SheyND]       GEORGETOWN     MINING    DISTRICT,    COLORADO.  1  1  (.» 
rone,  which  is  itself  the  richest  of  all,  but  seem  rather  to  have  been 
segregated  from  the  surrounding  sulphides.  Specimens  were  found 
n  which  seams  of  massive  polybasite  mixed  with  ruby  silver  cut 
hrough  primary  massive  lead  and  zinc  ores.  The  frequent  existence 
>f  well-crj  stallized  polybasite  and  ruby  silver  lining  i  ugs  and  fissures 
n  galena-sphalerite  ore  also  points  to  the  secondary  origin  of  the 
ireater  portion  of  these  minerals. 
Thai  all  of  the  galena  and  zinc  blende  is  no!  primary  is  shov  n  l>\ 
he  occurrence  along  open  crevices  of  fresh  and  apparently  recently 
leposited  crystals  of  these  two  minerals,  and  also  by  the  presence  of 
Tystals  of  galena  and  sphalerite  <m  top  of  crystals  of  siderite,  a 
oineral  which  sometimes  occurs  lining  reopened  lead-zinc  filled 
issures.  A  specimen0  from  the  Maine  nunc  shows  large  crystals  of 
>olybasite  with  good-sized  crystals  of  blende  and  galena  on  their 
'ace-.  The  polybasite  ci  ystals  are  also  covered  with  minute  specks  of 
lative  silver  which  is  evidently  secondary  to  the  polybasite.  Native 
diver  in  the  wire  or  flake  form  is  also  frequently  found  in  crevices 
ind  along  fault  fractures  partly  or  wholly  filled  by  vein  material. 
riiir-  is  probably  the  effect  of  descending  waters. 
Considerable  chalcopyrite  and  pyrite  are  also  secondary.  These 
ast-named  minerals  arc  found  in  isolated  seams  in  rock  and  also 
coating  the  sides  of  crevices.  Many  of  the  more  cupriferous  ores  of 
he  Empire  area  doubtless  owe  then-  greater  richness  to  the  enrichment 
rhich  has  resulted  from  the  leaching  of  the  ores  nearer  the  surface. 
The  bprnite  which  is  found  in  some  of  the  mines  is  later  than  and 
econdary  to  the  chalcopyrite,  as  shown  by  its  occurrence  in  definite 
treaks  along  fractures  cutting  both  chalcopyrite  and  pyrite. 
Small   amounts  of  argentite    (Ag^.S,  "silver  glance"),   acanthite 
A ii  S).  and  enargite  (Cu3AsS4),  are  also  to  be  classed  with  the  sec 
ndary  sulphides. 
().r'nl',\i  (1  >,;■;  s.   -Oxidi/ed  ore-  ioimd  in  the  Silver  Plume-George 
own  area  lie  in  a  comparatively  limited  zone,  extending  from  the  sur 
ace  down.     Forty  feet  is  a  good  average  depth  of  complete  oxidation. 
)ccasion{illy    -mall    pockets   of   oxidized    ore   have   been    found    far 
elow  the  point-  above  noted,  even  reaching  depth-  of  L,000  feet  or 
iore  below  the  surface  along  channels  occupied  by  descending  sur 
tee  water-.     The  ore-  iii   the  oxidized   /one     the  "sulphurets"  of 
le  miner-  -at  times  are  granular,  black,  easily  friable  masses,  while 
-rain  they  have  the  appearance  of  brown  clay,  often  stained  reddish, 
(llowish,  or  greenish.  No  analysis  of  these  oxide  ore-  has  as  yet  been 
ade.  but  they  probably  consist  in  part  of  lead  carbonates  or  oxide-. 
ack  silver  sulphide  ("  silver  black  "  of  the  miner-),  silver  chloride. 
'aek  oxide  of  copper,  etc. 
"Owned  by  Mr.  Randall,  of  Georgetown,  J».  C. 
