For several years past the drainage of the deep mines has been one of the most serious problems confronting the mine owners of the Cripple Creek district. Large sums of money have been spent for pumping by nearly all the principal producers. What the total amount pumped has been it is impossible to state, as few mines have kept any accurate record.
As is generally known among geologists and mining men, the Cripple Creek district is an area of eruptive or volcanic rock of an irregular elliptical shape from 3 to 5 miles in diameter, of unknown depth, and surrounded by an impervious granite rim. This volcanic mass has been thoroughly fissured by many successive eruptions and contains innumerable fissures, crevices and cavities of all sizes and shape.
These cavities are filled with water and, as has been stated by a practical mining man, the rock is saturated to the limit. It is, in fact, an immense cistern or reservoir, and has been said to resemble a water-soaked sponge set in a glass cup.
This eruptive mass assumes the shape of an inverted frustrum of a cone; that is, the area of horizontal sections are supposed to become less with depth. The contact of the granite walls with the volcanic rock dipping to center. The number and size of fissures and other openings will undoubtedly decrease with depth, until at very great depths, perhaps 5 or 6 miles, they will be absolutely closed by weight of rock above. We may, therefore, fairly conclude that the total amount of water per foot vertical will gradually become less with depth until the rock is perfectly dry.
Although no very exact data are available, we have some evidence that such is the case in the Cripple Creek district. Personally, I am of the opinion that considerable water will still be found at as great depths as it is practicable to mine.
Sources of the Water.
The question of the source of this water is of great practical importance. It is generally admitted by all who have studied the subject that it is entirely of meteoric origin. It is invariably cold, even in the deepest workings, and has none of the properties of water that has come from great depths.
It has been gradually stored up through a long period of time and largely prevented from escaping by the tight granite walls of the volcanic neck, as before stated. No continuous record of the annual precipitation in the district has ever been kept, but it probably amounts to an average of fully 16 ins.
In the year 1904 it is said to have been 24 ins. This is largely in the form of heavy showers during the summer season, and a very large proportion runs off on account of the steep slopes, which are for the most part bare. Just what proportion of the surface precipitation finds its way to the underground waters it is difficult to estimate, but it is no doubt much greater now than formerly.
The entire surface of the productive area is honey-combed with mine workings to depth of 10 to 100 and 150 ft, many of them entirely open. These openings no doubt catch and hold a large amount of water that would otherwise pass off by surface drainage.
For some time after the Cripple Creek district was first discovered it was generally considered a dry camp. The earlier shafts sunk were near the summits or upon the slopes of the various hills and considerably above what is now known to have been the original water level. The first water of consequence encountered in mining operations was in the Blue Bell tunnel, a short distance below the town of Anaconda, in the year 1892, at an elevation of 9,340 ft. and considerably below all of the shafts which had then been sunk.
This tunnel was but a few hundred feet in length and was driven entirely for development purposes. It penetrated the granite rim to the contact and was driven northerly along the contact for a short distance. I visited this tunnel shortly after the water was encountered and noticed it frequently thereafter, but never made any attempt to measure the flow. My opinion is that it never exceeded 300 gals, per min. and, perhaps, was not over 200 gals.
Water was so scarce in those days that it was something of a curiosity. Owing to this scarcity of water it was considered a valuable find, and probably determined the location of three large mills that were built in Squaw gulch immediately below it during the next 2 years. The flow from this tunnel continued for about 4 years at a nearly uniform rate, but probably had little effect in lowering the general water level. The flow ceased entirely shortly after the Moffat or Ophelia tunnel cut the contact a short distance to the north in 1896.
The first mine that was troubled with water to any extent was the C. O. D. mine, situated in Poverty gulch, just east of the town of Cripple Creek and near the well-known Gold King mine, one of the first discoveries in the district.
I think that the first station pump installed in the camp was in the 350-ft. level of the C. O. D. mine. Water had first been encountered about 25 ft. above, or at an actual elevation of about 9,500 ft., early in the year 1896. This pump was said to have a capacity of 1,000 gals, per min., but as the work progressed more water was encountered and the pump was drowned some time during the month of May, 1896.
The water only rose about 20 ft. above the station. In September a pump was started at that point, and by raising 560 gals, per min. for a few weeks the station pump was recovered. The cross-cut to vein was then bulkheaded and sinking of shaft resumed to the 8th, or 555-ft. level., with an average flow of less than 100 gals, per min.
No cross-cuts were made to vein on 8th level at this time, and in May, 1897, the property was closed temporarily.
→ Meantime, in December, 1896, the Moffat or Ophelia tunnel, about 1 mile to the south of the C. O. D. mine, had been driven through the granite to the contact with the eruptive rock, where a flow of water estimated at from 2,000 to 2,500 gals, were encountered.
Within 60 days from that time the workings of the C. O. D. mine were practically dry down to nearly the 8th level. It seems quite certain that at the same time the Ophelia tunnel drained many of the other properties on the west side of the district, notably the Moon-Anchor, Anchoria-Leland and Blue Bell tunnel.
At various times during the year 1896 most of the present deep shafts of the district had been sunk to and below the original water level and were obliged to begin pumping. They soon demonstrated the fact that Cripple Creek instead of being a dry camp, was, on the contrary, a very wet camp, and before the end of the year pumping machinery was being brought in by the carload.
While the actual elevation at which water was first encountered in the several shafts varies from 50 ft. to 100 ft, the average actual elevation of the original water level is not far from 9,500 ft. And that corresponds fairly well with the elevation of the lowest notches in the surrounding granite rim.
