Download By CM Sehwellnus~ D.Se., and J. Willemse, M.Se., Ph.D.

TITANIUM AND VANADIUM IN THE MAGNETIO IRON ORES
23
TITANIUM AND VANADIUM IN THE MAGNETIC IRON ORES OF THE
B USHVELD
By C. M.
Sehwellnus~
COMPLEX.
D.Se., and J. Willemse, M.Se., Ph.D.
(Communicated by permission of the Honourable the Minister of Mines.)
[PLATES
III-V.]
ABSTRACT.
The Bushveld iron ores contain up to 1·5 per cent. V 2 0ij' This constituent is fairly
evenly distributed in individual bands of ore, but some bands are richer than others.
The highest concentration occurs in the lower band of the Principal group of magnetic
iron ore bands. The vanadium is not present in a mineral which can be separated from
the ore by physical means. If a suitable method of separation could be operated the
potential ore reserves would probably exceed 1,000,000 tons V 2 0ij'
The same ores also contain from about 8 per cent. to 25 per cent. Ti0 2 • The titanium
is contained in the ilmenite which occurs in the ores either as granules, or else as exsolution
lamellae in maghemite (or magnetite). When in granular form the ilmenite can be
separated magnetically. The content of granular ilmenite, rather than the total percentage of Ti0 2 , will, therefore, indicate the results to be expected from ,methods of
magnetic separation.
There is an antipathetic relation between V 2 0 S and Ti0 2 in the iron ores.
INTRODUCTION.
Magnetic iron ores occur as magmatic segregations in the basic rocks of the
Bushveld igneous complex. These segregations are in the form of bands which
are usually continuous for miles along the strike, and probably persist to great
depths.
Most of the ore is found as several superimposed bands in the upper part
of the Main zone of the complex. They are referred to as the Principal group
of bands. In the western Bushveld complex this group stretches from north of
Pretoria, westwards as far as the Pilansberg. Here they bend north-eastwards
and continue intermittently as far as the Crocodile river, the total length of
strike being about 110 miles. In the eastern Transvaal (Lydenburg area) the
bands are known over a distance of strike of some 100 miles. From the Principal
group of magnetic iron ore bands in this sector, only one sample was at our
disposal, namely, from the farm Uitvlugt 137.
In several isolated localities, magnetic ore, either in small outcrops or as
discontinuous bands, occurs in the basic i'OC~S at horizons well below the Principal
group of bands. One such seam in the Rustenburg area is situated in the lower
part of the Main zone of the complex. It was sampled at one locality (Goedgedacht 409). Ore in the Critical zone was available for investigation from the
Lydenburg area (De Goede Verwachting 313, and Eerstegeluk 348).
The relative position in the complex: of the various zones and of the bands of
magneticiton ore is clear from t~e tables of analyses (Tables 1-3) and from
Fig. 11.
24
TRANSACTIONS OF THE GEOLOGICAL SOCIETY OF SOUTH AFRICA
MAGNETITE BAND IN THE·
MAGNETITE BAND" ON
GOEDGEDACHT 409
CRITICAL ZONE
NORTH·WEST OF RUSTENBURG
LYDENBURG DISTRICT
Scale: 1 Inch:: 500 Cape Roods
Scale: 1: 250,000
/
,
GO{;:EDACHT
",
/.....
/1
I
409
'"
X
;
R 15-23
"
/
Magnetite Kop
Fig. 2
Fig. 1
MAGNETITE KOP ON GOEDGEDACHT 409
s.
N.
Hard lumpy material
,
Talus ,,"
"
..
,
....
""
.. "
Fia.3
FIGs. 1, 2 & 3.
TITANIUM AND VANADIUM IN THE MAGNETIC IRON ORES
25
Although it has been known for some time that the magnetic iron ore of the
Bushveld complex carries some titanium and vanadium, nothing was known
about the distribution of these constituents in the different superimposed bands
and along or across the strike of individual occurrences.
The authors are indebted to Dr. L. T. Nel and Professor B. V. Lombaard
for critically reading the manuscript.
LOCALITIES SAMPLED.
The bands of magnetic iron ore have been sampled at intervals over a
strike distance of about 60 miles from the farm Goedgedacht 409 in the Rustenburg district eastwards to the farm De Onderstepoort 496, north of Pretoria.
Two samples from the Oritical zone of the eastern Transvaal (Lydenburg
district ) have been analysed.
.
The diagrams (Figs. 1-10) clearly show where and over what thickness
samples were taken, except for the sample from Uitvlugt 137, the exact locality
of which is not known. Where it was necessary, and possible, trenches were dug
to expose the ore. Unless otherwise stated, all samples taken were channel
samples 2 inches wide and 1 inch deep at right angles to the dip of the bands.
1.
Goedgedacht 409, Rustenburg district (Figs. 1 and 3).
This occurrence is situated in the Main zone about halfway between the
Merensky reef and the lowermost exposure of the Principal group of iron ore
bands. It, therefore, represents a band which has hitherto not been known in
the complex. The samples were taken at the Goedgedacht trigonometrical
beacon which is situated on a koppie composed of massive magnetic iron ore
belonging to this band, some 23 feet thick. Samples R. 15-R. 23.
2.
Rooiwal 751, Rustenburg district (Figs. 4, 5 and 6).
(a) The lower band was sampled about 900 yards east of the school.
Three samples, R. l-R. 3, represent the upper 34 inches (±) of the seam. The
lower contact is not exposed but the thickness is certainly much more than
34 inches, probably 5 or 6 feet.
(b) The upper band was sampled where it forms part of the northern
bank of a spruit some 500 yards east of the road through the farm. At this locality
the seam is about IIi feet thick. Samples R. 4-R. 14.
3.
Boschpoort 16, Rustenburg district (Fig. 4).
On this farm a prominent outcrop of iron ore is situated well above the
lower band. The outcrop is about 25 feet wide and was chip-sampled.
Sample R. 24.
4.
Berseba 503, Rustenburg district (Fig. 4).
Near the western boundary of the farm, two seams are exposed which,
according to their position, would appear to belong to the middle band of the
Principal group. They are higher-lying than 3 (above).
