Duluth Metals Provides Metallurgical Update on Twin Metals Minnesota Project

  • Positive results from various metallurgical options considered for the Twin Metals Minnesota Project
  • Good metal recoveries to both a bulk concentrate and to separate copper (~25% Cu, <1% Ni) and nickel (~10% Ni, <5% Cu) concentrates were achieved during recent pilot plant programs;
  • Good metal extraction from bulk concentrate using the CESL™ process;
  • Good recoveries of gold and platinum group elements from CESL™ residues by sulfur flotation.

TORONTO, July 18, 2013 /CNW/ - Duluth Metals Limited ("Duluth Metals") (TSX: DM) (TSX: DM.U) is pleased to announce significant progress on various metallurgical options being considered during pre-feasibility on the Twin Metals Minnesota Project ("Twin Metals").  Some of the most recent test results from an ongoing comprehensive metallurgical testwork program aimed at defining the optimal process flowsheet for the recovery of copper, nickel, gold, platinum, and palladium to payable products are summarized below. This metallurgical testwork program involved mineralogical assessments, laboratory bench scale testing, and pilot plant testing with independent laboratories.

The metallurgical testwork included flotation programs to develop and prove two separate flotation options: the first being the option to produce a bulk copper-nickel concentrate; and the second option being to produce a marketable copper concentrate and a marketable nickel concentrate.

Testwork was conducted on both the bulk concentrate and the nickel concentrate using the CESL™ process. Teck Resources Limited ("Teck") has developed the CESLTM hydrometallurgical process that effectively recovers copper, nickel and PGM's from bulk copper-nickel-PGM concentrates, which Duluth and Twin Metals are considering as a concentrate processing alternative. Both concentrates from the Maturi group of deposits have been successfully processed at bench and pilot scale at Teck's hydrometallurgical facility in Richmond, B.C. More detailed summary reports for the two approaches (selective flotation and CESLTM processing) are available on the Duluth Metals website at www.duluthmetals.com.

Vern Baker, President of Duluth Metals stated, "This metallurgical test work is quite encouraging. The Twin Metals project now has two viable processing alternatives for the project that can be evaluated during the pre-feasibility. The pilot plant work has shown that either a CESL™ process or production of marketable flotation concentrates can be effectively operated with the Twin Metals resource."

The test programs were conducted to establish initial parameters for engineering design of the Twin Metals processing plant. One important component of the program was a flotation pilot plant campaign at the ALS Metallurgy facility in Kamloops BC, where Maturi material derived from drill core was processed to demonstrate both bulk concentrate and separate concentrate flowsheets. The flotation test work was successful at demonstrating the ability of the flowsheets to achieve high base and precious metals recovery to either a bulk concentrate or to separate copper and nickel concentrates,

A second component of the test work included a six week pilot plant operation of the CESL™ process at Teck's hydrometallurgical facility in Richmond, British Columbia. CESL™ work established good overall recoveries of metal into three products: cathode copper, a mixed (nickel and cobalt) hydroxide, and a precious metals flotation concentrate.

Head grade assays are supported by the Resource Estimate, and verified under the standard QA/QC program of the respective independent commercial laboratory responsible for executing the metallurgical testwork program. Similarly, the actual testwork protocols, sample collection, assay reconciliation, and metallurgical balance at laboratory scale and pilot plant level are all developed under each commercial laboratory's standard QA/QC protocols.


Twin Metals has been working since early 2012 on a comprehensive metallurgical testwork program aimed at defining a commercially viable process flowsheet that will recover copper, nickel, gold, platinum, and palladium to payable products. This metallurgical testwork program included mineralogical assessments, laboratory bench scale testing, and pilot scale testing.

A variety of samples have been tested as part of the metallurgical test program. In particular to the flotation flowsheet development and pilot plant programs undertaken in 2012 and 2013, the majority of samples were obtained from a large PQ drilling campaign which acquired almost 70 tons of mineralized material.

Metallurgical Testing

Two flotation flowsheets were investigated. The two flowsheet circuits considered primary grinding and multi-stage flotation including rougher, regrinding of the rougher concentrate and two or three stages of sequential cleaning.

