PARTOF
THE
PLANTOF
THE
POTASH COMPANY OF AMERICAFROM
THE
AIR
NEW MEXICO SYLVINITE Occurrence and Mining R. M. MAGRAW Potash Company of America, Cadsbad, N. Mex.
T
HE first commercial discovery of sylvinite in the Carlsbad area (or in the New World) was made in 1925 by the late V. H. McSutt. He recognized crystals of the mineral sylvite in the cuttings of an oil well and, after confirmation of his opinion by analysis, secured authorization to prospect the area for potash minerals by diamond drilling. The results obtained from the cores secured from such drilling justified the exploitation of the deposit. The United States Potash Company was formed to take over the development and operation of the property through permits and leases from the Government. A shaft was sunk approximately 1000 feet to the deposit, which was found to average 12 to 14 feet in thickness over a considerable area. A mill was erected to grind the ore to a maximum of about 10 mesh; the product produced in this form was marketed as manure salts (25 per cent potassium oxidegrade). Later thiscompany constructed a refinery and sank a second shaft about 1800 feet from the No. 1 or hoisting shaft for ventilation purposes. At and before the time McNutt made his discovery, the United States Government, through the Geological Survey and the Bureau of Mines, was making intensive search for potash-bearing minerals throughout that part of the Permian Basin. They did not, however, prove any workable deposits of sylvinite until some time subsequent to the McNutt discovery. The work performed by these agencies and the geological data obtained are of inestimable value to present operating companies and the people of the United States.
The Potash Company of America secured prospecting permits from the New Mexico and the Federal Government in the spring of 1931 and, after an intensive drilling campaign carried out through the following two years, their No. 1 shaft was started in March, 1933. Holes were drilled to the top of the salt through the overburden (composed of blow sand, gypsum, clay, anhydrite, water-bearing limestone, and of unconsolidated sand which verges in some cases to quicksand) by the use of percussion drills or “spudders.” The thickness of the overburden varies from about 300 to as much as 600 feet, the average being about 400 feet. Casing was run to the top of the salt or to an impervious bed immediately below the top of the salt, a saturated solution of potassium chloride-sodium chloride brine was used to prevent etching of the core, and in most instances the core equaled or approximated 100 per cent. Occasionally the total length of the core, as assembled in the core boxes, exceeded the depth of the hole; this was due to inability to fit the numerous sections of the core perfectly. The nonrotating inner core barrel used in most of the later drilling was developed by A. S. Ruellan, of the United States Potash Company, and perfected by the Sullivan Machinery Company. Modifications of this core barrel are now considered standard equipment for salt coring. The use of such a core barrel eliminates much cross fracturing of the core and prevents grinding of the individual sections one upon the other, with consequent loss of an indeterminate length of the core as actually cut by the drill. 861
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INDUSTRIAL. AND ENGINEERING CHEMISTRY
VOL. 30, NO. 8
(Above) CARS “IN TRAIN”BEINQ EMPROTARY DUMP; ORE Is THEN TO A PAN CONVEYOR FEEDDELIVERED INQ A CRUSHIR (Center) HOISTINGMACHINERYWITH t MOTOR-GENERATOR SET AT THE LEFT
TIED BY A
(Below) SECTIONOF THE REFINERY SHOWING BALLMILLS AND CLASSIFIERS IN THE FOREGROUND, AND FLOTATION MACHINESIN THE BACKGROUND
Sinking The No. 1shaft was planned as a hoisting shaft and consists of three compartments; each one is 61/a X 5 feet in the clear. Two compartments are used for hoisting, and the third is for pipe lines, cables, ladders, etc. The ore body was struck at a depth of 998 feet in December, 1933. Some difficulty was experienced as a result of water encountered a t several horizons and one area of quicksand. It was necessary t o seal both water and sand by reinforced concrete side walls which, with dividers or buntons, were poured monolithically in about 300 feet of this shaft. The heaviest flow of water encountered was 235 to 250 gallons per minute. This flow came from limestone at a depth of 255 feet; it had a hydrostatic head, as determined after it was placed under control, of 84 pounds per square inch. The main stream was led into a pipe extending through the concrete form, an open valve being placed on the end of the pipe which permitted the water to spill into the shaft. After the concrete had been poured and allowed t o set, the valve was closed and a pressure gage attached which disclosed the pressure just cited. This water can be closed off entirely or allowed to flow by its own head to a 300,000-gallon sump, where it can be pumped out to the surface by a deep well pump and used wherever required around the plant. In the No. 2 or air shaft, located 700 feet from the No. 1 shaft, a flow of 1000 gallons per minute was encountered a t the same horizon. This flow was under the same p r e s s u r e i . e., 84 pounds per square inch. The flow entered the shaft through