A history in detail of the pumping done at all of the properties which have been obliged to pump would be difficult to obtain and would probably be somewhat tiresome. Very few have kept careful data of their work. The largest quantities have been pumped by the Portland, Elkton, El Paso and Mary McKinney mines. These properties, as well as many others, have been repeatedly flooded when attempting to work at any great depth below the general water level.
The theory of a common water level has been largely discussed by the engineers and mine managers of the district, and many facts presented to prove or disprove such a condition. Personally, I am of the opinion that for all practical purposes there is a common water level over a very large part of the district, covering, in fact, all but the extreme easterly portion.
The main facts in support of this opinion are: The original water level was found to be practically the same in all shafts sunk to that depth. The Elkton, Mary McKinney, Morning Glory, Moon-Anchor, C. O. D., Portland and other shafts have had their water lowered by tunnel drainage to substantially the same extent, although, perhaps, not to the same actual level.
It requires considerable head or pressure to force the water through the rock, and the fact that one mine may be pumping water on a level 40 ft. or 50 ft. higher than that on which a mine a mile away is dry cannot be accepted as proof that a practical common water level does not exist. There is little doubt but that there are much more direct and open connections between the various mines of the west side of the district than between them and the mines of the south and east sides of Battle mountain or Bull hill.
A History of Tunnel Drainage.
While a great many tunnels have been driven in the Cripple Creek district only 4 have encountered a flow of water of any consequence, namely, the Blue Bell, Ophelia, Standard and El Paso. The Newell tunnel on Grouse mountain might also be included, but there is no evidence that the small flow from this tunnel had any effect on the water level of the district.
The Blue Bell and Ophelia tunnels have been referred to and described, briefly, above.
The Standard Tunnel.
The Standard tunnel was started in the latter part of the year 1895 at an elevation of 9,034 ft. on the westerly slope of Beacon hill, a short distance below the old El Paso shaft. At that time the water level, where not locally lowered by pumping, was from 9,290 ft. at the Portland to about 9,350 ft. at the Elkton and Mary McKinney.
The tunnel was driven easterly in the granite towards the Beacon hill phonolite plug, reaching the contact after numerous delays, about July, 1898. But little water was encountered until the El Paso vein or dyke was cut in the granite at a distance of 1,330 ft. from the portal. Here a flow of about 250 gals, per min. was opened.
The contact was reached in a distance of about 1,900 ft. from the portal and the flow there increased to 1,000 gals, per min. Work was suspended for a time and thereafter progressed but slowly, the flow of water increasing so rapidly as to seriously interfere with the work of driving. By. Jan. 1, 1899, it had penetrated the phonolite from 400 ft. to 500 ft. and the flow had increased to about 7,500 gals, per min.
I visited the tunnel at about this time and was greatly surprised at the quantity of water being discharged. It was by far the largest stream of water I had seen coming from any opening in the district up to that time, and I felt convinced that a large underground reservoir had been opened.
I made no attempt to measure the flow and think no one else did. Driving, however, was slowly continued, numerous additional water courses were cut, and finally such a heavy flow was encountered, or accumulated, rather, that work had to be suspended. I have no exact record of this date, but it was probably early in the spring of 1899.
I visited the tunnel at the portal shortly after and distinctly remember that the water was flowing out with a strong current the full width of the tunnel (8 ft.) and almost knee deep. The engineers in charge, and others, estimated that the flow amounted to from 17,000 gals, to 18,000 gals per min. I don't think any attempt was made to get a correct measurement of it, and am inclined to think that it could hardly have been 18,000 gals, at the time I saw it.
The flow may have amounted to that for a short time after the principal water course was cut. I feel sure that it was at least twice the maximum amount which afterward flowed from the El Paso tunnel and which I repeatedly measured and found to be 6.800 gals, per min. This heavy flow continued with little variation for probably 6 months or more, and then began slowly to decrease.
In a year from that time, or about July 1, 1900, the flow was estimated at 8,000 gals. I did not visit the locality again until the early spring of 1901, and the flow had then greatly diminished, and probably did not exceed 1,000 gals, per min. At that time all of the deep shafts on the west side were below the water level (below the Standard tunnel) and pumping heavily, raising in the aggregate 5,000 gals, to 6,000 gals, of water.
By the end of the year 1901 the Standard tunnel was practically dry and has discharged no water since, except what was pumped into it from the lower levels of the El Paso mine. The total amount discharged by this tunnel was not less than 13,000 millions of gallons, an amount probably exceeding the total quantity pumped by all the mines of the district up to the time of its completion.
It is doubtful if the water discharged through that tunnel could have been pumped to the surface by the mines then pumping for a less sum than $1,000,000, and it did not cost the principal mine owners a dollar. It was certainly the star performer of its day in the drainage line. There is no doubt but that it drained the eruptive rock over a very large portion of the district.
Such a vast volume of water could not have come from any small drainage basin. It also furnished striking proofs of the connection of the water courses of the Beacon Hill phonolite plug with the main eruptive area. The sudden stoppage of the flow in the Ophelia tunnel, over a mile away to the north, shortly after the heavy flow began in the Standard indicates a very close connection between the two water courses, a connection which, in my opinion, follows very near the contact between the granite rim and the volcanic neck.
I think the mine owners and managers, as a rule, did not fully realize the great benefits of the Standard tunnel for some time after it had ceased discharging water. At that time nearly all the mines continued to struggle with the water at depths of from 50 ft. to 100 ft. lower than the Standard tunnel.
The Elkton Co., especially, in its efforts to open their eighth level, pumped continuously during the years 1901 and 1902 from 2,000 galls, to 3,000 galls, per minute. In fact, to use a common expression, they nearly "went broke" pumping water. In the latter part of the year 1902 they gave up the attempt to develop the mine below the water level, pumping was stopped and the water rose slowly to nearly the seventh level, or an elevation of about 9,050 ft.
