Charles George Warnford Lock.

Economic mining: a practical handbook for the miner, the metallurgist and ... online

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The lumps of mineral, as they are taken from the mine, consist of
bundles of hard fibres, lying parallel to one another, and strongly
bound together. They vary in colour from light grey to brown, and
the general appearance of a fine sample of asbestos is suggestive of
the interior of the riven trunk of a tree. By the exervise of a littlo
care, threads may be separated, many feet or even yards in length,
the oontiniiity being perfect from end to end, the o^oneral appear-
ance and strength being very similar to those of flax. It is this
quality of length and strength of fibre that distinguishes Italian
ttbestos from aU other. The best comes from Eniarese; the most
fire-proof from Usseglio; that of Campiglia Souna has long fibres,
bat is often in a state of decomposition ; on the whole, the mineral
from Yaltellina has the strongest fibres.

Asbestos of inferior quality is found in a number of localities in
the United States, but these are for the most part of no more than
znineralogical interest, and have never become important producers.
The total amount of asbestos mined in the United States in 1889 was
bat 30 tons ; in 1890, the product was only 71 tons, the production in
eadi year being limited to Oalifomia. In 1 89 1 the output was 66 tons.
The American mineral is adapted only for grinding, for paints and
cements, for boiler and steam-pipe covering, &c.

African asbestos is dark blue in colour, and while the length of
the fibre is about the same as the Canadian, it is altogether wanting
in fire-resisting power. Whilst Italian asbestos contains nearly 80
per cent, magnesinm silicate and only about 3 per cent, iron oxide,
this African asbestos only contains about 50 per cent, silica and no
less than 40 per cent, iron oxide. It will not stand much heat with-
out disintegrating and becoming quite rotten, this effect being pro-
bably due to the fact that a portion of the iron is in the form of a
ferrous salt. By exposure to air and heat this salt oxidises, and
alters the composition of the asbestos to such an extent that it is
easily charred.

A considerable quantity of asbestos, somewhat resembling the
Canadian in character and formation, has been imported from beyond
the Ural Mountains in East Bussia. This fibre, although darker in
odIout than the Canadian asbestos, is certainly superior to the African,
but has very little commercial value.



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1 66



ECONOMIC MINING.



In oompoBition, asbestos is essentially a hydrated magnesium
silicate. The following analyses are interesting for oomparison :•—





Caoadlau.


Italkn.




a


h


c


d


1


u


SUica


40-57


40-52


8906


40-9


40-3


41-69


Magnesia (and lime) .. .. ..


41-5


42-05


40-07


33-2


43-37


37-84


Alumina


•9


2-1


3-69


6-6


2-27


2-57


Iron oxide


2-81


1-97


2-41


5-75


•87


3-01


Potash


,,


,,


,,


traces


,,


•85


Soda


,,


,,


,,


•68


••


1-41


Chlorine


,,


,,


, ,


-25






Water


13*55


13-46


14-48


.,


13-72


304


Loss (organic matter, Ac ) . . . .


••




•3


12-5


••


9-5d



NoTK.— ^ is Tery finest quality ; d, average commercial ; i, average oommerdaL

A curious feature of Canadian asbestos is that while it is perfectly
fireproof and acid-proof, it is easily damaged if exposed to rain or
water when newly mined, becoming hard and woody.

Asbestos is used in making liquid and fireproof paints, roofiog,
piston and valve packing, flat packing, covering steam-pipes and
boilers, fireproof cements, sheet and roll millboard, flooring, felt,
tubes for carrying electric wires, lamp- wicks, <&c. It is often used in
combination with hair felts and other substances.

All asbestos goods may be classed, as regards their process of
manufacture, under two heads — paper and yam. The paper may be
worked up in various ways, and the yam may be twisted, plaited, or
woven, but the crude material is niade to assume one of these two
forms before it is worked into the finished article.

The crude asbestos is brought in bass containing 1 to 2 cwt. each.
When unpacked, it is found in pieces of all sizes from that of a man's
hand to such as a man can scarcely lift. These have first to be opened
out to free the fibres from one another, and from the non-fibrous
material by which they are bound together. For this purpose a
machine has been devised consisting of two rollers covered with teeth
of pyramidal form. These revolve, as a rule, at equal peripheral
speeds, and at the same time have a sideways motion in relation to
each other, so that the asbestos, which is fed in with the fibres lying
parallel to the line of motion, is both crushed and separated at the
same time. By the direct pressure, the binding agents are separated,
and then the loosened fibres are combed apart by the reciprocating
motion, which, however, is not sufi&ciently great to interfere with
their parallelism. In the subsequent operations there is nothing
special, the short fibre being dealt with like paper pulp, and the long
fibre being spun and woven as a textile.

