The Emma Mine, Little Cottonwood Canyon, Utah.
THERE often seem to be vicissitudes in the working life of a mine, like that in the life of an individual who, after a long struggle, becomes suddenly rich, and again, after a short period of flashy display and recklessness, becomes sud-denly poor again, to the astonishment of himself and those around him. This has been the experience of the Emma Company, starting out, in 1871, with a mine whose deposit was then described in the repor's as a lake of mineral, whose value was considered as scarcely over-eestimated in the price paid for it ($5,000,000) ; a mine so vast that one of the directors declared that 100 or even 1,000 tons extracted scarcely made an impression upon it. It seems strange that this magnificent property should have been exhausted in the space of two years, and that now the only prospect seems to be a winding up of the concern and an abandonment of the property they paid such an enormous price to obtain. That the estimates placed upon this property were too high in the first place, is evi-dent ; for, although it is said that about $2,000,000 have been already produced, still this amount could not be said to have been in sight when the mine was purchased, and, as any mining engineer knows, this amount should have been in sight to justify the purchase of the mine at the price paid for it, as it is always a correct rule in limestone formations to base the value of the mine upon the ore, and at the utmost to allow not more than two and one-half times the value of the ore in sight at the value of the mine. If this two millions of dol-lars had been in sight in the mine at the time of its purchase, and all questions as to title definitely settled, then the purchase money was still excessive, as the developments were insufficiently forwarded to tell the actual condition of the mine on either its dip or strike. To say that it was part of the same vein that comprised the Flagstaff, South Star, Vallejo, Caledonia, and North Star mines, was to start from an hypothesis not yet proved to be more than a strong conjec-tures, and we have seen how often the strongest conjectures in mining have failed. It only illustrates the great risk of expending large sums of money where the prospect of remuneration is even in part based upon hypothetical con-clusions.
The present condition of the mine may be taken from the reports of different persons made to the Company.
Mr. GEO. ATTWOOD, the general manager, reports the property is in a most unfortunate condition, all accessible pay ore having been extracted.
Mr. E. S. BLACKWELL reports: The future of the mine depends entirely upon virgin ground.
Mr. CLARENCE KING reports: The great Emma ' ' Bonanza," the object of such wide celebrity, the basis of such extravagant promises, is, with insignificant excep-tions, worked out.
Mr. A. MURRAY, F. R. S , reports: In my opinion the famous Emma mine is exhausted, end nothing more is to be expected from it but the leavings of the old workings, the scrapings of the walls, the ore which may have been en-tombed by the cave, the old fillings, and the second class ore on the dump.
These were the reports made in 1873, and if the condition could be even more discouraging, it certainty was so at the time of my visit in December, 1874. The engine shaft had been then sunk to a depth of about 82 feet below where the last trace of ore had been found and was in hard crystalline limestone; from that point down in the old workings, the creeping of the ground was slowly crushing the strongest timbers; the walls, wherever accessible, were picked clean, and all the drifts ended in solid limestone, without a trace of ore in sight. In the old workings a mass of broken timbers, limestone and mine fillings, princi-pally the refuse breccia that had been once rejected in sorting the ore, was all that remained of the famous lake of mineral upon which the small matter of ex-tracting a thousand tons or so was to make no impression.
But is the Emma Mine really exhausted? So far as the works h ve anything to show, it is; but unless geo-logical evidences are utterly at fault, it is not ; and here a few words in regard to the ore formations of the district and their mode of occurrence may serve to explain a feature that is not generally understood. About a year ago, I published a geological map of the district and ex-plained it by a set of sections and two articles published in the Utah Mining Gazette. In the first article I showed that the Granite Mountain, to the East of the Emma, was undoubtedly an intrusive one, and subsequent ob-servations have not only confirmed the opinion I then expressed, but have also fully satisfied me of the cor-rectness of an opinion I then held, viz.: that the num-erous dykes of porphyry which traverse the sedimentary rocks of the district are all connected with the mass of this mountain, and are, in fact, spurs of the granite mass itself. These, in two instances, are first seen at the base of the mountain, putting out into the sedi-mentary rocks as apparently true granites, and gradually changing in appearance until the true porphyritic struc-ture and appearance entirely prevail. They continue, and finally give out, in the limestone or quartzites, and in no instance have I been able to trace any connection between the porphyries and the Western Granite Moun-tains. Another phase is, that the ore deposits all seem to be of more recent origin than the porphyry dykes, and to be in almost all cases where the deposits are im-portant, in more or less intimate connection with, or in close proximity to, the dykes, in several marked instances occupying the fissures of the dykes from which a part of the porphyry has been removed by pseudo-morphic action. It would seem as if the formation of the ore deposits was a secondary effect of the porphyritic eruption. The strike of the veins is also conformable to that of the dykes, except in one or two unimportant in-stances.
