Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
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.