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Case Studies

Bruce A. Kennedy, Editor

9.4 Morenci/Metcalf

John L. Bolles
Gary A. Loving
James L. Madson

INTRODUCTION

One of the large copper properties in the world today is The Phelps Dodge Morenci, Inc. operation located near the confluence of the San Francisco and Gila rivers in eastern Arizona (Fig. 9.4.1).

Figure 9.4.1.

The Morenci operation encompasses two operating open pit mines, two concentrators, extensive dump leaching, two copper precipitation plants, a large solvent extraction/electrowinning facility including three separate solvent extraction circuits, two power plants, shops and maintenance facilities necessary to support those operations, and a townsite where most of the employees live. It is the largest of Phelps Dodge Corp.’s copper mining and processing complexes, normally producing about 50% of the company’s new copper output.

Early History

First discovery of mineralization in the district was recorded in 1864. The earliest production of any consequence occurred in 1872 when copper oxide ore of very high grade was mined and processed by direct smelting methods. Some of that early copper production was hauled overland by mule- and oxen-train to Kansas City, Missouri.

By the 1880s, a number of companies were operating in the district. These included the Detroit Copper Mining Co., the Arizona Copper Co., the Longfellow Copper Co., the Shannon Copper Co., and several smaller companies.

Phelps Dodge’s entry into the region, and in fact into copper mining, occurred in 1881 when it acquired partial ownership of Detroit Copper Mining Co.

Ownership in the district was gradually consolidated until only the Detroit Copper Mining Co. and the Arizona Copper Co. remained. After 1897 Phelps Dodge assumed full ownership of the Detroit Copper Mining Co. In 1921, Phelps Dodge purchased the Arizona Copper Co. to become sole operator in the district.

With the exception of some surface glory holing, all mining prior to 1932 was by underground methods. Both high-grade copper oxide and copper sulfide veins were mined. As mining progressed, exploratory drilling revealed a very large low-grade deposit of disseminated chalcocite, called the Clay ore body, in porphyry host rock.

Initiation of the Morenci Open Pit Copper Mine

Pioneer exploratory work on the Clay ore body by Arizona Copper Co. and later by Phelps Dodge Corp., revealed that the porphyry copper deposit lay beneath 60 to 150 m (200 to 500 ft) of leached capping. Phelps Dodge began a systematic drilling program on the Clay ore body in 1928 to confirm and augment information gained earlier by Arizona Copper and Detroit Copper companies. The drilling, which continued until November 1930, confirmed the existence of more than 181 Mt (200 million st) of material averaging slightly more than 1 % copper.

One of the key questions to be resolved was whether to mine the ore by underground block caving or by the open pit method. In considering the choice the following items were studied:

Minimum dilution of the ore, maximum recovery of the ore, low maintenance costs, favorable production costs, production flexibility, uniform ore production and stripping rates, availability of space to locate waste and leach dumps, good physical layout for haulage systems, minimum pre-ore stripping, 209 Mt (230 million st) of ore at 1.06% Cu, and a waste to ore ratio of 1:1.

After a year of investigation, it was determined that the open pit mining method could recover about 10% more copper, reduce final average mining costs by more than 30%, and could ultimately yield from 20 to 25% greater profits.

Development of the mine, however, was only one phase of the large and costly enterprise. The old No. 6 Concentrator and its various units at Morenci were inadequate to process the huge tonnage that the new mine was designed to produce and the old facilities were not advantageously located. Further evaluation indicated that it would not be economically feasible to enlarge and modernize these existing facilities.

A decision was made to construct a new infrastructure—crushing plant, mill, smelter, power plant, and auxiliary facilities necessary for a major mining operation.

The site selected for the crushing plant, mill, smelter, and other units would lie almost halfway between the towns of Morenci and Clifton and would allow the ore to be delivered by favorable haul from the mine over a significant portion of the mine’s life. By the time the preliminary study was completed, the United States had entered the Great Depression and development was suspended pending improvement in the economic climate.

In 1937, encouraged by the economic outlook, Phelps Dodge reactivated the Morenci Project. In June, the company made a public offering of $20,285,000 of 15-year convertible 3½% debentures. They soon were sold and work on the mine and related facilities began. The balance of the total estimated cost of $35 million came from corporate earnings as the work progressed.

