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Geochemical insight on gem opal formation and highly weathered rhyolitic ignimbrite layer from Delanta area, south Wollo, northern Ethiopia

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Abstract

A large amount of gem-quality opals is found in south Wollo/Delanta woreda, especially in Wegel Tena and Tsehay Mewucha localities in central Ethiopia. Petrographic investigation shows the host rock comprises porphyritic rhyolitic ignimbrite with quartz, plagioclase, and alkali feldspar phenocrysts. The matrix is composed of glass shards and is mostly weathered into clay, with a small proportion of biotite, hornblende, opaque minerals, and lithic fragments. Geochemically, the rhyolitic ignimbrite displays a pattern typical of silicic volcanic rocks from the area, with depletions of Ba, K, Sr, P, and Ti due to feldspar, apatite, and Fe-Ti oxide crystal fractionation. The rhyolitic ignimbrite is characterized by light REE-enrichment pattern ((La/Lu)N = 7.05–14.65) with slight negative Eu anomalies. The opal samples show lower REE than the rhyolitic ignimbrite, with stronger negative Eu anomalies and more positive Ce anomalies than the host rhyolitic ignimbrite. The Eu and Ce anomalies indicate that the fluid responsible for opal precipitation is associated in part with feldspar dissolution under variations in redox conditions, respectively. Therefore, as demonstrated in previous studies, we concluded that the Delanta opal is formed through intense weathering and alteration of rhyolitic ignimbrite before the eruption of the overlying thick and welded rhyolitic ignimbrite.

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References

  • Abduriyim A, Kitawaki H, Furuya M, Schwarz D (2006) “Paraíba”-type copper-bearing tourmaline from Brazil, Nigeria and Mozambique: chemical fingerprinting by LA-ICP-MS. Gems Gemol 42:4–21

    Article  Google Scholar 

  • Aguilar-Reyes BO (2004) Microstructural study of opal: application to the destabilization by whitening. PhD dissertation, University of Nantes, Nantes, France, pp 174

  • Ansori C (2010) Model mineralisasi pembentukan opal banten. Jurnal Geol Indones 5:151–170

    Google Scholar 

  • Ayalew D, Yirgu G (2003) Crustal contribution to the genesis of Ethiopian plateau rhyolitic ignimbrites: basalt and rhyolite geochemical provinciality. J Geol Soc London 160:47–56. https://doi.org/10.1144/0016-764901-169

    Article  Google Scholar 

  • Ayalew D, Barbey P, Marty B, Reisberg L, Yirgu G, Pik R (2002) Source, genesis, and timing of giant ignimbrite deposits associated with Ethiopian continental flood basalts. Geochem Cosmochim Acta 66:1429–1448. https://doi.org/10.1016/S0016-7037(01)00834-1

    Article  Google Scholar 

  • Ayalew D, Gibson S, Yirgu G, Ali S, Assefa D (2020) Pedogenic origin of Mezezo opal hosted in Ethiopian Miocene rhyolites. Can Mineral 58:231–246. https://doi.org/10.3749/canmin.1900059

    Article  Google Scholar 

  • Baker J, MacPherson CG, Menzies MA, Thirlwall MF, Al-Kadasi M, Mattey DP (2000) Resolving crustal and mantle contributions to continental flood volcanism, Yemen; constraints from mineral oxygen isotope data. J Petrol 41:1805–1820

    Article  Google Scholar 

  • Barnes JD, Paulick H, Sharp ZD, Bach W, Beaudoin G (2009) Stable isotope (δ18O, δD, δ37Cl) evidence for multiple fluid histories in mid-Atlantic abyssal peridotites (ODP Leg 209). Lithos 110:83–94. https://doi.org/10.1016/j.lithos.2008.12.004

    Article  Google Scholar 

  • Bartoli F, Bittencourt-Rosa D, Doirisse M, Meyer R, Philippy R, Samama JC (1990) Role of aluminium in the structure of Brazilian opals. Eur J Mineral 2:611–619

    Article  Google Scholar 

  • Beccaluva L, Bianchini G, Natali C, Siena F (2009) Continental flood basalts and mantle plumes: a case study of the Northern Ethiopian plateau. J Petrol 50(7):1377–1403

    Article  Google Scholar 

  • Berhe SM, Desta B, Nicoletti M, Tefera M (1987) Geology, geochronology and geodynamic implications of the Cenozoic magmatic province in W and SE Ethiopia. J Geol Soc Lond 144:213–226

