EconomicGeology Vol. 81, 1986, pp. 2022-2028 MINGORA EMERALD DEPOSITS (PAKISTAN): SUTURE-ASSOCIATEDGEM MINERALIZATION A. H. KAZMI, GeologicalSurveyof Pakistan,42-R, Block6, PECHS,Karachi, Pakistan R. D. LAWRENCE, Geolog•tDepartment,OregonState Universitel,Corvallis,Oregon97331 j. ANWAR, GemstoneCorporationof Pakistan,Peshawar,Pakistan L. W. SNEE,* GeologyDepartment,OregonState University,Corvallis,Oregon97331 AND S. HUSSAIN GemstoneCorporationof Pakistan,Peshawar,Pakistan Introduction The Indian subcontinentsequence The Mingoraemeralddepositsare locatedat the northernedge of Mingora,SwatDistrict, about 130 milesnortheastof Peshawar(Fig. 1). They havebeen knownand sporadicallymined since 1958 (Davies, 1962; Kazmi, 1983). Jan(1968) andJanet al. (1981) discussed the petrographyof the deposit.Gubelin (1968, 1982) publisheda gemologicaldescriptionof the Mingoraemeralds.Mingoraemeraldswere sold in world marketsfor more than 20 yearsby names other than Mingora (or Pakistan).These emeralds were introducedworldwide under their own locality name after exhibitionof a large consignmentof cut andpolishedstonesin the TucsonGem andMineral show(U.S.A.)in 1981 (Herzberg, 1981). The presentstudyindicatesthat the emeraldsare found exclusivelyin metamorphosed ophioliticmrslangeof the suturezonebetweenthe Kohistanisland arc andthe Asiancrustalplate (Fig. 1). The geologic settingof the Mingoraemeralddepositsandtheir origin are describedin this paper. This sequencecomprisesfour lithostratigraphic units(Table 1), whichare exposedeastof Mingora. The PrecambrianManglaurschistis the oldestandit wasprevasivelyintrudedby the Swatgranite(early Paleozoic?)whichoccursasa massivesheetlikebody intrudedinto the Manglaurschist.Bothof themwere foldedsubsequentlyinto an antiform,the outer part of whichis largelycomposedof a coarseleucocratic augengneiss.The presenceof beryl in theserocks (Kazmiet al., 1984) issignificantfromthe standpoint of emeraldparagenesis. The Alpuraischistis composed of severalhundred metersof siliceousschistandcalcareousquartz-micagarnetschist.The Alpurai schistis probablyunconformableontopof the ManglaurschistandSwatgneiss and is overlainby Saidu calcareousgraphite schist which is at upper greenschistto lower amphibolite metamorphic facies.The AlpuraiandSaiduschists are probablyof late Paleozoicto Mesozoicage(Kazmiet al., 1984). The upperpart of the Saiduschisthasbeen overthrustby the Indussuturem61anges comprising Regional Geology an imbricatezonewith slicesof Saiducalc-graphite Structurallythe Mingoraareaiscomposedof three schist,talc-dolomiteschist,and Mingora ophiolite tectonostratigraphic groupsof rocks(Table 1). From m(•lange(Fig. 2). northto souththeseare (1) the Kohistanarcsequence (Jan,1977, 1980; Tahirkheliet al., 1979; Bard, 1983) which hasbeen thrust over (2) the Indus suturem(•- The Indus suturemdlangegroup langegroup (Kazmi et al., 1984) which in turn has The Indus suturem(•langescomprisefragmented been obductedonto (3) the Indian subcontinentse- blocks derived from oceanic crust, volcanic arcs, quence(Figs. i and 2). The Indus suturemf•lange trenches,andcontinentalmargins,rangingfromPregroupandthe Indian subcontinentsequenceare sig- cambrian(?)to Late Cretaceousin age;they are set nificantfromthe standpoint of emeraldmineralization in a ductile matrixof volcaniclastic to pelitic schist, and are briefly discussed