The rocks appear to have been originally talcose and chloritic schists, sometimes micaceous, inclosing masses of argillite, and of quartz which appears to have been massive enough at certain points to assume the character of a vein, and parallel to the stratification which has the usual north-western strike and easterly dip of the region. All this mass of material which at Quail Hill is certainly three hundred feet wide, and possibly twice that, and with a linear extent exceeding one thousand feet, appears to have been very highly impregnated or mineralized by sulphurets, chiefly of iron, with a portion of copper, zinc and lead. The sulphurets have undergone almost total decomposition throughout the entire mass, leaving soft ochraceous deposits of a rusty red and yellow color, and staining the rocks with brilliant colors, a peculiarity which the miners have characterized by the name of “Calico rocks.” This decomposition or oxidation of the sulphurets, has extended to a point as low as atmospheric influences extend, or probably to a point where water is permanently found, which at Quail Hill is assumed to be about 170 feet below the outcrop of the mass, or crest of the hill. Dykes of porphyry and of other rocks, commonly called intrusive, are seen dividing these great ore channels in a direction conformable to the line of strike. But the decomposition which has affected other portions of the ore channel, appears also to have changed them, for they are found to be reduced completely to the condition of kaolin and lithomarge, or kindred alterations of feldspathic rocks. The outlines of the feldspar crystals are still easily distinguished, although the mass of the dykes is completely friable.
The zinc blende which is found in small quantities at Whisky Hill, and the vitreous copper also to some extent, appear to have escaped decomposition. The copper ores appear to have been confined to a portion of the deposit, as is indicated in the section exhibited, while the auriferous sulphuret of iron has been co-extensive with the ore channel, the cubical cavities left by the decay of its crystals being found in all the outcrops both in the quartz and in the ‘calico rocks,’ resulting from the decomposition of feldspathic and talcose or chloritic constituents.
Accompanying the entire mass of decomposition at both localities, occur both gold and silver, disseminated with remarkable uniformity in all parts of the orey ground. At Whisky Hill, films of metallic silver are visible upon the talcose masses stained green by malachite or chrysocolla; the gold is rarely seen in situ, being mostly obscured by the very rusty and highly-stained character of the associated materials. But it is rare that on washing a small quantity of any of the contents of these great deposits, gold is not found in angular grains or small ragged masses, from the size of a few grains’ weight, to impalpable dust. Nuggets of several pennyweights occur occasionally. This gold has evidently accompanied the sulphurets and been left in its present position and condition by their decomposition. There can be little doubt that the gold of the gulches adjoining these deposits has been derived from them. At Whisky Hill, the gulch gold ceases to be found as soon as the limits of this deposit are passed, and the same is true at Quail Hill. The occurrence of deposits of this nature throughout the range of the foot-hills, seems to offer the best solution which has suggested itself of the origin of the placer gold which is found in situations so far removed from the gold belt of the upper Sierras, and away from sources usually recognized as those to which placer gold may be referred.
Experiments made by myself and by others on a considerable scale, the details of which will appear elsewhere, show that the amount of the precious metals disseminated in the average mass of vein stuff and decomposed materials of every name at Quail Hill, is considerably in excess of the general average tenor of gold veins in California. The mean of my own trials gave to the ton of 2,000 lbs. by assay:
| Gold | $35.14 |
| Silver | 15.08 |
| $50.22 |
While from the working of carefully prepared averages in considerable quantity by milling process, the tenor of the precious metals was:
| Gold | $29.18 |
| Silver | 5.91 |
| $35.09 |
The extremely friable condition of the entire mass of these auriferous materials renders their extraction and treatment easy and comparatively inexpensive.