Hostname: page-component-77c89778f8-fv566 Total loading time: 0 Render date: 2024-07-17T14:13:59.978Z Has data issue: false hasContentIssue false
  • English
  • Français

Optical image and microchemical analysis of gold grains from a weathered profile of the Minvoul greenstone belt, northern Gabon

Published online by Cambridge University Press:  30 August 2019

Mario Iglesias-Martínez Open the ORCID record for Mario Iglesias-Martínez [Opens in a new window] ,
Berta Ordóñez-Casado Open the ORCID record for Berta Ordóñez-Casado [Opens in a new window]  and
Edgar Berrezueta Open the ORCID record for Edgar Berrezueta [Opens in a new window]
Mario Iglesias-Martínez*
Affiliation:
Escuela Técnica Superior de Ingenieros de Minas, Universidad Politécnica de Madrid, c/Ríos Rosas, 21, 28003 Madrid, Spain
Berta Ordóñez-Casado
Affiliation:
Instituto Geológico y Minero de España, c/Matemático Pedrayes, 25, 33005 Oviedo, Spain
Edgar Berrezueta
Affiliation:
Instituto Geológico y Minero de España, c/Matemático Pedrayes, 25, 33005 Oviedo, Spain
*
Author for correspondence: Mario Iglesias-Martínez, Email: mario.iglesiasm@alumnos.upm.es
Get access Rights & Permissions [Opens in a new window]

Abstract

Morphological characterization and quantification of gold particles by optical image analysis (OIA) and by compositional analysis of microprobes using scanning electron microscope and electron microprobe analysis techniques were carried out on gold grains from the Minvoul area (Archean greenstone belt in Gabon). Large grains of almost pure gold were found throughout a weathering profile, which consisted of saprolite, mottled clay zone, iron duricrust, pisolitic gravels and yellow latosol. In the deeper horizons, gold was dissolved as shown by corrosion features on the surface of particles with average sizes of 2.6Φ and 2.35Φ in the saprolite and mottled clay zones, respectively. The occurrence of secondary gold in the duricrust was indicated by the larger size of the nuggets (average, 1.8Φ), the high fineness (> 995 in average) and the close textural relationship between gold and neoformed iron oxyhydroxides. The uppermost horizons composed of yellow latosol and pisolitic gravels were interpreted as transported materials based on their size distribution (average 0.85Φ and 1.34Φ), sorting and shape parameters. The best morphological parameter to describe the whole weathering profile was found to be the perimeter/area ratio. The highest ratios were recorded in the saprolite (average 0.192 μm−1), and decreased towards the surface (average 0.057 μm−1). The combination of the OIA technique and the microchemical analysis of gold grains allowed us to define specific morphological and compositional characteristics of the gold particles for each horizon. Both methods proved to be of great utility to understand gold concentration, dissolution and dispersion processes in supergene environments.

Keywords

goldlateriteweatheringoptical image analysisGabon
Type
Original Article
Information
Geological Magazine , Volume 157 , Issue 2 , February 2020 , pp. 307 - 320
Copyright
© Cambridge University Press 2019 

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Antweiler, JC and Campbell, WL (1977) Application of gold compositional analyses to mineral exploration in the United States. In Developments in Economic Geology Vol. 9, pp. 17–29. Amsterdam: Elsevier.Google Scholar
Averill, SA and Zimmerman, JR (1986) The riddle resolved: the discovery of the Partridge gold zone using Sonic drilling in glacial overburden at Waddy Lake, Saskatchewan. Canadian Geological Journal, Canadian Institute of Mining and Metallurgy 1, 14–20.Google Scholar
