44  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1906,   I'AKT    I. 
group  of  which  the  Granite  is  the  most  important  member  cut  both 
granite  and  sedimentary  rocks,  but  do  not  extend  very  far  from  ( lie 
contact.  This  points  to  the  granite  or  to  some  later  igneous  rock 
below  it  as  the  probable  source  of  the  ores.  ■ 
PRACTICAL   DEDUCTK  >  \  S . 
The  country  to  the  north,  east,  and  south  of  the  Granite-Bimetallic 
lode  is  traversed  by  silver-gold  veins,  which  are  smaller  and  of  lower- 
grade  but  otherwise  of  the  same  general  character  as  the  granite  vein] 
Their  strike  varies  less  than  25°  from  east  and  west  and  in  most  places 
is  a  little  north  of  east,  approximately  parallel  to  the  granite  vein. 
Nearly  all  dip  more  than  70°  to  the  south.  They  traverse  both  the 
granite  and  sedimentary  rocks  and  cross  the  contact,  where  they  are 
commonly  displaced  by  faults  apparently  of  small  throw.  Their 
walls,  like  those  of  the  Granite  vein,  are  well  defined  in  the  granite 
but  much  less  sharply  defined  in  the  sedimentary  rocks,  especially 
in  the  limestone,  where  they  become  replacement  veins.  At  some 
places  they  are  faulted  by  cross  faults  other  than  those  at  the  granite 
contact.  The  Headlight  vein,  which  cuts  across  the  bedding  of  lime- 
stone, is  displaced  by  a  number  of  normal  faults  that  follow  the  bed] 
ding  planes  of  the  limestone.  The  ore  minerals  are  essentially  the 
same  as  those  of  the  Granite  vein,  though  there  appears  to  be  a  higher 
percentage  of  rhodochrosite  in  the  veins  where  limestone  is  the 
country  rock.  Near  the  surface  this  alters  to  black  manganese  oxide, 
which  has  been  mined  to  a  small  extent  for  that  metal.  The  'Front 
vein  is  the  most  important  of  this  group  of  silver  veins  and  has  pro- 
duced several  hundred  thousand  dollars'  worth  of  ore. 
Of  the  veins  in  the  granite  to  the  north  of  the  Granite-Bimetallic 
lode  a  number  have  been  prospected  for  more  than  a  thousand  feet 
along  the  strike,  and  considerable  stoping  has  been  done.  None  of 
them,  however,  has  produced  much  more  than  $100,000  in  silver  and 
gold,  and  few  have  paid  for  the  work  expended  on  them.  Though 
they  are  persistent  along  their  strike,  easily  followed,  and  many  of 
them  of  satisfactory  grade,  they  are  in  few  places  of  payable  width. 
From  analogy  with  the  Granite  vein  the  depth  at  which  the  rich- 
esl  ore  should  be  found  in  these  veins  is  from  200  to  700  feet  below 
the  surface,  and  the  tops  of  the  richest  ore  shoots  should  be  found 
not  more  than  400  feet  deep  and  in  most  places  much  nearer  the 
apex  of  the  vein.  Considerable  prospecting  has  been  done  at  this 
depth  in  secondary  sulphide  ores.  In  the  country  to  the  northeast 
and  east  of  the  Granite  mine  there  are  numerous  outcrops  of  quartz 
veins  that  have  been  prospected  only  superficially.  If  there  are 
shoots  of  rich  ore  in  these  veins,  their  highest  point  will  likely  be 
found  almost  invariably  within  200  feet  of  the  surface,  though  it  is 
possible  that  the  highest  point  of  some  will  be  100  or  in  a  few  places 
even  200  feet  lower. 
