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  Geological 
  Society 
  :— 
  

  

  zones, 
  impregnated 
  with 
  sulphides 
  and 
  tellurides, 
  and 
  is 
  most 
  

   abundant 
  in 
  the 
  lodes 
  in 
  the 
  quartz-dolerite. 
  

  

  The 
  rocks 
  for 
  purposes 
  of 
  description 
  are 
  divided 
  into 
  

  

  (A) 
  Sedimentary. 
  — 
  Of 
  these 
  the 
  most 
  distinctive 
  are 
  conglomerates 
  and 
  

   grits, 
  the 
  former 
  containing 
  pebbles 
  of 
  quartzite 
  and 
  of 
  albite-porphyry. 
  

  

  (B) 
  Igneous. 
  — 
  These 
  are 
  often 
  very 
  highly 
  altered 
  by 
  metamorphism 
  

   (inducing 
  schistosity 
  and 
  partial 
  recrystallization) 
  and 
  by 
  metasomatic 
  action. 
  

   They 
  include 
  : 
  

  

  (1) 
  Fine-grained 
  amphibolites 
  ; 
  altered 
  basic 
  igneous 
  rocks 
  — 
  probably 
  lavas 
  

  

  and 
  tuffs. 
  

  

  (2) 
  Fine-grained 
  greenstones 
  ; 
  slightly 
  schistose 
  aggregates, 
  probably 
  

  

  related 
  to 
  the 
  fine-grained 
  amphibolites 
  in 
  origin. 
  

  

  (3) 
  ' 
  Calc-schists 
  ' 
  : 
  whitish-green 
  rocks, 
  which 
  are 
  closely 
  connected 
  with 
  

  

  the 
  greenstones 
  and 
  merge 
  into 
  them. 
  

  

  (4) 
  Peridotites, 
  serpentines, 
  etc., 
  often 
  filled 
  with 
  carbonates, 
  but 
  perhaps 
  

  

  comprising 
  originally 
  enstatite-peridotites 
  as 
  well 
  as 
  other 
  types. 
  

   These 
  rocks 
  form 
  the 
  eastern 
  part 
  of 
  the 
  northern 
  end, 
  and 
  include 
  

   talc-magnesite 
  rocks 
  and 
  fucbsite-magnesite 
  rocks. 
  

  

  (5) 
  Hornblende-rocks 
  or 
  pyroxene-amphibolites, 
  probably 
  occurring 
  as 
  

  

  dykes 
  in 
  the 
  peridotites. 
  

  

  (6) 
  Lustre-mottled 
  amphibolites, 
  containing 
  remains 
  of 
  felspar, 
  and 
  

  

  originally 
  hornblende-dolerites. 
  

  

  (7) 
  Epidiorites, 
  uralitized 
  and 
  saussuritized 
  gabbros 
  or 
  ophitic 
  dolerites, 
  

  

  not 
  very 
  numerous. 
  

  

  (8) 
  Quartz-dolerites 
  and. 
  their 
  derivatives— 
  amphibolites 
  usually 
  coarse- 
  

  

  grained, 
  with 
  a 
  considerable 
  amount 
  of 
  interstitial 
  micropegmatite. 
  

   This 
  is 
  the 
  important 
  rock 
  of 
  ' 
  The 
  Grolden 
  Mile.' 
  It 
  contains 
  very 
  

   coarse 
  pegmatitic 
  veins, 
  and 
  is 
  often 
  to 
  a 
  great 
  extent 
  albitized. 
  It 
  

   presents 
  a 
  great 
  variety 
  of 
  types 
  due 
  to 
  different 
  stages 
  and 
  kinds 
  of 
  

   alteration, 
  and 
  many 
  of 
  these 
  phases 
  are 
  difficult 
  to 
  recognize 
  as 
  

   derived 
  from 
  the 
  quartz-dolerites. 
  

  

  (9) 
  Albite-porphyrites 
  (with 
  hornblende 
  andbiotite) 
  and 
  albite-porphyries. 
  

  

  Secondary 
  minerals 
  are 
  common 
  in 
  the 
  rocks 
  of 
  this 
  group. 
  

  

  (10) 
  Jaspers 
  and 
  graphitic 
  schists. 
  These 
  traverse 
  all 
  the 
  other 
  rocks, 
  

  

  occurring 
  as 
  lodes 
  or 
  bands, 
  and 
  may 
  closely 
  resemble 
  sedimentary 
  

   schists. 
  They 
  sometimes 
  are 
  found 
  running 
  on 
  each 
  side 
  of 
  dykes 
  

   of 
  albite-porphyry. 
  Their 
  mode 
  of 
  origin 
  is 
  not 
  quite 
  certain, 
  but 
  

   they 
  are 
  intimately 
  connected 
  with 
  the 
  igneous 
  rocks. 
  

  

  The 
  relation 
  and 
  the 
  sequence 
  of 
  the 
  rocks 
  of 
  Kalgoorlie 
  are 
  next 
  

   discussed. 
  

  

  The 
  greenstones, 
  fine 
  amphibolites, 
  and 
  calc-schists 
  are 
  regarded 
  

   as 
  the 
  old 
  ' 
  country-rocks,' 
  into 
  which 
  the 
  others 
  are 
  intrusive. 
  

   They 
  are 
  probably 
  a 
  complex 
  of 
  basic 
  lavas, 
  ashes, 
  etc. 
  greatly 
  altered. 
  

  

  The 
  quartz-dolerites, 
  hornblende-dolerites, 
  and 
  pyroxenites 
  are 
  

   very 
  closely 
  related 
  one 
  to 
  the 
  other, 
  and 
  show 
  every 
  grade 
  of 
  

   transition. 
  Probably 
  the 
  peridotite 
  group 
  is 
  merely 
  the 
  early 
  basic 
  

   facies 
  of 
  the 
  quartz-dolerite 
  series, 
  and 
  the 
  porphyries 
  and 
  porphy- 
  

   rites, 
  which 
  were 
  the 
  last 
  rocks 
  intruded, 
  are 
  regarded 
  as 
  being 
  

   derived 
  from 
  the 
  same 
  magma. 
  

  

  The 
  metasomatic 
  changes 
  and 
  origin 
  of 
  the 
  ores 
  are 
  then 
  con- 
  

   sidered. 
  The 
  great 
  characteristic 
  of 
  this 
  goldfield 
  is 
  the 
  prevalence 
  

   of 
  albitization 
  in 
  the 
  auriferous 
  districts. 
  From 
  this, 
  and 
  from 
  a 
  

   general 
  consideration 
  of 
  the 
  rock-facies 
  developed 
  from 
  the 
  magma, 
  

   it 
  seems 
  probable 
  that 
  we 
  have 
  in 
  Kalgoorlie 
  an 
  instance 
  of 
  the 
  

   production 
  of 
  auriferous 
  lodes 
  by 
  rocks 
  belonging 
  to 
  the 
  same 
  class 
  

   as 
  the 
  pillow-lavas 
  and 
  their 
  diabases 
  and 
  soda-granite-porphyries 
  

   (the 
  spilitic 
  suite 
  of 
  igneous 
  rocks). 
  

  

  