The El Paso Tunnel.
It now became apparent, at least to the mine owners of the western side of the district, that some form of co-operation in drainage must be adopted. Estimates made by mining and pumping experts showed that the underground storage water probably amounted to 60,000,000 gals, per vertical ft. for the larger part of the district, and in addition to this that unknown portion of the surface precipitation finding its way to the ground water level.
The cost of pumping such a quantity, even on a large scale, and by the most economical methods, seemed prohibitive. They therefore wisely decided to attempt the drainage of their mines by the tunnel method. Careful surveys showed that by a tunnel about 5,800 feet in length the district could be drained to a depth of 240 ft. below the Standard tunnel, and at an estimated cost of not exceeding $100,000.
An important advantage of a tunnel at that particular elevation was, that it would connect at the proper grade with the 600-ft. level of the El Paso mine, which was running in nearly the same direction as the proposed tunnel, directly towards the portal, and thereby save some 700 ft. of drifting.
Drifts could also be run from the westerly end of the El Paso sixth level towards the portal, and easterly from the El Paso shaft towards phonolite contact and Elkton main shaft. In December 1902, the Cripple Creek Drainage Tunnel Co. was organized with a capital of $80,000 subscribed by the principal mines of the western part of the district.
The site selected for the portal was at the Junction of Cripple creek and Arequa creek. On January 25, 1903, a contract was let to the El Paso Mining Co. to drive this tunnel at the rate of $14 per lineal ft., the size to be 4½ x 7 ft. in the clear. The elevation of floor at portal was 8,786, and the grade was 0.28 ft. per 100 ft., or 1 in 357. The total distance to be driven to connect with the westerly end of the El Paso 600-ft. level was 4,074 ft.
Work was begun at once, and to expedite matters two intermediate shafts were sunk at distances of 505 feet and 2,325 feet from portal, respectively, the first 40 ft. deep and the latter 216 ft. Ingersoll machines, 3½-in., were used, with an average air pressure of 125 lbs.
Three shifts of men were worked but, owing to the very hard nature of the rock, the average progress for all headings was only 5.8 ft. per day for the time actually worked. There were for a large part of the time as many as four headings to work upon, and never less than two. The portal heading connected with the westerly heading of the 40-ft. shaft before the 215-ft. shaft had been sunk to the tunnel level.
The greatest progress made in a month at any one heading was 286 ft., made in the month of July, 1903, from portal heading. The greatest total progress made in any one month was 783 ft. at 4 headings, also during the month of July.
The work was completed and connection made with the El Paso 6th level on Aug. 31, 1903, requiring about 7 months' time. The average progress was 582 ft. per month. There were fully 2 weeks' delay caused by labor troubles.
While the tunnel proper was being constructed a drift was driven from the El Paso main shaft eastwardly to tap the contact and strong water courses beyond that were known to exist in the Standard tunnel almost immediately above. This was driven for a distance of nearly 500 ft. until a flow of 50 gals, per min. had accumulated by the end of May, 1903.
Work was then suspended in this drift until connection was made with portal. It was resumed in September, 1903, and the drift driven 678 ft. farther, cutting the granite-phonolite contact and going about 300 ft. beyond. Five distinct water courses were cut in the phonolite running nearly at right angles to the course of the tunnel. This drift was finally stopped about the middle of February, 1904, the total flow from the tunnel at that time amounting by actual measurement to 6,500 gals, per min.
The total cost of the El Paso tunnel is said to have been $90,000, including intermediate shafts, which would make an average of $17.15 per linear foot of tunnel. A flume or box was prepared at portal 4 ft. wide. 4 ft. deep and 100 ft. long, with a fall of about 3 ins. All of the water discharged passes through this flume and was carefully measured every week by myself or assistants for 1 year after the tunnel was completed. Since then the flow has been measured at irregular intervals and not oftener than once a month.
A Lallie electric current meter is used and the average of 6 readings of 100 sees, each is taken to obtain the correct velocity of current. This velocity multiplied by the area of water section gives the flow in cu. ft. per sec.
* * * * * *
The total flow from the El Paso tunnel from the time of its completion (September, 1903) to the end of the year 1905 cannot be given with reasonable accuracy, and the flow for the years 1906 and 1907 can be estimated fairly close. The total discharge up to the end of the year 1905 amounts to 5,675,000,000 gals.
The total discharge for the years 1906 and 1907 I estimate to be 2,486,000,000 gals., or a total to the present time of 8,161,000,000 gals. This is equivalent to approximately 25,000 area ft., i. e., an area of 25,000 acres covered to a depth of 1 ft. The area of eruptive rock is roughly 9.6 sq. miles, or 6,150 acres.
This amount of water would cover the area to a depth of 4 ft. Assuming but one-half of eruptive area to be drained, it would be 8 ft. deep, in which case the water would amount to 5% of cubic contents of rock drained. This enormous quantity of water would weigh 33,864,000 tons. A very interesting question is, what would it have cost to pump it?
The average height to which it would have been raised, by the mines doing the pumping, could not be much less than 600 ft. The actual pumping costs in the Cripple Creek district are difficult to ascertain. I think none of the mines has kept exact records of the cost of pumping. The same battery of boilers has usually furnished steam for hoisting and other purposes, as well as for pumping. Fuel is the chief item, and that has probably cost the same at all the mines, about $6 per ton.
* * * * * *
I have concluded, from information given, that the cost is not less than $125 per 1,000,000 gals. To put it in a more familiar form, the cost of pumping 1,000 gals, per min. a height of 600 ft. would, at this rate, amount to $5,500 per mo. The average cost at the Leadville joint pumping shaft is $100 per 1,000,000 gals, raised 700 ft. under most favorable conditions.
