THE BARITE DEPOSITS OF MISSOURI 93 



dike in the southern part of the Central district. How much later 

 this was intruded is unknown, but the writer suggests that the 

 movement of the igneous material came during the deformation 

 of the Cretaceous. If this is correct, the mineralization in the 

 other district as well as that in the Central district can possibly 

 be connected with this deformation. 



Corroborative evidence 



In the study of these deposits, many features have been de- 

 termined which are not described in previously published accounts 

 of barite studies. These facts led to a careful search of the lit- 

 erature to determine to what extent other deposits of barite be- 

 longed to the class of deposits made by the concentration of the 

 materials from the surrounding rocks, and to what extent they 

 possessed the characteristics of those deposits known to owe 

 their origin to igneous rocks. 



Mode of occurrence of barite in other deposits. Some of the 

 points to be considered are the common mode of occurrence of ba- 

 rite in those mineral veins where the origin is accepted as being 

 due to deposition by hot solutions ascending from igneous rocks, 

 its mineral associates in those deposits, and in what rocks they 

 are found. As to the first point, barite is in practically every 

 case among the very last of the gangue minerals to be deposited. 

 The barite veins at Aspen, Colorado, are an exception, but Spurr* 

 states that the usual order of mineral deposition is reversed at 

 Aspen. The conditions there are abnormal. As an excellent ex- 

 ample of barites having been deposited last, the Freiberg de- 

 posits may be cited. There the third and youngest series of veins 

 are baritic. As a rule, the recognition of the order of deposition 

 of the minerals in a given deposit is rather difficult, especially 

 where deposition was rapid and the minerals overlap, or where 

 periods of deposition occurred. This is responsible for the com- 

 mon, indefinite statement that certain minerals were among the 

 last to crystallize. 



In most mineral deposits the mineral associates of barite in- 

 variably include galena, sphalerite, and pyrite, while quartz, flu- 

 orite, calcite, dolomite, siderite, rhodocrosite, marcasite, and 



'Spurr, J. E., Econ. Geo!., vol. 4, p. 301. 1909. 



