RVING.] 
OURAY   DISTRICT,   COLORADO. 
59 
Uuartzite 
:^-r-Eg|gP Clay  shale 
•md  follows  the  shales  in  a  thin  band  between  the  two  separated  por- 
tions of  the  fissure. 
Ore  and  gangue  minerals. — The  ore  minerals  found  in  these  silver 
pins  are  of  three  classes :  (1)  Original  sulphides,  (2)  oxidation  prod- 
ucts, (3)  secondary  sulphide  enrichment  minerals. 
The  original  sulphides  occur  in  largest  amount  in  the  deeper  por- 
tions of  the  mines,  but  in  many  eases,  as  in  the  Bachelor,  extend 
upward  to  the  top  of  the  vein  beneath  the  black  shales.  They  are 
argentiferous  galena  and  an  antimonial  sulphide  of  copper — locally 
ffllled  gray  copper — which  carries  very  high  values  in  silver  and  is 
probably  related  to  freibergite.  Chalcopyrite  and  pyrite  often  occur 
intermingled  with  the  other  sulphides,  and  sphalerite  is  generally 
present,  though  often  subordinate 
in  amount.  Extensive  oxidation  has 
taken  place  near  the  surface  and  na- 
tive silver  has  been  developed  in  large 
amount.  Its  position  shows  that  it 
has  in  all  cases  been  reduced  during 
the  process  of  oxidation. 
This  is  strikingly  true  in  the  Cal- 
liope mine,  where  a  deep  gulch  cuts 
directly  across  the  strike  of  the  vein. 
The  line  that  separates  the  native  sil- 
ver from  the  unaltered  sulphide  ore 
follows  closely  the  topography,  pass- 
ing down  beneath  the  gulch  at  a  depth 
slightly  less  than  that  between  it  and 
the  tops  of  the  hills  on  either  side. 
'[Thus  in  a  profile  of  the  vein  the  out- 
prop  would  show  a  deep  U-shaped 
Repression  where  intersected  by  the 
l^ulch,  and  the  line  between  the  two 
raids  of  ore  would  show  the  same  profile,  slightly  less  accentuated, 
flie  same  relations  occur  also  in  the  Black  Girl  vein. 
\  Bodies  of  ruby  silver  occur  occasionally  in  the  veins,  but  are  rarely 
found  at  great  depths  below  the  surface.  They  are  thought  to  be  the 
'esult  of  secondary  sulphide  enrichment  of  the  gray  copper  ore, 
>etween  the  zone  of  oxidation  and  the  zone  of  unaltered  sulphides. 
The  gangue  minerals  are  quartz,  barite,  secondary  silica,  a  pinkish 
carbonate,  probably  containing  magnesium  and  manganese,  and  coun- 
try rock.  The  secondary  silica  is  usually  light  grayish  in  color  and 
learly  secondary  when  examined  microscopically.  The  barite  is  very 
jbundant  and  occurs  in  places  in  such  large  amounts  as  to  almost  com- 
letely  fill  the  vein.     Among  the  silver  veins  the  Bachelor  vein  is  of 
Quartzite 
Clay  shale 
Quartzite 
Clay  shale 
Fig.    3- 
Type   of   silver-bearing   vein 
unmodified. 