The total yearly production is about 6000 to 9000 tons of Canadian,
and about half that quantity of Italian. The trade being in fev
hands prices fluctuate arbitrarily, ordinary figures being 20/. a ton
for Italian and 8/. to 152. a ton for Canadian.



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NON-METALLIFEROUS MINERALS. 167



ASPHALT.

OuGiHALLY applied speoificallj to a peculiar substance found in a
single localitj — on the shores of the Dead Sea — ^the term asphalt is
BOW used generioally to denote a great number of semi-solid bitumens
or bituminous rooks, differing widely from each other in chemical
composition and in behaviour under the influence of heat and of re-
sgentsL The original substance, of which very little is seen now,
WES defined as having a sp. gr. of 1*0 to 1 * 2, fusing at 212° F., dis-
Bolving in five times its weight of naphtha, insoluble in water and in
alcohol, emitting a strong smell of pitch, and burning with a bright
flame. All bituminous minerals are supposed to be derived from
vegetable matters acted on by water, other conditions probably being
exdusion of air, and presence of heat or pressure, or both.

Until the remarkable impetus given to the asphalt industry in
California and Utah in 1888, me Pitch Lake in the island of Trinidad,
and the deposits of Seyssel, in France, Yal de Travers, in Switzerland,
and Limmer, in Brunswick, furnished the bulk of the world's supply.
Cuba produces asphalt of excellent quality, some of which has been
imported into the United States. Venezuela has furnished a small
portion of the supply in the past, and a few tons of bituminous lime-
stome are produced annually in the island of Sicily. In Mexico large
deposits of asphalt are reported.

The American discoveries have led to a multiplication of names
without any corresponding usefulness, each deposit apparently re-
ceiving a new appellation. Thus we have albertite, aspnaltum, brea,
elaterite, gilsonite, grahamite, maltha, piauzite, uintite (or uintahite),
wolongonzite, ieind wurtzilite.

The most important European source of asphalt is a limestone
hiU impregnated with bitumen close to the town of Seyssel, on the
Bhone. The product varies much in appearance and in the propor-
tions of bitumen and limestone, but contains no other substance.

The Yal de Travers mine is very different from that of Seyssel.
It is much richer in bitumen, but of considerably less extent. The
bed of asphalt is covered with a thin layer of soil, underneath which
is another layer of earthy asphalt, varying in thickness from 2 ft. 6 in.
to 3 ft. The bed itself is circular in form, about 22 ft. thick and
1 60 yd. diam. It contains 12 or 13 per cent, of bitumen, and it was
the first kind ever employed in the construction of pavements.

These two mines are by far the most important Enropean sources
r»f asphalt ; but there are several smaller ones from which an equally
good product is obtained, e.g. those of Challonge, Gbavaroche,
Hanosque, Lobsann, Dallet. and Pont du Chateau. There is also a
large mine at Maestu, near Yittoria, in Spain, the product of which is
of a very fine quality ; but access to this mine can only be gained by



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i68 ECONOMIC MINING.

means of mules and oxen, which is a serious drawback to its snccessfal
workine.

Asphalt is ordinarily obtained from the mine by blasting, like
other rocks. This is sometimes carried on in the open air, as at
Seyssel and Yal de Travers, and sometimes in underground workin};6,
as at Challenge and Chavaroche. In winter, owing to the hardness
of the rock, the work is much easier than in summer, when it is more
or less soft and sticky. It sometimes happens that the elasticity of
the mineral cannot be overcome by gunpowder, in which case it must
be hewn out with the pick. In the very hot weather, the miners
work for only a few hours in the morning, before the rock has had
time to soften under the influence of the sun. These remarks do
not, of course, apply to the extraction of the rock from underground
workings, where these obstacles are avoided by the unvarying low
temperature of such workings. The blocks of mineral should never
be piled up in high heaps, as in such a oa^e an elevation of tern-
perature would cause the undermost blocks to crumble to piecee,
when, should the fragments become mixed with rain-water, the sub-
sequent operations are much impeded.

