64 IOWA ACADEMY OF SCIENCES. 



RECENT DEVELOPMENTS IN THE DUBUQUE LEAD 

 AND ZINC MINES. 



BY A. G. LEONARD. 



During the pa&t year or two there have been some important 

 developments in the Dubuque district. New lead mines have 

 been opened up, new ore bodies have been discovered, and the 

 Durango zinc mine, the largest in the state, has been still 

 further developed. 



About one mile west of the city is located the mine of the 

 Dubuque Lead Mining company, which has been worked only 

 about a year and a half. It is on the west end of the old level 

 range which has been followed for nearly three miles and has 

 yielded considerable ore from various points along its length. 

 When the mine was visited in November, 1895, there were 

 seventy -five men employed and the place presented a lively 

 appearance. The three shafts are 210 feet deep with a steam 

 hoist on one and gins on the other two. The company has 

 just erected a concentrator at the mine for the purpose of 

 crushing and cleaning the ore. This was made necessary by 

 the fact that in this mine much of the Galena occurs scattered 

 through the rock, sometimes in particles of considerable size. 

 The limestone is crushed aid the lead then separated from it 

 by washing. The ore-bearing dolomite forms a zone from two 

 to four feet wide and contains an abundance of iron pyrites. 

 This latter mineral is often found here crystallized in beautiful 

 octahedrons with a length of from one-fourth to three-fourths 

 of an inch. Besides being disseminated through the rock the 

 Gal%na occurs in large masses in what is probably the fourth 

 opening, and it likewise fills the crevice above for some dis- 

 tance. The ore body is apparently an extensive one; 700,000 

 pounds cf lead have already been raised. Work in this mine 

 is made possible only by the constant operation of a steam 

 pump which keeps the water below the opening where the ore 

 occurs and thus allows the miners to reach the deposits. 



