STONE

(By J. M. Chelini, Montana Bureau of Mines and Geology, Butte, Mont.)

Dimension stone and crushed and broken stone are the principal products of the stone industry. Dimension stone consists of natural blocks or slabs that are cut to definite shapes or sizes (Key, 1960b, p. 794). Crushed and broken stone consists of large irregular fragments of rock usually mined or quarried and crushed or ground to smaller size (Key, 1960b, p. 804). The raw material for the stone industry includes igneous, metamorphic, and sedimentary rocks. The principal varieties of rock used for dimension stone are limestone, granite, and marble, whereas many kinds of rock are used for crushed and broken stone. Broad classifications are "traprock," which in the trade is considered to be all dark dense fine-grained igneous rocks; and "granite," which includes all the lighter colored, coarser grained igneous rocks. Gneiss, a metamorphic rock, is usually grouped with granite. Sandstone and quartzite are locally used in large amounts. Limestone, a calcareous rock that includes dolomite and marble, is used in great quantities for fluxing in smelters and in the manufacture of lime. Of the crushed stone produced, nearly 75 percent is limestone, 8 percent is traprock, 6 percent is granite; the remainder is sandstone and miscellaneous rock types.

Dimension stone for interior use must be attractive in color and texture, have reasonable strength, and resist abrasion and cleaning solutions. For exterior use where it will be subjected to weathering, it must possess, in addition, resistance to stresses set up by repeated expansion and contraction, and resistance to chemicals naturally present or introduced into the atmosphere. Tests have been devised by the Bureau of Standards to determine these properties as well as the physical properties of toughness, elasticity, and density (Kessler and others, 1940 and 1927).

Physical features of rocks that determine their usefulness as dimension stone include jointing, sedimentary layering, and secondary cleavage. These are planes of weakness that influence the size and shape of the blocks that can be quarried. If properly distributed they may facilitate quarrying; if not, they may prohibit extraction of large-sized blocks.

The principal uses of dimension stone are in exterior and interior walls, windowsills, steps, fireplaces, piers, columns, trim, wainscoting, flooring, and ornamental structures such as arches. A large market has been developed in recent years for "split stone," "strip stone," ashlar, and rubble as veneer on residences and other small buildings. Other important uses are for monuments, curbing, flagging, paving, and roofing (Currier, 1960, p. 7).

The principal uses for crushed and broken stone are for concrete aggregate, road stone, and railroad ballast; however, large quantities are used in riprap and terrazzo.

Rigid requirements by consuming industries have produced many different specifications for crushed stone; therefore, reference is made to reports of the following organizations: American Association of State Highway Officials, American Roadbuilders Association, and U.S. Department of Commerce.

In 1961 the value of dimension stone sold or used by producers in the United States was $88,093,000 ($230 million in 1999); the value of crushed and broken stone was $862,467,000 ($8.6 billion in 1999); and the value for all stone was $950,560,000 (Cotter and Jensen, 1961, p. 1139). During the same year, Montana stone production was worth $1,849,000, or only about 0.2 percent of the national total.

Numerous varieties of rock suitable for dimension stone can be found in many parts of the State, and stone has been quarried in the State for many years. However, not uncommonly a dimension-stone quarry was opened to produce stone for a specific project and then abandoned. Similarly, abandoned crushed and broken stone quarries are numerous owing to the plentiful and widespread occurrences of the raw material within the State. For economic reasons, producers move portable plants to new sites as existing markets shift.

At present, sandstone and quartzite for crushed and broken stone are being quarried by Victor Chemical Works in Beaverhead County (fig. 39, locality No. 1); by Russken Mining Co. in Deer Lodge County (No. 2); by Ideal Cement Co. in Gallatin County (No. 3); by Lyons Construction Co. in Missoula County (No. 4); by the Great Northern Railway Co. in Cascade County (No. 5) and in Flathead County (No. 6); and by the Northern Pacific Railroad in Park County (No. 7). Limestone is quarried in a number of counties in western Montana. (See chapter on Limestone.)

Sandstone and quartzite are quarried for dimension stone by Montana Stone, Inc., in two quarries near Neihart in Cascade County (Nos. 8 and 9). At these quarries a very brilliant tan to maroon, and tan and maroon banded ashlar and flagstone are produced. The quarries are in the Flathead quartzite of Cambrian age. A green picture slate is quarried by the same company in Lewis and Clark County (No. 10). The Sesco Co. is quarrying a tan and chocolate-brown banded quartzite from the Striped Peak formation of Pre-cambrian age near Thompson Falls (No. 11).

Granite for the manufacture of monuments is quarried intermittently by Trevillion-Johnson Memorials Co. from three quarries within a 5-mile radius of each other in Jefferson County (No. 12). Granite is quarried near Gardiner, Park County (No. 13), by the Livingston Marble & Granite Works. This same company quarries travertine in the same area for manufacture of rubble, ashlar, and polished building stone. (See Chapter on limestone).

Travertine is also quarried near Gardiner by the Montana Travertine Co., which produces at present only rubble for exterior and interior veneer. Montana Stone Inc. quarries travertine northwest of Lewistown for manufacture of rubble (No. 14). See also Building stone in Montana, by R.B. Berg, MBMG Bulletin 94, 1974.

SULFUR

Pyrite, iron sulfide, in Mineral Museum, Butte

(By C. E. Erdmann, U.S. Geological Survey, Great Falls, Mont., and U. M. Sahinen, Montana Bureau of Mines and Geology, Butte, Mont.)

Sulfur is a nonmetallic element that constitutes only 0.06 percent of the earth's crust, yet is found widespread in nature, both in the native form and in combination with other minerals. Chief commercial sources are from deposits of native sulfur, from hydrogen sulfide (H₂S) gas associated with natural gas and petroleum, and from metallic sulfide ores such as pyrite (FeS₂). A potential source not utilized at present are the very large and widespread sedimentary deposits of gypsum (CaSO₄·2H₂0) and anhydrite (CaSO₄).

The uses of sulfur are so widespread and important that it is often mentioned as an indicator of economic development. Largest consumer is the fertilizer industry which like the chemical, petroleum, rayon, and steel industries, uses it in the form of sulfuric acid (H₂SO₄). Large amounts are used by the paper industry for sulfite pulp, and the insecticide and rubber industries are major users of elemental sulfur. Annual consumption of sulfur in the United States in recent years has generally been in excess of 5 million long tons. US sulfur consumption in 1999 was 13.3 million metric tons.

No commercial deposits of native sulfur are known in Montana, although small occurrences have been noted in a few places. Montana has produced important quantities of sulfuric acid from metallic ores, however. Metallic sulfides are found in every mining district in the State, and as the ores from these districts are smelted, the sulfur is driven off as sulfur dioxide, which is recovered and manufactured into sulfuric acid. The Butte district provides by far the greater bulk of the ores smelted at Anaconda, Mont. Sulfuric acid produced there was formerly used at the plant in the manufacture of treble superphosphate fertilizer; but since Anaconda has ceased fertilizer manufacture, the acid is marketed as such in tank cars, and much, if not all of it, finds its way into fertilizer industry in other States.

Up until 1959 pyrite concentrate from low-grade pyritic ores from the Butte district was made at Anaconda at a rate of about 50,000 long tons of equivalent pyrite annually. Production ceased after 1959 because of no intracompany demand for sulfuric acid.

Deposits of pyritic ores outside of the Butte district have been suggested as possible sources of sulfur for sulfuric acid, but to date no investigation has proceeded to the stage of delineating any such deposits.

In Montana there are extensive deposits of gypsum and anhydrite (calcium sulfate) interbedded with Paleozoic and Mesozoic strata, and deposits of sodium sulfate occur in intermittent lakes of Chouteau County in central Montana and in Sheridan County in northeastern Montana; but these materials are valuable mineral commodities in their own right and are not utilized as sources of sulfur or sulfuric acid.

Large quantities of hydrogen sulfide gas (containing 94.1 percent sulfur) are found in natural gas from some of Montana's gas fields. Because of its highly toxic nature and unpleasant odor it must be removed before marketing the gas for domestic or industrial consumption when the concentration reaches 0.04 percent. Gas that contains more than this is known as sour gas.

Much of the petroleum and natural gas from the Paleozoic formations in the Rocky Mountain area contains hydrogen sulfide, and where present in sufficient amount it has become an important source of elemental sulfur. Concentrations are highly variable, even from place to place in the same formation or reservoir and range from traces to more than 16 percent in the Tensleep sandstone at Elk Basin oilfield in Carbon County. On the whole, in Montana they are decidedly low. Those available from the Madison (Mission Canyon) limestone in Kevin-Sunburst Dome in Toole County, for example, range from 0.069 to 3.73 percent in the Rim Rock pool. The gas associated with the Mississippian, Silurian, and Ordovician oil on Cedar Creek anticline in the southeastern part of the State is for the most part considered "sweet." Where the amount of gas is sufficient for commercial use, but the hydrogen sulfide content is low, as at the Reagan field or Pine field, the H₂S is extracted and flared to prevent the possibility of dangerous accumulations in local topographic depressions.

The problem of what concentration of hydrogen sulfide is worth recovering for sulfur therefore becomes a matter of business judgment involving mining factors, but a plant working with small percentages obviously requires very large reserves of gas. Thus, a sulfur plant in Wyoming, which operates on what is considered a minimum profit byproduct basis, extracts 9 or 10 long tons of sulfur per day from 15 million cubic feet of gas with an H₂S content of 2.5 percent, the beneficiated gas being delivered to a pipeline for commercial and domestic use. On the other hand, in some States where the H₂S concentration is sufficiently great to be processed for sulfur alone, and where no market for gas in available, the beneficiated gas may be returned to the reservoir to maintain pressure.

Production of elemental sulfur in Montana has developed some interesting discrepancies. The only plant that processes hydrogen sulfide gas originating in Montana is situated in Wyoming. This is the Pan American plant in the Elk Basin field, which handles over 16 million cubic feet of gas per day to extract some 60 or 70 long tons of sulfur daily from Tensleep sandstone gas with an H₂S content of about l6 percent and Madison limestone gas with 2 or 3 percent H₂S. Approximately 20 percent of the sulfur attributed to the Tensleep and about 8 percent of the sulfur from the Madison is considered to come from the Montana portion of the field. Conversely, the only sulfur plant in Montana is the Montana Sulphur & Chemical Co. installation at Billings which produces about 50 long tons of sulfur per day from waste gases, mainly hydrogen sulfide and carbon dioxide, received from local refineries of the Continental Oil Co. and the Humble Oil Co. The origin of the hydrogen sulfide, however, is mainly from oil imported from Wyoming.

