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COMMISSION
  
OF
  
INQUIRY
  
INTO
  
SAFETY
  
AND
  
HEALTH
  
IN
  
THE
  
MINING
  
INDUSTRY 
 
27 
 
-Narrow Width of Mineralisation 
 
A large fraction of the reefs worked by mines in the Witwatersrand system is less than 1 m 
in width.  This feature of the mineralisation impacts in a number of ways on the hazards of 
the extraction of the reefs. 
 
Firstly, the limited space obtained during the mining of these reefs prevents the application 
of any other mining technique employed safely and successfully elsewhere.  Furthermore, 
as no other region of economic significance has similar geometry, no mining industry 
outside South Africa persues the solution to this problem.  The platinum mines have 
essentially the same difficulty.  The solution must therefore be found in South Africa. 
 
Secondly, the narrowness and lateral persistence of the reefs result in “tabular” stope 
excavations that are in the region of one metre in width and tens or even hundreds of metres 
in the other two directions.  Such geometry leads to exceptionally high stress concentrations 
at the edges of these excavations.  These areas of high stress concentration include stope 
faces that are the working places of many miners. High stresses cause intensive rock 
fracturing and frequent rockbursts, which in turn are responsible for the greatest hazards to 
miners. 
 
Thirdly, due to the narrow width of mineralisation a large area must be mined in each year 
to produce the planned tonnage of gold (e.g. 619 t in 1993).  The recovery of this tonnage 
requires the extraction of reef over an area of some 20 to 30 km
2
.  Due to reasons explained 
earlier, the extraction of such a huge area, unfortunately, must be achieved by employing a 
rudimentary and very labour intensive method of mining.  This technology prevents the 
effective utilisation of stope faces, and each mine is forced to maintain excessively long 
stope faces, and long, often tortuous communication lines.  It is difficult to control, 
supervise and inspect such widespread operations.  In short, men working in such mines 
tend to be in a perilous situation. 
 
3.2.3  Current Methods of Combating Rockbursts 
 
Formal research into the alleviation of the rockburst hazard started in 1953 and during the 
following four decades a number of defensive methods have evolved.  There are essentially 
two approaches to the mitigation of the rockburst problem, which can be considered as 
strategic and tactical. 
 
The aim of the strategic approach is to diminish the likelihood of encountering rockburst 
prone situations in mines.  The common features of this approach are firstly, that they 
involve decisions that will affect the mine in the long term, and secondly, that the beneficial 
effects become significant only after the mining of a large, more or less contiguous area.  
Hence, the lapse of time may be measured in years. 
 

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COMMISSION
  
OF
  
INQUIRY
  
INTO
  
SAFETY
  
AND
  
HEALTH
  
IN
  
THE
  
MINING
  
INDUSTRY 
 
28 
 
The known strategic measures for mitigating the seismic hazard assume two forms.  The 
first involves the optimal layout design to reduce the theoretical stress concentrations, and 
the second incorporates regional support into the system to minimise the convergence of the 
stope walls.  Two versions of regional support have been suggested and tried so far.  Due to 
the relative simplicity of implementation, regional support based on stabilising pillars was 
the first system that was experimented with in some deep mines.  In this system about 15% 
of the reef is left behind, in a predetermined pattern of pillars, to interrupt the spans and 
hence reduce the magnitude of stope convergence.  The second involves the introduction of 
backfill into the stopes to minimise stope convergence through the reduction of available 
volume. 
 
Conceptually, if these systems are implemented well, they should bring considerable relief.  
Unfortunately, in practice, neither method is perfect and both have significant shortcomings. 
 
Both versions could lead to significant cost increases associated with backfill and / or loss 
of extractable reserves.  The pillars, since they are significant stress raisers could, and 
sometimes do bring with them certain hazards.  As a result of those and other difficulties, 
the strategic rockburst counter measures have not been implemented as widely or 
effectively as one would hope. 
 
The purpose of tactical measures is twofold.  They are intended to reduce the frequency of 
the occurrence of rockfalls, and to minimise the destructive effect of seismic events.  
Essentially the use of improved face and gully support falls into this category.  Effectively 
applied tactical control measures tend to become effective shortly after installation, but of 
course, their widespread introduction takes time.  Several new support systems have been 
developed during the last few decades.  The Commission heard evidence that, 
disappointingly, these support systems are not used as widely as they should be, and even 
when they are employed, they are often not used to the best advantage. 
 
The Commission’s recommendations in Chapter 10.5.1 will refer to the need for increased 
use of these systems. 
 
3.2.4  Future Projection of Hazards Arising from Rock Failure 
 
The submission of the COM contains some very disturbing information concerning the 
future perils associated with rock failure in deep gold mines.  A safety competition 
operating in South African mines called the C S McLean competition, has rules which 
subdivide gold mines into three groups, that is, shallow, deep and ultra deep mines (p 44 of 
the submission). 
 
The depth limits between these groups increase from year to year, presumably due to the 
natural deepening of the workings due to the dip of the reefs.  On page 45 a tabulation is 
given in which both fatality and reportable accident rates are given for the period 1989 to 
1993.  The arithmetic means of the rockburst fatality rates for the periods of five years are 
0,13, 0,24 and 0,84 for the shallow, deep and ultra deep mines, respectively. 
 
These are very disconcerting figures.  The rate for ultra deep mines is 3,5 and 6.3 times 
greater that those for deep and shallow mines respectively. When this information is 
considered in the light of the data given by the Chamber on 
  
 
 

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