COPPER    DEPOSITS    OF    HARTVILLE    UPLIFT,    WYOMING.  99 
many  places  either  an  iron-stained  limestone  or  hematite.  The  vein- 
lets  of  ore  do  not  extend  beyond  these  iron-rich  substances  in  so  many 
places  that  the  natural  inference  is  that  the  iron  acted  as  the  precipi- 
tant. Under  the  microscope  a  thin  section  of  this  ore  shows  that  the 
copper  ores  occur  as  veinlets  cutting  the  hematite  and  limestone  and 
rim  the  hematite  as  if  it  had  acted  as  the  precipitant.  Limonite  is 
contemporaneous  with  the  copper  minerals.  Since  the  hematite  is 
locally  the  iron-rich  base  of  the  Guernsey  formation  recrystallized, 
extending  down  into  joints  in  the  limestone  enlarged  by  solution,  it  is 
possible  that  the  ore  is  all  of  post-Carboniferous  age.  The  lenses  of 
copper  ore  in  pre-Cambrian  limestone  are  certainly  in  some  places  and 
probably  everywhere  post-Carboniferous  in  age,  and  were  formed  by 
descending  waters,  the  probable  source  of  the  copper  having  been  the 
Guernsey  formation. 
Lenses  in  schist  and  other  pre-Cambrian  formations. — Similar  lenses 
of  ore  with  definite  downward  limitations  occur  in  pre-Cambrian 
schist,  quartzose,  and  jaspery  rocks  and  in  the  chloritic  schist  derived 
through  mashing  from  basic  igneous  rocks.  In  schist  he  ores,  chryso- 
colla,  and  malachite,  and  in  some  places  chalcocite  and  azurite,  occur 
as  thin  sheets  in  the  planes  of  schistosity  and  in  small  cross  fractures. 
Microscopic  examination  also  shows,  in  addition  to  innumerable  tiny 
fractures  filled  with  malachite,  some  replacement  of  quartz  by  mala- 
chite. At  some  places  these  deposits  decrease  in  width  with  depth 
and  at  others  they  extend  downward  from  blanket  deposits  of  the 
Guernsey  sandstone.  The  majority  of  them,  at  least,  are  thought  to 
have  been  formed  by  descending  waters,  and  the  source  of  many 
was  probably  the  Guernsey  formation.  Since  the  gray  quartzose 
rocks  and  the  jasper  are  very  brittle,  the  ramifications  of  the  copper 
veinlets  through  them  are  most  complex. 
Lenses  in  iron  ore  and  heavily  iron-stained  jasper. — The  most  impor- 
tant example  of  the  lenses  in  iron  ore  and  jasper  is  the  Sunrise  mine, 
now  the  most  productive  iron  mine  west  of  the  Mississippi,  but  in  the 
eighties  an  important  copper  mine.  It  is  situated  on  the  southward- 
facing  slope  of  a  steep  hill  in  the  north-central  portion  of  sec.  7,  T.  27 
N.,  R.  65  W.  Its  total  copper  output  is  given  by  Knight  as  1,395,287 
pounds,  valued  at  $209,282.  The  copper  content  ranged  from  6  to  20 
per  cent,  with  an  average  yield  of  15  per  cent.  Knight  states  further 
that  the  ore  carried  from  2  to  3  ounces  of  silver  per  ton.  The  slag  from 
the  Fairbank  furnace,  where  the  ore  was  smelted,  is  now  being  shipped 
to  smelters  by  C.  A.  Guernsey,  of  Guernsey,  who  states  that  it  averages 
5  or  6  per  cent  of  copper.  Malachite,  leached  from  the  slag  since  the 
shut-down  of  the  furnace,  occurs  upon  the  surface  and  in  the  cavities 
of  the  slag  fragments. 
The  country  rock  of  the  copper  ore  at  Sunrise  is  schist,  iron  ore 
(hematite),  and  an  impure  flint  which  is  stained  by  either  limonite 
