DIAMOND PAGE — Rupert sizes up South African pipe

The third hole of a delineation drilling program on the past-producing Crown kimberlite pipe in South Africa has intersected more than 467 metres of potentially higher-grade, hypabyssal-phase kimberlite.

Vancouver-based Rupert Resources (rup-v) can earn up to a 75% interest in the subsurface portion of the mine and up to a 50% interest in a tailings reprocessing project.

Hole 3 is a 670-metre stepout north of hole 1, and is being drilled back toward the first hole at a -55 angle. Hole 3 first encountered hypabyssal kimberlite at a downhole depth of 476.3 metres and, at last report, the rock type was unchanged at a depth of 944 metres.

Rupert President Neil Briggs says the hole has deviated downward only slightly.

The upper part of the intersection has been shipped to Lakefield Research for microdiamond analysis.

Rupert has drilled four holes to date. The first was drilled to the north at an angle of -60. It cut a 20-metre interval of hypabyssal kimberlite at a downhole depth of 647 metres before intersecting a further 191.5 metres of the same rock starting at 713.5 metres. The hole bottomed out in hypabyssal kimberlite at a downhole depth of 905 metres.

A total of 84 macrodiamonds and 303 microdiamonds was recovered from 269.03 kg of core samples taken between 713.5 and 898.7 metres downhole.

The second hole, collared 230 metres north of the first, was designed to test a subsurface protrusion of the pipe, termed the “bulge.” The vertically drilled hole was stopped at 431.5 metres after failing to encounter the hypabyssal kimberlite. At a depth of 333.3 metres the hole intersected a 30.7-metre-long interval of tufficitic kimberlite breccia, and then continued through a complex, highly fractured zone of lava, shale and shale-rich kimberlite breccia to the end of the hole.

The fourth hole tested a smaller satellite pipe, 30 metres west of the main pipe. Drilled at -85, the hole intersected 174.8 metres of hypabyssal kimberlite starting at 226.2 metres. Hole 4 was completed to a depth of 442.8 metres.

The Crown kimberlite is a deep-seated, multi-phase pipe. It was intermittently mined from 1902 to 1931, producing 701,346 carats from the treatment of almost 4.5 million tonnes of kimberlite, which equates to a recovered grade of 15.7 carats per 100 tonnes.

The Crown pipe was mined out by open-pit and underground chambering methods to a depth of 165 metres and partially mined to a depth of 240 metres. Prior to the mine’s closure, underground development on the 335-metre level uncovered the large “bulge” in the pipe.

The mine closed during the Great Depression as a result of poor diamond market conditions and never reopened.

The Crown pipe is roughly circular in shape and, at surface, covers an area of 1.4 ha, increasing with depth to 2 ha at the 165-metre level. Rupert says the hypabyssal phase of the pipe has very steep and somewhat irregular margins. Drilling to date indicates that the hypabyssal kimberlite extends to a vertical depth of at least 805 metres below surface, with a true width of up to 200 metres. This represents a 470-metre downward extension from the 335-metre development level. The pipe remains open to depth.

Rupert is preparing to examine the feasibility of dewatering and refurbishing the old underground workings to provide access for drilling and bulk sampling. The main shaft has collapsed near surface.

The company is also in the midst of negotiating a contract for a scoping study, which would examine the capital and operating costs of establishing a new underground mine.

Another important part of the project is the reprocessing of the old tailings dumps. Rupert is carrying out a due diligence evaluation of the surface dumps by directing and monitoring the processing of approximately 200,000 tonnes of tailings through an on-site, 200-tonne-per-hour pan plant.

After a detailed survey of the dump piles, Rupert has estimated that they contain 4.4 million tonnes averaging 10 carats per 100 tonnes.

Four small parcels of diamonds totalling 301 carats that were recovered from the tailings sold for an average US$113 per carat.