Thomas_et_al_1994_Spodumene

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Unusual spodumene pegmatites from the
Late Kibaran of southern Natal, South
Africa
ARTICLE in ORE GEOLOGY REVIEWS · APRIL 1994
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ELSEVIER Ore GeologyReviews 9 (1994) 161-182
()RE ( ;E( )IL )( ,Y
RI:XIFAVS
Unusual spodumene pegmatites from the Late Kibaran of southern
Natal, South Africa
R.J. Thomas a, D. Biihmann b, W.D. Bullen a, A.J. Scogings c and D. De Bruin b
"GeologicalSurvey, P.0. Box 900, Pietermaritzburg, 3200 South Africa
bGeologicalSurvey, P. Bag X112, Pretoria, 0001 South Africa
¢507Roper St., Baileys Muckleneuk, Pretoria, 0181 South Africa
(Received March 9, 1993;revised version accepted August 10, 1993)
Abstract
Significant quantities of spodumene have been identified from a number ofleucocratic pegmatoid bodies which
crop out on The Corner, near Highbury, Port Shepstone District, in the southern part of the ~ 1 Ga Natal Meta-
morphic Province. The mineralized rocks form part of a suite of sub-concordant, predominantly aplitic sills which
intruded high-grade mafic gneisses of the Mucklebraes Formation. The entire package lies within a synformally
folded klippen structure. The spodumene-bearing sills, which are up to 15 m thick, were emplaced at several struc-
tural levels along the northern limb of the synform. These white, coarse-grained rocks are composed of quartz,
albite, microcline and spodumene, with traces of white Li-mica, garnet, graphite and very rare beryl. Pale yellow-
ish-green to pink spodumene, symplectically intergrown with quartz (SQI), forms irregular to ovoid poikilocrysts
up to 40 cm across. This texture is characteristic of spodumene that has replaced primary petalite and the compo-
sition of the SQI is comparable with published petalite analyses. This isochemical inversion model is supported
by an observed volume change, evidenced by the radial cracks which commonly surround isolated SQI crysts. The
P-T conditions of formation of SQI are consistent with near-isobaric cooling models which have been proposed
for this part of the Natal belt. Geochemical analyses show that the Li-pegmatites are highly siliceous with variable
K/Na ratios and low Fe. Trace-element abundances (including H20 and F) are low, with the exception of Rb. The
largely anhydrous mineral assemblages (coupled with the absence of other mineral phases typically associated with
Li-pegmatites), textural relationships and geochemistry suggests that the Highbury Pegmatites crystallized from
relatively high-temperature, volatile-poor liquids under conditions of lowfH2o and low fo2. Consequently, the Li-
pegmatites are considered to be late-stage differentiates of the characteristically anhydrous garnet leucogranites
and charnockites of the Margate Suite, with which they share many mineralogical and geochemical similarities.
The lithium may have been scavenged from country rock metasediments during anatexis. A simple gravimetric
test shows that the spodumene can be efficiently beneficiated to a product with ~ 7% Li20. In view of the increas-
ing economic importance of Li-minerals and the easily accessible position of the Highbury Pegmatite, coupled
with feldspar and dimension stone as possible by-products, the prospects for future exploitation are considered
favourable.
1. Introduction
The pure white, sheet-like aplite and leuco-
pegmatite intrusions of the Highbury area, some
18 km north of Port Shepstone (Natal), form an
integral part of the ~ 1 Ga Natal Metamorphic
0169-1368/94/$07.00 © 1994Elsevier Science B.V. All rights reserved
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t 62 R.J. Thomas et al. / Ore Geology Reviews 9 (1994) 161-182
Province (Fig. 1). The rocks were first described
by Thomas (1988), who referred to them as
"alaskitic granite" and noted that, in addition to
quartz, two feldspars and very sparse white mica,
the rocks commonly contained garnet and
graphite. In one area, Thomas (1988) also re-
ported an abundance of large, rounded, optically
continuous "patches" of poikilitic clinopyrox-
erie, thought to be diopside, on the farm The
Corner. However, during routine mineralogical
investigations by the senior author, the clinopy-
roxene was re-identified as spodumene. In view
of the widespread interest currently being shown
in spodumene, both by the glass industry (e.g.,
Kingsnorth, 1988) and as a source of lithium
salts, a more detailed petrological study and eco-
nomic evaluation of these rocks was initiated.
This paper reports the results of that study and
compares the Highbury rocks with other Late
Kibaran pegmatites in southern Africa.
2. Nomenclature
The term "alaskite", used by Thomas ( 1988 ),
is now considered inappropriate, as it has now
been established that K-feldspar is only locally
the dominant feldspar (following Le Maitre,
1989). For the most part, the intrusions are al-
bite-dominated, medium-grained, extremely
leueocratic (Colour Index ~ 1), with saccharo-
idal texture and are best termed "aplite". How-
ever, this paper focuses on the coarse-grained
spodumene-bearing phase, termed here the
"Highbury Pegmatite", after Highbury farm
which lies to the south of The Corner, where the
majority of the Li-rich rocks crop out (Thomas
et al., 1993).
3. Geological setting and field relationships
Two discrete tectonostratigraphic terranes
have been recognised in the southern part of the
Natal Metamorphic Province (Thomas, 1989).
The granulite-grade Margate terrane in the south
is juxtaposed against the amphibolite-grade
Mzumbe terrane to the north along the Melville
Thrust (Fig. 1). In the Highbury area, north of
the Melville thrust, an outlier of granulite facies
marie rocks (the Mucklebraes Formation) has
been identified. This outlier was interpreted by
Thomas ( 1989 ) as a small Margate Terrane klip-
pen which is bounded at its base by a zone of
ductile thrusting. The pegmatitic and aplitic
rocks under review here form a number of sub-
concordant sill-like bodies that occur in a ~ 150
m thick zone within the mafic pyroxene gneisses
and granulitic calc-silicates of the Mucklebraes
Formation. After the intrusion of the pegmati-
tic/aplitic sheets, the klippen was folded into an
open, east-west-trending periclinal synforrn
(Thomas, 1989). The foliation in the gneisses,
and hence the contacts of the pegmatite sills, dips
centripetally towards the axis of the synform at
shallow angles (generally < 30 ° ). Consequently,
the aplitic bodies now define a broadly arcuate
outcrop, measuring ~ 8 km by 3 km, around the
western, southern and eastern limbs of the syn-.
form (Figs. 1, 2). They appear to be regionally
transgressive, having been emplaced at a slightly
lower structural level in the west.
Outcrops of the pegmatite are poor except
along the densely-bushed, NE limb of the syn-
form, where it locally forms prominent 20-m-high
white cliffs, on the farm The Corner, overlook-
ing the Mzumbe River Valley (Fig. 2): The in-
termittent nature of the outcrops along consis-
tent structural levels suggests that the thickness
of individual pegmatite sheets may vary along
strike due to tectonic pinching and swelling. In
this case, pegmatite mega-boudins may be ex-
pected to be elongated along the local S- to SW-
plunging stretching lineation direction, Samples
of the pegmatite were also obtained from a stra-
tigraphic borehole (the Mzumbe Borehole) lo~.
cared some 300 m south of the outcrops on The
Corner (Fig. 2 ). Correlation of the outcrops with
the borehote core is good, suggesting that the
pegmatite sheets dip at ~ 20-25 ° to the south in
this region.
Significant concentrations of spodumene have
been discovered in this area, in pegmatite out-
crops along a strike length of > 1kin, centred ap-
proximately on the Mzumbe Borehole site (Fig.
3 ). The spodumene occurs throughout a number

R.J. Thomas et al. I Ore Geology Reviews 9 (1994) 161-182
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I
-TAMORPHIC PROVINCE
3HBURY PEGMATITE
:e tectonic plutons
040 - 1070 Ma)
:umbe Terrane
irgate Terrane
[oO°°o° o-,1
Fig. 1. Regional geological setting and location of the Highbury Pegmatite.