(a) The lower of these was chip-sampled at right angles to the strike
across the outcrop over a distance of about 25 feet. Sample R. 26.
26
TRANSACTIONS OF THE GEOLOGICAL SOCIETY OF SOUTH AFRICA
LOCALITY MAP SHOWING WHERE SAMPLES WERE COLLECTED
RUSTENBURG DISTRICT
Scale: 1 Inch =2 MUes
LOWER MAGNETITE BAND ON ROOIWAL 751
N.
R 2 (12")
R 3110")
s.
Massive magnetite ~
___- - - - - -
~
Gabbro
~
UPPER MAGNETITE BAND ON R.oOIWAL 751
N.
s.
Massive magnetite
......... ---- ...
Gabbro
Fig. 6
FIGs. 4, 5 & 6.
TITANHJ"M AND VANADIUM IN THE MAGNETIO IRON ORES
27
(b) The upper one is a few hundred yards north of (a) and was also chipsampled across the outcrop over a distance of 30 feet at right angles to the
strike. Sample R. 25.
Waaikraal Mine, Rustenburg district (Fig. 4) ~
.An appreciable amount of magnetite had been dumped alongside the
opencast working of this abandoned mine and the iron ore material on the dumps
was chip-sampled. Sample R. 27.
5.
6.
Sjambok Zyn Kraal 52, Rustenburg district-Profile along the De WildtHebron Road (Figs. 7 and 10).
(a) The lower band was chip-sampled at right angles to the strike over
33 feet of outcrop. Sample R. 28.
(b) The second band is well exposed in a small spruit to the east of the
road and about 1,000 yards north of (a). The seam is one foot thick. Samples
R. 29 and R. 30, represent the upper and lower halves, respectively.
(c) The third band is only 3 to 4 inches thick and is exposed in the small
spruit about 125 yards north of (b). Four channel samples were taken about
3 feet apart along the strike and made into one sample, R. 31.
(d) The fourth band crops out some 1,200 yards north of (b) along the road.
It is about 24 inches thick. R. 32 represents the lower 12 inches and R. 33 the
upper 12 inches.
(e) The upper band is exposed some 400 yards north of (d) alongside the
main road. The ore was further exposed by a small trench, and it was found
that there were two massive seams separated by yellowish-weathering· decomposed gabbro. R. 34 is from the lower seam (18 inches thick), and R. 35 from
the upper one (24 inches thick).
7.
Klipfontein 482, Pretoria district-Profile along the Pretoria-Hebron Road
(Figs. 7 and 9).
(a) The lower band is exposed in a road-metal quarry west of the road.
The lower contact is not exposed. Samples 1-6.
(b) The middle band crops out one mile towards Hebron on the west of
the road. The outcrops were chip-sampled. Sample 8.
(c) Half a mile north-east of the road the upper band appears at the
surface on the slopes of a hill. The outcrop is very much weathered, but was
nevertheless chip-sampled at right angles to the strike over a distance of 25 feet.
Sample 7.
8.
The Sphynx-pyramids Profile North of Pretoria (Figs. 7 and 8).
(a) The lower band is exposed in a quarry next to the Pretoria-Warmbaths
road. Samples 9-17. Sample 17 (a) represents red clay from cracks and joints in
the lower portion of the seam.
(b) The uppermost exposed band which may, however, actually be the
middle horizon of the Principal group is in a furrow beside the railway line,
some 1,000 yards north of (a). The band lies very flat and is undulating.
Sample 18.
.
28
TRANSACTIONS OF THE GEOLOGICAL SOCIETY OF SOUTH AFRICA
LOCALITY MAP SHOWING WHERE
SAMPLES WERE COLLECTED
PRETORIA DISTRICT
Seale : 1 Inch= 4.694 Miles
Bushveld granite
LOWER MAGNETITE BAND ON
LOWER MAGNETITE BAND ON
DE ONDERSTEPOORT 496
KLIPFONTEIN 482
a
Fig.
Fig. 9
MAGNETITE BANDS ON SJAMBOK ZYN KRAAL 52
N.
.~5
.10 Miles
Miles
125 Yards
R33t12",
R34{lS")
. ; :.'
.. : :. "-Disseminated ore
...
(Not sampledl
Fig. 10
FIGS.
7, 8, 9 & 10.
.55 Miles
s.
TITANIUM AND VANADIDM IN THE MAGNETIC IRON ORES
29
Uitvlugt 137, Belfast District .
.A sample of iron ore which seemingly comes from the Principal group of
bands in the eastern part of the Bushveld complex was submitted to the Geological Survey for identification. The sample is rich in ilmenite, mostly of the
lamellar type. No analysis was carried out, and the concentration test on this
material proved very disappointing (vide Table 3).
9.
De Goede Verwachting 313 and Eerstegeluk 348, Lydenburg District (Fig. 2).
On these farms, some years ago, Professor B. V. Lombaard collected
samples of magnetic iron ores from the Critical zone between the Merensky reef
and the chromitite bands.
10.
L.622 comes from a band at the boundary between Eerstegeluk 348 and
De Goede Verwachting 313.
L. 623 was collected at the foot of the hill on which the south-west beacon
of Eerstegeluk 348 is situated. The material at this site is represented by large
quantities of rubble.
MINERAGRAPHY OF THE ORES.
Only the mineralogical constitution of the ores will be considered and the
relation of the minerals to one another. For more detailed descriptions of the
ore minerals the reader is referred to a recent paper by Frankel and Grainger
(1 pp. 101-110*).
The following minerals are present in 45 sections examined :-magnetite,
ilmenite, spinel, sulphide, maghemite, haematite (martite) and occasional
silicates and secondary minerals like goethite.
Magnetite is a comparatively rare constituent of the Bushveld iron ores.
