Lopo Vasconcelos Dept. Geology Eduardo Mondlane University Maputo, Mozambique

Transcription

1 Lopo Vasconcelos Dept. Geology Eduardo Mondlane University Maputo, Mozambique

2 1. INTRODUCTION Located in SouthernAfrica; km 2 Complex geo-tectonicframework,ageing from Meso-Archaean (2907 My) to Quaternary. KarooSupergroup (KSG) KSG presents generally 2mainepisodes: significant coaldeposits. sedimentary formations: U. Carboniferous L. Jurassic graben & half-grabenbasins igneous formations: simultaneous with topmost Upper Karoo sediments L. Jurassic Irregular distribution of KSG: Only igneous episode: Libombosmonoclinaland AngocheBasalts Only sedimentary formations: Metangulaand other Niassaand CaboDelgado grabens Areas where both exist Teteand Center Main coal occurrences

3 2. GEOLOGY OF THE MAIN MOZAMBICAN KAROO BASINS Geology of coal basins very diverse: Widespread geographical locations Different geologic/tectonic frameworks Different sedimentation environments Different evolution histories Different coal types/qualities Age: Upper Carboniferous Lower Jurassic Thick sedimentary sequences deposited in continental basins KAROO: Strata unconformably overlying the Precambrian basement followed by bimodal igneous formations of Lower Jurassic age and/or unconformably overlain by Middle Jurassic or younger strata. Bimodal Igneous formations

4 2. GEOLOGY OF THE MAIN MOZAMBICAN COAL (KAROO) BASINS SEDIMENTARY IGNEOUS

5 2. GEOLOGY OF THE MAIN MOZAMBICAN KAROO BASINS Karoo basins geodynamically subdivided into (Hobday 1986 in Cairncross1989): Foredeep basins Intracratonicsag basins Rifts Mozambique: Grabens/Half-grabens In general: more arid and warm conditions fluvial/lacustrine clasticsediments (COAL) sediments of glaciogenic/ /temperate and deltaic origin

6 2. GEOLOGY OF THE MAIN MOZAMBICAN KAROO BASINS Zambezi Valley: divided into W and E areas, separated by Precambrian rocks in Songoarea. Western: E-W trend; Eastern: NW-SE trend; Each of these areas: subdivided into structurally controlled smaller sub-basins. Three main basins: Chicôa-Mecúcoè Sanângoè-Mefídezi Moatize-Minjova (NW and SE extensions to Nkondeziand Mutarara) correspond to the Zambezi Mobile Belt between the Zimbabwe & Congo Cratons.

7 2.1. KAROO IN METANGULA BASIN (Niassa) No evidence of basal conglomerates of glacial origin (Dwyka); Outcrops of Ecca (coal)(permian) and Beaufort (Permo-Triassic) restricted to the southern tip of the basin Oriented NE-SE, border faults NW-SE faults: Rio Moola and Txiune Faults Verniers et al (1989) Beaufort up to 600 m thick Upper Karoo up to 6 km thick Ecca: -subdivided into 3 horizons: K2, K3 and K4. K2 local basal conglomerates, coarse grained gritty sandstones, siltstones, mudstones and thin coal beds. 343 m K3 K4 Coal beds avg. 20 cm in a sequence m thick. no coal, cross-bedded sandstones with intercalations of siltstones and mudstones. coal present amidst cross-bedded sandstones. two coal-bearing series Upper Lower 1-4 m thick coal seams cm thick 1-4 m thick coal seams cm thick Beaufort: argillaceous siltstones & reddish silty argillites, several levels of reptile fossils. Upper Karoo (Triassic-Jurassic): sedimentary rocks forming fluvial cyclic sequences, contemporary with the graben subsidence.

