90 UNIVERSITY OF MISSOURI STUDIES 



Order of filling. — The barite appears with or without 

 quartz. The deposits in the Proctor dolomite are without quartz, 

 and it is absent from many of those in the Potosi dolomite also. 



The solutions deposited pyrite or marcasite, first; on the 

 dolomite as a rule, but on the drusy quartz if any was present. 

 This was followed by the deposition of sphalerite and galena, 

 always contemporaneously if both are present, but either may be 

 found alone. In the Central district chalcopyrite might have been 

 deposited at this time, altho it is of no importance in any of the 

 deposits. The barite follows the others. If all the preceding 

 minerals are missing, which is not uncommon, the barite is de- 

 posited on the dolomite. In either case very irregular contacts 

 with the dolomite may result. Possibly there are two generations 

 of barite, but of this there is no certainty. A slight overlapping 

 was observed between the barite and the chalcopyrite, the latter 

 having been deposited near the close of the mineralization period. 

 The group of minerals typical of these deposits is a common one. 

 It is found in many deposits in other regions, where the order of 

 deposition is commonly the same as that above, but this depends 

 upon the depth, the temperature, the solutions, and other variable 

 factors. 



Replacement. — The very irregular contact of the barite with 

 the dolomite in the disseminated deposits is evidence of replace- 

 ment. In a few instances the barite had replaced the dolomite 

 between the areas of pyrite, where the latter had not completely 

 covered the vein walls. Thus the barite partly enclosed the 

 pyrite. The boundaries of these masses present the concavo- 

 convex surfaces which Irving^ cites as evidence of replacement. 

 The numerous stringers connected with the veins are also evi- 

 dence of replacement as they run out in all directions and do not 

 follow joints, cracks, or other openings. They usually pinch out 

 at a distance of from a few inches to two or three feet. The 

 Potosi and the Proctor formations show no evidence of being dif- 

 ferently adapted to replacement. Replacement does not appear 

 to be very important in the Central district, where cave or fis- 

 sure filling predominates. 



•Irving, J. D., "Replacement Ore-bodies," Econ. Geol., vol. 8, p. 649. 

 1911. 



