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Gemmology Volume 26 No The Journal of Gemmology Volume 26 No. 1 January 1998 The Gemmological Association and Gem Testing Laboratory of Great Britain Gemlnological Association and Gem Testing Laboratory of Great Britain 27 Greville Street, London ECIN 8SU Tel: 0171 404 3334 Fax: 0171 404 8843 e-mail: [email protected] Website: www.gagtl.ac.uk/ gagtl President: Professor RA Howie Vice-Presidents: E.M. Bruton, AE. Farn, D.G. Kent, RK. Mitchell Honorary Fellows: RA Howie, RT. Liddicoat Jnr, 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. Monnickendam, L. 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, L. Bartlett, B.Sc., M.Phil., FGA, DGA, E.M. Bruton, FGA, DGA, CR Cavey, FGA, S. Coelho, B.Sc., FGA, DGA, Prof. AT. Collins, 8.Sc., PhD, AG. Good, FGA, DGA, CJ.E. Hall, 8.Sc. (Hons), FGA, G.M. Howe, FGA, DGA, G.H. Jones, B.Sc., Ph.D., FGA, M. Newton, B.Sc., D.Phil., H.L. Plumb, B.Sc., FGA, DGA, RD. Ross, B.Sc., FGA, DGA, P.A Sadler, B.Sc., FGA, DGA, E. Stern, FGA, DGA, Prof. I. Sunagawa, D.Sc., M. Tilley, GG, FGA, CM. Woodward, 8.Sc., FGA, DGA Tb.e JotJnra1o.£G~nunology Editor: Dr R.J~. Harding A$st'stant Ed1.tor$:M~J. a'Donoghue, P:G .. Read AssQeiat~ E,d.,#Pf'5: S~M. M!lietson (LOi1dott), Dr C.E.S. Alps (Leid~n), G~B9Sshart (ll.,'tt~~)j' Ptof.A.'t C~i (Lond.ll>:tll. Dr J.W. HlUTis (Gla$gow), Prof. RA. Howie (Derbyshire), Dr J.M.. Ogden. (Cambridge). .. Or J.E. Shigl~(Carlsbad;)~ &0,£. DoC. Smith (Paris), E. stem (London), Prof-I. Sunagawa Cf~kYo), Dr M. Superchi (Mil~lil),C.M.Woodward (London) Production Editor:M.A. Burland Vol 26, No.1, January 1998 ISSN: 1355-4565 Turquoise from Hubei Province, China Qi Lijian, FGA, DGA, Yan Weixuan, FGA, DGA, and Yang Mingxin, FGA China University of Geosciences, Wuhan, 430074, P.R. China ABSTRACT: The turquoise deposit in Yunyang district, Hubei Province, China, is characterized by its large scale, complex and variable ore-body types and colour varieties, compared with similar bodies outside China. The copper and phosphorus in the deposit originate mainly from finely dispersed sulphides in layered carbonaceous-siliceous slates, and from colloidal apatites (collophane) that occur in an irregular and patchy distribution pattern. The host rocks favourable for the formation of the turquoise are relatively rich in silica, copper and phosphorus and relatively poor in potassium, calcium and magnesium. The ore occurs mainly in lenticular bodies compressed between the layers. The distinctive mineralization is controlled by lithology, structure and the effects of ground water movement. The colouring mechanism of the turquoise results from a combination of [Cu (H20)4]2+, Fe3+ and Fe2+ ions. The colouring ions and the existing form and content of H20 limit directly the colour of the turquoise. The turquoise deposit can be considered as having been formed by a process of secondary leaching. Keywords: turquoise, mineral deposit, secondary leaching 1 Introduction unyang in Hubei Province, located in the eastern section of the Qinling fold Yzone at the intersection of Hubei, Henan and Shanxi provinces (Figure 1), is well known not only for its high-quality turquoise but also for its excellent carving techniques and life-like handicrafts (Figure 2). The exceptionally long mining history of turquoise can be deduced from the 20 turquoise beads unearthed with Qijia cultural relics of late Neolithic Age, located in Yongjing County, Gansu Province, China. This indicates a mining history of about 3200-3800 years (Hao Yongwei et al, 1982). Figure 1: Location map of the turquoise deposits At present, the holes for extraction of the in Hubei. Bai He is approximately 500 km NWof turquoise ore are readily apparent (Figure 3). Wuhan. © Gemmological Association and Gem Testing Laboratory of Great Britain ISSN: 1355-4565 Figure 3: AncientAncient cavescaves where turquoise waswas mined.mined. 2 Figure 4: Turquoise deposits at Yungaisi,Yungaisi, Yunxian County,County, Hubei. Hubei. Figure 2: Turquoise carving 'A picture ofof Paradise' (32x48x27 (32x48x27 cm). cm). Photo: Photo: Yuan Yuan Jiaqi. Jiaqi. ThThee complecomplexx metallogenimetallogenicc anandd geologicalgeological conditionconditionss ooff ththee turquoiseturquoise,, ththee variousvarious morphologiemorphologiess ooff ththee ororee bodybody,, ththee widwidee spatialspatial distributiodistributionn ooff ththee turquoisturquoisee anandd ititss irregularirregular occurrencoccurrencee iinn thithiss districdistrictt havhavee attracteattractedd littllittlee attentioattentionn frofromm ththee GovernmenGovernmentt foforr a lonlongg timetime.. IInn 19801980,, a teamteam