The total cost of pumping is not directly proportional to the height lifted or the quantity pumped. That is, it does not cost twice as much to lift 1,000 gals. 1,000 ft. as to lift it 500 ft. All the items of cost except fuel would be practically the same in both cases. Probably fuel costs only would be directly proportional, or nearly so, to the height lifted or the quantity pumped.
But, assuming the average cost of lifting 1,000,000 gals. 600 ft. in the Cripple Creek district to be $125, then the El Paso tunnel has earned to date fully $1,000,000, and it is still at work'. And it works every minute of the day and every day of the year. There is no expense connected with it and no flooding of levels on account of labor strikes or accidents to machinery.
This tunnel has lowered the general water level of the district, as shown by the subsidence of water at the Elkton shaft, a total of 160 ft. Perhaps the average reduction would not be so much. I have prepared a diagram showing the relation between discharge of water from the tunnel and falling of water at Elkton and Mary McKinney shafts. The line showing fall of water at Elkton is complete and correct, as the elevation of the water level there has been carefully taken at least once a month since the tunnel was completed. The Referenced Diagram was not included in the source text.
Assuming that the subsidence of water at the Elkton shaft is a fair average of the fall over that portion of the district affected by the tunnel, then it has required the discharge of an average of 51,00,000 gals, to lower the general water level 1 ft. vertical; and this does not include what may have been pumped during the same time.
But from July 1, 1906, until the end of 1907 the fall of water at the Elkton was only 10 ft., although the tunnel continued to discharge steadily about 2,000 gals, per min. From which I infer that a large part of the flow (the 2,000 gals.), perhaps one-half of it, is that portion of the surface precipitation which finds its way to the ground water level.
The water in the Elkton shaft is stationary at about 40 ft. above the elevation of the easterly end of the El Paso tunnel, showing that it requires about that much head, or pressure, to force it through the mile or more of intervening rock.
If we are to judge by the flow from El Paso tunnel and fall of water at the Elkton shaft, then the total amount of water per foot vertical is increasing rather than decreasing with depth. During the last three months of 1903 the discharge per foot lowered was 22,500,000 gals.; for the year 1904 it was 40,063,000 gals., and for the year 1905 it was 57,000,000 gals.
Mr. Mudd, in his report made in 1902, estimated that to lower the water in the district 300 ft. vertically below the original water level required an average discharge of nearly 67,000,000 gals, for each foot. Assuming his estimate to be correct, the amount of water per foot vertical is decreasing with depth.
There is undoubtedly a constant addition to the ground water, or storage water, from the surface. How much it amounts to it is impossible to state. The fact that for nearly 6 mos. from October, 1906, to March, 1907, the tunnel continuously discharged nearly 2,000 gals, per min. without appreciably lowering the water in the Elkton shaft would seem to indicate that 2,000 gals, per min. is about that addition.
A rough calculation shows that this would require nearly, if not quite, one-third the average annual precipitation over a large part of the district. It is hardly possible to believe that so large a proportion as that finds it ways to the ground water level, and I am inclined to think that there is some underground flow coming into the northern or northeasterly part of the district from the direction of Gillett or Pike's Peak.
There is a large area in that direction of a higher average level than the district, that has been largely fissured and carries numerous dikes. It is not unlikely that some of these dikes are connected with the main volcanic neck of the mineral-bearing area.
Referring again to the estimate of the number of gallons discharged per vertical foot during the years 1904 and 1905 it will be seen that this constant flow of 2,000 gals, per min. is a much larger proportion of the total flow during the year 1905 than 1904. For that reason it may be that the total amount of storage water only per vertical foot is not increasing with depth.
After the El Paso tunnel was completed in the early part of the year 1904 very little pumping was done in the district (except by the El Paso Co. from below the tunnel level) until May of 1907. At that time the Granite M. Co. began pumping and bailing from below the 9th level of their Gold Coin shaft at the rate of about 1,200 gals, per min.
In about 2 mos. they had beaten the water down to their 12th level, 300 ft. deeper, and were holding it there by pumping 750 gals, per min. Before beginning to pump, the water in the Gold Coin shaft had been standing for some time at an elevation of about 8,873 ft., or 10 ft. above the level of the water at the Elkton shaft.
Within a few days after pumping had begun at the Gold Coin shaft a fall in water at the Elkton was perceptible, and by the time the Gold Coin 12th level was recovered it had fallen 4 ft. Prior to that time it had not fallen perceptibly for several months.
During this same period of pumping at the Gold Coin shaft the water in the Strong mine subsided 16 ft. and at the Portland 35 ft. There is no connection of the Gold Coin drifts below the water level with the workings of other mines and the shaft is located in the granite several hundred feet from the eruptive contact.
I mention this to show that there is certainly a connection of the water courses of Battle mountain with those of the Elkton, even at the great depths now reached.
The El Paso tunnel was the first in the district driven solely for drainage purposes, and in that respect it has been an entire success. It was considered by many in the light of an experiment. It has fully demonstrated that a tunnel driven through the granite rim of the southwestern side of the district to the phonolite plug of Beacon hill will effectively drain the larger part of the producing area.
In that respect it has corroborated the evidence furnished by the Ophelia tunnel in 1896 and the Standard tunnel in 1898. It should have been driven to a greater depth, but there was doubt in the minds of some as to the results, and others had nearly exhausted their ore reserves above the water level and wanted relief at the earliest possible moment.
And now we come to the Gatch Park tunnel, under construction.
The Cripple Creek Deep Drainage Tunnel.