    Article  Google Scholar 

  • Campbell KA, Guido DM, Gautret P, Foucher F, Ramboz C, Westall F (2015) Geyserite in hot-spring siliceous sinter: window on Earth’s hottest terrestrial (paleo) environment and its extreme life. Earth Sci Rev 148:44–64. https://doi.org/10.1016/j.earscirev.2015.05.009

    Article  Google Scholar 

  • Caucia F, Marinoni L, Leone A, Adamo I (2013) Investigation on the gemmological, physical and compositional properties of some opals from Slovakia (“Hungarian” opals). Period Di Mineral 82(2):251–261

    Google Scholar 

  • Chauviré B, Rondeau B, Mazzero F, Ayalew D (2017) The precious opal deposit at Wegel Tena, Ethiopia: formation via successive pedogenesis events. Can Mineral 55(4):701–723

    Article  Google Scholar 

  • Chauviré B, Rondeau B, Alexandre A, Chamard-Bois S, La Carole C, Mazzero F (2019) Pedogenic origin of precious opals from Wegel Tena (Ethiopia): evidence from trace elements and oxygen isotopes. Appl Geochem 101:127–139

    Article  Google Scholar 

  • Clarke JDA (2003) The occurrence and significance of biogenic opal in the regolith. Earth Sci Rev 60(3–4):175–194

    Article  Google Scholar 

  • Coulie E, Quideleur X, Gillot PY, Courtillot V, Lefèvre JC, Chiesa S (2003) Comparative K-Ar and Ar/Ar dating of Ethiopian and Yemenite Oligocene volcanism: implications for timing and duration of the Ethiopian traps. Earth Planet Sci Lett 206:477–492

    Article  Google Scholar 

  • Curtis NJ, Gascook JR, Johnson MR, Pring A (2019) A review of the classification of opal with reference to recent new localities. Minerals 9(5):299. https://doi.org/10.3390/min9050299

    Article  Google Scholar 

  • Day R, Jones B (2008) Variations in water content in opal-A and opal-CT from geyser discharge aprons. J Sediment Res 78(4):301–315. https://doi.org/10.2110/jsr.2008.030

    Article  Google Scholar 

  • Dowell K, Mavrogenes J, McPhail DC, Watkins JJ (2002) Origin and timing of formation of precious black opal nobbies at Lightning Ridge. In: Roach IC (ed) Regolith and Landscapes in Eastern Australia. CRC LEME, Perth, pp 18–20

  • Dutkiewicz A, Landgrebe TCW, Rey PF (2015) Origin of silica and fingerprinting of Australian sedimentary opals. Gondwana Res 27:786–795

    Article  Google Scholar 

  • Ebinger CJ, Sleep NH (1998) Cenozoic magmatism throughout East Africa resulting from impact of a single plume. Nature 395:788–791. https://doi.org/10.1038/27417

  • Ebinger CJ, Yemane T, WoldeGebriel G, Aronson JL, Walter RC (1993) Late Eocene-recent volcanism and faulting in the southern main Ethiopian rift. J Geol Soc London 150:99–108

    Article  Google Scholar 

  • Eckert AW (1997) The world of opals. Jone and Wiley & Son, INC, New York and Chichester, pp 448

  • Elzea JM, Rice SB (1996) TEM and X-ray diffraction evidence for cristobalite and tridymite stacking sequences in opal. Clays Clay Miner 44:492–500

    Article  Google Scholar 

  • Fritsch E, Rondeau B (2009) Gemology: the developing science of gems. Elements 5:147–152

    Article  Google Scholar 

  • Fröhlich, (2020) The opal-CT nanostructure. J Non Cryst Solids 533(2):1–8. https://doi.org/10.1016/j.jnoncrysol.2020.119938

    Article  Google Scholar 

  • Gaillou E, Delaunay A, Rondeau B, Bouhnik-le-Coz M, Fritsch E, Cornen G, Monnier C (2008) The geochemistry of gem opals as evidence of their origin. Ore Geol Rev 34(1–2):113–126

    Article  Google Scholar 

  • Gallacher AD (2001) Geochemistry of sedimentary opal, Hebel, Southern Queensland (unpublished Doctoral thesis). School of Earth Sciences, Melbourne Vic: The University of Melbourne

