EIACP (PC-RP) on Environmental Problems of Mining

Champion Reef Gold Mine

The Mine

This mine went into regular production in the year 1891 and was the second deepest mine in the field having reached a depth of over 2800 m below the field datum (which was at the surface of the mine at an altitude of 893.3 m above Mean Sea Level). The gold-bearing quartz reef worked in the mine occurred in a narrow strip of pre-Cambrian hornblende schist which was surrounded by the complex of gneissic and granitic rocks which cover the greater part of Southern India.

Most of the gold production of the Kolar goldfield came from the Champion Lode and its branches. This lode persists through all the mines. It strikes almost due north and dips towards the west at an angle of 40 degree to 50 degree near the surface to more than 85 degree in the deepest part of the mine. The Champion Lode had been subjected to a number of intrusions of pegmatities, particularly in the deeper levels. Numerous faults had been encountered in the Champion Reef Mine, the largest being the Mysore North Fault. Rich ore shoots were found near both edges of this fault and below the 68th horizon and on the south side of the fault there was a unique ore-body of great magnitude known as the Glen Ore Shoot. It was in this ore-shoot that the two accidents took place. This ore-shoot extended from the 68th level (1938 m below field datum) to the 97th level (2783 m below field datum) which was being developed then. The main body of the shoot covered an area of approximately 23.5 hectare of which some 15.5 hectare had been exhausted. Between the 76th and 82nd levels the ore-shoot attained a maximum horizontal length of about 427 m, the average quartz width being 97 cm. One of the main characteristics of the ore-body was the lack of any well-defined hanging or foot wall, the lode channel being 12 to 15 m wide. The Mysore North Fault ran at a slight angle to the ore-body in the footwall and at the 80th level it varied in distance from 9 m at the northern fringe to 55 m at the southern fringe from the reef.

Method of working

The Gifford’s shaft was the main artery of the mine from the surface to the 70th level, a single lift of about 2000 m. From the bottom of this shaft, the lower levels of the Glen Ore shoot were served mainly by three vertical shafts, namely, Heathcote’s, White’s and Osborne’s shafts. From these shafts, cross-cuts were driven through the country rock to reach the reef which was divided up into rectangular blocks by levels and winzes or raises. Levels were at intervals of about 30 m above the 89th level while below that level the interval was reduced to 23 m. The intervals between winzes or raises varied from 60 m in the upper part to over 90 m in the lower part of the Glen Ore shoot. The rectangular blocks of ore were removed by stoping operations. The voids thus created being packed with granite masonry immediately above and below the levels and at the sides of ore chutes and ladder-ways and with “dry granite” blocks in between the chutes and man-ways. Such packs were intended to control ground movement and to prevent caving in of the walls.

The accident which occurred on 19.4.1952

At 10.07 a.m. on 19.4.1952 a very severe rock-burst occurred and it was followed by another almost equally severe rock-burst at 11.21 a.m. The first rock-burst had affected the stopes and levels in White’s shaft area between the 80th and 82nd levels. At 10.45 a.m. the Assistant Agent reported by telephone that 16 men appeared to be missing and that bursting and heavy ground movements were continuing in the area and were preventing a detailed inspection. The Chief Underground Agent, who was on the surface, instructed him to organize rescue squads and as soon as the ground movements quietened down, rescue work was to commence but on no account were unwarranted risks to be taken. At 11.35 a.m. the Assistant Agent reported that the exact number of men missing was 20, seven on 80th level, nine on 81st level and four on 82nd level and that the whole area was still disturbed by ground movements. The Underground Agent was deputed to take charge of the situation and at 12.50 p.m. when the ground movements had decreased sufficiently, the Agent and the Assistant Agent inspected the affected areas and found the three levels choked to varying degrees and over varying distances. The Rill stope above 80th level was found choked. Attempts were made to contact any person who was alive in the area by hammering on the compressed air pipes in the levels and by shouting, but no reply was heard. After the Chief Underground Agent, the Inspector of Mines and the Mine Superintendent had made detailed inspections of the affected area by about 4 p.m., they came to the conclusion that with the severity of damage they had observed, there was hardly any possibility of any of the 20 missing persons being alive.

Nature and extent of damage

Despite the violent nature of the rock-burst, the damage done by it was local and confined to a small area of workings. The 80th level was partially choked over a distance of 42 m. Further south of this area, about 44 m of the level had still been choked up as a result of a rock-burst in 1947 and 6 men who were caught in this rock-burst were engaged in clearing the old choke and re-setting the level. The Rill stope above the 80th level was fully choked; similarly the ladder-way to 79th level was choked to within 10m of that level.

The 81st level was the worst affected. It was completely choked over a distance of 55 m. The flat-back stope 9 m above the level, which was completely choked as a result of the 1947 rock-burst, was being cleared between the second and third chutes. The cleared portion of this stope was again choked as also were the chutes leading to the stope. The steel sets in the level were badly buckled and twisted and the granite masonry pack-wall above the sets, originally 1.5 to 1.8 m thick, was reduced to a thickness of only 0.6 to 0.9 m.

The 82nd level was not so badly damaged. The steel sets were buckled over a distance of 27 m but complete closure had not taken place. The Rill stope face and the flat-back 9 m from the bottom of the rill as well as the ladder-ways and chutes leading to the stope were completely choked.

