ORE    DEPOSITS    IN    THE    VICINITY   OF    LAKE    CITY,   COLO. 
By  J.  D.  Irving. 
INTRODUCTION. 
The  town  of  Lake  City,  which  has  a  population  of  TOO,  is  situated 
in  the  San  Juan  Mountains  in  the  southwestern  portion  of  Colorado, 
at  the  junction  of  Lake  Fork,  a  tributary  of  Gunnison  River,  and 
Henson  Creek. 
The  region  in  which  the  mining  developments  have  been  carried' 
on  is  extremely  rugged  and  precipitous,  and  cliffs  in  many  places 
rise  1,000  feet  above  the  level  of  the  streams.  The  mountain  peak' 
in  the  vicinity  are  among  the  highest  summits  in  the  State  of  Colo 
rado,  Uncompahgre  Peak,  9  miles  to  the  northwest  of  Lake  Citj 
having  an  altitude  of  14,306  feet. 
The  ore  deposits  described  in  this  paper  are  located  along  th< 
courses  of  Lake  Fork  and  Henson  Creek.  They  extend  along  Lata 
Fork  to  a  point  5  miles  south  of  the  town,  and  along  Henson  Creel 
westward  through  Henson  and  Capitol  City  for  a  distance  of  1< 
miles.  Very  little  prospecting  has  been  done  at  any  considerabl 
distance  from  the  streams,  and  practically  all  of  the  active  mininj  | 
has  been  carried  on  along  the  comparatively  accessible  bluffs  adjacen 
to  them. 
GEOLOGY. 
All  the  rocks  exposed  in  the  mining  region  are  of  igneous  origii 
They  may  be  divided  into  the  following  fairly  distinct  groups: 
1.  Volcanic:  Rhyolitic  flow  breccias,  tuffs,  and  agglomerates;  andesitic  tufi  I 
and  agglomerates. 
2.  Intrusive:  Intrusive  andesite-porphyries ;  intrusive  pyroxene  audesites  I 
intrusive  diabase:  intrusive  latite. 
The  exact  sequence  of  these  various  rock  types  has  not  yet  been  d< 
termined  in  detail.    It  is  possible,  however,  to  give  a  brief  preliminar 
outline  of  the  more  prominent  geologic  features.     The  hills  whit 
form  the  sides  of  the  canyon  of  Henson  Creek  are  composed  large]) 
of    rhyolite    flow    breccias.     These    frequently    form    perpendiculd 
cliffs  which  rise  500  or  600  feet  above  the  stream  bed.     They  ajij 
characterized  by  a  prominent  banding,  which  often  imparts  to  tl 
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