Mount Hope Mine Expands

By C.H. Vivian, Compressed Air Magazine, March 1945

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An extensive improvement program has recently been completed by the Warren Foundry & Pipe Corporation at its Mount Hope iron mine, situated near Dover, N.J., within an hour's ride of New York City and reputed to be the oldest operating mine in the nation. The new facilities include a deep shaft, two electric-driven hoists to serve it, a modern lump-ore treatment plant and fine-ore concentrating mill, a water-supply system, a change house for miners, and a heating plant. Underground, new pumps have been provided, new crushing plants built, additional electrical and haulage equipment installed, and considerable development work done to gain access to the ore bodies. The improvements will enable the mine greatly to increase production, reduce unit costs, and increase the grade of its products. Further, by providing access to deeper portions of ore bodies now being mined as well as additional deposits previously not within economical reach, they will insure many years of output.

The program was initiated in 1941 in response to a request by the War Production Board for increased iron production. The Mount Hope Mine is one of the few properties that yield magnetite, and the particular virtue of its ore is that a large proportion of it is obtained in lump form, which is much in demand for use in open-hearth steel furnaces. The only other magnetite producers in the country are three more in New Jersey, a group in the Adirondacks of New York State, one in eastern Pennsylvania, and another at the eastern end of the Mesabi Range in Minnesota.

The current improvements were financed by the Warren Foundry & Pipe Corporation through a $4,000,000 loan, against which it issued 10-year sinking-fund notes. The engineering for the new surface facilities and the shaft was done by the J.G. White Engineering Corporation of New York. The mining company's own staff planned the underground work other than shaft sinking. It was originally hoped that the project could be finished in nineteen months from the starting date, but the manpower shortage delayed construction, especially of the shaft, and all units of the program were not ready for operation until the early part of this year. The fine-ore mill, however, has been in service since January, 1944, its completion having been rushed because of a fire in June of 1943 that destroyed the plant formerly in use. During the remainder of 1942, fine ore brought up through the existing Brown Shaft was stockpiled, and after the new plant was put in operation that material was transported to it for processing. The new mill also handled the fine ore produced through the Brown Shaft during 1944.

As revamped, the plant is designed to produce and treat 3000 tons of crude ore per day, or more than four times the maximum output obtainable with the older facilities. When the underground development work now underway is finished there will be five horizontal haulageways instead of one. These will be at the previously existing 1000-foot level and at the 1700-, 2100-, 2300-, and 2500-foot levels. All will provide means of access to several different ore bodies, and the two lower ones will make it possible to reach parts of the veins that have not been worked.

The hoisting equipment consists of two Nordberg units - one for a double-deck man-and-materials cage capable of transporting 60 men at a time, and the other for operating counterbalanced 10-ton ore skips. The man hoist is driven by a Westinghouse 900-hp. motor and the ore hoist by two similar units. These are of the direct-current type, and motor-generator sets are furnished to convert the incoming power-line alternating current for their use. One of these sets is made up of a 2000-hp. synchronous motor driving two 750-kw. generators and the other has an 800-hp. motor and one 750-kw. generator. The man hoist has a single, divided 12-foot drum the cable on one side of which is attached to the cage and that on the other to a 14-ton counterweight that runs in one of the shaft compartments. The ore hoist has two 14-foot drums. Each of the four hoist drums is wound with 3400 feet of Bethlehem 1-7/8-inch wire rope having a hemp center. The speed of the hoists is regulated independently of their loads, and the torque is automatically limited by means of Westinghouse Rototrols. This device consists of two small direct-current generators that replace most of the switches, relays, and resistors conventionally used for the purpose. The man hoist operates at a maximum speed of 800 feet per minute when carrying persons and 1200 feet when carrying materials only. The ore skips travel at a maximum speed of 1800 feet per minute. Adjacent to the hoist house is the compressor house in which are three new Ingersoll-Rand Class PRE machines each of which has a piston displacement of 3864 cfm. and is driven by a Westinghouse 700-hp. synchronous motor. The air from each machine passes through a horizontal aftercooler to extract moisture, and the output of all three units is piped down the shaft through a 12-inch main.

