Waldemar Lindgren.

Mineral deposits online

. (page 63 of 84)
Online LibraryWaldemar LindgrenMineral deposits → online text (page 63 of 84)
Font size
QR-code for this ebook

the magma. Weinschenk also applies this theory to its occur-
rence in many areas of regional metamorphism, but this view is
probably not justified.

In studying the contact-metamorphic graphite from Ticon-
deroga, New York, E. S. Bastin showed by experiments that the
contemporaneous quartz crystals had not been exposed to a
temperature of 575 C. While a very high temperature is neces-
sary for the manufacture of artificial graphite, the transformation
can evidently be effected in nature at a much lower degree of

3. Lastly, graphite occurs in veins, sometimes 2 or 3 feet
wide, having the appearance of resulting from the filling of open
fissures, and in this form the mineral usually possesses a marked
transverse fibrous structure. Such veins are found in igneous
rocks like pegmatites and granites, and also in the surrounding
metamorphosed sediments. Fine examples are seen in the
graphite regions of New York, Canada, and Ceylon.

The origin of this type is less easy to explain. As the veins
are usually found near intrusive contacts where high heat pre-

1 T. H. Holland, Mem., Geol. Survey India, vol. 30, 1901, p. 201.

2 G. O. Smith, Bull. 285, U. S. Geol. Survey, 1906, pp. 480-483.

3 Geologic Folio 161, U. S. Geol. Survey, 1908.


vailed, it may be conjectured that they were formed by deposi-
tion from gaseous carbon compounds, such as carbon monoxide
or cyanogen compounds, perhaps with metals; in some of these
graphites the ash contains much iron. The prevailing opinion
is that the carbon is derived from surrounding sediments and
was deposited shortly after the intrusion, but E. Weinschenk 1
and others consider it as originating from exhalations of igneous
origin. The Ceylon veins, described by the same author, contain,
in addition to graphite, quartz, rutile, orthoclase, apatite, pyrox-
ene, and pyrite. Calcite is contemporaneous and intergrown
with the graphite. Finally there are, both here and at other
places described by Weinschenk, kaolin and the corresponding
iron compound, nontronite, and these occurrences are held to
support the theory of igneous derivation. This view is assuredly
not justified, as the possibility that such highly hydrated
compounds can be formed by igneous exhalations is decidedly
remote (p. 328). Types 2 and 3 form many valuable graphite

Occurrences.- Deposits of graphite have been found in a
number of States in the Union, but few are of economic impor-
tance; many of them are graphite slates or clays which are util-
ized as pigments or as lubricants.

A part of the domestic supply of "crystalline" graphite is ob-
tained from New York; the mines are located in Essex, Warren,
Washington, and Saratoga counties, in the Adirondack region, 2
and the largest mine, that of the American Graphite Company,
has been worked for 30 years. The rocks are pre-Cambrian
crystalline schists of sedimentary origin. The principal bed
worked is a dark silver-gray quartz-graphite schist and is said
to average about 6 per cent, graphitic carbon. Elongated
quartz grains, muscovite, apatite, pyrite, and graphite, the latter
in thin and ragged flakes, averaging about 1 millimeter in length,
are the constituents. Two beds are known, one about 8 feet
thick, the other from 3 to 20 feet. Excavations have extended
for 2,000 feet along the gentle dip of the thicker bed, the greatest

1 Abhandl. Bayer. Akad. d. Wissensch., vol. 21, 1901, pp. 218-335.

* E. S. Bastin, Econ. Geol, vol. 5, 1910, pp. 134-157.
D. H. Newland, New York State Museum, Butts., 1905 to 1916. Annual
reports of the graphite industry.

Ida H. Ogilvie, Bull. 96, idem. (Geological map.)
H. L. Ailing, The Adirondack Graphite Deposits, Bull. 199, New York
State Museum, 1918.


depth below the surface being 250 feet. The associated rocks
are garnetiferous gneisses and limestones of the Grenville series.
The sediments are metamorphosed by intrusion and injection
of granite and gabbro of Laurentian and possibly Algoman age.