164 R.J. Thomas et al. I Ore Geotog.: Reviews 9 (1994) 161-182
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0 2 km
Alluvium
Highbury pegmatite ( ,ann"" spodumenebearing)
Garnet leucogranite (Margate Granite Suite)
Mucklebraes Formation
4/24 Dip and strike of foliation
Mzumbe gneiss (sheared)
/4' Thrust zone
Fig. 2. Geological map of the Highbury Pegrnatite and environs. Note the position of the Mzumbe Borehok:
of sills and there is no evidence to suggest that
the host bodies show any systematic vertical
zonation in the fashion typical of lithium peg-
matites (e.g., Norton, 1983). This does not,
however, preclude the possibility of lateral zon-
ation. A systematic search of the entire Highbury
Pegmatite field failed to reveal further spodu-
mene mineralization. The garnetiferous aplites
constituting the vast bulk of the intrusions ap-
pear to be barren, so the Li-pegmatites may have
formed as a result of lateral fractionation within
the intrusive system.
In outcrop the rocks are typically granular, un-
foliated to poorly foliated in texture. However,
elongated trains of small garnets locally define a
weak fabric parallel to intrusion margins and to
the layering in the country rocks. The pegmatites
are clearly intrusive into the gneisses of the
Mucklebraes Formation, but were emplaced
prior to the development of the regional synfor-
mal structure. The upper and lower contacts ob-
served in the Mzumbe Borehole are typically
sheared. In the southern part of the synform, the
rocks are aplitic and more strongly fotiated. These
rocks closely resemble garnet-leucogranites of the
Margate Suite, a voluminous syntectonic leuco-
granite-charnockite association of the Margate
Terrane (Thomas, 1988 ). Thus, despite the often
unstrained appearance of the core areas of the

R.J. Thomas et al. I Ore Geology Reviews 9 (1994) 161-182 165
X S / 3 0 ° 30' E B ~ ' ~ / ~ ~ 0b~100 m
/ ~":~'-~'" "'~/ ~ ~ . . . . . . /
v ........~...........-:~-- i .~..J ~"--0 J" • ~'~= ~.~.~ • ~.~,....~ . . . . (- , . ~
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I / "....I . "~ j THECORNER ";-" TO1
:"
~o/ Contours at 40 m intervals• Mzumbe Borehole site /-
• Spodumene pegmatite outcrop f Road
........... TrackSpodumene pegmatite
• outcrop / boulders
Farm boundary
.:~i~' Interpretedextent of i
'~:~ spodumene pegmatite • TC 2 Sample Site
O Barren pegmatite / aplite A ~ B Line of section
200
100
A
Mzumbe
MUCKLEBRAES
~.:~
lorehole
Outcrop of mainspodumene
pegmatite zone
CORNE~ Large bolders (outcrop?)
~:'~i::i:~ ~ _f
~'
4_ Spodumene pegmatite
~ . Intersectionsin borehole
250 Metres 5C)0
Bottom (2943m)
Fig. 3. Detailed geological map of the spodumene-bearing pegmatites on The Corner and N-S section through the Mzumbe
Borehole.

166 R.J. Thom tz~et al. / Ore Geology Reviews 9 (1994) 161-182
pegmatites, they clearly represent a syn- to late
tectonic intrusive suite.
4. Petrographic characteristics
In hand specimen, the extremely leucocratic
pegmatites and aplites are strikingly white, with
extremely low marie mineral contents (< 1%).
The coarse-grained pegmatitic phases contain
feldspar crystals up to 30 cm in length ( ~ 5 cm
average). Aplitic phases are typically medium-
grained (2-5 mm), saccharoidal, though inequi-
granular. In addition to quartz and feldspar, small
( < 1 mm) flakes of graphite are locally conspic-
uous, along with minute (< 1 mm), pale pink
and brown garnet. In the Li-rich phase, spodu-
mene occurs in equant, ovoid to irregular crys-
tals, up to 40 cm across, in graphic and symplec-
tic intergrowth with quartz (SQI, for
Spodumene-Quartz-Intergrowth, modified after
Burt et al., 1988). At their densest, these crysts
are closely packed and can constitute up to 70%
of the total rock. No pure spodumene crystals
have been observed. The SQI crysts tend to be
extremely inconspicuous and elusive in the field.
but they form grey patches on weathered sure-
faces (Fig. 4) and can be observed in glancing
sunlight as large, optically continuous, poikilitic
cleavage surfaces. On polished surfaces, the
coarse-grained intergrowths typically resemble
graphic textures, with regularly oriented, angular
quartz grains enclosed within optically continu-
ous spodumene (Fig. 5). The spodumene is white
to pale yellow-green or pink, though light-brown
shades have locally been observed. In certain lo-
calities where the SQI crysts are relatively sparse
and not in mutual contact, they are commonl)
surrounded by radial cracks, suggesting that a
significant volume change has taken place at
some stage in their genesis. One 10 x 5 mm cry,s-
tal of light-blue beryl was recorded in the spo~
dumene pegmatites. It is doubtless the mineral.
ogical simplicity, coupled with the cryptic habit
and unremarkable colour of the spodumene that
has prevented the earlier discovery of the High-
bury Li-pegmatites.
The pegmatites, with ve~, low mica content~
Fig. 4. Field appearance of the Highbury Pegmatite, with grey patches of spodumene-quartz intergrowth, showing typ~c:finega-
tive-weathering. The unremarkable appearance of the outcrops is probably why the spodumene was only recently recog¢fiscd.

R.J. Thomas et al. / Ore Geology Reviews 9 (1994) 161-182 167
Fig. 5. Graphic spodumene-quartzintergrowth (SQI) in cut surface through sample of the topmost mineralizedpegmatite in the
Mzumbe borehole, with quartz (dark grey) and spodumene (pale grey) (Scale in centimetres).
Fig. 6. Typical appearance of SQI in thin section. Field of view is 4 mm across.
are thus typified by anhydrous mineral assem-
blages. Despite a uniformly leucocratic appear-
ance, the mineralogy is highly variable with re-
spect to quartz and feldspar ratios. Quartz makes
up between 18 and 50% of the rocks, while the
plagioclase/K-feldspar ratio varies markedly.
The majority of rocks are plagioclase-domi-
nated, with up to 70% albite and as little as 2%

68 R.J. Thomas et aL / Ore Geology Revwws 9 (1994) 161-182
ig. 7. Photomicrograph of fibrous spodumene-quartz intergrowth at the edge of a poikilitic SQI crysL Field ot v~c
?,ross.
Fig. 8. Photomicrograph of symplectic spodumene-quartz intergrowth. Field of view is 2 mm across.