The size, quantity, and cost of the equipment and facilities required for a task of such magnitude taxed the imagination. The new mine at Morenci was to become a huge, complex, and thoroughly mechanized industrial operation.

To provide for the great increase in personnel that the new operation required, Phelps Dodge laid out a new townsite. The company built more than 300 housing units that would be rented to employees at nominal rates. The project also included the expansion of recreation and school facilities and the construction of a new hospital with the most modern equipment.

In 1937, the pre-ore stripping of 44 Mt (49 million st) of overburden commenced at the Morenci mine with shovels and trucks developing 15-m (50-ft) high mining benches and railroad access. The trains were added later to handle the movement of large tonnages of material over long distances including ore deliveries to the Morenci primary crusher. The physical features of the topography permitted the installation of the main line haulage tracks outside final pit limits and also permitted the favorable downhill movement for an estimated 85% of the material to be handled.

Copper concentration studies were resumed in 1938 following a six-year hiatus to test various types of equipment and to develop a final concentrator flowsheet. Ground was broken for the new concentrator and smelter in 1939. The first copper anode was poured on April 26, 1942.

Wartime Expansion

The Morenci operation was designed to process 22.7 kt (25,000 st) of copper ore per day. However, in 1941 the nation was facing international war, and the federal government urgently requested Phelps Dodge to expand the Morenci Project by 80%, to a capacity of 41 kt (45,000 st) of copper ore per day. Responding to this request, the company designed, constructed, and completed a major expansion project in slightly more than two years.

By the close of World War II, Phelps Dodge had spent approximately $42 million on the Morenci project and the federal government’s Defense Plant Corp. had provided an additional $26 million. The facilities provided by the U.S. government were sold to Phelps Dodge after the war ended.

The Postwar Years

Additions and improvements raised the capacity of the Morenci concentrator to its present level 59 kt (65,000 st) of copper ore per day with a corresponding increase in mining rates.

Major improvements in recent years have included construction of the largest solvent extraction/electrowinning complex in the United States to recover copper leached from mine dumps. The mine dumps contain copper-bearing material with grades too low for processing through the concentrator.

Since the initiation of the Morenci mine in 1937, about 2.0 Gt (2.2 billion st) of rock have been moved, of which about 690 Mt (760 million st) were ore averaging 0.86% copper. Approximately 530 Mt (584 million st) of material remain to be mined under current plans. The present Morenci pit covers some 595 ha (1,470 acres), measuring about 2.9 km (1.8 miles) north to south and 2.4 km (1.5 miles) east to west. Mining, which began at 1691 m (5,550 ft) above sea level, has continued down to the 1219 m (4,000 ft) level. Current mine plans indicate that the final bottom of the pit will beat the 1021 m (3,350 ft) elevation.

Metcalf, A Second Open Pit in the Morenci Ore Body

In 1970, development of the nearby Metcalf mine was initiated to replace, insofar as overall company production is concerned, the production lost when the open pit and underground mining operations ceased at Bisbee, Arizona, in 1974 and 1975 (Fig. 9.4.3). The Metcalf development, operated as part of the Morenci Branch, also required construction of a new concentrator built southwest of the Morenci concentrator.

Figure 9.4.3.

The Metcalf copper deposit is an upfaulted portion of the Morenci ore body and is located a short distance north and on the opposite side of Chase Creek from the Morenci open pit mine. Development of the Metcalf area began in 1870 when Robert Metcalf struck a rich copper oxide vein upstream from Clifton. Metcalf returned to the area about two years later and located the Longfellow claim and mine. The mine was acquired by the Lezinsky brothers, then by the Arizona Copper Co., and finally by Phelps Dodge in 1921 as part of the acquisition of the Clay ore body.

Exploration drilling at Metcalf began in the 1960s and in 1969 the company announced plans to develop the Metcalf mine. By December, 1974, the Metcalf project was substantially completed—at a cost of almost $200 million.