8 2.1. KAROO IN METANGULA BASIN (Niassa) VPDM (2012) There are seams with small coal proportion (N1C1: 29% coal). Total thickness: 96.2 m Sterile layers: 65.4 m (68%) Coal 30.8m (32%) Sterile 16.4 m Coal 14.4m 15%

9 2.2. KAROO IN TETE Border faults parallel to Zambezi Mobile Belt Faults filled with dolerite dykes (igneous episode Dip of strata: (45 near the border faults) Lower Jurassic Rift General Sequence of Formations LOWER KAROO VúziFormation (base Upper Carboniferous) Fluvial-glaciogenic characteristics Basal conglomerates, sandstones, coallyargillites and siltites. Isolated patches, lowest depressions of Pre-Karoo landscape

10 2.2. KAROO IN TETE Moatize Formation (Permian) Occurrence of thick coal deposits (Nr seams 6-8). Lays unconformably either on Precambrian rocks or on the Vúzi Formation. Moatize area 340 m Other areas: from some to hundreds of meters White to gray arkosic sandstones, micaceous sandstones with fossil flora of Glossopteris and Gangamopteris, amongst others, and black argillites with coal seams. Moatize 6 seams Mucanha-Vuzi 6 seams Benga area 4 seams(?) Sanangoe 8 seams Thicknesses Lateral extension Great variation André seam, w/ Matindeseries above, Moatize Matinde Formation (Mid.-U. Permian) White sandstones, sometimes arkosic and conglomeratic, with cross bedding. In some areas, Matinde Fm. can present some coal seams.

11 2.2. KAROO IN TETE LOWER-UPPER KAROO Cádzi Formation Transition from Lower-Upper Karoo -Permian/Triassic. Composed of medium to coarse grained arkosic sandstones with cross-bedding, with some limestones and carbonates sandstones UPPER KAROO Middle Triassic/Upper Jurassic 2 sedimentary formations, different types of sandstones. Igneous Formations Large scale cross-bedding in Cádzi Formation Several igneous formations Basalts, rhyolites, andesites, etc. Dolerite dykes which burn coal. Zumbo Formation Lualádzi Formation Carumacáfuè Mountains consisting of Zumbo Formation Red dunes resulting from the weathering of the Lualádzi sandstones Great Dyke in Moatize River

12 2.2. KAROO IN TETE 1. MUCANHA-VÚZI AREA (Chicôa-Mecúcoè) Several borehole programs: thickness of the Karoo sequence in the Chicôa-Mecúcoè area, especially in Mucanha-Vúzi sub-basin varies a lot. Cross sections: half-graben structure evident, Deepening of the basin to the west and to the south, as a consequence of the complicated faulting affecting this basin _ Seams dipping southwards and westwards. 6 Coal zones named M1-M6 (CPRM, 1983) or B0-B5 (Lächelt, 2004) S W N E SW NE

13 2.2. KAROO IN TETE 2. SANÂNGOÈAREA NW-SE oriented syncline, SE plunging and obliterated by a border fault, Precambrian rocks to the North. Coal outcrops are well visible. Dolerite dykes and sills (have little influence on coal). Basin cut by faults perpendicular to the synclinal axis

14 2.2. KAROO IN TETE 3. MOATIZE AREA VALE CONCESSION (Moatize) RIO TINTO CONCESSION (Benga) ChipangaSeam -Moatize River

15 2.2. KAROO IN TETE 3. MOATIZE AREA Basin divided into several sections defined either by natural boundaries or tectonic structures Graben oriented NW-SE and limiting faults, the biggest being Border Fault Sediments somewhat folded, with anticline and syncline axes with a prevalent NW-SE direction Several faults cut the basin, provoking vertical throws reaching 100 m. Doleritic dykes ( Great Dyke cuts the NW part of the basin). Outcrops of several coal seams: Great Dyke 1. Sousa Pinto 2.Chipanga 3. Bananeiras 4. Intermédia 5. Grande Falésia 6. André

16 2.2. KAROO IN TETE 3. MOATIZE AREA Lachelt(2004) VALE (2009)

17 2.3. COAL-BEARING FORMATION Mucanha-Vúzi Sanângoè Moatize Metangula m ~200 m ~340 m ~100 m

