52  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   L906,   PART    I. 
Distribution  of  ore  in  the  deposits. — The  distribution  of  ore  in  the 
ore  zone  is  extremely  irregular.  The  largest  and  richest  body  of 
ore  was  the  Cornish  ore  shoot,  a  rudely  cylindrical  mass  inclined  from 
the  horizontal  toward  the  west,  and  occupying  approximately  thl 
Cornish  stope,  described  on  page  46.  Above  this  and  connected  with 
it  is  the  Square  Set  ore  shoot,  which  continues  upward  at  a  steeper 
angle  to  the  surface.  The  Showers  ore  shoot,  about  100  feel  west 
of  the  engine  station,  is  in  line  with  the  other  two,  but  a  large  irregtj 
lar  body  of  magnetite  is  situated  between  them.  The  magnetitl 
forms  the  northwestern  boundary  and  a  part  of  the  base  of  the 
Cornish  ore  body.  The  three  ore  bodies  appear  to  be  connected 
to  the  south  of  the  magnetite  body  by  coarsely  crystalline  calcitl 
and  quartz.  The  plane  of  these  ore  bodies  is  near  the  center  of  the 
ore  /one  and  makes  a  small  angle  with  its  strike,  trending  more 
nearly  east  and  west.  Still  another  group  of  ore  bodies  occurs  to 
the  north  of  this  one,  lying  jelose  to  the  north  Granite  contact.  It 
is  not  connected  by  ore  with  the  Cornish  group.  Of  the  northern 
group  the  Lake  ore  shool  is  by  far  the  largest  and  most  productive! 
The  shape  of  thi~>  ore  body  was  nearly  that  of  a  thin  cylinder  about 
320  feet  long  -approximately  the  shape  of  1  he  Lake  stope,  describe! 
on  page  46.  Its  northwest  end  is  connected  by  low-grade  sulphidl 
ore  with  an  ore  body  just  below  and  a  little  farther  north  on  the 
65-foot  level,  below  which  there  are  still  others  <>n  the  1  10-foot 
and  214-foot  levels.  In  these,  however,  the  ore  does  not  extend 
eastward  a-  far  as  in  the  Lake  ore  body.  All  the  ore  bodies  of  this 
group  are  closer  to  the  uortheast  wall  than  to  the  southwest  wall 
and  are  north  of  and  below  the  Cornish  group.  The  Square  Set  and 
Cornish  stopes  are  connected  1>\  ore,  as  are  the  Lake  stopc  and  the 
-tope  on  the  65-foot  level.  If  the  central  point  of  each  of  the 
bodies  is  plotted  not  more  than  three  such  points  fall  in  approx 
mately  the  same  plane.  Since  any  three  points  have  a  comm 
plane,  it  is  clear  that  the  ore  bodies  are  not  related  to  a  plane  like 
ore  shoots  in  a  fissure  vein.  The  ore  occurs  in  general  a  lew  feet 
away  from  the  granite,  and  only  in  the  Lake  stopc  and  its  continu- 
ation «»n  t he  level  below  did  the  stoping  extend  to  the  granite.  Owing 
to  the  close  confinement  of  the  ore  zone  between  the  granite  walls 
no  point  in  (he  zone  is  more  than  200  feet   from  granite. 
Genesis  of  tin  ore.  The  form  and  general  character  of  the  ore 
bodies  show  that  they  are  replacement  deposits.  They  can  not 
be  classed  as  replacement  veins  or  stocks,  for  their  boundaries  are 
approximately  cylindrical  or  rudely  spherical,  and  a  single  ore  body 
does  not  extend  very  far  in  any  one  direction.  Taken  as  a  whole 
they  show  little  or  no  alignment. 
Of  the  minerals  of  contact-metamorphic  origin  amphibole,  calcite, 
garnet,  mica,  and  epidote  are  present  in  the  ore  zone;  but  of  these,  so 
ore 
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