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By Frank E. Chase

Retreat mining is one of the most hazardous operations conducted underground. One of the keys to miner safety and an efficient recovery of the reserves is to design adequately sized production pillars to prevent pillar squeezes, excessive pillar spalling, severe floor heave, roof falls, and pillar bumps. Currently, few pillar design approaches are available which consider the abutment pressures generated by the gob. The Bureau of Mines is developing a method called Analysis of Retreat Mining Pillar Stability (ARMPS) to aid in the design of retreating sections. Back analysis of 42 case studies indicates that ARMPS can be helpful in predicting stability during retreat mining operations.

Jan 1, 1993

By A. J. Richardson

Before the development of the underground stoping and mining costs can be considered, certain facts about the ore body, the proposed mine, markets, etc., must be known or determined. In the case to be studied, the zinc-lead mineralization occurred with a narrow vertically dipping structure of undetermined length and vertical extent. Exploration completed to date has revealed 6.5 mil¬lion st t of proven reserves. A further 820,000 st of in¬dicated reserves has been outlined and this tonnage is considered capable of being expanded by a factor of approximately four after more detailed drilling. After studying the market conditions and completing a very preliminary feasibility study, it was decided that production would be 730,000 stpy (or 2000 stpd) of ore. First year production would be at the rate of 1500 stpd. The main design criteria for the selection of the min¬ing methods are minimizing surface subsidence, maxi¬mum recovery of the ore body, maximum degree of grade control, maximum productivity, and safe working conditions. Two basic extraction systems are considered capable of meeting these requirements: mechanized cut¬and-fill stoping and sublevel long-hole stoping with filling. The primary development system of the mine has been designed to give maximum flexibility in stoping systems and layout and to permit changes if considered necessary as a consequence of actual production ex¬perience. At the present time, access to the mine is by a circu¬lar concrete lined vertical shaft, 16 ft diam, sunk to a depth of 1380 ft. Two exploration levels have been driven within the ore zone at depths of 165 and 1246 ft below the surface outcrop. The development to date had the objective of sampling the mineralization and produc¬ing detailed information on the outline of the ore body and the distribution and controls of zinc and lead values. In an attempt to satisfy the basic design criteria for the mine, it was decided that production would be best achieved by a combination of 40% sublevel long-hole stoping and 60% cut-and-fill mining. Costs of exploration and capital development of per¬manent underground facilities are normally written off over the life of a mine. Production expenditures, on the other hand, are of a temporary nature and are normally charged as and when incurred as an operating expense. Reasonably accurate predictions of mine production costs can be built up from engineering design and estimates of individual mine activities for ultimate inclusion in the comprehen¬sive data required for financial decision making. The simulated operations can be costed on a detailed basis in the form of a monthly operating budget. The budget format can be generalized or detailed, depending upon the scope of the project. However, ex¬perience suggests that a fairly detailed format has the advantage of assuring that all significant cost items are included. For underground costing it is suggested that the budget structure include five major cost centers (i.e. development, diamond drilling, ore extraction, hoisting/ transportation, and general mine expense). These in turn are detailed under numerous subheadings. The mechanism for compiling an operating budget will be illustrated. Because of its relative simplicity, ore extraction under sublevel long-hole stoping has been chosen for illustration. All other activities, simple or complex, can be estimated in similar fashion. BLOCK AND STOPE DEVELOPMENT Long-hole blocks, used where advantageous, will be up to 250 ft in height, depending upon the vertical con¬tinuity of the mineralization, and approximately 300 ft long. Drawpoints will be at 36-ft intervals and serviced by loading crosscuts driven from a footwall drift parallel to and close to the ore zone. Pillars between the stopes will be 50 ft wide. Stopes will be drilled off with vertical rings of blastholes drilled from sublevels approximately 60 ft apart vertically. This drilling will be done by percussion drilling machines (31/2 in.) mounted on a trackless drilling rig. Load¬haul-dump (LHD) equipment will be used to move broken ore from the drawpoints to the orepass connecting to rail haulage systems. On completion, long-hole stopes will be backfilled to prevent caving and to facili¬tate later pillar removal. From a planned stope layout, a forecast of produc¬tion and development is made in Table 1. Table 1. Block Tonnage and Stope Development Quantity Ore Waste Total ore block 375,000 st 2 stopes 310,000 st 1 pillar 65,000 st Access crosscuts, 4 at 100 ft 400 ft Drill sublevel drifts, 6 at 300 ft 1800 ft Stope raises, 3 at 250 ft 750 ft Undercut sublevel drifts, 2 at 300 ft 600 ft Loadout crosscuts at 35-ft intervals 550 ft 100 ft 3300 ft 500 ft Total development footage 3800 ft Tons per ft of development 987 st