Bassot, JP, Caen-Vachette, M, Vialette, Y and Vidal, Ph (1986) Géochronologie du socle gabonais. Rapport préliminaire sur les mesures d·âge (zone Monts de Cristal, Mitzic-Oyem, Makokou Est et zone de Fougamou). Ministère des Mines, Gabon (Organisation des Nations Unies, Service Géologique), Libreville, Gabon and Département de Géologie et de Minéralogie, Université de Clermont-Ferrand 11, France.Google Scholar
Berrezueta, E and Castroviejo, R (2007) Reconocimiento automatizado de menas metálicas mediante análisis de imagen: un apoyo al proceso mineralœrgico. I: ensayo metodológico. Revista de Metalurgia 43, 294–309.Google Scholar
Berrezueta, E, González-Menéndez, L, Ordóñez-Casado, B and Olaya, P (2015) Pore network quantification of sandstones under experimental CO2 injection using image analysis. Computers and Geosciences 77, 97–110.CrossRefGoogle Scholar
Berrezueta, E, Ordóñez-Casado, B, Bonilla, W, Banda, R, Castroviejo, R, Carrión, P and Puglla, S (2016) Ore petrography using optical image analysis: application to Zaruma-Portovelo deposit (Ecuador). Geosciences 6, 30.CrossRefGoogle Scholar
Bowell, RJ (1992) Supergene gold mineralogy at Ashanti, Ghana: implications for the supergene behaviour of gold. Mineralogical Magazine 56, 545.CrossRefGoogle Scholar
Boyle, RW (1969) Hydrothermal transport and deposition of gold. Economic Geology 64, 112–5.CrossRefGoogle Scholar
Butt, CRM (1984) The nature and origin of the lateritic weathering mantle, with particular reference to Western Australia. In Geophysical Prospecting in Deeply Weathered Terrains (eds Doyle, HA, Glover, JE and Groves, DI), pp. 11–29. Geology Department and Extension Service, University of Western Australia, Special Publication no 6.Google Scholar
Butt, CRM and Hough, RM (2006) Crystallographic controls on the weathering of gold. In Proceedings of Regolith 2006-Consolidation and Dispersion of Ideas, 26–7. CSIRO Exploration and Mining, Bentley, Western Australia.Google Scholar
Castroviejo, R, Berrezueta, E and Lastra, R (2002) Microscopic digital image analyses of gold ores. A critical test of the methodology, comparing Reflected Light and SEM. Minerals and Metallurgical Processing 19, 102–9.Google Scholar
Chapman, RJ, Leake, RC, Moles, NR, Earls, G, Cooper, C, Harrington, K and Berzins, R (2000) The application of microchemical analysis of alluvial gold grains to the understanding of complex local and regional gold mineralization: a case study in the Irish and Scottish Caledonides. Economic Geology 95, 1753–73.Google Scholar
Chevallier, L, Makanga, JF and Thomas, RJ (2002) Notice explicative de la carte géologique de la République Gabonaiseà 1/1.000.000. Gabon: Éditions DGMG, 195 pp.Google Scholar
Colin, F, Lecomte, P and Boulange, B (1989) Dissolution features of gold particles in a lateritic profile at Dondo Mobi, Gabon. Geoderma 45, 241–50.CrossRefGoogle Scholar
de Oliveira, SMB and Campos, EG (1991) Gold-bearing iron duricrust in Central Brazil. Journal of Geochemical Exploration 41, 309–23.CrossRefGoogle Scholar
de Oliveira, SMB and de Oliveira, NM (2000) The morphology of gold grains associated with oxidation of sulphide-bearing quartz veins at Sao Bartolomeu, central Brazil. Journal of South American Earth Sciences 13, 217–24.CrossRefGoogle Scholar
DiLabio, RNW (1991) Classification and interpretation of the shapes and surface textures of gold grains from till. In Gisements Alluviaux d’or (Alluvial Gold Placers/Yacimientos Aluviales de Oro). Paris: ORSTOM, pp. 297–313.Google Scholar
Dos Santos, JF (1984) O ouro elúvio-laterítico do de’ósito de Jatobá-MT. In Proceedings of the XXXIII Congresso Brasileiro de Geologia, Rio de Janeiro. Anais, Sociedade Brasileira de Geologia, Vol. 8, pp. 4012–23.Google Scholar
Edou-Minko, A (1988) Pétrologie et Géochimie des Laterites à ‘stone-line’ du Gîte d’or d’Ovala. Application à la Prospection en zone Équatoriale Humide (Gabon). France: Université de Poitiers. Thèse Science 147 pp., published thesis.Google Scholar
