42 
CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1906,  PART    I. 
be  a  remnant  of  primary  ore  that  was  not  involved  in  movement  sub- 
sequent  to  veining  and  was  therefore  in  a  position  unfavorable  to 
rface 
Fig.  3.— Generalized  section  of  Granite  vein. 
illustrating  occurrence  and  association  of  min- 
erals, a,  Poor  oxidized  ore;  b,  rich  oxidized 
ore;  c,  rich  sulphide  ore;  d,  poor  sulphide  ore. 
The  horizontal  position  of  theareas  represenl 
ing  the  various  types  of  ore  is  without  signifi- 
cance as  to  their  position  in  the  vein,  hut  the 
areas  show  approximately  the  relal  Lveamounl 
of  each  type  at  various  depths.  The  width  of 
the  vein  is  greatly  exaggerated  with  respect  to 
its  vertical  extent. 
enrichment.  The  low-grade  pyrite 
crystals  which  occur  locally  in 
druses  are  of  secondary  origin  and 
of  more  recent  age  than  the  massive 
pyrite  of  the  vein. 
Distribution  of  pay  ore. — The  man- 
ner of  occurrence  of  ore  in  the  vein 
is  shown  in  fig.  3.  In  this  figure  no 
attempt  is  made  to  show  the  hori- 
zontal position  of  the  various  types 
of  ore  in  the  vein,  but  the  areas  show 
quantitatively  the  relative  amounts 
of  each  type  of  ore  at  various 
depths.  Eaeli  of  these  zones  is  cut 
by  zones  above  it,  and  the  upper 
zones  descended  farther  where  the 
brecciation  of  the  vein  favored  the 
downward  circulation  of  water. 
The  pay  ore  is  practically  limited  to 
the  enriched  oxide  and  theenriched 
sulphide  zones,  though  a  consider- 
able amount  of  the  low-grade  pri- 
mary ore  has  been  mined. 
The  principal  ore  body  is  a  tabu- 
lar mass,  in  the  main  from  2  to  10 
feel  wide  and  about  4,500  feel  long. 
The  surface  slopes  to  the  west  and 
consequently  the  greatest  depth  is 
obtained  in  the  eastern  portion  of 
the  mine,  where  the  ore  extends 
downward  more  than  2,600  feel  be- 
low the  surface.  The  west  end  of 
the  ore  body  has  been  explored  to  a 
depth  of  about  1,600  \'oo\.  Be- 
tween the  eastern  and  western 
boundaries  the  ore  is  continuous  in 
the  upper  levels,  but  in  the  lower 
levels  a  large  part  of  the  vein  near 
the  central  portion  of  the  mine  is 
narrow  or  of  too  low  grade  to  work'. 
The  form  of  the  shoot  of  payable 
ore,  therefore,  is  something  like 
that   of   a    flat  arch,  the  ore   pitch- 
