SPPRK 
CAKIt 
,,AVXD]       GEORGETOWN    MINING    DISTRICT,    COLORADO.  107 
themselves  were  probably  intruded  in  part  along  old  faults  in  the 
gneisses,  granites,  diorites,  and  pegmatites.  Along  these  old  lines  of 
weakness  the  later  movements  probably  successively  occurred. 
NATURE    OF    THE   ORES. 
The  Georgetown  district  possesses  a  great  variety  of  ores.  The 
values  are  principally  in  silver,  gold,  lead,  zinc,  and  copper,  in  the 
order  named.  Silver  is  found  in  small  amounts  in  the  native  slate 
as  "  wire  silver,"  associated  with  ore  minerals  or  by  itself  in  seams  of 
(fractured  rock.  As  a  rule,  however,  the  silver  occurs  in  various 
mineral  compounds  associated  with  galena  and  zinc  blende.  In  the 
low-grade  ores  the  values  lie  in  the  galena  and  zinc  blende,  and  sepa- 
rate silver  compounds  ordinarily  can  not  be  distinguished.  The  light- 
brown  or  yellow  "  resin  zinc  "  seems  to  be  more  favorable  for  carry- 
ing silver  values  than  the  dark-brown  or  black  sphalerite.  In  high 
grade  sulphide  ores  the  silver  values  lie  chiefly  in  tetrahedrite  and 
polybasite;  ruby  silver  and  tennanite  also  occur.  Tetrahedrite,  poly- 
basite,  and  tennanite  come  under  the  miner's  term  "  gray  cOpper." 
The  so-called  strictly  silver  ores  often  average  $2  in  gold,  especially 
if  considerable  pyrite  is  present. 
Gold   in    the    free   state   was    formerly    obtained    in    considerable 
amounts  from  placer  deposits  and  from  surface  outcrops  of  veins  in 
jthe  vicinity  of  Empire.     This  gold  was  recovered  by  sluicing  methods 
nd  through  the  agency  of  stamp  mills.     A  limited  number  of  string- 
rs  or  "  seams  of  native  gold  up  to  the  width  of  a  lead  pencil  in  thick  - 
ess  "  °  were  found  several  years  ago  in  granite  in  the  Hidden  Treas- 
ure mine,  near  Empire. 
|  At  present  the  gold  is  obtained  chiefly  from  pyrite-chalcopyrite 
)res.  While  free  gold  is  found  in  this  class  of  ores  in  very  limited 
quantities,  the  major  portion  is  intimately  combined  with  the  sul- 
phides. The  copper  content  of  the  minerals  seems  to  be  closely  con- 
nected with  the  gold  values,  for  unless  chalcopyrite  is  present  or  the 
pyrite  is  more  or  less  copper  bearing  the  ore  is  usually  too  low  grade 
o  ship.  Assays  of  pure  chalcopyrite  have  given  as  high  as  25  ounces 
n  gold.  Around  Empire  ores  carrying  $10  or  over  in  values  can  be 
profitably  mined. 
A  small  mass  of  rich  silver-gold  telluride  ore  was  also  found  in  the 
rriffith  mine,  at  Georgetown. 
The  ore  in  many  of  the  mines  is  chiefly  galena  and  sphalerite,  with 
me  pyrite  and  chalcopyrite  and  a  small  amount  of  silver.     The 
ercentages  of  the  minerals,  galena,  blende,  chalcopyrite,  and  pyrite, 
the  ore  change  so  in  different  parts  of  the  region  that  an  infinite 
"Verbal  communication,  Mr.  David  Ward,  Empire. 
