9()  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   1906,   PART    I. 
FISSURE    VEINS    IN    PRE-CAMBRIAN    FORMATIONS. 
The  Copper  Bottom  prospect,  owned  by  Henry  Metz  and  situated 
in  the  south-central  part  of  the  SE.  J  sec.  23,  T.  29  N.,  R.  65  W.,  is 
located  probably  on  a  fissure  vein.  At  the  time  of  the  writer's  visi| 
the  shaft  was  15  feet  deep.  The  country  rock  is  a  slightly  silicified 
dense  yellowish  limestone  of  pre-Cambrian  age,  which  is  cut  by  thin 
seams  of  hematite.  The  vertical  vein,  which  strikes  N.  20°  W.,  cuts 
across  the  steeply  dipping  limestone.  There  is  a  fault  of  small 
throw  on  the  east  side  of  the  vein,  and  fragments  of  limestone  are 
included  in  the  vein  matter.  On  the  east  side  of  the  shaft  the  vein  is 
4  inches  wide  at  the  surface  and  22  inches  at  the  bottom  of  the  shaft 
on  the  west  side  the  vein  comes  in  3  feet  from  the  bottom  and  there 
only  as  a  thin  stringer.  The  limestone  for  a  distance  of  1  foot  or 
either  side  of  the  vein  is  heavily  iron  stained.  An  assay  of  an  average 
sample  collected  by  the  writer  across  the  vein  on  the  east  side  of  tip 
shaft.  1.")  feet  from  the  bottom,  contained  a  trace  of  gold,  2  ounces 
per  ton  of  silver,  and  24.64  per  cent  of  copper.  The  predominant  on 
is  the  brownish  form  of  chrysocolla,  blotched  with  irregular  masses  o 
green  chrysocolla  in  the  center  of  which  is  some  malachite  and  rare! 
a  little  azurite.  Tennantite  °  occurs  in  irregular  masses  up  to  1  foo 
in  length.  Although  chrysocolla  is  on  the  whole  slightly  older  thai 
malachite  and  the  latter  older  than  azurite,  these  ores  with  tennantill 
are  approximately  of  the  same  age.  Incrusting  tiny  cavities  in  thii 
ore  is  some  quartz,  which  in  turn  is  coated  with  younger  calcitl 
Clearly  later  than  these  ores  and  gangues  and  occurring  in  cracks  i] 
them  are  knife-edges  of  malachite,  azurite,  and  a  black  sooty  coppe 
oxide  or  sulphide.  The  thickening  with  depth,  together  with  it. 
position  along  a  fault,  lead  to  the  belief  that  this  deposit  is  thll 
oxidized  portion  of  a  fissure  vein.  The  apparent  thickening  wit  i 
depth  may.  however,  be  local. 
The  Charter  Oak  prospects,  owned  by  Lauck  &  Stein,  are  situate*! 
on  the  south  side  of  McCanns  Pass,  near  the  center  of  the  SE.  {  sec.  2( , 
T.  27  X.,  R.  65  W.  The  deposits  lie  beneath  apparent  gossans  <f 
limonite  and  hematite,  in  pre-Cambrian  muscovite  schist  and  grad 
quartzose  beds.  Malachite,  chrysocolla,  and  chalcocite  occur  ii 
fractures,  in  one  place  within  a  cupriferous  belt  4  feet  wide  and  ii 
another  place  along  a  vein  t  feet  wide  cutting  across  the  verticil 
schist .  The  schist  near  the  copper  is  said  to  assay  from  80  cents  1a 
$27  in  gold  and  2  to  5  ounces  of  silver.  The  amount  of  developmeiij 
at  this  point  is  small,  but  these  deposits  have  the  appearance  of  bciia 
the  oxidized  /one  of  a  copper  vein. 
a  W.  T.  Schaller  states  concerning  specimens  submitted  to  him:  "  Both  samples  contain  the  cc  J 
stituents  of,  and  probably  are,  tennantite." 
