Bansome.]  COETJR    D'aLENE    DTSTBICT,  IDAHO.  295 
The  Standard-Mammoth  and  Hecla  mines  are  probably  on  a  single 
fissure  zone,  but  the  actual  continuity  is  broken  by  a  northwest- 
southeast  fault,  dipping  northeast,  against  which  the  vein  abuts  at 
the  eastern  end  of  the  Standard-Mammoth  mine.  Between  this 
fault  and  the  Hecla  shaft  the  vein  is  unknown.  In  the  Standard- 
Mammoth  and  Hecla  mines  the  general  country  rock,  as  in  all  of  the 
large  Canyon  Creek  mines,  is  the  Burke  formation.  The  ore  occurs 
in  a  zone  of  combined  Assuring  and  shearing,  partly  as  the  filling  of 
fissures  and  partly  as  a  replacement  of  the  sericitic  quartzite.  The 
lode  has  no  definite  walls  and  usually  ranges  from  4  to  10  feet  in 
width.  In  the  Hecla  mine  the  ore  usually  occurs  on  one  side  of  a 
dark  narrow  dike,  of  which  no  microscopical  examination  has  yet 
been  made,  but  which  resembles  a  fine-grained  diorite.'  Very  rarely 
a  little  ore  occurs  as  a  replacement  in  the  dike.  A  little  of  the  same 
rock,  although  discontinuous  and  much  more  decomposed,  occurs 
with  the  Standard-Mammoth  vein. 
r 
E 
to, ^, 
Scale  of  feet 
.0              ?00           -400           600           800 
*<^n 
X 
/B\ackJ?ear 
vein 
, veiV" — 7                          TS^ 
T "            /      Helena-Fnsco 
' Gem  shaft                           shaft 
Fig.   18. — Plan  of  veins  in  the  Helena-Frisco  mine. 
The  Tiger-Poorman  lode  is  generally  similar  to  the  Standard- 
Mammoth,  the  ore  being  usually  from  3  to  15  feet  in  width.  In  the 
eastern  part  of  the  mine  the  lode  exhibits  a  well-marked  linked  vein 
or  imbricated  structure. 
In  the  Wardner  deposits,  as  exemplified  in  the  Bunker  Hill  and 
Sullivan  and  Last  Chance  mines,  there  is  one  dominant  fissure, 
locally  known  as  the  "  foot  wall,"  which  strikes  northwest  and  dips 
southwestward  at  an  angle  of  38°.  The  rocks  on  both  sides  of  this 
fissure  are  sericitic  quartzites  of  the  Burke  formation.  Those  in  the 
hanging  wall  are  much  more  fissured  than  those  in  the  foot  Avail, 
and  it  is  in  the  fissured  hanging-wall  quartzite  that  the  ore  bodies 
occur.  No  ore  of  importance  has  yet  been  found  in  the  quartzite 
of  the  foot  wall  in  these  mines.  Although  the  main  fissure  was  un- 
doubtedly formed  prior  to  the  deposition  of  the  ore,  it  has  also  been 
a  plane  of  later  movement,  as  shown  by  slickensided  surfaces  on  the 
ore,  and  it  is  always  accompanied  by  soft  gouge. 
The  zone  of  fissured  quartzite  in  which  the  ore  bodies  occur  has  a 
maximum  width,  measured  perpendicularly  to  the  foot-wall  fissure. 
of  about  300  feet.     Within  this  zone,  sometimes  in  contact  with  the 
