Background to the Liberia and Sierra Leone implosions

Liberia and Sierra Leone are tragic examples of what happens when central authority collapses and warlords emerge as de-facto rulers over large portions of the national territory. Horrors inflicted on non-combatants and the well publicized trading in conflict diamonds served to focus world attention on these two small countries sharing a common border. Both countries have experienced mixed success with outside military intervention for peace keeping and nation building purposes. What has happened is all the more distressing when one considers each countrys prospects at birth under the political and economic aegis of arguably two of the most powerful and enlightened countries of the time, Great Britain in the case of Sierra Leone and the United States in Liberia.     

Background to the Liberia and Sierra Leone implosions

Liberia and Sierra Leone are tragic examples of what happens when central authority collapses and warlords emerge as de-facto rulers over large portions of the national territory. Horrors inflicted on non-combatants and the well publicized trading in conflict diamonds served to focus world attention on these two small countries sharing a common border. Both countries have experienced mixed success with outside military intervention for peace keeping and nation building purposes. What has happened is all the more distressing when one considers each countrys prospects at birth under the political and economic aegis of arguably two of the most powerful and enlightened countries of the time, Great Britain in the case of Sierra Leone and the United States in Liberia.     

The nature and location of the suture zone in the Rokelide orogen, Sierra Leone: Geochemical evidence

The boundaries of the West African Craton mark the location of a continuous suture zone that records Neoproterozoic to Early Cambrian oceanic closure. The western part of the circum-West African suture zone extends through the line of outcrop of the Mauritanide, Bassaride and Rokelide mountain belts. Our geochemical analyses are consistent with the idea that igneous and metamorphic rocks of the Rokelide and Southern Mauritanide mountain belts of West Africa occupy a suture zone that records the closing of a Neoproterozoic to Early Cambrian ocean basin during the Pan-African orogeny and final assembly of Gondwana. The closing of that basin was marked by the collision between Archean rocks of the Leo massif of the West African Craton and reactivated Archean and Paleoproterozoic rocks that now outcrop nearer to the coast of Africa in Sierra Leone and Liberia. Within the Rokelides, the geochemistry of the Kasewe Hills volcanic rocks and Marampa amphibolite indicate that remnants of an arc system are caught up in the suture zone. The geochemistry of Guingan schists that outcrop along strike of the Rokelides is compatible with the idea that the metamorphosed equivalents of the Marampa and Kasewe Hills arc volcanic rocks extend through the Bassarides and into the Southern Mauritanides.     

The Kasila Group,Sierra Leone,an interpretation of new data

Recent geological mapping and U/Pb age determinations show that the Kasila Group has many of the characteristics shown by the Limpopo Belt and other high-grade linear metamorphic belts. The Kasila Group appears to form the southwestern periphery of the dominantly low-grade West African Archaean Craton.     

The nature and location of the suture zone in the Rokelide orogen,Sierra Leone: Geochemical evidence

The boundaries of the West African Craton mark the location of a continuous suture zone that records Neoproterozoic to Early Cambrian oceanic closure. The western part of the circum-West African suture zone extends through the line of outcrop of the Mauritanide, Bassaride and Rokelide mountain belts. Our geochemical analyses are consistent with the idea that igneous and metamorphic rocks of the Rokelide and Southern Mauritanide mountain belts of West Africa occupy a suture zone that records the closing of a Neoproterozoic to Early Cambrian ocean basin during the Pan-African orogeny and final assembly of Gondwana. The closing of that basin was marked by the collision between Archean rocks of the Leo massif of the West African Craton and reactivated Archean and Paleoproterozoic rocks that now outcrop nearer to the coast of Africa in Sierra Leone and Liberia. Within the Rokelides, the geochemistry of the Kasewe Hills volcanic rocks and Marampa amphibolite indicate that remnants of an arc system are caught up in the suture zone. The geochemistry of Guingan schists that outcrop along strike of the Rokelides is compatible with the idea that the metamorphosed equivalents of the Marampa and Kasewe Hills arc volcanic rocks extend through the Bassarides and into the Southern Mauritanides.     

Petrochemistry of eclogites from the Koidu Kimberlite Complex,Sierra Leone

Petrography, mineral and bulk chemistry of upper mantle-derived eclogites (garnet and clinopyroxene) from the Koidu Kimberlite Complex, Sierra Leone, are presented in the first comprehensive study of these xenoliths from West Africa. Although peridotite-suite xenoliths are generally more common in kimberlites, the upper mantle sample preserved in Pipe Number 1 at Koidu is exclusively eclogitic, making this the fifth locality in which eclogite is the sole polymineralic xenolith in kimberlite. Over 2000 xenoliths were collected, of which 47 are described in detail that include diamond, graphite, kyanite, corundum, quartz after coesite, and amphibole eclogites. Grossular-pyrope-almandine garnets are chromium-poor (<0.72 wt% Cr₂O₃) and fall into two distinct groups based on magnesium content. High-MgO garnets have an average composition of Pyr₆₇Alm₂₂Gross₁₁, low-MgO garnets are grossular- and almandine-rich with an average composition of Gross₃₄Pyr₃₃Alm₃₃. Clinopyroxenes are omphacitic with a range in jadeite contents from 7.7 to 70.1 mol%. Three eclogites contain zoned and mantled garnets with almandine-rich cores and pyrope-rich rims, and zoned clinopyroxenes with diopside-rich cores and jadeite-rich rims, and are among a very rare group of eclogites reported on a world-wide basis. The bulk compositions of eclogites have ranges comparable to that of basalts. High-MgO eclogites (16–20 wt% MgO) have close chemical affinities to picrites, whereas low-MgO eclogites (6–13 wt% MgO) are similar to alkali basalts. High-MgO eclogites contain high-MgO garnets and jadeiterich clinopyroxenes. Low-MgO eclogites contain low-MgO garnets, diopside and omphacite, and the group of primary accessory phases (diamond, graphite, quartz after coesite, kyanite, and corundum); grospydites are peraluminous. Estimated temperatures and pressures of equilibration of diamond-bearing eclogites, using the diamond-graphite stability curve and the Ellis and Green (1979) geothermometer, are 1031°–1363° C at 45–50 kb.K _D values of Fe-Mg in garnet and clinopyroxene range from 2.3 to 12.2. Diamonds in eclogites are green, yellow, and clear, and range from cube to octahedral morphologies; the entire spectrum in color and morphology is present in a single metasomatized eclogite with zoned garnet and clinopyroxene. Ages estimated from Sm-Nd mineral isochrons range from 92–247 Ma. _Nd values range from +4.05 to 5.23. Values of specific gravity range from 3.06–3.60 g/cc, with calculated seismic Vp of 7.4–8.7 km/s. Petrographie, mineral, and bulk chemical data demonstrate an overall close similarity between the Koidu xenolith suite and upper mantle eclogites from other districts in Africa, Siberia and the United States. At least two origins are implied byP-T, bulk chemistry and mineral compositions: low-MgO eclogites, with diamond and other accessory minerals, are considered to have formed from melts trapped and metamorphically equilibrated in the lithosphere; high-MgO eclogites are picritic and are the products of large degrees of partial melting, with equilibration in the asthenosphere. Fluid or diluted melt metasomatism is pervasive and contributed here and elsewhere to the LIL and refractory silicate incompatible element signature in kimberlites and lamproites, and to secondary diamond growth.     

Temporary labour migration and sustainable post-conflict return in Sierra Leone

Economic and social development indicators suggest that the small West African state of Sierra Leone is among the poorest countries in the world. Sierra Leone’s economy and quality of life deteriorated rapidly during a decade of political instability and civil war in the 1990s, when many people fled their homes and abandoned their livelihoods due to the rebel insurgency. This paper examines the post-war reconstruction scenario in Sierra Leone and presents recent evidence from two rural communities in the Eastern Province that were badly affected by the conflict. The paper considers the links between the farming and diamond mining sectors, which, despite severe dislocation during the conflict period, have proved to be remarkably resilient. It is argued that seasonal labour mobility associated with this dual economy has not only continued to be a key ingredient in sustaining livelihood portfolios, but is actually an essential pre-condition for the creation of an enabling environment for sustainable post-conflict return.

A primary platinum occurrence in the Freetown Layered Intrusion, Sierra Leone

The primary source of the alluvial platinum-group minerals (PGM) of the Freetown Layered Intrusion, Sierra Leone, has been unknown since their discovery 70 years ago. This is a report on work in progress to establish a primary occurrence related to the igneous layering. New whole-rock major and minor element analyses and precious metal assays show that at key horizons there is a significant change in the silicate mineral compositions and in Cu, Cr and Ni, as well as in Pt and Pd, comparable to those encountered in other PGM-bearing layered intrusions. Anomalous (0.1 to 0.4 g/t) Pt levels occur in pyroxene troctolites, which maintain these levels along strike. Received: 30 July 1999 / Accepted: 2 December 1999     

Petrogenesis of the Fe-Ti intrusive complexes in the Sierra Leone region, Central Atlantic

The study of melt inclusions in Cr-spinels from melanocratic troctolites provided the first direct information on the physicochemical parameters of enriched magmatic systems that produced high-Fe and high-Ti intrusive complexes in the Sierra-Leone region (Central Atlantic, 6°N). These complexes are made up of predominating hornblende Fe-Ti oxide gabbronorites and gabbrodiorites with subordinate amount of ultramafics, diorites, quartz diorites, and trondhjemites. The study of melt inclusions and rocks showed that the majority of gabbroids of the Central Atlantic (Sierra Leone area and 15°20′ Fracture Zone) were derived from N-MORB-type melts, whereas differentiated Fe-Ti-oxide rocks were crystallized from other melts, which were preserved as inclusions in the Cr-spinels from the melanocratic troctolites of the Sierra Leone region. The ion-microprobe study of these inclusions yield direct evidence on the elevated water content (up to 1.24–1.77 wt %) in the parental melts of Fe-Ti oxide rocks. Data on trace and rare-earth element distribution together with high (La/Sm)_N and (Ce/Yb)_N ratios in the inclusions indicate the possible influence of deep plume source on the generation of these magmas. Simulation based on melt inclusion data testifies that high-Fe intrusions of the Sierra Leone area were crystallized from the water-saturated magmas at relatively low temperatures (1020–1240°C). It was shown that the geochemically enriched Fe-Ti melts were presumably formed regardless of N-MORB-type magmatism predominant in Central Atlantic, under the influence of new mantle plume that caused melting of hydrated oceanic lithosphere.     

地面高精度磁法在塞拉利昂洛琴铁矿区的应用

塞拉利昂位于赤道附近,属于低纬度地区。在低纬度区,以水平磁化为主的条件下,磁性体所产生的ΔT磁异常以负异常为主,正异常伴生。通过对磁资料进行倒相180°、化赤、化极处理方法的对比,认为在不考虑剩磁、磁性体退磁作用的情况下,结合当地地质情况,倒相180°的处理方法能够展现该区的磁场特征,以此作为基础资料对全区的磁异常进行解释。利用不同高度的向上延拓处理,有效地排除了浅层干扰,突出深层异常特征,再结合最大坡度法、经验切线法、欧拉奇次方程法确定其磁性体的埋深和水平大致位置,最后,采用二度半人机交互反演拟合磁性体大致的形态,通过布设钻探施工,验证结果与推断吻合较好。     

