The present paper deals with the Cumberland field, or, as it is probably
better known, the Comox field. This field occupies a strip three miles
wide and six miles long, running from the Puntledge river in a southeasterly
direction to just south of Cumberland, and situated along the western edge
of the Cretaceous lowland which forms the east coast of Vancouver Island.
In these 18 square miles there have been opened up eight mines, two of
which are still operating.
These sedimentary rocks are of Cretaceous age and are divided lithologically into two formations, the Comox and the Trent River. The Comox formation consists essentially of sandstone, principally white in colour and with a calcareous [p.1254/1255] cement. It is in this formation that the coal seams occur. In all, there are more than ten seams, and they vary in thickness from 2 inches to 8 feet; but only three of them are over 3 feet and workable. These embrace the lower seam, now being worked in No. 4 mine; the upper bench of this seam, which has been worked in No. 4 mine; and what is known as the upper seam, which is the one No. 5 mine workings are in.
The Comox formation attains a thickness of over 700 feet in this area. Overlying it is the Trent River formation, consisting essentially of shale with thin sandstone beds distributed through it. This formation is of no importance as far as coal is concerned, as no workable beds have been found in it.
The whole lowland has been uplifted and given a northeast tilt. The basement rocks have also been folded, and the overlying sediments have conformed to these gentle open folds of the underlying rocks. The faults due to the folding are in most cases clean, sharp, normal faults, and they occur in zones, the most noted of which is the west slope of No. 5 mine. Here there is a regular network of faults having two general directions, N.60°-70°E. and N.10°W. Most of the faults have a vertical displacement of less than 10 feet, but in some the throw is much greater than this. These fault zones are the source of a great deal of trouble in working or developing the mine.
The measures above No. 4 mine dip to the northeast, while at No. 5 mine the dip swings round slightly to the north. This gives rise to a pitching syncline, and it is in this basin that the best coal is obtained. Over the anticline to the east the coal is very poor.
During the glacial period the area was covered with ice, which moved in an easterly direction to the strait of Georgia. The remnants of the ice may still be seen in the hills at the head of Comox lake. The glacier scoured the surface and then; in retreating, deposited a thin mantle of glacial till or boulder clay on the rocks. This in turn was covered with a coat of stratified drift, which is over 100 feet thick in places. A general uplift of the region followed, and subsequent erosion has given rise to the present-day surface. [p.1255/1256]
Of the eight mines which have been opened in this field, only two, Nos.
4 and 5, are now in operation.
No. 1 Slope. – The mine is opened by two slopes. No. 1 slope is driven due north, half across the pitch, while No. is turned off, just inside the mouth of the opening, at an angle of 45 degrees to the east, which is the full pitch of the seam. At a point 4,800 feet from the surface, No. 1 slope is turned parallel with No. 2, and driven in this direction to a point 9,400 feet from the surface. Levels have been turned off to the right and left, the lowest being Nos. 20 East and West, levels. The slope has been driven about 200 feet beyond No. 20 West level.
At a point 6,000 feet from the surface, an upthrow fault was encountered. A level landing was made at this point, and a level rock tunnel driven through the fault. After coal was reached the slope was continued. The only part of the mine now operating is on the lower side of this fault. Nos. 16, 17, 18, 19 and 20 West levels are being worked, but all the workings above and on the east side have been either finished or abandoned. In order to consolidate the workings on the west side, and to improve haulage conditions, No. 15 West level (which was turned off just inside the fault and which had been abandoned) was reopened, and from it a slope, No. 4, was driven due North to cut off the faces of the levels below.
Until this fault was encountered, all the operations had been on the pillar and stall system; but as, on the inside of fault, the coal was much thinner than on the outside, it was decided to change the method of working. Accordingly, when No. 4 slope was driven, cutting off the levels below No. 15, the system was changed over to longwall, and all subsequent operations conducted from this slope have followed this system. [p.1256/1257]
At the present time two new slopes are being started below No. 20 West level. One of these is being driven N.45 °E, and is practically a continuation of No. 1 Main slope. The other trends due north, or about parallel to the No. 4 slope. These three slopes open up a fairly large area.
