48 
CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1006,  PART    I. 
The  Meagher  limestone  has  been  extensively  reerystallized  near  the 
granite  intrusive,  and  within  the  entire  ore  zone  it  lias  been  change! 
to  a  marble  of  which  the  grain  varies  greatly.  The  commonest  faciei 
is  a  white  or  light-gray  marble  composed  of  interlocking  grains  of 
calcite  that  are  a  little  smaller  than  grains  of  wheat.  Very  com- 
monly this  grades  into  a  marble  composed  in  the  main  of  interlocking 
crystals  of  calcite  several  inches  in  diameter.  As  the  grain  of  the 
marble  increases  a  considerable4  proportion  of  quartz,  iron  oxides,  and 
iron  and  copper  sulphides  begins  to  appear,  and  in  the  coarsest  vari- 
eties these  minerals  are  as  a  rule  present  in  considerable  quantities 
The  coarsely  crystalline  calcite  occurs  throughout  the  ore  zone,  buti 
is  most  abundant  near  the  granite  contacts. 
Magnetite  is  present  throughout  the  ore  zone  as  large,  irregular 
bodies  that  have  apparently  no  relation  to  the  bedding  planes  of  the 
rocks.  These  bodies  are 
con  lined  to  the  lime- 
stone and  occur  on  all 
levels.  The  magnetite 
bodies  are  rudely  ellip- 
soidal in  outline,  and: 
some  of  them  are  at 
least  100  feet  in  diam- 
eter. One  of  the  largerr 
masses  lies  just  west  of 
the  engine  station  and 
forms  in  part  the  west 
wall  of  the  Cornish  stope.. 
Mica  veins. — Veins 
composed  of  green  mica 
occur  in  many  places  at  the  contact  between  granite4  and  limestone 
or  magnetite  and  limestone,  and  apart  from  the  contact  Iheyhave' 
been  noted  cutting  the  magnetite.  These  veins  are  from  1  to  3; 
inches  wide  and  are  composed  of  crystals  of  green  mica  about  an  inch< 
in  diameter.  They  are  probably  of  pegmatitic  origin  and  are  of  later 
age  than  the  granite  and  the  magnetite,  and  they  may  represent  am 
end  phase  of  the  granitic  intrusion. 
Age  relations. — The  general  relations  of  the  various  rocks,  as  showm 
by  their  contacts,  can  be  briefly  stated.  Shale  and  limestone  are 
the  earliest  rocks,  and  limestone  is  cut  by  granite  and  magnetite  and 
by  veins  of  mica  pegmatite.  Granite  cuts  the  sedimentary  rocks 
only  and  does  not  cut  magnetite.  Magnetite  cuts  limestone  and 
probably  follows  the  granite  in  age.  The  mica  veins  cut  all  the 
other  rocks  and  are  therefore  of  later  age. 
The  recrystallization  of  the  limestone  continued  after  the  granite 
had  solidified  and  had  been  fractured.  Numerous  veins  of  t  he  calcite 
cut  the  granite.     Fig.  4  shows  a  block  of  granite  40  feet  below   the 
Fig.  i.  Granite  block  surrounded  and  cul  by  coarsely  crystal- 
line calcite,  quartz,  pyrite,  and  chalcopyrite,  10  Eeel  belov 
northwesl  end  of  Lake  stope,  Cable  mine,  a,  Calcite,  quartz, 
pyrite,  and  chalcopyrite;  b,  granite. 