Due to the extremely rugged terrain at the mine site, it was necessary to locate the concentrator for Metcalf ore adjacent to the Morenci concentrating and smelting complex. However, the primary crusher was located near the mine. After the Metcalf ore is crushed using a 1.52 m (60 in.) gyratory crusher at the mine, the ore was hauled approximately 8 km (5 miles) by rail to the concentrator. The facility was designed to handle 27 kt (30,000 st) of ore per day, although it has a proven capacity of 41 kt (45,000 st) of ore per day.

Pre-ore stripping resulted in the removal of 68.6 Mt (75.6 million st) of overburden. To maintain ore development, a stripping ratio of 2.5:1 was required. However, that ratio was not achieved for several years following startup due to economic constraints. Since production began in 1974, 39 Mt (43 million st) of copper ore averaging 0.76% copper have been mined. All material mined since stripping began totals about 220 Mt (242 million st).

During the years 1977 through 1980, a very substantial portion of the Metcalf concentrator ore supply was provided from the Morenci open pit. Early in 1981 the Metcalf open pit was shut down, the entire 100 kt/d (110,000 stpd) of ore production for the two concentrators (Morenci and Metcalf) was shifted to the Morenci mine along with the mining equipment to take advantage of the lower waste-to-ore ratios and slightly higher ore grade. There remains about 0.9 Gt (1.0 billion st) of material to be mined at Metcalf

Consolidation of Potential Mining Areas at Morenci

Phelps Dodge completed the consolidation of all potentially minable copper properties in the Morenci district in 1981. This was accomplished through purchase of the Western Copper property for $10 million. The property, acquired from Hanna Mining Co., consists of 81 patented claims covering 754 ha (1,862 acres). The property is located on the east side of Chase Creek at the eastern limit of the Morenci mine and at the southern limit of the Metcalf mine. It is part of the Morenci copper mineralization, as is the Metcalf deposit. Portions of the Western Copper property are included in the final pit limits of both the Morenci and Metcalf mines.

The relatively low elevation of the Western Copper property makes it ideally suited for use as a waste disposal area for both the Metcalf and Morenci mines. Substantial reductions in haulage costs are anticipated because of shorter distances and favorable grade compared to disposal of Metcalf waste on dumps located at higher elevations north and east of the Metcalf mine.

MINES DEVELOPMENT

As previously indicated, the construction of a major copper mining complex in a remote setting requires a great amount of auxiliary development. In addition to direct mine and plant structures and equipment, a significant amount of pre-mine fact gathering, planning, and design, as well as support facility logistics development are required.

Water Supply Development

Because of the increased copper production brought on by the expansion of the Morenci mine and concentrator in the 1940s, there also was a corresponding need for additional water. In order to meet this water demand, innovative arrangements were developed to import the majority of the required water from various sources outside the Morenci district. To accomplish this, several dams, pumping plants, pipelines, powerlines, and support facilities were constructed, as shown in Fig. 9.4.2.

Figure 9.4.2.

In 1947 Horseshoe Dam was the first constructed retention structure for the collection of surface runoff, followed by Jacques Dam in 1954 and Blue Ridge Dam in 1965. Then, through various agreements and water exchanges, Phelps Dodge was permitted to divert water from the Black River, 43 km (27 miles) northwest of Morenci, and transfer it into Eagle Creek. The water diverted from the Black River flows south to the lower reaches of Eagle Creek where it is pumped 9.6 km (6 miles) to Morenci. A well field in the upper Eagle Creek area also has been developed to augment surface water sources with groundwater as necessary.

Water use by the entire Morenci Branch operations consists of 30.837 Mm³ (25,000 acre-ft) per year of which 617 000 m³ (500 acre-ft) per year are used by the mines for dust control, cleaning of equipment, change room services, and other minor uses. Water is pumped to head tanks located near the top of the mine and then gravity fed to the place of use. Rubber hose of 38 mm (1.5 in) diameter is used to furnish water to the open pit mining faces. This provides a flexible, inexpensive transport system.

Utilities

Electrical power is distributed to the Morenci mine through two 46 kV power transmission lines. This power line feeds a 15 MVA substation in the bottom of the Morenci pit. Voltage is transformed down from 46 kV to 4,160 V and is distributed from the substation through radial power lines placed perpendicular to the mining faces. Switchhouses are located at the bottom of selected wooden power poles in active mining areas from which insulated electrical cable provides power to the mining equipment.

