NEWS RELEASE: Duluth Metals Provides Metallurgical Update on Twin Metals Minnesota Project

July 18, 2013

  • 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 CESLTM process;
  • Good recoveries of gold and platinum group elements from CESLTM residues by sulfur flotation.

TORONTO, Ontario, July 18, 2013 – 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 CESLTM 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

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 CESLTM 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 CESLTM process at Teck’s hydrometallurgical facility in Richmond, British Columbia. CESLTM 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.

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