124  ONTKIBUTIONS    TO   ECONOMIC    GEOLOGY,  1906,  PAKT    I. 
From  all  the  analyses  thus  far  published  of  the  nickel  silicates  oi 
New  Caledonia  and  of  Riddles  it   appears  that  the  average  content 
of  nickel  in  the  New  Caledonia   minerals  is  higher  than  that  in  the 
genthite  of  the  Kiddles  deposits.     Perhaps  sufficient  amounts  of  the 
Riddles  ores  have  not  been  smelted  to  permit  safe  estimates  to  be 
made  of  their  average  nickel  content;  but  the  treatment. by  different! 
methods  of  about  20  tons  of  the  ore,  which  constituted  the  shipments' 
made  by  the  Oregon   Nickel  Mines  Company,  gave  results  varyi 
from  5  to  8  per  cent  in  nickel.     Two  specimens,  taken  by  the  writ 
as  average  samples  of  the  ore,  were  analyzed  in  the  Survey  laborato 
by  George  Steiger.     The  results  were  5.35  and  4.94  per  cent  of  nicke 
Each  of  the  two  analyses  also  showed  0.11  per  cent  of  cobalt.     T 
New    Caledonia    ores    now    being   shipped    to    the   smelters   contaj 
between  6  and  7  per  cent  of  nickel. 
The  gangue  consists  of  quartz,  iron  oxides,  and  serpentine.  T 
quartz,  the  mosl  abundant  of  these 'minerals,  is  in  general  of  a  whitiJ 
color,  but  the  surface  of  much  of  it  has  a  yellowish  to  brownish-rJ 
tint,  due  to  a  coating  of  iron  oxide.  The  quartz  appears  to  be  chiefly 
chalcedonic,  but  in  places  it  has  a  weak  greenish  color,  resembling 
chrysoprase,  a  mineral  that  has  been  shown  to  be  present  in  these 
deposits."  The  iron  oxides  are  of  a  distinctly  yellow  to  reddish- 
brown  color,  and  the  evidence  is  clear  that  these  oxides  represent  one 
of  the  final  products  of  decomposition  of  the  serpentine,  which  is 
itself  produced  by  the  alteration  of  the  peridotite. 
THE   DEPOSITS. 
The  deposits,  which  lie  Hat,  occur  as  brecciated  and  conglomerate 
irregular  masses  on  the  surface  of  the  peridotite  and  consist  of  silica. 
nickel  silicate,  iron  oxide,  and  serpentine,  with  a  very  subordinate 
anioimi  of  chromite.  The  most  st  riking  feature  of  the  ore  is  t  he  grea 
color  of  the  nickel  silicate.  Where  the  ores  have  been  exposed  t< 
weathering  action  for  a  considerable  time,  these  nickel  silicates  hal 
been  dissolved  and  carried  away  and  a  honeycombed  quartz  skeletoi 
remains.  Tn  some  of  the  cavities  of  this  skeleton  are  found  pulveru- 
lent iron  oxides,  which  can  readily  be  shaken  out,  only  the  siliceous 
cement  of  the  former  brecciated  or  conglomeratic  mass  being  left. 
Such  materials  lie  on  the  surface  of  a  considerable  part  of  the  nickel 
area  and  have  served  as  a  guide  to  prospecting.  A  portion  of  this 
material  has  been  transported  mechanically  to  its  present  location. 
In  some  places  the  brecciated  ore  consists  of  irregular-shaped  frag- 
ments of  serpentine  breaking  down  to  hydrated  iron  oxides.  The 
fragments  are  cemented  by  silica  and  nickel  silicate,  which  were  prob- 
"  Kunz.  <;.  !■'..  Gems  and  Precious  Stones,  p.  122. 
