DIAMOND PAGE — Crown pipe yields more diamonds for Rupert

A delineation drilling program at the former-producing Crown diamond mine in South Africa is providing Rupert Resources (RUP-V) with a better understanding of the mine’s deep-seated kimberlite pipe.

With four holes completed and a fifth in progress, drilling has encountered kimberlite to a vertical depth of over 800 metres below surface.

Microdiamond results were recently announced for the third hole of the program, which was drilled back towards the first hole at a minus 55 angle, some 670 metres north of hole 1.

Hole 3 intersected a 501.1-metre-thick interval of kimberlite and kimberlite breccia, with included rafts of country rock, starting at a downhole depth of 476.3 metres. The hole was shut down in kimberlite at a depth of 977.4 metres downhole. The 501.1-metre-long interval represents a horizontal width of 270 metres and a vertical extent of 420 metres.

A collection of 18 samples weighing a total of 402.55 kg and representing a non-continuous 253.2 metres of varying degrees of kimberlite purity, yielded 80 macrodiamonds (greater than 0.5 mm) and 191 microdiamonds. Approximately 77% of the recovered diamonds are said to be “white transparent.” In a recent edition of Canaccord Capital’s daily investment report, mining analyst David James describes the latest results as “quite good,” but notes that an underground bulk sampling program, and possibly the testing of other targets on the Crown property, are needed before Rupert’s potential is fully understood.

The microdiamond results from hole 3 compare with hole 1, which yielded 84 macros and 303 micros from 269.03 kg of core samples taken between 713.5 and 898.7 metres downhole.

Rupert holds the right to acquire up to a 75% interest of the subsurface portion of the Crown mine, and up to a 50% interest in a tailings reprocessing operation. The Vancouver-based junior is required to make a combination of cash payments and expenditures totalling US$15.8 million, of which, US$5.6 million can be paid from project profits.

The Crown mine operated intermittently from 1902 to 1931, producing 701,346 carats from the treatment of nearly 4.5 million tonnes of kimberlite, which equates to a recovered grade of 15.7 carats per 100 tonnes. The largest diamond recovered weighed 86.5 carats. The mine closed during the Great Depression and never re-opened.

An additional 396,000 carats are believed to be contained in tailings from past production, at an average grade of 10 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 240-metre depth. The kimberlite pipe is roughly circular in shape and, at surface, covers an area of 1.4 ha. The pipe increases in area with depth.

A substantial “bulge” on the southern side of the pipe was encountered during development work on the 335-metre level, prior to the mine’s closure.

A second, smaller satellite pipe, 30 metres west of the main pipe, was discovered during mining operations in 1921. The satellite pipe is not exposed at surface and is thought to join the main body at depth. The fourth hole of Rupert’s drilling program tested the satellite pipe. Collared at minus 85, the hole intersected 174.8 metres of hypabyssal kimberlite starting at 226.2 metres. Microdiamond results are expected shortly.

Hole 6 was drilled through the satellite pipe and, at last report, was in the main part of the pipe at a downhole depth of 669.2 metres.

Drill core samples are being split, sealed in buckets at the drill site and shipped to Lakefield Research in Ontario for analysis by caustic dissolution methods. Petrographic examinations and mineral chemistry studies will be performed on sections of the retained core.

Former owner De Beers Consolidated Mines (DBRS-Q) estimated the Crown pipe contained a resource of 20.3 million tonnes to a depth of 440 metres, with a predicted average grade of 32 carats per 100 tonnes. De Beers acquired the inactive mine in 1939 and held on to the property for nearly 60 years before disposing of it in the early part of 1997.

The Crown pipe is composed mainly of tufficitic kimberlite breccia and hypabyssal kimberlite with varying degrees of purity depending on the abundance of country-rock xenoliths.

The major types of kimberlite encountered in hole 3 was linked by a micaceous kimberlite matrix, which Rupert says is consistent with a single intrusive phase.

Drilling indicates that to a vertical depth of 600 metres, the Crown pipe is composed of mostly impure hypabyssal kimberlite to kimberlite breccia, with a relatively large proportion of country-rock fragments. This material is similar to the 4.5 million tonnes mined from the upper portion of the pipe by past operators.

Below 600 metres, the kimberlite has fewer country-rock xenoliths and much higher diamond counts. Rupert expects the in situ grade will be considerably higher than 30 carats per 100 tonnes.

The company is examining the feasibility of dewatering and refurbishing the old underground workings to provide access for drilling and bulk sampling.

Rupert is in the process of raising additional funds that will go towards an underground program.

As part of its evaluation of the Crown mine, Rupert is directing and monitoring the processing of approximately 200,000 tonnes of tailings through an on-site, 200-tonne-per-hour pan plant. The large-scale, bulk-sampling program is designed to determine an accurate grade and value of the diamonds in the tailings. An initial 301-carat parcel of diamonds recovered from the tailings sold for an average of US$113 per carat.

George Albino, a Toronto-based mining analyst with Sprott Securities, reports that an additional 1,200 carats of diamonds, which he viewed on a recent property visit, are worth an estimated US$55 per carat. He considers the 1,200-carat parcel to be a better representation of the tailings diamonds.