It is often absent in polished sections. -In exceptional instances it may constitute
up to 40 or 50 per cent. of the ore, but is usually very much less, perhaps in the
vicinity of 5 per cent. The magnetite sometimes forms irregular patches in the
maghemite (Plate V, Fig. 1) in which case it displays a typical moth-eaten
pattern with fretted, embayed and exceedingly irregular outline. This pattern
is considered to be due to replacement. The identification of the various minerals
in such a pattern is somewhat doubtful. The unreplaced parts consist of what is
presumably magnetite, conspicuously brown in colour and distinctly, though
weakly anisotropic when examined in the strong light of an arc lamp. This
brown magnetite is surrounded by altogether isotropic magnetite, less brown in
colour and this in turn by maghemite which is feebly anisotropic. It is possible
that the brown magnetite represents a titaniferous variety.
In the opinion of the writers the relationship of maghemite to magnetite
and the whole maghemite problem requires further investigation. The presence
or absence of arizonite (Fe 2 0 3 • 3Ti0 2) in the Bushveld ores should also receive
attention in a detailed mineralogical study, as this mineral appears to be widespread in ilmenite sands.
* Figures in brackets refer to the literature at the back.
30
TRANSACTIONS OF THE GEOLOGICAL SOCIETY OF SOUTH AFRICA
Ilmenite has three different modes of occurrence, viz. : As individual grains.
As intergranular ilmenite.
As exsolution lamellae.
1.
2.
3.
As Individual Grains.
These are often twinned and reach diameters exceeding 5 mm. (Plate III,
Fig. 1). When abundant they are usually much smaller in size. Ilmenite in this
form is comparatively rare and has b(jen found in any quantity only in the
magnetic iron ores of the Critical zone. (Sample L. 623). The ores with predominantly granular ilmenite lend themselves to a physical method of concentration of the ilmenite.
1.
I ntergranular Ilmenite.
This mode of occurrence is very similar to that just described, the only
difference being that the ilmenite is present as drawn out irregular grains which
fill interstitial spaces between grains of maghemite or magnetite. Such ilmenite
bodies rarely exceed 1 mm. in width but may be up to 5 or 6 mm. in length.
They often branch (Plate III, Fig. 2.) This ilmenite can also be freed by fine
grinding, but it is rare in the ores examined.
2.
3.
Exsolution Lamellae.
-These are crystallographically orientated and so minute that they can
usually be seen distinctly only under high magnification (Plate IV, Fig. 1).
Frankel and Grainger (1 p. 103) measured the minute ilmenite lamellae and found
them to average 51..\ in width and 181..\ in length. Occasional ones measure 1 mm.
across and it is therefore possible that at least some of the exsolved material
could be freed from the accompanying minerals by very fine grinding. This
mode of occurrence of the ilmenite appears to be characteristic of the upper
band.
Spinel ex solution spindles, crystallographically orientated, have very
often been observed under high magnification (Plate V, Fig. 2). The mineral is
conspicuous but certainly not abundant. It is confined to maghemite and
magnetite and when ilmenite lamellae are present the spinel is often clustered
as fine grains on such lamellae. The spindles are always very much smaller than
the minute ilmenite lamellae.
Sulphide.-In almost every section, minute specks of sulphide, apparently
chalcopyrite, were seen under high magnification. They are distributed throughout the ore, and according to Frankel and Grainger- (1 p. 108) are 1 to 21..\ in
diameter.
M aghemite is the commonest and most widely distributed mineral in the
Bushveld magnetic iron ores.
Haematite (Martite) is easily distinguished from maghemite by its higher
reflectivity and its anisotropism. When. the ore consists almost wholely of
maghemite the martite is usually absent or only present in small quantities. In
magnetite, partially replaced by martite, the ilmenite lamellae are not disturbed
(Plate IV, Fig. 1). The martitisationof magnetite along crystallographic directions is often conspicuous.
_TABLE l.
)..
CHEMICAL ANALYSES OF MAGNETIC IRON ORES
_.!~I_SiO,
R14
R.12
R.10
R. 7
R. 4
..
..
..
..
..
3·35
1·40
2·84
3·9H
2·60
16·21
20'41
19·93
15·17
19'26
5·24
2·77
3·02
5'12
1·82
',<it
MIDDLE BANDSR.24 . .
It.26 . _
18 ..
AI.0 3
TiO.
UPPER BAND-
0·83
2·47
1'46
Fe,03
59·25
58'46
61'49
56·69
63'40
Cr,03
0·02
0·04
0'02
0'02
0'02
'V.Os
0·4
0·0
0·0
0'4
0'4
FeO
9'19
12·07
8·62
11·50
9·05
MnO
0·24
0·43
0·38
0'40
0·38
NiO
0'03
nil
nil
nil
nil
MgO
CaO
0·59
0·70
0·58
0·80
0'84
0'28
0·56
0'50
0·56
0 '56
~'51
).' 4&
a;'o - ~ t
'1.< ., t
"'f\~"lo,
14 '85
16'00
18'82
4'10
3·14
2'83
67'23
69'47
55'58
tr.
0 ·02
0·19
0·5
0·7
0'4
9·19
5'75
17'53
0'20
0 ·23
0'33
tr.
tr.
nil
0'66
0'67
0·93
0'16
0 ·44
0'50
12·60
11·69
8·23
13'00
13·69
12·17
4·24
3'84
4·92
8·91
3 '41
0 ·74
3·85
16·41
70'27
67·24
61'00
73 ·78
68'67
65'80
37'53
0'23
0'31
0'22
0 ·33
0'23
1 ·00
0·23
1 '1
1 '1
1·3
1'3
1'1
1 ·5
0 '6
5·75
10'63
4,,31
2·59
9'48
10 ·34
2 '87
0'25
0 ·07
0·25
0 '15
0·30
0 ·30
0·09
0·02
0·07
0'05
0·07
0'08
0·06
0·07
0'80
1'33
0·80
0·78
1·04
1·23
-0·07
0'56
0·07
0·34
0'39
0'45
0'22
0'81
14'37
6'61
24·43
0·27
0·20
0·20
tr.
tr.
tr.
1·24
0'43
0·64
11·50
0 ·20
0·07
1'49
I~·.!.
- - - - - - - - _~~_I_~~
Na.O
R,O
-
-
-
nil
--
-
-
nil
-
-
-
*
H~O+
H,O-
Total
Ap.
Ab.
An.
