Mining and Scientific Press, Vol. 10, No. 14, p. 216 (April 8, 1865)

"THE MOUNT DIABLO MINES. CONTINUED."

In continuing the description of the Mount Diablo mines, from our issue of the 26th March [sic], we come now to the Summit of Zion Copper Mine, located on the extreme northerly point of the spur which reaches out from the main Mount Diablo, as described in a previous article, and upon its westerly declivity. The approach to the mine is from the west, and up quite a steep acclivity, up which, however, a good road might be constructed with comparatively little labor, from the level of the valley below. Some $4,000 (we write from memory) has been expended upon the mine, under the general direction of the Secretary, J. F. Williams, Esq., of Martinez. A tunnel has been run in so as to strike the vein at nearly right angles with its line of direction, which is nearly north and south. After passing through the vein, a few feet, so as to make sure of cutting it, the foreman went back and commenced an incline, the vein dipping directly under the tunnel, and in conformity with the slope of the hill. After following the incline some fifty feet in depth, (our distances are all written from memory and of course are only approximate), a drift was started to the right, and run northerly upon the vein, some twenty or thirty feet, the indications of copper in the meantime sensibly improving. The incline was subsequently driven downward some thirty feet further, to the water level, where another drift was started, also to the northward. This is all the work which has been done upon the mine, except to sink a shaft some fifty feet in depth from the croppings, to ascertain the probability of the existence of a vein in depth. This was the first work done upon the mine, and the development was such as, in the opinion of the directors, to warrant the commencement of the tunnel already described. The work upon this mine has been most judiciously laid out, and we doubt whether another mine can be found in the State, worked by a company, where a better show has been made for the money expended. This is a most encouraging indication to the shareholders, and should be considered an additional inducement for them to continue the work of development so judiciously and economically conducted thus far. A careful examination of the mine, as now opened, has satisfied us that the company has a true vein, with well defined walls--both upper and lower. The foot wall upon the incline is almost as smooth and even as a floor, throughout its whole extent ; the dip, however, from the first drift to the bottom of the incline has taken a sharper pitch, which is an encouraging indication. The vein-rock is quartzose, carrying a large quantity of mundic. As the workmen have descended, the indications of copper have constantly increased, giving reasonable evidence that at a greater depth a concentrated vein of sulphurets may be looked for. The vein was first struck in a depression, or gorge, between two ridges. It is seldom, especially in either silver or copper, that a concentrated paying vein is found immediately beneath such a surface. The managers of this mine have done well in running a drift along the course of their vein, in order to prove it in depth under the higher portion of the ground, because it is well known to miners that chimneys, or the more concentrated portions of copper and silver veins, are usually found beneath the elevated portions of the surface ground. If the same economy is practiced in future that has characterized operations in this mine heretofore, it will require but a small additional amount to prove its value.

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