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British Geological Survey
TECHNICAL REPORT WC/94/1 Overseas Geology Series
THE INDUSTRIAL MINERAL RESOURCE POTENTIAL OF UGANDA
A Report prepared for the Overseas Development Adminisaation under the ODAIBGS Technology Development and Research Programme, Project 9111
Keyworth, Nottingham, British Geological Survey, 1994
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THE INDUSTRIAL MINERAL RESOURCE POTENTIAL OF UGANDA
CONTENTS
INTRODUCTION
PROFILE OF UGANDA TODAY
GEOLOGICAL FRAMEWORK
PRODUCTION AND TRADE OF UGANDAN INDUSTRIAL MINERALS
ESSENTIAL INDUSTRIAL MINERALS
Carbonate rocks Clays Evaporites and Brines Feldspar Phosphate Rock Sand and Gravel Silica sand Stone Sulphur
OTHER INDUSTRIAL MINERALS
Asbestos Barite Bauxite Bentonite Diatomite Garnet Graphite K-rich rocks Kyanite Li-minerals Mica Nepheline S yenite Quartz crystal Pozzolanas Rare earth minerals Talc Vermiculite Zeolites
REFERENCES
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LIST OF FIGURES
Fig. 1 Geography of Uganda.
Fig. 2
Fig. 3
Simplified geology and industrial mineral domains of Uganda.
Carbonatite/alkaline intrusive centres of southeast Uganda, based on Davies (1 956).
Simplified geology of the Western Rift around Lake Edward and Lake George showing the locations of key industrial mineral deposits
Plasticity of selected Ugandan clays.
Geology of the Sukulu carbonatite complex, based on Williams (1959).
Geology of the Bukusu carbonatite/alkaline complex, based on Baldock (1967).
The Busumbu phosphate deposit.
Silica sand deposits around Lake Victoria.
Simplified geology of the Pakwach area showing the location of diatomite deposits.
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8
Fig. 9
Fig. 10
LIST OF TABLES
Table 1
Table 2
Table 3
Table 4
Table 5
Table 6
Table 7
Table 8
Table 9
Table 10
Table 11
Industrial Mineral Domains of Uganda.
Uganda industrial mineral production since 1965.
Ugandan imports of industrial minerals 1992.
Essential industrial minerals in Uganda.
Lake Katwe: extremes of lake brine composition 1967.
Reserves (in tons) of mineral salts at Lake Katwe.
Analyses of Ugandan feldspars, from Pallister (1959) and Mathers and Mitchell (1992).
Chemistry of phosphate rock samples from Busumbu, for locations see Fig. 8.
Apatite content of phosphate rock samples from Busumbu.
Elemental reserves in the pyrite tailings stockpile near Kasese.
Grading and exfoliation tests on Namekara vermiculite from Bloomfield (1973).
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LIST OF PLATES
Plate 1
Plate 2
Plate 3
Plate 4
Plate 5
Plate 6
Plate 7
Plate 8
The Tororo Rock carbonatite plug, southeast Uganda.
Calcitic carbonatite (sovite) from Limekiln Hill near Tororo.
Quaternary lacustrine limestone from Hima in the Western Rift.
Traditional brickmaking at Seta near Kampala.
Brickclay pit at Seta near Kampala.
Brine lake within a Quaternary tuff ring in the Western Rift.
Sukulu Hills carbonatite complex from the northeast.
Silica Sand beach deposit on the shores of Lake Victoria at Diimu fishing village.
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THE INDUSTRIAL MINERAL RESOURCE POTENTIAL OF UGANDA
INTRODUCTION
It is now over thirty years since the last systematic description of Uganda’s mineral resources
was published by the Ugandan Government (Barnes, 1961). Although dated, this account still
remains the logical starting point for any investigation for water, hydrocarbons, geothermal
energy, metallic or industrial mineral resources within the country. This serves to illustrate the
sustained value of such compilations. This document is not intended to replace the still useful
account of Barnes (1961), but rather to up-date information on Uganda’s industrial mineral
sector.
An industrial mineral is ’any rock, mineral, or other naturally occurring substance of economic
value, excluding metallic ores, mineral fuels and gemstones’. A vast range of industrial minerals
is consumed by society since they provide the primary raw materials for the construction,
cement, chemical, fertilizer, metallurgical, ceramics and glass industries. Clearly industrial
minerals are literally and commercially the foundation stones of development! An evaluation of the industrial mineral potential of a country like Uganda can be expected to identify the basic
raw material needs of industry, to aid with efficient resource planning and management, help
in the discovery of new deposits and indicate how locally produced materials can substitute for
imports.
Presented here is a compilation of the substantial body of information on Uganda’s industrial
minerals that has been produced since 1961. This has involved a comprehensive review of the
numerous unpublished internal reports produced at the Ugandan Department of Geological
Survey and Mines (DGSM) since 1961 together with published geological accounts, fresh field
evaluations of selected mineral deposits, and the characterization of key raw materials carried
out in the UK at the laboratories of the British Geological Survey (BGS). A clear distinction is made in this report between the industrial mineral commodities that are ’essential’ for Uganda’s
current domestic needs and ’other’ commodities with more specialized applications that are not
generally required in significant volumes by local industry.
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This streamlined approach to the production of an up-dated national industrial mineral inventory
is very cost-effective and is highly replicable. Indeed it could, and should, be carried out
periodically by all countries to form an essential part of the information infrastructure that any
government must provide to attract investment and ensure economic growth. Through this
particular collaboration the BGS has assisted the DGSM to provide such information for
Uganda. Publication of this account is particularly timely since it coincides with the 75th
Anniversary of DGSM (formerly the Geological Survey of Uganda).
This document is being widely disseminated to interested parties in government and the private
sector both in Uganda and elsewhere. With Uganda’s economy recovering steadily there is now
a need for a detailed evaluation of several of the most critical industrial mineral prospects
described in order to establish available reserves for industry, and the installation at DGSM of
a computerized database containing details of all these mineral prospects for consultation by
investors and industry.
This account of the industrial mineral resource potential of Uganda has been prepared as a
collaborative effort between BGS and DGSM which is a component of the Ugandan Ministry of Water and Mineral Development. Funding for the UK input has been provided by the
Overseas Development Administration (ODA) of the Foreign and Commonwealth Office (FCO)
as part of the ODA-BGS Technology Development and Research (TDR) project ’Minerals for
Development’. The Ugandan input has been provided by DGSM. The provision of some logistic
support from the United Nations Department of Economic and Social Development (UNDESD)
through their Mineral Investment Promotion Project (UGA/89/001), which is being implemented
jointly with DGSM, is also gratefully acknowledged.
PROFILE OF UGANDA TODAY
Uganda is landlocked, covering an area of about 236,000 km2 lying astride the Equator in East
Africa (Fig.1). Uganda has common borders with Sudan in the north, Kenya to the east,
Tanzania and Rwanda in the south and Zaire to the west.
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Fig. 1 Geography of Uganda.
KEY
- - - - lmernational
- Railways
- Main roads
boundaries
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Much of Uganda comprises gently rolling country at elevations of about 1000 - 1500 m with
Lake Victoria - Africa’s largest lake and source of the River Nile - occupying the southeastern
corner. In the extreme west segments of the Western Rift are occupied by broad flat elongate
valleys with large lakes whilst the adjacent uplifted blocks such as the spectacular Ruwenzori
Mountains rise to over 3000 m. The extreme southwest of the country around Kabale is mountainous and heavily forested. In the southeast the large stratovolcano of Mount Elgon
straddles the border with Kenya.
The population of Uganda according to the 1991 census is about 17 million. The capital,
Kampala, is located just north of Lake Victoria, with a population of about 750,000. The eight
largest cities combined contain only 10% of the population, which is predominantly rural.
The transport and communications infrastructure was largely destroyed by the political unrest
of the seventies and early eighties, but it is gradually being repaired. Most major roads south
of latitude 1”N are now in good order. The rail network is in need of maintenance and repair;
it is of vital importance to Uganda since many imports enter the country by rail via the port of Mombasa on the Kenyan coast. The country’s only major airport is located at Entebbe on the
shores of Lake Victoria some 30 km south of Kampala; most regional cities have small airstrips.
Boat services operate to Kenya and Tanzania across Lake Victoria, from the Ugandan ports of Jinja and Port Bell near Kampala.
Jinja lies to the east of Kampala and is a major industrial centre located close to the Owen Falls Dam and Hydroelectric plant which provides most of the country’s electric power supply.
The currency is the new Uganda Shilling (current exchange rate = Ug Sh 1275 = f 1). The
economy of Uganda was decimated by the unrest between 1972 and 1985, and precise
information on many financial aspects are still lacking. After several years of relative peace and
stability production in 1988 finally recovered to 1972 levels! Steady growth continues and was
estimated at 3.4% in 1990. Agriculture and Food Processing are the key elements of the Gross
National Product, the raw value of minerals currently contribute less than 0.1 % to the overall
economy although this considerably understates their importance when one considers the added
value that occurs in processing and manufacturing them into finished products. Exports are
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predominantly of coffee with small amounts of tea and cotton. The principal trading partners
are the United States and the European Community countries.
GEOLOGICAL FRAMEWORK
The simplified geological map presented (Fig. 2) contains five categories: crystalline
Precambrian basement, Precambrian - Palaeozoic sedimentary ’cover’ sequences, Cretamus - Tertiary carbonatite/alkali intrusives, Tertiary - Quaternary volcanics and Quaternary
sediments. For the purposes of evaluating the industrial mineral potential of Uganda each of these five categories can be considered as a distinct domain containing a characteristic and
predictable suite of industrial minerals (Table 1). This classification also provides a broad guide
for targetting any future mineral exploration. The principal characteristics of these mineral
domains are outlined below.
The Precambrian Crystalline Basement (Domain A, Fig. 2, Table 1) is widespread covering
about 75% of Uganda’s land area. This terrain is predominantly composed of gneisses,
granitized rocks and granites with associated pegmatites. Whilst most of the basement rocks are
probably of Archean age, some of the granites are younger since they cut parts of the overlying
late Precambrian ’cover’ sediments. Subordinate lithologies within the basement include strongly
metamorphosed and deformed amphibolites, quartzites, marbles, and other metasediments and
metavolcanics. The areas underlain by basement commonly comprise low-relief plains on which
prolonged in-situ alteration has led to the development of thick weathering profiles and lateritic soils.
Many of the lithologies within the basement provide good hard rock suitable for use as blocks
or in crushed form as sized coarse aggregate for construction. Granite is the principal lithology
extracted although minor amounts of amphibolite have also been exploited. The availability of
rock is however limited to areas where basement rocks crop out as opposed to the extensive
tracts where this is covered by a thick residual soils. These soils do however provide good clay raw materials for the brick, tile and pottery manufacturing industries. Iron concretions within
lateritic soils also constitute an adequate source of coarse aggregate. Locally the basement rocks
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D,WA II IK AI INI I IT 11 I I 111 11 I I 11 11 I W Z A I I lrim T I I I I I I
SYMmOL -UN
Tororo /
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@ D Tertiary-Quaternary Volcanics
Lake Creteceous-Tertiary Carbonstite I Victoria Alkali I m s ~ v e Centres
Pracambrian-Paleeozoic Sedimentary a 'CovefSeguence ------ .L A Crysalline Precambrien Basement
0 m*. TANZANIA
, 32 34'
Simplified geology and industrial mineral domains of Uganda.
6
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are rich in minerals such as graphite, garnet, corundum, talc, asbestos and kyanite, although
most of the occurrences documented (Barnes, 1961) are either subeconomic or require proper
evaluation. However, many of these commodities are used in such small quantities in the
domestic market that they are unlikely to be mined in the foreseeable future.
The remaining industrial mineral potential of the basement lies in small, but economically
important, pegmatites developed around the peripheries of granite stocks and batholiths. The
pegmatites tend to occur in swarms but individual bodies rarely exceed 100 m x 40 m. Many
industrial minerals have been won from pegmatites principally by artisanial methods; these include; quartz crystal, sodic and potassic feldspar, sheet mica (muscovite), beryl, spodumene,
rare earth-bearing minerals and kaolin.
In some parts of Uganda (about 12%) the basement is overlain by extensive tracts of variably
metamorphosed and deformed Sedimentary ’Cover’ Sequences (Domain B, Fig. 2, Table 1). Generally the upper parts of these formations tend to be weakly metamorphosed and little deformed; however at progressively lower structural levels the metamorphic grade and extent
of deformation tend to increase. The principal lithologies are terrigenous and include arenamus
and rudaceous clastics with intercalated argillites and locally metavolcanics. Most of these
’cover’ sequences are Precambrian in age and include the widespread Buganda-Toro and
Karagwe-Ankolean systems in the south and southwest, and the Bunyoro and Kyoga series
which occupy an east-west trending belt around Lake Kyoga in the heart of the country (Fig.2).