C
-
-
2·0
4·0
3·5
4 ·0
3·9
0·5
1·4
-
1'2
3 ·1
3·5
3'1
0'8
-
0·8
1 ·1
2·0
H·2
1·1
-
- - - ----
tr.
tr.
tr.
tr.
tr.
tr.
tr.
nil
tr.
tr.
4'14
2·61
2·32
4'16
1 '45
0 '50
0 ·22
0'24
0'40
0·04
99 '44
99'67
99'94
99·21
99·82
-
tr.
tr.
tr.
tr.
tr.
tr.
I-55
1·69
1 ·46
0·08
0 ·13
0·05
99 '35
100·51
100 ·00
-
tr.
tr.
tr.
tr.
tr.
tr.
.tr.
tr.
nil
nil
nil
0·03
0'10
0'63
0·23
0'05
0·04
1·66
99·95
100·51
99·73
99·94
99·61
99'46
98'27
-
-
-
0·8
tr.
tr.
2'25
1 ·5]
4'46
1·89
2'11
1·53
10 ·21
-
3·9
0·8
2·3
2·7
2 '8
1·5
.. ~o
.I,S
-
1·9
I Spm.
En.
lip.
Fa.
Mt.
Ilm.
-
12 ·3
2·5
5'0
10·3
0'6
-
-
32'5
40·4
3U·2
30'1
37 ·7
47·6
50·2
48 '1
49·4
53'3
3'6
1·3
3'6
4'8
3'5
1·3
3·9
0 ·2
-
29'1
31·1
36'4
61·3
57'1
52·3
4·0
4·0
4'2
24·8
22'3
15·9
25'5
27'3
23·3
62·8
64 ·3
46'5
63·6
66·8
62'0
4'6
7'6
4'6
4·4
-
1 '6
-
0·9
-
-
-
-
-
-
2·8
Hm.
------
1
T,OWER BAND
It. 2
9
10
11
14
17
..
..
..
2'25
1'47
9·2
2'02
1·63
1'42
23'21
..
..
17 (a)
I
BAND ABNORMALL! DEVELOPED ON GOEDGEDACHT 400
R_22 __
R.18 ..
R.15 ..
0-30
24-09
2-85
55-10
1·75
1'14
8 ·01
21'32
1·35
3·99
62 '92
46·31
tr.
0·05
0·2
0'2
0·5
18·76
, 3 '12
60'68
0'32
0 ·9
0-02
CRITICAL ZONE-
L. 6~3
I
1'50
ROOIWATER IGNEOUS COMPLExt-
I
1 '25
l
18'40
I
2·72
-
0'03
-
-
nil
-
-
0'20
0·07
0'16
0 '44
0'16
nil
nil
0'16
0 '04
-
-
-
2·7
3'1
20'8
3'1
0·3
-
5·8
-
-
-
-
-
-
-
-
3 '1
tr.
0·68
8·77
0·23
-
1'07
tr.
-
-
II
-
7'1
0·38
6·96
0 ·04
tr.
nil
tr.
1'52
9·85
1·83
0'07
0·89
0'08
100·57
99'61
100·69
0·4
-
-
-
0'5
0·3
-
-
46·6
45·7
6·5
-
-
-
-
1 '1
3'1
-
2·0
-
14·2
40·7
35·2
3·7
-
-
tl'.
nil
1·01
0·08
99·79
-
-
1·2
-
1·5
1 ·4
i-
-
36 '3
53·3
6'3
-
I
1,.
66 ·70
-
-
nil
nil
nil
nil
0 '14
I
0·15
100'11
* V.Os determinatiolls in Bushveld magnetic ir,on orcs by E. C. liaumann, other constituents by C. J. Liebenberg, Department of Chemical Services.
t Quoted from (6, p. 121), analyst: C. F. J. van der Walt, Department of Chemical Services.
I
I
I
TITANIUM AND VANADIUM IN THE MAGNETIC IRON ORES
31
Coulsonite ?-The Bushveld magnetic iron ores carry from 0 to 1·5 per cent.
V20 S ' No definite mineral could be detected to account for the va.nadium.
Dunn and Dey (2 p. 131-132) are of the opinion that in the Indian titaniferous
magnetite this element is present in coulsonite. It is either isomorphous with
magnetite or it may well be a vanado-maghemite, i.e., FeO (FeV)20s or (FeV)20s'
Frankel and Grainger agree with the latter possibility and state that the term
coulsonite might be applied to maghemite which is rich in vanadium.
A polished section of the Indian ores from the Union Geological Survey
collections was investigated and the maghemite therein is very similar under the
microscope to that of the Bushveld, a. fact also pointed out by Frankel and
Grainger. Maghemite grains with cores of very fine felt-like constituents amongst
which hematite is also apparently present, were ~hown by Frankel and Grainger
to be comparatively rich in vanadium (Plate IV, Fig. 2). N. N. Chatterjee
(2 pp. 185-186) in discussing the introduction of the new name, coulsonite,
strongly disputes the existence of a separate mineral.
Silicates.-Small irregular patches of silicate gangue are sometime~ present,
but considering the ore as a whole the quantity of this constituent is negligible.
The magmatic separation of the iron ore in the basic rocks was very clean and
excluded silicates of any amount.
Goethite.-Cracks and intercrystalline spaces of the more decomposed
ores carry fair amounts of this mineral. The amount present depends on the
degree of decomposition of the ores.
CHEMICAL COMPOSITION OF THE ORE.
When the original investigation was started, some of the analytical results
were urgently required and the Ti02 was accordingly determined colorimetrically.
These values were subsequently found to be too high. Many samples were,
however, not re-analysed and the original values of such samples are still given
in Table 2. They are indicated by asterisks and serve to show the general trend
in composition of the ore. They are not taken into consideration in the plotting
of the curves and the discussion.
In view of the varying degree of alteration of the analysed material one
is at once faced with the problem of representing the analytical results in a comparable manner. A norm calculation proved very unsatisfactory in view of the
fact that the water content is not eliminated in this way and that minerals
like rutile, figure prominently in such calculated norms. Consequently it was
decided upon to apply the katanorm calculation as suggested by Niggli
(3 pp. 295-217) and largely to ignore the state of oxidation of the iron in the
building of the ilmenite molecule. The molecular proportions of V20 S and Cr20 S
were added to Fe20 s, and MnO and NiO to FeO. Since the values here concerned are very small, the final results are hardly effected by these additions.