Three miles northwest of Ticonderoga, in the same region,
coarse graphite plates are irregularly distributed throughout the
contact zone between pegmatite and pegmatitic granite and the
schists and limestones which these rocks intrude. Contact-
metamorphic minerals, like scapolite, pyroxene, and vesuvian-
ite, occur in this zone. The graphite also forms veins, 1 to 2
inches wide, which cut across both the schist and granite. The
deposits at this locality have been worked for a number of

In the last years the production of flake graphite from a belt
of Paleozoic mica schist in Clay county, Alabama, and adjacent
region has acquired considerable importance. The ore contains
about 3 per cent, graphite.

A deposit containing graphite in veins similar to those of
Ceylon has recently been found near Dillon, Montana. 1 The
veins occur along a contact zone of granites and pegmatites,
intrusive in pre-Cambrian schists and calcareous rocks which
have been contact-metamorphosed.

At several places in New Mexico 2 intrusions of basic igneous
rocks have altered the coal-beds of the Tertiary or Cretaceous
formations. At Madrid the coal was converted to anthracite.
Near Raton the intrusions have turned the coal into a coke-like
material, but at one place 7 miles southwest of Raton a number
of sills produced exceptionally intense metamorphism, convert-
ing the coal to graphite. Graphite also occurs in irregular
masses in the diabase and has a more or less columnar texture
normal to the faces of the igneous rock.

Similar conditions produced the important deposit of amor-
phous graphite of Santa Maria, in central Sonora, Mexico. Ac-
cording to F. L. Hess 3 several coal-beds, attaining a maximum
thickness of 24 feet, have been subjected to contact metamor-
phism and folding by intruding granite and are converted into
amorphous graphite. The mam vein averages 86 per cent.

J A. N. Winchell, Econ. Geol, vol. 6, 1911, p. 218. E. S. Bastin, Econ.
Geol, vol. 7, 1912, p. 435.

2 W. T. Lee, Mineral Resources, U. S. Geol. Survey, pt. 2, 1908, p. 733.

3 Idem, p. 734.



graphitic carbon and furnishes a good material for the manu-
facture of lead pencils.

The graphite deposits of Ceylon 1 are among the most pro-
ductive in the world, yielding about 38,000 short tons a year
of high grade product. The mineral is said to occur as veins,
varying in width from 12 to 22 centimeters. The mines are from
100 to 500 feet deep. The rough material often contains up to
50 per cent, impurities and is hand picked and sorted.

According to Bastin the veins are found in a fine-grained acidic
or basic gneiss to which he applies the name granulite. The
rock contains quartz, feldspar, garnet, pyroxene, biotite, etc.

FIG. 253. Vertical section of graphite veins, Buckingham Township,
Quebec. After A. Osann.

Some crystalline limestone is also present. The gneisses are
intruded by granites and pegmatites. In the last few years
Madagascar is rivaling Ceylon. In 1917, 35,000 tons are said
to have been produced, the quality of flake graphite being about
the same as that of the domestic output.

The Siberian deposits, in the Batagol Mountains near Irkutsk,
yield material of great purity, which formerly supplied the lead-
pencil industry. L. Jaczewski, 2 describing the Alibert mines in
this region, states that the graphite occurs in a nepheline syenite

1 J. Walther, Zeitschr. Deutsch. geol. Gesell., vol. 41, 1889, p. 359.

E. Weinschenk, Op. cit.

E. S. Bastin, Econ. Geol., vol. 7, 1912, pp. 419-443 (with literature).
2 Neues Jahrb., 1901, 2, ref. p. 74. (Original in Russian.)



close to the contact of a schist that also contains graphite, the
latter, as well as the inclusions in the igneous rock, being con-
sidered of organic origin. This conclusion is vigorously at-
tacked by E. Weinschenk. 1

The deposits at Passau, in Bavaria, comprise few veins; the
graphite occurs in a crushed, schistose rock and Weinschenk
regards the deposits as caused by volcanic emanations. The
occurrences hi Moravia are apparently similar.