The Gatch Park Tunnel.
In the early part of the year 1904, and shortly after the completion of the El Paso tunnel, I became convinced that within a few years a deeper tunnel would be required, and that as several years might be needed to drive it, it should be started as soon as possible. A careful study of the topographical maps prepared by the government Geological Survey, and some personal knowledge of the country, very soon decided that the best sites for tunnels of any length would be along the Cripple Creek canon, in a southwesterly direction from Beacon hill and the El Paso shaft.
I made some careful preliminary surveys, running random lines and levels along the bottom of the canon for a distance of fully 6 miles from the El Paso shaft. I then prepared plans and sections for 3 different tunnels and presented them to the drainage tunnel committee, of which Mr. Sherwood Aldrich was then chairman.
These three proposed tunnels were designated by me as No. 1, No. 2 and No. 3, but were afterwards called the "Cape Horn," "Gatch Park" and "Window Rock" tunnels. To compare them with each other and with the El Paso tunnel I will give the principal details:
The elevation of the collar of the El Paso main shaft is 9,365 ft.
|Name of Tunnel.
El Paso Tunnel.
El Paso Shaft.
El Paso Shaft.
|Distance to Main
|Estimated Cost Per
Vertical Ft. Drained.
|$ 409 (Actual cost)
|Roosevelt Park (Gatch Park)
These three tunnel sites, as well as the El Paso and Standard tunnels, arewere shown upon the maps and section exhibitednot included with the source articles. All are projected on Gatch Park section. This will give a clearer idea of their relative positions, lengths and depths.
A careful comparison of these plans and estimates discloses a great advantage in favor of the Window Rock scheme. It is only 2,650 ft. longer than the Gatch Park site, but gains 353 ft. greater depth. The grade of the Cripple Creek canon increases considerably from near the portal of the Gatch Park site to fully one-half mile below the Window Rock site.
Hence, the Window Rock site gives more depth per linear foot of tunnel than either of the other two above. This advantage is also shown by the estimated cost per vertical foot of depth drained, which is $468 in the Window Rock site as compared with $581 in the Gatch Park site.
The tunnel committee, and mine owners interested, discussed the subject frequently, but no decision was made or action taken for more than a year, when in the summer of 1905 Mr. D. W. Brunton, the eminent mining engineer of Denver and expert in tunnel matters, was engaged to examine the situation. Mr. Brunton made a thorough investigation and study of the question and an exhaustive report to the mine owners.
He strongly recommended drainage by means of a deep tunnel and also strongly favored the Window Rock site. His principal reasons were that while the Window Rock tunnel was of reasonable length it gained sufficient depth to forever preclude the necessity of another tunnel. Also, its great advantage in the matter of cost per vertical foot drained.
In this connection I wish to state that very few important mining districts are so favorably located for drainage by a single tunnel as is Cripple Creek, and this is true from a geological as well as topographical view.
In comparison with the Leadville district Cripple Creek is highly favored in this respect. In the year 1891 I was employed by Leadville mining men upon surveys for a tunnel to drain the Carbonate hill mines and what were known as the down-town mines. Careful investigations showed that the best and about the only practicable site for the portal was at Malta, about 3 miles west of the city of Leadville.
A tunnel driven straight from that point towards the Maid of Erin shaft on Carbonate hill (and at that time the nearest deep shaft) would have been over 3½ miles long and gained less than 800 ft. depth. As compared with this the Window Rock tunnel, of practically the same length, gains 1,653 ft. depth at the El Paso shaft, or over twice as much.
The Leadville tunnel was not driven, owing largely to the decline in the price of silver at about that time, but it would undoubtedly have saved many times its cost in pumping. What are known as the down-town mines (the Bohn, Sixth Street, Coronado, Penrose and others) have since been almost constantly struggling with heavy flows of water and have spent millions of dollars in the aggregate to drain their ground.
After accepting Mr. Brunton's report no decisive action was taken by the Cripple Creek mine owners for over 1.5 years. I am not fully informed of the cause or causes of the delay. Nearly all realized that a tunnel must be driven if they were to continue mining at depth, or else additional and costly pumping machinery installed at nearly all mines, with constant heavy expense for running.
Probably the chief causes of delay were a failure to agree upon the proportion of cost to be borne by the several mines and the tunnel site to be adopted. Many insisted upon the Window Rock tunnel site, and others, who desired as speedy relief as possible from water, favored the Gatch Park tunnel.
Finally, in March, 1907, the Cripple Creek Drainage & Tunnel Co. was organized and the Gatch Park tunnel site selected for operations. I was engaged by the tunnel company to make final surveys of the line from the portal to the EI Paso shaft, and bids were invited for its construction. At that time $378,500 had been subscribed by the leading mining companies.
Buildings were erected; power, compressors and other machinery were installed, and active work begun about June 1, 1907. Probably no more important enterprise has been inaugurated in the Cripple Creek district since the construction of the Short Line Railway.
In some respects it is far more important than that. The tunnel line, as finally located, runs from the portal N. 44° 20' E. to a point 65 ft. easterly from the S. E. corner of the El Paso main shaft. Its total length to that point is 14,484.5 ft.
From that point it turns to the east, running about N. 70° 30' E. directly towards the Vindicator No. 1 shaft, a distance of approximately 12,650 ft. more, passing about 50 ft. south of the Elkton main shaft, 600 ft. south of the Moose shaft, 850 ft. south of the Blue Bird shaft and 200 ft. north of the Last Dollar shaft. The total length from the portal to the Vindicator shaft is 27,134 ft., or 5.14 miles.
