516 



THK ORE-DEPOSITS OF BORAH CREEK, 



slight alteratioa of the walls of the lode. In his examination 

 of the ore deposits of Monte Cristo,* Mr. Spurr has given an 

 ideal diagram of tlie se- 

 quence of the ores in this 

 district. This is here 

 reproduced (text fig. 6), 

 sliglitly modified, for com- 

 parison with the order 

 ob.served in the Borah 

 Creek Mine. A corrc's- 

 ponding diagram (text fig. 

 7) has been drawn for the 

 sequence of ore-deposition 

 in the Borah Creek Lodes. 

 There is a very striking 

 similarity between the 

 structure of the two ore- 

 bodies. 



Text-fig. 6— Modification of Mr. J. E. 

 Spurr's diagram illustrating sequence of 

 ore-deposition at Monte Cristo, Wash- 

 ington. 



B, Beginning of crystallisation— E, End 

 of crystallisation — 1, quartz —2, arseno- 

 pyrite — ."}, pyrite — 4, chalcopyrite — 5, 

 pyrrhotite — 6, blende — 7, galena — 8, real- 

 gar — 9, stibnite — 10, calcite. 



Summary. 



The Borah Creek Mine is situated in the New England Dis- 

 trict of New Soutli Wale.s, within two miles of the Gwydir 



River. The lode is a solid 

 granite, of a very acid 

 nature, which has intruded 

 an older and more basic 

 granite. The "acid granite," 

 as Mr. Andrews has termed 

 it, has been shown by 

 several writers to be inti- 

 mately related to the tin- 

 deposits occurring along its 

 margin. The Borah Creek 

 Lode crosses the contact 



Text-fig. 7. — Diagram illustrating 

 sequence of ore-deposition at Borah 

 Creek. 



B, Beginning of crystallisation — E, End 

 of crystallisation — 1, arsenopyrite — 2, 

 pyrite -3, chalcopyrite —4, sphalerite — 

 '}, stannite — f>, galena — 7, quartz. 



* Spurr, J. E., "Ore-deposits of Monte Cristo, Washington, Twenty- 

 Second Annual Report U.S. Geol. Surv., Pt.ii., Ore-deposits, p. 840. 