microcline. However, there is a complete spec-
trum of feldspar ratios through to rare K-feld-
spar dominated rocks with up to 65% microcline
and only ~ 5% albite. Grain size is also highly
variable, with granular textures typical, but in
many rocks an interlobate, amoeboid inter-
growth is seen, where embayed grains of quartz
and feldspar form a distinctive interlocking
texture.
The spodumene can only be distinguished op-
tically from diopside on the basis of its lower ex-
tinction angle ( ~ 22 ° ). As noted above, it only
occurs in the form of poikilitic crystals, sym-
plectically intergrown with quartz and modal
analyses have shown that the spodumene: quartz
ratio in these intergrowths is consistently ~ 60: 40
(Fig. 6). The quartz inclusions tend to be coarser-
grained (up to 2 cm long) and sub-angular in the
centres of large SQI crysts. However, these often
grade into a symplectic intergrowth of minute,
rounded quartz vermicles reminiscent of myr-
mekite in spodumene at the contact with feld-
spar grains. These myrmekitic textures com-
monly grade into fibrous intergrowths at the
margins (Fig. 7 ). Smaller SQI grains ( < 2 mm)
are typically entirely symplectic (Fig. 8 ). Minor
quantities of skeletal muscovite are seen in thin
section, whilst accessory graphite (occurring as
opaque flakes), garnet (forming small, rounded
grains) and rare chlorite complete the accessory
mineralogy.
The rocks are characteristically unaltered,
though some embayment and replacement of
spodumene and feldspar by late-stage quartz is
locally apparent. Xenomorphic and granular
textures result from this alteration. However,
spodumene is typically unaltered, except locally
by albite, and no replacement by other Li-rich
secondary phases such as eucryptite, lepidolite,
etc., was observed (c.f. most spodumene depos-
its). Microcline (perthitic in places) is either
partially or wholly replaced by albite which em-
bays and, in places, completely encloses K-feld-
spar crystals, suggesting that extensive, late-stage
sodium metasomatism has taken place. Evi-
dence of post-crystallization strain is common,
as shown by bent twin lamellae in plagioclase and
undulose extinction in quartz. This supports the
interpretation of the pegmatites as syn- to late
tectonic.
5. The Mzumbe borehole
This borehole was sunk with the idea of ob-
taining a complete stratigraphic section through
the Mucklebraes Formation to the base of the
klippen structure, and to provide information on
the Highbury Pegmatites. From outcrop it was
Table 1
Modal percentage of spodumene in the Highbury Pegmatite in the Mzumbe borehole
Depth Vertical True SQI* Spodumene
(m) thickness thickness (%) (%X 0, 55 )
(m) (m)
Appr.%
Li20
113.5-128.9 15.4 14.3 44.9 24.7 2.0
132.3-135.0 2.7 2.5 41.9 23.0 1.9
136.2-143.1 6~9 6.4 42.5 23.4 1.9
181.1-191.3 10.2 9.5 22.1 12.1 1.0
192.4-196.2 3.8 3.5 9.7 5.3 0.4
216.8-225.6 8.8 8.2 < 1 << 1 -
229.3-241.5 12.2 11.3 < 1 << 1 -
*Poikilitic spodumene percentages were determined from core samples in the following manner: A line, drawn from the top of
each pegmatite intersection to the bottom, was subdivided into 12.5 mm increments. The mineral (spodumene or other) occur-
ring at each increment margin was noted. For example, the uppermost pegmatite sheet was subdivided into ~ 1100 increments
and the volume percentage of spodumene determined therefrom. These results represent the mean of two separate runs. True
thicknesses were determined assuming a dip of 22 °.

70 R.J. Thomas et at. /Ore Geology Reviews 9 (1994) 161-182
O"
r-
£1-
03
0
©
0
% modal spodumene
0 50 1O0
0
- MZ 28
-ME 29
5
MZ 30
200
50.
MZ
56
15
0
- MZ 34
0
- MZ 36
2
250
~ Highbury
pegmatite
m
Ii
L_
------] Mucklebraes
Formation
6
E
p = pegmatite > 15 cm thick
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5 xz
d)
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known that the pegmatites occur as multiple in-
trusions, though it was not possible to ascertain
their precise number or thickness. The borehole
was sited at an elevated location north of the ax-
ial trace of the regional synform (Fig. 2 }. From
mapping, however, it is known that at least one
~2-m-thick spodumene-rich sill occurs at a
higher structural level than the top of the bore-
hole. The ~250 m deep borehole penetrated
seven separate sills of Highbury Pegmatite greater
than 2 m in vertical thickness (maximum 15.4
m) and several minor sheets less than ! m thick
(Fig. 9 ). The upper and lower contacts of the sills
dip generally at ~ 22 ° to the south, indicating
that the true thickness of the sills is approxi-
mately 93% of the apparent thickness (Table 1
Contacts of the sills with the count,'3' rock
gneisses are subconcordant with the gneissose
layering, locally sheared, but often clearly intru-
sive. The contact zones tend to be enriched in
garnet and graphite, suggesting that these min-
erals might represent contaminants from the
country rocks. Spodumene-quartz intergrowths
tend not to be developed in these marginal zones
up to 50 cm from the contacts. Apart from the
typically barren contact zones, there does not ap-
pear to be any systematic mineral zonation
throughout the sills, and SQI occurs randomly
within the wide, central mineralized zone. The
modal distribution of SQI in the thickest sills in
the Mzumbe Borehole is shown graphically in
Fig. 9. Of the seven sills with a thickness of more
than 2 m intersected, the topmost set of three
contains the most significant spodumene miner-
alization (Table 1). This group of sills, which
occur from 113.5 m to 143.1 m depth, have a to-
tal thickness of 25 m and have, on average, > 40%
modal SQI. The method of determination of
modal SQI-content in the core, along with the re-
suits obtained, are given in Table 1. Using a con-
servative, optically-determined spodu-
mene:quartz ratio of 55:45 for the SQI, this
Fig. 9. Distribution of Highbury Pegmatite sills in the
Mzumbe Borehole. The histograms show modal percent spo-
dumene in the five main mineralized sills in the Mzumbe
Borehole. Numbers prefaced by MZ refer to borehote samples,

R.J. Thomas et al. /Ore Geology Reviews 9 (1994) 161-182 171
represents >23% modal spodumene, which in
turn equates with ~ 2% Li20. The subequal spo-
dumene concentrations in the upper three peg-
matite bodies suggests that they probably repre-
sent a single, branching intrusion. Below this
zone, spodumene grades are lower. A 10.2 m
thick pegmatite at 181 m depth contains about
half the SQI values of the upper three ( ~ 22%),
whilst the intrusions below 200 m are effectively
barren.
6. Mineralogy and geochemistry
6.1. XRD analysis
A powdered sample of spodumene pegmatite
(TC 3) was subjected to X-ray diffractometry
(XRD) at the Geological Survey Laboratories in
Pretoria. This confirmed that quartz, plagio-
clase, microcline and spodumene are the major
mineral species, along with accessorywhite mica,
garnet and graphite. Other samples of coloured
spodumene (yellow-green,light brown and pink
varieties) were analysed and gave identical spec-
tra. In one sample, minor chlorite was identified
and the macroscopic identification of a single
grain of beryl was confirmed. Mineral concen-
trates obtained from TC 3 were also analysed by
XRD. The analysis showed the garnet to be a Mn-
rich almandine and the white muscovite mica
was confirmed as a dioctahedral 2M1 mica. A
systematic XRD search of a number of borehole
samples for other Li-phases such as eucryptite or
petalite proved fruitless.
6.2. Major and trace-elementgeochemistry
Whole-rocksamples
Major and trace-elementanalyses of five ( 1-5
kg) samples from outcrops of the pegmatite and
six ( ~ 1 kg) borehole samples were made at the
Geological Survey laboratories in Pretoria. For
comparative purposes, the outcrop samples an-
alysed included rocks with (TC 2 and 3) and
without spodumene (TC 1, 4, 5). The majority
of elements were analysed by X-ray fluorescence
(XRF). Major element concentrations were ob-
rained from fusion discs according to the method
of Norrish and Hutton (1969). Trace elements
were analysed by XRF on pressed powder pellets
of the core samples. The appropriate back-
ground and interference corrections from other
spectral lines were made, while mass adsorption
correction procedures were carried out for ma-
trix effects. Li20 and F were determined by wet
chemical analysis. A LECO analyser was used for
the determination of structural H20, CO2 and S.
The results of the eleven whole-rockanalyses are
given in Tables 2 and 3.
The great variation in feldspar content seen in
thin section is naturally reflected in the Na20/
1(20 ratio, ranging from 0.5 to 2.5. As expected,
SiO2 is high (73.8-78.6%), and the high alu-
mina (14.0-18.8%) reflects either a high feld-
spar or spodumene content. Trace-element
abundances are uniformly low except for Rb
(~ 500 to > 900 ppm). Rb values rise sympa-
thetically with K20 and K/Rb ratios are ex-
tremely low (~20-50). One sample (MZ 34)
contains anomalously high V, Cr and Ba. F con-
centrations range from 100 to 350 ppm, lower
than most typical granites (e.g., Middlemost,
1985), and reflecting the extremely low modal
mica content of the pegmatite. When plotted on
the Rb-Sr-Ba ternary diagram of E1Bouseily and
E1Sokkary ( 1975), the Highbury Pegmatites plot
within the field of "highly differentiated
granites".
Li20 in SQI and white mica separates
In addition to whole-rock samples, separates
of SQI and white mica were analysed for Li20 by
wet chemical techniques. Spodumene-quartz
concentrate from sample MZ 28 contained 4.67%
Li20, corresponding to 58% spodumene, a figure
consistent with the modal determinations. Wet
chemical analyses of a hand-picked white mica
concentrate from TC 3 returned an Li20 content
of 0.51%, showing it to be a lithian muscovite
according to the criteria of Newman and Brown
(1987).
Spodumene separates
A simple beneficiation test was devised in or-
der to ascertain the Li20 content of the spodu-
mene in the pegmatites. Two spodumene-rich