Also included are very small patches of Palaeozoic Karoo sediments which crop out on the
northern fringes of Lake Victoria.
These sequences appear to have been little exploited for industrial minerals and whilst little has
been written about their potential it is probably limited. As in the basement the more durable
lithologies such as massive quartzite beds tend to be used as a source of building stone and
crushed rock aggregate. The only other important indications of potential include kaolinized
deposits in the Karagwe-Ankolean and Karoo sediments. Argillaceous beds within the sequences may offer a possible raw material for local brick, tile and cement manufacture.
Occupying a minute part of Uganda’s land area, but nevertheless of major economic importance,
8
are about a dozen small Carbonatite/Alkali Intrusive Complexes (Domain C, Fig. 2, Table
l), which are scattered throughout eastern Uganda. These complexes include small intrusive
plugs, as well as larger ring complexes such as Sukulu and Bukusu in the southeast, which
contain annular and arcuate intrusions of carbonatite, syenite and ultrabasic rocks. These
intrusive centres are Cretaceous to Tertiary in age and are evidence of some of the earliest
volcanism associated with the doming and later rifting of this part of East Africa.
These small intrusive centres contain considerable industrial mineral reserves and potential. The
carbonatite intrusives offer a scarce source of carbonate rock for lime and cement manufacture
within an area dominated by basement terrain. Apart from the carbonatites themselves, it is the
thick residual soils commonly developed on the complexes, that contain important concentrations
of industrial minerals such as apatite (for phosphate) vermiculite, zircon, barite and pyrochlore
(rare earth elements). Magnetite is the principal mineral present in these soils and is easily
removed from the other species by crushing followed by magnetic separation. To date these
soils have only been worked and processed on a regular basis to produce phosphate concentrates for fertilizer manufacture.
Tertiary - Quaternary Volcanic Rocks (Domain D, Fig. 2, Table 1) cover about 3% of Uganda’s land surface. This category comprises lavas, pyroclastic rocks (mainly tuffs) and
closely associated volcaniclastic sediments. These deposits occupy two main areas. In the east
of the country they form the Miocene Mount Elgon stratovolcano and the nearby smaller
extrusive centres (Fig. 2); these are chiefly characterized by nepheline-bearing lavas and tuffs
(Na-rich and undersaturated). In the southwest around Fort Portal and the Western Rift, K-rich pyroclastics form several tuff cones and rings. These deposits are relatively recent as shown by
their fresh geomorpholgical expression and the fact that similar examples just across the border
in neighbouring Zaire are still active.
Apart from the utilization of the volcanic lavas and tuffs as a local building stone and source
of aggregate the Tertiary - Quaternary volcanics are not utilized as industrial minerals. One
possibility is use of strongly potassic rocks as a direct application petrofertilizer. Given the
geological setting and chemistry, bentonite and zeolite-rich deposits would be expected to occur
within intercalated volcaniclastic sediments and altered tuffs; other possible industrial minerals
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likely to occur within this domain, but presently unreported, include scoria and volcanigenic
sulphur.
The final category Quaternary Sediments (Domain E, Fig. 2, Table 1) includes deposits that
have accumulated in active depositional environments such as the Western Rift, major drainage
tracts, swamps and beaches fringing major lakes, and in poorly drained depressions and
glacigenic deposits developed principally in the Ruwenzori Mountains in southwest Uganda. The
deposits are predominantly clastic gravels, sands, silts and clays together with biogenic and
chemical deposits including limestones and diatomite. Also included for convenience in this
domain are the mineral salts contained in lake brines and the porewaters of lake sediments and also hot springs.
Quaternary deposits provide an abundant source of industrial raw materials including sand and
gravel (aggregates), limestone, common clays, silica sand, gypsum, ball clays and salt (from
brines). Diatomite deposits are also known to occur; bentonite and zeolite-rich beds are likely
to be present although their recognition in the field is not always easy so they sometimes go
unreported. In addition to common salt, brines also offer a potential source of many other Na-,
Mg- and K-salts.
PRODUCTION AND TRADE OF UGANDAN INDUSTRIAL MINERALS
Uganda’s production of key industrial mineral commodities since 1965 is summarized in Table
2; this shows the marked decline in output that accompanied the political unrest of the 1970s
and early 1980s. Since then, recovery has been slow with production levels, where known, still
well below those of 1970. The restricted level of activity in the manufacturing industry sector
means that imports of industrial mineral commodities are also limited; details for 1992 are
presented in Table 3. Most imports either originate in Kenya or are imported through Kenya,
which reflects the strong dependence of landlocked Uganda on her neighbour. Of particular note are the volumetrically significant imports of cement and salt which Uganda is currently forced to buy. Despite the obvious demand for these commodities, Uganda’s installed production
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Table 2.
Aggregates
Asbestos
Common clay
Cement
Gypsum
Lime
Limestone
Phosphate (apatite conc)
salt
Uganda industrial mineral production since 1965. Data in tonnes. Source DGSM Entebbe
1965 1970 1975 1980 1985 1990 1992
NA
0
NA
NA
0
19,606
197,403
16,381
302,07 8
163
40,234
194,858
0
21,278
292,033
30,3 18
NA
0
15,893
97,438
0
92 1
NA
NA
NA
0
10,667
NA
0
55 1
76
0
NA
0
NA
NA
0
1,175
35
0
20,047
0
NA
14,000
0
NA
18
25
39,417
0
NA
NA
1,982
NA
1 ,OOo
NA
5,516 2,277 NA NA NA NA NA
NA: not available
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Table 3. Ugandan imports of industrial minerals 1992. Source: Uganda Revenue Authority
COMMODITY TONNAGE MAIN SOURCES
Natural abrasives
Bricks and tiles
Dimension stone
Cement
Chalk
Glass
Gypsum
Kaolin and bentonite
Lime
Phosphate
Silica sand
Refractory bricks
salt
Sulphuric acid
9.9
672.1
78.9
136,919.4
239.5
285.2
95.8
67.5
170.6
56.5
49.8
892.4
54,489.6
120.1
12
Kenya
Kenya, United Arab Emirates
Kenya, United Arab Emirates
Kenya, Tanzania
Kenya
Kenya, China
Spain, Kenya
Kenya, Denmark
Kenya
Germany, Kenya
Kenya
UK, India, China
Kenya
Kenya
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facilities are largely inoperative and require investment to enable repair and provide working
capital.
At present Uganda’s principal manufacturing industries and their industrial mineral requirements
are:
1. Food manufacturing and processing (sugar, grain, vegetable oils and bakeries). Industrial
minerals needed for food production include manufactured and direct application fertilizers, and
Carriers for agrochemicals. In processing food, lime is used for sugar refining, salt as a
preservative, bentonite for clarifying vegetable oils and diatomite as a filter-aid.
2. Beverages and tobacco (breweries, distilleries and soft drinks manufacturers; tobacco
processing). Drinks manufacturers require filter-aids such as diatomite together with small
quantities of gypsum and salt.
3. Textile industry (mills). Few industrial mineral needs.
4. Steel and metal products (including a rolling mill using recycled scrap and factories
manufacturing sheets, wire, nails and tools). Limited use of industrial minerals for present
recycling operations.
5. Construction (cement, lime, bricks and tile factories).
Extensive utilization of aggregates (natural and cfushed), common clay (bricks, tiles and cement
raw material), carbonate rock (lime and cement) and gypsum (cement).
6. Leather products (tanning factories and shoes).
Requires modest amounts of kaolin, lime and chemicals.
7. Printing, publishing and paper (small printers and paper mills using recycled paper). Kaolin is required for paper making but only in limited amounts at present as all production is by
recycling.
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8. Others (wood working, chemicals, paints and plastics).
Mainly requiring specialized manufactured chemical products, carbonate rock and kaolin as
fillers in plastics; paints include small quantities of many industrial minerals such as talc, kaolin,
barite, carbonate rock and pigments.
In this account the industrial minerals of Uganda are grouped under two headings. Considered first are commodities which constitute essential industrial minerals for Uganda’s domestic
consumption and foreseeable development, In times of economic prosperity these commodities
can be expected to be needed in relatively large quantities: for example, limestone for lime and
cement manufacture or common clay for bricks, tiles and pottery.
The second category, other industrial minerals, includes those commodities which although
not presently worked are either known to occur or for which the geological conditions are very
favourable. These are generally higher-value commodities with more specialized industrial uses
for which domestic demand is likely to remain very limited. Such commodities usually require
considerable beneficiation; examples include graphite, kyanite and barite. Given Uganda’s landlocked position, and unreliable transport links to port facilities, these deposits would need
to be amongst the world’s biggest, or best, to become viable as exports.
ESSENTIAL INDUSTRIAL MINERALS
Table 4 shows the industrial minerals that are regarded as ’essential’ for Uganda’s domestic
needs. Only about half of these commodities are actively being extracted since much of the
manufacturing industry is still on a care and maintenance basis. Despite over eight years of stability since President Museveni and his National Resistance Movement came to power in
1986, economic recovery is gradual.
Table 4. Essential industrial minerals in Uganda.
Commodity Principal uses
Carbonate rocks Lime, cement, fillers Clays
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Ball clay Common claylshale
Kaolin
Evaporites & brines
Gypsum
salt Feldspar
Phosphate rock
Sand & gravel
Silica sand
Stone
Sulphur
Ceramics Bricks, tiles and cement
Paper, fillers
Ceramic moulds, cement retarder
Hu man/ani mal consumption , chemicals
Glass and ceramics
Fertilizers
Coarse and fine aggregate
Glass and fillers (silica flour)
Construction and as crushed rock aggregate
Fertilizers and chemicals
Carbonate rocks
Introduction
Although carbonate rocks are found in each of Uganda’s five mineral domains, overall they are of restricted extent, and absent in large parts of the country. Since Uganda has not experienced
marine incursions for more than brief intervals of Phanerozoic time (the last 570 million years),
unmetamorphosed marine limestones, common in many other parts of the world, are absent.
Instead Uganda relies chiefly on intrusive carbonatites and Quaternary tufaceous limestones
(travertines) as her primary sources of carbonate rock. Marbles are common in selected parts
of the basement and its sedimentary cover, but most are remote from the industrialized areas.
Carbonate rocks are fundamental raw materials for the manufacture of cement and lime, and a reliable supply of these commodities is critical for any country. Carbonates for cement need to contain little magnesia which makes many of the deposits, in particular most of the marbles,
unsuitable for this use. Relatively pure lime (CaO) is needed for certain applications such as sugar refining, whilst as a soil conditioner, lime with a reasonable
Carbonate rocks for use as fillers should be relatively easy to grind
a very bright white powder.
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Mg-content is beneficial.
to fine sizes and produce
Resources
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Dolomitic marbles occur within the Karasuk Series of the Basement Complex (Domain A) close
to the Kenyan border in easternmost Uganda. These Karasuk marbles are well developed on
1: 100 OOO geological map sheets 27 and 36 and described in the accompanying memoirs (Fleuty,
1968; Macdonald, 1961). Similar marbles are also reported from adjacent sheets 9, 18 and 26
(unpublished) together with very small occurrences on sheet 45 (Trendall, 1961). Chemical analyses of the marbles are limited, the following compositional ranges - CaO 20.15 - 54.80%,
MgO 0.63 - 21.12% - are stated in Ministry of Water and Mineral Development (1992).
Dolomitic marbles are also present in the Madi Series which forms part of the 'Cover' sequence
(Domain B) east of Moyo adjacent to the Sudanese border. Located in the Gweri Hills region,
these dolomitic marbles occur as thin beds containing accessory minerals such as tremolite and
phlogopite. Anyoli (1977) reports four analyses of the deposit which average 73.7% CaCO,,
13.1% MgCO,, 4.0% SO2, 1.44% Fq03 and 1.12% A1203. Available reserves are put at 4.8
million tonnes by Kabagambe-Kaliisa (1978) but they are regarded as unsuitable for cement
manufacture.
The Carbonatite/Alkali intrusive centres of eastern Uganda (Domain C) are an important source
of carbonate rock. Fairly pure calcitic carbonatite (sovite) is the principal lithology of interest
since it can be used in both cement and lime manufacture. The four most southerly centres
Sukulu, Tororo, Bukusu and Butiriku (a.k.a. Sukululu), are shown in Fig. 3; these lie close to
industrial facilities and populated areas so their economic potential has been investigated in
detail. Carbonatite is also known to be present in several other more remote centres in northeast
Uganda including Napak, Toror and Lolekek but these have not yet been evaluated in detail.
