Back in January, Canadian gold mining junior Osisko Development Corp with its flagship Cariboo Gold Project, located near Wells, central British Columbia, announced that a new Sandvik MT720 continuous miner (roadheader) had been delivered to the Cariboo site. The company is using the technology for drift development at the existing Bonanza Ledge Phase II mine and the planned Cariboo mine which are both part of the overall Cariboo plan.

The former has an estimated production of 62,000 oz over an initial two years with further exploration upside near existing workings and is starting production this quarter; Cariboo production start is expected in 2023 with the feasibility study tracking for H2 2021 and permits expected in 2022 with a short construction period thereafter. It is the flagship asset capable of producing over 200,000 oz/y. Both mines will see ore processed at the permitted and scalable 1,000 t/d existing QR Mill.

The roadheader was assembled in February 2021 and is presently being commissioned in drift development at Bonanza Ledge Phase II. It has cut over 100 m of drift (5.8 m wide x 5.3 m of height) with up to 7 m of advancement achieved during a 12 hour shift including rock support, services installation and mucking. The company states: “This equipment is engineered to mechanically cut the hard and abrasive rock mass and is expected to improve the development performance by 25%, and to reduce costs by 50% compared to traditional ‘drill and blast’ development.”

Both roadheader and drill and blast development will be used for the Cariboo mines with an estimated monthly development rate of 200 m per face and 300 m with multiple faces with an average 11 km/year of development peaking at 16 km/year using two roadheader crews and 3-4 conventional crews. Mine production will use longitudinal retreat long-hole stoping using a combination of cemented rock fill, uncemented rock fill and paste fill with 30 m sub-levels. The company add that automation will be a major focus.

The company has also announced positive results of recent test work aimed at confirming the use ore sorting to improve the processed grade of mineral resources at the project. It commissioned TOMRA in the last quarter of 2020 to complete ore sorting tests using a XRT sensor on a sample of approximately 2,200 kg of ore coming from the Cariboo Gold project. After screening to remove the fine particles (size less than 10 mm), approximately 1,800 kg of sample, corresponding to medium grade mineralised material typically encountered around high grade veins and replacements, was tested by the TOMRA sorter. For the Cariboo Gold Project, grades higher than 4.0 g/t will go directly to flotation where metallurgical tests yields gold recovery of 98.3%. Grades lower than 4.0 g/t are sent to a pre-concentration ore sorting process. The business case for ore sorting includes:

• 10 g/t Au is the approximate in situ grade of vein material based on core logging data. Statistics show 100% or more increase in grade by using a XRT sensor driven ore sorter to remove unmineralised rock from sulphide rich vein material.
• 93.1% gold recovery with ore sorting, 98.3% gold recovery from flotation concentrate and overall recovery of 91.3% (ore sorting + flotation + leaching).
• 50% of waste rock can be removed after the initial crushing by utilising the XRT sensor ore sorter for less than $2.00 per tonne. 50% less material goes to the grinding and flotation circuit.
• 25% estimated savings in processing costs and 7% of overall operating costs; 30% estimated savings in capital costs; 50% reduction in process water and power requirements for the concentrator.
• Eliminates the requirements for a Tailings Storage Facility (TSF) for the concentrator located in Wells. Only 13% of all extracted ore will generate tailings that will be stored at the existing QR mill TSF as filtered tailings

“Combining the two new tests done at the TOMRA facility with the previous 21 tests done at the Steinert facility in Kentucky, USA, more than 4,700 kg of mineralisation was tested with commercially available ore sorting technology. The average combined recovery of gold from all tests was approximately 93.1% and a mass pull of 42.6%. Using the ore sorting as a primary pre-concentration process reduces overall processing costs by removing mechanically, unmineralised material (57.6% in tests done). In the case of the Cariboo Gold project, this translates to important cost savings on the capital expenditures and operation expenditures for the mill facility by reducing the requirement to process 50% to 60% of the extracted mineral resource tonnage from the mine. This translates to approximately $5.00/tonne of operation expenditures savings and a concentrator feed grade increase from 80 to 100%.”

The benefits of ore sorting technology are also substantial from an environmental perspective by reducing the energy required for the communition circuit, the amount of processing reagents and water needed for processing and more importantly, enabling the Cariboo Gold Project to have no tailings storage facility near the community of Wells. Sorted material can be transported and deposited within the existing waste pile adjacent to the Bonanza Ledge mine currently in operation.

Sean Roosen, Chair and CEO of Osisko, commented: “he results from the TOMRA tests validate the favorable mineralogy of the Cariboo Gold Project for ore sorting technology. These new tests, completed on medium grade material, demonstrate the potential to provide a higher grade, ore sorter concentrate, at a low cost, to be further upgraded via a standard flotation process, to the planned concentrator facility in Wells, BC. It will also enable us to substantially reduce the amount of process water, chemicals and energy required in comparison to conventional processing. The Sensor Sorting Technology is used in many industries including metals and plastics recycling as well as vegetable and fruit sorting which are far more challenging. This is another step to demonstrating our ongoing commitment to best environmental practices.”

In the coming months, Osisko Development plans a second ore sorting test at the TOMRA test facility in Wedel, Germany to provide even further confidence for this design improvement of the Wells concentrator. The company also expects to receive approval to begin development of an underground access for a 10,000 t bulk sample in the second quarter of 2021. The bulk sample permit intends to replicate the Cariboo Gold Project’s mining conditions by mining two stopes and processing the mineralized material through an ore sorter on site. A new ore sorter was purchased in the last quarter of 2020 and is expected to arrive in Wells during the third quarter of 2021 with test work beginning before year end.