Abstract:

Longhole Open Stoping (LHOS) is a widely used mining method. LHOS is considered a “bulk” mining method that is generally applied to steeply dipping deposits. LHOS is generally thought to be a relatively safe and efficient mining method and can be applied in either a transverse or longitudinal orientation with or without backfill.

One of the challenges in designing a LHOS mine is selection of the optimum stope size (height, width, and depth). Larger stope sizes increase the productivity of the stope cycle and reduce the total mine development required to extract the ore. Unit operating costs are reduced with larger stope dimensions. Larger stope sizes introduce geometric simplification of the mining shapes which reduces the selectivity of the method. This could lead to a lower reserve tonnage at a lower head grade. Larger stope sizes also introduce a higher risk of geomechanical instability in the exposed walls of the stope and potentially more unplanned dilution. Decreasing stope size yields greater selectivity, improves ground stability, and reduces the amount of unplanned dilution. These benefits come at a premium in terms of lower stope productivity and higher unit costs.

Selection of the optimum LHOS size has traditionally been done using a combination of empirical, experiential, and analytical methods. This process can be subject to personal and professional bias. Torex Gold Resources Inc. (Torex) initiated a study to create a process and evaluation tool to integrate all relevant design criteria and remove bias from the stope size evaluation process. This paper presents the process flowsheet and the Excel based assessment tool developed by Torex and their strategic partners at SRK (Canada) and BWB Consulting Services Inc.

Biography of the presenter: Mr. Buss is a Professional Mining Engineer and Project Manager with over 30 years of progressive experience on four continents. A graduate of Queen’s University at Kingston, Mr. Buss gained his early operational experience as a miner and shiftboss in the Witwatersrand gold mining district of South Africa. He developed a technical specialization in rock mechanics and further advanced this skill set on his return to Canada to work with Inco Ltd (now Vale.) During some 20 years with Vale he continued to expand his technical experiences into mine engineering and planning. He later specialized in project development. Prior to leaving Vale he held the position of General Manager- Mining Projects with accountability for advancing and constructing underground mining projects in Vale’s North American operations. Mr. Buss then took on an executive role in the junior gold mining sector as Vice President – Project Development with Lake Shore Gold (now Pam American Silver) in the historic Timmins Gold Camp. Mr. Buss is currently President of BWB Consulting Services Inc. where he provides strategic guidance to mining companies on operational efficiency, mineral deposit economics, and project evaluation. He provides expert advice and due diligence reviews in support of investment, mergers, and acquisition activities. Mr. Buss actively volunteers with industry, academic, and professional organizations as well as community based volunteer organizations. He is a member of PEO, CIM, PDAC, and PMI. He holds a board position with the Centre for Excellence in Mining Innovation and maintains close contacts with the mining departments at several Canadian Universities. Mr. Buss married his university sweetheart in 1986. They have one daughter, who is working towards attaining her CPA designation. In his personal time, Mr. Buss enjoys golfing, fishing, and travel.

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Clifford Lafleur