One of the 46 kV power lines extends past the Morenci substation to the Metcalf mine. This voltage is then transformed at two 5 MVA substations to feed the shops, the Metcalf solvent extraction plant, and primary crusher. The total connected load in the Morenci and Metcalf mines is about 25 megawatts.

Natural gas is provided to the Reduction Works area through two main pipelines: a 152 mm (6 in.) and 203 mm (8 in.) line, both at 4100 kPa (600 psi). The natural gas then is redistributed to the Morenci mine shops through a 102 mm (4 in.) feeder line at 621 kPa (90 psi). The annual mine consumption is about 708 m³ (25,000 ft³). Propane, delivered by truck, is used at the Metcalf offices and shop area, since an active mining area is located between the Morenci mine shops and the Metcalf mine shops.

Compressed air at about 621 kPa (90 psi) is provided to the Morenci mine shop area from the Morenci power plant through a 152 mm (6 in.) pipeline. Compressed air at about 758 kPa (110 psi) is provided to the Metcalf shop area by two stationary 10 m³/min (355 cfm) air compressors located at the Metcalf shop area and distributed through a 102 mm (4 in.) pipeline.

Fire protection for the mine complex is provided through the use of fire hydrants located near principal mine buildings, fire extinguishers on mobile equipment, and water trucks equipped with fire hoses or water cannons. A volunteer fire department trained to fight industrial fires is also available.

Mine Planning and Mine Engineering

Before development of Morenci/Metcalf mines could begin, it was essential to determine the location of the copper ore body, thickness of the overburden, grade of the ore, type and character of the rock to be milled, and location of dumping areas. This was accomplished by drilling a portion of the 1,450 vertical diamond drill and churn drill holes now in the data base, as well as extensive sampling and some diamond drilling from the underground workings.

For the surface drilling, 122-m (400-ft) grid with a center hole in each 122-m (400-ft) square initially was used. Later, this was modified to eliminate the center holes. The ore body at the Morenci/Metcalf mines is a large porphyry copper deposit. The dominant rock types that host ore are monzonite porphyry, granite, and granite porphyry, with minor amounts of limestone, shale, and quartzite.

Sulfide ore mineralization is typified by supergene chalcocite and covellite replacing pyrite, chalcopyrite, and minor amounts of bornite. This sulfide mineralization occurs in veins, veinlets, microveinlets, and disseminations.

Oxide ore minerals present within the mining limits include azurite, malachite, tenorite, brochantite, chrysocolla, and cuprite. Minor amounts of native copper are encountered locally. Minor amounts of gold, silver, and molybdenite also are included in the ore and are collected with the copper sulfides in the concentrating process.

The material in the minable reserve is classified into three separate materials: ore, leach, and waste. Material classifications by contained copper are as follows:

Ore	≥0.40% Cu
Leach	≥0.20% Cu	≤0.39% Cu
Waste		≤0.19% Cu

Material that is above 0.40% copper, but exhibits more than half of the contained copper as oxides, is reclassified as leach and handled accordingly.

In evaluating the drilling results, the area of influence of each drill hole was determined by using the polygonal technique. Drill hole assays averaged in 15-m (50-ft) vertical increments corresponding to the mining levels were used in assigning polygonal block grades for each drill hole. An average density of 0.354 m³/t (12.5 ft³/st) was used to calculate tonnages included within the polygonal blocks. In the absence of geological information, drill holes that ended in ore were not projected downward. Drill holes that ended in non-ore material were projected downward as waste to determine a boundary for adjacent holes.

Final copper reserve mining slopes are set at 51° based on geological evidence, rock strength characteristics, shape of the banks, and length of the slope. Initially, the Morenci pit mining limits were projected to be on a 45° overall slope, but were changed to a 37° overall slope, and later to a 51° overall slope.

The final reserve slopes are calculated using an economic model based on the value of the copper recovered from a block of material and the amount of overburden removal that the specified value can support.