fromfrom thethe HubeiHubei BureauBureau ofof GeologGeologyy anandd MineraMinerall ResourceResourcess carriecarriedd ououtt a reconnaissance geologicageologicall survesurveyy ooff ththee turquoisturquoisee deposidepositt aatt 1:200,001:200,0000 scalescale.. IInn 19821982,, ZhanZhangg HuifenHuifen,, JianJiangg ZechunZechun,, et ah,al., frofromm ththee GuiyanGuiyangg GeochemistrGeochemistryy InstitutInstitutee undeunderr ththee AcademAcademyy SinicSinicaa madmadee a detailedetailedd investigatioinvestigationn intintoo ththee turquoisturquoisee mineralogmineralogyy iinn thithiss districdistrictt anandd oonn ththee basibasiss ooff thithiss iitt wawass evidenevidentt thathatt mormoree needeneededd ttoo bbee donedone.. FoForr ththee paspastt severaseverall yearsyears,, ththee first-namedfirst-named authoauthorr anandd hihiss colleaguecolleaguess iinn ththee GemmologicaGemmologicall InstitutInstitutee ooff ththee UniversitUniversityy ooff ChinChinaa (Wuhan(Wuhan)) havhavee climbeclimbedd ththee QinlinQinlingg J.J. Gemm., 19981998,26,1,1-12, 26, 1, 1- 12 mountains,mountains, havehave investigatedinvestigated severalseveral tunnelstunnels whichwhich werewere stillstill beingbeing activelyactively minedmined andand havehave exploredexplored severalseveral abandonedabandoned cavescaves inin orderorder toto tracetrace thethe originorigin ofof thethe turquoiseturquoise andand toto prospectprospect forfor newnew occurrencesoccurrences (Figure 4) 4).. StratigraphicalStratigraphical andand lithologicallithological featuresfeatures TheThe ore-bearingore-bearing bedbed hashas beenbeen identifiedidentified asas thethe LowerLower CambrianCambrian ShuigoukouShuigoukou FormationFormation (E(e^g) jsg),, partpart ofof a regionallregionallyy metamorphosedmetamorphosed rockrock successionsuccession (Bao(Hao YongweYongweii et aI.ah,, 1982)1982).. ItsIts lithology isis composedcomposed mainly mainly of ofcarbonaceous-siliceous carbona­ ceous-siliceous slates,slates, carbonaceouscarbonaceous claclayy andand siliceoussiliceous slates,slates, bandebandedd thin-layethin-layerr siliceoussiliceous slates,slates, carbonaceoucarbonaceouss micmicaa quartzquartz rocks, calcareoucalcareouss micamica quartz-schistsquartz-schists andand carbonaceouscarbonaceous claclayy marbles.marbles. ThThee turquoiseturquoise Figure 6: Collophane (Apa)(Apa) and and quartz quartz (Si) (Si) occuroccurss mainlmainlyy inin ththee firstfirst threethree typetypess ofof rocksrocks.. along aa bedding bedding plane plane in incarbonaceous-siliceous carbonaceous-siliceous ThThee carbonaceous-siliceouscarbonaceous-siliceous slateslatess (th(thee hosthostss ooff slate, x60. x60. the turquoiseturquoise oreore bodies)bodies) havehave been been universally univer­ sally silicifiesilicifiedd anandd recrystallizerecrystallizedd intointo massivmassivee typicatypicall ofof quartz,quartz, carbonaceouscarbonaceous materialmaterialss andand slatslatyy quartzitquartzitee (Figure 5) 5).. This Thi srock roc kis i sgrey gre yto t o sericite,sericite, cacann bbee observeobservedd (Figure 6), 6), together togethe r blacblackk anandd characterizecharacterizedd mainlmainlyy bbyy aann witwithh colloidacolloidall structurestructuress anandd isotropiisotropicc areas.. intermediate-to-finintermediate-to-finee granulagranularr structurestructure,, anandd a 3 3 FielFieldd observationobservationss shoshoww thathatt ththee intensitintensityy ooff densdensee anandd harhardd texturetexture.. ThThee rocrockk iiss composedcomposed mineralizationmineralization,, ororee bodbodyy morphologmorphologyy anandd ororee ooff quartquartzz (80-85%)(80-85%),, carbonaceoucarbonaceouss materiamateriall qualitqualityy ooff thithiss districdistrictt araree alalll controllecontrolledd bbyy ththee (10-15%)(10-15%),, sericitsericitee (3-5%)(3-5%),, anandd albitalbitee (<1%)«1%).. lithologlithologyy (Figure 7). 7). ThThee carbonaceoucarbonaceouss siliceousiliceouss slateslatess frofromm ththee stronglstronglyy mineralizemineralizedd segmensegmentt ooff thithiss districtdistrict contaicontainn mormoree ooff ththee patchpatchyy colloidacolloidall apatitesapatites Figure 7: Mineralized intermediate toto thickly thickly (collophane)(collophane).. IIff thithiss rocrockk iiss sectionesectionedd anandd bedded carbonaceous-siliceous carbonaceous-siliceous slates slates.. The marker The marker observed through thethe microscope,microscope, the the features, features, indicates the the mineralization. mineralization. Figure 5:5: Thin Thin section section of ofcarbonaceous-siliceous carbonaceous-siliceous slate,slate, finefine toto medium medium grained grained,,
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