18 3. PROPERTIES OF MOZAMBICAN COALS In general, the Mozambican Permian coals are: Bituminous, with rank varying from high to low volatile bituminous coals, occasionally anthracitic Richer in Vitrinite than in Inertinite, Very low Liptinite content, In general ash yield is high, Minerals are finely intergrown with the organic matrix, thereby posing difficulties in liberation during beneficiation 3.1. PETROGRAPHY Dominance of vitrinite; Moatize with somewhat more inertinitic coals; Low content of liptinite (Mucanha-Vúzi) or almost absence (Moatize-Minjova-Mutarara). References to the petrography of coals from other regions were found only for Metangula coals: Mineral-rich (28% -48%); Vitrinite varying from 36% to 51%; Liptinite in the range 1.9% to 2.5%.

19 3.1. PETROGRAPHY Fluorescence of Moatize coals Fusinite with clay minerals Left: natural light; right: blue light. All: 600 x

20 3.1. PETROGRAPHY

21 3.2. RANK Moatize: increase in rank with depth: from 1,28% in Grande Falésia(Bituminous B) to 1,51% in S. Pinto (bituminous A). Minjova: %VR ranging between 1,36-1,43% -MVB (or bituminous B) to these coals Mucanha-Vúzi: lower rank than Moatize, %VR that varies between 1,00-1,10%, approximate border between HVB-MVB (bituminous B). Benga are MVB (bituminous B). %VR(max) varies from 1,16% in Top Chipanga Seam to 1,27-1,29% in Middle Chipanga and 1,27-1,37 in Bottom Chipanga, i.e., increases with depth. Mutarara: Rrbetween 1,93-3,86%, showing an anthracitic stage, some coal in LVB (many dolerite intrusions) No information was found concerning reflectance of coals from the Metangula Basin. Reports refer to Bituminous C-D Moatize

22 3.3. PROXIMATE ANALYSIS, CALORIF IC VALUE & TOTAL SULFUR RAW Coal Ash generally high; Less Chicoa- Mecucoe Max Metangula & Mutarara Sulfur Varies significantly; Higher: Metangula, Mucangadzi, Bohoziand some Moatize coals Basin Locality Sample H2O (%, ad) Ash (%, ad) Volatile Matter (%, ad) GCV (MJ/kg, ad) Sulfur (%, ad) Metangula unknown range of 27 samples 1,8-2,6 31,6-85,2 n.d. 14,78-26,48 0,30-3,50 Chicôa- Mecúcoè Mucangádzi R. range of 27 samples (trench) 5,9-11,5 16,4-45,1 19,7-28, Vúzi R. range of 28 samples (trench) 2,4-15,9 9,4-34,8 24,0-33, Bohozi R. range of 36 samples (trench) 1,3-14,2 12,7-35,2 21,0-28, Massínduè R. range of 18 samples (trench) 2,7-16,0 11,0-30,8 21,3-28, Mucanha R. range of 5 samples (trench) 1,0-1,8 13,8-33,0 19,5-26, Luângua R. range of 56 samples (trench) 0,8-11,2 13,8-37,7 14,9-28, Sanângoè License 871L Moatize- Mutarara- N condézi Moatize Section 6 Zone 8 (drilling) 4,2 52,9 14,9 13,25 1,06 Zone 7 (drilling) 4,0 42,5 21,9 17,30 1,24 Zone 6 Upper (drilling) 3,7 35,1 25,1 20,28 1,06 Zone 6 Lower (drilling) 3,2 41,6 23,5 18,25 1,23 Zone 5 (drilling) 3,2 45,7 21,5 16,16 1,01 Zone 4 Upper (drilling) 3,9 34,5 25,6 22,07 1,25 Zone 4 Lower (drilling) 2,6 48,6 21,7 17,30 1,28 Chipanga/Chi. 3 Mine (undg./chan.) 0,9 13,7 17,2 29,98 0,74 Chipanga/Chi. 8 Mine (undg./chan.) 0,6 17,6 17,1 29,66 0,50 Sousa Pinto (avg., drilling) 0,84 56,07 12,15 13,80 1,10 Chipanga L. (avg., drilling) 0,83 32,86 16,92 19,31 4,42 Chipanga M. (avg., drilling) 0,85 42,84 15,51 15,83 3,83 Moatize Chipanga U. (avg., drilling) 0,87 38,11 16,38 17,73 4,11 Central Section Bananeiras U. (avg., drilling) 0,92 38,09 16,74 17,57 4,03 Intermédia (avg., drilling) 1,04 41,76 16,30 16,45 3,77 Grande Falésia (avg., drilling) 1,04 43,74 16,75 15,62 3,80 André (avg., drilling) 1,20 36,18 18,68 21,37 3,81 Mutarara Boreholes (range 171 samples) 0,2-1,4 33,5-89,8 4,1-35,5 2,78-22,8 0,03-2,53 Ncondédzi Potential exp. thermal products +8 (ar) +22 n.a (ar) +1

