NEAR THE PINOS-CHAMA SUMMIT.
“Geologically,” we are told on high authority, “the veins of the district are very young, probably having been formed at the close of the cretaceous or the beginning of the tertiary period. The enormous eruptions of the trachytic lava cover a continuous area of more than five thousand square miles. Stress has been laid upon the impregnation with mineral matter of certain volcanic strata,—a phenomenon that occurs throughout a large tract of country. This shows that at the time of the eruptions such conditions existed as were favorable to the formation of that class of minerals generally termed ores. It is furthermore to be observed that these impregnations occur mainly in the younger strata. Although the inference can not be drawn that the fissures were formed at the same time, or shortly after the deposition of the trachytic lava, it is allowable to assume that at such a period the material for filling these fissures was existing near the locality where but lately so thorough an impregnation had taken place. The fact that the fissures extend at a number of points, downward, through the older metamorphic rocks, makes it improbable that they should have been formed by contraction of the cooling masses. Singular as it may seem, these lodes are devoid of that which is usually classed as surface-ore. Immediately from the surface the perfectly fresh minerals are taken out. The gangue is hard and solid. An exception is made, of course, although only to a slight extent, by pyrite, which decomposes very readily when exposed to the action of atmospheric influences. This characteristic may be explained in various ways,—by the rapid decomposition and breaking off of the wall-rocks, carrying with them portions of the gangue and ore; by the less intense effect of atmospheric agencies; by the character of the minerals composing the ore, and by the comparatively short time that these fissures have been filled. The latter view is the one that would appear as the most acceptable.
“A difficult question arises, when a decision is to be made, as to the causes that have produced the formation of the fissures that were afterward filled. Accepting the theory that volcanic or plutonic earthquakes have probably produced the larger number of all lode systems,—and such we have in this case, it will be necessary to find whence came the requisite force. Along the highest portion of the quartzite mountains we have an anticlinal axis which can be traced westward for nearly forty miles, an upheaval that must have a very perceptible effect on regions adjoining. The idea at first presented itself that this might have given rise to the formation of the fissures, but evidence subsequently discovered demonstrates that long before the eruption of the trachyte, this disturbance had occurred.
“About twenty miles west from the center of the mining region is a series of isolated groups of volcanic peaks. The highest one of these, Mount Wilson, reaches an elevation of 14,285 feet above sea level, or about 5,000 feet above the valley. Lithologically these groups must be considered younger than the lode-bearing rock of the Animas, and must therefore have become eruptive later. It seems quite possible that the disturbance produced by these eruptions may have resulted in the formation of the present fissures, which subsequently were filled from that source which supplied so much mineral matter to other neighboring rocks in the form of impregnation.”
This ore, then, may be set down as principally galena,—a lead ore of silver, frequently enriched by gray copper (tetrahedrite). The high percentage of lead makes smelting the most rational process of treatment, and they are generally to be classified as smelting ores.
In several localities, however, of which Parrott City and Mount Sneffels are chief examples, rich ores of silver are found, nearly or quite devoid of lead. These come mainly into the group of antimonial ores, with chlorides and sulphides also. Popularly these ores,—barring the chloride,—are termed “brittle silver,” and on account of the absence of lead, they are unfit for smelting, but must eventually be treated by a milling process in which the pulp is subjected to the action of mercury in amalgamating pans, where the silver is separated from the quartz and collected by the quicksilver. Antimonial ores, prior to amalgamation, will require chlorination, that is, roasting with salt, as is done at the Ontario mine, Utah; while the chlorides and sulphides of silver can be treated directly, without roasting, as at the mines of the Comstock lode, Nevada.
The foregoing remarks apply generally to all of the mining districts mentioned in the present chapter; and their uniform nature is readily explained by the fact that the whole neighborhood is of the same geological age, character and origin.
The mines in the immediate vicinity of Silverton, my starting point, are situated upon, or rather in, the lofty mountains which hem in the little park. Southward of the town, easily recognized by its cloven peak, stands the Sultan, thirteen thousand five hundred feet in altitude. Its most noteworthy mines are the “North Star,” “Empire,” “Jennie Parker,” and “Belcher.” Tower and Round mountains, next northward, contain several ledges of low-grade galena ores of silver.
Crossing the Animas to the eastern side, King Solomon wears as the central jewel in his crown another “North Star.” It stands upon his very brow,—one of the loftiest silver deposits in the world, almost fourteen thousand feet above the restless surf of the Pacific. Here, too, the ore is galena and gray copper of extraordinarily high grade. A marvelous trail has been cut through the woods and then nicked into the almost solid rock of the bald mountain-crest, far above timber-line, or built out upon balconies of logs, along which burros carry to the mine all its supplies, and bring down its product. On King Solomon are several other noteworthy claims, such as the “Shenandoah,” “Eclipse,” and “Royal Tiger.”