In all circumstances in calculations where oxides such as Ti02 and V20 S
take part, their distribution cannot always be effected according to hard and
fast rules, because the metal valency is generally not known with certainty.
According to J'akob (4 p. 270) one can just as well regard titanium as trivalent
instead of tetravalent in calculating the ilmenite molecule and then add equivalent molecular amounts of ferric oxide. The nett result would not be affected
'32
TRANSACTIONS OF THE · :GEOLOGICAL SOCIETY OF SOUTH AFJl,ICA
VARIATION IN COMPOSITION OF BUSHVElD MAGNETIC IRON ORES
10
r~'~d
Prlflc/.
pal
9
Group Mlddl. Nlld
.3
..,
1 ;\
~~
1 .\ \ .
...
~
LolI"I' band a
,0
0 0'"
;.
"'"--.• · A
~2,/
/
I
/
/
/
4!1
i
•..
.!::
/
/
/
B.nd on 5
.1
Ooedltdacllt
4D.
..
./
4\
'T,
2
\
4
\
\
\i
' +~
r
\ <
\~
\
\
Meren.ky reef 0
-.c:
.
...
horIzon
0
~
~
·1
-
--
,
--l----
-\ - - - - - - \
,
0.5
I
t
~V,O,
1,.0
1.5
20
30
40
~lIm
FIg. 11
and Hm+Mt
50
60
TITANIUM
TABLE 2.
AND
VANADIUM
DETERMINATIONS
RUSTENBURG
DISTRICT
PRETORIA
DISTRICT
LYDENBURG
DISTRICT
r~----------------------~A~----------------------~, ,_------------------~A~------------------~,~
409
."
."
0..
0..
~
~
C\)
~c
0..
~
V)
l-
E
<IS
u
:E
C\)
lri02
%
1V20 5
Bands
Main
~c
~
u
C\)
R14
R13
R12
R11
RIO
R9
R8
R7
R6
R5
R4
12"
12"
It
12"
12"
If
it
12·
12"
12·
18·
16-21
20'3·
20'41
21-1·
19·93
20'7·
20-7·
1H7
20·3*
20-3·
19-26
10
R3
R2
R1
Zone
10 - 13-2'"
12" 12·60
12" 12'9·
0·9
1-1
1'3
Lower
Band "C
24' 25'0·
36" 24-09
36" 25'0·
3s" 24-5·
36" 25'5·
3S" S'01
3S" 23'5·
~16 36' 24'0R15 36" 21'32
%
V)
%
1V20 5
~
,0..
E
<IS
_V)
R35
R34
0'4
0·2
0'0
0·0
0'0
0·2
0-2
0'4
0'4
0-2
0-4
Bands
R23
R22
R21
R20
R19
R18
R17
~ %
."
."
C\)
C\)
0..
0..
~
~
j
~
F=
."
C\)
0.
E
C\)
%2 1v2~
TiO'
24· 18'09
18" 20'3·
0-2
0'4
~
~
C\)
0. ~ Ti0
0..
.!:!
2 1V20 5
E
<IS
V)
F= % % en~
17-9'"
7
0-3
~c
l~
C\)
1V295
%'
%
Ti02
0. Ti0 V 0.
E
2 2
<IS
V)
%
%
:
?
R24
{
C\)
C\)
Ti02 1V20 5 0.. Ti021v20 5 0..
E Ti02
<IS
%~ ~ %
Upper
Band <
Principal
Group
of
Middle
0.
482
E
E
E
DE ONDERSTE, i DE GOEDE
N'ERWACHTINC
POORT
496
313
KLIPFONTEIN
52
I
C\)
C\)
SJAMBOK
ZYN KRAAL
BERSEBA
503
BOSCHPOORT
16
ROOIWAL
751
GOEDGEDACHT
14,85
0·5
R25
R26
18'5"
16,0
0'5
0'7
R33 12" 12'3111
R32 12' 7·S·
R31 3" 16'7·
R30 6" 13·25
R29 6" 16·S·
9'43
R28
0'2
0-0
0'4
0'4
0'5
0-7
18-82
8
20'0·
0·3
18
27
1
2
3
4
5
6
It 14'1'"
1-3
12"
1-5
1-5
9
10
11
12
13
14
15
16
17
6" 11-69
10· S'23
6" 13-00
1" 13-412~
13'9It' 13·69
It' 14-412" 14'7·
4" 12·17
15-1·
It 15'4·
12" 15-1·
12· 15'112" 15'1·
1·3
1-5
1-5
0·4
1-1
1'3
1·3
1'2
1'3
1-1
1-4
1·2
1-5
0'2
0·2
0'0
0-0
0'4
0,2
0·2
0·4
0·5
L623 18·76
L622 24'0·
Critical{
Zone
Analyses Indicated thus· were urgently required
and the Ti 0 3 determined co/orimetrical/y.
Values probably too high.
0·9
0·2
All V2 0 5 determinations and analyses
indicated thus'" by E. C. Haumann
Other analyses by C.J.liebenberg
TITANIUM AND VANADIUM IN'THE 'MAGNETIC IRON ORES
33
in the least. There is no scientific background for regarding titanium tetravalent
or trivalent in the ilmenite molecule. He further points out that the existence of
trivalent titanium in the. mineral kingdom might be much more widespread
than has hitherto been assumed.
Walker (5 p. 19) has shown that in lodestone from Bon Accord titanium is
probably trivalent and present in the maghemite. He suggests that the name
maghemite should be reserved for the combination (Fe Ti)20a rather than for
ferro-magnetic ferric oxide as proposed by Wagner. Frankel and Grainger
(1 p. 105) have also indicated that after allowing for the ilmenite laths the
amount of titanium in maghemite is about 10 per cent. (Ti02). The large quantities of rutile in the norm, already remarked upon, also support the view that the
titanium might be linked with ferric oxide.
From a perusal of the analyses (Tables 1, p and 3), and also from the plotted
results (Fig. 11) the following deductions appear permissible.
