54  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1906,  PART    I. 
composed  in  part  of  pyrite,  for  many  of  them  contain  pseudomorphl 
after  that  mineral.  The  gold  of  the  replacement  veins,  so  far  as  they 
have  been  developed,  is  finer  than  that  of  the  Cable  mine,  and  there 
are  no  placers  of  importance.  Good  ore  bodies  have  been  found 
below  barren  or  low-grade  gossans;  but  thus  far  the  highest  points  od 
tin4  ore  shoots  have  everywhere  extended  within  50  or  100  feet  of  the 
surface  and  at.  most- places  nearer.  The  trend  of  these  veins  can 
usually  be  made  ont  by  trenching  or  by  digging  shallow  pits.  The 
most  favorable  place  for  prospecting  is  at  the  intersection  of  two 
veins. 
Much  of  the  magnetite  carries  from  20  to  SO  cents  a  ton  in  gold,  and 
ai  some  places  it  has  been  prospected  with  the  hope  that  in  depth  it 
will  change  to  a  sulphide  ore  carrying  gold  of  payable  grade.  The 
large  bodies  of  magnetite,  however,  are  unquestionably  of  primary 
origin  and  will  continue  to  be  magnetite  as  far  down  as  they  extend. 
The  pyrite  ore  of  the  veins  alters  to  limonite  and  hematite,  carrying 
small  grains  of  magnetite  and  nowhere  to  large  masses  of  magnetite. 
The  presence  of  the  small  magnetite  grains  in  the  oxidized  ore  has  no 
diagnostic  value,  for  they  are  present  in  the  oxidized  ore  of  practical^ 
every  ore  deposit  in  the  Philipsburg  area,  and  a  large  number  of  these 
are  ordinary  fissure  veins  and  in  no  sense  replacement  deposits. 
RESUME. 
The  Granite-Bimetallic  lode  is  a  typical  fissure  filling  of  simple 
structure  and  of  remarkable  persistence  both  horizontally  and  verti- 
cally. Surface  waters  have  leached  the  values  from  its  apex  and  to 
a  variable  depth  of  50  to  300  or  loo  feet  below  the  surface.  Below 
ihi-  zone  is  one  of  enriched  oxidized  ores  in  which  the  values  are 
largely  horn  and  native  silver.  Next  below  is  a  zone  of  enriched  silver 
sulphides,  unquestionably  of  secondary  origin,  and  the  primary  ore, 
t  he  deepesl  in  I  he  vein,  is  a  low-grade  sulphide  ore  carrying  silver  and 
gold. 
The  Cubic  ore  body  is  a  cont  act  -met  ;i  morphic  deposit  of  rather! 
uncommon  character,  bin  resembles  most  such  deposits  in  having  no 
definite  shape.  The  country  rock  is  for  the  most  part  limestone  and 
has  undergone  the  usual  change  due  to  contact  met  amorphism.  The 
ore  minerals,  aside  from  the  presence  of  considerable  coarse  gold,  are 
those  commonly  associated  with  ores  of  cont  act-met  amorphic  origin. 
As  :i  rule  the  ore  is  not  immediately  ;it  the  contacl  of  the  granite,  but 
may  occupy  any  position  in  the  ore  zone. 
So  far  as  their  larger  structural  features  are  concerned  the  ore 
deposits  of  the  two  mines  are  so  unlike  that  they  can  scarcely  be 
compared.  A  list  of  nearly  all  the  minerals  noted  in  the  two  mines, 
with  short  notes  upon  their  occurrence  or  position  in  the  deposits,  is 
given  in  the  subjoined  table.     This  list  was  made  previous  to  micro- 
