Oroco Restates Resource Estimate On Cerro Prieto Project And Releases Results Of Preliminary Metallurgical Studies
May 11, 2009
VANCOUVER, British Columbia – (May 11, 2009) Oroco Resource Corp. (TSX-V:OCO) (“Oroco” or “the Company”) is pleased to announce restated resource estimates on its 100% owned Cerro Prieto project as well as the results of preliminary metallurgical studies.
The Company previously released resource estimates (see January 27, 2009 News Release) based on gold equivalent cut offs which were calculated prior to the completion of metallurgical tests. In the opinion of the British Columbia Securities Commission, it was inadvisable to use gold equivalent cut offs because a portion of the resource was based on zinc and lead content in the oxide zone of the deposit and metallurgical tests with respect to zinc recovery had not yet been completed and, while the area of the higher grade gold and the higher grade zinc overlap, they are not totally coincident.
Having now received preliminary metallurgy demonstrating high percentage recoveries of gold (up to 91.5%) and zinc (up to 85.3%), Giroux Consultants Ltd. (“Giroux”) has provided the Company with redefined resource estimates, first using gold cut offs and, second, using zinc cut-offs, as set out in the following tables. In the opinion of Giroux, these resource estimates indicate a potential open pit scenario. (For tables of resources at different cut off grades please refer to the NI 43-101 compliant amended technical report dated April 14, 2009 (the “Report”) filed on Sedar).
RESOURCE ESTIMATES
A. Using a 0.50 g/t Gold Cut-off
| ESTIMATED RESOURCES IN OXIDE ZONE |
| Category |
Tonnes
> 0.50 Au g/tCut-Off |
Au
(g/t) |
Ag
(g/t) |
Pb
(%) |
Zn
(%) |
| Indicated |
7,450,000 |
1.24 |
12.8 |
0.41 |
1.04 |
| Inferred |
140,000 |
0.99 |
11.2 |
0.73 |
1.98 |
The following table shows gross contained metal within the estimated resources from the tables above. However, potentially recoverable amounts of each metal will be reduced by metallurgical and other recovery factors.
| Category |
Tonnes
> Cut-Off |
Au
(ounces) |
Ag
(ounces) |
Zn
(pounds) |
| Indicated |
7,450,000 |
297,000 |
3,066,300 |
170,765,900 |
| Inferred |
140,000 |
4,500 |
50,400 |
6,109,500 |
Correlation coefficients and plots for the various elements indicate that, while overlapping, the higher grade gold and zinc zones are not completely correlated. As a result, the resource estimates using a gold cut-off do not include all higher grade zinc blocks. Therefore, Giroux has calculated separate resource estimates using a zinc cut-off as set out in the following tables As the zinc cut-off resource estimates contain many of the same blocks as included in the gold cut-off estimates, the zinc cut-off estimates should not be added to the gold cut-off resource estimates.
B. Using a 0.50% Zinc Cut-off
| ESTIMATED RESOURCES IN OXIDE ZONE |
| Category |
Tonnes
> 0.50% Zn Cut-Off |
Au
(g/t) |
Ag
(g/t) |
Pb
(%) |
Zn
(%) |
| Indicated |
20,440,000 |
0.43 |
8.7 |
0.38 |
1.20 |
| Inferred |
6,290,000 |
0.13 |
14.5 |
0.30 |
1.04 |
The following table shows gross contained metal within the estimated resources from the tables above. However, potentially recoverable amounts of each metal will be reduced by metallurgical and other recovery factors.
| Category |
Tonnes
> Cut-off |
Au
(ounces) |
Ag
(ounces) |
Zn
(pounds) |
| Indicated |
20,440,000 |
282,600 |
5,717,400 |
540,597,100 |
| Inferred |
6,290,000 |
26,300 |
2,932,400 |
144,176,900 |
METALLURGY
The Company retained SGS de Mexico, S.A. de C.V. (“SGS”), under the direction of the Company’s consultant, Mr. Art Winckers of Arthur H. Winckers and Associates (“Winkers”) to conduct a preliminary metallurgical study on sample rejects from drill holes CP009 and CP019, two holes that are considered to be representative of the deposit.