A mine planning staff is located at Morenci to develop annual and long-term mine plans, as well as to review district copper ore reserves, and to prepare feasibility studies for improved mining methods. Presently the polygon method of reserve calculation is under review and efforts are being made to reevaluate the district’s mining reserves through computer-generated block modeling and geostatistics. Other feasibility studies focus on improving mining efficiencies and alternatives to the conventional haulage methods.

The inter ramp slope for final mining limits is 51° with a uniform bench height of 15 m (50 ft) and a working bench width of 30 to 61 m (150 to 200 ft) in most areas. Because of the topography at the Metcalf mine, only truck haulage is used, while the Morenci mine uses both truck and rail haulage. All mine trackage is standard 1,435-mm (56.5-in.) gage. The maximum available degree of curvature for main line track is 12°. The main line is constructed of 60-kg (133-lb) rail and normally is located outside pit limits or placed in a semipermanent location. It is a heavily traveled route and therefore consists of double track: one for the loaded trains and the other for empty trains.

The main truck haulage system is designed so that the maximum ramp grade is 10% and ramp width is 30 m (100 ft). This 30-m (100 ft) width allows for large berms on each side of the ramp as well as a drainage ditch. Runaway truck ramps and crash berms built of reverberatory furnace slag are provided for downhill hauls. The minimum radius of curvature for the main haulage road is 61 m (200 ft).

Internal truck ramps are used where necessary and can be narrower than main ramps. Dump loads are designed to be on an adverse grade of 2 to 3% to allow for settlement and to limit the possibility of a truck rolling backwards through the dump berm.

Equipment Selection

The decision regarding type of haulage equipment was based on the following factors: Topography of the area, tonnage to be removed, speed and distance that material must be moved, and overall economics.

The selection of rail haulage equipment was based on the layout of the final track haulage system. To determine the final layout, the maximum safe grade and the size of the train first had to be ascertained.

The train size also had to be flexible enough to meet the varying operating conditions with the maximum car size. Maximum grade was determined to be 4% with a most efficient train size being eight 30.6-m³ (40-yd³) self-dumping side dump cars. Because of the interchangeability and the need to facilitate train dispatching, the same type and size cars were used both for copper ore deliveries to the primary crusher and for waste and leach material deliveries to the mine dumps.

In the original selection of the locomotive power to be used, serious consideration was given to total electrification of the rail haulage system, but because of frequent changing of the bench track as well as narrow mining benches and heavy blasting, this concept was abandoned. The decision thus was made to use an overhead trolley electrification system only on the main line track system in combination with diesel-electric and battery-electric locomotives for bench and dump track.

Plans for a track extension in 1955 called for the electrification of an additional 8 km (5 miles) of main track. However, due to the high cost of such a venture and improvements over the previous two decades in diesel-electric locomotives, all trolley electric locomotives were replaced with 1306-kw (1,750-hp) diesel-electric locomotives. These larger locomotives also were capable of improving efficiency by pulling longer trains.

The present fleet of locomotives consists of 3895-kW (1,200-hp), 13 1306-kW (1,750-hp), 21 1343-kW (1,800-hp) and 12 1492-kW (2,000-hp) diesel-electric locomotives. The present railroad car fleet consists of 200 32.9-m³ (43-yd³) side dump cars, and 53 90-t (100-st) bottom dump cars used only for ore deliveries from the Metcalf primary crusher to the Metcalf concentrator.

Although the Morenci open pit has historically been a rail haulage mine, truck haulage has become increasingly important over the years. The decision to use trucks in the preliminary stripping operations was based on the need to prepare the mine for rail haulage and the success of truck haulage in other large-scale excavations.

Initially, a fleet of 18 17.2-m³ (22.5-yd³) trucks was used to open new levels, to remove overburden from the upper benches and to build railroad access. The fleet in 1970 was upgraded to 47 90-t (100-st) trucks and in the 80s, the old truck fleet was phased out and replaced with 28 154-t (170-st) trucks. Trucks in the Morenci mine now are used for all direct production from the active mining faces while rail is used to transfer ore to the Morenci and Metcalf concentrators.

The selection of loading equipment was based on the following factors: loading rate, size and type of material being loaded, haulage unit being loaded, and life of the operation.