The best European asphalt is lime carbonate (containing some-
times slight traces of silica) impregnated naturally with bitumen, is
the proportion of about 7 or 8 parts of bitumen to 93 or 92 parts of
the limestone. The mineral is found in layers interposed between
beds of ordinary limestone, especially in the Upper Jurastsic forma-
tion, and presents the following physical characteristics : —

Its colour is a deep chocolate, almost black. Its fracture also i
resembles chocolate in appearance and colour; it is granular and
irregular, without any plane of cleavage ; its colour is deeper accord-
ing as it is worked in the direction of the stratification or perpen-
dicularly to that direction ; it is deeper and more floury in the first
case, and drier and clearer in the second. Each individual mine has
its own particular shade. In consistence, it varies with the tern-

Eerature ; it is very hard and sonorous when cold, but softens when
eated, until at 120° to 140° F. it falls to powder. Its average sp. gr.
is 2*235. Its structure varies in difierent samples.

Asphalt of the best quality may be known by the following con-
ditions : — The grain is fine and homogeneous, and does not exhibit a
particle of ordinary or white limestone. The rock is often lined with
streaks of a darker colour than the rest, which give it very much the
appearance of a tiger^s skin. Other samples contain crystals of lime
carbonate, impregnated with bitumen like the rest, sometimes of con-
siderable size. All these varieties are perfectly good so long as tbey
are completely penetrated by the bitumen. Bad qualities may bs
recognised as follows : — Sometimes the rock is regularly impregnated,
but the proportion of bitumen is as low as 6 per cent., when it can be
worked only with much difficulty. iSometimes the limestone is very
hard and much cracked, the cracks being filled with bitumen, bo that,
when broken, the fracture appears brownish black, like the good
samples, but when examined with the microscope, the impregnation
is seen to be very incomplete. Samples of this kind are frequently met
with in Auvergne. Sometimes the limestone, while it appears rich ia



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NON-METALLIFEROUS MINERALS. 169

bitumen, contains clay, which, being impenetrable, spoils the homo-
geneity, and canses the fissures so often seen in streets paved with
the material ; the presence of clay in the sample is easily recognised.
Some bituroinons limestones, that of Lobeann/ for instance, contain
an oily principle besides the bitumen, which renders them greasj, and
spoils the consistence of "mastic" made from it; this oil may be
removed by distillation, after which the asphalt is fit for use. When
asphaltio rock has been long exposed to the air, the bitumen on the
gnrfaoe dries up, to a depth of about *01 in. This desiccation, which
is due to the slow evaporation of the bitumen, is sufficient to discolour
the asphalt so much that it becomes similar in appearance to ordi-
nary omestone ; blocks of this kind, which are suspected to contain
bitnmen, must be broken up to ascertain the colour of the interior,
ling evaporation rarely extends farther into the rock than ^ in.

Inferior asphalts, such as the bituminous limestones of Auvergne,
contain clay, silica, magnesia, iron salts, &c. The Auvergne samples
contain also traces of arsenic. As a general rule, it may be stated
that samples of asphalt are valuable in proportion as they are free
from these foreign matters. It is seldom necessary to make a quali-
tative analysis of asphalt, but it is often required to determine the
proportion of bitumen. Following is a simple method. A quantity
(about 200 grm.) of the substance is reduced to a fine powder, and
dried by exposing it in a current of air heated to a temperature higher
than 230^ F., but not above 300°, since above this temperature the
bimmen may be altered by the vaporisation of certain essential oils.
After well mixing this powder, 100 grm. is taken and placed in a
beaker ; 100 grm. pure carbon bisulphide is then poured upon it, and
the mixture is well stirred with a glass rod. After resting a moment,
it is poured into a weighed filter, having another beaker placed
heneath. More carbon bisulphide is poured upon the limestone
remaining in the first beaker, well stirred, allowed to stand, and the
dear portion is again added to the filter ; this is continued until the
powdered limestone is perfectly white, and the last portions of carbon
bisolphide added exhibit no tinge of brown. The limestone is then
dri^ whilst the liquid in the filter is running through. When
perfectly dry, the limestone and the filter are weighed together, and
after deducting the weight of the filter, the weight of the washed
Hmestone is obtained, and, by difference, the weight of the bitumen
removed by the carbon bisulphide.

The production of asphalt in Germany reaches 40,000-50,000 tons
jeariy, with a value of about 7«. 6d. a ton ; that of Italy, 30,000-
40,000 tonS; worth about 20«. a ton ; that of Spain, 200-600 tons at
7^ ^ French statistics are comprehensive of all bituminous sub-
stances, which average about 200,000 tons per annum, estimated at
About 5«. a ton.

