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1 Dipartimento Ingegneria Chimica dei Materiali, delle Materie Prime e Metallurgia, Università degli Studi di Roma "La Sapienza", Via Eudossiana 18, 00184 Rome, Italy
2 Dipartimento di Scienze della Terra, Università di Siena, Via delle Cerchia, 2, Siena, Italy
3 Department of Mineral Engineering, Faculty of Engineering, "A. Neto" University, C.P. 1756 Luanda, Angola
* E-mail address of corresponding author: giovanna.saviano{at}uniroma1.it
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Abstract |
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 TOP Abstract INTRODUCTIONGEOLOGICAL SETTINGKAOLIN CHARACTERISTICSKAOLIN FORMATION MODEL AND...ACKNOWLEDGMENTSREFERENCES |
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Mineral exploration tools have been evaluated during this study to assist in future kaolin exploration in the Cunene anorthosite complex.
Isotopic analysis of O and D indicates that Ca-feldspar alteration is essentially due to meteoric fluids, over a different range of temperatures. Furthermore, the presence of quartz-feldspar veinlets in the kaolinite bodies could be the result of hydrothermal activity linked to post-anorthosite granite intrusions of the so-called ‘red granite’. Kaolinite from Cunene plots on or close to the kaolinite line into the ‘warm temperature in tropical region’ area (surficial samples). Samples from drill-holes plot on the left and show the largest displacement from the KS line; these samples also have a relatively reduced 
D range of values (–65 to –98
). However, if supergene processes take place in the presence of waters of meteoric origin at temperatures similar to typical surface temperatures, the clays thus formed should plot either in the vicinity of the KS line or be displaced towards lower O18 and higher D, depending on both the temperature and relative proportion of clay to water.
Key Words: Angola • Clay-forming Fluids • Cunene Anorthosite Complex • Isotope Analyses • Kaolin • Mafic Rocks
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INTRODUCTION |
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TOPAbstractINTRODUCTIONGEOLOGICAL SETTINGKAOLIN CHARACTERISTICSKAOLIN FORMATION MODEL AND...ACKNOWLEDGMENTSREFERENCES |
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GEOLOGICAL SETTING |
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TOPAbstractINTRODUCTIONGEOLOGICAL SETTINGKAOLIN CHARACTERISTICSKAOLIN FORMATION MODEL AND...ACKNOWLEDGMENTSREFERENCES |
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).
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Based on K-Ar dating of plagioclase within the anorthosite, Silva et al.(1973) suggested an age range between 2098 ± 51 and 2151 ± 42 Ma for the Cunene complex. Carvalho (1990) gave an older age for the complex of >2160 Ma and stated that it was affected by the Eburnean, Kibarian and Panafrican orogenic cycles. Ashwal and Twist (1994) observed that the xenoliths in the complex are Upper Archean (~2700 Ma) to Lower Proterozoic (2400 Ma) in age, and that the complex itself is cross-cut by the ‘Red Granites’ that have ages between 2200 and 1200 Ma. A recent study of the Mevaiela kaolin by Gomes et al.(1994) defined a Rb/Sr age of 1300 Ma for an anorthosite sample collected near the Mevaiela kaolin deposit. Additional age studies are ongoing (Mayer et al., 2000)
Brittle deformation appears to have played a role in the formation of the kaolin. In the study area a clearly-defined system of NNW–SSE trending fractures intersects a less pronounced ENE–WSW system (Figure 2); the latter system also appears to cross-cut the cover of the Upper Kalahari Formation at the eastern margin of the outcropping anorthosite. The two fracture systems have a horizontal component of movement and often form small grabens that are a few tens to a few hundreds of meters long. Some fractures in both systems are filled by dykes and veins of norite and diabase.
