In• I EBOOO E9000 Eloooo Ellooo E12000 £13000 £14000 £15000 N12000 Nl1000 N10000 N9000 N8000 N7000 MEQB REGIONAL COPPER-NICKEL This document is made available electronically by the Minnesota Legislative Reference Library as part of an ongoing digital archiving project. http://www.leg.state.mn.us/lrl/lrl.asp A PRELIMINARY REPORT DETAILS OF THE UNDERGROUND MINE MODELS Steven Po Oman William A. Ryan REGIONAL COPPER-NICKEL STUDY MINNESOTA ENVIRONM~NTAL QUALITY BOARD FEBRUARY, 1978 REPORT. The reader is cautioned t""""""",V","¥Y$i'li!! use, quotation or reproduction of this material without first contacting the authors, since the . document may experience extensive revision during review. TABLE OF CONTENTS Page EXECUTIVE SUMMARY 1 INTRODUCTION 2 ADVANTAGES OF UNDERGROUND MINING 3 Environmental Impacts 3 Se1ectivi ty 4 Protection From Weather 4 DISADVANTAGES OF UNDERGROUND MINING 5 Economy 5 Development Period 6 Recovery of Ore 7 Safety 8 Labor Availability 9 Subsidence 10 MINING METHODS 11 MINE PLANNING 19 BLASTHOLE OPEN STOPING 21 PREPRODUCTION DEVELOPMENT 21 Shafts and Hoists 27 MINING OPERATIONS 34 Scheduling 34 Mine Design 34 Stope Development 37 Stope Mining 38 Transportation 39 Underground Crushing 40 Vent i1 ation 40 Compressed Air 43 Pumping Facilities 44 Ground Support 45 Underground Maintenance Facilities 45 Page MINING COSTS 47 Equipment Requirements 47 Supplies 51 Manpower Requirements 51 Summary of Costs 54 ROOM-AND-PILLAR MINING 56 Major Ad.vantages 56 Major Disadvantages 58 Development and Mining 58 Mining Costs 59 SUMMARY 64 APPENDIX A: GLOSSARY OF MINING TERMINOLOGY 67 APPENDIX B: UNDERGROUND MINING METHODS 69 APPENDIX C: DUST CONTROL TECHNIQUES 83 APPENDIX 0: HYDRAULIC BACKFILLING 93 REFERENCES 97 TABLES Table Page 1 Percent ore recovery for different underground 7 mining methods 2 Mine injury statistics for 1976 9 3 Underground mining methods 12 4 Applications of underground mining methods 14 5 Geologic and mechanical criteria in large-scale 15 mining methods 6 Advantages of various underground mining methods 18 7 Hoist design parameters 32 8 Underground mine equipment requirements - initial 49 and additional capital requirements 9 Schedule of capital additions and replacements 50 10 Supplies and materials requirements 51 11 Manpower distribution for the underground mine model 52 12 Average wage rates for hourly and salaried personnel 53 13 Blasthole open stoping capital costs 54 14 Blasthole open stop~ng operating costs in $/ton of 55 Cu-Ni ore 15 Room-and-pillar capital costs 62 16 Room-and-pillar operating costs in $/ton of Cu-Ni ore 63 17 Comparison of blasthole open stoping and room-and- 65 pillar mining models FIGURES Figure Page 1 Comparison of development rates during 22 preproduction and normal production operation 2 Generalized cross-sectional view of the blasthole 24 open stoping mining levels 3 Typical circular shaft arrangements 31 4 View of a stope in a blasthole open stoping mine 35 5 Room-and-pillar full face and multibench mine 57 6 Section through room of typical full face and 60 bench mining operation 7 Life cycle of the room-and-pillar mine 61 8 Variation of mining costs with capacity 66 0-1 Flow diagram of a hydraulic sandfill system 95 Page 1 EXECUTIVE SUMMARY This report creates two models of hypothetical underground copper-nickel mines located near the basal contact of the Duluth Complex in northeastern Minnesota (St. Louis and Lake counties). The mine models have been developed by the Minnesota Environmental Quality Board (MEQB) Regional Copper-Nickel Study in order to determine potential environmental impacts, approximate mining costs, and the requirements of an underground mine in terms of equipment, supplies, land, and manpower. Several assumptions form the framework for development of the hypothetical mine models. The mines are designed to produce 7,938,000 metric tons (mt) (8,750,000 short tons (st)) of ore per year over a mine life of 30 years. An additional 635,000 mt (700,000 st) of waste 'rock will be produced annually. The cut-off grade (stated in terms of percent copper) is set at 0.60 percent copper. The average grade of the ore is 0.80 percent copper and 0.20 percent nickel. The mining methods chosen as the most applicable to underground mining of the Duluth Complex are room-and-pillar mining and blasthole open stoping. For modelling purposes, room-and-pillar mining will be used where sub­ stantial reserves of fairly flat lying ore exist. The dip angle must be less than 20 0 and the thickness of the mineralization is restricted to less than 25 meters (m) (82 feet (ft)). Blasthole open stoping will be employed when the height of the ore zone is greater than 25 m (82 ft). Using the models as examples, the report outlines: 1) the activities of the pre­ production development period; 2) the major features of the mining methods, including the equipment involved; and 3) the costs associated with each mining method. ' A work force of about 1000 people