- Overall recoveries of >90%, including gravity, expected -
TSX: VTR
TORONTO, Nov. 22 /CNW/ - Volta Resources Inc. ("Volta" or the "Company") (TSX: VTR) is pleased to announce that recent metallurgical tests undertaken by SGS South Africa (Pty) Limited ("SGS") indicate that between 40% and 55% of gold at the Kiaka Project should be recoverable by gravity separation in less than 3% of the mass. SGS concludes that overall recoveries of >90% could be expected from a fairly standard process route that includes crushing, milling (to 50% passing 75 micron), gravity concentration with intensive cyanidation of the concentrate, finer milling of the gravity tailings followed by CIL treatment. The Company also commissioned a 60 day column heap leach trial on high grade and low grade bulk samples which indicated overall gold extraction by heap leaching of 51.5% and 55.9% respectively.
Kevin Bullock, CEO of Volta said, "We are encouraged by the results obtained from testing the amenability of the Kiaka ores to gravity separation. The combination of recoveries of up to 55% of the gold upfront in a gravity circuit and the gravity tails proving amenable to direct cyanidation, point to overall recoveries in excess of 90% for both high and low grade ores at Kiaka. The relatively lower dissolution attained in the column heap leach trials will mean that we will now focus our further efforts in discerning an appropriate process route that will comprise optimized comminution, gravity separation and conventional CIL components for Kiaka."
Volta shipped two bulk (each greater than 300 kg) samples to SGS laboratories in Johannesburg, South Africa in order to undertake gold deportment and dissolution test work for ores from the Company's Kiaka Gold Deposit in Burkina Faso. The two bulk samples comprised selected quarter core samples from four exploration boreholes which were composited to each be representative of high grade and low grade portions of the deposit. To homogenize, SGS crushed each bulk sample to <20mm size, blended and then split into representative sub-samples as required by the test program.
Gravity concentration and CIL treatment of gravity tailings
To determine the Kiaka ores' amenability to gravity separation two ~8 kg sub-samples of each bulk sample were split from the bulk samples. The sub-samples were milled to a target grind of 50% passing 75 micron. Assayed head grades (50g fire assay) for the high grade and low grade samples averaged 2.12 g/t Au and 0.63 g/t Au, respectively. These were then subjected to gravity separation by Falcon Gravity Separator to yield gravity tails and concentrates as detailed in the table below. Approximately 39% and 54% of the gold reported to the gravity concentrate from a mass pull under 3% for both the high grade and low grade samples, respectively.
| Gravity Separation | Mass
(g) | Mass
% | Au Grade
g/t | Au Distribution
% |
| High Grade | Gravity Tails | 7,948.11 | 97.22 | 1.65 | 60.66 |
| Gravity Concentrate | 227.39 | 2.78 | 37.40 | 39.34 |
| Head | 8,175.50 | 100.00 | 2.64 | 100.00 |
| Low Grade | Gravity Tails | 8,009.94 | 97.53 | 0.39 | 46.20 |
| Gravity Concentrate | 203.22 | 2.47 | 17.90 | 53.80 |
| Head | 8,213.06 | 100.00 | 0.82 | 100.00 |
Note that the calculated head grades of 2.64 g/t and 0.82 g/t for the high grade and low grade samples, respectively are significantly higher than the assayed head grades of 2.12 g/t and 0.63 g/t for these same samples. The discrepancy is probably due to a nugget effect caused by sporadic larger gold grains that are more likely to be included in the larger 8kg sample than the 50g sample used for deriving the fire assay head grade.
