Mineral Potential of Malawi 4 Deposits Resulting from Residual Weathering, Produced for the Ministry of Energy and Mines of Placer and Rift-Related Sedimentation

Ministry of Energy and Mines REPUBLIC OF MALAWI

Mineral potential of Malawi 4 Deposits resulting from residual weathering, Produced for the Ministry of Energy and Mines of placer and rift-related sedimentation. (bauxite, Malawi by the British Geological Survey under saprolitic nickel, Ti±REE±Zr, gold and gemstone the auspices of the UK Department for International placers, etc.) Development.

;:Kao " Chitipa ;:BC Karonga

;:Fe Nyika plateau

LAKE

BC ";: MZUZU

Kao " Likoma ;: island MZIMBA

MA Section dredge and floating concentrator:

LAWI Chipoka mineral sands pilot project, Lake Malawi

Au !Õ

" NKHOTA KOTA Cenozoic deposits African surface Superficial deposits (residual to eluvial, colluvial, and with thick residual soils and dambos alluvial to lacustrine) contain important mineral resources Gyp Kao !Õ : Ti ; !Õ in Malawi. They cover large tracts of the Lake Malawi "Senga Salima " Gla " Dia Ti &' Mchinji !Õ littoral, the Shire Valley and the Lilongwe-Kasungu and Ni BC !Õ ;: ;: " BC Kao " Chipoka Mzimba plains. Residual and placer deposits developed ;: ;: Au, Ti LILONGWE !Õ " Mon, Ti during the Cenozoic as a consequence of complex Linthipe Dia Au !Õ !Õ &' evolving geomorphic cycles of weathering, erosion and Mangoche " deposition under varying climatic conditions. Residual

Kao deposits include bauxites, clays, saprolitic nickel and ;: Lake Kao Malombe Gla Recent lacustrine, alluvial ;: Balaka gemstones. Dambos are a potential source of gypsum, " &' and colluvial deposits Cor ;: !Õ Kao ;:Kao brick clays and silica sand. Heavy mineral alluvial Mineral deposits/occurrences Au Al placers with ilmenite, rutile, monazite, zircon, gold and/ !Õ ;: Lake !Õ Alluvial/Colluvial " Chilwa ZOMBA or gemstones have largely developed along the major ;: Mwanza Residual/Eluvial " BC rivers and around the lakes of the East African Rift Valley. &' Sedimentary !ÕCor ;:"" LIMBE BLANTYRE ;: BC They are also a potential source of columbite-tantalite, Al, Kao Gla Silica Sand Dia Diatomite ;: cassiterite, PGM’s, etc. Lacustrine deposits in the Malawi Au Gold BC Brick clay Rift include diatomite, phosphate, and unconsolidated Ti Titanium Ni Nickel Mulanje Mts Al Bauxite Kao Kaolinite marls. The thick sediment fill of the rift is a target for Mon Monazite Gyp Gypsum hydrocarbon exploration. Ti Cor Corundum !Õ

" Nsanje January 2009

1096_Malawi_brochure_4_final.indd 4 16/01/2009 14:23:07 Landforms the thickness of the sedimentary fill in content, high aluminium content, vitreous The Malawi uplands (750–1350 m) on the the northern part of the lake is > 2 km and textures and high porosities. western side of the country represent the thickens to >4 km near the major border African Surface which dominated the scenery faults. The sedimentary sequences generally Bauxite has developed from the prolonged at c.30 Ma. This is a composite erosion thin towards the south and in the Lower Shire weathering of syenogranitic rocks that form surface resulting from at least 100 Ma of valley are of the order of 1.6 km. Mulanje Mountain which rises 600–700 m continental denudation, characterised by above the surrounding Phalombe plain. The low relief and deep regolith profiles that The sediments of Lake Malawi consist Mulanje bauxite resource has been known developed by protracted and aggressive of homogeneous diatomites, pelagic since 1924 and has been explored by the weathering and differential leaching. diatomaceous oozes, varved diatomite muds, Anglo American Corporation (1934), the British Low lying areas are occupied by dambos turbidites, littoral sand sheets and extensive Aluminium Company (1951–58) and Lonrho or clay-filled bottomlands with sluggish deposits of ferro-manganese nodules. Turbidite (1969–72) amongst others. Six extensive drainage. At the culmination of this prolonged channels and coarse clastic deposits are bauxite areas have been identified but the peneplanation episode most elevations on found off many of the major rivers and border best deposits occur on the Lichenya and the African Surface probably rose no more faults even in water depths of several hundred Linje plateux at an elevation between 1800 than c.200 m above the pediment. Stripping metres. These are most common in the and 2000 metres. The bauxite is a trihydrate of this surface began in the Miocene with northern lake basin where large deltas have gibbsite which overlies kaolinite and has the initiation of the western arm of the East developed off the Ruhuhu and North and South goethite and quartz as the main contaminants.

