]9S  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1906,  PART    I. 
the  surface  at  the  Sunrise  mine  the  soft  ore  equals  the  hard  ore  in 
bulk,  while  on  the  lowest  levels  hard  ore  greatly  predominates.  In 
the  Lone  Jack  tunnel,  which  after  entering  the  hill  gains  consider- 
able depth  beneath  the  surface,  the  soft  ore  gradually  decreases  in 
amount  from  the  entry  of  the  tunnel  to  the  breast,  and  at  the  latter 
point  is  practically  absent.  Alteration  of  the  hard  ore  into  the  soft 
by  percolating  waters  is  well  exemplified  by  the  presence  of  soft  ore 
along  channels  of  maximum  water  circulation.  There  is  also  reason 
to  believe  that  soft  ore  originates  from  the  hard  through  shearing, 
since  it  occurs  along  many  fault  planes  in  the  ore  bodies. 
The  mammillary,  grape,  and  stalactitic  forms  of  hematite  are 
clearly  younger  than  the  hard  ore  and  in  most  places  are  younger 
than  the  soft  ore.  The  mammillary  ore  occurs  in  fractures  cutting 
the  hard  and  soft  hematite,  while  the  grape  and  stalactitic  ores  cover 
cavities  in  the  older  varieties.  Some  of  the  mammillary  ore  was 
undoubtedly  formed  after  the  deposition  of  the  detrital  ore  at  the 
base  of  the  Guernsey  (Carboniferous)  formation. 
Limonite  is  a  product  of  the  surface  alteration  of  the  other  iron- 
ore  minerals.  It  occurs  as  pseudomorphs  after  both  hematite  and 
siderite.  Great  rounded  bodies  of  limonite  associated  with  an  iron- 
stained  flint  are  found  in  the  Lone  Jack  and  Sunrise  open  pits  imme- 
diately beneath  the  Carboniferous  rocks.  The  limonite  and  flint 
grade,  on  the  one  hand,  into  schist  and,  on  the  other,  into  hematite 
and  are  evidently  a  product  of  the  surface  alteration  of  the  schist. 
Siderite  occurs  in  cavities  in  the  hematite  and  is  clearly  younger  than 
it.  After  the  deposition  of  the  siderite  came  that  of  quartz  in  small 
crystals.  Quartz  is  in  turn  at  places  coated  with  calcite.  Of  earlier 
origin  than  either  the  quartz  or  the  calcite  are  the  copper  ores. 
These  copper  ores  were,  in  the  main,  deposited  after  the  Guernsey 
formation  had  been  laid  down,  and  in  consequence  the  quartz  and 
calcite  were  evidently  formed  in  Carboniferous  or  post-Carboniferous 
times. 
GRADE  OF  ORE. 
The  ore  of  the  Hartville  iron  range  is  a  high-grade  hematite,  some 
masses  of  which  contain  over  68  per  cent  of  iron,  although  the  ore 
as  a  whole  will  probably  not  average  over  60  per  cent.  The  iron 
content,  where  the  contact  of  the  ore  and  country  rock  is  a  fault, 
usually  holds  its  grade  up  to  the  fault  plane.  The  iron  content  in 
the  Sunrise  mine  increases  perceptibly  with  depth,  indicating,  perhaps, 
a  considerable  redeposition  of  iron  at  depths  through  secondary 
processes.  The  ore  of  the  Hartville  iron  range  examined  by  early 
writers  was  very  low  in  phosphorus,  many  samples  showing  only  a 
trace.  At  the  present  time  much  of  the  ore  shipped  is  of  a  non- 
Bessemer  grade.  The  earlier  analyses  are  believed  by  the  officers  of 
the  Colorado  Fuel  and  Iron  Company  to  have  been  made  from  picked 