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) . Deformation is superposed on the tectonics as a result of the emplacement of the anorthositic complex. The NNW–SSE alignments are clearly connected to a fault system which is weakly convergent towards the north and the vertical throw of which has resulted in the formation of the horst and graben complex. In addition to this principal tectonic system, one can also recognize a transverse ENE–WSW system in the Mevaiela area, as well as WNW–ESE and NNE–SSW systems that delimit the depressions. Figure 2 shows the principal kaolin deposits aligned along NNW–SSE faults west of Mevaiela (black stars). To the north and south of Mevaiela, large kaolin occurrences are found in small valleys which trend parallel to the transverse faults. This information will be discussed in detail in the exploration methods section. |
KAOLIN CHARACTERISTICS |
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TOPAbstractINTRODUCTIONGEOLOGICAL SETTINGKAOLIN CHARACTERISTICSKAOLIN FORMATION MODEL AND...ACKNOWLEDGMENTSREFERENCES |
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).
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reports the chemical compositions of six anorthosite samples (LU9-LU14). The samples LU12, LU13 and LU14 were collected progressively closer to the kaolin main excavation, and a single kaolin sample was collected from the deposit itself (CAO15). For sample locations see Figure 3.
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Table 2 reports some analytical results from four kaolin samples. Sample CAO was collected from a vast unquarried kaolin outcrop located to the south of the principal excavation, while samples CAO1, CAO2 and CAO3 were taken from the main excavation (Figure 3) and are unprocessed; samples CAO1-10 µm, CAO2-10 µm and CAO3-10 µm represent the <10 µm fraction from the same samples after processing.
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).
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radiation, 20 mA, 40 kV, speed 1°/min) was used for the analysis of the outcropping kaolin samples and for anorthosite. Small quantities of pure kaolinite were obtained by handpicking. Where handpicking was not possible, samples were disaggregated and the different fractions separated by standard aqueous sedimentation techniques. Organic matter was destroyed by oxidation with 30% hydrogen peroxide and the purified samples washed thoroughly with deionized water. Fe oxide and hydroxides were not removed (a study of Fe content and crystallinity of these kaolinites is in progress).
The XRD pattern in Figure 4a represents the kaolin sampled from the principal excavation (CAO15, Table 2) and it shows well ordered kaolinite with minor plagioclase (5–10%) and calcite and traces of halloysite (Fiori et al., 1989). The XRD patterns obtained for samples CAO4 and CAO5, from the kaolinized outcrop, shows the same well ordered kaolinite with small quantities of plagioclase (Figure 4b,c). The Hinckley index (Hinckley, 1954, 1963; Murray, 1989; Murray and Lyons, 1956) for kaolinite crystallinity estimated for samples CAO4 and CAO5 (bulk kaolinized rock for the <2 µm fraction) and the Range and Weiss index (Range et al., 1969; Mackenzie, 1972) for samples CAO4, CAO5 and CAO15 (bulk and finest) are listed in Table 3. Figure 4d shows the diffraction pattern of an unaltered anorthosite sample.
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The chemical results indicate that the kaolin samples are contaminated by significant amounts of Ca and Si, while the XRD results outline a dominant kaolinite composition with variable quantities of calcite. This is present as radiating fibrous calcite nodules. These nodules are frequently found on the ground, especially near the altered areas, and may prove an important exploration tool.
Differential thermal analysis
Differential thermal analysis (DTA) was performed using a Stanton-Redcroft STA 780 series instrument. Based on DTA curves of a number of kaolin clays (Mackenzie, 1972), the patterns in Figure 5a,b show the first endothermic peaks at 100–150°C due to the loss of free or adsorbed water and a decomposition peak at 540–550°C (for pure kaolinite, decomposition occurs at 590°C) indicating quite a low crystallinity (Jasmund and Lagaly, 1993). The characteristic endothermic peaks for kaolinite and halloysite occur at ~550–600°C and are all of a similar magnitude, such that the total kaolin content in a mixture can be estimated but the individual proportions cannot be ascertained (Grimshaw, 1971). The DTA curve for the radiating calcite nodules CAO6 is also shown (Figure 5c) with the calcite endothermic peak at 880°C.
