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Wednesday, 27 August 2008

"cyanide " The mill tailings of Kolar gold mines

B. R. Krishna and F. H. Gejji (Curr.
Sci., 2001, 80, 1475–1476) have highlighted
the environmental pollution
being caused by the dumping of the mill
tailing (sand) in the Kolar gold mines
area. It is true that there are about 32
million tonnes of this sand, which
makes up the 15 dumps spread out
along 8-km long distance in the mine
area. These sands have been causing
considerable environmental health hazards
to the people of the Kolar gold
field. During the months of June/July
when the weather is dry and windy,
these sands are carried eastward to
Robertsonpet and Andersonpet areas,
over a distance of 3 km. The finer particles
get air-borne and finally settle
down up to a radial distance of 4 km.
With the onset of monsoon, the rainwater
carries these sands further down
onto tank beds.

These sands are essentially
made up of grains of quartz and
amphibole minerals, with a fineness
varying the <>

The authors’ apprehension that these
sands cause health hazards like silicosis,
lung cancer, etc. is not based on
facts. According to Gowda and Shenoi1
of M/s Bharat Gold Mines Medical Department,
‘although the gold mines are
100 years old, so far there is no reported
occurrence of silicosis in any of the
employees of the Kolar gold mines.
They further confirm that silicosis, as
seen in the famous Rand gold mines of
South Africa, does not exist in the Kolar
gold field. However, a form of pneumoconiosis
(lung disease) is commonly
found in underground mine workers and

Table 1. Major constituents of sand in
the Kolar gold mines area

Constituent -------Light- coloured ----Dark- coloured

Calcium oxide --------8.4 ---------------7 .6
Silica -------------------56.0 --------------51.8
Aluminium oxide ----11.9 --------------8.2
Ferrous oxide -------10.2 --------------18.9
Magnesium oxide ---8.6---------------- 6.3
Loss of ignition-------2.0---------------- 3.9

their most recent study (1973–1978) on
5893 workers has shown a decline in
the prevalence rate of pneumoconiosis.
The mill tailings have so far not caused
any respiratory health hazards or skin
diseases or allergies to the people of
Kolar gold field area. At best, these
sands can be considered as a nuisance
and should be ignored as innocuous.
As for the possible industrial use of
these mill tailings, so far all attempts
made in the past have proved to be either
futile or uneconomical. In the early
fifties, the British engineers mixed
these tailing sands with Portland cement
and after reinforcing with steel rods,
manufactured fence-posts pillars, slabs,
etc. Since these products lacked the
required strength, they all cracked up
and broke. In another attempt, during
the 1980s the Bharat Gold Mines Ltd
(BGML) supported a S&T project by
the Cement Research Institute of India
(CRII) for manufacture or Portland/
Pozzoland cement by blending
these tailings with high-grade limestone
obtained from Bagalkot in Belgaum
district. Although technically it was
found feasible, the final assessment was
that economically it was not viable for
two reasons:

(1) For each tonne of mill
tailings, four tonnes of high grade limestone
had to be procured from Bagalkot
area and transported over 400 km distance.

(2) All the major constituents like
SiO2, Al2O3, MgO and Fe2O3 were almost
double in percentage compared to

Krishna and Gejji’s contention that
about 20–22 million tonnes of these
tailings has been lost due to denudation
is not correct. The total quantity of tailings
generated during the last 120 years
is about 35 million tonnes and the present
(1999) estimate is 32 million tonnes.
The difference of 4 million tonnes
is accounted for as follows:

(i) Tailings
used for filling voids underground for
sand stowing: during 1956–1980, 1.6
million tonnes2; during 1980–2000, 1.4
million tonnes (BGML source); total,
3.0 million tonnes.

(ii) The balance 1
million tonne may be accounted for

During 1981–1989 about 2,03,500
tonnes of tailing sand found around

Walker’s shaft in the Nundydroog area
was treated and 106 tonnes of scheelite
(tungsten ore) was recovered as a byproduct
by BGML. The mill tailing
sands contain about 0.75 g of
gold/tonne of sand. So during 1986–
1998, BGML treated 3.8 lakh tonnes of
sand and recovered 328 kg of gold by
heap leaching technology. This involved
transportation of sand for 3 km
distance to an uninhabitated area which
in turn created air pollution enroute.
This apart, the cost of other inputs like
labour, power, cement, cyanide, transport,
etc. was prohibitively high and
hence in January 2000 BGML closed
down this plant also, as part of its final
winding-up operations.

