Charles George Warnford Lock.

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

. (page 34 of 76)
Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 34 of 76)
Font size
QR-code for this ebook

it is 3 ft. thick and crops out at the surface, whereas in others it
dwindles down to a few inches, or is found at depths varying from
3 ft to 20 ft. These two conditions, thickness of deposit and depth
of strata, taken together with the richness of material in phosphoric
add, are of oourse the chief points for consideration in the economic
urorking of Uie beds on an industrial scale.

In tiie two kinds of deposits, the ''Biver " and the "Land,'* the
naterial is of practically the same chemical description. Both have
been worked extensively and have proved to be of great commercial
Talne, the first especially so, since it is obtained by the simple and
inexpensive process of dredging, and is thus raised and washed from
all adhering impurities by one and the same operation.

The xoSl and nodules are found in very irregular masses or blocks,
of extremely hard conglomerate, and of variegated colours, weighing
from less than ^ oz. to more than 1 ton. The mean specific gravity
of the material is 2*40, and it is bored in all directions by very smaU
boles. These holes are the work of innumerable Crustacea, and are
BOW filled with sands and days of the overlying strata. Sometimes
the rock is quite smooth or even glazed, as if worn by water ; at others
it is rough and jagged.

Interspersed between the nodules and lumps of conglomerate
are the fossilised remains of various species of fish, and some
animals, chiefly belonging to the Eocene, Pliocene, or post-Pliocene

Very careful analyses of a large number of the samples of " land
rock" taken from working pits and made by Wyatt gave, after being
well dried at 212° F., the following average : Moisture, water of com-
bination, and organic matter lost on ignition, 8 per cent. ; lime
I^osphate, 59*63 per cent. ; lime carbonate, 8*68 per cent. ; iron and
aluiiana(calculated as oxides), 6 * 6 per cent. ; magnesia carbonate, * 73
per cent.; sulphuric acid and lime fluoride, 4*8 per cent.; sand,
nliciouB matters and undetermined, 11*56 per cent.

The cost of producing one ton of •* river rock " in dry marketable
wndition is generally allowed to be about 5*25 dels, per ton, includ-
ing 2*00 dofi. royalty, and, with a properly constructed plant, well
nukiiaged land companies with no royalty to pay, place their cost of
production at about 4 dels., delivered free alongside vessels in
Charleston harbour.

Digitized by



As a raw material of the first class in the manafacture of soluble
and available phosphates. South Carolina rock will continue to be
everywhere held in the highest esteem. In Europe it is also veiy
popular, and, being of unvarying Quality, has yielded results that
cannot be surpassed by any other pnosphate as an all-round staple,
uniform, and reliable article.

No absolute opinion can be expressed as to the probable extent
and capacity of the yet untouched or unexploited deposits, but it may
probably be safely estimated at about 30 miles. Placing the yield of
this area at the present average of 750 tons to the acre, we ooncla^ion
would be that the State may still produce about 14,000,000 tons.

The annual production of Carolina phosphate is about 400,000 io
500,000 tons, but in 1892 it fell to 350,000. The selling price in
foreign markets has been 6<2. per unit, which was fixed with tlie
object of killing competition, while it entailed a loss to the producer.

The existence of nodular amorphous phosphate deposits in Florida
is not a matter of recent discovery, for they were found in various
directions manv years ago, but were never believed to be of suffident
importance eitner in quantity or quality to merit the serious attentioD
of capitalists. The geologiod formation in which the deposits occur
has been very fully described in Wyatt's * Phosphates of America,' and
may be broadly summed up here as being composed of: —

1st. Original pockets or cavities in the Yicksburg limestone, filled
with hard and soft rock phosphates and d6bris.

2nd. Mounds or beaches rolled up on the elevated points, and
chiefly consisting of huge boulders of phosphate rock.

3rd. Driffc or disintegrated rock, covering immense areas, chieflv
in Polk and HiUsboro counties and underlying Peace Biver and iti

The work of exploration or prospecting has now extended all ovei
the State in each of these varieties of the formation, and actoa]
exploitation on the large scale by regular mining and hydraulici
methods has been commenced at various points.