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) (Keller, 1977a, 1977b; Keller et al., 1977). In this study, the textures which are considered to be the most significant are books of kaolinite plates and individual, randomly oriented kaolinite flakes, as well as tubular forms (‘rolled-up’ halloysite plates) and elongated plates which have a very fibrous texture. Figure 6 shows the most frequent and important morphologies, photographed using secondary electron signals. The first two images of raw kaolinite, coated with a thin graphite film, clearly show the lithological fabric: (1) the form of the kaolinite books (Figure 6a) suggests that they form directly from feldspars, while (2) the tubular kaolinite forms are clearly visible as alteration of feldspar surfaces (Figure 6b).
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Figure 6c shows that small kaolinite flakes (<125 µm size fraction) occur near curved or linear kaolinite books. Similar sized clay flakes also exhibit micro-scalloped and slightly crinkled edges (Figure 6d), while small, elongate and randomly oriented kaolinite flakes range in size between 75 and 125 µm. Tubular, rolled-up plates of what is probably halloysite (Figure 6e) (Bates and Jackson, 1980) are surrounded by a matrix of essentially hexagonal flakes of kaolin (125 µm size fraction) (Figure 6f). In spite of the fact that the kaolinite books appear weak and delicate, they maintain their integrity after dispersion in water and filtering, and thus these features are also present in the finest fraction. Furthermore, the images show a relatively open, porous and permeable texture in which the kaolin books are surrounded by smaller, randomly oriented kaolinite crystals.
Isotope analyses
Some kaolin and anorthosite samples were analyzed for 18O SMOW and selected kaolin samples have also been analyzed for D/H. Each sample represents the mixture of three sub-samples as described above. These measurements were performed to define the type of fluid responsible for anorthosite alteration and kaolin formation (Sheppard, 1969, 1977; Lawrence and Taylor, 1971, 1972; Taylor, 1974; O’Neil and Kharaka, 1976; Suzuoki and Epstein, 1976; Fornaseri, 1980; Bird and Chivas, 1988; Savin et al., 1988; Longstaffe, 1989; Rye et al., 1992; Fei Zheng, 1993).
Although the unaltered anorthosite 18O values are within the range reported for terrestrial mantle rocks, the 18O values for the kaolin samples collected from the main excavation are quite different (Table 4). These values appear to confirm different temperatures of water at the surface and at depth. It is assumed that the higher temperature in the lower level of the kaolinite body is due to mixing with warm waters related to the crosscutting ‘red granites’ (Figure 7) while the surficial occurrences show constant temperature caused by cold meteoric waters (Figure 8) (Eslinger, 1971; Land and Dutton, 1978; Rieti-Shati et al., 2000; Nicholson, 2000). Furthermore, the particle morphologies of kaolinite, similar for different size fractions (Figure 6), and the crystallinity indexes of samples from different depths (study in progress) show no heterogeneity which would indicate the minor possibility of recrystallization or neoformation of the kaolinite (Giral-Kacmarcik et al., 1998). Sample CAO318 only, collected in a small excavation, shows isotope values similar to that of the deepest samples collected from the drill-holes but in this case the kaolinite is closely linked to the occurrences of ‘red granite’ and quartz-felspar veinlets (Seal and Rye, 1992). The D vs. 18Oo SMOW plot for the kaolins is shown in Figure 9 (modified after Mizota and Longstaffe, 1996). The kaolinite line (KS) (Savin and Epstein, 1970a, 1970b) is a best-fit line through kaolins interpreted to be in isotopic equilibrium with meteoric waters at Earth-surface temperatures (Hassanipak and Eslinger, 1985; Sheppard et al., 1969; Sheppard and Gilg, 1996; IAEA, 2001a, 2001b).