several crevices; therefore a little different procedure was necessary in this case. The crevices were excavated back for a distance of about 4 feet in dovetail shape. Bell-shaped reducers from 10 to 6 inches were then grouted into place, and the water was permitted to flow into the bottom of the shaft from which it was pumped to the surface by a deep well turbine. After the c e m e n t h a d t h o r o u g h l y set, a 6-inch header was run around three sides of the shaft and connected to the several bleeder pipes. By means of a T and nipple a 6-inch valve was attached t o one end of this header. The suction pipe of the turbine wa~sshortened and a hose run from the valve to the bottom of the pump barrel. The arrangement worked satisfactorily, and from then on, the bottom of the shaft was comparatively dry. One end of this header was permitted to remain open so that the water flowed freely to the pump as before. Lining the shaft with reinforced concrete was then undertaken; after the concrete was thoroughly seasoned, the valve was closed and apressure gage attached, the indicated pressure being 84 pounds. This water is also under such control that any part or all of it can be utilized.
AUGUST, 1938
INDUSTRIAL AND ENGINEERING CHEMISTRY
The No. 1 or hoisting shaft is used as a downcast for air. The No. 2 shaft, which was sunk primarily for an air and escape way, is used as the upcast. The air circulation is induced by a 5 X 7 foot Jeffrey fan, powered by a 125-horsepower synchronouo motor. This fan is capable of passing 150,000 cubic feet of air per minute a t a water gage of 3 l / 2 inches. The air current can be reversed in a few minutes by opening two doors and closing other doors. Reversal of the current, however, is resorted to only during periods of extreme cold; a t such times it is necessary to make the reversal in order to keep ice from forming in the hoisting shaft.
System of Mining The sylvinite bed occurs as a blanket formation, with a gentle rise from east to west. Minor folding occurs, however, and in some cases quite heavy grades have been encountered. These folds, as well as the general pitch, are attributed largely to the Guadalupe uplift, although some of the cross folds or rolls are undoubtedly due to irregularities existing on the floor of the basin a t the time of deposition. The generally horizontal character of the deposit permitted the projection of mining operations along lines similar to those adopted by modern coal mines. The room-and-pillar system was selected as most satisfactory, both from the standpoint of operating economy and of the ultimate recovery of a maximum tonnage of the ore originally in place. The ratio of ore extracted to ore left in pillars is about 60 to 40 and is more or less empirical, although supported by data furnished by G . S. Rice of the Bureau of Mines. No effort has been made to recover ore from the pillars. None is contemplated for the immediate future because if caving occurred, water could enter from the overburden with disastrous results. Pillars of ample dimension to support the roof and to permit ultimate recovery are left in place with the thought that, when the present mine is developed to the boundaries of the deposit or t o the economic limit as determined by haulage costs, the life of the property might be prolonged by the systematic robbing of the pillars. It is believed that the salt overburden, which is roughly 600 feet, is sufficiently elastic so that, with removal of supports, it will bend until it meets the floor instead of caving. But the chance of losing the mine from an influx of water is of too much moment t o warrant gambling on a theory a t this time. When the condition mentioned occurs, however, the odds will be in favor of the operation since the mine will be otherwise exhausted. Triple entries are driven, the air is split at each panel, and an adequate supply is circulated to each working face. The return air is conducted to the upcast shaft through separate air courses and passes through concrete overcasts or undercasts a t the several intersections. Stoppings or bulkheads, used to close the crosscuts or abandoned working places and thus to force a continuous supply of fresh air to the operating faces, are constructed from fine salt-i. e., “bug dust”-resulting from the undercutting operation. This is mixed with saturated brine and handled like concrete. When properly tamped, it sets so rapidly that practically no forms are required. Two posts wedged between the floor and roof a t the appointed place, with one board which is moved upward as the work progresses, are all that is needed. There is some shrinkage which shows a t the top of the structure. This necessitates a little trowel work, but then the structure is airtight and heavy shooting can be performed within a distance of a few feet without damage to the stopping. The sylvinite is overlain by about 600 feet of salt or other solution deposits. This makes an excellent back so that no timbering is required. The thickness of the salt below the sylvinite varies from 600 to 800 feet. The bed itself, as de-
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veloped in the mine of the Potash Company of America, varies from 4 to a little over 8 feet in thickness, with an average of S2/3 feet.