The graphite deposits of Canada are contained chiefly in Buck-
ingham and Grenville townships, Quebec, near Ottawa. The pro-
duction in 1917 was about 3,700 long tons. These deposits,

FIG. 254 Vertical section of graphite vein in limestone, Grenville district,
Quebec. After A. Osann.

which have been described by A. Osann, 2 show particularly clear
relations to contact-metamorphism. The rocks are largely
gneiss, quartzite, and crystalline limestone of Grenville age
cut by granite, pegmatite, and diorite. Graphite is widely
distributed in fissure veins or lenticular masses in these intrusions
or near their contacts, also as disseminated flakes in limestone
or gneiss (Figs. 253 and 254). Associated minerals are apatite
and scapolite, often appearing in the wall rocks of the veins,

X E. Weinschenk, Op. cit.

E. Weinschenk, Zur Kenntniss der Graphitlagerstatten., Abhandl. Bayer.
Akad. d. Wiss., vol. 19, 1899, pp. 511-563.

2 Ann. Rept., Canada Geol. Survey, 1899, pp. 660-820. See also Cirkel's
report quoted above.


also biotite, titanite, wollastonite, and pyrite. The analogy of
these deposits with the apatite veins is striking and the conclusion
seems justified that they were developed by igneous emanations
shortly after the close of the intrusive activity.

Production and Uses. The production of natural graphite in
the United States has varied considerably, owing to the large
quantities of low-grade material used for paints and fertilizers.
The output of flake graphite from New York State is about
1,500 tons per annum. Alabama, in 1917, produced 3,100 tons;
the total domestic output of flake graphite in 1917 was 7,000
tons. Much larger is the production of artificial graphite now
manufactured in electric furnaces at Niagara Falls at the rate of
5,000 tons per annum, from anthracite coal mixed with a small
percentage of ash. In addition about 20,000 to 42,000 tons of
graphite are imported from the .highly productive mines in
Ceylon, Mexico, Korea and Madagascar. Ceylon graphite sold
in New York (1911) for 7 to 9 cents a pound, but during the war
the price rose to 30 cents. Domestic No. 1 Flake brought 13
to 18 cents per pound in 1917. It should contain 90 per cent,
graphitic carbon.

There is a great demand for graphite from many branches of
industry. The inert and heat-resisting nature of the "crystal-
line" graphite makes it particularly valuable for crucibles, the
fibrous Ceylon product being most suitable for this purpose.

Graphite is extensively used as a lubricant, with oil, and for
this purpose the artificial mineral, which is "deflocculated,"
causing it to remain indefinitely in suspension in oil, is especially
employed. Other uses are for pencils, foundry facings, polish-
ing powder, paint, electrodes, and, strange to say, as an adul-
terant for fertilizers; it is claimed that it prevents absorption of
moisture and caking.

The low-grade material from New York State is concentrated
at the mines by crushing, washing on buddies or other appliances,
and settling, but the details of the process have not been made
public. Present practice in Clay County, Alabama, includes
dry crushing, drying and water flotation. 1


Some varieties of garnet, especially almandite, are mined and
used as abrasive material. In the State of New York there are
1 Irving Herr, Eng. and Min. Jour,, April 11, 1917.


several deposits of this kind. 1 The garnets occur in highly
altered rocks of somewhat uncertain history but are probably
the result of contact metamorphism.


General Features. The deposits thus far described lie close
to the well-defined contact of an intrusive rock with a sedimen-
tary series. There are deposits, however, in which the mineral
association points to the same mode of origin, but which are not
clearly related to any given contact. This may result from a
sloping or irregular contact of a large batholith, so that a point
on the surface that is several miles from the contact horizontally
may be only a few thousand feet from it in a vertical direction.
General metamorphism, without special development of mineral
deposits, appears to have been effected by such conditions at the
northern end of the great batholith of Idaho between the Clear-
water and St. Joe rivers. 2 During a long and deep immersion
into the abyssal zone, metallic gases given off by magmas may
have penetrated farther from the intrusion than they have near
the surface. It is also possible that erosion may have cut away
the metallizing dike or mass, so that its relation to the deposit
is no longer apparent.