A further carbonatite is reported from western Uganda at Bwera near Kasese; preliminary
studies in 1974 indicated its small size and poor quality (Ministry of Water and Mineral Development, 1989).
Despite the installation of a cement factory adjacent to the Sukulu complex, most of the
carbonatite in this centre contains too much MgO (typically 3.5%) and P205 (3.7%) for cement
manufacture in accordance with, for example, British Standards. Some of the carbonatite has
16
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e e 0 a e e a a 0 e e e 0
0
e 0 a 0
however been used for the manufacture of lime which is utilized for building and road
stabilization .
The nearby Tororo centre however has proved to be a satisfactory source of calcium carbonate
for the manufacture of cement at the Uganda Cement Industry factory. The centre comprises
the Tororo Rock plug (Plate 1) and three smaller hillocks named Limekiln, Cave and Reservoir
hills. Sovite carbonatite from Limekiln Hill (Plate 2) has been quarried extensively, it contains on average less than 1.0% MgO although the P,O, content remains high at 1.7%, yielding 2.4% in the clinker which just exceeds the recommended maximum of 2.25%. This difficulty can be
overcome by the addition of low-phosphate lime and/or fluorite to the batch.
The carbonatites of the Tororo centre have recently been reappraised in a study commissioned
by the African Development Bank and implemented in 1988 by Scancem. The author has not
had direct access to the findings but discussions with cement industry personnel suggest that extraction will continue at Limekiln Hill, where good quality reserves are put at 7 million
tonnes. Extraction here is hampered by mafic dykes up to 3 m wide cutting the carbonatite;
these are being individually extracted for aggregate. Additionally the variable chemistry of the
carbonatite means that selective extraction from the adjacent Cave and Reservoir hills is feasible
(75 million tonnes of medium-grade material), and the same also applies to parts of the Sukulu
complex.
The extensive Bukusu centre farther northeast also contains crescentic outcrops of carbonatite
(Baldock, 1967) which are in parts mantled by thick residual soils. Chemical analyses of the carbonatites indicate the majority to be relatively low in magnesia (most <2.0%) although some
varieties are high in either silica, magnesia or iron oxides or a combination of the three. The
pure sovites contain 48.6 - 54.5% CaO with very little MgO (<0.2%) and appear suitable for
cement manufacture.
The most northerly of the four centres that has been investigated in detail is the Butiriku centre
close to the southern flanks of Mount Elgon and southeast of Mbale. This centre is largely
mantled by residual soils and its solid geology has been deciphered by traditional geological
surveying coupled with geochemical and geophysical surveys and drilling. Carbonatites make
17
- 1-N
- 0 b5N
7 MBALE
SUKULU
TORORO
F
F
TORORO
BUTlRlKU
F
F
Late Tertiary-Quaternary volcanics E3
I F I Fenitisedrocb
Crystalline basement granites 0 0 5 10
kilometres
Fig. 3 Carbonatite/alkaline intrusive centres of southeast Uganda, based on Davies ( 1956).
18
e a a 0 a a a e 0 a e e a a
a
up a small portion of this centre and include Bukiribo Hill near Bududa. This occurrence was
evaluated by a drilling programme in 1982. The study was undertaken with assistance from a
Turkish firm and considered the potential for siting a cement factory nearby. Unfortunately the investigations proved only three million tonnes of good quality carbonatite suitable for cement
manufacture and the initiative was halted.
At Katumeth, which lies at the foot of the southern slope of Moroto Mountain, Macdonald
(1961) recorded the presence of a hard porcellaneous dolomitic limestone with chalky
intercalations very close to the base of the Tertiary Moroto volcanics (Domain D) which in this
area rest unconformably on the basement. Up to 3.7 m of the deposit has been proved in pits.
Three analyses including pure and impure carbonate lithologies gave the following
compositional ranges: MgO 9.93 - 15.72% and SO2 1.09 - 19.86%.
Several small limestone deposits are reported from the Quaternary sediments (Domain E) on the
floor and flanks of the Western Rift in the vicinity of Lake George and Lake Edward. These
deposits are predominantly composed of tufaceous limestones (= travertines) deposited around
the sites of former mineral springs. The deposits are believed to be principally lacustrine
chemical precipitates deposited in higher-level, more extensive predecessors of the present rift
valley lakes.
Three principal deposits have been investigated in detail (Fig. 4) and worked for limestone;
occurrences have also been reported from other localities.
The largest known deposit is the Hima limestone located southeast of the village of Hima which
is on the Mbarara - Fort Portal road about 15 km northeast of Kasese. The outcrop is roughly
triangular in shape and covers about 2.5 km2 of the Kisinga Flat, These limestone beds also
extend laterally beneath other Quaternary sediments as shown by sections along the incised
valley of the nearby Hima River (Bames, 1956).
Within the outcrop area several small knolls are thought to represent the loci of old springs; at
one Bmes (1956) reported that an old vent could still be seen, suggesting that the uppermost
layers are very recent indeed. Near the surface the deposits are principally dark grey compact
20
Basement and 'Cover' sequence
- Railway
30E / )) Mbarsra
Fig. 4 Simplified geology of the Western Rift around Lake Edward and Lake Gmrge showing the locations of key industrial mineral deposits
21
a a a e e a a e a e a 0 a e a 0 a 0 a 0 0 e 0 0 0 0 0
0 0 0
0 0 0 0
micritic limestones with a vughy texture, abundant gastropod shell fragments and subordinate
clay seams. A persistent clay bed up to 5 m thick has been encountered in boreholes, and
separates distinct upper and lower limestone beds (Barnes, 1956) which on average are each over 5 m thick. The abundant gastropods within the upper few metres of the deposit, many of
which retain their ornamentation, have been identified as the genus Limicolana and most
probably L. martensiana which is a terrestrial form; this suggests that the springs that deposited
this tufaceous limestone were marginal to, rather than within, the lake.
Extensive chemical analyses have been performed on this deposit and are reported by
McConnell (1953) and Barnes (1956). These show the limestones to be of low- to medium- chemical grade with variable magnesium and insoluble residue contents, most samples analysed fall within the following limits: CaO 35 - 52 %, MgO 1.5 - 10 % (exceptionally up to 16%),
P205 0.1 - 1.5 %, and insoluble residue 1 - 10 %.
Several exploration programmes have been mounted using pitting and drilling to evaluate the
available reserves. In the first systematic study Barnes (1956) calculated total reserves of 23 million long tons of which 18 million long tons were proven (measured). This estimate included
only 3.25 million long tons from the lower limestone bed. Several subsequent studies have
produced varied estimates; these are contained in confidential preparatory company reports but
are synthesised in a study by the Ministry of Water and Mineral Development (1992). The most
recent evaluation was carried out by Hima Cement Industries and indicated about 18 million tons
of measured reserves of which 14 million tons are suitable for cement manufacture. These reserves are equally distributed between the two limestone beds.
In 1968 a cement factory was installed at Hima to utilize the deposit, but for much of its life
this has only produced a fraction of the installed 300,000 tpa capacity due to civil unrest, lack
of working and investment capital and unreliable power supplies. To date about one million long
tons of limestone have been extracted from shallow (up to 3 m deep) pits (Plate 3). Whatever
the exact reserves it seems certain that sufficent material exists to supply the cement factory,
for at least 25-30 years, even at its original installed capacity,
22
a a a a a a a a
a a a e a a @ a
a a a a e a a a a a a a m
e a
a
The second important occurrence is the Muhokya limestone deposit located astride the
Mbarara - Fort Portal road between mileposts 90 - 97 (128 - 140 km) around the village of Muhokya which lies about 10 km south of Kasese (Fig. 4).
In this vicinity patches of grey compact tufaceous limestone form a discontinuous outcrop incised by numerous boulder and gravel-filled channels containing recent fluvial deposits derived
off the adjacent upland areas. McConnell (1953) provided the first detailed description of the
deposit, recording sections which showed up to 4.5 m of limestone resting on green clays. The
basal 1.2 m consisted of a hard liver-coloured recrystallised limestone which when fned
produced excellent lime for use as whitewash.
The six analyses reported by McConnell (1953) and two further unpublished ones produced at
BGS, indicate that these limestones are of moderate to high purity with compositions in the
ranges: CaO 51.03 - 54.50%, MgO 0.07 - 2.28%, SO2 trace - 3.82%, A1203 + F%O3 0.09 - 3.10% and P20, trace - 0.76%.
The deposit has been used intermittently for lime manufacture since 1945, several small companies are involved, with the largest, the Equatorial Lime Company currently producing
about 2.5 - 3 tons of lime per working day. Calcination is by a vertical shaft kiln fuelled by
charcoal and dry grass. The output is utilized in road construction (for binding and stabilizing
the soil), sugar refining, tanning, and as lime mortars and whitewash. J
The total reserves were estimated by McConnell (1953) to be about 250,000 tons, this must be
Viewed as a very cautious estimate and it is likely that detailed geological surveying would
delineate several times this volume of material.
A third deposit the Dura limestone is located on the eastern side of the Western Rift, north of Lake George, at the point where the Dura (Dwemkorebe) River flows westwards out onto the
valley floor (Fig. 4). Mineral springs are still active today at this locality. Access is difficult
by road but the deposit lies alongside the Kasese - Kampala railway.
24
e e a e a a
a 0 Q
0 a
e e 0 0
e e a
e a e e a a e I)
e a a
The deposits contain three distinct lithologies: powdery marls which are well-developed in the
lower parts of the deposit and as intercalations at higher levels, brown and grey compact
travertines which make up the upper parts of the deposit, and reniform satin spar (relatively
pure calcite) which comprises about 20% of the overall deposit. Barnes (1954) estimated that
the whole deposit contained 1 - 2 million tonnes of good limestone; Seal (1957) estimated the
deposit north of the Dura River at 6 million tonnes of which about 2 million tonnes were of
'good' quality. In this area the deposit is on average 6.5 m thick. Seal also reported the average
chemical composition of the northern part of the deposit as CaO 46%, MgO 2%, Fq03 1%, SiOz 6% and PzOs 0.1 %.
Other deposits of limestone in the region have been reported from Kikorongo, 12 miles south of Kasese (McConnell, 1953), at Katerera on the road from Kichwamba to the fishing village
on Lake George, near the fish landings at Lake Katwe and Katungulu (Ministry of Water and
Mineral Development, 1992), and in the volcanic field that flanks the eastern margin of the Rift around Rubirizi, at Lake Kigezi and Lake Kyamwiga (see published geological map sheets SA 36-1 scale 1:250 OOO and sheet 76 scale 1:lOO 000). Whilst these additional deposits are
probably associated with other mineral springs, and likely to be of restricted extent, they shauld
nevertheless be evaluated.
In addition to the deposits described above there are many other reported Occurrences of small
calcrete and travertine deposits within Quaternary valley infills in Uganda. These deposits are
almost always closely associated with mineral springs and/or outcrops of carbonate rocks such as carbonatites or marbles. Most are too small to provide a regular source of carbonate for
industry but might be used for ad-hoc production of lime for local agriculture and road stabilization. Details of these occurrences can be found on the published geological maps and accompanying sheet memoirs of the Geological Survey of Uganda. Two further deposits
however are worthy of individual mention.
In the extreme southwest the tufaceous Kaku limestone crops out within Quaternary alluvium
along the Kaku River valley about 7 miles northwest of Kisoro. Reserves were estimated at 1
million tonnes (Roe, 1944) but later revised to 4 million tonnes (Ministry of Water and Mineral
Development, 1992). Six chemical analyses of the travertine show the following variations in
25
a 0
a m 0
e
e 0
a 0 e 0
e 0 a a a e e a a
a 0
0 0 a 0
e e a 0 0
0
composition: CaO 50.05 - 50.62%, MgO 2.39 - 3.38%, SO2 0.73 - 2.39%, Al,03 0.18 - 0.68%, FqO, 0.30 - 0.93% and P20, trace - 0.15%.
In eastern Uganda a soft chalky limestone up to 2.5 m thick was recorded by Macdonald (1961)
1.25 miles north of Akomelioret trigonometric station (on 1: 100 000 geological map sheet 36),
but the extent of the deposit at this locality has not been established.
clays
Introduction
Clays are one of tlle most fundamental raw materials for industry and in particular the
construction sector. The overall term 'clays' is used here to encompass several industrial
mineral commodities that are of importance in Uganda. Common clayhhale tends to contain a mixture of several clay mineral species together with other components such as sand, &t or
organic material. It is used in large quantities in cement, brick and tile manufacture.