Mechanized Mining Methods Sullivan undercutters, equipped with 7l/rfoot cutter bars, are used to undercut the ore a t the point of contact with the salt. The average depth of cut is 7 feet, and the height of kerf is 6 inches. It was found necessary to reduce the rate of feed, or traverse, of the machine across the face from the usual 16 to 24 inches per minute because the salt, while no harder than some coals, is tough and rubbery and dissipates heat much more slowly. Hence, when permitted to travel at the high rate of speed used in coal mining, the bits were soon made so hot that they burned or failed. The bits now employed are tipped with an alloy metal and then ground to the proper shape. After the undercutting cycle is completed, the face is drilled; Jeffrey post drills with auger bits are used for this operation. The conventional round in a 14 X 7 foot face is twenty-eight holes. Owing to the nature of the ore, it is essential that the holes be carefully spaced t o avoid “bootlegging,” with consequent excessive use of explosive. There is no overbreak in any direction; hence the holes are literally filled with powder almost to the collar, although it has been found that the fiame result is accomplished with a 7/s-inch powder as with one of larger diameter. “Gelamite” (40 per cent strength, ll/~,inch powder) is used as primer to give a kick to the bottom of the hole, as well as to make it easier to insert the detonator. Powder 7/s-inch in diameter is used for the balance of the hole. Delayed-action detonators are employed. Because of the rubbery nature of the ore, with consequent close spacing of holes and excessive use of powder. the cost of shooting is a major item. The tonnage of ore broken per pound of powder ranges from one-fifth to one-third as much as that broken in the average coal or hard rock mine. As a safety measure a separate electric circuit is carried throughout the mine for shooting purposes. This circuit is dead a t all times except momentarily when shots are being fired. Shots are fired from the station a t the bottom of the shaft when the shift changes and after all the men on the shift have checked out. An electric switch is placed a t the entrance to each working place; each panel, or section of the mine, is also protected by a suitable switch; and the master switch, which is locked a t all times except during the moment of firing, is located a t the station. The shot firer, the last man to leave the faces, closes the several switches in rotation as he comes out. He then unlocks and closes the master switch, and the shots are fired. The induced ventilation of the mine ensures the removal of smoke and fumes from the working places between the time of the firing of shots and the arrival of the oncoming shift. Broken ore is loaded out by mechanical means; development, or narrow, work is handled by Jeffrey mobile loaders. Booms, or wide work, are loaded by Sullivan dragline loaders. These machines were built to a special design and will deliver to a mine car on the same track o n which the machine is operating or, by turning it go”, to a car or train of cars moving slowly on a parallel track.
