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Gemmology Volume 26 No The Journal of Gemmology Volume 26 No. 2 April 1998 The Gemmological Association and Gem Testing Laboratory of Great Britain Gemmological Association and Gem Testing Laboratory of Great Britain 27 Greville Street, London EC1N 8SU Tel: 01714043334 Fax: 01714048843 e-mail: [email protected] Website: www.gagtl.ac.uk/gagtl President: Professor RA Howie Vice-Presidents: E.M. Bruton, AE. Faro, D.G. Kent, RK. Mitchell Honorary Fellows: RA Howie, R.T. Liddicoat Jill, K. Nassau Honorary Life Members: D.J. Callaghan, E.A Jobbins, H. Tillander Council of Management: CR Cavey, T.J. Davidson, N.W.. Deeks, RR Harding, I. Thomson, V.P. Watson Members' Council: AJ. Allnutt, P. Dwyer-Hickey, R Fuller, J. Greatwood, B. Jackson, J. Kessler, J. Monhickendam, 1. Music, J.B. Nelson, P.G. Read, R Shepherd, CH. Winter Branch Chairmen: Midlands ~ G.M. Green, North West -I. Knight, Scottish - B. Jackson Examiners: AJ. Allnutt, M.5c., Ph.D., FGA, S.M. Anderson, B.Sc. (Hons), FGA, 1. Bartlett, B.Sc., M.Pbil., FGA, DGA, E.M. Bruton, FGA, DGA, CR Cavey, .FGA, S. Coelho, B.Sc., FGA, DGA, Prof. AT. Collins, B.Sc., Ph.D, AG. Good, FGA, DGA, CJ.E. Hall, B.Sc. (Hons), FGA, G.M .. Howe, FGA, DGA, G.H. Jones, B.5c., Ph.D., FGA, M. Newton, B.Sc., D.Phil.,H.1. Plumb, B.Sc., FGA, DGA, RD. Ross, B.Sc., FGA, DCA, P.A Sadler, B.5c., FCA, DCA, E. Stern, FGA, DGA, P rof. I. Sunagawa, D.5c., M. Tilley, GG, FGA, CM. Woodward, B.Sc .., FGA, DGA The Journal of Gemmology Editor: Dr RR Harding Assistant Editors: M.J. O'Donoghue, P.G. Read Associate Editors: S.M. Anderson (London), Dr CE.s. Arps (Leiden), G. Bosshart (Zurich), Prof. AT. Collins (London), Dr J.w. Harris (Glasgow), Prof. RA Howie (Derbyshire), Dr J.M. Ogden (Cambridge), Prof. AH. Rankin (Kingston upon Thames), Dr J.E. Shigley (Carlsbad), Prof. D.C Smith (Paris), E. Stern (London), Prof. I. Sunagawa (Tokyo), Dr M. Superchi (Milan), CM. Woodward (London) Production Editor: M.A Burland Vol 26. No.2, April 1998 ISSN: 1355-4565 Distinctive gem corundum suites from discrete basalt fields: a comparative study of Barrington, Australia, and West Pailin, Cambodia, gemfields F.L. Sutherland1, D. Schwarz2, E.A. Jobbins3, R.R. Coenraads1 and G. Webb1 1. Geodiversity Research Group, Australian Museum, Sydney, Australia 2. Giibelin Gemmological Laboratory, Lucerne, Switzerland 3. Caterham, Surrey, U.K. ABSTRACT: Barrington, Australia, and West Pailin, Cambodia, basalt fields yield remarkably similar 'metamorphic' corundums (including ruby) and 'basaltic' type blue corundums. These represent different underlying sources tapped by basaltic eruptions. The 'metamorphic' suites have high chromium/low gallium chemistry, with Ga203 contents <0.01 wt% and Cr203/Ga203 ratios above 3. The 'basaltic' suites show higher Ga203 (up to 0.04 wt%) and Cr203/Ga203 ratios below 1. The 65 absorption spectra of blue 'metamorphic' sapphires are dominated by Fe3+ bands in the ultraviolet (375, 387 nm) and visible region (450, 460, 469 nm). A broad Fe2+ - Ti4+ charge transfer band lies between 550-750 nm, without significant Fe2+ - Fe3+ charge transfer absorption toward the near infrared that is typical of blue 'basaltic' sapphires. Most