Resource World Magazine

a u g u s t / s e p t e m b e r 2 0 1 5 www.resourceworld.com 49 rocks because of their potential for the neutralization of the acid leach solution. The ISR copper operations use 0.5% sulfuric acid which is similar in acidity to lemon juice; • The mineral deposit should be at reasonable depth. Risks associated with isR methods include: • Reduced copper recoveries: at depth due to hydrological con- ditions; due to low fracture density, poor porosity or aquifer connectivity; due to short circuiting of leaching solutions along major sets of fractures; due to reduced flow rates because of gypsum precipitation on fissures as a result of copper carbonates leaching; • Reduced uranium recovery due to the trapping of silt and clay in the pores of the sandstones by the underground water flow; • Increased acid consumption due to acid neutralization by carbonates; • Increases in the price of sulfuric acid (leaching agent) during periods of increased phosphate consumption; • Increased well costs due to bad ground requiring well screens and larger boreholes; • Environmental risks associated with the pollution of the pro- ducing aquifer especially when the body of water has other downstream users; • No standalone commercial ISR copper operation ever existed. While ISL uranium operations have been successfully carried out for decades in different countries and environments, the ISR of copper was undertaken at several operating mines as com- plementary to hardrock mining only and some of the method's shortcomings were readily visible. At Glencore's Mufulira Mine in Zambia several cases of contamination of the adjacent town's water resources were recorded over the last decade. Arizona oper- ations proved safer: BHP's San Manuel Mine and its Pinto Valley Mine with the Miami unit operated over a decade without major issues. At the San Manuel Mine injection wells treated rubbleized (blasted/fragmented) low-grade ore from the underground mine. The pregnant solution was recovered from both recovery wells and directly from the underground. In the initial phase 10% of the solution was lost to surrounding ore and country rock; were the mine located in an inhabited area it could have possibly cre- ated contamination problems. cOpper Current ISR copper projects comprise the excelsior Mining [MIN-TSXV; OTCQX-EXMGF; 3XS-FSE] Gunnison Project, taseko Mines' [TKO-TSX; TGB-NYSE MKT] Florence Project, and Copper Fox Metals' [CUU-TSXV; CPFXF-OTC] Van Dyke Project, all located in Arizona. uraniuM According to the World Nuclear Organization, in 2013, 47% of world uranium was from in-situ leaching (ISL) operations. Australian ISL mines (Beverley, Four Mile, and Honeymoon) use sulfuric acid as complexing agent and hydrogen peroxide as oxi- dant. Kazakh ISL mines use only acid but in higher concentrations as acid leaching gives higher uranium recovery (70-90%). US ISL mines use an alkali leach (60-70% recovery) due to the presence of acid neutralizing limestone and gypsum in its aquifers. The production life of an individual ISL well pattern is one to three years in the US (most of the uranium being recovered in the first six months of operation), and up to 1.5 years in Australia (70% of uranium recovered in the first year). The flow capacity of injection wells is always on a downward trend through its productive life. The pregnant solution is recovered in a resin/polymer ion exchange (IX) or liquid ion exchange (solvent extraction-SX) sys- tem. At closure time contaminated water drawn from the aquifer is either evaporated or treated (reverse osmosis) before reinjec- tion. In the US strict environmental regulations stipulate that water is to be restored to parameters that allow its pre-mining use. In Australia the ISL aquifers water is very poor and has no use; therefore no treatment is required as water quality reverts to its original condition over time. Upon decommissioning, an ISL site is easily reverted to its original state through wells capping, facilities removal and reveg- etation of the evaporation pond. pOTash Deep seated potash (sylvite) and table salt (halite) beds are mined through an in-situ mining method called solution mining. In Saskatchewan alone there are 8 billion short tons of potash reserves (at less than 1,100 m depth) amenable to conventional mining, and some 11 billion short tons of potash reserves recov- erable through solution mining. Water or halite-rich brine is injected at the base of the potash beds promoting potash dissolu- tion and the creation of underground caverns filled with brine. The saturated brines are then pumped to the surface through recovery holes where they would be evaporated and the crystal- lized product would be sent to the processing plant. Solution mining projects are less risky than the copper ISR projects but still face risks associated with the continuity of pot- ash beds, their quality, and potential processing risks. In Saskatchewan, potash solution mines are represented by Mosaic's Belle Plaine Mine and PotashCorp's Patience Lake Mine. Solution mines projects include Vale's Kronau Project and Western Potash Corp.'s Millennium Project. rOcK salT Solution mining is successfully applied in mining part of the 8,500 square miles of rock salt beds that underlie New York State. The resulting salt caverns could be used for the safe storage of hydrocarbons and of different types of wastes. Lithium Brines (saline basin brines, geothermal water, and oil field brines) are also exploited and lithium, boron and potassium are being economically recovered from them. n

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