Diversified major Rio Tinto has completed the drilling of ten bulk trenches to conclude its sampling programme on Canadian junior Star Diamond’s Star kimberlite, using a new technology.

The trench cutter sampling rig that Rio Tinto Exploration Canada (RTEC) used at Star, which is located in the Star-Orion South diamond project in Saskatchewan, has a design sampling depth of 250 m below the surface.

“This ambitious sampling programme required significant time to assemble all the components on site, but once it commenced the trench cutter has operated efficiently and successfully, recovering a large (estimated to be about 8 271 wet tonnes) bulk sample from the Star kimberlite,” Star Diamond senior VP for exploration and development George Read said on Tuesday.

The trench cutter programme had been designed to recover high-quality kimberlite samples that ensured diamond breakage was minimised.

“The successful use of this new trench cutter sampling rig technology for the recovery of kimberlite bulk samples also has the ability to revolutionise future bulk sampling and mining of kimberlites, particularly for kimberlites characteristic of the Fort à la Corne diamond district of central Saskatchewan,” commented Read.

The trench cutter sampling rig consists of a Bauer BC 50 cutter mounted on a Bauer MC 128 duty-cycle crane. The depth of each trench is determined by kimberlite thickness.

The ten holes completed on the Star kimberlite included a total of 2 351 m of trench cutter drilling and intersected a total of 1 215.5 m of kimberlite. This kimberlite was pumped to surface and recovered using a kimberlite separation unit (KSU), with samples loaded and stored in cubic metre bulk bags.

The KSU is designed to recover kimberlite fragments between 80 mm and 0.85 mm from the trench cutter sampling rig slurry. Kimberlite collected is being stored in a secure storage area, until the on-site bulk sample plant (BSP) has been fully assembled and commissioned.

The BSP is at an advanced stage of construction. Once construction is completed, RTEC intends to commission the BSP using existing Orion South kimberlite that was originally collected by Star Diamond from the underground bulk sampling programme, performed in early 2009.

Read said that the use of Orion South material for commissioning the BSP would help ensure that the BSP was operating at its design capacity before starting to process the trench cutter samples that were collected from RTEC’s 2019 bulk sampling programme.