INVESTIGATION    OF    IRON    ORES   AND    NONMETALLIF- 
EROUS  MINERALS. 
By  Edwin  C.  Eckel,  Geologist  in  Charge. 
INTRODUCTION. 
The  work  which  can  be  carried  on  by  the  Survey  in  the  investigation  of  iron  ores  and 
the  nonmetallic  products  differs  very  markedly  from  that  which  is  either  required  or 
practicable  in  the  examination  of  gold,  silver,  copper,  lead,  and  zinc  deposits.  The  differ- 
ences between  the  two  lines  of  work  are  based  on  fundamental  differences  between  the 
products  treated.  In  the  one  case  we  have  usually  to  deal  with  small  bodies  of  ore  of  high 
unit  value  occurring  at  scattered  localities  and  requiring  little  else  than  mining  to  make 
it  a  valuable  product.  In  dealing  with  iron  ores  and  the  nonmetals,  on  the  other  hand, 
we  encounter  minerals  of  low  unit  value,  widely  distributed  over  the  country  and  usually 
occurring  in  large  bodies,  whoso  industrial  value  depends  chiefly  on  nongeologic  factors, 
such  as  composition,  transportation,  facilities,  milling  methods,  etc. 
These  facts  have  influenced  the  work  of  the  Survey  in  dealing  with  iron  and  the  non- 
metals  in  two  ways.  First,  a  proper  report  on  such  products  requires  very  careful  detailed 
stratigraphic  and  areal  work  and  can  hardly  be  undertaken  profitably  unless  a  satisfactory 
topographic  base  is  available.  Second,  the  products  owe  so  much  of  their  possible  value 
to  purely  technologic  and  industrial  conditions  that  a  complete  report  on  them  requires 
consideration  of  many  subjects  not  directly  connected  with  the  geology  of  the  deposits. 
For  this  reason  Survey  reports  on  the  iron  ores,  fuels,  structural  materials,  etc.,  must 
necessarily  contain  matter  relative  to  the  industrial  relations  of  these  products,  which  is 
not  necessary  in  reporting,  for  example,  on  a  deposit  of  high-grade  gold  ore.  The  economic 
work,  furthermore,  must  generally  be  carried  on  in  close  connection  with  detailed  area! 
and  stratigraphic  examinations;  and  for  the  best  results  a  very  accurate  topographic  base 
is  essential. 
A  further  essential  difference  between  the  work  possible  on  the  two  classes  of  products 
lies  in  the  fact  that,  in  general,  the  geologist  can  point  out,  in  advance  of  actual  exploration, 
where  workable  deposits  of  limestone,  clay,  coal,  and  iron  ore  are  likely  to  occur.  Further- 
more, in  many  cases  he  can  make  a  close  estimate  of  the  total  tonnage  available  in  any 
area — an  estimate  which  would  be  impossible  in  dealing  with  gold,  copper  ores,  etc.  It 
is  probable,  for  example,  that  a  careful  geological  examination  of  a  southern  red-hematite 
district  would  enable  the  geologist  to  estimate  the  total  quantity  of  ore  with  a  limiting 
error  of  less  than  10  per  cent,  and  this  is  a  grade  of  accuracy  very  different  from  that  pos- 
sible in  dealing  with  the  irregular  bodies  in  which  the  ores  of  gold,  silver,  copper,  lead, 
and  zinc  usually  occur. 
IRON,  MANGANESE,   AND  ALUMINUM   ORES. 
Iron  ores. — For  many  years  past  the  Lake  Superior  district  has  furnished  two-thirds  of 
the  iron  ore  produced  in  the  United  States.  The  geologic  problems  connected  with  these 
ore  deposits  are  of  great  complexity,  and  the  importance  of  the  subject  naturally  caused 
this  to  be  the  first  iron-ore  district  to  be  taken  up  in  a  detailed  way  by  the  Surve\ .     A 
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