From a letter in the Grass Valley _Tidings_ we make the following
extracts:
The Spenceville Copper Mining Company have 43 acres of copper-bearing
ground and 100 acres of adjoining land, which was bought for the timber.
There are a hoisting works, mill, roasting sheds, and leaching vats on
the ground, and they cover several acres.
On going around with Mr. Ellis, the first place we came to was the mine
proper, which is simply an immense opening in the ground covering about
one half of an acre, and about 80 feet deep. It has an incline running
down into it, by which the ore is hoisted to the surface. Standing on
the brink of this opening and looking down, we could see the men at
work, some drilling, others filling and running the cars to the incline
to be hoisted to the surface.
The ore is found in a sort of chloritic slate and iron pyrites which
follow the ledge all around. The ore itself is a fine-grained pyrite,
with a grayish color, and it is well suited by its sulphur and low
copper contents, as well as by its properties for heap roasting. In heap
roasting, the ore is hand-broken by Chinamen into small lumps before
being hoisted to the surface. From the landing on the surface it is run
out on long tracks under sheds, dumped around a loose brick flue and on
a few sticks of wood formed in the shape of a V, which runs to the flues
to give a draught. Layers of brush are put on at intervals through the
pile. The smaller lumps are placed in the core of the heap, the larger
lumps thrown upon them, and 40 tons of tank residues thrown over all to
exclude excess of air; 500 lb. of salt is then distributed through the
pile, and it is then set afire. After well alight the draught-holes are
closed up, and the pile is left to burn, which it does for six months.
At the expiration of that time the pile is broken into and sorted, the
imperfectly roasted ore is returned to a fresh roast-heap, and the rest
trammed to the