Mesothorium is a radio-active element always found in thorium minerals. Until quite recently it has been thrown away in the manufacture of thorium nitrate; but it is now being produced as a by-product, and is useful as a substitute for radium in luminous paints, and for therapeutic purposes.
GEOLOGICAL AND GEOGRAPHICAL DISTRIBUTION
The principal sources of monazite are Brazil and India, although it has been mined successfully in the United States in the Carolinas and in Idaho. It has been found in Swaziland, Africa, and in Australia, and also, to a limited extent, in native rock and in placers in Ekaterinburg, Russia.
Monazite is usually found in the gravels of small streams or bottom lands, although it is sometimes found in the soil of hillsides. In Brazil and India it occurs mainly in the beach sands of the sea coast. In places it is found in small crystals in gneiss, granite and pegmatite rocks. As these rocks become disintegrated, the crystals are washed into streams and with other heavy sands are deposited in the stream beds. On the coast of Brazil, the monazite grains from the crystalline rocks of the coastal mountains are concentrated by the waves of the sea.
United States.
—The deposits of the Carolinas cover an area of several hundred square miles east of the Blue Ridge Mountains. In North Carolina, the counties of Cleveland, Burke, Alexander, Rutherford and Lincoln furnish the richest deposits. In South Carolina the only deposits of value are in the counties of Cherokee and Greenville. Practically all of the monazite mined in the Carolinas is derived from gravels in streams and bottom lands, the miners usually following the stream courses. The gravels vary greatly in thickness, and it is therefore difficult to make a true estimate of the average, but in general the monazite-bearing gravels are between 1¹⁄₂ and 2¹⁄₂ feet thick. The top soil in the bottom lands averages 3 to 6 feet thick and may be 7 feet or more.
The deposits in the State of Idaho are near Centerville and Idaho City. In the future, under more favorable conditions of price, transportation, etc., these deposits may possibly become a commercial source of monazite. Almost all of them contain small quantities of gold. The gravel beds are considerably thicker than those in the Carolinas, and with the gold content might be more profitable were it not for labor being higher priced.
Monazite has been found in Colorado, in the Newland Gulch district, 20 miles south of Denver, where it occurs in gravels that carry considerable gold.
Brazil.
—There are three kinds of monazite sand deposits in Brazil; the deposits within the government lands along the coast; deposits lying behind the government coastal lands, which are private state possessions or belong to private parties; and inland deposits. The bulk of the monazite is derived from coast sands in the states of Espirito Santo and Bahia, the sand being washed by means of oscillating tables or sluice boxes. The coast lands are the property of the federal government for 33 meters inland, measuring from the point where the sea waves wash the beach at mean high tide. This uncertain method of marking property has of course given rise to disputes when boundaries are established.