The grade adopted is 0.3 ft. per 100 ft., or about 1 in 333. This gives a total rise from the portal to the El Paso shaft of 43.5 ft. The elevation of grade at portal is 8,033.8 ft., making its depth below the surface at the El Paso shaft 1,288 ft., at the Elkton shaft 1,640 ft. and at the Vindicator shaft 2,100 ft.
It is expected to lower the present water level about 730 ft. The granite-phonolite contact and the so-called Black Bell water courses should be cut about 1,000 ft. easterly from the El Paso shaft, if we may judge by the tunnels driven above. At 8,000 ft. from the portal an intermediate shaft is being sunk which will be 680 ft. deep to the tunnel level.
The power for carrying on the work at the portal heading is furnished by the Gold Belt Cons. Electric Co. of Cripple Creek by wires carried from the Cripple Creek stations, and is paid for on meter measurements at the rate of about 1½ cents per kw. hour. A kilowatt is estimated at 1.33 h. p. The total cost for power at the portal heading for the 8 months ending Jan. 31 has been $3,520, or an average of $2.45 per foot driven.
This includes the power necessary for operating the fan or blower and air motor as well as the compressor. At the intermediate shaft, now sunk to a depth of 90 ft., the power for hoisting is furnished by steam, and for the compressors by electricity. I have no data regarding cost of power at this shaft.
Little progress has been made there for the reason that we were compelled to wait nearly 3 months for the required machinery. Since Dec. 16 nothing has been done at the shaft, waiting for a new contract to be let.
The rock in which the tunnel is being driven is designated as Pike's Peak granite by government geologists. It is a reddish, coarse-grained rock, usually deficient in the dark-colored constituents, and much of it rather poor in quartz. It frequently has a schistose or gneissic structure. It is one of the oldest rocks of the region and almost entirely surrounds the eruptive area.
There are no indications upon the surface along the tunnel line or in the bed of the Cripple Creek canon, immediately west of the center line, that the tunnel will pass through anything but the Pike's Peak granite. The summit of Grouse mountain, just to the east, is covered with a phonolite overflow, but probably no dikes or branches from this rock extend across the line of the tunnel; at least none are found at the surface.
This granite has so far proven very hard to drill and exceedingly difficult to break. There are very few seams or joint planes in the rock, or, as a miner would put it, "There is nothing to break to."
It is to be hoped that in places it will have a more sheeted, "blocky" structure, so that it can be more easily broken.
The total progress made to Feb. 1 amounts to 1,438 ft., or an average of about 180 ft. per month for the time since work actually began. As there have been several short but unavoidable delays, due to change of contractors, etc., the average progress may be put down at about 200 ft. per month.
The section of the tunnel is 7 ft. wide by 10 ft. high in the clear. It has been designed for use as a transportation as well as drainage tunnel, the intention being to lay a double track resting upon stulls and giving a clear space of 2 ft. the entire width of the tunnel for a waterway. This should be ample to accommodate any flow of water than can possibly be encountered.
It is not expected that any water courses will be cut until the El Paso shaft is reached, and possibly not until the phonolite contact beyond is cut. There are no springs showing in the Cripple Creek canon either above or below the tunnel site, and no water was opened in any of the tunnels above until the granite rim was penetrated.
I have prepared sections of the tunnel showing the usual methods of drilling the holes and breaking the ground. The chief obstacle to progress so far has been the difficulty of breaking the center or cut holes. In many cases it has been found necessary to load and shoot them a second time, or even a third time.
Holes are usually drilled to a depth of 5 ft. from the face and from 300 lbs. to 350 lbs. of 60% powder are used at each round. Ventilation is effected by means of a 16-in. pipe carried along the righthand side of the tunnel, about 6 ft. above the floor and to within 100 ft. to 150 ft. of the face.
A force blower at the portal sucks the smoke out very rapidly after each blast, so that it is possible to go to the breast in 15 min. or 20 min. after each round is fired.
→ A new contract has just been let for driving the tunnel, and the section is to be changed to one of 10 ft. wide by 7 ft. high in the clear.
At one side a water channel will be cut in the floor 6 ft. wide by 3 ft. deep, and one of the tracks carried over it by ties extending across the full width of the tunnel. Personally, I am in favor of driving a tunnel for drainage purposes only, and making it of as small a section as is consistent with the most rapid progress.
We do not know that the tunnel will ever be needed for transportation purposes. There are no mills or railroads at the portal of this tunnel or below it, and none are ever likely to be constructed in that locality. Three to five miles is a long distance to tram waste or ore, either.
It can be hoisted from depths as great as 2,000 ft. more cheaply than it can be hauled to the portal. If it is found later on that transportation is desirable, the tunnel can be quickly enlarged to provide for it and, probably, at little greater cost. But there is no uncertainty about the drainage feature.
We do know that we want drainage, and want it as speedily as possible. Some of the mines in the district will exhaust their ore reserves above the present water level before the tunnel can be completed. They must then either cease mining or install expensive pumping plants on their lower levels.
When it becomes possible to mine for 200 ft. or 300 ft. below the present bottom levels they will then feel much better able to enlarge the tunnel. If it appears desirable to do so.
How long will it take to complete this tunnel, and what will it cost?
It now appears probable that it will take much longer to drive this tunnel than was anticipated. Mr. Brunton's estimate of the length of time required was 2.1 years to reach the El Paso shaft. He based this estimate on the assumption that the intermediate shaft could be sunk at the rate of 3½ ft. per day, and the portal and shaft headings could be driven 10 ft. per day.
It now seems practically impossible to make such progress in the kind of rock so far encountered. Probably 90 ft. per month in the shaft and 250 ft. per month in the portal heading is as good as can be expected. Assuming such a rate of progress to be made beginning with March 1, 1908, I estimate that it will require from 36 mos. to 42 mos. to reach the El Paso shaft.