African Rift system. Residual deposits are Rukuru Rivers. An average analysis yields 43.3% Al2O3, poorly preserved in the eastern and southern 13.3% free quartz, 2.2% combined silica,

parts of the country due to the greater rift- Bauxite 14.2% Fe2O3, 1.8% TiO2, <5.0% kaolinite and related uplift and denudation. Alluvial placer Bauxite comprises variously hydrated 28.8% LOI. Total reserves on the mountain deposits, which are an important source for aluminium oxides (gibbsite, diaspore, etc) and are estimated to be >50 Mt. Lonrho showed gemstones, precious metals, titanium and constitutes the principal ore of aluminium. that the two main deposits amount to 28.8 Mt

rare metal minerals, largely formed during It forms as a result of intensive surficial using a cut-off grade of 30% Al2O3 with an this recent period of rift tectonics. weathering on well drained plateaux in average depth of 4.5 metres. A feasibility study regions with wet tropical climates. The executed by MET-CHEM Canada Inc.on behalf The Malawi Rift comprises a segment process of bauxitisation involves intense of MIDCOR in 1993 estimated 25.6 Mt bauxite of the western branch of the East African leaching of the protolith and/or regolith at a grade of 43.3% and proposed a mining Rift System that extends for about 800 km and dissolution/desilicification of kaolinite. output of 580,000 tpa of bauxite to produce from southern Tanzania to the Shire Valley Lateritic (silicate) bauxites comprise >75% of 200,000 tpa alumina for an annual production in southern Malawi. The rift structures the World’s bauxite resources. They can form of 100,000 tonnes of aluminium. extend further south by the Shire trough in from various silicate rocks (granite, gneiss, Malawi and Urema graben in Mozambique. syenite, basalt, shale) but are preferentially The bauxitic outliers on Mulanje Mountain are The Malawi Rift is largely occupied by Lake derived from lithologies with low silica associated with remnants of the African Surface Malawi at an average elevation of 474 m which overflows southwards into the Shire River and joins the Zambezi. The lake is 570 km long, 50–90 km wide and some 700 m Lake Chilwa Mulanje Mountain(s) deep i.e. >200 m below sea level. The rift viewed from the south shoulders reach c.1300 metres higher than the rift floor after erosion. Chanbe Lichenya Basin The Malawi Rift is largely non-volcanic but Plateau hot springs are located at various places along the western and southern parts of the lake area. The Malawi Rift is at an early stage of development. It began to subside in during the late Miocene and major rifting took place in northern Lake Malawi at 6–5 Ma. The Lake Malawi basin consists of seven linked half-graben units (typically 120 km x 40 km) Perspective image using natural colour Landsat 7 band composite 1,2,3 from data acquired alternating asymmetrically along a single axis. on 26/05/02 coupled with elevation data from the Shuttle Radar Topography Mission – The seismic reflection profiles show that SRTM. Released on the NASA Website (Earthobservatory.nasa.gov).

1096_Malawi_brochure_4_final.indd 5 16/01/2009 14:23:09 cost open pit or strip mining. Lateritic nickel deposits are estimated to comprise 73% of the worldwide continental nickel resources.

Lisungwe Mineral Resources Ltd have identified deposits of nickeliferous saprolite on the Chimwadzulu and Chimimbe ultramafic bodies close to the western border of Malawi with Mozambique and Zambia respectively. Surface pitting indicated that both deposits have estimated non-compliant resources in excess of 3.0 Mt of ore grading better than 0.5% nickel.