No. 2 Slope. — The main slope was driven down a distance of 7,800 feet at which point some poor coal was struck and development was stopped. Levels had been turned off to right and left as in No. 1 slope, the lowest being Nos. 20 East and West; but the only levels operating now are from Nos. 16 to 20 on the east side. A fault was encountered on the east side, and it cut off the coal. Prospecting along this fault was carried out in Nos. 15, 16, and 17 East levels, but the examination was evidently conducted in a different direction in No. 15 level from that followed in Nos. 16 and 17. In No. 15 the original lower seam was picked up, while in Nos. 16 and 17 another seam, referred to above as the Upper Bench and lying about 40 feet vertically above the lower seam, was found. This new seam was opened up and extensively worked in Nos. 16 and 17 levels. No. 15 East level, on the other hand, continued to operate in the original lower seam until a point was reached where it became necessary to leave a barrier pillar between it and No. 5 Mine lower seam workings. The levels below No. 17 were stopped when the fault was reached, and the pillars were withdrawn. No. 15 East level, which had been abandoned for some considerable time, was re-opened, and from it a slope trending due east was started inside the fault. On account of the thickness of the seam in this section, the pillar and stall system of mining was adopted. The slope is now down past the face of No. 17 level.
Another slope, also running due east, was started off No. 20 East level. A pillar 200 feet thick was left below the No. 20 East level, and then the longwall method was followed. The slope is now down 950 feet, and there are 24 places in the section. A new slope has also been started off No. 20 West level. It trends N. 45 °E., or parallel to No. 2 slope, and it is now down 300 feet from the level. This slope will also be on the longwall system. Places are being turned off ready for operation. [p.1257/1258]
These six slopes, three on No. 1 and three on No. 2, constitute the development scheme for the future, and they are giving access to territory hitherto untouched. At the same time, they have created serious problems in haulage and ventilation.
Haulage. — The haulage on Nos. 1 and 2 slopes is effected by a double drum hoist operated by a 500-h.p. motor. This is the same hoist which had been in use at the mine as a steam hoist. Both drums are loose and clutch-operated on a common shaft, so that hoisting may be done on both slopes at the same time or on either slope separately. There are 7,500 feet of rope on each drum. The main hoist on No. 1 slope operates to the No. 15 West level, a distance of 6,900 feet. From here a storage battery locomotive is used between No. 4 slope and the bottom of the main slope. Auxiliary hoists are used to raise cars from No. 20 level, and also from No. 4 slope, to No. 15 level, where they are picked up by the motor. Other auxiliary hoists are used to gather the coal from the new slopes below No. 20 level and place it on the landing at No. 20.
On No. 2 slope, the main hoist runs to No. 17 East level, a distance of 6,400 feet. All coal from below this point is raised by an auxiliary hoist on No. 17 level, whence it goes to the main surface landing.
Only two sizes of auxiliary hoist are used, 50 and 100 h.p. respectively. These hoists are all of the same make and are interchangeable.
Haulage at the face and on the levels is done by mules.
Ventilation. — Ventilation is probably the most serious problem confronting us in the operation of this mine. A Sullivan multi-blade fan, producing 165,000 cubic feet per minute. is used. This fan ventilates the entire mine. On account of the great distances the air has to be carried, and the number of stoppings required, the leakage naturally is considerable To help reduce this leakage, stoppings are being rebuilt and "gunited" with the cement gun. In doing this, wire netting is first nailed to the face of the stopping, in order to give the required bond for the cement. It is possible to get a much better seal around the edge of the stopping by the "gunite" method than by any other process. Cracks and breaks in the strata are also readily sealed up in this way. [p.1258/1259]
The return airways are being enlarged to permit the passage of larger quantities of air.
A Sirocco fan, which was used at No. 7 mine and which has a capacity of 200,000 cubic feet per minute, is being installed. When this installation is complete, it is proposed to make Nos. 1 and 2 slopes entirely separate so far as ventilation is concerned The present fan will be used to ventilate No. 2 slope while the new one will ventilate No. 1. With the completion of this installation, it is expected that there will be more than sufficient air for all requirements.
Pumping. — There is not a great deal of water to handle in this mine. All pumps used are turbines, varying in size from single-stage to nine-stage. On account of the excessive length of slope and the amount of pipe required, two ten-inch bore holes were put down and cased. The bore hole on No. 1 slope is at No. 19 East level, that on No. 2 slope at No. 14 level.