The geology of part of an orogenic belt in western Sierra Leone,West Africa

Zusammenfassung Die Sierra Leone unterteilt sich in zwei Haupteinheiten. Die östliche ist ein Teil des festen präkambrischen westafrikanischen Kratons und besteht aus hochgradig metamorphem Gestein und Granitgneisen. Die Strukturen verlaufen in vorherrschend NE-Richtung. Der westliche Teil enthält Elemente eines orogenen Gürtels, nämlich der Rokeliden, die entweder im späten Präkambrium oder frühen Paläozoikum entstanden sind und nach NNW streichen. Die Gesteinsserien, die den orogenen Gürtel bilden, setzen sich aus dem Kasila-System, einer unbenannten Gneisgruppe östlich davon, den Rokel River Series und den Marampa Schists zusammen. Die sich an das Kasila-System, umbenannt in Kasila-Gruppe, anschließenden Gneise und wahrscheinlich auch die Kasila-Gruppe selbst können mit dem Gestein des Kratons verglichen werden, sind jedoch während der Entstehung der Rokeliden neu überprägt worden. Sie bilden die Basis der Mulde, die Sedimente und vulkanisches Gestein aus den Rokel River Series und den Marampa Schists enthält. Die Rokel River Series sind neu benannt und unterteilen sich in die Rokel River Gruppe mit sechs Formationen und in die Taban Formation, die aus nach-orogener Molasse besteht. Die Marampa Schists sind neu benannt in Marampa Formation. Das Ausmaß der Metamorphose steigert sich über die Rokeliden nach WSW, und die Marampa Formation ist der am stärksten metamorphisierte Teil der geosynklinalen Ausfüllung.

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Sierra Leone is divisible into two major structural units. The eastern one is part of the stable Precambrian West African craton and consists of high grade metamorphic rocks and granitic gneisses. The foliation has a dominantly NE trend. The western unit contains the elements of an orogenic belt named the Rokelides, which formed in either late Precambrian or early Palaeozoic, and trends NNW. The rock groups which comprise the orogenic belt are the Kasila System, an unnamed group of gneisses on the east of it, the Rokel River Series and the Marampa Schists. The gneisses adjacent to the Kasila System, renamed Kasila Group, and also, probably, the Kasila Group can be correlated with rocks in the craton, but were refoliated during the Rokelide orogenesis. They constituted the basement to the geosyncline which contained sediments and volcanic rocks of the Rokel River Series and Marampa Schists. The Rokel River Series is renamed, and divided into Rokel River Group which contains six formations, and the Taban Formation which is post-orogenic molasse. The Marampa Schists are renamed the Marampa Formation. The intensity of metamorphism and deformation increases across the Rokelides towards the WSW and the Marampa Formation is the most highly metamorphosed part of the geosynclinal infilling.

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Résumé Le Sierra Leone peut se diviser en deux principales sections structurales. La section orientale fait partie du craton stable précambrien de l'Afrique occidentale, formé de roches métamorphiques de haute qualité et de gneiss de granit. La foliation a principalement une direction NE. La section occidentale contient les éléments d'une ceinture orogénique appelée les Rokelides qui ont été formées soit vers la fin de la période précambrienne, soit au début de la période paléozoique et en direction NNW. Les groupes rocheux qui comprennent la ceinture orogénique sont le Kasila System, un groupe de gneiss sans nom situé à son côté est, la Rokel River Series et les Marampa Schists. Les gneiss avoisinant le Kasila System, renommé Kasila Group et en toute probilité le Kasila Group également peuvent être rattachés aux roches du craton mais auraient été refoliés pendant l'orogenèse Rokelide. Ils ont formé la base du géosynclinal qui contient des sédiments et des roches volcaniques de la Rokel River Series et des Marampa Schists. La Rokel River Series a été renommée et divisée en Rokel River Group qui contient six formations et la Taban Formation qui est la mollasse post-orogénique. Les Marampa Schists ont été renommés la Marampa Formation. L'intensité du métamorphisme et de la déformation augmente vers WSW à travers les Rokelides, et la Marampa Formation est la partie la plus métamorphosée de l'accumulation géosynclinale.

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塞拉利昂中部马卡利地区金矿特征及成矿远景

塞拉利昂中部马卡利地区出露有大片的太古界花岗-绿岩带地质体,其金矿资源丰富。通过矿产勘查和成矿规律研究表明,金的来源与太古界花岗-绿岩带地体密切相关。岩金矿床类型为含铁建造金矿床,主要赋存于绿岩带的绿片岩中及含铁建造的片岩中,受褶皱和断裂构造控制;砂金矿的类型为河流冲积型砂金矿,主要分布在花岗-绿岩带内及其周边河流中的全新统冲积层中下部砂砾石层中。重砂异常和地球化学异常区内具备良好的岩金、砂金成矿地质背景和找矿前景,实施砂金-岩金综合找矿方法,找矿潜力巨大。     

New Rb-Sr age determinations on the Archaean basement of Eastern Sierra Leone

The Archean basement of Sierra Leone is a typical example of granite-greenstone terrains found in ancient continental nucleii. Reconnaissance field mapping showed that the area can be subdivided into old gneiss, which predates the greenstone belts, and young granite which is later than the greenstone belts.New Rb-Sr whole-rock age determinations on two suites of old tonalitic gneiss yield ages of 2786 ± 49 Ma and 2770 ± 137 Ma, which either reflect the time of formation of the original tonalites or their metamorphism. Three new Rb-Sr whole-rock age determination on young granites yield ages of 2786 ± 143 Ma, 2780 ± 79 Ma and 2770 ± 50 Ma, which are interpreted as the time of emplacement. The widespread occurrence of similar young granites, throughout the Archaean of West Africa, suggests that these results date a major event in the evolution of this segment of the crust.A published Pb-Pb age of the old gneiss and the new ages of the young granite bracket the age of the greenstone belts to 3000-2770 Ma. However, if the Rb-Sr ages of the old gneiss reported in this paper reflect the time of their formation, the age of the greenstone belts is tightly bracketed to ca. 2770 Ma. There is no isotopic evidence for rocks substantially older than 3000 Ma in the West African Archaean.     

Hydrothermal Mineralization in the Sierra Leone Fracture Zone (Central Atlantic Ocean)

The analysis of data on the location of hydrothermal fields, seismicity, and satellite altimetry evidences that in mid-ocean ridges with low spreading velocity hydrothermal fields tend to be grouped in areas with generally low seismic activity and at intersections of discontinuities and rift zones. Based on this assumption, the Sierra Leone Fracture Zone was studied in 2000 during cruise 22 of the R/V Akademik Nikolaj Strakhov.The study of gabbrodolerite and dolerite showed that sulfide ore minerals in them were formed both by hydrothermal and magmatic processes. The analysis of melt inclusions demonstrated that magmatic complexes formed from a high-temperature (1210–1255°C) low-potassium melt of the N-MORB type. Investigations of fluid inclusions revealed that gabbro and dolerite formed under the influence of an active hydrothermal system at a temperature of 205–226°C. Thus, the Sierra Leone Fracture Zone is considered to be perspective for the discovery of a new hydrothermal field.     

Towards an understanding of man-firewood relations in Freetown (Sierra Leone)

This paper examines ‘folk’ evaluation and classification of firewood as a means towards understanding man-firewood relations in Freetown. It demonstrates how access to ‘wood views’ renders comprehensible identifiable spatial and temporal patterns in firewood exploitation and utilisation. It is argued that the extension of the ethno-scientific approach beyond mere identification of wood categories to the examination of the relationship between cognition and action generates information capable of informing efforts towards short-term gains and/or long-term development policy aimed at a more efficient management and utilisation of the firewood resource. The article concludes by emphasising the need for an understanding of the view both from ‘above’ (technological forestry) and ‘below’ (folk ecology) of man-firewood relationships in the Freetown area in order that meaningful co-operative modifications based on a blend of sodo-cultural and ecological considerations, on the one hand, and economic and technological factors on the other, can be effected.     

Groundmass oxide minerals in the Koidu kimberlite dikes,Sierra Leone,West Africa

Petrology and oxide mineral chemistry are presented on 5 kimberlite dikes that are classified into three groups: (1) one dike is highly carbonated and highly oxidized (> MH) and is characterised by chlorite+Mn-titanomagnetite+rutile+hematite (after chlorite)+maghemite (after titanomagnetite), with ilmenite and perovskite being absent; (2) three dikes are typified by atoll-textured spinels +phlogopite+euhedral Mn-picroilmenite, of intermediate oxidation state (WM-FMQ) with coexisting deuterically serpentinized olivine+Ni-Fe alloys and magnetite; (3) the remaining dike records an early crystallization event under very low ( WM) redox conditions that precipitated anionic-deficient spinels and a Mg-Ti-Cr-wüstite-type phase, followed by late stage more oxidizing (=FMQ) Mnpicroilmenite.Spinels are complexly zoned and crystallization trends among the dikes are diverse, underscoring the fact that no single compositional trend, or evolutionary sequence is typical of kimberlites. Ilmenites are euhedral, and criteria for groundmass crystallization are established. Extraordinarily high MnO (max 17 wt%) contents and high geikielite (62 mole%) concentrations expand the ilmenite field typically assigned to that of kimberlites. Zirconium, Nb and Cr are present in concentrations of 0.5–3 wt% (as oxides) in ilmenite. These highly incompatible elements, along with Mn, are concentrated in late stage melt fractions. The high pyrophanite contents, which are more typical of silicic alkali suites, are accompanied by phlogopite in the Koidu dikes.Objective evaluations of kimberlite-carbonatite relations, as outlined in the literature, cannot be made based on the oxide mineral group. Much of the compositional data for oxides in kimberlites are on mantle-derived xenolith suites and are not from oxides derived from the crystallization of kimberlitic melts.Assessments of the fO₂'s of kimberlites have considerable potential in evaluating diamond survival through redox reactions. Manganese-rich (+Nb, Zr, Cr) ilmenites are typical of many kimberlites and should be considered in the suite of index minerals employed in prospecting.     

Gravity stratification in the Freetown Basic Igneous Layered Complex,Sierra Leone,West Africa

An area of 78 sq. km in the vicinity of Freetown is mapped for the first time. By systematic mapping and study of about 1,500 thin sections, nine macro layered units have been recognized in this lowest exposed part of the intrusion. Each unit grades upward from magnetite or olivine-rich layers, through pyroxene-rich to plagioclase-rich rock. Field data of fine-scale layering, ‘false-bedded’ layers and slumping are given. These and other sedimentary structures and features indicate that the Freetown magma was convective. It is suggested that rhythmic layering in the Freetown basic intrusion originated from slow accumulation of density-sorted crystals which precipitated simultaneously from the magna-pulses.     

Land access constraints for communities affected by large-scale land acquisition in Southern Sierra Leone

While national figures of land availability are used to justify accepting large-scale land investors, not very much is known about the local level realities of land availability. By combining remotely sensed data with fieldwork, system dynamics modelling and qualitative research methods, we examine local level realities of land use and availability in the Malen Chiefdom of Southern Sierra Leone. Here, local communities are experiencing the outcomes of large-scale investments in oil palm for biodiesel and other industrial purposes by the SOCFIN Agricultural Company. We find that beyond agricultural production, there are other land uses that are vital for the socio-cultural, economic and environmental realities of communities. The Company does not respect engagements promised to local people to set aside buffer zones around living areas to serve as biodiversity corridors. Local communities are severely deprived of agricultural land and other land resources. The operations of SOCFIN do not take account of present or future land needs of local people. A baseline requirement of food crop land should be set aside for each community, to ensure the attainment of food security in communities affected by land acquisitions. Such baseline requirement should be augmented with local level needs assessments to meet new demand for cropland necessitated by changing demography. This model of land planning can be applied to other land use and additional engagements of large-scale land investors.