The first flowsheet involved production of a bulk concentrate that would require onsite processing rather than direct sale to smelters. Results of the bulk flotation showed very high copper recoveries and solid nickel recoveries. Concentrate grades and recoveries can be found in the summary reports available on our website.

The second flowsheet (selective flotation) involved production of a marketable copper concentrate and a marketable nickel concentrate. The sequential flotation tests indicated very little loss of copper recovery and minimal nickel recovery losses in comparison to the production of a bulk concentrate. Testwork indicated that nickel deportment to the copper concentrate was minimal. Copper concentrates of almost 25% copper with less than 1% nickel, and nickel concentrates of approximately 10% nickel with less than 5% copper were achieved. Ongoing testwork is focused on upgrading the nickel content of the nickel concentrate. Specific values and trends are represented in the summary reports available on our website. Note that these results were achieved during bench and pilot plant programs using the composite ore samples as described above; additional testwork programs are planned to investigate variability in ore response to the flotation flowsheet as a mine plan is developed for the deposit.


Three concentrates from the Twin Metals project were successfully processed through Teck's hydrometallurgical research facility utilizing the CESL™ process for approximately a six week period in Q1 of 2013. The concentrates processed through the pilot plant consisted of three different concentrates from the Twin Metals resource. The first concentrate was a bulk concentrate (all metals floated in one concentrate) made from a mixed sample of material from the Maturi and Birch Lake deposits. The second concentrate was a bulk concentrate made from material derived from the western portion of the Maturi deposit. The third concentrate was a nickel concentrate derived as one of two products from the ALS flotation pilot plant during the period when a separate copper and nickel concentrate was being produced from ore from the western portion of the Maturi deposit.

The concentrate characteristics were:

  • Maturi Bulk #1 - produced from Maturi East and Birch Lake deposits (17.0 % Cu, 3.7 % Ni and 20.4 g/t TPM (Total Precious Metals or TPM = Platinum+Palladium+Gold));

  • Maturi Bulk #2 - produced from Maturi West deposit (15.5 % Cu, 4.1% Ni and 9.0 g/t TPM);

  • Maturi Ni-Cu - produced from Maturi West deposit after separation of a high grade Cu concentrate ( 6.9 % Cu, 8.0 % Ni and 10.6 g/t TPM).

The main goals for each of the concentrates were to determine optimal base metal extraction while also recovering precious metals. Multiple variables were tested in the leaching circuits to determine the optimal operating conditions for recovery of metals.

Overall CESL™ pilot plant metal recoveries from concentrate are presented in Table 1. The results for the two bulk samples are combined due to limited run time for the second sample.

Table 1: Maturi Metal Recoveries from Concentrate
Concentrate   Metal Recovery
      % Cu % Ni
Maturi Bulk #1     93.7 96.1
Maturi Bulk #2    
Maturi Ni-Cu     91.2 97.6

Recovery of Precious Metals from CESL™ residue

Precious metals including gold, platinum and palladium remain in residue throughout the leaching process and are recovered from the residue via flotation.  A weighted precious metals recovery from the leach residue of 90.9%, 82.6%, and 88.1% for Maturi Bulk #1; 88.2%, 52.5%, and 78.8% for Maturi Bulk #2;  and 75.0%, 75.0% and 75.0% for Maturi Ni-Cu was achieved for gold, platinum, and palladium respectively.

Compositions of the flotation products for each concentrate processed are presented in Table 2.

Table 2 - Precious Metals Flotation Concentrate Product
Concentrate S (t)
Maturi Bulk #1 85.8 81.4 6.1 11.0 33.0
Maturi Bulk #2 93.8 91.4 4.1 5.3 19.8
Maturi Ni-Cu 97.0 94.6 2.5 6.8 21.4

Although not integrated within the pilot plant flowsheet, bench testwork was performed to further upgrade the material to elemental sulphur and a separate Precious Metals cake using sulphur melting. The grade of the Precious Metals cake for the Maturi nickel-copper concentrate would be approximately 225 g/t assuming the cake retained an elemental sulphur grade of 45%.

Further metallurgical testing will be conducted during pre-feasibility in order to optimize the selected process and flowsheet design.