It will be seen, by reference to the geological section accompanying this paper, that the Emma Mine is also connected with a dyke of porphyry, and as far as the dyke can be traced upon the surface, or in the workings of the adjacent tun-nels, its direction of strike is in conformity with that of the Emma ore vein. That it has been instrumental in the formation of the vein is a highly probable conjecture, as it has been traced to near the mouth of the Vallejo tunnel, and I have also found in the ores of the mine slight traces of matter similar to that of which the dyke is composed. Passing to the North of the ore deposit is a deep-ly marked line of fault; this fault was, I believe, first found in the main shaft of the mine and afterwards in the Illinois tunnel, where it is exposed by a level run by the North Star Co. for a distance of about 300 feet, and also by a shaft sunk from the tunnel level to a depth of about 90 feet. The grooving of the walls of the fault and the condition of the faulted rocks go to show that the throw was from above, or rather a sinking of what might be called the hanging wall of the break. This, as will be observed, crosses the line of dip of the vein, and has, without doubt, carried that portion of the vein contained in the sunken rocks to a considerable depth below its original position, leaving a dirty trail of ore for some distance below the upper portion of the vein, and also crushing into the lower part of the ore chamber a sufficient quantity of limestone to fill that portion and give it the appearance of a limestone floor. So compact and hard has this become that only a close examination can detect the difference between it and the crystalline lime of the wall rocks. This compact nature has been caused probably by the heat genera'ed by the friction of the walls or sur-faces of the fault, and the same cause has produced another effect upon the ores contained in the lower part of the mine—that is, changing the ores from sulphides into oxides. To no other cause can we attribute the anomalous con-dition of the ores below the water level of the mine, for long and almost uni-versal experience has shown that in all ordinary cases the change of ore at the water level is from oxides to sulphides; but here is a case so unusual that, so far as I know, no explanation has ever been offered before, and in examining the break, as exposed in the Illinois tunnel, we find the friction surfaces of the rocks to have been changed into a compact marble, on each side of the break, of the most beautiful description, owing to crystallizing together of fragments of the different colored rocks. This feature does not appear, to any extent, at least, in the mine, owing to the more homogeneous condition of the rocks lying near the granites, which were probably metamorphosed long before the forma-tion of the ore deposit.
It will be observed that in the geological section I hive carried out a continua-tion of the vein below the break, marked "supposed lower ore body." While this may be considered pure theory, there are good reasons for supposing the ore to continue below the fault. It happened that at the time of my visit to the Emma mine I was engaged at the South Star and Titus mines, and found so many points of resemblance between the break in the two mines that I at once set to work to trace out, if possible, the connection of the fault in the South Star with that in the Emma. I have succeeded thus far in tracing it from the Flagstaff on the West to the Vallejo, and from the Emma on the East to the Caledonia, through the North Star, and Monitor, and Magnet mine. It is also said to exist in the Caledonia, though I have not seen it myself. If this should prove to be correct, then we have a distinct chain of evidence through all the mines situated upon the Emma vein, of the existence of this remarkable displacement, slight in the Flaggstaff, being a throw of less than 20 feet, increasing in the South Star to about 45 feet, and of unknown depth in all the mines to the East of the Val-lejo; it has been proved in the South Star, and the ore found to continue uninter-ruptedly downwards, thus proving that the rocks have in former times con-tained a continuous vein of ore, which was subsequently broken, and the lower portion carried downwards, as shown in the geological section. That the entire chain of mines belong to the vein appears to me very probable, as in all cases, even in the western end of the Emma, there is clear evidence of a difference be-tween the foot and hanging walls, forming what may be termed a strata vein, or a vein lying between the beds of limestone. The hanging wall is undoubtedly of Devonian age, though highly metamorphosed on the eastern end ; while the foot wall may probably be termed Silurian, though I am inclined to refer it also to the Devonian era.
THEORETICAL CONCLUSIONS.
We have shown that the connection of the line of fault is continued through-out the entire length of the vein as far as known; that the fault has been passed in the South Star mine, and so far as developed, the ore continues downwards; that the vein is probably a contact one between different beds of limestone, and we might even extend these points of resemblance by showing a similarity in the ores of the different mines; but the evidence given may be supposed to convey all that is required to give strong grounds for believing that the Emma mine is not exhausted, and that there is good reason for a further extension of explora-tions downwards.
J. H. MORTON.
