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the available CaF is 75 per cent, or 5 points above the standard; but a spar containing 85 per cent CaF, and 10 per cent SiO, would be penalized 10 points, for the available CaF2 is only 60 per cent.

Although prices are normally quoted f. o. b. mines or the nearest railroad shipping point, regardless of the location of the deposit, the prices in the Illinois-western Kentucky field actually set the level of prices in the country (with the exceptions noted later). The cost of fluorspar in Chicago is, then, the southern Illinois mine. price plus freight from mine to Chicago. The price of fluorspar (for Chicago markets) f. o. b. Colorado mines must be equal to or lower than the cost of Illinois-Kentucky spar in Chicago (the nearest large eastern market) minus the freight rate from the mine in Colorado to Chicago. This mine price for Colorado mines also holds, theoretically at least, if shipments are made to consumers in Colorado or other western States. In practice the prices received for western fluorspar depend somewhat upon competitive conditions among western mines. In normal times little western fluorspar has reached eastern markets, and there have been but few western markets. The total consumption of all grades of fluorspar in the far western States has been estimated at not more than 10,000 tons per year, most of it of fluxing grade. Western fluorspar producers must compete among themselves for this business. Little eastern fluorspar has ever been shipped to far western markets.

Imported fluorspar has also been an important factor in setting the price level for the country. Before the war low-priced imported fluorspar, chiefly from England, could be shipped profitably as far west as Pittsburgh from the port of entry. Although this fluorspar was of lower grade than the domestic product, its delivered price more or less set the price for domestic fluorspar. During the war imports were so small and demand so great that this factor was of little importance. Since the war imports have been resumed, but British costs of production, ocean freights, and railroad freight rates have increased so much that competition between imported and domestic spar has only been important close to the Atlantic seaboard. An import duty on fluorspar was first imposed by the tariff act of 1909, when a duty of $3 per long ton was put into effect. In 1913 this was reduced to $1.50 per long ton. By the tariff act of 1922 the import duty on fluorspar was increased to $5.60 per long ton. This duty has not been high enough to exclude imported spar, for it is now shipped as far west as Youngstown, Ohio. A few shipments of German fluorspar have been made by barge canal from New York. City to Buffalo. Acid-grade spar, and to a lesser extent glass and enamel grade spar, can probably be imported economically because their unit value is higher. In general, the delivered price of imported fluorspar must be somewhat lower than that of domestic

fluorspar of the same grade, due to uncertainty and irregularity of shipments and greater variation in quality.

Another factor in the price situation has been the policy of certain large consumers to encourage the development of new mines (sometimes in remote localities) by making contracts with such producers at prices higher than those for similar grades from the IllinoisKentucky district.

One factor in the price situation which was perhaps more important in the past than it is now is the practice of small producers, particularly in western Kentucky, to cut prices to make quick sales or compensate for irregular shipments. The tonnage sold under such conditions, though not large, has tended to disturb price levels. Pre-war fluorspar prices were so low that fluorspar mining in general was not profitable, partly due to destructive price cutting between large producers, partly to the low price at which imported spar could be obtained, and partly to a mistaken impression that our fluorspar deposits were practically inexhaustible.

During the war the demand became so acute that prices rose rapidly. In 1918, while some producers were making deliveries on old contracts at $5 to $10 per ton (for gravel grade), extreme prices received for gravel spar for prompt delivery reached $38 to $45 per ton. Average annual prices actually received during a period of rapid price changes do not reflect accurately the condition of the market or the price levels reached over short periods.

The table shows the average range in fluorspar prices from 1910 to 1924.

Fluorspar prices per short ton at mines or local shipping point

1

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1 Figures for 1910-1923 were compiled by the U. S. Geological Survey; for 1924 by the Bureau of Mines.

In June, 1922, the following prices per short ton prevailed in the Illinois-Kentucky district f. o. b. cars at mines or nearest railroad shipping point:

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Acid grade, ground, bulk (packages $4 per ton extra)

40.00

In October, 1922, prices were advanced to the following levels:

Gravel grade:

85 per cent CaF2 and not over 5 per cent SiO2--

85 per cent CaF2 and not over 6 per cent SiO2-

80 per cent CaF2 and not over 5 per cent SiO2--

Glass and enamel grade, ground, bulk_.

Acid grade, ground, bulk (packages $4 per ton extra).

No. 1 lump--

No. 2 lump__.

$21.50

21.00

20.00

35.00

45.00

30.00

25.00

In September, 1926, the price of gravel-grade fluorspar, f. o. b. Illinois, was $18 a ton. For the preceding year the price was $17.50 to $18.50 a ton.

INDIVIDUAL DISTRICTS AND MINES

ILLINOIS-WESTERN KENTUCKY DISTRICT

The most important fluorspar-producing region in the United States and probably in the world is the Illinois-western Kentucky district which centers about Rosiclare, on the Ohio River, in Hardin County, Ill. The largest producing mines are in Hardin County, Ill., and in Crittenden and Livingston Counties, just across the Ohio River in Kentucky. Smaller and less important deposits occur in Pope County, Ill. and in Caldwell, Christian, Lyon, and Trigg Counties, Ky.

