220 



METASOMATIC PROCESSES IN A CASSITERITE 

 VEIN FROM NEW ENGLAND. 



By Leo A. Cotton, B.A., B.Sc, JuxVior Demonstrator in 

 Geology, University of Sydney. 



(Plates xviii.-xx.) 



The chief workers on the origin and occurrence of tin in New- 

 England are Professor David, B.A., F.R.S., and Mr. E. C. 

 Andrews, B.A. The former worked chiefly in the Enaraaville 

 District, and made the relations of the Tertiary basalts to the 

 deep leads his main investigation.* Since Professor David's 

 work was published, mining enterprise has caused more attention 

 to be paid to lode-tin mining. Mr. Andrews, as a later w^orker, 

 has consequently paid somewhat more attention to this phase of 

 the subject. In his papers on the geology of New Englandf he 

 has dealt at some length with the igneous formations. The 

 granites, which occupy the largest portion of New England, he 

 has grouped into three classes — (l)The "blue granite." (2) The 

 *' sphene-bearing granite." (3) And the "acid granite." Of 

 these it is the " acid granite " with which the cassiterite veins 

 of New England appear to be associated. 



Mr. Andrews considers that these veins are the result of 

 intruding solutions, of a very acid nature, into the acid granite. 

 From his observations on the minerals developed in these veins, 

 and their resemblances to foreign occurrences, he has expressed 

 his opinion that the processes involved are chiefly of a metasomatic 

 nature. 



* Geology of the Vegetable Creek Tin-mining Field. Mem. Geol Survey 

 N. S. Wales. Geology No. 1(1887). 



+ " The Geology of the New England Plateau, with special reference to the 

 Granites of Northern New England." Rec. Geol. Survey N. S. Wales, Vol. 

 viii., pp.108 and 196(1905-07). 