Both deposits are still open along strike, down plunge and at depth. Potentially View of Chimimbe hill, from the north-east. recoverable quantities of ferro-chrome and inherited from the Paleogene (70–40 Ma) of highly-disordered kaolinite with halloysite, magnetite are also present. bauxite-forming event which involved top-down have plasticity indices between 20 and 40. bauxitisation of mature kaolinitic mantles. The clay could form the basis for production Chimwadzulu hill is the type locality for Nyala Bauxite deposits are rare in East Africa which of earthenware, stoneware, aluminosilicate rubies and nickel exploration was suspended has been influenced by rift-related uplifts. refractories and sand moulds. upon re-issue of the primary licence to Nyala. Within the Malawi rift these appear to be Initial exploration work shows Ni grades from preserved at elevations of 1800–2000 m. Reserves amounting to 0.5 Mt and 0.6 Mt 0.3%–1.0% at half metre intervals over a have been delineated also at Senzani and sample depth of two metres. The resource Bauxitisation was the dominant process on Nkhande respectively. estimate based upon a depth of three metres the planated summit of Zomba mountain is equivalent to 12,000 t of metallic nickel (2134 m) which is at a similar altitude to the Lateritic/saprolitic nickel recovered at 80%. Mulanje deposits. Bauxite development up to Lateritic nickel deposits form by prolonged three metres thick occurs beneath a layer of and pervasive weathering of ultramafic rocks Chimimbe Hill rises from an extensive soil one metre thick. The greatest thickness in tropical to subtropical climates. They peneplain (African surface) about 80 km east occurs at the border of the plateau. The typically develop from serpentinitic rocks that of Lilongwe and is just 12 km from paved bauxite is being supplanted by kaolinitisation have a significant background level of nickel highway and railroad access and 6 km from under current weathering conditions. (c. 0.3%). Being restricted to the weathering a power line. The Chimimbe Hill surface mantle they tend to be tabular, flat and mineralisation overlies an east-dipping Kaolinitic clays areally large and therefore amenable to low lenticular ultramafic sheet emplaced into Substantial resources of kaolinitic clays suitable for the production of ceramic wares occur at Linthipe in the Dedza district and at Senzani and Nkhande in Netcheu district. At Linthipe, the clays formed as a result of in situ weathering of a meta-anorthosite body within the Basement Complex. The Linthipe meta- anorthosite, composed of 95% labradorite, forms a negative topographic feature covering 230 km2.The weathering profile passes upward from bedrock through slightly altered meta-anorthosite to kaolinitic saprock and into a saprolite of plastic kaolin on top and overlain by distinctive thin pale grey savannah soils. Four groups of deposits each containing between 1.0 and 3.5 km2 of clay 0.7 to 1.7 m thick have been outlined. The total area amounts to 7.6 km2 with indicated reserves of 15 Mt. The clays, which consist principally Lisungwe exploration camp and colluvial fan (red soils) on the east side of Chimimbe hill.

1096_Malawi_brochure_4_final.indd 6 16/01/2009 14:23:11 Early metallurgical test work fertiliser (either by manufacture of compound indicates that 85% of the nickel phosphate or by direct application) and for contained in the non-magnetic the production of phosphoric acid and various fraction of the potential ore can other chemicals. According to present practice be rapidly extracted using hot for apatite to be directly applied to the soil

sulphuric acid at atmospheric the average P2O5 content of the ore should be pressure. Potentially economic > 16% and the Fe content <5% and it should quantities of ferro-chrome and be free of potential contaminants. magnetite may also be recovered with simple magnetic/gravity The Kangankunde and Chilwa Island methods of separation. carbonatites, contain only small amounts of

primary apatite but the P2O5 concentration in The conservative estimate residual and eluvial phosphate accumulations

of 3 Mt constitutes in excess range from 1.32 to 8.9% P2O5 with an average

of 15,000 tonnes contained of 2.5% P2O5. Eluvial soils overlying the nickel. Sulphuric acid will be a pyroxenite near Ligowe carry an average of significant cost factor and its 7.8% chlorapatite, and weathered pyroxenite ready availability may be critical 1.6 km further south contains 12% apatite. Other to the viability of this venture. eluvial phosphate accumulations are reported from the Chingale metapyroxenite (estimated Rotary air blast (RAB) drilling to a nominal depth of 20 m Numerous ultramafic bodies with reserves 8.76 Mt at 3.76% P2O5), the Bilira meta- using a small mobile tracked rig (hole diameter 12 cm) at elevated Ni values occur within pyroxenite (mean 1.42% P2O5) and the Mlindi the Chimimbe Hill prospect. the basement complex (see ultrapotassic pyroxenite to syenite complex. Brochure 2). Exploration for lateritic/saprolitic Mchinji sandstones of the Muva Supergroup. nickel mineralisation, which depends upon At Mlindi, two areas with apatite-rich The ultramafic body dips at about the same the preservation of deep weathering mantle, residual soils were delineated overlying the angle as the hillslope and mostly comprises should focus on the African peridotite but there is extensive development planation surface in the 8455600

of talc schist in the SE part of the hill which west-central part of the 8455500 FOOTWALL may be part of the exposed hangingwall. The country. SANDSTONE 8455400 sheet is cut by NNE-trending faults. ALLUVIAL FLATS Phosphate 8455300

