RADIUM AND URANIUM RESOURCES OF THE UNITED STATES
General Statement.
—The commercially important deposits of ores of radium and uranium in the United States are, so far as yet known, confined to the carnotite regions of southwestern Colorado and southeastern Utah, and the pitchblende deposits of Gilpin County, in eastern Colorado. In Connecticut, North Carolina and elsewhere, uraninite, pitchblende and other uranium minerals have been found; and near Mauch Chunk, in Pennsylvania, small quantities of carnotite have been discovered, but these occurrences are, so far as known, in quantities too small to be of commercial value.
Colorado and Utah.
—The carnotite deposits of southwestern Colorado and southeastern Utah are the most important sources of radium and uranium in the world. In Colorado the largest quantities of ore have come from many mines in Montrose County, especially in Paradox Valley, while Mesa, San Miguel, Dolores, Rio Blanco, Routt and other counties have been producers. In southeastern Utah the ores are carnotite, as in southwestern Colorado, and occur especially in Grand, Emery and San Juan counties, but have not been worked to the same extent as in Colorado.
The carnotite of Colorado and Utah occurs as an impregnation in sandstones and shaly sandstones, mostly in the McElmo and the La Plata formations, lying at the top of the Jurassic beds and below the Cretaceous sandstones and conglomerates of the region. The deposits seem to have been formed by the precipitation of carnotite from solution along certain strata of these formations, and the material occurs along bedding planes, in fissures and small cavities, in layers or irregular masses from a fraction of an inch to several inches in width, and sometimes as a general impregnation of the sandstone for several feet in thickness. It seems to be especially abundant in strata impregnated strongly with vegetable or animal matter, and is often in unusual quantities in lignitized or petrified trunks of trees. This phenomenon suggests the influence of organic matter in precipitating and segregating the carnotite.
The rocks carrying the carnotite lie horizontally or dip at low angles in most parts of the Colorado region; in Utah they lie often in the same way, but occasionally dip at steep angles. Where they appear on the surface, the carnotite sometimes impregnates certain strata for several hundred feet or more along the outcrops, but more generally it occurs in spots along them, with little or no carnotite in the intervening spaces. As these outcrops are followed into the hillsides, the ore appears to be even more irregular in its distribution than on the surface, and in many or most cases it becomes much scarcer the further it is explored underground, until within 10 to 40 or 50 feet from the surface it often mostly or entirely disappears. There are exceptions to this feature, but the gradual and often rapid decrease in quantity and grade of the carnotite ore as it is followed into a hill is generally recognized. This fact suggests that the carnotite may have been redissolved in the sandstone and carried to the surface by capillary action in this arid climate, forming rich, superficial efflorescences.
In many of the carnotite deposits, vanadium minerals occur independently of the vanadium in the carnotite, but this association is not always observed. They occur in sandstone and often give it a dark-gray or blackish color.
In eastern Colorado several mines near Central City, Gilpin County, have produced limited quantities of pitchblende. Among these are the Kirk, the Wood, the Belcher, the Alps, the German and the Calhoun mines. The pitchblende occurs as a subordinate constituent in the gold-bearing veins of that country. The veins intersect old metamorphic rocks intruded by igneous rocks. The mines of Gilpin County are today producing little if any pitchblende, and the total production has been small, amounting in all probably to only a few tons. Much more pitchblende, however, was let go to waste in former days when the mines were worked for other ores and the value of uranium was not recognized.
Production.
—The United States is today by far the largest producer of radium and uranium ores in the world, and is also the largest producer of manufactured radium and uranium compounds. Before the war, England, France and Germany, especially Germany, imported large quantities of American ores and extracted the radium in a refined state as its different salts, much of which was returned to the United States for sale. Now, however, American ores are almost entirely treated in the United States, with the exception of a little shipped to England and possibly to France. The Standard Chemical Co., of Pittsburgh, was a pioneer in this work, and others quickly followed, among them the National Radium Institute, of Denver; the Schlesinger Radium Co., of Denver; the Chemical Products Co., of Denver; the Cummings Chemical Co., of Lansdowne, Pa.; the Radium Luminous Materials Corporation, of New York, and others.
Before the discovery of radium in 1898, but little attention was given to uranium ores in America, though some little pitchblende was shipped from the Central City, Colorado, region for use in making uranium compounds. Shortly after the discovery of radium, however, mining was begun on the carnotite of southwestern Colorado, and from 1900 to 1910 several companies were formed to work these ores both in Colorado and Utah. The pitchblende of Central City also began to attract renewed attention. For a few years active work was done in prospecting for it, but the quantities have so far proved to be small. A few tons probably represent the total amount derived from these mines since the search began. In the meantime, however, the production of carnotite increased rapidly until 1915, when it greatly decreased on account of the curtailment of shipments to Europe. In the latter part of 1916, however, the production increased again, on account of the increased consumption of ore in this country, and in 1918 the production was very active, largely on account of the increased use of radium not only in medicine but especially in luminous paints.
The amount of radium and uranium ores produced in the United States, or in fact anywhere, during a given period, is difficult to determine, on account of the different bases on which reports are made, but it may be said that the tonnage is small compared with that of ores of commoner metals, a few thousand tons being a large amount of carnotite, and simply a few tons or pounds being a large amount of pitchblende. Though the mining of radium and uranium ores in the United States began about 1900 or shortly before, no very large quantities were produced until 1912, when about 1,100 tons were mined, consisting chiefly of Colorado carnotite. The production gradually increased to several thousand tons yearly, practically all of which is carnotite from Colorado and Utah.