sruRR.]  ORES   OF   GOLDFIELD,    NEV.  137 
silver  is  usually  practically  absent,  though  the  shipping  ore  from  the 
Combination  mine  contains  from  1  to  3  ounces.* 
Deposition  of  rich  ore  during  oxidation. — The  origin  of  this  rich 
ore  is  important  to  consider  in  order  to  judge  the  future  chances  of 
the  district.  Most  of  that  which  has  been  extracted  up  to  the 
present  time  has  been  oxidized  ore.  The  ores  are  mixed  sulphides 
(usually  in  large  part  pyrite)  and  oxides  up  to  near  the  surface. 
The  oxidized  material  which  follows  cracks  and  seams  is  usually 
found  to  be  several  times  (sometimes  several  hundred  times)  as  rich 
as  the  unoxidized  portion.  The  irregular  spongy  nature  of  the  free- 
gold  particles  in  such  oxidized  material  completes  the  proof  that  this 
is  gold  that  has  been  dissolved  and  redeposited  in  concentrated  form 
during  the  process  of  oxidation.  Iron  sulphate  derived  from  oxida- 
tion of  the  pyrites  is  the  probable  agent.  A  peculiar  yellow  coating, 
pointed  out  to  the  writer  as  the  best  sign  of  values  in  the  oxidized 
ores,  was  shown  by  Doctor  Hillebrand  to  be  a  basic  ferric-alkali 
sulphate,  containing  both  sodium  and  potassium — perhaps  jarosite. 
Other  sulphates,  such  as  alum  and  gypsum,  are  abundant.  These 
oxidized  ores  are  prepared  for  shipment  by  screening,  the  fines  being 
shipped  and  the  coarse  quartz  rejected.  This  is  a  rather  crude 
method  of  treatment.  Some  specimens  of  ore  from  the  waste  or  low- 
grade  dumps  have  been  found  by  the  writer  to  show  under  the  micro- 
scope a  large  amount  of  free  gold. 
Rich  sulphide  and,  telluride  ore. — As  the  ground-water  level  at 
Groldfield  is  unusually  high  for  this  desert  country,  water  having  been 
sncountered  in  several  shafts  at  from  150  to  200  feet,  it  is  plain  that 
his  oxidized  ore  is  only  a  temporary  supply.  In  the  Combination  and 
he  Florence  mines,  however,  sulphide  ores  of  very  high  grade  have 
j)een  encountered  below  the  oxidized  zone.  In  these  mines  a  dark- 
£ray  copper-bearing  mineral  is  most  intimately  connected  with  the 
*old,  being  very  rich.  A  specimen  from  the  Combination,  analyzed 
)y  Doctor  Hillebrand,  proves  to  be  a  sulpho-salt  of  copper,  antimony, 
jnd  arsenic,  which,  so  far  as  qualitative  composition  goes,  may  be 
etrahedrite.  Tellurium  is  also  present  in  this  ore;  and  the  same  ele- 
ment has  been  reported  elsewhere  in  the  district.  Therefore  the  sul- 
fide ores  may  also  be  very  rich.  Moreover,  while  the  difference 
ctween  the  oxidized  and  unoxidized  portions  of  the  ores  within 
(he  oxidized  zone  is  in  general  so  great,  certain  shoots  occur  in  the 
xidized  zone,  as  in  the  January  and  the  Jumbo,  where  the  unoxi- 
Assays  from  the  Blue  Bull  mine  at  Goldfield  made  by   Mr.   A.    Hamilton   show   much 
iore  silver  (up  to  73  ounces).      In  five  assays  the  proportion  of  gold  to  silver  by  weight 
1  :  50,   1  :  52,   1  :  51,   1  :  137,  and   1  :  382.     All  these  samples   were  from  depths  of  35 
•i  |>  40  feet  except  the  last,  which  was  from  the  outcrop.      In  a  sixth  specimen  the  propor- 
■   Ion  was  reversed,  being  silver  to  gold,  1  :  37,  by  weight.      (Courtesy  of  H.  C.  Morris.) 
