90 Transactions. 



Art. IV. — Notes on the Distribution of Ores in Horizontal 

 Zones in Vertical Depth. 



By Professoi- James Park, M.A.Inst.M.E., M.Inst.M. and M., 

 F.G.S., Director Otago UniveTsity School of Mines. 



[Read before the Otago Inititnte, Hth August, 1905.] 



It has been clearly demonstrated by mining operations in the 

 United States, England, and elsewhere that while in many 

 veins the metallic sulphides are intimately mixed without 

 any definite arrangement, in other veins, particularly those 

 of lead, zinc, and iron, there is a more or less orderly distribu- 

 tion in horizontal zones in a vertical direction : that is, there 

 are certain horizontal zones each of which is characterized by 

 a dominant sulphide. 



This arrangement of the metallic contents of a vein in more 

 or less horizontal zones was noticed in Cornwall many years 

 ago ; and no better example could be found than that presented 

 by the celebrated Dalcoath Mine, which commenced as a tin- 

 mine, at a lower depth yielded nothing but copper, and again 

 below that, tin. 



In the great lead- and zinc-mining region of Ozark, in the 

 lower Mississippi Valley, the vertical distribution of the ores, 

 according to Bain,* is as follows :— 



(1.) Oxidized zinc and lead ores, with galena. 

 (2.) Blende, with a little galena. 



(3.) Iron-sulphide predominates, and increases with 

 depth. 



Spurr.f in his report on Monte Cristo mining district, in 

 Washington, states that the quartz, p^Tite, chalcopyrite, pyrr- 

 hotite, blende, galena, realgar, stibnite, and calcite show a 

 marked tendency to aggregate themselves in horizontal zones 

 in the order named above. 



Rickard mentions the orderly distribution of ores in Colo- 

 rado. J Weed states that in the Castle Mountain district, in 

 Montana, the order appears to be galena on top, passing into 

 highly zinciferous ores below, and these into low-grade pyTite.§ 



* H. F. Bain, U.S. Geol. Survey, Twentv-second Annual Report, 

 Part II, p. 161. 



t J. H. SpuiT, foe. clL, p. 841. 



J. J. A. Rickard, Trans. Inst. Min. and Met. London, Vol. vi, 1899, 

 p. 196. 



§ Weed and Pirsson, Bull. 1.39. U.S. Geol. Survey, 1896. 