in this paper (for further serpentinite,or talc-dolomiteschist.Three thrust informationseeKazmi et al., 1984). faults,the Shangla,Makhad, and Charbagh-Kishora complexintothreem61ange * Presentaddress:U.S. GeologicalSurvey, Box 25046, Mail thrusts,slicethism(•lange Stop 905, Federal Center, Denver, Colorado 80225. units (Fig. 1). From north to south these are the 0361-0128/86/631/2022-7$2.50 2022 Downloaded from https://pubs.geoscienceworld.org/segweb/economicgeology/article-pdf/81/8/2022/3489074/2022.pdf by China University of Geosciences Beijing user on 04 November 2018 SCIENTIFIC COMMUNICATIONS •• • œ0œ3 ISLAMABAD AS,A. PLAT• I.Granite 2.Platform•shelfdeposits KOHISTAN ISLAND ARC I,Granite 2 .Vo•con•cs• o•iolites • Diorites,a•hiboli•s I•IAN etc PLATE •.Plotf•m•shelfmolasse deposits ' Thrust MMT= Main Mantle Thrust MKT=Maln Karakaram ThrUst fault •oOO0oOoO•• Go Ooo o .... • ..... o ß % o Q•O • • o o ß • /o. ,oO•• • oø o O ß Kishoro ß ' ß ß •_ + • ß{ :,- +. 4..r,. ß . ß +. + + + +.+ + .F+ +.I Em•ald mines +++ + ..i. + +, .•. + + +- •, +4*+++++ •+++++++++ , KOHISTAN ISLAND ARC INDUS •[-• Amphibolite Thrustfault Alluvium ++++• SUTURE ZONE INDIAN PLATE Shongla blueschist melange Saidu calc.graphitic schist ] Chorbogh greenschist melange Alpuroi colc.garnetiferous schist • Mingoro ophiolitic melange •.•-1Swat granite gneiss Mo .ncjlaur cryst. schist and granite gneiss FIG. 1. Ceologic map of the Mingora-Alpurai area. Shangla blueschist m•lange,the Charbaghgreenschist roclastic,metasediment,and metachert set in a matrix m•lange,andthe Mingoraophioliticm•lange.North- of talc-chlorite-dolomite schistandcalcareous quartzward the Main mantle thrust (MMT) zone of Tahir- mica-chlorite schist. kheli et al. (1979) alongwith the overridingKohistan Geologyof the Mingora Emerald Deposit island-arcsequenceencompasses all of theseunits. The Mingoraemeralddepositspreadsover an area The Mingora ophioliticm•lange formsa narrow north-south-trending wedgeandcontains the Mingora of about180 acresat the northernmarginof Mingora emeralddeposits.In decreasingorder of abundance, (whichincludesthe Islamiatrench,the Farooqmine, it iscomposedof blocksofserpentinite,talc-dolomite andthe Carrel'strench,mine œandmine 3). schist,greenstonemetabasalt,greenschistmetapySchistoserocksstriking north-southand dipping Downloaded from https://pubs.geoscienceworld.org/segweb/economicgeology/article-pdf/81/8/2022/3489074/2022.pdf by China University of Geosciences Beijing user on 04 November 2018 2024 SCIENTIFIC COMMUNICATIONS parallelnorth-south trending normalfaults(Figs.2 TABLE1. Stratigraphyof the Mingora Area and 3). The Islamiatrench and mine 2 are straddled Kohistan •c •-•,•--•-,--•.,,•Kohtstan Sequence by a set of conjugatenormalfaultswhichwere the principalavenuesfor the mineralizingfluids. Thrust•ww•..,-•• At the Mingoraminesfrom westto eastthe following tectonostratigraphic sequenceis exposed:Charbagh greenschist m•lange --> thrust --> Mingora ophioliticm•lange-->thrust-->Saiducalcareous graphitic schist. The Charbaghgreenschist m•langecomprises metabasaltsandmetapyroclastics. The Saiducalc-graphite schistoccupiesthe area east of the minesand has Shanglablueschist melange •• • ß• Shangla •rust • Charbaghgreenschist melange • • ,v•,,----•Makhad Thrust • Mingora ophiolitemelange •-==----• --• been described earlier. Charbagh-Kishora Saidu calc-graphite • • Emeraldmineralizationis confinedto the Mingora ophioliticm•lange.This unit is composed of a thick, heterogeneous massof talc-dolomite schistcontaining tectonizedclastsof serpentinite,dolomite, greenschist,and graphiticschist,rangingfrom lessthan 2 schist Al•urai calc-mica-ga•etschist • • •• ••wat -I• •t.