NIOBIUM (COLUMBIUM) AND TANTALUM 



449 



weathered, so that some of the heavy resistate 

 minerals may be recovered from the saprolite by 

 simple placer-type methods. 



Columbite-tantalite and other niobium-tantalum 

 minerals occur in pegmatites throughout the world, 

 but only a few deposits have been sufficiently rich 

 to be mined solely for these minerals, and they are 

 more commonly a coproduct or byproduct of mica, 

 beryl, or cassiterite operations. In the United States, 

 intermittent recovery of niobium-tantalum minerals, 

 chiefly columbite, has been made from almost all 

 areas where pegmatites are found (Barton, 1962). 

 The Harding pegmatite, in Taos County, N. Mex., 

 was an important source of tantalum during World 

 War II and supplied about 3 tons of microlite con- 

 centrates during a brief period when tantalum was 

 in very short supply (Montgomery, 1947). By 1946, 

 about 17,200 pounds of microlite had been produced 

 from the deposit (Berliner, 1949) . The unusual con- 

 centration of tantalum in the pegmatite is thought 

 by Montgomery (1950) to have been derived from a 

 genetically related granite in which tantalum is 

 largely concentrated in sphene. 



The present major source of tantalum in North 

 America is a pegmatite, the Bemic Lake deposit in 

 southeastern Manitoba, that, has been estimated to 

 contain about 2 million tons of ore containing 0.23 

 percent TaaOs (Howe, 1968). Like the Harding peg- 

 matite, it is a complexly zoned deposit containing 

 lithium and beryllium as well as tantalum and 

 niobium. The principal ore mineral at Bemic Lake 

 is the uncommon mineral wodginite which occurs 

 mainly in a potassium feldspar-muscovite-quartz- 

 beryl zone lying below the quartz core (Grice and 

 others, 1971). 



PLACER DEPOSITS 



Concentrations of niobium and tantalum minerals 

 in various types of placer and residual deposits have 

 been significant sources of these elements. Individual 

 deposits of these types commonly are small but may 

 be sufficiently numerous in a local area to constitute 

 an economically important district. , 



Resistate heavy minerals such as columbite or 

 tantalite, when released from their host rock by 

 weathering, may accumulate essentially in place and 

 become enriched in the rock debris by chemical and 

 mechanical removal of other less durable and lighter 

 weight minerals. Such accumulations in eluvium may 

 constitute economic deposits minable by placer 

 methods. 



Transport and redeposition by running water can 

 form concentrations of niobium and tantalum min- 

 erals in alluvial placers, the richest being in or near 



the source area at some site where the velocity of 

 the water is reduced to the point where the heavy- 

 mineral grains can no longer be transported. This 

 reduction of velocity can result from many factors 

 largely related to the geomorphic history of the 

 terrain. 



Heavy-mineral concentrations formed along sea 

 beaches by wave action are important sources of 

 monazite, zircon, and rutile. Niobium and tantalum 

 minerals, however, are rarely reported from these 

 placers, but it is quite probably that unsuspected 

 niobium enrichment either from independent nio- 

 bium minerals or from carrier minerals would be 

 found by analytical studies of sea-beach concen- 

 trates. 



Consolidated equivalents of sea-beach placers are 

 found in sedimentary rocks; notable are those of 

 Cretaceous age in Wyoming and other western 

 States. Some of these fossil placers are large enough 

 to constitute possible future sources of titanium, zir- 

 conium, and rare earths. A niobium-bearing opaque 

 radioactive mineral found in the Wyoming deposits 

 and tentatively identified as euxenite could be a co- 

 product of these placers if they were exploited 

 (Houston and Murphy, 1962). 



The most important placer deposit of niobium and 

 tantalum known in the United States is at Bear 

 Valley, Valley County, Idaho. The placer was mined 

 from 1955 through 1959 by two dredges with a com- 

 bined capacity of 8,000 cubic yards per day, and 

 during the period of operation 1,050,000 pounds of 

 combined niobium and tantalum oxide was pro- 

 duced from the euxenite and subordinate columbite 

 recovered from the deposit (Barton, 1962). It has 

 been estimated that there is sufficient unmined 

 ground to permit 30 years' mining at the same rate 

 of operation (Mining World, 1958). 



The placer area is in a glaciated valley in the gran- 

 itic rocks of the Idaho batholith ; the richest placers, 

 which have been partially mined, are in the upper 

 part of the valley where the source of the valuable 

 minerals is thought to be a 6-square-mile area of 

 quartz diorite and associated pegmatites (Mackin 

 and Schmidt, 1956). The euxenite content of the 

 quartz diorite is very irregular and may range from 

 a trace to 0.05 pound per cubic yard ; this has been 

 enriched to about 1 pound per cubic yard in the 

 placers, where the euxenite is accompanied by a 

 large suite of other heavy minerals, some of which, 

 with their estimated tenor in pounds per cubic yard, 

 are as follows: Columbite (0.2), ilmenite (20), mag- 

 netite (5), zircon (0.05), garnet (5), and monazite 

 (0.5). 



During the processing of the placer sands, euxen- 



