VANCOUVER, BRITISH COLUMBIA--(Marketwired - Mar 3, 2015) - Columbus Gold Corporation (TSX VENTURE:CGT)(CBGDF) ("Columbus Gold") is pleased to announce the results of the final two phases of comprehensive metallurgical test work from Columbus Gold's 100% controlled Montagne d'Or Gold Deposit, Paul Isnard Project, in French Guiana.
The results of Phase I tests were released on January 8th, 2015, where three gold recovery process options were investigated on two master composites, which included initial evaluations of 1) whole-ore cyanidation, 2) gravity concentration followed by cyanidation of gravity tailings, and 3) gravity concentration followed by gold/silver flotation from the gravity tailings. The initial test work indicated that the ore types of the principal Upper Felsic Zone ("UFZ") and subsidiary Lower Favorable Zone ("LFZ") are highly amenable to the three metallurgical processes with gold recoveries ranging from 95% to 97%.
Highlights of Phase II and III metallurgical test work include:
- Large-scale gravity + rougher flotation testing on master composite resulted in a combined gold recovery of 95.9% from the UFZ master composite and 96.0% gold recovery from the LFZ master composite.
- Rougher flotation concentrates was upgraded in one stage of cleaner flotation to produce a cleaner flotation concentrate that contained about 17-18 g/t Au and 34-72 g/t Ag. After one stage of cleaning a combined gravity + cleaner flotation gold recovery of about 94% Au was achieved.
- Cyanidation studies conducted on the cleaner flotation concentrates demonstrated that over 97% of the gold contained in the cleaner flotation concentrate could be extracted.
- Gravity + cyanidation gold recovery on ten variability test composites varied from 93.5% to 97.3%, and averaged at 95.8% including 33% gravity recoverable gold.
- Bond ball mill work index testing of the UFZ and LFZ variability composites confirmed the moderate hardness of the Montagne d'Or rock. The lower than expected hardness has a significant impact on reducing the energy needs for the project.
Phase II Metallurgical Test work
Phase II was undertaken on the UFZ and LFZ master composites, which included large-scale flotation studies to evaluate the extent to which the flotation concentrates can be upgraded, as well as the downstream concentrate cyanidation behavior.
Large-scale gravity + rougher flotation testing with approximately 80 kg of each master composite resulted in a combined gold recovery of 95.9% from the UFZ master composite and 96.0% gold recovery from the LFZ master composite. This included 31.6% gravity gold recovery from the UFZ composite and 32.6% gravity gold recovery from the LFZ composite. The gravity cleaner concentrate, representing approximately 0.01% of the original mass, contained greater than 4 kg/t Au and 3 kg/t Ag, suitable for direct smelting. Rougher flotation concentrates, which contained 15-16% of the original mass, was upgraded in one stage of cleaner flotation to produce a cleaner flotation concentrate that contained about 17-18 g/t Au and 34-72 g/t Ag. After one stage of cleaning a combined gravity + cleaner flotation gold recovery of about 94% Au was achieved.
Cyanidation studies conducted on the cleaner flotation concentrates demonstrated that over 97% of the gold contained in the cleaner flotation concentrate could be extracted. This resulted in an overall gold recovery of 91.7% from the UFZ master composite and 93.3% gold recovery from the LFZ master composite. Gold recovery in each process stage is summarized in Table 1.
Table 1 - Gold Recoveries After Gravity Concentration, Cleaner Flotation and Cyanidation of Cleaner Concentrate
| Comp. ID |
Process Route |
Mass Recovery, % |
Gold Recovery, % |
| UFZ Master Comp. |
Gravity Concentration |
0.01 |
31.6 |
| Gravity + Rougher Flotation |
14.67 |
95.9 |
| Gravity + Cleaner Flotation |
5.83 |
93.3 |
| Gravity + Cleaner Flotation + Concentrate Cyanidation |
5.83 |
91.7 |
| LFZ Master Comp. |
Gravity Concentration |
0.01 |
32.6 |
| Gravity + Rougher Flotation |
16.20 |
96.0 |
| Gravity + Cleaner Flotation |
6.38 |
94.5 |
| Gravity + Cleaner Flotation + Concentrate Cyanidation |
6.38 |
93.3 |
Phase III Confirmatory Test work
The Phase I and Phase II metallurgical studies conducted for Montagne d'Or were focused on the testing two UFZ and LFZ master composites. This was followed by the Phase III study on variability composites to evaluate the impact of spatial and grade variations throughout the deposit. A total of ten variability test composites, including six representing the UFZ, three representing the LFZ and one representing saprolite (oxidized mineralisation) were created for the Phase III program.
