UNIVERSITY OF CALIFORNIA PUBLICATIONS 



BULLETIN OF THE DEPARTMENT OF 



GEOLOGY 



Vol. 8, No. 1, pp. 1-15 Issued January 8, 1914 



IS THE BOULDER "BATHOLITH" A 

 LACCOLITH ? 



A PROBLEM IN ORE-GENESIS 



BY 



ANDEEW C. LAWSON 



CONTENTS 



PAGE 



Introduction 1 



Vagueness of the Term Batholith 3 



Distinction between Laccolith and Batholith 4 



Laccolith 4 



Batholith 6 



Criteria Applied to the Boulder Intrusive 8 



Size 8 



Structural Features 9 



Metamorphism 12 



Consequences of the Laccolithic Hypothesis 13 



Magmatic Concentration of Sulphides 13 



Access of Meteoric Waters 14 



Conclusion 15 



INTBODUCTION 



The granite (quartz-monzonite) in which the mines of Butte, 

 Montana, are situated was stated by Weed 1 in 1899 to be a batholith 

 and was named by him the "Boulder batholith." The statement 

 was accompanied by a brief account of the intrusive relations of the 

 granite to the surrounding rocks at Elkhorn and Helena. Since 

 then various writers who have discussed the geology of this intrusive 



1 Granite Koeks of Butte, Montana, and Vicinity, Jour. Geo!., vol. 7, p. 737, 

 1899. 



JAN 20 1914 