Until 1956, all the underground workings
where the gold ore has been extracted,
were being supported by timber
of granite, which was very expensive.
After studying some of the Australian
gold mines, BGML also started making
use of these sands with water to fill up
the stoped-out areas. From 1956 to
2000, BGML used about 3 million tonnes
of sand for supporting the underground
workings. Perhaps, this is the
best use the mill tailings have been put
to so far.

The suggestion of Krishna and Gejji
of making use of these sands for the
manufacturing of hollow bricks, solid
columns, reinforced slabs, an additive
for Portland cement, for manufacture of
stoneware pipes, bottles and bangles,
etc. may not be feasible as these tailing
sands do not possess the required physical
and chemical attributes as specified
for the respective industries.

According to Ganapathi Prabhu3,
BGML under technical guidance, undertook
an afforestation programme on the
tailing dumps, to contain the dispersal
of these sands. Hybrid eucalyptus saplings
were successfully grown after
spreading red-earth and green manure
as foundation on the dumps. With good
care, the saplings grew into adult trees.
The greenery was evident and prevented
the sand from denudation. Since January
2000, the maintenance of these
plantations has been given up by
BGML, as it has wound up all its operations.
Now it is left to the Karnataka
Forest Department to look after these
plantations, to mitigate the environCORRESPONDENCE
mental pollution of the Kolar gold field

About 6 years ago, an Australian
company came up with a project of recovering
the residual gold (0.75 g/
tonne) from the mill tailings by in situ
heap leaching technology. However,
due to the proximity of these dumps to
the dwellings of workers, etc. the project
did not materialize.

Now that BGML has abandoned its
mining and metallurgical operations
since January 2000, there is nothing
anybody can do. The people in and
around Kolar gold fields have to coexist
with the dumps and tolerate its
nuisance until a new solution is found.
The Building Research Institute at Roorkee
may have some answer for the
utilization of these sands.

1. Gowda, A. M. S. and Shenoi, B. V.,
Bharat Gold Mines Ltd (BGML), Centenary
Souvenir, 1980, pp. 43–45.

2. Devaraj, V. G., BGML Centenary Souvenir,
1980, pp. 104–106.

3. Ganapathi Prabhu, K. in National Seminar
on Recent Development in Exploration,
Exploitation of Minerals in India,
Mining, Geological and Metallurgical
Institute of India, 1990, pp. 165–166.

1126, Geetha Road,
Kolar Gold Field 563 122, India


Para 1 of the article by J. V. Subbaraman
confirms the prevalence of environment
pollution hazard. It also
substantiates the same, not only on
the mine workers, but also on the
local population living at a considerable
radius surrounding the mining area,
where the mill tailings are heaped as

Para 2 identifies pneumoconiosis
(lung diseases), which is invariably
associated with the respiratory system
of all living beings. As far back as from
1917, various miners’ diseases resulting
from the gold mining by milling process
are being studied and identified by
the National Institute of Miners’
Health founded at site in the Kolar Gold

Afforestation efforts towards retarding
the environment pollution hazard,
affirm the pollution hazard – a very
expensive scheme, but not yet a permanent
remedy. The major constituents of
the mill tailings being about 55 to 60%
of silica dust and the balance also of
other amphibole minerals, establish the
fact that lung diseases are caused by
inhalation of the silicious dust. (ref:
Souvenir of the 50th year of Independence
– 1997).

Coming to bulk productive utilization
of the tailings, the technical feasibility
of developing the puzzolonic characteristics
is in consonance with our scheme.
Only the research and experimentations
are conducted in the wrong direction by
the Cement Research Institute of India,
with support from Bharat Gold Mines
Ltd, as a S&T project. As far back as in
1974 we had suggested the scheme
for the same, since fast-consumption of
the tailings is the only permanent solution.

The statement that the total mill tailings
generated over the past 120 years
is only 35 million tonnes, of which only
one million tonne is lost by denudation,
is not correct. The historical gold production
data of the Kolar gold mines
are: 51.124 million tonnes of ore are
milled and gold produced is 800.3 tonnes,
as furnished by the Indian Bureau
of Mines for the total period of a little
over 120 years, ending on 31 March

*Satya Sai, 22(A)
S. M. Layout, V Phase,
J. P. Nagar,
Bangalore 560 078, India
†No. 60, BTS Road,
Wilson Garden,
Bangalore 560 027, India