Charles George Warnford Lock.

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

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tents of the hopper emptied, and by elevating the rod it is tigbtlr
closed. This furnace is charged by lifting the air-tight cover ani
dumping 1600 lb. of ore into the hopper. The cover is then let dova*
the plug at the bottom of the hopper is lowered, and the charge ii
admitted into the furnace. The body of the furnace is modelled aft^
the cupola. Below the charging floor the furnace is encircled br »
pipe, with which smaller pipes, or delivery tubes, leading from xss^
are connected. The mercurial vapours ascend in the furnace, throogi
the delivery tubes to the outside conducting pipes, and thence to ts
condensing chamber. About 20 ft. below the piping is the fiii^
floor, where 3 fireplaces lead into the body of the furnace, and are f^
with wood 4 ft. long; 12 ft. beneath the firing floor is the groo^
floor and point of discharge ; between it and the firing floor the bcdy
of the furnace constitutes a cooling chamber for the roasted ore, wbii
is from time to time raked from three points of discharge at the bi»
of the furnace. This furnace, which is principally used for the higbtf*
grade ore, has a capacity of 19,200 lb. in 24 hours. „,

The condensing chamber attached to the tierras furnace ^^
serve as a representation of those in use at these works. Tbi*
chamber is 35 ft. long, 20 ft. high, and 20 ft. wide. The intOTX ^

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ooled by 11 pipes the length of the chamber. Any unoondensed
rapouTS which may pass through the chamber are conducted into a
Ine where, by the aid of a fan, they are conveyed a distance up an
Qcline 900 ft. to a brick stack 80 ft. high.

The chief consumption of mercury is in metallurgical operations
or recovering precious metals. The English trade is in few hands
nd oontroU^ by powerful capitalists. The market value is abou
«. a lb.y but is not constant.

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Both geographically and mineralogioally nickel is a wide-ranging
metal, yet commercial supplies are drawn from restricted areas. The
principal ores of nickel are : —

Millerite, BulpMde, NiS oontaining 64 per cent nickeL

Niooolite, arsenide, NiAs ^ 44 „

Pentlandite, snlphide, (NiFe)8 .... „ 34} ,,

Annabergite, hydrated arseBiate .... „ 33} ^

Gersdorffite, sulph-anenide, Ni(ABS/ .. ,, 32^ „

Siegenite, cobalt pyrites ^ 29-30 „

Gamierite (nonmeaiteX indefinite silicate „ 7-26 »,

Nickeliferoos pyrrhotite and ohalcopyrite ^ 3 „

Previous to the New Caledonian discoveries, Cornwall prodooed
some nickel ore from the Pengelly, the Fowey Consola, and the
St. Austell Consols mines. The ore tiien realised 80-84Z. a ton ; now
it is only wortJi 15-202. In Scotland some nickeliferous pyrrhotite
canjing 3 per cent, metal was raised at one time.

Li Germany, nickel ore has been discovered recently in the
Schlei&teinthal, Upper Harz, in spiriferous sandstone of the Uppa
Devonian formation. In the fault fissure, which is plainly marked by
selvages, and also in the adjacent country rock, are found streaks and
veinlets of nickel ore. The width of these veinlets varies frtim 1 to
12 in. The vein matter consists of fragments of the country rock,
caldte and pyrite, together with the nickel mineral, which is a sulph-
arsenide. Galena and blende, which occur in the other veins of the
district, are wanting. The proportion between mineral and vein
matter is variable, but not infrequently the whole of the screak is
solid mineral. The clean ore carries 30 per cent. nickeL The dty
slate and mica schist district near Schneeberg, Saxony, oontaii^
numerous lodes in a zone 6 miles by 2.

In Sweden, nickeliferous pyrrhotite is found in some abundance,
notably at St. Blasien, Elefra (Smaland), and Saffmyra (Daleoailia>
These mines have Ions been worked, the ore affording ^-2^ per cent
nickel and some cobalt. The production of metallic nickel 20 yeai»
ago was 60-80 tons per annum, now it is only 10-15.

Norway* produces yearly 5000-7000 tons of nickel ore (pyrite and
pyrrhotite), principally at Moss, RingeriKC, Snarum, and Tra^erd. In
some mines, rich ore has been found, &ough in small bodies, e. g.
7 per cent, at Beiem, and 5^ per cent, in other places ; but while in
the best mines first-class smelting ore up to 3^^ per cent, can be
sorted out, the bulk is much lower. In 1870, a yield of -8-1 -3 per

• J. H. L. Vogt, Zeit f. Prakt. GeoL, 1893, p. 143.

