The Tlicory of Copper Deposit ion — Lane. 2:)j 
THE THEORY OF COPPER DEPOSITION. 
By Ai-FKEi) C. Lank, State Geologist, Lansing. Mich.* 
Diuin;;- the past few years there has hecii a lively interest 
in the theory of the origin of ore deposits, and r(^cently two 
works have been pnhlished by the Institute of Mining Engi- 
neers and by the Engineering and Mini':-^ j\>nrnal, which give 
a very good account of the j-jresi : . sl;ite of the controversy, 
and references enough to carry one pretty well over the whole 
field of the latter. f In these discussions our deposits of iron 
ore and copper oi lake Superior have been frequentlv used as 
illustrations of the various theories by those who take part 
in tlie discussion. In view of these facts, it seems proper to 
give a review of what is known concerning the copper of lake 
Superior :iiul of the theories regarding the same. There is also 
a practical i:iierest involved in the disci.osion. As we shall 
shortly see, all the best authorities at present agree that the 
copper has been deposited by water, but there is some dififer- 
eiice of opinion as to whether the water current is a de- 
scending one and copper was deposited and a circulation pro- 
duced l)y gravity, or ascending, and the circulation due to 
one or more jirincipal causes, which we may call as a common 
name, volcanic, meaning thereby that they are connected with 
the interior heat of the earth. Xow, it is a common notion 
among the practical Cornish miners of the copper country, al- 
though I do not remember to have seen the statement in 
print, that the copper is liable to occur under high ground. 
To understand what is meant by the expression "high 
ground," we must remember that at the present day the bulk 
of the copper is deposited in bedded lodes. It would be per- 
haps more correct to say that it comes from lodes whose strike 
•.Advance sheets from the Annual Report for 190.3, reprinted from The 
Michigan .Ai/ner. January and Fetjruary, 1 9(14-. It should be understood that 
the title in a general magazine like the Amkkican Geologist is too broad, for 
the article has reference solely to the deposits of Keweenaw Point, and the 
author does not wish to apply either facts or conclusions to other deposits, 
such as the sulphides, whose history he believes to be difterent. 
t Genesis of ore deposits. Reprinted papers from Volumes xxiii, xxiv, xxx 
and xxxi of the Transactions of the .American Institute of Mining Kngincers. 
Published by the Institute at the oftice of the Secretary, New York City. 1902. 
Ore Deposits, a discussion republished from the Engineering and Mining 
Journal, New York City, 1903. 
See also Geological Survey of Michigan, vol. i, Part II, p. 4-3. Vol. vi. 
Part I, p. 216. 
Vet more recent: Trans. Am. Inst. Min. Eng.,Oct., 1902. "Igneous Rocks 
and Circulating W aters as Factors in Ore Deposition," by J. F. Kkmp; "Ore 
Deposits Near Igneous Contacts," by W. H. Wred, and discussion of same. 
Annual rc])ort of the State Geologist (of .New Jersey ). 1902. "Copper De- 
posits of New Jersey." l)y Wai.tkk Hakvkv Whed. "The Chemistry of Ore 
Deposition," by Wai.trk P.Jen.nev. 
