BLACK SANDS OF PARACALE. 943 
all the gold, although it is probably equivalent to the actual 
recovery to be expected of the dredge. When we amalgamated 
the original sample we were able to save only 39.7 per cent of 
the total gold present, or about 76 per cent of the free gold. 
There was an actual loss of 24.3 per cent in gold which floated 
off and was not caught by the mercury nor saved with the 
tailings. When testing the ground, under the methods of rough 
treatment practised, it is unquestionable that there is a loss of 
gold due to such floatation. 
The amalgamation tests on lot 2 are given as follows: 
TABLE XXV.—Amalgamation tests. Lot No. 2. 
Weight Gold Gold . 
Product. No. of se eeey ot saved, {saved per| gold mnie, of Dscren bi 
sample. : | weight. |tonofore.| © : ee 2 
Grams.| Pesos. | Mgrms. | Pesos. |Percent.| Pesos. Pesos. 
Original through 1 900 114. 20 40.58 54.10 47.5 59.50 (—)0. 60 
60-mesh. 2 950 109. 60 26.60 32. 60 30.0 67. 30 (—)8. 70 
Original through 3 680 110. 80 29. 40 51.70 46.6 64.40 | (+)0.29 
100-mesh. 4 110 114. 20 31.15 52. 90 46.4 58.10 | (—)3.11 
i 
The screen test of the ore through 60- and 100-mesh shows the 
following: 
TABLE XXVI.—Screen tests. Lot No. 2. 
(—) 150- 
Product. 60-mesh. | 80-mesh. |100-mesh.|150-mesh. Gan. 
Per cent. | Per cent. | Per cent. | Per cent. | Per cent. | 
Through 60-mesh --_______---_--------------.--- none 13.6 21 20.3 45.1 
Through 100-mesh -_-__-------------------------- none none none 10.28 89. 72 
As seen from Table XXV, the amalgamation tests at 60-mesh 
show an average of 38.7 per cent recoverable, while at 100-mesh 
an average of 46.5 per cent was obtained. It is evident that 
finer grinding releases more gold and increases the extraction. 
However, it is clear that the increase is only nominal and not 
as great as might be expected from the difference in fineness. As 
shown by the screen tests tabulated in Table XXVI, the 100- 
mesh product contained 89.72 per cent through (—)150-mesh, 
while the 60-mesh product contained only 45.1 per cent through 
(—)150-mesh. This indicates that on this lot, fine grinding is 
not a very efficient method of liberating the gold. Furthermore, 
the maximum recovery of only 46.5 per cent is altogether too 