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c^nt. from ore assaying • 9-1 • 5 per cent, was satisfactory ; now dressing
is resorted to so that the yield from the smelter is 1^-2^ per cent. In
the best mines, the cost of producing 1 metric ton of 2 per cent, ore
varies from 6«. to 12^., and avenges about 9«.

The Canadian mines at Sudbury, Ontario, were originally worked
for copper, which, though present in somewhat greater proportion than
he nickel, has an inferior value. The nickel and copper bearing
nineral deposits apparently in most instances form portions of igneous
nasses, consisting of diorites, diabases and their corresponding altered
bnns. The name '* greenstone " is commonly applied to the group,
rhese masses are usually extremely irregular in surface outline, but
n the main appear to be conformably bedded with the crystallised
edimentary strata, quartzites, schists, greywaokes and clay slates of
he Huronian masses, and the gneisses of the Laurentian masses.
Granite, syenite or felsite frequently intervenes between the green-
tone and the Laurentian gneisses, and again massive quartzite is in
mmediate contact. The nickel and copper-bearing greenstone, as
ndicated by surface exposures, is chiefly included in Huronian strata,
requently in the vicinity of the contact with Laurentian masses, and
Ifio, apparently, to a limited extent occurs within the Laurentian
trata. It has not been determined by developments thus far whether
he character and quality of the deposits vary materially according to
heir position. Large and small deposits and relatively high gntde
ad low grade mineral aggregates, occur within relatively narrow
mfines, under the several conditions. The richest ores, however,*
3 determined by analyses of average samples, have been derived from
eposits in the vicinity of the irregular contact between the Huronian
ad Laurentian formations.

The mines may be roughly divided f into 8 classes : — (a) those
hich are composed of extremely massive pyrrhotite, and are of such
lormous extent that as yet no idea of their boundaries has been
btained ; (h) those which contain more rock material, and which are
988 extended in size, though much richer in both copper and nickel ;
'.) those which are not only as extensive as (a) but nearly as rich

As an example of class (a), the Stobie mine may be cited. Before
eing opened at all, it simply appeared to be an immense rounded
ill of red gossan. As to the length, tbe outcrop shows it to continue
I a more or lees unbroken condition for some miles. Upon removing
lis gossan, which consists of a brown iron ore in regular stratified
yers (the product of the decomposition of the pyrrhotite), the un-
tered pyrrhotite in a massive condition is encountered within
-6 fL of the surface. At intervals limited bands of rock occur, and
xatsionally considerable horses of diorite or of mixed ore and rock ;
at as a rule the ore is massive pyrrhotite, with occasional pockets

very pure chalcopyrite, and not infrequently rounded and even
igular occluded masses of diorite, from the size of a chestnut
) to boulders weighing many tons. The position of the ground is

* E. B. Bash, '♦ The Sudbury Nickel RegioD," En. and Min. Jl.
t E. D. Peters, ^ The Sudbury Ore Deposits," Trans. Amer. Inst Min. Eogs.,

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favourable for open-<)ast work, and miners are at present sinmLy taking
the whole hill down as they go, on a level with the valley. They haTe
in some places already out over 100 ft. across the ore, thns obtaining
a fine face for blasting down in great quantities (several hundred tooE
at a blast), by putting 8-10 air-drilled holes, 10 ft. deep, and firing
with a dynamo. Besides the open cut, two tunnels have been driTcai
a further 60 ft across the body, always in massive ore.

Class (&) is represented by the Copper Cliff mine. The ore here
is sometimes much intermixed with diorite, and ooours in irr^g^uUi
masses of several thousand tons each, situated apparently be^raen
two cleavage-planes in the country rock, so that new deposits an
found by drifting. Although there are absolutely no stringers of on
or veinlets of quartz to connect these ore-bodies, the country rofSL in
their vicinity ia usually speckled to a greater or less extent with ora,
and this is oiften the only indication of immediate proximity to a larg<e
ore-bodv. I^he shaft is down 700 ft on a slope of about 40^, and &
ore still continues.

The ore delivered to the smelting fomaoee from the whole districi
averages about two-thirds the gross weight hoisted &om the mines;
and after this hand-picking the mean assay is Ij^ per cent, nickel
and 1-^ per cent copper, with minute quantities of gold md

The genesis of these ore bodies has been much debated, and while
the earlier opinions were based on the eruptive igneous theory, later
investigators have found reasons for believing in a possible aqueonsl
origin.* So also, the question whether the nickel is a constitiieoti
of the eangue or of the pyrrhotite has received different replies, andj
as this nas a bearing on the method of dressing the ore, it will bel
referred to subsequently.

