site sides of the fault. In this way not only may the exact position of the fault be determined, but its approximate throw and perhaps its dip may be estimated, and much useless shaft sinking may be saved.

AUGER AND POST-HOLE DRILLING

Where the zone of surface weathering is deep, as it usually is in the western Kentucky district, and where the soil is relatively free from large pebbles and rocks, a less common condition, the earth auger or post-hole drill may be used to advantage. The fluorspar in this weathered zone is usually a loosely coherent gravel that an auger picks up easily. Extensions of several smaller veins in Kentucky are said to have been found in this way. Often several holes are started and abandoned later because of rock obstructions before one hole deep enough is completed. In spite of this disadvantage the method, where applicable, may be the cheapest and quickest available.

SUGGESTED IMPROVEMENTS IN PROSPECTING METHODS

To find new veins or continuations of known veins is constantly becoming more difficult and expensive. All areas known to be mineralized have been carefully searched many years for surface indications and probably all the easily discoverable deposits are now known. In addition, much prospecting, most of it very unsystematic, has been done in areas where no visible outcrops of fluorspar could be found.

At present, if the opening up of new ore is to equal production, prospecting must be done more efficiently and systematically. It should be possible to block out an area and prospect it so thoroughly that little doubt can exist as to the presence or absence of important deposits of fluorspar. Present methods are too slow and expensive for such prospecting; they must be improved or new methods devised.

For finding veins or faults where no outcrops exist and the soil covering the solid rock is thick, trenching at right angles to the supposed strike seems to offer the greatest possibilities. Instead of trenching by hand a form of drag-line scraper specially designed for this purpose might be used. Such a device might have a rather narrow scraper and be driven by a portable gasoline engine. In unconsolidated material relatively free from large bowlders the scraper should cut long, deep trenches much more rapidly and cheaply than they can be dug by hand.

Where the sinking of prospect shafts is necessary or desirable the following equipment is suggested: On a heavy motor truck or trailer

could be mounted a small gasoline engine, a small geared hoist, and a belt-driven air compressor large enough to run one drill of the jack-hammer type. The hoist and compresser should be so placed, on opposite sides of the engine, that either could be run independently. With this portable outfit prospect shafts could be sunk through soil or solid rock much more rapidly and probably more cheaply than by present methods. Possibly, too, the same engine and hoist could be used to run a drag-line scraper.

MAPS AND RECORDS

In all prospecting, whether successful or unsuccessful, accurate maps and records should be kept which should show: The exact location of the drift, shaft, trench, or bore hole, its direction, its depth or length, the elevation of the collar of the opening, the material passed through, and the position of contacts, the date of work, and the names of the men in charge. Many small-scale operators, particularly some of the smaller ones, have not appreciated the need for such records, assuming that if they found and mined the spar no records were necessary; if they found no spar the records were useless. This, of course, is not true, for only through the gradual accumulation of data on formations and the presence or absence of favorable indications can future prospecting and development be done intelligently. Information obtained from a prospect deemed unfavorable may, when added to similar data from another prospect, give information of great value.

For example, in an area of branching and step faulting, as in western Kentucky, differences in elevations of the same bed in nearby prospects may indicate a fault between, and this fault may be mineralized.

A company in Illinois that keeps good records has devised a graphic method of keeping data on churn-drill holes. In addition to the regular records, it makes on thin cardboard a chart for each hole, showing, to scale, the depth of the hole and the exact boundaries. between the different formations encountered. Then drill cuttings that represent the materials of each different formation are glued to the chart in their proper places. In this way a controversy as to the proper identification of a formation or its similarity to material found in other holes may be settled at any time.

DEVELOPMENT

Few fluorspar mines in the United States maintain an adequate policy for the systematic development of fluorspar reserves in advance of mining. In the southern Illinois district several of the

larger companies develop their property systematically; their policy is to keep each of the principal shafts much deeper than its lowest working level, often a hundred feet deeper. Provision for lateral development is, in a way, partly made through the shrinkage-stope method of mining commonly used. One large shrinkage stope provides many working places and blocks out a large tonnage of ore. In addition, drifts are usually driven in advance of working stopes, commonly at least 100 feet and often much more.

In Illinois few shafts are used and lateral development is most important, in contrast to the Kentucky practice of using many small shafts. In Illinois it is often necessary to drive long development drifts through pillars of waste in pinches to reach known blocks of ore beyond. Such work is expensive, but has the merit of exploring thoroughly and sometimes finding ore in a block of ground that otherwise might never have been touched.

In the western Kentucky district very few mines have been developed systematically. Much mining has been on contract under short-term leases. The small operators have not had the incentive or the capital to do any development, but have mined out small patches of easily accessible ore from small temporary shafts. The need of adequate development is appreciated by the larger Kentucky operators and more attention will probably be given it in future. At Wagon Wheel Gap, Colo., where the deposit is opened by adit tunnels, development is kept far ahead of mining by the extension of tunnels, the driving of new tunnels at low levels, and the connecting of tunnels by raises.