Less common, and of considerably higher value, are clays which are dominated by a single clay
mineral such as kaolinite-rich clays which can be used either as ballclay for ceramics, or as kaolin (china clay) which has many uses including that of a filler. In contrast to ball clay the
production of useable kaolin nearly always requires substantial beneficiation.
Bentonites and other single species clays, have not been mined or reported from Uganda.
Domestic demand for them is restricted; the likelihood of their occurrence is discussed in the
section on other industrial minerals below.
Uganda possesses extensive clay deposits which include primary/sedentary clays produced by
alteration of materials in situ, and alluvial/secondary clays which are produced by the
transportation and deposition of the clay particles as detrital sediments. In this account the clay deposits are described in general terms with regard to the Industrial Mineral Domain in which
they occur. The widespread residual soils developed in Uganda are considered as an integral
26
a 0
e
a a
0
a 0 0 a e 0
a e
a 0
0 e 0
a a e I)
0 Q 0
0 0
0 e e
part of the underlying geological unit even though their age/development is comparatively
recent. The boundary between such residual deposits and alluvial clays in the present swamps
and drainage tracts is often in reality transitional.
Resources
Clay deposits associated with the crystalline basement (Domain A) include thick residual clayey
soils that blanket large areas and much older clays produced by the hydrothermal alteration of discrete bodies such as pegmatites.
Residual clays developed on the granitoid rocks which constitute much of the basement (Plates
4, 5) tend to be predominantly kaolinitic, and considered as potential ceramic raw materials
would show low wet to dry shrinkage, low plasticity and a very refractory nature. Whilst those
clays developed on amphibolite lenses within the basement and basic schists of the 'cover'
sequence (Domain B) have a tendancy to have a high smectite content and are thus likely to produce ceramic clays with higher wet to dry shrinkage and plasticity and less refractory
properties.
Clay deposits are also present within the 'cover' sequences as variably metamorphosed
argillaceous sedimentary rocks generally of mixed type, which constitute an important
component of many of these sequences and as kaolinitic hydrothermal alteration products of the sedimen ts .
Clays are also an important constituent of the Quaternary sedimentary deposits (Domain E) which floor many of the present-day basins and drainage tracts in Uganda. Their composition is governed by the drainage basin; those from small isolated swamps closely reflect the local
conditions whereas those along major river valleys tend to be more mixed in composition (Gill,
1965).
Details of the most important clay deposits that have been extracted or investigated are as
follows:
27
a 0
a 0 a e e 0 a e e 0 e e e e 0
e e a e 0 0
0 0
e a 0
0
a 0 e e e
Common claykhale
Clays have been dug since the 1940s around Kajansi, some 12 km south of Kampala on the
road to Entebbe. Uganda’s largest mechanized brick and tile factory is located here. Present
production is about 65-70 tons of products per day. The area is underlain by both granitoid
rocks of the basement and metasediments of the Buganda-Toro Series ’cover’ sequence. Most
of the clay used is dug from the alluvial clays of the adjacent valley of the River Kajansi which
drains eastwards to Lake Victoria.
Sections in the working face show up to 2.5 m of alluvial sandy clay, pale grey at depth but
pale brown in the upper metre. Within the clay are patches of medium grained sand occurring
as thin beds and perhaps also as channel infills. These ’waste’ lenses are not dug. Ample
reserves, perhaps enough for 100 years, have been proved adjacent to the pit. The clay is
composed of fine feldspar and quartz with kaolinite and smectite. The clay fraction (< 2pm)
comprises about two-thirds of the sample and is essentially kaolinite and smectite. The liquid limit is 38, the plastic limit 20 and plasticity index 18 (Fig. 5). The clay shows optimum
moulding properties for brickmaking and has an ’ideal’ firing temperature of around 1100°C
(Mathers and Mitchell, 1992).
Brickclays have also recently been investigated in the Namanve valley about 10 Km northeast
of Kampala (Musisi, 1986; Tuhumwire, 1988; Tuhumwire & Katto, 1990). The alluvial deposit
is located on the floor of the Namanve valley and comprises up to 2.5 m of grey plastic clay.
The deposit is surrounded by deeply weathered granitoid basement. A representative sample
(GSMD Ref No. NV/XL 7/P3) has been examined to provide some basic data on this clay.
The sample as a whole contains mainly quartz with kaolinite, feldspar and smectite. The clay
fraction constitutes about 45.5% of the sample and is mainly kaolinite with some smectite. The liquid limit is 31, the plastic limit 17 and the plasticity index 14 (Fig. 5). The clay has
acceptable brickmaking properties; vitrification is gradual with no evidence of bloating and on firing produces an attractive cream-buff colour (Mathers & Mitchell, 1992).
29
Drying shrinkage
L a3 0
; a w
3
t h
B T c)
v1
I .- - L
30
e 0
a 0
e
e a e e 0 0
e a e e 0
e e a
0
0 a 0
0 a 0 0
a 0
e I)
In the 1940s and 1950s bricks were made using clay from this vicinity; however following
recent investigations and pressure from competing mining and environmental lobbies it was
decided to reforest the area, so the deposit has been sterilized for the foreseeable future.
Common clayhhale is also required in considerable quantities for cement manufacture. The
cement plant at Hima near Kasese in the Western Rift utilizes Quaternary alluvial clays
deposited by the nearby Hima River but no data are available on these deposits. In the east the
cement factory at Tororo utilizes a weathered and kaolinized basement rock which crops out on the eastern outskirts of the town of Mbale. This deposit has been characterized by Mitchell &
Fortey (1993) and comprises weathered granite-gneiss (a mixture of quartz, feldspar and mica)
together with about 15% kaolinite.
Ballclays
The Mukono clay has been dug for many years from alluvial-residual clays in the valley near
Mukono, northeast of Kampala. This area is underlain by granitoid basement rocks covered with
thick residual soils. The clay has mainly been utilized as a ballclay in the preparation of ceramic
ware, laterly mainly for African Ceramics Ltd who have a nearby factory. Present extraction
is very small since the factory is presently on a 'care and maintenance' basis.
Data on this clay are presented by Mitchell (1992) and summarized here. X-ray diffraction
studies show it to be composed essentially of quartz and kaolinite (38%) with some albite and
smectite. The liquid limit is 30, the plastic limit 17, and the plasticity index 13 (Fig. 5).
Contrary to the observations of Gill (1965) this clay is of relatively low plasticity. Raw
brightness is 38%, which only improves to 46% on firing - poor values for a ballclay. The clay contains 3.4% sand, 51.7% silt and 44.9% clay.
Kaolins
Hydrothermal kaolin deposits have been reported from many localities in Uganda, and include those associated with pegmatites (e.g. Mutaka), and those produced by alteration and
weathering of sedimentary rocks (e.g. Koki and Namasera).
31
e 0 e e a a e 0 a a
0 a a 0
0 a 0 0
e e e 0
0 0 a 0 0 0
a 0 0 0
Primary hydrothermal kaolins occur in the swarm of pegmatites associated with the post-tectonic
granites of the Kibaran Orogenic Belt in southwest Uganda. An inventory of these occurrences
is given by Reedman (1969) and an account of their emplacement, crystallization history and
diagenesis by Reedman & Lowenstein (1971). Most of the pegmatites are of restricted
dimensions and typically contain a core of quartz flanked by feldspar-rich margins. Many other
minerals of economic importance (beryl, feldspar, and metallics) are found within these
pegmatites, and further details are given later in this report. Some of the pegmatites are almost
completely kaolinized whilst others retain relatively fresh feldspars.
The largest of these intrusions - the Mutaka pegmatite - is partially kaolinized. Material has
been investigated as a potential source of kaolin for use as a filler in paper and other
commodities, and used in raw form in ceramic manufacture.
Investigations by Mitchell (1992) show that unprocessed bulk samples of the Mutaka kaolin
contain about 65 % kaolinite (including halloysite) with some K-feldspar, quartz and mica. The
< 63 pm fraction contains 82 % kaolinite and can be upgraded by hydrocyclone to a product
containing 87% kaolinite with 54% of particles < 2 pm in diameter (recovery 35%). This
fraction has a raw brightness of 80% and a fired brightness of 87%. Transmission electron
microscopy shows subhedral to rounded kaolinite plates and halloysite rods. These data and
others contained in confidential reports seen by the author indicate that a good-quality kaolin
filler can be produced from this deposit.
Given the complexity of a pegmatite coupled with a variable degree of kaolinization, extraction of minerals such as kaolin has to proceed on a piecemeal, or trial and error basis, and will rely
heavily on the experience of artisanial workers. It is probable that similar deposits are present
within the other pegmatites of southwest Uganda and these can be expected to present similar
logistical mining difficulties.
Kaolin deposits produced by leaching of banded shales of the Karagwe-Ankolean 'cover'
sequence have been reported from Kisai near Rakai in Masaka (also referred to as the Koki kaolin) and near Kasambia in Ankole.
32
e 0 0 0 a a 0
e e e e e a a e
The Kisai (Koki) deposit is reported by Barnes (1961) to comprise 2.5 M tonnes and have
potential for use as either a filler, a carrier or a ceramic raw material. Mitchell(l992) examined
a grab sample from this deposit and reported a kaolinite content of only 16%’ a poor colour and
difficulties in up-grading the material. The Kasambia deposit was examined in the field by
Plummer (1969) who concluded it to be very impure and not economical to work.
The Namasera kaolin deposit is located about 5 Km north of Kasanje west of Kampala. The
kaolin is a hydrothermal alteration product of feldspars within aplitic rocks of the basement and
is thus similar to the pegmatite type of occurrence. The deposit is covered by a latente duricrust
which caps Namasera Hill. This occurrence was investigated by Sharma (1972) who estimated
reserves of 64,OOO tonnes of material that could be utilized in ceramic.
Further investigation of a grab sample of the material by Mitchell (1992) indicated a kaolin content of only 18% with quartz as the major component. Washing, screening and then passing
through a hydrocyclone permitted separation of a fine overflow product containing about 80%
kaolinite with clay-grade material constituting 79% of the sample. However the brightness of this upgraded fraction was disappointing, reaching only 50% in the raw state and 66% in a fued sample.
Other localities in the Kampala-Entebbe area that contain low-grade kaolins are reviewed by
Kabagambe-Kaliisa (1 976) and include Buwambo and Migade (kaolinized pegmatites) together
With Combe Hill and Buku Hill (altered sedimentary ’cover’ rocks).
Evaporites and Brines
Introduction
Gypsum and salt are the principal commodities that have been produced domestically from either
evaporite deposits or brines. All Uganda’s potential sources of these raw materials occur in
Quaternary sediments (Domain E) or in associated lake and interstitial brines. In the case of brines, their composition is often such that several mineral salts can be derived from them.
33
a e a 0 rn e o
e
a 0
e 0
a a 0
e 0
rn 0 0 0
0 0
e e e 0 0
0 0 0
0
Gypsum is mainly required for addition to cement clinker where it acts as a retarder enabling
the slow growth of a strong interlocking crystal structure within the cement. Additionally in
Uganda it is currently used in small quantities for the manufacture of ceramic moulds and
writing chalk for schools.
Salt is needed for human and animal consumption and also has an important role in food
preservation. It is also a fundamental raw material for the chemical industry, although this
sector is not yet developed in Uganda. Other important evaporite minerals that are likely to be
of use within Uganda include soda ash or trona (Na2C03) used principally in glass making, and
nitrates and potassium salts for fertilizer manufacture. In recent years brines associated with
saline alkaline lakes in many arid regions have become important internationally as a source of elements such as bromine and iodine.
Resources
Uganda’s best known salt reserves are those in the lake and interstitial brines of Lake Katwe
which lies on the northern shore of Lake Edward in the Western Rift. Lake Katwe is one of a
cluster of small lakes in this vicinity which are confined within Quaternary tuff rings (Plate 6); Katwe’s brines contain a higher proportion of NaCl than the adjacent lakes.
Lake Katwe covers up to 2.5 km2 and comprises a circular western portion about 1.5 km in
diameter from which an arm branches off to the northeast. The lake has a maximum depth of about 75 cm although this is substantially reduced during the prolonged dry seasons. Systematic
sampling of the lake brine throughout 1967 was reported by Morton (1973) and revealed the
following compositional extremes, which resulted from the effects of dilution during the wet
season and evaporation in the dry season.
Table 5 Lake Katwe: extremes of lake brine composition 1967.