During the Phase III program each of the variability composites was tested to evaluate their response to two process options that included: 1) gravity concentration followed by cyanidation of gravity tailing, and 2) gravity concentration followed by gold flotation from the gravity tailing.
All ten variability test samples responded well to the gravity + cyanidation and gravity + flotation process options. The test results at optimum test conditions are presented in Table 2 with major findings summarized below:
- Gravity + cyanidation gold recovery on the ten variability test composites varied from 93.5% to 97.3%, and averaged at 95.8% including 33% gravity recoverable gold.
- Gravity + flotation on the nine UFZ/LFZ variability composites resulted in gold recoveries that ranged from 67.5% to 98.7% and averaged 90.9% into a combined gravity + cleaner flotation concentrate that averaged about five weight percent of the feed. Combined gold recovery from the saprolite composite was 69.5%.
- Cyanidation of the cleaner flotation concentrates was not conducted due to the limited amount of concentrate produced. However, high gold extractions can be expected based on the Phase II cyanidation studies conducted on flotation concentrates produced from bulk testing of the UFZ and LFZ master composites.
Table 2 - Summary of Gold Recoveries from Montagne d'Or Variability Composites
| Zone |
Variability Composite ID |
Response to Gravity+Cyanidation |
Response to Gravity+Flotation |
Au
Recovery, % |
Tailing Grade, g/t Au |
Gravity+Ro.
Au
Recovery, % |
Gravity+Cl.
Au
Recovery, % |
Tailing Grade, g/t Au |
| Upper Felsic Zone ("UFZ") |
UFZ-VC1 |
95.7 |
0.11 |
95.5 |
94.8 |
0.12 |
| UFZ-VC2 |
96.3 |
0.04 |
88.8 |
85.6 |
0.10 |
| UFZ-VC3 |
96.8 |
0.11 |
99.0 |
98.7 |
0.04 |
| UFZ-VC4 |
93.5 |
0.07 |
98.1 |
97.5 |
0.03 |
| UFZ-VC5 |
94.9 |
0.08 |
79.1 |
67.5 |
0.25 |
| UFZ-VC6 |
95.9 |
0.15 |
97.8 |
97.5 |
0.09 |
| Lower Favorable Zone ("LFZ") |
LFZ-VC1 |
95.9 |
0.13 |
98.4 |
98.2 |
0.06 |
| LFZ-VC2 |
95.7 |
0.04 |
87.6 |
86.1 |
0.08 |
| LFZ-VC3 |
97.3 |
0.04 |
93.5 |
92.4 |
0.08 |
| Average for Fesh Rock |
95.8 |
0.08 |
93.1 |
90.9 |
0.09 |
| Saprolite |
95.9 |
0.04 |
75.4 |
69.5 |
0.20 |
Head analyses and Bond grindability work indices for each of the variability composites are presented in Table 3. Metallic screen assays and the 20-51% gravity recoverable gold obtained from the gravity test work confirmed the presence of coarse gold in the Montagne d'Or variability test composites. Bond ball mill work index testing of the UFZ and LFZ variability composites confirmed the moderate hardness of the Montagne d'Or test composites.