All things considered, the outlook for improvement of production of elemental sulfur from Montana is not attractive chiefly for the following reasons: (1) Except for the northern part of the Elk Basin field, which is already contributing hydrogen-rich sulfide gas to a plant in the southern part of the field in Wyoming, the volume and H₂S content of natural gas from the State is low; (2) Montana is literally surrounded by large refineries in adjacent States that treat rich concentrations of hydrogen sulfide in large volumes of gas. Even if a new discovery of hydrogen sulfide suitable in quality and quantity were to be made in Montana its competitive position against these established plants probably would be poor. Chief among these large sulfur plants are: The Texas Gulf Sulphur Co. plant at Worland, Wyo., which produces about 85 long tons of sulfur per day; the Signal Oil & Gas Co. at Tioga, in the Williston Basin of North Dakota, which produced about 107,180 long tons of sulfur during the first 6 months of 1962; and the British American Oil Co. plant in the Pincher Creek gas condensate held in southwest Alberta, which is capable of processing 170 million cubic feet of crude natural gas per day to recover 780 long tons of sulfur.

TALC AND PYROPHYLLITE

(By P. L. Weis, U.S. Geological Survey, Spokane, Wash.)

Talc is a hydrous magnesium silicate. It is a very soft white, gray, or green micaceous mineral that occurs only in metamorphic rocks. It forms from serpentine, which in turn may be formed by the regional or contact metamorphism of magnesium-bearing rocks such as dunite, pyroxenite, and dolomite. The deposits themselves are generally closely associated with serpentine; more rarely they are enclosed by quartzite, phyllite, gneiss, or even granite.

Pyrophyllite, a hydrous aluminum silicate, resembles talc very closely in physical properties and appearances, hence is substituted for talc in some industrial applications. It also characteristically occurs in metamorphic rocks (Chidester and Worthington, 1962).

Talc has several physical properties which make it useful in industry. It is extremely soft, chemically inert, and has low thermal and electrical conductivity. Several grades are marketed but steatite, the purest of the common commercial grades, and "lava," a pure, massive, fine-grained variety extensively used in the electrical industry, are the most valuable. They are machined or preformed into intricate shapes and fired for use as insulator plates in vacuum tubes and related electronic equipment.

Talc is used extensively as a filler in rubber, paint, paper, and roofing material, in the manufacture of high-fusion ceramic products such as high-frequency insulators, and it is used in the manufacture of whiteware, glazed wall, and floor tiles, and similar products, and as a carrier for insecticides. Special uses include: white shoe polish, cosmetics, dusting powders, finishing agent for leather and nails, lubricant for gunpowder, and crayons for marking hot metal castings and ingots. Prices for best quality talc in the period 1950-60 commonly ranged from about $9 to $12 per ton for the crude material at the mine. (In 2001, the price of processed talc was $118 per ton.) Pyrophyllite is competitive with talc in most uses where color is not a factor, and prices are, therefore, about the same as for talc.

Montana has possibly the largest reserve of steatite-grade talc in the United States (Engel and Wright, 1960, p. 840). All of the known deposits are in the highly metamorphosed rocks of the Cherry Creek Group in Beaverhead and Madison Counties, and all appear to have formed from serpentenized dolomitic marble. The greatest production has come from the Smith-Dillon deposit on Axes Creek, about 11 miles southeast of Dillon (fig. 40, locality No. 1). The mineral occurs there both as thin veins and stringers, and as large masses of exceptional purity. The deposit is being worked by Tri-State Minerals Co.

Similar deposits occur about 8 miles to the northeast (Keystone mine) and about 3 miles to the south (Timber Gulch deposit). Talc, at these two deposits, contains some impurities, however, and neither is being worked at present, although both contain large reserves of talc suitable for many commercial purposes (Perry, 1948, p. 6).

Talc deposits are also worked at Johnny Gulch, about 20 miles south of Ennis, Madison County (No. 2). Considerable lava talc was produced, but known reserves of this grade appear small. Large quantifies of ceramic-grade talc remain, and limited amounts of cosmetic-grade talc are also present.

Talc occurs on Granite Creek, north of Virginia City (No. 3), and on Idaho Creek, southwest of Virginia City (No. 4), but these deposits appear to have less potential value than those described above. A deposit of good-quality talc was found in Cambrian rocks just south of Helena (No. 5), but was worked out a number of years ago.

Pyrophyllite occurs in a deposit about half a mile northeast of Argenta, 12 miles northwest of Dillon (No. 6) which appears to be of commercial quality and of sufficient size to permit exploitation, provided a suitable market can be found.

Current production figures are not available for Montana talc deposits. However, 250,000 tons, worth nearly $3.5 million, was produced during the period 1952-61. See also Talc and chlorite deposits in Montana, by R.B. Berg, MBMG Memoir 45, 1979.

THORIUM AND THE RARE EARTHS

(By P. L. Weis, U.S. Geological Survey, Spokane, Wash.)

Thorium and the rare earths are closely related in chemical properties, hence they are considered together in this report. Thorium is the only natural radioactive element other than uranium that constitutes a potential source of atomic power. Natural thorium cannot be used in nuclear reactions but it can be converted to U²³³ in a breeder reactor and then used in the same, way as uranium (0lson and Adams, 1962). Although uranium reactors are apparently simpler and cheaper to build and fuel at present, much research is being done to develop the use of thorium for atomic power in the future. Thorium is used as an alloy with magnesium, in gas mantles, refractories, polishing compounds, and chemical and medical products.

The rare-earth metals comprise fifteen elements. Lanthanum, cerium, praseodymium, neodymium, samarium, and europium are generally considered to form the cerium group. Yttrium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, lutetium, and ytterbium make up the yttrium group.

Rare-earth metals and their compounds are used for a wide variety of purposes, although none are used in large quantities (1960 consumption in the United States was equivalent to about 1,800 tons of rare-earth oxides) (US consumption in 1999 was 17,700,000 metric tons of rare-earth oxide). Cerium is used in sparking alloys, are carbons, and in the glass industry. A variety of rare-earth elements are used in the iron and steel industries. Rare-earth oxides are used as polishing agents. A variety of minor uses exist, and considerable research is in progress to investigate further uses.

Principal minerals containing important amounts of thorium are few; thorite, thorogummite, and thorianite are the most common ones. Monazite, a cerium phosphate, commonly contains thorium as well as the rare earths. The euxenite group consists of several similar minerals that contain thorium and the rare earths along with tantalum, niobium, and uranium. Bastnaesite is a rare-earth carbonate. Thorium- and rare-earth-bearing minerals, although widely distributed in igneous and metamorphic rocks, are most abundant in alkalic rocks and carbonatites, in syenites and granites, in gneisses, and in veins, especially those associated with alkalic rocks. Because these minerals are, in general, resistant to weathering, most of the world supply of thorium and rare-earth minerals is found in placer accumulations.

The Lemhi Pass area of Montana and Idaho (fig. 41, locality No. 1), near the crest of the Beaverhead Range, contains a considerable number of thorium-bearing quartz veins that cut metamorphic rocks of the Belt Series (Sharp and Cavender, in press). Some veins are more than 1,000 feet long and, in places, are as much as 35 feet thick (Armstrong, F. C., written communication, 1954). They consist of red to white quartz with barite, feldspar, thorite, specular hematite, and hydrous iron oxides, and with less widespread rare-earth minerals, and copper and iron sulfides (Anderson, 1958). Some of the veins locally contain as much as 20 percent ThO₂; average grade may be about 0.50 percent in some deposits (Sahinen and Crowley, 1959).

Thorium reserves in the Lemhi Pass area are estimated to be about 100,000 tons of ThO₂ in ore of probable commercial grade at current prices ($1.75 to $2.25 per pound of ThO₂ in 20 to 30 percent thorium concentrates) (Baker and Tucker, 1962). (In 2001, the price of thorium oxide was $82-$107 per kilogram, depending on purity.)

Upper Cretaceous sandstones (Virgelle and Horsethief sandstones, St. Mary River formation) (Nos. 2, 3, and 4) in Glacier, Pondera, and Lewis and Clark Counties contain fossil black-sand placer concentrations (Stebinger, 1914) that are a potential source of monazite (Armstrong, 1957; Murphy and Houston, 1955), as well as zircon, ilmenite, and magnetite, and may constitute a worthwhile source of thorium and rare-earth elements.

Deposits of uncertain origin containing monazite, rare earths, and relatively small amounts of thorium, together with columbite and rutile, are known in southern Ravalli County (No. 5). The deposits are in a group of schists, gneisses, amphibolites and carbonate rocks that extend from the headwaters of the West Fork of Bitterroot River, south into Idaho (Abbott, 1954; Sahinen, 1957; Anderson, 1958; Crowley, 1960). They may constitute a resource with considerable potential for the future, although their grade and location do not appear to be favorable for immediate exploitation.

Carbonatite veins in the Bearpaw Mountains on the Rocky Boy Indian Reservation, Hill and Chouteau Counties, contain as much as 3.5 percent rare earths (Pecora, 1956, p. 1546) (No. 6). This is much less than the amount present in Mountain Pass carbonatite in California; nevertheless, the Bearpaw deposits may be a potential source of rare earths at some future date.

Other occurrences of thorium minerals in Montana are shown on the accompanying map (fig. 41). Most are in placers or associated with pegmatites. Their potential is unknown, but it appears likely that the principal reserves are in the four areas listed above. Thorium-bearing placer deposits of unknown potential are also known near Victor, Ravalli County (No. 7).

Although some of the deposits of thorium and rare earths have been known for a number of years, only a very small amount has been produced in Montana. Recent developments make it appear likely that this situation may change in the future. Much depends on the advances in technology that may come about as a result of current and projected research. Market conditions do not favor increased production at present, but the demand for thorium as a source of atomic energy, and of rare earths for a number of developing uses, may increase considerably in the not-too-distant future. At that time, some of the Montana deposits may well prove to be highly important.

TITANIUM

(By P. L. Weis, U.S. Geological Survey, Spokane, Wash.)

Titanium is a light, lustrous, white metal. It is stronger for its weight than most metals, and is both strong and markedly corrosion resistant at temperatures up to 1,000º F. It is therefore used in airframes, jet engines, in a variety of apparatus exposed to salt water, and in heat exchangers, reactors, pumps, valves, and other equipment used in the chemical industry. Titanium is alloyed with other metals to increase corrosion resistance. Titanium metal is difficult and expensive to produce, and did not become available in usable amounts until 1948 (Lynd, 1960, p. 851). High cost is still one of the chief obstacles to its widespread use.

The chief use of titanium is in the form of titanium oxide, a brilliant white material with very high refractive index and great light-scattering ability. It is therefore without peer as a white pigment in paints, paper, rubber, and a wide variety of other materials, but the oxide is also used extensively for welding rod coatings. Titanium dioxide pigment production was a $3-billion-a-year industry in the U.S. in 1999. Titanium nitride, boride, and carbide are used in cutting tools, abrasive stones, and dies.

Titanium is a constituent of a large number of minerals, but only two are now, or are likely to become, ores. Ilmenite, iron titanium oxide, is the chief ore mineral. It occurs in large massive deposits associated with anorthosite and pyroxenite in several places in the world, and is also recovered from placer concentrations in beach sands. Rutile (TiO₂) is a widespread accessory mineral in igneous rooks but, with or without associated ilmenite, it forms minable concentrations in some ore bodies that are also typically associated with anorthosite. Like ilmenite, rutile occurs in beach sands in some places.