50 The initial programme of pitting covered an area Carbonatites and other 8455200

of 1 x 0.5 km with some pits reaching a depth alkaline igneous rocks 61 62 8455100 CHIMIMBE HILL 12 of 7 metres. Hand-held XRF analyses indicate commonly contain elevated 60 49 39 59 8455000 6 grades of 0.3% to 1.3% nickel and 0.3% to 2% 56 phosphate concentrations 58 57 33 32 34

chrome. The peridotitic bedrock yields 0.2–0.8% 22 in the form of fluorapatite. 8454900 2 55 54 23 27 31 35 Ni. The explored area remains open at both Weathering of these 36 11 52 53 28 8454800 24 1 8 7 40 ends and down-dip to the east. The present igneous rocks leads to 37 10 51 48 25 26 41 8454700 3 phase of rotary air blast (RAB) drilling on an natural enrichment in 29 38 30 18 80-metre square grid to a target depth of 20 m apatite and other resistant 19 21 42 8454600 4 17 14 44 20 13 43 to determine the true thickness of saprolite minerals (e.g. magnetite, 15 8454500 ore grades (typically 10–20 m) has yielded pyrochlore, monazite) 16 45 5 encouraging results including the identification mostly by removal of 8454400 46

of near-surface enrichment zones. Infill holes soluble carbonate minerals 47 8454300 9 initially on a 40 m grid and possibly deeper and gravitational sorting. Drill hole holes will be drilled where required. Deep weathering profiles 8454200 Pit overlying and derived from 8454100 Base of hill

There is an extensive talus apron and apatite-rich carbonatites 0100 200 300400 m colluvial spread on the pediment to the can produce economic east of the hill which carries not only high eluvial deposits. 503100 503200 503300 503400 503500 503600 503700 503800 503900 504000 504100 Ni-Co but also exploitable ferrochrome. This Apatite is an essential raw Sampling plan of Chimimbe Hill and eastern pediment, showing extends up to 400 metres from the break of material that is widely pitting and drill holes to November 2008 courtesy of Lisungwe slope as two outwash fans. used as a phosphatic Mineral Resources Ltd.

1096_Malawi_brochure_4_final.indd 7 16/01/2009 14:23:13 metapyroxenite with estimated probable reserves of 2.4 Mt with grades of 7% to

14% P2O5.

Gypsum Gypsum is a hydrated form of calcium sulphate that can be used in the manufacture of drywall plaster board linings, a plaster ingredient, Plaster-of-Paris for casting moulds, etc., a fertiliser and soil conditioner, in Portland cement, medicines and pharmaceuticals. Calcined gypsum can be used for drinking water defluoridisation in areas of Malawi where dental fluorosis is Processing plant at Chimwadzulu Mine — soon to be replaced (photo courtesy of Nyala prevalent. Malawi currently imports most of Mines Ltd.). its gypsum requirements (c. 6000 tpa). quartz and, more importantly, low levels heavy minerals have accumulated in the The dambos of Dowa and Lilongwe district of deleterious impurities, particularly clay, weathering mantle and include residual, contain deposits of crystalline gypsum. The iron oxides and refractory minerals, such colluvial and eluvial deposits. Mdika and Mponela dambos in the Dowa as chromite. Silica sands are essential raw district are estimated to have a combined materials for glass manufacture and a wide The Chimwadzulu Hill deposit is essentially resource of >500,000 tonnes at a grade of range of other industrial and horticultural an eluvial gemstone deposit yielding both 6–10% gypsum. applications. rubies and sapphires that has developed over a meta-(ultra)basic complex from Dambos are seasonally flooded channelless Glass sand for colourless glass containers which they are ultimately derived (see

shallow valleys that have developed on the generally has an iron content of <0.035% Fe2O3, brochure 2). The Ministry of Mines, Natural

