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in it. The shale produced ammonia as well as oil, and the
sulphate of ammonia was now one of the principal products without
which shale could hardly be profitably worked. The shale seams
were about six in number, and varied in thickness from two up to
fifteen or more feet. The principal shales were known as the
Raeburn Fields, Broxburn, Dunnet, and Pumpherston shales, but
at some places these seams were divided into several parts, each of
which was workable. Good shale produced 30 gallons of crude
oil and 40 or 50 Ibs. of sulphate of ammonia per ton. The shale
fields were far from regular in form, and the whole area was much
folded and faulted, and was at places invaded by large sheets of
intrusive basalt. The author described in detail the geological
features" of the various shale fields worked by about ten different
companies, with a total capital of nearly ,2,000,000. The industry
was an important one, and the author thought great credit was due
to the Scottish companies for the inventive genius, perseverance,
and pluck they had shown in carrying on the industry for many
years, in face of the fierce competition from America and other
places, where the oil spouted up ready made, and no great skill
was required to win it from the soil. The principal shale fields
were those of West Calder, Mid Calder, Pumpherston, Broxburn,
Philpstown, Hopetoun, Dalmeny, Straiten, and Burntisland, but
shale was not being worked at all these places. The author
exhibited a geological map he had prepared, showing the probable
geographical extent of the available shale measures, and illustrated
the paper, which was a long one, by numerous vertical and horizontal
sections across typical areas in West and Mid Lothian.



A vote of thanks was accorded to the author.

16



THE CARBONIFEROUS LIMESTONE COAL-FIELDS OF
WEST LOTHIAN."

Paper by H. M. CADELL.



Abstract.

THE carboniferous limestone series of Linlithgowshire (or West
Lothian), immediately covering the oil shales, was about 2000 feet
in thickness, and was marked by three upper limestone beds, and
by two or more similar marine beds at the base, between which
were found the coal measures of Bo'ness and the district at and
to the south of Bathgate. The series was characterised by a
great development of volcanic rocks, basalt, and tuffs, which were
interstratified with the coal seams of Bo'ness and Bathgate. Be-
tween these localities the volcanic rocks were very thick, and
occupied the position of the coals and non-volcanic strata. In
the centre of the area, to the south of Linlithgow, there was a
volcanic bank over 2000 feet thick, where no coal had apparently
been formed; but to the north and south of this nucleus the trap
rocks thinned away, and the coals began to increase. The Bo'ness
coalfield contained more workable and generally better seams than
the Bathgate field, and the author exhibited a series of vertical
sections showing the relative proportion of coal-bearing and
volcanic rock along the strip of carboniferous limestone ground
extending for 12 miles southward from Bo'ness. He said he had
often been asked to trace the Bo'ness coal seams into the Bathgate
district, and state which seams in the one coalfield corresponded
with those in the other. His answer in this paper was that there
was really no connection between them, as the volcanic rocks had
apparently produced a barrier in the carboniferous sea, on each
side of which different strata were being laid down during most of
the coal producing period. It was not till the upper limestones
were deposited that the volcanic bank became . sufficiently sub-
merged for the sea to flow continuously across it, and permit of
the uninterrupted deposit of sedimentary rocks.



Mr. J. G. Weeks, the Chairman, and Mr. James M'Murtrie -took
part in the Discussion, and the author replied.

A vote of thanks was accorded to the author.



"THE TARQUAH GOLD-FIELD, GOLD COAST,
WEST AFRICA."

Paper by A. R. SAWYER.



Abstract.

THE Tarquah gold-field is situated in the Gold Coast colony. It
is connected with the coast at Sekondi by a narrow gauge (3^ feet)
railway. This railway, which is being constructed to Koomasi,
is already open for traffic between the village of Tarquah (situated
somewhere about the centre of the south-eastern edge of the gold-
field) and Sekondi, a distance of 40 miles; and its course from
Tarquah is as far as Cinnamon Bippo, a distance of about 7 or 8
miles along the south-eastern edge of the gold-field. There it
leaves the south-eastern outcrops and cuts across country to the
same outcrops, which have been shifted forward in a north-westerly
direction. The railway passes on to these new outcrops about 17
miles from Tarquah, and continues along them to Aponsu, a
distance of 40 miles from Tarquah.

