BERYLLIUM 



91 



bearing pegmatites. The crystals of spodumene and 

 beryl may be very large, which permits them to be 

 recovered by hand sorting in rather simple mining 

 operations. 



The coarse zoned pegmatites have yielded nearly 

 all the beryl used in industry. 



HYDROTHERMAL DEPOSITS 



The hydrothermal deposits that are of most in- 

 terest as actual or potential sources of beryllium 

 ore are mainly hypothermal types formed at high 

 temperature and at least moderate depth, and epi- 

 thermal types formed at shallow depths. These de- 

 posits have provided a very small proportion of the 

 total supply of ore but will become dominant in the 

 near future. 



HYPOTHERMAL DEPOSITS 



Hypothermal deposits are generally quartz-rich 

 moderately coarse-grained veins and beryl-bearing 

 granite, both associated with greisen. In North 

 America they are most commonly mined for tung- 

 sten, but a few have yielded tin minerals, and the 

 ones near Lake George, Colo., were mined for beryl 

 and bertrandite. Other examples of beryllium- 

 bearing hypothermal deposits are those near Lost 

 River, Alaska; in the Bagdad area, Arizona; in the 

 Mineral and Sheeprock Ranges, Utah; and in the 

 Mount Wheeler and Eureka areas, Nevada. Most of 

 these are veins in silicate rocks ; a few, as in Nevada, 

 are in carbonate rocks; and in the Sheeprock and 

 Mineral Ranges beryl is dispersed in granite. 



Contact-metasomatic deposits are hypothermal 

 replacement bodies in carbonate rocks, most com- 

 monly along or near contacts of intrusive rocks. 

 They contain a wide variety of silicate minerals and, 

 rather uncommonly, helvite. Much of the beryllium 

 reported in these deposits is contained in idocrase 

 or other minerals of low-beryllium content. The de- 

 posits at Iron Mountain, N. Mex., have been thor- 

 oughly studied. Others are at Iron Mountain, N.H., 

 and in the Victorio Mountains, N. Mex. 



MESOTHERMAL DEPOSITS 



The mesothermal deposits that yield most of our 

 lead, zinc, and copper are notably poor in beryllium. 

 A little helvite has been found in deposits rich in 

 rhodochrosite or rhodonite near Philipsburg, Mont., 

 and Silverton, Colo., but these deposits show no 

 promise as sources of beryllium. 



For convenience, the chrysoberyl deposits of the 

 Seward Peninsula, Alaska, are included here, al- 

 though they might also be grouped with the hypo- 



thermal deposits with which they are associated. 

 These replacement bodies in limestone consist 

 largely of very fine grained fluorite, diaspore, and 

 chrysoberyl, and they lack silicate gangue minerals. 

 They contain some of the largest known resources 

 of beryllium and of fluorite and may form the basis 

 for a multiproduct mining operation. 



EPITHERMAL DEPOSITS 



Concentrations of beryllium minerals in epither- 

 mal deposits were overlooked for many years because 

 they are not closely associated with the famous 

 gold- and silver-bearing sulfide deposits of this 

 genetic type. Instead, they are in sulfide-poor altered 

 rocks that contain small amounts of fluorite as the 

 only readily recognizable economic mineral. The 

 largest known beryllium deposits are the epithermal 

 mantos at Spor Mountain, Utah, in which a rhyolite 

 ash bed containing as much as 65 percent of lime- 

 stone and dolomite in pebbles and cobbles was re- 

 placed by montmorillonite, silica, fluorite, adularia, 

 and bertrandite. The ore is too fine grained to be 

 beneficiated, but nearly all the beryllium can be 

 leached from it with acid. A somewhat similar de- 

 posit is a few miles north of Iron Mountain, N. Mex. 



Large veins of quartz, calcite, adularia, and ber- 

 trandite cut monzonite in the Gold Hill district, 

 Utah, and are unusual in that they contain no fluor- 

 ite and are not in calcareous host rocks. 



REGIONAL DISTRIBUTION OF BERYLLIUM DEPOSITS 



Pegmatite deposits of Paleozoic age have been 

 found along much of the Appalachian Mountains 

 from Nova Scotia to central Alabama. Beryl is 

 widespread in the northern Appalachians, but is 

 largely restricted in the southern Appalachians to 

 the tin-spodumene belt near Kings Mountain, N.C., 

 the Amelia-Powhatan County area, Virginia, and 

 the Troup County area, Georgia. Pegmatites of Pre- 

 cambrian age yield beryl in the Black Hills, S. Dak., 

 northern Colorado, northern New Mexico, and 

 south-central Wyoming. Beryl-bearing pegmatites 

 are not as productive elsewhere in the west. 



Nonpegmatitic deposits have an entirely different 

 distribution. Most are in the block-faulted regions 

 of the West, and a few are in strongly faulted areas 

 in Alaska, the Mississippi Valley, and northern New 

 England. The beryllium deposits are in, and prob- 

 ably are features of, fluorspar metallogenic prov- 

 inces, especially in the West, where they commonly 

 are associated with igneous rocks of middle or late 

 Tertiary age. Many of the deposits are in limestone 

 or dolomite. 