African planation surface in the northern for flat glass in the range 0.060 to 0.1% Fe2O3, Resources and Environment (2004) recorded 3 and central parts of Malawi. The gypsum and for coloured containers 0.2–0.3% Fe2O3. a grade of 75.6g/m for the Chimwadzulu accumulates along with magnesium Closely-sized grades (generally 0.5-1.0mm) of Hill gemstone deposit. The ruby resource sulphate, calcrete nodules etc. at the silica sand are the principal filtration medium was estimated to be 247 kg (Yager, 2001). margin of the dambo floors during dry used by the water industry. The regolith which is commonly 2–4 metres season through upward discharge of deep thick (max. 20 m) includes a basal clayey water at the spring line. At the Kasangadzi Substantial deposits of good quality silica sands saprolite. The distribution of the gemstones Dambo, 5 km NW of Mponela the gypsum occur in dambos in the Mchinji area of central is highly localised. Current throughput horizon has an average thickness of 0.9 m Malawi. Recoverable reserves in six dambos is 20–25m3 per day with a production and is overlain by 0.5–1.0 m thick sticky amount to 1.6 Mt with 96–99% (average 97%) of about 300 gm of gem quality rough

black cotton soils (vertisols). At the Livuno SiO2 and 0.12–0.2% iron oxide. The Lake stones per month. The rubies account for Dambo in Dowa West the gypsum clay Chilwa — Chiuta sand bar is estimated to approximately one third of the gems and is 0.5–0.7 m thick with an average grade contain 25 Mt of glass sands averaging 92.7% range from pink to red to orange to the rare

of 7% amounting to a total estimated SiO2 and 0.62% iron and are suitable for the pinkish orange known as padparadscha reserve of >300,000 tonnes of the +2 mm manufacture of brown (amber) quality glass sapphire. Single crystals up to 40 carats fraction. Mining of these gypsum resources containers. have been recorded. Unlike most other ruby is generally regarded as difficult due to deposits of its type the colour is completely flooding and the hardness and stickiness of Further beneficiation would improve the natural and they are marketed under the these gypsum bearing soils. The Geological quality of the sand to make it suitable for name of ‘Nyala rubies™’ through the Survey Department undertook detailed manufacture of plate and window glass and Columbia Gem House. The sapphires need assessments of the gypsum deposits in reasonably clear glass containers. heat treatment. The deposit is currently Livuno and Katete dambos and concluded worked by Nyala Mines Ltd. who are that they could be worked as a small-scale Placer deposits installing a new plant with a 300–400 m3 labour-intensive operations. At Chimwadzulu Hill in the Kirk Range per day capacity and are planning exploit (gem-quality corundum), Thambani, the deposit by systematic contour terracing Silica (industrial) sands Mwanza (opaque corundum and zircon), of the hill to bedrock. This should increase Silica sands contain a high proportion Makoko, Nsanje (industrial corundum) production to > 3.5 kg/month including 2 kg

of silica (up to 99% SiO2) in the form of and at Kapiridimba (kyanite and rutile) of pink to red ruby.