Jan 1, 1982

By Valerio Violo, Antonio Raschillà, Livia Cicinelli

"The Cityringen project foresees the construction of a new circular metro line in and around the city center of Copenhagen. Both drives, the north and the south one, required the TBMs to be equipped in order to cope with contaminated water table and soil. The north drive mined in water contaminated with chlorinated compounds, including chloroform and vinyl chloride, while the south TBMs excavated in a highly benzene contaminated area, becoming the first TBMs to complete such a challenge. Despite the pollution and the stricter operative procedures, the production has been extremely successful with record up to 520 m in one month and 32 m in one day. 1 INTRODUCTION The Cityringen is an extension of the existing metro line. The 15 km long twin tunnels will form a new circular line with 21 new stations (17 + 4 crossovers). When finished it will interchange with the existing metro, rail and bus infrastructure at key locations around town, taking 90% of Copenhagen citizen at less the 600m from a metro station (Figure 1). The Contract has been awarded in April 2011 to the Copenhagen Metro Team (CMT), a joint venture between the Italian companies Salini Impregilo, Tecnimont and Seli SpA. Tunnels are being excavated with 4 Seli-Kawasaki EPB TBMs, two of which manufactured in Denmark by Seli Tunneling Denmark ApS, which is also operating them. At the moment this article is written 50% of the tunnels have been completed and over 40% handed over for the electromechanical works. Seli Tunnelling Denmark is a Danish company constituted in 2012 as a subsidiary of Seli SpA for this project and subsequently acquired by the Salini Impregilo Group in 2015."

Jan 1, 2016

By V. Arad, S. Arad

Besides the conservation and closing activities, an important issue to achieve is the environmental rehabilitation of the mining perimeters, also assuring the continuity and sustainable development of the mining activity in the Jiu Valley. Modifying and depleting the soils by mining works and dumps of mineral waste as a result of coal mining and tailing is one of the important aspects. The paper’s aim is to analyze which are minerals and resources policies of our government and to adopt measures for sustainable development in the coal mining in this region. The measures to reduce the instability risk for the mining works and waste dumps, which could affect the underground mining constructions or the related surface areas, were consider. It is most important to establish the priorities in order to obtain a high efficiency by combining the measures according to the environmental analysis and risk assessment.

Jan 1, 2005

By C. Pitzer

"Safety performance in many companies and even industries has stalled in the last decade. Accidents rates are at a “plateau” and yet, serious accidents and fatality rates are not. In more dramatic cases, such as in the BP Texas Refinery disaster, organizations that have “exemplary” safety statistics, suddenly have a catastrophic or multi-fatality event occurring. Classic examples are the Piper Alpha disaster and NASA’s Challenger and Columbia disasters, the BP’s Deepwater Horizon Rig disaster in the Gulf of Mexico. Looking into the causes of these accidents provides an insight into the events and deficiencies that led up to the accident, but what are the common features in the organization’s mindset, or its culture? What characterizes these organizations’ decision-making, their approach to safety and to risk and are there features that can be delineated? The research and review presented in this paper covers a period since1995, which started in the Australian resource industry and since then covered international events. The features of these organizations are summarized as the seven deadly delusions of near zero organizations (NZO) that suffered unexpected disasters, based on extensive research by the author. More recently, the massive West Fertilizer plant explosion in Texas, and the Train Disaster in Lac-Mégantic, Quebec, Canada underlined the same trends. Organizations may experience calamities not because they are bad, or unsafe, but because they have become “cult-like”. INTRODUCTION The train disaster of 6 July 2013, in the small town of Lac-Mégantic in Quebec, Canada, in which 47 people were killed, had many strange pre-cursorsso-called “black swan” events that have occurred in many different industries. Black swan events are so rare, that there is almost zero chance that they will ever occur again, but they are so calamitous that the responses to these are emotional and irrational, (but necessary) and in those responses, the seeds for other, different black swan events are put into place. It is not what we don’t do, or do wrong, that causes modern disasters, it is what we do. The same things in the culture that make us successful, may also cause the disasters. We slowly, incrementally and insidiously ‘float’ into disaster. One such Black Swan event: The Piper Alpha Oil Rig disaster, killing 167 men in the North Sea on the 6 September 1988, was one of the most pivotal events in safety around the world. It changed the thinking and focus of governments, whole industries and led to numerous books and papers. It resulted in new legislation, textbooks and a critical self-examination by the oil and gas industry."

