﻿W. 
  H. 
  Weed 
  — 
  Gold-hearing 
  Hot 
  Spring 
  Deposit. 
  167 
  

  

  mine, 
  and 
  a 
  microscopical 
  and 
  chemical 
  examination 
  of 
  the 
  

   sinter, 
  both 
  confirm 
  this 
  hypothesis. 
  It 
  is 
  therefore 
  necessary 
  

   to 
  add 
  this 
  form 
  of 
  deposit 
  to 
  those 
  already 
  recognized 
  in 
  the 
  

   classification 
  of 
  ore 
  bodies. 
  

  

  As 
  but 
  little 
  is 
  generally 
  known 
  of 
  the 
  Mount 
  Morgan 
  mine 
  

   a 
  few 
  notes 
  condensed 
  from 
  Dr. 
  Jack's 
  report* 
  are 
  inserted 
  : 
  

  

  This 
  remarkable 
  ore 
  deposit 
  forms 
  the 
  upper 
  portion 
  of 
  the 
  

   hill 
  known 
  as 
  Mount 
  Morgan, 
  whose 
  summit 
  is 
  about 
  500 
  feet 
  

   above 
  the 
  surrounding 
  lowland, 
  and 
  is 
  some 
  1200 
  feet 
  above 
  sea 
  

   level. 
  The 
  rocks 
  in 
  the 
  immediate 
  vicinity 
  of 
  the 
  mine 
  are 
  

   bluish-gray 
  quartzites 
  forming 
  part 
  of 
  a 
  much 
  disturbed 
  series 
  

   of 
  beds 
  of 
  Carbonifero-Permian 
  age. 
  These 
  beds 
  are 
  inter- 
  

   sected 
  by 
  numerous 
  dikes 
  of 
  igneous 
  rocks, 
  mainly 
  rhyolite, 
  

   and 
  intrusive 
  bodies 
  of 
  diorite 
  and 
  other 
  eruptives. 
  Reefs 
  of 
  

   gold-bearing 
  quartz 
  are 
  common 
  in 
  this 
  area 
  of 
  metamorphic 
  

   rocks. 
  

  

  The 
  workings 
  of 
  the 
  mine 
  show 
  that 
  the 
  siliceous 
  sinter 
  

   forms 
  a 
  surface 
  covering 
  upon 
  the 
  slopes 
  of 
  the 
  " 
  mount." 
  In 
  

   such 
  situations 
  it 
  has 
  been 
  found 
  to 
  be 
  usually 
  without 
  gold, 
  

   but 
  the 
  cup-shaped 
  mass 
  of 
  sinter 
  forming 
  the 
  central 
  core 
  and 
  

   summit 
  of 
  the 
  hill 
  is 
  impregnated 
  with 
  brown 
  ironstone 
  carry- 
  

   ing 
  as 
  high 
  as 
  169 
  86 
  oz. 
  of 
  gold 
  to 
  the 
  ton. 
  

  

  The 
  tunnels 
  driven 
  through 
  the 
  ore 
  body 
  at 
  various 
  levels 
  

   show 
  that 
  the 
  sinter 
  though 
  generally 
  an 
  unbroken 
  mass 
  is 
  

   sometimes 
  formed 
  of 
  large 
  angular 
  blocks, 
  as 
  if 
  the 
  deposit 
  

   had 
  been 
  shattered. 
  A 
  dike 
  of 
  igneous 
  rock 
  now 
  thoroughly 
  

   decomposed 
  and 
  kaolinized, 
  cuts 
  the 
  quartzites 
  and 
  extends 
  

   upward 
  through 
  the 
  sinter. 
  There 
  is 
  no 
  hydrothermal 
  activity 
  

   whatever, 
  in 
  the 
  vicinity 
  of 
  the 
  mine, 
  at 
  the 
  present 
  day, 
  

   though 
  hot 
  springs 
  occur 
  in 
  other 
  parts 
  of 
  Queensland. 
  

  

  The 
  sinter 
  which 
  Dr. 
  Jack 
  has 
  sent 
  as 
  representative 
  of 
  that 
  

   forming 
  the 
  main 
  body 
  of 
  the 
  ore 
  deposit 
  he 
  describes 
  as 
  " 
  a 
  

   very 
  light, 
  frothy, 
  spongy 
  or 
  cellular 
  rock, 
  so 
  light 
  from 
  the 
  

   entanglement 
  of 
  air 
  in 
  its 
  pores 
  as 
  to 
  float 
  in 
  water 
  like 
  

   pumice." 
  In 
  thin 
  section 
  this 
  material 
  is 
  dark 
  between 
  crossed 
  

   nicol 
  prisms 
  ; 
  its 
  structure 
  and 
  general 
  appearance 
  is 
  that 
  of 
  

   a 
  hot 
  spring 
  deposit, 
  though 
  no 
  sinters 
  quitejike 
  it 
  have 
  as 
  yet 
  

   been 
  found 
  by 
  the 
  writer. 
  It 
  can 
  be 
  positively 
  stated 
  that 
  this 
  

   material 
  is 
  not 
  a 
  pumice, 
  but 
  is 
  a 
  hot 
  spring 
  deposit. 
  The 
  anal- 
  

   ysis 
  JSTo. 
  1 
  of 
  the 
  following 
  table 
  was 
  made 
  in 
  the 
  Laboratory 
  

   of 
  the 
  TJ. 
  S. 
  Geological 
  Survey 
  by 
  Mr. 
  E. 
  A. 
  Schneider, 
  shows 
  

   this 
  sinter 
  to 
  be 
  a 
  remarkably 
  pure 
  form 
  of 
  opal. 
  

  

  Analysis 
  No. 
  II, 
  of 
  a 
  sinter 
  from 
  the 
  Yellowstone 
  Park, 
  was 
  

   made 
  by 
  J. 
  E. 
  Whitfield 
  in 
  the 
  laboratory 
  of 
  the 
  U. 
  S. 
  Geological 
  

  

  * 
  Mount 
  Morgan 
  Gold 
  Deposits. 
  Second 
  Report 
  by 
  Robert 
  L. 
  Jack, 
  Govern- 
  

   ment 
  Geologist, 
  Queensland, 
  Australia, 
  1889. 
  

  

  