In the United States, lenticular masses of nickeliferous pyrrhotite,!
imbedded in gneisses and schists, have been found in many plaoee,!
assaying up to 8 per cent, nickel, but not contributing to the indns-j
trial supply. The only important mine is the Gap, in PennsylvaniA^i
the output of which is rapidly declining. Here the ore (nullehte,
pyrrhotite, chalcopvrite, siderite, &a) occurs as a lining on andl
superficial (6-80 ft) impregnation of an enormous lenticular mass of
hornblende enclosed in micaceous schists, adjacent to a great trap
dyke. The ore, originally only worked for its copper, camee 1-3 per j
cent, nickel. Other American localities may be briefly mentioned as
follows: — Millerite at Benson, Arkansas; arsenide and sulphide |
associated with cobalt, at the Gem mine, Colorado; nickeliferous
pyrrhotite at Dracut, Massachusetts; siegenite with pyrite in the
lead ores of Mine La Motte, Missouri ; niccolite and aimabei^te in
veins permeating a ledge 30 ft. wide, at Cottonwood, Nevada;!
gamierite in connection with serpentine, at Webster, N. Cardinm ; '
pyrrhotite, chalcopyrite, and gamierite, at Biddies, Upper Dad's Creek,
and Bock Point, Oregon.

New Caledonia ranks second in importance for production of
nickel, and so widely is the metal distributed that mining concessions '
covering over 7000 sq. miles are said to be in actual operation, though
• E. B. Bush, op. oit

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Harland,* as late as 1892, places the number of mines at that date at
324 (of which only 80 were working), comprising an area of over
120,000 acres. The nickel deposits occur exclusively in the pre-
dominating common massive serpentine, almost invariably in elevated
positions, and capped with ironstone carrying 4r-8 per cent, chromium
sesquioxide. The nickel ores occur, as a general rule, in irregular
veins and strings in the fissures and joints of the rock, ramifying in
every direction, and forming a stockwork or network of smaU veins.
Occasionally they are met with as persistent veins extending some
hundreds of feet in length and to a moderate depth, and in these cases
partaking of some of the characteristics of a regular lode. Veins occur
2-3 ft- thick, with good regular walls and a regular dip, and taking
at times a lenticular form 4-5 ft. thick. It is generally held, however,
by the French engineers, that these are not tme fissure lodes. At a
depth of about 300 ft., the gamierite gives way to magnesia silicate
exclusively— no nickel As to their origin, it would seem that they
are segregated veins, and inasmuch as the enclosing serpentine carries
*25-*75 per cent, nickel, there can be little doubt that the filling of
the veins and joints has been caused by lateral secretioD, or the
leaching out of the metal from the serpentine and its subsequent
deposition. The ore is exclusively gamierite (hydrated silicate of
nickel and magnesia), no trace of arsenide or sulphide having been
fonnd ; and while two varieties, a green and a brown (called " choco-
lat "), are distinguished, investigations by A. C. Claudet prove that
the latter owes its colour to associated limonite.

The methods of working the deposits are by regular mining, when
the ore bodies are fairly persistent and of good width ; and by open
quarrying, when they are less than 6-12 in. wide, and when stockworks
occur. Sometimes both systems come into operation in different parts
of the same deposit ; and often, when underground mining is pursued,
the irregularities and crossings of the veins render the workings very
intricate. Quarrying is done in terraces from the top downwards,
each terrace having a wide floor on which the rock is blasted down,
and where the ore is prepared for market. Each quarry has a face of
nearly vertical rock, 80-40 ft. high, and a floor 60-120 ft. wide. Deep
holes are drilled by " jumpers " in the face of the quarry, and blasted
with dynamite. The rock, being very jointed, breaks down in large
lumps or blocks, which have subsequently to be reduced by heavy
hammers or shot-holes to a convenient size for setting free the veins
and strings of ore, and for easy removal of the dead rock in waggons
or barrows. Boughly speaking, every joint and fissure of the rock is
filled with ore, the veins thus ramifying in every direction varying
in size from a knife-blade thickness up to 6 in. or more, but the
smaller are the more common and numerous, and hence, to secure all
the ore, it becomes necessary to blast down the whole mass of rock.
Occasionally these small veiDs have a white filling of magnesia
silicate only. Transportation to depot is accomplished by ropeways,
of an exceedingly rudimentary description where the distance is
small — a single wire rope with tough forked sticks in lieu of pulleys ;

• J. Garland, *• Nickel Mining in NeW Caledonia," Trans. Inst. Min. and Met.,
Ui. 121.

