UNIVERSITY OF CALIFORNIA PUBLICATIONS 



BULLETIN OF THE DEPARTMENT OF 



GEOLOGY 



Vol. 10, No. 20, pp. 361-382, pis. 25-27, 3 text-figures November 8, 1917 



THE GEOLOGY AND ORE DEPOSITS OF THE 

 LEONA RHYOLITE 



BY 



CLIFTON W. CLARK 



CONTENTS 



PAGE 



Character and Purpose of the Work 362 



Physical Features of the Area 362 



Pre-Reeent Erosional Surface 363 



Geological History 364 



Distribution of the Rhyolite 365 



Nature of Surface upon which Lava Flowed 365 



Age of the Rhyolite 366 



Faulting 366 



General Features of the Rhyolite 367 



Petrographical Characters 368 



Felsite Faeies .„. 368 



Felsophyric Facies '. 369 



Vitrophyric Facies 369 



Microlitie Facies 369 



Distribution of the Different Faeies — 370 



Summary of the Microscopic Study 371 



Chemical Characters 371 



Pyrite Deposit - - 372 



Location - 372 



Underground Development 373 



Occurrence 373 



Mineralogy - 374 



Metallographic Study of the Ore 374 



Genesis of the Ore 375 



The Relation of Fracturing to the Ore Deposit 377 



The Reducing Effect of the Rhyolite _ 377 



Summary 37 