Edou-Minko, AE, Colin, F, Trescases, JJ and Lecomte, P (1992) Altération latéritique du gîte aurifére d’Ovala (Gabon), et formation d’une anomalie superficielle de dispersion. Mineralium Deposita 27, 90–100.CrossRefGoogle Scholar
Ehrlich, R, Kennedy, SK, Crabtree, SJ and Cannon, RL (1984) Petrographic image analysis; I. analysis of reservoir pore complexes. Journal of Sedimentary Research 54, 1365–78.Google Scholar
Folk, RL and Ward, WC (1957) Brazos River bar: studying the significance of grain size parameters. Journal of Sedimentary Research 27, 3–26.CrossRefGoogle Scholar
Freyssinet, P, Butt, CRM, Morris, R and Piantone, P (2005) Ore-forming processes related to lateritic weathering. In Economic Geology 100th Anniversary Volume (eds Hedenquist, JW, Thompson, JFH, Goldfarb, RJ and Richards, JP)., pp. 681–722. Society of Economic Geologists, Littleton, Colorado.CrossRefGoogle Scholar
Freyssinet, P, Zeegers, H and Tardy, Y (1987) Néoformation d’or dans les cuirasses latéritiques: dissolution, migration, précipitation. In Mécanique, Physique, Chimie, Sciences de l’univers, Sciences de la Terre (ed. Maignien, R), pp. 867–74. Liège, Belgium, UNESCO, Comptes rendus de l’Académie des sciences, 305.Google Scholar
Freyssinet, P, Zeegers, H and Tardy, Y (1989) Morphology and geochemistry of gold grains in lateritic profiles of southern Mali. Journal of Geochemical Exploration 32, 17–31.CrossRefGoogle Scholar
Grant, AH, Lavin, OP and Nichol, I (1991) The morphology and chemistry of transported gold grains as an exploration tool. Journal of Geochemical Exploration 40, 73–94.CrossRefGoogle Scholar
Grove, C and Jerram, DA (2011) jPOR: an ImageJ macro to quantify total optical porosity from blue-stained thin sections. Computers and Geosciences 37, 1850–59.CrossRefGoogle Scholar
Guindon, DL and Nichol, I (1982) Speciation of free gold in glacial overburden, Grant 76. In Geoscience Research Grant Program, Summary of Research 1981–1982 (ed Pye, EG). Ontario Geological Survey, Miscellaneous Papers, vol. 103, p. 65.Google Scholar
Hallbauer, DK and Utter, T (1977) Geochemical and morphological characteristics of gold particles from recent river deposits and the fossil placers of the Witwatersrand. Mineralium Deposita 12, 293–306.CrossRefGoogle Scholar
Hérail, G (1984) Géomorphologie et Litologie de l’or Détritique (Piémonts et Bassins Intramontagneux du Nord-Ouest de l’Espagne). Paris: CNRS.Google Scholar
Higgings, MD (2006) Quantitative Textural Measurements in Igneous and Metamorphic Rocks. Cambridge: Cambrigde University Press, 265 pp.CrossRefGoogle Scholar
Hirdes, W (1984) Different populations of gold particles as outlined by their silver content: a regional investigation in the Precambrian Kimberley Reef Placer of the East Rand Goldfield, Witwatersrand, South Africa. In Syngenesis and Epigenesis in the Formation of Mineral Deposits (eds Wauschkuhn, A, Kluth, C and Zimerman, RA), pp. 247–59. Berlin: Springer-Verlag.CrossRefGoogle Scholar
Hough, RM, Butt, CR and Fischer-Bühner, J (2009) The crystallography, metallography and composition of gold. Elements 5, 297–302.CrossRefGoogle Scholar
Iglesias-Martínez, M (2015) Rapport annuel d’activités 2014–2015, Craton del Congo Exploraciones. SARL, du Permis de Recherche G9-580 Minvoul. Libreville-Madrid.Google Scholar
Iglesias-Martínez, M (2016) Rapport annuel d’activités 2015–2016, Craton del Congo Exploraciones. SARL, du Permis de Recherche G9-580 Minvoul. Libreville-Madrid.Google Scholar
Iglesias-Martínez, M, Espí, JA and Edou-Minko, A (2018) Geological setting of gold mineralization of the Minvoul greenstone belt (Ntem complex, northern Gabon). Journal of African Earth Sciences 147, 1–10.CrossRefGoogle Scholar
Jardine, MA, Miller, JA and Becker, M (2018) Coupled X-ray computed tomography and grey level co-occurrence matrices as a method for quantification of mineralogy and texture in 3D. Computer and Geoscience 111, 105–17.CrossRefGoogle Scholar