(1) The vanadium pentoxide (V 20 S ) content in the magnetic iron ores of the
Bushveld complex varies .from nil to 1·5 per cent. The lower band in the
Principal group of bands contains the most vanadium.
(2) The titanium dioxide (Ti0 2 ) content in the ore varies from 8 per cent.
to 24 per cent. The lower band in the Principal group of bands carries on an
average the least titanium.
(3) There is an antipathetic relation between the titanium and vanadium
contents. While there is an increase in titanium in the upward succession in the
Principal group of bands, the 'vanadium decreases correspondingly. The antipathetic relation persists at lower .horizons and is clearly indicated by the curves
V2 0 S and Ilm (Fig. 11). On the other hand there is a sympathetic relation between
the V20 S content and the Hm+Mt.* value of the ore (cf. the marked parallelism
of the corresponding curves, Fig. 11).
(4) The band of magnetic iron ore on Goedgedacht 409 (i.e., below the Principal
group of bands) and also the one in the Oritical zone of the complex do not fall in
line with the variation observed in the Principal group.
Oontrary to expectation these two bands show relatively very high Ti0 2
values-up to 24·09 per cent. which i& the highest value yet recorded in the Bushveld magnetic ores. They are low in vanadium. These bands together form a
separate entity showing the same characteristics as the Principal group of bands,
i.e., an increase in titanium and a decrease in vanadium towards higher horizons.
This anomaly in the general trend of the variation, occurring below the Principal
group of iron ore bands, is also known from other curves depicting trends of
differentiation in the basic rocks of the Bushveld complex.
* In plotting these curves the average of all the analyses at each horizon was taken
into consideration except for the Hm+Mt. values of the lower band where one abnormally
low value was discarded. It represents an analysis of decomposed gabbro with ore (Sample
10), and as the alkalis were not determined the silica was probably wrongly used in building
hypersthene instead of alkali-feldspar. In this way there remained relatively little iron
for the building of Hm.
34
TRANSACTIONS OF THE GEOLOGICAL SOCIETY OF SOUTH AFRICA
(5) The sympathetic relation of the H m + M t. and V 20 5 curves and the antipathetic relation of these two curves and the Ilm curve indicate that the V20 5 is
contained in the magnetite (or maghemite) and not in the ilmenite. This contention is further supported by the fact that the V20 5 content shows a considerable increase in the magnetic fractions of the magnetically separated ore
(see Table 3 : L. 623 (a) and (b) ).
(6) Across individual bands of ore there is no appreciable variation in the
content of either vanadium or titanium. The only exception is formed by the
band on Goedgedacht 409 where one sample (R. 18) gave 8·01 per cent. Ti0 2 as
against an average for the band of more than 20 per cent. Ti0 2 • This sample is,
however, not typical of the band as a whole, as it is weathered and the rocks
have been crushed at this point. The original titanium content has probably been
diluted through the addition of other constituents.
(7) The Cr2 0 a content of the ore is generally low and often nil-a lnaximum
of 1·0 per cent. being recorded. There appears to be a concentration of
chromium in the ore from the Critical zone and in the lower band of the Principal
group, with a general decrease or disappearance upwards. The trend of the
Or20 a values is thus, in general, the same as that of the V20 5 , and the chromium
is also considered to be associated with the magnetite (maghemite) rather than
with the ilmenite. This contention is also borne out by the analytical results
of the magnetically separated portions (see Table 3).
(8) Manganese seems to increase slightly towards the upper horizons.
(9) The phosphorus content of the ore is generally very low. A high concentration of this constituent (6·96 per cent. P 20 5 ) is recorded in sample R. 18
(Goedgedacht 409). As previously pointed out this sample was obtained from a
crush zone passing through the ore band. The material is very limonitic and the
phosphorus is probably present in the form of a hydrated iron phosphate. This
constituent was probably secondarily concentrated and might have been derived
from the overlying ore which contains more P 20 5 (0·38 per cent. in Sample R. 24)
than any other.
(10) The clay in cracks and joints within the ore has not been enriched with
either vanadium or titanium, but carries only small amounts of both these
constituents (Sample 17 (a)-4·4 per cent. Ti0 2 and 0·6 per cent. V20 5 ).
(11) The sample from Waaikraal 206 is so low in titanium (0·5* per cent.
Ti02 and 0·2 per cent. V 20 5 ) that it is considered to represent an altered ferruginous sediment. There are quartzites in the vicinity and the presence of these
supports the contention of a sedimentary origin of the iron ore. It is, of course,
also possible that this magnetite represents a pneumatolytic product derived
from the magma of the Red granite.
(12) An analysis of magnetic iron ore from the more southerly of the two
" magnetite" bands in the Rooiwater complex (Kent, 6, p. 121) is given for comparison (Table I). Should this sample represent the upper band in this complex,
as it apparently does, the chances are that the other known band is poorer in
titanium and richer in vanadium.
* Colorimetric
small.
determination by E. C. Haumann and reliable since Ti0 2 content is
35
TITANIUM AND VANADIUM IN THE MAGNETIC IRON ORES
CONCENTRATION TESTS.
As stated before, it seems very doubtful whether the vanadium can be
concentrated by a physical method. In the United States it was found, after
careful research that, although methods of extraction are technically practicable,
vanadium could be obtained more cheaply from other sources (7 p. 908).
Frankel and Grainger (1 p. 108) arrived at the conclusion that" the intimate
association of the minerals in this ore would militate against the successful
concentration of any of its constituents by physical methods." Although these
authors had material at their disposal from only a few localities, their statement
holds for most of the magnetic iron ore in the Bushveld complex. In the present
investigation an attempt was made to concentrate the ilmenite by means of a
physical method, viz., magnetic separation. Mr. P. C. Hinsbeeck, technical
assistant in the Geological Survey laboratory, kindly assisted with the concentration tests.
It was found that if the ore with ilmenite in the granular form (Plate III,
~-'ig. I) were ground to a requisite state of fineness, the ilmenite could be freed
by a hand magnet. The magnet attracts all the minerals except the ilmenite and
minerals like silicates, limonite, etc., which latter, however, are only present in
negligible amounts. Much of the ilmenite when in intimate association with the
other minerals is, of course, picked up with the magnetic minerals like magnetite
and maghemite. The results of the various tests are given in Table 3.