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), and show the largest displacement from the KS line; these samples also have a relatively reduced D range of –65 to –98. However, if supergene processes take place in the presence of waters of meteoric origin at temperatures similar to typical surface temperatures, the clays thus formed should plot either in the vicinity of the KS line or be displaced towards lower O18 and higher D, depending on both the temperature and relative proportion of clay to water. It is conceivable that those of surficial samples with the greatest O18 depletion were originally deeper and warmer clays partially reequilibrated during supergene activity to a kaolinite with a composition defined by the KS line. The low range of D, and the appreciable range of O18 values (from 9 to 20) either indicates that the different clays formed over a wide range of temperature, in the presence of water with similar D values but different O18 values, and finally the relative proportion of exchangeable clay to water, or that the spread reflects different degrees of retrograde (supergene?) exchange. |
KAOLIN FORMATION MODEL AND EXPLORATION TOOLS |
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TOPAbstractINTRODUCTIONGEOLOGICAL SETTINGKAOLIN CHARACTERISTICSKAOLIN FORMATION MODEL AND...ACKNOWLEDGMENTSREFERENCES |
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The kaolin deposits in the anorthositic Cunene complex are unusual in that they occur in basic rocks (Silva 1990; Schenato and Formoso, 1993; Gomes et al., 1994), in contrast to some of the world’s largest deposits, e.g. in Cornwall, southwestern UK (Durrance et al., 1982; Bristow, 1990 ) or in other areas throughout the world (Comsti, 1969; Damiani and Trautman, 1969; Hunter and Urie, 1969; Marumo et al., 1982, 1995; Lombardi and Mattias, 1987 Lombardi and Mattias, 1995; Harris et al., 1999).
Notwithstanding this unusual occurrence, the kaolin is, aside from other economic properties (Gomes et al., 1994), essentially white in color and pure in composition. Compared to the kaolin formed in intermediate or acidic felspathic rocks, only Ca is significantly more enriched in the Cunene kaolin.
Basic data relating to the genesis of the deposit are as follows:
On the basis of these data one can summarize the formation process as follows. Meteoric water penetrated the faults and fractures in the anorthosite and was reheated due to the presence of high geothermal temperatures, possibly related to granitoid intrusions emplaced after the anorthosite. This might establish a convective system like those observed in other kaolinite areas (Durrance et al., 1982; Fehn, 1985). The weakly acidic meteoric water interacted with the anorthosite, remobilizing the alkaline and alkaline-earth (Ca2+, Mg2+, Na+, K+) cations. However, these acidic super-gene solutions can apparently alter the isotopic composition of pre-existing hypogene clays. Iron, present in small concentrations in the anorthosite, was oxidized and immobilized in small limonite concretions. The alkaline and alkaline-earth cations, along with silica which is more soluble in basic solutions, were deposited some distance from the rock-water interaction zone where the kaolin was generated. Furthermore, Ca was liberated by the alteration of Ca forming Ca(HCO3)2, due to the presence of CO2; a small amount of the calcium bicarbonate was subsequently precipitated out as the calcite nodules found throughout the weathered areas. Quartz veinlets cutting the kaolin deposits could have formed during subsequent hydrothermal interaction, although the primary fluid phase was meteoric water.
Mineral exploration tools
Information gathered during this study has defined the feasibility of various techniques for future kaolin exploration in the Cunene anorthosite complex.
(1) At a regional scale, satellite photos and photogeology aided in defining altered zones within the anorthosite. In fact, initial photogeology outlined whitish zones that were subsequently found to be kaolinized when examined in the field. However, the Ca concentrations are much higher in this deposit, probably due to the fact that the surface samples are contaminated by carbonate incrustations formed during the alteration of the feldspars.
The eastern margin of the anorthosite complex also shows some kaolinized areas. For example, as reported on the 1:250,000 scale geological map of Angola (sheet South D-33/U), the anorthosite appears intensely bleached and kaolinized a few km to the SE of the main kaolin excavation; it is possible that in this eastern sector, some of the kaolin is covered by Tertiary ochre sands related to the Kalahari system (Figure 10). The photogeology study revealed not only bleached areas in the anorthosite complex but also the presence of tectonic lineaments (such as fractures or faults) along which the altering fluids would have preferentially acted.
