1317 Pf RETITE, Ca(UO2)3(Seo3)Z(OH)4. 4H2O, a NEW CALCIUM URANYL SELENITE from SHINKOLOBWE. SHABA" ZAIRE RENAUD VOCHTENI

1317

The CanadinnMine ralo gist Vol. 34, pp.1317-1322(1996)

PfRETITE, Ca(UO2)3(SeO3)z(OH)4. 4H2O, A NEW CALCIUM URANYL SELENITEFROM SHINKOLOBWE.SHABA" ZAIRE

RENAUDVOCHTENI Laboratoriumvoor chemische en fusische mineralogie, Departement Scheikunde, Universiteit Antwerpen, MiddelheimlaanI, 8-2020 Antwerpen, Belgium

NORBERT BLATON ANDOSWALD PEETERS Laboratorium voor analytische chemie en medicinale flsicochemie, Farulteit Farmnceutische Wetenschappen, Katholieke Universiteit leuven, Van Evenstrant 4, 8-3000 Leuveu Belgium

MICMLDELIENS Instint royal desSciences rnturelles de Belgique,Koninklijk belgischInstituut voor Natuurwetenschnppe4 Sectionde Min4ralogie et Pttrographie, Rue Vautier 29, B-10a0Bruxelles, Belgium

ABSTRACI

Piretite, ideally Ca(UO)3(SeO3)2(OH)4.4H2O,is a new mineral from the Shinkolobweuranium deposit in Shaba Zaire, that occursas crustsin associarionwith an orangemasuyite-like U-Pb oxide on the surfaceof uraninite samples.The crystals are lemon-yellol,in color with a peady luster; they do not fluoresce under ultraviolet light. Cleavage: {001} good. Dno = 4.00 g/cm3and D"a, = 3.87 glcm3(empirical fonnula), 3.93 g/cm3(idealized formula); Huor, = 2.5. optically biaxial negative,2V = 33(5)', cl 1.54(calc.),p 1.73(l) and1 1.75(1), with opticalorientation X ll c, f ll a, Zll b. Tlnedispersion r > I is weak, and the crystals are nonpleochroic.Piretite is orthorhombic,space group Pmn2, or Pmnm, with the following unit-cell pammetersrefined from powderdata: a 7.010(3), b 17.135(7), c 17.606(4) A, V 2114.8(1)L3 , a:b:c 0.409:7:1.02i7, Z = 4. The forms recognizedare {100} {010} {001}, tenacityis weak,and the fractureis uneven.The strongestten reflections of the X-ray powder pattern ld(in A)(l)hkry are: 8.79(80)002,8.56(40)020, 5.57(20)013, 4.43(20)130,4.30(30)131, 3.51(100)200,3.24(40)220, 3.093(50)115, 3.032(100)151 and 1.924(40)237.Electron-microprobe and thermo- gravimetricanalyses gave: CaO 3.57, UO3 72.00, SeO219.29, H2O 8.00, total 102.86wt.Vo. The empiricalformula is 0.76 CaO'3.02UO3'2.09 SeOr'5.33 HrO. Piretite resultsfrom the alterationof uraninite and primary selenium-bearingsulfides suchas penroseite, in the presenceof Ca derivedfrom the host rocks.The nameis chosento honor the Belgian crystallographer Paul Piret. Holotype material is depositedin the mineralogicalcollection of the Royal Belgian lnstitute of Natural Sciences, Brussels,Belgium. Keywords:piretite, new mineral species,calcium uranyl selenite,Shfukolobwe, Shaba, Zaire.

SoNqr4arns

La piretite, de formule id6ale Ca(JO)3(SeOr)r(OFl)a.4HrO,est un nouveaumindral du glte uranifbre de Shinkolobwe, Shaba,Zarre. lr min6ral se prdsenteen cro0tesi la surfaced'6chantillons d'uraninite associ6ei un oxyde oranged'U-Pb semblabled la rnasuyite.La couleur des cristaux estjaune citron avecun 6clat nacr6;il n'y a aucunefluorescence aux rayons ultraviolettes.l,e clivage {001} est bon. D."" = 4.00 et D"a"= 3.87 (formule empirique), 3.93 (formule id6a1e); HMoh"= 2.5. Optiquementbiaxe n6gative2V = 33(5)", cr 1.54(calc.),p 1.73(1)et y 1.75(l), avec orientationoptique X ll c, f ll a, Z ll b. La dispersionr > v est faible, et les cristaux sont non pl6ochroiques.La piretite est orthorhombique,grou_pe spati^\Pmn2t, ort Pmnm, avec les parambtresde la maille a 7.010(3),b 17.135(7),c 17.606(4)A, y 2114.8(1)A3, a:b:.c0.409;l;1.027 porr Z = 4.I*s formesdes cristaux sont: { 100} {010} i001 }; la tenacit6est faible, et la casswe,irr6gulibre. Irs dix raiesles plus intensesdu spectrede diffraction X (m6thodedes poudres) ld (enA)Q)hktl sonr 8.79(80)002,8.56(40)020, s.57(20)0r3,4.43(20)130,4.30(30)131, 3.51(100)200, 3.24(40)220,3.093(50)11s, 3.032(100)151 et r.924(40)237.t-es aralysesi la microsonde6lectronique et thernogravim6triquesont donn6:CaO 3.57,UO3 72.00,5eO219.29,H2O 8.00, total 1,02.86/a.La formuleempirique est 0.76 CaO,3.02UO..2.09SeOr.5.33 H"O. lr mindralrdsulte de 1'alt6rationde I'uraniniteet de sdl6niuresprimaires, tet que ta pemos6ite;le calcium provierft de la jangue du gite uranifbre.Le nom est e I'honneur du criskllographe belge Paul Phet. l€ min6ral est enregistrddans la collection min6ralogiquede l'Institut royal des Sciences naturellesde Belgique,d Bruxelles,Belgique. Mots-cl6s.'piretite, nouvelle espbce mindrale, s6l6nite d'uranyle et de calcium,Shinkolobwe, Shaba, Zatre.

I E-mail address.'[email protected] 1318 THE CANADIAN MINERALOGIST

IN'rRoDUciloN Monruolocv, Pnvsrcal PnoPm.rms eNp OcflRnsNcE Piretite, ideally Ca(UO)3(SeO3)2(OI|a'4H2O,is a new uranyl selenitemineral from Shinkolobwe,Shabq Piretite occlus as elongatetablets lemon-yellow in Zahe. T\e Shinkolobwe uranium deposit has been color that possessan irregular outline. The streak is exploited for uranium until 1960, and is world- pale yellow. The crystals have a mean length of famousfor its rich associationof secondaryminerals. 2-3 mm anda width of aroundL mm, but somecrystals More than forty uranium-bearingspecies have been are acicularprisms up to 5 mm in length. The mineral identified; twenfy-sevenwere describedfor the fust is transparentto translucent,with a pearly luster. The time from this deposit.This abundanceof secondary tablets are flattened on (001), have a good {001} uraniumminerals is mainly due to two factors: (l) the cleavage,and are in somecases cracked and sfrongly large variety of primary sulfides, selenides and striated parallel to the elongation. The forms of the tellurides associatedwith uraninite" combined with crystalsare {100}, {010} and {001}. The tenacityis t}re elements of the host rocks (calcium, barium, weak, andthe fractureis uneven.The photomicrograph magnesium)provide complex chemistry, and (2) the (Fig. 1), uken by scanning electron microscopy exceptional thickness of the alteration zone, which (SEM), shows a typical associationof stackedtablets locally reachesmore than 100 meters. of piretite. The crystals are gbnerally of poor quality The original sampleof piretite was collected at the and occur as curvedsheets. Figure 2 showsthe acicular time of the activity of the mine, and was given to shapeof a hollow crystal with rough faces.The Mohs the authorsby Gilbert Gauthier.The mineral and the hardnessis 2.5. The density,measure-d by flotation in mineral trame were approvedby the Commissionon Clerici solutionat25"C, is 4.00 g/cmr.The calculated New Minerals and Mineral Names, IMA. The type density basedon the empirical formula is 3.87 g/cm3, specimenof piretite is stored as R.C. 4717 in the and that basedon the idealizedformula is 3.93 g/cm3. mineralogicalcollection of the Royal Belgian Institute The higher value of the experimentally determined of Natural Sciences,Brussels, Belgium. The mineral is density may be explained by the presenceof some named for Paul Piret, hofessor of Crystallography, micro-inclusions of uraninite in the crystals. The University of t ouvain-la-Neuve,Belgium, who has piretite found in the Shinkolobwedeposit results from been involved in the description of thirty-four new the alteration of primary veins of uraninite associated mineralspecies. with selenides,such as pentoseite,or associatedwith