Table 3 - Head Characterization of Montagne d'Or Variability Composites
| Items |
Units |
Upper Felsic Zone ("UFZ") |
Lower Favorable Zone ("LFZ") |
Saprolite |
| UFZ-VC1 |
UFZ-VC2 |
UFZ-VC3 |
UFZ-VC4 |
UFZ-VC5 |
UFZ-VC6 |
LFZ-VC1 |
LFZ-VC2 |
LFZ-VC3 |
| Au |
g/mt |
2.07 |
0.84 |
2.36 |
1.22 |
0.93 |
2.87 |
3.65 |
1.29 |
1.01 |
0.96 |
| Ag |
ppm |
2 |
2 |
2 |
2 |
2 |
6 |
9 |
3 |
5 |
1 |
| Cu |
% |
0.07 |
0.07 |
0.10 |
0.09 |
0.02 |
0.21 |
0.29 |
0.02 |
0.06 |
0.04 |
| Bwi |
kWh/mt |
12.25 |
10.13 |
9.03 |
10.19 |
9.74 |
12.77 |
11.61 |
11.57 |
12.08 |
6.83 |
The metallurgical tests were conducted by Bureau Veritas Commodities Canada Ltd., Inspectorate Metallurgical Division, under the direction and supervision of Mr. Eric Olin of SRK Consulting (U.S.) Inc. The metallurgical tests are an integral part of a Preliminary Economic Assessment ("PEA") on the Montagne d'Or deposit to be completed in the spring of 2015, which will include an updated resource estimate incorporating the results of the Phase II Diamond drilling program (126 holes, 25,570 m) and a preliminary environmental assessment.
The test work is being funded by Nord Gold N.V. (LSE:NORD LI) as part of a minimum US$30 million exploration and development program pursuant to which they can earn a 50.01% interest in Montagne d'Or and the Paul Isnard mineral claims, by completing a bankable feasibility study no later than March 2017.
Eric Olin, of SRK Consulting (U.S.), Inc., MSc, MBA, RM-SME and a Qualified Person under National Instrument 43-101 has reviewed the metallurgical information contained in this release.
ON BEHALF OF THE BOARD,
Robert F. Giustra, Chairman & CEO
Neither the TSX Venture Exchange nor its Regulation Services Provider (as that term is defined in the policies of the TSX Venture Exchange) accepts responsibility for the adequacy or accuracy of this release.
This release contains forward-looking information and statements, as defined by law including without limitation Canadian securities laws and the "safe harbor" provisions of the US Private Securities Litigation Reform Act of 1995 ("forward-looking statements"), respecting Columbus Gold's: indications that ore types of the UFZ and LFZ are highly amenable to the three metallurgical processes tested; metallurgical tests; completion of new mineral resource estimate; completion of a preliminary environmental assessment; completion of the PEA; projected funding of drilling programs by Nord Gold N.V. pursuant to the terms of the option agreement and the related completion of a bankable feasibility study ("BFS"). Forward-looking statements involve risks, uncertainties and other factors that may cause actual results to be materially different from those expressed or implied by the forward-looking statements, including: the ability to acquire necessary permits and other authorizations; environmental compliance; cost increases; availability of qualified workers and drill equipment; competition for mining properties; risks associated with exploration projects including, without limitation, the accuracy of interpretations; mineral reserve and resource estimates (including the risk of assumption and methodology errors and ability to complete a new resource estimate by the proposed target date or at all); whether the ore types of the UFZ and LFZ are highly amenable to the three metallurgical processes tested; the ability to complete the preliminary environmental assessment by the proposed target date or at all; the ability to complete the PEA by the proposed target date or at all; dependence on third parties for services; non-performance by contractual counterparties; title risks; risks associated with Nord Gold N.V. electing not to exercise its option and make the related option payments and the ability to complete the BFS by the stated deadline or at all; and general business and economic conditions. Forward-looking statements are based on a number of assumptions that may prove to be incorrect, including without limitation assumptions about: whether the planned metallurgical tests are appropriate for the site; general business and economic conditions; the timing and receipt of required approvals; availability of financing; power prices; ability to procure equipment and supplies including, without limitation, drill rigs; and ongoing relations with employees, partners, optionees and joint venturers. The foregoing list is not exhaustive and Columbus Gold undertakes no obligation to update any of the foregoing except as required by law.