manganese mining in kilifi

kiwara hill manganese occurrence near kilifi, kenya | the diggings

kiwara hill manganese occurrence near kilifi, kenya | the diggings

The Kiwara Hill Manganese Occurrence is near Kilifi, Kenya. The site was first discovered in 1908. Ore mineralization has been found at this location and the size of the deposit is estimated to be small, however the precise grade, tonnage, and extent of the mineralization are not known. There has been no production and little to no activity other than routine claim maintenance since the mineral discovery. The ore mined is composed of pyrolusite with waste material consisting primarily of goethite and quartz. The ore body extends 630.00 meters (2,066.93 feet) long, 370.00 meters (1,213.91 feet) wide, and 0.12 meters (0.39 feet) thick. The host rock in this area is sand & gravel.

1 World-class significance is determined by total endowment of the contained commodity. This includes all past production and remaining reserves. Each commodity is considered separately and commodities cannot be combined to arrive at a significant size. The tonnage thresholds are from the mine model grade-tonnage studies. As of June 2008, many entries were classified as significant under less strict rules.

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manganese deposit - an overview | sciencedirect topics

manganese deposit - an overview | sciencedirect topics

Manganese deposit occurrences are within Kilifi district along the coast, Samburu and Moyale Districts in the Rift Valley and in parts of Isiolo in Eastern Province. Production of this mineral has commenced albeit in a small scale.

Copper occurrences have been reported within various parts of the country including Mwingi, Taita-Taveta and West Pokot where some operators have obtained exploration licences to determine their economic viability.

Manganese deposits and IFs of Neoproterozoic age are extensively but discontinuously developed in association with glacial deposits. In addition, iron-rich shales are relatively common in contemporaneous, glacially influenced successions (e.g., Young, 2002). The latter relationship was re-emphasized by Canfield et al. (2008) to infer a return during the late Neoproterozoic to Archean-style anoxic, ferruginous ocean conditions. Significant iron and manganese accumulations in association with glacial deposits are present in a number of Neoproterozoic successions worldwide, although for other Neoproterozoic IFs a clear stratigraphic or temporal relationship with ice ages has not been established (e.g., Cabral et al., 2011; see also Appendix 1).

Presently available geochronological constraints and stratigraphic correlations imply that IFs are at least temporally related to the Sturtian (~715Ma) and Marinoan (~635Ma) glaciations, although some uncertainty exists regarding a number of Neoproterozoic glacial events, their ages and duration, and chemostratigraphically based correlations (e.g., Kendall et al., 2009). The Rapitan IF and Franklin igneous event on Victoria Island in Canada are both ~715Ma (Heaman et al., 1992; Macdonald et al., 2010), supporting a genetic relationship among volcanism, mantle processes, and deposition of IF at least on the basin scale. Neoproterozoic IFs are typically enriched in Mn and P and have high Co, Ni, and Cu contents (Halverson et al., 2011; Klein and Beukes, 1993; Planavsky et al., 2010a,b; see also Chapter 9.11). Highly positive sulfur isotope values in shales and manganese formations overlying Neoproterozoic glacial diamictites have been related to Rayleigh distillation in low-sulfate oceans, which were highly susceptible to the development of anoxic ferruginous conditions and hydrothermal delivery of iron and manganese into shallow basins during mantle plume breakout events (Liu et al., 2006). Importantly, IFs were deposited during deglaciation as indicated by the presence of dropstones in IFs and interlayering with tillites. Poor age constraints for other Neoproterozoic IFs do not warrant correlation with Neoproterozoic mantle plume events, although several such events occurred during the late Neoproterozoic (e.g., Ernst and Buchan, 2001). However, almost all Neoproterozoic IFs are spatially and temporally linked with submarine mafic and felsic volcanic units. Some basins hosting IFs of this age also contain coeval VMS deposits (e.g., Buhn et al., 1992; Cabral et al., 2011), suggesting a proximal hydrothermal source of metals. Most of these IFs were deposited either in closed rift basins or on reactivated continental margins (e.g., Trompette et al., 1998).

Neoproterozoic IFs generally comprise laminated and nodular hematite, massive magnetite, hematitic mudstone, and jasper (Figure 16). Lenticular and nodular chert and jasper are less common, but are present within laminated jasper beds (Yeo, 1981). Banded cherts, similar to those in Archean and Paleoproterozoic IFs, are absent. Furthermore, the thickness of Neoproterozoic IFs is highly variable over relatively short distances. GIFs and intraformational conglomerates containing hematite pebbles developed locally at the top of the Rapitan Iron Formation and in the Jacadigo Group, Brazil, but coated grains are uncommon (Klein and Beukes, 1993a; Klein and Ladeira, 2004). REE patterns for Neoproterozoic IFs have either no or slightly positive Eu anomalies, and either no or slightly negative Ce anomalies (Derry and Jacobsen, 1990; Fryer, 1977; Halverson et al., 2011; Klein and Beukes, 1993a; Klein and Ladeira, 2004; Liu et al., 2006; Lottermoser and Ashley, 2000), likely indicating a high degree of dilution of locally derived, hydrothermal fluid by mildly oxidized seawater. Models that are generally accepted for Phanerozoic manganese deposits (see Chapter 9.11) are probably also applicable to the origin of Neoproterozoic IFs. These models infer anoxic conditions with enhanced submarine volcanism in the deeper parts of isolated to semi-isolated basins and manganese precipitation occurring at the redox boundary on the shallow margins of the basins. Another factor, in addition to mantle plume events and tectonics, which could have contributed to deposition of IF, is dramatic sea-level fall during ice ages. Sea-level fall would decrease the overlying hydrostatic pressure and shift equilibrium in the seafloor hydrothermal systems toward higher Fe/H2S ratios, thus promoting larger Fe fluxes into the oceans (Kump and Seyfried, 2005). In sum, although the occurrence of Neoproterozoic IFs supports long durations of glaciations and the existence of redox-stratified basins, they do not require extreme snowball Earth conditions in order to form.

Figure 16. Rapitan Iron Formation at Cranswick River, Mackenzie Mountains, Northwestern Territories, Canada. (a) Nodular and banded jasper interlayered with hematite bands and overprinted by anastomosing hematite. (b) Jasper nodules and lenses in massive hematite. (c) Banded jasperhematite iron formation with dropstone overprinted by anastomosing hematite. (d) Jasper nodules and lenses in massive hematite.

The Vani manganese deposit is a fossil stratabound hydrothermal deposit formed by the penetration of hydrothermal fluids through a lithified pyroclastic tuff. Two types of deposit have been recognized: high-temperature hydrothermal Mn deposits formed initially when the hydrothermal fluids penetrated faults and fissures within the volcaniclastic sandstone and bedded hydrothermal Mn deposits formed subsequently as the cooling hydrothermal fluids migrated along the bedding planes of the volcaniclastic sandstone. Both are late-stage, low-temperature deposits. Mineralogical analysis showed that the principal manganese minerals present are (in decreasing order of abundance) cryptomelane, pyrolusite, hollandite, ramsdellite, coronadite and romancheite with jacobsite, franklinite and hydrohetaerolite present in minor amounts. On average, the high-temperature hydrothermal Mn deposits appear to be marginally enriched in pyrolusite, ramsdellite and perhaps coronadite and jacobsite and depleted in haematite compared to the bedded hydrothermal Mn deposits but these variations are not statistically significant. Variations in the abundances of minerals between individual samples are much greater with pyrolusite, cryptomelane and hollandite varying between low and very abundant and ramsdellite, coronadite, romanechite and barite between absent and very abundant. However, no systematic patterns in the relative abundances of the various minerals could be observed. The compositional data also showed wide variations in element concentrations between samples. On average, the high-temperature deposits are significantly enriched in Mn and the bedded deposits in Na, K, Mg, Ca, Al, Ti, Fe, Zn, Zr, Nb, Ce, Hf and Th. This reflects the fact that the high-temperature deposits formed first when the Mn concentration in the hydrothermal fluids was higher. The bedded deposits formed subsequently and are characterized by higher concentrations of lithogenous elements derived from the associated volcaniclastic sandstone. However, no well-defined patterns of association between the ore-forming elements could be observed in the samples. Nonetheless, these data demonstrate that the Vani manganese deposit is a Mn-Ba-Pb-Zn-As-Sb-W-rich hydrothermal deposit which is similar in mineralogy and composition to the epithermal vein deposits of the southwestern United States. Based on a comparison with the JADE submarine hydrothermal field in the Okinawa Trough, it is suggested that Pb, Zn As and Sb may have been leached as chloro complexes from felsic rocks of the Aegean intracontinental Arc by deeply penetrating chloride-rich hydrothermal fluids during the formation of the Vani manganese deposit, although a magmatic contribution is possible. The high positive Eu anomalies in the deposit confirm that leaching of the divalent Eu2+ from the host rocks took place at temperatures greater than 250C during this time.

The marine manganese deposits (MMD) include manganese nodules (also called polymetallic nodules or ferromanganese nodules), slab-type ferromanganese encrustations, and cobalt-rich crusts. Although first recovered in 1868 from the Kara Sea, off Russia (erstwhile the USSR), probably the first detailed scientific investigation of MMD was made during the HMS Challenger expedition (187276, Fig. 1.1). This study followed the recovery of manganese nodules onboard on March 13, 1874 from the seafloor between Hawaii and Tahiti in the Pacific Ocean. The recovery of manganese nodules possibly led to one of the greatest advances made in the world of science. In subsequent years, manganese nodules and crusts were collected from several basins of the worlds oceans. However, it was not until the late 1950s that scientists were able to convince industrialists to explore the manganese nodule deposits of the central Pacific Ocean for their economic potential. In fact, because of the initiative of Mero (1965), manganese nodule deposits were soon considered as possible sources of metals such as manganese (Mn), nickel (Ni), copper (Cu), and cobalt (Co).

Even though some minerals have been retrieved from oceans already, it is only over the last three decades that the exploration of mineral resources from the deep seafloor has been carried out. Detailed examinations of earlier data indicate a possibility of recovery of massive sulfides, cobalt-rich crusts, and manganese nodules from the deep sea by the middle of this century because the demand for raw material is consistently increasing. However, constraints remain on the inadequate information of the resources (e.g., grade, geographical extension, future market demand), and whether environmentally responsible mining technology could be developed in the future. The MMD, as mentioned previously, are attractive from both commercial and academic angles, with manganese nodules taking the center stage. Accordingly, this book focuses almost entirely on nodules, and hence we use nodules throughout the text to represent manganese/polymetallic/ferromanganese nodules.

The nodules are generally potato shaped, porous, and of black earthy color of 210cm in diameter (Fig. 1.2AC). The nodules grow at an extremely slow rate (about 15mm per million years) and occur at water depths between 4000 and 6000m on the seafloor. They host several metals of high commercial interest (with high enrichment index; Table 1.1). The wet density of nodules is close to 2g/cm3, moisture dry mass (water content) 40%, and porosity 50%. The nodules have layers of thick dark-colored oxides arranged alternately with thin light-colored silica-rich layers around a nucleus (Fig. 1.2D). The dark layers are formed of crystallized hydroxides of Mn and iron (Fe). The well-crystallized minerals, 10 manganite (todorokite) and 7 manganite (birnessite), are enriched in Mn, Ni, and Cu, while the cryptocrystalline minerals such as vernadite and -MnO2 have significant Fe and Co (Burns and Burns, 1977).

(A) values in %, (B) Columns 2 and 3 in percentage. Figures in million metric tons. PGE, platinum group elements. Ocean reserve is from the Clarion-Clipperton Zone in the Pacific Ocean (ISA, 2010). Terrestrial reserves are economically recoverable reserves as of today.

(A) values in %, (B) Columns 2 and 3 in percentage. Figures in million metric tons. PGE, platinum group elements. Ocean reserve is from the Clarion-Clipperton Zone in the Pacific Ocean (ISA, 2010). Terrestrial reserves are economically recoverable reserves as of today.

Several schools of thought exist regarding the origin and growth of the nodules on the seafloor. The metals may have been supplied by seawater, dead organisms, volcanic magmatic emanations, weathering of seafloor rocks, and following reaction of hot water with the underlying basalts and subsequent leaching and venting of metals. The processes for the formation of nodules have, however, been ascribed largely to two mechanisms: hydrogenous (slow precipitation of metals from seawater) and diagenesis (remobilization of metals through the underlying sediments, cf. Bonatti, 1983).

Kennecott and Newport Shipbuilding Company (1962) was the first to show interest in the sampling the nodule deposits, while Arrhenius (1963) detailed the geochemical composition of nodules and suggested a metallurgical process to extract metals from nodules. Although Bezrukov (1960) was a pioneer researcher of nodules, it took more than two decades for Russia to start its exploration program. In the 1960s several companies initiated investigations to explore, exploit, and process the nodules (Mero, 1965). In 1972 the National Science Foundation (USA) commenced a program to study the origin of the nodules by involving several laboratories. The area of interest was the eastwest-trending equatorial North Pacific nodule belt between the Clarion and the Clipperton fracture zones (Horn etal., 1972). It is in this Horn area (named after the scientist D.R. Horn) that most countries and mining groups concentrated their future nodule exploration programs.

In the worlds oceans there are four potential areas from where nodules could be explored and recovered commercially, because of their high abundance, rich grade, and largely even/gentle seafloor topography (Fig. 1.3). The areas are: (1) Clarion-Clipperton Zone (CCZ, Equatorial North Pacific Ocean), (2) Peru Basin (Southeast Pacific Ocean), (3) Cook Islands (east of Australia in the central South Pacific Ocean), and (4) Indian Ocean Nodule Field (IONF within the Central Indian Ocean Basin, CIOB). In this second edition of the book (the first edition was published in 2008) we seek to review the distribution, nature, abundance, origin, and formational process of nodules and crusts of one of these areas: the IONF. In addition, the methods of exploration, resource estimation, environmental impact of mining, mining techniques, extractive metallurgy, and economic feasibility of the nodule deposits are discussed. Special attention is given to modeling the dynamics of nodule formation in the IONF. The book also examines the legal and commercial perspectives of starting a deep-sea mining venture.

Figure 1.3. The four most potential nodule-rich areas in the worlds oceans with nodule abundance in kg/m2: IONF and Penrhyn Basin (Cook Islands) (>5 kg/m2), Peru Basin (10 kg/m2), and Clarion-Clipperton Zone (15 kg/m2).

Most iron and manganese deposits form directly from seawater, and, because of their redox sensitivity, are likely to respond to changes in the oxidation state of the oceans. Iron ore deposits have long been studied for evidence of effects of the evolving ocean-atmosphere system. Manganese does not, however, show as clear a pattern of secular evolution as does iron. The mass-age distribution of manganese ore deposits (Fig. 11) shows three specific episodes of enhanced manganese accumulation:

The first two correspond to times of iron deposition, but the third does not. There are also times in Earth history when very little manganese was deposited. Notable periods are the Early Archean, which may reflect poor preservation of crust of that age, and an apparent gap from 2700 to 2300Ma that may also be a statistical aberration. A well-defined gap in sedimentary rock-hosted deposits is also evident between 1800 and 1120Ma, although some large volcanic rock-hosted accumulations did form in this time period. The two Precambrian pulses of manganese accumulation and the mid-Proterozoic gap correspond closely to the frequency of black shale deposition, which had flourished at 20001800Ma, was drastically reduced after 1800Ma, and then flourished again at 800600Ma.

During the three periods of major manganese deposition, mineralization appears to be controlled by local basin tectonics, whereas iron deposits respond more to global parameters such as declining heat flow. The locality-dominated distribution of manganese deposits may be the result of the intracratonic euxinic basin mechanism for manganese enrichment. The structure of the water mass in these basins provides a large reservoir from which manganese is mobilized and a very steep redox and sulfur gradient to produce separation from iron. The Archean Earth lacked these basins, and they were likewise poorly developed in much of the Proterozoic owing to low sulfate. Intracratonic euxinic basins then proliferated again in the Phanerozoic, concentrating at times of continental break-up.

All of Myanmar's more promising manganese deposits are east of the Salween, and most are in an north-trending belt north of Mong Yawng. The district, which in the 1990s accounted for several percent of world manganese production, includes the Seemon (Wansa Lo), Na Yaung, and Phan Min deposits, and Mong Yu in Wa State. Htay Win and Min Chit Thu (2012) and Minn Chit Thu etal. (2014) provide some information on the Ahr-Ye (Maw We?) deposit north of Tachilek where cryptomelane, manganite, rhodonite, and braunite occur as thin veins and layers within rhyolites, dacites, and associated folded sedimentary rocks. The association with sediments suggests, but does not require, manganese deposition by a supergene replacement process. Than Zaw (2013, unpublished presentation) reports an andesite dyke cutting ore beds or layers at Ahr-Ye where open pit workings are more than 50m deep. The volcanic rocks are altered to chlorite and epidote, either hydrothermal or metamorphic, and strongly silicified. Details of other deposits are even more limited although reports of stratabound manganese ore in sedimentary rock suggest the possibility of carbonate replacement. Perhaps because of proximity to the China border, much of the ore has been mined and exported with no record of mine geology.

Leaving aside supergene enrichments, manganese deposits are generally divided into two groups: deepwater volcanic-hosted deposits and shallow-water sediment-hosted deposits. The deepwater volcanic-hosted deposits are generally smaller than the sediment-hosted deposits and represent proximal exhalites into oxidized, deepwater environments. Sediment-hosted Mn deposits are generally associated with redox-stratified basins, in which hydrothermal Mn was upwelled onto an oxidized shelf (e.g., Force and Cannon, 1988). Cycling of Mn occurs in zones of high organic productivity where upwelling Mn is oxidized, then subsequently reduced during organic matter remineralization, and finally precipitated as Mn carbonates either in pore waters or in the lower part of the water column, where high ambient Mn and bicarbonate concentrations are sustained. Deposition of Mn deposits in the Proterozoic and Phanerozoic is generally interpreted to indicate shallow-water oxidizing conditions and deeper-water anoxic or sulfidic conditions (e.g., Force and Cannon, 1988).

There are few cases of middle-to-late Archean Mn deposits (Maynard, 2010; Roy, 2000, 2006) or Mn enrichments (e.g., Alexander et al., 2008). Some of these deposits are presently in tropical areas with deep weathering (India and Brazil), and others have been preserved in high-grade metamorphic terrains, which complicates interpretation of their original mineralogy and the processes that led to Mn enrichments. These deposits are associated with bimodal volcanics and iron formations and only rarely with black shales. This contrasts with the larger Proterozoic and Phanerozoic Mn deposits that are commonly associated with zones of high organic productivity and black shales. The formation of the Archean Mn deposits is attributed in at least some cases to local oxygen production by photosynthesizers (Roy, 2006). Nonbiological precipitation of Mn from seawater requires an oxidation state in excess of that required for iron oxidation. However, biologically mediated Mn(II) oxidation at submicromolar oxygen concentrations has been demonstrated in the Black Sea suboxic zone and a multicopper oxidase, a metalloenzyme, was implicated as the catalytic agent (Clement et al., 2009).

The Mn cycle in the Archean oceans is not well understood. It is suspected that the hydrothermal flux of manganese to Earth's oceans was likely larger in the Archean than it is today and that Mn was present in relatively high concentrations (comparable and even likely larger than those in the deep part of the Black Sea (8M)) in solution in Earth's early oceans. In contrast, it has been recently suggested that mantle convection, and therefore subduction and plate tectonics, may have actually been slower in the Archean (Korenaga, 2008). The sinks for Mn in these early oceans are thought to have been different than those today since the oceans had a very different redox structure. This is inferred to have limited the efficiency of concentration mechanisms associated with oxidation and precipitation, leading to organic matter remineralization and Mn coprecipitation with carbonates. This may be supported by the observation that the typical separation of Fe and Mn observed in younger deposits that reflects these redox processes is not observed in Archean successions. It appears that sinks associated with photochemical oxidation of Mn are not likely, as Anbar and Holland (1992) showed in laboratory experiments that this process is inefficient. Veizer et al. (1982) suggested that higher Fe and Mn contents of Archean carbonates indicated Fe and Mn coprecipitation with carbonates, but this sink is difficult to quantify using the carbonate record because it is hard to distinguish between synsedimentary and postdepositional, diagenetic enrichments. It is possible that Fe could have acted as a local redox shuttle in Archean environments, where Fe was oxidized in the upper part of the water column via anoxygenic photosynthesis, then delivered as Fe oxyhydroxide particles to the deeper part of the water column and sediments, where it was reduced via organic matter remineralization to produce dissolved inorganic carbon (CO32). Reactions between Mn dissolved in seawater and bicarbonate generated in the deep part of the water column at the sedimentwater interface and in pore waters may have led to direct precipitation of Mn carbonates without a Mn oxide intermediary. This model predicts that Mn enrichments and Mn deposits could have formed in settings distal from hydrothermal sources, with high organic productivity and low sedimentation rates. In these settings, hydrothermal plumes highly diluted and distilled by Fe oxyhydroxide precipitation could have delivered waters with low Fe/Mn ratios. The testable predictions of this model are that the hosting lithologies should have highly negative Fe isotope values and lack Ce anomalies.

The situation changed dramatically with the GOE. Manganese deposits first appeared at economic grades in the rock record at the GOE. These deposits show a progressive increase in the separation of Mn and Fe. For example, the Rooinekke Formation (Koegas Group, South Africa) and Hotazel Formation (Postmasburg Group, South Africa) deposited shortly before/at the early stage of the GOE and during the GOE, respectively, show some Fe enrichment. However, the 2.22.1Ga Mn deposits of the Birimian Supergroup (West Africa), Franceville Group (Gabon), and Gangpur and Sausar Groups (India) are not directly associated with iron enrichments (Bekker et al., 2003; Roy, 2006). The latter 2.22.1Ga Mn deposits are ultimately associated with black shales, resembling younger Phanerozoic deposits in this aspect. The secular trend of Mn deposits thus broadly agrees with other redox indicators for the atmosphereocean system, mainly implying little to no redox separation between Fe and Mn before ~2.4Ga, a progressive increase in Fe and Mn separation between ~2.4 and 2.2Ga, and redox separation of Fe and Mn similar to the Phanerozoic after ~2.22.1Ga.

The overwhelming majority of available isotope data for modern carbonate-manganese deposits belong to lacustrine or shallow marine sediments. Particularly oceanic manganese carbonates are rather weakly studied with regard to their isotopic composition, a shortcoming resulting from the insufficient degree of surveying thus far carried out in those regions of the global ocean most likely to contain such carbonates.

The Guatemala depression of the Pacific Ocean, as is known, is one of the known regions of the global ocean to feature wide development of manganese carbonates in modern sediments. The isotope data for oceanic sediments that are available in the literature (Coleman et al., 1982; Pedersen and Price, 1982) refer to samples of carbonates taken in precisely this region. The former work (Coleman et al., 1982) provides a detailed study of the material and isotopic composition of carbon and oxygen in 17 samples of carbonates rich in manganese that were uncovered at wellsites 503A and 503B (south of the Guatemala depression). The range of measured variations in isotopic composition in these samples ranged from 3.8 to 1.2 for 13C and from 4.06 to 5.99 (relative to the standard PDB) for 18O. The isotope data previously obtained by this books author (Sval'nov and Kuleshov, 1994) turned out to be analogous (Table 2.2, Fig. 2.4): the 13C values vary within the range of 2.5 to 1.1, and 18O values within the interval 34.937.1 (relative to the standard SMOW).

Fig. 2.4. 13C vs. 18O in carbonate nodules of Guatemala depression (Panama Basin, Pacific Ocean). 1Foraminifera from nodules, 2foraminifera from enclosing sediments, 3nodules from stations 3884, 3895, and 3899; 46nodule from station 3899, horizon 295300cm: 4loose nodule, 5outer shell, 6inner part; 7data (Coleman et al., 1982).

The data cited above are substantially distinct from the isotope data particular to lake and sea manganese carbonates in that the 13C values are higher in the former. At present, there is no means for comparing the isotopic composition of the studied rhodochrosites with analogous accumulations from other parts of the offshore areas of the global ocean. However, as will be shown below, rhodochrosites from the sediments of the Guatemala depression are substantially distinct in terms of their isotope characteristics from analogous accumulations in other types of water bodies in that the former have higher contents of the heavy isotope 13C. This is evidently connected with the specific conditions of the formation of manganese carbonates in the sediments of this region of the global ocean.

It has been established that practically all of the studied carbonate-manganese accumulations (fossil as well as modern sea and lake; Kuleshov, 1999, 2011a,b) are characterized by low 13C values. This is due to the fact that Mn carbonates in sedimentary series are formed in a stage of diagenesis with active participation by isotopically light carbon dioxide. The latter forms during the oxidation of organic matter in the environment of the sediments themselves. For this reason, it can be proposed that the generation of Mn carbonates in sediments of the Guatemala depression during diagenesis has occurred in several other, fairly specific conditions distinguished by the insignificance of the role of CO2 of organic origin in this process. The formation of manganese carbonates occurred principally as a result of the dissolution and redeposition of biogenic calcium carbonate of the sediments (evidently, shells of foraminifera and limy skeletal remnants of other organisms).

For certain samples available to us, it was possible to study different genetic varieties of manganese carbonates contained within a single sample. Thus, the isotopic composition of the carbon of the rhodochrosite from the host sediment and from carbonate nodule of the same interval of core sample 3899 turned out to be identical: 13C varies within the range 2.5 to 2.0 (samples 2851, 2852, 2857, 2859). Furthermore, for certain nodules, their inner part is distinguished by a higher values of 13C (1.9, an. 2853) in comparison with that of their outer part (2.3, an. 2852). Analogous results have been obtained in an earlier work (Coleman et al., 1982), which found that for two samples out of the five studied, there was a gradual increase from the periphery toward the center in the heaviness of the isotopic composition of the carbon.

On the whole, the isotopic composition of carbonate-manganese matter is not dependent on its form of occurrence in the sediment (ie, nodule, dispersion, etc.). The observed insignificant variation of the values of 13C and 18O, within different samples as much as within the boundaries of a single nodule (as was proposed in the work; Coleman et al., 1982), was to all appearances connected with local conditions (ie, permeability of the sediment, physical-chemical heterogeneity, etc.) of the generation of Mn carbonates.

By way of comparison, the isotopic composition of carbon and oxygen in the foraminifera collected from the host sediment as well as from the carbonate-manganese nodules themselves was studied (Table 2.3). Here was manifest a constant difference in the isotopic composition of foraminifera and of manganese carbonates from nodules. The former are characterized on the whole by higher 13C values (approximately 2) in relation to that of the nodules. This difference is evidently due to the different isotopic composition of the original bicarbonate and by the temperature of the generation of carbonate matter. As is well known, bicarbonate of the upper horizons of the hydrosphere is characterized as a rule by higher 13C valuesa consequence of the higher bioproductivity of the near-surface horizons of the water column. Therefore, carbonate from foraminifera, which form from bicarbonate of surface waters, should have heavier 13C values.

Thus, it can be stated that authigenic manganese carbonate in the sediments of the Guatemala depression (Pacific Ocean) is represented by calcium rhodochrosite and was formed mainly as a result of the dissolution and redeposition of limy shells of foraminifera and skeletal fossils of other organisms. Furthermore, the isotopically light carbon dioxide that formed as a result of the oxidation of Corg plays a sharply subordinate role in this process. One source of manganese of the studied nodules was the host sediments, and occasionally also Fe-Mn concretions, which supplied Mn as it was remobilized during the process of diagenesis.

A principal feature of the formation of Mn carbonates in the sediments of the Guatemala depression is the low geochemical activity of organic matter in this process, which resulted in the relatively high values of 13C in the studied nodules.

Despite the accumulation of a vast array of data on the geology of manganese deposits and particularly pertaining to the chemical composition of manganese rocks and ores, many questions of manganese ore-genesis remain only partially answered. This is the case, first and foremost, with genetic models of the formation of the principal industrial types of manganese ores that are contained in such giant deposits and manganese-ore basins as the Kalahari (Republic of South Africa), groups of Oligocene deposits of the Paratethys (Ukraine, Georgia, Kazakhstan, and Bulgaria), the northern Urals (Russia), the Gulf of Carpentaria (Groote Eylandt, Arnhem Land, and elsewhere in Australia), and others.

breaking the odds; bringing china home the mining gallery africa

breaking the odds; bringing china home the mining gallery africa

A short stint at a Kilifi-based manganese mining plant in 2018 is what introduced Eng. Cyrus Njonde to the art of machine fabrication. This labour-intensive skill bridges the gap of importing expensive mining equipment for Kenyas mining investors, particularly for small and medium mining enterprises. Dadson Mwangi, also a mining engineer has thrown his weight into research efforts in his studies at the Jomo Kenyatta University of Agriculture and Technology (JKUAT), in order to develop affordable and quality mining systems.

The Pan African Equipment launched its first office in Nairobi late last year, injecting Kshs 500 million into the mining industry in a bid to satisfy the growing demand for mining equipment, in the last few years. Veteran companies like The Atlas Copco, Mantrac, JCB specialized on heavy construction equipment like excavators, wheel loaders, jaw crushers, drill rigs, generators and compressors. However, as the demand for heavy machinery increased so did the need for lighter, smaller and inexpensive mining gear. The likes of hand drills, submersible pumps (used to remove water from a mine pit) winches (they help to pull materials from vertical pits), portable jaw crushers for commercial crushing of ballast and conveyor belts. Chinese companies such as the Nile Equipment Limited then proliferated the Kenyan market to provide the latter to miners. Nile Equipment has already setup a godown and an agency office in the capital, Nairobi, and was soon followed by Camco, another Chinese mining equipment supplier.

Back in Kilifi, Eng. Cyrus received a vibrating screen consignment at work whose body parts needed to be installed for operations. The companys assembly unit took a few days putting up the screen whose learning curve, Cyrus discovered, was not that steep. The thought to innovate and improvise pieces with local materials came to mind around the same time that Eng. Dadson was seeking affordable mining solutions for gold miners in Western Kenya.

It didnt take long for a mining investor in Nairobi to reach out to Cyrus asking him to put together an improvised vibrating screen dubbed off the original, he had seen on his social media platforms. Cyrus consulted with Eng. Dadson whose research path had led to a collaboration with JKUAT in the designing and fabrication of a smaller, efficient gold mill. The machine which grinds hard rocks into powder, graced the Mining 4I innovation forum as a prototype, and elicited a lot of feedback. The Strathmore extractive department, Extractive Baraza sponsors the forum which runs every year.

The Nairobi-based investor ordered a vibrating screen and conveyor belt system set meant to separate manganese pebbles into three different sizes as needed by the processors. The budget in play was $16,000 compared to the $23,000 needed to import a new unassembled unit, inclusive of customs clearance, agents and transport from the port of Mombasa to the investors location. The former cost covers a fortnights worth of work in comparison to the latter whose work worth includes nothing short of 40 days to complete.

There are numerous counterarguments on the efficiency of local fabrications compared to manufactured equipment, but they do not dismiss the necessity for affordable mining gear as expressed in Mr. Kazungus context, the beneficiary and an investor based in Kilifi. Local fabrication is set to be the alternative for mining practices in Kenya and other developing countries.

Speaking with Mr. Harun Mwangi, the CEO for Speed Craft Kenya Ltd, a local fabricator and installations experts, the affinity for these services needs to be tapped at this time when the nation is growing exponentially in minerals discovery and development. Collaborations with technical institutions which have advanced machineries to fabricate, cut and shape well designed mining equipment will reduce the budgets induced by imports by a large margin while contributing to the countrys GDP.

There are also serious private centres for mechanical innovation to link with for instance Gearbox Kenya , which is capable of producing mechanical intellectuals who can design and deliver a functional machine to an investor. It is the high time for the Kenyan mining sector to understand the needs of the industry and anticipate to fill the gap with resources, financial or otherwise. Private investors and the Kenyan artisanal mining sector need to be equipped with small mining machinery for them to realize their full potential in mining practice. This will not only improve production but also emphasize safety practices thereby mitigating a lot of mine accidents.

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