spitrr.]  ORE    DEPOSITS    OF    TONOPAH,    NEVADA.  105 
In  the  Montana  Tonopah  the  chief  vein  shows  in  places  a  breccia- 
tion  and  subsequent  cementation.  Both  the  original  material  and 
the  subsequent  cement  are  of  quartz  and  rich  black  silver  ores,  and 
seem  to  have  been  deposited  under  about  the  same  conditions.  The 
inference  is  that  the  strain  which  originally  produced  the  fracture 
zones  kept  on  during  their  cementation  by  the  circulating  mineral- 
izing waters,  and  that  in  this  case  this  strain  resulted  in  the  local 
shattering  of  the  cement  and  the  subsequent  healing  by  similar 
materials. 
Primary  ores. — At  the  time  of  the  writer's  first  investigation  of 
Tonopah,  in  the  autumn  of  1902,  only  the  oxidized  ores  of  the  upper 
levels  of  the  Mizpah  were  available  for  examination.  From  a  micro- 
scopic study  of  these  he  found  that  the  original  metallic  mineral  was 
still  present  in  minute  grains.  It  was  black  in  color,  and  he  supposed 
it  to  be  a  rich  silver  sulphide.  Subsequent  to  this  investigation  the 
primary  sulphide  ores  were  found  in  the  Montana  Tonopah  mine,  and 
the  correctness  of  the  forecast  above  mentioned  was  shown.  In  the 
Montana  Tonopah  the  ores  are  quartz  veins  carrying  in  places  very 
large  amounts  of  the  rich  black  antimonial  sulphide  of  silver,  steph- 
anite.  This  stephanite  is  undoubtedly  primary.  Besides  the  quartz, 
as  gangue  mineral,  there  is  another  having  a  milky  appearance, 
but  otherwise  looking  much  like  the  quartz.  This  is  a  variety  of 
orthoclase  (valencianite).  Some  of  the  stephanite  may  contain  some 
copper,  making  it  a  kind  of  polybasite.  Chalcopyrite  is  very  com- 
monly present  and  is  probably,  in  part  at  least,  primary,  although 
this  is  not  certain. 
Secondary  sulphides. — Throughout  the  Tonopah  district  argentite 
and  ruby  silver  occur  in  greater  or  less  abundance,  sometimes  adding 
considerably  to  the  value  of  ores,  but  they  do  not  occur  in  such  quan- 
tities as  the  stephanite  ores  or  the  oxidized  products.  Wherever 
found  the  argentite  and  the  ruby  silver  are  unquestionably  secondary, 
having  formed  from  the  alteration  of  the  stephanite.  They  occur 
along  cracks  in  the  primary  sulphide  ore  and  are  occasionally  found  in 
the  oxidized  or  semioxidized  ore.  The  chalcopyrite  above  mentioned, 
as  observed  in  the  Montana  Tonopah  ore,  seems  to  occur  chiefly  as 
small  streaks  cutting  the  original  stephanite  ore,  giving  it  the  appear- 
ance of  being  secondary  to  the  latter.  In  some  cases  it  occurs  along 
cracks  and  is  undoubtedly  secondary.  It  is  veiy  likely  that  some  at 
[least  of  this  mineral  has  been  formed  from  the  copper  contained  in 
the  cupriferous  silver  sulphide.  Some  pyrite  is  also  undoubtedly 
secondary.  Pyrite,  however,  is  relatively  rare  in  these  ores — much 
jmore  so  than  in  the  country  rock. 
Oxidized  ores. — In  the  Mizpah  vein  the  oxidized  zone  extends  nearly 
down  to  the  700-foot  level.  Observation  shows,  however,  that  the 
Limit  of  oxidation  is  extremely  irregular.  For  examine,  the  oxidation 
Extends  much  deeper  along  the  vein  than  some  distance  away  from  it 
