388  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY-,  1005. 
state  without  apparent  chemical  change,  is  unknown.  One  of  the  veins  shows  an  outcro  >\ 
40  feet  broad  and  traceable  through  a  distance  of  several  hundred  feet.  Others  show  less*  r'l 
outcrops,  but  the  amount  exposed  is  large.  However,  in  such  outcrops  but  two  dimension  J 
are  known,  and  an  estimate  of  the  amount  of  magiiesite  available  is  merest  guesswork. 
Although  these  deposits  have  been  known  for  a  long  time,  they  have  not  been  worked  unt 
the  past  year  owing  to  their  distance  from  a  railroad.     There  are  a  number  of  veins  in 
group  around  a  small  valley,  so  arranged  as  to  be  excellently  located  for  working  by  adits  an .' 
an  aerial  tram.     The  first   magnesite  was  shipped  from  the  mine  in  November.     The  vei 
that  is  being  mined  strikes  about  N.  30°  W.,  dipping  steeply  south  westward.     It  is  pierce 
by  several  adits  on  different  levels,  and  a  crosscut  at  one  place  entered  the  vein  for  35  fee 
without  going  through  it.     A  drill  hole  S  feet  long  at  the  end  of  the  crosscut  was  said  not  t ; 
have  reached  the  other  side.     The  vein  had  been  developed  through  a  length  of  betweei ; 
250  and  300  feet.     The  magnesite  is  pure  and  white,  the  crosscut  looking  as  if  freshl; 
whitewashed.     As  is  to  be  expected  in  a  serpentine  area,  faults  have  occurred,  cutting  th 
•  vein  in  a  number  of  places,  both  hanging  and  foot  walls  being  fault  planes. 
Mining  is  carried  on  by  means  of  an  open  cut  in  which  the  magnesite  is  quarried  andallowe< 
to  fall  through  an  upraise  to  an  adit  below,  whence  it  is  moved  in  cars  to  the  aerial  tram 
The  tram  drops  600  feet  in  the  2, .500  feet  to  the  bunkers.  The  skips  are  placed  500  fee 
apart  and  each  carries  1,000  pounds.of  magnesite. 
Close  to  the  magnesite  veins  are  small  impregnation  veins  of  chromite,  about  250  yard)  I 
southeast  of  the  present  workings.  The  chromite  occurs  in  grains  from  the  size  of  a  pet" 
downward  and  can  be  clearly  seen  to  spread  from  joints  in  the  serpentine.  The  chromite  if  i 
accompanied  by  a  pale  lilac-colored  chlorite,  probably  either  kotschubeite  or  kammereria 
A  small  amount  of  work  has  been  done  on  the  veins,  but  the  prospects  do  not  seem  to  hav< 
been  encouraging. 
A  little  cinnabar  is  said  to  have  been  found  in  the  neighborhood,  and  two  mercua 
mines  are  being  developed  within  a  radius  of  I  or  5  miles. 
CHILES    VALLEY. 
Chiles  Valley  is  situated  in  Napa  County  and  its  nearest  shipping  point,  Rutherford,  is  84- 
miles  by  rail  north  of  San  Francisco.  Magnesite  was  mined  in  the  valley  at  a  point  about 
10  miles  from  the  railroad  by  Stanley  &  Bartlett  for  twelve  years,  bul  the  mines  have,  not 
been  operated  for  the  last  five  years,  being  too  far  from  the  railroad  to  compete  with  points 
having  better  shipping  facilities.  During  the  time  that  the  mines  were  worked  many  thai 
sands  of  tons  of  magnesite  were  mined  and  burned  at  this  place.  As  pure  magnesite  loss 
more  than  half  its  weight  by  being  burned,  a  large  saving  could  be  made  in  haulage  by  getting 
ridofth  \ carbon  dioxide,  if  the  material  was  to  be  used  as  magnesia.  Manzanita,  a  hard- 
wooded  shrub  making  a  hot  fire,  was  largely  used  for  fuel. 
The  country  rock  is  here  also  the  (/oast  Range  serpentine,  somewhat  more  inclined  to.a 
blue-bla<  k  color  than  at  the  Livermore  deposits.  The  deposits  are  on  the  west  side  of  the 
valley  in  a  small  serpentine  hill  skilled  by  a  public  road,  and  consist  of  a  number  of  veins 
which  vary  in  thickness  from  1  foot  to  6  feet  and  are  said  to  have  been  as  much  as  12  feet  wide. 
Where  seen,  however,  the  larger  veins  were  much  mixed  with  serpentine  and  other  impuri- 
ties. Much  faulting  occurs  with  the  veins,  and  both  the  hanging  and  foot  walls  are  generally 
fault  planes.  The  serpentine  is  much  broken  in  the  neighborhood  of  the  veins,  the  inter- 
stices being  filled  by  smaller  veins  of  magnesite. 
On  the  foot  wall  of  several  of  the  veins  extensive  silicification  has  taken  place,  the  serpen- 
tine being  hardened  through  2  or  3  feet.  The  veins  are  often  brecciated  and  cemented  with 
less  pure  material  of  yellowish  color,  while  the  original  magnesite  is  a  clear  white.  Fre- 
quently in  the  brecciated  portions  each  fragment  is  covered  by  magnesite  in  radial  crystals, 
forming  a  coating  up  to  half  an  inch  thick  and  varying  in  color  from  crystalline  clearness  to 
delicate  green  and  yellowish  green.  Cracks  in  the  serpentine  are  also  filled  with  the  same 
crystalline  magnesite.  This  form  is  strikingly  different  from  the  ordinary  magnesite.  which 
in  these  deposits  shows  no  crystal  form  to  the  unaided  eye.  In  places  crevices  in  the  vein 
have  a  velvety  black  coating  of  pyrolusite  (manganese  dioxide),  making  the  rock  look  as  if  it 