The asphalt of Trinidad is found in a so-called " lake " (really a
plain), situated about 100 ft. above the sea and about 2 miles from
the sea-shore, at the village of La Brea (" Pitch "), 40 miles from
Port of Spain. The area of the deposit is over 100 acres, and the
depfth ascertained by rough borings varies from 18 ft. at the margin
to 78 ft in the middle. On this basis, the deposit must contain some

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170 ECONOMIC MINING.

millions of tons, and certainly the removal of neai'ly a quarter of a
million tons has not appreciably lessened it. The deposit appears
as a level tract of brownish material having an earthy appearance.
Cracks or fissures, having a width and depth of a few feet, appear
here and there over the surface ; some are filled with rain-water, omers
with soil blown there by the wind and giving support to a scrabby
vegetation.

Travellers have reported that the deposit is liquid in the middle,
but such is not the fact. Carts and mules can be driven everywhere
on its surface. The material is dug with a pick and shovel, loaded
into carts, and hauled to the beach. Here it is placed in baskets,
which are carried by coolies wading through the surf to lighters, and
from these lighters it is loaded on vessels. During the voyage the
material unites into a solid mass, and has to be removed again by the
use of the pick and shovel. On being unloaded, it is placed for about
5 days in large tanks heated by a slow fire. The moisture is expelled,
the roots of treeis and other vegetable matters are skimmed off the sur-
face, the earthy matter with which it is combined settles by gravity,
and the refined product is run off into barrels. This refining is in
reality a mere heating to a liquid condition, in order to allow the
sediment to deposit ; and great care is taken not to heat the material
to a point which will in any way change its chemical condition, or
produce distillation.

The crude asphalt has the following properties: sp. gr. 1*28;
hardness at 70^ F., 2 * 5 to 3 in Dana's scale ; colour, chocolate brown ;
analysis: —

Bitumen 89*83

Earthy matter 33*99

Vegetable matter 9*31

Water 16*87

100*00

The earthy matter consists mostly of clay, and the rest is very
fine sand. The refined asphalt has the follcwing properties : — sp. gr.
1 • 49 ; hardness at 70° F., 2*5; colour, black ; breaks with a oon-
choidal fracture ; bums with a yellowish-white flame, and in burning
emits an empyreumatic odour ; analysis : —

Bitumen (by CS,) 59*86

Earthy matter 35*82

Vegetable matter 4*32

10000

An analysis of the pure bitumen dissolved out by CSj gave

Carbon 85*89

Hydrogen 1106

Sulphur \ 2*49

Unknown, poBsibly oxygen 0*56

10000

After treatment with petroleum residue, in order to make asphalt
paving cement, the bitumen soluble in CSj varies from 68 -6 to 70
per cent.



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NON METALLIFEROUS MINERALS. 171

The approximate cost of the crude product per ton delivered f.o.b.
is ld«., made up as follows : — rock, 5«. ; cartage, 4«. ; boating, 3«. 3(2. ;
export dnty, 9a. The annual shipments are about 90,000 tons crude
and 10,000 tons hpwree (purified), about 10 per cent, of the former and
90 per cent, of the latter coming to Europe. The selling prices in
1892 were 28« 6rf. a ton for crude, and 68«. 6(£. for pure, f o.b.

The bituminous sandstone of California is found in large quanti-
ties at various points between San Francisco and Los Angeles. It
contains about 12 to 18 per cent of bitumen, and the rest is quartz
sand, in grains about ^ in. diam. The material is sufficiently soft
to yield to the heat and pressure of the hand. Within the last few
years it has come into use for paving purposes and coating iron pipes
on the Pacific coast. The rock is quarried, broken to fragments of
about 2 in^ heated in kettles by steam (which causes it to fall into
poirder), and then, while still hot, taken to the street and compressed
by rolling or tamping. Reports as to its quality as a paving material
are conflicting.

In 1888 a large deposit of bituminous rock containing an un-
Qsnally large percentage of asphalt was discovered in Ventura county,
California. This mineral contains 24 per cent, of bitumen, the
other constituents being silica (about 64 per cent.), iron oxide, and
calcium carbonate. Its high percentage of bitumen increases its
value, and the price ranges from 32«. to 22. per ton, while the bitu-
minous rock of San Luis Obispo and Santa Cruz is valued at about
10«. per ton at the mines. Deposits of a nature similar to the Ventura
product are also being operated in Santa Barbara county.

The Ventura mine is situated 6 miles from San Buenaventura.
The lode presents an excellent illustration of the general character
of the asphalt deposits of the locality, which are true fissure veins in
a mass of grey silicious clay. It was indicated on the surface by a
mere seam 7 to 15 in. thick; but when stripped it was found to
iocreaae rapidly, both horizontally and downward, so that at the
depth of 66 ft. from its surface cropping and 60 ft. horizontally from
the same, its thickness is 5 ft., and the material has improved in
quality. The strike of the vein is 30^ N. ; its pitch, 66° to 70°,
a30° W.