• granite -i--- cm to hundreds of meters in size. These clasts are set in a fine to coarse ductile matrix of talc-chlorite-do- unconfo•ity Manglaur • •• • • . c•stallzne %,-l• lomite schist(Fig. 4). The talc-chlorite-dolomite schistis the mostubiquitous rock in the Mingora emerald mines. It is a schist gn• grayishto greenish-white,greenish-gray,or greenbrown, fine- to medium-grained,soft,well-foliated, andshearedrockthat formsthe matrixof the Mingora 25 ø to 75 ø west crop out in the mine area.Westerly ophioliticm•lange.Talc, chlorite,and dolomiteare dipping thrust faults have formed severaltectonic the main constituents.Fuchsite,quartz, pyrite, antiblocks.Mine 3, the Carrelstrench,the Farooqmine, gorite, actinolite,chromite,and magnetiteoccurin and the Islamia trench are located adjacentto two lesser amounts. - MINGORA EMERALD A MINES --->' B Emerold deposits WEST EAST o 125 250 575 SCALE CHARBAGH GREENSCHIST MELANGE MINGORA OPHIOLITIC MELANGE INDIAN I. Talc dolomite schist melange '>•Greenschist Metasomatised picotire schist • • Thrust fault Normal faul• _•_0 Foliationdip PLATE SEQUENCE SAIDU SCHIST 2. Greenschist I. Calc. chlarite schist with marbl•enses 5. Dolomite 2. Calc. graphitic schist 4. Colc. graphitic schist 5. Serpentinite ALPURAI CALC. GARNET with marble lenses • with amphibolite lenses ALLUVIUM/COLLUVIUM SWAT FIG. 2. Geologiccrosssectionof the Mingora area. Downloaded from https://pubs.geoscienceworld.org/segweb/economicgeology/article-pdf/81/8/2022/3489074/2022.pdf by China University of Geosciences Beijing user on 04 November 2018 GRANITE GNEISS SCHIST SCIENTIFIC COMMUNICATIONS ,. 20 25 ß M•NGO•:•C• CiTY 0 I )Mingora emerald 40 80 I I SCALE 120 Im mine area and fence r.•_• Operatingmines :_-"-'•? Abandoned mines .... ]Areo _• . • coveredby geological map EXPLANATION CHARBACH GREENSCHIST MELANGE "--:':• '"' Greenschi•t Metasomatised picarite schist MINGORA OPHIOLITIC MELANGE I. Talc-chlorite-dalomite schist 2'-• 2.Serpentinite 3. Dolomite .-;.'.• Saidu Calc. graphitic schist • ..... ._L60 Calluvium Thrust fault • Farooq Mine Normal fault • Carrel's Trench Foliation dip I$1amia Trench • • Mine 2 Mine 3 FIG. 3, Geologicmap of the Mingoraemeraldmines. In the ophiolitic m•lange serpentiniteclastsare more abundantin the upper andwesternpart of the m•langezoneandarepracticallyabsentin the lower andeasternpart (Fig. 3). The greenschist clastsrange in composition from a chlorite-antigorite schist(metadunite)to actinolite-tremolite-chlorite schist(metavolcanic)to albite-biotite-clinozoisite-sphene sem- ischist(metadiabase) to albite-chlorite-epidote-quartz granofels(metagabbro).The dolomiteclastsare medium to coarsegrained and vary from a few centimetersto hundredsof metersin length.At places,for examplein mine 3, the dolomite containsstockwork of milky white quartz veins associated with fuchsite and chlorite (Fig. 5). In thin sectionsof suchrocks, Downloaded from https://pubs.geoscienceworld.org/segweb/economicgeology/article-pdf/81/8/2022/3489074/2022.pdf by China University of Geosciences Beijing