Interior of Tunnel

As the advent of the Roosevelt drainage tunnel into the great water pocket of Cripple Creek, the breccia-filled volcano, is the great event of the year in the Colorado mining field, it will be of interest to recall the leading features of the drainage system of Cripple Creek as described by Messrs. Lindgren and Ransome of the U. S. Geological Survey, who were aided in their investigations by special reports of Messrs. Victor G. Hills, Charles J. Moore and S. W. Mudd and were indebted for many facts pertaining to the water history of the mines and tunnels to Mr. S. Aldred and Messrs. Countryman and Jacquith, the two last gentlemen at that time being engineers of the El Paso drainage tunnel.

Original Water Surface.

The annual precipitation in the district is moderate, the average being about 16 in. annually. The ground surface water is not usually deep, deep shafts in the main volcanic neck encountering water at moderate depths.

The Blue Bell tunnel began to drain the district at a very early stage in mining development. It was running a copious stream of 200 gals, a minute when all other mines were practically dry. The higher water levels, owing to the gradual slope and drainage westward of the district, are eastward, averaging 9,000 ft. above the sea.

As shafts were deepened ground water seriously interfered with mining and mines began pumping in 1895. The burden of draining the district devolved upon a few of the deeper and wetter mines. Attention was consequently turned to tunnel drainage.

Earlier Drainage Tunnels.

The Ophelia tunnel enters the granite at the west base of Gold hill at an elevation of 9,268 ft. In December, 1896, it was 2,600 ft. long, discharging 2,000 gallons per minute. This water came from the breccia or from open fissure zones connected with the main volcanic nest. The tunnel flowed for a year, becoming dry in 1898, when the Standard tunnel began to drain the district.

The Standard tunnel began 1896 in granite. It aimed at the phonolite plug of Beacon hill. In February, 1896, it cut the El Paso vein, whence issued 250 gallons per minute, and when the phonolite was reached it increased to 1,000 gallons and by greater penetration attained to 18,000 gallons.

Work was abandoned June, 1899, at 2,800 ft. length. By the end of 1901 the tunnel was dry, having lowered the water levels in Beacon, Gold and Raven hills mines.

The NewettNewell tunnel in Grouse hill has not reached the phonolite or volcanic neck or encountered any important flow.

The El Paso tunnel (the lowest except the present Roosevelt) is in Arequa gulch, a mile S. W. of the El Paso shaft with which it connected September 6, 1903. The El Paso slowly lowered the water in the Mary McKinney and Elkton, showing a connection through open fissures between the Beacon hill phonolite and the main volcanic neck.

Nature of the Great Water Pocket.

The drainage records show that the volcanic neck filled with porous breccia and eruptive rocks contains a body of water prevented from escaping into the streams of the region by its impervious surroundings of granite rock. The tunnels are dry till they penetrate the volcanic breccia or cut open fissures extending into it.

The underground water of the central part of the Cripple Creek district is to be regarded as an underground body of water bounded by the steep walls of the old volcanic crater. (Rock known as more abundant than water and instead of a lake the water is rather contained as in a sponge in a glass cup.)

This water is not volcanic water ascending from great depths, but supplied by rain and snow falling on the surface of the district. The underground water of the region may be regarded as occupying a number of separate basins.

The water does not flow with equal freedom in all directions and through all rocks of the volcanic neck.

Sections of Cripple Creek Volcano Showing Porous Water-Bearing Breccia. Adapted From U.S. Geo. Survey

Water Records in the History of the Mines.

An account of the behavior of the water in some of the principal mines will show its general character.

• In July, 1903, water in the Portland showed 557 ft. above the pumping level of the adjoining Stratton's Independence.
• In 1904 the Portland fell only 26 ft., though pumping had been continuous in the neighboring mine, and the El Paso tunnel had been draining the district for several months.
• In August, 1903, Portland water fell 2 to 3 in. per week.
• In April, 1904, Elkton water was 15 ft. lower than Portland, whereas, in July, 1903, 17 ft. higher.
• In July, 1889, the Portland was pumping 1,500 gallons per minute from the 800-ft. level, while the Elkton 40 ft. deeper, was dry.
• The Eclipse, between the Portland and Elkton, had on April 19, 1904;
• a water level 491 ft. above that of the Portland
• 520 above that of the Ajax
• and 506 ft. above that of the Elkton. This is the most remarkable case of difference of water level in the district.
• The Elkton mine shows that the water circulates mainly through open fissures and not through the general mass of the country rock and is confined to these fissures.

The existing drainage tunnels (prior to the Roosevelt) have tapped the breccia volcanic neck from the west or southwest, and have shown their effects principally in the West Side group of mines. The Ophelia tunnel, down far into the breccia and through several open fissures, drained the mines of Raven and Gold hills to its level.

The Standard tunnel, aimed at the phonolite plug of Beacon hill, found water derived from its connection by open fissures with the main volcanic neck. It lowered the water of the West Side mines, including those of Gold hill and Poverty gulch.

Although the East Side group of mines, such as American Eagle, Logan, Blue Bird and Last Dollar, are among the deepest in the district, their shafts have had little trouble with underground water. Water that was encountered in some of them soon receded with depth, due perhaps, to this part of Bull hill being drained by mines and tunnels to the west.

Some of the deepest shafts have always been dry.

The behavior of the water in five of the mines of this East Side group shows them to have a common water basin, an artificial change in the water level of any one mine being followed by adjustment in the others.