Jan 1, 2016

By Steve Kral

In December 2013, the Colorado Department of Transportation (CDOT) completed the widening of the eastbound tunnel on Interstate 70 (I-70) from two lanes to three. Work on the westbound tunnel began earlier this year and is scheduled for completion in December. The Twin Tunnels project is located in the mountains about 55 km (35 miles) west of Denver. They were bored during the 1960s when I-70 was being built and became the main access to Colorado?s growing number of ski areas and the state?s Western Slope. Throughout the decades following their construction, traffic on I-70 continued to increase and now the tunnels have a major bottleneck. Com-mutes to and from the mountain resorts, particularly on weekends, have become long and slow. Adding a third lane through the tunnels will help alleviate the congestion. (A complete report on the project can be found in T&UC, December 2013, page 61.) Once the eastbound tunnel was completed late last year, CDOT authorized the funding to begin work on the westbound side. That made economic sense, as the equipment used on the eastbound tunnel needed to only be shifted across I-70 to begin work on the westbound side, rather than removing it in December and bringing it back in March when construction began on the westbound tunnel. Work on the westbound tunnel uses essentially the methods that were used on the eastbound tunnel ? removal of the existing concrete lining and using drill-and-blast methods for tunneling widening. The main difference between the two tunnels is that the westbound side requires more blasting on both ends to widen I-70 to three lanes.

By C. D. Secrest

Visiting Spring Canyon, a historic coal mining district near Helper, Utah, I was impressed by the great accomplishments that had taken place there. A tour book of the region tells of a period that began in the early 1900's, when the land was still very much the Old West, when settlers lived out their lives in coal company towns and produced a resource that was to build a nation (Cunningham, F., 1990). Between 1912 and the early 1970's, 11 mines had come and gone in that narrow canyon less than 15 kilometers long. Spring Canyon is a historic district now, but I could not dwell too long on the richness of its history. I was there to look for evidence of PCBs.

Jan 1, 1993

By G. Pierson

Explanations of commodity price levels, or movements, commonly focus on the supply and demand fundamentals of the particular commodity, or else are assigned to speculative activity. Comparisons of metal price histories with monetary and other economic data support the argument that the supply of and demand for money are no less important in price determination than are the supply and demand of the commodity itself. That these relationships should exist is evident in the price identity and are consistent with monetary theory. The patterns developed have limited usefulness as predictors, but their recognition is essential for the construction of price scenarios for planning purposes.

Jan 1, 1996

By J. J. Gusek

There are hundreds of passive treatment systems accepting mining influenced water (MIW) throughout the world. Some systems do not perform to design expectations while others, including volunteer systems, have successfully operated relatively unattended for decades. The primary reasons for this situation include the common misconceptions that (1) a “cookbook” approach to design is valid for a wide array of MIW chemistries and site conditions, and (2) low maintenance means “no maintenance.” Passive treatment systems for MIW are typically manmade ecosystems that are designed to handle a specific range of metal loading conditions and MIW geochemistry. Thus, when design conditions are exceeded, the suite of microbial to macroscopic ecosystems may be slow to recover or mature. This should be no surprise to designers. But when a particular system fails, it may be inappropriately attributed to the technology, not the design. This paper presents a standard “phased” design protocol that appears to work and provides examples of sub-par performance of selected passive treatment systems.

Jan 1, 2002

By E. DeLilia

For the past 30 years, surface mines have moved toward more highly mechanized, automatic systems that continuously mine overburden and ore to in-crease productivity, lower operating costs and minimize manpower needs. To achieve these goals, mine operators must be involved in every step of the machine procurement process. Several factors are involved in making the machines operate economically and efficiently: ? Prudent engineering. ? Proper planning. ? Realistic feasibility studies. ? Effective specification. ? Thorough training of the mine personnel.