Tom Pugsley, Director of Duluth Metals is the Qualified Person for Duluth Metals in accordance with NI 43-101 of the Canadian Securities Administrators, and is responsible for the review of the technical content of this press release.

About Duluth Metals Limited

Duluth Metals Limited is committed to acquiring, exploring and developing copper, nickel and platinum group metal (PGM) deposits. Duluth Metals has a joint venture with Antofagasta plc on the Twin Metals Minnesota Project, located within the rapidly emerging Duluth Complex mining camp in north-eastern Minnesota. The Duluth Complex hosts one of the world's largest undeveloped repositories of copper, nickel and PGMs, including the world's third largest accumulation of nickel sulphides, and one of the world's largest accumulations of polymetallic copper and platinum group metals. Aside from the joint venture, Duluth Metals retains a 100% position on approximately 40,000 acres of mineral interests on exploration properties adjacent to and nearby the Twin Metals Minnesota LLC joint venture.

About Twin Metals Minnesota LLC

Twin Metals Minnesota, LLC, is a joint venture company, 60 percent owned by Duluth Metals Limited and 40 percent by Antofagasta plc. Twin Metals was formed in 2010 to pursue the development and operation of a copper, nickel and platinum group metals (strategic metals) underground mining project within the Duluth Complex in northeastern Minnesota. Twin Metals holds mineral and land assets of approximately 32,000 acres of leased and permitted land, including mineral resources prepared in compliance with the requirements of NI 43-101.

This press release contains forward-looking statements (including "forward-looking information" within the meaning of applicable Canadian securities legislation and "forward-looking statements" within the meaning of the US Private Securities Litigation Reform Act of 1995) relating to, among other things, the results of drilling operations of Duluth Metals and exploration and mine development.  Generally, forward-looking statements can be identified by the use of words 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 statements that certain actions, events or results "may", "could", "would", "might" or "will be taken", "occur" or "be achieved".  Duluth Metals has relied on a number of assumptions and estimates in making such forward-looking statements, including, without limitation, the prices of copper, nickel and platinum group metals (PGMs) and the costs associated with continuing exploration and mining development.  Such assumptions and estimates are made in light of the trends and conditions that are considered to be relevant and reasonable based on information available and the circumstances existing at this time. A number of risk factors may cause actual results, level of activity, performance or outcomes of such exploration and/or mine development to be materially different from those expressed or implied by such forward-looking statements including, without limitation, whether such discoveries will result in commercially viable quantities of such mineralized materials, the possibility of changes to project parameters as plans continue to be refined, the ability to execute planned exploration and future drilling programs, possible variations of copper, nickel and PGM grade or recovery rates, the need for additional funding to continue exploration efforts, changes in general economic, market and business conditions, and those other risks set forth in Duluth Metals' most recent annual information form under the heading "Risk Factors" and in its other public filings.  Statements related to "reserves" and "resources" are deemed forward-looking statements as they involve the implied assessment, based on realistically assumed and justifiable technical and economic conditions, that an inventory of mineralization will become economically extractable.  Forward-looking statements are not guarantees of future performance and such information is inherently subject to known and unknown risks, uncertainties and other factors that are difficult to predict and may be beyond the control of Duluth Metals.  Although Duluth Metals has attempted to identify important risks and factors that could cause actual actions, events or results to differ materially from those described in forward-looking statements, there may be other factors and risks that cause actions, events or results not to be as anticipated, estimated or intended.  Consequently, undue reliance should not be placed on such forward-looking statements. In addition, all forward-looking statements in this press release are given as of the date hereof.  Duluth Metals disclaims any intention or obligation to update or revise any forward-looking statements, whether as a result of new information, future events or otherwise, save and except as may be required by applicable securities laws.  The forward-looking statements contained herein are expressly qualified by this disclaimer.





SOURCE: Duluth Metals Limited

For further information:

Mara Strazdins
Vice President Investor Relations and Corporate Communications
Telephone: (416) 369-1500 ext. 222
Email: mstrazdins@duluthmetals.com
Webpage:  www.duluthmetals.com

Vern Baker
Telephone: (651) 389-9990
Email: vbaker@duluthmetals.com

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