While going in upon this vein for 100 ft. in an open cut, it was
found to expand into several '* pockets " of 7 to 16 ft. diam., from
which great masses of material were extracted ; the whole output from
this cut alone was 1400 tons. At one point a wall of the " ore "
appeared sideways overhead. This proved to be a "spur" vein
Joining the other at an oblique angle, with a thickness of 3 to 4 ft.,
increasing to 6 ft of clear asphalt, about 90 ft. from the entrance of
the cut.

The spur vein was found to expand into a huge pocket, which,
when mined out, formed an irregular chamber about 30 ft. square by
12 to 15 ^at one point 30) ft. high, frx>m which 450 tons of material
were obtained.

The variability of thickness and ihe tendency to the formation of
•'pockets," introduces an element of uncertainty which, fortunately,
aeems generally to run in the direction of an increase of mass. This

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172 ECONOMIC MINING.

sporadic expansion into large masses appears to be a oharacteristic of
these asphalt veins; and the regular vein body itself, as a role,
increases downward.

The material is a brownish black, nniform mass, of conchoidal
fracture ; yielding somewhat nnder light blows of the hammer, but
splintering tinder heavy ones, so that it can readily be blasted. The
sp. gr. is about 2. On heating to about 450^ F. it softens into a
mushy condition, but does not attain fusion without the aid of some
^'fluxing" or thinning substance. An attempt to replace the some-!
what tiresome process of drilling blast-holes by the use of hot iron
bars failed to give satisfactory results.

Assays show that the total bitumen fixed at 212^ F., while ranging
within the several veins from a minimum of 15*28 per cent, to as
much as 22*75 per cent., will in each case, on the average, be dose
upon 20 per cent. — generally above. The fixed residue or ash is in
all cases a silicious clay, usually containing but little sand and about
3 per cent, of lime carbunate ; occasionally occur streaks, or " horses,'*
in which is a notable admixture of either coarse sand or nests of
peculiar gravel hardened by lime carbonate, gypsum, and iron pyrites.
At some points the floor clay, or footwall, is so strongly imbued with
bitumen that, while inferior in quality to the vein mass, it can never-
the^ss be profitably used for certain purposes.

There are several deposits of bituminous rock in San Luis Obispo
and Santa Cruz counties, in which the peculiar features of asphalt
formations are strikingly illustrated, clearly showing that they belong
to no particular era or age ; they are found at various altitudes, and
with no uniform character in appearance, hardness, or chemical com-
position. Deposits of solid asphalt and springs of viscid, oily material,
commonly called " brea," occur in places not 1000 ft. apart, and yet in
strata of unquestionably different periods of formation. The bitu-
minous rock of San Luis Obispo and Santa Cruz is a sandstone
thoroughly impregnated with bitumen. It is used almost entirely
for street paving, and for that purpose is probably more easily and
cheaply prepared than any of the asphalt products. The only treat-
ment necessary is to steam it, so as to thoroughly mix its ingredients
and soften it for spreading to a uniform thickness and a smooth even
surface. Analyses gave : —

Sand 65-917

Bitumen 16*255

Iron and alumiDa • 8*405

Calciutu carbonate 8*212

Magnesium carbonate 1*003

Undetermined 0*208

100*000

An important deposit is worked in Uintah Valley, about 100 miles
from Price, Utah. The vein is described as a regular fissure, cutting
across the country for 12,000 ft., or more, in length, and 3 to 4 ft. thick.
It has been opened by 14 shafts or pits, aggregating 700 ft. in depth.
The surface-portions of the mineral are fissured and cracked by weather-
ing, are more or less contaminated with sand and earthy matters^ aad
are regarded as of second quality, while the portions below are oom-

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NON-METALLIFEROUS MINERALS, 173

pftct and pnre. The mineral is obtained in masses several inches in
dUnL, and apparently free from mechanically disseminated impurities.
It breaks with a oonchoidal fracture, is very brittle, and is readily
redaced to powder in a mortar. Hardiiess, 2 to 2*5. Sp. gr. 1*065 to
1-070. C!oloar, black, brilliant, and lustrous ; streak and powder, a
rich brown. It is a non-conductor of electricity, and is electrically
excited by friction. Analysis gives : —

Cbrbon 7843

Jlydrogen 10-20

Nitrogen 2*27

Oxygen 8*70

Aah 0-40

100-00



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