1(52 
CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1905. 
In  the  examination  for  precious  metals  a  separate  kilogram  sample  of  each  product  of  the 
concentrating  tables  is  mixed  with  water  in  a  2-gallon  bottle.  To  this  is  added  a  small 
quantity  of  sodium  amalgam,  and  after  mechanical  agitation  for  about  thirty  minutes  it  is 
found  possible  to  extract  practically  all  the  free  gold,  platinum,  and  iridosmium,  It  has 
been  found  that  the  platinum  and  iridosmium  will  stick  to  the  sodium  amalgam  as  long  as 
the  sodium  is  not  all  converted  by  water  into  sodium  hydroxide.  As  in  some  instances 
the  gold  has  been  found  to  be  so  coated  with  martite  and  other  oxides  of  iron  as  to  defeat 
amalgamation,  each  product  is  also  examined  by  fire  assay  to  determine  the  total  gold  and 
platinum. 
In  the  treatment  of  class  2  the  sands  are  sized  through  an  8-mm.  screen.  What  remains 
on  this  screen  is  hand  picked,  and  the  screenings  are  passed  over  a  2-mm.  screen.  What 
remains  on  this  screen  is  jigged  for  the  separation  of  heavy  minerals.  The  concentrates  of 
the  hand  jig  are  hand  picked.  The  material  going  through  the  2-mm.  screen  is  again 
sieved  through  a  half-millimeter  screen,  and  the  coarse  and  fine  materials  are  run  separately 
after  appropriate  sampling  on  one  of  the  tables.  All  the  above  concentrates  are  subjected 
to  the  same  final  examination  as  the  sands  of  class  1. 
Results. — The  following  table  gives  a  synopsis  of  the  results  obtained  by  the  concentration 
of  various  sands; 
Results  of  concentration  of  black  sands. 
a.  Lots  in  which  a  high  per  cent  of  the  gold  and  platinum  were  concentrated  into  a  small 
bulk. 
Record 
num- 
ber. 
Localrl  y  from  which  sample 
was  obtained. 
Material. 
Amount. 
Actual  value  of 
gold  ami  plati- 
num in  product. 
OREGON. 
Coos  County: 
P102a 
not 
P68a 
P68a 
P67a 
PG7a 
Concentrates 
Tailings,  including  No.  2  con- 
centrates. 
Through  2  mm.  on  J  mm.: 
Concentrates  Nos.  1  and  2. 
'failings 
Through  £  mm.: 
Concentrates 
Tailings  and  No.  2  concen- 
trates. 
Through  2  mm.  on  J  mm.: 
Concentrates 
Tailings  and  No.  2  concen- 
trates. 
Through  2  mm.  on  \  mm.: 
Concentrates  No.  1 
Tailings 
Through  \  mm.: 
Concentrates 
Tailings 
Pounds 
20 
423.  5 
1.497 
22.5 
19 
222.5 
37 
393.5 
11 
37.5 
Dollars. 
1.819 
.129 
.0022 
.0008 
2. 015 
.277 
Per  cent. 
93.  37 
6.63 
73.11 
20.  83 
87.87 
12.11 
.940 
90.77 
.028 
2.67 
6.713 
99.93 
.004 
.07 
.623 
99.82 
.001 
.18 
