70  CONTRIBUTIONS    TO   ECONOMIC    GEOLOGY,  1904.        [bull.  260. 
barred  by  overlying  bands  of  impervious  shales,  or  until  they  found 
some  porous  layer  along  which  it  was  possible  for  them  to  circulate 
in  a  lateral  direction.  The  alkaline  waters  dissolved  the  quartzite, 
depositing  at  the  same  time  their  burden  of  metallic  sulphides  by 
molecular  interchange,  With  the  sulphides  much  of  the  dissolved 
quartzite  was  redeposited  as  a  matrix  between  the  grains.  The  alka- 
line waters  being  now  deprived  of  their  metallic  contents,  still  con- 
tinued to  flow,  and  penetrating  beyond  the  deposit  which  they  had 
formed,  dissolved  out  immense  empty  cavities  in  the  quartzite.  As  a 
final  phase  of  their  activity  some  of  the  silica  was  deposited  as 
crystalline  druses  of  quartz  on  the  walls. 
A  period  of  rest  then  ensued  and  erosion  carved  the  Uncompahgre 
Valley,  leaving  the  quartzite  in  its  present  elevated  position.  Mete- 
oric waters  charged  with  oxygen  percolated  through  the  outer  portion 
of  the  rocks  near  the  brow  of  the  hill  and  oxidized  the  outer  portions 
of  sulphides  to  ferric  sulphates.  These  ferric  sulphates  attacked  the 
gold  and  carried  it  down  in  solution  to  the  unoxidized  sulphide  in  the 
lower  portions  of  the  ore  masses  and  were  then  reduced  to  ferrous 
compounds.  As  ferrous  salts  have  no  solvent  effect  on  gold,  it  was 
precipitated  in  the  free  condition  in  the  Lower  portions  of  the  deposits. 
The  value  of  the  ores  is  almost  entirely  in  gold.  Silver  is  subor- 
dinate, although  as  much  as  120  ounces  is  sometimes  found,  especially 
when  gray  copper  and  galena  occur  mingled  with  pyrite,  Hie 
values  are  unusually  high,  some  of  the  ore  yielding  as  high  as  30 
ounces  in  gold.  At  the  time  the  mine  was  visited  the  ore  would 
average  when  sorted  about  $00  per  ton.  Owing  to  high  freight  ani 
smelter  charges  $35  per  ton  is  considered  the  lower  limit  for  sulphides. 
In  the  early  days  of  mining  the  values  were  uniformly  higher  than 
at  present. 
Between  1889  and  January,  1905,  the  mine  has  produced  23,641,316 
pounds  of  ore,  valued  at  $1,464,923.35.  This  would  give  an  average 
value  of  $123.12  per  ton,  or,  roughly,  6  ounces  of  gold  per  ton  of 
sorted  rock. 
This  agrees  very  closely  with  the  average  values  obtained  from 
the  Bright  Diamond  quartzite  ores  and  the  most  important  of  the! 
other  similar  though   smaller  deposits  found  along  the  outcrop  oi 
the  Dakota  quartzite. 
Much  of  the  ore  is  shipped  direct.  It  is  transported  in  a  wire 
rope  tramway  from  the  mouth  of  the  mine  across  the  Uncompahgn 
Canyon  to  the  ore  bins  along  the  side  of  the  railroad.  A  mill  adjoin 
ing  the  ore  bins  has  been  used  to  concentrate  the  leaner  sulphides 
It  is  not  in  operation  at  the  present  time. 
The  tramway  is  a  striking  feature  of  the  mine.  It  has  a  tota 
length  of  4,100  feet  and  a  span  across  the  canyon  of  1,800  feet.  Th 
highest  point  of  this  span  is  900  feet  above  the  bottom  of  the  valley 
