238  CONTRIBUTIONS    TO   ECONOMIC    GEOLOGY,  1904.        I  bull.  260. 
along  beds  in  marmorized  limestone  in  the  vicinity  of  fissures  and 
intrusives.  Smaller  but  more  uniform  veins  of  argentiferous  lead 
ore  traverse  all  rocks,  are  largest  in  limestone,  and  most  numerous 
in  the  vicinity  of  intrusives. 
ORIGIN  OF  THE   ORES. 
It  is  sufficient  for  present  purposes  to  state  that  in  general  it 
appears  that  the  large  bodies  of  copper  ore  were  formed  through 
replacement  of  limestone  directly  or  indirectly  under  the  influence  of 
igneous  magmas;  that  the  argentiferous  lead  ores  were  deposited 
from  aqueous  solutions  in  northeast-southwest  fissures,  mainly  by 
filling,  partly  by  replacement,  and  that  the  disseminated  copper  in 
monzonitic  intrusives  is  secondary. 
RECENT  DEVELOPMENTS. 
The  rapid  and  extensive  development  of  its  mining  industry  in 
recent  years  lias  placed  Bingham  not  only  in  the  lead  of  copper- 
producing  camps  in  Utah,  but  among  the  great  copper  camps  of  the 
country.  In  15)00  the  mines  of  this  district  produced  only  a  little 
over  a  hundred  thousand  tons  of  ore;  in  1904  they  are  reported  to 
have  produced  nearly  a  million  tons  of  copper  ore  alone.  The  recent 
striking  advance  of  Utah  in  the  production  of  the  precious  metals  is  || 
also  due  mainly  to  this  great  increase  in  the  output  of  copper  ore  at 
Bingham;  for  the  ordinary  sulphide  copper  ore  of  this  camp  car- 
ries, as  above  stated,  from  10  cents  to  $1  in  gold  and  from  2  to  5 
ounces  in  silver,  while  some  of  the  black  copper  sulphide  ores  run 
high,  a  sample  from  one  of  the  large  mines  affording  58.0  ounces 
silver  and  $76  in  gold. 
The  period  from  1890  to  1900  was  characterized  by  consolidation  of 
large  tracts  under  individual  companies  and  extensive  underground 
exploration  of  several  great  properties.  This  exploration  resulted  in 
opening  large  bodies  of  the  primary  copper  sulphide  ore  and  consid- 
erable rich  black  sulphide  ore.  Then  followed  an  epoch  of  prepara- 
tion for  extraction,  shipment,  and  reduction  on  a  large  scale.  These 
preparations  have  now  been  completed,  and  in  the  last  two  or  three 
years  one  property  after  another  has  settled  down  to  shipping 
regularly. 
The  leading  producer  of  the  camp,  the  Highland  Boy  mine  of  the 
Utah  Consolidated  Company,  has  conducted  extensive  underground 
development  and  yearly  added  to  its  surface  improvements.  Under- 
ground, the  mammoth  No.  1  ore  shoot  has  been  followed  down  more 
than  100  feet  farther,  from  the  Nos.  7  and  7i  levels  to  No.  8  level,  and 
proved  to  maintain  great  size  and  paying  values.  A  large  new  ore 
body  has  been  discovered  in  the  hanging-wall  limestone,  100  feet 
