NOTES  ON  THE  GEOLOGY  OF  THE  GOLDFIELDS  DISTRICT, 
NEVADA. 
By  J.  E.  Spure. 
INTRODUCTION. 
Interest  has  been  aroused  in  the  new  camp  of  Goldfields,  Esmeralda 
County,  Nev.  This  district  is  situated  23i  miles  southeast  of  Tono-. 
pah  and  about  6  miles  due  east  of  the  old  mining  camp  of  Montezuma. 
Recently  some  good  values  in  gold  have  been  found;  several  hundred 
people  have  gone  there,  and.  ore  has  been  sacked  for  shipment  from 
some  of  the  mines. 
The  writer  visited  this  district  in  June,  1903,  shortly  after  it  had 
been  located,  and  while  only  a  few  men  were  working.  Some  good 
assays  had  been  reported  at  this  time,  while  other  attempts  did  not 
succeed  in  finding  much  over  a  trace  of  gold.  The  district  then 
was  known  as  the  "Grandpa,"  but  the  name  has  since  been  changed. 
The  writer's  visit  was  a  flying  one,  and  no  close  examination  was  made, 
but  such  notes  on  the  geology  as  were  taken  may  prove  of  interest. 
GENERAL  GEOLOGY. 
Topographically  the  district  shows  a  number  of  low  ridges.  To  the 
west  are  basalt-capped  mesas,  leading  up  into  the  higher  mountains  in 
the  vicinity  of  Montezuma.  The  part  of  the  district  examined  con- 
sists of  one  of  the  ridges  mentioned,  which  runs  in  a  north-south 
direction;  this  was  followed  for  a  distance  of  about  2  miles.  On  the 
north  end  of  the  ridge  the  rock  is  a  very  much  altered  rhyolite,  show- 
ing strong  flow  structure,  a  glassy  groundmass,  and  porphyritic  crys- 
tals of  quartz,  orthoclase,  and  biotite,  which  are,  however,  almost 
always  decomposed.  Near  the  north  end  of  the  ridge  the  igneous  rock  is 
chiefly  alaskite  (quartz-feldspar  rock),  sometimes  of  granitic  structure, 
sometimes  coarse  and  pegmatitic,  frequently  very  fine  grained.  A 
variation  of  this  is  quartz-muscovite  rock  which,  when  fine  grained, 
resembles  somewhat  metamorphosed  quartzite.  Some  of  these  quartz! 
muscpvite  rocks  seem  to  have  been  originally  such,  while  in  other 
portions  the  muscovite  seems  to  have  formed  in  little  blades  at  the 
expense  of  original  orthoclase  feldspar.  A  process  of  endomorphism 
similar  to  that  described  by  the  writer  in  similar  rocks  at  Belmont/'  is 
aSpurr,  J.  E.,  Quartz-muscovite  rock  from  Belmont,  Nev.:  Am.'Jour.  Sci.,  4th  ser.,  vol.  10,  1900,  pp. 
351-358. 
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