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and the cost of a double iDstallation 1968 ft long, witii 2 steel oaUes
1 in. diam. and hemp guide ropes, oarrying a load of 4 bags or 600 Ik,
is given at only 2002. The oost of ore mined, dressed to about 7-8
per cent, nickel (6 per cent, is the minimum marketable), and deliToed
on ship-board, varies from 6«. to 40-60«. a ton, 40«. being perhaps about
the average.

Treatment, — Practically the whole world's supply of nickel is
famished by the pyrrhotite of Canada and the gamierite of Ne#
Caledonia, and it will be appropriate to discuss the preparation of tbe
metal from each of these sources first.

As to the nickeliferous pyrrhotite there oomes the initial questioa
of how the nickel occurs. Dr. S. H. Emmens has asserted* positiTdy
that the niqkel is not as a constituent replacing part of the iron in ^
pyrrhotite, that magnetic separation wUl give a rich nickel concen-
trate, and that the nickel is possibly an essential constituent of the
gangue and not of the pyrrhotite. On the other hand, it is shown t
that for several years the Canadian Copper Company has be^i sorting
its ores, making four grades of the mine output, by boys, who, judging
by the eye alone, separate: — (a) the average mixed oopper-nidrel ore;
(h) the copper pyrites ; {e) the pyrrhotite or nickel ore ; (d) ^e rode
or diorite. What results are obtained will be seen by the following
averages : —

Oopper Cliff mixed ore . .
Stobie mixed ore .. ..
Evans mixed ore
Copper Cliff picked Cu ore
Stobie picked Cu ore
EvaiiB picked Cu ore
Copper Cliff picked Ni ore
Evans picked Ni ore . .
Average diorite rock



















p. c


16 -S

(contained as shota of ore)

The fact that in the picked pyrrhotite or nickel ore from ^
Copper Cliff mine the nickel is 91 per cent, of the total copper-niokd
contents, while in the same mine before sorting it is only 45-5 per
cent, of the two metals, shows very conclnsively that nickel is not s
constituent of the diorite, bnt that it always accompanies and is fomid
in the pyrrhotite, whether it be an essential mineralogical constituent
thereof or not.

Before hand-picking, the ore is broken by sledge-hammers to soit
a Blake breaker, and from the latter it passes through revolving
screens which separate it in 3 sizes — 4 in., If in., and } in. Metal-
lurgical treatment commences with pile roasting, to remove the
sulphur and oxidise the iron as much as is practicable. The roast-
jard is nearly ^ mile long and 100 ft. wide, so that the length of tie

* Can. Min. and Mech. Bev., Ang. 1893.

t D. H. Browne, En. and Blin. JI., Dec. 2, 1893.

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is limited by the width of the ground. After allowing space to
fjset around them and for drains, about 80 ft. is left for the length.
They are about 40 ft. wide, and, as the ore is piled about 7 ft. high
on Uie wood, hold about 800 ton^. They are built in the usual
manner, about 30 cords of wood being sufficient to kindle a pile.
After the main body of the pile is built up of coarse ore, a layer of
ragging or medium ore is put on, 6-12 in. thick, according to the
supply on hand, and this is covered in the usual manner with fines.
By interposing a layer of rotten wood and chips between the ragging
md fines, both these smaller sizes are roasted more perfectly uian
isoaL In general, the whole heap is well enough oxidised to take it
lirect to the smelter without re-roasting any portion. A heap of
JOO tons bums about 60 days if properly managed. Very great car©
las to be exercised, or the combustion becomes too rapid, and a great
)art of the sulphides in the ore melt down into a solid matte, which
B most difficult to break up, and which carries far more sulphur than
9 permissible. Almost the entire success of the smelting process
tepends upon a good roast. If the sulphur is not properly removed,
great quantity of low-grade matte is formed, into which the iron
^oes, leaving the silica witiiout sufficient flux, and making the
amaoe run ^owly and badly. If it is reduced to the normal amount
f 7-8 per cent sulphur in the roasted ore, a rich matte is formed in
omparativelv small quantity, thus lessening freight and treatment
liarges. The iron which was combined with the sulphur is
loroughly oxidised, and is thus in a condition to combine at once
ith the silica, forming exactly the flux required, and making a
^pid, dean and fluid run in the furnace. The importance of this
nioess cannot be exaggerated. The roasting is done by contract at
very small figure, both for fuel and labour. By a second contract
is dug out of the heaps, which are frequently so fritted together as
require light blasting. A very successful method of heap-roasting
to build two heaps in the ordinary manner, allow them to bum out
)oat one-half, and become thoroughly cooled on the sides, and then
lild a third heap in the passage-way between them. A bed of wood
t the bottom, and a single layer on the sloping sides of the two
teral heaps, provide ample fuel to start No. 3, which not only
idergoes a thorough burning itself, but also sets the unroasted
>ping sides of the two adjoining heaps on fire again, and thus roasts
cuething like 50-100 tons of material that ordinarily is nearly raw.
\VA method, besides greatly lessening the percentage of unroasted
3, also adds some 60 per cent, to the capacity of an ordinary roast-
onnd. Practically the same plan is followed at Bio Tinto (see
431). The roasted ore goes to the smelting furnace, a steel water-
;ket of the Uerreshoff pattern, rectangular, with rounded comers,
d a slight convexity all around, so that it really approaches an
^1; its section, at the tuyers, is 3 by 6 ft., and it has 11 2^in.
yers, 5 on each side and 1 at one end, the discharge-opening being
the other end ; it is 6 ft. high from tuyers to charge-door, and is
unbroken water-jacket the entire distance from the cast bottom-
to to the charging-door. Above the threshold of this opening is a
j^iDg of boiler-iron, lined with fire-brick, which lasts as long as