TABLE 3.
RESULTS OF CONCENTRATION TESTS.
NON-MAGNETIC FRACTION.
,-
Mode
granular 11menite
TiO.
in
sample
per
cent.
_ _ _ _ _ _ 1_ _ -
UITVLUGT 137-
Weight
of
sample
(gms.)
Mesh
of
sieve
used.
~------------~
Per- I
centage
con-SiO.
centrate
per
excent.
tracted
V.06
TiO.
per
cent.
per
cent.
FeO
per
cent.
Cr.O.
per
cent.
Fe,Os
per
cent.
_ _ _ _ _ _•_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
5·12
80
4·3
105·18
12·85
80
50
13·6
5·1
\
MIDDLE BANDR.24 (a)* I 14·15
R.24 (b)*
-
-.
14·85
BAND ABNORMALLY DEVELOPED ON GOEDGEDACHT 409-1
R.22 ..
0 ·05
24 ·09
11 ·3
50
4·8
R.15 ..
17·7
21·32
11·05
50
12·9
R.15-23
(a)*
54·42
40
1·8
(b)*
51·52
4·1
50
(c)*
22·73
80
6·0
(d)*
74·95
100
6·0
CRITICAL ZONEL.622 .. I 14·3
24·0
L.623 (a)
22·3
18·76
(b) Magnetic fraction
56·96
12·42
80
80
112.5
17·8
----------
I
3·20
23·76
1·60
3·42
34·66
25·12
2·70
2·70
2·60
24·86
26·70
27·60
27·50
~:I
0·76
I
I
I
42·70
10. 56
1
0·36
1·50
~31
0·46
33·05
9·20
14·37
70·42
* For explanation, see text.
All analyses by C. J. Liebenberg.
The following procedure was adopted in carrying out the concentration tests.
After the polished sections had been examined and the amount of granular
ilmenite determined with the integrating stage, a, few of the samples were
selected for treatment. Sample R. 15-R. 23 (excepting R. 18) is a composite
36
TRANSAOTION.S OF 'rlfE I'GEOLOGICAL SOCIETY' OF SOUTH AFRICA
sample representing the whole thickness of the band on Goedgedacht 409. The
sample was coars~ly crushed and quartered to about 200 grams. It was then
ground so as to pass through the coarsest of· four superimposed sieves with
varying meshes Crable 3). The material passing through each mesh waS magnetically treated and the non-magnetic fraction was analysed. The results are·
self -explanatory.
The magnetic separation was done in the following manner :-The finely
ground material was spread over a clean sheet of paper and a hand magnet
passed over it. With the material in thick layers much ilmenite was also picked
up by the magnet. A thin spreading was therefore essential. On repeating the
process two or three times no granular ilmenite worth mentioning was left
behind. Magnetic treatment under water was also tried out with equally good
results, except that much of the fine powder was lost on decanting. The concentrates obtained were mounted and polished in order to investigate their
purity. The unweathered material gave the purest product.
The following conclusions are drawn from the results (Table 3) of the concentration tests :~
(1) The modal percentage of granular ilmenite is the only indication of the
possible amount of magnetically separable ore. The Ti0 2 content has very little
bearing on this point, for example, L. 623 and R. 22 carry, respectively, 18·76
and 21·32 per cent. Ti02 : in the former ilmenite is present chiefly in granular
form, whilst in the latter this mineral is probably not all exsolved from the
magnetite.
(2) The crushing must be fine enough to separate the smallest grain of
ilmenite from adhering magnetite. An 80-mesh sieve proved the most suitable
(Table 3, Sample R. 15-R. 23, (a), (b), (0) and (d)) .
.(3) . Unweathered pure ore is desirable, since secondary minerals and
silicates go with the ilmenite fraction on concentration.
(4) The amount of non-magnetic material in individual outcrops varies as
is illustrated by the results obtained for R. 24. The same more or less applies. to .
R.15. R.24 (a) represents the results obtained by treating the hand specimen
collected for. the preparation of a polished section, whereas R. 24 (b) indicates
that obtained by treating the sample collected for chemical analysis. The latter
should be representative of the outcrop sampled. The non-magnetic con-.
centrate obtained in each case was very impure.
(5) The Cr20 a content of the non-magnetic fraction is low. So is the
V 20 5 •
(6) From the limited number of samples investigated it seems as if the
magnetic iron ore from the Critical zone contains much more granular ilmenite
than similar ores higher up in the pseudo-stratigraphical sequence.
ECONOMIC CONSIDERATIONS.
Vanadium.-:-Nearly all titaniferous iron ores are said to contain some
vanadium, generally less than 0·5 per cent. V20 5 , but occasionally the vanadium
c?ntent may reach 7 per cent. or more as at Dublabera, India. The recovery of
TITANIUM AND VANADIUM IN THE MAGNETIC IRON ORES
3;7
vanadium from ~uch ores has frequently been proposed. Large-scale experiments have. been conducted in Swedish steelworks, and in 1932 a plant was
erected at Kertsch, in the Orimea, in which ". ferro-titanium and vanadium "
were made from iron slags" making the Soviet Union independent of foreign
sources." (7 p. 908). As stated before, in the United States it has been found
technically practicable to extract vanadium from such ores.
The quantities of vanadium in the Bushveld ores varies from 0 to 1·5 per
cent. (V20 5) and should the Union of South Africa have to become independent
of foreign supplies it may be worth investigating the processes of separating
the vanadium from the ore.
The lower band of the Principal group of bands of magnetic iron ore carries
the highest vanadium values, the maximum content being 1·5 per cent. V20 5.
There is no marked lateral or vertical variation in the vanadium content of
individual bands.
With regard to the ore reserves, an estimate based on the assumptions
that the above-mentioned band is 3 feet thick, persists for 100 feet along the dip
and is uniform in composition at 1·25 per cent. V20 5, indicates that the known
occurrences of this band alone will yield in round figures 1,000,000 tons V20 5.
