One of the most promising mineral locations in Contra Costa is the quicksilver mine near the eastern base of the main summit of Mount Diablo. This mine has been known to the Tribal Communities from time immemorial. A very aged native, who has given up the roving habits of his race, and "located" in the vicinity of this mine, says that from the time of his boyhood all the natives in that region have been in the habit of resorting to that place for obtaining the red paint (sulphate of mercury) with which they were accustomed to bedaub themselves on all occasions of great festivity or when preparing for battle. 

The same use, it will be recollected, was made of the same substance at the New Almaden mine. So little attention was paid to mining matters about Mount Diablo, that it is only quite recently that the value of this mine has been brought to the notice of capitalists. It was first located by Mr. Welch, who, in connection with several of his friends, took it up a year or two ago. They ran a short cut into the face of the hill, and sunk a shaft some thirty-five feet in depth on the ledge, at which point they cut through-'the vein, which was thus proven to be continuous and about ten feet in thickness. 

This shaft was partially filled up at the time of our visit to the mine. The ore is very rich, the quicksilver being brought freely to the surface whenever the ore is exposed for a short time in a fire. Repeated assays of average rock have uniformly yielded most satisfactory results. The vein rock proper is accompanied with a large amount of earthy matter, known by the Mexicans as "tiros," precisely as it is found at the New Almaden mine, near San Jose. A large amount of free quicksilver can be washed from this earth by the ordinary pan process, securing, at the same time, large quantities of pure sulphuret of mercury, in the form of fine crystals, like sand. 

It is said that a man can make fair wages by merely panning out the native quicksilver. It may not be out of place in this connection to state that the party of Mexicans who were employed to do the work of the New Almaden Company, proposed to take the mine and open it thoroughly by tunnels and shafts for extensive working, and take merely the ore which they might raise for their pay--thus making the mine pay for its own development. The proprietors did not see fit to accept their offer, but preferred to associate themselves with capitalists and develop it on their own account. 

As a further evidence of the richness of this mine, it may be noticed that a small stream of water, which runs down the mountain, the most of the year, across the vein, has been taken up as a quicksilver placer; the locators intending to sluice out the bed of the stream for the free quicksilver, and the large deposit of rich boulders of ore and finely divided sulphuret sands which abound in the same. A handsome prospect of quicksilver can be obtained from a panfull of earth taken up at random, almost anywhere in this stream, for two or three thousand feet from the mine.

The holders think they have got a "good thing" of it, and will commence operations as soon as the next rainy season sets in. The original owners of the mine, which is called after its locator, the "Welch Claim," have made an arrangement with Mr. Ogilsby, a capitalist, well known as the owner of the Ogilsby road over a portion of the Sierra, to put up furnaces and the necessary machinery for working the mine. The work of putting up this machinery has already commenced, and we understand the retorts will be ready for work in about two or three months. Experts and persons who have long been connected with the working of the ores of the New Almaden mine, say that this is quite as promising as that was at the start.

The millions of profit which have been derived from the Almaden make the proprietors of the Welch claim almost fancy themselves millionaires also. We trust they may become so in reality. Three extension locations have been made upon the north and one upon the south of the original location, known as the Union Company, which presents quite as well defined a vein as that of the original Welch Company, and much more favorably located for working ; beyond which there is no appearance of the vein, and, indeed, such is the formation of the mountain, that there is scarcely a possibility of its being found any further. 

Some work has been done on the southern extension--a short cut run, in which the vein is exposed, and a location made for a tunnel, at a point which presents a most favorable opportunity for a thorough opening of the vein at a very moderate cost. The location of this vein is very favorable for profitable and economical working. It is situated within three or four hours' ride from San Francisco, and within eleven miles of good water communication, over nine miles of which there already exists an excellent and almost perfectly level county road. 

The other two miles are now being constructed by Mr. Ogilsby, who, by the way, is famous for building good roads. We shall not be surprised to see Mount Diablo, before long, presenting a formidable rival to the Old and New Almaden mines, which have for so many years controlled the quicksilver market of the world. 

This discovery, should it prove as valuable as it now promises to become, will be most opportune for the present increasing demand for this prime necessity for working ores of the precious metals is calling loudly for a new and additional source of supply, without which, the mining public may well fear a monopoly which may, at no distant day, exert a disastrous influence on the world's supply of gold and silver.