1096_Malawi_brochure_4_final.indd 8 16/01/2009 14:23:14 The Thambani eluvial corundum and the shore of Lake Malawi and along the The reserves of beach sands around Chipoka/ zircon deposit, 60 km WNW of Blantyre, Shire River. Heavy mineral sand deposits Salima along the western shore of Lake is derived from pegmatites that intrude comprise high density minerals (SG > 4.2) Malawi are estimated to be 700 Mt with nepheline syenite gneisses over an area that occur as disseminated, lenticular or an average grade of 5.6% total heavy of c.260 km2 of the Precambrian basement. layered concentrations within the sands minerals. The sands contain ilmenite, rutile, The deposit was worked intermittently and most commonly include Ti minerals, monazite, garnet and minor zircon. Other between 1923 and 1952 and produced gold, cassiterite, zircon, monazite and minerals present include amphibole, ortho- over 1745 tonnes of abrasive quality garnet. By far the most important resource and clinopyroxenes, magnetite, titanite, corundum. The opaque corundum from in Malawi is the Ti mineral sand deposits. apatite, orthite, epidote and chromite. The Thambani graded A1 on alumina content. The high strength-to-weight ratio, exploitable bed is up to five metres thick. Known reserves amount to over 100,000 corrosion resistance, bio-compatibility and Allied Procurement Agency and Mineral tonnes with good prospects for extending non-toxic characteristics make titanium Sands Ltd. of South Africa conducted a pilot the available resource to over 500,000 mt. ideal for strategic and critical applications suction dredging and processing operation There is obvious potential for discovering in the aerospace, military and medical along the shoreline to the north of Chipoka in gem quality material. fields. Ti oxide is the main component 2006 with the intention of starting large scale of white pigments in paints, paper and exploitation of zircon and rutile. Contained Alluvial Gold ± PGM plastics. resources of zircon and rutile at Chipoka Bay Alluvial gold has been reported in the amount to 6.7 Mt and 3.6 Mt respectively. Lisungwe river system in the Kirk Range Three heavy mineral sands deposits have area, the Dwangwa river and its tributaries been investigated. They include the colluvial In the Mangochi district large resources of straddling the districts of Nkhotakota and deposits at Tengani in Nsanje district, the heavy mineral sands occur at Makanjila on Nkhata Bay in central Malawi and in the beach sands in the lakeshore districts of the southeastern lake shore of Lake Malawi. areas of Nathenje and Mwanza. Salima, Nkhotakota and Mangochi and the Sand dunes extend 6 km inland along a 20 km sand bar at Lake Chilwa in the Zomba district. shoreline and up to 100 metres above the The Lisungwe River and some of its current water level of the lake. Reserves are affluents draining the Manondo gold district In the Tengani area at the foot of the estimated at 800 Mt grading at an average of contained some of the richest alluvial gold east-dipping Mulaka Hills the reserves of 13.0% total heavy minerals with ilmenite (5.2%) concentrations and have been worked colluvial heavy mineral sands and gravels being the dominant economic commodity. intermittently. The Likudzi River, a tributary are estimated at 108 Mt with a heavy of the Lisungwe draining an area of faulted mineral content ranging from 3.5 to 35% Millenium Mining Ltd. of Australia have ultramafic sheets additionally carries PGM averaging 0.34% rutile and 1–14% ilmenite. considered the development of the Makanjila minerals (e.g. ferroplatinum). The Lisungwe Other estimates put the rutile: ilmenite and Salima Bay mineral sands deposits with and Likudzi yielded coarse angular gold ratio in the heavy mineral fractions in the a view to producing 500,000 tpa of ilmenite indicating a proximal source. range 1:12 to 1:4. An assessment by the which would have been smelted at Chipoka. Geological Survey Dept. in 1997 indicated A co-product would be high quality pig iron. The alluvial gold potential is limited but its 2.5 Mt of heavy mineral sands grading at occurrence is a useful indicator of bedrock 3% ilmenite and 0.3 Mt containing 0.3% sources. rutile. Elevated contents of Ti minerals mainly occur on the interfluves between the In the Nathenje area alluvial gold is Nkande and Namyala rivers. spatially related to outcrops of calcsilicate granulites or skarns. The main sources The Mpyupyu Hill colluvial heavy mineral of the gold, however, appear to be shear sands contain over 11.9 Mt grading at 3.8% zone-hosted concordant quartz stringers ilmenite and 0.01% rutile (MMNRE, 2004). in the paragneisses and pyritised veins in These heavy mineral sands spread across carbonatised schists. Gold occurrences have the Lake Chilwa flooplain on which the been documented for the Malindi-Makanjira eastern foothills of the Zomba plateau level area in the Mangochi district also but off. Between Mpyupyu Hill and the present- attempts to trace the gold so far have been day shoreline of Lake Chilwa, two separate inconclusive. sand bodies have been delineated that total of about 15 Mt with an average grade Heavy Mineral Sands of 6.93% ilmenite, 0.38% zircon, 0.02wt% Malawi hosts at least two billion tonnes rutile, 0.04% leucoxene and 0.06% garnet Exposed heavy mineral sand layers at the of mineable heavy mineral sands around (Dill, 2007). shoreline north of Chipoka.