172 R.J. Thomas et aL / Ore Geology Reviews 9 (1994) 161-182
Table 2
Major element analyses of outcrop samples of the Highbury Pegmatite
Wt% TC-1 '[C-2 TC-3 TC-4 T(-5
SiO2 71.88 74.16 75.76 74.68 - 1,05
TiO2 0.09 0. I 1 0.09 0,10 0, ]i)
A1203 17.03 1570 15.83 14.81 ~6,34
Fe203* 0.23 0.19 0.23 0.10 0.22
MnO 0.13 o.12 0.06 <0.0i 0t2
MgO 0.17 0.07 0.14 018 0.15
CaO 0.93 0.28 0. l 1 0,37 ~).52.
Na20 7.72 5.79 3.15 5,83 ,~.6~,
K20 0.95 i,70 2.08 3.44 .7 :
Li20 0.04 1.33 2.03 < 0,01 0,05
P205 0.04 0.05 0.03 0.05 ~.).05
H20- 0.06 0.13 0.09 0. i i 0,02
H20+ 0.39 0.38 0.51 0.24 0.17
C02 0.19 0.07 O.13 0.35 ;}.13
Total 100.51 100,07 100.25 t00,21 98.98
*Total Fe as F%O3.
Sample descriptions: TC 1: medium-grained albite aplite; TC2: albite-spodumene pegmatite; TC3: spodumene pegmatite: TC4:
albite pegmatite; TC5: fine-grained aplite.
Highbury Pegmatite samples were selected, TC 3
(fresh spodumene pegmatite with SQI from out-
crop) and MZ 36 (SQI from the Mzumbe bore-
hole). In addition, NS (spodumene from Nou-
mas No I pegmatite, Namaqualand) was selected
for comparative purposes. The samples were
hand-crushed in a pestle and mortar. TC 3 was
sieved to yield a - 1000/+ 500/t fraction, while
MZ 36 was sieved to obtain - 1000/+ 500/t and
- 500/+ 75 # fractions. The resultant fractions
were then subjected to heavy liquid gravimetric
separation using bromoform (S.G. = 2.9),
washed in acetone and air-dried. Iron impurities
in the sample were removed magnetically. Major
element and Li20 analyses were undertaken on
the separates by the techniques described previ-
ously (Table 4 ).
The spodumene samples from both sieve frac-
tions of MZ 36 give Li20 values of ~ 7%, some-
what higher than those from natural outcrop (TC
3, with 6.5% lithia). Li20 values from Highbury
are higher than those obtained from the Noumas
spodumene, but lower than the Durabees (Nor-
rabees) spodumene (Bischoff and Bischoff,
1988). In general, major element compositions
of the Highbury spodumene fall within the ranges
quoted in Deer et al. (1974), with respect to
m1203(~25-27%), CaO (<0.1%), and alkalis
(0.1-2%). With regard to the latter, whilst K20
is always low in spodumene (<0.2%), Na20 is
variable up to 2%, as seen in the Noumas sam-
ple. The Highbury spodumene concentrates con-
tain ~ 0.4% total Fe, similar to the typical value
of ~0.5% (Deer et al., 1974).
6.3. Microprobeanalyses
In order to obtain precise mineral chemical
data from a number of spodumene grains and to
test for compositional variability, seven grains
from two samples of pale yellowish green spo-
dumene from the Mzumbe Borehole (MZ 28 and
MZ 36) were selected for microprobe analysis,
along with three grains of a pale pink variety (TC
2). In addition, albite, microcline and mica
analyses were made, to confirm the petrographic
and chemical analyses. The analyses were made
on a Jeo1733 Microprobe using wavelength tech-
niques at the Geological Survey Laboratories in
Pretoria (Table 5). The compositions of all
grains analysed are very similar to the spodu-
mene separates analysed by XRF (Table 4), with
SiO2and A1203values of ~ 64% and ~ 18%, re-
spectively. Furthermore. very little composi-

R.J. Thomas et al. / Ore GeologyReviews 9 (1994) 161-182
Table 3
Major and trace-element analyses of core samples of the Highbury Pegmatite from the Mzumbe Borehole
173
Wt% MZ 28 MZ 29 MZ 30 MZ 34 MZ 56 MZ 36 Petalite
SiO2 74.69 74.13 71.56 73.05 72.07 77.63 78.00
TiO2 0.11 0.09 0.11 0.11 0.10 0.10 -
A1203 15.05 17.37 16.80 15.60 15.80 16.61 17.00
Fe203* 0.59 0.48 0.26 0.40 0.34 0.26 0.04
MnO 0.13 0.07 0.03 0.04 0.08 0.07 0.00
MgO 0.14 0.21 0.03 0.19 0.11 0.13 0.00
CaO 0.41 0.17 0.18 0.53 0.30 0.04 0.00
NazO 4.22 2.67 3.10 3.20 6.45 0.30 0.07
K/O 2.63 1.78 7.45 4.96 4.03 0.12 0.05
Li20 1.49 2.47 1.01 0.60 0.04 4.59 4.74
P20~ 0.04 0.04 0.05 0.04 0.04 0.02
H20- 0.20 0.01 0.01 0.01 0.01 0.01 0.00
H:O + 0.10 0.19 0.64 0.18 0.14 0.04
CO2 - 0.08 0.10 0.43 0.16 0.14
S <0.01 <0.01 0.01 0.01 0.01 <0.01
Total 99.70 99.67 100.89 99.81 99.72 100.26 99.99
(Valu~ inppm)
F 350 200 100 250 150
U 7 <6 <6 6 <6
Pb 15 14 25 19 17
Rb 674 477 > 900 > 900 642
Th 5 6 <5 <5 5
Y 8 <5 <5 <5 10
Nb 23 20 14 6 58
Sr 9 7 20 29 9
Zr 37 18 20 26 21
Mo 2 2 <1 1 1
Ga 38 30 37 31 35
Zn 32 67 39 14 69
Cr 7 112 61 268 53
V 7 9 8 264 9
Ba < 5 8 7 261 15
*Total Fe as Fe303.
Sample descriptions: All samples are leuco-pegmatite with varying modal proportions of quartz, albite, microcline and spodu-
mene, except MZ 56 which has no visible spodumene and MZ 36 which is SQI.
Petalite analysis is from SW Finland, in Deer et al. (1974).
tional variation throughout the seven grains is
apparent. Significantly, Fe203 contents of the
grains range from 0.3% to 0.5%, typical of spo-
dumenes in general (Deer et al., 1974), confirm-
ing the mineral separate XRF data. Fe203 values
from twelve microprobe analyses of pale pink
spodumene grains range from 0.14 to 0.32%, with
a mean of 0.28%. These samples have concom-
mitently higher MnO values which range from
0.22 to 0.33% (mean=0.28%). The low Fe and
higher Mn content of these spodumene grains
probably accounts for their pink colour. Anal-
yses of the plagioclase and K-feldspars showed
them to be almost pure albite and microcline re-
spectively (Table 5). Micas from the two sam-
ples are within the range of typical muscovites
(e.g., Newman and Brown, 1987).

