Star Diamond acquired Newmont's interest in the broader Fort à la Corne joint venture in June 2017 and concurrently entered an option to joint venture agreement with Rio over up to 60%, which it dubbed Project FalCon.
The company said Rio had used new sampling technology at its Star kimberlite, with the trench cutter sampling rig able to reach up to 250m below surface and it had been designed to recover high quality kimberlite samples and minimise diamond breakage.
"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, Canada," senior vice president exploration and development George Read said.
He said a bulk sample plant was at an advanced stage of construction on site and would be commissioned using existing Orion South kimberlite from a 2009 programme, before testing this year's Star samples.
A 2018 preliminary economic assessment had estimated 66 million carats could be produced from the Star and Orion South kimberlites over a 34-year mine life.
The base case had outlined an IRR of 19% with a 3.4-year payback.
A study released in March this year confirmed "unusually high proportions" of rare Type IIa diamonds at both Star and Orion South.
Star Diamond had C$4 million in working capital at June 30.
Its shares spiked to 38c in October last year after the Saskatchewan environment ministry approved the project.
They were as low as 18c in August and closed 2.4% lower yesterday to 20.5c, capitalising it about $84 million (US$63 million).