GRANITE-BIMETALLIC    AND    CABLE    MINI'S,  MONTANA.  43 
ing  in  both  directions  away  from  the  keystone,  which  is  assumed  to 
be  about  300  feet  west  of  the  Ruby  shaft.  The  rich  ore,  however,  is 
closely  related  to  the  topography  of  the  country  and  occurs  for  the 
most  part  between  200  and  800  feet  below  the  apex  of  the  vein. 
Where  other  veins  unite  with  the  Granite  vein  along  a  nearly  verti- 
cal line,  there  are  no  marked  effects  of  enrichment;  but  the  richest  por- 
tion of  the  vein  occurs  just  above  the  union  of  several  veins  which 
joined  along  a  nearly  horizontal  line.  This  is  the  great  bonanza, 
east  of  the  Ruby  shaft,  between  levels  3  and  8. 
Probable  genesis. — The  bonanza  ores  of  the  mine  are  unquestionably 
the  result  of  secondary  enrichment  by  descending  waters;  but  it  can 
not  safely  be  assumed  that  the  'primary  ores  were  everywhere  even 
approximately  of  equal  tenor.  The  great  bonanza  east  of  the  Ruby 
shaft  was  very  much  richer  than  secondary  ore  occupying  elsewhere 
a  similar  position  in  the  vein,  and  probably  resulted  from  primary 
ore  of  relatively  high  grade.  The  average  of  the  low-grade  ore  in  the 
lower  levels  of  the  mine  carries  about  25  ounces  in  silver.  The  aver- 
age in  the  bonanza  east  of  the  Ruby  shaft,  as  shown  by  annual  mill 
runs,  was  about  175  ounces.  This  rich  zone  has  an  average  vertical 
extent  of  about  400  feet,  and  if  we  assume  that  it  has  resulted  from 
the  enrichment  of  a  primary  ore  carrying  25  ounces  of  silver  in  a  vein 
of  constant  width,  it  would  require  6  times  400  feet,  or  2,400  feet  of 
25-ounce  vein  material,  to  produce  this  bonanza,  and  the  original 
vein  before  denudation  would  then  have  had  a  vertical  extent  of  at 
least  5,000  feet.  Near  the  Blaine  shaft,  between  levels  3  and  7,  the 
ore  averaged  about  100  ounces  for  a  vertical  distance  of  about  350 
feet.  If  this  ore  has  resulted  from  the  enrichment  of  25-ounce  rock, 
it  would  require  the  erosion  of  1,050  feet  of  the  vein  from  above  its 
present  apex,  provided  all  of  the  values  were  redeposited.  This 
would  give  a  minimum  vertical  extent  of  about  2,850  feet  for  the 
original  vein  here  before  denudation.  There  has  probably  been  more 
than  2,400  feet  of  erosion  since  the  granite  was  intruded  into  the  sedi- 
mentary rocks,  for  the  Flathead  quartzite,  the  earliest  Cambrian  for- 
mation, now  outcrops  at  the  contact  with  the  granite.  The  entire 
Paleozoic  section  above  the  Flathead,  as  well  as  later  sedimentary 
rocks,  has  probably  been  eroded  from  the  quartzite  since  the  intru- 
sion. If  the  vein  was  formed  soon  after  the  solidification  of  the  granite 
there  has  been  ample  erosion  to  account  for  any  probable  amount  of 
enrichment,  but  as  it  is  likely  that  the  ore  east  of  the  Ruby  shaft 
was  primarily  richer  than  that  west  of  the  Blaine  shaft,  an  estimate 
below  2,400  feet,  so  far  as  the  vein  itself  is  concerned,  appears  to  be 
safer.  In  either  case  the  vertical  extent  of  the  vein  was  very  great, 
and  when  this  is  considered,  together  with  its  persistence  horizontally 
and  its  width  in  the  lower  levels  of  the  mine,  it  appears  very  probable 
that  the  ore  was  deposited  by  ascending  waters.     The  veins  of  the 
