Engineering & Mining Journal

SEP 2018

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Page 43 of 75

NARROW VEIN MINING 42 E&MJ • SEPTEMBER 2018 AMC has conducted numerous studies to reduce dilution for mechanized narrow vein mining methods in operating mines. Meth- ods have included long hole open stoping (LHOS) and mechanized cut and fill (CAF). Dilution can be classified as planned or unplanned. Planned dilution accounts for waste material incorporated into the stope when designing practical mining shapes. Planned dilution will depend on the vein geometry, thickness, orebody dip and lo- cal ground conditions. Unplanned dilution consists of waste, which is mined due to overbreak, which may result from poor drilling or blasting or as any waste incor- porated during mucking. This article pres- ents a high-level discussion of a study con- ducted by AMC to determine the optimum (minimum) dilution that could be reason- ably applied to a narrow-vein orebody. Vein Characterization The dilution study began with vein characterization. The broad aim was to identify the general variability in vein width, geometry, and lateral ex- tent (strike and dip) and to iden- tify geotechnical conditions that may determine the applicability of various mining methods. The findings included: • Consistent vein strike 1,500 m; • Vein width ranging from 0.5 m to more than 5 m; • Ground condition ranging from poor to good, across strike and depth extents; • Cemented rockfill and waste rock con- sidered to aid ground support; and • LHOS and CAF used at the mine, with potential to optimize sublevel spacing and mining sequence. Optimized Dilution Scenarios Using the results of the vein character- ization study, it was concluded that the minimization of dilution for LHOS and CAF would be based on: • Vein widths of 1.5 m, 2.25 m, 3.5 m and 5 m; • Varied ore drive dimensions, and rectan- gular and shanty-back profiles; and • Orebody dips of 61°, 66°, 68° and 72°. Formulae AMC utilized the following formulae to determine dilution. Dilution ratios were calculated for planned and unplanned dilution. Total dilution is the sum of planned and unplanned dilution (Figure 1.1 and Figure 1.2). This method has been selected from numerous alternatives for calculating dilution. The optimum dilution is a trade-off against ore recovery. Given the value of the ore for this case study, recovery was given priority over dilution, with a target recovery of 100%. Benchmarking and Case Studies AMC used benchmarking and case studies to identify dilution experienced at different narrow-vein mines, guide equipment selec- tion, drill-and-blast designs, and technical services procedures and recommendations. Equipment AMC examined the existing fleet of stope equipment (jumbos, LHDs, long- hole drills, and bolters) at the mine and established optimal drill-and-blast designs for the selected vein widths, dips, drift pro fi les (square and shan- ty), drift size (height and width), and mining methods, which could immedi- ately be implemented to reduce dilution, without additional equipment purchases. Reducing Dilution With Narrow-vein Mining A plan that considers drive size, blast design and quality control provides the best results By Paul Salmenmaki Figure 1.1—Minimum dilution is achieved by using the optimal equipment and smaller ore drives for the LHOS methods.

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