user on 04 November 2018 2026 SCIENTIFICCOMMUNICATIONS /Serpentinite '•',I ',',',I I ',',', .... "•'•"' Talc-dolomite •ii',',',lltl] schist • •/f Dolomite •I•Y•4f "•""•• Debris • 0 Fault I 4 I I I 8 LImonitlc Im SCALE (By Aman Ah Shah) Disseminated / talc-dolomite emerald schist mtnerahzation FIG. 4. Sketch showinggeologicsectionat the Farooq mine, Mingora. crystals of emeralds areeasilyseen.Thereispervasive faultsfilledin by limoniteandveinletsor stringers of alterationof the dolomiteto ferruginous dolomiteand quartzandcalcite.Emeraldmineralizationis largely siderite. confinedto limonitizedfaultandjoint planesandbetEmerald ter productionis commonlyobtained from points Mineralization where two mineralized fractures intersect. Emerald Mingoraemeraldsare nonpegmatiticandare commonlyassociated with one or more of the following features(1) faultsand fractures,(2) limonite zones, (3) calcitenodulesand veinlets,and (4) quartzveins andstockworks.At the Mingoraminesthe following crystalsalsooccurin quartz and calcitealongthese fractures.This type of deposithasyielded excellent euhedralstonesof goodqualityand sizethoughthe productiontendsto be relativelysporadic. four of the Mingoradepositcontainsintenselyfractured dolomitefilled with stockworks of quartz (Fig. 5), distinct modes of emerald occurrence are present. 1. Emerald disseminations along a well-defined linear shearzone.Thistype of mineralizationis characteristicof the centralquarry of mine 2. The host rock is composedof gray to greenish-graysheared talc-chlorite-dolomiteschistwhich is interspersed with talc-rich and dolomite-richlayers and lenses. Smallshearjoints, with no significantdisplacement, crisscross the mineralized zone with numerous ex- 3. Emeralds associated with stockworks. Mine 3 which contain the emeralds in association with fuch- siteandtourmaline.Many smallmicroscopic euhedral crystals of emeraldsmaybe seenin fuchsiteveinslined by chlorite. Emeraldsfrom suchdepositsare commonlyof lighter color. 4. Emeraldsalongtensiongashes.At the Islamia trench talc-chlorite-dolomiteschistoccursalong a faultblockof greenschist anddolomite.Largetension gashesfilled in by quartzlensesup to 2 m in diameter posedslickensidedplanes.Mineralizationoccursbe- and 1 m thick have formed in the talc-chlorite-dolotween two parallel normalfaultsalonga shearzone mite schist. Emeralds occur in a 15- to 30-cm-thick which has been limonitized and contains a few scatlayer of talcoserock surroundingthe quartzlenses. tered quartzveins.In thiszoneemeraldcrystalsoccur Large (up to 30-caratsize)euhedralemeraldcrystals in sporadicallyscatteredpocketsor nests5 to 15 cm of gooddeep greencolor and clarity havebeen obacross.Smallercrystalsare disseminated pervasively tainedfromsuchdeposits.Eachmineralizedlensmay throughoutthe matrix of the mineralizedzone. The yield 1,000 to 5,000 caratsof goodstones. emerald is commonlyassociatedwith fuchsiteand tourmaline.The emeraldmineralization at the Farooq mineis similar.Thistype of depositisfairlyconsistent Physicaland chemicalproperties in its mineralizationand enrichmentandhasyielded Comparedwith other emeraldoccurrencesof the the best productionquantitativelyand qualitatively. world (Gubelin, 1968, 1982), Mingoraemeraldsare 2. Emeraldsin fracture filling along nacrowli- uniquefor their deepgreencolor,relativelyhighremonitizedjoint planesor fault planes.In