Frc. l. SEM photomicrogtaph of piretite showing stacked curved tablets. Scalebar: 100pm. PIRETTIE, A NEW SPECIESFROM SHINKOLOBWE.ZAIRE 13t9

FIc. 2. SEM photomicrograph of a hollow acicular prism of piretite with rough faces. Scale bar: l0 um.

selenium-containing sulfides such as linnaeite, measuredwith a Carl Zeiss Jena MD-100 micro- siegenite,or vaesite, all in the presenceof calcium densitometer.The pattem is unique and could not be from the dissolution of the upper Cambrian matchedwith that of any phasein the ICDD Powder carbonaceoushost-rocks of the S€rie des Mines. Diffraction File. Piretite forms stacked ag$egates on the surface of Single crystals of piretite were examined using uraninite. An orange uranyl-lead oxide arrangedin Weissenbergmethods employing filtered Cu-radiation. microcrystalline flecks and veinlets is the only Film data of the 0, I and2levels for a crystal mounted associateduranyl mineral. Its X-ray powder pattem along the c axis indicate orthorhombic symmefy. is very nea.rto that of masuyite[Pb3U8O2?.I0H2O] Systematicabsences give the spacegroups Prm2l or (PDF 13-408). Pmnm. The refined unit-cell parameters are: a7 .010(3),b 17.135(7), c 17.606(4) A, v Zt 14.8(1)A3, Oprrcal Cnenacrnmsrrcs a;b:c 0.409;l;1.027,Z = 4; they were obtainedusing tle d-values of 32 powder-diffractionlines. The The mineral is biaxial negative with a measured indexing of these lines is conformable with single- 2V value of 33(5)' (Tobi method).The indices of crystal Weissenbergdata. The program PIRIIM refraction were deterrninedat 589 nm: cr 1.54 (calc), (Werner 1969) was used for unit-cell refinement. P 1.73(l) and1 1.75(l). The dispersionis weak,and Figure of merit values are M(20) = 8, F(20) = L4 the crystalsare nonpleochroic.The optical orientation (0.02L4,70).A tully indexedpowder pattern is givenin isXff c, YllaandZll b. Dispersionis weak,r> v. Table l.

X-ney CnysralI-ocRAplry Cmutcal CorraposmoN

The X-ray powder-diffraction data were recorded Crystalsof piretite were chemically analyzedusing with a Guinier-Hiigg camerausing monochromated a CamecaSX-50 electronmicroprobe with a beamsize CuKal radiation (), = 1.5406A) operatedat 40 kV and of 2 pm operating at 15 kV and a beam current of 20 mA. Synthetic fluorphlogopite (SRM-675) was 20 nA. Except for the major components,no peaksqf used as a calibrant for tle lower O-values.and silicon elementswith an atomic numberof 6 or greaterwere powder (SRM-460) was usedfor the higher 0-values. significantly abovethe detectionlimit, indicating that The relative intensities of the diffraction lines were piretite is essentially a pure Ca-U-Se phase. The t320 TTIE CANADIAN MINEMLOGIST

