98 
CONTRIBUTIONS   TO    ECONOMIC    GEOLOGY,  1905. 
made  by  which  the  company  exchanges  ore  with  the  Britannia  Company,  near  Vancouver, 
sending  it  the  basic  ore  and  receiving  in  exchange  the  highly  siliceous  ores  of  the  Britannia 
mine.  The  Coppermount  smelter  was  also  in  operation  in  the  latter  part  of  1905  and 
promises  to  be  a  steady  producer  in  the  future. 
One  mine  on  Prince  William  Sound  was  a  steady  producer  during  1904,  shipping  ore  to 
the  Puget  Sound  smelter. 
The  Nikolai  greenstone  forms  a  remarkable  body  of  igneous  rock,  extending  along  the 
Alaska  Range  for  nearly  300  miles,  lifted  and  upturned  with  the  Carboniferous  limestone 
about  its  holders,  but  not  breaking  through  the  rock  or  sending  out  dikes  or  arms  into  it. 
This  great  body  of  rocks,  which  consists  mainly  of  intrusive  masses,  but  in  part  contains 
amygdaloidal  surface  lavas,  is  cupriferous  over  a  very  extensive  area,  and  in  places,  as 
Bonanza  Creek  (Copper  River)  carries  disseminated  bornite  and  veins  of  glance  in  wh 
appears  to  be  fresh  rock,  together  with  associated  magnetite  and  pyrrhotite."  According 
to  Schrader  and  Spencer  the  Nikolai  greenstone  consists  of  volcanic  flows  varying  laterally 
and  vertically  and  constituting  a  unit  compared  with  adjacent  rocks  It  is  composed  of 
green  to  red  feldspar,  with  augite,  a  less  amount  of  chlorite,  a  little  serpentine,  and  some 
accessory  magnetite.  The  rocks  are  mainly  altered  basalts.  Locally  they  contain  metallic 
copper,  which  is  secondary.  Both  the  greenstone  and  the  adjacent  sedimentaries  are 
fractured  and  the  fissures  become  veins.  The  copper  occurs  in  the  fissures  in  the  greenstone 
or  in  the  sedimentaries  only  near  the  contact  with  the  greenstone,  b 
The  best-known  mines  of  the  Prince  William  Sound  or  Copper  River  district  are  in  the 
Bonanza  Creek  basin,  which  lies  across  the  range  from  the  coast  and  is  reached  by  a  two 
weeks'  journey  with  saddle  and  pack  mules.  The  ore  occurs  in  a  vein  which  crosses  at  90c 
the  contact  between  the  Nikolai  greenstone  and  Carboniferous  limestones  upturned  about  it,! 
The  vein  shows  a  pay  streak  of  4  feet  of  40  to  50  per  cent  ore,  consisting  of  bornite  andi 
glance,  the  vein  itself  being  about  11  feet  wide,  if  the  parallel  (issuring  is  included.  Thf 
fracture  is  distinctly  traceable  into  the  limestone,  where,  however,  it  is  barren  and  filled 
with  limestone  fragments  cemented  by  calcite.  The  vein  was  traced  by  II.  V.  Winchel 
for  over  half  a  mile  into  the  limestone  and,  being  above  timber  line,  it  is  well  exposed 
particularly  where  it  crosses  a  70-foot  cliff.  Although  carefully  examined  and  samplec 
it  does  not  show  even  a  trace  of  copper  throughout  this  extent  in  the  limestone.  The  on 
occurs  only  where  the  vein  is  incased  in  the  greenstone,  and  a  40-foot  shaft  sunk  in  th< 
greenstone  shows  this  ore  to  be  a  surface  enrichment . 
ARIZONA. 
Mining  is  Arizona's  chief  industry,  and  copper  the  principal  product,  the  Territory  beinfi 
second  in  the  United  States  and  fourth  in  the  world  in  the  amount  of  its  copper  production 
Production  of  copper  in  Arizona,  1903  and  190J/.,  by  counties. 
County. 
1903. 
1904. 
County. 
1903. 
1904. 
Pounds. 
63, 264,  488 
257,022 
7,740,843 
52,839,856 
31,931 
15,000 
Pounds. 
90,850,611 
333,754 
14,677,561 
59,  537, 295 
1,480 
3,039,219 
Pinal. . 
Pounds. 
84,000 
4, 162 
23, 999, 628 
9,043 
Pounds. 
186,63 
27.00 
30, 826, 28 
1,20 
Yavapai 
Gila 
Yuma 
Total 
Graham 
Mohave 
148, 245, 973 
199,481,04 
Pima 
a  For  a  description  of  the  Nikolai  greenstone  see  Schrader,  F.  C,  and  Spencer,  A.  C,  Geology  an< 
mineral  resources  of  a  portion  of  the  Copper  River  district,  Alaska:  House  Doc.  No.  546.  56th  Cong. 
2d  seas.,  L901. 
b  For  details  concerning  the  copper  deposits  of  various  localities  see  op.  cit.,  pp.  82,  89. 