1096_Malawi_brochure_4_final.indd 1 16/01/2009 14:22:58 Development of the smelter with a planned Source area Lacustrine basin capacity of 250,000 t/yr titanium slag would Vertisol Debris flow Lateritic deposits Iron ore Bog Iron ore be dependent upon obtaining power supplies old Mud flow Saprolite deposits from Mozambique. peneplain Talus creep Vertisol to sheet Stream flow floods deposits Fluvial Saprock deposits Lacustrine sediments Fluvio-deltaic deposits Lacustrine Diatomite is an amorphous biogenic modern deposits silica comprising porous siliceous skeletal peneplain remains of diatoms. It is very light weight, chemically inert, abrasive and highly Basement Complex and Chilwa absorbent. Diatomite is used as a filtration Alkaline Igneous Complexes aid (drinks, medicine, petrol, chemicals, Residual-eluvial Eluvial-colluvial placer Fluvial Fluvial-deltaic Lacustrine dyes, swimming pools, etc.), heat insulation placer eg Ti, Fe-Cr placer placer material, a functional filler (rubber, eg gemstones colluvial-elluvial eg Zi-Zr-REE eg Zi-Zr-REE Fe-Al-Ni (pathfinder minerals) �Au

paper, cosmetics, toothpaste, chinaware Chimwadzulu Tengani-mulaka Hill TenganiMyupyu Hill-Kachulu Salima products, etc), a chemical carrier (catalysts, Thambani Chimimbe (E) Mwanza activators, pesticides and fertilisers) and a Linthipe bonding agent. It has many environmental Schematic cross-section (modified after Dill & Ludwig (2008)). applications as a dessicant, for oil absorption and waste water treatment. of southern Lake Malawi. The uppermost limonite-opal facies. Nontronite nodules Songwe unit (max thickness 115 m) comprises are most common near diatomite deposits Diatomites and diatomaceous clays occupy a white laminated varved sequence with and in proximity to geothermal sources. the shallowest, highly productive settings sporadic beds of homogeneous diatomaceous There are several distinct nodules horizons mud. The couplets of light (100% diatoms) with limonite-opal types toward the base –dark (50% diatoms) laminae are seasonal and ferro-manganese types near the top. LAKE MALAWI SEDIMENT FACIES phytoplankton blooms with an overall Vivianite (iron phosphate) nodules and (adapted from Johnson and Davis 1989) sedimentation rate of 1mm /yr. No resource crusts are also present. The various iron- 10º estimates are available. rich sediment layers range in thickness from 13 cm to >80 cm and are separated by N Iron±manganese deposits siliciclastic muds and silts. Extensive fields of ferromanganese nodules up to 50 cm thick and comprising up to The Lake Malawi type of iron enrichment is 11º 95 wt% of the sediment occur off the an example of a precursory to mature phase Nkhotakota shoreline and on the slopes of of precipitation of metalliferous muds of Red tilt-block structures at Mbenje and Likoma Sea-type deposits. Islands. The nodules are typically 1–8 mm diameter and range from relatively pure ferric Calcareous/marly sediments 12º nodules (<2% Mn) to spheroids containing Very large quantities of unconsolidated marls

Diatom ooze >60% Mn. These fields occur at the present with 20–45% CaO and <2% MgO occur in parts sediment/water interface and are largely of the bed of Lake Malombe in the Mangochi Silt confined to water depths of 80–160 m i.e. district that could be used for the production Silty diatom clay above the anoxic-oxic boundary at 200–250 of natural cement and hydraulic lime. These

Sand 13º metres depth. Known regions with high calcareous sediments are highly variable in Shelf concentrations of ferromanganese nodules terms of carbonate content which tends to always occur at the boundary between increase with distance from the shoreline and Slump littoral sands and detrital muds. Sporadically decrease with increasing depth below surface high Ag and Au values reported for nodules giving way to sands at depths of 3 to 4.5 m.

14º from Likoma and Mbenje are significant in terms of economic potential. Hydrocarbon potential 0 100 km 75% of Africa’s petroleum has been

34º 35º Nodular iron-rich deposits overlie diatomite generated during the past 30 Ma and 50% or coarse grained clastic sediments in the of it lies in reservoirs of Eocene to Holocene Distribution of diatomite and diatomaceous southernmost part of the lake but these age. Rift basins are well known as prolific clays in the Lake Malawi sediments. are predominantly of the nontronite and hydrocarbon-bearing provinces worldwide.