The reefs in the Tarquah gold-field are undoubtedly con-
glomerates, occurring in a sandstone-and-quartzite formation.
These rocks occur as fine and coarse grained, and in some cases so
coarse-grained as to become grits. They often contain scattered
pebbles. There is no doubt that these sandstones and grits become
quartzitic in depth. These rocks differ in no wise from the same
rocks on the Rand, except in the fact, which the reefs also share,
that they contain a very large quantity of iron oxide, which mostly
occurs in irregular thin bands or veins, giving the sandstone or
quartzite a " striped ' ; appearance.

The thickness of this sandstone-quartzite formation is not easily
determined, owing to probable duplication and to scarcity of
available outcrops. The writer estimates the thickness, however,
at between 4000 and 8000 feet. Overlying this formation and
conformable with it, occurs a thick slightly arenaceous clay-slate
formation, containing a few thin, fine-grained sandstone beds' He
found the clay slates about three miles from the Wassau mine, and
these still continued where he left off his examination. At this
point, the clay-slate formation had a dip of from 5 to 10 degrees,
and dipped consequently at a slightly flatter angle than in the



220 THE TARQUAH GOLD-FIELD.

south-western portion of the goldfield. This formation the writer
estimated to be at least 1000 feet thick. In whatever direction the
quartzites dip, these slates, which invariably accompany them, dip,
owing to their conformability, in the same direction. They form a
useful index of the position of the reefs, as will appear further on.
These two intimately connected formations make up the gold-field,
and although the slates are not auriferous, they certainly overlie the
quartzites, with the conglomerate-reefs contained therein.

The enclosing formations are, so far as the writer can judge,
mostly basic igneous rocks, and schists and slates derived from
them. These rocks contain white auriferous quartz-reefs, like
those at Preston and Crockerville, generally with a trend parallel
to the prevailing trend of the conglomerate outcrops.

The gold-field has a tendency to a long synclinal shape trending
about 40 degrees north-east. The continuity of the syncline south-
westward is disturbed. Powerful dynamic forces have there thrown
the sandstone-quartzite formation almost at right angles to the
syncline.

With numerous comparatively small disturbances, the sandstone-
quartzite formation forming the south-eastern edge of the syncline,
which consequently dips in a north-westerly direction, extends as far
as the neighbourhood of the village of Busumchi, a total distance
from Tamsoo of about 20 miles. Here another powerful disturb-
ance appears to have thrown the whole formation north-westward
about four miles, as there the peculiarly striped quartzite formation
appears strongly, with a strike parallel to that of the large syncline
and a north-westerly dip.

The resemblance between the Witwatersrand and Tarquah
synclines, with respect to the large disturbances occurring at either
end, is striking. The Detchikroom disturbance corresponds to
the large Witjpoorte fault and the Busumchi disturbance to the
Boksburg fault, which throws the Moddersfontein series some
miles to the north. Just as the Randfontein series there strike at
right angles to the Rand, so here the Detchikroom disturbance
strikes at right angles to the large Tarquah syncline.

The matrix of the reef consists invariably, near the surface, of
sandstone composed of quartz-grains, white mica, and iron oxide,
which becomes compact and quartzitic in depth. At the extreme
ends of the syncline, namely at Teberibi and Tamsoo to the
south-west, and near Busumchi to the north-east, the matrix is
schistose. This characteristic is due to shearing, no doubt produced
by the earth movements which prevailed during the occurrence of
the great disturbances at each end of the known syncline. The
pebbles vary in size up to 8 inches, and near the surface are invari-
ably coated with white mica. They consist mostly of white quartz.
Darker quartz-pebbles and dark indurated slate-pebbles also occur.



THE TARQUAH GOLD-FIELD. 221

Patches of talc and red clay occur. The quartz pebbles are
opaque, translucent and sugary or saccharoidal, in some cases being
very friable. Under the microscope, the quartzites and con-
glomerates nearly all show evidence of strain and crushing from
shearing.

Unlike the pebbles of the Rand banket, in which gold occurs
very rarely if at all, the Jarquah conglomerate pebbles occasionally
contain gold. The quartz-reefs from which they are derived must
have been more or less auriferous, like some of the quartz-reefs now
being worked in the neighbourhood of Prestea, and by the Ashanti
<Goldfields, Limited. The principal amount of gold occurs, however,
like on the Rand, in the matrix.

The unaltered condition of the haematite both in the quartzites
and conglomerates, down to the depth at which it has been found,
is remarkable. It is not improbable that pyrites will be found to
replace haematite in the matrix at a greater depth.

The dykes, in or about this gold-field, consist mostly of basic
igneous rocks, but a few examples of intermediate igneous rocks
occur. Dolerites and diabases are the only representatives of the
basic igneous rocks. The few intermediate igneous rocks are
diorite (the plutonic or deep-seated form) and andesite (porphyrite)
the volcanic form, which usually occurs as a dyke.

