122  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1905. 
Bingham  is  the  most  important  copper  district  of  Utah.  A  monograph  describing  the 
district,  by  J.  M.  Boutwell,  has  recently  been  published  by  this  Survey.  The  conclusions 
reached  by  Boutwell  a  as  to  the  genesis  of  the  Bingham  deposits  are  as  follows: 
In  Mesozoic  or  early  Tertiary  time  intrusive  bodies  of  monzonite  invaded  a  mass  of 
quartzites  and  limestones,  producing  contact  metamorphism,  with  the  intrusion  of  pyritous 
copper  sulphides  as  replacement  of  marmorized  limestone.  After  the  cooling  of  the  upper 
part  of  the  intrusive  monzonite  to  at  least  partial  rigidity  it  and  the  inclosing  sedimentary 
rocks  were  fractured  by  persistent  northwest-southeast  fissures.  Heated  aqueous  solu- 
tions from  the  deeper  unconsolidated  portions  of  the  magma  ascended  through  these 
fissures,  altering  the  fissure  walls  and  introduced  additional  metallic  material,  adding  to 
the  deposits  in  the  limestones,  altering  the  monzonite  and  adding  copper,  gold,  and  silver 
as  auriferous  chalcopyrite,  pyrite,  and  molybdenite  to  the  monzonite.  Two  periods  of 
mineralization  are  clearly  defined  -first,  that  of  contact  metamorphism,  with  intergrowth 
of  ore,  garnet,  etc.;  second,  after  actions,  producing  the  disseminated  ores  and  the  lodes. 
The  site  of  the  ore  bodies  was  determined  by  selective  preference  of  mineral  solutions 
for  deposition  in  certain  beds,  a  preference  quite  as  marked  with  different  limestone  beds 
as  it  is  between  limestone  and  quartzite.b  The  disseminated  ores  c  were  deposited  by 
hydrot hernial  action  subsequent  to  the  date  of  the  igneous  intrusion,  and  the  sulphides 
are  now  undergoing  normal  superficial  alteration.  The  ores  occur  in  the  joints  of  the  rock 
as  a  mossy  coating  of  quartz  and  sulphides,  but  also  in  the  body  of  the  rock,  especially 
associated  with  dark  ores  of  ferromagnesian  minerals,  principally  secondary  (?)  biotite. 
The  productive  ground  was  coextensive  with  monzonite  exposures,  as  may  be  seen  by 
comparison  of  the  geologic  and  economic  maps.  All  the  monzonite  was,  however,  not 
mineralized,  and  it  was  only  where  extensive  fracturing  permitted  the  access  of  the  deep- 
seated  solution  that  mineralization  was  extensive  enough  to  form  workable  ore  deposits! 
In  the  Utah  Company's  claims  an  average  assay  of  6,000  samples  corresponds  closely  to 
t  he  grade  of  ore  now  milled,  showing  1.98  per  cent  of  copper,  0.016  ounce  of  gold,  and  0.15 
ounce  of  silver  per  ton. 
The  Nevvhouse  or  Cactus  mine,  in  Beaver  County,  is  now  one  of  the  regular  producers 
of  the  State.  A  description  of  this  property,  by  S.  F.  Emmons,  is  given  in  Bulletin  No.  260, 
page  242.  The  mine  is  A\  miles  northwest  of  Frisco,  in  the  San  Francisco  Mountains, 
and  is  reached  by  a  branch  line  of  the  San  Pedro,  Los  Angeles  and  Salt  Lake  Railroad. 
The  ore  consists  of  coarsely  crystalline  pyrite,  with  a  little  chalcopyrite  and  rarely  sooty 
sulphide.  The  deposit  is  a  shear  or  crush  zone  in  monzonite,  15  to  30  feet  wide,  the  ore 
cementing  fragments  and  filling  cracks  and  crevices  in  the  shattered  rock.  The  ore  zone 
is  vertical  and  is  developed  to  a  depth  of  600  feet  by  a  shaft  and  a  crosscut  tunnel  over  aj 
mile  long.  While  the  mine  yields  some  smelting  ore,  the  main  product  is  concentrating 
ore  treated  in  an  800-ton  mill  and  concentrated  6  into  1.  The  shear  zone  is  a  strong  fault 
zone,  traceable  for  a  mile  or  more  across  the  mountain  slopes  running  toward  the  Horn 
'Silver  fault. 
The  Park  City  district,  though  better  known  as  a  producer  of  argentiferous  lead  ores, 
yields  an  important  and  rapidly  increasing  output  of  copper  ore.  Copper  is  commonly 
present  as  tetrahedrite  (gray  copper),  or  f ah  lore,  in  the  high-grade  silver  ores,  the  average 
of  such  ores  (allying  about  2.5  per  cent  of  copper,  40  per  cent  of  lead,  and  60  ounces  of 
silver  per  ton,  while  the  crude  ore  sent  to  the  concentrators  carries  1 .5  per  cent  of  copper. 
The  ore  occurs  in  fissure  lodes  and  as  masses  in  limestone,  the  bulk  of  the  ore  now  extracted 
coming  from  the  bedded  ore  bodies  in  limestone.  The  northeast-southwest  fissures,  with 
steep  northwesterly  dip,  are  wide  and  persistent  veins,  2  to  35  feet  wide,  carrying  narrow 
pay  streaks  of  high-grade  ore. 
The  "bedded"  deposits  are  replacements  of  and  occur  in  certain  layers  in  Upper  Carbon- 
iferous and  Permian  limestones,  the  ore-bearing  layers  being  inclosed  in  quartzitc.  Both 
lodes  and  replacement  bodies  occur  intimately  associated  with  porphyry  intrusions. 
a  Prof.  Paper  U.  S.  Geol.  Survey  No.  38,  1905,  p.  229.  b  P.  128.     Sec  fig.  2.  c  p.  172. 