Another important element could be the characterization of the post-anorthosite granitoid intrusions, if such intrusions acted as a ‘thermal engine’ for the meteoric fluids.
(2) A more detailed survey over the flat areas is required as dark montmorillonitic clays and sands often cover vast kaolinized zones around Mevaiela; typically these zones are only visible in the erosional beds of small seasonal streams.
Finally, the mapping of carbonate nodule occurrence could be of great assistance considering their abundance on the surface of kaolinized areas. These nodules testify to an alteration process which caused the liberation of Ca from Ca feldspars and the subsequent precipitation of these radiating fibrous calcite nodules.
In conclusion, it is clear that the Mevaiela area was affected by feldspar alteration to a much greater extent than was previously suspected. The commercial potential, in terms of quality and quantity, needs to be tested using an appropriate network of shallow boreholes. Part of this network has already been established in the areas around the old mine, and the initial results appear to be very encouraging in terms of the continuity of the mineralized body and the quality of the kaolin.
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ACKNOWLEDGMENTS |
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TOPAbstractINTRODUCTIONGEOLOGICAL SETTINGKAOLIN CHARACTERISTICSKAOLIN FORMATION MODEL AND...ACKNOWLEDGMENTSREFERENCES |
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Footnotes |
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(Received 13 January 2003; revised 20 January 2005)
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REFERENCES |
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TOPAbstractINTRODUCTIONGEOLOGICAL SETTINGKAOLIN CHARACTERISTICSKAOLIN FORMATION MODEL AND...ACKNOWLEDGMENTSREFERENCES |
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Ashwal, L.D. and Twist, D. (1994) The Cunene complex, Angola/Namibia: a composite massif-type anorthosite complex. Geological Magazine, 131, 579–591.
Bates, R.L. and Jackson, J.A. (editors) (1980) Glossary of Geology, 2nd edition. American Geological Institute, Falls Church, Virginia, USA, 751 pp.
Bird, M.I. and Chivas, A.R. (1988) Stable-isotope evidence for low-temperature kaolinitic weathering and post-formational hydrogen-isotope exchange in Permian kaolinites. Chemical Geology (Isotope Geoscience Section), 72, 249–265.[CrossRef]
Brindley, G.W. and Robinson, K. (1948) Structures of methalloysite. Mineralogical Magazine, 28, 393–406.[GeoRef]
Bristow, C.M. (1990) The genesis of the China Clays of south-west England: a multistage story. 27th Annual Meeting of the Clay Minerals Society, Columbia Missouri, abstract, p. 27.
Carvalho, H. (1990) Complexo Gabro-Anortositico do SW de Angola/NW da Namibia. Istituto de Investigaçâo Cientifica Tropical, série Ciências da Terra, Lisboa, 2, 1–66.
Comsti, F.A. (1969) Kaolin deposits of Philippines. Proceedings of the Symposium ‘Kaolin Deposits of the World’, B: Overseas Countries. 23rd International Geological Congress, Prague (M. Malkovsky and J. Vachtl, editors), 16, 67–74.
Damiani, L. and Trautman, F. (1969) Les depots de kaolin francais. Proceedings of the symposium ‘Kaolin Deposits of the World’; 23rd International Geological Congress, Prague (M. Malkovsky and J. Vachtl, editors), 15, 141–178.
Durrance, E.M., Bromley, A.Y., Bristow, C.M., Heath, M.J. and Penman, J.M. (1982) Hydrothermal circulation and post-magmatic changes in granites of south-west England. Proceedings of the Usher Society, 5, 304–320.
Fehn, U. (1985) Post-magmatic convection related to high heat production granites of south-west England: a theoretical study. In High Heath Production (HHP) Granites, Hydrothermal Circulation and Ore Genesis (XX and XX, editors). Institution of Mining and Metallurgy, London.