The writer has not seen any granite either in or about this gold-
field, nor has he seen any between Sekondi and Tarquah. Typical
hornblende-biotite-gneiss occurs on the coast near Sekondi, and is
quarried there for building purposes, but he has not seen any such
rock in or about the Tarquah gold-field.

The writer stated in a paper on the Witwatersrand gold-field,
read before the North Staffordshire Institute of Mining and
Mechanical Engineers on October 4th, 1889, that "The length of
their (bankets) extension, coupled with the steepness of their dip,
justly suggested a continuation downwards for a considerable dis-
tance."* Just as on the Rand the length of outcrop indicated
continuity in depth, so here the long known lengths of outcrop
warrant the same conclusion. The view expressed in 1889 has been
so splendidly confirmed on the Rand that he did not see how it
could be otherwise here.

The rocks surrounding the Tarquah gold-field are mostly of basic
igneous origin. At Prestea, a graphitic schist-layer occurs in close
proximity to the quartz-reef. The Prestea reef is a bedded quartz-
reef, and has a strike of north 48 degrees west with a dip 60 degrees
to the north-east.

There is no question in the writer's mind as to the permanency
of the conglomerate-beds in depth. They differ in thickness at

* Trans. Inst. Min. Eng., 1889, vo1 - x -



222 THE TARQUAH GOLD-FIELD.

the different mines, but it may be broadly stated that these beds
are considerably thicker at the south-western end of the synclme
than at the north-eastern end, and that the thicker they are the
lower the grade.



A vote of thanks was accorded to the author.



" BRICK-MAKING."
Paper by GEORGE L. ALLEN.



Abstract.

IN making clay into bricks the only forces that can be used are
natural crystallization and artificial cohesive attraction. The former
process is best suited to clays naturally plastic, and the latter for
dry clays; while a combination of the two may be satisfactorily
employed in treating certain classes of raw material. These methods
may be termed the plastic, the dry press, and the semi-plastic, and
the manufacturer who wishes to found a successful business must
satisfy himself at the beginning as to ^vhich method is most suitable
for his material.

PLASTIC CLAY BRICKS. In making plastic clay bricks, one very
important matter is to see that the clay is well mixed at the face.
The waggon which conveys the clay to the machinery should contain
a regular admixture of the various stratas of the clay bed, as
different sections usually require different treatment in drying and
burning.

It is important that the physical or natural condition of the
clay should be entirely broken up, and this should be accomplished,
as far as possible, by first passing it through a mixing mill and
rollers before it reaches the pug mill. The pug mill alone is too
often relied upon for thoroughly mixing and shredding the clay.
The duties of the pug mill are to consolidate the clay and press it
through the die into a continuous column. This column should
be thoroughly compact, free from lamination, and have a fine,
polished surface, clean and unbroken at the corners. Several
machine makers are now making a speciality of a double-shafted
pug mill, fitted with expression rollers, to produce this result.

CUTTING TABLE. A most convenient hand power cutting table
is one which travels longitudinally as well as laterally known as
the " Simplex " cutting table. The whole operation is performed by
one attendant with one handle. A few power cutting tables are in
use, some automatic and some not; but it is evident that, to super-
sede a hand table that requires but one attendant, the coming
cutter must be automatic. The " Raymond " and the American
Clayworking Machinery Co.'s automatic cutters have a most har-
monious arrangement of all parts, and make a perfectly straight cut.



224 BRICK-MAKING.

DRIERS. The old fashioned sysrem of open-air drying is, or
ought to be, a thing of the past. Nowadays drying floors and tunnel
dryers are recognised necessities. Tunnel dryers are of recent
introduction into this country, but already some are giving good
results, though their increased cost of construction may be against
their general adoption for some time. The requisites in a drier
are :- Non-liability to damage the green bricks, perfect regulation of
the heat and air circulation, economy in construction and working;
and the method which best achieves these results can only be
obtained by varied experiment and careful observation.

KILNS. The modern continuous kiln is fast superseding older
types; it is being rapidly perfected, and the day is not far distant
when it will be used for burning all kinds of material. A continuous
kiln, to give the best results, must always be built to suit the material
it is intended to burn, and the nature of the material must always be
taken into consideration in designing the kiln.

