COPPER    DEPOSITS    OF    HARTVILLE    UPLIFT,    WYOMING.  97 
At  several  places  near  Haystack  Peak,  copper  minerals  fill  tiny 
fractures  or  incrust  cavities  in  pegmatite  or  pegmatitic  quartz  dikes. 
Ohalcopyrite  and  chalcocite  are  original  and  malachite  and  covellite 
are  their  alteration  products.  Sulphides  are  rather  abundantly  present 
in  the  center  of  the  NE.  J  sec.  26,  T.  27  N.,  R.  65  W.,  as  cement  to 
a  breccia  of  schist.  A  sample  collected  at  one  of  these  prospect 
shafts,  on  the  dump,  which  at  the  time  of  examination  was  boarded 
over,  gave  a  trace  of  silver,  but  no  gold,  copper,  or  nickel. 
LENSES    OF    COPPER    ORE    DEPOSITED    BY    DESCENDING    WATERS. 
The  most  common  copper  deposits  in  the  Hartville  uplift  are  len- 
ticular or  wedge-shaped  masses  of  carbonates,  silicates,  and  oxides 
and  secondary  sulphides  which  narrow  with  depth  and  finally  disap- 
pear. These  deposits,  which  occur  in  the  Guernsey  and  several  of 
the  pre-Cambrian  formations,  are  believed  to  have  been  laid  down  by 
descending  waters,  the  ore  presumably  having  been  leached  from  the 
Guernsey  or  from  some  formation  that  was  once  superimposed  upon  it, 
but  was  removed  by  erosion  prior  to  the  deposition  of  the  Hartville 
formation. 
Lenses  in  the  Guernsey  formation. — Copper  deposits  in  the  Guernsey 
formation  are  practically  confined  to  the  immediate  vicinity  of 
Guernsey,  the  only  deposit  of  consequence  being  that  of  the  Green 
Mountain  Boy. 
The  Green  Mountain  Boy  mine  is  situated  approximately  half  a 
mile  east  of  the  town  of  Guernsey,  at  the  head  of  a  broad  valley. 
The  production  has  been  variously  estimated  at  300  to  500  tons, 
valued  at  $36,000  to  $60,000.  The  ore  is  said  to  have  averaged  37 
per  cent  copper,  with  from  one-third  to  one-half  ounce  of  silver  to 
each  per  cent  or  unit  of  copper,  the  total  values  averaging  at  the  time 
of  shipment  $155  per  ton.  The  silver,  which  was  closely  associated 
with  chalcocite,  was  patchy  in  distribution,  some  assays  of  high  value 
having  been  obtained. 
The  country  rock  is  the  upper  part  of  the  light-gray  or  white  hori- 
zontal Guernsey  limestone  which  at  the  horizon  of  the  main  workings 
contains  many  lenticular  masses  of  brown  flint.  The  flint  nodules  are 
from  2  inches  to  4  feet  long,  and  from  one-half  inch  to  6  inches  wide. 
Calcite-lined  cavities  2  to  3  feet  long  occur  in  the  limestone.  The 
original  lens  was  of  chalcocite  and  is  stated  to  have  been  60  feet  long, 
30  feet  wide,  and  from  5  to  9  feet  thick.  The  long  diameter  of  this 
podlike  mass  lay  east  and  west  across  the  valley.  At  the  surface  con- 
siderable malachite  was  associated  with  the  chalcocite,  but  as  the 
lens  was  followed  into  the  hill  malachite  decreased  in  amount. 
The  open  cut  and  the  three  tunnels  from  it  now  open  to  inspection 
show  but,  little  ore,  and  the  tunnels  are  barren  30  feet  southwest  of 