An interesting feature of the shaft installation is a carrier-current signal system that makes it possible to transmit signals to and from the surface by the man-cage hoisting cable. This supplements the usual shaft signal wiring and has various advantages. Signals, can be sent from within the cage, even when it is moving, and a signal previously given the hoist operator can be changed anywhere en route up or down the shaft. This saves time and promotes safety when repairs are being made in the shaft, for under the conventional system, signal stations are available only at the levels and orders must be shouted by the repair crew to a man at the nearest level and then relayed by him to the surface. It is claimed that the system works equally well in wet or dry shafts, and there is no danger of signal wiring being severed or torn out by ore spilled during hoisting. This electronic cable-signaling system was developed by R.L. Rutherford of Superior, Ariz. It was first used in 1938 in deep shafts of the Magma Copper Company in Arizona and has since been adopted by several other large mines.

The Mount Hope property is believed to have been first worked in 1715, and it has been an intermittent producer ever since. Its total output is something more than four million long tons. The history of the mine was given in our March, 1941, issue. Since 1912, all production has been through the Brown Shaft - a 68 degree incline that extends 100 feet below the 1000-foot level. The ore bodies outcrop at the surface and are lath-like formations that have upward-disposed edges and that slope underground toward the northeast at an angle of 15° from the horizontal, with indications of steepening to around 19° with increasing depth. Their sides incline southeastward at an angle of 55° to 90° from the horizontal. There are several of these ore bodies, all parallel and disposed over all area 550 feet wide. Individual veins are from 6 to 40 feet wide, generally around 200 feet high, and of undetermined length, as no workings have penetrated deep enough to discover how far they go into the earth. In the zone penetrated by the Brown Shaft the ore bodies have been displaced 150 feet horizontally and 380 feet vertically by a fault plane that runs approximately at right angles to the vein system. This fault, called the Mount Hope Fault, divides the old workings into two sections, known as the north and south workings.

The property has been mined by running inclined drifts underneath the ore bodies from the 1000-foot level, those extending southward from the shaft bottom sloping upward and those extending northward being inclined downward, Stopes, generally about 210 feet long and with 30-foot pillars between them, are opened above the drifts to the full width of the vein and mined by the shrinkage system. As the ore is drilled and blasted off in successive overhead slabs, only enough is withdrawn after each shot through chutes installed below to afford the miners ample headroom for taking off another slice. This procedure is continued until the stope has reached the top of the ore body. The entire stope is then filled with broken ore that can be withdrawn as needed.

Most of the south workings have been depleted, because earlier operators followed the veins downward several hundred feet before the Brown Shaft was sunk. Consequently, the bulk of the production in recent years has been coming from the north workings, and the inclined drifts have been pushed continually deeper its they followed the dipping ore bodies. This has progressively lengthened the haul required to deliver the ore to the main 1000-foot haulage level, and thence to the shaft bottom for hoisting to the surface. The longest of the drifts, which is under the Taylor Vein, now extends for more than 4200 feet. Ore has had to be hoisted through it in two stages, then transferred to cars on the 1000-foot level, and again transferred into a skip at the shaft bottom. This multiple handling of ore and the progressively greater distance from the shaft at which the miners have been working have inevitably added to production costs and prevented appreciably increasing the output. This was the situation in 1941 when the Government appealed for more ore to further the war effort. The only logical answer was a new development program such as is now being carried out.