In several of the mines, notably in those of Marion and Gtrai
counties, there are immense deposits of phosphatic material, proved b^
actual experimental work to extend in many cases over uninterrupted
areas of several acres. The deposits in each case have shown theuh
selves to be combinations of the *' original pocket " and the '' mound ""
formation, and the superincumbent material, or overburden, u
principallv sand, and may be fairly said to have an average depUi oi
about 10 ft. The phosphate, immediately underlying it, is sometin^f
in the form of enormous boulders of hard rock, cemented togetha
with clay, and sometimes in the form of a white plastic or frial^
mass resembliuK kaolin, and probably produced by the natural di&
integration of the hard rock by rolling, attrition, or coucussion. Tb<
actual thickness of the deposits is too variable to be computed witl
any accuracy into an average, but it has been known to reach a depti
of 50 ft., and a little over 2 acres only has yielded more than 20,0t>'
tons of good ore, without signs of exhaustion. Directly outsdde of tl»
limits of these combined " pockety " and " mound " tormations, tb*
deposits of phosphate seem to abruptly terminate, and to give placv

Digitized by



to an unimportant drift, which sometimes crops ont at the surface, and
which may he followed in all directions over the immediate vicinity
without leading to another pocket of exploitable value.

The same geological phenomena are prevalent in nearly every
section of the country, with the exceptions of Polk and Hillsboro
coimties, where they are somewhat modified. We are, therefore,
warranted in declaring that the Florida phosphates of high grade
occur in beds of an essentially pockety, extremely capricious, uneven
and deceptive nature.

Sometimes the pockets will develop into deep quarries, and will
probably yield large quantities of various merchantable qualities.
At other times they will be entirely superficial, or will contain the
phosphate in such a mixed condition as to render profitable exploi-
tation impossible.

In the case of the " pebble " or *• drift " deposits this capridous-
neasis much less marked ; in fact an unusual degree of r^ularity may
be flaid to characterise their occurrence in the extensive area in which
they have been found, and which may be roughly said to take its
point of departure in Polk county, a little to the south of Bartow, and
thence to practically continue with a gradually narrowing tendency
to within a very short range of Charlotte Harbour. The country is
flat and swampy, and is intersected at frequent intervals by the
Alafia, Manatee, Peace, and others rivers, rivulets, and streams.

Pit-sinking is now going on over a wide area, and it has been
practically demonstrated that this section of Florida is more or less
underlaid with a nodular phosphate stratum of a thickness varying
from a few inches to 30 ft., and covered by an overburden that may
be fiurly averaged at about 8 ft

The actual chief working centre for ** pebble " phosphates is Peace
Biver, which rises in the l^igl^ Iftke lands of Polk county and flows
rapidly southward into tiie Gulf of Mexico. Its course is extremely
irregular, and its bottom is a constant succession of shallows and deep
basins. Lakes Tsala-Opopka and ChilHcohatchee and Pains and
Whidden creeks are its chief tributaries and the main sources of its
phosphate deposits, the pebbles being washed out from their banks
and borne along their beds by the torrential summer rains.

Prof. Cox ascribes the Florida phosphate deposits to the minerali-
sation of ancient guano. They occur in much-weathered Eocene
limestone, filling the numerous potholes. The sand which forms the
overburden, covering almost the entire peninsula of Florida, has, in
Cox's opinion, been blown over from the sea beaches.

The pebbles, when freed ft'om impurities and dried, are of a dark
blue colour and are hard and smooth, varying in size from a grain of
rice to about 1 in. diam. Their origin is mainly organic, and they
are intimately mixed up with the bones and teeth of numerous extinct
spedee of animals, birds, and fish.

The river deposits are said to all proceed from the banks of " drift,"
fiitnated on the higher lands in Polk county, the pebbles being all of
the same size, and differing only in that ^ose of the land are of a
lighter colour, and imbedded in a matrix of sand and clay, to which
they frequently bear the proportion of about 20 per cent by weight.

Digitized by




The chemical compoeitioii of Florida phosphates and more especi-
ally of those known as *' hard rock " or '' boulder," is irregular and
variable. Nor is the physical aspect any more uniform, for while in
some regions it is pOTfectly white, in others it is blue, yellow, or
brown. In many instances it is practically free from iron and
alumina, but in some districts it is heavily loaded with these com-
mercially objectionable constituents. A large proportion of the land
rock is very soft when damp, but becomes perfectly hard when dried.

The following average analyses by Wyatt are presented for the
purpose of generally illustrating the composition of Florida phos-
phates : —

Boulders, oarefoUy seleoted andl

cleaned (120 samples) .. ../
Boulders and debris, as mined (237)

samples) .. j

Soft white phosphate (148 sampl^)
Pebble from Peace Biver, as markO

eted (84 Bamples) j

Pebble and drirt beds, Polk connty,!

washed and dried (92 samples) . . /

of lime.