The cost, also, is very likely to exceed the original estimates by fully 20%. But even should it cost 100% more than the original estimate, the mine owners cannot afford to abandon it, for it will in the end save many times its cost in pumping alone. Its saving in pumping costs is not the only advantage.
It will save largely in other mining costs, and particularly labor. Experienced mine managers will tell you that men will not do nearly as much work in wet ground as in dry. They are continually hampered by heavy rubber garments and boots, and have other disadvantages.
Some managers have estimated that it costs 33% more to mine in wet ground. The ore in dry ground is mined and marketed in much better condition. There is no loss in "fines" washed away by the water and largely pumped to surface.
Our richest ores are sylvanite bearing quartz and fluorite. The sylvanite occurs in slender prismatic crystals that are very brittle and easily pulverized by the blasting of enclosing rock. The specific gravity is not so great but that a considerable portion of the finest part may be washed away by flowing water, carried to the sump, pumped to the surface and lost.
Samples of the "fines" taken from the bottom of the sump in pump station on the 800-ft. level of the El Paso mine, showed values of $160 per ton. And this sump was about 600 ft. from the ore shoot.
Its Influence on the Future of the Cripple Creek Mining District.
The completion of this tunnel will mark the beginning of another era of activity and prosperity for the Cripple Creek district. Perhaps it will not create another mining stock boom. I hope not. But there will be a greater production, more real prosperity, than at any time since the days of 1900 and 1901.
It is somewhat hazardous to predict the future of any mining district. To use a common expression, "No one can see into the ground," but I feel decidedly optimistic about the future of Cripple Creek and the developments below the present water level after this tunnel is completed.
I hardly think that the maximum production of $18,000,000 of 1900 will ever again be reached, but I do believe that the present production of perhaps $10,000,000 to $12,000,000, per year can be maintained for several years, and that will be sufficient to enable Cripple Creek to retain its rank of the leading gold mining district of this country.
It is quite possible that the total annual production will decline somewhat before the tunnel is completed. While ore bodies now opened will be largely worked out to water level during the next three years, new ore bodies will undoubtedly be opened from time to time, and the total production thus maintained.
As an illustration of the possibilities in the way of discovery of new ore bodies above water level, I will mention the "Little Clara" ore shoot, belonging to the Work Mining Co. This ore shoot was discovered about two years ago and has since produced about $1,500,000. The ground was supposed to be reasonably well developed by workings done years before.
A shaft had been sunk directly over the ore body to a depth of 135 ft., and a drift near the bottom driven to within 25 ft. of the top of shoot. The Callie shaft had been sunk to the depth of 480 ft, missing the westerly edge of the ore shoot only 30 ft. to 40 ft., and the Ophelia tunnel was driven directly under it and about 40 ft. below.
But the vital question is, will our principal fissures and larger ore shoots continue to greater depths?
There is no doubt but that there is a decrease in the number of fissures and ore shoots, for the reason that many of them have united. But the decrease is probably not so great as seems apparent at first. The lower levels have not been so thoroughly developed as those near the surface, the prospecting at depth being usually confined to the vicinity of the large ore shoots which have been followed from the surface or upper levels.
Our main fissures, though usually narrow, are persistent and well-defined, and will continue to much greater depths than have yet been reached. The ore shoots are all intimately connected with the fissures and dikes, many of them having been followed from the surface to the deepest levels and are there as large and rich as at any point above.
The laws governing the deposition of ores and minerals in fissures are not well known, the general theory being that hot alkaline waters and vapors circulating through the deep-seated rocks' dissolve the more readily soluble constituents. These solutions or vapors ascend through the porous volcanic rocks along fissures and lines of least resistance. At certain places chemical reactions take place and the mineral contents of the solutions will be precipitated, that is, deposited in a solid form upon the walls of the fissure.
The causes of the chemical reactions are usually a reduction in heat and pressure or a change in the nature of the rock forming the walls of the fissure, or a retardation of some kind, of the circulation. We are probably unable to reproduce artificially the physical and chemical conditions which cause such reactions.
It is supposed that the ores of the Cripple Creek district were formed later than the latest actual eruptions and later than the basic dikes, which were the latest dikes formed.
This is proven by the fact that there is very little faulting and very few faults in the ore-bearing fissures. The ores were deposited in the fissures of a volcanic mountain of a much greater height than the present highest points in the district. It is estimated that the erosion has been from 1,000 feet near the center of this volcanic cone to 500 feet at its base.
If this be true, then many of our present ore shoots are over 2,000 feet below the original surface, or the surface in existence at the time of ore deposition. It would certainly have been a much better mining camp some thousands of years ago than now. But the fact that ore shoots are still large and well-defined at depths of 1,500 ft. and at depths of 2,000 ft. below the surface, that existed when they were originally deposited, would make it reasonable to suppose that they will continue for a few hundred feet deeper.
Probably the best indications as to what will be found at the depth of the Gatch Park tunnel are the ore shoots now actually developed in the lowest levels of our deepest shafts. This evidence is decidedly encouraging. I have questioned the mine managers of our principal mines regarding these developments and have personal knowledge of some of them.
At the El Paso mine on the 800-ft. level, which is 200 ft. below the present water level, the ore shoot was large, the fissure well-defined, and the richest ore ever mined in that property was shipped. On the 1,000-ft. level, at an elevation of 8,360 ft., over 400 ft. below the present water level, the veins were still well-defined and the ore as good as above.
This level is at the lowest actual elevation at which ore has been mined in the district.