the northern fractiveindices(1.588 to 1.596), andspecificgravity and southernquarriesof mine 2, the talc-chlorite- (2.75 to 2.78). Microprobe analyseson Mingora dolomite schist,the host rock, showscrenulate folds, emeralds(Table 2) showhigh Cr•O• (up to 1.79%) shearing,and dismembermentby numeroussmall andFeO (1.02%). Neutronactivationanalyses (Snee, Downloaded from https://pubs.geoscienceworld.org/segweb/economicgeology/article-pdf/81/8/2022/3489074/2022.pdf by China University of Geosciences Beijing user on 04 November 2018 SCIENTIFIC COMMUNICATIONS 2027 EAST WEST Quarry Quartz Talc-chlorite / Sketch showing section of a part of the mineralized zone at Mine 5 (see box at right) • dolomiteschist I. Dolomite •,• 2_.Dolomite with st. ringers ofquartz and fuchsite veins Dolomite (with quartz lenses and veins) bearing emerald mineralisation '[1• 5. Dolomite withnumerous parallel fuchsite veins and malachite stains 14. • Quartz 0 i 5. Scree 5 i0 i i SCALE 15 Im FIG. 5. Sketchshowingsectionof the mineralizedzone of mine 3, Mingora. unpub.data)indicatehighcontents of vanadium (up controlledandthey were formedduringshearingand to 1% V203). These chemicalcontentsare consistent the last-stage alterationof the Mingoraophioliticm•withemeraldmineralization in anophiolitic m•lange. lange.Mineralizationis alsolithologicallycontrolled by the talc-dolomiteschistandapparentlytookplace in two phases.The disseminatedemerald depositsof the mine 2 centralquarryand the Farooqminewere The emeraldsformed late after major deformation probably formed earlier. At these mines emeralds was complete. Their mineralizationis structurally mainly occur in the groundmassof the talc-chloritedolomiteschistwith no significantquartzcalciteveins or stockworks in the vicinity.It is likely that thisearTABLE2. ChemicalAnalysis(wt %) of MingoraEmeralds lier phase was more pneumatoliticand may have (avg 11 analyses) formedat a highertemperature.The higher permeSiO2 63.89 ability and porosity of the talc-chlorite-dolomite TiO2 0.00 schist,the pervasiveshearedtexture, and the preexConclusions Al•O3 FeO 1 12.65 0.55 MnO 0.02 MgO 2.23 CaO 0.02 Cr•O3 Others• 1.34 19.33 • FeO = total iron • MostlyBeO Microprobeanalyses by Ellen D. Mullen and M. Schaffer istence of chromite in these rocks favored their se- lective mineralizationduring this earlier pneumatolitic phase.The mineralizingfluidsprobablycontained high volatiles,low water, very little silica, and substantialreducediron. This alsoexplainsthe disseminated nature, smallersize, better gem quality, and presenceof a well-definedmineralizedzone despite the fact that there are no surficial veins to mark its extent. Downloaded from https://pubs.geoscienceworld.org/segweb/economicgeology/article-pdf/81/8/2022/3489074/2022.pdf by China University of Geosciences Beijing user on 04 November 2018 2028 SCIENTIFIC COMMUNICATIONS Emerald mineralization in stockworks and calcite- work on the emeralds. We also thank Therese Belden quartzfissurefillingsat the Islamiamineandmine3 for preparationof this manuscript. suggests that theseemeraldsformedlater duringa more hydrousphasewhen the mineralizingfluids June5, 1985; May 21, 1986 containedrelativelylargeramountsof silica,carbon REFERENCES dioxide,beryllium,andboron.At theseminesemerald mineralizationwas apparentlyprecededby limoni- Bard,J.P., 1983, Metamorphicevolutionof an obductedisland arc:Exampleof the Kohistansequence(Pakistan)in the Himtizationandwasfollowedby the depositionof calcite alayancollided range:Univ. PeshawarGeol. Bull., v. 16, p. and quartz. 