THE COLLIERY GUARDIAN

AND

JOURNAL OF THE COAL AND IRON TRADES.

Vol. CVIII.	FRIDAY, OCTOBER 16, 1914.	No. 2807.

Hydraulic Stowing in the Gold Mines of the Witwatersrand.*

By B. C. GULLACHSEN.

The hydraulic stowing of mine workings is a subject
that is coming more and more into prominence iri the
mining world; and although there are many detractors
of the system in this country, the most conservative of
British mining engineers must, by now, be convinced of
its practical utility. That Great Britain should be one
of the last mining countries to adopt hydraulic stowing
is only in keeping with its old tradition of caution;
but one cannot think that the coal mining industry of
this country will hesitate much longer in adopting the
system.

It is not the object of this paper to deal with
hydraulic stowing in general, but with the method as
employed at the gold mines of the Witwatersrand in
particular. In the Transvaal hydraulic stowing was
first used in the gold mines about the middle of 1909,
but credit is often given to the late President Kruger
for having several years previously suggested that the
unsightly residual sand dumps, which were then com-
mencing to make themselves objectionable, should be
conveyed underground to fill up the excavated portions
of the mine.

The first mine at which hydraulic stowing, or “ sand-
filling ” as it is more generally called on the Rand, was
commenced was the Village Main gold mine, to be
followed shortly afterwards by the Ferreira gold mine,
and by June 1910 the Village Main was sending under-
ground about 1,200 tons of sand daily. During 1911
several more mines were equipped, and in the annual,
report of the Central Mining and Investment Company
for 1912 it is stated that at seven mines of this group
alone 984,650 tons of sand were stowed into the
worked-out stopes. At the present date 15 mines on
the Rand have installed hydraulic equipment, and more
are to follow in the near future.

Hydraulic stowing on the Rand may be divided into
two systems—namely: (1) sand taken from dumps;
and (2) sand taken direct from the cyanide vats. In
the first of these two systems the sand to be used for
stowing is taken from the mine dump (the dump
consisting of the residual sand after the gold has been
extracted).

into the dump and washes the sand away into launders.
The pulp then proceeds direct into a small shaft, from
the bottom of which the pulp is conveyed into the
workings by means of launders.

Unless, as in the case of the Robinson mine, the sand
can be washed direct into the workings from the dump,
this system has the disadvantage that the sand must be
shovelled from the dump into trucks and then conveyed
to the collecting bins, an expense not incurred by the
other system. When sand from old dumps is used,
considerable quantities of lime must be added in order
to neutralise the sulphuric acid formed by the decom-
position of the pyrites. Another disadvantage of using
old dump sand is that the sand is mixed with a
considerable quantity of colloidal slime, the presence of
which is very objectionable underground.

Sand Taken Direct from the Cyanide Vats.

This system was first employed on a large scale at the
Simmer and J ack mine, although current sand residue
had previously been employed to some extent at the

Fig 5.-Side
Barricade

Fig’ 2.-Launder with
Hardwood Lining
and Corner-pieces

Fig 3.--V-shaped Launder
with Hardwood
Corner-pieces

Fig 6 -Rock-ash
Barricade

Fig 4.-Concrete
Launder

r-

i.r2 FEET e INCHES

IN DIAMETER
F

Fig 8.—Sand filling for the Extraction of Pillars
of Rich Ore left as Supports in Outcrop Mines

__________--_____--MiRt-JOW_____________________________!
,	,___— ______----------t----1’ninth level /

1=
I

It is interesting to note that in this system the ore
hoisted from the mine about a fortnight previously is
returned again minus its gold content, and that a ton
of the ore which occupied a space of 12 cubic feet in situ

in the mine yields about the same volume of sand for
return underground, after the ore has been well crushed
and classified into 50 per cent, sand and slime
respectively.

Conveyance of the Sand Down the Mine.