absorption spectra of 'metamorphic' corundums represent a combination of Fe/Ti/Cr-bands, with variable relative intensities. Keywords: corundum, sapphire, ruby, sapphirine, absorption spectra, trace elements, basalt, Barrington (Australia), Pailin (Cambodia) Introduction widely separated basalt fields, Barrington in Fast Australia and South East Asia East Australia and West Pailin in Cambodia, exploit rich corundum deposits from and show that they contain mixed ruby and • / their basalt fields, in significant mining, sapphire suites of remarkable similarity. processing and cutting industries (Mumme, Two distinctive gem corundum suites 1988; Hughes, 1990, 1997). East Australia appear in eluvial and alluvial deposits produces sapphire and rare ruby (Coldham, from the Barrington basalt province in 1985; Olliver and Townsend, 1990; Sutherland, New South Wales, one typical of East 1991), while SE Asia produces both sapphire Australian sapphire fields and the other and ruby in abundance (Vichit, 1992). In this associated with rubies (Sutherland and paper we describe corundum suites from two Coenraads, 1996). Besides typical Australian © Gemmological Association and Gem Testing Laboratory of Great Britain ISSN: 1355-4565 corrodedcorroded blue-green-yelloblue-green-yelloww zonedzoned sapphiressapphires PreliminaryPreliminary examinationexamination ooff WesWestt PailiPailinn (Coenraads,(Coenraads, 1992a,1992a, b;b; Sutherland,Sutherland, 1996;1996; GuoGuo etet materiamateriall showedshowed itsits similaritysimilarity ttoo thethe al.,al, 1996),1996), ththee BarringtonBarrington provinceprovince alsoalso yieldyieldss BarringtoBarringtonn suites,suites, includingincluding sapphirinesapphirine aass anan anan abundantabundant pastel-colouredpastel-coloured sapphire-rubysapphire-ruby intergrowthintergrowth inin thethe rubyruby associationassociation (analysis(analysis suitesuite (Sutherland(Sutherland et al.,al, 1993;1993; SutherlandSutherland andand bbyy K.K. Williams).Williams). A mormoree detaileddetailed Coenraads,Coenraads, 1996).1996). RecognitionRecognition ofof thisthis lastlast suitesuite investigationinvestigation ofof samplessamples collectedcollected bbyy JobbinsJobbins promptedprompted a re-examinatiore-examinationn ofof rubyruby andand waswas carriedcarried outout bbyy personnepersonnell frofromm thethe sapphiresapphire collectedcollected fromfrom basaltbasalt fieldsfields aroundaround AustraliaAustraliann MuseumMuseum anandd GiibelinGiibelin PailiPailinn bbyy E.A.E.A. JobbinsJobbins inin 19741974 (Berrange(Berrangé andand GemmologicalGemmological Laboratory,Laboratory, Switzerland.Switzerland. ThisThis JobbinsJobbins,, 1976;1976; JobbinsJobbins andand Berrange,Berrangé, 1981).1981). worworkk includesincludes gemmologicalgemmological studiestudiess onon Figure 1: Distribution ofof basaltic basaltic rocks rocks (stippled (stippled areas) areas) and mainand maindrainages, drainages, Barrington Barrington volcano volcano province, 250 250 km km north north of ofSydney, Sydney, New New South South Wales. Wales. Corundum/zircon Corundum/zircon suites suitesare marked are marked by inclined by inclined crosses. The The numbered numbered sites sites are are basalt basalt age-dating age-dating sites, sites,with thewith following the following ages, 1: ages, 44-54 1: m.y., 44-54 1A: m.y., 1A: 54 m.y.,m.y., 2:2: 3737 m.y.,m.y., 2A:2A: 4242 m.y., m.y., 3: 3: 52-54 52-54 m.y., m.y., 4: 4: 59 59 m.y., m.y., 5: 5: 54 54 m.y. m.y. (based (based on onSutherland Sutherland and and Fanning, 1996). 