98 Transactions. 



Art. VI. — Notes on the Origin of the Metal-bearing Solutions 

 concerned in the Formation of Ore-deposits. 



By Professor James Park, M.A.Inst.M.E., M.Inst.M. and M. 

 (Lond.), F.G.S., Director Otago University School of 

 Mines. , 



[Bead before the Otago Institute, Sth Augiist, 1905.] 



Ore-deposits may be divided into two genetic classes — namely, 

 those deposited by metal-bearing solutions, and those formed 

 by direct magmatic segregation in an igneous magma. The 

 former include the majority of ore-deposits of economic value ; 

 the latter are comparatively rare and unimportant. 



It is manifest that the waters concerned in the formation 

 of ore-deposits of the first class must be either (a) meteoric 

 and descending, or {b) magmatic and ascending. 



Descending waters are believed to gather their mineral 

 contents from the rocks through which they percolate. They 

 are said by Van Hise and other writers to descend to great 

 depths by gravitative stress, and to move laterally towards 

 open channels and fissures, where they deposit mineral matter. 

 In this we find the basis of the theory of lateral secretion. 



Hot ascending solutions are held to be genetically connected 

 with igneous masses — that is, they are either directly magmatic, 

 or they are liberated from sedimentaries in the form of gases' 

 and aqueous vapour. In this conception we have the funda- 

 mental basis of the theory of ascension of solutions. 



Theory of Lateral Secretion. 



According to this theory it is assumed that meteoric waters 

 percolating through the country rock, by the aid of carbon- 

 dioride and alkalies dissolve out certain constituents, which 

 are afterwards deposited in fissures and cavities. 



The origin of the theory is unknown, but it is certain that 

 Delius, in 1770, Gerharde, in 1781, and Lasius, in 1789, were 

 supporters of it, the latter basing his argument upon a careful 

 examination of the veins of the Hartz Mountains.* 



In 1847 Professor Bischof, of Bonn, a distinguished geologist 

 and chemist, in his fascinating " Text-book of Chemical and 

 Physical Geology," discusses the chemical processes which take 

 place when meteoric waters and different kinds of aqueous 



* Georg. Lasixis, " Observations on the Hartz Mountains," Hanover, 

 17SH : " Ores and Minerals," Vol. ii. 



