IDAHO    SPRINGS    MINING    DISTRICT,    COLORADO.  39 
until  they  finally  die  out.  There  are  also  special  cases  of  crossing  or  intersecting  veins 
or  lodes. 
An  excellent  example  of  a  branching  lode  is  found  in  the  Fraction-Kitty  Clyde  vein  and 
branches.  The  first  type  is  well  illustrated  by  the  Little  Mattie-Newton  vein.  In  the  Li!  I  le 
Mattie  mine  there  are  two  porphyry  dikes  running  parallel  to  one  another  or  else  one  large 
porphyry  dike  which  splits  into  two  or  more  parts,  separated  by  huge  masses  of  gneiss 
and  pegmatite.  The  vein  runs  approximately  parallel  to  the  dikes,  at  some1  places  entirely 
in  porphyry  and  at  others  with  pegmatite  or  gneiss  on  both  walls.  Minor  veinlets  or  feeders 
enter  this  main  vein  at  long  intervals.  Moreover,  the  main  vein  itself  splits  up  at  both 
ends  into  several  strong  but  less  productive  veins,  and  these  become  an  example  of  the 
branching  type.  The  New  Era  and  Great  Western  veins  also  run  parallel  to  each  other 
and  are  only  about  75  feet  apart.     A  minor  cross  vein  intersects  both  of  these  parallel  veins. 
The  crossing  of  veins  is  well  illustrated  by  the  intersection  of  the  Black  Eagle  and  Bis- 
mark  veins. 
PAY    SHOOTS. 
Junctions  of  two  large  veins  or  of  branches  or  feeders  with  a  main  vein  are  frequently 
sites  of  ore  deposition.  Most  of  the  ore  in  such  cas:s  is  on  the  main  vein,  but  some  ore 
is  also  found  along  the  cross  or  branch  veins  for  some  distance  from  the  junction. 
In  veins  parallel  with  and  at  or  near  the  contact  of  a  porphyry  dike,  pay  shoots  are  some- 
times found  at  the  junction  of  minor  branches,  but  they  commonly  occur  irregularly  along 
the  fractured  zone.  This  irregular  distribution  of  the  shoots  may  possibly  be  accounted 
for  in  the  following  manner.  Porphyry  or  other  wall  rock,  when  intensely  altered,  often 
changes  to  a  clay-like  mass  which  is  soft  and  tends  to  close  up  any  fissures  running  through 
it.  As  this  clay-like  substance  is  practically  impervious  to  the  ore-bearing  solutions,  these 
solutions  are  diverted  into  the  more  open  channels  or  spaces  between  the  clayey  portions 
and  there  deposit  the  ores.  This  deposition  may  be  the  result  of  mingling  with  othc  r  solu- 
tions or  of  replacement  of  the  strained  or  crushed  and  pulverized  rock  along  the  fractured 
zone. 
In  the  Little  Mattie  mine  crushed  pegmatite  and  gneiss  zones  are  inclosed  between  two 
dikes  of  porphyry.  As  the  dikes  converge  the  "  horse  "  of  gneiss  and  pegmatite  is  gradually 
replaced  by  quartz  and  ore,  until  finally  the  space  between  the  porphyry  dikes  is  filled 
completely  by  ore  and  gangue  material,  no  pegmatite  or  gneiss  being  visible.  Some- 
what similar  ore  bodies  have  been  formed  by  the  replacement  of  porphyry  instead  of  peg- 
matite and  gneiss.  In  such  cases  the  vein,  which  is  entirely  in  porphyry,  splits  and  incloses 
a  mass  of  porphyry  2  or  3  feet  in  diameter.  This  mass  is  composed  mainly  of  crushed  but 
comparatively  unaltered  porphyry;  but  in  places  this  grades  first  into  porphyry  partially 
replaced  by  ore  and  quartz,  and  then  into  solid  ore  and  quartz,  showing  no  trace  of  the 
original  porphyry. 
The  Little  Mattie-Newton  vein  is  crossed  by  several  later  and  leaner  veins.  One  of  these, 
the  so-called  "cross  vein,"  faults  the  Little  Mattie  vein  from  10  to  25  feet.  This  vein, 
while  carrying  only  low  values  itself,  seems  to  bear  a  definite  relation  to  the  ore  bodies, 
for  a  series  of  them  are  found  to  lie  one  above  another  immediately  east  of  the  "crors 
vein."  The  Chicago-Bismark  and  the  Guy  Irving  veins  likewise  intersect  the  Little 
Mattie-Newton  vein.  The  first  of  these,  the  Bismark,  is  crossed  by  the  Black  Eagle  vein 
and  is  faulted  by  it  about  6  feet.  An  ore  body  was  found  at  this  intersection.  The 
Waltham-International  and  the  Amethyst  veins  are  examples  of  other  large  veins  of  com- 
paratively little  mineralization  which  cross  the  main  belt  of  northeast-southwest  veins. 
PERSISTENCE    OF    FAULT   MOVEMENTS. 
Movements  occurring  after  the  solidification  of  the  porphyry  dikes  caused  ussures  which 
contained  loose  angular  fragments  of  porphyry  and  the  older  rocks.  Subsequent  deposition 
of  ore  in  these  fractures  formed  a  consolidated  breccia  with  the  ore  minerals  constituting 
the  matrix. 
