Charles George Warnford Lock.

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

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higher than that of Luxemburg, these figures would indicate thst^
have the cheapest iron ores of all the great iron-producing countri
even when allowance has been made for diflferenoes in the rate
wages. Nor is our position less favourable as regards cost of
port : in general, the iron ore mines are less than 30 miles from
place at which they are smelted ; in Continental countries, and in
United States, no similar advantages exist

The only two countries in Europe other than our own that app
♦ J. T. Smith.

Digitized by



to po8B60B any considerable deposits of iron ores adapted for the making
of nigh-class Bessemer iron are Spain and Sweden.

Spain has two districts that are nnnsuaUy rich in ores of high
quality. Up to the present time, Bilbao has ttimed out about
40 million ton of ore ; and an estimate made in 1884 put the total
quantity of nnworked ore in the Sommorostro district at 50 million
tons, which would be reduced, if it still held good, to less than
30 million at the present time. Farther inland are large virgin fields
of ore, which are computed to add another 40 million tons. This
would meet the present demand, along with the ores of Sommorostro,
for perhaps 20 years. The ores of the South of Spain are virtually
oDtoQched, although, so far as can be ascertained, they are of at least
as high a quality, and probably can be worked fully as cheaply, as
those of the Nor&. Between Malaga and Garthagena there are some
large and easily-worked deposits of hi^h-class ores, a few of them
mnning up to as much as 65 per cent, iron, and at least one or two
>f them within 20 miles of the coast. The ores of the South of Spain
ire well adapted for the Bessemer and open hearth processes, and it
a general characteristic of these ores that they contain considerably
nore manganese than those found in the North, reaching up to as
nuch as 4^ per cent., and averaging in some districts 3j^ per cent. ;
vhile they exist both as hematites and as magnetites, the former
KX»8ionally running more or less into spathic ore. It has been found
hat ores of this class are admirably adapted for mixing with other
dgb-class ores, such as the hem^t^ of West Cumberland and Lake
Superior. The mining of these ores has at present hardly commenced ;
*ut labour is vei^ cheap in the South of Spain, being little more than
ne-half of what it costs in the North. On the other hand, there is the
rawback of greater cost of transport.*

The rocks associated with the Bilbao iron ore belone to the Creta-
eous formation. Blue limestone and shales are found above it, and
imestone and schistous grit below it. The latter is recognised as the
cor of all the deposits. The ores are classed as follows : — ru&to, a
rown hematite or hydrated ferric oxide (FcjOs + HjO), which forms
tie great bulk of all now produced ; cam^nil^ a red hematite or ferric
xide (FeiOj), containing a somewhat less quantity of water in com-
ination ; vena dulce, also a hydrated feme oxide (FcsOs), found in
dns, is of a soft and porous nature, and is more or less intimately
ixed with both of the above kinds ; spathic ore, siderite or ferrous
krbonate (FeCOj). The upper portion of the deposits generally con-
Bts of rybio. It is fall of cavities, some of which contain earth and
ay ; and, consequently, it requires more careful selection than the
Jier kinds. It has always a honeycombed appearance. Brown
^matite and spathic ore are sometimes found mixed in broad bands,
cs^Uv called pedrisco. The deposits are all of aqueous origin.

The quality of the Bilbao ores for smelting purposes is exceedingly
)od ; in other words, they are easily fused. Bubio contains on an
rerage about 50 per cent metallic iron, as delivered in cargoes, and
mpanU a little less. Down to a certain depth in the mines the
tality seems to improve. Beduced metallic yield generally arises

/^J. T. Smith.

Digitized by VjOOQIC



from want of care in selection, or from wet weather at the mines., when
the mineral is so coated with mnddj water that it is difficult to detect
impurities. In the annexed table are average analyses of the foor
kinds of Bilbao ore, compared with good Cumberland hematite Mid
the best ore raised in the Forest of Dean.*

In examining these analyses the following points seem noteworthy.
Rubio and campanil do not differ much in riclmess ; but in the former
case the allied minerals consist more largely of silica and oombined
water, and in the latter case of lime and carbonic acid. Yena is richer
in iron and manganese, and freer from silica, than either of the two
kinds previously named. In lime and carbonic acid it is on a par witk
rubio, and in freedom from combined water it is more than equal 'o
campaniL It is, therefore, the richest and purest of the three kisdii
Gkx>d Cumberland hematite ore excels rubio and campanil, in the |m>-
portion of iron it contains, also in freedom from combined water and
moisture ; but it has considerably more silica and alumina, and some-
what more sulphur and phosphoric acid. The best ore obtained fron
the Forest of Dean is considerably richer in iron than rubio and cam-
panil, and almost equal to vena ; and if there was only sufficient of it,
and it could be cheaply raised, there would be much leas need t»
import from abroad than is now the case. Spathic ore has less iron,
and more silica, combined water, carbonic acid, and sulphur, than anj
of the others named. If calcined, however, it loses 25 per cent
of its original weight, and then becomes nearly as rick and pure is












Purple Red









per ad

Peroxide of iron, FejO, . .






