Allied Nevada Gold Corp.

Allied Nevada Gold Corp.

November 12, 2010 08:01 ET

Allied Nevada Reports Additional Metallurgical Test Results Confirming Milling Recoveries of 86.6% for Gold and 84.1% for Silver

RENO, NEVADA--(Marketwire - Nov. 12, 2010) - Allied Nevada Gold Corp. ("Allied Nevada" or the "Company") (TSX:ANV)(NYSE Amex:ANV) is pleased to announce that is has received metallurgical test results from additional composite samples for its Hycroft mine located near Winnemucca, Nevada. The Company has included the new composite test results in a geologically representative metallurgical model, which includes all metallurgical test results received to date for milling oxide and sulfide mineralization. Based on the 39 composites included in the model, average recoveries, based on rock type and tonnage weighted, are expected to be 86.6% for gold and 84.1% for silver (compared with previous test work which indicated recoveries of 87.2% for gold and 81.7% for silver). Test work demonstrates that these recoveries may be achieved through a grind-flotation (to create a concentrate)-cyanidation of tailings circuit. Previous aqua regia test results indicate the flotation concentrate is very amenable to oxidation processes typically practiced within the industry, with recovery of 98.5% of the gold and 99.3% of the silver. Management believes that this metallurgical model provides a more accurate view of the metallurgical characteristics and recovery expectations at Hycroft. It is expected that, based on preliminary indications, gold and silver mill recoveries will improve with optimization of the metallurgical testing process. 

"The metallurgical model is providing us with a good sense for what we should expect metallurgically from the various rock types on the property," commented Scott Caldwell, President & CEO. "While we understand that there remains a significant amount of work to be completed, these continued positive steps provide confidence as we move forward with the milling project feasibility study."

Currently, 46 additional composite samples are being metallurgically tested using the grinding-flotation of the sulfides to create a concentrate and cyanidation of the tailings flow sheet. This test work continues to provide data for the milling metallurgical model. Master composites will be constructed by domain for optimization test work. Five one thousand (1,000) kilogram bulk samples have been obtained for pilot plant testing simulating the proposed milling-flotation-tail cyanidation flow sheet. Flotation concentrate will be evaluated using various oxidation processes including roasting and autoclaving. Material from each bulk sample will be submitted for comminution and grindability test work. The size and geometry of this deposit allow the flexibility to blend mill feed for optimum metallurgical performance such as gold and silver grades, sulfide content and ore hardness.

Management estimates that approximately 30% of the required metallurgical testing has been completed for a milling feasibility study, expected mid-2011. Due to the very large size of the current mineral resource and the scope of the milling scenario, management intends to conduct sulfide test work on a significant number of composite samples, distributed throughout the deposit. Management believes that this level of test work will allow for final flow sheet and plant design and that this test work will be completed by mid-2011.

Further details of historical metallurgical test results are contained in the recently filed NI 43-101 compliant Amended and Restated Technical Report dated September 23, 2010 and filed with SEDAR.

Sulfide Metallurgical Characteristics

The goal of the sulfide metallurgical program is to provide information for the anticipated mill feasibility study, expected to be completed in the second half of 2011. All testing to date has been completed to a feasibility study standard.

The previously announced results indicate:
  • Sulfide mineralization is amenable to simple, conventional flotation technology.

  • Coarse grind to 100 microns.

  • Bond work index of 15.6 kWh/t, or equivalent to a moderate hardness.

  • Rougher flotation and cyanidation of the tailing indicates overall recoveries averaging approximately 88% for gold and 86% for silver.

  • Sulfide sulfur content of the cleaner concentrate is approximately 25%. This level of sulfur has produced an exothermic reaction in pressure oxidation, roasting and smelting operations. This type of exothermic reaction will reduce the amount of energy required to operate these process plants, reducing overall process costs.

  • Overall flotation concentration in excess of 20:1.

  • Direct relationship between recovery of sulfides and metals.

