294  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.         [bull.  200. 
ing,  the  displacement  could  in  no  case  be   measured,  and  there  is 
usually  no  observable  difference  in  the  rock  on  each  side  of  the  fissure. 
The  region,  as  has  been  shown,  contains  many  large  faults  that  have] 
left   their   marks   upon   the   geological    structure.     But   these   struc-j 
turally  important  faults  are  not  ore-bearing. 
The  productive  fissures  are  occasionally   simple   fractures.     Usui 
ally,  however,  they  exhibit  complexity  of  various  kinds. 
In  the  Morning  mine  are  two  nearly  parallel  zones  of  Assuring 
about  1,000  feet  apart.  The  northern  one,  known  as  the  Morning j 
vein,  conforms  approximately  to  the  cleaA7age  of  the  sericitic  Burke] 
and  Revett  quartzites  in  which  it  occurs,  Assuring  and  cleavage] 
being  so  closely  related  that  the  structure  may  be  termed  a  shear 
zone.  The  average  width  of  this  zone  is  about  9  feet.  The  south.1 
ern  zone,  known  as  the  You  Like  vein,  is  similar  in  character  but  nar-l 
rower,  being  only  about  G  feet  wide.  In  both  lodes  the  ore  occurs  to 
some  extent  in  small  branching,  irregular,  or  lenticular  veinlets,  but! 
the  ore  is  mainly  a  replacement  of  the  country  rock  and  as  a  whole  has 
no  definite  walls. 
In  the  Gold  Hunter  mine  are  three  nearly  parallel  lodes,  which! 
with  minor  intermediate  ones,  constitute  a  shear  zone  about  70  feed 
wide,  of  which  a  small  part  only  is  productive.  Structurally  this] 
zone  resembles  the  Morning  and  You  Like  veins,  but  is  less  persistent,] 
and  the  productive  parts  of  the  lode,  as  they  are  followed  along 
their  strike,  lose  their  identity  in  the  slaty  cleavage  of  the  Wallace 
and  probably  St.  Regis  formations,  which  form  the  country  rock  of 
this  deposit.  The  Gold  Hunter  lode  is  supposed  to  be  a  continuation] 
of  the  You  Like  vein.  While  this  is  probable,  the  continuity  has 
not  been  established.  The  Gold  Hunter  and  Morning  zone  of  shear- 1 
ing  and  Assuring  probably  continues  west-northwest  to  Canyon  Creek, 
where  it  seems  to  be  represented  by  the  fissures  of  the  Helena-Frisco 
mine,  which  is  in  the  Burke  formation.  The  lodes  worked  in  the 
Helena-Frisco  are  three  in  number,  known  as  the  Black  Bear,  Frisco,, 
and  Gem  veins.  They  are  apparently  parts  of  a  single  faulted  lode, 
as  shown  in  fig.  IS,  but  as  the  mine  was  only  in  small  part  accessible 
at  the  time  of  visit  this  hypothesis,  which  is  strongly  supported  byj 
the  maps  of  the  underground  workings,  could  not  be  fully  verified. 
The  three  veins,  moreover,  are  not  identical  in  structure  or  in  characa 
ter  of  ore,  and  it  is  possible  that  the  transverse  faults  are  older  than 
the  ore.  The  Black  Bear  vein  is  rarely  over  3  feet  wide  and  is  a 
simple  filled  fissure  with  very  little  metasomatic  replacement.  The 
Frisco  vein  is  also  in  the  main  a  simple  fissure,  but  a  considerable 
part  of  the  ore  occurs  as  a  replacement  of  the  country  rock.  The  ( Jem 
vein  is  much  like  the  Frisco.  It  splits  up  and  can  not  be  followed 
after  entering  the  intrusive  mass  of  syenite  on  the  west. 