174 R.J. Thomas et al. / Ore Geology Revwws 9 (1994) 161-182
Table 4
Major element analyses of spodumene separates from the Highbury Pegmatite; analyses of two Namaqualand spodunienes are
shown for comparison
Wt% TC 3 MZ 36A MZ 36B NS ,~AB218,':
SiO2 65.15 63.75 63.86 59.39 :440
TiO2 0.10 0.11 0.11 0. !t) ~,!!3
AI203 25.32 26.48 26.83 26.93 ' I(;
Fe203* 0.35 0.39 0.39 (I.5~ i.~!2
MnO 0.26 0 12 0.14 0.1; i.!o
MgO 0.21 0.18 0.17 0.28 } if)
CaO 0.03 0.03 0.04 0. t i ~.()2
Na20 0.25 0.25 0.27 2.08 ~.2t)
K20 0.09 0~08 0.10 15I) ~~2
Li20 6.50 7.06 7.03 5.49 "62
P205 0.30 0.02 0.02 0.07. ;.00
H20- 0.34 t).09 0.18 1 3; ).48
H20 + 0.84 0,3~ 0.44 2.3' (>~
CO2 0.18 0.13 0.17 0.18
S <0.01 -00i <0.01 0.01
Total 99.92 99.00 99.75 100.52 ~.).2i~
*Total Fe as Fe203.
Sample descriptions: TC 3: pale yellowish-green spodumene separate (pegmatite outcrop); MZ 36A: pale yellow spodumenc
separate, - 1000/+ 500/.t fraction (borehole core ); MZ 36B: pale yellow spodumene separate, - 500/+ 75 ~tfraction (borehote
core); NS: large spodumene crystal, Noumas No. 1 pegmatite, Namaqualand; AAB2186: Spodumene, Durabees (Norrabees i,
Namaqualand (Bischoffand Bischoff, 1988 ).
7. Petrogenesis
Spodumene is one of the diagnostic minerals
of complex Li- pegmatites, usually occurring in
well-defined zones within intrusive bodies, typi-
cally in association with other Li-phases such as
petalite, eucryptite, lepidolite, amblygonite, etc.
Stewart (1978 ) has shown that most Li-pegrna-
tires have comparable Li-contents ( --, 1.5% Li20 )
and that the presence and distribution of spodu-
mene (LiAISi206), petalite (LiAISiaOm) and
eucryptite (LiAISiO4) is not controlled by com-
positional differences, but rather by varying P/T
conditions during crystallization. In the system
albite-quartz-eucryptite-H20, petatite will crys-
tallise at high temperatures and low pressures,
whereas spodumene is the stable phase at lower
temperatures and higher pressures, according to
the reaction: l~talite-,spodumene + 2 quartz. Eu-
cryptite is the stable phase at low temperatures
and pressures and is commonly found as a low-
temperature alteration product of spodumene.
Further experimental work on the system eu-
cryptite-silica-H20 by London (1984) generally
confirmed Stewart's findings and provided a pe-
trogenetic grid for Li-pegmatites at low to mod-
erate pressures (0.5 to 6.0 kbar) at temperatures
between 350 and 950°C.
Spodumene usually forms large to extremely
large, discrete crystals up to several metres in
length or, less commonly, spodumene-quartz in-
tergrowths. However, SQI is a relatively com-
mon feature of Li-pegmatites, having been de-
scribed, for example, from Zimbabwe (Cooper,
1964; Grubb, 1973), Dakota (Norton, 1982)
and the Tanco pegmatite (Burt et al., 1988).
However, SQI appears to occur in two distinct
morphological habits, possibly depending upon
the P- T conditions of formation:
( 1) Coarse-grained, graphic spodumene-quartz
intergrowths: These textures have been recorded
from Zimbabwean and South African pegma-
tires, where they have been interpreted as the
crystallization products of eutectic melts (e.g.,
Grubb, 1973; Bischoff and Bischoff, 1988).
However, Stewart ( 1978 ) demonstrated that in

R.J. Thomas et al. / Ore Geology Reviews 9 (1994) 161 - 182 175
Table 5
Microprobe analyses of selected spodumene, feldspar and mica grains from the Highbury Pegmatite; note that the low totals
reflect the 6-7% Li20 present in the spodumene
MZ 28 (Spodumene) MZ 36 (Spodumene)
Wt% A B C D A B C
TC 2
(Spodumene)
Mean*
SiO2 65.44 65.22 65.34 65.75 65.21 65.14 65.22 65.82
A1203 28.47 28.26 28.25 28.35 28.50 28.62 28.49 28.73
Fe203 0.52 0.55 0.54 0.47 0.33 0.42 0.43 0.26
MnO 0.12 0.10 0.13 0.16 0.11 0.11 0.11 0.28
MgO nd nd nd nd 0.04 nd nd
Na20 0.10 0.10 0.12 0.12 0.12 0.14 0.12 0.15
Total 94.65 94.25 94.49 94.85 94.43 94.45 94.37 95.24
MZ 28 MZ 36
Wt% Microcline Mica Albite Mica
SiO2 63.76 45.88 68.27 45.71
TiO2 nd nd nd 0.11
A1203 19.63 39.48 20.48 34.35
Fe203 0.06 0.81 nd 3.62
MnO nd 0.04 nd 0.11
MgO nd 0.10 nd 0.98
CaO nd nd 0.17 nd
Na20 0.65 0.38 11.02 0.34
K20 15.47 9.64 0.11 10.25
Total 99.57 96.33 100.05 95.47
Or 94.0 0.7
Ab 6.0 98.5
An - 0.8
N.B. nd= <0.04% (detection limit).
Sample descriptions: MZ 28 = yellowish green spodumene; MZ 3628 = pale yellowish green spodumene; TC 2 = pink spodumene.
*Mean of 12 analyses.
N.B. Mica totals are low because they exclude Li20, H20 , F, etc.
the system NaAISi3Os-SiO2-LiA1SiO4-H20, the
eutectic growth of quartz and spodumene does
not occur at magmatic temperatures in typical
zoned complex pegmatites. Under magmatic
conditions feldspar-quartz-spodumene assem-
blages crystallise, and quartz-spodumene assem-
blages will only form after the cessation of mag-
matic crystallization by some process, such as
sudden pressure loss (possibly caused by wall-
rock fracturing), causing super-saturation in Li,
leading to the precipitation of a spodumene-
quartz eutectoid. Petalite is typically absent from
such pegmatites, though late replacement of spo-
dumene by eucryptite is found (e.g., Bischoffand
Bischoff, 1988 ).
(2) Fine-grainedsymplecticspodumene-quartz
intergrowths:Cooper (1964), noting the similar
LizO, SiOe and A1203 contents of acicular spo-
dumene-quartz intergrowths and petalite from
Bikita, suggested that both crystallized from the
same liquid phase "under slightly different con-
ditions". Subsequently, Norton (1982) has sug-
gested from geochemical and textural data that
fine-grained spodumene-quartz intergrowths in
the pegmatites of the Black Hills, Dakota, repre-
sent post-crystallization breakdown products of