The new shaft, called the New Leonard has been sunk vertically into the ground 1750 feet to the east of the Brown Shaft at the surface and 1450 feet on the 1000-foot level. The latter had already been driven far northward of the vertical extension of the new shaft before it was sunk and is, accordingly, available as a haulageway to it as well as to the Brown Shaft, which will be continued in operation for the time being. In addition, another level, at a depth of 1700 feet from the surface, was driven from the North Elizabeth incline northward, to the lowest workings of the Taylor ore body and southward toward the new shaft while the latter was being put down. It was carried beyond the line of the new shaft and southward of the fault to tap the Teabo Vein which outcrops far south of the Brown Shaft and which, because of its dip, lies roughly 1000 feet below the bottom of the latter shaft.

As the existing facilities for treating the ore were inadequate for handling the increased production from the new shaft, it was necessary to include new milling plants in the scheme. This was desirable for another reason because progress in the practice of concentrating magnetite ore had been so great since the older plants were built as to render them comparatively inefficient.	The lump-ore mill at the Brown Shaft was the first of its kind. Prior to its construction in 1937 all magnetite ore was crushed, concentrated by the magnetic process, and the concentrate was sometimes sintered to give it the body and physical strength required of material charged into blast furnaces. By utilizing a system of passing a conveyor belt over magnetic pulleys, the Mount Hope management was able to offer steel mills magnetite lump ore (pieces 5/8 inch and larger) for their open-hearth furnaces. The magnetic equipment was supplemented by a picking belt where trained workers further segregated ore and waste rock. This was required because lumps with ore only partly exposed might ride over the magnetic pulleys with the rock side up and consequently be attracted. By means of these facilities the mine was able to produce around 67-1/2 percent of its shipping product in lump form averaging 62 percent in iron content. The fine ore was crushed and concentrated into a product averaging approximately 66 percent iron. In a typical year, 69 percent of the crude ore hoisted was marketed and 31 percent went to the dump as waste.

By contrast, the new facilities are expected to turn out up to 75 percent of the shipping product in the form of lump ore and to yield as high a grade of both lump and concentrate as any magnetite mine in the country, with a general ratio of concentration of 1.5 to 1. Using the old lump-ore mill and the new fine-ore mill, there was treated last year a total of 242,000 tons of material, consisting of 195,000 tons of crude ore and of 47,000 tons, of so-called middlings from the old lump-ore plant that had been stockpiled during the latter half of 1943 after the fire in the old dry-concentrate mill. Because of the inclusion of these middlings, and the further fact that the crude ore was considerably diluted with rock as a result of the large amount of development work done in the mine, the total material treated last year had an average iron content of only 37.4 percent, as compared with it normal average of 46-48 percent. Despite these unfavorable factors 131,300 tons of ore was recovered, amounting to 54.3 percent of the quantity processed. Of this ore 61,325 tons, or 46.7 percent, was in the form of concentrates and 70,000 tons, or 53.3 percent, in lumps. The concentrates averaged 65.79 percent iron, in the dry state, and the lump ore averaged 61.40 percent iron. The new fine mill recovered 93.9 percent of the theoretical iron content of its input, and the tails had an average iron content of 4.55 percent iron, in the dry state.

Under the new operating set-up, crude ore is crushed to a maximum size of 6 inches in underground jaw-type crusher stations, loaded from pockets into skips, and hoisted and dumped into a crude-ore storage bin adjacent to the base of the headframe and having a capacity of 1600 tons. From this bin the ore is conveyed by belt to the top floor of the 7-story lump-ore plant from which it passes successively downward. It is first screened to produce two sizes: one under 5/8-inch mesh, which is conveyed directly to the fine mill for processing, and the others 5/8 inch to 6 inches, which undergoes treatment in the lump-ore plant. The larger material first goes over two magnetic pulleys arranged in series. There are two of these installations, and the flow is changed from one to the other every eight hours as the magnets become heated and lose some of their effectiveness. The magnets attract and segregate not only pieces that are rich in ore but also those that are largely rock with some areas of exposed ore. Further separation is therefore desirable to obtain lump ore high in iron content. To effect it, the material is passed from the magnets to a double-deck screen that produces three sizes: 6 - 2-1/2 inches, 2-1/2 - 1-1/2 inches, and 1-1/2 inches to 5/8 inch.