Diagnostic leach analysis of representative sub-samples of the gravity tailings was then undertaken. This entailed milling the material to a target grind of 80% passing 75 micron and then following sequential solubilizing of the least-stable minerals via various pre-treatments.
| Sequential Treatment of Gravity Tailings | High Grade | Low Grade |
| Au g/t | Cum. Au Distrib. % | Au g/t | Cum. Au Distrib. % |
| Direct Cyanidation | 2.273 | 85.36 | 0.35 | 66.38 |
| Cyanidation CIL proxy | 0.003 | 85.47 | 0.06 | 78.18 |
| HCL digestion | 0.199 | 92.94 | 0.04 | 86.54 |
| HNO3 digestion | 0.006 | 93.20 | 0.01 | 88.84 |
| Carbon Assoc. | 0.034 | 94.46 | 0.02 | 92.04 |
| Occluded in Quartz | 0.148 | 100.00 | 0.04 | 100.00 |
| TOTAL | 2.663 | 100.00 | 0.52 | 100.00 |
Reagent consumption for the cyanidation tests of the high grade and low grade gravity tailings were 1.66 kg/t NaCN and 1.08 kg/t NaCN and 0.70 kg/t CaO and 0.63 kg/t CaO, respectively.
SGS concludes that overall recoveries of >90% could be expected from a fairly standard process route that includes crushing, milling (to 50% passing 75 micron), gravity concentration with intensive cyanidation of the concentrate, finer milling of the gravity tailings followed by CIL treatment.
Heap Leach Trials
Four representative sub-samples of each of the high grade and low grade bulk samples were split and crushed to 6mm, 8mm, 10mm and 12mm screen sizes. Simulated heap leach tests were undertaken on the 8 samples in order to ascertain the optimal crush size to use for column leach test work. This entailed bottle rolling each sample for 7 days in excess leach conditions. The results are summarized in the following table.
| Parameter | High Grade | Low Grade |
| | 6mm | 8mm | 10mm | 12mm | 6mm | 8mm | 10mm | 12mm |
| Solution Grade g/t | 1.74 | 1.45 | 1.24 | 1.36 | 0.40 | 0.35 | 0.34 | 0.38 |
| Residue Grade g/t | 0.86 | 0.59 | 1.79 | 1.68 | 0.30 | 0.26 | 0.31 | 0.36 |
| Calc. Head Grade g/t | 2.60 | 2.04 | 3.03 | 3.04 | 0.70 | 0.61 | 0.65 | 0.74 |
| Assay Head Grade g/t | 2.51 | 2.22 | 2.94 | 3.26 | 0.69 | 0.59 | 0.70 | 0.76 |
| Accountability % | 103.7 | 91.8 | 103.0 | 93.4 | 102.8 | 102.5 | 93.54 | 98.6 |
| Au % Extraction based on Calc Head Grade | 66.95 | 71.06 | 40.87 | 44.73 | 57.40 | 57.02 | 52.32 | 51.63 |
| NaCN Consumption kg/t | 4.01 | 4.01 | 4.36 | 4.16 | 4.42 | 4.39 | 4.27 | 4.36 |
| CaO Consumption kg/t | 0.34 | 0.31 | 0.40 | 0.12 | 0.09 | 0.10 | 0.02 | 0.22 |
The simulated heap leach tests revealed that the best gold dissolution was achieved for the 6mm top size fraction with 66.95% for the high grade sample and 57.40% for the low grade sample. These tests show that gold dissolution can be vastly improved by increasing the fineness of the ore presented for simulated heap leaching.
Volta also commissioned a column heap leach test on each of the low grade and high grade samples. An amount of ~80 kg of the <6mm material was split from each bulk sample. Head grade analyses was undertaken in duplicate for each sample, returning average grades of 2.51 g/t and 0.69 g/t for the high grade and low grade samples, respectively. The material was placed in a 190mm diameter column, simulating a heap height of 4.0m. A leach solution containing cyanide (NaCN) and lime (CaO) was then pumped into the column at a rate of 10lh/m2. After saturation of the column, approximately 4,200 ml of pregnant solution was collected from the columns every 24 hours and analyzed for gold, NaCN and CaO concentrations for a period of 60 days. A summary of the overall gold extraction is provided in the following table.