176 R.J. Thomas et al. / Ore Geology Reviews 9 (1994) 161-182
originally magmatic petalite. In the Black Hills
intergrowths, spodumene occurs as acicular
crystals, typically only ~ 5 mm in length, inter-
grown with quartz. Norton ( 1982 ) noted that the
normative compositionsof SQI from Dakota plot
in the petalite field on a feldspar-quartz-eucryp-
tite diagram and show a close correspondence to
petalite-albite-quartz rocks. He thus suggested
that the SQI resulted from the breakdown of pri-
mary petalite upon cooling. In support of this,
pegmatites with fine-grained SQI of this type
often contain petalite in other zones and petalite
pseudomorphs or relicts are often present in the
SQI (e.g. Bikita- Cooper, 1964; Tanco -- Burt
et al., 1988). Similarly, London and Burr
(1982a) ascribed coarse-grained symplectic
quartz-spodumene intergrowths from the Tanco
Pegmatite in Manitoba to the isochemical break-
down of primary petalite. The spodumene-petal-
ite inversion has important economic implica-
tions for the glass ceramics industry where a low-
iron, high lithia product is required. Although
petalite has a lower Li-content than spodumene
(theoretical maxima of ~ 4.9% and ~ 8.0%, re-
spectively), it cannot accommodate as much iron
in its lattice (~ 0.05% versus up to 2% in spo-
dumene). The conversion of petalite to spodu-
mene + quartz thus provides an efficient natural
two-fold concentration of lithium, without the
problems of high-Fe content that accompanies
the crystallization of primary spodumene.
The composition of SQI from the Highbury
Pegmatite is almost identical to that of petalite
(~78% SiO2, ~ 17% A1203, ~4.5% Li20, and
little else, see Table 3). In addition, the symplec-
tic-fibrous character of the SQI is comparable
with those described from Tanco. Further field
evidence in support of this model is provided by
the radial cracks that have been observed to lo-
cally surround SQI crysts. Clearly then, the phys-
ico-chemical characteristics of the SQI in the
Highbury Pegmatite points to an origin by the
second (petalite transition) type. Furthermore,
as the experimental work by Stewart ( 1978 ) has
shown that the magmatic eutectic growth of
quartz and spodumene is unlikely to occur at the
relatively low temperatures associated with the
Li-bearing zones of complex pegmatites, those
intergrowths which have been described as eu-
tectic textures (e.g., Grubb, 1973; Bischoff and
Bischoff, 1988) should perhaps be re-inter-
preted in the light ofthe petalite transition model.
At very high temperatures fl-spodumene or
virgilite will crystallise (London, 1984), though
the latter has only been recorded in nature from
high-temperature, silica-rich volcanic glasses
(French et al., 1978). London (1984) con-
firmed these results by means of additional ex-
perimental data on the system LiAISiO4-SiO2-
H20 and erected a complete petrogenetic grid for
Li-rich pegmatites (Fig. 10). This grid is partic-
ularly useful since, as noted earlier, the stability
relations in Li-aluminosilicates are primarily a
function of P and T and are largely independent
of the compositions and proportions of the other
phases present. Thermobarometric estimates
from southern Natal, suggest peak P-T condi-
tions of > 800 °C at ~ 4-6 kbar during the main
regional tectogenesis (e.g., Thomas et al., 1992).
Subsequent cooling from peak temperatures ap-
pears to have been prolonged and near-isobaric
(Grantham et al., 1993). This proposed P-T-t
path is supported by the data from the Highbury
Pegmatites. Field evidence suggests that the
Highbury Pegmatite was emplaced after peak
J~
J<
n
Spod + Qtz
Ecr+/ Pet + Qtz
Otz/
/
B Spod
2;0 300 400 5;0 600 700 800
T (°C)
Fig. 10. Suggested P-T crystallizationpath for the Highbury
Pegmatite. Inferred paths for the Tanco and Bikita pegma-
tites are shown for comparison (after London, 1984):

metamorphic temperatures and pressures. Un-
der these conditions, the late-stage Li-enriched
magma would crystallise within the field of pe-
talite stability. Prolonged near-isobaric cooling
would give rise to the breakdown of petalite to
the observed symplectic SQI intergrowths. There
is no textural evidence in the SQI to suggest that
the low P and T reaction of spodumene to eu-
cryptite+ quartz has occurred, possibly suggest-
ing that pressures remained above 2 kbar at tem-
peratures below 300°C. This is particularly
relevant in situations of decreased fH20, which
has the effect of enhancing the stability field of
eucryptite+ quartz. Figure 10 shows a possible P-
T crystallization path for the Highbury Pegma-
rite, compared to that suggested for two major
Li-pegmatites.
The discovery of significant quantities of spo-
dumene in the Highbury Pegmatite, suggested
that they might represent the exposed part of a
typical complex, zoned lithium pegmatite. How-
ever, several important features militate against
such an interpretation. Firstly, whilst a regional
lateral zonation may be present throughout the
pegmatite-aplite suite, no systematic vertical
zonation has been recognized and no other com-
plex pegmatite mineral assemblages were found.
In addition, the extreme dearth of micas and the
absence of typical complex Li-pegmatite para-
geneses means that the Highbury Pegmatite can-
not easily be fitted into any standard classifica-
tion of pegmatitic rocks (e.g., Cameron et al.,
1949; Cerny, 1991 ). This is in part due to the
almost totally anhydrous mineralogy as a result
of the low content of volatile elements, such as
H20, F, etc. The anhydrous nature of the High-
bury Pegmatite magma is further demonstrated
by the lack of alteration to secondary Li-phases,
seen commonly in volatile-rich Li-pegmatites
(e.g., London and Burt, 1982b). The unusual
presence of graphite suggests emplacement un-
der conditions of low fo2. Similarly, apart from
enrichment in Li20, the Highbury Pegmatite is
not enriched in any of the expected trace ele-
ments (except Rb) for which analyses are avail-
able (e.g., P205, U, Th, Nb, Y). Nevertheless,
the high Li20 and Rb content, and the very low
K/Rb ratios testify to the highly fractionated na-
ture of the Highbury Pegmatites.
It has earlier been noted that the Highbury
Pegmatites are petrographically similar to the
voluminous garnet leucogranites of the Margate
Suite, which crop out extensively in southern
Natal. This suite is also characterized by anhy-
drous mineral assemblages (quartz + feldspar +
garnet _+minor biotite) and contains charnock-
itic (quartz + feldspar + hypersthene) phases
(Thomas et al., 1991). The Margate Granites are
similarly characterized by high Rb, variable K/
Na ratios and low volatile contents and were em-
placed under conditions of lowfo: (Grantham,
1988). It is thus reasonable to suggest that the
Highbury Pegmatites might represent late-stage,
volatile-poor differentiates of the Margate leu-
cogranites that are enriched in lithia, silica and
Rb.
As to the source of the Li, Stewart (1978)
pointed out that to achieve a LieO content of
~ 1.5%, it would be necessary to perfectly frac-
tionate at least 70 times more parental magma
with ~ 100 ppm Li than the resulting pegmatite.
In the case of the Highbury Pegmatites, there is
certainly enough parental garnet leucogranite
magma, but it remains obscure as to why all the
Li is concentrated in one place, without the cor-
responding concentration of other incompatible
phases, except Rb. More plausibly, Stewart
(1978) suggested that Li was enriched in the
source magma by anatectic melting and scaveng-
ing of Li-rich metasediments (meta-evapo-
rites? ). The presence of Li lowers the minimum
melting temperature of the granite system by at
least 75 °, allowing for heterogeneous Li-enrich-
merits, that can then be further concentrated by
fractionation. The immediate host rocks of the
Highbury Pegmatites are mafic gneisses and
granulites. However, farther south the country
rocks to the Margate Suite granites are granulite
facies metapelitic and calc-silicate gneisses of the
Leisure Bay Formation and marbles and dolo-
mites of the Marble Delta Formation. It is not
inconceivable that at least some of these rocks
might represent originally evaporitic deposits,
modern-day examples of which are known to host
large, low-grade Li-brines.

