86  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1905. 
The  contact  metamorphic  deposits  and  the  veins  related  to  them  have  been  exposed  by 
deep  erosion. 
3.  The  eruption  and  solidification  of  surface  lavas  was  also  followed  by  assuring  and  the! 
deposition  of  gold  and  silver  bearing  veins,  but  these  phenomena  were  less  normal  and  gen- 
eral than  the  fissuring  of  the  intrusive  slocks.  They  probably  took  place  only  where  direct 
connection  with  the  eruptive  focus  and  with  the  deep-seated  magmas  could  be  established. 
The  veins  contained  in  the  volcanic  (lows  have  suffered  comparatively  little  from  erosion 
and  their  present  level  is  thus  near  the  surface  of  original  deposition. 
COPPER  DEPOSITS   IN    SEDIMENTARY    ROCKS. 
Copper  is  widely  distributed  through  certain  sedimentary  beds  in  New  Mexico,  which 
are  usually  referred  to  as  the  "Red  Beds"  and  assigned  an  age  varying  from  Upper  Carbon- 
iferous or  Permian  t<>  Triassic  or  Jurassic.  Nor  is  this  development  entirely  confined  to 
New  Mexico,  but  recurs  in  the  Plateau  Province  of  Utah  and  Arizona  and  extends  eastward 
into  northern  Texas.  In  their  general  aspect  the  distribution  and  origin  of  the  copper  in 
the  "Red  Beds"  have  been  discussed  by  Emmons,  a 
In  New  Mexico  t  hese  cupriferous  beds  are  exposed  and  have  been  prospected  over  a  broad 
belt  extending  across  the  Territory  in  a  northwesterly  direction.  The  best-known  occur- 
rences are  at  Nacimiento  and  Cuba,  Sandoval  County;  at  Ilerosa,  Rio  Arriba  County;  at 
Tecolotc,  nea;-  Las  Vegas,  San  Miguel  County;  and  in  the  Sandia,  Man/.ano,  San  Andreas, 
and  ( tecura  ranges  in  central  New  Mexico.  The  localities  where  most  work  has  been  done 
are  at  Nacimiento  and  along  the  eastern  base  of  the  Oscura  Mountains.  In  all  eases  the 
copper  ores  occur  partly  oxidized,  partly  as  chalcocite  in  the  sandstones.  Redud  ion  plants 
have  been  erected  at  Estey,  in  the  Oscuras,  as  well  as  at  Senorito  and  Tecolotc.  Shipments 
of  glance  ore  have  been  made  from  the  first  two  places,  but  at  present  these  deposits, 
though  certainly  extensive,  furnish  only  an  insignificant  part  of  the  copper  production  of 
the  Territory. 
Opinions  are  very  much  divided  as  to  their  age  and  origin.  Probably  the  most  prevalent 
view  is  that  the  ores  were  deposited  at  the  same  time  as  the  inclosing  sediments  by  sea  or 
lake  water  which  contained  copper  in  solution.  The  deposits  are  not  strictly  confined  to 
the  Permian  or  Triassic,  but  occur  also  in  the  lowest  Cretaceous  as  well  as  the  in  Upper 
Carboniferous.  Our  studies  of  the  copper-bearing  sandstones  have  not  progressed  far 
enough  to  justify  the  expression  of  a  definite  opinion  concerning  them.  However,  the 
t  heory  of  deposit  ion  stated  above  seems  improbable.  At  least  two  ot  her  possibilit  ies  exist : 
Either  the  copper  was  deposited  by  adsorption  in  the  clayey  sandstone  of  cupriferous  solu- 
tions ascending  on  fault  fissures,  or  it  was  leached  from  older  deposits  in  adjacent  ranges 
which  may  have  been  land  areas  during  the  deposition  of  the  "Red  Beds,"  carried  down  by 
the  streams,  and  precipitated  byprocesses  of  adsorption  in  the  sediments  near  the  shores. 
Leaching  and  redeposition  may  even  be  going  on  at  the  present,  time.  Mr.  Schrader,  who 
has  examined  the  deposits  in  the  northern  part  of  the  Territory,  inclines  toward  this  second 
view.  It  is  also  supported  by  the  fact  that  older  pre-Cambrian  copper  deposits  occur  in 
many  of  the  ranges,  at  the  foot  of  which  the  cupriferous  "Red  Beds"  extend. 
There  is  evidence  in  favor  of  each  of  these  hypotheses.  At  any  rate  it  seems  certain  that 
precipitation  by  absorption  from  dilute  solutions  of  copper  salts  h  has  played  an  important 
part  in  the  formation  of  these  bedded  copper  ores. 
a  Emmons,  S.  F.,  Contributions  to  economic  geology,  1904:  Bull.  U.  S.  Geol.  Survey  No.  260,  L905, 
pp.  221-232. 
b  Sullivan,  Dr.  E.,  The  chemistry  of  ore  deposition;  precipitation  <>f  copper  by  natural  silicates:  Eco- 
nomic Geology,  vol.  1,  No.  1,  pp.  67-73. 
