"kaxsome.1™  I         CRIPPLE    CREEK    DISTRICT,    COLORADO.  91 
but  rarely  contain  enough  of  the  precious  metals  to  form  ore.  Native 
gold  appears  to  be  absent  from  the  telluride  ores,  except  as  it  may  be 
set  free  by  the  oxidation  of  these  tellurites. 
The  usual  gangue  minerals  of  the  ores  are  quartz,  fiuorite,  and 
dolomite.  Roscoelite  and  rhodochrosite  are  also  found  in  places. 
Oelestite,  or  sulphate  of  strontium,  while  never  present  in  large 
amount,  frequently  occurs  as  little  acicular  crystals  in  the  quartz 
vugs  of  the  lodes.  Calcite  occurs  interstitially  in  much  of  the  breccia 
near  the  ore  bodies,  but  is  rarely  found  in  distinct  crystalline  form 
with  the  ore  minerals.  Secondary  potassium  feldspar  is  common  in 
the  ores;  it  is  especially  abundant  in  the  ores  inclosed  in  granite,  par- 
ticularly those  in  the  Pikes  Peak  type.  This  feldspar  has  the  compo- 
sition of  orthoclase  or  microcline.  and  is  formed  by  the  recrystalliza- 
tion  of  the  original  potassic  feldspar  contained  in  the  rocks.  In  the 
granitic  ores  of  the  Stratton's  Independence,  Portland,  Ajax,  and 
Elkton  mines  this  secondary  feldspar  is  the  principal  gangue  min- 
eral. 
Oxidized  ores,  while  still  worked  in  many  properties,  are  of  rela- 
tively less  importance  than  when  Penrose  described  the  district. 
They  contain  the  characteristic  dull  gold,  often  in  pseudoinorphous 
skeletons,  resulting  from  the  oxidation  of  the  tellurides,  associated 
with  tellurite  (tellurium  dioxide),  emmonsite  or  durdenite  (both 
hydrated  ferric  tellurites),  and  probably  other  oxidized  compounds  of 
tellurium  and  iron.  These  minerals  occur  in  association  with  kaolin, 
alunite,  and  ferruginous  clays.  The  deep  workings  of  the  present 
day  show  that  kaolin  is  always  connected  with  oxidation,  and  is  not  a 
product  of  the  original  mineralization  of  the  district,  as  was  supposed 
by  Penrose. 
The  Cripple  Creek  ores,  as  a  rule,  contain  very  little  silver,  the 
average  proportion  being  about  1  ounce  of  silver  to  10  ounces  of  gold. 
In  the  Portland  and  Stratton's  Independence  mines  the  proportion  is 
very  much  less,  the  silver  from  the  Portland  in  1901  amounting  to 
only  2.4  ounces  for  each  100  ounces  of  gold.  In  the  Blue  Bird. 
Doctor-Jack  Pot,  Conundrum,  Pointer,  and  other  mines  containing 
notable  amounts  of  tetrahedrite  or  galena,  the  proportion  of  silver 
rises,  considerably  above  the  average. 
The  average  value  of  the  Cripple  Creek  ores  lies  probably  between 
$30  and  $40  per  ton.  In  some  of  the  larger  mines  the  average  value 
sinks  to  about  $25  per  toil.  From  a  lower  economic  limit  of  about 
$12  per  ton  the  values  of  individual  shipments  swing  through  a  wide 
range  up  to  ores  carrying  $3,000  or  $4,000,  or  even  $8,000,  per  ton 
Occasionally  smaller  amounts — 1  or  2  tons— have  yielded  as  much 
as  $50,000  per  ton. 
