144 ECONOMIC GEOLOGY 



chloride. Meteoric waters transferred the sodium chloride down- 

 ward and in their downward transition they dissolved the copper 

 as copper chloride. Reactions between the original minerals of 

 the volcanics and the copper solution gave rise to native copper, 

 calcium chloride and soduim silicates. 



The following assemblage of facts bearing on the source of the 

 copper in the Lake Superior district is taken directly from the 

 masterly work of A. C. Lane on the Keweenaw Series of Michigan. 



(A) The dissemination of copper in small quantities through- 

 out the formation. The average from several thousand feet of 

 drilling at the Clark-Montreal mine was 0.02 per cent. Hardly 

 a single amygdaloid fails to carry less than 0.02 per cent, copper, 

 and when the copper content reaches 0.5 per cent, it is nearly 

 an ore. 



(B) The occurrence of native copper in similar formations of the 

 red rock associated with salt waters and lavas elsewhere, notably 

 in the New Jersey Triassic, in the Bolivian Puca sandstone, in 

 Nova Scotia, around Oberstin, in the Naho melaphye region, and 

 in Alaska. 



(C) The general absence of native copper outside the Keween- 

 awan, in the Lake Superior region, but 



(D) Native copper has been found in iron ore (generally thought 

 to be formed by the action of downward working waters) in a few 

 places. 



(E) The water in the formation is of three kinds. 



(a) At and near the surface soft and fresh with sodium in 

 quantities more than sufficient to combine with the chlorine. 



(6) At some distance (generally 500 to 2000 ft., before it attracts 

 attention, unless especially sought) the chlorine is higher and the 

 water is charged with common salt. The line between the two 

 classes of waters is often quite sharp. 



(c) At greater depths a strong solution of calcium chloride 

 contains some copper. 



(F) The middle water b often contains more salt than it could 

 possibly have were it a mixture of a and c. 



(G) The lines between the different kinds of waters are not 

 regular, yet the lowest water probably always comes within 2000 

 or 3000 ft. of the surface. 



(H) The amygdaloids seem, other things being equal, to contain 

 rather stronger (more saline) water than the conglomerates. 

 (I) An unequally heated solution corresponding to mine water 



