MMONS.] 
INVESTIGATION    OF    METALLIFEROUS    ORES. 
23 
In  1902  Mr.  Waldemar  Lindgren,  of  the  corps  of  economic  geolo- 
gists of  the  Survey,  published  a  paper  on  "  The  geological  features 
)f  gold  production  of  North  America.*''1  This  was  a  far  more  impor- 
ant  contribution  to  the  subject,  from  the  geological  standpoint,  than 
he  previous  one,  because  in  the  decade  just  elapsed  the  economic 
vork  of  the  Survey  had  increased  far  more  rapidly  than  in  the  previ- 
>us  decade,  and  already  it  included  within  its  scope  most  of  the  great 
;'old-producing  districts  of  the  country.  Mr.  Lindgren  was  therefore 
uabled  to  make  a  somewhat  detailed  classification  of  the  sources  of 
old,  based  on  ^geological  age,  the  inclosing  rock,  and  the  character  of 
eposits.  The  information  on  which  this  classification  Avas  based, 
owever,  was  in  no  measure  furnished  by  the  division  of  mining  and 
iineral  resources  of  the  Survey,  because,  although  Congress  had,  in 
900,  permitted  the  collection  by  the  Survey  of  the  statistics  of  gold 
nd  silver,  and  added  $20,000  to  the  annual  appropriation  for  this  pur- 
pose, up  to  1903  the  figures  given  in  the  volume  on  Mineral  Resources 
rere  still  merely  a  condensed  copy  of  those  published  by  the  Director 
f  the  Mint. 
In  Mineral  Resources  for  1903  segregated  statistics  of  the  produc- 
on  of  gold  and  silver  are  given  for  some  of  the  precious-metal  pro- 
ucing  States,  but  they  contain  no  geological  information  whatever, 
ud  are  too  imperfect  to  furnish  much  aid  in  the  segregation  of  that 
roduct  on  geological  grounds.  In  view  of  the  importance  of  this  sub- 
let, however,  it  has  been  judged  best,  even  in  the  absence  of  as  com- 
lete  information  as  could  be  desired,  to  prepare  such  reviews  of  the 
roduction  of  the  respective  metals  during  the  past  year  as  shall 
arnish  a  more  philosophical  discussion  of  the  industry  than  can  be 
erived  from  the  contemplation  of  a  column  of  figures. 
The  discussion  of  the  year's  production  of  gold  and  silver  has  been 
ltrusted  to  Mr.  Lindgren,  who  has  classified  these  products  according 
>  geological  age  and  according  to  the  character  of  the  ores  from 
hich  they  have  been  derived.  The  latter  classification,  which  it  is 
elieved  has  never  before  been  made,  divides  the  ores  into  (1)  placer, 
v  detrital  deposits,  and  (2)  ores  from  rock-in-place.     The  latter  class 
further  subdivided,  according  to  mineralogical  composition,  into 
iree  classes,  based  primarily  upon  the  different  processes  required 
pr  the  extraction  of  the  precious  metals  from  their  matrix.     These 
e  siliceous  ores,  copper  ores,  and  lead  ores.    The  percentage  of  the 
tal  production  derived  from  the  four  classes  thus  established  is  as 
dIIows  : 
old 
lver 
Placers. 
Siliceous 
ores. 
Copper 
ores. 
Lead 
ores. 
15.2 
0.1 
74.3 
22.2 
5.0 
34.7 
5.4 
42.9 
a  Trans.  Am.  Inst.  Min.  Eng.,  vol.  33,  p.  790. 
