In early June, Rio Tinto (NYSE: RIO; LSE: RIO) began a planned bulk sample program at Star Diamond’s (TSX: DIAM) Star-Orion South diamond project, 60 km east of Prince Albert, Saskatchewan.
The 10-hole program will take place this summer at the Star kimberlite. A 20-hole program is also planned to follow at Orion South.
In 2017, Rio signed an option to earn up to 60% of the project for a total investment of up to $71.5 million over 7.5 years. However, it won’t earn an interest (51%) in the project until it completes the ﬁrst two phases of work: a 10-hole bulk sampling program (or $18.5 million in spending) within the ﬁrst three years, plus another 10-hole program (or $18.5 million in spending) within 18 months.
In order to prepare for the bulk sample, Rio has had to tap some new technology. The company has opted to use a modiﬁed Bauer trench cutter rig – normally used in civil engineering projects – for the task. The rigs will dig rectangular holes 3.2 by 1.2 metres to depths of up to 250 metres.
“The successful use of this new Trench Cutter sampling rig technology for the recovery of kimberlite bulk samples has the ability to revolutionize future bulk sampling and mining of kimberlites, particularly for kimberlites characteristic of the Fort à la Corne diamond district of central Saskatchewan,” said senior vice-president exploration and development, George Read in a release.
The rig has been modiﬁed to minimize diamond breakage.
Star-Orion South is a low grade project (around 14 carats per tonne), but is known to host large stones and rare, high value, Type IIa stones. A recent study of a 10,000-carat parcel of stones from the project showed that 26.5% of Star diamonds and 12.5% of Orion South diamonds are Type IIa vs. only about 2% of mined diamonds globally.
Rio is also building a bulk sample process plant onsite, which will be ready before the end of the year.
– This article originally appeared in the June 2019 issue of Diamonds in Canada magazine.