Silver Lake Sugar Zone Mine Expansion

CLIENT: Silver Lake Resources
PROJECT: Sugar Zone Mill Expansion

PROJECT TYPE: Brownfield
LOCATION: Ontario, Canada
SERVICE SCOPE: Design Engineering


The Sugar Zone process plant was originally designed to produce doré bars via a gravity circuit as well as a concentrate via a flotation and dewatering circuit.  The design feed throughput was 600 tpd, although, upon commissioning, the operations team had achieved a throughput of 700 tpd on numerous occasions.

The client commissioned Halyard to complete a feasibility study which tabled options for increasing the throughput of the process plant to 1,200 tpd.

The challenge of this undertaking was expanding the process plant throughput within a relatively small footprint.  Also, the client wanted to consider additional processing including on-site leaching to eliminate the need to sell the concentrate, all the while considering downtime of the existing process plant during the expansion’s construction.


The following options were identified and studied:

  • Expansion of the existing process plant without the addition of leaching.
  • Expansion of the process plant with the addition of a Merrill-Crowe process.
  • Expansion of the process plant with the addition of a carbon-in-leach circuit.

Several factors such as capital and operating costs, equipment availability, operations complexity, economics of final products and constructability were taken into consideration when selecting a suitable expansion method.

Expansion of the process plant without the addition of on-site leaching prevailed as the most economical and suitable solution to achieve the 1,200 tpd throughput.


The study was completed in 4 months with three separate process designs, including mass balances, water balances and equipment sizing being completed for each option.  Capital cost estimates for mechanical equipment, civil works, structural steel and electrical were generated for each process option within the tight timeline.  Halyard were responsible for sections 13 and 17 of the NI 43-101 feasibility study technical report and sign-off by the relevant Qualified Persons (QPs).