Canadian Mining Journal


DIAMONDS: Bauer trench cutter used for bulk sample

Bauer’s expertise includes a trench cutter sampling rig hard at work at the Star-Orion South diamond project. (Image: Bauer Maschinen)

SASKATCHEWAN – Exploration continues at the Star kimberlite, part of the Star-Orion South project 60 km east of Prince Albert. The project is owned by Saskatoon’s Star Diamond Corp. and optioned to Rio Tinto Exploration Canada.

As operator of the project, Rio Tinto had recommended the use of a trench cutter sampling rig built by Bauer Maschinen of Germany. The manufacturer says this is the first time that this technology will be used in an exploration project to sample Kimber lite at depth of up to 250 metres.

The trench cutter sampling rig consists of a Bauer BC 50 cutter mounted on a Bauer MC 128 duty-cycle crane. The is designed to sample large volumes of kimberlite by excavating a rectangular hole of 3.2 by 1.5 metres. Each 10 metres of advance down the hole in the kimberlite, will yield some 100 tonnes of sample. The cutter head has been designed to excavate kimberlite fragments up to 80 mm in diameter, which are then pumped in a slurry to surface.

The trench cutter sampling rig was tested in October 2018, prior to winter shutdown, with the first hole reaching a depth of 37.1 metres below surface. The rig successfully excavated the sand and till overburden and returned a substantial proportion of large fragments from the till. Despite performing well, performance of the trench cutter was negatively impacted by the commissioning of the first desanding plant, which did not operate at design capacity.

A redesigned kimberlite separation unit has been manufactured and delivered to site. This KSU is designed to recover kimberlite fragments between 80 and 0.85 mm from the trench cutter sampling rig slurry. Washed kimberlite material will then be collected in cubic metre bulk bags for delivery to an on-site bulk sample plant. Assembly of this plant is currently underway.

The trench cutter sampling rig and associated KSU were designed by Rio Tinto to minimize diamond breakage during sample excavation, washing and bagging. Washed kimberlite material will help ensure optimal performance of bulk sample plant. Final diamond recovery is to be conducted by Rio Tinto at a secure off-site facility.

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