Tracks and Transportation The track gage is 42 inches. Fifty-two pound rail is used on the main line and 30-pound rail elsewhere. The ore cars are of the Card rotary-dump type and are equipped with 14inch semisteel wheels with chilled treads, 3I/*-inch heattreated axles, Timken bearings, double brakes, and spring bumpers with swivel drawbars which permit passage of the
LOADING SYLYINITE
cars through t,he dumping device “in train.” Cars are 100 feet in capacity and 38 inches high above the rail. When properly loaded they carry an merage of 5 tons of ore. Loading equipment is serviced by 5-ton’Mancha storage battery locomotives, powered b ~ Exide r batteries. A battery charging station near the shaft is equipped with an overhead crane so that a battery can be changed in about 11/2minutes. The usual service train consists of six cars which are spotted at tlie loading machines in rotation. After the full train is loaded, it is placed on a near-by sidetrack; after an equal number of empties have been delivered. it is picked up by a 10-ton condination t.rolley-cable reel Baldwiri-Westin~~iouse bar-steel frame locomotive and hauled to the main sidetrack from which trains, or trips, of thirty cars or more are rnade up for transport to the bottom of the shaSt by 15-ton Baldu-inWestinghouse straight trolley-type locornotives. Trains arc then pulled past the station and shunted from the main line to a parallel track which leads to the dump. After passing over a scale, the loaded cars go throiigh the rotary dump one at a time. They are dumped “in train” and are fed to the dump automatieally by means of dogs or car stops actusted by tlie dumping mechanism. After the ore falls from the car while rotating in the dump, it drops into a hopper of I5-ton capacity, from which it is delivered by a pan feeder to a % X 54 inch single-roll, insertedtooth Jeffrey crusher, which breaks it down t,o about %inch maximum size. This primary breaking facilitates liandling through the skip loaders, surface storsge bins, etc. Delivery from the crusher is to a skip pocket that d l store about 100 tons of ore. From the pocket i t is drawn hy two Link-Belt automatic skip loadors directly into the &ips. These pieces of mechanism, which are actuated by the skips themselves, ensure uniform loading of the skips with a minimum of spillage. Two skips, wliich are of the underslung topdumping type and 5-ton net capacity, run in balance at a rope speed of 1250 feet per minute; the hoisting and dumping cycle is completed in ahont I’/* minutes.
Hoisting and Power The hoist, a double cylindrical drum Nordberg, is operated by a 400-horsepower 3Wvolt direct-current motor, which receives its current from a Ward Leonard motor-generator fiywheel set; the curve of the primary power chart is thus held to almost a straight line.
The drums are 5 X 9 feet and spool the full length of the inch Lang-Lay rope in one lap, thus eliminating niuclr abrasion. The head frame is 128 feet high and of steel con.. struetion. The height is necessary for hopper or bin room to permit surge storage betveen the shaft collar and the grinding mill. The power plant contains five Diesel units, aggregating 4000 horsepower. Primary current is generated at 2300 volts. alternating current.
Self-sufficiency of the Plant Owing to the isolation of the plant, it liss been necessary to install and eyiiip a modern machine shop, as well as a gen-. era1 supply department where needed repairs and supplies. can be had upon demand. Xany annoying and expensive delays have heen prevented by the functioning of these two (if?partments. -4 two-story laboratory building, 32 feet wide and 68 fcct long. for plant control and research vrurk provides ample facilities Sor this department. The control laboratory is on the. ground floor and is without windows, so that infiltration of dust is minimized. A uniform temperature is assured by a combination heating and air-conditioning piant which serves tlie entire building, as well as the adiscent general offices.. Other departments on the ground floor include a grinding or. sample preparation room, a resoarch or experimental room, storage space, etc. The second story provides staff offices, a. large draft.ing room, and a research or analytical iaboratory. During the peak shipping season ss many as thirteen thousand determinations are rnade per month. Change roonis. equipped with showers, lavatories, toilets. individual steel lockers for street clothes, and chairis with hooks and basket for workclothes, are provided Eor both mine and refinery employees. Condortable quarters for key employees have been provided. These include a number of homes, modern in every way, for those who are married. as well as a modern comhination mess hall, amusement hall, and apartment building forthe single members of the staff. A majority of the employees, however. live in Carisbad, vhich is located on the Pecos River ahout 23 miles southwest of the plant,. Working and living. conditions connected with potash nrining in Xew Mexico. can he compared favorably with those of any other industry. in the United States. R B C ~ X Y May F D 10, 1938.
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