will be necessary for the mine to function at a production rate of 7,938,000 mt/year. The costs associated with the two mining methods are summarized below. Blasthole Room-and- Operating Costs--$/mt of Cu-Ni ore Open Stoping Pillar Mining Development 2.05 0.52 Ground Control .26 Drilling .30 085 Blasting .12. .33 Haulage .76 1.82 Crushing and Hoisting .35 .33 Power and Fuel .30 .33 Maintenance (non-allocatable) .58 .58 Supervision and Services 1.05 1.10 General .35 .39 Total $5.86 $6.51 Capital Costs $130,400,000 $112,200,000 The m~n~ng glossary fo~nd in Appendix A may aid in understanding some of the mlnlng terms used ln this report. Page 2 INTRODUCTION The copper-nickel mineral resources of northeastern Minnesota can be removed from the ground by open pit mining, underground mining, or combina­ tions of both methods. A preliminary report on ~Ren pit mining of the Duluth Complex has already been prepared by the Minnesota Environmental Quality Board (MEQB) Regional Copper-Nickel Study. Underground mining will be examined in this report. Underground mining methods must be considered when the depth of a mineral deposit is such that removal of the overburden makes surface mining tech­ niques unprofitable or when external factors prohibit the operation of a surface mine. Determining the optimum underground mining method requires careful analysis of geologic, economic, and environmental data. By using a less rigorous approach, room-and-pillar mining and blasthole open stoping were chosen as the mining methods most suitable to the development and mining of the mineral resources of the Duluth Complex. Both methods are high productivity mining methods which incorporate the latest developments in underground mining equipment. The hypothetical mine models developed in this report attempt to typify the mining practices that may be employed in northeastern Minnesota. Although no two mines are alike, there are enough similarities between mines (and mining methods) that much of the information found in this report will re­ main valid even if different mining methods are actually utilized. Page 3 ADVANTAGES OF UNDERGROUND MINING The advantages of underground mining are basically the disadvantages of open pit (or surface) mining. Similarly, the inverse is true; that is, the disadvantages of underground mining relate to those areas where sur­ face mining holds an advantage. The major advantages of underground mining over open pit mining are lessened environmental impacts, greater selectivity, and reduced exposure to weather. Environmental Impacts Much less land surface is necessary for the operation of an underground mine than for an open pit mine of the same production size. At the very least, an underground mine will require that land be available for the mine entrance and access roads. Commonly, additional land is utilized for ventilation shafts, multiple mine entrances, buildings, stor~ge areas, and waste rock dumps. (However, a mining company could decide to dispose of the waste rock in suitable underground openings and thus eliminate the problem of placing waste rock above ground.) Because less land is needed for an underground mine than for an equivalent open pit mine, there should be less disruption of the plant and wildlife species that inhabit or use the surrounding area. With less surface activity occurring, dust and noise generation should be reduced accordingly. Finally, the magnitude of the reclamation program for an underground mine is greatly diminished because of the absence of an open pit and a network of roads, and the reduced size of the waste rock dumps. This results in lower reclamation costs for underground mining than for open pit mining. DRAFT REPORT· The reader is calr~ioned c~ncernil1g use, quotation or reproduction of thIs ,material witllout 'first contacting the author:s, SlIlc,e, the , document may experience e~tenslve reVISion dUring review. Page 4 Selectivity Underground mining methods make it possible to economically mine mineral deposits which are too small, irregular, and/or deeply buried to extract using surface mining methods. Mining methods exist which can be applied to irregularly shaped deposits, narrow veins, discontinuous veins, and small pockets or lenses of ore. Using these methods, the mineral laden rock can be removed without having to handle large quantities of low- grade ore and/or waste rock. As a rule, the more selective mining methods are only applicable to deposits where the value of the ore is high enough to justify the generally lower productivity associated with selective mining. On the other hand, underground mining of low-grade deposits must be performed as efficiently as possible in order to be economical., which usually means that large scale total extraction mining methods must be used. However, even these large scale methods offer more selectivity than open pit mining which ultimately removes all the material that overlies the ore at a given depth.