DRY PRESS BRICKS. Up to the present time little has been done
in this country in the making of dry press bricks, though in other
countries, particularly in the United States, the best quality of
facing bricks is made by this system. Where it has been tried in
Britain it has not been altogether successful, but this result is due
to a want of knowledge of the material best suited to this method,
and ignorance of the machinery best fitted for it. Briefly stated,
the method is as follows : The clay is first thoroughly dried, pre-
ferably by being left for some time under a shed with a hot floor.
It is then thoroughly ground in perforated mills, and being next
elevated to the top of the building, it is there sifted, the finer
particles of clay being delivered by rhones down through a hopper
to the press, while the coarser material is returned to the mill.
The fine clay is next delivered through a charger into moulds, where
by plungers with increasing degrees of force it is formed into com-
pleted bricks. It is to be noted that different qualities of clay
require different degrees of pressure.

These bricks require more careful steaming and harder burning
than the bricks made by the plastic method.

SEMI-PLASTIC SYSTEM. This system is generally applied where
the material is of a shaley nature. The material is ground as
already described in the dry press system, and is led from the
rhones into a double-shafted mixing mill, where it is stirred up and
mixed with a small quantity of water. From the mixing mill the
clay is delivered into the pug mill, and from there it is pressed into
moulds in a circular revolving table, or in a cylinder, according to
the class of machine. From the moulds the bricks are then
delivered automatically to the press, where under considerable



BRICK-MAKING. 225

pressure they are finished and taken direct to the kiln. This method
of brick-making is best suited for treating the refuse heaps of coal
and iron-stone mines, where these are used for making bricks.



Mr. J. A. Longden, Mr. A. Gilmour, Mr. A. Weatherilt, and Mr.
H. B. Nash took part in the Discussion.

A vote of thanks was accorded to the author.



THE BUFFELSDOORN AND ADJACENT DISTRICTS
OF THE NORTHERN KLERKSDORP GOLD-FIELDS,
TRANSVAAL."

Paper by WILLIAM SMITH.



Abstract.

I. GEOLOGY.

ALTHOUGH much has been learned and recorded by competent
geologists and mining engineers of the general formation of the
Klerksdorp district, still there is much to be done before the all
important point, the exact position of the Main Reef payable beds,
is located along the lines of the formation. There can be little
doubt that these beds will be traced from Randfontein to Klerks-
dorp.

The generally recognised succession of beds as known on the
Rand and neighbouring districts can be more or less distinctly
recognised and traced over the Klerksdorp district, with this
difference, that the country generally is more disturbed and
broken up by the presence of intrusive igneous rocks, and con-
siderable areas are covered by the overflows from dykes and other
centres of eruption. The disturbances caused and the extensive
areas covered by the igneous action has rendered progress in
prospecting very limited, and in most cases it has been attended
with uncertainty and much expense. Boring on a large scale and
to great depths is now well understood and carried out on the
Rand, and it only requires that a systematic plan of prospecting
by bore-holes be employed to settle the question of the position
of the payable reefs. The fact that large areas are covered with
sheets of ancient lava need not deter one from piercing them with
the drill, as in all probability they will be found of a reasonable
thickness, especially near the edges of the overflow, and merely
a cover to the older gold-bearing formations.

The succession of strata from below upwards is as follows :
(i) Granites; (2) Schists; (3) Old and New Quartzites, Sandstones
and Shales with Gold-bearing Conglomerates; (4) the Black Reef,
lying unconformable to the above named ; (5) Dolomites ; and (6)
the Magaliesberg and Gatsrand Sandstones and Quartzites.

Granite is found in large bosses appearing to the north and
west of Buff elsdoorn ; and resting on these bosses are the shales,
sandstones, and quartzites of the Rand formation; and towards



BUFFELSDOORN DISTRICT OF KLERKSDORP GOLD-FIELDS. 227

the east, the overlying Black Reef and Dolomitic Limestone, with
a large area of igneous rock underlying and forming the footwall
of the Black Reef. Igneous rock also occurs in large masses to
the west of the Palmietfontein farm, and to the north on Cyfer-
fontein farm. From the Doornfontein farm, about ten miles north
of Buffelsdoorn, a rock similar to the Hospital Hill shales (which
are generally taken as tjje index to the Main Reef series) can be
traced in a north-easterly direction for several miles, and this
would indicate that the Main Reef should be found on a more or
less parallel line at about one mile to the south-east or on the
Witrandjesfontein, Tweelingsfontein, and Rooikop farms.