The absence of notable east, west or northeast-south-west fissures in this zone explains the failure of existing tunnels to drain the mines near the eastern side of the volcanic neck.

On March 27, 1906, the El Paso mine, opened to the 1,000-ft. level or 400 ft. below the drainage tunnel, was flooded. On breaking through the El Paso phonolite dike the miners encountered an unexpected flow of water estimated at from 5,000 to 7,000 gallons per minute, which drowned the pumps and in six hours filled the mine to the 600-ft. level.

This event shows that the fissuring along the C. K. & N. vein constitutes an open and effective watering to a depth of 400 ft. below the present drainage tunnel.

Ideal Section Showing Drainage Tunnel Entering Crater

Geological Conditions.

The drainage of Cripple Creek is not scattered in underground streams through the district, but is centered in the breccia filling the volcanic crater of the Cripple Creek volcano, which has been likened by Ransome and Lindgren to a cup filled with a water-soaked sponge.

The center of the Cripple Creek district is occupied by an eroded volcanic neck appearing on the surface in plan like the relics of volcanic necks described by Geikle in the south of Scotland.

The Cripple Creek area was a granitic plateau, not differing much from what appears there today. This, by repeated and tremendous eruptions, was split by a great chasm.

The granite above the volcanic hearth was shattered and fragments of it blown into the air, falling back in a more or less comminuted condition into the pit and over the surface. Eruptions of phonolite, latite phonolite and syenite followed. Successive paroxysms shattered and comminuted the products of earlier outbursts. The breccia of the volcanic throat shows a great intermingling of different rock fragments indicating that the chasm, after being filled with breccia and pierced by intrusions, was more than once cleared and refilled.

A cone was built up around the orifice composed of the fragments.

The descending walls of the crater, as well as the contents of the pit, are well shown in many of the mines.

In the Portland mine at Victor the contact between the breccia and the granite walls shows an irregular surface of granite plunging deeply under the breccia in a N. and E. direction dipping from 70 degrees to vertically and sometimes overhanging the pit. The granite here forms a promontory jutting into the breccia filled funnel.

The Granite, Dead Pine and Stratton's Independence are ranged along this contact.

The Golden Cycle shaft, 1,000 ft. deep, is wholly in breccia.

In the Midget mine and GoodwellGoodwill tunnel the contact between granite and breccia is vertical and the gneiss is shattered at the contact.

The breccia of the northwest slope of Gold hill occupies a pit produced by explosive volcanic activity. The pit here is a marginal embayment of the central volcanic abyss.

Its floor pitches steeply south attaining a depth from the surface of 1,500 to 3,000 ft. These embayments, characteristic of the crater, are due to the tendency of the volcanic forces to find relief in a lateral as well as an upward direction as they neared the surface.

In the Ophelia tunnel the dip of the granite wall is from 70 to 80 degrees. At Anaconda and Mary McKinney it is vertical.

In the Elkton there is a local granite promontory jutting northeast into the breccia overhanging the crater. Later faulting movements occur near the original contact due to subsequent movements (perhaps to a subsidence and collapse of the filling of the crater after the intrusion of matter ceased).

In the Isabella mine granite appears on the 800-ft. level at contact sloping 45 degrees.

From these observations made by Messrs. Lindgren and Ransome it is evident that the breccia mass extending from Goldfield to Carbonate hill and from Guyot hill to Cameron occupies the throat of a volcano. The same is true between Gold hill and Goldfield, Victor and Altman. The breccia of Gold hill may fill a separate vent; also those in the outlying district about Mts. Rhyolite, Pisgah and Mineral hill the Fluorine mine and Copper mountain.

The volcanic breccia filling the crater is a structureless unstratified agglomerate of fragments of all the volcanic and igneous rocks found in the region, including the granite.

Deep down in the breccia in the Jackpot, Morning Glory, Independence and Elkton mines remains of silicified and carbonized trees have been found, relics of those that originally grew on the granite plateau and were entombed in and buried in the volcanic eruption.

Flow of Water Making a Waterfall
at the Roosevelt Drainage Tunnel Portal Site

The tunnels, including the great drainage tunnel, are dry as long as they are in the granite, but while they penetrate the breccia or cut open fissures extending into it, there is apt to come a sudden rush of water down the adjacent water level.

The central water zone may be said to be restricted to the breccia filled crater confined and bounded by steep rock wells. Some have supposed that in the center of the crater is an underground lake, but it is more probable that the water is absorbed and held under great hydrostratic pressure within the sponge-like breccia mass.

This water-absorbing breccia has been aptly compared to a sponge in a glass cup.

The water may be conceived to be not unlike that of artesian water when struck by a well. This artesian water does not exist as an underground lake, but rather as a zone of water soaked, porous rock under tremendous pressure.

This pressure, when released by a bore, causes the water in the porous rock to rush upwards in the form of a spray or fountain. The same, we believe, will be the case when the breccia is exploited by the arrival of the drainage tunnel.

The granite traversed has so far proven dry. No mineral veins or mineralized dikes have, we understand, been cut or encountered by the tunnel, despite its great depth, probably because the majority of it runs parallel with the strike of these rather than cuts across their course.

We will look forward with great interest to future developments. The accompanying sections, adapted from those of the United States Geological Survey, will show clearly the relation of the granite cut by the tunnel to the water zone in the breccia filling the crater of the Cripple Creek volcano.