Date Water depth S.G. Na K CO3 C1 SO, (cm) (gm4
17.1.67 38 1.30 145 31 55 125 91 24.5.67 61 1.09 39 11 12 42 15
34
Overall
46 1 124
a e a a 0 a 0 a a a a
a
a a
e a a e a e a 0 a a a 0 a e
a a e i.
Pitting and drilling beneath the lake floor has revealed a thick sequence of evaporites and
associated crater-infill sediments. In the upper (lacustrine) parts of this sequence three zones can
be identified:
Upper zone max. 6 m Trona, minor burkeite with accessory halite and hanksite, thin
mud layers, 9.7% insolubles.
Middle zone max. 5 m Massive burkeite and trona, low mud, 7.1 % insolubles.
Lower zone max. 30 m Trona interbedded with muds which pass down into muds.13.2 %
in solubles.
These deposits constitute a large reserve of soda ash (trona) shown in Table 6 below. Whilst
the evaporites contain little crystalline salt (halite) their interstitial brines are rich in sodium and
chloride ions, having a similar composition to that of the lake brines in the dry season (Table
5). The following estimated reserves for the entire brine - evaporite body have been calculated
(based partly on Morton, 1973).
Table 6 Reserves (in tons) of mineral salts at Lake Katwe.
NaCl 1,700,000
Na2S0, 2,000,000
Na2C0, 17,500,000
K2SQ 700,000 KC1 425,000
KBr 10,000
Pumping is the most effective means of extracting the interstitial brines and tests were carried out on some of the exploratory boreholes (reported by Morton, 1973) and in later feasibility
studies by German concerns. These showed that due to the high transmissivity of the evaporite
deposits yields of concentrated brine at a rate of about 13,000 gallons per hour could readily
be achieved from a series of boreholes. This would be sufficient to maintain production of about
36
a a a a a a a a a a a a a a a a a a a a a a a e a a a a a a a a a 0
50,000 tpa of salt which could probably be sustained for at least 10 years before any decline in
brine strength (and thereby production) would become evident.
Salt has been produced by traditional methods from the brines of Lake Katwe for many
centuries. By the middle of this century a regular output of several thousand tonnes per annum
was achieved (Barnes, 1961). After several unsuccessful attempts to start mechanized
production, a German firm, Thyssen Rehinstalin Technick, installed a chemical plant at Katwe
in 1975. This enabled salt and various other minerals to be separated from the brines. The plant
worked for a few years until it failed due to corrosion of the poorly-designed heat exchanger
tubes. Subsequent attempts to repair the installations and restart production during the mid
eighties hit financial problems and the plant has since remained in inoperative.
Salt was also won by traditional methods for a brief period in the 1950s from Lake Bunyampaka (Kasenyi) which also lies within a tuff ring, north of the Kazinga Channel near Lake George.
Many of the other volcanically controlled lakes in this region contain sulphur which makes them
unsuitable for salt production (Barnes, 1961).
Very small quantities of salt have also been extracted from hot springs at Kibiro in the Lake
Albert section of the Western Rift. This, together with records of saline water encountered
during oil exploration drilling in the same basin, gives credence to the idea that recoverable
brines may exist at depth within the pores of the thick rift valley sediments.
Gypsum is very scarce in Uganda, the only occurrences being of disseminated crystals of gypsum/selenite within alluvial Quaternary clays (Domain E). The gypsum is thought to have
originated diagenetically possibly by the interaction of volcanigenic sulphur with calcareous
sediments. These deposits are of low-grade and require substantial beneficiation to produce
saleable concentrates of gypsum.
The most important Occurrence of this type is around Kibuku at the boundary of the rift with
the northem-most extension of the Ruwenzori range. Around the point where the Kisege River
leaves the upland area and flows out onto the rift floor a sequence of sandstones and clays
belonging to the Kisegi - Kaiso Beds is exposed. Gypsiferous clays up to 6 m thick crop out
37
0
a a a a e 0
e e 0
e e 0 0 a a a a a a a
a 0
e 0 0 0 0
a a e 0 0
a
over an area of about 2 km2. On average the clays contain 10% gypsum providing total reserves
estimated at 1.2 million tonnes (Kabagambe-Kaliisa, 1977). The gypsum comprises transparent
selenite crystals commonly 10 - 20 cm in diameter embedded in the clay and forming narrow
crosscutting veins. The richest seams lie close to the surface, crystals also abound as float
where they have accumulated as a lag deposit following washing away of the host clay.
Artisanial extraction of the gypsum crystals using hand tools and screening has taken place in
the last couple of years at Kibuku in order to supply the cement factory at Hima some 120 km away. Total production by mid-1992 was of the order of 1,500 tonnes, which has been sufficient
to meet the factory’s demand as it is only operating at about 10% of its installed capacity.
Should the Hima factory return to full production it seems unlikely that the deposits at Kibuku
could supply all the demand.
Two other geologically similar deposits have been investigated but no extraction has occurred. The first is in the Quaternary alluvium of the Kashara River which drains into Lake Mburo in
eastern Ankole. An area of 6 km’ to the north of the 1,ake was investigated by pitting and revealed a discontinuous 30 cm layer of gypsiferous clay usually at depths less than 2 m. Detailed pitting of the most promising area covering 55,000 m2 indicated about 1.1 million
tonnes of gypsiferous clay capable of yielding about 2.6% gypsum. The low gypsum content,
coupled with the subsequent establishment of a game reserve at this locality, make it unlikely
that this deposit will ever be worked.
The second prospect lies around Kanyatete amd Muhokya on the Lake George flats. The richest
concentrations of gypsum in these localities barely exceed 1% of the host clays, making them
uneconomic to work.
Feldspar
Introduction
Whilst feldspar is a common mineral in many sedimentary, igneous and metamorphic rocks,
38
0 a 0 0
0 0
0 a a 0 0 0 e a 0 8 a 8 a a e 0 a a
a e e a
0
0 8 a a
relatively pure concentrations of the mineral which are of economic value are rare. These usually include occurrences in pegmatites and very feldspathic sandstones (arkoses). It is the
alkali (Na, K) feldspars that are principally sought by industry as a source of alumina and alkali elements. The latter constitute a useful flux in industrial processes such as glassmaking and the
fkng of ceramic ware. The alkali feldspars are more commonly associated with granitoid rocks
and their derivatives, whereas more calcic feldspars tend to occur in more basic igneous rocks.
Small amounts of feldspar have been mined from pegmatites in various parts of Uganda and
used principally in the production of ceramic ware and to a lesser extent in abrasive powders.
None of these sites are currently producing feldspar although small quantities have been
excavated from the Mutaka pegmatite from time to time.
Resources
The mode of occurrence of minerals in pegmatites mi1ita;s agains. mechanized mining and the
precise quantification of available reserves. Mining of these bodies in Uganda has traditionally
been artisanial, simply involving the use of hand tools to excavate and trace pockets of the
required mineral. In the absence of any significant demand for feldspar in Uganda it is probable
that this piecemeal approach will continue.
Several pegmatitic occurrences of microcline feldspar are mentioned by Barnes (1961): at
Bulema Mine in Kigezi, Nyabakweri in Ankole, Wabiyinja and Nakabale in Buganda, and
Lunya in Kyaggwe. Feldspar from the latter locality was exported to Kenya for use in ceramics
during the 1940s (Pallister, 1959). It is probable that many of the pegmatites in southwestern
Uganda, which have not been heavily kaolinized, contain recoverable quantities of microclhe
feldspar.
Published analyses of the chemistry of the feldspars that have been extracted are limited to the following:
39
Table 7 Analyses of Ugandan feldspars, from Pallister (1959) and Mathers & Mitchell (1992).
Mutaka Lunya Lunya
white microcline green microcline white orthoclase
SiO, 64.82 63.71 63.73
A1203 19.41 19.51 19.37
Fe203 0.53 0.14 0.48
K20 13.23 15.00 15.00
Na20 2.04 1.75 1.75
These are potassic types which have been used almost exclusively in the production of ceramic
ware.
Phosphate Rock
Introduction
No mineral is more important to life - plant and animal - than phosphate. It is an important
constituent of the genetic material DNA and its compounds are essential to the energy functions of all living systems. Phosphate occurs in all igneous and sedimentary rocks; its average content
is 0.1 - 0.2%. In igneous rocks such as carbonatites crystalline hydroxy fluorapatite
Ca5(P04),(OH,F) is the commonest phosphorus-bearing mineral, whereas in marine sedimentary
rocks (phosphorites) fine grained fluorapatite (francolite) C%(PO,CO,OH),(F,OH) predominates.
Rocks containing economic concentrations of phosphorus are termed phosphate rock, most
economic deposits containing at least 20% P205.
Phosphate rock is used primarily in the manufacture of NPK fertilizers which are essential for intensive agriculture. Such fertilizers are widely used in low latitudes where many soils are phosphorus deficient. Under certain conditions, for example on acidic soils, ground phosphate
rock can also be applied successfully as a direct application fertilizer.
40
a e * 0 0
a 0
e e
a e e 0
0 0
e
a 0
e
a 1,
0 e a 0 0 * e 0
e
Sedimentary phosphates have not been recorded in Uganda and so the carbonatite complexes
in the eastern part of the country constitute the only potential source of phosphate rock. Whilst
the apatite content of the crystalline carbonatite is low, the thick residual soils that commonly
develop on it contain high concentrations of relatively insoluble minerals such as magnetite and
apatite. These constitute an important source of phosphorus in Uganda; the residual deposits
from the Sukulu and Bukusu carbonatite/alkali intrusive complexes have been utilized
commercially and details are given below.
Resources
The most important phosphate rock resources are those of the deeply-eroded Sukulu intrusive
complex (Plate 7), located some lOkm southwest of Tororo. The complex is about five kilometres in diameter and contains ridges and knolls composed of carbonatite and attendant
breccias which are flanked by several depressions and valleys in which residual soils, locally
over 50 m thick, are found (Fig. 6). The detailed geology of this complex is described by Williams (1959).
Total reserves of residual soils at Sukulu have been calculated to be about 230 M tonnes
averaging 12.8 % P205, (Bearden-Potter Corporation, 1982). The soils are composed essentially
of magnetite and apatite together with accessory goethite, crandallite, quartz, pyrochlore and
zircon. The apatite content is variable, and can locally exceed 30% of the soil, but typical
assays indicate 1 1 - 15 % P205.
Between 1962 and 1978 the company Tororo Industrial Chemicals and Fertilizers (TICAF)
extracted the residual soils from an opencast pit in the North Valley (Fig. 6). According to
Bloomfield (1973), the dug soil was slurried at the pit, passed through magnetic separators and
a hydrocyclone and then pumped about lkm to the plant. The slurry was then ground to -150
mesh (< 106 pm) followed by further magnetic separation and desliming. The pH was then
controlled by adding caustic soda and a flotation agent added before a two-stage froth flotation
extraction of an apatite concentrate (about 41.5 % P20,). Over the period of operation (1962-78) about 2.16 M tonnes of soil were processed to produce 160,000 tonnes of apatite concentrate.
41
a 0
e e 0 a e 0 a e a 0 c 0 0 0
e 0 a m 0
0 e a 0 0
0 a
0 0 0 e
Carbonatite Sukulu-tvDe soil . I
Savite-breccia Laterite
0 A
fi h
A
\. . . . . . . . . . . . . . . . . . FEET
0 0 0- 500 loo0 1500
METRES
n . . . . . . . . . . . . . . . . . . . . . . . . .
Fig. 6 Geology of the Sukulu wbonatite complex, based on Williams (1959).
42
a 0 a 0 * 0
e 0 a 0
e 0 .. 0
a 0 a 0 0 0
a 0
e 0 0
0 a 0 a
0 0
e
The concentrate was treated with strong sulphuric acid which produced about 21 % water-soluble
P20s which was sold as single superphosphate fertilizer. Some 22,390 tonnes of this product
were manufactured in 1969.
In the eighties the Sukulu soils were re-evaluated in a series of studies by the Bearden-Potter
Copration (1982) and on their behalf by McClellan & Cooper (1982) and the International
Fertilizer Development Center - IFDC (1983, 1984a, 1984b, 1984c, 1985). These studies
investigated and identified the processing requirements to produce a wide-range of manufactured
phosphate compounds for use in fertilizers. The results are summarized in IFDC (1988).
Attempts have also been made to assess the processed concentrates as a direct application
fertilizer, tests over three years were generally not very encouraging although the use of a
partially acidulated product was effective (Rwakiseta-Tanaako, 1987).
