BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 24, pp. 293-300 June 10, 1913 



PKE-CAMBRIAN" STRUCTURE OF THE NORTHERN BLACK 



HILLS, SOUTH DAKOTA, AND ITS BEARING ON THE 



ORIGIN OF THE HOMESTAKE ORE BODY 1 



BY SIDNEY PAIGE 



(Read before the Society December SO, 1912) 



CONTENTS 



Page 



Introduction 293 



Rocks 294 



Structure 294 



Position and form of the ore body 299 



Character of the replaced rocks 299 



Summary 300 



Introduction 



It is the purpose of this paper to suggest the hypothesis that the Home- 

 stake ore body is in the main a replacement deposit in a calcareous slate 

 series, and that it owes its position to the presence of a strong fault and 

 its form to its replacement character and to structural factors. 



These conclusions are not stated as final, as further study of this 

 problem is contemplated. Paleozoic and Tertiary rocks cover and igneous 

 intrusions in places obscure observations, while the examination under- 

 ground was very incomplete. 



The Black Hills are an oval-shaped mountainous tract, trending nearly 

 north, on the extreme western edge of South Dakota. Physiographically 

 this mountainous tract is the dissected core of an oval-shaped domical 

 uplift which involves rocks as late in age as Tertiary. 



Erosion has stripped the cover from this oval dome and etched the 

 underlying basement series of pre-Cambrian schists. 



Tt is with this underlying pre-Cambrian basemenl series that this paper 

 lias to do, and solely with that portion confined to the northern end of 

 Hie structural dome. 



1 Published with the permission of the Director <>f the U. S. Geological Survey. 

 Manuscript received by the Secretary of the Society February 24, li'i:?. 



(298) 



