308  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1905. 
mill  was  built  several  years  ago,  which  obtained  a  small  product,  but  apparently  without 
sufficient  profit  to  give  encouragement  to  continued  operations. 
The  granite  area  of  the  Bighorn  uplift  has  been  extensively  prospected  for  metallic  min- 
erals, but  the  results  appear  to  be  not  encouraging.  Small  amounts  of  free  gold  occur  in 
quartz  veins  connected  with  the  diabase  dikes  in  the  granite,  but  the  values  are  low.  There 
are  several  prospects  on  the  headwaters  of  East  Fork  of  Big  Goose  Creek.  The  work  was 
begun  in  1898  and,  although  the  results  have  appeared  promising,  no  ore  has  been  pro- 
duced. A  350-foot  tunnel  is  projected  at  one  of  the  mines.  The  rock  is  a  dark-gray  gran- 
ite containing  some  pyrite  and  a  trace  of  copper.  Assays  of  gold  showing  $4  a  ton  are 
reported.     In  one  opening  $12  of  gold  and  $7  of  silver  a  ton  were  found. 
Considerable  prospecting  has  been  done  in  two  large  dikes  southeast  of  Willitt  Creek. 
The  minerals  are  galena  and  pyrite,  occurring  in  small  streaks  in  quartz  along  diabase  con- 
tacts. A  few  small  prospects  have  been  made  in  a  quartz  vein  about  a  mile  north  of  Tongue 
River  Cabin.  A  mine  on  the  ridge  southwest  of  the  mouth  of  South  Fork  of  Tongue  River, 
belonging  to  the  Nickel  and  Copper  Refining  Company,  has  been  worked  at  intervals  since 
1896,  but  is  now  abandoned.  There  is  a  shaft  180  feet  deep,  with  buildings  and  extensive 
machinery.  The  shaft  is  sunk  along  the  contact  of  a  large  dike  of  peridotite  and  a  quartz 
vein,  but  apparently  very  little  mineral  was  found.  It  is  stated  that  platinum  was  one  of 
the  principal  objects  of  the  enterprise.  Extensive  prospecting  was  done  at  intervals  along 
the  dike,  which  has  a  length  of  about  3  miles.  Traces  of  gold  are  found  in  gravels  and  sands 
along  some  of  the  streams  flowing  out  of  the  mountains,  but  they  have  not  been  sufficiently 
promising  to  lead  to  any  placer  mining. 
Rich  gold  prospects  have  been  found  in  the  crystalline  rock  area  in  the  center  of  the 
Bridger  uplift,  7  miles  southwest  of  Deranch.  Very  promising  prospects  of  gold  have  been 
found  recently.  The  metal  appears  to  be  free  and  is  partly  in  quartz  veins  and  partly 
in  association  with  copper  ores.  The  extent  of  the  deposit  has  not  been  ascertained,  but 
numerous  claims  have  been  located,  and  doubtless  these  will  soon  be  thoroughly  explored. 
Very  little  prospecting  has  been  done  in  the  high  ridges  about  Cloud  Peak,  and  possibly 
some  of  the  great  dikes  which  traverse  the  granite  in  that  region  may  carry  minerals  of 
value,  such  as  gold  or  even  platinum,  and  the  rare  earths,  some  of  which  now  have  consider- 
able economic  importance.  The  dike  rocks  contain  magnetite  and  titanic  iron,  but  they 
are  intimately  intermixed  with  the  other  constituents,  and  consequently  are  of  no  value 
Assays  of  ordinary  rock  from  the  two  largest  dikes  showed  no  traces  of  valuable  metals. 
COPPER. 
Copper  minerals,  mainly  malachite  and  red  oxide,  appear  occasionally  in  the  granite, 
and  in  the  vicinity  of  Bull  camp  and  Okie's  store  considerable  prospecting  has  been  done. 
Small  amounts  of  moderately  high  grade  ores  are  obtained,  mainly  from  quartz  veins  in 
the  vicinity  of  the  diabase  dikes.  The  principal  prospects  are  east  and  southwest  of  Bull 
camp,  one  of  the  most  extensive  being  near  Beaver  Creek,  3  miles  east-southeast  of  that 
place.  Here  a  shaft  has  been  sunk  40  feet,  but  only  a  small  amount  of  copper  ore  was 
obtained.  Apparently  the  mineral  is  in  minute  veins  widely  scattered  through  the  rock, 
and  no  bodies  of  economic  importance  appear. 
On  a  branch  of  South  Fork  of  Wolf  Creek,  southwest  of  Walker  Prairie,  several  efforts 
have  been  made  to  develop  a  copper  mine  in  a  15-foot  quartz  vein  in  the  granite.  A  shaft 
has  been  sunk  56  feet  and  crosscuts  made.  The  ore  is  mainly  malachite,  occurring  in  irregu- 
lar veins  in  the  quartz.  Some  galena  also  occurs  and  part  of  the  vein  carries  gold  amount- 
ing to  from  $3.50  to  $4  a  ton.  The  quartz  vein  at  this  locality  extends  about  3  miles 
southwest  and  the  same  distance  east  of  the  opening,  passing  under  Deadwood  sandstones 
at  Walker  Prairie.  Near  its  northeast  end,  at  Walker's  mine,  where  it  is  about  25  feet 
wide,  it  has  been  prospected  to  some  extent.  A  small  amount  of  pyrites  was  obtained 
which  carried  small  values  of  gold. 
