80  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1905. 
Peak  mines  in  Luna  County,  from  the  Granite  Gap  mine  and  others  in  Grant  County, 
and  from  the  Magdalena  mines  in  Socorro  County.  The  mining  of  zinc  ores  has  become 
an  important  industry  in  the  Magdalena  district  of  Socorro  County  and  promises  to, 
become  so  in  the  Tres  Hermanas  district  in  Luna  County.  The  metal  produced  in  1904 
is  reported  as  having  a  value  of  $899,589,  a  considerably  larger  amount  than  is  repre- 
sented by  the  silver,  gold,  copper,  or  lead  industry. 
GEOGRAPHIC  DISTRIBUTION  OF  DEPOSITS. 
The  Great  Plains  and  the  Plateau  Province  of  eastern  and  northwestern  New  Mexico 
do  not  contain  metalliferous  deposits  except  local  iron  and  copper  ores  distributed  in] 
sedimentary  rocks.  On  the  other  hand,  the  metallic  ores  are  present  in  every  mountain 
range  in  the  Territory.  They  occur  in  the  continuation  of  the  Rocky  Mountain  system] 
in  northern  New  Mexico,  in  the  Zuni  uplift,  in  the  Sandia,  Magdalena,  San  Pedro,  Man- 
zano,  San  Andreas,  Oscura,  Organ.  Mimbres,  and  almost  all  of  the  small  desert  ranges 
of  southwestern  New  Mexico.  They  also  occur  in  the  broken-down  edge  of  the  Plateau 
Province  about  Silver  City  and  in  several  of  the  huge  rhyolite  fields  in  the  southwestern. 
part,  extending  from  the  Mogollon  Mountains  into  Socorro  County. 
By  far  the  majority  of  metalliferous  deposits  are  found  in  the  southwestern  quarter  of 
the  Territory,  and  in. this  area  most  of  the  important  deposits  extend  in  a  curved  line 
from  Socorro  through  llermosa,  Chloride,  Kingston,  Hillsboro,  Lake  Valley,  Cooks  Peak, 
Santa  Rita,  and  Pinos  Altos  to  Silver  City  and  the  Mogollon  Mountains  near  the  Arizona 
line. 
There  is  little  indication  of  an}'  regularity  in  the  geographic  distribution  of  the  different 
metals  within  the  metal-bearing  region. 
(iE()LOGICAI>    DISTRIBUTION   OF  DEPOSITS. 
Almost  every  known  type  of  deposit  is  found  in  New  Mexico.  Then'  are  ores  of  copper 
and  iron  contained  in  sedimentary  beds;  normal,  sharply-defined  fissure  veins,  carrying 
gold,  silver,  lead,  copper,  or  zinc;  wide  shear  zones,  stringer  leads,  and  lenticular  bodies 
of  or*s,  both  in  intrusive  rocks  and  in  the  old  pre-Cambrian  schists;  irregular  replacement 
deposits,  usually  in  Ordovician,  Silurian,  or  Carboniferous  limestone;  irregular-contact 
deposits,  containing  copper,  lead,  and  zinc,  but  usually  poor  in  gold  and  silver,  along  the 
boundaries  between  intrusive  rocks  and  limestones  of  any  age;  and  finally  gold-bearing 
gravel  beds  of  Tertiary  or  recent  age. 
In  a  general  way  the  pre-Cambrian  schists  contain  fahlbands,  shear  zones,  and  veins  o: 
copper  and  zinc  sulphides,  low  in  gold  and  silver;  the  Paleozoic  limestones  are  apt  to  har- 
bor the  irregular  copper,  lead,  and  zinc  deposits,  often  greatly  enriched  by  processes  of 
oxidation  and  in  places  containing  much  silver;  the  intrusive  porphyries  and  granites  con- 
tain fissure  veins  with  gold,  silver,  or  both,  and  (in  most  cases)  minor  amounts  of  the  base 
iik  tals;  and,  finally,  the  flows  of  rhyolite  and  andesite  inclose,  at  some  places,  fissure  veins 
rich  in  gold  and  silver,  but  commonly  with  relatively  small  amounts  of  copper,  lead,  and 
zinc. 
AGE   OF  THE  DEPOSITS. 
I 
In  the  gold  placers,  as  well  as  in  some  of  the  bedded  iron  and  copper  deposits,  the  valu- 
able metals  were  introduced  or  laid  down  at  the  same  time  as  the  accompanying  rock  was 
formed.  These  deposits  are  often  called  syngenetic.  The  important  ore  bodies  of  the 
majority  of  New  Mexico  mines  belong  to  the  class  of  epigenetic  deposits,  in  which  the 
metals  were  introduced  at  a  time  when  the  surrounding  rocks  had  already  been  formed. 
During  the  present  reconnaissance  particular  attention  was  given  to  the  question  of  age, 
in  the  hope  of  discerning  the  main  epochs  of  ore  formation.  The  results  have  justified 
this  and  it  has  been  shown  that  certain  physical  characteristics  of  the  deposits  in  general 
distinguish  these  several  epochs,  even  if  the  criteria  are  not  always  sufficent  to  determine 
age  in  the  absence  of  general  geological  evidence. 