The systems of dealing with the sand on the surface
having been discussed, the next point is the lowering of
it down the mine. There are two methods of doing
this, namely:—(1) By means of pipes ; and (2) by means
of boreholes. In the first case the pipes are hung in the
shafts, care being taken to make them quite secure, on
account of the very considerable vibration caused by the
passage of the thick pulp through them. The pipe line
must also be easily accessible, so as to allow of the easy
and rapid removal of the lengths of pipes that become
worn through. A great objection to the sand-filling
pipe lines being installed in the shaft is that, in the
event of a pipe becoming worn through, or bursting, a
considerable quantity of pulp is discharged into the
shaft, causing a very objectionable mess.

Sand-filling at the Geldenhuis Deep Gold Mine.

The sand at the dump is shovelled into trucks, which
are then taken by an endless-rope haulage to the
collecting bins, situated near the entrance to the mine.
The sand is tipped into these bins, which are furnished
with folding doors, through which the sand is able to
pass when required. Projecting through these doors
are short lengths of 3-in. piping, having a flat-shaped
nozzle-end, and perforated along its length with small
holes. Water under pressure is turned into this pipe,
and is injected into the surrounding sand, which is then
washed through the doors into the launder. In the
event of the sand coming through too thickly, more
water may be added in the launder from the water pipe
provided for that purpose at the end of the launder.
The pulp flows down the launder, which has a gradient
of about 15 degs., into a box-shaped receptacle at the
top of the shaft, from which box the pulp is conveyed
through 6 in. cast iron pipes to its desired destination
underground.

At the Robinson gold mine the arrangements are
different, as at this mine the dump was so conveniently
situated to the mine workings that it was found
unnecessary to convey the sand to storage bins. The
sand is washed direct from the dumps by means of
high-pressure water thrown on to it by hydraulic
monitors with 3 in. nozzles, which force of water breaks

* From a paper read before the North of England Institute
of Mining and Mechanical Engineers.

City and Suburban mine. The essential feature of this
system consists of using the sand as soon as it is
discharged from the cyanide vats, thus doing away with
the cost of transporting it to the top of high dumps,
whence, as in the first system, it has again to be
shovelled into trucks and transported to the collecting
bins. What was at first looked upon as a grave objec-
tion to this system was the presence in current sand-
residue of dangerous quantities of potassium cyanide,
and it was found to be absolutely necessary to destroy
the cyanide before the sand could be used. This was
accomplished by introducing into the water a small
amount of permanganate of potash solution, thus
converting the poisonous cyanide into harmless cyanate.

In this system it is a great advantage if the sand
treatment vats are situated so that the sand immediately
on being discharged can be mixed with water and
permanganate and run direct into the mine. As
frequently occurs, the vats are placed some considerable
distance from the borehole or entrance to the mine, in
which case, as at the Simmer and Jack installation, the
pulp has to be pumped to the position where it is
required. The pulp then passes through de-watering
cone classifiers, the underflow from which is then
discharged into the borehole or pipe-line leading
.to the mine workings, while the overflow runs or is
pumped back to the mixing bin, when it is again utilised
to bring up more sand.

It was at first considered that boreholes would be
impracticable, on account of their becoming choked,
but in practice this is not the case if the borehole is of a
reasonably large diameter. Boreholes 7 or 8 inches
in diameter have been found to give very little trouble
through choking. If a borehole should become choked,
it can be cleared by running a small amount of water
into it for a few hours. Boreholes have the great
advantage over pipe lines that after once the first cost
has been met, there is no upkeep cost, as in the case of
a pipe line. There is also the additional advantage that
they can be put down at the very best point for the
distribution of the filling material underground, thus
avoiding in many cases the great lengths of more or less
horizontal piping necessary when the pipe line is taken
down the shaft, and which are so liable to become
choked.

Boreholes are in use at the Simmer and Jack and
Robinson Deep mines; that at the Simmer and Jack
was put down by means of a jumper drill at a rate of
8 ft. per day, and at a cost of 17s. to 20s. per foot. The
Robinson Deep borehole was bored by a steel shot drill
to a depth of 1,700 ft. in nine months, and cost £2,625. or
a little over 30s. per foot. The borehole at the Simmer
and Jack mine has now been in use for four years,
and no trouble whatever has been experienced with it.

After the stowing material has reached the bottom of
the shaft or borehole, the next consideration is the