105-184. Comparedto the othermajoremeralddeposits in the world (Colombia,India, Tanzania,Zambia,etc. reviewedin Sinkankas,1981), the geologicsettingof the Mingoraemeralddepositis unique.The Mingora depositformedin ophioliticm•lange(Late Creta- Davies,R. G., 1962, A greenberyl (emerald)near Mingora,Swat State:Punjab Univ. Geol. Bull., v. 2, p. 51-52. Gubelin, E. J., 1968, GemmologischeBeobachtungen am neuen SmaragdausPakistan:Der Aufschluss, Sonderheft18, p. 110116. -- 1982, Gemstonesof Pakistan:Emerald, ruby, and spinel: Gemsand Gemology,v. 18, p. 123-139. ceousto Eocene, Kazmi et al., 1984) along an active continentalcollisionalzonesubsequent to subduction Herzberg, C., 1981, Pakistandebutsfirst officialgemstonecollection: New York, National Jewellery, 1 p. and metamorphism. Within the suturezonethere is Jan,M. Q., 1968, Petrographyof the emerald-bearing rocksof no sourcerockfor beryllium;thus,it apparentlycame Mingora(SwatState)andPrangGhar (MohmandAgency),West Pakistan:Univ. PeshawarGeol. Bull., v. 3, p. 10-11. from an extraneoussource.It is postulatedthat the 1977, The Kohistanbasiccomplex,a summarybasedon Swatgranitegneisswasthe sourceof berylliumand -petrologicalresearch:Univ. PeshawarGeol. Bull., v. 9beryllium-bearingfluids which found easy access recent 10, p. 36-42. throughthe nearby,sheared,chromium-rich ophiol- -1980, Petrologyof the obductedmaficandultramaficmeitic m•lange.The carbonate-rich environment of the tamorphitesfrom the southernpart of the Kohistanislandarc sequence:Univ. PeshawarGeol. Bull., v. 13, p. 95-107. m•langewasconducive to theprecipitation andcrystallization of emeralds. Acknowledgments We are pleasedto acknowledgethe permission Jan,M. Q., Kamal,M., and Khan, M. I., 1981, Tectoniccontrol over emerald mineralization in Swat: Univ. Peshawar Geol. Bull., v. 14, p. 101-109. Kazmi,A. H., 1983, Reporton the economicgeologyanddevelopmentprospectsof Swatemeraldmines,Mingora:Pakistan, GemstoneCorp., unpub., 105 p. granted bytheGovernment ofPakistan todothiswork Kazmi, A. H., Lawrence, R. D., Dawood, H., Snee, L. W., and andthe encouragement givenusby Kalim-ur-Rehman Hussain,S. A., 1984, Geologyof the Indus suturezone in the Mirza of the GemstoneCorporationof Pakistan.LawMingora-Shangla area of Swat:Univ. PeshawarGeol. Bull., v. rencewasa Fulbrightlecturerat PeshawarUniversity 17, p. 127-144. (1981-82) andKazmia Fulbrightresearchscholarat Sinkankas,J., 1981, Emeraldand otherberyls:Radnor,Pennsyl- OregonStateUniversity(1983) duringpart of this work.Partialsupportwasprovidedby NationalScienceFoundationgrantsINT 80-13158 and81-18403. vania, Chilton Book Co., 665 p. Tahirkheli, R. A. K., Mattauer, M., Proust, F., and Tapponnier, We thank Hamid Daud and Tahseen Ullah Khan for P., 1979, The Indian-Eurasian suturezonein northernPakistan: Synthesis andinterpretationof dataat platescale,in Farah,A. andDeJong,K. A. eds.,Geodynamics of Pakistan:Quetta,Pak- assistance in the field and Ellen Mullen for analytical istan Geol. Survey, p. 125-130. Downloaded from https://pubs.geoscienceworld.org/segweb/economicgeology/article-pdf/81/8/2022/3489074/2022.pdf by China University of Geosciences Beijing user on 04 November 2018