Iron end














In mining the hard rock or high-grade boulder deposits, careful
selection of the different qualities and accurate sampling and analysn
of the different piles before shipment are essential. There is at present
no remunerative market in America for the richest grades, and it k
therefore probable tbat for some time to come the major pcrtion will
be exported.

Foreign buyers will make no contracts for raw material containing
a higher maximum than 3 per cent, of oxides of iron and alumina, ana
shipments must be made within this limit by miners who would
establish a good reputation. This necessitates great experience and
perfect harmony between the miners and chemist.

The most rational plan is to first crush the rock to a suitable sizv
as it comes from the mine, say, 1^ in., next to pass it through washeifl
and screens, and finally diy it by hot air, avoiding direct contact witli
fire. The cost of production under these conditions averages aboul
5 dols. per ton, delivered on the cars. The actual selling price fai
Florida phosphates, both '* hard rock " and ** pebble," in good market-
able condition, that is to say with no more than 1 per cent, of moistun
and a guaranteed maximum of 3 per cent, of the combined oxides oi
iron and alumina, is about 4j^. per unit delivered free on board can
at the mines. The prices paid at the end of 1891, for Florida phos-
phate delivered f o.b., were 6 dols. (25f.) a ton for pebble of 60-65 pei
cent, and 9 dols. (37«. 6d.) for hard rook of 75-80 per cent.

Where the deposits liave been denuded or come directly to the
surface, it is easy to collect the nodules, and by a slight washing from
adhering sand to prepare them for the market. But where the layo^

Digitized by



roiks deeper, a great quantity of saperinonmbeiit earth has to be
thrown aside, often as much as 6 ft. in depth. If excavation were
not then systematically conducted all profit would be soon absorbed
by too much handling of the bulky material. Fortunately the level
Datura of the country (there is scarcely an elevation of more than
30 ft in the whole region) allows the easy laying of tramroads into
the midst of the fields or woods where mining is done. In open fields
this is a regular and simple matter when aU other conditions are
favourable ; but when the rock lies too deep, or not at uniform depths,
or is not thick enough, nor rich enough, nor near enough to trans-
portation, the problem becomes more complicated. It costs about 1 dol.
('k. 2<L) a ton to mine. Pits 6 by 12 ft. are dug to the rock, which
is then carefully laid aside. The usual price is 25 cents (12^.) per
vertical foot removed. Transportation and washing cost about 1 doL,
and all other expenses of handling, drying, storing, &c., 1 dol. more,
making the total cost of rock, clean, dry, and gle


The presence of pyrite, sometimes in pieces ^ in. across, and dis-
tributed irregalarlj tjirongh the phosphatic rock, is characteristic of
^e black phosphate. It occurs also in the black shale, and the
solpbates of iron and alumina resulting from the action of the
snlphnric add (derived by atmospheric oxidation of the pjrite) upon
the Bbale can be seen enorustine the shale at several localities.
Several years ago Dr. Phillips made experiments with a crude phos-
phate containing considerable quantities of iron and alumina, to
asoertain if the phosphoric acid could be rendered available, without
treatment with sulphuric acid in the ordinary manner. By roasting
the finely ground rock with from 3 to 5 per cent, of sulphur a satis-
^ctoiy yield of " available " phosphate was obtained. There is no
doabt but that this method could be applied to a sulphurous phosphate,
if at any time the alumina should become objectionable. As long,
however, as it keeps below 4 per cent, it will not seriously interfere
with the treatment of the rock in the usual way.

Canada produces large quantities of a phosphatic mineral called
"apatite," which is derived from veins in the primitive rocks. It is
remarkable for containing calcium chloride and much fluoride, but no
i^bonate. The phosphate-bearing district is not extensive. Taking
the dty of Ottawa as a base, a glance at the map will show a section
)f ooontry north of that point, lying between two large tributaries of
the Ottawa river, which flow southward through the Laurentian
Siila, named respectively the Gatineau and the Lievre. This section,
nth a belt of 4 or 5 miles in width east and west of each of these
iven, is the true phosphate country; beyond this the mineral is
kpparently wanting, and here it is where mining is carried on.

