Edmonton – April 27, 2022 – Benchmark Metals Inc. (the “Company” or “Benchmark“) (TSX-V: BNCH) (OTCQX: BNCHF) (WKN: A2JM2X) – is pleased to announce advanced metallurgical laboratory test results for the Company’s 100% owned Lawyers gold-silver Project. The testwork has provided gold leach recoveries averaging 93%, and silver recoveries of approximately 65% from the Amethyst Gold Breccia (AGB) and Cliffs Creek resources. The advanced test work confirms a simple preliminary design using conventional whole rock cyanide leaching and incorporating Merrill Crowe zinc precipitation to produce on-site gold and silver Dore. The test work builds a large data set throughout the main Amethyst Gold Breccia (AGB) and Cliffs Creek resource areas, in addition to composites representing potentially the first years of mining in a conceptual mine plan. The Lawyers Project is located in the historic mining region of the Golden Horseshoe, located in north-central British Columbia (BC), Canada.
Jim Greig, President and Director, commented, “The results demonstrate exceptional gold recovery from rocks utilizing a conventional and proven method that results in pouring gold and silver Dore bars. Technical results and participation from miners like Yamana Gold in Benchmark Metals continues to validate the potential to become Canada’s next major gold and silver mine.”
Ian Harris, VP Engineering, commented, “We are very encouraged by the metallurgical test results that demonstrate robust recovery on a standard conceptual mining schedule and support using a straightforward, proven, industry norm, processing flow sheet. The growing data set is now incorporated into our modelling and supportive of the evaluation of multiple mining scenarios for future feasibility level evaluations.”
The metallurgical program was advanced and coordinated by F. Wright Consulting Inc., under the direction of Frank Wright, P. Eng. Mr. Wright is an independent metallurgical consultant, with extensive experience in precious and base metal process development. He is the qualified person as defined by National Instrument 43-101.
The supporting studies have been conducted by several globally recognized laboratories including:
- ALS Laboratory – Kamloops, BC: for detailed comminution testing;
- BV Mineral Process Laboratories – Richmond, BC: for optimization and variability gravity treatment and bottle roll leaching studies;
- FLSmidth Inc. – Salt Lake City, Utah: for leach response confirmation, gravity pre-treatment, and filtration test work, and;
- SGS Mineral Services – Lakefield, Ontario: for treatment circuit simulation for the leach process, liquid/solid separation, and Merrill Crowe.
Various mineralogical studies have also been performed on AGB and Cliffs Creek samples that indicate the gold is primarily present as fine native particles. Depending on the sample specimen, the silver occurs predominantly as acanathite (Ag2S), or electrum, often as coarser particles of 200 microns or greater, although it can be fine grained as well. To a lesser extent native silver is present.
Image #1 – Core sample from the Cliff Creek Deposit representing the largest mineral resource area
Selected drill core from drill hole 21CCDD085, containing electrum and native silver grading 77.9 grams per tonne (g/t) gold and 1,675 g/t silver or 98.84 g/t gold equivalent (*AuEq).
Metallurgical Testing Results
The recent laboratory studies suggest processing by grinding to a targeted feed particle size 80% passing (P80) range of 106 to 125 microns, incorporating gravity pretreatment by centrifugal concentration, followed by conventional cyanide leaching of the gravity tailing. These moderate operating conditions provide excellent gold recoveries, that consistently exceed 90%. The majority of the gold is yielded within 24 hours of leach retention time. More intensive treatment procedures provide minimal improvement to the overall gold recovery.
As is typical for this type of mineralization the silver leach dissolution is more challenged, averaging approximately 65%. Generally higher silver recovery occurs in the Cliffs Creek Zone, as compared to AGB. The silver recovery benefited from an additional 12 hours of leach retention time, along with elevated sodium cyanide (NaCN) addition and increased pH (with lime). Additional more aggressive procedures such as use of lead nitrate, oxygen, finer grinding, further lixiviant, and elevated caustic can offer some limited further improvement to silver recovery. However, the more aggressive treatment procedures were not deemed to be economically beneficial at this time. Further optimization of silver recovery will be undertaken in the future as mill head grade and metal pricing accuracy improve towards more detailed economic evaluation.
These reported test results are additional to prior optimization testing, and to preliminary data previously reported in June 2021. The following Table provides a summary of the most recent bottle roll data obtained under ambient conditions, with 36 hours of leach retention time at 40 wt.% solids, and pH~11. This recently completed laboratory program consists of a further 40 variability samples conducted on AGB zone, and 25 variability samples from the Cliffs Creek zone. The variability samples originate from drill core assay rejects composited in length to each represent potential mining bench heights of ~10 m. Separately included in the Table are Year 1 to Year 5 annual composites that were blended based on the most recent conceptual mining schedule.
Table 1: Summary Table of Variability Test Results – Gold and Silver Leach Recovery
The results confirm the initial metallurgical evaluation that with modest operating conditions a positive process response is expected from both the principal mineral zones of the Lawyers property. This is especially true for gold, which is the primary metal value, and shows recovery in the low to mid ninety percent range for samples obtained spatially and at depth to well represent the known resource. The initial metallurgical data has been incorporated into the preliminary economic assessment anticipated for issuing near the end of the second quarter of 2022. Following this, the current data, along with further evaluation to be undertaken will be used in the upcoming Feasibility Study.
The technical content of this news release has been reviewed and approved by Michael Dufresne, M.Sc, P.Geol., P.Geo., a qualified person as defined by National Instrument 43-101.
About Benchmark Metals
Benchmark Metals Inc. is a Canadian based gold and silver company advancing its 100% owned Lawyer’s Gold-Silver Project located in the prolific Golden Horseshoe of northern British Columbia, Canada. The Project consists of three mineralized deposits that remain open for expansion, in addition to +20 new target areas along the 20 kilometre trend. The Company trades on the TSX Venture Exchange in Canada, the OTCQX Best Market in the United States, and the Tradegate Exchange in Europe. Benchmark is managed by proven resource sector professionals, who have a track record of advancing exploration projects from grassroots scenarios through to production.