MINING METHODS

Although the methods used in mining fluorspar differ greatly in different mines and in different districts, all mines may be divided into three main groups, as follows: (1) Open-cut mines; (2) mines opened by drifts or tunnels; and (3) mines opened by shafts. Of these three groups the third is by far the largest and most important.

OPEN-CUT MINES

In the western Kentucky field and at a few of the smaller mines in southern Illinois and elsewhere the fluorspar veins outcrop or lie so close to the surface that open-cut mining is possible. These mines are nearly always very small and the fluorspar is removed entirely by hand labor.

In western Kentucky and at a few mines in southern Illinois surface deposits of soft residual gravel or lump spar mixed with clay and sand are worked by open pits, usually to depths of not 99113°-27-3

more than 30 feet. The fluorspar is removed by pick and shovel and trammed in small cars or wheelbarrows to a log washer close by. Usually the spar is so soft that no drilling or blasting is

necessary.

Although many shallow deposits may be mined economically by open cuts, use of open cuts is inadvisable if the vein continues in depth and later mining must be underground. This is particularly true where the vein and its walls are disintegrated and soft at the surface. At many deposits in western Kentucky the surface has been so cut up by open-pit mining that subsequent underground mining has been greatly hampered and much ore lost by "mud runs " and by streams of water entering the workings from the open cuts above.

When an outcrop of residual fluorspar is discovered, prospecting should be done to prove the downward continuation of the deposit. If the ore proves to be of minable width in the solid rock below, a shaft should be sunk, preferably in the footwall, and mining started at such a depth that a strong pillar of solid-vein material can be left to support the surface. After all of the deep-lying ore has been removed the surface ore may be taken; in other words, the surface ore should be mined last. This policy is now followed by the larger companies in the Illinois field.

DRIFT MINES

Many fluorspar deposits that are in a region of rugged topography and dip at a high angle (as at Wagon Wheel Gap, Colo.), and many more or less horizontal bedded deposits that lie above the general level of the surrounding country (for example, the deposits near Cave in Rock, Ill., and at the Nakaye mine, N. Mex.) can be opened by drifts or tunnels instead of shafts. Where conditions warrant, drifts and tunnels are preferable, because no hoisting and often no pumping is required. Where the veins dip at a high angle the methods of mining need not differ greatly from those used in shaft mines and require little comment here. The description of the mining method at Wagon Wheel Gap, Colo., will be interesting in this connection.

There are only a few bedded fluorspar deposits, and the only ones in the United States that have been worked at all systematically are near Cave in Rock, Ill. Those parts of the beds that contain fluorspar of minable thickness, usually more than 24 inches, are opened by drifts and the spar is extracted by a modified room-and-pillar method, such as is sometimes used in coal mining. The methods used at Spar Mountain mine illustrate this.

SHAFT MINES

Shaft mines differ greatly in size, productive capacity, methods of working, efficiency of operation, and many other respects. They range in size from small pits 30 to 40 feet deep, worked on contract by two or three men who use a hand windlass for a hoist, to the very large mines, several hundred feet deep, which employ hundreds of men and have extensive mechanical equipment. Some of the larger mines employ definite systems of mining, but unfortunately these mines are far in the minority. There are only a few really large mines (chiefly in southern Illinois), and there are a great number of small mines (chiefly in western Kentucky). At a few of these smaller mines some semblance of a definite system is attempted, but usually the ore most easily extracted near the surface has been removed as cheaply and rapidly as possible with little regard to future mining.

At those deposits which are worked by leasing to contractors for brief periods short sections of the vein, often 150 feet along the vein, mining is without system. Such mines are commonly opened by small (often 4 by 4 feet or even smaller) single-compartment cribbed shafts sunk on the vein. As soon as the shaft reaches the base of the barren surface material very narrow drifts, untimbered if possible, are run from the shaft along the vein.

If developments in this drifting are favorable, it is customary to sink the shaft 20 to 40 feet deeper and again run drifts in each direction, usually to the boundaries of the leased section. Then removal of the mineral by overhand stoping begins. Only such timber is used as is absolutely necessary to hold the ground during mining and to provide standing room to keep the miners up to the back of the stope. If all of the mineral above this level is extracted before the termination of the lease, the shaft may again be deepened 20 to 40 feet and another slice mined out.

In such mining very little dead work is done to follow the vein through pinches; often all of the easily accessible ore is extracted, or the workings cave before the termination of the lease and the mine is abandoned. In a relatively short time the workings are wholly inaccessible, and more systematic mining later is greatly hampered. Sometimes such deposits are mined again by similar inefficient unsystematic methods and the workings once more left to cave. Much ore is lost and deposits have been reported as worked out when only the part near the surface has been explored. Adequate maps are rarely made of the old workings, and subsequent mining is difficult and expensive.