Fei Zheng, Y. (1993) Calculation of oxygen isotope fractionation in hydroxyl-bearing silicates. Earth and Planetary Science Letters, 120, 247–263.[CrossRef][ISI][GeoRef]
Fiori, C., Fabbri, B. and Ravaglioli, A. (1989) Materie Prime Ceramiche: Studi, Ricerche e Tecnologie in Italia. Vol. 3, Faenza Editrice, Rome, 1242 pp.
Fornaseri, M. (1980) Lezioni di Geochimica. Veschi, Rome, 824 pp.
Giral-Kacmarcik, S., Savin, S.M., Nahon, D., Girard, J.P., Lucas, Y. and Abel, L.J. (1998) Oxygen isotope geochemistry of kaolinite in laterite-forming processes, Manaus, Amazonas, Brazil. Geochimica et Cosmochimica Acta, 62, 1865–1879.[CrossRef][ISI][GeoRef]
Gomes, C., Velho, J. and Guimarâes, F. (1994) Kaolin deposit of Mevaiela (Angola), alteration product of anorthosite: assessment of kaolin potential for application in paper. Applied Clay Science, 9, 97–106.[GeoRef]
Grimshaw, R.W. (1971) The Chemistry and Physics of Clays and other Ceramic Materials. Ernest Benn Limited, 1024 pp.
Harris, C., Compton, J.S. and Bevington, S.A. (1999) Oxygen and hydrogen isotope composition of kaolinite deposits, Cape Peninsula, South Africa: low-temperature, meteoric origin. Economic Geology, 94, 1353–1366.[Abstract][GeoRef]
Hassanipak, A.A. and Eslinger E. (1985) Mineralogy, crystallinity, O18/O16, and D/H of Georgia kaolins. Clays and Clay Minerals, 33, 99–106.[Abstract][CrossRef][ISI][GeoRef]
Hinckley, D.N. (1954) Variability in "crystallinity" values among the kaolin deposits of the coastal plain of Georgia and South Carolina. Clays and Clay Minerals, 11, 229–235.
Hinckley, D.N. (1963) Variability in ‘crystallinity’ values among the kaolin deposits of the Coastal Plain of Georgia and South Carolina. Proceedings of the 11th National Conference – Clays and Clay Minerals, 229–235.
Hunter, D.R. and Urie, J.C. (1969) Kaolin deposits of Swaziland. Proceedings of the Symposium ‘Kaolin Deposits of the World’, B Overseas Countries, 23rd International Geological Congress, Prague (M. Malkovsky and J. Vachtl, editors), 16, 67–74.
IAEA/WMO (2001a) Global Network of Isotope in Precipitation the GNIPDatabase. http://isohis.iaea.org
IAEA (2001b) Isotope Hydrology Information System. The ISOHIS Database. http://isohis.iaea.org
Jasmund, K. and Lagaly, G. (1993) Tonminerale und Tone. Steinkopf Verlag, Berlin, p. 38.
Keller, W.D. (1977a) Scan electron micrographs of kaolins collected from diverse environments of origin – IV. Georgia kaolin and kaolinizing source rocks. Clays and Clay Minerals, 25, 311–345.[Abstract][CrossRef][ISI][GeoRef]
Keller, W.D. (1977b) Scan electron micrographs of kaolins collected from diverse environments of origin – V. Kaolins collected in Australia and Japan on field trips of the sixth and seventh clay conference. Clays and Clay Minerals, 25, 347–364.[Abstract][GeoRef]
Keller, W.D., Galán, E. and Mattias, P.P. (1977) Scan electron micrographs of clays from field trip localities of the VIII International Kaolin Symposium, Spain and Italy. Proceedings of the 8th International Kaolin Symposium and Meeting on Alunite, Madrid, 10 pp.
Köstlin, E.C. (1974) The Cunene basic complex, northern Southwest Africa. Contributions to the Precambrian Geology of Southern Africa (A. Kröner, editor). University of Cape Town, Department of Geology, 15, 123–135.
