Irving.]  ORE    DEPOSITS    NEAR    LAKE    CITY,    COLO.  83 
GOLD-BEARING  FISSURE  VEINS. 
The  gold-bearing  fissure  veins  are  those  which  produce  chiefly 
gold,  Avith  usually  subordinate  silver.  Only  two  veins  of  this  char- 
acter have  so  far  been  at  all  productive.  These  are  the  Golden  Fleece 
and  Black  Crook.  The  Black  Crook  vein  can  hardly  be  distinguished 
as  a  gold  vein,  as  it  has  produced  much  silver  ore;  but  its  upper  por- 
tions contained  large  quantities  of  fine-grained,  brownish,  iron  pyrite 
with  high  values  in  gold.  Except  for  this  occurrence  it  might  be 
placed  among  the  less  prominent  silver-bearing  veins. 
According  to  a  statement  made  by  the  management  the  Golden 
Fleece  mine  has  produced  $1,400,000  and  has  been  sufficiently  prom- 
inent to  warrant  a  brief  description.  It  is  situated  on  the  west 
bank  of  Lake  Fork,  about  5  miles  south  of  Lake  City,  opposite 
Lake  San  Christobal.  The  country  rock  consists  of  tuft'  and  breccia 
interbedded  with  andesite  flow  breccia  and  cut  by  a  small  dike  of 
diabase  or  related  rock.  The  bedding  of  the  tuffs  dips  in  a  gen- 
eral way  toward  the  west,  although  it  is  so  much  disturbed  and 
distorted  and  so  confusedly  related  to  the  flow  breccias  that  it  can 
not  be  said  to  show  airy  constant  dip.  The  workings  of  the  mine  con- 
sist of  four  tunnels,  the  upper  three  running  in  on  the  vein  in  a 
westerly  direction.  The  highest  is  about  1,000  feet  from  the  bottom 
of  the  creek.  The  two  successively  lower  ones  are  100  and  200  feet 
below.  The  fourth  and  lowest  is  an  adit  a  short  distance  above 
the  stream  bed  level.     It  is  2,100  feet  in  length. 
In  its  outcrop  the  vein  formed  a  ridge  about  25  feet  in  width,  with 
a  nearly  westerly  strike  projecting  above  the  surrounding  rocks  for  a 
distance  of  about  125  feet.     This  ridge,  together  with  the  rocks  at  its 
base,  slopes  eastward  in  the  direction  of  strike  at  an  angle  of  about 
i>0°.     In  depth  the  vein  assumes  a  more  regular  character,  but  even  in 
the  lower  levels  the  ore  is  a  more  or  less  broken  and  confused  mass  of 
tuff  fragments,  gangue,  and  ore  minerals.     The  uppermost  tunnel  of 
the  mine,  570  feet  west  of  the  opening,  encountered  an  abrupt  wall 
of  rock  dipping  west  about  30°.     This  wall,  or  roof,  as  it  may  more 
properly  be  called,  reappeared  in  the  two  lower  levels,  but  has  not 
yet  been  encountered  in  the  lowest  tunnel.     The  rock  on  the  western 
4de  of  this  plane  consisted  of  a  very  coarse  breccia  composed  of  large 
)owlders  of  yellowish-colored  tuff  cemented  together  by  a  volcanic 
naterial  of  the  same  character  as  the  bowlders  themselves.     There  is 
ittle  doubt  that  it  is  a  true  volcanic  breccia.     It  was  at  first  consid- 
ered to  be  a  simple  fault,  but  a  tunnel  was  run  into  it  for  a  distance 
f>f  more  than  1,500  feet  and  failed  to  reveal  any  other  rock  than  the 
breccia  first  encountered.     It  therefore  seems  probable  that  there  is 
lere  a  heavy  volcanic  breccia  which  has  been  faulted  into  its  present 
osition.     That  the  plane  is  distinctly  a  fault  plane  is  shown  first 
