Charles George Warnford Lock.

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cases the ore is seldom continuous for any great distance, but is ibuni



After Forbes, Proc. Qeol. Soc., Nov. 1860.

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METALLIFEROUS MINERALS. 417

scattered through the metalliferous sandstones, in irregular patches
or spots of a white or greenish-white colour, fall of small grains of
metallic copper : the colour of these spots, forming a striking contrast
with the deep red colour of the rest of the bed, affords, at first sight, a
sure indication of the presence of the metal. This discoloration seems
to indicate some chemical change having taken place, apparently con-
nected with the reduction of the copper to the metallic state, and the
formation of the sulphate of lime (gypsum) in these beds ; and Forbes
concluded that this change has been caused by the evolution of
sulphurous fumes penetrating into the pores of the strata, at the time
of the eruption of the dioritic rocks of Comanche and the Cerro de las
Esmeraldas, situated respectively to the north and south of the
metalliferous district of Corocoro, and the protrusion of which through
these Permian beds caused the fault itself and the accompanying
dislocations of the strata. The sandstone he supposes to have been,
previously to this disturbance, calcareous, and more especially so in
the cupriferous parts, in which he regards the copper as having been
present in the state of oxide or carbonate associated with carbonate
of lime. Sulphurous acid, by combining with the oxygen of the oxide
of copper to form sulphuric acid, would reduce the copper to the
metallic state, whilst at the same time the sulphuric acid thus formed,
acting upon the carbonate of lime, would produce the sulphate of lime
(or gypsum) invariably accompanying these deposits. It is interesting
to note that vanadium is present here as in the Permian Eupfer^
schiefer of Thuringia.

The metallio copper is the main object of exploration, and in a state
of powder, resulting from the crushing and washing of the cupriferous
sandstones, is exported in large quantities to Europe under the namo
of '* copper-barilla." The want of coal or wood in this barren region
prevents the ores of copper being worked or concentrated to a suffi-
ciently high percentage for exportation, — ^the only smelting works
being supplied with fuel from the excrement of llamas — it being
oonsidered that 100 quintals (each quintal ^ lOH lb.) of llama dung
will smelt 80 quintals of " copper-barilla " ; and the reverberatories
are built with two chimneys. The annual product is about 6000 tons
of barilla, carrying 66 per cent, copper.

Chili. — While in 1865 Chili was responsible for half the world's
production of copper, it now affords about one-fourteenth ; the most
aooeesible and richest deposits have been worked out, and mining and
metallurgy have not been improved to keep pace with the needs of
greater depths and poorer ores. The chief producing districts are
Coquimbo, Atacama, Lota, Coronel, Valparaiso, and Tocopilla, in the
order named. The principal reduction and smelting worxs are those
of Cousino & Yattier at Maitenes, of Lambert at Coquimbo, and those
of Chanaral, Guaycan, and Tongoy.

Germany. — The chief productive ores are chaloopyrite and copper
glance. The pyrites bed in the coal measures of Rommelsberg, near
Goslar, in the Hartz Mountains, is a deposit 600 m. long and 80 m.
thick, and is composed of copper pyrites, galena, blende, fahlerz, and
iron pyrites, with heavy spar, calc-spar, and quartz. It was first
worked over 900 years ago.

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4i8 ECONOMIC MINING.

\

The most important source of copper in Germany is Mansfeld, cm'
the south-eastern extremities of the Hartz Mountains. The geological
formation of this district is exceedingly simple, as, with the exception
of an occurrence of melaphyre in the Wepper Valley, the whole region
is composed entirely of stratified rocks, of which the " Bothliegendes"
forms the lowest member, then the '* Zechstein," and uppermost the
" Bunter Sandstein," which consists of red clay-slates, red sandstone
and shales, oolitic beds, and thick masses of gypsum. The Eoih-
liegendes forms the base of the " Kupferschiefer " ^copper shale). The
Zechstein formation consists of two principal divisions, the lower
comprehending the ** Rupferschiefer-Flotz," or cupriferous seam, and
the *' Dach,*' or the Zechstein proper ; while the upper consists o)
*' Stinkstein," " Asche," and " Ranch wacke," with gypsum and various
clays.