The water is pumped from the respective slopes up these bore-holes to
the surface. The main pump on No. 1 slope is below No. 19 East level; it
is a 7-stage pump with a capacity of 350 gallons per minute, and it is
driven by a 150-h.p. motor, direct connected. The height of lift at this
point is 780 feet vertical. In No. 2 slope the main pump is stationed at
No. 20 West level and is a 9-stage pump with a capacity of 350 gallons,
driven by a 200-h.p. motor. The vertical lift here is 1,180 feet. The auxiliary
pumping is done by single and 3-stage units driven by 10 and 25 h.p. motors,
The pitch of the seam is N.40°E. and the dip about 8 degrees. Two
inclines, Nos. 1 and 2, were raised off the East level and worked by the
pillar and stall method. These have now been worked out and the pillars
extracted. No. 1 slope [p.1259/1260]
was sunk at a point 1,050 feet from the shaft bottom. This slope was driven down 1,500 feet, at which point development work was stopped on account of the large amount of rock in the seam. Levels were turned off east and west. Those on the west side struck the fault running through the shaft bottom and those to the east were stopped on account of the excessive amount of rock in the seam. The average thickness of the seam is about 7 feet, but it includes three bands of rock. To the east these rock bands increase in thickness, and as the aggregate thickness of the seam remains about constant, the bands of coal become thinner and thinner until there is considerably more rock than coal in the seam.
No. 2 slope was driven down at a point 3,650 feet from the shaft bottom and was stopped 850 feet from the level. Here the thickness of the top bench of rock was nearly 4 feet so it was decided to open up the levels being driven east by longwall, making the thick band of rock the roof. The section now has 18 places working, and the longwall system is used throughout. Boreholes immediately ahead of the section show that there has been a displacement of the strata here. There are evidently two large faults just ahead of the present workings, and, within a short distance, they will entirely cut off this portion of this mine.
A tunnel was driven through the fault on the west side of the shaft and the seam located; its thickness, however, is much less than on the east side. Most of the rock bands are absent, and there is about 3½ feet of coal. Here a slope was driven, and it is still being developed, being now down a distance of 2,600 feet. Levels were turned off right and left. In the levels to the right the seam has about the normal thickness, and this section was worked by pillar and stall. To the left the coal is thinner and was opened by the longwall system. A regular network of faults was met with, in the area, and they have considerable retarded the development of the levels. So numerous were they that it was impossible to open up any continuous section of face containing more than 3 or 4 places.
The faults have two general directions: N.60°-70°E. and N.10°W. They are sharp, well defined, and have displacements ranging from one foot to ten feet, and occasionally even more The slope is at present being driven through a fault whose extent [p.1260/1261] has not yet been determined. The faulting has greatly retarded the development of the area, which would have been ideal for longwall operation had it been undisturbed. Although, as stated, the slope has been driven 2,600 feet, only a few working places are being operated on it.
Mine Water. — Next to the extensive faulting, the greatest problem
in this mine is the handling of the water, which is present in large volume.
Moreover, the water is comparatively acid, as the following analyses will
|Shaft bottom, No.5 Mine||Top of No.1 incline||Bottom of No.1 dip||Bottom of No.2 incline|
|Organic and volatile matter||117||227||128||274|
|Ferric oxide (Fe2O3) plus small amounts of alumina (Al2O3)||1,455||749||172||1,396|
|Sulphur trioxide (SO3)||2,878||2,190||1,323||2,363|
|Chlorides as Cl||241||191||142||142|
|Free acid as H2SO4||286||221||220||427|
The acidity of the water is such that it rapidly attacks metals with which it comes in contact. Pumps of a special acid-resisting alloy were accordingly made in the company's own shops, but even with these the cost of maintenance was very high. Nos. 5 and 6 shafts being connected underground both in the upper and lower seams, it was decided to hoist the water by bucket from No. 6 shaft, which at this time was not producing coal. Self-filling and self-emptying cylindrical buckets, with a capacity of 600 gallons each, were used. Two hoists per minute can be made, giving a hoisting capacity of [p.1261/1262] 1,200 gallons per minute. During the winter months, the water is heaviest, this hoist is making two trips per minute and running, on an average, about 22 hours per day, which means a discharge of over one and a half million gallons of water per day. Three five stage pumps are maintained at the bottom of No. 5 shaft for use in case of breakdown of the hoisting apparatus at No. 6 shaft.
Pumping to the shaft bottom from the various slopes is effected by 3- and 5-stage turbine pumps.
Haulage. — The main haulage on the East level is by electric
trolley locomotive. A storage battery locomotive is used on the level from
the bottom of No. 2 slope. Electric auxiliary hoists of the same size and
type as those in No. 4 mine are used here. Haulage at the faces and short
levels is done by mules.