BARITE 



79 



Custer County, Colo. In most of the deposits in the 

 Eastern and Midwestern States an association with 

 igneous activity is not obvious. 



Most of the barite in veins and cavity fillings is 

 dense and gray to white, and is associated with 

 many other minerals including the minerals of the 

 metallic ores as already mentioned. The grade of 

 the barite ore varies by deposit and within deposits. 

 The deposits commonly have sharp contacts with 

 wallrocks ; large-scale replacement of the host rocks 

 by vein minerals is rare. Within individual districts, 

 the deposits commonly are scattered and irregular, 

 and range in thickness from a few inches to a few 

 feet and in length from tens to hundreds of feet. 

 Barite cementing of breccia along fault zones forms 

 thin deposits of small extent in the eastern United 

 States. On weathering, fault-breccia deposits may 

 form bodies of residual ore. 



Barite deposits in collapse and sink structures 

 are common in central Missouri where they are 

 known as circle deposits, and in the Appalachian 

 States. The deposits have yielded rich ore but the 

 individual bodies tend to be small. On weathering, 

 these deposits also form valuable bodies of residual 

 ore. 



The barite and other - minerals of the vein and 

 cavity-filling deposits are typical of an epithermal 

 suite precipitated from low-temperature solutions. 

 Many geologists agree that most vein deposits con- 

 taining barite in the Western States had such an 

 origin. A hydrothermal origin also is postulated for 

 many deposits in the midcontinent region and in the 

 Eastern States where the term "telethermal" has 

 been applied to indicate that the solutions traveled 

 farther from their source, and therefore, were some- 

 what cooler than those generally termed "epither- 

 mal." Evidence has been accumulating in the past 

 decade to suggest that some barite and minerals of 

 base metals may form vein deposits from circulat- 

 ing ground waters (meteoric or supergene water). 



RESIDUAL DEPOSITS 



Residual barite deposits in unconsolidated mate- 

 rial are formed by weathering from preexisting 

 deposits. Many residual deposits of commercial in- 

 terest lie within the clayey residuum derived from 

 Cambrian and Ordovician limestone and dolomite, 

 especially in southeastern Missouri (Brobst and 

 Wagner, 1967) and the Appalachian region (Brobst 

 and Hobbs, 1968). These include deposits in the 

 major barite districts at Sweetwater, Tenn. (Maher, 

 1970, p. 13) and Cartersville, Ga. (Kesler, 1950), 

 and many lesser known districts in Alabama and 

 Virginia. 



Most residual barite is white and is translucent 

 to opaque; it occurs in discrete mammillary, fib- 

 rous, platy, or dense fine-grained irregular masses 

 most of which range in longest dimension from 

 about 1 to 6 inches. Small amounts of pyrite, galena, 

 and sphalerite occur in or on some of the barite, 

 and locally some lead and zinc may be minor by- 

 products of barite mining. Chert and jasperoid are 

 common in many deposits. Incompletely weathered 

 rock fragments, and red, yellow, or brown clay 

 typically make up the rest of most deposits. 



The grade of the ores varies greatly, but com- 

 mercial mining now requires a minimum of about 

 220 pounds of recoverable barite per cubic yard of 

 residuum. Much of the typical ore in major districts 

 has 200-300 pounds of recoverable barite per cubic 

 yard of residuum. 



Deposits in Washington County, Mo., are in re- 

 siduum overlying bedrock 10-15 feet below the sur- 

 face. The deposits at Cartersville, Ga., are in re- 

 siduum that is as deep as 150 feet. Commercial 

 deposits are commonly many acres in extent, but 

 the shape of the residual deposit depends on the 

 shape of the original deposit. Deposits derived from 

 solution channels and vein systems tend to be 

 elongate, and those derived from sink structures 

 tend to be circular. 



Ribs or pillars of carbonate bedrock protrude up- 

 ward into the residuum at many deposits. Some of 

 the ribs contain veins filled with barite, fluorite, 

 quartz, calcite, and locally some sulfide minerals 

 including pyrite, chalcopyrite, galena, and spha- 

 lerite. In other deposits, only thin veinlets or dis- 

 seminated lumps and pods of barite occur in the 

 carbonate bedrock. The source of the barite in 

 residual deposits generally has been assumed to be 

 epigenetic (introduced) hydrothermal vein material 

 left after the host rock has been chemically de- 

 stroyed. 



Today's knowledge of mineralogy and crystallog- 

 raphy suggests that any barium that was trapped 

 in precipitating carbonate will fit into the lattice 

 of aragonite, which seems to be a common primary 

 precipitate of calcium carbonate. Because of the 

 differences in ionic radii of the cations and the 

 crystal structure, barium will not fit into the lattice 

 of calcite or dolomite. Thus, when aragonite is con- 

 verted to calcite or dolomite, any structurally in- 

 cluded barium is expelled from the lattice. It seems 

 reasonable to suppose that any sulfate present in 

 the pore fluids might then fix the barium as barite 

 in veinlets or nodules in the carbonate rocks. If the 

 pore fluid is chloride-rich, and sulfate-poor, the 

 expelled barium might be converted to the very 