Protoxide of iroD, FeO ..






Protoxide of manganese 1
11\ per cent, MnO . . /






Peroxide of manganese |^
69i per cent., Bln,0, ..j






Alumina, A1,0, .. ..











1 If

Magnesia, MgO .. ..






Silica, SiO,







Carbonic acid, CO, .. ..






Sulphur, 8







Phosphoric acid, RO. . .
Combined water, lijd . .






9 00







99-74 1



Loss by calcination . .









14 00




Metallic iron, dry, Fe . .





Iron in damp ore ..




40 -bo


Iron in calcined ore





^ I

* .

\, HtacU Brit. Assu






The miniog condsts in the removal of ore by cutting away in
vrels or steps, 30-60 ffe. high, and a considerable length. In some
888 a tunnel is made at or below the lowest level of the ore, and
driven in as far as the working £ioe. A shaft and side entrances
e made down to it, and through these the ore is shot and loaded
to tracks. The quarry levels are worked gradually down to and
en below the tunnel. But in the latter case a shell of unworked
ineral is retained round it, to protect the rolling stock from the
suits of blasting, &a It is customary to drill deep holes into the
>rking faces with a succession of jumpers, longer and larger ones
ing employed until a depth of nearly 30 ft. is reached. A
aU oharge of dynamite is tnen inserted, and fired by a fuse. This
larges the end of the hole into a chamber, into which is introduced
arger quantity of d3mamite, and the explosion of this brings down
onsiderable quantity of mineral. No machine drilling is in use.
K>nt 2000-3000 tons are the largest quantities usually brought
prn by a single blast. Vena ore can be easily got with a pick,
ter disintegration by blasting, the fiallen masses are immediately
acked by men and boys with hammers, wedges, and crow-bars, and
it up into piecesof a portable size; impurities are here separated,
1 taken to the spoil heap. The cost of quarrying and selecting
ies considerably, according to circumstances. In a few campanil
Qes it is as low as 1<. per ton ; but in rubio mines, where more
action is necessary, it goes up to 2«. Of this, 2^.-4^. per ton is
explosiTcs and tools, and the rest for labour.
T^^o kinds of aerial tramways are used : about 20 miles of Hodg-
's and 2 miles of Bleichert's. In Hodgson's system an endless steel
e rope is made to travel by means of an engine fixed at the lower
^ The buckets are hooked on to the rope at intervals, and move
h it, passing over the pulleys as they come to them. The fall
kets travel in one direction, which is generally down hill, and the
^tj buckets in the opposite direction on the return rope. At either
uintis they are switched on to an outer rail, to be loaded or tipped,
a ran round on two rollers attached to the hanger, and finally
)red on the return rope. At each "angle" for changing the
<rtian of the route they are switched by hand. Stretches must
exceed 2 miles each ; there may be sevenJ endless ropes on each
of trestles, but two is the most usuaL The quantity conveyed is
at 2000 tons per rope per week of 72 hours. Each bucket holds
vt^ and one passes every 26 seconds, which is equivalent to 28
\ per hour. The place where the hanger bears upon the wire
» is furnished with a seating of rubber, which acts as a spring, and
IS the rope without damaging it. The system will not do where
inclination exceeds 1 in 4, as then the hangers slip upon the rope
wb\ -weather. To obviate this difficulty, Bleichert's system was
oduced. In this the main rope is stationary, the buckets travel-
on ity as on a rail, and being hauled by a subsidiary rope ; when
gradient exceeds 1 in 4 the traffic becomes self-acting. But it is
3 costly in construction and in maintenance, and it is not capable
nplication on the same trestles. 1 he two ropes only \^t a single
, a» compared with one rope lasting two years in Ho<lg«on*s

