RPA's March 2016 technical report for Mandalay Resources on the Cerro Bayo project in Chile's Aysén region records 2015 recoveries of 91% for silver and 87% for gold, and FloatStar automation adding almost 1% to recovery.
The Technical Report on the Cerro Bayo Project, Region XI (Aisén), Chile, was prepared by RPA Inc. for Mandalay Resources Corporation and dated March 15, 2016. The Cerro Bayo plant has a capacity of 1,650 t/d and makes about 31 t/d of flotation concentrate, grading 70 to 120 g/t Au and 10,000 to 13,000 g/t Ag. The report describes the process as simple: crushing, SAG milling, hydrocyclone classification, ball milling, flotation, thickening, filtration and concentrate storage.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Report date | March 15, 2016 | Not applicable | RPA Inc. for Mandalay Resources Corporation |
| Plant capacity | 1,650 | t/d | About 31 t/d of concentrate |
| Concentrate grade | 70 to 120 g/t Au; 10,000 to 13,000 g/t Ag | Not applicable | Flotation section gives 80 to 120 g/t Au |
| Ore milled, 2015 | 456,128 | t | 33% Dagny, 52% Delia NW and SE, 15% Fabiola |
| Recovery, 2015 actual | 91 Ag, 87 Au | % | 1% and 2% above budget |
| Long-run recoveries | 93.3 Ag, 90.7 Au | % | RPA considers these achievable |
| Jaw crusher | 42 x 48 inch, 200 hp | Not applicable | Product 80% minus 6 inches |
| SAG mill | 18 x 9.25 ft, 1,340 hp | Not applicable | 12% ball charge of 4 inch balls |
| Ball mill | 11.5 x 18.0 ft, 1,340 hp | Not applicable | 38% charge of 2.5 inch balls |
| Grind | 70% minus 200 mesh (74 µm) | Not applicable | Not applicable |
| Concentrate filter cake moisture | 8 to 9 | % | Larox filter, eight-minute cycles |
Overview
Ore from the underground is trucked to stockpiles near the jaw crusher, colour-coded by silver grade: green at 150 g/t, brown at 151 to 250 g/t, orange at 251 to 500 g/t and red above 500 g/t. The plant supervisor tells the loader operator how much to take from each pile to give an average mill feed grade.
The FloatStar automation system raised recovery by almost 1% after start-up. With MillStar and a new PLC, it improves recovery and operation by responding immediately to needed adjustments. The plant is controlled from an Allen Bradley SLC 500 PLC. Planned additions include flotation level sensors, pressure gauges, density meters and two Blue Star on-line analyzers.
Key Process Stages
Crushing. A loader feeds the hopper of a 42 by 48 inch Allis Minerals jaw crusher (200 hp). Product at 80% minus 6 inches goes by a 900 mm belt to a 1,500 t silo.
Grinding. Two Skako vibrating feeders and a weightometer belt feed an 18 by 9.25 ft Marcy/Allis Minerals SAG mill with a 1,340 hp motor. An internal trommel returns material over 10 mm to the mill. The minus 10 mm fraction is pumped to four 381 mm (15 inch) Warman cyclones, whose underflow goes to an 11.5 by 18.0 ft ball mill, also 1,340 hp. The final product is 70% minus 200 mesh (74 µm).
Flotation. A column cell does flash flotation to recover coarse liberated gold and silver straight to final concentrate. The rougher and scavenger circuit, seven 14.2 m³ Wemco cells with 28 minutes of residence time, makes a low-grade concentrate of about 30 g/t Au and 1,500 g/t Ag. Six 4.25 m³ Agitair cleaner cells and a 10 m by 1.10 m column cell raise it to final grade. The collectors are potassium amyl xanthate (X-350) and Aerofloat A-3477, both prepared at 5% strength, and the frother is MIBC.
Dewatering. A 9 m thickener with Superfloc A-110 raises the concentrate from about 25% to 60% solids. It is then filtered on 6.2 m² Larox filters, one operating and one standby, to 8 to 9% moisture, and trucked to the port of Chacabuco for shipment.
Tailings. Rougher and scavenger tails, which carry no commercial value, are thickened in six 6 inch Warman cyclones, with the water recycled, and deposited in the tailings facility. The tailings dam was raised to 318 m in 2014 and was scheduled for a further 2 m raise in 2016.
Additional Interesting Data and Summary
Mandalay bases its recovery assumptions on testwork and actual plant results. The Dagny and Fabiola test samples cover a wide grade range, and there are no known deleterious elements or processing factors that significantly affect recovery. In 2015 the plant milled 456,128 t, about 18% of it from ore development drifts. Silver and gold production were below budget, because 12 days were lost to a strike during collective agreement negotiations.
In summary, Cerro Bayo is a compact SAG-ball and flotation plant that blends graded stockpiles and uses flash and column flotation to make a very high-grade silver-gold concentrate, recovering about 91% of the silver and 87% of the gold in 2015.
Key Processes
- Grade-coded stockpiles and blended crusher feed
- Jaw crushing and silo storage
- SAG milling with trommel and ball milling to 74 µm
- Flash flotation in a column cell
- Rougher, scavenger, conventional cleaner and column cleaner flotation
- Concentrate thickening and Larox pressure filtration
- Cyclone-thickened tailings with water recycle
Source: Technical Report on the Cerro Bayo Project, Region XI (Aisén), Chile, prepared by RPA Inc. for Mandalay Resources Corporation, March 15, 2016.
Earlier report summaries
Earlier versions of this profile, based on older technical reports, are retained below for source traceability. Dates and figures reflect each report’s own effective date and are superseded by the current information above.
Cerro Bayo Project — 2012 Technical Report
Cerro Bayo Project — 2012 Technical Report
| Company | Mandalay Resources Corporation |
| Date | 2012-03-16 |
| Commodities | Gold, Silver |
Executive Summary
This NI 43-101 Technical Report from March 2012 details the recovery methods and historical performance of the Cerro Bayo Project operated by Mandalay Resources Corporation. The report highlights significant operational data spanning from 2002 to 2011, with a focus on gold and silver recovery rates. Historical data from 2002 to 2008 shows average recoveries of 92.2% for gold and 94.7% for silver, with daily throughput averaging 1,053 tonnes in 2007. The project utilizes an underground mining method characterized by a “retreat” approach, which impacts ore recovery strategies as re-entry into mined stopes is not possible.
Performance in 2011 indicated lower grades and recoveries compared to budgeted amounts, largely due to the inclusion of ore from outside the modeled resource areas, specifically the Fabiola, Dagny, and Bianca veins. Approximately 17% of the milled tonnage came from a low-grade stockpile, and over 60% of underground mining occurred outside the planned resource model. Despite these variances, the report concludes that historical recovery figures are achievable with strict adherence to the mine plan. The processing circuit includes crushing, grinding, and flotation, with no leaching methods currently employed.
The report provides a comprehensive overview of the plant’s mill performance, including head grades, concentrate grades, and metal production figures. It emphasizes the profitability of recovering sterilized ore left behind due to the retreat mining method. The data suggests that while operational challenges exist regarding grade control and resource modeling, the project remains viable and capable of meeting recovery targets when operating within the planned resource boundaries.
Website: https://www.juniorminingnetwork.com/junior-miner-news/press-releases/1038-tsx/mnd/111651-mandalay-resources-corporation-completes-sale-of-cerro-bayo-mine-to-equus-mining.html
Report Date: 2012-03-16
Region: Aysén
Commodity: Gold, Silver
Ore type:
