MINEFINDERS SELECTS METALLURGICAL PROCESS FOR DOLORES
April 29, 2004
VANCOUVER, BRITISH COLUMBIA – Minefinders Corporation Ltd. (the “Company”) (TSX: MFL / AMEX: MFN) has selected a combined flotation and heap leach mineral recovery process for the final feasibility study on its Dolores gold-silver deposit located in Chihuahua, Mexico. The selection was made after extensive evaluation of standard heap leach, flotation, agitated cyanide leaching, and pulp agglomeration, individually, and in combination with each other.
In the selected process, high-grade and sulfide ores containing the majority of the project gold and silver will be preferentially directed to the mill and flotation plant, while low-grade ores will report directly to the leach pad for standard, low-cost heap leach processing. The addition of flotation to the Dolores mine plan is expected to substantially increase the overall percentage recovery of contained silver, while maintaining the percentage recovery of contained gold at favorable levels approximating those previously announced.
The evaluation of the different process scenarios was completed on the basis of estimated capital and operating costs and on recovery information generated from laboratory metallurgical testing. Following this analysis, it was determined that a combined flotation with heap leach recovery operation would provide the flexibility required to maximize returns at current and higher precious metals prices and remain cost effective in a lower price environment. The final bankable feasibility for the project will be based upon optimization of this operating scenario.
Mark Bailey, Minefinders’ President and CEO commented: “The final selection of the Dolores operating process marks a major milestone in the commercialization of the project. While the metallurgy at Dolores has always been very good, we have taken the time necessary to ensure that all of the possible recovery processes have been thoroughly evaluated, so as to maximize the project’s potential.”
Projected Flotation Recoveries
Flotation test results from composited ore-grade intervals (shown in the first table below) from the Dolores deposit demonstrated a highly efficient recovery process, yielding enhanced gold recovery and very significantly increased silver recovery. These recovery efficiencies are expected to have a particularly positive financial impact, due to the increase in sulfide resources within the project area, the discovery of potentially important base metal concentrations, and recent increases in silver prices.
The table indicates the projected total recoveries for each ore-type, based on results from SGS Lakefield lock-cycle and other testing, using the proposed process, i.e. recovered gold and silver in the flotation concentrate is then cyanide leached and combined with gold and silver recovered from the leached tails to provide the “Total Recovery” percentages:
|
Composite Type |
Flotation Au |
Flotation Ag |
Total Recovery Au |
Total Recovery Ag |
|
Mixed Oxide/sulfide ore |
65 % |
67 % |
93 % |
82 % |
|
Sulfide ore |
91 % |
90 % |
90 % |
94 % |
|
Sulfide/base-metal ore |
92 % |
90 % |
* |
* |
* total recovery results for sulfide/base-metal ores are pending
Metallurgical samples were composited to represent dominant ore-types found throughout the Dolores deposit and sent to SGS Lakefield Research Limited of Ontario, Canada for testing. The three ore-types selected include: 1) Composite 1 - mixed oxide and oxide/sulfide ores, 2) Composite 2 - simple sulfide ores, and 3) Composite 3 - sulfide ore with a significant base-metal (Pb-Zn) component. Each composite was subjected to a wide series of flotation tests using a range of variables in an effort to optimize flotation recoveries and processing. The table indicates that leaching of mixed and oxide tails, although requiring an additional circuit, provides a significant contribution to total recovery; and that leaching of sulfide tails may not be necessary. A cost/benefit analysis of this issue is ongoing.
An additional 15 samples, totaling 105 kilograms, are undergoing variability testing to further characterize flotation response to the different rock types and oxidation states of ore-grade material from the Dolores deposit. Flotation testing is ongoing for the sulfide-base metal composite which has produced marketable lead and zinc concentrates which could be sent to a smelter to further enhance project economics.
Projected Heap Leach Recoveries
Heap leach recoveries from lower grade ores are estimated from recovery data indicated by the 32 columns of composited Dolores material tested and/or compiled by McClelland Labs of Sparks, Nevada. While additional data from ongoing column leach tests are being accumulated, the test results to date are sufficient to provide the projected recoveries presented below:
|
Composite Type |
Recovery Au* |
Recovery Ag* |
|
Oxide ore |
78 % |
45 % |
|
Mixed ore |
70 % |
50 % |
|
Sulfide ore |
59 % |
59 % |
* total recovery results for sulfide/base-metal ores are pending
Metallurgical samples were composited to represent dominant ore-types found throughout the Dolores deposit and sent to SGS Lakefield Research Limited of Ontario, Canada for testing. The three ore-types selected include: 1) Composite 1 - mixed oxide and oxide/sulfide ores, 2) Composite 2 - simple sulfide ores, and 3) Composite 3 - sulfide ore with a significant base-metal (Pb-Zn) component. Each composite was subjected to a wide series of flotation tests using a range of variables in an effort to optimize flotation recoveries and processing. The table indicates that leaching of mixed and oxide tails, although requiring an additional circuit, provides a significant contribution to total recovery; and that leaching of sulfide tails may not be necessary. A cost/benefit analysis of this issue is ongoing.
An additional 15 samples, totaling 105 kilograms, are undergoing variability testing to further characterize flotation response to the different rock types and oxidation states of ore-grade material from the Dolores deposit. Flotation testing is ongoing for the sulfide-base metal composite which has produced marketable lead and zinc concentrates which could be sent to a smelter to further enhance project economics.
Projected Heap Leach Recoveries
Heap leach recoveries from lower grade ores are estimated from recovery data indicated by the 32 columns of composited Dolores material tested and/or compiled by McClelland Labs of Sparks, Nevada. While additional data from ongoing column leach tests are being accumulated, the test results to date are sufficient to provide the projected recoveries presented below:
* presumed 100% passing –3/8 inch crush
Summary
It is expected that the proposed combination of flotation and heap leach circuits will ensure optimal project returns and substantially increase Minefinders’ leverage to current and higher gold and silver prices at moderate projected capital and operating costs. Details of the Dolores project economics will be released in conjunction with the completion of the feasibility study.
About Minefinders
Minefinders is a highly successful precious metals exploration company with its advanced Dolores gold and silver deposit and several ongoing exploration projects in Sonora, Mexico. The Company is presently working on completing a feasibility study on the Dolores deposit and conducting exploration drill programs on its other prospects. Mark H. Bailey, MSc., P.Geo., a Qualified Person as defined by National Instrument 43-101, supervised the preparation of the technical information in this release.
On Behalf of the Board of Directors
MINEFINDERS CORPORATION LTD.
Mark H. Bailey
President and Chief Executive Officer
For further information please visit our website at www.minefinders.com, or contact the Company at
Tel: 1 (866) 687-6263 or Fax: (604) 687-6267.
Safe Harbor Statement under the United States Private Securities Litigation Act of 1995: Statements in this release that are forward-looking, including statements relating to the size, and growth in size, of the Company’s mineral resources and the timing of the further exploration and development of the Dolores project, are subject to various risks and uncertainties concerning the specific factors identified above and in the Company’s periodic filings with the Ontario Securities Commission and the U. S. Securities Exchange Commission. Such information contained herein represents management’s best judgment as of the date hereof based on information currently available. The Company does not intend to update this information and disclaims any legal liability to the contrary.
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