  • Gauthier JP, Mazzero F, Mandaba Y, Fritsch E (2004) Opal from Ethiopia: usual gemology and unusual characteristics. Rev Gemmol AFG 149:15–23

    Google Scholar 

  • George R, Rogers N, Kelley S (1998) Earliest magmatism in Ethiopia: evidence for two mantle plumes in one flood basalt province. Geology 26:923–926

    Article  Google Scholar 

  • Goryniuk MC, Rivard BA, Jones B (2004) The reflectance spectra of opal-A (0.5–25μm) from the Taupo Volcanic Zone: spectra that may identify hydrothermal system on planetary surfaces. Geophys Res Lett 31:L24701. https://doi.org/10.1029/2004GL021481

    Article  Google Scholar 

  • Gübelin E (1986) Les opales mexicaines. Revue de Gemmologie (a.f.g.) 88:3–8

    Google Scholar 

  • Guthrie GD, Bish DL, Reynolds RC (1995) Modelling the X-ray diffraction pattern of opal-CT. Am Mineral 80:869–872

    Article  Google Scholar 

  • Harnois L (1988) The CIW index: a new Chemical Index of Weathering. Sediment Geol 55:319–322

    Article  Google Scholar 

  • Hofmann C, Courtillot V, Feraud G, Rochette P, Yirgu G, Ketefo E, Pik R (1997) Timing of the Ethiopian flood basalt event and implications for plume birth and global change. Nature 389:838–841

    Article  Google Scholar 

  • Iler RK (1979) The chemistry of silica: solubility, polymerization, colloid and surface properties and biochemistry of silica. John Wiley and Sons, New York, NY

    Google Scholar 

  • Johnson ML, Kammerling RC, DeGhionno DG, Koivula JI (1996) Opal from Shewa Province. Ethiopia Gems Gemol 32(2):112–120

    Article  Google Scholar 

  • Jones B, Renaut RW (2004) Water content of opal-A: implications for the origin of laminae in geyserite and sinter. J Sediment Res 74(1):117–128

    Article  Google Scholar 

  • Jones JB, Segnit ER (1971) Nature of opal part I: nomenclature and constituent phases. J Geol Soc Aust 18:57–68

    Article  Google Scholar 

  • Kiefert L, Hardy P, Sintayehu T, Abate B, Woldetinsae G (2014) A new deposit of black opal from Ethiopia. Gems Gemol 50(4):302–315

    Google Scholar 

  • Kieffer B, Arndt N, Lapierre H, Bastien F, Bosch B, Pecher A, Yirgu G, Ayalew D, Weis D, Jerram DA, Keller F, Meugniot C (2004) Flood and shield basalts from Ethiopia: magmas from the African superswell. J Petrol 45:793–834

    Article  Google Scholar 

  • Koivula JI, Fryer CW, Keller CP (1983) Opal from Queretaro, occurrence and inclusions. Gems Gemol 19(2):87–98

    Article  Google Scholar 

  • Langer K, Flörke OW (1974) Near infrared absorption spectra (4000–9000 cm-1) of opals and the role of “water” in these SiO2-nH2O minerals. Fortschr Mineral 52:17–51

    Google Scholar 

  • Le Bas MJ, LeMaitre RW, Streckeisen A, Zanettin B (1986) A chemical classification of volcanic rocks based on the total alkali-silica diagram. J Petrol 27(3):745–750

    Article  Google Scholar 

  • Liang Y, Zhang J, Liu Y, Tang X, Li Z, Ding J, Wang Y, Yang S (2020) Evidence for biogenic silica occurrence in the lower Silurian Longmaxi Shale in Southeastern Chongqing. China Minerals 10(11):945. https://doi.org/10.3390/min10110945

    Article  Google Scholar 

  • Liesegang M, Milke R (2014) Australian sedimentary opal-A and its associated minerals: implications for natural silica sphere formation. Am Mineral 99:1488–1499

    Article  Google Scholar 

  • Lynne BY, Campbell KA, Moore JN, Browne PRL (2005) Diagenesis of 1900-year old siliceous sinter (opal-A to quartz) at Opal Mound, Roosevelt Hot Springs, Utah. U.S.A. Sediment Geol 179:249–278. https://doi.org/10.1016/j.sedgeo.2005.05.012

    Article  Google Scholar 

  • Martin E, Gaillou E (2018) Insight on gem opal formation in volcanic ash deposits from a supereruption: a case study through oxygen and hydrogen isotopic composition of opals from Lake Tecopa, California, U.S.A. Am Min 103:803–811. https://doi.org/10.2138/am-2018-6131