23 3.3. PROXIMATE ANALYSIS, CALORIF IC VALUE & TOTAL SULFUR QUALITY OF SIZED FRACTIONS AND WASHED PRODUCTS Comparisons not always possible given the different sampling techniques and objectives of each investigation.

24 3.3. PROXIMATE ANALYSIS, CALORIF IC VALUE & TOTAL SULFUR QUALITY OF SIZED FRACTIONS AND WASHED PRODUCTS MINJOVA sized fractions Parameter (air dry) ROM 20 x 5 ROM 10 x 0,5 ROM 5 x 0,5 ROM -0,5 Moisture, % 1,3 1,3 1,2 1,5 Ash, % 27,2 18, ,7 Volatiles, % 18,5 20,5 18,9 20,6 Fixed Carbon, % 53 59,7 56,5 61,2 Gross CV, MJ/kg n.a. n.a. n.a. n.a. Total Sulfur, % n.a. n.a. n.a. n.a. METANGULA Parameter Ministry of Geology, 1981 Washed (19 samples) (cut-off density not known) VPDM (2012) Drill core samples of seams N3, N23, N2, N12, N1C1, N1C2, N1C3, N1C4 F 1.50 F 1.90 Moisture, % 1,8 3,0 6,28-7,90 4,99-6,40 Ash, % (air dry) 15,4 26,8 12,30-14,88 28,18-35,29 Volatiles, % (air dry) 27,2 32,2 32,80-34,55 27,21-29,58 Gross CV, MJ/kg 30,19-33,20 25,46-26,50 18,25-21,28 Sulfur, % 1,30 1,40 1,20-2,72 0,98-3,99 Parameters (air dry) SANÂNGOÈ Primary and Middlings Products for the -25mm +10mm -10mm+0.5mm fraction fraction Primary product composite of all zones F1,40 Middlings product composite of all zones F1,60 Primary product composite of all zones F1,40 Middlings product composite of all zones F1,60 Wash Yield (%) Moisture (%) Ash (%) Volatiles (%) Fixed Carbon (%) GCV (MJ/kg) Total S (%) BENGA

25 4. RESOURCES Lack of reliable numbers that illustrate the real situation. The Mining Directorate of Mozambique (DNM, 2013) compiled a table of coal resources(jorc) with the information provided by the coal companies : TOTAL of 25,439 million tonnes; Inferred -11,348 million tonnes; Indicated -10,496 million tonnes Measured 3,585 million tonnes Numbers apply to 16 licenses: 10 from Moatize-Ncondézi- Mutarara 2 from Sanângoè-Mefidézi 3 from Mucanha-Vuzi 1 from Metangula

26 6. CONCLUSIONS Much work is still required, especially of scientific nature, and most especially in the remote areas such as western Tete and NiassaProvinces to which access remains a challenge. In general, Mozambican Permian coals are medium to low volatile bituminous, with some areas having high volatile bituminous, and a few others reaching the anthracite stage. Petrographically speaking, these coals are mainly vitrinitic. Total sulfur content of sized and washed products typically around 1%, with some horizons having higher contents. Almost all basins/sub-basins coals can be beneficiated to yield both coking coals and thermal coal fractions. Resources and Reserves still do be evaluated with more studies and exploration works.