The Bukusu complex is Uganda's, and probably Africa's largest carbonatite/alkali centre being
some 13 Km in diameter. It lies between Tororo and Mbale (Fig. 3). In contrast to Sukulu,
carbonatites at Bukusu are poorly developed. The principal Occurrences form crescentic ridges
in the south and western segments of the complex; these carbonatites contain 2-15% apatite and
are embedded within ultramafic intrusives. Thick (up to 60 m) residual soils are developed on the carbonatites (Baldock, 1973; Bloomfield, 1973).
Phosphate rock has been mined from small pits along a ridge at Busumbu in the extreme south
of the complex (Fig. 7). This occurrence is unusual since the phosphate occurs both as crystalline apatite in residual soils containing about 15% P20s (locally known as "soft" rock)
and also as a secondary phoscrete (a concretionary hard pan) rich in francolite and averaging
30% PzOs ("hard" rock).
This occurrence was described in a series of reports on the evaluation of reserves, mine status
and processing written by staff of the Uganda Geological Survey between 1950 and 1960. The
most important are by Taylor (1954, 1955, 1960). Mining at Busumbu commenced in 1944 and
continued to 1963. Until 1956 the "hard" rock was blasted, excavated, crushed and screened before being exported to Kenya for the manufacture of citric-soluble soda phosphate through mixing with soda ash and calcining. The undersize material (< 1") was used locally as a direct-
43
0
0 0
a
0 e a a 0
0 e 0 a 0 0 a 1)
0
0 0 e 0 e 0
e 0 0 0
.
Fig. 7 Geology of the Bukusu carbonatite/alkaline complex, based on Baldock (1967).
44
application fertilizer which was found to be beneficial owing to the relative solubility of
francolite compared to crystalline apatite. From 1956 onwards a change in customer
requirements meant that the "hard" rock production was discontinued and was replaced by %oft"
rock and naturally occurring mixtures of the two. This loose soil was up-graded to the required
P205 content by screening and magnetic separation prior to shipment. The "hard" rock quarried during this later phase was stockpiled on the quarry floor where it remains. Production
throughout the 1950s was at maximum 6,000 tpa of processed ore. Taylor (1960) estimates an
output of 12,000 tonnes for the period 1955-60. Production ceased on a large scale in the early 1960s when TICAF established their operation to manufacture fertilizers from the soils of the
Sukulu complex about 25 km to the southwest. Remaining reserves at Busumbu were cited by
Hadoto (1992) as: "hard" rock 18,300 tonnes (av. 30% P205), 13,000 tonnes of "mixed" rock
(av. 21% P2O5) and at least 1 M tonnes of soft rock (av. 15% P205).
A recent inspection of this occurrence by the author confirmed that the site is still much as described by Taylor in the 1950s with the dumps of "hard" rock still present around the now
overgrown pit. Samples were collected for analysis and the results are presented in Fig. 8 and
Tables 8 and 9. It is interesting to note that occurrences of "hard"' rock are elongate with a
tendancy to follow the trend of the ring intrusions. Their distribution may well be controlled by
lithological contacts, faults or shear zones within these intrusives. Some support for the latter
possibility is afforded in Mitchell & Fortey (1993) who report that many of the grains in
samples of "hard" rock appear to have been affected by cataclastic processes.
The Busumbu ridge is also being re-evaluated as part of the DGSM - UNDESD Minerals
Project and the available reserves of "hard" rock have reportedly been extended by new discoveries. The future importance of this occurrence hinges on whether ground "hard" rcok
can be used as a low-cost source of water-soluble direct application phosphate fertilizer with
demonstrably superior properties to those of fine ground apatite. Agronomic studies are in progress to investigate this possibility.
Many of the other carbonatite/alkali centres of eastern Uganda have bodies of carbonatite
intrusives on which residual soils are developed; these include Tororo, Butiriku, Nap& and
Toror. The deposits at Tororo appear to have been sterilized by urban expansion. The potential
45
0
0 a 0
,/' /-----_ Small, degraded, disused quarry r,./'
__.e-
___. 5hoo 4,' ,./ _,-
/ / ///'&@& -- - __ -.- -. /
/ / P' / @g,
/ /
/ *... ..'- / ,/ SM23
/ / %
/ _/," ,/'
/ ,I'
_._ /' I'
/- /
/
,/' / /'
/'
0 Quarryface
*---- I '
'--__- I ) Dumpedrock
Outcrop of Phoscrete
0 fwt 400
I I 0 m a n s 100
SM2O 0 Sample location
Track ------
-- 3aw -- Contour, height in feet
Fig. 8 The Busumbu phosphate deposit.
46
m m - 0 3 0 O d d
m b - - 0 0 0 0 0
O o ; 0 V i N m
b * 0 0 - M
O N O W N N 0 0 0
m CI
E cn
3
2 m VI
47
a e e e Table 9 0
Apatite content of phosphate rock samples from Busumbu.
OS a m pl e (Wt %) ratio
e 0 OSM18 Busumbu Mine dump 24 0.49 aSM19 Busumbu Mine dump 55 1.28 eSM20 Busumbu Mine outcrop 86 1.38 a S M 2 1 Busumbu Mine dump 17 1.38 eSM22 Busumbu outcrop (4) 67 1.24
SM23 Busumbu outcrop (2) 69 1.39 a 0
A pat i t e con ten t CaO : P20 j
w N.B. Apatite calculated from P205 content and assuming pure apatite to contain 42% P&.
0
48
e a 0 0 0 e e 0 0 a e a 0
0 a e 0
e
0
0 a a e
a e 0 0 a 0
at Butiriku is limited and has been outlined by Reedman & Mullingar (1974). To date the
phosphate potential of the other sites has not been fully evaluated since large reserves are proven
at Sukulu which is much more favourably placed with regard to existing infrastructure and
markets.
The possibility of utilizing phosphatic sediments (10% apatite) found the Lower Bugisu Series
Crertiary) of Nkokonjeru Mountain and around the flanks of Mt Elgon has also been mentioned
by Davies (1956) and Bloomfield (1973). These deposits are probably derived from a concealed
mbonatite in this region but are unlikely to provide an economic source of phosphate rock.
Sand and Gravel
Unconsolidated sand and gravel deposits suitable for use as a local source of coarse and fine aggregate are found widely within the Quaternary Sediments (Domain E) of Uganda. Most of the worked deposits are from alluvial or beach systems and are taken to include the deposits
found in the present day river courses and on beaches. Clearly the best deposits are to be found
in association with the major rivers, around the major lakes and at the margins of Quaternary
sedimentary basin such as the Western Rift. Extraction tends to be haphazard and sporadic
depending on local construction needs; estimates of the volumes extracted are thus likely to be well below the actual volumes used. A further source of coarse aggregate that has been utilized
locally is the abundant pebble-sized iron-concretions that are found within strongly developed
lateritic soil profiles.
Silica sand
Introduction
Beach deposits rich in silica have been reported from the shores of Lake Victoria and the isl ids
within the lake. The location of these deposits is usually controlled by the presence of quartzites
in the basement and "cover" sequences from which high silica sands can be derived. Several
49
e 0 a 0
a
e a a
e a a a 0 a e a a a a a 0 a e a
0 0
0 0 e e
promising deposits are mentioned by Barnes (1961) and some basic grain size and chemical data
presented; however most of these occurrences have not been investigated in detail. Since these
silica sands form attractive white beaches which are located in the more developed part of
Uganda, they must also be viewed as an important asset for tourism and so extraction may need
to be carefully planned and regulated.
The principal use of silica sand is in glass making. Chemical purity is important in this
application since even modest iron, chromium and titanium contents preclude use in colourless glass, coloured (container) glass specifications are less stringent. Grain size is also important
in glass making since coarse or poorly-sorted sands require more energy for fusion. Silica sands can also be ground for use as a filler (silica flour), for example to give strength in ceramic
batches.
Resources
Deposits of silica sand on the south side of Kome Island near Bega Point (Barnes, 1961) and
at Bukakata east of Masaka (Pallister, 1959) were extracted in the 1950s and 1960s for use in
the container-glass factory at Jinja and for export to Kenya. Barnes (1961) reports exports of
about 6,000 tpa from Kome Island at that time.
Several other localities are known to have high silica beach sands (Fig. 9); these include the
beaches at Entebbe, Nyimu, Nyoba and Nalumuli Bays and Kabugoga in Kyaggwe southeast of
Kampala, and Ziro Island in Busoga east of Jinja (Bames, 1961). In a brief study of the glass
sand potential of two of these occurrences, Trendall (1956) estimated resources of 200,000 tonnes at Nalumuli Bay and 50,000 tonnes at Nyimu Bay.
More recently reported is a large deposit at Diimu (Dumu) southeast of Masaka initially
evaluated by Mukinda (1972, 1973). The site is currently being studied as part of the DGSM - UNDESD project. Mukinda’s study worked southwards from Diimu fishing village (Plate 8)
using the shoreline as a baseline. The beach sediments were sampled on crosslines every 50 m for a distance of 6.5 km (almost to Malembo fishing village). Over most of this distance
samples were collected from pits located 5-10 m and 25 m from the shore producing two
50
'1
*
I I I I I I I I I I I I I I I I I I
5 a a
z N z t-
I
51
e a e e e a
a a a a
a
e 0 e a e 0 e e e 0 0 e e 0
@ 0 0 0 0 0 0 0
0
samples every 50 m. A second older beach deposit - the "old" deposit - forming a low ridge
about 100 m inland was also sampled systematically. Pits were terminated at the base of the
sand or the watertable whichever was encountered first. The maximum thickness of the deposit
is about 2.5 m with the average about 1.0 m.
In his first report Mukinda (1972) presents results for the first 2.5 Km of the beach from Diimu
southwards. Grain size distribution, magnetic separation, analysis of FqO, content and heavy
mineral identification together suggest that the present day beach deposit is mostly suitable for
making coloured glass with little beneficiation; reserves were estimated at about 100,OOO tonnes.
The "old" deposit however is too coarse and impure for use.
In his follow-up study (Mukinda, 1973) examined a further 4 Km of the beach southwards
toward Malembo. Whilst this study is less thorough it does suggest that over much of this
southerly stretch the beach and "old deposit" sands are too coarse for glassmaking.
Grain-size data and analyses of three grab samples from around Diimu village are also reported
by Mitchell & Fortey (1993) who concluded that untreated, they are suitable for coloured glass
and that they could be readily upgraded for colourless glass production. The deposit is currently
being re-evaluated as part of the UNDESD-DGSM minerals project.
One point that needs to be borne in mind in assessing beach sediment resources is that they
often show considerable grain-size and compositional variation normal to as well as along the
shoreline as shown by the brief study of Lido Beach, Entebbbe, reported in Mitchell and Fortey
(1993).
Stone
Much of Uganda is underlain by hard durable crystalline and indurated rocks in the basement
(Domain A), the sedimentary 'cover' sequence (Domain B), and the carbonatite/alkali intrusive
centres (Domain C). In areas where these lithologies are not overlain by deeply weathered soil
profiles, and so can be easily dug, they provide a useful raw material with which to produce
53
e e e e e e e e e 0 e a e e e e e
a
a e
e e e e e e e 0
a e e e
crushed rock aggregate and building stone.
Particularly favoured lithologies are the basement granite-gneisses, quartzites within the ’cover’
sequence, and carbonatites each of which provide good-quality crushed aggregate. Although of inferior quality in terms of durability amphibolites have also been used in the Jinja area. The lavas and tuffs of the Tertiary - Quaternary volcanic fields (Domain D) are generally of low
strength and are not a viable source of material (Barnes, 1961). Uganda has abundant supplies
of stone for aggregate, but extraction is generally on a small scale for specific construction
projects and production statistics are very difficult to compile with any reliability.
Sulphur
Introduction
Sulphur is a key industrial mineral with applications in most industries, in particular for the
chemical industry. Sources are of two types; naturally occurring ’voluntary’ sources including elemental sulphur and sulphur minerals, and ’involuntary’ sources produced as by-products of
other industrial processes such as oil refining and base-metal smelting. Uganda presently lacks
the industrial installations that are able to produce ’involuntary’ sulphur but has several possible
’voluntary’ sources which are described below although to-date none of these have been used
to produce sulphur. Uganda’s principal requirement for sulphur is for manufacturing basic chemicals such as sulphuric acid which are utilized in many industrial processes, for example
in the manufacture of NPK fertilizers.
Resources
Sulphide mineralization is well developed within amphibole schists of the basement Middle
Kilembe Series which crop out in the southern part of the Ruwenzori Mountains in western
Uganda. Copper, occurring as chalcopyrite, was mined at Kilembe between 1956-77; pyrite
tailings meanwhile were stockpiled nearby close to the railhead at Kasese. Kisutu (1989)
provides the following reserve estimates for the stockpile of about 1.1 M tonnes.