The general dip of the formation is from 30 to 45 degrees
south-eastward, and the strike trends from north-east to south-west.
The igneous rock is chiefly amygdaloidal diabase, with other basic
rocks. Coal is found in small basins overlying the dolomite; and
one of these areas, situated near Koekemoer station, has been
opened out and worked by the Buffelsdoorn Estate and Gold-
mining Company (Limited). Large deposits of good coal are
found south of Klerksdorp and the Vaal river in the Orange River
Colony, and the coal is supplied to the Klerksdorp gold-mines at
a reasonable price.

II. THE BUFFELSDOORN ESTATE AND GOLD-MINING COMPANY

(LIMITED).

This mine, one of the best equipped mines of the district, began
in a small way, with but trifling development and a 10 stamps
battery, and to-day has 200,000 tons of ore-reserves, and 100,000
tons of 4.97 dwts. gold-slimes conserved in dams. The mining
and other rights are situated on the Buffelsdoorn (660), Request
(137), Rietfontein (632), Eliazar (617), Rietkuil (337), Palmiet-
fontein (697), and Stilfontein (381) farms.

The mine-workings comprise one main inclined shaft, 1,245
feet deep, the No. i west inclined shaft, 524 feet deep, and the
No. 2 west inclined shaft, 539 feet deep. These shafts are con-
nected by six levels; the seventh level is connected with No. i
shaft, and is being driven westward to No. 2 shaft; and the eighth
and ninth levels are being driven westward from the main inclined
shaft towards No. i shaft.

The surface equipment consists of: (i) The battery-plant, (2)
the cyanide-plant, (3) the electric-plant, (4) the pumping-plant, and
(5) the air-compressing plant. The battery-plant consists of 170
stamps of the ordinary gravitation heavy type pattern. Details of
the plant are given in the paper.

The average working costs per ton of stone milled are as follows :
Mining, los. 9-94d. ; redemption of capital, 45.; transport, 4-54d. ;



228 BUFFELSDOORN DISTRICT OF KLERKSDORP GOLD-FIELDS.

prospecting, o.84d. ; milling, 33. 5-42(1 ; cyanide treatment, 23.
2.5yd.; native labour supply, 3-59d. ; and the total cost of 2is.
2. pod. would be reduced about 10 per cent, if waste-rock, broken
and thrown out in the sorting process, was taken into account.

The writer apologises for the brevity of the paper, which was
written on the veldt, but hopes, at some future date, when he has
left his regiment and returned to civil life, to write an extended
paper.



A vote of thanks was accorded to the author.



"THE CULM-MEASURE TYPES OF GREAT BRITAIN."
Discussion on Paper by W. A. E. USSHER.



This paper was read at a previous meeting of the Institution of
Mining Engineers (see Transactions, 1900, Vol. XX., p. 360).

Mr. Ussher referred to and quoted from a paper entitled " Notes
on Certain Granitoid Fragments from the Culm Conglomerates"
by Mr. A. R. Hunt.

Mr. James M'Murtrie took part in the Discussion.
The meeting was then adjourned.



WEDNESDAY, 4th SEPTEMBER, 19O1.

Mr. JAM^S S. DIXON in the Chair.

"THE PRODUCTION OF COPPER AND ITS SOURCES
OF SUPPLY."

Discussion on Paper by M. EISSLER.



This paper was read at a previous meeting of the Institution of
Mining Engineers (see Transactions, 1901, Vol. XXL, p. 315).

Mr. A. H. Bromly continued the Discussion.



"THE IMPERFECT PULVERISATION OF ROCKS BY
MEANS OF STAMPING, AND SUGGESTIONS FOR
ITS IMPROVEMENT."

Paper by E. D. CHESTER.

Abstract.

THIS paper explains the cause of the imperfect crushing by stamps
as at present operated, owing to the restriction set up through using
a fine screen, and trying to reduce the material at one operation,
and suggests crushing in series and classifying. A trial run on
hard Perthshire conglomerate in a stamp mill running at 94 drops
per minute, with 1200 Ib. stamps and yj inches drop, by first
crushing through a screen 100 holes to the square inch, proved
that 86.3 per cent, would pass through a 900 screen at the rate of
9.29 tons per stamp per 24 hours. The coarse sands not passing
the 900 screen were recrushed in a battery of 1200 Ib. stamps, drop-
ing 4 inches, drops per minute, 144, resulting in 2.6 tons per stamp.
The two above results give an average of 6.277 tons per stamp.
Another quantity of rock was then crushed in accordance with the



Online LibraryInternational Engineering Congress (1901 : GlasgowReport of the proceedings and abstracts of the papers read → online text (page 20 of 37)