At any rate such ore-bodies are termed deposits due to igneous
metamorphism, rather than contact-metamorphic deposits.

Ores of copper, zinc, lead, and iron are included in this class.
Many representatives are found among the obscure deposits in
the pre-Cambrian of Scandinavia.

Boundary District. At Phoenix 3 and Greenwood, in British
Columbia near the international boundary, are a number of ore-
bodies which in the last decade have yielded about 125,000 tons
of copper. The geology of the region is complex. A thick series
of volcanic rocks (porphyrites) , both clastic and massive, crystal-
line limestones, and argillites, all of upper Paleozoic age, is
intruded by a granitic batholith of probable Jurassic age and
smaller masses of syenite.

1 W. J. Miller, Garnet deposits of Warren County, N. Y., Econ. Geol,
vol. 7, 1912, pp. 493-501.

2 F. C. Calkins"and E. L. Jones, Bull. 530, U. S. Geol. Survey, 1913,
pp. 75-86.

3 O. E. LeRoy, Mem. 21, Canada Geol. Survey, 1912.


The large ore deposit of the Granby Company lies in a miner-
alized zone which represents a part of the limestone replaced by
epidote, garnet, etc. The ore-bodies are lenses or large masses
one of which is 2,500 feet long and 900 feet wide and has a maxi-
mum thickness of 125 feet: The dip becomes flat in depth and
the ore ceases at a vertical depth of 675 feet. Fig. 255 represents
the somewhat clearer condition at the adjoining Brooklyn Mine.
The ore consists of chalcopyrite, pyrite, hematite, and magnetite,
with andradite, actinolite, and epidote. Calcite and quartz
fill the interstices between the lime-iron silicates. The ore as
smelted contains from 1.2 to 1.6 per cent, copper with 0.04 ounce
of gold and 0.3 ounce of silver per ton. The original limestone
which appears in some remnants near the ore-body is compara-

FIG. 255. Generalized section of Brooklyn ore-body, Phoenix, B. C. o,
ore-body; Is, limestone; g, gangue; j, jasperoid. Scale 400 feet =1 inch.

tively pure and contains from 1 to 10 per cent, of silica and little
or no iron. Magnetite, epidote, and garnet formed contempora-
neously; somewhat later but partly overlapping came the de-
velopment of chalcopyrite, pyrite, and hematite. The limestone
is in large part converted to jasperoid, the alteration appearing
to have taken place before the development of the ore.

No large bodies of igneous rocks appear in or near the deposits,
and the nearest small outcrops of granodiorite are 1 to 2 miles
away; one of these outcrops has been locally replaced by garnet,
epidote, and actinolite. Deep drilling below the deposits failed
to disclose intrusive rocks. It is held that the ores were formed
by igneous emanations of iron, silica, and copper which traversed
the limestone laterally from some unit of the intrusive series
that is now eroded.

Ducktown, Tennessee. The copper ores at Ducktown have
been worked since about 1848 and still maintain an output of
8,000 tons of copper a year. In addition, about 700 tons of
sulphuric acid is now obtained daily from these ores. The
district, which lies in the mountainous area of the southern



Appalachians, has been the subject of repeated geologic investi-
gation by C. Heinrich, J. F. Kemp, and W. H. Weed. Lately,
W. H. Emmons and F. B. Laney 1 have examined the deposits.
According to Emmons and Laney the deposits are contained in
a highly compressed metamorphosed and schistose series of
arkose sediments of Cambrian age, consisting of poorly sorted
conglomerates, grits, sandstone, and shale. Garnet and stauro-
lite have developed abundantly in the rocks, the staurolite
following certain horizons persistently. Thin lenses of limestone

Schist Ore Zone Gossan Chalcocite

FIG. 256. Cross-section of Mary mine, Ducktown, Tennessee.
After W. H. Emmons, U. S. Geol. Survey.

were contained in the series and are exposed in some places in
the mines; they are now crystalline and contain layers of biotite
and muscovite. Here and there are small ill-defined lenses of a
highly metamorphic rock looking like a diorite-pegmatite and
consisting of quartz, feldspar, hornblende, and garnet. These
peculiar phases are now believed to be the result of strong meta-
morphism of the arkose sediments. Dikes of gabbro, later than
the mineralization, are intruded in the sediments.

