82  CONTRIBUTIONS    TO   ECONOMIC    GEOLOGY,  1904.        [bull.  26^ 
den  Treasure  ores  it  is  subordinate;  in  others  it  is  higher  in  amouni 
in  the  upper  lodes  and  abundant  below ;  and  in  some  eases,  as  in  tht 
Moro  mine  and  the  Yellowstone  Gulch  properties,  it  forms  more  thai 
50  per  cent  of  the  ore  minerals,  so  that  its  removal  constitutes  one  o: 
the  most  serious  problems  of  exploitation. 
The  gangue  minerals  are  quartz,  rhodonite,  rhodochrosite,  and  bar 
ite.     The   ore   minerals   are   usually   scattered   through   the   gangui 
minerals  in  more  or  less  irregular  bands.     A  definite  sequence  o 
deposition  can  frequently  be  determined,  but  space  is  hardly  availa 
ble  here  for  such  discussion.     A  replacement  of  the  country  rock  b 
silica  has  often  extended   for  considerable  distances  from  the  vein 
and  the  fragments  of  the  country  rock  which  are  included  within  th 
vein  are  usually  altered  to  a  dense  black  silica.     Alteration  of  othe 
kinds  also  extends  to  even  greater  distances  from  the  fissures,  bi 
replacement  has  not  been  a  serious  factor  in  the  extension  of  value 
into  the  wall  rock,  and  commercial  operations  are  confined  to  the  vei 
tilling.     Clay  selvages  may  often  be  observed  in  the  upper  portions  c 
the  ore  body,  but  they  disappear  in  depth,  the  veins  being  tight] 
frozen  to  their  Avails. 
Values. — In  the  upper  portions  of  the  veins  the  values  have  bee 
uniformly  high,  especially  where  pockets  of  ruby  silver  have  bee 
discovered.  A  single  bonanza  at  times  produces  as  high  as  15,01 
ounces  of  silver  .per  ton.  These  masses  are,  however,  exceptional,  ar 
in  the  zone  of  unaltered  sulphides  the  silver  values  are  contained  in  tv 
of  the  ore  minerals,  the  galena  and  tetrahedrite.  The  galena,  whe 
solid,  usually  carries  about  22  ounces  of  silver  per  ton,  rarely  run  nil 
above  80  when  unmixed  with  tetrahedrite.  The  tetrahedrite,  or  an 
monial  copper  sulphide,  usually  carries  the  larger  portion  of  the  s 
ver,  and  is  thought  to  be  related  to  the  argentiferous  variety  kno\  j 
as  freibergite.  It  carries  silver  ranging  in  value  from  30  to  ma: 
thousand  ounces  per  ton,  and  where  richest  in  silver  has  usually 
more  brilliant,  greasy  luster  than  where  it  is  barren  of  valu 
Where  galena  carries  very  high  values  in  silver,  it  will  be  genera' 
found  to  be  mingled  with  large  proportions  of  this  freibergite. 
Treatment  of  ores. — A  small  smelter,  known  as  the  Crook  smelt 
was  originally  operated  at  Lake  City  for  the  Ute  ores,  but  was 
operation  only  a  short  time.  Most  of  the  ore  mined  has  been  shipr. 
for  treatment  to  other  smelting  centers  or  concentrated  at  the  mil 
and  the  concentrates  shipped  for  further  treatment.  Ores  conta 
ing  high  percentages  of  lead  usually  gain  the  precedence  over  ill 
other  ores  in  the  cost  of  treatment.  Large  mills  are  located  at  il 
Hidden  Treasure  and  Ute  mines  in  Henson  Creek.  From  the  smal  j 
mines  only  such  ores  as  may  be  profitably  shipped  are  now  mined. 