The largest size, 6 to 2-1/2 inches, is fed to a picking belt that has stations for fourteen workers. As the material travels along, they allow the high-grade ore to remain on the belt, which conveys it to storage bins or railroad cars. They pick off rock that is essentially devoid of ore and place it on a belt leading to a waste-rock pile. An intermediate product, middlings, goes by way of another belt to a 2-inch jaw crusher and thence over a magnetic pulley. That portion of it which contains enough ore to be attracted by the magnets is carried back to the head of the circuit for reprocessing, while that rejected by the magnets passes to a cone crusher which reduces it to 1/4-inch size before it joins the other material going to the fine mill. The 2-1/2 to 1-1/2-inch material is fed over a magnetic-drum separator that produces lump ore, rock, and half-and-half. The 1-1/2 to 5/8-inch material undergoes similar treatment in another magnetic drum of different current intensity. In both cases, the half-and-half is crushed to 1/4-inch size and goes to the fine mill.

All the material under 5/8 inch that is separated out in the lump-ore plant is conveyed to the top floor of the 7-story fine mill. This is a wet-process plant, which is somewhat more efficient than the dry process formerly used but is mainly more desirable front the health standpoint because it produces no dust. During its progress through the mill the material is carried by water. The incoming ore is distributed by an overhead regulating feeder to two vibrating 8-mesh screens. Material that is too large to pass through the screen is fed to a rod mill on the first floor to be ground and then pumped back to the screen. From the screen it goes to magnetic machines, known as roughers, which produce a rough concentrate and tailings. The rough concentrate passes to a series of vibrating screens that separate it into four sizes. These are further treated in six magnetic finishing separators that were designed by Harry Davenport, now superintendent of the Mount Hope property and formerly in charge of the old dry mill. Four of these machines handle the two intermediate sizes, which are the greatest in quantity, while one suffices for each of the two other sizes.

The products in all cases are concentrates and tailings. The latter, as well as the tailings from the rougher separators used to effect the first concentration, go through a special rougher separator that is known as a policeman. It yields tailings and middlings, which latter pass to a rod mill for grinding and then back over one of the finishing separators. Tailings are dewatered by a drag rake and then conveyed to a dump. Concentrates are dewatered in a rotary vacuum-type filter and transferred to a large bin, or directly to railroad cars. Both travel on separate belts housed in the same enclosed bridge, which contains steam pipes to prevent the materials from freezing during cold weather.

The fine-ore mill uses a great amount of water, and a supply is also needed for the miner's change house and other purposes. To furnish it, a reservoir was created by erecting a low earth dam at the end of a peat bog south and east of the new surface plant. It receives the runoff from 1250 acres of higher land surrounding it and also the water pumped from the mine. Although the reservoir has a surface area of 216 acres exposed to the evaporative rays of the sun, the water level was not perceptibly lowered during the unusually hot and dry summer of 1944. From a pump house containing two 1500-gpm. and one 3000-gpm. pumps, reservoir water is elevated to a water tank that rises 138 feet above the ground surface. The plant supply is obtained from the tank by gravity flow. After water has been used in the fine-ore mill, it is run into the reservoir at a location where it will soon be withdrawn. This permits the solids carried to settle out and provides the pumps with clear water at all time.