54
e m e e e e e 0 e 0
e * a e a e e e e e a e
e e e e e e a e a a
Table 10. Elemental reserves in the pyrite tailings stockpile near Kasese.
Element % Potential reserves
Sulphur 42.4 466,400 tons
Cobalt 1.35 14,850 tons
Copper 0.36 3,960 tons Nickel 0.17 1,870 tons
A further 350,000 tons of pyrite sulphur are thought to remain unmined within the Kilembe
concession whilst further reserves could probably be located in adjacent areas. Plans have
recently been advanced to bioleach the stockpile to produce cobalt for export.
Other potential, but minor sources of sulphur include the brines of Lake Katwe which contain
H,S which could be converted to sulphur or sulphuric acid as a by-product of salt production.
The presently moribund salt factory near Lake Katwe has the capacity to produce about 500 tpa
of by-product sulphur.
OTHER INDUSTRIAL MINERALS
The 'other' industrial minerals considered in this section are commodities which have seldom,
if ever, been worked as industrial mineral raw materials in Uganda.
Domestic demand for most of these commodities is very limited or non existant, and is likely
to remain so for the foreseeable future. Deposits of a size and quality suitable for export
internationally are geologically rare and the chances of encountering new occurrences of this sort must be considered very slight.
Asbestos
Asbestos is a generic term applied to fibrous varieties of several silicate minerals of which
55
a e a 0 a a 0
0 0
Q a 0
e 0 0
0 e 0
0
6
a 0
0
e 8 0 0 e 0 * a
chrysotile (fibrous serpentinite) is the most important. Chrysotile usually occurs in stockworks
of thin veins within serpentinized ultramafic bodies in basement terrains. Asbestos has mainly
been used for its resistance to heat and chemical attack in textiles and for its strength and
insulation properties in cement-based products. The world market for asbestos is declining
rapidly due to concerns over the health and safety aspects of its use, future exploration and
exploitation of this commodity appear unlikely.
Barnes (1961) reports that several minor occurrences of asbestiform anthophyllite and tremolite
are known from amphibolites in the basement terrain (Domain A) of West Nile, Acholi and
Karamoja. These deposits are in remote locations and there has been no sustained working of the deposits.
Subsequent more detailed evaluations have been carried out on a deposit at Nakapiripirit in
Karamoja (Mboijana, 1974) and Anzaiya near Arua in West Nile (Kabagambe-Kaliisa, 1976)
although in both cases the poor quality of the deposits meant that no firm estimate of available
reserves was attempted.
Barite
Barite (BaSO,) is the most abundant of the barium minerals; it occurs in sedimentary, igneous
and metamorphic rocks of all ages. Its mode of occurrence is variable, and includes veins,
residual deposits and stratiform layers. Barite is utilized in many ways including applications
in drilling muds, chemical manufacture and as a filler. Barite is commonly produced as a by- product of mining for metallic ores.
Barnes (1961) reported a promising occurrence of barite at Mugabuzi Hill in northwest Ankole
associated with haematite lenses in granite-gneiss of the basement. A detailed study of this
prospect was undertaken in the early 1980s and is summarized in Ministry of Water and Mineral
Development (1989), the prospect of recovering significant amounts of barite does not seem to
be supported by this later study.
56
Another potential source of barite is the residual soils of the Sukulu carbonatite complex which
contain accessory barite. If the soils were once again worked for the phosphate content, by-
product barite could probably be produced during beneficiation providing sufficient demand
existed.
Two other very small occurrences of barite are mentioned in Barnes (1961) in a pegmatite near
Katoma Hill in western Ankole and as veinlets in brecciated basement gneiss along the Lolachat
River in Karamoja.
Bauxite
Bauxite is an impure mixture of aluminium oxide minerals such as gibbsite, boehmite and
diaspore. The most abundant bauxite deposits occur as lateritic soils which blanket long-
established erosion surfaces in many tropical and semi-tropical locations. Commercially useful
deposits require an A1203 content of at least 45%. Most bauxite mined is used in the
metallurgical industry to manufacture aluminium, however some finds use as an industrial
mineral in the manufacture of chemicals and as a cement raw material.
Some of the lateritic soils developed in south central Uganda are known to contain a substantial
A1203 content. These deposits are up to 3 m thick and are widely distributed forming flat-topped
hills in the area at two principal altitudes; between 4200-4800 ft and 3400-3800 ft (Bracewell,
1962). A report of diaspore from Kawere Island in Lake Kyoga in 1920 was not substantiated
by subsequent detailed examination.
Bentonite
Bentonite is the commercial term applied to smectite (mon tmoril1onite)-rich clays and includes variants rich in sodium and calcium. Sodic forms are relatively rare in nature, and are noted for
their ability to swell by absorbing considerable amounts of water, in addition they have a high
dry strength and moderate wet (green) strength. Conversely calcic forms have a low dry strength
57
a 0
a 0 e e a 0 m 0
a e
e 0 0 a
0 0
c e 0
0 0 a 0 a 0
0 0
e
but high wet strength. Calcic forms can be converted into sodic forms for use in industrial
applications.
Most deposits of bentonite occur in Cretaceous or younger strata generally in beds less than 5
m thick. High-purity beds less than 1 m thick can be worked economically. Most deposits result
from the in-situ weathering of metastable volcanic products such as glass and ash. Bentonite is
used in a very wide ranging series of industrial applications including drilling muds (Na
varieties) as a binder for foundry sands and pellets, as a carrier for agrochemicals, and in clarifying vegetable oils.
There are surprisingly few reports of bentonitic clays in Uganda despite the widespread
development of Tertiary-Quaternary sediments with closely associated volcanism. This may
reflect the difficulty of identifying bentonite in hand specimen from other clay deposits rather
than its general absence. Indeed most studies of clays in Uganda to date have focused on clay
deposits close to the major urban areas that are required for the manufacture of bricks, tiles and
pottery. Bentonite-rich clays can be expected to be common within sediments intercalated with
the Tertiary - Quaternary Volcanics (Domain D), in the Quaternary Sediments (Domain E) and
in soils developed on basic - ultrabasic lithologies within the basement (Domain A).
Gill (1965) cites evidence for bentonite within the Quaternary sediments of eastern Uganda.
Here black cotton soils typically rich in smectite are developed on alluvial deposits in northwest
Sebei, central Karamoja and north Teso, these deposits are referred to as the Sebei Clay (Ollier
& Harrop, 1959).
Other reported occurrences include the valleys fringing Lake Victoria south of Lunyo and the
sediments in the Lake Albert segment of the Western Rift north of Butiaba and near Buhuka in
the south. Further evidence on the widespread occurrence of bentonite-rich clays within the
Quaternary sediments are afforded by the study of the Kibuku clay by Mathers & Mitchell
(1992). The study indicates a smectite content of 34% for this clay which hosts the gypsum
deposits described above.
58
0
a
e
a a
e
0
0
* 0 e
8 e 0
* a
0
e a e e
a a a *
Diatomite
Diatomite is a soft, pale-coloured sedimentary rock composed mainly of the skeletal remains
of diatoms - minute aquatic algae commonly 20-200 pm in diameter. Diatomites are found as thin beds (usually less than 5 m) within marine and lacustrine sedimentary sequences and usually
in close proximity to active volcanism which provides the abundant soluble silica necessary to
build the diatom skeletons. Commercially useable deposits are invariably late Tertiary - Quaternary in age. Processed diatomite powders have a unique physical structure, are
moderately refractory and chemically inert. They are used in a wide variety of industrial
applications but principally as filter-aids, fillers and mild abrasives.
Beds of diatomite have been identified in the Quaternary sediments (Domain E) of the Western
Rift, located on the western bank of the Albert Nile around Pakwach (Hepworth, 1957). Three principal occurrences are known around Panyango, Atar and Alui (Fig. 10).
Around Panyango, approaching 100 m of almost horizontal Quaternary deposits crop out along
the west bank of the Albert Nile. A broad tripartite sand-clay-sand sequence can be recognised,
with the clay-rich middle unit being about 35 m thick. In the upper 15 - 20 m of this clay-rich
unit six diatomite beds are present with an aggregate thickness of about 6 m; the thickest
individual bed is about 3.65 m thick (’12ft bed’). Visual inspection led Hepworth (1957) to
conclude that the material was of moderate to good quality and he estimated that 75,000 - 100,OOO tons of available reserves would be available assuming stripping to a limit of about 5
m of overburden.
In the occurrence near Atar (Fig. lO), Quaternary sediments are exposed in a low eroded fault
scarp; here about 1 m of variable diatomite is overlain by 2.5 m of overburden. Near Alui a 1.5
m bed of diatomite is present beneath 1.0 m of overburden whilst a further bed 0.9 m thick
occurs about 15 m up the sequence. Mubiru (1978, 1983) described pitting programmes to
investigate the deposits at Panyango, Atar and Alui. Unfortunately the maps showing the
locations of these pits have apparently been lost and therefore the work is thus of little value.
Mubiru (1983) reported that 33 out of 44 pits sunk at Panyango proved diatomite and 48 out of
54 at Atar were also successful. The Alui deposit was shown to be impure and pits suggested
59
e a 0 8 e e 8 * c 0 a 0 0
a 0 r )
e 0 e ii
b ’m N
I
I
I i
x x x x x x
x x x : x x x x
2 N
X I ? 2%- \ x x x x
Rift Sediments
60
0 e 0 a .. 0
c, * 0 e e 0 @
a 0 8
0
0
0 0 c 0 e 0
0 0 a a
it had a limited lateral extent.
These deposits have not been visited during the compilation of this work because of the security situation in the north of the country. A sample, presumably from the investigations of Mubiru
and most probably from Panyango, has been evaluated at BGS Keyworth, the detailed results
are reported in Mitchell (1992) and Mathers & Mitchell (1992). The sample was shown to
contain mainly amorphous silica (diatoms) and 39% kaolinite, chemical analysis showed SiO,
63.33 % , A1203 21.86% and FqO, 2.75 % . A study of a diatomite sample from the Panyango deposit is also mentioned in Ministry of Water and Mineral Development (1989) having been
carried out by a UNDP worker. This reports that 84% of the sample tested was between 53 pm
- 2 pm and this fraction comprised almost pure diatomite; this is clearly at variance with the
BGS findings (39% kaolinite) but may well reflect variation within the deposit.
Further diatomite Occurrences are known around Parombo (Sheet 29/1) 30 miles west of
Pakwach, and in the valleys of the Umvosa and Amboso rivers 50 miles north of Pakwach
(Sheet 1311) where a 2 m bed of diatomite is reported to occur (Barnes, 1961; Mubiru 1983).
Garnet
Almandine garnet is used widely in industry as an abrasive due to its hardness and high
resistance to physical and chemical attack. Garnet is a common mineral in high grade
metamorphic rocks. Barnes (1961) observes that weathering of garnet-bearing gneisses in the
basement rocks of Karamoja may provide a possible source of garnet should it be required.
Unfortunately much of the garnet that was present in schistose rocks has been altered to
limonite.
Graphite
Graphite is produced as the result of metamorphism of organic material in sediments.
Amorphous (microcrystalline) graphite tends to be present in a finely disseminated form in low-
grade metamorphic rocks; with increasing grade it is converted to coarsely crystalline flakes of
61
graphite commonly up to about 25mm across. Deposits tend to be stratabound reflecting the
original sedimentary distribution of organic material. Most economic deposits come from
Precambrian basement terrains and typically contain 10- 15 % graphite; these require up-grading
to produce concentrates prior to transport. Graphite is a very good electrical and thermal
conductor and is extremely refractory. Most graphite is utilized as either a refractory material
as in bricks and crucibles, as a lubricant, or as a conductor in batteries and brake linings.
Barnes (1961) provides details of several occurrences of graphitic lithologies within the
basement (Domain A). Gneisses are locally known to contain up to 25% graphite in Karamoja and also occur in West Nile. A 15 cm layer of almost pure graphite hosted by quartzite has also
been recorded in a tributary valley of the Mobuku River in the Ruwenzori Mountains. A limited
pitting and benching programme was also carried out on an occurrence at Ngora, Kitgum
District, Karamoja (Sheet 24/2) and reported by Obur (1975). The locations of eleven known
occurrences of graphitic basement rocks are shown in Barnes (1961, Figure 17).
