70  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1905. 
free.  The  original  deposition  was  without  much  doubt  an  impregnation  of  the  country  rock,  ] 
as  is  the  case  with  the  secondary  minerals.  There  is  a  notable  resemblance  between  these] 
deposits  and  those  of  Kawich  and  certain  of  those  of  Goldfield. 
Gold  Crater  is  dependent  for  its  water  supply  on  tanks  located  on  the  basalt  mesa  and  on  1 
two  wells,  respectively,  3  and  9  miles  distant.  Fuel  for  mining  purposes  is  obtainable  f%m 
the  Stonewall  Mountains.     Goldfield  is  27  miles  distant. 
Stonewall  Mountains. — The  Stonewall  Mountains  lie  17  miles  southeast  of  Goldfield  and 
are  of  notably  symmetrical  form.  The  predominant  formation  of  the  mountains  is  a  rhyo-J 
lite  flow,  which  is  cut  by  monzonite-porphyry.  Quartz  veins  and  stringers  are  very  abun-j 
dant,  particularly  on  the  north  border  near  Stonewall  Spring.  These  quartz  veins  and! 
stringers  fill  faults,  joints,  and  the  cavities  of  brecciation,  in  both  formations. 
The  most  prominent  vein  follows  a  fault  scarp  immediately  south  of  Stonewall  Spring. 
The  fault  strikes  S.  65°  W.  and  dips  70°  NW.  The  quartz  vein  is  in  some  places  simple  j 
and  40  feet  wide,  while  in  others  it  is  complex  and  composed  of  many  parallel  veins.  Brec- 
ciation  often  accompanies  the  faulting,  the  interstices  between  fragments  of  the  country] 
rock  being  filled  with  quartz.  The  quartz  is  white  or  colorless,  rarely  greenish  yellow,  and! 
is  beautifully  crustified.  Vugs  with  quartz  crystals  or  mammillary  quartz  are  common. 
The  quartz  has  locally  been  fractured  and  slightly  displaced,  and  a  second  quartz  has  filled' 
the  cavities.  Heavy  limonite  and  slight  azurite  stains  were  noted  in  the  quartz,  while 
pyrite  is  locally  developed.  Prospectors  report  traces  of  gold  at  a  number  of  places. 
Timber  and  water  are  at  hand  in  abundance. 
Oak  Spring. — Oak  Spring  is  situated  50  miles  northeast  of  Bullfrog.  Here  massive 
rounded  hills  of  Carboniferous  limestone  and  sandstone  are  injected  by  irregular  masses  of 
biotite-granite.  The  limestone  near  the  contact  is  steeply  tilted  and  has  been  altered  to  a 
white  marble  containing  brown  garnet ,  epidote,  tremolite,  and  other  metamorphic  minerals,  j 
The  contact  facies  of  the  granite  contain  rather  abundant  crystals  of  pyrite,  probably  oM 
pyrogenic  origin.  Tertiary  lavas  and  sediments  form  mesas  which  surround  the  older! 
rocks. 
In  granite  1^  miles  nearly  due  south  of  Oak  Spring,  quartz  veins  striking  N.  30°  E.  and< 
dipping  15°  NW.  and  from  6  inches  to  3  feet  wide  have  been  staked.  The  quartz  is  white 
and  slightly  sugary.  Some  is  intensely  brecciated,  the  cracks  being  stained  by  hematite 
and  limonite.  Vugs  with  small  quartz  crystals  occur.  Sulphides,  sparingly  present,  are! 
pyrite,  chalcopyrite,  galena,  and  zinc  blende,  named  in  the  order  of  their  abundance. 
From  these  the  following  secondary  minerals  are  derived:  Hematite,  limonite,  malachite, 
azurite,  and  cerussite.  A  coating  of  a  greasy  mineral  in  silvery  tablets  frosts  some  of  the 
cavities.  The  values  in  this  ore  are  said  to  be  gold,  with  less  silver.  These  deposits  are 
similar  to  the  second  and  third  vein  systems  at  Trappmans  Camp. 
The  pegmatitic-quartz  veins,  abundant  in  a  small  granite  mass  three-fourths  of  a  mile 
east  of  south  of  the  spring,  contain  pyrite  crystals,  as  do  the  less  acid  pegmatites  and  the 
surrrounding  and  genetically  related  granite.  This  quartz  is  said  to  carry  good  gold  and 
silver  values,  presumably  in  the  pyrite. 
Three  hundred  yards  southwest  of  Oak  Spring  and  down  the  same  ridge  is  a  25-foot' 
shaft  in  Carboniferous  limestone,  here  locally  horizontal.  A  vein  2  feet  wide  which  st  i  ikes 
N.  35°  E.  and  dips  70°  NW.,  cuts  the  limestone.  The  vein  is  formed  of  malachite,  chryso- 
colla,  and  a  jaspery  quartz  which  is  deeply  stained  by  blotches  of  manganese  dioxide  and 
limonite.  Striking  vugs  in  malachite,  lined  with  later  azurite  which  in  turn  is  covered  with 
clear  quartz  crystals,  resemble  copper-sulphate  crystals.  Massive  yellowish-gray  cerussite 
(lead  carbonate)  is  also  present.  Post-mineral  faulting  has  occurred.  The  secondary 
minerals,  which  alone  are  seen,  partially  replace  the  limestone  and  partially  fill  preexistiiJ 
cavities. 
The  so-called  turquoise  mine  at  Oak  Spring  is  a  small  cut  in  the  metamorphic  Carbonif- 
erous limestone  H  miles  south  of  the  spring  and  three-fourths  of  a  mile  from  the  granite  con- 
tact. Two  veins  strike  north  and  south  and  dip  65°  W.,  apparently  parallel  to  the  bedding 
of  the  limestone,  which  is  here  partially  marmorized  and  silicified.     The  wider  vein  varies 
