bansome.]  COEUR    D'ALENE    DISTRICT,  IDAHO.  297 
been  locally  faulted.     As  a  rule  the  ore  passes  gradually  into  the 
unmineralized  quartzite. 
In  the  Granite  mine  the  ore  occurs  in  extremely  irregular  masses 
in  a  tongue  of  metamorphosed  and  fissured  quartzite  which  projects 
into  the  intrusive  mass  of  syenite  north  of  Gem. 
Character  of  the  ores. — The  most  characteristic  minerals  of  the 
lead-silver  ores  are  galena  and  siderite.  Both  of  these  minerals  occur 
us  the  rilling  of  fissures  and  as  metasomatic  replacements.  In  many 
instances  the  galena  directly  replaces  sericitic  quartzite.  But  in  sonic 
large  ore  bodies,  particularly  those  at  Wardner,  the  quartzite  was  first 
replaced  by  siderite,  which  was  in  turn  replaced  by  galena.  All 
stages  may  be  seen  from  siderite  that  is  traversed  by  little  reticulating 
veinlets  of  galena,  to  complete  replacement  by  the  lead  sulphide. 
That  galena  was  formed  at  more  than  one  period  is  shown  by  the  fact 
:hat  masses  of  coarsely  crystalline  galena  are  sometimes  traversed  by 
veinlets  of  a  more  compact  variety  of  the  same  mineral. 
Pyrite  and  sphalerite  are  found  in  all  the  deposits.  The  latter  is 
Darticularly  abundant  in  the  Granite  mine.  Elsewhere  it  is  a  minor 
constituent  of  the  ore  and  many  of  the  deposits  are  remarkably  free 
Prom  it.  The  average  quantity  of  zinc  in  the  concentrates  from  the 
Federal  Company's  mines  is  about  4.5  per  cent.  While  most  of  the 
nines  working  above  the  main  drainage  lines  of  the  district  show 
10  impoverishment  of  the  ore  through  an  increase  of  pyrite  and  sphal- 
erite, the  conditions  in  the  lower  levels  of  the  Helena-Frisco,  Tiger- 
Poorman,  and  Standard-Mammoth  indicate  that  such  a  change,  prob- 
ibly  a  gradual  one,  may  be  expected  at  considerable  depths. 
Tetrahedrite  occurs  in  bunches  in  the  galena  of  the  Wardner  and 
Vlullan  mines  and  in  the  Standard-Mammoth.  It  is  never  very  abun- 
lant  and  always  indicates  ore  rich  in  silver.  It  appears  to  be  rather 
nore  abundant  near  the  surface  than  at  great  depth. 
Chalcopyrite  is  very  rare  in  the  mines  at  Wardner.  In  the 
Standard-Mammoth  mine,  however,  it  is  fairly  common,  though 
lever  found  in  large  masses,  and  it  occurs  also  in  the  Tiger-Poorman, 
Telena-Frisco,  and  Granite  mines.  It  is  frequently  closely  associated 
vith  pyrrhotite,  particularly  on  the  bottom  level  of  the  Tiger-Poor 
[nan.  Pyrrhotite  was  detected  also  in  the  concentrates  from  the 
Morning  mine.  Small  quantities  of  stibnite  occur  in  the  Gold  Hunter 
ode. 
In  addition  to  the  prevailing  siderite,  quartz  forms  a  subordinate 
part  of  the  gangue  in  all  the  large  mines.  Barite  was  noted  in  the 
Standard-Mammoth,  Gold  Hunter,  and  Morning  mines,  and  a  little 
;alcite  in  the  Hecla  mine.  As  a  general  rule,  the  quartz  is  more 
ibundant  in  the  low-grade  portions  of  the  ore  bodies. 
The  minerals  found  in  the  oxidized  zone  are  cerussite,  cerargyrite, 
