Engineering & Mining Journal

OCT 2017

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REGIONAL NEWS - U.S. & CANADA 10 E&MJ; • OCTOBER 2017 www.e-mj.com Mining will be by a combination of conventional cut-and-fill and shrinkage mining methods, using two-boom electric hydraulic drill jumbos, 3.5-yd 3 LHDs, 20- mt haul trucks, scissor-lift bolters, and other rubber-tired support equipment. The PEA assumes upgrading of the existing mill and tailings management fa- cility, which have been on care and main- tenance since 1999. Mill throughput of 600 mt/d is assumed to be achievable by modernizing controls and instrumenta- tion of the reagent and grinding circuits and installation of new pumps. The mill flowsheet consists of a sin- gle-stage crushing circuit and a two- stage grinding circuit followed by cyanide leaching. The leached gold is collected in a carbon-in-pulp (CIP) circuit, subse- quently stripped using mild caustic, and collected on stainless steel mesh cath - odes by electrowinning. The product from electrowinning is refined into doré bars in an induction furnace. Pure Gold benefits from existing per- mits, including the Environmental Compli- ance Approval, which allows for operation of a 1,089-mt/d mill and CIP circuit, with discharge of treated tailings to the existing tailings facility. This permit will require updating due to regulatory changes. Over the coming months, Pure Gold will focus on completing a detailed project development schedule that will provide a critical path to a production decision, in- cluding detailed engineering and permit- ting. Resource definition drilling from the Madsen ramp will test for extensions to the current mineral resource, and exploration drilling from surface will seek to identify and extend new zones of gold mineraliza- tion close to existing mine infrastructure. Minnesota Releases Dam Safety Permits for PolyMet The Minnesota Department of Natural Resources (DNR) released two draft dam safety permits and a public waters work permit for public review and comment. These are two of the major permits Poly- met Mining needed to build and operate its NorthMet copper-nickel-precious met- als project in northeastern Minnesota. The draft public waters work permit is required for a culvert extension to widen Dunka Road, the connecting road be- tween the plant and mine site. Dam safety permits establish the de- sign, construction and operating parame- ters to ensure long-term, safe and stable operations of facilities that impound water. PolyMet has proposed two facilities to im- pound water: an existing tailings basin and a new hydrometallurgical residue facility. The DNR posted the draft permits for a 30- day public review and comment period. "These draft permits account for three of nine permits that have been no- ticed for public review and comment this summer," said Jon Cherry, president and CEO, Polymet Mining. "We are pleased with our progress and look forward to the rest of the draft permits being released." PolyMet will reuse this basin and in- corporate additional engineering controls into the design to ensure it remains sta- ble and protects nearby natural resources during and after operations. Using the ex- isting tailings basin affords less wetland impacts and beneficial reuse of a brown- field site. The new hydrometallurgical res- idue facility will impound water and solids from the hydrometallurgical processing plant, and will have a double liner con- tainment system. "The tailings basin was one of the most studied aspects of the NorthMet project during the comprehensive state and federal environmental review of the project that concluded in 2016," Cherry said. "We take the design, construction and operation of the tailings impound- ment very seriously and have taken extra measures to ensure a safe and stable de- sign. The science shows that not only can we be protective of water and other nat- ural resources, but we will make a sub- stantial contribution to addressing legacy reclamation issues at the site." Other permit applications currently under review by the state include a water quality permit, an air emissions permit and the Permit to Mine. MSHA Proposes Changes to Workplace Examination Rules The U.S. Mine Safety and Health Admin - istration (MSHA) published two proposed rules in the Federal Register that would change the final rule on examinations of working places in metal and nonmet- al (M/NM) mines that was published on January 23. The first proposed rule would make limited changes to the final rule, according to MSHA. It would require that an examination of the working place be conducted before work begins or as min- ers begin work in that place, and that the examination record include descriptions of adverse conditions that are not correct- ed promptly and the dates of corrective action for these conditions. It would pro- vide mine operators additional flexibil- ity in managing their safety and health programs and reduce regulatory burdens without reducing the protections afforded miners. The proposed rule would continue to permit mine operators with consecutive shifts or those that operate on a 24-hour, 365-day basis to conduct an examination on the previous shift. Comments on the proposed changes to the final rule must be received by mid - night EST on November 13. The second proposed rule would further delay the effective date of the final rule. The proposed extension would offer addi- tional time for MSHA to provide stakehold- ers training and compliance assistance. The Madsen Project will likely become Ontario's next gold mine.

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