COBALT 



149 



HYDROTHERMAL DEPOSITS 



Hydrothermal deposits (formed from heated solu- 

 tions) locally have been important sources of cobalt, 

 and some of them are the only deposits mined chiefly 

 for this metal. The hydrothermal deposits may be 

 subdivided into two major classes: (1) vein de- 

 posits, and (2) replacement deposits. 



In the United States, the vein deposits of the 

 Blackbird district, Idaho, contain 1.6 percent copper, 

 0.6 percent cobalt, and lesser amounts of nickel and 

 precious metals (Vhay, 1964, p. 68). The aggregate 

 tonnage of the ore in the district was reported in 

 1959 to contain 15 million to as much as 225 million 

 pounds of cobalt (Bilbrey, 1962, p. 27), equivalent 

 to hypothetical resources in the classification of this 

 report. In the Goodsprings district, Nevada, hetero- 

 genite forms envelopes around bodies of copper min- 

 erals. Large amounts of rock in many small bodies 

 contain 0.3-0.5 percent cobalt (Vhay, 1952). Some 

 cobalt occurs in the base metal veins of the Coeur 

 d'Alene district, Idaho. Veins containing uranium, 

 zinc, silver, nickel, and cobalt (0.09 percent) occur 

 in the Blackhawk district. New Mexico (Gillerman 

 and Whitebread, 1956). Several thousands of tons 

 of cobaltian manganese ores (0.01-0.5 percent co- 

 balt) occur in the Luis Lopez hot springs deposits. 

 New Mexico. In Connecticut, veins with cobalt occur 

 at Great Hill; and at the Booth mine, north of 

 Bridgeport, at least two bodies of pyrrhotite contain 

 0.01 percent cobalt. 



In Canada, veins that contain as much as 10 per- 

 cent cobalt occur in the great silver-arsenide deposits 

 of the Cobalt-Gowganda region, Ontario (Berry, 

 1971). Cobalt occurs with uranium in ore now pro- 

 duced in the Northwest Territories (Andrews, 1962, 

 p. 99). 



Many veins containing an average of 1.2 percent 

 cobalt with nickel, iron, and silver occur in the Bou 

 Azzer area, Morocco, near the contact of serpentinite 

 and diorite with granite and mica schist of Precam- 

 brian age (Orcel and Jouravsky, 1936). 



Hydrothermal replacement deposits containing 

 cobalt minerals occur in the Bawdwin mine, Burma. 

 The ore body consists of silver, lead, and zinc min- 

 erals that have replaced greatly sheared rhyolitic 

 tuifs that are overlain and underlain by sedimentary 

 rocks. The cobalt occurs in gersdorffite. The ore has 

 an average grade of 0.5 percent cobalt, but during 

 smelting of the ore the cobalt content is increased to 

 8-4 percent in the nickel speiss (Sharma, 1944). At 

 Outokumpu, Finland, large reserves in a copper-rich 

 sulfide deposit contain 0.2 percent cobalt, chiefly in 

 the mineral linnaeite. The ore minerals replace 



quartzite, serpentinite, and other rocks of the Kare- 

 lian schist (Vahatolo, 1953). 



An extensive shear zone has been mineralized by 

 small amounts of pyrite and sphalerite for at least 

 15-20 miles along the east foot of Catoctin Mountain, 

 Va. Surface samples from about a half dozen locali- 

 ties along the strike suggest that although the grade 

 of sulfide minerals is low, the distribution of the 

 minerals is uniform. The cobalt content is 0.007- 

 0.05 percent. 



The geologic features of deposits of the Mississippi 

 Valley type have been summarized recently by Sny- 

 der (1968, p. 277-284). The deposits occur chiefly 

 in carbonate rocks of Cambrian to Pennsylvanian 

 age on the flanks of broad domes. The ore consists 

 mostly of sulfides of lead, zinc, iron, and copper. Sul- 

 fides of cobalt and nickel occur in a few districts. 

 Fluorite and barite are major minerals in some dis- 

 tricts, and minor in others. Cadmium, silver, ger- 

 manium, and arsenic also are reported in some dis- 

 tricts. All these ore materials probably were de- 

 posited from hydrothermal brines at temperatures 

 not over 125°C. 



The cobalt and nickel content of the Mississippi 

 Valley ores is of particular interest because of the 

 records of past production. At the south end of the 

 old lead belt, especially in the Fredericktown and 

 Mine La Motte areas of southeast Missouri, cobalt 

 and nickel sulfides (siegenite, millerite, bravoite, and 

 several unidentified minerals) associated with chal- 

 copyrite and sphalerite locally were abundant, es- 

 pecially in places where the mineralized dolomite of 

 the Bonneterre Dolomite pinches out against the 

 Precambrian rocks in the core of the St. Francois 

 Mountains (Kline and others, 1961). Siegenite-rich 

 ores were the source of the cobalt produced in the 

 southeastern part of the old lead belt in the early 

 days of mining, as well as from 1944 to 1961. 



The metal ratios in the ore of the Bonneterre-Flat 

 River areas in the northern part of the old lead belt 

 were estimated by Snyder and Gerdemann (1968, p. 

 349 ) . The data indicated that cobalt and nickel were, 

 respectively, 20 and 40 times more abundant than 

 silver, but only the silver was recovered. Nearly all 

 the 300,000 Troy ounces of silver produced in Mis- 

 souri in 1965 came from the Bonneterre-Flat River 

 area of the southeast district (Kiilsgaard, 1967, p. 

 71). 



Cobalt and nickel sulfides associated with chalcopy- 

 rite and sphalerite are locally abundant in the lead 

 deposits of the Viburnum Trend now in production 

 on the west side of the St. Francois Mountains. These 

 deposits also occur in the Bonneterre Dolomite in a 

 belt about 27 miles long and have an average min- 