The bituminous marl constituting the copper schist, or shale, liei
with great regularity on the Bothliegendes. The metalliferous con-
tents of the schist occur as a rule in the form of a " Speise," or very
fine particles, which in transverse fracture give a metallic reflectioc
in sunlight. A golden colour shows a predominance of chalcopyrite
a violet, blue, or copper-red colour, the preseuce of erubescite ; mon
rarely the colour is steel-grey, from copper glance ; and sometime^
bluish-grey, from the presence of galena. The Speise consists princi-
pally of sulphuretted ores of copper, but there also occur argentite.
l)Iende, galena, and iron pyrites. Although none of the layers o)
Kupferschiefer is barren, it is only in a few bands that the ok
occurs in workable quantities. The thickness of the productive seair
varies from 2\ to 5 in., and contains 2 to 3 per cent, copper with 5 u
10 lb. silver to the ton of copper.

From the report recently issued by the " Mansfeld'schen Kup^r-
Fchieferbauenden Gewerkschaft " for the year 1891, it appears tlwi
the quantity of copper shale mined during the year was 521,696 ton^,
which included 51,719 tons of " DachljKsrge " (an inferior quality
shale), or a decrease of 14,793 tons from 1890, due to the inability
to get rid of the water in the lower levels. They were thus fon»i
to work, at a greater cost, the higher levels, which are much poorer
in both copper and silver. The cost of mining amounted to 38*21
marks (about 39«.) per ton, which was 2*29 marks more than in 189('.
The total quantity of ground excavated was 1,533,500 sq. ul, or
102,600 sq. m. less than in the previous year, which makes 2- 94 sq. m.
to the ton of shale. At present, of a total quantity of 1 1,562,100 sq m.
of excavated ground, 3,793,700 sq. m. are under water. The furnaces
altogether smelted 512,828 tons of shale, against 543,470 tons in 185K).
The black copper production was 39,331 tons, against 40,854 tons in
1890. The yield per ton of ^hale was 75 k (165 lb. J black copptr.
The copper yield was 30*45 A; (70 lb.) copper, and '18 k (4J oz.) silver
per ton.

India. — A recent writer * has described extensive copper working*
in Singhbhum, Hazaribagh, Kulhari, and Singhana districts, whid^
seem to deserve attention.

Nova Scotia. — At numerous points .the sandstones and shaltfr
• * Times of India,' Oct 25, 1890.