Digitized by



system. The relative costs of oonstruction are — Hodgson's, about
2000Z. per mile, single line ; Bleichert*s, about 4000Z. But the latter
system is capable of conveying nearly one-half more than the fonner
per annum. The cottt of transport is about the same in each ^sm.
viz. l\dL, to \n. ^r ton per mile. In both systems a powerfnl brab;
is required to regulate the speed, and tightening apparatus to ke«p
the rope in uniform tension. In addition, there are a number of self-
acting rope and drum inclined planes, built by the Consett Irai
Works, near Durham. These operate at a cost of 3<2.-4d. a ton.*

Sweden and Lapland possess enormous iron ore deposits. Tb
Swedish ores are remarkably free from phosphorus, Dannemora odti-
taining only '003 per oent., Persberg -004- '005 per cent^ Ston
Bispberg under * 01 per cent. ; but in Grangesberg, and in GelliT&m
Eirunavara, and other places in Lapland, the percentage readies 4-6,
or even more.f

The Gellivara and neighbouring deposits are of gigantic propcr-
tions, and official surveys report of them : — (a) that the ore is afl
more or less magnetic, the metallic iron contained being in the cofr
dition of protoxide, peroxide, or magnetic oxide, or a combinati(K) ^
these ; (6; that it is found in lodes or veins, which, together witii tbi
bedrocks in which they lie, appear to have had an intrusive origin, izk
are usually more or less distorted ; (c) that the lodes are assocUl^
with gneiss, quartz, felspar, granite, hornblende, and mica scbist
corundum, fluor-spar, calcHspar, actinolite, adamantine, asbestos, epi
dote, and garnets are also found in or about them ; (^) that the pH «
phorus is in the form of apatite (Ca32P04), and can to a great exted
be separated by hand-picking ; (e) that ore sufficiently free froa
phosphorus for acid steel purposes is but a portion, say one-fifth, <
the whole.

The deposits of limonite now in process of formation in someo
the Swedish lakes, and from which they are periodically dredged, &r
geologically interesting, but not economically important.

The iron ores of the island of Elba, once deemed so importui
embrace specular ore, hematite, limonite, magnetite, and spattiic oa
bonate. The veinstuff is quartz, and the ores generaUy contaai
titanium and manganese. The deposits are ascribed to ferrugiiioi
thermal springs. ,

The United States produce some 16 million tons of iron ore yesiQ
The relative importance (in tons) of the different kinds in 1880 u
1890 is shown in the following figures : —

1880. 1890.

Hematite 2^ million 10} miJlion

Magnetite 2^ „ 2J „

Limonite 2^ „ 2| „

8iderit6 .. 1 „ \ n

Pennsylvania leads in limonite, Michigan in hematite. New Yod
in magnetite, and Ohio in siderite, mining no other kind. The ■!
famous iron-ore mine in the country is that at Cornwall, PemMjl
vania, which has been in operation since 1740, and has yielded i

* J. Head, Brit. Abboc. f H. Lnndholm.

Digitized by VjOOQIC


ban 10,000,000 tons of magnetite. The production of limonite is more
ddely extended than that of any other variety ; it is raised in 24
tates, hematite in 17. magnetite in 13, and siderite in 8. The aver-
a;e contents of metallic iron in the ores of the United States was
1-07 per cent by the census of 1880, and 61*27 per cent, by that
r 1890. The richest ores (60 per cent.) are mined in Minnesota, and
le poorest (40*7 per cent.) in Georgia and North Carolina. With
je exception of the Cranberry mines in North Carolina, which in
392 produced 18,433 tonfs no Bessemer ore of any moment is mined
i the Southern States.

