BLACK SANDS OF PARACALE. 221 
In assaying the screen products after division into magnetic 
and nonmagnetic products, the greatest differences in duplicate 
assays occurred in the products containing the most free gold. 
This was true notwithstanding the fact that the majority of the 
free gold had previously been eliminated by amalgamation. 
These assay differences are shown in Table IV in which the 
pulp was bucked through 150-mesh and then assayed in trip- 
licate. The maximum differences are given. 
TABLE 1V.— Showing assay variations in screened products. Lot No. 1. 
Maximum assay differences 
in triplicate assays. Gold amal- 
A080 SS gamated for 
Magnetic |Nonmagnetic oae Bones 
product. product. a 
Mesh. Pesos. Pesos. Pesos. 
10 15. 60 10. 94 23. 96 
20 5.96 10. 60 89. 22 
40 none 10. 60 12.16 
60 none none 
80 none 1,24 
100 none 1.24 3.04 
150 none none 
(—) 150 none none 38.68 
As shown by Table IV, the triplicate assays check almost per- 
fectly in the finer screen products, but check very poorly in the 
10- and 20-mesh. Evidently this is due to the greater abun- 
dance of free gold in the coarser meshes (see column 4) which 
makes the assay sampling exceedingly difficult even when the 
pulp is pulverized through 150-mesh. The table also shows 
that the magnetic products check in their respective assays very 
much closer, as a rule, than do the nonmagnetic products. This 
distinction is due, likewise, to the free unamalgamable gold re- 
maining in the nonmagnetic portion. The theory that the free 
gold is the cause of variations in duplicate pulp assays is also 
borne out by the fact that in the majority of cases little difficulty 
was encountered in obtaining close checks on products after 
amalgamation; whereas, before amalgamation, in assaying the 
heads, great differences occurred and frequently required from 
6 to 8 assays in order to obtain a dependable average. 
ASSAYING OF THE CONCENTRATES. 
Occasionally some free gold was caught where the sample was 
put through 60-mesh preparatory to the final splitting. As a 
rule, however, the gold was so brittle as to be reduced in size 
along with the remainder of the sample. When the final sample 