No commercial deposits of titanium minerals are known in Montana. Fossil beach sands containing ilmenite are present in the Virgelle, St. Mary River, and Horsethief formations of Cretaceous age in Glacier, Pondera, and Lewis and Clark Counties (Murphy and Houston, 1955), but reserves and grade have not been established. Although they may contain enough titanium to be a potential source in the future, they are too low grade and too far from existing markets to be of commercial value at present. (See fig. 41, thorium and rare earths in Montana, for the location of these deposits.)

TUNGSTEN

(By A. E. Weissenborn, U.S. Geological Survey, Spokane, Wash.)

Tungsten is a white metal which is ductile when pure and which has superior mechanical properties at high temperatures. Its melting point of 3,410º C. is higher than that of any other metal. Its uses are based chiefly on the extreme hardness and wear resistance of tungsten alloys and carbides; on the ability of tungsten alloys to retain hardness at elevated temperatures; and on the high melting point, low vapor pressure, or favorable electrical and thermionic properties of pure tungsten (Holliday, 1960, p. 903). Because of these characteristics, tungsten is used extensively in the machine-tool industry and is a metal of high strategic value.

---

Table 8. Mine production of tungsten in Montana, 1950-62
(in Short-ton-units of WO₃;
1 short ton unit= 20 pounds WO₃)

1950	none
1951	60
1952	none
1953	840
1954	40,680
1955	72,660
1956	73,800
1957	39,600
1958	(1)
1959	none
1960	(2)
1961	(2)
1952	none
	(1) production from Brown's Lake and Red Button Mines; (2) production from Red Button Mine

The United States has been considered deficient in tungsten resources, and except for the period 1953-65, consumption has exceeded domestic production. However, a large domestic productive capacity was demonstrated between 1950-56 under the influence of the price incentive of the Government stockpiling program. In the peak year of 1956, domestic production was nearly four times the average annual production achieved from 1946 through 1950, the 5 years immediately preceding the start of the program.

In the United States tungsten occurs principally in quartz veins that contain scheelite (calcium tungstate, which forms an isomorphous series with powellite, the calcium molybdate), minerals of the wolframite group (iron and manganese tungstates) or both, and in contact metamorphic deposits. Most of the tungsten deposits of the Western United States, including Montana, are related spatially to intrusive bodies of Cretaceous or early Tertiary age (Lemmon and Tweto, 1962, p. 1).

Tungsten has been produced in Montana from numerous lode deposits and from some alluvial deposits, in part in conjunction with the mining of gold (fig. 42), but until 1954 Montana's tungsten output was insignificant. The entire production from 1900 to 1951 amounted only to the equivalent of 33,760 short ton units of WO₃, or about 0.40 cent of the domestic production of 10,216,720 short ton units (U.S. Bureau of Mines Minerals Yearbook, 1954, p. 1289). Previous to 1954 maximum shipments in any one year were in 1946 and these amounted only to the equivalent of 5,040 short ton units of WO3, most of which was produced from the Henderson Gulch gold-tungsten placers. In 1952, under the influence of the Government buying program and Government aid to exploration available through the Defense Minerals Exploration Administration, there was a great increase in the exploration of Montana tungsten deposits. Montana production reached an all time high of 73,800 short ton units (table 8) and Montana became the fourth largest tungsten-producing State. Production dropped rapidly at the termination of the Government domestic stockpiling program in December 1956, and at the end of 1958 no tungsten mines were operating in Montana. The Red Button mine was reopened in late 1959 but was closed again in December 1961. In 1962 there were no tungsten mines operating in Montana.

Tungsten deposits are found in Beaverhead Counts along the eastern edge of a quartz monzonite pluton that forms the backbone of the Pioneer Mountains (Myers, 1952, pp. 16-17). In the Brown's Lake-Lost Creek area most of the tungsten deposits that from present knowledge give promise of commercial grades and tonnage lie in contact-metamorphosed carbonate rocks of the Amsden formation of Pennsylvanian age along the eastern edge of the main quartz monzonite mass, although older limestones have been mineralized in places south of Birch Creek. Five known areas of contact-metamorphosed Amsden formation are recognized between Birch Creek and Brown's Lake.

The chief producer has been the Brown's Lake or Ivanhoe deposit on Rock Creek about 6 miles northwest of Glen (fig. 42, locality 20). Up to the time it was closed in 1957 the mine produced 625,107 tons of ore averaging 0.35 percent WO₃ and during the brief span of its operation it ranked high among domestic producers (Pattee, 1960, p. 6). The deposit has long been known and a few hundred pounds of concentrates had been shipped, but previous to 1951 the low grade of the tactite and the high molybdenum content of the scheelite discouraged development.

The tungsten is found chiefly as fine-grained high-powellite scheelite in tactite near the base of the Amsden formation. The scheelite occurs mostly as tiny crystals sprinkled through interstitial quartz and the outer shells of garnet crystals (Myers, 1952, p. 39). Concentrates prepared at the Glen mill were shipped to Salt Lake City for refining. The successful operation of the property was due in large part to the development of a method of metallurgical treatment by which a high recovery was made from a low-grade ore (Mining World, 1955).

The Lost Creek deposits (No. 21) are about 3 miles southeast of the Brown's Lake mine and are in a similar geologic environment. The deposits were explored intensively in 1952 and 1953. Production from 1952 to August 1956 totaled 21,150 short tons of ore averaging 0.18 percent WO₃ (Pattee, 1960, p. 12), the grade of the ore produced being considerably lower than that from the Brown's Lake mine. The ore was treated at the Glen mill.

The Red Button, or Calvert, mine (No. 19) is reported to have been discovered in 1956 and was operated in 1957 and 1959-60. In 1960 the grade of the ore shipped was 1.13 percent WO₃ (U.S. Bureau of Mines Minerals Yearbook 1960, 1961 v. 3, p. 610). The ore occurs in recrystallized limestone of probable Precambrian age near the contact with a quartz monzonite intrusive. Other tungsten occurrences are known in this area, and some exploration has been done on the Fool Hen prospect about 2 miles to the southeast.

Numerous other tungsten occurrences in Beaverhead County are known in the Utopia or Birch Creek district (No. 22) south of the Lost Creek deposit and in the Bald Mountain district (No. 22a) still farther south. All are along the edge of the intrusive. Many of these are described by Pattee (1960).

In Deer Lodge and Granite Counties, tungsten occurs in quartz veins near granitic intrusives in the Flint Creek and Anaconda ranges (Walker, 1960). Some contact deposits also occur. Many of these vein deposits were explored during the 1950's with the assistance of Defense Minerals Exploration Administration contracts.

Tungsten occurrences are numerous in the Black Pine-Henderson districts, north of Philipsburg. The chief production has come from a placer in Henderson Gulch (No. 7) where scheelite was identified in the black sand concentrate in 1933. According to Walker (1960, p 17), from 1942-49 dredging yielded $940,000 in gold and scheelite; a total of 142 tons of scheelite concentrate containing 63 percent WO₃, was produced. The average gold content was 15.5 cents per cubic yard; the average tungsten recovery was 0.06 pound WO₃ per cubic yard. In the vicinity of Henderson Gulch, sediments of the Pre-cambrian Newland Formation have been intensely metamorphosed by a granodiorite intrusive. Scheelite from the granodiorite and the contact zone is the probable source of most of the scheelite in the placer. Eluvial material on the adjacent hill slope also contains small amounts of scheelite (Walker, 1960, pp. 17-20).

The Combination (Black Pine) mine (No. 6) is in the eastern part of the John Long Mountains about 3.5 miles southwest of the Henderson Gulch placer. During its main period of production from 1882 to 1897 it produced a notable amount of silver from quartz-tetrahedrite veins with other sulfides (Emmons and Calkins, 1913, pp. 252-253). The principal ore-bearing structure of the mine is the Combination vein, one of four known parallel veins. The veins are enclosed in quartzite of the Precambrian Spokane Formation, and conform generally to the bedding. Huebnerite is a minor constituent of the ore and occurs as disseminated grains and in irregular concentrations which form narrow tungsten-rich bands or lenses of limited extent. In 1947 and 1948 the U.S. Bureau of Mines explored the property (Volin and others, 1952). Further exploration was done in 1952 and 1953 with the aid of a Defense Minerals Exploration contract. Only a small amount of tungsten ore was produced.

Other occurrences of tungsten in the district are the Bear and Float prospect and the Double Eagle prospect, both of which adjoin the Combination property, and the Franz prospect about 6 miles northwest (No. 5). All are similar to the occurrence at the Combination mine, as is the Sunrise vein on Sunrise Mountain, north of Henderson Gulch. At the Argo mine in the Harvey Creek district (No. 4), T. 10 N., R. 16 W., to the north, tungsten occurs in a gold quartz bedding vein in the Belt series.

Tungsten minerals have been noted at a number of prospects in the Philipsburg area (Walker, 1960, pp. 20-25) but there is no recorded production of tungsten from any of these properties.

At least 17 tungsten occurrences are known in two closely spaced areas about 14 miles west of the city of Anaconda (Nos. 17 and 18). The tungsten is found in quartz veins or replacements in Paleozoic limy sedimentary rocks intruded by several small granodiorite outliers of the Philipsburg batholith. A large granodiorite stock lies about a mile north of Silver Lake (Walker, 1960, p. 28). The Trigger mine has produced about 1,000 tons of ore, averaging 1 percent WO₃ (Walker, 1960, p. 29, table 3) from replacement deposits in the Jefferson Formation. Smaller production has come from the H. L. M. and Storm Lake or Tarlach properties. The latter was explored in 1953 and 1954 by the Sunshine Mining Co.

Another tungsten area is in the Foster Creek district (No. 16) on the east slope of the Flint Creek range, approximately 8 miles west of Anaconda and 5 miles northeast of Silver Lake, where at least 15 occurrences of tungsten are known. The Tip Top, Day, and Smith prospects have shipped small amounts of tungsten ore, but none has made any substantial production. Tungsten occurs in veins and shear zones and in tactite bodies. Tungsten grade of some of the surface showings is good but exploration has failed to find extensions of the ore in depth (Walker, 1960, pp. 44-52).

In the Marysville district of Lewis and Clark County (No. 9), veins mined chiefly for their gold content are found in and around a granodiorite stock about 3 square miles in extent. The stock intrudes the Helena limestone and the overlying Empire shale, and is surrounded by a contact aureole half a mile to a mile wide. Although the district produced much gold, there has been little activity in recent years. Scheelite was recognized in 1941 in placer concentrate from gold dredging in Piegan Gulch. Subsequently, scheelite-bearing tactite bodies were found in six or seven localities in the contact aureole (Knopf, Adolph, written communication, 1942). One of these localities, a tactite body on the Prentice property adjoining the Drumlummon mine, was explored in 1953 and 1954 by Ottawa Tungsten Co.

In Colorado Gulch (No. 10), 9 miles west of Helena, scheelite-bearing garnetiferous tactite masses are found on both sides of the gulch. The area is along the northern border of the Boulder batholith where the intrusive rocks are in contact with Three Forks formation and the Madison limestone (Knopf, Adolph, written communication, 1942).

