LEAD AND ZINC ORES. 1 145 



Associated with the sphalerite and galena are large amounts of marcasite 

 and pyrite. For much of the region the workings have not extended far 

 below the level of ground water, but in certain districts they have reached 

 a considerable depth. In some places, as at Granby, Mo., a deep exploration 

 has shown pyrite and marcasite to dominate at the lowest level reached. 



Under the present heading a full consideration of the concentration by 

 ascending waters is excluded; but in order to consider the secondary work 

 of descending waters it is necessary to outline the work of the first concen- 

 tration by ascending waters. 



In the Upper Mississippi Valley the order of occurrence of the minerals 

 at many openings from the wall to the center of the veins or to the druses 

 is marcasite, ferriferous sphalerite, galena in cubic crystals; or is sphalerite, 

 galena. In some cases the order is marcasite, blende, these two being 

 repeated perhaps several times. Not infrequently the galena of the first 

 succession is followed by marcasite and (very subordinate in Quantity) 

 galena in octahedral crystals. Occasionally between the galena and the 

 second marcasite is ferriferous sphalerite in small amount. If the druses 

 are not fully closed by the sulphides there usually follows calcite, and 

 occasionally barite on the calcite. Thus if there were a full succession at 

 any one place, it would be (1) marcasite, (2) ferriferous sphalerite, (3) galena 

 in cubic crystals, (4) ferriferous sphalerite, (5) marcasite, (6) galena in 

 octahedral crystals, (7) calcite, (8) barite. 



In the Lower Mississippi Valley sequences similar to those in the 

 Upper Mississippi Valley occur in certain places, but in the best known and 

 most productive district, that of southwestern Missouri, there seems to be 

 no regular sequence for the sulphides. According to Bain, the general 

 order of deposition for this district, within the openings, was dolomite, 

 metallic sulphides, and chert. "To some extent these processes were con- 

 temporaneous or recurrent, but as a whole they occur successively in the 

 order named." As to the relations of the sulphides to one another, Bain 

 says: "Blende rests on galena and galena on blende indiscriminately, and 

 both cover and in turn are covered by iron sulphide." b Also blende and 

 galena are in many cases intimately intermingled. 



a Bain, H. F., with Van Hise, C. R., and Adams, G. I., Preliminary report on the lead and zinc 

 deposits of the Ozark region : Twenty-second Ann. Kept. U. S. Geol. Survey, pt. 2, 1901, p. 162. 

 » Bain, H. F. , cit. , pp. 151-152. 