1096_Malawi_brochure_4_final.indd 2 16/01/2009 14:22:59

Title Malawi Size 86 x 170 port Fig 11 1st proof Drawn by: P Lappage 2nd proof Corrections by P Lappage 3rd proof Corrections by P Lappage 4th proof Corrections by highly anoxic conditions. Potential Brochures in the series on the Mineral N Livingstone reservoir rock in the form of deltaic Potential of Malawi basin sandstones is being deposited 1. Mineral deposits associated with aliro DZ Cham locally along the lake margins and alkaline magmatism. orth N RU extend into the lake. Project PROBE 2. Mineral deposits associated with the UHU R GH ROU T (1985–87) revealed four sedimentary Basement metamorphic and igneous rocks. 0 50 km sequences in the lake stratigraphy 3. Mineral deposits associated with

y Usisya/Mbamba e and further indicated potential for sedimentary and volcanic cover rocks: l l basin a V hydrocarbons in the shallow waters Karoo and post-Karoo.

n in the central parts of the lake, 4. Deposits resulting from residual

especially around the lakeshore weathering, placer and rift-related

districts of Nkhotakota and Salima. sedimentation.

Z D ro ali am A A key factor in evaluating prospectivity Sources Ch B AM NI H is determining the presence or Geological Surveys Department bulletins, A UG Chamaliro DZ M RO T absence of mature source rocks. memoirs and reports. Thick sequences of the Lake Nyasa Mining Journal Annual Reviews. Group extend as far south as 13o15’S US Geol. Survey Minerals Yearbook. Major Pre-Rift but at present geological evidence Minex Company annual reports and release Dislocation zones Metangula basin is lacking that thermal maturity has updates on the Worldwide Web. Normal faults been reached. Sequences of Karoo Dill, H.G., 2007. Journal of African Earth

Transfer/ sediments intersect the lake axis at Sciences 47, 153-173. Accommodation Zones two locations. Therefore the possibility Dill, H.G. & Ludwig, R.-R., 2008. Ore Geology also exists for source/reservoir rocks Reviews 33, 411-434. STRUCTURE MAP of Karoo age succeeded by post-Karoo Report by Mintek and its contractors 2002. OF LAKE MALAWI Mesozoic reservoir rocks capped by Lisungwe PLC (pers comm). the Miocene to Recent lake sediments. Nyala Mines Ltd. (pers comm). Adapted from Schalz and Scott (1989), Project PROBE. Despite the overall stratigraphic Contact details Tectonically-derived topography is the similarity between half-grabens in the rift Secretary for Energy and Mines prime control on both sedimentary system each sub-basin is filled independently Private Bag 350, Capital City, processes and facies distribution of so that details of lithostratigraphy vary. Lilongwe 3, Malawi hydrocarbon source rocks, reservoirs and Therefore, the source rock potential of the rift Tel: +265-1-789488/Fax: +265-1-788689 seals in syn-rift successions. Reservoirs are system can only be identified after each half- email: [email protected] abundant throughout continental syn-rift graben is drilled. successions but good seals tend to be The Director, uncommon. Potential reservoirs and seals Helium Department of Mines, P.O. Box 251, Title Malawi Size 76 x 150 port can be identified by integrating sequence Natural gas resources in Lake Kivu, one of Lilongwe, Malawi Fig 10 1st proof Drawn by: P Lappage stratigraphic concepts with the predicted the great lakes on the western arm of the Tel: +265-1-755303/Fax: +265-1-757235 2nd proof Corrections by P Lappage 3rd proof Corrections by spatial facies distribution although this East African Rift lying on the border between email: [email protected] 4th proof Corrections by can be difficult to interpret in non-marine the Democratic Republic of the Congo and systems because of rapid lake level changes. Rwanda, contain 5–10% helium. Gas-rich The Director waters with an estimated reserve of 50 Geological Survey Department, P.O. Box 27, Previous exploration projects in the billion m3 occur at a depth of > 300 metres. Zomba, Malawi Lake Malawi basin have demonstrated By analogy, Lake Malawi, one of the deepest Tel: +265-1-524166/Fax: +265-1-524716 the existence of thick sedimentary rock lakes on the rift system could be a source of email: [email protected] sequences and structures that could trap helium-rich natural gas also. The northern hydrocarbons beneath the northern part end of the lake is considered particularly Head, BGS International of Lake Malawi and in the Lower Shire favourable for helium accumulation and British Geological Survey, Kingsley Dunham valley. In the northern part of Lake Malawi, retention. See also brochure 3. Centre, Keyworth, Nottingham NG12 5GG where the sedimentary sequences reach United Kingdom their greatest thickness (>2.5 km), shallow Tel: +44-(0)115-9363466 cores from the lake bottom indicate organic- Fax: +44-(0)115-9363474 rich sediments are being deposited under email: [email protected]

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