The deposits are elongated, roughly tabular masses, some of
them curved, lens-shaped, or folded, striking northeast and mostly
dipping southeast (Fig. 256). The ore beds are parallel to the

1 Preliminary report in Bull. 470, U. S. Geol. Survey, 1911, pp. 151-172.


strike of the schists and average 60 feet in width. The primary
ore is a coarsely crystalline mass of pyrrhotite, pyrite, chalcopyrite,
zinc blende, specularite, magnetite, actinolite, calcite, tremolite,
quartz, pyroxene, garnet, zoisite, chlorite, mica, graphite, titanite,
and feldspars, all of practically contemporaneous crystallization.

Much of the ore is almost massive pyrrhotite and pyrite.
Along the strike and dip the ore may grade into a lime silicate
rock of gangue minerals and these in places grade into crystalline
limestone. The contact between schist and ore is sharp or
gradational within a few inches. The beds have been worked
to a maximum depth of 1,000 feet. A thin but rich chalcocite
zone due to enrichment by surface waters was found at a depth
of 50 feet (p. 853), but below this the ores contain 1.5 to 3.0
per cent, copper, a small amount of silver, and a trace of gold.
The ores from the Mary mine now average 2.5 per cent. It is
held that the ores are formed by the replacement of thin limestone
beds; all the abundant gangue minerals are in fact rich in lime.
The replacement is believed to have been effected by igneous
emanations, as a general association of minerals is typical of
normal contact deposits. At the time of ore formation the rocks
were at a high temperature and deeply buried, and it is thought
probable that the emanations from some intrusion far below the
surface, which had little effect on the schist, caused mineralization
in the limestone beds. The mineralization fell within the epoch
of dynamometamorphism; some deformation of the ore has taken
place since its deposition.

Franklin Furnace, New Jersey. l - The great zinc-manganese
deposits of northern New Jersey are of exceptional complexity
and interest. Known since 1650 and actively worked since
1860, they now yield annually about 700,000 short tons of ore
containing about 120,000 tons of zinc The treatment of the
crude ore by magnetic concentration yields franklinite, "half
and half," and willemite; the first is used for the manufacture
of zinc oxide for paints and leaves a manganiferous residue
which goes to the blast furnace to make spiegeleisen; the second
is also used for zinc white; and the third after further concen-
tration yields a product of willemite from which a high-grade
spelter (zinc) is made.

*A. C. Spencer, H. B. Ktimmel, J. E. Wolff, and Charles Palache,
Geologic Folio 161, 1908.

See also review by C. K. Leith, Econ. Geol, vol. 4, 1909, p. 265.



The two ore deposits of Mine Hill and Sterling Hill, 3 miles
apart, are situated along a belt of pre-Cambrian crystalline
limestone adjoined on the west by coarse gneisses of igneous
origin. Cambrian limestone covers these rocks to the east and
west. Both deposits form canoe-shaped beds in the pre-Cam-
brian limestone. The Mine Hill ore bed (Fig. 257) is closely
adjoined along its west flank by the gneiss, the contact of which
is parallel to the ore-body. The ore mass is thus a layer varying
from 12 to 100 feet in thickness and, bent upon itself, forms a
long trough or one-half of a canoe with sides of unequal height,
the keel pitching north at a gentle angle.


FIG. 257. Plan of outcrop and levels and vertical section of Mine Hill ore-
body, Franklin Furnace, New Jersey. After A . C. Spencer, U. S. Geol. Survey.