Wherever the Clinton stage of the Upper Silurian outcrops, it
JDoet invariably contains one or more beds of red hematite, inter-
ratified with shales and limestones. These ores are of extraordinary
irsistenoe. In general, the Clinton ore is characterised by a high
^rcenta^e of phosphorus, and is seldom, if ever, available for Bes-
mer pig ; it is chiefly employed for ordinary foundry irons, the
»roentage of iron varying much. These hematites have undoubtedly
iginated in some ca^es by the weathering of ferruginous limestones
>ove the water level. The unaltered limestones at the bottom of a
ine at Alalia, 250 ft. from the surface, contained but 7 • 76 per cent.
>n, while the outcrop a£forded 57 * 52 per cent. ; in another case there
IS a gradual increase of lime from a trace at the outcrop to 30*55
r cent, at 135 ft. Geologists have explained these beds as due to
e bringing of iron in solution into the sea of the Clinton age, and
its deposition as small nodules, or as ferruginous mud, forming an
litic mass, as in the modem Swedish lakes. The structure of the
3 varies : (a) it is a replacement of fossils, such as crinoid stems,
>llascan remains, <&c. (fossil ore) ; (6) sniail oolitic concretions, like
xseed (flaxseed ore, oolitic ore, lenticular ore) ; (c) elsewhere it is
own as dyestone ore. In many places it is really a highly ferrugi-
as limestone, and below the water level in the unaltered portion it
en passes into limestone, while along the outcrop it is quite rich.
The important Lake Superior deposits are b<»dies of hematite, both
I and specular, soft and hard, in metamorphic rocks; they vary
lely in shape, although at times are quite perfectly lenticular ; and
I usually associated with jasper and chert, having for a footwall a
atively impervious rook of some sort. Magnetite is at tiroes
«ent. They are of varying physical structure and associations,
e five principal ore-producing belts or districts (also called
injces," as they follow ranges of low hills) are the Marquette, the
nominee, the Gogebic or Penokee-Gogebic, the YermiUon Lake,
I the Mesabi (Mesaba). The geology of these districts has been a
ject of much controversy. The ore bodies were in earlier years
lerally regarded as true beds of greater or less extent, and often of
At irregularity. They approximate a lenticular shape in the
iplest development, as is shown in the less disturbed districts, but
the Marquette region this is at times obscured by the excessive
tnrbances. They often follow the foldings of the walls, particu-
\y in synclinal troughs. Later developments have brought out the
t that the ore bodies are associated with some underlying rock that
elatively impervious. The favourite one is the so-called " soaprock,"

Digitized by



an altered igneous intrusion that is chiefly in dykes. Beds of jaspei
seem to play the same r6le. Van Hise notes 4 deposits : (a) on tbii
contaot of a quartzite conglomerate (the base of the Upper Marquette
and the ore-bearing formation ; (6) on soaprock, which gradei intj
massive diorite ; (c) on dykes of soaprock, which follow along or cut
across the ore-bearing formations ; (d) interbodded in the jasper d
chert On the east the soft hematites (limonites) are first met ; tbei
in going west the red and specular hematites ; and then the magDeti>:
character increases, until at the western end of the district the mag
netites are most abundant.

In the Menominee district, the geological Roction immedifttel}
associated with the ore involves {a) 1200 ft. of silioious (" Norway ^
limestone ; (6) 1000 ft. of the Quinnesec ore group, consisting of lim^
stone, silicious or jaspenr slates, hydromica schists and slates, and on
bodies ; (c) the Lake Hanbury slate group, overlaid unoonformabh
by Potsdam sandstone. The ore occurs along two or three plsnei i
deposition in 6, and not far from contact with a. Fig. 140 iUustntef *
the general structure : a, silicious (Norway) limestone ; b, QoinneM
ore group ; c, Lake Hanbury slates ; d, Potsdam sandstone ; t^ ni
ore ; /, blue ore.

FiQ. 140. — Ibon Deposits: Menominse.

Li the Penokee-Gogebic district the rocks are less metamorpbod
The strata run E.-W. with a N. dip of 60°-«0°, and with no snbcrf
nate folds ; they consist of cherty limestone at the base, followed \
quartz, slates, quartzite, iron ore, and ferruginous cherts, and fio^
slate and schists ; and are traversed by dykes. The ore is a soft, r«j
somewhat hydrated hematite, with more or less manganese, which i
often considerable, and is most abundant in the southern mines ; ^
specular is rare. Van Hise has proved the ore bodies to be in ^
troughs formed by the intersection of northerly dippins^ cwnf*
quaitzites, and southerly dipping trap dykes. He has traced the 'mA
to a source in the layers of cherty car
ites and above them. From this
percolating water, and has been depc
where it has replaced the original ca

The ores from Tower and Ely, in
high-grade Bessemer, and are produc

In the Mesabi district,t the o

♦ J. Fulton, Trans. Amer. Ini
t J. F. Kemp, * Ore Deposits.

