90  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.        [bull.  260. 
tive  value,  while  the  really  important  mines  would  be  embraced  by  a 
circle  of  about  half  that  radius,  with  its  center  near  the  summit  of 
Raven  Hill.  That  scattered  deposits  of  greater  or  less  value  may  be 
found  in  outlying  portions  of  the  district  is  by  no  means  improbable. 
But  the  close  dependence  of  the  typical  Cripple  Creek  ores  upon  the 
main  volcanic  center,  and  the  consequent  remarkable  compactness  of 
the  gold-bearing  area,  are  features  highly  characteristic  of  the  dis- 
trict and  are  likely  always  to  remain  so. 
UNDERGROUND    DEVELOPMENT. 
At  the  time  of  the  earlier  survey  the  deepest  shafts,  those  of  the 
Moose,  Pharmacist,  and  Anna  Lee  mines,  were  down  only  about  400 
feet,  while  few  of  the  other  mines  were  over  200  feet  in  depth.  Many 
subsequently  prominent  mines  were  then  mere  prospects  or  had  not 
been  located. 
The  deepest  shaft  at  present  is  the  Lillie,  which  is  over  1,500  feet 
deep,  although  the  Stratton's  Independence  shaft,  1,400  feet  deep,  has 
the  lowest  sump  in  the  district.  The  American  Eagle  shaft  is  nearly 
as  deep  as  the  Lillie,  while  there  are  about  twenty  other  shafts  over 
1,000  feet  in  depth,  and  at  least  100  shafts  deeper  than  the  deepest 
workings  existing  in  1894. 
The  amount  of  drifting  and  crosscutting  accomplished  since  the 
earlier  survey  is  more  than  commensurate  with  the  increased  number 
and  depth  of  the  shafts,  and  the  district  is  further  intersected  in  vari- 
ous directions  and  at  different  levels  by  two  long  tunnels  run  forr 
drainage  purposes  and  by  a  dozen  or  more  extensive  adits. 
CHARACTER  OF  THE  ORES. 
The  characteristic  feature  of  the  Cripple  Creek  ores  is  the  occur 
rence  of  the  gold  in  combination  with  tellurium,  chiefly  as  calaverite, 
I  »ul  partly  also  as  the  more  argentiferous  sylvanite,a  and  probably  to 
a  minor  extent  as  other  gold,  silver,  and  lead  tellurides.     The  tellu- 
rides  are  frequently  associated  with  auriferous  and  highly  argentifer- 
ous tetrahedrite,  with  molybdenite,  and  occasionally  with  stibnite 
While  these  minerals  have  not  yet  been  closely  studied,  preliminary 
examination  indicates  that  their  contents  in  gold  are  due  to  an  inti- 
mate mechanical  mixture  of  tellurides.     Pyrite,  Avhile  widely  dissemi 
nated  through  the  country  rock  and  of  common  occurrence  in  the 
fissures,  is  rarely  sufficiently  auriferous  to  constitute  ore.     Such  of  th< 
pyritic  ores  as  have  been  tested  reveal  the  presence  of  tellurium,  indi 
eating  that  the  ore  is  a  mixture  of  pyrite  and  gold-silver  tellurides 
Galena  and  sphalerite  occur  in  small  quantities  in  many  of  the  mines 
a  Calaverite  (AuAg)  Te.> :  tellurium,  57 .  \  per  cent:  gold,  39.5  per  cent  ;  silver,  '.\.\  pe 
cent.  Sylvanite  (AuAg)  Te2 :  tellurium,  <">'-!.  1  per  cent;  gold,  24.5  per  cent;  silver,  13. 
per  cent. 