| Sample | Au % Extraction | Reagent Consumption |
| | Based on calc head grade | NaCN | CaO |
| High Grade | 51.47 | 2.83 | 1.95 |
| Low Grade | 55.89 | 2.88 | 1.98 |
After leaching, the ore beds were washed with water for 4 days at the same rate as the leach solution and then allowed to drain. A profile analysis of the solids contained in the columns was then carried out (top, middle and bottom). This was followed by 48 hour batch dissolution tests (CIL) on the profile sub-samples of the heap leach column tails, which were subjected to milling to a target grind of 80% passing 75 micron. The average results for top, middle and bottom samples from the column tail profiles are presented in the following table.
| Sample | Column Tails
Head Gold Grade | Residue | Carbon | Reagent Consumed | Dissolution
Au % |
| Assay g/t | Calc g/t | Au g/t | Au g/t | NaCN kg/t | CaO kg/t | (on calc head) |
| High Grade | 1.18 | 1.22 | 0.15 | 35.67 | 2.62 | 0.05 | 87.52 |
| Low Grade | 0.36 | 0.37 | 0.06 | 8.39 | 2.50 | 0.05 | 83.11 |
The column leach test results point to a process route that is unlikely to include a heap leaching component at this stage.
The work described above was undertaken under the guidance of Johan O'Connel, Operations Manager for the Metallurgy and Mineralogy Division at SGS South Africa (Pty) Limited in Johannesburg, South Africa. Under the guidelines of National Instrument 43-101, the qualified person for the Kiaka Gold Project is Mr. Guy Franceschi, Vice President, Exploration for Volta. Mr. Franceschi is a member of the European Federation of Geologists and has reviewed and approved the contents of this news release.
Volta is a mineral exploration company primarily focused on becoming a leader in the identification, acquisition and exploration of gold properties in West Africa. The Company is currently fast-tracking its flagship Kiaka Gold Project, located in Burkina Faso, towards a development decision.
Forward Looking Information Caution:
This press release presents "forward-looking statements" within the meaning of Canadian securities legislation that involve inherent risks and uncertainties. Forward-looking statements include, but are not limited to, statements with respect to the future price of gold and other minerals and metals, the estimation of mineral reserves and resources, the realization of mineral reserve estimates, the capital expenditures, costs and timing of the resources, the realization of mineral reserve estimates, the capital expenditures, costs and timing of the development of new deposits, success of exploration activities, permitting time lines, currency exchange rate fluctuations, requirements for additional capital, government regulation of mining operations, environmental risks, unanticipated reclamation expenses, title disputes or claims and limitations on insurance coverage. Generally, these forward-looking statements can be identified by the use of forward looking terminology such as "plans", "expects" or "does not expect", "is expected", "budget", "scheduled", "estimates", "forecasts", "intends", "anticipates" or "does not anticipate", or "believes", or variations of such words and phrases or state that certain actions, events or results "may", "could", "would", "might" or "will be taken", "occur" or "be achieved". Forward-looking statements are subject to known and unknown risks, uncertainties and other factors that may cause the actual results, level of activity, performance or achievements of Volta to be materially different from those expressed or implied by such forward looking statements, including but not limited to: risks related to international operations, risks related to the integration of acquisitions; risks related to joint venture operations; actual results of current exploration activities; actual results of current or future reclamation activities; conclusions of economic evaluations; changes in project parameters as plans continue to be refined; future prices of gold and other minerals and metals; possible variations in ore reserves, grade or recovery rates; failure of equipment or processes to operate as anticipated; accidents, labour disputes and other risks of the mining industry; and delays in obtaining governmental approvals or financing or in the completion of development or construction activities. Although the management and officers of Volta believe that the expectations reflected in such forward-looking statements are based upon reasonable assumptions and have attempted to identify important factors that could cause actual results to differ materially from those contained in forward-looking statements, there may be other factors that cause results not to be as anticipated, estimated or intended. There can be no assurance that such statements will prove to be accurate, as actual results and future events could differ materially from those anticipated in such statements. Accordingly, readers should not place undue reliance on forward-looking statements. Volta Resources does not undertake to update any forward-looking statements that are incorporated by reference herein, except in accordance with applicable securities laws.
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