Digitized by



Animikie) and over the quartzite (Pewabio) ; the ore bodies are all
»uth of the granite ridge called the Giants' range. Upon the
K)uthem islopes of this range lie the green schists of the Eeewatin,
mconibrmabljr i»verlain by the Pewabio quartzite ; on this rests the
)re-b6aring rock, jasperj quartzite (" taoonite ") ; over this, in order,
.'ome greenish silicious slates and cherts, black slates (Animikie), and
^eat masses of gabbro. On the flanks of the Giants' range the dip
8 steep, but it flattens out nearly to horizontality away from the
^nite. The ore bodies lie on the southerly slopes of low hills, and
re found immediately below the mantle of glacici drift, which yaries
ip to 100 ft. in thickness. The ore is (a) soft, blue, earthy, and
andy hematite, and (6) hard specular ; with these are limonites and
>aint ores. The sections show at times 50 ft and more of excellent
lematite, which may be of exceptional purity and far below the
Bessemer limit of phosphorus, or which may slightly exceed it, but
Q general it is quite high-grade, silicious, low phosphorus ore. The
re bodies may be directly on the Pewabio quartzite, as seems usual,

Fig. 141.— Ibon Dbposits: Biwabik.

r else entirely in the taconite. They fade out into the latter along
le dip. They are regarded as having originated by replacement of
16 taconite. This rock sometimes contains calcareous streaks, that
sive perhaps aided in furnishing the carbonic acid, which, it is
lOQght, has dissolved the silica of the quartzite (taconite) in the
^placement process. Fig. 141 illustrates a section at the Biwabik :

green schist; 6, quartzite; c, banded ore and taconite; d, slates;

glacial drift ; /, ore. When the surface is stripped o£f, the ore is
tnnd in flat deposits, covering 60 or more acres, and 20-90 ft. thick,
est pits are sunk in places 117 ft. deep by pick and shovel, with-
it a single drill hole or blast of powder. In other spots there may
5 20 or 30 ft, in a pit which is too hard to pick. This can be thrown
>wn in large quantities when there is once a face on it, and can then
) loaded by hand or steam-shovel. Where no blasting is required,
le expense of loading cars by hand labour will not exceed 25 cents
#.) per ton; by steam shovel it may reach 10 cents (5d.). Where
te ore is hard enough to blast, the expense of excavating and loading
K cars may reach & cents (1«. 8d.). When the surface is removed,
le ore is practically in a huge stock-pile, containing, in some instances.

Digitized by



aeyeral miUioiiB of tonEU At the maximiim cost of miTiiTig thk
hand, and in hard ore, the cost of stripping and placing ore on
is 48 cents (2«.) per ton. The minimum cost is 11*2 cents, (r
The ayerage is about 29*5 cents (1«. 3<2.). But as there is moio
ore than hard, the average may be expected to be about 25 cents '
The average quality of 145 samples from 12 mines gives :
61*05; silica, 6*18; phosphorus, -0544. Manganese was found
54 of these samples varying in amount from - 06 to 1 * 657 per
and with an average of -667. Of the 12 mines the Biwabik
the best showing, giving as an average of 60 samples : iron, 63
silica, 3-46; phosphorus, -0455.*

Iron Mountain, Missouri, consists of felspar porphyries, m(^«
less altered, and seamed with one large parent mass of ore, and
numerable minor veins that radiate into the surrounding rook. U]
the flanks of the porphyry hill rests a mantling succession of i
mentary rocks, that dip away on all sides. The lowest member
conglomerate of ore fragments, weathered porphyry, and residual
left by its alteration, and now the principal source of ore. It
mined underground, hoisted and washed by hydraulic methods, "
those employed in the auriferous gravels of California, and
jigged. The apatite has largely weathered out of it.

Beds of magnetite, often lenticular interstratified with Arched
gneisses and crystalline limestones, are extensively developed in th
Adirondacks, in the New York and New Jersey Highlands, and )
western North Carolina. Titanium is often present in such amonDl
as to render the ore valueless ; and apatite is always found, althon^
it may be in very small quantity. Chlorite, hornblende, angiti
epidote, quartz, felspar, and a little calcite are the common associatd
minerals. The Adirondacks are very largely knobs of a rock, wbid
is chiefly labradorite, with some hypersthene and other bisilicato
and variously called labrador-rock, norite, hypersthene-rock, anoc
thoeite, &c. Associated with it, especially in the foothills, are gneia
and crystalline limestones, in the former of which occur the magneiiti
deposits now wrought ; but there are also large bodies of magnetit
in true igneous gabbros. The Chateaugay ore body is really a bed o
gneiss very rich in magnetite, rich enough in places to afford a mer
chantable ore; great part of it, however, requires oonoentratacu
Commercially the Adirondack ores are divided into (a) high in phos
phorus but low in sulphur ; (6) low in both phosphorus and sulphur
(c) pyritous ; (eJ) titaniferous. Under d come numerous beds whid
are worthless, out which, if the titanium could be neutralised, wonlc
be very valuable. Mineville is by far the most productive region

Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 55 of 76)