Lane, GR, Martin, C and Pirard, E (2008) Techniques and applications for predictive metallurgy and ore characterization using optical image analysis. Minerals Engineering 21, 568–77.CrossRefGoogle Scholar
Larizzatti, JH, de Oliveira, SMBD and Butt, CRM (2008) Morphology and composition of gold in a lateritic profile, Fazenda Pison ‘Garimpo’, Amazon, Brazil. Journal of South American Earth Sciences 25, 359–76.CrossRefGoogle Scholar
Lawrance, LM and Griffin, BJ (1994) Crystal features of supergene gold at Hannan South, Western Australia. Mineralium Deposita 29, 391–98.CrossRefGoogle Scholar
Leake, RC, Chapman, RJ, Bland, DJ, Stone, P, Camero, DG and Styles, MT (1998) The origin of alluvial gold in the Leadhills of Scotland: Evidence from internal chemical characteristics. Journal of Geochemical Exploration 63, 7–36.CrossRefGoogle Scholar
Leake, RC, Styles, MT, Bland, DJ, Henney, PJ, Wetton, PD and Naden, J (1995) The interpretation of alluvial gold characteristics as an exploration technique. British Geological Survey, Keyworth, Technical Report WC/95/22.Google Scholar
Lecomte, P (1988) Stone line profiles: Importance in geochemical exploration. Journal of Geochemical Exploration 30, 35–61.CrossRefGoogle Scholar
Leistel, JM, Deschamps, Y, Feybesse, JL, Husson, Y, Lambert, A, Leduc, C, Milési, JP, Chassignol, AL, Chêne, F, Heinry, C, Lançan, B, Lannez, P and Ralay, F (2001) Évaluation du potentiel aurifère du craton gabonais. Internal report of French Geological Survey (BRGM), RC-51121-FR. Orléans, France.Google Scholar
Loen, JS (1994) Origin of placer gold nuggets and history of formation of glacial gold placers, Gold Creek, Granite County, Montana. Economic Geology 89, 91–104.CrossRefGoogle Scholar
Mann, AW (1984) Mobility of gold and silver in lateritic weathering profiles; some observations from Western Australia. Economic Geology 79, 38–49.CrossRefGoogle Scholar
Michel, D (1987) Concentration of gold in situ laterite from Mato Grosso. Mineralium Deposita 22, 185–9.CrossRefGoogle Scholar
Morrison, GW, Rose, WJ and Jaireth, S (1991) Geological and geochemical controls on the silver content (fineness) of gold in gold-silver deposits. Ore Geology Reviews 6, 333–64.CrossRefGoogle Scholar
Nakagawa, M, Santosh, M, Nambiar, CG and Matsubara, C (2005) Morphology and chemistry of placer gold from Attappadi Valley, Southern India. Gondwana Research 8, 213–22.CrossRefGoogle Scholar
Njiosseu, ELT, Nzenti, JP, Njanko, T, Kapajika, B and Nédélec, A (2005) New U-Pb zircon ages from Tonga (Cameroon): coexisting Eburnean–Transamazonian (2.1 Ga) and Pan-African (0.6 Ga) imprints. Comptes Rendus Geoscience 337, 551–62.CrossRefGoogle Scholar
Ouangrawa, M and Yongue, FR (2001) L’or, le zircon et la tourmaline: traceurs de l’origine des matériaux des profils latéritiques d’Afrique. African Journal of Science and Technology 2, 25–43.Google Scholar
Owona, S, Ondoa, JM, Tichomirowa, M, Ratschbacher, L, Tchoua, MF and Ekodeck, GE (2012) New 207Pb/206Pb-Zr evaporation, metamorphic 87Rb/86Sr-WR-Bt ages and tectonic imprints in the Archean So’o Group (Ntem Complex/Congo craton, SW Cameroun). Global Journal of Geological Sciences 10, 99–109.Google Scholar
Pirard, E (2004) Multispectral imaging of ore minerals in optical microscopy. Mineralogical Magazine 68, 323–33.CrossRefGoogle Scholar
Pirard, E, Lebrun, V and Nivart, JF (1999) Optimal image acquisition of video images of reflected light. European Microscopy and Analysis 60, 9–11.Google Scholar
Ramanaidou, ER, Horwitz, RC and Morris, RC (1991) Channel iron deposits. AMIRA Project P75G-Restricted Report 399R, CSIRO Exploration and Mining, Australia.Google Scholar
Russ, JC (1992) The Image Processing Handbook. Boca Raton, FL: CRC Press, 444 pp.Google Scholar