The new shaft is one of the largest and deepest ever put down in the eastern part of the country. Including a 3-1/2 foot sump, it is 2674 feet deep. It measures 12 feet 6 inches by 18 feet 3 inches inside its concrete lining, which has an average thickness of 15 inches and a minimum of 8 inches. The shaft was sunk under contract by the Underpinning & Foundation Company, New York. The cage, skips, landing chairs, ore-pocket steelwork were made by the Union Iron Works, Elizabeth, N.J. Excavating and concreting were done concurrently, that phase of the work having been started on November 7, 1941, and completed on March 3, 1944. The setting of steel and installation of cages, skips, pipes, cables, etc., consumed an additional eleven months, and the finished shaft, ready for operation, was turned over to the mining company on February 1, 1945. In addition to constructing the shaft proper, the contractor cut stations at five levels and at four of them built skip-loading pockets, each 28 feet high, 18 feet 3 inches wide, and 23 feet deep. The operations involved the excavating and removal of approximately 27,000 cubic yards of rock, measured in the solid, and the placing of some 8000 cubic yards of concrete in forms.

As the prevailing gneiss country rock reaches the surface at the site selected, the work required drilling and blasting from the outset. A temporary steel head-frame 65 feet high was put up to get operations underway, and the permanent 148-foot steel headframe now serving the mine was erected while sinking was in progress. As soon as the latter was completed, it was utilized by the contractor. It is equipped with sheave wheels 12 feet in diameter and 120 feet above the ground surface. A Lidgerwood electric hoist, driven by a 600-hp. motor and wound with 1-1/4-inch nonspinning wire rope, way used for the sinking operations. This unit, which had previously seen service on one of the shaft sinking jobs of the Delaware Aqueduct of the New York City water-supply system, was equipped with brakes operated by compressed air. The air was ordinarily obtained from the contractor's distribution lines, but a small Ingersoll-Rand air-cooled compressor was set up in the hoist house for emergency service. A smaller air hoist was employed in erecting the permanent headframe and thereafter served as a standby, pinchhitting on three occasions for the main hoist when it became incapacitated because of power failure. Round buckets of 1-1/4-cubic-yard capacity were used during the early stage of the work for handling men, muck, and materials and were later replaced with similar ones of 2-cubic-yard capacity. Guides were run down the shaft for 1650 feet, below which point the bucket swung free.

Drilling was done with both Jackhamers and drifters. Because they can be moved about more readily and require no time for setting up, Jackhamers were utilized wherever relatively soft ground was encountered and drifters in harder ground. Two veins of ore were passed through, one being entered at a depth of 1500 feet below the surface and the other at about 2160 feet. Approximately half of the work was done by Jackhamers and half by drifters. All drills were of Ingersoll-Rand make, there being fourteen wet-type S-68 Jackhamers and six DA-35 drifters on the job. When drilling with Jackhamers, eight machines were ordinarily used. When drifters were employed, four were in service, being mounted two each on two bars set up across the shorter dimension of the shaft. Compressed air was delivered to manifolds, from which there were hose takeoffs to the individual drills. In each of the latter was interposed an air-line oiler to insure adequate lubrication at all times.

A drill round consisted of from 52 to 56 holes averaging from 8 to 10 feet deep. A V-cut was made extending across the midsection between the sides of the opening. These holes were shot first, and those at either side of them were then fired progressively so as to break to this continually widening cut. The center section was always shot and mucked a foot or two lower than the rest of the bottom. This provided a sump which all water drained and kept the remaining areas dry.

Hollow, round 1-1/8-inch Jackrods and 4-point Jackbits were used with the Jackhamers. Starters had a maximum diameter of 2-1/4 inches, and a reduction of 1/8 inch in gauge was made with each succeeding bit change. A total of 34,00O bits was employed in sinking the shaft. Hollow, round 1-1/4-inch conventional sharpener steel was utilized with the drifter drills, holes being started with bits of 2-3/8-inch gauge. The time required to drill a round varied from 4 to 8 or 9 hours, depending upon the hardness of the rock. As each hole was completed, it was blown out with compressed air and stopped with a wooden plug to mark its location and to keep out dirt.