The rocks of the mountain range that traverses this district are
omposed of pyroxene, representing the so-called " spotted gabbro " of
Norway, intermixed with quartzite, orthoclase, mica, gneiss, and
rTstaUine limestone. The phosphate itself varies much, according
locality. It is found in crystals sometimes of large dimensions ; in
A^^sses, varying from compact to coarse granular; in strata of a
imellar texture, and in a friable form. The latter is very abundant,
nd is known as ** sugar phosphate," often so decomposed as to take
he appearance of pure sand, soft enough to be dug out. The colours
f the phcepbate are very varied, consisting of green of different
bades, blue, red, and brown of all shades, yellow, white, and cream
:>]oured. Occasionally beautiful crystals are met with, large and
erfect at both ends, and enveloped in calc spar, or occasionally a
rosy cavity is struck, known in miners' parlance as a " vug," con-
unine sometimes one large or a number of small independent
rystak 8h( oting from the sides, or standing erect in the cavity. In
oe of the mines on the Lievre, crystals of a gigantic size have been
let with, some weighing individually as much as 1000 lb.

Professor Harrington, of the Geological Survey stafif, says as a
lie the apatite-bearing veins of the Ottawa region are characterised
ktber by a want of regularity or order in the arrangement of their
nvstituents than by any degree of symmetry. Veins with sharply
sfined widls, as in metalliferous lodes, are rarely seen, the vein and
'Untry rock merging into each other. Dana says such a blending of

Digitized by VjOOQIC


a yein with the walls is a natural result when its formation in a
fissure takes plaoe at a high temperature during the orystallisation of
the containing rock. Dr. Sterry Hunt, who nas made Laurentian
rocks his study for upward of 30 years, regards many of the apatite
veins as fissures or cavities which have been filled by the deposition
of materials derived from the adjacent strata. One striking featnie
developed in this mining is the great irregularity of the depositB;
but taking into consideration the extremely disturbed character of
the Laurentian rocks, this is not to be wondered at.

At the North Star Mine, with a view to testing the depth of tbe
deposits, a test shaft was sunk where the vein on the surface was not
more than 3 or 4 in. wide ; the shaft was proceeded with till, at a
depth of 30 ft., the vein increased to a width of 2 ft., ranging after
that from 1 to 4 ft. till a depth of 80 ft. was attained. Here tbe
phosphate almost disappeared, but at a depth of 120 ft. a vein 1 ft
wide was reached, which gradually kept on increasing. At a deptli
of 166 ft. a body of phosphate was penetrated occupying the whole
width of the shaft. Sinking was still continued, and now, at a depth
of 266 ft, the entire floor and sides are pure phosphate, and a drift
run for some distance at the 200 ft. level shows solid ore.

In addition to the yield of pure phosphate in large masses, it OfXAr
sionally happens that large quantities of it are mixed with mica,
pyroxene, and other foreign substances, and if shipped in that state
the value of the whole cargo would be materially deteriorated. To
get rid of this extraneous matter a process known as ** cobbing*" i)
resorted to, which consists in the separation by hammers of the ore
from its matrix, an easy operation, owing to the more friable conditios
and softness of the phosphate as compared with the intrusive mate-
rials. This is done in a hut or oobbing-house, on solid tables ca
stands. On one side of the building are tramcars or wagons, intc
which the refuse is thrown as broken ofi^ while the phosphate thxie
cleaned is thrown into another receptacle on the other side. Boji
and old men are employed at this work, which no machinery has ye<
been found adapted to perform. In spite of every care used, Isjgi
quantities of phosphate are thrown aside at present which, with ai
improved system, may yet prove of value.

The composition of Canadian phosphate varies as follows : —


Phosphoric acid 80*84 to 41*54

Lime.. 42*72 „ 54*74

Alumina and iron oxides and flaorine . . 3 * 03 „ 13 * 32

Insoluhle silioioas matter * 59 „ 13*50

Trihaaic phosphate of lime 67-32 „ 90*68

Competition between South Carolina and Florida low-grade phoi
phate has practically killed Canadian seconds, and the only marke
now left open for the 70 per cent, grado is in Chicago and the Wester
States. ^ sale of 1000 tons for Chicago was recently made at 6*3
dol. per ton for ground 65 per cent, in bags, free on board 4
Buckingham, P. Q.

The cost of production of Canadian phosphate is estimated at aboi

Digitized by



12 dol. per ton of 2240 lb., free on board ship at Montreal. The
selling prioee in 1892 ranged from 13 to 14*50 doL per ton.

Norw^ian apatite dif^rs from Canadian in containing no oalcinm
fluoride. Sometimes the oalcinm chloride exceeds 4 per cent.