TABLE 1. X-RAY POWDER-DIFFRACTION DATA Tnmvnr SresLrrY FORPIRETITE The thermal stability of piretite was studied with hkl 4*(A) d-'"(A) I a TGA 2950 thermogravimetric analyzer, TA of 5'C/min and a 0ll 12.30 12.28 10 Insfruments, with a heating rate 002 E.79 8.80 EO constantN2-flow of 50 ml/min. The TGA curve shows 020 8.56 8.57 40 that dehydrationand dehydroxylationdo not take place o2l 7.70 5 in distinct steps. 101 6.52 6.51 5 20 022 6.15 6.14 hrnensD SpsglRoscopv UIJ 5.57 )-f,J 20 130 4.43 4.43 20 131 4,30 4.29 JU The ffiared spectrumwas recordedusing the KBr r32 J.vo 3.96 5 dispersiontechnique (1 mg sample in 300 mg KBr) 024 3.92 3.92 l0 with an Ati-Mattson Genesis Fourier transform 200 3.51 3.50 100 infrared spectrometer, which covers the range 015 3.45 3.45 5 presented 142 3.38 3.38 t 40H000 cm-l. The infrared specfium, in 220 3.24 t.za 40 Figure 3, is characterizedby the vibrations of H2O ll5 3.093 3.095 50 molecules,OH, UO2and SeO3 groups. The absorption l)l 3.032 3.033 100 bandsat about3303 and 1623cm-t aredue to HrO, and lt< 2.952 2.954 20 correspond to stretching and deformation modes, 016 2.895 2.892 20 absorptionbands is )11 2.841 2.839 ) respectively.The assignmentofthe 462 2.715 2.716 10 summarizedin Table2. 1.45 , 5?{ 2.536 ) 017 2.487 2.488 ) RELATroNsnPsro OIIDR SPscEs t71 2.291 2.291 5 073 2.257 2.259 5 ln addition to guilleminite, piretite is the second 330 2.162 z-to5 l0 Selenium 156 2.124 2.124 10 uranyl seleniteto be found at Shinkolobwe. 236 2.493 2.093 ) in southern Shaba is mainly concentrated in the 038 2.053 2.054 10 Musonoi copperdeposig which also containslocalized n?s 2.409 2.010 ) uranium mineralization.Th:is deposit, located 200 km 237 L.924 t.924 40 eastof Shinkolobwe,is the type locality for four of the 228 1.821 1.821 5 five known secondary uranyl selenites previously described: demesmaekerite[Pb2Cu5(UO)2(SeO3)6 Guinier-Hnggcamera, Cu,(ar radiation. Intensities (OH)6.2H2O1(Cesbron et al. 1965), deniksite measuredwith Carl Zeiss JenaMD-100 microdensito- (Cesbronet al. l97l), meter. lCua(UOzXSeO3)2(OH)6'H2O) guilleminite [Ba(UO)dSeOs)zOz@2O)3]l (Cooper & Hawthorne 1995) and marthozite [Cu(UO)3(SeO)3 (O}I)2.7H2O1(Cesbron et al.1969). The last secondary following standards were used: wollastonite (Ca), syntheticUO2 (r, Analytical Reagentselenium (Se). H2O contentwas determinedthermogravimetrically. A thermogravimetric analysis (TGA) reveals a total weight-loss of 8.00 wt.Vo. Five elecfon-microprobe analysesca:ried out on each of five different crystals TABLE 2. INFRARED ABSORPTION BANDS OF yield the proportion (wt.Vo) of major components: PIRETITE Cao 3.57 4.07 Uq 72.o0 p0.6G-73.40],Seo2 [3.w l, Wavenumber(cm') A$signment 19.29 118.60-20.201.The oxide formula calculatedon the basisof 14 O atomsis: 0.76 CaO'3.02Uq'2.09 3303(s,b) vrHzO t SeOr.5.33 H2O. The empirical formula, taking into 2en $) v2H2O I *r accountelectroneutrality, is: Can.ru(UO)r.02(Seo:)z.or 1623G) 6 H2Q 1483(w) ** (OH)il8.3.64H2O. The ideal formula is: Ca(UO)3 6Hrg 898(s) v:UQ * (SeO)2(OH)a.4H2O.Piretite is soluble in dilute HCI 8ls (w) vrSeor * without effervescence. 732(s) v:Seot t Calculation of the Gladstone-Dale relationship 468(m) v:Se(!: * using the constantsof Mandarino (1981) yields a "good" compatibility index between physical and s: strong;m: medium,w: weak,b: broad ri chemicaldata using the measureddensity U - (Ky'Kc) * Kbanclehal& Verna (19?6); Monis aral = 0.0567'1. o991). PIRETTIE. A NEW SPECIESFROM SHINKOLOBWE.ZAIRE t32l

