COPPER    MINES    OF    THE    UNITED    STATES MONTANA.  Ill 
completed.  Lump  copper  is  common  and  can  often  be  recognized  by  the  light -colored 
patches  of  decomposed  rock  surrounding  it. 
Joints  and  long  slip  planes  are  of  frequent  occurrence  and  may  mark  a  change  in  the 
copper  content,  the  rock  on  one  side  being  richer  or  poorer.  As  a  rule  the  cross  courses 
consist  of  bands  from  a  few  inches  to  2  feet  wide  of  crushed  rock  seamed  with  white  calcite. 
They  dislocate  the  copper  lode  but  slightly  and  seldom  contain  copper.  In  general,  the 
mineralization  of  the  amygdaloidal  lodes  is  diffused  and  irregular  and  the  richer  rock  lies 
against  the  hanging  wall. 
The  conglomerate  lodes  have  been  the  richest  in  the  history  of  the  region.  The  bed 
known  as  the  "  Allouez,"  or  as  the  "Albany  and  Boston  conglomerate,"  is  from  8  to  25  feet 
thick.  It  is  underlain  by  3  or  4  feet  of  sandstone,  resting  in  turn  upon  trap  rock,  and  it 
is  overlain  by  a  foot  of  clay  gouge  with  4  to  5  feet  of  shattered  trap  rock  above  it,  and 
then  the  normal  hard  trap  rock  forming  the  hanging- wall  bed.  Like  the  amygdaloid, 
the  conglomerate  is  also  traversed  by  well-marked  joints  and  slips.  The  pebbles  range 
in  size  from  a  pigeon's  egg  to  bowlders  as  large  as  a  man's  head.  The  rock  composed  of 
mailer  pebbles  is  more  favorable  for  copper,  and  the  best  ore  occurs  where  the  cementing 
material  is  less  firm,  the  copper  favoring  the  permeable  rock.  In  the  Franklin  mine  the 
foot-wall  sandstone  thins  out  in  depth,  and  the  copper  extends  from  the  conglomerate 
into  the  underlying  amygdaloid.  The  dip  is  about  18°.  The  ore-bearing  beds  sometimes 
lie  close  together;  for  example,  the  " Osceola  conglomerate"  lies  800  feet  east  of  the  "Cal- 
lmet  conglomerate." 
A  knowledge  of  the  geology  of  the  region  is  essential  to  successful  prospecting.  The 
rap  beds  are  so  nearly  alike  that  identification  is  ordinarily  impossible,  but  occasionally 
some  mineralogieal  characteristic  will  serve  as  a  guide,  as,  for  example,  the  foot  wall  of 
:he  "Kearsarge  amygdaloid"  is  a  bed  marked  by  large  feldspars.  Usually  the  amygdaloid 
ayers  weather  more  readily  than  the  compact  trap  incasing  them,  and  hence  show  infre- 
quent exposures  and  are  covered  with  drift  and  soil.  The  conglomerate  beds  resist  erosion 
md  form  occasional  outcrops. 
DEVELOPMENT. 
The  following  lodes  are  worked:  The  Calumet  conglomerate  is  developed  by  the  Calumet 
md  Hecla  Company.  The  Kearsarge  amygdaloid,  which  lies  2,130  feet  east  of  the  Calumet 
md  Hecla  conglomerate,  is  worked  by  the  Calumet  and  Hecla,  the  Allouez  (on  the  under- 
ay),  the  Akmeek,  and  the  Tecumseh  companies.  The  Franklin  and  Rhode  Island  com- 
panies are  both  trying  to  locate  ore  in  this  lode.  The  Osceola  amygdaloid,  which  lies  2,200 
eet  east  of  the  Calumet  conglomerate,  is  worked  by  the  Calumet  and  Hecla  Company  and 
:he  Tamarack  Company.  The  Baltic  lode  is  worked  by  the  Superior,  the  Baltic,  and  the 
ITri-Mountain  companies,  and  has  been  prospected  by  the  Rhode  Island  Company,  but 
aroved  too  lean  in  their  ground  to  yield  a  profit.  The  ore  in  this  lode  is  spotty,  good  ore 
Jternating  with  lean.  The  Pewabic  and  Allouez  lodes  have  proved  too  lean  to  work  in 
he  Rhode  Island  Company  ground.  The  Knowlton  and  Butler  lodes  are  worked  by  the 
Vlass  Copper  Company.  The  Montreal  River  lode  is  worked  by  the  Keweenaw  Company, 
ind  the  Calumet  and  Hecla  Company  is  reopening  the  old  Manitou  property  near  Lac  la 
belle. 
MONTANA. 
I  The  copper  production  of  Montana  continues  to  dominate  the  entire  industry,  amounting 
;o  the  enormous  total  of  335,000,000  pounds  in  1905.  Although  for  many  years  past  this 
uState  has  furnished  about  40  per  cent  of  the  copper. production  of  the  United  States,  it  will 
eiot  quite  reach  this  figure  for  1£05,  as  the  increase  in  Arizona  has  been  extraordinarily 
apid.  The  production  of  the  State  is  almost  entirely  from  the  Butte  mines,  but  a  small 
amount  is  reported  from  Beaverhead  County,  mainly  from  the  Indian  Queen  mine,  and  from 
Meagher,  Jefferson,  and  Madison  counties,  these  four  counties  yielding  gold-copper  ores. 
The  copper  ores  of  Montana  furnish  18  per  cent  of  the  gold  production  of  the  State  and  80 
Bull.  285—06 8 