In Lincoln County, scheelite has been reported (Lemmon and Tweto, 1962, p. 12) in a lead-zinc vein on Callahan Creek, about 8 miles west of Troy (No. 1). At this locality, veins with sphalerite and galena in a silicate gangue are enclosed in argillitic and quartzitic sediments of the Prichard and Burke formations (Calkins and MacDonald, 1909, pp. 99-102).

Gibson (1948, p. 87) mentions scheelite as a constituent of a, quartz vein with galena and tetrahedrite at the Midas mine near Howard Lake, 21 miles south of Libby (No. 2). The country rock consists of calcareous shales of the Wallace formation.

Lemmon and Tweto (1962, p. 12) list an occurrence of scheelite in quartz streaks in a sheer zone at the Waylett prospect on Miller Creek (No. 3) a short distance southeast of the Midas mine.

Numerous quartz-tungsten veins are known in the Potosi district, Madison County (No. 23), in extremely rugged country southwest of the town of Pony. These are associated with aplitic or alaskitic phases of the Tobacco Root batholith and are entirely within the batholithic rocks. These have been described by Hart (Tansley and others, 1933, p. 32) as follows:

"The tungsten mineral huebnerite occurs as seams in wide, massive, white quartz veins or dikes of pegmatitic character. Along the hanging wall, fluorite filling may be noted. The huebnerite occurrences, although of great extent, vary greatly in intensity and only lenslike zones constitute possible ore reserves, but it is apparent that under favorable market conditions the veins would warrant further exploration."

In the Jardine-Crevasse Mountain district, Park County (No. 25) -- also known as the Sheepeater district--scheelite occurs with gold and arsenic, and was recovered for many years as a byproduct of gold mining. It is interesting to note that the Jardine mine is one of the earlier commercial sources of tungsten to be discovered in the United States. Total production of scheelite through 1942, all of which came from the Jardine mine, is estimated at about 400 tons of concentrate with an estimated value of $305,000 (Seager, 1944, p. 1). In addition to gold, silver, and tungsten, the mine produced minor amounts of lead and copper, and a considerable quantity of arsenic, it being one of the few mines in the country where arsenic was a valuable byproduct. The mine continued in operation until 1948, when a fire destroyed the cyanide plant. Production during the period 1942-48 was probably about 15 short tons of 60 percent WO3.

The gold-tungsten-arsenic deposits of the Jardine-Crevasse Mountain district are found as replacement veins in Precambrian metamorphic rocks. Two types of veins are recognized: (1) quartz veins in quartz-biotite schist and biotite quartzite; and (2) arsenopyrite veins in quartz-cummingtonite schist. The veins of the first type contain more tungsten and less gold than those of the second (Seager, 1944, p. 45).

In Powell County, several scheelite contact-metamorphic deposits have been found in the Ophir district (No. 8) 20 miles west of Helena on Snowshoe, Ward, Carpenter, and Ophir Creeks. Scheelite occurs scattered through garnetiferous tactite masses in the Madison Limestone. A small shipment of tungsten is reported to have been made from the Arnold and Ladysmith properties on Snowshoe Gulch in 1943 (Hobbs, S. W., written communication, 1944).

In the Ogden Mountain mining district (No. 8a) east of Helmville, gold-quartz veins with scheelite are found in rocks of the Belt series surrounding a quartz monzonite stock and also in the quartz monzonite stock itself. Scheelite is also said to occur in placer gravels. Some exploration was done in 1952 and 1953 on the New Progress and Old Timer claims, but there is no record of tungsten ore having been shipped from the area.

Huebnerite has been recognized (Weed, 1912, pp. 81-85) in some of the veins at Butte, Silver Bow County (No. 15), but has not been recovered commercially from the ore.

The presence of huebnerite in a quartz-silver shoot on the Birdie vein has long been known, and some tungsten ore is said to have been shipped in 1916. The mine is on the western slope of the Continental Divide, about 4 miles east of Butte, and is in granitic rocks of the Boulder batholith. The property was reopened and explored for tungsten by the West Slope Mining Co. during the period 1952-55. Sahinen (personal communication) also reports a scheelite-powellite occurrence in tactite along a limestone-quartz monzonite contact in the Highland district, 15 miles south of Butte.

Other localities where tungsten has been reported are in Broadwater County at the Diamond Hill mine (No. 13), near Kendall in Fergus County (No. 12), in the Woodville district in Jefferson County (No. 14), in the emigrant district in Park County (No. 24) and in tactite, near the Yogo Peak deposits in Judith Basin County (No. 11). Little is known about most of these occurrences.

The future outlook for tungsten mining in Montana depends on demand and economic factors. No tungsten mines are operating in Montana at the present time. Previous to 1953, Montana's small tungsten output came from mining of quartz veins usually with gold, silver, or other metals and as a by product from placer gold mining. With some possible exceptions, the tungsten-rich veins tend to be narrow and the ore shoots scattered, spotty, and marginal in grade. Some of them probably could be mined successfully during periods of high tungsten prices, and should gold prices increase, some tungsten might be recovered as a byproduct from lode gold or placer gold mining. The total amount of tungsten that could be recovered from these sources, even with abnormally high tungsten prices, would, however, be small.

The tactite deposits typified by the Brown's Lake or Red Button deposits are in a very different category. They can produce large tonnages of ore and probably can operate successfully at an appreciably lower price level than most of the vein mines. Experience during the Government tungsten program has shown that, given sufficient price incentive, the United States is not deficient in tungsten resources, but possesses a very substantial domestic productive capacity. Remaining known reserves of the Montana tactite deposits are probably insufficient for sustained large-scale production, but well-planned exploration might bring in new ore reserves. Not all of the numerous tactite bodies in Montana contain tungsten ore bodies, but prospecting of tactite bodies in carbonate sediments near their contacts with the younger granitic intrusive rocks might discover ore bodies similar to those at the Brown's Lake and Red Button mines.

These probably could not be worked profitably at present price levels of tungsten but the better ones might be able to produce, at price levels less than the $65 per unit price, which was current during the tungsten-buying program of the 1950's. The Montana tactite deposits thus are an important potential source of tungsten. (In 2001, the price of tungsten was $64 per metric ton unit (mtu) WO₃, with 7.93 kg tungsten per mtu.)

URANIUM

(By A. E. Weissenborn and P. L. Weis, U.S. Geological Survey, Spokane, Wash.)

Uranium is a mixture of the isotopes U²³⁸, U²³⁵, and U²³⁴. U²³⁸ can be converted to plutonium, which, along with U²³⁵, can be used in nuclear reactions. Atomic power and nuclear weapons are, therefore, the chief uses for uranium; minor amounts are used in the chemical, ceramics, and electrical industries.

Uranium is widely scattered in many types of rocks. The principal domestic sources of uranium are deposits in terrestrial sedimentary rocks. The largest and most numerous of these deposits are in sandstones and conglomerates in which uranium minerals occur as pore fillings and impregnations. Less important uranium deposits are found in lacustrine limestones. Coals and coaly sediments interbedded with clastic terrestrial sediments commonly contain minor concentrations of uranium; in a few localities the coals beds may contain up to several percent uranium and some deposits have been mined. Uranium is widespread in small concentrations in certain marine black shales and phosphorites such as the Permian Phosphoria Formation which underlies large areas of Idaho, Utah, Wyoming, and southwestern Montana (Schnable, 1955; Butler and others, 1962). Uranium is also found in many areas in veins, commonly of Tertiary age. Uranium is relatively soluble, and ground water solutions commonly transport and redeposit small quantities to places where its radioactivity is readily noticed. As a result, large numbers of small "radioactive occurrences" of little value are known.

Montana has not been an important producer of uranium. Numerous occurrences are known, however, and some deposits appear to have significant economic potential. (See fig. 43.) Production data for Montana is as follows:

Because of security restrictions which were in effect at the time, production data from 1949 to 1952 are not available.

Explanation: Green circles=peneconcordant with sedimentary features of the enclosing rocks; solid=1,000 to 1,000,000 tons of ore; large open circle= 1 to 1,000 tons; small circle=occurrences. Red squares=veins, breccia zones, stock-works, and related types. Sizes as for green symbols. For detailed distribution of Phosphoria, see Fig. 30. "Ore" means production plus reserves, containing at least 0.1% U3O8. Occurrences include less than 1 ton, recognizable uranium minerals, or at least 0.01% U3O8.

The first discovery of uraniferous vein deposits in Montana was made in 1949 on the W. Wilson and adjacent claims near Clancy (Roberts and Gude, 1953a) and at the Free Enterprise mine near Boulder (Roberts and Gude, 1953b) in the northern part of the Boulder batholith. Subsequently more than 100 radioactivity anomalies were detected (Becraft, 1956, p. 117), all but 2 of which are in quartz monzonite, granodiorite, or related rocks of the Boulder batholith. In this area uranium is associated with chalcedony veins and vein zones which locally contain a Little silver (Knopf, 1913 p. 103). Examples are the W. Wilson vein in the Clancy area and Free Enterprise vein near Boulder. A similar occurrence is at the Red Rock mine, one of the examples of uraniferous veins in prebatholithic volcanic rocks (Becraft, 1956, p. 120).

In the same area uranium also is associated with lead-silver veins and with minor amounts of zinc and copper as at the Comet and Gray Eagle mines or with mixed-type veins intermediate between the chalcedony and the lead-silver veins as at the Lone Eagle mine (Becraft, 1956, pp. 120 and 121). In all cases the uranium is believed to have been emplaced in a late stage of mineralization.

Uranium ore has been produced from only a very few of the numerous radioactive veins. A few tons of high-grade ore and about 150 tons of low-grade ore were produced from the Free Enterprise mine (Roberts and Gude, 1953b, p. 147) and several hundred tons of moderate-grade ore were mined from the W. Wilson mine (Becraft, 1956, p. 120). A small tonnage was produced from the Lone Eagle mine and a few tons have been obtained from other properties. No mines in the area are currently producing uranium ore.

Secondary uranium minerals are found coating small joints and fractures in Belt series quartzites near Saltese, Mineral County, but no production is known (Weis and others, 1958, p. 21).

Uraniferous veins or shear zones have been reported from Mineral, Ravalli, Beaverhead, and several other counties in western Montana (Butler and others 1962).

In the Pryor Mountains in Carbon County, tyuyamunite (Ca(UO₂)₂(V0₄)₂5-8.5 H₂O) occurs in soft clayey material and silicified breccia that fills caves and solution cavities in the Madison limestone (Jarrard, 1957, p. 36). The largest productive mines of the Pryor Mountains are in Wyoming, but a number of deposits have been found in Montana. Although the individual ore bodies are small, the grade of the ore is relatively high and most of the Montana production of uranium has been from the Pryor Mountains.