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METALLIFEROUS MINERALS, 419

isent irregular bedded masses and layers of copper ores, principally
iy snlpliurets, with films and coatings of carbonate, and associated
th fossil plants, to whose presence their deposition is attributed,
therto, attempts to find them in workable amounts have not been
jcessftil, though a Permo-carboniferous sample from Carribou, near
Jtou, gave 40 per cent, copper, 25^^ sulphur, 11 iron, 2 cobalt,
ime, \ manganese. In the Triassic formation, most noticeably at
irgaretville, copper ores, principally carbonates with native copper,
I found in veins in the trap and ash. These veins have been ex-
•red several times without success. No records have been made
the "low-grade" values of these rocks, but there is reason to
)po8e from the frequent occurrence of copper ores over so wide an
»nt of territory that, locally, beds may be found carrying the
eeminated metal in amounts of economic value.*
Persia. — Copper is very plentifully distributed throughout Persia,t
i close to Semnan is a very interesting deposit, where considerable
antities of copper exist, chiefly as carbonate, with a little sulphate
d oxide. The ore is found in small veins and disseminated through
day stone which, in some cases, is still quite plastic, in others is so
ghly silicified as to resemble agate and jasper. It has clearly been
posited by the action of mineral waters, as there can be seen layer
ter layer of material permeated throughout by salts of copper. In
tne cases the little seams or veins of copper carbonate are over \ in.
ick. The workings are very rough and irregular, but go down a
nsiderable depth, and at a fairly steep angle ; layer after layer of
« copper-bearing stuff being passed through, with comparatively
iiren ground between. The deposits are very similar to some in the
ate of Guerrero, Mexico, where the ore occurs in precisely the same
W8 of formation, further proof of the mineral-spring character of
« deposits being in each case given by the seams of crystallised
rpsum which are found with the copper salts. Average samples
we 2-3 per cent, copper.
Scandinavia. — What will probably prove to be very important
pper deposits exist at Sulitelma, but have hitherto been unde-
sloped owing to transport difficulties. The pyrites carry a small
sxcentage of zinc, but are very free from other impurities, and
ment copper made from these is entirely devoid of antimony,
Knic, and bismuth.
Spain. — The celebrated cupriferous pyrites beds of Eio Tinto, San
Ingos, and Tharsis occupy a great metalliferous belt, over 100
» long and 30 miles wide, partly in Spain and partly in Portugal,
^ country rocks are Upper Devonian slates, striking 16*^ to 25^N.
[W. and with a nearly vertical dip, often much altered into talc
AN &C., by intrusions of quartz, quartz-syenite, granite, diabase,
I felspar porphyry. There are four principal *' lodes " (? bedded
^s), all occurring at or near the junction between the porphyry
I the slate, and attaining sometimes to the enormous thickness of
to 600 ft. Fig. Ill illustrates the formation: a, pyrites vein,

L* E. Gilpin, ** Geological Relations of Nova Sootia Minerals," Trans. Amer. Instt
f- EnKs.. 188D.
t J. Maetcar, ** Notca on Persian Mines," Trans. In*t. Min. and IMet., iii.

2 K 42



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420



ECONOMIC MINING.




Fig. 111. — CoppEB Dkposits,
Rio Tinto.



worked out at &, and capped by gossan e; <2, slates; 0, porpbyry;
The minerals composing the vein matter vary oontinually, and 6»
brace the sulphides of iron, lead, and zinc, as well as most Tarietiei
of cupreous pyrites. The mining operations are conducted on a
enormous scale, probably the largest in Europe. In the magnfisiai

limestones of Permian age, in Astunu
are very extensive deposits of melaooniti
giving 75 per cent, copper when sept
rated, and the whole mineral nuk>8 assay
ing over 6 per cent.

United States. — ^The copper of tb
Lake region (chiefly Michigan state
<KScnrs native, with some silver, in boti
sedimentary and interstratified igneoQ
rocks of the Eeweenawan system; as
cement, binding together and replaoBj
the pebbles of a porphyry conglomerate ; or filhn^ the amygdoks i
the upper portions of the interbedded Hheets of igneous rock ; or a
irregular masses, sometimes of enormous size, in veins, with a gangn
of calcite, epidote, and various zeolites ; or in irregular maseea alon
the contacts between the sedimentary and igneous rocks.*

Of the three principal mining districts — Keweenaw Point, on tlJ
end of the Point ; Portage Lake, in the middle : and Ontonagon, a
the western base. Portage Lake is now almost the only producer.
In the Keweenaw Point district most of the mines are on ori_
fissures, which hnve later become much enlarged by the alteration
the walls. They are usually 1 to 3 ft. broad, but may reach 30 ft.
the looser textured rocks, and these expansions are also richer
copper ; the veins stand nearly vertical and cross the beds at lij
angles, while the metallic masses, both large and small, occur
tributed through the gangue. The best known mines are CI
Phoenix, and Copper Falls.

