﻿52 
  ME. 
  T. 
  L. 
  WALKEK 
  Otf 
  THE 
  [Feb. 
  1 
  897, 
  

  

  quantity. 
  The 
  pyrrhotite 
  often 
  contains 
  crystals 
  of 
  magnetite 
  and 
  

   biotite, 
  which 
  are 
  consequently 
  older 
  than 
  the 
  pyrrhotite 
  con- 
  

   taining 
  them. 
  By 
  examining 
  some 
  specimens 
  one 
  might 
  conclude 
  

   that 
  the 
  ores 
  had 
  crystallized 
  before 
  the 
  silicates, 
  while 
  an 
  exami- 
  

   nation 
  of 
  other 
  specimens 
  would 
  lead 
  to 
  the 
  opposite 
  conclusion. 
  

   The 
  ores 
  are, 
  in 
  fact, 
  to 
  be 
  regarded 
  as 
  constituents 
  of 
  the 
  rock 
  T 
  

   which 
  at 
  a 
  few 
  places 
  along 
  the 
  border 
  of 
  the 
  eruptive 
  have 
  been 
  

   concentrated 
  by 
  differentiation, 
  so 
  that 
  the 
  ore-deposits 
  are 
  norite 
  or 
  

   greenstone, 
  which 
  is 
  rich 
  enough 
  in 
  chalcopyrite 
  and 
  nickeliferous 
  

   pyrrhotite 
  to 
  be 
  of 
  commercial 
  value. 
  The 
  quantity 
  of 
  the 
  ores 
  in 
  

   the 
  rock 
  increases 
  gradually 
  towards 
  the 
  border, 
  till 
  it 
  often 
  consti- 
  

   tutes 
  three-fourths 
  of 
  the 
  rock. 
  Sometimes 
  the 
  ores 
  and 
  silicates 
  

   are 
  finely 
  intermingled, 
  while 
  at 
  other 
  times 
  comparatively 
  pure 
  

   masses 
  of 
  pyrrhotite 
  and 
  chalcopyrite 
  are 
  included 
  in 
  the 
  silicate- 
  

   groundmass. 
  These 
  masses 
  of 
  pure 
  ore 
  vary 
  from 
  a 
  few 
  lines 
  

   to 
  a 
  foot 
  in 
  longest 
  diameter. 
  In 
  other 
  cases 
  the 
  ores 
  appear 
  to 
  

   form 
  the 
  groundmass 
  in 
  which 
  the 
  silicates 
  are 
  included. 
  Near 
  the 
  

   contact 
  the 
  grain 
  of 
  the 
  ores 
  is 
  fine, 
  and 
  the 
  proportion 
  of 
  chalco- 
  

   pyrite 
  and 
  pyrrhotite 
  is 
  often 
  so 
  large 
  as 
  to 
  form 
  deposits 
  of 
  economic 
  

   importance, 
  while 
  farther 
  from 
  the 
  contact 
  the 
  ore 
  becomes 
  coarser- 
  

   grained 
  and 
  the 
  quantity 
  of 
  silicates 
  increases 
  till 
  it 
  can 
  no 
  longer 
  

   be 
  worked 
  at 
  a 
  profit. 
  The 
  nickel 
  percentage 
  of 
  the 
  pyrrhotite 
  

   varies 
  greatly, 
  but 
  may 
  be 
  safely 
  stated 
  as 
  ranging 
  from 
  3 
  to 
  7 
  for 
  

   the 
  deposits 
  which 
  have 
  been 
  worked 
  on 
  a 
  large 
  scale. 
  There 
  

   are, 
  however, 
  many 
  deposits 
  which 
  contain 
  less 
  than 
  3 
  per 
  cent, 
  of 
  

   nickel, 
  but 
  these 
  are 
  at 
  present 
  of 
  no 
  special 
  value. 
  

  

  Yogt, 
  in 
  describing 
  similar 
  nickel-deposits 
  in 
  Norway, 
  regards 
  the 
  

   pyrrhotite 
  and 
  chalcopyrite 
  as 
  rock-forming 
  minerals, 
  and 
  believes 
  

   that 
  they 
  took 
  their 
  present 
  form 
  at 
  the 
  time 
  of 
  the 
  solidification 
  

   of 
  the 
  rock 
  containing 
  them. 
  He 
  refers 
  to 
  the 
  rock 
  rich 
  in 
  

   pyrrhotite 
  as 
  ' 
  pyrrhotite-norite,' 
  and 
  observes 
  that 
  the 
  ores 
  generally 
  

   diminish 
  with 
  the 
  distance 
  from 
  the 
  contact. 
  He 
  regards 
  the 
  ores 
  

   as 
  the 
  most 
  basic 
  rock-constituents, 
  and 
  considers 
  that 
  the 
  pyrrhotite- 
  

   norite 
  is 
  related 
  to 
  the 
  greenstone 
  in 
  the 
  same 
  way 
  as 
  basic 
  borders 
  

   on 
  granite-stocks 
  are 
  to 
  the 
  granite. 
  Both, 
  he 
  maintains, 
  have 
  been 
  

   formed 
  by 
  differentiation 
  of 
  once 
  homogeneous 
  magmas. 
  My 
  obser- 
  

   vations 
  lead 
  me 
  to 
  think 
  that 
  the 
  same 
  relations 
  obtain 
  in 
  the 
  case 
  

   of 
  the 
  Sudbury 
  chalcopyrite-pyrrhotite 
  deposits. 
  

  

  Occasionally 
  small 
  masses 
  of 
  titaniferous 
  magnetite 
  are 
  associated 
  

   with 
  the 
  pyrrhotite. 
  An 
  analysis 
  of 
  such 
  a 
  mass 
  from 
  Murray 
  

   Mines 
  showed 
  the 
  presence 
  of 
  18*34 
  per 
  cent, 
  of 
  titanic 
  acid. 
  At 
  

   other 
  points 
  along 
  the 
  border 
  of 
  the 
  Whitson 
  Lake 
  eruptive 
  similar 
  

   masses 
  of 
  titaniferous 
  magnetite 
  occur. 
  Portions 
  of 
  norite 
  which 
  

   are 
  rich 
  in 
  titaniferous 
  magnetite 
  might 
  well 
  be 
  so 
  named 
  as 
  to' 
  

   indicate 
  the 
  presence 
  of 
  magnetite 
  as 
  an 
  essential 
  mineral. 
  Similar 
  

   peripheral 
  separations 
  of 
  titaniferous 
  magnetite 
  are 
  frequent 
  in 
  

   connexion 
  with 
  the 
  gabbros 
  of 
  Minnesota, 
  as 
  Bayly 
  has 
  recently 
  

   pointed 
  out. 
  

  

  About 
  100 
  yards 
  south 
  of 
  the 
  office 
  at 
  Murray 
  Mines 
  a 
  

   porphyritic 
  facies 
  of 
  the 
  greenstone 
  occurs. 
  The 
  groundmass 
  is- 
  

  

  