Uranium-bearing lignite deposits underlie an area of approximately 13,000 square miles in North and South Dakota and adjacent parts of eastern Montana, near the eastern edge of the Great Plains physiographic province (Densen and Gill, 1956, pp. 413-418; Gill, 1959, pp. 167-179). The mineralized lignite beds occur throughout 2,000 feet of fluviatile deposits of Paleocene and late Cretaceous age. Overlapping the lignite-bearing sequence with marked regional uniformity are 250 feet or more of mildly radioactive tuffs and bentonitic clays of Oligocene and Miocene age. The uranium-bearing lignite beds underlie the more prominent buttes. Field evidence suggests that uranium was leached from the tuffs and concentrated in the underlying lignite. Megascopically identifiable uranium minerals are rare. Where they occur they coat or fill thin joints and fractures in the lignite and associated rocks. According to Densen and Gill (1956 pp. 4, 18) incomplete data indicate that deposits of radioactive lignite in eastern Montana and adjacent parts of North and South Dakota aggregate about 90 million tons. The beds average about 4 feet in thickness, and contain about 0.008 percent uranium. The uranium content of ash from the lignite ranges from 0.05 to 0.1 percent. The lignite beds are therefore a significant potential source of uranium particularly if uranium can be extracted from ash of lignite used industrially. The discovery of lignite containing as much as 5 percent uranium in the Cave Hills area of South Dakota suggests that other high-grade deposits of considerable size might be discovered.

Becraft (1958) has described uraniferous shale and lignite beds in the Townsend and Helena Valleys in Lewis and Clark, Broadwater, and Jefferson Counties. The uranium-bearing beds are in the lower part of a Tertiary sedimentary unit that consists largely of thin-bedded tuffs locally altered to bentonite. The uranium presumably was leached from the tuffs by meteoric water and concentrated in the carbonaceous shale and lignite. None of the uranium occurrences appear to be commercial, but they suggest that similar Tertiary sedimentary rocks which are present in many of the major valleys and intermontane basins in western Montana may be worth prospecting for uranium, particularly if they include light-colored, fine-grained tuff, bentonite, and coaly or carbonaceous beds.

Uranium is present in small amounts in all the bedded phosphorite deposits of southwest Montana (Swanson, 1960). The phosphorite occurs as part of the two phosphatic shale members of the Phosphoria formation of Permian age (McKelvey and others, 1959). Estimates by Swanson (1960, and oral communication) indicate that in the area south of Butte 35,000 short tons of uranium is present in rock 3 feet or more thick containing 31 percent P₂O₅ (acid-grade rock), with an average uranium content of 0.0090 percent. In rock of that thickness containing 24 percent P₂0₅ there are more than 400,000 tons of uranium, with an average content of 0.0066 percent. Estimates for the area farther north, which includes the deposits being mined near Garrison and Maxville, are not yet available. These figures reflect the total estimated phosphorite reserve, not just that part now accessible to mining. Uranium is recovered from some of the phosphorite mined in Florida, which is of comparable grade, but has not been recovered from any mined in the western field.

Although additional uranium discoveries very possibly could be made in veins and in deposits similar to those in the Pryor Mountains, production from these sources cannot be expected to be large. If the need were great enough, very large quantities of uranium could be recovered from the uraniferous lignite deposits of eastern Montana and from the phosphorite deposits of western Montana. Montana therefore is an important potential source for the future production of uranium.

VERMICULITE

(By P. L. Weis, U.S. Geological Survey, Spokane, Wash.)

Vermiculite is a hydrated magnesium-aluminum silicate mineral that expands greatly when heated. It occurs in nature as a platy brownish to greenish mineral with micaceous cleavage, and resembles biotite in appearance. When heated to about 1,500° F., vermiculite expands from 10 to as much as 30 times its original volume. Natural vermiculite is soft, and deposits have often been recognized by the presence of mica-like flakes in a slippery soil that forms over the bedrock.

Minable bodies of vermiculite are generally found in intrusive bodies of pyroxenite, or less commonly with pyroxenite layers in metamorphic rocks. Commercial deposits require ore that contains a large proportion of vermiculite (30 to 50 percent or more), and the vermiculite must be sufficiently expandable so that the final product weighs from 4 to 10 pounds per cubic foot.

Expanded vermiculite is a good thermal insulator at temperatures ranging from subzero to 2,000°F; it is lightweight, fireproof, granular, and free flowing; it is inert and will not decompose or decay; it is sterile and harmless to handle; it has the properties of a mineral sponge and will absorb large amounts of liquids and still remain free-flowing (Myers, 1960, p. 894). These properties result in its extensive use as loose grains as an insulator, or mixed with portland cement, clay, or plaster for lightweight aggregate, fireproof insulation, refractory blocks, and related products. It is used as a mineral filler, as a carrier for insecticides, fertilizers, and pesticides, as a culture medium for starting seeds and cuttings, and as a soil conditioner, in addition to a great many miscellaneous uses. The domestic industry produces about 200,000 tons of vermiculite annually.

Montana has large reserves of vermiculite. The large deposit controlled by the Zonolite Co. near Libby, Lincoln County, which began operation shortly after World War I, was the first deposit exploited in the United States (fig. 44, No. 1).

The Libby deposit consists of masses of vermiculite formed by hydrothermal alteration in a large body of pyroxenite (Pardee and Larsen, 1929, pp. 22, 24). The deposit is cut by dikes of syenite, and it contains masses of hydrobiotite, biotite, and amphibole. The ore body is one of the largest ever worked; production ranged from a few hundred tons a year in the early 1920's to 20,000 tons in 1940 and to 75,000 tons in 1946. Present production is considerably greater. Reserves of ore-grade material are extensive.

Vermiculite deposits of a similar type are known near Hamilton, Ravalli County (No. 2) (Perry, 1948, p. 28), where the material also occurs in pyroxenite associated with syenite and pegmatite dikes. The vermiculite may be of commercial quality, but the amount of reserves is not known.

The vermiculite deposits near Boxelder on the Rocky Boy Indian Reservation, Hill County (No. 3), are also associated with syenite and pegmatite. The Bearpaw Mountains, in which the deposits occur, are largely made up of an unusual potassium-rich group of igneous rocks. The deposits themselves appear to be limited in size, but commercial-quality material is believed to be present.

Vermiculite also occurs in metamorphic rocks of the Precambrian Pony series (Perry, 1948, p. 32). Such deposits that have been investigated include those near Pony (No. 4), Virginia City (No. 5), and Ennis (No. 6), Madison County and near Dillon (No. 7), Beaverhead County. The vermiculite at these places is found in schistose bands and layers. Although the vermiculite is generally fine grained, some commercial-quality material exists at these deposits, and reserves may be large.

METALLIC AND INDUSTRIAL MINERAL RESOURCES

SELECTED REFERENCES

Abbott, A. T., 1954, Monazite deposits in calcareous rocks, northern Lemhi County, Idaho: Idaho Bur. Mines and Geology Pamph. 99, 27 p.

Altschuler, Z.S., Clarke, R.S., Jr., and Young, E.J., 1958, Geochemistry of uranium in apatite and phosphorite: U.S. Geol. Survey Prof. Paper 314-D, p. 45-90.

Am. Assoc. of State Highway Officials, 1955, Standard specifications for highway materials and methods of sampling and testing, pt. 1: Washington, D.C., 257 p. Am. Roadbuilders Assoc., 1957, The highway construction industry in a long-range national highway program: 16 p.

Anderson, A. L., 1958, Uranium, thorium, columbium, and rare earth deposits in the Salmon region, Lemhi County, Idaho: Idaho Bur. Mines and Geology Pamph. 115, 81 p.

Anderson, S.B., 1959, Study reveals Mississippian series possibilities: North Dakota Geol. Survey Rept. Inv. No. 31.

Anderson, S. B., and Hansen, D. E., 1957, Halite deposits in North Dakota: North Dakota Geol. Survey Rept. Inv. No. 28.

Andrichuck, J. M., 1955, Mississippian-Madison Group stratigraphy and sedimentation in Wyoming and southern Montana: Am. Assoc. Petroleum Geologists Bull. v. 39, no. 11, p. 2170-2210.

Armstrong, F. C., 1957, Eastern and central Montana as a possible source of uranium: Econ. Geology, v. 52, no. 3, p. 211-224.

Armstrong, F. C., and Full, R. P., 1950, Geologic maps of Crystal Graphite mine, Beaverhead County, Montana: U.S. Geol. Survey open-file maps.

Baillie, A. D., 1955, Devonian System of Williston Basin: Am. Assoc. Petroleum Geologists Bull., v. 39, no. 5, p. 575-629.

Baker, D. H., Jr., Greenspoon, G. N., and Washington, W. F., 1962, Copper:

U.S. Bur. Mines Minerals Yearbook 1961, v. 1, p. 495-534.

Baker, D. H., Jr., and Tucker, E. M., 1962, Thorium: U.S. Bur. Mines Minerals Yearbook 1961, v. 1, p. 1209-1214.

Banning, L. H., and Rasmussen, R. T. C., 1951, Processes for recovering vanadium from western phosphates: U.S. Bur. Mines Rapt. Inv. 4822, 44 p.

Barrell, Joseph, 1907, Geology of the Marysville mining district, Montana, A study of igneous intrusion and contact metamorphism: U.S. Geol. Survey Prof. Paper 57, 178 p.

Bateman, A. M., 1950, Economic mineral deposits, 2d ed.: New York, John Wiley & Sons, Inc., 916 p.

Becraft, G. E., 1956, Uranium deposits of the Boulder batholith, Montana: U.S. Geol. Survey Prof. Paper 300, p. 117-121.

Becraft, G. E., 1958, Uranium in carbonaceous rocks in the Townsend and Helena Valleys, Montana: U.S. Geol. Survey Bull. 1046-G, p. 149-164.

Binyon, E. 0., 1952, North Dakota sodium sulfate deposits: U.S. Bur. Mines Rept. Inv. 4880, 41 p.

Blixt, J. E., 1933, Geology and gold deposits of the North Moccasin Mountains Fergus County, Montana: Montana Bur. Mines and Geology Mem. 8, 25.

Brobst, D. A., 1958, Barite resources of the United States: U.S. Geol. Survey Bull. 1072-B, p. 67-130.

Brobst, D. A., 1960, Barite, in Industrial minerals and rocks, 3d ed.: Am. Inst.

Mining Metall. Petroleum Engineers, p. 55-64.

Butler, A. P., Jr., Finch, W. I., and Twenhofel, W. S., 1962, Epigenetic uranium in the United States: U.S. Geol. Survey Mineral Inv. Resources Map MR-21.

Calkins, F. C., and MacDonald, D. F., 1909, A geological reconnaissance in northern Idaho and northwestern Montana: U.S. Geol. Survey Bull. 384, 112 p.

Calvert, W. R., 1909, Geology of the Lewistown coal field, Montana: U.S. Geol. Survey Bull. 390, 83 p.

Cameron, E. N., and Weis, P. L., 1960, Strategic graphite--a survey: U.S. Geol. Survey Bull. 1082-E, p. 201-321.

Campbell, A. B., 1960, Geology and mineral deposits of the St. Regis-Superior area, Mineral County, Montana: U.S. Geol. Survey Bull, 1082-I, p. 545-612.

Caro, R. J., 1949, Anaconda phosphate plant, beneficiation and treatment of low-grade Idaho phosphate rock: Am. Inst. Mining Metall. Engineers Trans., v. 184, p. 282-284.

Carter, G. J., Kelly, H. J., and Parsons, E. W., 1962, Industrial silica deposits of the Pacific Northwest: U.S. Bur. Mines. Inf. Circ. 8112, 57 p.