Lawrence, J.R. and Taylor, H.P., Jr. (1971) Deuterium and oxygen-18 correlation: Clay minerals and hydroxides in quaternary soils compared to meteoric waters. Geochimica et Cosmochimica Acta, 35, 993–1003.[CrossRef][ISI][GeoRef]
Lawrence, J.R. and Taylor, H.P., Jr. (1972) Hydrogen and oxygen isotope systematics in weathering profiles. Geochimica et Cosmochimica Acta, 36, 1377–1393.[CrossRef][ISI][GeoRef]
Lombardi, G. and Mattias, P. (1987) The kaolin deposits of Italy. L’Industria Mineraria, 6, 1–34.
Longstaffe, F.J. (1989) Stable isotopes as tracers in clastic diagenesis. Pp. 201–277 in: Burial Diagenesis (I.E. Hutcheon, editor). Short Course, 15, Mineralogical Association of Canada, Ottawa, Ontario.
Mackenzie, R.C. (1972) Differential Thermal Analysis. Vol. 2, Academic Press, London, 1382 pp.
Marumo, K., Matsuhisa, Y. and Nagasawa, K. (1982) Hydrogen and oxygen isotopic compositions of kaolin minerals in Japan. Pp. 315–320 in: Proceedings of the International Clay Conference 1981. Developments in Sedimentology, 35. Elsevier Science Publishers, Amsterdam.
Marumo, K., Longstaffe, F.J. and Matsubaya, O. (1995) Stable isotope geochemistry of clay minerals from fossil and active hydrothermal systems, southwestern Hokkaido, Japan. Geochimica et Cosmochimica Acta, 59, 2545–2559.[CrossRef][ISI][GeoRef]
Mayer, A., Sinigoi, S., Miguel, L.G., Morais, E. and Petrini, R. (2000) Kibaran ages in the Kunene Anorthositic Complex. P. 110 in: Geoluanda 2000 International Conference, Luanda, Abstracts volume.
Mizota, C. and Longstaffe, F.G. (1996) Origin of Cretaceous and Oligocene kaolinites from the Iwaizumi clay deposit, Iwate, northeastern Japan. Clays and Clay Minerals, 44, 408–416.[Abstract][CrossRef][ISI][GeoRef]
Morais, E., Sinigoi, S., Mayer, A. and Miguel, L.G. (2000) Kunene gabbro-anorthosite Complex: coalescence of discrete crystal mush intrusion. Geoluanda 2000, International Conference, Luanda, Angola, Abstracts volume, p. 110.
Murray, H.H. (1989) Kaolin minerals: their genesis and occurrences. Pp. 1–25 in: Hydrous Phyllosilicates (S.W. Bailey editor). Reviews in Mineralogy, 25. Mineralogical Society of America, Washington, D.C.
Murray, H.H. and Lyons, S.C. (1956) Correlation of paper coating quality with degree of crystalline perfection of kaolinite. Clays and Clay Minerals, 4, 31–40.
O’Neil, J.R. and Kharaka, Y.K. (1976) Hydrogen and oxygen isotope exchange reaction between clay minerals and water. Geochimica et Cosmochimica Acta, 40, 241–246.[CrossRef][ISI][GeoRef]
Pickering, S.M., Jr. and Murray, H.H. (1994) Kaolin. Pp. 265–277 in: Industrial Minerals and Rocks. Society of Mining, Metallurgy and Exploration, Inc., Littleton, Colorado, USA.
Prasad, M.S., Reid, K.J. and Murray, H.H. (1991) Kaolin: processing, properties and applications. Applied Clay Science, 6, 87–119.
Range, K.J., Range, A. and Weiss, A. (1969) Fire clay type kaolinite or fire clay mineral? Experimental classification of kaolinite-halloysite minerals. Proceedings of the International Clay Conference, Jerusalem, Israel University Press, pp. 3–13.
