96  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1905. 
introduction  of  labor-saving  devices  at  the  smelters  and  the  improved  mechanical  arrange- 
ments which  have  lowered  the  cost  of  treatment  and  so  led  to  the  mining  of  lower-grade 
ores.  The  cheapened  smelting  costs  have  added  a  long  lease  of  life  to  various  old  proper- 
ties by  enabling  bodies  of  lean  and  previously  unworkable  ores  to  be  reckoned  as  ore ; 
reserves,  while  pyritic  smelting  has  led  to  a  demand  for  pyritic  ores  as  a  fuel  flux  to  be  added 
to  siliceous  ores. 
If  it  be  true,  as  an  eminent  metallurgist  has  epigrammatically  expressed  it,  that  "roast- 
ing is  a  crime  and  concentration  a  felony,"  the  ores  now  concentrated' will  some  day  be 
treated  direct  in  the  blast  furnace,  mixed  with  pyritic  ores,  as  is  now  being  done  at  the 
Pittsmont  smelter  at  Butte. 
It  has  not  been  found  practicable  nor  is  it  especially  desirable  to  separate  the  production 
of  milling  and  of  smelting  ores.  At  Butte,  Mont.,  the  smelting  ores  form  from  0  to  10  per 
cent  of  the  total  amount  mined,  the  proportion  varying  at  the  different  mines.  The  entire 
production  of  the  Utah  and  of  the  Boston  companies  of  Bingham,  Utah,  will  be  milling 
ores,  and  at  everyone  of  the  Arizona  camps  the  proportion  of  milling  ores  used  is  increasing 
each  year. 
The  California  ores,  like  those  of  Ducktown,  Tenn.,  are  basic  sulphide  ores,  an  ideal 
material  for  pyritic  smelting. 
Copper  ores  can  be  grouped  commercially  into  smelting,  concentrating,  and  leaching  ores. 
All  three  kinds  of  ore  often  occur  at  the  same  mine,  but  the  distinction  holds  good  in  a  gen- 
eral way.  Smelting  ores  may  be  either  pyritic,  with  an  excess  of  iron,  or  siliceous,  carrying 
an  excess  of  silica,  though  the  lower-grade  siliceous  ores  are  often  classed  as  concentrating 
ores.  Pyritic  ores  are  found  at  Ducktown,  Tenn.,  and  at  the  mines  of  Shasta  County,  Cal., 
whila  the  smelting  ores  of  Butte  are  well-known  examples  of  siliceous  ores  which  need 
basic  flux  added  to  them  to  insure  successful  treatment. 
In  some  cases,  owing  to  the  physical  character  of  the  ore  and  the  minute  tntergrowth  of 
ore  and  gangue  minerals,  concentration  is  not  feasible.  In  such  cases  direct  smelting  with 
the  production  of  a  low-grade  matte  is  possible,  provided  basic  ores  can  be  obtained.  In 
any  case  the  loss  in  wet  concentration  is  considerable,  varying  from  20  to  35  per  cent. 
In  recent  years  self-fluxing  ores  have  been  found  at  a  few  localities  as,  for  example,  at 
the  Boundary  Creek  region  in  Canada  and  in  the  mines  of  the  Saddle  Mountain  Company 
on  Cola  River,  Arizona  and  in  such  cases  ores  particularly  low  in  copper  may  he  treated 
at  a  profit,  provided  coke  can  he  obtained  at  a  reasonable  figure.  The  utilization  of  low- 
grade  garnetiferous  contact-metamorphic  ores  is  still  a  problem  for  the  metallurgist,  and 
although  various  attempts  have  been  made  to  treat  such  ores,  particularly  in  the  San 
Pedro  mines  in  New  Mexico,  success  has  not  been  attained. 
The  Lake  Superior  ores  may  be  called  ideal  concentrating  ores,  as  the  native  metal  is 
tough  and  does  not  slime,  as  do  the  brittle  sulphides  when  they  are  pulverized  to  liberate 
t  he  metallic  contents. 
From  a  geological  standpoint  the  producing  copper  deposits  of  the  United  States  may  be 
grouped  as  follows : 
(a)  Deposits  in  altered  limestones,  showing  eontaet-metamorphic  characters,  and 
adjacent  to  eruptive  rocks  (Morenci  type)  in  part  characterized  by  deposits  of  group  b. 
(/>)  Deposits  in  fissured  and  altered  igneous  rocks,  in  part  as  veins,  in  part  as  dissemina- 
tion and  impregnation  of  shattered  or  porous  rocks  of  other  kinds  (Morenci). 
(c)  Replacement  veins  in  sheeted  granitic  rock  (Butte  type). 
(d)  Lenticular  masses  of  solid,  nearly  pure,  pyritic  ore  in  shear  zones  in  igneous  rocks 
(Shasta  County  type). 
{e)  Lenticular  deposits  (similar  to  d  in  shape  and  mineral  character)  m  metamorphic 
schists  (Ducktown,  Term.,  Ely,  Vt.). 
(/)  Deposits  of  native  copper  in  altered  amygdaloidal  basic  lava  and  interbedded  con- 
glomerates (Lake  Superior). 
(g)  Normal  fissure  veins  and  impregnations  of  similar  genesis. 