On the ninth level of the Elkton mine, just below the water level, the developments are limited, but they show, as far as they go, that the ore shoots are fully as large and the grade of ore higher than on the eighth level, 100 ft. above. The ninth level was opened up and worked for a few months in the summer of 1905, the general water level at that time being 65 ft. higher.
It required the pumping of 850 gals, per min. to hold the water at the ninth level, and the quantity increased as drifts were extended upon the vein.
The ore shoots opened on the lower levels of the Mary McKinney mine are said to be as large and productive as upon any of the levels above.
On the 1,100-ft. level of the Gold Coin shaft, belonging to the Granite Mining Co., high-grade ore is known to exist. This level is now about 160 ft. below general water level, and 100 ft. below the water at the tenth level, where about 750 gals, are being pumped.
The Strong mine, on its tenth level (elevation about 8,800 ft.) and where there is now being pumped 1,000 gals, per min., has as good ore and as large ore shoots as upon any levels above. The Gold Coin and Strong shafts are sunk in the granite several hundred feet from the contact.
At the Portland property, on the 1,300-ft. level of the No. 1 shaft, developments have been in progress but a short time, but the developments so far are decidedly favorable. One ore shoot has been opened for a length of about 775 ft., and no doubt many others will be found. While this ore shoot is somewhat narrower than above, the grade of ore is said to be much higher.
This ore on the 1,300-ft. level is fully 1,500 ft. below the surface, directly over it. Pumping is going on at the rate of 600 gals, per minute from this level, which is probably 60 ft. below the general water level in that end of the district.
When the Portland Co. ceased pumping in December, 1902, the water rose to 12 ft. above the eleventh level; when they resumed sinking from the twelfth to the thirteenth level, water was again encountered at 30 ft. below the twelfth level, showing that it had subsided about 142 feet in something over 5 yrs.
This I consider largely due to the heavy flow from the El Paso tunnel during the same period. Very little pumping was done during this period.
At the Golden Cycle mine, on the 1,200-ft. level, the developments so far show that the ore shoots are fully as large, and the grade of ore better, than in most of the levels above. Pumping at the rate of 100 gals, to 200 gals, per min. is going on.
At the 1,200-ft. level of the Vindicator mine, developments so far prove that the ore is just as good and the ore shoots as large as upon any levels above. They are pumping 200 gals, per min. from this level.
At the Findley mine, on the fourteenth and fifteenth levels, the ore bodies are fully as large and upon the whole of as good an average grade as any above.
The Isabella mine has recently opened probably the largest ore shoots ever found in that property on its ninth, tenth and eleventh levels, and the average grade of ore, with possibly one exception, is as high as in any other shoot it has ever had.
This information is obtained directly from the mine managers and superintendents, and I have no reason to doubt it. With such showings on our deepest levels, are we not justified in spending $500,000, or more, if necessary, in constructing a tunnel to drain this valuable territory to a depth of 730 ft. below the present water level.
What will such a tunnel add to the life of the camp? I think that in most of the large properties it takes from one to two years to thoroughly develop and mine the ore from one level to the next, or from 100 ft. vertical of ground. At the Elkton mine, since 1896, it has required on an average nearly two years' mining to each 100 ft. depth.
Probably, if they had not been troubled with water, less time would have been required. About the same time (2 yrs.) has been required at the El Paso and Mary McKinney properties. While many other properties have reached depths of 1,200 ft. or more in 12 yrs. to 15 yrs., that does not mean that they have exhausted their ores at the rate of 100 ft. vertical per annum.
Probably 1½ yrs. time for each 100 ft. of depth would be a fair average, and upon that basis, the tunnel now under construction will add fully ten years to the life of Cripple Creek, assuming that mining is carried on no deeper. But it seems probable that there will be somewhat less storage water at that depth, so that mining operations can be carried on to greater depths by pumping to the tunnel level.
The necessary lift will be much less than at present, and if large quantities of water are still encountered, probably a central pumping station, supported by all the deep mines, can be established to handle the water at minimum cost. It seems very unlikely that any deeper tunnel will ever be constructed.
This tunnel, in its course from the El Paso to the Vindicator mine, will intersect many of the principal veins, dikes and water-courses of the district at great depth and to that extent will be valuable, and worth all it costs in the way of prospecting only. When connected with the various deep shafts near the line of tunnel, it should also prove of great value in the way of ventilation.
This tunnel will benefit all properties in the district directly or indirectly, and all should be willing to contribute something to its construction, even though their deepest workings are still well above the present water level. There are very few properties of importance, whose ground has not been drained either by the pumping of their neighbors or by some of the tunnels heretofore constructed.
The Cripple Creek district is a vast storage reservoir which has now been drained by tunnels and pumping to an elevation of about 8,820 ft., or nearly 700 ft. below the average original water level.
The total amount of storage water per vertical foot at the present level is not less than 50,000,000 gals., and there is as yet no positive evidence of a decrease.
There is a constant addition to this storage water from meteoric waters of probably 1,000 gals, per min. There are more or less perfect connections of the main underground water-courses over a large part of the district, and for all practical purposes a common water level exists.
The cost of pumping this water at a joint pumping station, and under the most favorable conditions, would be not less than $100 per 1,000,000 galls., or $5,000 per vertical ft., or $3,700,000 to the level of the tunnel under construction.
To hold the water at that level when reached would require the continuous pumping of 1,000 gals, to 2,000 gals per min., lifted a height of 730 ft., to the lowest possible outlet.
The cost of draining the same ground by a deep tunnel will not be in excess of one-fifth of the cost by pumping. Tunnel drainage has other advantages in addition to saving in pumping expense.
The developments in our deepest levels are such as to justify the expectation that valuable ore shoots will extend to the depth of the tunnel level or deeper.