bain.]  LEAD    AND    ZINC    RESOURCES    OF    UNITED    STATES.  271 
output  of  the  Rico  mines  brings  Dolores  into  the  column  of  pro- 
ducers. The  geology  of  the  district  has  been  described  by  Messrs. 
Cross  and  Spencer"  and  the  mines  by  Mr.  Ransome.6 
Xo  comprehensive  study  of  the  Colorado  zinc  resources  has  yet 
been  made.  Up  to  the  last  few  years  zinc  has  been  a  source  of  los-  to 
the  smelters  and  penalty  to  the  miners,  and  ores  high  in  zinc  have 
cither  remained  unmined  or  been  thrown  into  the  dump.  It  is  there- 
fore difficult  to  get  a  clear  idea  as  to  just  how  valuable  they  may  be. 
The  complex  nature  of  the  ores  makes  their  treatment  very  difficult, 
but  the  zinc  industry  seems  now  to  be  making  very  rapid  progress. 
New  Mexico. — In  the  southwestern  part  of  this  Territory,  near 
Hanover,  are  some  deposits  of  blende  and  smithsonite.  which  have 
been  described  by  Blake. c  These  have  yielded  a  considerable  tonnage 
of  zinc  carbonate  from  surface  workings.  The  blende,  because  of  its 
intimate  mixture  with  garnet  and  other  heavy  gangue  minerals,  has 
not  proved  of  much  value.  The  ore  occurs  in  bodies  of  considerable 
size  in  limestones  of  presumably  Carboniferous  age  and  apparently 
in  close  association  with  igneous  rocks.  The  carbonate  mined  went 
principally  to  Mineral  Point,  Wis.,  for  treatment,  and  up  to  1803  the 
shipments  were  important.  At  present  the  output  of  the  district  is 
approximately  1,000  tons  per  annum. 
More  recently  zinc  has  been  shipped  in  quantity  from  the  Magda- 
lena  district  near  Socorro.  The  ore  occurs  here  in  the  Graphic  and 
Kelley  mines,  which  have  in  the  past  produced  important  amount-  of 
lead  and  silver.  The  occurrence  is  described  by  Mr.  Keyes.d  The 
zinc  occurs  in  a  great  plate  of  Carboniferous  lime-tone  preserved  on 
the  back  of  a  block  of  ancient  >diists  thrown  up  by  faulting.  AlSSO- 
ciated  with  the  ore  bodies  are  intrusive  and  eruptive  rocks  of  compar- 
atively recent  age.     The  ore  occurs  at  four  horizon-: 
(a)  The  "contact  vein,"  which  lies  at  the  base  of  the  lime-tone 
and  between  the  latter  and  the  schists  and  greenstones. 
(b)  The  "Silver  Pipe  vein."  GO  feet  above  the  contact  and  devel- 
oped along  a  bed  of  very  pure  white  limestone  under  a  cover  of  more 
siliceous  rock. 
(c)  The  "outer  or  west  vein,*'  80  feet  above  the  Silver  Pipe  vein 
and  also  in  the  limestone. 
(d)  The  "surface  vein." 
|- 
"Cross,  Whitman,  and  Spencer,  A.  c.  Geology  <>f  the  Rico  Mountains,  Colorado: 
Twenty-first  Ann.  Kept.  U.  S.  Geol.  Survey,  pt.  2,  1900,  pp.  15-165. 
b  Ransome,  F.  L..  The  ore  deposits  of  th°  Rico  Mountains,  Colorado:  Twenty-second 
Ann.  Rept.  C.  S.  Geol.  Survey,  pi.  2.  1902,  pp.  229   398. 
rP>!ai<e,  W.  I'..  Zinc-  ore  deposits  of  southwestern  New  Mexico:  Trans.  Am.  Inst.  Min. 
Bng.,  vol.  24,   1894,  pp.   is?    195. 
'' Koyes,  C.  R.,  Zinc  carbonate  ores  of  the  Magdalena  Mountains:  Mining  Magazine  (in 
press). 