Santosh, M, Philip, R, Jacob, MK and Omana, PK (1992) Highly pure placer gold formation in the Nilambur Valley, Wynad Gold Field, Southern India. Mineralium Deposita 27, 336–9.CrossRefGoogle Scholar
Shang, CK, Satir, M, Siebel, W, Taubald, H, Nsifa, EN, Westphal, M and Reitter, E (2001) Genesis of K-rich granitoids in the Sangmelima region, Ntem complex (Congo craton), Cameroon. Terra Nostra 5, 60–3.Google Scholar
Smith, RE and Anand, RR (1992) Mount Gibson Au deposit, Western Australia. In Regolith Exploration Geochemistry in Tropical and Subtropical Terrains (eds Butt, CRM and Zeegers, H), pp. 313–6. Amsterdam: Elsevier, Handbook of Exploration Geochemistry no. 4.Google Scholar
Spring, KR (2007) Cameras for digital microscopy. Methods in Cell Biology 81, 171–86.CrossRefGoogle ScholarPubMed
Styles, MT (1995) Alluvial gold characterisation in exploration planning: Project summary report. BGS Technical Report WC/95/38. British Geological Survey, Nottingham, United Kingdom.Google Scholar
Suh, CE and Lehmann, B (2003) Morphology and electron-probe microanalysis of residual gold-grains at Dimako, Southeast Cameroon. Neues Jahrbuch für Mineralogie-Monatshefte 6, 255–75.CrossRefGoogle Scholar
Tchameni, R (2004) Monozircon and Sm-Nd whole rock ages from the Ebolowa greenstone belts: Evidence for the terranes older than 2.9 Ga in the Ntem Complex (Congo craton, South Cameroon). Journal of Cameroon Academic Sciences 4, 213–24.Google Scholar
Tchameni, R, Mezger, K, Nsifa, NE and Pouclet, A (2000) Neoarchaean crustal evolution in the Congo Craton: evidence from K rich granitoids of the Ntem Complex, southern Cameroon. Journal of African Earth Sciences 30, 133–47.CrossRefGoogle Scholar
Thiéblemont, D (2013) Evidence for an aeolian origin of the Holocene lateritic surface cover of Gabon (Central Africa). Quaternary International 296, 176–97.CrossRefGoogle Scholar
Thiéblemont, D, Castaign, M, Billa, M, Bouton, P and Préat, A (2009) Notice explicative de la carte géologique et des ressources minérales de la République Gabonaise à 1/1 000 000. Ministère des Mines, du Pétrole et des Hydrocarbures (DGMG), Libreville.Google Scholar
Toteu, SF, Van Schmus, WR, Penaye, J and Michard, A (2001) New U–Pb and Sm–Nd data from north-central Cameroon and its bearing on the pre-Pan African history of central Africa. Precambrian Research 108, 45–73.CrossRefGoogle Scholar
Townley, BK, Herail, G, Maksaev, V, Palacios, C, de Parseval, P, Sepuldeva, F, Orellana, R, Rivas, P and Ulloa, C (2003) Gold grain morphology and composition as an exploration tool: application to gold exploration in covered areas. Geochemistry, Exploration, Environment, Analysis 3, 29–38.CrossRefGoogle Scholar
Vicat, JP, Léger, JM, Nsifa, E, Piguet, P, Nzenti, JP, Tchameni, R and Pouclet, A (1996) Distinction, au sein du craton congolais du sud-ouest du Cameroun, de deux épisodes doléritiques initiant les cycles orogéniques éburnéen (Paléoprotérozoïque) et panafricain (Néoprotérozoïque). Comptes Rendus de l’Académie des Sciences. Série 2. Sciences de la terre et des planètes 323, 575–82.Google Scholar
Von Gehlen, K (1983) Silver and mercury in single gold grains from the Witwatersrand and Barberton, South Africa. Mineralium Deposita 18, 529–34.CrossRefGoogle Scholar
Webster, JG and Mann, AW (1984) The influence of climate, geomorphology and primary geology on the supergene migration of gold and silver. Journal of Geochemical Exploration 22, 21–42.CrossRefGoogle Scholar
Wilson, AF (1984) Origin of quartz-free gold nuggets and supergene gold found in laterites and soils: a review and some new observations. Journal of the Geological Society of Australia 31, 303–16.Google Scholar
Zhihui, H and Fletcher, WK (1991) Distribution and morphological characteristics of visible gold in Harris Creek (82L/2). British Columbia Geological Survey. Geological Fieldwork, paper 1992–1. Vancouver, Canada.Google Scholar