Jan 1, 1995

By Bernard L. Merlo

INTRODUCTION Modern mine management is constantly striving to develop improved mining methods which will not only increase productivity, but will also provide a safer work environment and make the most efficient use of our natural resources. Progress can be seen in this area by tracing mining methods through history. Work that was originally done with hand tools progressed with the age of mechanization to conventional mining, matured to continuous and longwall mining, and the advent of short¬wall mining, a combination of continuous and longwall, has recently been seen. This new method of shortwall mining provides a promising method for safe and ex¬pedient coal extraction. This study focuses upon the planning, design de¬velopment, and operation of the first producing short¬wall unit in the US which was operated in the Pittsburgh coal seam in northern West Virginia. MINE DESCRIPTION The mine is located in northern West Virginia at Grant Town in the heart of the high volatile Pittsburgh coal seam. Originally opened in 1901, the mine has be¬come one of the largest in the US, encompassing an area of approximately 103.6 sq km (40 sq miles). The seam being mined was the high volatile Pittsburgh seam which ranged in thickness from 1.8 to 2.96 m (6 to 91/2 ft). Three types of mining methods were employed: con¬tinuous mining, longwalling, and shortwalling, with each type accounting for 50%, 30%, and 20% of total pro¬duction, respectively. A total of 630 contract and super¬visory personnel were employed to produce the mine's designed annual tonnage of 1.8 Mt (2 million st). There were ten producing sections, eight continuous miners, one longwall, and one shortwall, operating a total of 22 unit shifts per day. Eight shafts, varying in depth from 80.2 to 194.2 m (263 to 637 ft) provided entrance to the Pittsburgh coal seam. These shafts were used for ventilation, portaling, coal hoisting, supply, and emergency escape hoisting. Ventilation was achieved by means of three exhaust fans which provided 707.9 m3/s (1.5 million cfm) of air to the mine and removed approximately 141 584 m3 (5 mil¬lion cu ft) of methane per 24 hr period. The room-and-pillar method was used for secondary recovery with designed barrier blocks between panels of 61 m (200 ft) in width. A double row of blocks was left around each gob area to provide efficient bleeder action

Jan 1, 1982

By Joseph Keenan

In March of 1994, Dynatec Mining Limited entered into a contract with PCL Civil Constructors to carry out the underground excavations for the Algonquin Power Corporation’s15 Megawatt Nagagami hydro-electric power station located near Hearst, Ontario, Canada. Dynatec completed the work for this project in early October 1995. Dynatec Mining Limited’s work included the excavation of a 175 meter long penstock driven at a grade of -25% to a 4000 m3 powerhouse located 50 meters below the intake elevation. A 1200 meter long tailrace was driven from the Nagagami River to connect with the powerhouse. Two 50 meter raises were driven from the powerhouse to surface to pro-vide access for equipment and personnel. The excavation of the tailrace tunnel(5.8m x 5.9m) was completed using Dynatec’s Long Round Jumbo Technology.

Jan 1, 1997

By P. D. Rao, D. E. Walsh

A pilot-scale study was performed to evaluate the potential for gravity concentration of gold from -13 mm (-1/2 in.) crushed ore from Ester Dome, AK. 9.04 t (9.94 st) of crushed ore were sampled and processed through a Pan-American jig-Wilfley table pilot plant. Plant products were sampled for assay and material balance calculations. Gold recovery through one stage of jigging and two stages of tabling was 17.4% at a concentration ratio of 615:1. Concentrate grade was 766.3 g/t (22.4 oz/st). The feed grade to the plant was calculated at 1.71 g/t (0.05 oz/st). Jig tailings, primary table tailings and secondary table tailings grades were 1.44 g/t (0.042 oz/st), 1.30 g/t (0.038 oz/st), and 5.47 g/t (0.16 oz/st, respectively. Significant coarse, free-milling gold values were shown to remain in the, jig tailings. Concentrate mineralogy is discussed.