Titanium.-One of the largest and purest ilmenite-magnetite deposits so
far described is the Blaafjeldit deposit of the Titan Oompany at J ossing Fjord,
in Sogndal, south of Egersund, Norway. After concentration there is 42 per cent.
Ti0 2 in the ore and part of it is said to contain 45 per cent. The Norwegian <?te
as shipped runs from 36 ·88 to 43 ·88 per cent. Ti02 • These ores contain 0·476
to 0·20 per cent. V20 5 ; 0·065 to 0·05 per cent. Or20 a ; 0·06 to 0·02 per cent.•
P205 and 0 ·62 to 3 ·28 per cent. Si02. Since about 1920 this Norwegian deposit
has been worked for the production of titanium white, and it was on this deposit
'that the titanium white industry was started (7 pp. 898-906).
In the United States the largest deposits of titaniferous iron ores are those
of the Adirondacks where bodies of ilmenite-magnetite are enclosed in anorthosites and dark gabbro or norite. The ore which varies in Ti02 content from
7 to 23 per cent. was too lean, however, to compete with the ilmenites that were
marketed just before the outbreak of the present war. It is claimed that
100,000,000 tons of ore have been proved.
Russia is said to possess several deposits, the largest of which seems to be
in the Ilmen mountains, where one deposit is reputed to contain 400,000,000
tons of ore. The ores contain 15 per cent. Ti02 and when magnetically concentrated give a product with 43 per cent. Ti02 and an iron concentrate' with 65 per
cent. Fe (7 p; 901-902).
Besides these deposits of titaniferous magnetite, there are the beach deposits,
e.g., of Travancore, India, where the reserves are said to be immense and the
concentrates contain between 51 and 60·3 per cent. Ti0 2.
The Bushveld complex deposits can in no way compete as far as grade of
ore is concerned with the beach deposits, but the Ti02 content compares favourably with other deposits of similar nature. An analysis of the concentrates from
the deposits in the Oritical zone of the Lydenburg area (L. 623) indicates 42·7 per
cent. Ti0 2 and is equal to the best quality concentrates from Norway and Russia.
38
TRANSACTIONS OF THE GEOLOGICAL SOCIETY OF SOUTH AFRICA
Professor B. V. Lombaard, of the University of Pretoria, verbally furnished
the following information regarding the available reserves of ilmenite-magnetite
ore on the farms Eerstegeluk 348 and De Goede Verwachting 313. On Eerstegeluk
the ore was only seen as rubble, and in his opinion there are thousands of tons on
the surface. A systematic search might reveal the solid outcrop. On De Goede
Verwachting a band of ore could be followed for a few miles and the quantities
are said to be expressible in tens of thousands of tons. Further south, on
Kennedy's Vale 253 another large exposure occurs. From the information to
hand it can thus safely be concluded that the available reserves are appreciable
and should the extraction of ilmenite from Bushveld rocks be contemplated, this
area merits further attention. An important factor is the proximity of these
deposits to water and rail. Steelpoort station is only five to six miles distant.
Only a relatively small portion of the magnetic iron ores of the Bushveld
complex have been investigated, and it is very likely that if a more detailed
field and laboratory investigation be carried out, the reserves- of magnetic iron
ore containing granular ilmenite in recoverable amounts, might prove to be
immense.
BIBLIOGRAPHY.
(1) FRANKEL, J. J. and GRAINGER, G. W.: "Notes on Bushveld Titaniferous
Iron-ore." S. Afr. J. Sci., XXXVII, 1941, pp. 101-110.
(2) DUNN, J. A. and DEY, A. K.: "Vanadium-bearing Titaniferous Iron-ores in
Singbhum and Mayurbhanj, India." Trans. Min. geol. Inst., India, XXXI, 3, 1937,
pp. 117-184.
(3) NIGGU, P.: "Ueber Molekularnormen zur Gesteinsberechnung."
Schweiz.
-min. petrogr. Mitt., XVI, 1936, pp. 295-317.
(4) JAKOB, J.: "Zwei Analysen von Ilmenit." Schweiz. min. petrogr. Mitt., XVII,
1937, pp. 269-270.
(5) WALKER, F. L.: "Lodestone from Bon Accord, Transvaal." Univ. Toronto
Stud. (Engng.) geol., 29, 1930, pp. 17-19.
(6) KENT, L. E.; VAN EEDEN, O. R.; PARTRIDGE, F. C. and BRANDT. J. W. :
" The Mineral Deposits of the Murchison Range." Mem. 36, geol. Surv. S. Afr., 1937.
(7) HESS, F. L. and GILLSON, J. L.: "Industrial Minerals and Rocks." Amer.
[nst. min. (metall.) Engrs., 1937, pp. 893-910.
TRANS. GEOL. SOC. S.A., VOL. XLVI.
PLATE Ill.
FIG. I.-Ilmenite (I) as individual grains, and maghemite (Mh). Note the
twinning lamellae in the ilmenite. Oritical zone, De Goede Verwachting 313,
Lydenburg district. 60 x, nicols partially crossed.
FIG. 2.-Intergranular ilmenite (I) in maghemite (Mh). Middle band, Klipfontein 482, Pretoria district.
60 x, nicols partially crossed.
TRANS. GEOL. SOC. S.A., VOL. XLVI.
PLATE IV.
FIG. l.-Exsolution lamellae of ilmenite (i) in magnetite (M). Large grain of
ilmenite (I). The highly reflecting mineral is martite (h) replacing the magnetite. Oritical zone, De Goede Verwachting 313, Lydenburg district.
250 x, crossed nicols, oil immersion.
FIG. 2.-Possible coulsonite (0) in maghemite (Mh). Lower band, Klipfontein 482, Pretoria district. 250 x, crossed nicols, oil immersion
TRANS. GEOL. SOC. S.A., VOL. XLVI.
PLATE V.
FIG. I.-Moth-eaten pattern of titaniferous (?) magnetite (m) grading
through magnetite (M) into maghemite (Mh). Main zone, Goedgedacht 409.
Rustenburg district.
500 x, oiUmmersion.
FIG. 2.-0rientated spindles of spinel (8) in maghemite (Mh). Lower band,
Klipfontein 482, Pretoria district.
500 x, oil immersion.