In the Portage Lake District the mines are either in conglomi
(Calumet and Heola, l*amarack. Peninsula, &c.) or in amygdak
strongly altered diabase, certain very sooriaceous sheets of which
known as ash-beds (Quincy, Franklin, Atlantic, &c.). In the •
glomerates the copper has replaced the finer fragments, so as to ap]
like a cement, and often the boulders themselves, or particular
rals in them, are permeated with copper. The metal occupies
small cavities of the amygdaloids, and in the open or shattered
it fills all manner of irregular spaces, often in fragments of great sise|
it is associated with calcite, zeolites, epidote, and chlorite. 1

In the Ontonagon district the copper follows planes approximate^
parallel to the bedding of the sandstones and igneous rocks, and ij
one mine at least (National) along the contact between the two ; it i
quite irregular in its distribution, but has the same associates.

In practice the mines are classed as ''mass," ''amygdaloid,
and " conglomerate," according to the size of the masses of copper a
to the character of the enclosing rock. l*he original souroe of th
copper w€w thought bjr early investigators to be the eruptive rook
themselves, and that witii them it had come in some form to the vox
* J, F. Kemp, « Ore Deposit^.*

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METALLIFEROUS MINERALS. 421

koe, and bad been snbeeqnently concentrated in the cayities. Pumpelly
^feired it to copper sulphides, distribute through the sedimentary
IS well as the igneous rocks, from which circulating waters have
eached it out as carbonate, silicate, and sulphate. Although the
raps are said by Irving to be devoid of copper except as a secondary
ntroduction, it is probable that their basic minerals may be its source.

Willie the deep explorations on these wonderful deposits, which
lave now attained a depth of 4000 ft. from the surface, show the
opper contents to be well maintained, it is noteworthy that the
luality of the metal, at least for electric purposes, is not up to its
brmer high standard. The great reduction in thn cost of electrolytic
fwfmfng and the high quality of the product render the trade less
lependent on Lake copper, and widen the field from which high-
juality metal can be drawn.

As an example of the low point to which cost of production has
Men brought on these mines, the following figures (1891) relating to
the Atlantic mine are quoted from Birkinbine : —

Total rock stamped 297,030 tons

Concentrates produced 5,089,7001b.

Refined copper produced 8,653.6711b.

Yield of copper per ton .. 12*3 lb.

9, percent. *615

G roes valne of product per ton 91*5467 (6«. 3(2.)

Ooet per ton of mining, self cting, and breaking . . . . $0 * 9529

^ transportation $0-0386

^ stamping and separating $0*2582

„ freight, smelting. &c $0*1847

^ construction account $0*1107

^ total $1*5451

THe stamping in this case is done by 5 Leavitt steam stamps with
l^in. cylindera The aggregate product of these stamps is 1000 tons
a day. The ore, when it comes up from the mine, is first picked
orer by hand, to remove barren rock, and then crushed to about the
Bze of broken coal. The cost of treating the ore, from the time it is
dumped at the shaft mouth to the time it arriyes at the stamps in the
concentrating mill, is about 7 c. (3^.), so that the total cost from the
ahaft month to the smelting operation is 33 0. (1#. 4j^.) per ton of
lock snitable for milling.

Folio-wing is a summary of the Wolverine mine, for 1894 : —

Book hoisted 108,220 tons

„ stamped .. .. * 76,440 tons

Mineral produced 1,852,2351b.

Beflned copper produced .. 1,611,8571b.

Tieldof copper per ton stamped 21*08 lb.

„ percent 1*05

Co6t per ton of rock hoisted $1145 (4a 9d.)

« stamped .. $1*625(6^ 9d.)

Sinking 279*2 ft.

cost per a $11*18 (46i.7d.>

Drifting 2304*6 ft.

„ cost per ft. $5*97 (25a)

Btoping 4587*7 fiithoms

„ cost per fathom $8*89(37«.)

Bock discarded as poor .. 31,780 tons

percent 29

Yield of copper from mineral, per cent 87*02

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422



ECONOMIC MINING.



