MINERAL    DEPOSITS    OF    NEW    MEXICO.  83 
with  garnet  and  chalcopyrite,  the  latter  carrying  a  little  gold.  A  system  of  narrow  aurif- 
erous quartz  veins,  on  one  of  which  the  celebrated  Ortiz  mine  was  worked,  intersects  the 
porphyry  of  the  Ortiz  Mountains  and  has  yielded  rich  placer  deposits.  The  Sun  Pedro 
laccolith  has  produced  contact-metamorphic  copper  deposits  with  economically  important 
ore  bodies  of  chalcopyrite,  accompanied  by  garnet  gangue,  in  Carboniferous  limestone.  Here 
again  a  system  of  small  but  rich  fissure  veins  intersects  the  laccolith  and  even  extends  for  a 
short  distance  into  the  sedimentary  rocks. 
At  Jarilla,  Otero  County,  a  laccolithic  mass  of  porphyry  has  bulged  up  the  Carboniferous 
limestones  and  in  certain  strata  has  produced  contact  deposits  carrying  gold  values,  with 
garnet,  epidote,  and  hematite  gangue.  In  the  porphyry  and  extending  out  into  the  sedi- 
mentary rocks  are  quartz  veins,  some  of  which  carry  principally  gold  and  some  gold  and 
copper.  Erosion  of  these  veinlets  has  formed  the  well-known  placers  at  the  eastern  foot  of 
the  hills.^ 
The  conspicuous  Organ  Range  in  Donna  Ana  County,  east  of  Las  Graces,  is  continued 
southward  into  the  Franklin  Range  and  northward  into  the  San  Andreas  Range.  The 
Organ  Range  consists  chiefly  of  granite  with  associated  porphyries,  and  this  granite  has 
been  regarded  as  pre-Cambrian  by  several  writers.  This  is  erroneous,  though  it  is  possible 
that  the  pre-Cambrian  complex  may  be  present  in  some  parts  of  the  range.  The  granite 
forms  a  large  laccolithic  stock  intrusive  into  Carboniferous  limestone  and  probably  con- 
tinues northward  into  the  little-explored  San  Andreas  Range.  For  a  distance  of  several 
miles  the  limestone  is  contact  metamorphosed,  with  the  development  of  garnet  and  pay- 
able bodies  of  now  partly  oxidized  chalcopyrite.  Deposits  of  lead  and  zinc  ores  occur  short 
distances  away  from  the  contact  in  the  limestone.  The  granite  is  traversed  by  a  system 
of  east-west  fractures,  which  contain  quartz  with  gold  or  silver  bearing  sulphides. 
The  small  but  conspicuous  mountain  group  of  Tres  Hermanas  rises  near  the  Mexican 
boundary  in  the  southern  part  of  Luna  County.  In  the  northerly  foothills  lead  and  zinc 
deposits  associated  with  garnet  and  wollastonite  and  of  typical  contact-metamorphic 
character  have  been  formed  where  granite  adjoins  the  Carboniferous  limestone.  Until 
recently  only  lead  ores  were  mined  at  Tres  Hermanas,  but  lately  large  quantities  of  oxi- 
dized zinc  ores  have  been  discovered.  Here  again  the  granite  contains  a  number  of  narrow 
quartz  veins  with  silver-bearing  lead  ores. 
Near  Hachita,  in  southern  Grant  County,  the  low  Apache  Hills  show  irregular  intrusions 
of  monzonitic  porphyries  through  Paleozoic  limestone.  Contact  metamorphism  with 
garnet  and  chalcopyrite  is  in  evidence  along  the  boundary  line  of  the  formations,  and 
from  one  of  the  deposits,  called  the  Apache  mine,  oxidized  copper  ores  are  shipped,  which 
occur  in  an  extremely  coarsely  crystalline  limestone. 
The  Hachita  Range  consists  of  folded  and  faulted  Carboniferous  and  probably  Cretace- 
ous strata  (Comanche  formation),  with  a  network  of  porphyry  dikes  and  sills.  Limestone 
and  dikes  are  cut  by  a  system  of  northeasterly  trending  fissure  veins  which  contain  galena 
and  zinc  blende.  In  at  least  one  place,  "The  Copper  Dick"  mine,  where  payable  copper 
ores  are  found,  the  Cretaceous  limestone  has  been  converted  into  garnet  and  chalcopyrite. 
A  large  laccolithic  mass  of  porphyry  domes  up  the  strata  at  Santa  Rita,  Hanover,  and 
Fierro,  in  Grant  County.  At  the  two  latter  places  limestones  in  contact  with  the  intrusive 
rock  have  been  metamorphosed  and  contain  low-grade  deposits  of  chalcopyrite,  in  places 
with  considerable  amounts  of  zinc  blende.  Garnet,  epidote,  and  magnetite  are  abundant 
gangue  minerals.  Throughout  the  district  ore-bearing  fissures  occur1,  principally  in 
the  porphyry.  In  these  gold  values  are  generally  low,  but  copper  and  sometimes  lead 
and  zinc  are  more  important.  Where  little  quartz  is  present  and  the  veins  consist  princi- 
pally of  narrow  streaks  of  sulphides,  secondary  enrichment  has  doubtless  played  an  impor- 
tant part  in  the  formation  of  ore  of  workable  grade. 
Narrow  veinlets  carrying  cupriferous  pyrite  in  porphyry  occur  in  the  Burro  Mountains. 
Concentration  by  descending  waters  has  here  likewise  probably  induced  the  formation  of 
disseminated  chalcocite  and  has  raised  the  ore  to  its  present  grade. 
At  Pinos  Altos,  north  of  Silver  City,  limestones  tilted  up  by  a  mass  of  porphyry  are  ml 