SGS was asked to deliver results for precious metal extraction using a cyanide leach and for zinc extraction using a sulphuric acid leach. Highlights of the results of the tests include
- Gold – using a grind size of 80% minus 200 mesh and a NaCN concentration of 3 g/l extracted an average of 91.5% of the gold and 35% of the silver over 6 tests in a 96 hour leach.
- Gold – using the minus 10 mesh fraction and a 0.25 g/l sodium cyanide concentration on an overall composite sample resulted in 85% gold extraction and 19.7% silver extraction within less than 48 hours.
- Zinc – using a grind size of 80% minus 200 mesh, and a sulphuric acid addition of 31 kg/t extracted an average of 64% of the zinc and 13% of the silver in a 6 hour leach. Winckers noted that the relatively low recovery was probably a result of the short leach time.
- Zinc – using the minus 10 mesh fraction on an overall composite sample and a sulphuric acid addition of 35.8 kg/t resulted in an 85.3% zinc extraction and a 13.0% silver extraction within less than 72 hours.
- Lead – lead was not recoverable above 10% in any of the tests attempted.
Winckers concluded that: “The results of these very preliminary leach tests are viewed as promising considering that high zinc and gold extractions were obtained with low lixiviant additions that are not considered to be optimized.”
The 85.3% zinc recovery using only 35.8 kg/t of sulphuric acid indicates the lack of problematic carbonate rock and silicate minerals in the Cerro Prieto Project. Most producing zinc oxide deposits are in carbonate hosts and many also contain zinc silicate minerals. As zinc is extracted using sulphuric acid, and carbonate rock neutralizes sulphuric acid, extraction of zinc in carbonate hosts requires either a very high amount of sulphuric acid (up to 200 kg/t) to digest both the carbonate and the zinc or a very costly alternative method to reduce the carbonate rock prior to extraction of the zinc. Zinc silicates are also difficult to extract requiring either very high rates of acid use or other, very costly, alternate techniques. The preliminary zinc extraction rates achieved indicate that zinc silicates are also not a problem in the Cerro Prieto mineralization.
With respect to the positive metallurgical tests and the restated resource, Ken Thorsen, President and CEO of Oroco, states: “We are pleased with the recoveries established for gold and zinc in the preliminary metallurgical studies, particularly given the significant zinc values in the gold rich upper part of the structure which is being modeled as an open pittable resource. Looking forward, we are initially focusing on increasing the oxide gold resource and on the development of a potential cost efficient open pit operation that will extract not just the estimated gold cut-off resource, but the additional portion of the estimated zinc cut-off resource not included in the gold cut-off estimate.”
The Company intends to continue the metallurgical testing and has a consultant preparing a preliminary assessment that will initially focus on open pit mining of the oxide gold resource. The results of these activities will assist in determining a plan going forward on the established resource.
The Company is also planning to drill the remaining 650 meters of strike length of the mineralized zone at the north end of the property where trenching results and drill hole CP023 have established the continuation of the mineralized zone. The initial program will focus on expanding the oxide gold resource and will total approximately 8,000 meters. An additional 2,000 meters of drilling are planned to test the deeper sulphide mineralization.
Mr. Giroux, of Giroux Consultants Ltd., and Duncan Bain, of Duncan Bain Consulting Ltd., the authors of the Report, have read and approved the contents of this News Release. The resource estimates are classified as Indicated Mineral Resources and Inferred Mineral Resources, consistent with the CIM definitions referred to in NI 43-101. These estimates are filed in a technical report, compliant with NI 43-101, on SEDAR. Mineral resources, which are not mineral reserves, have not demonstrated economic viability. Oroco is not aware of any environmental, permitting, legal, title, taxation, socio-political, marketing or other issues, which may materially affect the estimate of mineral resources.
Kenneth R. Thorsen, B.Sc., P. Geo., is a director and officer of the company and is a ‘qualified person’ for the purposes of National Instrument 43-101 Standards of Disclosure for Mineral Properties of the Canadian Securities Administrators and has verified the data (including sampling, analytical and test data) and prepared or supervised the preparation of the information contained in this news release.
For further information, please contact:
Mr. Ken Thorsen, President and CEO
Oroco Resource Corp.
Tel: 604-688-6200
kthorsen@orocoresourcecorp.com
Neither 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.
