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HIGHFIELD RESOURCES JUNE 2016 • E&MJ; 47 www.e-mj.com plant will ultimately produce 90,000 mt/ month of granular K60 MoP product (or 1.08 million mt/y of GMoP), which will require more than 6.3 million mt/y of run- of-mine (RoM) ore. Highfeld completed its DFS in March 2015. As the company turned its at- tention to construction and ultimately production, it made several realizations during the underground design and equipment selection process that would improve operational effciencies. This in- formation was used to further optimize the Muga project and company released an optimized DFS in November 2015. The measured and indicated mineral resource estimate is 224.5 million mt at an average grade of 13.4% K 2 O based on a minimum 1.5-m bed thickness and grade cutoff of 8% K 2 O-in-sylvinite. The estimate also includes beds thinner than 1.5 m where the grade exceeds 12%, satisfying the 8% K 2 O-in-sylvinite at 1.5 m cutoff. Recognizing that the K 2 O contained in carnallite is unlikely to be recovered in the proposed ore treatment method, it was not included. The sylvinite mineralization occurs in seven beds, ranging in depth from 100 m to more than 1,500 m. The original mine plan targeted four beds in two areas, an eastern zone and a western zone (See Fig- ure 2). The new mine plan was altered to include an additional sylvinite bed, which extended the mine life to 47 years from 24 years. Instead of relying solely on road-head- ers, the company elected to use a com- bination of continuous miners and road- headers to increase productivity in both production and infrastructure develop- ment. By increasing the number of main headings from one to three, they could reduce ramp up risks and increase oper- ational effciency. The size of the main- line underground conveyor and storage system, and the decline conveyor were all increased so they could provide a steady feed of 1,500 mt/h to the process- ing plant. Importantly this also enables further expansion with the company believing that Muga has the potential to produce around 2 million mt of potash for a period of more than 30 years. The various mining horizons will be accessed using two straight 5- x 7-m declines approximately 2.5 km and 2.6 km in length. "Spain has a rich heritage of tunneling and infrastructure develop- ment," Schlumpberger said. "When we tendered for the ramp construction, we had 10 choices for contractors." The eastern decline reaches the min- eralized horizon at 440 m below surface and the western decline approximately 452 m below surface. "We will use the east ramp for conveyance," Schlumpberg- er said. "The west ramp will be entry and emergency egress and primary ventilation. As the mine develops, we will sink some short shafts to assist with ventilation." At the bottom of the decline, min- ers will drive two sets of main headings (north and east) using a three-entry sys- tem with panel belts for the development sections running perpendicular to the mains. "We decided to use a three-entry system for development," Schlumpberger said. "It offers more options than a single heading as far as ventilation, regress and production effciencies." Depending on the geology and bed height, the room-and-pillar mining meth- od will use a combination of continuous miners and road-headers to minimize dilution. "The use of road-headers gives us some fexibility with regard to selec- tively separating the sylvinite from the halite," Schlumpberger said. "The con- tinuous miners are more productive than road-headers and the increased tonnage offsets the poor selectivity." A little less than 20 years ago, Sierra del Perdón was extracting sylvinite using both room-and-pillar and longwall mining methods. The use of the longwall mining method lends credence to the compe- tence and uniformity of the ore body and more importantly the lack of an aquifer, Schlumpberger explained. "The lack of an aquifer is one of our strategic advantag- es," he said. "If a potash operation en- counters an aquifer above the beds they are usually forced to use shaft access. When a decline pierces an aquifer, water fows down the ramp into the mine. Potash miners do not like water. With shafts, they can freeze their way through the aquifer and isolate the water from the operation." Sinking shafts is an expensive prop- osition that can exceed more than $500 million as is currently being demonstrat- ed by BHP in its Jansen potash project. "Muga's two declines, including the con- veyor system will cost less than $30 mil- lion," Schlumpberger said. The decline conveyor will trans- port RoM ore to permanent storage buildings on the surface. "Those will be designed in-country," Schlumpberger said. "Any place we can use in-country design, we are using it. If we need a spe- cialized contractor with potash experi- ence, then we use foreign contractors." Highfeld intends to use paste backfll- ing, however, this will not be implemented until Muga's Phase 2 begins construction. Backflling will increase the life-of-mine extraction ratios for each panel from 55.7% to approximately 80%, and also provide long-term geotechnical stability, minimizing the risk of subsidence. Recovering GMoP Highfeld has engaged several globally recognized consultants, who are world leaders in the processing of sylvinite ores and have been involved in the de- sign process for many plants, to de- velop and supervise the completion of Figure 2—Mine panel confguration by east and west zones across the four principle mining seams.