K-rich rocks
K-rich rocks are required for the manufacture of NPK fertilizers and can also be utilized as a
direct application fertilizer. Uganda does not possess thick sedimentary evaporite sequences
which are the source of most of the world’s potash, although some of the Tertiary - Quaternary
Volcanics (Domain D) in the southwest of the country have moderately potassic lavas and tuffs
which exceptionally reach 6.67% K,O (Nixon & Homung, 1973). These deposits are unlikely
to form a commercial source of potassium for fertilizer manufacture. They might however, be
utilized locally as a direct application fertilizer, provided agronomic trials can demonstrate that
the potassium is soluble and benefits plant growth.
Potash could also be produced as a by-product of salt extraction from the brines of Lake Katwe and also Lake Bunyampaka (Kasenyi) according to Barnes (1961).
62
Kyanite
Kyanite (A1,Si05) is a highly refractory mineral found mainly as blue coarse bladed crystals
forming radiating and interlocking aggregates in the high-grade metamorphic rocks of basement
terrains. It is principally used in the manufacture of heavy-duty refractory bricks; commercial
grades must contain at least 56% A1203 and 42% SO2.
Several occurrences of kyanite in Uganda were noted by Barnes (1961); brief details are as
follows.
In West Nile a muscovite-garnet-kyanite schist crops out along the road from Parombo to Erusi Hill; kyanite constitutes about 10% of the rock. The adjacent Azi Hill, however, contains a
kyanite-rutile-schist with up to 80% kyanite which forms a 300 m-long ridge. Chemical analysis
of this schist indicates over 50% A120, and 5 % Ti02, strongly suggesting that it is derived from
a residual bauxitic laterite.
In Eastern Kigezi further occurrences have been described from a belt of strongly
metamorphosed Karagwe-Ankolean schists overlying granitic intrusions north of the Rubaare - Lugalama - Kitanga road (see geological sheet 1: 250 000 36-1 Mbarara). Within this belt
coarse-bladed kyanite occurs at Kamera Hill although it is allegedly unsuitable for refractory
use due to the presence of mica along cleavage planes. At nearby Ihunga Hill similar deposits
are also present and have been examined by Reedman (1967) and Rubondo (1985). These deposits occur as aggregates within quartz veins with individual bladed kyanite crystals reaching 15 cm in length.
Li-minerals
The most commercially important Li-minerals are found in pegmatites and include spodumene,
petalite, amblygonite and lepidolite. These minerals provide lithium for the manufacture of a
whole series of important lithium chemicals utilized by industry as well as lithium metal.
63
Lithium minerals are present in pegmatites in Buganda, Ankole and Kigezi provinces and
include occurrences of primary spodumene and alteration products such as amblygonite and
zinnwaldite. Details of many minor occurrences are provided by Barnes (1961), Reedman &
Lowenstein (1971) and Reedman (1969) but most are of academic, rather than economic,
interest. Commercial production of amblygonite for export took place from the Mbale Estate
pegmatite between 1949-54 during this period over 500 tons of amblygonite concentrate was
produced.
Mica
The mica group of minerals are characterized by their perfect basal cleavage which enables them to be split into very thin flexible sheets. The commercially useful micas are muscovite and
phlogopite. Commercial mica is derived principally from pegmatites. Large sheets of shaped
mica are termed sheet mica whereas finer pieces are used to produce ground mica. Demand for
sheet mica traditionally used for example as a capacitor or optical filter, is in decline,
conversely ground mica is used increasingly in applications such as in jointing cements and as a filler in paint and plastics, and as a lost-circulation material in drilling muds.
In Uganda muscovite mica is found in simple pegamtites intruding the basement rocks in many parts of the country. Barnes (1 961, p 82-83) gives a comprehensive list of occurrences mainly
in the Karamoja-Acholi, West Nile and Buganda regions. Sheet mica was intermittently
produced until 1966 mainly from pegmatites in West Nile. The total production for the period
1943-66 is estimated at about 22 tons of trimmed sheet mica. The declining world demand for sheet mica and the absence of domestic demand in Uganda make it unlikely that these deposits
will be worked in the future.
Nepheliie Syenite
Nepheline Syenite is an intrusive igneous rock common in alkali centres and is essentially
composed of alkali feldspars and nepheline. In some countries it is used as a source of alumina
64
0 a 0 a
a e
e * a * 0 e a
8
e
.i
0
e 0
e e e 0
0
and alkalis in glassmaking and in ceramic batches especially where other sources of these
elements (e.g. soda ash, feldspar) are difficult to obtain.
Whilst nepheline-bearing intrusives occur associated with the carbonatite/alkali centres in eastern
Uganda their remote location, chemistry, variability and limited extent make it unlikely that they
would ever be developed (Allen & Charsley, 1968).
Quartz crystal
Quartz crystal has traditionally been used for the manufacture of lenses, prisms and for its
piezoelectrical properties in electronic circuits. Natural raw materials for these applications have
largely been replaced by synthetically produced quartz and other materials.
Limited amounts of quartz crystal were mined in the Buhweju area and exported during the
second world war, the crystals were located in alluvial gravels from which placer gold has also
been won. It is unlikely that there will be a renewed demand for quartz crystal.
Pozzolanas
A pozzolana is any raw material capable of reacting with lime in the presence of water to form materials with beneficial cementitous properties. The addition of up to 30% of such material to
cement can produce substantial savings in energy and other manufacturing costs whilst
producing a stronger cement and, by reducing permeability, improves resistance to chemical and
physical degradation. Commonly used pozzolans include volcanic ashes and various forms of
silica including diatomite.
The use of pozzolanic materials in Uganda has not yet been attempted on a large-scale despite the benefits mentioned above. Some initial research has however been carried out into the
effectiveness of certain natural, vegetable and manufactured raw materials as pozzolanas in the
production of lime-pozzolana and portland-pozzolana cements (W. Balu-Tabaaro, unpublished
65
e 0 a 0 m a a e
0 * 0
e
0 e e 0 e I.
0
0
0 a 0
0 0 0
information). These studies show the suitability and potential of volcanic ash around Kisoro in the extreme southwest of the country. Abundant supplies of similar material also occur in and
around the flanks of the Western Rift near Fort Portal, Kasese and the Kazinga Channel.
Rare earth minerals
Rare earth elements (REEs) as their name suggests are uncommon in nature, economically
viable concentrations are therefore unusual and tend to occur in very specific geological settings.
The most common of the REE-bearing minerals are monazite, bastnaesite and xenotime.
Monazite and xenotime are found mainly as placers in mineral sand deposits usually derived
from granite-gneiss basement terrains. Bastnaesite and pyrochlore on the other hand are
principally found in association with carbonatite intrusions.
A comprehensive list of Occurrences where REE-bearing minerals are known to be present has
been given by Barnes (1961, pgs 78-80). The most important of these being monazite in
basement rocks and sediments derived from them. Provisional inspection of these deposits
suggests that they are not of exploitable size.
Talc
Talc is a hydrous magnesium silicate with characteristic softness, a greasy feel and pearly lustre.
It tends to occur as foliated or massive aggregates and is commonly white or pale green. Most deposits are impure mixtures of talc and closely allied minerals such as chlorite and serpentinite,
in a commercial sense the term talc often includes such mixtures.
Commercially viable deposits occur either as metasediments commonly including dolomitic
horizons or as serpentinized ultrabasic bodies. Talc is usually a late-stage product. Talc finds
use as a bright absorptive filler in a variety of products including paint, paper, plastics and
rubber and extremely pure forms are used in the cosmetics and pharmaceutical industry.
66
A useful review of talc occurrence in Uganda is provided by Nyakaana (1989) who discusses
five deposits. The Lolung - Moruamakale iiltrabasic mass located about 20 Km northeast of
Moroto, Karamoja contains layers of talc schist (Morton, 1969). Individual lenses of white fairly
pure talc locally exceed l m thick and extend for up to 10 m along strike. Deposits from this
locality need mineralogical examination to verify the grade of the deposit.
Two further alleged occurrences of 'good quality' talc are reported from opposite Manengo - Itega church near Kyamuhunga in Bushenyi District and Kisinga in Bwera (Nyakaana, 1989).
Unfortunately detailed mineralogical investigation of representative grab samples from these
localities, coupled with field inspection of the former, has shown the deposits are essentially
composed of chlorite with subordinate talc (Mitchell 1992, Mathers & Mitchell, 1992) although
this would not preclude their use as a low-grade filler.
Other probably uneconomic occurrences of 'talc' mentioned by Nyakaana (1989), about which
little is known, are at Rwimi (Kyanaroke) Falls on the Rwimi River near Kisomoro southwest
of Fort Portal and at Nampunge Hill, Busiro northwest of Kampala.
Vermiculite
Vermiculite is a hydrated sheet silicate with similarities to the mica group of minerals. It tends
to form as a supergene alteration product of ultramafic intrusive rocks which are commonly associated with granitic or carbonatitic magmatism. Vermiculite contains a water interlayer
parallel to the prominent basal cleavage. On rapid heating the water converts to steam forcing
apart the layered structure to give an expanded lightweight product which contains up to 90%
air. This product finds applications as a lightweight aggregate, as a thermal and acoustic
insulation material, as a carrier for chemicals and a rooting medium in horticulture.
Vermiculite occurrences in Uganda have been reviewed by Mboijana (1974) and are restricted
to the carbonatite/alkali volcanic centres of Bukusu and Sukulu in eastern Uganda. The
occurrences of the Bukusu centre are regarded as the more promising.
67
At Bukusu deeply weathered semicircular outcrops of ultramafic
rocks such as mica pyroxenites and glimmerites contain variable amounts of vermiculite in the residual soils. The most promising locality is the Namekara deposit where Taylor (1956) carried
out detailed pitting and trenching. The study indicated that beneath a magnetite rubble
overburden up to 3 m thick, some 125,000 tons of recoverable good-quality coarse vermiculite
flakes are present within 15m of the surface, with about twice this amount of additional poorer
grade material. In general the better quality vermiculite for exfoliation tends to be darker in
colour and have a brighter lustre. Bloomfield (1973) reports the results of grading and
exfoliation study of a large crushed bulk sample, these are given below in Table 11. Even lower
exfoliated densities (likely to meet international specifications) should be attainable if higher
firing temperatures are used on up-graded concentrates from which magnetite has been separated
(Bloomfield, 1973).
Table 11 Grading and exfoliation tests on Namekara vermiculite from Bloomfield (1973).
Waste Coarse Medium Fine
Percentage 22.8 44.2 9.4 23.6
Exfoliation temp ( O C) 600 450 500
Exfoliation factor 4 3 3 Density (lb/ff') 10.2 12.4 13.8
Within the Bukusu complex vermiculite has also be recorded at Nakhupa, Sekusi, Surumbusa
and Kabatola. Only the latter occurrence is likely to contain appreciable quantities of vermiculite
suitable for exfoliation (Mboijana, 1974).
At Sukulu vermiculite is known to occur at depth below the North Valley but this occurrence
is unlikely to be of commercial interest (Bloomfield, 1973).
Zeolites
The zeolite group of minerals comprise about 40 naturally occurring hydrated alumino-silicates
68
0 e 0 1)
a 0
I. e * e a 0
e a
a
whose basic SiO, tetrahedra are arranged in rings, producing passageways through the molecular
structure. Zeolites form as low-temperature alteration products of fresh volcanic glass, feldspars
and clay minerals. Economically interesting deposits are usually altered volcaniclastic and
pyroclastic deposits which commonly show zonation of mineral assemblages. Zeolites are
metastable and m e in pre-Mesozoic strata.
Zeolites have a wide range of uses due to their properties of ion exchange, water and gas
absorption, and catalysis (Clifton, 1987). To date most zeolites used in industry are manufactured synthetically, but where large volumes are required as for example as a pozzolana
or in fertilizers, natural zeolites are favoured. Of particular importance to developing countries
are applications in agriculture and environmental protection (Parham, 1989). The principal
zeolites mined are clinoptilolite, mordenite, chabazite, phillipsite and the possibly carcinogenic
fibrous variety erionite.
With the exception of the amygdaloidal type of Occurrence within lavas of Mount Elgon (Davies
1952), zeolites have not been reported from Uganda. Clearly the geological environment is very
favourable for their formation within pyroclastic and volcaniclastic sediments associated within
the Tertiary- Quaternary Volcanics (Domain D) and Quaternary Sediments (Domain E) close to penecontemporaneous volcanic centres. The presence of zeolites in such deposits is easily
overlooked since they are commonly fine grained and difficult to recognise without recourse to
mineralogical techniques such as X-ray diffraction. Carefully targetted reconnaissance
exploration work is recommended, if demand for the commodity can be established, as the
chances of encountering potentially useful deposits of zeolites are regarded as high.
0 a
69
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e
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