2 p

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the furnace does. The oharge-door is situated at one long side of tlw
furnace, while the flue opening is opposite to it. The entire flue, u
well as the iron charging-platform, rests on a series of girdera ud
I-beams, supported by the stone walls of the building and by three
iron columns. The flue enters into a series of zigzag dust-duunben
outside of the building, oonnected with a stack 60 ft. high and 5 d
square inside from bottom to top. The water-space in the famaoe e
only 2 ill. wide, instead of 6-8 in. The chief peculiarity is the front
connecting-reservoir or "well." It is a circular, cast-inm, wate^
jacketed vessel, mounted on 4 stout wheelfs and so designed thtt \^
hole in one side connects directly with the outlet-hole of the fanuoe.
This forms a connecting channel, a few inches in length, l^orongblr
protected by water-cooUngj through which the molten sla^ and msstt
flow out of the fnmace as rapidly as they are formed. Tbey thm
escape the influence of the blast ; and any possibility of the formatioo
of the great bugbear of copper-smelters, masses of metallic ins
(" sows " or " salamanders "), is completely avoided. The slag vA
metal separate very perfectly in this quiet, spacious reservoir, and
the slag flows in a continuous stream over the jacketed lip at a height
of 10 in. above the outlet-hole of the furnace. This ingeniow
arrangement completely traps the blast, and prevents foul slag. Tbe
matte is tapped at intervals of 10-20 minutes through a septnte
bronze water-cooled tap-hole casting, which is bolted to one nde ^
the well, and which is plugged with clay in the usual maimer.
Owing to its proximity to the hot stream of molten matter from ^ \
furnace, the tap-hole never chills. When the operation of tappiu? j
fakes place, the furnace-man simply drives a ^in. steel bar throogli
the clay plug with a few light taps of a carpenter's hammer. I^
matte flows quietly into a slag-pot, and the small tap-hole in tJhf
casting is closed, without any chance of failure, by a clay plug ^ I
usual. There is no interruption of the blast. For the better prt- 1
servation of the cast-iron plates which form the floor of the buildist; |
around the furnace, a circle is cut in the plate just where the ftreac^
of slag naturally falls, and into this is introduced a shallow caet-in^
basin. The slag drips into this without injuring the plates, vA ■ '
taken out from time to time by the fork, and thrown into the sla^
pot. The basin stands two months or more before it is destrqre
and is replaced at a cost of 3«., and without loss of time to the fnrnac
Ore and fuel are accurately weighed, and sampled; the nttt
produced is daily sampled, as well as accurately weighed, before it
dumped from the pot, and the slag is sampled from every potful a
assayed once every 24 hours. By properly mixing the three dilfere*
ores, flux is dispensed with. The fuel used is Pennsylvania oikA<
the best quality, 1 ton of which smelts 7-8 tons of ore. The oap*:it
of each furnace is about 125 tons per 24 hours. The matte or r^tilc
produced carries 27-30 per cent, copper and 16-19 per cent nidw.
The refining of the matte is performed in two ways : —
(a)* The matte is bessemerised in converters with a silidrs
lining, the latter uniting with the oxidised iron to form a slag, whip
the copper and nickel remain as sulphides. The enriched m«tte
• 8. H. Emmens, Mineral Induatry, 1898. p. 352.

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next calcined in a reverberatory furnace to remove moet of the
foilphnr, afterward roasted with salt, and the copper chloride is

Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 65 of 76)