TITANIFEROUS    IKON    ORE    OF    IRON    MOUNTAIN,  WYOMING.       209 
mechanical  impurities,  but  biotite,  olivine,  and  feldspar  are  sporadic- 
ally distributed  throughout  its  mass.  Olivine  is  particularly  abun- 
dant in  portions  of  the  small  dike  300  feet  east  of  the  main  mass. 
The  iron  ore  is  cut  by  rather  closely  spaced  joints  and  by  slickensided 
fracture  planes.  In  consequence,  the  outcrop  is  angular,  and  its 
surface  is  littered  with  square  blocks  broken  from  the  ore  in  place. 
Weathering  has  broken  down  the  iron  ore  mechanically  and  pro- 
duced some  chemical  changes.  Many  weathered  surfaces  are  pitted 
by  reason  of  the  complete  removal  of  olivine  and  feldspar  grains  and 
the  partial  removal  of  biotite.  On  joint  surfaces  and  along  other 
fractures,  limonite  and  less  frequently  hematite  has  been  formed 
from  the  magnetite  by  percolating  waters. 
As  seen  under  the  microscope  the  ore  in  some  specimens  consists 
principally  of  titaniferous  iron  with  a  little  spinel.  Other  thin  sec- 
tions show  considerable  olivine,  while  biotite  and  labradorite  are 
present  in  many  specimens  and  in  a  single  section  a  crystal  of  what 
appears  to  be  brown  hornblende  was  noted. 
Analyses  of  the  iron  ore  are  given  in  the  following  table: 
Analyses  of  iron  ore  from  Iron  Mountain,  Wyoming. 
A. 
B. 
c. 
D. 
E. 
F.a 
G. 
Fe203 
45.03 
17.96 
.76 
23.49 
3.98 
2.45 
"'23.32" 
48.97 
24.55 
&  2. 15 
23.18 
49.47 
47.21 
25. 80 
1.21 
22.43 
83.43 
FeO 
Si02                                
1.64 
Ti02 
C20.68 
14.06 
AI2O3             
Cr203 
.16 
.11 
Cr 
Mn02 
1.53 
1.11 
.47 
1.56 
1.44 
Trace. 
1.14 
CaO 
.22 
ZnO 
MgO.    .                   
S 
.04 
d.011 
.03 
1.14 
.03 
P 
.  036 
Total  
99.78 
45.49 
"'50 "83" 
98.88 
53.33 
100. 556 
49.66 
34.29 
58.40 
a  Other  constituents  not  tried  for. 
Insoluble  residue  in  acid. 
cTi  12.42. 
d  P205  .026. 
A.  Average  sample  across  width  of  dike  on  north  side  of  Chugwater  Creek.     Analysis  by  Dr.  Eugene 
C  Sullivan. 
B.  Analysis  by  J.  P.  Carson,  Fourth  Ann.  Rept.  U.  S.  Geol.  Survey  Terr.,  Hayden,  Washington,  D.  C, 
1871,  p.  14." 
C  Analysis  by  Prof.  O.  D.  Allen,  U.  S.  Geol.  Explor.  40th  Par.,  vol.  2,  p.  14. 
D.  Analysis  by  Professor  Richards,  Mass.  Inst.  Technology,  ibid,  p.  15. 
E.  Analysis  by  Prof.  R.  W.  Woodward,  ibid,  p.  14. 
F.  Analysis  by  W.  C.  Knight,  Univ.  Wyoming,  Bull.  Wyoming  Experimental  Station,  No.  14,  p.  177, 
1893. 
G.  Sample  of  Iron  Mountain  ore  smelted  at  Portland  Exposition,  loaned  by  Dr.  D.  T.  Day.     Analysis 
by  Columbia  Engineering  Works,  Portland,  Oreg. 
The  iron  content  is  fairly  high,  averaging  perhaps  50  per  cent,  and  the 
most  notable  feature  of  the  ore  is  its  high  titanium  content.  Of  the 
injurious  constituents  besides  titanium,  the  sulphur  in  three  anal- 
yses is  low  and  in  two  others  high,  while  phosphorus  in  the  three 
analyses  in  which  it  was  determined  is  below  the  Bessemer  limit. 