Holes were loaded with 40 percent Atlas gelatine dynamite, the average consumption ranging from 350 to 400 pounds per round. Primers were made up at the shaft bottom, electric blasting caps up to eight delays being used. Shooting was done from the surface or from shaft stations after all drilling equipment and men had been hoisted. The average advance in depth per round was approximately 6 feet. Mucking was done by hand shoveling. The time required to clean up a round was about twelve hours in the beginning. This gradually rose to 14-16 hours as depth increased and more time was consumed in hoisting and lowering the bucket. The maximum rope speed of the hoist was 750 feet per minute. The average time for a cycle of drilling and mucking wax 22-23 hours.

Tile maximum flow of water into the shaft was around 50 gpm. During the first 1000 feet of sinking this was pumped to the surface by Ingersoll-Rand Motorpumps, additional units being set up with depth until three were being used in series. During the remainder of the work the water was pumped to the 1000-foot level of the mine and raised from there to the surface by the mine pumps. Ingersoll-Rand NT-4 pumps served during this latter period. One unit handled the water down to the 17000-foot level. It was then stationed there and a second unit installed in the shaft as a booster to that point. The second pump was stationed at the 2500-foot level when the shift reached that depth. Two air-operated sump pumps were used at the bottom for pumping casual water into the hoisting bucket during mucking.

Concreting of the first 1000 feet of the shaft was ordinarily done once it week, and frequently twice weekly thereafter if "popping rock" was encountered, the aim being to keep the unlined section down to a safe distance for scaling the sides above the bottom. Six-foot steel forms were employed, and it was necessary to lower them from the surface each time they were set up and to hoist them out of the shaft after the concreting cycle had been completed. Concrete was hauled to the shaft head in transit-mix trucks front Kenvil, N.J., it distance of 8 miles, and was delivered directly into the shaft bucket. As depth increased, the time required to transport both forms and concrete in the shaft became progressively greater, and the work was slowed up proportionately. Normally, five rounds, equivalent to around 30 feet, were excavated and concreted weekly, and the best performance registered was 46 feet in one week.

Every 90 feet vertically, a bearer set of steel was anchored in the concrete, and these sets form part of the ordinary steelwork placed throughout the shaft to subdivide it into compartments. A 4-inch air line and a 2-inch water line to supply the drills, a 6-inch water discharge line, and two 8-inch ventilating ducts were all embedded in the concrete. Ventilating air was supplied from the surface until the 1400-foot level was passed, after that the blower was moved to that level. Air was normally blown down the shaft but after each blast it was exhausted for fifteen minutes to remove smoke and powder fumes.

Compressed air for the shaft-excavation work was furnished by an Ingersoll-Rand 14-inch stroke Class PRE-2 machine driven by a 200-hp. Westinghouse synchronous motor. During the summer of 1943, a bolt of lighting burned out the motor, and three I-R portable compressors were brought in to provide temporary service. They remained as standby units. The contractor maintained a blacksmith shop with complete Ingersoll-Rand equipment for reconditioning drill steel. Jackbits were resharpened by a J2 and a J3 grinder, and both shanks and threads were swaged on the Jackrods in a No. 50 sharpener. The same unit served for all reconditioning operations on the solid forged steel used by the drifter drills, and there were two 27P oil furnaces for heating the steel. All the steel and bits required for a round were sent down the shaft at one time. Jackbits were delivered in boxes having compartments for the different sizes. Used bit were places in another box on the shaft bottom to be brought to the surface for resharpening.

The steelwork that divides the shaft compartments consists of horizontal sets of 12- and 8-inch H-beams hung on 6-foot centers and interconnected by the steel guides. It was made up by the American Bridge Company and totaled approximately 1000 tons in weight. Installation was started at the shaft bottom and carried progressively upward. To facilitate this, the bucket that had been suspended from the hoist cable during the excavation operations was replaced with a platform that could be extended at the sides to give the workmen access to all parts of the shaft cross section. All seat angles, brackets, and guide supports were secured to the concrete lining with 1-inch bolts, 6-inches long, that were screwed into Star double-expansion shields of rustproofed malleable iron. Each shield necessitated the drilling of a hole 1-3/4 inches in diameter and 6 inches deep, there being an average of 40 of them for each set, or more than 17,000 in the shaft. They were put in with the S-68 Jackhamers that had previously been used in excavating. Drilling was done with Jackbits, the number required for the purpose being 3000.

