j« -i  twell.]  ORE    DEPOSITS    OF    BINGHAM,   UTAH.  237 
cents  to  $1,  and  silver,  averaging  from  2  to  5  ounces,  raise  the  total 
value  of  the  ore  per  ton — $11  to  $15 — well  above  the  commercial 
limit.  Tellurium  has  been  found  associated  with  some  of  the  black 
copper  sulphides,  in  one  instance  in  considerable  amount,  with  pro- 
portionately high  values  of  gold  and  silver.  Zinc  blende  occurs 
in  the  argentiferous  lead  ores,  but  is  not  saved. 
OCCURRENCE  OF  THE  ORES. 
The  productive  area  is  roughly  limited  to  a  region  that  is  char- 
acterized by  intrusives,  and  within  this  area  the  largest  ore  bodies 
occur  in  metamorphosed  limestones  adjacent  to  intrusives  and  fis- 
sures. 
The  copper  ores  occur  in  large  masses  in  metamorphosed  limestone, 
and  also  in  grains  disseminated  through  monzonitic  intrusives.  The 
large  bodies  lie  within  massive  marbleized  limestones  adjacent  to 
intrusives  and  fissures.  Associated  with  this  ore  in  the  coarsely 
crystalline  marbleized  limestone  are  the  following  minerals :  Garnet, 
epidote,  tremolite,  sphalerite,  specularite,  pyrrhotite,  etc.  The  ore 
bodies  are  in  the  form  of  lenticular  beds  lying  roughly  parallel  with 
the  bedding  of  the  country  rock,  and  exhibit  a  massive  banded  struc- 
ture which  is  continuous  with  the  bedding  of  the  inclosing  country 
rock.  These  beds  are  localized  into  elongated  lenticular  shoots  which 
dip  roughly  with  the  bedding  and  pitch  moderately.  These  shoots 
sometimes  assume  great  size,  being  several  hundred  feet  in  length 
along  their  strike,  nearly  200  feet  thick,  and  have  been  followed  down- 
ward continuously  for  several  hundred  feet. 
The  disseminated  auriferous  copper  ore  occurs  throughout  exten- 
sive stocks  of  mozonite,  but  particularly  in  areas  where  it  is  fractured, 
Essured,  and  altered.  Irregular  grains  of  chalcopyrite  and  cuprifer- 
us  pyrite  are  there  found  in  small  veinlets,  intergrown  with  second- 
ary silica,  sericite,  etc.,  chiefly  along  joint  or  fracture  planes,  and  sub- 
ordinately  in  altered  areas  immediately  adjacent  to  such  planes. 
Definite  shoots  have  not  been  proved. 
The  argentiferous  lead  ores  occur  in  veins  filling  fissures  which 
trend  northeast-southwest  and  traverse  all  kinds  of  rocks  known  in 
:he  district.  The  veins  are  widest  in  limestone  and  in  shales  which 
contain  calcareous  and  carbonaceous  matter.  Their  general  structure 
ls  a  rough  banding  parallel  to  the  walls  of  the  fissures,  but  these  bands 
ire  not  sharply  defined,  the  minerals  of  one  band  being  irregularly 
ntergrown  with  those  of  adjoining  bands.  The  relative  distribution 
)f  minerals  in  these  bands  indicates  that  the  general  order  of  deposi- 
tion from  older  to  younger  was  sphalerite  and  tetrahedrite,  pyrite, 
md  galena,  calcite,  quartz,  rhodochrosite,  and  barite. 
In  brief,  sulphide  copper  ore  occurs  chiefly  in  large  lenticular  shoots 
