GOLD   AND  SILVER 
LAKE  FORK  EXTENSION  OF  THE  SILVERTON 
MINING   AREA.  COLORADO. 
By  I..  II.  Woolsby. 
INTRODUCTION. 
The  Silverton  mining  district,  Colorado,  has  been  under  develop] 
menl  many  years  and  was  described  by  Ransome  and  others  "  after 
examination  in  1889  and   L900. 
What   may  be  considered  a  geologic  extension  of  (his  district   has 
been   opened    near   the   head   of   Lake    Fork  of  Gunnison  River,   at 
Whitecross  post-office,  about  14  miles  by  road  northeast  of  Silverton 
and  nearly  the  same  distance  southwest  of  Lake  City.     This  area  was 
hurriedly  covered  by  a  party  under  Mr.  Whitman  Cross  during  a 
reoonnaissance  of  the  San  Cristobal  quadrangle  in  the  summer  of  1906] 
and  the  mines,  especially  those  closely  surrounding  Whitecross,  will 
be  discussed  iii  the  present  paper  from  held  notes  taken  by  the  writer 
at  that  time. 
GENERAL   GEOLOGY. 
The  geology  along  Lake  Fork,  as  in  most  of  the  Silverton  area,  is 
that  of  an  intricate  igneous  complex.  Water-laid  rocks,  save  small 
amounts  of  fine,  stratified  tuffs,  are  the  exception.  Though  many 
geologic  relations  were  necessarily  undetermined  during  the  stay  at? 
Whitecross,  the  broad  geologic  features  of  the  region  may  be  slated. 
An  indeterminate  breccia,  consisting  largely  of  monzonitic  flow 
breccias  and  tuffs  and  including  some  fragments  of  granite,  occupies 
the  bottom  of  Lake  Fork  for  2  or  3  miles  east  of  Whitecross.  This 
breccia  is  extensively  invaded  and  covered  by  a  rhyolite  bearing 
prominent  quartz  phenocrysts,  apparently  the  same  rock  as  that 
forming  large  masses  on  the  higher  slopes  of  the  valley  and  especially 
on  the  ridges  and  peaks  to  the  east.  To  the  south  this  complex  lies 
against  a  granite  backbone,  which  has,  roughly  speaking,  an  east -west 
extension  for  several  miles  along  Cottonwood  Creek  and  Lake  Fork  lo 
the  east.     Near  the  mouth  of  Cottonwood  Creek,  however,  an  arm  of 
a  Ransome,F.L.,  Economic  geology  of  the  Silverton  quadrangle:  Bull.  '  .  S.  Geol.  Survey  No.  L82,  1903 
Cross,  W.,  Howe,  E.,  and  Ransome,  F.  L.,  Description  of  Silverton  disl  rid  :  Geologic  Atlas  I  [.  S.,  folio 
120,  U.  S.  Geol.  Survey,  1905. 
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