Jan 1, 1992

By Wade E. Cooper

INTRODUCTION How accurate are past and present employee radondaughter exposure records of underground uranium miners employed in the United States? This often-debated question is essential for future substantiation of safe exposure limits. An apparent discrepancy between company-reported exposures and Mining Enforcement and Safety Administration (MESA) projected exposures was detected in 1977. For these reasons a need for an updated comparison of these exposure data was indicated. This paper gives some of the conclusions of the earlier study and compares more recent exposure records compiled by the Atomic Industrial Forum, Inc., with projected exposures based on sampling by Federal mine inspectors. EARLIER STUDY In its 1977 Annual Report (U.S. Department of the Interior, 1978), MSHA's predecessor, the Mining Enforcement and Safety Administration (MESA), reported that there was "an apparent discrepancy between Federal inspection results and company records." Both company records and MESA's projections from samples taken during routine Federal inspections indicated reductions in the average exposure of underground uranium miners from 1975 to 1977, but the MESA projections were over 4 times higher than the company-reported averages. This apparent discrepancy however, was based on a comparison of exposure data reported for all U.S. underground uranium miners. This projection more closely represented the average exposure of U.S. underground uranium mine production workers who worked 1,500 hours or more during the year. Exposures of such workers are reported each year by the Atomic Industrial Forum, Inc. (AIF) in summaries of exposure data reported to the AIF by uranium mining companies throughout the United States. (The AIF exposure summary for 1979 appears as tables A-1 and A-2 in the appendix of this paper.) Assuming that the average exposure for each exposure range category is the midpoint of each exposure range category, table 1 compares the estimated average exposures for U.S. underground uranium mine production workers who worked underground 1,500 hours or more each year in 1975 through 1977 with the exposures projected by MESA for those years. [Table 1. - Average Exposure and Projected Average Exposure for U.S. Underground Mine Production Workers Who Worked Underground 1,500 Hours or More During the Year. Company, MESA?' Reported- Projected Year (WLM) (WLM) 1975 1.59 5.68 1976 1.84 4.64 1977 1.68 4.08 1 Atomic Industrial Forum, 1976, 1977, 1978. 2 U.S. Dept. of the Interior, 1978.] Table 1 indicates that, even after adjustment to ensure better comparability an apparent discrepancy between Federal inspection results and company reported exposures for 1975-1977 exists; however, the apparent discrepancy diminished over the 3 years. Slade, 1977, explained some of the discrepancy between company records and MESA projections of miners' average radon-daughter exposures as follows: 1) Concentrations of radon daughters in some work areas can vary greatly during any one day. A variation from 0.3 WL to 17.0 WL has been measured in the same stope on the same day. 2) Seemingly simple abatement problems indicated by the regular Federal and State inspections were solved simply by manipulating the mine ventilation. 3) The methods used by mine operators to compute cumulative exposures were such that high radiation readings were seldom or never reflected in the records. For example, a work area sampled on Monday indicated a radon-daughter level equal to 0.2 WL and this was recorded. It was sampled again on Wednesday of the following week and the level was 2.2 WL. The miners were withdrawn or told to fix the ventilation, and when this was accomplished the area was sampled and found to be at 0.2 WL again. Although the miners could have been working in the higher concentration up to 6 days, this reading might never be reflected in their records. If it was recorded, only a fraction of the day on which it was discovered would be entered into the cumulative exposure calculation (time-weighted average). 4) Some of the mines visited used a mine average radiation concentration, and every employee working underground was given the same exposure per unit of time spent underground. As a result of the 1977 study, more stringent sampling and recordkeeping standards were proposed and public hearings held in 1977. The resulting new and revised health standards on radon-daughter sampling and exposure recordkeeping became effective August 30, 1979 (Mine Safety and Health Administration, 1979). Prior to these new regulations, radondaughter sampling requirements were on an "as often as necessary" basis (Code of Federal Regulations, 1978). The new regulations required practically all active work areas in underground mines to be sampled at least once every 2 weeks, with many areas requiring weekly sampling. They also required calendar-year exposure records of all underground

Jan 1, 1981

By Atta Ur Rehman, Kwame Awuah-Offei

This paper examines the effect of bucket geometry (cutting-blade profile, floor profile and blade thickness), speed, motor power output and muckpile particle sizes on bucket penetration and draft for rubber tire loaders. The work uses a 1:16 scale model of a load-haul-dump (LHD) in full-factorial experiments to examine the effect of the variables on penetration and maximum draft. The results show that speed and motor output are positively correlated with penetration and draft, and muckpile particle size is positively correlated with penetration and negatively correlated with draft (p < 0.0014).