Approximately 450 men will be needed to operate the mine at its new capacity, but, in view of the manpower shortage, it is difficult to forecast how soon a full working force can be obtained. The present payroll of around 150 will be increased as rapidly as more employees become available. Meanwhile the kind of ore produced at Mount Hope is in demand, and existing agreements assure a market for virtually the entire capacity output for five years ahead.

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GENERAL VIEWS - The shaft headframe (in circle) rises 148 feet above the ground and the water tower 138 feet. Shaft transportation is handled by the two Lidgerwood electric hoists shown above. The 900-hp. man hoist is in the foreground and the 1800-hp. ore hoist is beyond it. One of the underground brusher stations where much is broken down to pieces 6 inches or under before hoisting is pictured at the far left. Upon reaching the surface, lump ore is first passed over magnetic pulleys which are so powerful that they attract some material that is not worth shipping. This is eliminated by men working at a picking belt, as illustrated at the left of the circle. In the top-center view the concentrate mill is in the foreground and the lump-ore plant and headframe are beyond it. Conveyor belts in the inclined trestles carry lump ore and concentrate to shipping cars and waste rock to dumps.

NEW SURFACE PLANT - In the foreground are temporary structures used by the contractors.

VERTICAL PROJECTION THROUGH ORE ZONE - This drawing shows disposition of the ore bodies and how their deeper sections will be reached through the New Leonard Shaft. Many older shafts are also shown, but production since 1922 has been through the Brown Shaft. The Mount Hope Fault, a shear zone up to 100 feet thick that has interrupted the continuity of the veins, is indicated near the center. The dotted horizontal lines show where three lower levels will be opened.

CROSS SECTION OF SHAFT - Drawing shows dimensions and uses of the six compartments. The shaded border indicated the concrete lining.

MINE COMPRESSOR PLANT - These three synchronous-motor-driven machines supply compressed air for operating rock drills, hoists, loading-pocket gates, ets., in the mine. They have a combined piston displacement of 11,592 cfm. The air delivered by them passes through the aftercoolers shown on the left wall and thence to receivers outside the building. A 12-inch main extends from the receivers down the shaft, and branch distribution lines on different levels serve the various working places.

CONCENTRATE MILL - Being magnetic, the ore is concentrated by passing it over electromagnetic drums and machines which attract the magnetite and allow the waste to pass on. Pieces larger than 5/8 inch are segregated in the lump-ore plant and marketed as lump ore. The remaining fine material goes to the 7-story concentrate mill where approximately 93 percent of its ore content is recovered. The view below shows a group of Davenport magnetic machines where the finished concentrates are produced. In the other picture, right, is a rotary vacuum filter in which the concentrates are dewatered before shipment; bottom-center, the Ingersoll-Rand vacuum pump that serves it; and, left, a rod mill used for grinding.

SHAFT SINKER - Luther Curtis, superintendent for the Underpinning & Foundation Company during the sinking of the new 2674-foot shaft.

DRILLING IN THE NEW LEONARD SHAFT - This picture was taken when the shaft was nearing the bottom. Four DA-35 drifters are mounted two each on cross bars spanning the narrower dimension of the opening. These machines were used in the harder rock sections, but approximately one-half of the drilling was done with hand-held Jackhamers. Note the concrete lining which has been extended almost down to the drilling floor.

SHAFT-SINKING EQUIPMENT - A in the contractor's blacksmith shop where drill steel was reconditioned. It shows a bit being forged on a piece of 1-1/4-inch steel in a No. 50 sharperner.