Sonoro Gold (TSXV: SGO | OTCQB: SMOFF | FRA: 23SP) is pleased to report the column metallurgical test results from the Company’s Cerro Caliche property in Sonora, Mexico returned an average recovery rate of 74% for gold.
The testing was conducted at McClelland Laboratories, Inc. (“MLI”) in Sparks, Nevada as part of a detailed scope of work. The material tested consisted of over 4,700 Kilograms of mineralized material used to prepare 52 drill core composites totaling 428 lineal meters, derived from ten 85-mm diameter PQ drill holes. Column leach test gold recovery obtained at the 80% minus 12.5 mm feed size averaged 74% over approximately 90 days.
There were no obvious variations in gold recovery related to ore zone or material type (vein breccia vs. stockwork). Cyanide consumption for the 12.5 mm feeds ranged from 0.36 to 0.80 Kg NaCN/mt (sodium cyanide per metric tonne) and averaged 0.55 kg NaCN/mt.
Key findings are as follows:
- All of Cerro Caliche’s 43 variability composites and nine column composites contained little or no sulfur and little or no organic carbon with no signs of refractory behavior or preg-robbing observed during testing.
- Column testing on nine major composites confirmed heap leach amenability at both minus 50mm and 80% minus 12.5 mm feed sizes.
- No solution percolation, fines migration or solution channeling problems were encountered with little to no ‘slumping’ of ore charges occurring during leaching.
- The ore charges did not require agglomeration treatment.
- Head screen analyses showed that the column composites contained between 0.19 grams of gold per tonne (“g/t Au”) and 1.54 g/t Au with an average of 0.58 g/t Au average.
- Average silver grade for the column test composites was 5 grams of silver per tonne (“g/t Ag”) and owing to the low silver grade nature of the composites and low recoveries silver recovery data is considered semi-quantitative.
- There were no obvious variations in gold recovery related to ore zone or material type (vein breccia vs. stock work).
- Cyanide consumptions were low, and good pH control was maintained.
- Finer crushing (from minus 50 mm to 80% minus 12.5mm) improved gold recovery significantly for approximately one third of the composites tested.
- The average 74% gold recovery obtained at the 80% minus 12.5 mm feed size was approximately 8% higher than the average 66% average recovery from the minus 50mm feed size.
Sonoro’s (TSX.V: SGO) President and CEO, Kenneth MacLeod, stated, “We are pleased that the average recovery rate obtained from these definitive tests exceeds the projected 72% recovery rate used in the Company’s July 26, 2019, NI 43-101 Technical Report1 which provided the project’s maiden mineral resource estimate. We’re also pleased that the tests demonstrate similar positive metallurgical recoveries across the entire resource area.”
The recovery results are a critical component of the anticipated updated resource estimate, expected to be announced within the next few weeks. As previously disclosed, the Company engaged Micon International Limited (“Micon”) to complete the updated resource estimate as part of a Preliminary Economic Assessment (“PEA”) to be prepared by D.E.N.M. Engineering Ltd. (“D.E.N.M.”). The resource estimate will include all prior and current exploration data up to April 2021. To date, the Company has drilled and assayed results from over 34,500 meters of drilling, including 24,221 meters of new drilling since September 2020. When combined with historical data, total exploration at Cerro Caliche totals over 47,500 meters within 433 drill holes and 9,704 surface samples.
The mineralization analyzed in the metallurgical tests derived from five major gold mineralized zones at Cerro Caliche including Japoneses, Cuervos, El Colorado, Cabeza Blanca and Buena Suerte with both stock work and vein breccia material types. Preliminary information regarding heap leach amenability and sample variability was generated from bottle roll tests as previously reported by the Company on March 3, 2021. These results were used in the formulation of the present column leach tests.
The column leach tests were conducted on each of nine composites at a minus 50 mm feed size and an 80% minus 12.5 mm feed size, to determine heap leach amenability and feed size sensitivity. These column test results confirmed all nine composites were amenable to simulated heap leach cyanide treatment. The smaller 80% minus 12.5 mm feed size produced the best gold recoveries which ranged from 61.3% to 80.6% and averaged 74% after approximately 90 days, with moderate increases recorded in some of the column tests as the leaching cycle was extended. Gold recoveries obtained at the minus 50 mm feed size ranged from 53.6% to 81.5% and averaged 66% after approximately 100 days.
Sonoro’s (TSX.V: SGO) Chairman, John Darch, commented, “These very positive metallurgical test results are a critical milestone as Micon can now finalize Cerro Caliche’s updated resource estimate and allow D.E.N.M. to complete the project’s PEA. We appreciate our shareholders’ patience and ongoing support as we work to transform Sonoro from explorer to developer and finally to gold producer.”
The metallurgical tests have determined the heap leach characteristics ofthe oxide mineralization at Cerro Caliche while quantifying estimated gold and silver recoveries from the various mineralized zones near surface and at depth. These tests also establish the optimal crushing sizes and associated process flow
Quality Assurance/Quality Control (“QA/QC”) Measures and Analytical Procedures
The PQ drill cores for metallurgical testing were drilled to normal industry standards, with the cores sequentially placed in 4-row plastic core boxes, then kept in secure storage and packed onto wooden pallets prior to shipping to MLI by DHL Couriers.
No QA/QC issues were noted with the results received from the laboratory. MLI maintains accreditation with ISO/IEC Standard 17025:2017, for fields of testing that include the fire assay and solution analyses used for the current metallurgical testing program.
Qualified Person Statement
Stephen Kenwood, P.Geo., a Director of Sonoro, is a Qualified Person within the context of National Instrument 43-101 (NI 43-101) and has read and approved this news release. Readers are cautioned that the presence of mineralization on historic mines adjacent to or on Cerro Caliche is not necessarily indicative of gold mineralization in the concessions held by the Company.
About McClelland Laboratories
MLI has been providing quality laboratory and consulting services to the minerals industry for over 33 years. Their services include metallurgical, environmental, analytical testing and consulting to meet their clients’ needs during all phases of project development, operation, and closure. MLI started as a lab dedicated to the gold, silver and copper industries and has expanded to provide services in a wide range of mineral markets.
MLI has an experienced staff of metallurgical, chemical, and environmental science and engineering professionals and technicians working in over 44,000 square feet of laboratory and office space in Sparks, Nevada. MLI works closely with their clients to design testing programs which meet their project objectives. The MLI philosophy is to design testing programs and procedures to produce the maximum amount of data to efficiently add value to their clients’ projects. MLI understands that attention to detail and quality of work, along with prompt professional service, are of utmost importance to their clients.