110  CONTRIBUTIONS    TO   ECONOMIC    GEOLOGY,  1904.        [bull.  260. 
(2)  The  Colorado  Central  type,  of  high-grade  silver  ore,  is  com- 
posed of  considerable  galena,  some  zinc  blende  (usually  yellowish 
•w  resin  zinc"),  characteristically  large  amounts  of  ruby  silver,  poly- 
basite  and  tetrahedrite,  and  only  faint  traces  of  pyrite  and  calcite. 
(3)  The  Mendota-Frostberg  type  (Maine,  Terrible,  Ocean  Wave., 
etc.)  is  composed  of  broad  and  exceptionally  strong  low-grade  zinc 
and  lead  ore  veins.  They  are  usually  large  fissures  containing  rub- 
ble cemented  by  heavy  dark-colored  zinc  blende,  considerable  galena 
varying  amounts  of  pyrite  and  chalcopyrite,  and  a  relatively 
small  amount  of  silver.  Besides  the  fissure  cavities,  there  are  fre 
quently  ore-filled  spaces  of  dissolution  in  crushed  portions  along  th< 
vein  zone,  and  also  in  the  granite  near  the  vein.  The  ore  is  chiefly  a 
the  junctions  of  veins. 
(4)  The  Republican  Mountain  type  (Mineral  Chief,  Boston 
Beecher,  Muscovite,  Sunburst,  Sceptre,  etc.)  is  characterized  by  pre 
dominance  of  lead,  small  amount  of  zinc,  considerable  pyrite,  lo\ 
content  of  silver,  a  little  siderite,  copper  pyrites,  gold,  and  sometime* 
gray  copper.  Physically  these  lodes  are  likely  to  be  strong  and. 
large,  but  are  in  places  entirely  unmineralized.  The  ore  seems  to  b 
richer  at  vein  junctions.  The  Sceptre-Sunburst  ore  is  a  variation  o 
this  class,  containing  a  characteristically  large  amount  of  siderit< 
with  comparatively  small  amounts  of  galena,  blende,  and  pyrite,  an 
slightly  more  silver. 
(5)  The  Democrat  Mountain  type  is  distinguished  from  the  lleput 
lican  Mountain  type  by  being  relatively  high-grade  ores,  compose 
chiefly  of  galena,  with  a  high  percentage  of  silver,  scarcely  any  iroi 
and  very  little  zinc.  The  ore  bodies,  though  small,  are  well  define* 
and  are  usually  located  near  crossings  or  junctions.  The  ore  bodi< 
are  all  located  near  the  surface,  the  veins  not  being  much  unrninera 
ized,  so  far  as  known,  below  a  depth  of  200  to  300  feet. 
(('))  The  Empire  type.  The  ores  of  this  type  are  made  up  almB 
entirely  of  low-grade  gold-bearing  pyrite  and  chalcopyrite,  with  i 
lead  and  zinc  and  only  a  trace  of  silver.  Normally  the  pyrite 
practically  without  gold  values,  Avhile  the  wholly  chalcopyrite  or 
contain  the  most  gold  values.  These  ore  bodies  appear  to  be  chief 
due  to  impregnation  and  replacement  of  the  wall  rock,  and  to  be  littl 
affected  by  junctions  or  crossings. 
(7)  The  Griffith  type.  This  is  a  gold-silver  ore,  with  varyii 
amounts  of  lead,  zinc,  and  cupriferous  pyrite,  chalcopyrite,  etc.  T 
this  class  belong  the  Griffith-Annette  ores,  which  are  predominant 
low-grade  gold-silver  ores  consisting  of  crystalline  iron  pyrite,  chalc 
pyrite,  galena,  and  sphalerite,  with  a  gangue  of  siderite,  quartz,  ai 
some  barite.  The  better  grades  of  ore  usually  have  the  most  galerii 
blende,  and  chalcopyrite.     Phenomena  show  that  the  galena-blenc 
