The Brucejack Gold Mine in the province of British Columbia, Canada commenced operation in the summer of 2017. It uses a Combimix mixer supplied by BHS-Sonthofen to stabilise the tailings – fine-grained residues from gold mining used for backfilling the mine. Among other things, the mixer sets itself apart with especially high availability at the remote location on Brucejack Lake.
The Valley of the Kings is a region in northwestern British Columbia with gold deposits occurring over more than 120,000 hectares. Brucejack is operated by Pretium Resources which has been extracting about 2,700 t of gold ore per day here since 2017. Nearly the same amount of residue is produced by the processing plant’s belt filter. Used to backfill the mines, these tailings first have to be stabilised with cement and water. BHS-Sonthofen supplied the corresponding technology, a Combimix mixer using the overflow process.
Just 40 km from the border with Alaska, the Valley of the Kings on Brucejack Lake poses challenges for both people and machines. Particularly heavy snowfall, low temperatures, and the region’s isolation make logistics difficult. Operation under these climate conditions puts great demands on the technology as well. Pretium places great emphasis on reliability, minimal maintenance, high availability of replacement parts, and fast on-site service for all components and systems.
The standards for the mixing technology were correspondingly high: For example, only massive steel components could be used to prevent possible corrosion in cavities. The mixer and all peripherals also had to be accepted and certified in accordance with the Canadian CSA Group standards. Strict requirements had to be met in the selection of motors, as well.
André Däschlein, Sales Director Mixing and Crushing Technology at BHS: “We examined the individual requirements point by point and implemented them. The reliability of our machines was a particularly important factor since the location is so remote.”
The filter cake, which is mixed with cement and water in the mixer, is very fine-grained and also supplied continuously. That is why a Combimix mixer was chosen, combining the mixing technology advantages of the BHS twin-shaft batch mixer operated in a continuous way. The Combimix mixer uses the overflow process: The material to be mixed is added at one end of the mixing trough and leaves the machine through an opening on the opposite end – a proven solution for fine material that does not settle on the bottom of the mixer due to its density.
For the ‘Brucejack’ project, BHS also equipped the mixer with a dual mixer mechanism that thoroughly breaks up, disperses, and homogenizes the filter cake, even at low rotational speeds. Considerably lower energy consumption compared to other mixer types is a welcome side effect of the lower rotational speed. The average retention time of the material to be mixed in the trough is about 1.5 to 2.5 minutes. It is regulated through the controlled addition of new material at the inlet.
To maximise the length of maintenance intervals and minimise downtime, BHS equipped the mixing trough with 28 mm thick and especially wear-resistant Optilong tiles. Fully automated lubrication is integrated for the same reason. It reaches all lubrication points (more than a dozen) and works according to a flexible, adjustable schedule. A special design feature of the BHS mixers also contributes to the mixer’s high availability. The mixer shaft bearings are physically separated from the seal to the mixing trough, so that the material to be mixed is kept away from the bearings. High-pressure cleaning was also installed for the first time for such an application.
The Brucejack gold mine equipped with BHS mixing technology commenced operation in the summer of 2017, and the Combimix mixer has been used continuously ever since. Tim Bates, General Superintendent Construction at Pretium Resources: “More than 2,700 t of ore are processed per day. To date the mixer has operated with no downtime, and no service calls from BHS were needed. We have found exactly the right partner with BHS-Sonthofen.” BHS also operates a subsidiary and a replacement parts warehouse in the US, providing additional security for the customer.