Initially 3.4-m³ (4.5-yd³) electric shovels were purchased for mine development. These shovels were much more efficient and dependable than earlier models and could load the large tonnages required on a daily basis. They also were compatible with the rail and truck haulage units. Shovel equipment life coincided with the expected mine life of 30 years. As the mine developed, shovels were upgraded to larger units. The shovel fleet currently consists of six 11.5-m³ (15-yd³), and six 16.8-m³ (22-yd³) electric shovels. In addition, two 9.2-m³ (12-yd³) rubber-tired front-end loaders are being used as backup production units or for special projects.

Initially, the selection of drilling equipment was based on the following factors: tonnage to be broken per day, size and depth of hole to be drilled, and type of material being drilled.

The large electric churn drill was selected at Morenci because its drilling rate and hole size would allow breakage of a maximum amount of material.

In 1940, all the primary drilling was performed by 12 electric churn drills using 229-mm (9-in.) diameter bits. Blast holes were drilled from 2.4 to 3 m (8 to 10 ft) below grade. Drill bits were reconditioned by a mechanical shaper and hardened for reuse. In 1956, a portion of the primary drilling was performed by large rotary drills capable of developing 311-mm (12¼-in.) diameter blast holes. The rotary drill used tricone bits and 10-m (33-ft) long steel sections. Two steel changes were required per hole. The present primary drill fleet consists of 10 rotary drills: 6 electric and 4 diesel-electric. The diesel-electric drills were used for the early development of the Metcalf mine, two of which have been converted to electric drills. Single pass drilling now is available with the larger drills as well as variable hole sizes ranging from 229 to 381 mm (9 to 15 in.) in diameter.

DESCRIPTION OF OPERATIONS—MORENCI MINE

Breaking Ground

In the Morenci pit, there are certain operating conditions that determine the pattern of blast holes and the powder loading ratios. Drilling access must be maintained and material must be available at each shovel on a continuous basis. To accommodate these constraints, hard toes and high bottoms resulting from unbroken rock, must be avoided.

Drilling and blasting practices in the Morenci open pit have undergone a slow evolution. Initially, 15-m (50-ft) benches were established using 229-mm (9-in.) churn drilled blast holes averaging 17.6 to 18.2 m (58 to 60 ft) in depth. Also, there was a tendency to lighten the burden on the holes in hard ground by decreasing the distance between holes and by shortening the length of the toe. This practice broke the toe well, although it resulted in poor fragmentation in the upper part of the bank. It also yielded a low tonnage per vertical foot of blast hole.

Later, it was found that the heavier the burden without overloading, the better the resultant fracturing. Currently, most blast hole drilling uses 311-mm (12¼-in.) diameter rotary bits.

A small amount of secondary drilling is accomplished with air drills equipped with 64-mm (2½-in.) button carbide bits.

During 1987, rotary drill blasts accounted for 70.7 Mt (77.9 million st) of broken ground in the Morenci pit and involved 402 km (1.32 million ft) of drilling. This resulted in 176 t of broken rock per meter (59 st per ft) of blasthole.

Throughout the years as the types of available explosives changed, the patterns and loading ratios also have varied. In the early days of the mine, gelatin dynamite was used. This was followed by bagged ANFO beginning in 1960. In the early 1970s, bulk, prilled ammonium nitrate was used and in 1980, a mixture of ammonium nitrate and aluminum was introduced.

Currently, ammonium nitrate and fuel oil account for about 50% of the explosive utilized in primary bank blasts, although aluminized ANFO in a 10% mixture occasionally is used. An increasing number of wet holes have been encountered that cannot be dewatered, sleeved, and blasted with ANFO. Consequently, such holes are loaded with a slurry form of ANFO.

Trucks outfitted with special compartments are used for loading the ANFO into blast holes. Ammonium nitrate prills, fuel oil, and flaked or granulated aluminum are augered or pumped separately from compartments to a nozzle where they are mixed with the other ingredients while being injected into the hole. Each hole is single primed with an in-the-hole delay cap in a 0.45-kg (¾-lb) cast TNT booster hung on a 20-grain downline. Individual holes are tied to a 25-grain trunkline, which is delayed on the surface between rows when a multiple row pattern is used. Slag, gravel, or drill hole cuttings scraped in with a backhoe serve as the stemming material. All blasts are initiated with an electric blasting cap by the blasting foreman. Typically, six benches are guarded against entry during a blast: one above the drill hole collars, the bench being blasted, and four below.