Although the general character and geology of the Illinois and Kentucky districts are the same, the economic phases of the fluorsparmining industry differ widely. In Illinois most of the production has come from the large Rosiclare vein, chiefly from the Rosiclare and Fairview mines, and from a subsidiary vein (or veins) at the Daisy and Blue Diggings mines. In Kentucky there are only a few moderately large mines, and past production has come from numerous small workings. In Illinois the owners almost invariably work the deposits, but in the past in Kentucky the properties have been largely worked by contractors, lessees, or even sublessees. In Illinois the three largest mines and a fourth, a smaller mine, have a direct railroad connection. In Kentucky a few mines have railroad connection. For these reasons the economic phases of the two districts will be treated here separately, although it is clearly recognized that for many purposes they should be considered as a unit.

GENERAL DESCRIPTION OF DEPOSITS

The area is underlain by a series of sedimentary rocks of Mississippian age (Paleozoic). These sedimentaries, which include limestones, sandstones, and shales, have been extensively faulted by a

series of steeply dipping intersecting block faults, often practically vertical; but the strata usually remain nearly horizontal and have also been intruded by a few small dikes and sheets of basic igneous rocks (lamprophyre and mica-peridotite) which are now so greatly altered that identification is difficult. The amount of vertical displacement along the faults is exceedingly variable; in some faults practically no displacement is evident and in others displacements of as much as 1,600 feet have been observed.

With the exception of one or two beds the fluorspar deposits occur as veins in faults. Although there seems to be no relation between the extent of the vertical displacement of the faults and the amount of mineralization, the major fault zones—that is, those of the greatest longitudinal extent-have usually contained the most important commercial deposits. The fluorspar may be deposited within the faults itself (as in the Rosiclare vein) or may be found chiefly in minor faults that are subsidiary to the main fault but are parts of the main fault system (as along the Columbia and Tabb vein systems). As noted, the most favorable location for important deposits is along the parts of the faults where one or both walls are limestone or highly calcareous shales or sandstones or in the parts of the fissures which have been filled with calcite earlier.

Calcite is the mineral most commonly associated with fluorspar; it is found in important quantities in nearly all large deposits. Silica as quartz is a common associate, but usually occurs in small amounts disseminated through the ore and is often absent. In parts of some veins galena is relatively common, but in others is missing. Sphalerite is present in but few veins, but in some places (for example, in part of the Rosiclare vein at Fairview) is found in fairly large quantities. Barite is generally absent, but occurs in minor quantities in parts of a few deposits (for example, at the Green mine, near Cave in Rock, Ill.). Clay, sand, or fragments of limestone, shale, or sandstone wall rocks are usually mechanically mixed with the fluorspar as it is mined. There is iron oxide in a few mines as solid limonite (as at the Stewart mine in Hardin County, Ill.) and in iron-stained residual clay and sand.

ILLINOIS

The Illinois fluorspar district occupies an area of gently rolling country of rather low relief. Near the Ohio River, where the most important mines are located, the surface is only a little above the normal river level, and when the river is high the water inundates the ground around the shaft collars.

Although weathering has probably been extensive, erosion has removed most of the products of weathering, particularly near the

river, and the present rock has little surface cover in many places. Vein outcrops can therefore be traced rather accurately.

The most important fault, with relation to production, is the Rosiclare fault or vein. The Daisy-Blue Diggings vein has been second in importance, if the assumption that these two mines work the same vein is correct. The third most productive source of fluorspar has been the bedded or blanket deposits of the Cave in Rock district. The remaining production has come from 12 or more small mines and prospects.

ROSICLARE VEIN

To obtain an adequate idea of the relative importance in the past of the Rosiclare vein in comparison with other operations, it might be noted that to date this vein has produced over 1,000,000 tons of fluorspar from two properties only; the Daisy-Blue Diggings vein has produced nearly 300,000 tons. The largest total production from any single property in Kentucky has been probably not over 40,000 tons, and the total past production of the State, according to Mineral Resources for 1925, has been 737,008 short tons.

The Rosiclare fault has been traced for about 42 miles along the strike, and has been developed over a length of about 9,000 feet by underground workings. This vein is known to carry fluorspar as deep as 500 to 600 feet in places. The vertical displacement at Rosiclare is 200 to 250 feet. The strike varies from nearly north and south to about N. 20° E. and averages about N. 17° E. The dip varies but usually ranges from 72° west to vertical and averages about 76° west. The width of the fluorspar vein varies from a tight pinch to 25 or 30 feet, for short distances. Parts of the vein that contain less than 2 feet of fluorspar are ordinarily worked only in development openings. The lengths of the pinches through which drifts have been cut to good ore on the other side vary from a few feet to at least 350 feet. On some levels the length of the barren parts are not known. The average width of ore is difficult to estimate, but it seems evident that the width decreases with depth, and that the "ore pockets" are shorter and the barren zones longer on the lower levels. From all the evidence now available the main parts of the ore body seem to maintain their width better and extend to greater depth in the part of the vein near the main shaft of the Rosiclare Lead & Fluorspar Mining Co. than in any other place. Here ore 6 feet wide occurs north of the shaft on the 600-foot level. Southwest of this shaft the Extension shaft of the Fairview Fluorspar & Lead Co. (now Franklin Fluorspar Co.) shows that at a depth of about 400 feet the vein filling is mostly calcite with little or no fluorspar. Similarly, to the northeast, at the main shaft of the

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