178 R.J, Thomas et a~, / Ore Geology Reviews 9 (1994) l O1-182
8. Comparison with other Li-pegmatites
8.1. General
Lithium pegmatites are a common feature of
many granitoid terranes worldwide, particularly
those of Precambrian age and typically in rela-
tively high-grade metamorphic environments.
However, large bodies with sufficient Li-min-
erals to be of economic value are scarce. The most
important include Gwalia-Greenbushes (West-
ern Australia), Tanco (Manitoba, Canada), Cy-
prus Foote-Kings Mountain-Bessemer City
(North Carolina, U.S.A) and Bikita (Zim-
babwe) (Anstett et al., 1990 ). Economic lithium
pegmatites are also known in Africa from Man-
ono in Zaire (Guenther and Ngulube, 1992) and
from the Karibib District of Namibia (the Pan-
African Helikon-Rubikon pegmatite belt; Rich-
ards, 1986). Lithium ores have also been ex-
ploited from Kibaran pegmatites in Burundi,
Rwanda and Uganda (e.g., Fransolet and Tack,
1990). These examples of economic Li-pegma-
tites are often complexly zoned, with Li occur-
ring in various mineral phases in different, well-
defined zones. For example, the Bikita Pegma-
tite contains spodumene, petalite, lepidolite,
amblygonite, eucryptite, pollucite and bikitaite,
complexly distributed through the intermediate
and core zones of the pegmatite (Cooper, 1964;
Wegener, 1981 ). Similarly, at Tanco, zones rich
in spodumene occur in the central zones with in-
termediate zones enriched in amblygonite, petal-
ite, lepidolite and pollucite (Butt et al., 1988).
The Li-minerals are consistently accompanied by
other characteristic complex pegmatite minerals
including tourmaline, beryl, columbite-tantalite,
cassiterite, apatite etc., along with other rare-
metal minerals. This association has been class-
ified as being characteristic of "LCT'" (Li-Cs-
Ta) pegmatites, derived from undepleted crustal
lithologies undergoing their first anatectic event
(Cerny, 1991 ). In such pegmatites, spodumene
crystals of extreme size are common (up to 5 m ).
8.2. Late Kibaran Li-pegmatites of southern
Africa
A number of Li-pegmatites are known from
southern Africa (see Keyser, 1976 ). Whilst some
of these are probably Archaean in age (e.g., Bis-
choff and Bischoff, 1988 ), many are associated
with the ~ 1 Ga Namaqualand Metamorphic
Province in the northwestern Cape, i.e. the west-
ern continuation of the Natal belt (Fig. 1). The
Late Kibaran pegmatites of the Namaquatand
Metamorphic Province are largely confined to the
"Pegmatite Belt", a narrow, E-W-trending tract
of land up to 30 km in width and approximately
450 km in length (Hugo, 1986), (Fig. i I ). Lith-
ium minerals, including spodumene, amblygon-
ite, tepidolite, zinnwaldite, petalite and triphy.-
tite-lithiophillite are found in complex.
berylliferous pegmatites, mainly in the western
portion of the belt. Individual bodies range from
over 2 km long and 70 m wide to small veinlets
and consist of coarse-grained quartz and feld-
spar along with muscovite, tourmaline and gar-
net (Von BackstrSm, 1976).
In the western sector of the Pegmatite Belt
spodumene has been extracted from the Noumas
No 1, Spodumene Kop Nos 1 and 2, Koker-
boomrand Nos 1 and 2, Groenhoekies and Nor-
rabees Nos 1 and 2 pegmatites (Fig. l I ). Lith-
ium-bearing pegmatites also occur in the
Groendoorn River gorge (Fig. 11 ). However, the
remoteness and inaccessibility of the gorge, cou-~
pled with the small size of the deposits, renders
them uneconomic (Nel, 1968). The Noumas
pegmatite has been worked intermittently since
1925 for a variety of commodities, including bis-
muth minerals, beryl, tantalite-columbite, mus-
covite, feldspar and for spodumene since t961
(Nel, 1968). The pegmatite ( 1 km long by l0 to
42 m wide) has been emplaced discordantly into
foliated granodiorite (Hugo, 1986). Single spo-
dumene crystals up to 1 m in length are charac.
teristic of the 1 to 8 m wide intermediate zone
and in places account for up to 50% of the min-
eral assemblage. Production of spodumene, a to-
tal of around 1000 t, from what is the largest
known mineralized pegmatite in Namaqualand
tapered off during the late 60's and early 70's
owing to lowered market prices and increased
operating costs. Grades have been calculated at
approximately 5 t spodumene per 100 t of peg-
matite material (Von Backstr6m, 1976l. An
analysis of the Noumas spodumene is given in

' I.19°
NAMIBIA f::::::t::::-~.~.~.-
::::::::::::::::::::::::::::::: UPINGTON
.,,~-.....,,,+..,-,, .... .- -, ,.- -', • • ~t
•
,, ! .v....X.X.X.X.)X-X-X.X.:.X-X.:-X-X.X..~~ - : : ; ~ . •...............................~.
~ ~ : - - .'.',',',',','.'.'.','"~ ~ ~:.','.','.','.'.'.'.'.'.'.'.'.'."t:
............ ~ . . . . . . . . . . • ..... ".'. - .j ..... •........ ', A
_ L z.4":'::':':':':':::':':':':':':':':':':':':'::':':~----:":::,;z ~;".:.:.:.:-:.:.:-:.:.:.:.:..',
~ t....:.:.:.:':-:':.:.:.:.:.:':':':':.:':':':':':':':':':':':~'~...-:-Y..:.:.:.:.:.~ "',:..~.:.:-:-:.:.:-:.:.:.%,
~ ~ . . ' . ' . I _ ~~ •v.v...'.. . . . . .... ,..v.v. ".'.'.....'.'.'.'.'.I EASTERN SECTOR .<,v.v.v.v.v...'-..-..,,, ....... : ,
~ : . - . . : ! ...... ~:.:.:.:.:.:.:.....:.:.............
t/....~ ~, .:':':~:'.2::2;~':,:;'.~':.,:'~,4.~..-~.~.:.:.:.:.:.:.:.:.:.:.:.:.:.:.S ",4":':':':':':':':':':':':':':':':':v.
"<.~'o7~o "-~'~ ~ x,'.'.'.'.'.'.'.'.'.'.'.-I 1 NOUMAS No 1 W:'''v "~,'"'""'"'"'""~~'.'.'.'.'.'.'.'.'.'/ ~.'.'.'.'. +u~4 "-'.'.'.'.'.'.', ~.
WESTERN SECTOR ",2-.~..~'," 2 SPODUMENE KOP No 1 ~:....:.:...lJ11))........,.....).~
3 SPODUMENE KOP No 2 v.v.v....v.v.v,v.v.
~:i:~) PEGMATITE BELT
--,,~.
• LITHIUM DEPOSIT
O
SPRINGBOK o LITHIUM OCCURRENCE
4 KOKERBOOMRAND No 1
5 KOKERBOOMRAND No 2
6 GROENHOEKIES
7 NORRABEES No 1
8 NORRABEES No 2
9 SWARTBERG
10 STRAUSSHEIM No 1
11 STRAUSSHEIM No 2
12 ANGELIERSPAN
0 50 100
i I I
SCALE km
'~v.'.'.'.v.'.'.v.v.v 0 "'-~.,,
"K"-X'X'X'X'X" 120 )/..x.
"~ 4~.,., ,.-.- ,,,:.. ,..~ ~.
SOUTH AFRICA
29 ° o
30 ° w
Fig. 11. Distribution of lithium mineralizationin the Namaqualand Metamorphic Province.
Table 6
A comparison of the main features of the Highbury Pegmatites with typical Li-pegmatites
Highbury pegmatites Typical Li-pegmatites
Multiple sheets, simple
Unzoned
Colour index ~ 1
Virtually anhydrous mineralogy (low H20, F, etc. )
Mineralogicallysimple
(quartz + albite + microcline+ spodumene)
White mica rare
Small ( < 40 cm ) spodumene crysts
Accessory garnet, graphite, no tourmaline, tantalite,
cassiterite, etc.
Usually dyke-like, complex
Complexly zoned
Colour index ~ 5
Hydrous phases common (high H20, F, etc. )
Mineralogicallycomplex--multiple Li-phases
Abundant white mica
Huge (up to 5 m) spodumene crystals
Rare-metal phases characteristic
Table 4. Pegmatites in the eastern sector of the
Pegmatite Belt are largely devoid of lithium min-
erals (Hugo, 1969).
The Natal belt, in contrast to Namaqualand, is
almost devoid of complex pegmatites. Although
mineralogically simple aplitic and pegmatitic
rocks are common (e.g., Evans, 1984; Thomas,
1988), spodumene has hitherto not been re-
corded from Natal. Clearly the Highbury Peg-
matite, with its simple largely anhydrous major
mineralogy, unusual accessory phases (gar-
net + graphite), absence of associated complex

