Speaking
of the fineness of gold in vein matter, he continues :—" A case in
point occurring at our works at Grass Valley a few days since is
deserving of mention in this connection. A sample of ore of hard,
glassy, and flinty appearance was consigned to the Fryers' Company for
treatment.
......The rock attracted attention on account of its barren
appearance, and was uniformly pronounced worthless by all to whom it was
submitted......On pounding.....the visible colors
were
so fine that they would have passed through an ordinary assay screen of
2,500 meshes to the square inch. This ore yielded on treatment . . . 80
dollars per ton. The elaborate experiments of Mr. Deetkin, of Grass
Valley, at the Eureka and Idaho mills, showeth that the 'gold contents'
of their rock crushed were 68-67/100 dollars per ton—assay value ; of
which 47-40/100 dollars
was saved by the mill, and 2-50/100 dollars by the concentrators ;
18-67/100 dollars, or about 27 per cent, of-the known contents, was
lost in the tailings ; 3-1/3 per cent, being very fine gold ; and yet
these two mines are not amongst the 'refractory' mines of the State."
As
I am not aware of there having been any observations made on the above
important subject, though a Mr. Thompson states the loss at 25 per
cent, only in Australia, there are no data to guide one to say from
what mines or mills that gentleman derived his observations, and upon
what kind of ores he based his calculations, and which, comparing the
great pains taken in California, as shown above, with our much less
effective efforts in the same direction, ought to be much more than
only a 25 per cent. loss ; so that there appears to be much room for
enquiry on this and kindred subjects by our practical mining experts.
And, consequently, as the loss of mercury in California during crushing
may not altogether prove uninteresting :—" Mr. Hague, of the Fortieth
Parallel Survey, made numerous experiments at the Sheffield Laboratory
of Yale College, which undoubtedly were conducted with great care and
consummate skill, and he considers that the loss of mercury may
be chiefly considered mechanical, and only to a limited extent
chemical. The more the mercury is ground, the greater the difficulty in
recovering it. If the consumption of iron is assumed to measure the
grinding effect given by the pans, the relation between the loss of
mercury ana that of iron should be in a certain degree proportionate.
According to his experiments, the loss of iron in batteries and pans
was from 9-1/4 to 12-1/3 lbs. per ton of ore. The data with respect to
the loss of
quicksilver.....justify the opinion that the loss is from 2-1/3 to
3 lbs. per ton of ore, and of iron castings, by wear and tear, about 10 lbs. per ton of ore,"