By D. Christofferson

As an alternative power source to eliminate trailing cables, ESD Corporation is installing a flywheel system on a shuttle car. Flywheel power is extracted by a high-speed generator, developed by Lear Siegler Corp., and the system -- including vacuum and lubrication and cooling auxiliaries -- is supplied by the aerospace group, Rocketdyne Division of Rockwell International. The flywheel system is being developed under a three-year contract with the Department of Energy. It is a follow-up contract to a previous DOE-contracted study by General Electric Co. in which it was shown that a flywheel can be a feasible power source for a shuttle car from technical, economic, and safety standpoints. This paper addresses the status of the program, design decisions established, and plans for laboratory test procedures and underground demonstration. The flywheel-powered shuttle car is a conventional 6-ton capacity shuttle car equipped with a 7-rotor flywheel energy storage package. The energy package is the sole source of power for the shuttle car through a complete mission duty cycle (MDC) of tramming to the miner, receiving a load of coal, and returning to the secondary haulage system. Energy stored in the system exceeds MDC requirements and waiting times to provide an ample margin of reserve energy. The energy storage system is recharged by spinning the rotors back up to maximum speed each time the shuttle car comes back to the seconaary haulage system. The electrical charge motor is connected to a power source to recharge the system while the load of coal is being discharged.

Jan 1, 1981

By V. R. Degner

The minerals industry trend toward very flotation machines, exceeding 10 m3, began in the late 1960&apos;s and responds to the continuing desire to achieve better plant economics through improved plant floor-space utilization, power requirements, and operational /maintenance manpower heeds. In general, as process design tonnage increases, the benefits of the larger flotation machine becomes more evident. The development of the larger flotation machine can be distingushed from earlier, smaller, machines in demanding a rational "scale-up" procedure to guide the basic design, thereby producing a machine prototype capable of satisfactory-operational evaluation at minimum cost. Proven flotation machine "hydrodynamic" scale-up consideration, successfully applied in the development of both the WEMCO No. 164 (28.3 m3) and No. 190 (42.5 m3) machine will be reviewed, and the resulting economic benefits of large flotation machines in high tonnage applications will be summarized.

Jan 1, 1985

By Jordi Vives-Costa, J. J. de Felipe, Lluís Sanmiquel, Maria Niubó

The article evaluates the convective heat transfer coefficient of ventilation air in a potash mine. The energy balance is obtained through thermal characterization of the ventilation air and rock, allowing for the calculation of heat transfer parameters. Different models for calculating the convective heat transfer coefficient are analyzed. The results indicate that the Pethukov–Kirilov, Gnielinski, and modified Dittus–Boelter models are optimal for this mine. The study also indirectly examines the conductivity of the adjacent rock, suggesting saturation throughout the studied section and the presence of liquid water upwelling in a specific section.

Apr 7, 2022

By S. K. Sharma, ANKUSH GALAV, G. S. P. Singh

Providing a suitable protective water barrier pillar (PWBP) is common to reduce inundation hazards in underground coal mines. The imperative factors influencing its performance include the water head acting on the pillar, cover depth, pillar width, strength properties, and permeability characteristics. The mechanical failure of such pillar is a stress-controlled phenomenon, whereas the hydraulic failure is a strain-based phenomenon. A finite-difference numerical modeling approach was developed to study the hydro-mechanical coupled behavior of protective water barrier pillars. The mechanical stability was evaluated in terms of the percentage of failed (ZoF) and intact zones. The influence of the strain-controlled weakening on the permeability of the flow medium was studied through the coupling of the mechanical and hydraulic effects. The coupled steady-state model was used to estimate the outflow rate and its hydraulic stability. The adequacy of the protective pillar was also investigated by assessing mechanical stability and capability to resist hydraulic pressure against the maximum expected water head. A seepage rate-based classification system has also been proposed to evaluate the seepage potential and assess the hydraulic stability. The model has been validated for two case studies at the cover depth of 136–189.5 m and the existing pillar width of 16–42 m against the water head of 25–141 m.

Aug 18, 2022

By L. R. Nelson

Cyprus Pima is a medium-sized open-pit copper mine located 35 km (22 miles) south of Tucson, AZ. The ore body was discovered using geophysical prospecting methods in 1953 and was originally worked as a small underground mine followed by small open-pit operations. As mining equipment grew larger and the economic ore grade dropped, the operation grew in size, through four expansions, to the present 50 500 tpd (56 500 stpd) milling rate. The remaining stripping ratio is about 2.5 to 1. Mining equipment includes 11 electric shovels ranging in size from 6 to 15 m3 (8 to 20 cu yd) and 42 diesel-electric haulage trucks ranging in size from 89 to 223 t (100 to 250 st). Mine planning is performed at Cyprus Pima to serve several functions. The most important is to plan ahead, one year at a time, to predict the ore grade and stripping requirements on a month-by-month schedule. This yearly plan is necessary for budget preparation and is revised once each quarter to incorporate variations in actual production experienced during the preceding quarter.

Jan 1, 1979