This report describes the processing route proposed for Bonanza Ledge ore at the QR Mine Cyanidation Plant, drawing on historical testwork and current plant design.
Report context
This technical report on the Cow Mountain project, part of the Cariboo Gold Project, has a final effective date shown in the NI 43-101 disclosure. The processing section outlines the intended milling of Bonanza Ledge run of mine ore at the QR Mine Cyanidation Plant near Likely, British Columbia. The QR Mill operated in February 2009 with QR Mine ore at a design throughput of 800 tonnes per day. BGM continued milling QR ore periodically from September 2010 until summer 2014, with the first gold pour from Bonanza Ledge ore on July 24, 2014.
Processing route
Historical metallurgical testwork
Metallurgical studies referenced in the report include work by IME (2003), McClelland (2006), and BC Mining Research Ltd. (BCMR, 2006). The 2003 IME study tested three composite samples labelled High (60.8 ppm Au), Medium (11.5 ppm Au), and Low (3.1 ppm Au), with gold recoveries of 96%, 50%, and 64%, respectively. The report suggests that "preg robbing" due to graphite was a possible explanation for the lower recoveries, though no specific depth or geological information was provided for the composite samples.
Periodic reports from Mr. Doug Watt (2005) discussed flotation studies and custom treatment at the Mt. Polley concentrator. The October 17, 2005 report stated that graphitic ore or interfaces could make up 10% to 15% of the ore to be mined, and suggested this ore could be preg robbing and difficult to separate from other ore types.
The 2006 McClelland study evaluated three composites with average gold head grades of 11.6 ppm, 14.3 ppm, and 17.2 ppm Au. Using direct cyanidation and carbon in leach (CIL) procedures, all three composites provided greater than 93% gold recovery. The conclusions noted that the composites were readily amenable to direct agitated cyanidation treatment and did not display notable preg robbing character. BCMR (2006) investigated dense media separation, findings considered encouraging for upgrading ore by rejecting lower grade gangue.
2009 testwork program
Mineral process testing during 2009 focused on generating data for utilizing the existing QR operating circuit. Samples were selected with the Int'l Wayside project geologist to represent variations in grades, lithologies, and mineralogy expected in the deposit. The assayed gold grade with an estimate of the sulphide content was the primary basis for sample selection. No observations or estimates of graphite were made in the geological logs for the selected samples.
The samples consisted of archived drill core from various areas of the conceptual open pit deposit, stored in core boxes at Wells, British Columbia. Core dated from the 2004 drill program, with additional samples from 2000 and 2003. A total of 12 composite samples were tested at two laboratories, each consisting of a contiguous section of drill core.
Ore characteristics
Head assays for the 12 composites showed gold content varying from 0.96 g/t Au to 42.7 g/t Au, with a correlation between gold grade and sulphide, arsenic, and silver content. Minor base metals were evident at less than 100 ppm Cu, less than 60 ppm Pb, and less than 120 ppm Zn. Organic carbon assayed from 0.25% to 1.46%. Graphitic carbon was measured at 0.03% or less in the last three samples listed. Total sulphur ranged from 5% to 20%, with a high ratio of sulphide sulphur to total sulphur indicating a low extent of sulphur oxidation.
X-ray diffraction on six samples showed the principal mineral was typically muscovite, with occasional moderate to significant quartz. Variable trace to moderate amounts of microcline, albite, dolomite, and pyrite were present. No graphite was identified in the XRD analysis. Solid SG ranged from 2.7 to 3.4. Ore samples exhibited a low crushing work index response, based on preliminary studies.
QR Mill process flowsheet
The QR Gold Mine has an existing mill utilizing carbon-in-pulp (CIP) process technology. Run of mine ore is delivered by haulage trucks to a stockpile near the crusher feed bin and grizzly. Material is fed into the crusher dump pocket using a front-end loader, with a grizzly screening coarse material into the primary jaw crusher. Fines discharge directly onto the jaw crusher discharge conveyor, which feeds the secondary crusher feed conveyor.
Material discharges into a standard secondary cone crusher, with product feeding onto the secondary crusher discharge conveyor and then to a screen feed conveyor. A double deck secondary sizing screen separates oversize material, which feeds into a short head secondary cone crusher. Screen fines and short head crusher discharge are transferred to the fine ore bin feed conveyor, feeding the fine ore bin. The mill feed conveyor withdraws material from this bin to feed the primary grinding ball mill.
The primary ball mill discharge feeds a cyclone. Cyclone undersize is split, with approximately two thirds feeding a secondary grinding ball mill. The remaining material is treated through a gravity concentration circuit for recovery of free gold, using a Knelson centrifugal concentrator with tabling for cleaning. Cyclone oversize reports to the pre-leach thickener, with thickener undersize feeding into leaching tanks. Material and solution from leach tanks feed into CIP tanks for carbon adsorption. Loaded carbon is sent for stripping, electrowinning, filtration, and smelting to produce doré.
The report notes that the presence of graphite has been mentioned, but analysis of the 12 composite samples indicated only three contained graphite, at very low levels from less than 0.01% to 0.03%. Should the ore contain larger amounts of graphite, the CIP circuit at the QR mill would not be as effective in recovering gold from cyanide solution as a CIL leach circuit due to potential preg robbing.
Tailings management
Tailings from processed Bonanza Ledge ore are stored at the former Main Zone pit at the QR site. Ongoing studies are evaluating the suitability and capacity of the Main Tailings Storage Facility. The QR permit allows tailings discharge in the Main Zone pit.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| QR Mill design throughput | 800 tonnes/day | Design |
| Cyanide leach time | 48 hours | Design |
| Carbon-in-pulp retention time | 6 hours | Design |
| Gold head grade range (12 composites) | 0.96 to 42.7 g/t Au | Testwork |
| Gold recovery, 2003 IME tests | 96%, 50%, 64% | Testwork |
| Gold recovery, 2006 McClelland tests | >93% | Testwork |
| Historical QR Mill recovery used | 93% | Historical operating data |
| Graphitic carbon in composites | ≤0.03% | Testwork |
| Total sulphur range | 5% to 20% | Testwork |
| Organic carbon range | 0.25% to 1.46% | Testwork |
Project website: https://www.canadianminingjournal.com/news/gold-cow-mountain-yields-high-grades-for-barkerville/
Technical qualifications
The report notes that the metallurgical work referenced was completed by IME (2003) and McClelland (2006). The 2003 IME composite samples did not identify specific depth locations or related geological information. The 2006 McClelland study evaluated three composites blended from 16 sub-samples with no resource origin location provided.
The report states that the 2009 samples were selected in conjunction with the project geologist, with the assayed gold grade and estimated sulphide content as the primary sample selection basis. No observations or estimates of graphite were made in the geological logs relating to selected samples. The report also indicates that the low crushing work index response was based on preliminary studies that should be confirmed with coarser crushed feed sample.
Source: Barkerville Gold Mines Ltd., Cow Mountain NI 43-101 Technical Report, Cariboo Gold Project, Final Effective Date, Sections 17.1 through 17.3.4.
