56  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1905. 
(2)  Reopened  pegmatitic  dikes:  The  quartz,  itself  of  pegmatitic  origin,  has  been  crushed, 
and  the  values  are  probably  due  to  the  same  period  of  mineralization  as  that  which  formed 
the  deposits  next  described  (3).  The  deposits  at  Lime  Point  and  some  of  those  at  Trapp- 
mans  Camp  are  of  this  origin. 
(3)  Massive  quartz  veins  in  fissures,  joints,  and  irregular  zones  of  brecciation:  The 
quartz  is  not  crustified.  The  chief  sulphide  is  pyrite.  although  galena,  chalcopyrite,  and 
sphalerite  sometimes  occur.  The  deposits  are  usually  gold  bearing,  although  with  the 
introduction  of  galena  silver  values  may  predominate.  These  ores  were  deposited  by  water, 
which  may  have  been  remotely  connected  with  the  granitic  intrusion.  Such  appear  to 
be  the  deposits  at  Old  (amp  and  some  of  those  at  Trappmans  Camp,  Oak  Spring,  and 
Southern  Klondike1. 
(4)  Impregnation  of  pyrite  along  joints:  This  is  an  unimportant  form  of  deposit  and  is 
seen  only  at  Trappmans  Cam  p. 
Deposits  in  diorite. — (1)  Quartz  veins:  This  is  the  type  of  deposit  at  Gold  Belt,  and  is 
similar  in  form  and  mineral  paragenesis  to  the  deposits  described  in  the  next  paragraph. 
Deposits  in  Paleozoic  sedimentary  rocks,  predominantly  limestone.  (1)  Quartz  veins  and 
irregular  masses  occupying  faults,  joints,  bedding  planes,  and  brecciated  zones,  usually  in 
the  neighborhood  of  granitic  intrusions.  Rarely  a  little  calclte  is  associated  with  the 
quartz.  The  original  sulplrdes  deposited  in  the  quartz  include  chalcopyrite,  galena,  pyrite, 
and  sphalerite.  In  the  veins  in  limestone  the  predominant  sulphides  are  chalcopyrite 
and  galena,  and  the  values  are  largely  silver.  In  quartzite  and  schist,  in  lime-silicate  rocks, 
composed  of  quartz,  garnet,  and  epidote,  and  in  limestone  zones  in  which  s  lie 'fication 
extended  beyond  the  quartz  vein,  pyrite  is  the  predominant  sulphide,  with  gold  values  alone 
or  in  excess  of  silver.  It  is  probable  that  the  relative  abundance  and  variety  of  sulphides 
was  determined  by  the  wall  rock,  the  more  siliceous  rock  tending  to  preclp'tate  from  the 
waters  auriferous  pyrite,  the  calcareous  rock  precipitating  argentiferous  galena  and  chal- 
copyrite. The  secondary  ores  of  this  subdivision  include  malachite,  azurlte,  chrysocolla, 
native  copper,  brochantite,  cerussite,  native  gold,  and  horn  s'lver,  while  chlorobrom  <ies 
of  silver  arc  reported.  Chalcocite  is  probably  of  secondary  origin.  Two  or  more  of  these 
ores  are" associated  with  hematite  and  limonite  or  with  a  heavily  stained  jaspery  quartz 
with  conchoidal  fracture.  Gypsum  and  at  one  place  sulphur  are  gangues  of  less  wide  dis- 
tribution. Cavities  in  the  secondary  ores  arc  often  frosted  by  later  quartz  crystals.  The 
Tokop  veins  belong  to  this  subdivision,  and  their  similarity  to  veins  in  the  granite  of  Old 
Camp  and  their  reported  passing  into  the  granite  beneath  indicate  that  the  quartz  veins 
in  the  granite  and  limestone  are  contemporaneous  in  age  and  of  like  origin.  The  Llda, 
Bare  Mountain,  and  Oriental  Wash  deposits  and  some  of  those  of  Chloride  Cliff,  Monte- 
zuma, Oak  Springs,  and  Southern  Klondike  arc  of  this  type. 
(2)  Veins  following  contacts.  These  occur  in  limestone  along  diorite-porphyry  d'kes 
and  sheets  and  at  Chloride  Cliff  along  a  mass  of  hornblende-gneiss.  The  dio:  ite-po:  phyry 
is,  without  much  doubt,  pre-Tertiary,  and  the  mineral  assocation  so  s  in  lar  to  that  in  the 
deposits  just  described  (1)  that  there  can  be  but  small  doubt  of  the  contemporaneous  or- 
gin  of  the  two  from  the  same  waters.  The  General  Thomas  and  some  of.  the  Montezuma 
prospects  are  of  this  type. 
(3)  Replacement  deposits:  In  the  Cuprite  mining  district  and  to  a  less  extent  Id  the 
General  Thomas  mine  the  sulphides  appear  to  replace  the  limestone  in  irregular  masses. 
The  Cuprite  deposits  are  at  a  considerable  distance  from  the  granite  masses,  and  in  these 
deposits  quartz  is  rare.  The  same  secondary  minerals  are  found  here  as  in  other  depos'ts 
in  the  sedimentary  rocks. 
TERTIARY    DEPOSITS. 
Gold  deposits  in  silicified  monzonites. — Gold  occurs  at  Kawich  and  Gold  ('rater  in  silicified 
and  kaollnlzed  monzonitic  rocks.  When  the  monzonitic  rock  was  silicified  pyrite  was 
deposited  in  open  fissures  in  it,  and  probably  partially  replaced  the  monzonite.  Dis- 
seminated pyrite  occurs  beyond  the  silicified  zone.     During  the  surface  alteration  of  the 
