ALUM  DEPOSIT  NEAR  SILVER  PEAK,  ESMERALDA  COUNTY,  NEV. 
By  J.  E.  Spurr. 
Locality. — About  10  miles  north  of  Silver  Peak,  Nevada,  there  lies, 
by  the  roadside,  a  deposit  of  alum  and  sulphur.  This  has  been  many 
times  located  and  prospected  as  a  sulphur  mine,  but  not  until  recently 
has  the  relatively  important  amount  of  alum  in  it  been  recognized. 
No  important  work  has  yet  been  done  on  the  deposit. 
Mode  of  occurrence. — At  the  locality  mentioned  there  is  an  elongated 
dike-like  or  neck-like  mass  of  rhyolite,  having  all  the  appearance  of 
being  intrusive  into  gently  folded  white  and  red  sedimentary  rhyolitic 
tuft's  of  Tertiary  age.  In  parts  the  rhyolite  is  easily  recognizable  as 
such;  in  other  portions  it  is  decomposed  to  a  white  powdery  variety. 
This  is  especially  true  of  two  portions  examined,  about  600  feet  apart; 
one  some  200  feet  in  diameter,  the  other  about  30  feet.  The  former, 
at  the  south  end  of  the  area,  contains  the  chief  alum  and  sulphur 
deposits.     The  latter  contains  sulphur,  but  no  alum. 
In  the  larger  area  the  decomposed  rhyolite  shows  sulphur  through- 
out, coating  all  cracks  and  crevices,  but  generally  not  over  a  fraction 
of  an  inch  thick.  With  the  sulphur  is  closely  associated  pure  alum, 
which  has  a  different  habit,  forming  veins,  some  of  them  several  inches 
thick,  that  split  and  ramify  irregularly  throughout  the  broken  masses 
of  altered  rhyolite.  Anatysis  in  the  chemical  laboratory  of  the 
United  States  Geological  Survey  shows  it  to  be  an  ordinary  potassium 
alum  (kalinite).  There  are  also  occasional  gypsum  seams,  of  the  same 
habit  as  the  alum,  but  much  less  abundant.  Bright-red  stains  are 
associated  with  the  sulphur  and  alum,  which  were  thought  in  the  field 
possibly  to  be  cinnabar.  The  small  quantity  represented  by  these 
spots  is  not  suitable  for  chemical  examination.  During  the  past  sum- 
mer, however,  Dr.  George  I.  Adams  has  investigated  the  Rabbit  Hole 
sulphur  mine,  in  northern  Nevada,  near  Humboldt  House  station,  on 
the  Southern  Pacific  Railway,  where  the  geology  appears  to  be  not 
greatly  different  from  that  of  the  place  being  described,  and  has  found 
there  similar  bright-red  stains.  Analysis  of  these  shows  them  to  be 
really  cinnabar  (sulphide  of  mercury),  and  there  can  be  little  question 
that  the  stains  of  the  deposit  near  Silver  Peak  are  of  the  same  material. 
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