60  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1905. 
been  traced  by  means  of  prospect  holes  at  least  1,000  feet.  At  one  prospect  hole  the 
vein  is  capped  by  a  gossan  of  spongy  limonite  9  feet  thick.  At  this  depth  some  malachite 
and  lessazurite  are  associated  with  the  limonite,  and  at  the  bottom  of  the  hole,  9  feet  deeper, 
the  vein  is  reported  to  have  run  12  per  cent  copper,  with  14  ounces  of  silver  and  $1.20  in 
gold  per  ton.  The  vein  is  from  2  to  5  feet  wide  and  on  its  borders  shows  a  gradual  passage 
from  totally  unaltered  limestone  to  pure  limonite.  These  secondary  ores,  on  the  border 
of  the  vein,  at  least,  are  a  replacement  of  the  limestone.  The  same  company  has  an  incline 
65  feet  deep  situated  on  a  shear  zone  in  practically  horizontal  limestone.  The  shear  zone 
strikes  N.  85°  E.  and  dips  60°  S.  A  streak  of  ore,  traceable  more  or  less  continuously 
for  900  feet  and  from  H  to  2\  feel  wide,  occupies  the  shear  zone.  The  ore  consists  of 
malachite,  azurite,  and  limonite,  associated  with  intensely  limonite-stained  chalcedony 
of  conchoidal  fracture.  The  sulphides  seen  were  chalcocite  and,  in  less  amount,  chalco- 
pyrite and  pyrite.  The  two  latter  are  undoubtedly  original.  Several  assays  of  the 
ore  are  said  to  have  averaged  between  0  and  10  per  cent  of  copper,  while  the  silver  values 
are  variable,  reaching  as  high  as  400  ounces  per  ton.  The  silver  is  evidently  intimately 
associated  with  the  copper  minerals,  the  iron  compounds  giving  no  silver  returns.  The 
average  ore  runs,  per  ton,  about  1  ounce  of  silver  to  1  per  cent  of  copper.  Gold  is  present 
in  traces  only.  Another  prospect  on  this  property  is  in  limestone  much  stained  by  limonite. 
Malachite  and  less  azurite  with  a  heavily  limonite-stained  chalcedonic  quartz  occur  in 
small  "kidneys"  throughout  the  limestone  and  in  narrow  seams  along  joint  planes.  Chal- 
copyrite  is  reported  from  the  surface  here,  but  is  not  abundant.  In  another  prospect 
irregular  lenses  of  the  same  ores  and  gangue  lie  in  a  narrow  shear  zone  in  the  limestone. 
Small  bunches  of  chalcopyrite  are  sporadically  distributed  in  the  dark  chalcedony. 
The  property  of  the  Tri-Metallic  Mining  Company  lies  one-half  mile  west  of  that  last 
described.  The  Cambrian  limestone,  although  gently  flexed,  is  approximately  horizontal. 
Intense  staining  by  limonite  is  characteristic  of  limestone  in  the  vicinity  of  the  ore.  Minor 
faults  were  noted,  hut  their  association  with  the  ore  deposits  is  not  intimate.  A  shipment 
of  picked  ore,  which  netted  $236  per  ton  (averaging  7  ounces  of  gold,  230  ounces  of  silver, 
and  19  per  cent  of  copper),  was  recently  made  from  a  surface  pocket  of  ore.  Chalcopyrite 
is  the  only  original  sulphide  present.  Chalcocite,  malachite,  and  azurite  with  dark-brown 
chalcedony  are  secondary  and  these  are  partially  at  least  replacements  of  limestone.  A 
few  masses  of  native  copper,  presumably  of  secondary  origin,  are  also  reported,  although 
they  were  not  seen  by  the  writer.  Chalcopyrite  was  apparently  originally  distributed 
in  the  limestone  in  masses,  which  so  far  as  known  do  not  exceed  one-half  inch  in  diameter. 
Later  these  scattered  particles  were  concentrated,  the  secondary  copper  minerals  appar- 
ently being  replacements  of  limestone. 
In  the  main  shaft  bunches  of  chalcopyrite  lie  in  the  limestone  in  association  with  coarse 
calcite  much  stained  by  limonite.  In  some  cases  the  chalcopyrite  has  been  brecciated 
and  the  narrow'  interstices  rilled  with  iron-stained  chalcedony.  The  ore  in  this  shaft  is 
said  to  have  occurred  in  "kidneys,"  sometimes  connected  with  other  "  kidneys"  by  narrow- 
ore  seams.  From  one  of  these  masses  1,900  pounds  of  ore  were  removed.  This  lens  of 
ore  was  4  feet  in  diameter  at  the  center  and  tapered  to  a  point  at  each  end,  the  total  length 
being  9  feet. 
Ore  examined  from  a  claim  owned  by  Mr.  E.  Oldt  showed  similar  characteristics,  a 
little  galena  and  white  quartz  of  apparently  equal  age  being  associated  with  pyrite  and 
chalcopyrite.  Again,  transparent  drusy  quartz  crystals  contemporaneous  with  or  later 
than  the  copper  and  lead  carbonates  and  brown  chalcedony  are  characteristic.  The  values 
in  this  ore  are  said  to  be  in  silver  and  copper. 
In  the  Cuprite  district  chalcopyrite  with  less  pyrite,  galena,  calcite,  and  quartz  appear 
to  have  been  deposited  as  sporadic  masses  in  the  limestone,  as  seams  along  joints,  and  as 
lens-shaped  bodies  along  shear  zones.  Later  these  ores  were  altered  by  descending  waters 
to  chalcocite,  carbonates,  and  oxides,  the  carbonates  and  oxides  in  large  part  replacing 
limestone.     Faulting   often   accompanied   or   preceded   the   change.     Contemporaneously 