The total area damaged by the rock-burst was roughly elliptical, the long axis of the ellipse being about 80 m along the dip of the reef and the short axis about 55 m along the 81st level.

Rescue operations

In order to recover the bodies, rescue operations were carried on without cessation from 12.50 p.m. on 19.4.1952 until the last body was found on 24.4.1952. These operations entailed (a) reclaiming the levels by taking out buckled steel sets, clearing debris and putting in new steel sets lagged with casuarina poles and packing of the voids around the sets with waste rock, (b) running debris from chutes, which sometimes necessitated the use of explosives in order to gain entry to the stopes, (c) re-building of chute-walls and ladder-ways, (d) clearing of debris from the stopes, and (e) making new ladder-ways into the stopes. The work was slow and tedious as it was carried out in dangerous ground severely crushed by the rock-bursts.

Conclusions

There were two remnants above 80 level and between 80 and 82 levels there were four large partially stoped blocks and two small remnants north of 1-N winze. Above and below these blocks and remnants, large areas had been stoped out. These remnants and partially stoped out blocks were acting as abutment for the stoped our areas and they were carrying abutment loads of considerable magnitude and were in a highly stressed condition. The rock-bursts which occurred in 1947 in the same area, although very violent and causing extensive damage between the 80 and 84 levels had not distressed the area. Even the present rock-bursts do not appear to have done so and the area between 80 and 82 levels continues to be in a highly stressed condition.

The heavy death toll in this accident was due to the fact that the rock-bursts took place at a time of the day when the maximum numbers of persons were at work in the area. There was no undue concentration of workers in the area for the purpose of ore production. In fact, of the 20 persons killed in the accident, 15 were engaged in work connected with the reclamation of a level and a stope damaged in the 1947 rock-burst and only 5 persons were engaged on work directly connected with the production of ore.

The accident which occurred on 30.6.1952

A very severe rock burst, which was both heard and felt over a wide area on the surface, occurred at 7.15 p.m. and affected the 86, 87 and 88 levels south of Heathcote’s shaft as follows:

• 86 level: The end of Heathcote’s shaft cross-cut was partially choked. The level was closed for about. 9 m on the north side and for about 88 m on the south side of the cross-cut.
• 87 level: The junction of the Heathcote’s shaft cross-cut and level was choked. The level was choked upto a point 82 m south of the cross-cut, that is, upto the bottom of 4-N Rill stope. The ladder-way into the stope above 87 level was also choked.
• 88 level: The level was unaffected for a distance of 3 m towards the south from Heathcote’s shaft cross-cut. From that point the steel-sets were buckled for a distance of 42 m and the level was fully choked for a further distance of 53 m. The ladder-way and chutes of the 4-N stope above the level were also choked. Immediately after the Occurrence, Section Agents led reconnaissance parties and tried to rescue any survivors. These reconnaissances revealed that 12 men were missing.

Rescue operations:

At 9.25 p.m. the rescue workers were successful in locating two men buried under the debris in 86 level immediately to the south of Heathcote’s shaft cross-cut. One was dead but the other was alive though seriously injured. The injured man was given first-aid and sent to the KGF hospital. A little later, the rescuers located another man buried but still alive in the stope below 87 level. It was gratifying that though the man was rescued several hours after having been buried under debris, he was, except for the shock, none the worse for the experience. In this stope the dead body of another pack-Waller was found. The rescue teams tried to contact the missing persons who might be alive by shouting and by signaling on the air-pipes and rails but there was no response. By mid-night it was concluded that there was little hope of recovering alive any more of the persons trapped in the area who in all probability, were beyond human help.

The levels that were damaged by this rock burst had been completely steel-setted with 34 kg, bull-headed rails around which the usual lagging of casuarina poles and black rock packing had been provided. These steel sets, which originally left an opening, 2.1 m high and 1.67 m wide, were so tightly crushed that air was prevented from passing along the levels. These broken and bent steel-sets had to be removed, sometimes by blasting, and after clearing the debris, new steel-sets were fixed and the usual lagging and packing executed. In some places the granite masonry pack-walls above the steel-sets had been crushed almost to powder and the debris ran into the levels while reclamation work was in progress thereby leaving large voids which had to be filled with new granite masonry. The progress of recovery work, therefore, was inevitably slow and at each point the daily rate was about 2 m. The last dead body was recovered after 44 days of continuous work in short shifts of 6 hours duration.

Conclusions

1. The rock-burst on 30.6.1952 occurred in a section of the mine where normal stoping operations were in progress and which was not regarded as a dangerous or abnormal area.
2. The rock-burst was due to abnormal stresses built up in a small area of ground at the junction of two stoping systems, the additional stress being due to the abutment load of ‘adjoining stoped out ground.
3. Preparatory stoping carried out many years earlier for considerable distances along the levels in advance of the stopes reduced the strength of the blocks of ground between the levels and set up stresses around the levels. These factors had a bearing on the rock-burst and accounted, to some extent, for the closure of the levels when the rock-burst occurred.
4. The Mysore North Fault which was situated in close proximity to the reef in the affected area was likely to be the cause of concentration of stress and perhaps it was a contributory factor in the building up of abnormal stresses which were relieved when the rock-burst occurred.
5. The rock-burst was not an indication of any inherent defect in the “V” sequence of stoping adopted since 1948 and in fact this sequence of stoping had been effective in reducing the frequency or rock-bursts.