    Article  Google Scholar 

  • Mazzero F, Gauthier JP, Rondeau B, Fritsch E, Bekele E (2009) Nouveau gisement d’opales d’Ethiopie dans la Province du Welo: Premières informations. [New deposit of Ethiopian opals in the Wollo Province: Early information]. Revue de Gemmologie a.f.g. 167:4–5 [in French]

  • McOrist GD, Smallwood AG, Fardy JJ (1994) Trace elements in Australian opals using neutron activation analysis. J Radioanal Nucl Chem 185:293–303

    Article  Google Scholar 

  • Merla G, Abbate E, Azzaroli A, Bruni P, Canuti P, Fazzuoli M, Sagr M, Tacconi P (1979) A geological map of the Ethiopia and Somalia and comment with a map of major landforms (scale 1:2,000,000). Consiglio Nazionale delle Ricerche, Frienze Italy, pp 95

  • Meshesha D, Shinjo R (2007) Crustal contamination and diversity of magma sources in the northwestern Ethiopia volcanic province. J Mineral Petrol Sci 102:272–290

    Article  Google Scholar 

  • Natali C, Beccaluva L, Bianchini G, Siena F (2016) Comparison among Ethiopia- Yemen, Deccan, and Karoo continental flood basalts of central Gondwana: insights on lithosphere versus asthenosphere contributions in compositionally zoned magmatic provinces. Spec Pap Geol Soc Am 526:191–215

    Google Scholar 

  • Nesbitt HW, Young GM (1982) Early Proterozoic climates and plate motions inferred from major element chemistry of lutites. Nature 299:715–717

    Article  Google Scholar 

  • Peucat JJ, Ruffault P, Fritsch E, Bouhnik-le coz M, Simonet C, Lasnier B (2007) Ga/Mg ratio as a new geochemical tool to differentiate magmatic from metamorphic blue sapphires. Lithos 98:261–274

    Article  Google Scholar 

  • Pik R, Deniel C, Coulon C, Yirgu G, Hofmann C, Ayalew D (1998) The northwestern Ethiopian plateau flood basalts: classification and spatial distribution of magma types. J Volcanol Geotherm Res 81(1–2):91–111

    Article  Google Scholar 

  • Pik R, Daniel C, Coulon C, Yirgu G, Marty B (1999) Isotopic and trace element signatures of Ethiopian flood basalts: evidence for plume lithosphere interactions. Geochim Cosmochim Acta 63(15):2263–2279

    Article  Google Scholar 

  • Pirajno F (2009) Hydrothermal processes and mineral system. Springer Berlin Germany, pp 1250. https://doi.org/10.1007/978-1-4020-8613-7

  • Rey PF (2013) Opalisation of the Great Artesian Basin (central Australia): an Australian story with a Martian twist. Aust J Earth Sci 60:291–314

    Article  Google Scholar 

  • Rodgers KA, Browne PRL, Buddle TF, Cook KL, Greatrex RA, Hampton WA, Herdianita NR, Holland GR, Lynne BY, Martin R, Newton Z, Pastars D, Sannazarro KL, Teece CIA (2004) Silica phases in sinters and residues from geothermal fields of New Zealand. Earth Sci Rev 66(1–2):1–61. https://doi.org/10.1016/j.earscirev.2003.10.001

    Article  Google Scholar 

  • Rondeau B, Fritsch E, Fritsch M, Renac C (2004) Opals from Slovakia (“Hungarian” opals): a re-assessment of the conditions of formation. Eur J Mineral 16:789–799

    Article  Google Scholar 

  • Rondeau B, Fritsch E, Mazzero F, Gauthier JP, Cenki-Tok B, Bekele E, Gaillou E (2010) Play-of-color Opal from Wegel Tena, Wollo Province. Ethiopia Gems Gemol 46(2):90–105

    Article  Google Scholar 

  • Rondeau B, Cenki-Tok B, Fritsch E, Mazzero F, Gauthier JP, Bodeur Y, Bekele E, Gaillou E, Ayalew D (2012) Geochemical and petrological characterization of gem opals from Wegel Tena, Wollo, Ethiopia: opal formation in an Oligocene soil. Geochem Explor Environ 12(2):93–104