Typical powder factors vary among the different rock types encountered in the Morenci pit; however, most average approximately 5.0 t broken per kg of explosive (2.5 st broken per lb, etc.).

Although the production work schedule is a 24-hr-per-day continuous operation, the drilling and blasting crews work a 40-hr week, seven days per week schedule. Drilling is conducted on a three-shift rotation and all blasting is done on day shift. Each drill shift will result in approximately 90 kt (100,000 st) of material when blasted.

Loading

Loading of haulage units is accomplished with 12 electric shovels varying in dipper sizes from 11.5 to 15 m³ (9 to 22 yd³). All shovels are powered by 4160 V via trailing power cables. Two 9.2-m³ (12-yd³) front-end loaders are used for cleanup operations and low bank loading and also serve as backup units to the shovels.

At Morenci, loading consists of production loading of all material at the mining face. Nonore material is delivered by truck to the dump while ore is delivered to several transfer locations. Once the ore has been delivered to the transfer site, it is reloaded onto trains and is transported to the concentrators.

Reloading of the ore is accomplished using three methods which include conventional 11.5 m³ (15 yd³) shovels, hydraulically operated drop chutes, or a mechanized feeder hopper.

Approximately 40% of ore is transferred onto rail by the drop chute method, 27% by the pan feeder and 33% conventionally. The pan feeder is the newest method of transfer loading incorporated at Morenci and consists of a large bin structure with a reciprocating pan feeder attachment at the base. The locomotive engineer operates the feeder and spots the train simultaneously resulting in a quicker, safer and more uniform loading process.

Construction of an in-pit crush convey ore handling system is scheduled for completion in 1989 which will replace all ore transfer at Morenci.

Shovel operators work three-shift-rotation on a continuous schedule. There are four shovel crews, each of which works seven days with two or three days off between shift changes. This schedule allows a continuous staffing with each employee working only one overtime day per month. In addition, a relief system for production personnel is utilized whereby employees are relieved at their equipment rather than being transported to the mine office or change room for relief.

Haulage

Haulage of material out of the Morenci pit is accomplished with trains and trucks. Presently all ore grade material is transferred onto trains for delivery to the concentrators. Trains are 15 33-m³ (43-yd³) capacity side dump cars mobilized by either 1306- or 1492-kW (1,750- or 2,000-hp) diesel-electric locomotives. The caboose is a side dump car that has been outfitted with an enclosed riding platform containing a seat, heater, two-way radio, and air gauges to indicate the pressures in the air brake systems. To provide a headlight for the caboose, an air-powered generator is used, operated by compressed air from the dump line on the train. Each train is operated by one employee via radio remote control. The remote-controlled locomotive system at Morenci is the largest of its kind in the world. The locomotive engineer carries a packset on his or her shoulders and a control head on the belt that enables the engineer to transmit signals to the throttle, all brake systems, wheel sanders, horn, and the headlights when he or she is located at either end of the train or on the ground in the near vicinity of the train.

Until the advent of remote control operation, two-man train crews, consisting of a locomotive engineer and a brakeman, were utilized. One-man operation of trains has significantly reduced the cost of train operation. Fail-safe features are built into the equipment, including automatic air application to stop the train whenever a coded tone radio command is not received clearly or whenever the locomotive engineer’s body assumes a position more than 45° off vertical. Remote control enables the driver to have full control of the train from the leading end—whichever direction he is traveling.

Computer-controlled dispatching of rail and truck traffic has been installed in the Morenci pit, similar to the system for dispatching haulage trucks in operation at Phelps Dodge’s Tyrone mine at Tyrone, NM. The system has increased effective operating time by reducing queuing at shovels and crushers. It incorporates on-board radio telemetry along with roadway sensors to measure and report train or truck location. With the addition of computerized dispatching, the productivity increases have offset the purchase cost of additional equipment to maintain production.

