres. The angled holes were positioned at the head of a prominent G10 pyrope indicator mineral train in the Sedna corridor. Geophysical surveys suggest the PST003 dyke extends for a distance of 500 metres in a northeast-southwest fashion. Each of the holes intersected narrow intervals of kimberlite, ranging from 0.15 to 1.52 metres in thickness. A composite 22.8-kg drill sample from the PST003 occurrence held 168 microdiamonds, based on a bottom stone cutoff of 0.105 mm.

In situ kimberlite was exposed in shallow hand-dug pits from which 4.1 tonnes of sample was collected for the analysis of larger, commercial-sized stones and grade. An additional 153.9 kg of kimberlite from the PST003 surface showing was separately analyzed for microdiamonds and yielded 1,208 rough stones using a higher cutoff of 0.15 mm, including the recovery of a number of highly encouraging larger diamonds. One of the biggest diamonds measures 2.9 by 2.58 by 0.96 mm and was caught in the upper 1.7-2.36 mm sieve size fraction. The next two biggest stones measure 3.04 by 2.02 by 0.66 mm and 1.88 by 1.34 by 1.32 mm.

Prospecting in the vicinity of unsourced, high-interest G10 indicator mineral till anomalies led to the discovery of the Notch and Jigsaw showings. Notch was found 3.5 km northeast of PST003. It has been trenched and tested with 11 widely spaced holes to about a 50-metre depth along a 3-km-long geophysical trend. The Notch kimberlite strikes north-south and is 0.7 to 1.5 metres wide.

A 210.1-kg sample of Notch, taken from the same site as a 6.1-tonne mini-bulk sample for which results remain pending, held 941 microdiamonds exceeding 0.15 mm in size. The largest stone measures 1.7 by 1.1 by 0.7 mm. This compares favourably to a previously reported composite 187.5-kg sample derived from outcrop and drill core that held 692 rough stones greater than 0.15 mm; the largest stone being 3 by 2.46 by 1.6 mm in size.

The Jigsaw kimberlite was found 20 km to the northwest under a thin layer of till along a prominent east-west trending, grassy linear. A magnetic high geophysical signature is traceable for more than 1 km. An initial 44.3-kg sample from the showing held 94 microdiamonds larger than 0.15 mm, including seven stones better than 0.5 mm in at least two directions.

A follow-up 282.6-kg sample has returned 868 microdiamonds, including 52 larger stones exceeding 0.5 mm in two dimensions. Two of the biggest diamonds measure 1.86 by 1.52 by 0.9 mm and 1.74 by 1.32 by 1.2 mm. An additional 5.7-tonne mini-bulk sample from Jigsaw is undergoing final analysis.

Table 1: Churchill Microdiamond Results Combined Drill Core and Surface Samples