LEAD  AND  ZINC. 
A  NEVADA  ZINC  DEPOSIT. 
By  II.  Foster  Bain. 
Introduction. — The  production  of  zinc  ores  in  the  Western  States  lias  begun  to  assume 
great  importance.  In  1905  the  number  of  producing  camps  and  the  total  shipments  were 
much  larger  than  in  1904.  Colorado,  with  Leadville  as  the  main  shipping  district,  con- 
tinued in  the  lead.  The  mines  of  the  Magdalena  Mountains  in  New  Mexico  made  heavy 
shipments.  Utah,  Idaho,  and  Montana  have  become  important  producers,  and  smaller 
shipments  have  been  made  from  other  States  and  Territories,  including  Nevada.  Impor- 
tant amounts  of  ore  have  been  brought  in  from  Mexico  and  some  from  British  Columbia. 
Old  mines  are  being  reopened,  new  mills  are  being  built,  and  everywhere  through  the  West 
the  zinc-ore  industry  is  attracting  large  attention.  In  the  summer  of  1905  the  writer  vis- 
ited the  main  zinc-producing  districts  of  the  West,  and  a  general  report  on  the  western 
zinc  industry  is  now  in  preparation  as  a  joint  publication  of  the  division  of  geology  and 
the  division  of  mineral  resources.  In  the  course  of  this  investigation  the  Potosi  mine  in 
southern  Nevada  was  visited,  and  certain  of  its  geologic  relations  were  found  to  he  so 
interesting  that  this  brief  separate  discussion  has  been  prepared. 
The  Potosi  mine  is  located  on  the  western  slope  of  Spring  Mountains,  about  latitude 
36°  N.,  longitude  115°  30'  W.  It  is  reached  by  a  30-mile  drive  from  Good  Springs  station 
on  the  San  Pedro,  Los  Angeles  and  Salt  Lake  Railway.  The  springs  from  which  the  sta- 
tion takes  its  name  are  about  7  miles  west  of  the  railway,  at  the  eastern  foot  of  the  moun- 
tains, and  mark  a  well-known  resting  and  camping  place.  The  mine  proper  is  near  the 
old  Mormon  trail  from  Salt  Lake  City  to  Los  Angeles  and  was  first  worked  nearly  half  a 
century  ago  to  furnish  lead  bullets  for  the  pioneers.  It  had  been  idle  for  many  years 
when  the  coming  of  the  railway  and  the  demand  for  zinc  led  to  its  reopening. 
The  mountains  have  been  visited  by  J.  K.  X.  Owen,  Gilbert,  Weeks,  Rowe,  and  Spurr. 
The  latter  has  summarized  existing  knowledge  regarding  them  as  follows:  a 
The  Spring  Mountain  Range  is  an  exceedingly  irregular-shaped  group  of  mountains,  lying  south- 
west of  Las  Vegas  Range,  and  separated  from  the  Kingston  Range,  farther  south,  by  the  Pahrump 
Valley.  The  general  trend  of  the  range  is  northwest  and  southeast,  and  its  length  in  this  direction 
is  about  60  miles,  and  at  its  northern  end,  in  the  neighborhood  of  Charleston  Peak,  the  total  width 
is  as  much  as  30  miles.  This  peak  constitutes  the  highest  portion  of  the  range,  being  10,874  feet  above 
the  sea,  and  is  a  conspicuous  landmark.  This  range  is  divided  Into  numerous  ridges,  which  run  in 
many  different  directions  without  much  visible  system.  At  at  hast  two  points  at  the  northern  base 
of  the  range  there  occur  warm  springs,  namely,  Indian  Spring  and  the  spring  at  White's  ranch  in  Pah- 
rump Valley.    This  is  interesting,  since  the  range  contains  few  igneous  rocks. 
Geology. — The  rocks  forming  the  mountains  consist  of  Cambrian,  Carboniferous,  and 
Jurassic  sediments,  and,  near  Good  Springs  proper,  a  small  area  of  basalt  with  at  least  one 
a  Spurr,  J.  E.,  Descriptive  geology  of  Nevada  south  of  the  fortieth  parallel  and  adjacent  portions 
of  California:  Bull.  U.  S.  Geol.  Survey  No.  208,  1903,  p.  104. 
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