80 



UNITED STATES MINERAL RESOURCES 



soluble chloride, in which case the barium could be 

 held in solution to be precipitated later, in place or 

 elsewhere, as barite when sulfate ions became 

 available. Connate water may play an important 

 role in the redistribution of barium in the carbonate 

 environment. The foregoing is perhaps an over- 

 simplification of a complex chemical process, but it 

 does offer an explanation of why calcite- and 

 dolomite-rich rocks generally contain such small 

 amounts of barium. Just as important perhaps is 

 the largely unevaluated role of organisms, especially 

 bacteria, in the mobilization and redistribution of 

 elements such as barium in the sedimentary en- 

 vironment under conditions of low temperature and 

 pressure. 



BEDDED DEPOSITS 

 Bedded deposits include those in which barite 

 occurs as a principal mineral or cementing agent 

 in stratiform bodies in layered sequences of rock. 

 The major deposits of commercial value in this 

 group are bedded concentrations of fetid dark-gray 

 to black fine-grained barite, some of which contain 

 millions of tons of barite easily beneficiated for use 

 in drilling mud and chemical plants. Deposits were 

 being mined in 1972 in Arkansas, California, and 

 Nevada. Geological details are available for some 

 deposits in Arkansas, including the major deposit 

 at Magnet Cove (Scull, 1958; Zimmermann and Am- 

 stutz, 1964) ; in Nevada, including deposits in the 

 Toquima Range (Shawe and others, 1969) and the 

 Shoshone Range (Ketner, 1965; Zimmermann, 

 1969) ; and in California, near Castella, Shasta 

 County (Weber and Matthews, 1967). The bedded 

 deposits and their origin are discussed in some de- 

 tail here because of the economic value of these 

 deposits and the good potential for finding more of 

 them in many parts of the world. 



Geologic features of the bedded deposits may be 

 summarized briefly. The dark beds of barite are a 

 few inches to 50 feet thick and extend over many 

 acres. The beds commonly occur interbedded with 

 dark chert and siliceous siltstone and shale. Some 

 ore zones are more than 100 feet thick. Some indi- 

 vidual beds of barite are massive, but more com- 

 monly the beds are laminated. The grains of barite 

 generally are less than 0.1 mm in diameter. Barite 

 nodules and rosettes make up a substantial part of 

 some barite beds, and a smaller part of some silty 

 or shaly beds. Some nodules have concentric rings 

 of barite, and the rosettes have a radially bladed 

 structure. Both structures suggest that room for 

 free grov^rth existed during deposition. Conglomer- 

 atic beds consisting of nodules and fragments of 



barite, chert, phosphate (apatite), and fragments 

 of rock in a fine-grained matrix of barite have been 

 found in the Toquima Range, Nev. (Shawe and 

 others, 1969, p. 248). Many small-scale sedimentary 

 textures and structures, as well as rhythmic alterna- 

 tions of beds have been described (Zimmermann 

 and Amstutz, 1964; Zimmermann, 1969). 



Many beds of ore in these deposits consist of 50- 

 95 percent barite. The chief impurity is fine-grained 

 quartz whose abundance is inverse to that of barite. 

 Small amounts of clay and pyrite are common. Car- 

 bonate minerals are rare. Spectrographic analyses 

 of many samples indicate that the environment of 

 these barite deposits is extremely low in calcium 

 and magnesium — the total of these two elements 

 generally is less than 1 percent. The most abundant 

 minor element is strontium; it occurs in amounts 

 up to about 7,000 ppm. The trace element suite is 

 limited, and the abundance of each element is un- 

 usually small as compared with the suite and abun- 

 dance of the trace elements in vein deposits. Man- 

 ganese and vanadium generally are each less than 

 50 ppm. Cobalt, copper, chromium, nickel, yttrium, 

 and zirconium each are less than 20 ppm. 



The beds of black bedded barite contain several 

 percent organic matter and characteristically give 

 off" the odor of hydrogen sulfide (HoS) when struck 

 with a hammer. The hydrogen sulfide is believed to 

 be the product of the decay of organic matter and 

 reduction of sulfate by anaerobic bacteria. Fatty 

 acids, hydrocarbons, and other organic compounds 

 (a geolipid fraction) have been extracted from sam- 

 ples collected in Arkansas, California, and Nevada 

 (Miller and others, 1972). The fatty acids identified 

 are considered to be biological markers for the 

 cell walls of bacteria that probably once lived on 

 or within the crystallizing barite masses. 



Rocks containing the black bedded deposits com- 

 monly are of mid-Paleozoic age even though they 

 are widely scattered geographically. The relation is 

 not fully understood, but is perhaps more than coin- 

 cidental. Most of the deposits in Arkansas are of 

 Devonian and Mississippian age ; those in California 

 and Nevada are mostly of Devonian age, although 

 some in Nevada may be of Ordovician age. Some- 

 what similar deposits at Meggen, Westphalia 

 (Ehrenberg and others, 1954), and in the Saarland 

 (Krebs, 1970) of western Germany also occur in 

 Devonian rocks. 



Earlier workers have proposed that the black 

 fetid beds of barite in Arkansas (Scull, 1958) and 

 Nevada (Ketner, 1965) originated by replacement 

 of carbonate rocks by barium-bearing hydrothermal 

 solutions stemming from intrusive igneous activity. 