From apatites alone it is diffionlt to make a dry and powdeiy
superphosphate, but by mixing them with lower grade phosphatic
mineralB carrying lime carbonate a good result is attained.

Phosphatic gnanos from the West Indies and other islands are less
abundant now 3ian formerly.

Sombrero rock or crust guano was at one time largely imported
into England. It is quarried on Sombrero, an islet about 2]^ miles
kmg, } mile wide, and not more than 20 or 30 ft. above the level of
the sea ; it is entirely composed of €his phosphatic substance. Frag-
ments of bones are found in the rock, and it is supposed to be a breccia
of bones of turtles and other marine vertebrata, coral debris, &o,^
collected before the elevation of the islet above the water, and
cemented together since by the droppings of birds carried down
through the mass b^ raius. It varies in colour and texture, some
being porous and friable, whilst other specimens are dense and com-
pact. JLater importations contained less iron and alumina and more
time carbonate than formerly, and from this it is inferred that the
rook (then worked from under the sea) is mined in close proximity to
the OOTal rock on whioh it rests. Analyses of Sombrero guano show : —


Triphosphate of lime 69 to 76

GarboDateoflime 2 „ 16

Iron and alumina 4 ., 10

Fluoride of caloimn 1},, 1}

Inaolvble matter 1 *> 2

When Sombrero euano is dissolved by itself, it makes a high grade
superphosphate of a light yellow colour.

Navassa guano, from tne coral island of that name in the Carib-
bean Sea, is of a reddish-brown colour, and consists of globular grains
of phosphate of lime, cemented into hard masses, ana contaminated
with a good deal of iron and alumina. It is found chiefly in the
cavities of the rocks which form the framework of the island. It
contains : —


Triphosphate of lime 55 to 70

Oaitonate of lime 4 „ 6

Oxidet of iron and alomina 15 „ 18

Iron and alnmina (as phoaphatea) 8 „ 10

Fluoride of ealoimn 1 „ 2

Insoluble matter 4 „ 5

'\ Superphosphate of lime, when made from Navassa alone, is ex-
sediogly hard and tough, and proportionately low in strength.

Cura^oa and Maiden Islands both furnish guanos in which the
hos^iate of lime is in an unmineralised state, and in a fine state of
Ivision ; they contain but little carbonate of lime, and are almost

\ from oxide of iron, alumina, and siliceous matter. They range in
Bality from 65 to 80 per cent, of tribasic phosphate of lime, the

Digitized by VjOOQIC


avera(2:e being about 70 per cent. The lower quaUties are, boweyer,
almost as yaluable proportionately as the higher, in conseqnenoe of
there being no oxide of iron, &a, to deteriorate the product, as id the
case of most of die inferior phosphates, and they are capable of yielding
superphosphates of high quality.

Numerous other phosphatic deposits deserve mention.

The Ayes Islands, off the coast of Venezuela, contain immeDfie
beds of guano, affordii^ over 88 per cent phosphoric add.

Coprolite beds at Stnta Mana di Leuoa, Southern Italy, afford
85 per cent, of calcium phosphate.

Kata Islands (Brazil; phosphates yield : —

Per cent.

Phosphorio acid 26 to 33

Lime 26 „ 37

Iron oxide 7 ^ ^^

Alnminw. • .. 9 ,» 12

In the Grellivara district of Northern Sweden apatite is foimd
intimately associated with magnetic iron (»:e, in proportions vaiyifig
from 10 to 60 per cent., but its separation is a difficult problem.

Near Taplow, two bands of phosphatic chalk have recently been
found overlying ordinary white flintless chalk. The proportion of
phosphate of lime present varies between 18 and 85 per cent.

Tunis and Algeria are reported as containing an enormous deposit
of phosphatic mineral lying in Eocene limestone beds, and estimated to
have 10,000,000 tons of 60 per cent, phosphate in sight. This phos-
phate contains less than 1 per cent, of iron and alumina, and very
little silica.

The yearly consumption of phosphatic minerals in the manufac-
ture of urtiflcial fertilisers is computed at 1^ to 2 million tons.

Digitized by




The term "pigments" properly includes all oolourin^ matters nsed
fo the preparation of paint, bnt in this instance it is restricted to
those whion are derived naturally from the mineral kin^om. They
ue few in number, but important on the score of abundance, cheap-
ness, and permanency.

BaryieB. — Barytee or sulphate of baryta, the most important of the

Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 34 of 76)