Chidester, A. H., and Shride, A. F., 1962, Asbestos in the United States: U.S. Geol. Survey Mineral Inv. Resource Map MR-17.

Chidester, A. H., and Worthington, H. W., 1962, Talc and soapstone in the United States: U.S. Geol. Survey Mineral Inv. Resource Map MR-31.

Clabaugh, S. E., 1952, Corundum deposits of Montana: U.S. Geol. Survey Bull. 983, 100 p.

Cole, L. H., 1926, Sodium sulfate of western Canada; occurrence, uses, and technology: Canada Dept. Mines, Mines Branch, Pub. 646, 160 p.

Condit, D. D., 1920, Oil shale in western Montana, southeastern Idaho, and adjacent parts of Wyoming and Utah: U.S. Geol. Survey Bull. 711-B, p. 15-40.

Corry, A. V., 1933, Some gold deposits of Broadwater, Beaverhead, Phillips, and Fergus Counties, Montana: Montana Bur. Mines and Geology Mem. 10, 45 p.

Cotter, P. G., and Jensen, N. C., 1962, Stone: U.S. Bur. Mines Mineral Yearbook 1961, v. 1, p. 1139-1167.

Cotter, P. G., and Mallory, J. B., 1962, Sand and gravel: U.S. Bur. Mines Minerals Yearbook 1961, v. 1, p. 1061-1090.

Creasey, S. C., and Scholz, E. A., 1945, Big Ben molybdenum deposit, Neihart mining district, Cascade County, Montana: U.S. Geol. Survey open-file report, 29 p.

Crittenden, M. S., and Pavlides, Louis, 1960, Manganese in the United States: U.S. Geol. Survey Mineral Inv. Resource Map MR-23.

Crowley, F. A., 1960, Columbium-rare-earth deposits, southern Ravalli County, Montana: Montana Bur. Mines and Geology Bull. 18, 47 p.

---1962, Phosphate rock: Montana Bur. Mines and Geology Spec. Pub. 25, 8 p.

Currier, L. W., 1960, Geological appraisal of dimension stone: U.S. Geol. Survey Bull. 1109 78 p.

D'Amico, K, J., 1962, Statistical summary of mineral production: U.S. Bur. Mines Minerals Yearbook 1961, v. 1, p. 135-182.

DeHuff, G. L., and Fratta, Teresa, 1959, Manganese: U.S. Bur. Mines Minerals Yearbook 1958, v. 1, p. 723-748.

DeMunck V. C., 1956, Iron deposits in Montana: Montana Bur. Mines and Geology Inf. Circ. 13, 49 p.

DeMunck, V. C., and Ackerman, W. C., 1958, Barite deposits in Montana: Montana Bur. Mines and Geology Inf. Circ. 22, 30 p.

Densen, N. M., and Gill, J. R., 1956, Uranium-bearing lignite and its relation to volcanic tuffs in eastern Montana and North and South Dakota: U.S. Geol. Survey Prof. Paper 300, p. 413-418.

Dougan, C. W., 1947, Dickite-clay deposit of Fergus County, Montana: Montana Bur. Mines and Geology Misc. Contrib. 9, 11 p.

Emmons, W. H., 1908, Gold deposits of the Little Rocky. Mountains, Montana: U.S. Geol. Survey Bull. 340, p. 96-116.

Emmons, W. H., and Calkins, F. C., 1913, Geology and ore deposits of the Philipsburg quadrangle, Montana: U.S. Geol. Survey Prof. Paper 78, 271 p.

Engel, A. E. J., and Wright, L. A., 1960, Talc and soapstone, in Industrial minerals and rocks, 3d ed.: Am. Inst. Mining Metall. Petroleum Engineers, p. 835-850.

Everett, F. D., and Agey, W. W., 1960, Field and laboratory studies of canal-lining materials, East Bench unit, Beaverhead and Madison Counties, Montana: U.S. Bur. Mines Prelim. Rept. 133 to Missouri Basin Field Comm.

------ 1961, Field and laboratory studies of canal-lining materials, Jefferson unit, Madison, Jefferson, and Broadwater Counties, Montana: U.S. Bur. Mines Prelim. Rept. 135 to Missouri Basin Field Comm.

Fisher, F. L., 1960, Germanium: U.S. Bur. Mines Minerals Yearbook, v. 1, p. 1252-1253.

Fleischer, Michael, 1961 Germanium content of enargite and other copper sulfide minerals: U.S. Geol. Survey Prof. Paper 424-B, p. 259-261.

Fulkerson, F. B., Kauffman, A. J., Jr., and Knostman, R. W., 1962, The mineral industry of Montana: U.S. Bur. Mines Minerals Yearbook, 1961, v. 3, p. 615-640.

Fulkerson, F. B., Knostman, R. W., and Petersen, N. S., 1962, The mineral industry of Idaho in 1962, Preliminary annual report: U.S. Bur. Mines Region I Area rept. B-97, 7 p.

Gale, H. S., and Richards, R. W., 1910, Preliminary report on the phosphate deposits in southeastern Idaho and adjacent parts of Wyoming and Utah: U.S. Geol. Survey Bull. 430-H, p. 457-535.

Geehan, R. W., and Katlew, Charles, 1954, Tungsten: U.S. Bur. Mines Minerals Yearbook 1951, p. 1285-1298.

Gibson, Russell, 1948, Geology and ore deposits of the Libby quadrangle, Montana: U.S. Geol. Survey Bull. 956, 131p.

Gill, J. R., 1959, Reconnaissance for uranium in the Ekalaka lignite field; Carter County Montana: U.S. Geol. Survey Bull. 1055-F, p. 167-179.

Goddard, E. N., 1940, Manganese deposits of Philipsburg, Granite County, Montana, a preliminary report: U.S. Geol. Survey Bull. Y22-G, p. 157-204.

Graham, C. E., and Robertson, F. S., 1951, A new dumortierite locality from Montana: Am. Mineralogist, v. 36, nos. 11-12, p. 916-917.

Greene, L. M., and Agey, W. W., 1960, Field and laboratory studies of canal-lining materials, Helena Valley unit, Lewis and Clark County, Montana: U.S. Bur. Mines Prelim. Rept. 131 to Missouri Basin Field Comm.

Hanson, Alvin, 1952, Cambrian stratigraphy in southwestern Montana: Montana Bur. Mines and Geology Mem. 33, 46 p.

Hart, L. H., 1935, The Butte district, Montana, in Copper resources of the world: Internat. Geol. Gong., 16th, Washington, D.C., 1933, v. 1, p. 287-305.

Havard, J. F., 1960, Gypsum, in Industrial minerals and rocks, 3d ed.: Am. Inst. Mining Metall. Petroleum Engineers, p. 471-486.

Heiligman, H. A., Mikami, H. M., and Samuel, D. G., 1961, Transvaal chromite in basic refractories [abs.]: Am. Ceramic Sec. Bull., v. 40, p. 585.

Heinrich, E. W., 1948, Deposits of the sillimanite group of minerals south of Ennis, Madison County with notes on other occurrences in Montana: Montana Bur. Mines and Geology Misc. Contr. 10, 22 p.

---1949, Pegmatite mineral deposits in Montana: Montana Bur. Mines and Geology Mem. 28, 56 p.

----1950, Sillimanite deposits of the Dillon region, Montana: Montana Bur. Mines and Geology Mem. 30, 43 p.

Herdlick, J. A., 1948, Investigation of the Four Chromes and other chromite deposits, Red Lodge district, Carbon County, Montana: U.S. Bur. Mines Rept. Inv. 4369, 13 p.

Hewett, D. F., Crittenden, M. D., Jr., DeHuff, G. L., Jr., and Pavlides, Louis, 1956, Manganese deposits of the United States, in Symposium sobre yacimientos de manganeso: Internat. Geol. Cong., 20th, Mexico 1956, v. 3, p. 169-230.

Holliday, R. W., 1960, Tungsten: U.S. Bur. Mines Bull. 585, p. 903-917. Hosterman, J. W., 1956, Geology of the Murray area, Shoshone County, Idaho: U.S. Geol. Survey Bull. 1027-P, p. 725-748.

Holmes, W. T., Holbrook, W. F., and Banning, L. H., 1962, Beneficiating and smelting Carter Creek, Montana, iron ore: U.S. Bur. Mines Rept. Inv. 5922, 21 p.

Howland, A. L., 1955, Chromite deposits in the central part of the Stillwater complex, Montana: U.S. Geol. Survey Bull. 1015-0, p. 99-121.

Howland, A. L., Garrels, R. M., and Jones, W. R., 1949 Chromite deposits of the Boulder River area, Sweetgrass County, Montana: U.S. Geol. Survey Bull. 948-C, p. 63-82.

Jackson, C. F., Knaebel, J. B., and Wright, C. A., 1935, Lead and zinc mining and milling in the United States; current practices and costs: U.S. Bur. Mines Bull. 381, 204 p.

Jackson, E. D., 1962, Stratigraphic and lateral variation of chromite composition in the Stillwater complex, Montana: Am. Mineralogist (in press).

Jackson, E. D., Dinnin, J. I., and Bastron, Harry, 1960, Stratigraphic variation of chromite composition within chromitite zones of the Stillwater complex, Montana [abs.]: Geol. Sec. America Bull., v. 71, no. 12, Dec. 1960, p. 1896.

Jackson, E. D., Howland, A. L., Peoples, J. W., and Jones, W. R., 1954, Geologic maps and sections of the eastern part of the Stillwater complex, in Stillwater County, Montana: U.S. Geol. Survey open-file report.

Jahns, R. H., 1960, Gemstones and allied materials, in Industrial Minerals and Rocks, 3d ed.: Am. Inst. Milling Metall. Petroleum Engineers, p. 383-441.

James, H. L., 1943, The Silver Star Chromite deposit, Madison County, Montana: U.S. Geol. Survey prelim. report.

---1946, Chromite deposits near Red Lodge, Carbon County, Montana: U.S. Geol. Survey Bull. 945-F, p. 151-189.

Jarrard, L. D., 1957, Some occurrences of uranium and thorium in Montana: Montana Bur. Mines and Geology Misc. Contr. 15, 90 p.

Jenkins, G. F., 1960, Asbestos, in Industrial minerals and rocks, 3d ed.: Am. Inst. Mining Metall. Petroleum Engineers, p. 23-53.

Johns, W. M., 1960, Progress report on geologic investigation in the Kootenai-Flathead area, northwest Montana, 2. southeastern Lincoln County: Montana Bur. Mines and Geol. Bull. 17, 52 p.

--- 1961, Progress report on geologic investigations in the Kootenai-Flathead area, northwest Montana, 3. Northern Lincoln County: Montana Bur. Mines and Geol. Bull. 23, 57 p.

Jones, Verner, 1931, Chromite deposits near Sheridan, Montana: Econ. Geology, v. 26, no. 6, Sept-Oct. 1931, p. 625-629.

Karlstrom, T. N. V., 1948, Geology and ore deposits of the Hecla mining district, Beaverhead County, Montana: Montana Bur. Mines and Geology Mem. 25, 87 p.

