GRANITE-BIMETALLIC    AND    CABLE    MINES,   MONTANA.  53 
far  as  can  be  determined  megascopically,  calcite  alone  is  intimately 
associated  with  or  is  a  part  of  the  ore.  Among  the  primary  ore  min- 
erals those  characteristic  of  deposits  of  contact-metamorphic  origin 
are  pyrite,  pyrrhotite,  chalcopyrite,  magnetite,  and  specularite.  In 
many  respects  the  ore  bodies  resemble  the  copper  deposits  of  the 
Clifton-Morenci  district  in  Arizona,  for  which  Lindgren  has  proved  a 
contact-metamorphic  origin.0  So  far  as  the  ore  itself  is  concerned 
the  association  of  minerals  is  much  the  same.  The  chief  difference  is 
that  the  Cable  ores  carry  considerable  gold  and  less  copper  than  those 
of  the  Clifton-Morenci  district.  The  bodies  of  magnetite,  the  mica 
veins,  and  the  ore  deposits  all  appear  to  owe  their  origin  to  the  intru- 
sion of  the  granite.  The  magnetite  represents  a  phase  of  contact 
metamorphism  when  substitution  was  complete  or  nearly  so.  The 
mica  veins  probably  represent  an  end  phase  of  igneous  intrusion, 
since  they  occupy  slip  planes  which  were  made  after  the  granite  had 
become  hard  and  after  the  magnetite  bodies  had  formed.  The  coarsely 
crystalline  calcite,  carrying  ore,  has  resulted  partly  from  substitution 
and  partly  from  recrystallization  of  the  country  ro^'k.  Silica,  iron, 
sulphur,  copper,  and  gold  were  added  and  some  lime  was  probably 
removed.  This  ore  has  certainly  been  extensively  recrystallized 
since  the  granite  became  hard  enough  to  break.  Fault  fissure's  that 
cut  both  granite  and  calcite  have  been  completely  healed  in  the 
calcite  in  such  a  manner  that  their  presence  would  not  even  be  sus- 
pected if  this  rock  alone  were  exposed.  Small  calcite  veins  also  cut 
the  granite.  Though  the  substitution  or  replacement  probably 
occurred  while  the  granite  was  still  soft,  recrystallization  on  an  exten- 
sive scale  continued  after  it  had  solidified. 
PRACTICAL    DEDUCTIONS. 
The  granite  comes  in  contact  with  limestone  at  several  places 
around  Cable  Mountain,  and  bodies  of  magnetite  similar  to  those  of 
the  Cable  mine  are  not  uncommon.  Near  the  granite  at  several 
places  are  ore  deposits  in  limestone  that  are  of  considerable  impor- 
tance; but  these,  so  far  as  present  developments  show,  are  not  of  the 
same  type  as  the  Cable,  being  replacement  veins  of  very  irregular 
width,  yet  clearly  related  to  fissures.  The  ore  is  much  the  same  as  the 
oxidized  ores  of  the  Cable,  the  ore  minerals  being  limonite,  hematite, 
specularite,  and  magnetite,  with  a  little  pyrite  and  pyrrhotite.  The 
values  are  chiefly  in  gold.  They  are  almost  invariably  largest  and 
richest  at  the  bend  of  a  fissure  or  at  the  intersection  of  two  fissures. 
Iron-oxide  gossans  are  very  common  in  the  vicinity  of  Cable 
Mountain,  but  in  most  places  they  carry  very  low  values  in  gold  or  are 
barren.     These  iron  caps  have  resulted  from  the  oxidation  of  an  ore 
a  Lindgren.  W.,  Copper  deposits  of  Clifton-Morenci  disl  rict,  Arizona:  Prof.  Paper  U.  S.  Geol.  Sun  ej 
No.  43,  1905,  pp.  126-164. 