180 R.J. Thomas et al. / Ore Geology Reviews 9 (1994) 161-182
pegmatite mineral phases and lack of vertical
zonation is quite atypical of Li-pegmatites both
worldwide and in the Late Kibaran of southern
Africa (Table 6) and can be considered to rep-
resent a unique form of Li-pegmatite.
9. Economic aspects
The potential economic implications of the
Highbury Pegmatites cannot be overlooked.
Spodumene was last produced in South Africa
from the Noumas Pegmatite No 1 (Fig. 11 ).
Since then, South Africa has been obliged to im-
port all its lithium requirements, either in min-
eral form (mainly spodumene) or as a com-
pound (lithium oxide, hydroxide or carbonate).
From 1988 to 1991 the total value of these im-
ports has approached $1 000 000 (South African
Minerals Bureau records). Principal uses of the
metal in South Africa are in the metallurgical,
electronics, petrochemical, plastics and chemi-
cal industries, while Fe-poor spodumene is used
in glass and ceramics. Clearly, the presence of an
economically viable lithium deposit in South Af-
rica, particularly in an accessible position near a
major industrialized centre, would be of great
benefit to the local economy, particularly as
worldwide demand for Li is expected to increase
(Alexander et al., 1992 ).
The results of the beneficiation analysis de-
scribed previously (Table 7) confirm the spo-
dumene: quartz ratio in SQI of approximately
60: 40 (sample MZ 36 ). The low Li20 values of
the float ( < 0.21%) show that this simplebene-
ficiation technique is an efficient means for be-
neficiating spodumene from the Highbury Peg-
matite. The results demonstrate further that this
efficiency is not significantly enhanced by crush-
ing and sieving finer than - 1000/+ 500/~. The
Fe-content of the greenish-yellow spodumene
( ~ 0.4% FezO3) is higher than the pate pink va-
rieties (Table 5), which contain ~0.2% Fe203.
Iron content is an important factor in the glass
and ceramics industries, so a detailed systematic
geochemical study over the entire pegmatite field
is necessary to establish the full range of varia-
bility of the Fe-content in the spodumene, with
the pink varieties constituting the most attrac-
tive exploration targets.
The size of the spodumene reserves is not
proven, though outcrops of more than 35% SQI
have been recorded intermittently over a t km
strike length. The amount of potential structural
disruption (by pinch-and-swell) has not been
precisely ascertained, though good correlation
with the Mzumbe Borehole and natural outcrops
suggests that bodies may be largely laterally con-
tinuous and that limited later faulting has oc-
curred. The down-dip extent of the mineralized
zone cannot be calculated with the present data
and clearly a future drilling programme would be
necessary to establish reliable estimates of ore
reserves. Nevertheless, from that which is known,
the Highbury Pegmatite appears to be a much
larger body than the lithium pegmatites of Na-
Table 7
Results of the spodumene beneficiation experiment with Li20 analyses
Sample Sieve fraction Recovery Li20 Mineralogy
(/t) ( wt% ) (wt%)
TC 3C - 1000/ + 500 ,u 34.7 (sink) 6.50
TC 3F - 1000/+ 500/1 65.3 (float) 0.17
TC 3 - - 2.03
MZ 36A - 1000/+500# 61.1 (sink) 7.06
MZ 36C - 1000/+500# 38.9 (float) 0.21
MZ 36B - 500/+ 75 # 58.5 (sink) 7.03
Z 36D - 500/+ 75 # 41.5 (float) 0.15
MZ 36 - 4.59
Spodumene ( +garnet
Quartz, feldspar, graphite
Whole-rock (spodumene pegmatite)
Spodumene
Spodumene
Whole rock (SQI)

maqualand and Transvaal and may be compa-
rable in reserves to a medium-sized deposit such
as Bikita. The easily accessible location of the
pegmatites (,,-100 km south of Durban), cou-
pled with their shallow-dipping geometry, are
additional strongly favourable considerations.
Furthermore, the uppermost sills are consis-
tently the most spodumene-rich, clearly an ad-
vantageous situation from a mining point of view.
Finally, it should be noted that not only does
the pegmatite have potential as a source of spo-
dumene, but the extensive aplitic phases could
also make an attractive dimension stone (Bullen
et al., 1992 ), and the high albite content of much
of the entire sill complex, may render feldspar a
useful by-product of any future mining venture.
Acknowledgements
The analytical work was performed at the
Geological Survey laboratories in Pretoria and
thanks are due to the following: Mrs. H.C.C.
Cloete, Dr. R. Edge, Mr. J.H. Elsenbroek, Mr. M.
Lekotoko, Ms. A. Peense and Mr. G. Trojak. The
authors would like to thank Mr K. Wilkinson for
access to the pegmatite outcrops and for permit-
ting the drilling operation on his farm in 1990.
Thanks are due to Ben Peterse and Koos Venter
of the Dep. Water Affairs in Howick for super-
vising the drilling and to Ms. D. Breytenbach of
the Minerals Bureau, Mr. P. van Eck of SAAR-
CHEM and Mr. P. Gauch6, owner of Blesberg
Mika (Pta) Ltd., for information about lithium
production, imports and uses in South Africa.
10. Conclusions
From the petrological study, it is suggested that
the Highbury Pegmatite represents a volatile-
poor, late-stage differentiate of the garnet leuco-
granite phase of the largely anhydrous Margate
Granite Suite. The source of the Li may be re-
lated to anatectic melting of Li-enriched meta-
sediments of the Margate Terrane. The pegma-
tires crystallized primary petalite that
isochemically reverted to symplectic spodu-
mene + quartz intergrowths (SQI) on near-iso-
baric cooling. Low-temperature replacement by
eucryptite has not been observed, though late al-
bitization is locally apparent. This is consistent
with the proposed P-T evolution of the southern
part of the Natal belt, which has been modelled
in terms of near-isobaric cooling from high tem-
peratures at moderate pressures (Grantham et
al., 1993).
From an economic point of view it has been
shown that the spodumene can be efficiently be-
neficiated from SQI by flotation, to give a prod-
uct with > 7% LIE0. In addition to low-Fe pink
spodumene, which may be pure enough to sat-
isfy the rigorous demands of the glass and ce-
ramics industries, the Highbury Pegmatites could
become an important source of Li-salts, with di-
mension stone and feldspar as possible by-
products.
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