Kessler, D. W., Insley, Herbert, and Sligh, W. H., 1940, Physical, mineralogical, and durability studies on the building and monumental granites of the U.S.: Natl. Bur. Standards Jour. Research, v. 25, p. 161-206.

Kessler, D. W., and Sligh, W. H., 1927, Principal commercial limestones used for building construction in the U.S.: Natl. Bur. Standards Tech. Paper 340, 94 p.

Key, W. W., 1960a, Sand and gravel: U.S. Bur. Mines Bull. 585, p. 701-715.

--- 1960b, Stone: U.S. Bur. Mines Bull. 585, p. 793-813.

Kinkel, A. R., Jr., and Peterson, N. P., 1962, Copper in the United States (exclusive of Alaska and Hawaii): U.S. Geol. Survey Mineral Inv. Resource Map MR-13.

Klepper, M. R., Weeks, R. A., and Ruppel, E. T., 1957, Geology of the southern Elkhorn Mountains, Jefferson and Broadwater Counties, Montana: U.S. Geol. Survey Prof. Paper 292, 82 p.

Knechtel, M. M., and Patterson, S. H., 1956, Bentonite deposits in marine Cretaceous formations of the Hardin district, Montana and Wyoming: U.S. Geol. Survey Bull. 1023, 116 p.

Knechtel, M. M., and Patterson, S. H., 1962, Bentonite deposits of the northern Black Hills district, Wyoming, Montana, and South Dakota: U.S. Geol. Survey Bull. 1082-M, p. 893-1027.

Knopf, Adolph, 1913, Ore deposits of the Helena mining region, Montana: U.S. Geol. Survey Bull. 527, 143 p.

Koschmann, A. H., and Bergendahl, M. H., 1962, Gold in the United States (exclusive of Alaska and Hawaii): U.S. Geol. Survey Mineral Inv. Resource Map MR-24.

Kuster, W. V., and Jensen, N. C., 1962, Gypsum: U.S. Bur. Mines Minerals Yearbook 1961, v. 1, p. 624-642.

Kuster, W. V., and Schreck, V. R., 1962, Fluorspar and cryolite: U.S. Bur. Mines Minerals Yearbook 1961, v. 1, p. 567-583.

Lemmon, D. M., and Tweto, O. L., 1962, Tungsten in the United States: U.S. Geol. Survey Mineral Inv. Resource Map MR 25 and accompanying text.

Lenhart, W. B., 1960, Sand and gravel, in Industrial minerals and rocks, 3d ed.: Am. Inst. Mining Metall. Petroleum Engineers, p. 733-758.

Lewis, R. W., and Tucker, G. E., 1962 Phosphate rock: U.S. Bur. Mines Minerals Yearbook 1961, v. 1, p: 973-992.

Lindgren, Waldemar, 1933, Mineral deposits, 4th ed.: New York, McGraw-Hill Book Co., Inc., 930 p.

Lovering, T. S., 1930, The New World or Cooke City mining district, Park County, Montana: U.S. Geol. Survey Bull. 811-A, p. 1-87.

Lyden, C. J., 1948, The gold placers of Montana: Montana Bur. Mines and Geology Mem. 26, 152 p.

Lynd, L. E., 1960, Titanium, in Industrial minerals and rocks, 3d ed.: Am. Inst. Mining Metall. Petroleum Engineers, p. 851-880.

McInnis, Wilmer, 1960, Molybdenum, in Mineral facts and problems: U.S. Bur. Mines Bull. 585, p 537-547.

McKelvey, V. E., Cathcart, J. B., Altschuler, Z. S., Swanson, R. W., and Lutz, Katherine, 1953a, Domestic phosphate deposits, in Soil and fertilizer phosphorus in crop nutrition, v. 4, p. 347-376, of Agronomy, a series of monographs prepared under auspices American Society of Agronomy: New York, Academic Press, Inc.

McKelvey, V. E., Swanson, R. W., and Sheldon, R. P., 1953b, The Permian phosphorite deposits of western United States: Internat. Geol. Cong., 19th, Algiers 1952, Comptes rendus, sec. 9, fasc. 11, p. 45-64.

McKelvey, V. E., Williams, J. S., Sheldon, R. P., Cressman, E. R., Cheney, T. M., and Swanson, R. W., 1959, The Phosphoria, Park City and Shedhorn Formations in the western phosphate field: U.S. Geol. Survey Prof. Paper 313-A, p. 1-47.

McKnight, E. T., Newman, W. L., and Heyl, A. V., Jr., 1962a, Lead in the United States: U.S. Geol. Survey Mineral Inv. Resource Map MR-15.

-----1962b, Zinc in the United States: U.S. Geol. Survey Mineral Inv. Resource Map MR-19.

McKnight, E. T., Newman, W. L., Klemic, Harry, and Heyl, A. V., Jr., 1963(?), Silver in the United States: U.S. Geol. Survey Mineral Inv. Resource Map MR-34 (in press).

Mann, John A., 1954, Geology of part of the Gravelly Range, Montana: Yellowstone-Bighorn Research Proj. Contr. 190, 91 p.

Mansfield, G. R., 1933, Some deposits of ornamental stone in Montana: U.S. Geol. Survey Circ. 4, 22 p.

Merewether, E. A., 1960, Geologic map of the igneous and metamorphic rocks of Montana showing locations of uranium deposits: U.S. Geol. Survey Misc. Geol. Inv. Map I-311.

Milner, R. L., 1956, Effects of salt solution in Saskatchewan [abs.], in North Dakota Geol. Sec. Williston Basin Symposium, 1st Internat., Bismarck, Oct. 1956: p. 111.

Mining World, 1955, How Minerals Engineering opens big low-grade tungsten deposits: Mining World, v. 17, no. 1, p. 3&43.

Murphy, J. F., and Houston, R. S., 1955, Titanium-bearing black sand deposits of Wyoming (and Montana): Wyoming Geol. Assoc. Guidebook, 10th Ann. Field Conf., Green River Basin, 1955, p. 190-196.

Myers, J. B., 1960, Vermiculite, in Industrial minerals and rocks, 3d ed.: The Am. Inst. Mining Metall. Petroleum Engineers, New York, p. 889-896.

Myers, W. B., 1952, Geology and mineral deposits of the northwest quarter of the Willis quadrangle and adjacent Brown's Lake area, Beaverhead County, Montana: U.S. Geol. Survey open-file report, 46 p.

Nordquist, J. W., 1953, Mississippian stratigraphy of northern Montana, in Billings Geol. Sec. Guidebook 4th Ann. Field Conf., Sept. 1953: p. 68-82.

Olson, J. C., and Adams, J. W., 1962, Thorium and rare earth in the United States (exclusive of Alaska and Hawaii): U.S. Geol. Survey Mineral Inv. Resource Map MR-28.

Pardee, J. T., 1918a, Ore deposits of the northwestern part of the Garnet Range, Montana: U.S. Geol. Survey Bull. 660-F, p. 159-239.

--- 1918b, The Dunkleberg mining district, Granite County, Montana: U.S. Geol. Survey Bull. 660-G, p. 241-247.

--- 1919, Some manganese deposits in Madison County, Montana: U.S. Geol. Survey Bull. 690-F, p. 131-147.

--- 1922, Deposits of Manganese ore in Montana, Utah, Oregon, and Washington: U.S. Geol. Survey Bull. 725-C, p. 141-243.

--- 1951, Gold placer deposits of the Pioneer district, Montana: U.S. Geol. Survey Bull. 978-C, p. 69-99.

Pardee, J. T., and Larsen, E. S., 1929, Deposits of vermiculite and other minerals in the Rainy Creek district, near Libby, Montana: U.S. Geol. Survey Bull. 805-B, p. 17-28.

Pardee, J. T., and Schrader, F. C., 1933, Metalliferous deposits of the greater Helena mining region, Montana: U.S. Geol. Survey Bull. 842, 318 p.

Pattee, E. C., 1960, Tungsten resources of Montana: deposits of the Mt. Torrey batholith, Beaverhead County: U.S. Bur. Mines Rept. Inv. 5552, 41 p.

Patterson, C. M., 1960, Lime and calcium: U.S. Bur. Mines Bull. 585, p. 463-472.

Patterson, C. M., and Schreck, V. R., 1962, Lime: U.S. Bur. Mines Minerals Yearbook 1961, v. 1, p. 799-826.

Pearson, W. J., 1960, Western Canada potash and its future prospects: The Engineering Journal, August 1960, p. 2.

Pecora, W. T., 1956, Carbonatites, a review: Geol. Sec. America Bull., v. 67, no. 11, p. 1537-1556.

Peoples, J. W., and Howland, A. L., 1940, Chromite deposits of the eastern part of the Stillwater complex, Stillwater County, Montana: U.S. Geol. Survey Bull. 922-N, p. 371-416.

Peoples, J. W., Howland, A. L., Jones, W. R., and Flint, Delos, 1954, Geologic map, sections, and map of underground workings of the Mountain View Lake area, Stillwater County, Montana: U.S. Geol. Survey open-file report.

Perry, E. S., 1948, Talc, graphite, vermiculite and asbestos deposits in Montana: Montana Bur. Mines and Geology Mem. 27, 44 p.

--- 1949, Gypsum, lime, and limestone in Montana: Montana Bur. Mines and Geology Mem. 29, 45 p.

Pierce, W. G., and Rich, E. I., 1962, Summary of rock salt deposits in the United States as possible storage sites for radioactive waste materials: U.S. Geol. Survey Bull. 1148, 91 p.

Popoff, C. C., 1953, Lead deposits of the Dunkleberg district, Granite County, Montana: U.S. Bur. Mines Rept. Inv. 5014, 41 p.

Prokopovitch, A. S., and Heidrich, H. V., 1962, Chromium: U.S. Bur. Mines Minerals Yearbook 1961, v. 1, p. 431-443.

Reed, G. C., 1949, Investigation of Sheep Creek iron deposits, Meagher County, Montana: U.S. Bur. Mines Rept. Inv. 4400, 9 p.

--- 1950, Mines and mineral deposits (except fuels), Park County, Montana: U.S. Bur. Mines Inf. Circ. 7546, 64 p.

-----1951, Mines and mineral deposits (except fuels), Broadwater County, Montana: U.S. Bur. Mines Inf. Circ. 7592, 58 p.

Reno, H. T., 1960, Iron: U.S. Bur. Mines Bull. 585, p. 403-421.

Roberts, W. A., and Gude, A. J., 3d, 1953a, Uranium-bearing deposits west of Clancey, Jefferson County, Montana: U.S. Geol. Survey Bull. 988-F, p. 64-87.

--- 1953b, Geology of the area adjacent to the Free Enterprise mine, Jefferson County, Montana: U.S. Geol. Survey Bull. 988-G, p. 143-155.

Robertson, A. F., 1950, Mines and mineral deposits (except fuels), Fergus County, Montana: U.S. Bur. Mines Inf. Circ. 7544, 76 p.

---1951, Mines and mineral deposits (except fuels), Cascade County, Montana: U.S. Bur. Mines Inf. Circ. 7589, 81 p.

Robertson, A. F., and Roby, R. N., 1952, Mines and mineral deposits (except fuels), Judith Basin County, Montana: U.S. Bur. Mines Inf. Circ. 7602, 51 p.