At the concentrators each train of ore is dumped pneumatically by the locomotive engineer. Each car is spotted at the dump pocket and a lever is pulled to open the valve that activates the dumping air cylinders.

Each train completes three to four cycles per 8-hr shift. The haulage operation, just as the loading operation, is continuous, operating 24 hours per day, seven days per week. A relief system for equipment operators identical to the loading operation relief plan is used.

The Morenci mine has a fleet of 28 haulage trucks rated at 154-t (170-st) pay-load capacity. Each of the trucks is powered by a 16-cylinder (1,600- or 1,800-hp) diesel engine that drives an a-c traction alternator that, in turn provides power to two d-c electric wheel motors that drive the rear dual wheels of the trucks. The trucks primarily are loaded by large electric shovels equipped with 16.8-m³ (22-yd³) dippers.

Historically, truck haulage in the Morenci mine accounted for less than 10% of the material moved. Recently, however, the accelerated development on the lower levels of the pit has increased truck haulage to 100% of total daily production while trains are utilized for ore transfer. Truck haulage will continue to be used in the Morenci pit in conjunction with other haulage methods. The in-pit crush and convey system that is scheduled to come on line by 1989 will replace rail haulage at Morenci.

REFERENCES

Cleland, R.G., 1952, A History of Phelps Dodge, 1834–1950, Knopf, New York, pp. 244–260.

Epler, W.C., 1975, “Production Begins at Phelps Dodge’s New $200 Million Metcalf Operation,” Pay Dirt, No. 430, Apr. 28, pp. 1–6.

Epler, W.C., 1981, “Morenci, First Investment Is Now Mainstay; Metcalf, Second Openpit on Morenci Orebody,” Phelps Dodge, A Copper Centennial, 1881–1981, Arizona Paydirt, pp. 36–62.

Fenzi, W.E., 1942, Some Aspects of Breaking Ground in the Morenci Open Pit Mine, private publication by Phelps Dodge Corp.

Fenzi, W.E. and Ormsby, L., 1956, “Rail Haulage at the Morenci Open Pit Mine,” Mining Congress Journal, Nov., pp. 86–90.

Hardwick, W.R., 1959, “Open-Pit Copper Mining Methods, Morenci Branch, Phelps Dodge Corporation, Greenlee County, Arizona,” Information Circular 7911, U.S. Bureau of Mines.

Hoppe, R., 1977, “Open Pit Copper Mining in Arizona,” Engineering and Mining Journal, June, pp. 95–100.

Langton, J.M., 1972, “Ore Genesis in the Morenci-Metcalf District,” paper presented at AIME Annual Meeting.

Larsen, J.U., 1947, “Some Phases of Drilling and Blasting Practices in the Morenci Open Pit,” paper presented at AIME Open Pit Subdivision Meeting, March 21–22, pp. 1–4.

Lawson, W.C., 1938, “Preliminary Stripping of the Morenci Open Pit, Arizona,” Technical Publication No. 980, AIME, Sept., pp. 1–15.

Lawson, W.C., 1940, “Preliminary Engineering at Morenci Open Pit,” Civil Engineering, Vol. 10, No. 8, Aug., pp. 510–513.

Lawson, W.C., 1947, “Laying Panel Track at the Morenci Open Pit,” Technical Publication No. 2189, AIME, July, pp. 1–13.

Orr, D.H., Jr., 1960, “Maintenance of Main Line Haulage Track in the Morenci Mine,” paper presented at Annual Arizona Section AIME Meeting, pp. 1–9.

Orr, D.H., Jr. and Berra, F.G., 1965, “One Man Remote Control Rail Haulage,” Mining Engineering, Apr., pp. 75–79.

Parsons, A.B., 1957, The Porphyry Coppers in 1956, AIME, New York, pp. 49–66.

Skillings, D.N., Jr., 1975, “Phelps Dodge Corp.’s Metcalf Porphyry-Type Project,” Skillings Mining Review, Vol. 64, No. 25, June 21, pp. 12–17.

Train, A., Jr., 1941, Ajo-Bisbee-Morenci, private publication by Phelps Dodge Corp., pp. 85–103.

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