In the Butte, Montana, oopper region, the veins Beem to baTs
been originally fissures or shear zones — but greatly enlarged by i»^
placement of the walls with ore — ^filled with oopper sulphides (boniit«r
chalcopyrite, d^o.) in a silioious gangue. Much silver is associated
with the oopper. At Butte is a north and south valley 6 miles widi
between high granite ridges on the east and lower rhyolite ridges aa
the west, and near the middle of this valley rises the butte of rby<>J
lite which gives the town its name. In the half of the valley esfll
of the meridian of the butte is a very dark basic granite, oonsistiog
of quartz, orthoclase, plap^ioclase, and an unusu^ amount of mica,
augite, and hornblende. In the part west and south of the butte is fl
highly acidic, light-coloured granite, containing quartz and orthoclatf
felspar with very little biotite. Quartz-porphyry dykes penetiati
the basic granite, and rhyolite dykes are encountered in the ore bodies
In the coarse granite east of the butte occur two distinct east-wotl
ore zones : the northern contains silver ores (chiefly sulphides of irwij
lead, silver and zinc) in a silicious gangue with much rhodonite ; thi
southern affords argentiferous copper ores (bomite, chalcooite, chalotv
pyrite, enargite, pyrite) in a silicious gangue. Scarcely any ooppei
is met with in the N. zone, and no manganese in the 8. zone (except
with zinc in the Gagnon vein), thus presenting the remarkable phe<
nomena of two parallel and adjacent systems of fissnres in the sanM
country rock being filled with very different ores. West of the butt^
in the acidic granite is a later-developed zone carrying silver and
mangane>e. As regards the source of the metalliferous minerals, i^
is probably to be sought in the eruptive rocks, for Emmons found •
•06 oz. silver per ton in the rhyolite and '09 oz. in the buttt
granite.

The yield of copper from the rock raised in Montana average^
about 7 per cent, as against less than 2 per cent, in the Lake region
but wages rule nearly double. The following figures relating ti
some of the Montana mines, though lacking in detail, are neverthdefl
interesting : —



MtaA.


Tom Ore
raised.


Cost of Mining.


Cost per torn.






1


$ «^ i


Colosa-Parrot


16,640


82,840


1-97= 8 3


Elra-Orlu


805


665


218= 9 1


Blaok-Rook


2,795


18,255


4-74 = 19 y


Parrot


53.155


184,575


3-47 = 14 5


Original


9,405


40,805


4-33 = 18


Glengarry


17,000


51,000


308 = 12 6


MooltoQ


940


7,403


7-87 = 32 9



The average is $3*29 (14«. Srf.) for the mines quoted, and
Dr. Ledoux has estimated the mean cost of mining in the Butte distrid
at $3 (12«. 6d.) per ton.

The Arizona and New Mexico mines have enjoyed an advantage

♦ 8. F. Emmons, "Notes on the Geology of Butte, Montana," Trans. Aib«
Inst. Min. Engs., xvi. 49.



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METALLIFEROUS MINERALS, 423

1 having ores yielding (in 1889) over 10 per cent, copper, and,
eing oxidised for the most part, they were readily reduced to black
xide.

The Santa Hita mines are found near the contact of a limestone
nd a large bed of eruptive rock, to all appearances a felsite. The
riginal openings were on native copper, cropping out in the felsite.
"he copper occurs in small pellets or shots scattered through the mass
f felsite, or in small flakes, leaves, or tabular masses, sometimes as
inch as 2 ft square, and not generally over \ in. thick. The presence
f these leaves and flakes precludes the idea that the copper is of the
fcme age as the felsite, and an integral part of this eruptive rock,
'he copper has undoubtedly been deposited subsequently to the
mption of the felsite, and in Assures formed at a later date. The
ative copper must, therefore, be held * to occur in true fissure veins,
Ithongh the irregularity of the deposition has been such that no
istinot vein can be found, and the copper-bearing rock presents
ather the appearance of a stocJctoerh^ having, however, a general
l-W. strike and almost vertical dip. In places near the surface, the
ative copper is altered into a beautiful pure red oxide. Near the
ine of junction of the felsite and limestone is a parallel series of veins,

2 which the ores assume an entirely different character (carbonates
nd oxides) and were formerly profitably mined and smelted, but in
epth, the rich oxides pinched out.