  • Key sulfides are pyrite, marcasite and pyrargyrite (Ag) (see Table).

  • Flotation concentration is amenable to roasting, smelting or pressure oxidation.

  • No metallurgical optimization test work has been completed for the variability tests. 

Composite Cleaner Flotation Concentrate Mineralogy  
Mineral Constituent Mineral Mass%
Pyrite/Marcasite 72.00%
Chalcopyrite 0.13%
Arsenopyrite 0.26%
Other Sulfides 0.07%
Quartz 16.60%
Feldspar 3.15%
Clays 2.01%
Micas 4.15%
Other Silicates 0.04%
Ti Oxides 0.19%
Other Oxides 0.04%
Native Sulfur 0.25%
Sulfates 1.04%
Carbonates 0.01%
Ag Minerals 0.01%
Other 0.05%
Total 100.00%

Multi-element analysis conducted on 154 holes drilled at Hycroft indicates that only trace amounts of mercury exist below 150 meters, predominantly where the sulfide mineralization occurs.

Heap Leach Metallurgical Characteristics

Current run-of-mine leach performance is consistent with historical gold recoveries of 56.6% and silver recoveries are averaging approximately 12% for a silver ounce to gold ounce production ratio of 2:1. The first crushing system became operational in the third quarter of 2010 and two additional crushers are expected to be added as more siliceous ore becomes available over the next 18 months. When combined with run-of-mine recoveries, crushing approximately 30% of the total current ore feed is expected to improve overall average recoveries to approximately 60% for gold and 14% for silver. 

The goal for oxide heap leach testing is to determine the optimum crush size for the oxide mineralization. Based upon the large size of the current oxide resource, management believes that additional column leach and grinding test work will be required on approximately 100 oxide composite samples. This test work is expected to be completed in the first half of 2011.

Cautionary Statement Regarding Forward Looking Information

This press release contains forward-looking statements within the meaning of the U.S. Securities Act of 1933 and the U.S. Securities Exchange Act of 1934 (and the equivalent under Canadian securities laws), that are intended to be covered by the safe harbor created by such sections. Such forward-looking statements include, without limitation, statements regarding the Company's expectations concerning the timing, results, indications, benefits of and resources needed for exploration, test work, the crushing systems and engineering assessments; management's expectations regarding recoveries, including the prospects for improving recoveries; expectations regarding potential growth and optimization opportunities; results of evaluation of underlying sulfide mineralization at Hycroft; results of evaluation of the benefits of crushing oxide mineralization; results of metallurgical testing on oxide and sulfide mineralization; reserve and resource estimates; and other statements that are not historical facts. Forward-looking statements address activities, events or developments that Allied Nevada expects or anticipates will or may occur in the future, and are based on current expectations and assumptions. Although Allied Nevada management believes that its expectations are based on reasonable assumptions, it can give no assurance that these expectations will prove correct. Important factors that could cause actual results to differ materially from those in the forward-looking statements include, among others, risks relating to uncertainties concerning reserve and resource estimates as well as those factors discussed in Allied Nevada's filings with the U.S. Securities and Exchange Commission (the "SEC") including Allied Nevada's latest Annual Report on Form 10-K and its other SEC filings (and Canadian filings) including, without limitation, its latest Quarterly Report on Form 10-Q. The Company does not intend to publicly update any forward-looking statements, whether as a result of new information, future events, or otherwise, except as may be required under applicable securities laws.

The technical contents of this news release have been prepared under the supervision of Scott Wilson of Scott E. Wilson Consulting Inc., who is a Qualified Person as defined by National Instrument 43-101. Scott Wilson is an independent consultant for Allied Nevada and is the Qualified Person for Allied Nevada Gold Corp.

Contact Information

  • Allied Nevada Gold Corp.
    Scott Caldwell
    President & CEO
    (775) 358-4455
    Allied Nevada Gold Corp.
    Tracey Thom
    Vice President, Investor Relations
    (416) 409-6007