The mines are opened by a vertical shaft 965 feet deep and an
incline 1,500 feet long. The ore forms transitions into the
limestone and at Sterling Hill the limestone between the flanks
also contains lean ore. Pegmatite dikes cut ore, limestone, and
gneiss. The ore is a coarse aggregate of franklinite, 50 per cent.;
willemite, 20 to 30 per cent. ; zincite, 2 to 6 per cent. ; and calcite,
3 to 11 per cent. Franklinite, (Fe,Mn,Zn)O.(Fe,Mn) 2 O 3 , con-
tains about 42 per cent, iron, 15 per cent, manganese and 12 per
cent, zinc; willemite, Zn 2 SiOi, 58 per cent, zinc; zincite, ZnO, 77
per cent. zinc. The four minerals mentioned are held to consti-
tute the original ore. Besides, there are a great number of rarer
minerals such as tephroite (Mn 2 SiC)4), zinc pyroxene (schefferite),
zinc amphibole, zinc spinel (gahnite), manganese garnet (poly-


adelphite), axinite (borosilicate of Al, Ca, Fe, Mn), apatite and
scapolite (containing chlorine), rhodochrosite, fluorite, zinc
blende, galena, arsenopyrite, chalcopyrite, and lollingite. Most
of these minerals are regarded as products of secondary meta-
morphism due to the pegmatite dikes. Many veins cut the
deposits, some of them containing the normal recrystallized ore
minerals, others distinctly later with sulphides associated with
calcite, albite, bornite, quartz, dolomite, etc.

In the older literature the deposits were considered of sedi-
mentary origin. The question of genesis was reopened in 1889
by F. L. Nason, who admitted the possibility of igneous origin.
Spencer believes that the original deposit was formed by the
injection of magmatic emanations from the gneiss intrusions into
the limestone. Participation in the general deep metamorphism
which affected this region in pre-Cambrian time has further
complicated the relations. It is certain that the texture of the
ore and the universal rounding or corroding of the ore minerals
point distinctly to igneous metasomatic action. The abundance
of the spinel minerals is indicative of high temperature.

Metasomatic Magnetite Deposits of Sweden. 1 Many of the
earliest known and longest worked of the Swedish iron deposits

1 Hj. Sjogren, The genesis of our iron ores (Swedish), Geol. For. Forhandl,
vol. 28, 1906, pp. 314-344. With discussion by Tornebohm, Hogbom,
Holmquist, Backstrom, etc.

Hj. Sjogren, The geological relations of the Scandinavian iron ores,
Trans., Am. Inst. Min. Eng., vol. 38, 1908, pp. 766-835.

Hj. Sjogren, The question of the origin of the iron ores in the older pre-
Cambrian series of Sweden, Geol For. Forhandl., vol. 30, 1908, pp. 115-155.

H. Johansson, The question of the origin of the middle-Swedish iron ores
(Swedish), Geol. For. Forhandl., vol. 28, 1906, pp. 516-538; vol. 29, 1907,
pp. 143-186, 232-255; vol. 30, 1908, pp. 232-235.

Review, Econ. Geol., vol. 5, 1910, pp. 494-498.

L. de Launay, L'origine et les caracteres des gisements de fer scandinaves.
Ann. des Mines (10), vol. 4, 1903, pp. 49-211.

See also a summary of recent literature by A. Bergeat in Fortschritte der
Mineralogie, etc., vol. 2 : Jena, 1911, pp. 43^4.

Excellent descriptions of individual districts are found in the guide to
the excursions of the Internat. Geol. Congress, Stockholm, 1910.

P. Geijer, Some problems in iron ore geology in Sweden and America,
Econ. Geol, vol. 10, 1915, pp. 209-239.

P. J. Holmquist, Swedish archaean structures and their meaning, Bull,
Geol. Inst. Upsala, vol. 15, 1916, pp. 125-148.

P. J. Holmquist, Structure and metamorphism of Swedish iron ores.
(Swedish) Geol For. Forhandl, April, 1913, pp. 233-272.



form irregular masses or lenses in rocks of upper Archean age.
They are either directly associated with crystalline limestone,

Online LibraryWaldemar LindgrenMineral deposits → online text (page 63 of 84)