1996). The The main main intrusive intrusive centre centre of Barrington of Barrington volcano volcano is marked is markedby a triangle by a (1555triangle m above (1555 m above sea level) andand the the original original extent extent of ofthe the volcano volcano before before dissection dissection is marked is marked by a dashed by a dashedperimeter perimeter (600-800 m m a.s.l.), a.s.L), after after Pain, Pain, 1983. 1983. 66 66 J.J . Gemm., 1998, 1998,26,2, 26, 2, 65-85 65-85 3km j N 67 67 Figure 2: Distribution of basaltic rocks (denser stippled areas) and drainages, Pailin district,district, Cambodia.Cambodia . Gem-bearing drainage is shown as continuous lines, with gem-barren drainages shown as short dashed lines. Volcanic ventsvents areare indicatedindicated byby trianglestriangles andand thethe mainmain basaltbasalt centrescentres areare PhnumPhnum KoKo Ngoap, Phnum 0O Tang forfor dominant fancyfancy coloured corundums, and Phnum Yat forfor dominant 'basaltic''basaltic' blueblue corundums. The main drainages are the O0 Chra and Stoeng Pailin rivers and the road toto Pailin is marked by a double line.line. The geological boundaryboundary betweenbetween youngeryounger basementbasement rocksrocks (coarse(coarse stipple) and older crystalline basement (unmarked) isis shown by a heavy line,line, and fault zones are markedmarked by long dashes.dashes. Diagram modified fromfrom BerrangéBerrange and Jobbins, 1976, and Jobbins andand Berrange,Berrangé, 1981.1981. corunducorundumm frofromm BarringtoBarringtonn anandd WesWestt PailiPallinn (CAMEC(CAMECAA microprobmicroprobee witwithh WDWDSS spectrospectro­­ anandd comparativcomparativee studiestudiess oonn sapphiresapphiress fromfrom metermeter;; R.RRR.. CoenraadsCoenraads,, F.LF.L.. SutherlandSutherland)) anandd EasEastt AustraliaAustralia,, frofromm centracentrall QueenslandQueensland comparisoncomparisonss ooff ththee corunducorundumm suitesuitess iinn (Anaki(Anakiee FieldsFields)) anandd NeNeww SoutSouthh WaleWaless discussiodiscussionn ooff theitheirr geologicageologicall originoriginss (Ne(Neww EnglanEnglandd FieldsFields)) anandd frofromm EasEastt PailinPallin.. (F.L(F.L.. Sutherland,Sutherland, D.D. Schwarz).Schwarz). StudieStudiess includincludee photographphotographyy anandd photophoto­­ micrography (G. Webb, E.A. Jobbins), trace micrography (G. Webb, E.A. Jobbins), trace GeologicaGeologicall settingsettingss elemenelementt anandd coloucolourr absorptioabsorptionn spectraspectrall studiestudiess (EDXRF(EDXRF,, UV-vis-NIUV-vis-NIRR spectrometry;spectrometry; ThThee BarringtoBarringtonn corundumcorundumss comcomee frofromm ththee DD.. Schwarz)Schwarz),, chemicachemicall analyseanalysess ooff inclusioninclusionss erodeerodedd BarringtoBarringtonn shielshieldd volcanvolcanoo iinn anandd intergrowthintergrowthss iinn WesWestt PailiPallinn corundumscorundums NeNeww SoutSouthh WaleWaless
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