Robertson, F. S., 1953, Geology and mineral deposits of the Zosell (Emery) mining district, Powell County, Montana: Montana Bur. Mines and Geology Mem. 34, 29 p.

Roby, R. N., 1949, Investigation of Running Wolf iron deposits, Judith Basin County, Montana: U.S. Bur. Mines Rept. Inv. 4454, 7 p.

----- 1950, Mines and mineral deposits (except fuels), Montana: U.S. Bur. Mines Inf. Circ. 7540, 43 p.

Roby, R. N., Ackerman, W. C., Fulkerson, F. B., and Crowley, F. A., 1960, Mines and mineral deposits (except fuels), Jefferson County, Montana: Montana Bur. Mines and Geology Bull. 16, 122 p.

Ross, C. P., 1950, Fluorspar prospects of Montana: U.S. Geol. Survey Bull. 955-E, p. 173-224.

Ruhlman, E. R., 1958, Phosphate rock. Pt. 1, Mining, beneficiation, and marketing: U.S. Bur. Mines Inf. Circ. 7814, 33 p.

Sahinen, U. M., 1939, Geology and ore deposits of the Rochester and adjacent mining districts, Madison County, Montana: Montana Bur. Mines and Geology Mem. 19, 53 p.

----1950, Geology and ore deposits of the Highland Mountains, southwestern Montana: Montana Bur. Mines and Geology Mem. 32, 63 p.

----1956, Preliminary report on sodium sulphate in Montana: Montana Bur. Mines and Geology Inf. Circ. 11, 9 p.

---- 1967, Mines and mineral deposits of Missoula and Ravalli Counties, Montana: Montana Bur. Mines and Geology Bull. 8, 63 p.

----1959, Metalliferous deposits in the Helena area, Montana, in Billings Geol. Sec. Guidebook 10th Ann. Field Conference, Sawtooth-Disturbed Belt area, Montana, 1959: p.129-140.

--- 1962, Fluorspar deposits in Montana: Montana Bur. Mines and Geology Bull. 28, 38 p.

Sahinen, U. M., and Crowley, F. A., 1959, Summary of Montana mineral resources: Montana Bur. Mines and Geology Bull. 11, 51 p.

Sahinen, U. M., Smith, R. I., and Lawson, D. C., 1958, Progress report on clays of Montana: Montana Bur. Mines and Geology Inf. Circ. 23, 41 p.

---1960, Progress report on clays of Montana: Montana Bur. Mines and Geology Bull. 13, 83 p.

___ 1962, Progress report on clays and shales of Montana, 1960-1961: Montana Bur. Mines and Geology Bull. 27, 61 p.

Sales, R. H., 1914, Ore deposits at Butte, Montana: Am. Inst. Mining Engineers Trans., v. 46, p. 3-109.

Sandberg, C. A., 1961, Distribution and thickness of Devonian rocks in Williston basin and in central Montana and north-central Wyoming: U.S. Geol. Survey Bull. 1112-D, p. 105-127.

Sandberg, C. A., and Hammond, C. R., 1958, Devonian System in Williston basin and central Montana: Am. Assoc. Petroleum Geologists Bull., v. 42, no. 10, p. 2293-2334.

Schafer, P. A., 1935, Geology and ore deposits of the Neihart mining district, Cascade County, Montana: Montana Bur. Mines and Geology Mem. 13, 62 p.

--- 1937, Chromite deposits of Montana: Montana Bur. Mines and Geology Mem. 18, 35 p.

Schnabel, R. W., 1955, The uranium deposits of the United States: U.S. Geol. Survey Mineral Inv. Resource Appraisals Map MR-2.

Seagar, G. F., 1944, Gold, arsenic, and tungsten deposits of the Jardine-Crevasse Mountain district, Park County, Montana: Montana Bur. Mines and Geology Mem. 23, 111p.

Sharp, W. N., and Cavender, W. S., Thorium deposits of the Lemhi Pass district, Lemhi County, Idaho, and Beaverhead County, Montana: U.S. Geol. Survey Bull. 1126 (in press).

Shenon, P. J., 1931, Geology and ore deposits of Bannack and Argenta, Montana:

Montana Bur. Mines and Geology Bull. 6, 80 p.

Shenon, P. J., and Taylor A. V., 1936, Geology and ore occurrence of the Hog Heaven mining district, Flathead County, Montana: Montana Bur. Mines and Geology Mem. 17, 26 p.

Sinkankas, John, 1959, Gemstones of North America: Princeton, N.J., D. van Nostrand Co., Inc., 675 p.

Spiroff, Kiril, 1938, Geological observations of the Block P. mine, Hughesville, Montana: Econ. Geology, v. 33, no. 5, p. 554-567.

Stebinger, Eugene, 1914, Titaniferous magnetite beds on the Blackfeet Indian Reservation, Montana: U.S. Geol. Survey Bull. 540,p. 329-337.

Stoll, W. C., 1950, Mica and beryl pegmatites in Idaho and Montana: U.S. Geol. Survey Prof. Paper 229, 64 p.

Stoll, W. C., and Armstrong, F. C., 1958, Optical calcite deposits in Park and Sweet Grass Counties, Montana: U.S. Geol. Survey Bull. 1042-M, p. 431-479.

Stone, R. W., 1911, Geologic relation of ore deposits in the Elkhorn Mountains, Montana: U. S. Geol. Survey Bull. 470, p. 75-98.

Swanson, R. W., 1960, Phosphate and associated resources in Permian rocks of southwestern Montana: U.S. Geol. Survey Prof. Paper 400-B, p. 65-66.

Swanson, R. W., McKelvey, V. E., and Sheldon, R. P., 1953, Progress report on investigations of western phosphate deposits: U.S. Geol. Survey Circ. 297, 16 p.

Tansley, Wilfred, Schafer, P. A., and Hart, L. H., 1933, A geological reconnaissance of the Tobacco Root Mountains, Madison County, Montana: Montana Bur. Mines and Geology Mem. 9, 57 p.

Taylor A. V., Jr., 1942, Quartz Hill district, near Divide, Montana, in Newhouse, W.H., ed., Ore deposits as related to structural features: Princeton, N.J., Princeton Univ. Press, p. 215-216.

Thayer, T. P., 1946, Preliminary chemical correlation of chromite with the containing rocks: Econ. Geology, v. 41, p. 202-217.

---- 1960, some critical differences between alpine-type and stratiform peridotite-gabbro complexes: Internat. Geol. Gong. Rept. 2lst Sess., Norden; pt.13, p. 247-259.

Tucker, H. A., 1960, Ferroalloys: U.S. Bur. Mines Bull. 585, p. 291-304. U.S. Congress, House Committee on Public Lands, Subcommittee on Mines and Mining, 1948, Strategic and critical minerals and metals, hearings, part I, manganese: U.S. 80th Cong., 2nd sess., Comm. Hearing no. 38, Feb. 12, 13, 24, 25, 27, 1948, 497 p. (see especially statements of F. A. Linforth, Butte, Mont., Mining geologist and engineer, Assistant to the Vice President, Anaconda Copper Mining Co., p. 279-298; and H. A. Pumpelly, Vice President, Domestic Manganese and Development Co., Butte, Mont., p. 338-351).

U.S. Dept. of Commerce, 1948, Coarse aggregates, simplified practice recommendation: Natl. Bur. Standards R. 163-48, 17 p.

Volin, M. E., Robey, R. N., and Cole, J. W., 1952, Investigation of the Combination silver-tungsten mine, Granite County, Montana: U.S. Bur. Mines Rapt. Inv. 4914, 26 p.

Waesche, H. H., 1960, Quartz crystal and optical calcite, in Industrial minerals and rocks: Am. Inst. Milling h4etall. Petroleum Engineers, p. 687-698.

Waggaman, W. H., and Ruhlmun, E. R., 1960, Phosphate rock. Pt. 2, Processing and utilization: U.S. Bur. Mines Inf. Circ. 7951, 36 p.

Walker, D. D., 1960, Tungsten resources of Montana: deposits of the Philipsburg batholith, Granite and Deer Lodge Counties, Montana: U.S. Bur. Mines Rept. Inv. 5612, 55 p.

Wallace, R. E., and Hosterman, J. W., 1956, Reconnaissance geology of western Mineral County, Montana: U.S. Geol. Survey Bull. 1027-M, p. 575-612.

Weed, W. H., 1900, Geology of the Little Belt Mountains, Montana, with notes on the mineral deposits of the Neihart, Barker, Yogo, and other districts: U.S. Geol. Survey 20th Ann. Rept., pt. 3-C, p. 257-461.

---1912 Geology and ore deposits of the Butte district, Montana: U.S. Geol. Survey Prof. Paper 74, 262 p.

Weed, W. H., and Pirsson, L. V., 1898, Geology and mineral resources of the Judith Mountains of Montana: U.S. Geol. Survey 18th Ann. Rept., pt. 3-D, p. 437-616.

Weis, P. L., Armstrong, F. C., and Rosenblum, Samuel, 1958, Reconnaissance for radioactive minerals in Washington, Idaho, and western Montana, 1952-1955: U.S. Geol. Survey Bull. 107-1-B, p. 7-48.

West, J. M., and Lindquist, A. E-I., 1962, Cement: U.S. Bur. Mines Minerals Yearbook 1961, v. 1, p. 391-429.

Westgate, L. G., 1921, Deposits of chromite in Stillwater and Sweetgrass Counties, Montana: U.S. Geol. Survey Bull. 725, p. 67-82.

Willey, E. C., Cressman, E. R., Pierce, H. W., and Cheney, T. M., 1954, Status of ownership of part of the lands on which phosphate-bearing beds crop out in southwestern Montana and northeastern Idaho: U.S: Geol. Survey open-file report, 10 p.

Wimmler, N. L., 1946a, Exploration of Southern Cross iron deposits, Deer Lodge County, Montana: U.S. Bur. Mines Rept. Inv. 3979, 14 p.

--- 1946b, Exploration of Choteau titaniferous magnetite deposit, Teton County, Montana: U.S. Bur. Mines Rept. Inv. 3981, 12 p.

---- 1948, Investigation of chromite deposits of the Stillwater complex, Stillwater and Sweetgrass Counties, Montana: U.S. Bur. Mines Rept. Inv. 4368, 41 p.

Winchell, A. N., 1914, The mining districts of the Dillon quadrangle, Montana, and adjacent areas: U.S. Geol. Survey Bull. 574, 191p.

Withington, C. F., 19G3, Gypsum and anhydrite in the United States (exclusive of Alaska and Hawaii): U.8. Geol. Survey Mineral Inv. Resource Map MR-33.

Witkind, I. J., 1959, Quaternary geology of the Smoke Creek-Medicine Lake -Grenora area, Montana and North Dakota: U.S. Geol. Survey Bull. 1073, 80 p.

Zeiglar D. L., 1956, Pre-Piper post-Minnekhata "red beds" in the Williston Basin (summary), in North Dakota Geol. Soc. Williston Basin Symposium, 1st Internat., Bismarck, Oct. 1956: p. 170-178.