216  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904. 
is  derived  almost  entirely  from  the  mines  of  Butte.  It  is  all  sulphide 
ore,  and  90  per  cent  of  the  output  of  the  mines  is  concentrating  ore, 
carrying  about  3.5  to  4  per  cent  copper,  which  is  concentrated  to 
a  20  per  cent  product  with  a  25  per  cent  loss,  before  going  to  the 
smelting  furnaces.  The  copper  occurs  largely  as  copper  glance, 
either  in  compact  shoots  or  disseminated  in  minute  veinlets  and  par- 
ticles through  altered  granite  or  the  normal  quartz-pyrite  vein  filling. 
Bornite  and  enargite  constitute  a  large  part  of  the  ore.  The  ore  oc- 
curs in  well-defined  replacement  veins  and  in  later  veins  which  fault 
them.  The  ore  bodies  are  in  places  enormous,  stopes  of  150  feet 
across  being  found  in  some  of  the  mines.  The  workings  extend  to  a 
depth  of  2,400  feet  and  are  still  profitable.  Owing  to  the  heavy 
timbering  required  and  the  high  wages  paid,  the  cost  of  mining  is 
relatively  high,  while  the  cost  of  metallurgical  treatment  of  such 
enormous  quantities  of  ore — 6,500  tons  a  day  being  treated  in  the 
Washoe  smelter — is,  everything  considered,  comparatively  low,  not- 
withstanding the  extremely  siliceous  character  of  the  ore. 
An  account  of  the  vein  system  and  geological  structure  will  be 
found  in  a  previous  bulletin.0 
Utah. — Copper  mining  in  this  State  began  only  a  few  years  ago, 
but  is  already  of  very  large  proportions.  The  principal  centers  of 
production  are  at  Bingham,  Park  City,  and  the  Frisco  district,  all 
described  elsewhere  in  this  volume. 
California. — Although  a  great  number  of  copper  deposits  are  scat- 
tered along  the  western  border  of  the  gold  belt  and  the  western  foot- 
hills of  the  Sierra  Nevada,  the  only  large  producing  mines  are  those 
of  the  Shasta  district,  in  which  great  lenses  of  pyritic  ore  occur  in  a 
shear  zone  traversing  metarhyolites,  etc. 
The  largest  ore  body,  that  of  the  Mountain  Copper  Company,  is 
a  solid  mass  of  pyrite  and  pyrrhotite  with  chalcopyrite,  in  sheared 
metarhyolite.  This  mass  is  100  to  400  feet  wide,  800  feet  long,  and 
600  feet  deep,  averaging  5.23  per  cent  copper,  with  2  ounces  silver 
per  ton  and  some  gold.  The  limonite  gossan  was  worked  for  many 
years  for  gold  and  silver.  The  ore  is  massively  schistose,  the  banding 
being  due  to  zinc  blende. 
The  Bulky  Hill  deposits,'J  in  the  same  county,  yield  barytic  ores  re- 
sembling those  of  Vancouver  Island. 
11  Bull.   F.  S.  Geol.  Survey  No.  213,  i>.  170. 
"See  Bull.  V.  S.  Geol.  Survey  No.  213  p.  123;  Bull.  U.  S.  Geol.  Survey  No.  225,  p.  172. 