Rye, R.O., Bethke, P.M. and Wasserman, M.D. (1992) The stable isotope geochemistry of acid sulphate alteration. Economic Geology and Bulletin of the Society of Economic Geologists, 87, 225–262.[Abstract][ISI][GeoRef]
Savin, S.M. and Epstein, S. (1970a) The oxygen and hydrogen isotope geochemistry of clay minerals. Geochimica et Cosmochimica Acta, 34, 25–42.
Savin, S.M. and Epstein, S. (1970b) The oxygen and hydrogen isotope geochemistry of ocean sediments and shales. Geochimica et Cosmochimica Acta, 34, 43–63.[CrossRef][ISI][GeoRef]
Savin, S.M. and Hsieh, J.C.C. (1998) The hydrogen and oxygen isotope geochemistry of pedogenic clay minerals: Principles and theoretical background. Geoderma, 82(1-3), 227–253[CrossRef][ISI][GeoRef]
Savin, S.M. and Lee, M. (1988) Isotopic studies of phyllosilicates. Pp. 189–223 in: Hydrous Phyllosilicates (exclusive of micas) (S.W. Bailey, editor). Reviews in Mineralogy, 19. Mineralogical Society of America, Washington, D.C.
Schenato, F. and Formoso, M.L.L. (1993) Mineralogical and geochemical aspects of the alteration of the Capivarita anorthosite to kaolin (Brasil). Proceedings of the 10th International Clay Conference, Adelaide, pp. 1–149.
Seal II, R.R. and Rye, R.O. (1992) Stable isotope study of water-rock interaction and ore formation, Bayhorse base and precious metal district, Idaho. Economic Geology, 87, 271–287.[Abstract][ISI][GeoRef]
Sheppard, S.M.F. (1977) The Cornubian Batholith, south-west England; D/H and O18/O16 studies of kaolinite and other alteration minerals. Journal of the Geological Society of London, 133, 573–591.
Sheppard, S.M.F. and Gilg, H.A. (1996) Stable isotope geochemistry of clay minerals. Clays and Clay Minerals, 31, 1–24.
Sheppard, S.M.F., Nielsen, R.L. and Taylor, H.P. (1969) Oxygen and hydrogen isotope ratio of clay minerals from porphyry copper deposits. Economic Geology, 64, 755–777.[Abstract][ISI][GeoRef]
Silva, A.T.S.F., Torquato, J.R. and Kawashita, K. (1973) Alguns dados geocronológicos pelo método K/Ar da regiâo de Vila Paiva Conceiro, Quilengues e Chicomba (Angola). Boletín Serviços de Geologia e Minas de Angola, 24, 29–46.
Silva, L.C. (1972) Maciço gabro-anortosítico do SW de Angola, observaçôes na regiâo do Pocolo. Revue Facultad de Ciências, Lisboa, 17, 253–277.
Silva, Z.C.G. (1990) Geochemistry of the gabbro-anorthosite complex of southwest Angola. Journal of African Earth Sciences, 10, 683–692.[GeoRef]
Silva, Z.C.G. (1992) Mineralogy and cryptic layering in the Cunene anorthosite complex of SW Angola and Namibia. Mineralogical Magazine, 56, 319–327.[CrossRef][ISI][GeoRef]
Suzuoki, T. and Epstein, S. (1976) Hydrogen isotope fractionation between OH-bearing minerals and water. Geochimica et Cosmochimica Acta, 40, 1229–1240.[CrossRef][ISI][GeoRef]
Taylor, H.P., Jr (1974) The application of oxygen and hydrogen isotope studies to problems of hydrothermal alteration and ore deposition. Economic Geology, 69, 843–883.[Abstract][ISI][GeoRef]
Vermaak, C.F. (1981) Cunene anorthosite complex. Pp. 578–590 in: Precambrian Geology in the Southern Hemisphere (D.R. Hunter, editor). Elsevier, Amsterdam.
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