    Article  Google Scholar 

  • Rossman GR (2009) The geochemistry of gems and its relevance to gemology: different traces, different prices. Elements 5:159–162

    Article  Google Scholar 

  • Shigley JE, Laurs BM, Renfro ND (2009) Chrysoprase and prase opal from Haneti, Central Tanzania. Gems Gemol 45:271–279

    Article  Google Scholar 

  • Simoni M, Caucia F, Adamo I, Galinetto P (2010) New occurrence of fire opal from Bemia, Madagascar. Gems Gemol 46:114–121

    Article  Google Scholar 

  • Smallwood A, Thomas PS, Ray AS (1997) Characterisation of sedimentary opals by Fourier transform Raman spectroscopy. Spectrochim 53:2341–2345

    Article  Google Scholar 

  • Smallwood A, Thomas PS, Ray A (2008) Comparative Analysis of Sedimentary and Volcanic Precious Opals from Australia. J Aust Ceram 44(2):17–22

    Google Scholar 

  • Sun SS, McDonough WF (1989) Chemical and isotopic systematics of oceanic basalts: implications of mantle composition and processes. Geol Soc Spec Publ 42(1):313–345

    Article  Google Scholar 

  • Thiry M, Simon-Coinçon R (1996) Tertiary paleoweatherings and silcretes in the southern Paris Basin. CATENA 26:1–26

    Article  Google Scholar 

  • Thiry M, Milnes AR, Rayot V, Simon-Coinçon R (2006) Interpretation of palaeoweathering features and successive silicifications in the tertiary regolith of inland Australia. J Geol Soc London 163:723–736

    Article  Google Scholar 

  • Ukstins IA, Renne PR, Wolfenden E, Baker J, Ayalew D, Menzies M (2002) Matching conjugate volcanic rifted margins: 86 40Ar/39Ar chrono-stratigraphy of pre and syn-rift bimodal flood volcanism in Ethiopia and Yemen. Earth Planet Sci Lett 198(3–4):289–306

    Article  Google Scholar 

  • Ullyott JS, Nash DJ, Whiteman CA, Mortimore RN (2004) Distribution, petrology and mode of development of silcretes (sarsens and puddingstones) on the eastern South Downs, UK. Earth Surf Process Landf 29:1509–1539

    Article  Google Scholar 

  • Wilson J (2014) The structure of opal-CT revisited. J Non Cryst Solids 405(1):68–75. https://doi.org/10.1016/j.jnoncrysol.2014.08.052

    Article  Google Scholar 

  • Winchester JA, Floyd PA (1997) Geochemical discrimination of different magma series and their differentiation products using immobile elements. Chem Geol 20:245–252

    Google Scholar 

  • Wolfenden E, Ebinger C, Yirgu G, Deino A, Ayalew D (2004) Evolution of the northern Main Ethiopian rift: birth of a triple junction. Earth Planet Sci Lett 224:213–228

    Article  Google Scholar 

  • Yu XY (2009) Colored gemmology, 2nd edn. Geological Publishing House, Beijing, China, p 10

    Google Scholar 

  • Zewdie S, Mammo W, Negassa G (2009) Opportunities for gem resource development in Ethiopia. EIGS, unpublished promotion report, Addis Ababa, Ethiopia, pp 31

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Acknowledgements

MM is highly grateful to Addis Ababa Science and Technology University (AASTU) for MSc program opportunity. This work is completed due to the kind and welcoming community of Dessie, Wegel Tena, and Tsehay Mewucha. Therefore, we greatly thank those community and government officials for their cooperation and hospitality. Finally, the authors thank the anonymous reviewers and associate editor for their constructive and detailed comments that improved the manuscript.

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  1. Department of Geology, College of Applied Science, Addis Ababa Science and Technology University, P.O. Box 16417, Addis Ababa, Ethiopia

    Mulugeta Milkias, Tesfaye Demissie & Daniel Meshesha

  2. Mineral Exploration, Extraction and Processing Centre of Excellence, Addis Ababa Science and Technology University, P.O. Box 16417, Addis Ababa, Ethiopia

    Mulugeta Milkias, Tesfaye Demissie & Daniel Meshesha

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Milkias, M., Demissie, T. & Meshesha, D. Geochemical insight on gem opal formation and highly weathered rhyolitic ignimbrite layer from Delanta area, south Wollo, northern Ethiopia. Arab J Geosci 16, 335 (2023). https://doi.org/10.1007/s12517-023-11426-w

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