The mines of the Clifton district form three classes, occurring in (a)
»ower Carboniferous limestone, (6) porphyry, and (c) granite. The ores
f a are oxides, primarily the red oxide or cuprite in a gangue of com-
act hematite, and malachite and azurite in a gangue of manganese ore
wad). The ores of h and c are oxides and oxy sulphides on the sur-
ace, changing into copper glance at a trifling depth, and into yellow
ulphnrets in the deepest workings. While in extent and number
be veins of h and c are considerably larger than of a, the latter are,
fj far, the most valuable and productive. One of the most important
uines is the Longfellow, which is an almost vertical fissure in strati-
ted limestone, at or near the junction with a dyke of felsite. In
tlaoes the vein, or branches of it, are at the contact of the limestone
jid felsite, there forming a true contact-vein. Again, branches of
he vein are entirely in felsite, and other branches entirely in lime-
tone. The formation is illustrated in Fig. 112: a, feleite ; 6, lime-
tone ; c, sandstone ; <f, porphyry ; «, deep adit ; /, upper adit. On
he rise of the vein above the upper adit large chambers of mangani-
erous ore containing blue and green carbonates of copper were found,
iveraging in bulk 17*17 per cent, copper, 26*80 SiOa, 16*29 Fe^Oa,
md 7*49 MnO. Fine bodies of rich oxidised ores have been worked
tn the porphyry to a depth of several hundred feet, but have always
pinched out and got lean.

The ores of classes h and c being found in a sUicious country-
rock, have a more silidous gangue, and contain more or less sulphur,
rheir development at Metcalf Hill is shown in Fig. 113; at the sur-
bce they form a ttockwerk a in the porphyry 6, while in depth all the

• A. F. Wendt, "Copper Ores of the South-west," Traus. Amer. Inst. Min.
Engs., XV. 23.



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424 ECO.

small branobeB, coyering 1(
vein c, which rapidly deter
The Coronado mines, of
of quartz-porphyry cuttin{
abutting against and being
present an extreme case o
samples at surface gave 6
vein is 5 to 15 ft. wide. Il




Fig. 112.— Copper Depg

LONOFBLLOW.

a, ore ; 6, quartz-porphyry
places the walls are very
decomposed and kaoliDised
where not so decomposed,
can be laid down as a la
through the south-west, ths



Fig. 114.— Copper Depo($it8,

COBONAIX).

of the country-rock are fa''
From the very nature of
composition is an accessory
glance in the Coronado mi
shoe, where the vein is



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METALLIFEROUS MINERALS. 425

fscattered through the gangne, which is practically a matn'x of kaolin
with imbedded rounded partides of quartz, nndoubtedlj in its original
form a quartz-porphyry. Wherever the copper glance in the Uoro-
nado mines has been followed down, it disappears at a depth of
150-200 ft from tiie surface, and either the yein becomes barren or
the glance is replaced by yellow sulphurets, sparingly disseminated
through tiie gangue. Experimental concentrations of these yellow
sulphurets gave assays of 8 per cent, llie average composition of
the silicious ores is 11-22 per cent, copper, 49-67 per cent. SiOj, and
?-9jkper cent. iron.

The mines occurring in granite are few and unimportant. The
)re is copper glance in a vein 10 ft wide, with good walls but very
rregular mineralisation.

Li the Warren (Bisbee) district, the principal mines are associated
»ith Lower Carboniferous limestone and felsite-porphyry. Here, too,
\ distinction can be made between veins and ores found in the lime-
itone and those in the silicious or eruptive rocks. The ores of the
alter are silicious, and within a few feet of the surface change into
sopper glance and at greater depth into pyrites; the ores of the
ormer are oxidised, and at a depth of over 400 ft. no trace of sulphur
las been discovered. All occur in true fissures;* and the two
principal producing mines of the district in every particular carry out
he description of " bed-veins " given by von Gotta. " The outcrop of
he ore starts between the bedding of the limestone ; and, as Cotta



Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 47 of 76)