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University of California Publications in Geology 



[Vol. 8 



mass have accepted without question Weed's interpretation of its 

 structure and it has become well known by his name. These writers 

 have been interested primarily in the study of the ore deposits, which 

 occur either in the supposed batholith or on its periphery, and the 

 assumption which has been made by them as to its batholithic char- 

 acter has had an important influence itpon their speculations as to 

 the genesis of the ores. Thus Weed 2 in 1912 says: "Though the 

 evidence is not conclusive, it is believed to indicate that the copper 

 and other metals of the quartz-pyrite veins are derived from mag- 

 matic emanations coming from a deep-seated mass of igneous magma." 



Kirk 3 concludes: "The two ultimate sources possible for these 

 ascending waters are, (1) meteoric, and (2) magmatic. The location 

 of these deposits many miles within a comparatively impervious 

 batholith renders difficult the conception that meteoric waters could 

 have gained access to a point where their ascent finally became pos- 

 sible. ... A supposition that appears to conform well with all 

 existing conditions is that the origin of both waters and ore was in 

 a cooling magma comparatively near the present surface — a state of 

 affairs which might well exist locally within a large batholith." 



Knopf 1 reaches a similar conclusion with regard to the older ore 

 deposits of the Helena region at the northern end of the intrusive 

 mass; although his chief argument for the magmatic supply of the 

 ore is based on the presence of tourmaline in the veins. He says : 



Although it seems clear that the ore deposits are closely linked in origin 

 with the intrusion of the quartz-monzonite, this causal connection may ulti- 

 mately be due either to (1) the heat furnished by the magma, thus stimulating 

 the circulation of meteoric waters and increasing their solvent powers, or 



(2) to the release of metalliferous solutions from the cooling magma, or 



(3) to combinations of (1) and (2). The current theory of ore deposits holds 

 that the presence of tourmaline, because of its content of boron and fluorine, 

 is proof that the deposits in which it occurs were formed by direct exhalations 

 from a cooling magma. In the ore deposits here considered the solutions that 

 carried the elements of the tourmaline carried also those of the metallic sul- 

 phides and the sulphides were formed contemporaneously with the tourmaline. 

 It is therefore probable that the ore-depositing solutions were of magmatic 

 derivation and represent the final manifestation of the intrusive energy of 

 the great monzonite invasion. 



- Geology and Ore Deposits of the Butte District, Montana, U. S. G. S. Pro- 

 fessional Paper 74, p. 97. 



3 Conditions of Mineralization in the Copper Veins at Butte, Montana, Eco- 

 nomic Geology, Vol. 7, p. 80, 1912. 



* Ore Deposits of the Helena Mining Eegion, Montana, U. S. G. S. Bull. 527, 

 pp. 51-53, 1913. 