\1oo

\^90 o Fes E (te F80

Wavenumber(cm-r)

Ftc. 3. Fourier-transforminfrared spectrumofpiretite from 400 to 21000cm-l

uranyl selenite described is haynesite tle Commissionon New Minerals andMineral Names, [(UO)r(SeOr)2(O]t)2.5H2O1@eliens & Piret 1991) IMA. for valuable comments.We thank the referees from the Repetemins, in Utah. Piretite differs from Dr. Peter C. Bums, the AssociateEditor Andrew C. the other yellow secondaryuranium minerals at the Robertsand the Editor. Robert F. Martin. for critical Shinkolobwedeposit by its stackingof striatedtablets reading and comments,which improved the clarity of and its pearly luster. Guilleminite, the other uranyl this paper. selenile known from Shinkolobwe,occurs as microcrystalline or powdered amber-yellow-coloredcrusts RffERmlCFS on uraninile. The yellow uranyl selenite, haynesite, whosemorphology and stateof aggregationof crystals Crsnnor.r,F., Bamrr, B. & Oosrunsoscn,R. (1965):La resemblesthat of piretite, has a vitreous luster and is demesmaekerite,s6l6nite hydrat6 d'uranium, cuiwe et only known from a uranium deposit hosted by the plomb.Bull. Soc.fr. Minlral. Cristallogr.88,422425. Morrison Formation in Utah, of Upper Jurassic age @eliens& Piret 1991). OosrmBoscr,R. & Prmnor,R. (1969):Une nouvelleespdce min6rale: la marthozite,uranyl-s6l6nite ACKNowmDGm/mNTs de cuiwehydrat6. Ball, Soc,fr. Miniral. Crtstuilagr.92, n8-283. We thank the National Fund for Scientific Research ftmncn, R. Vr.nsBEK,T. (1971): La deniksite, (NFWO) for financial support awarded & to one of us Cua(UO)(SeO3)2(OH)6.H2O,une nouvelle espdce (R9, and Dr. F. Mees of the University of Ghent for mindrale.BaIl. Soc.fr. Min6ral. Cristallogr. 94, 53+537. the determinationof the indices of refraction. We are also indebtedto Ing. J. Jansensof the Laboratory of Coopm, M.A. & Hewrnonre, F.C. (1995):The crystal struc- Inorganic Chemistry, University of Antwerp for ture of guilleminite, a hydratedBa-U-Se sheetstructure. recording the TGA curve, Mr. J. Wauthier of the Can.Mineral. 33. 1103-1 109. Deparhrcnt of Geosciencesof the Universit6 de Louvain-la-Neuve for the electron-microprobe DH.im{s,M. & PRE'I,P. (1991):la halnesite, sdl6nitehydrat6 analises, and to Mrs. D. Dielen for typing the d'uranyle, nouvelle espbcemin6rale de la mine Repete, manuscript.We are also indebtedto somemembers of comtdde SanJuan, Utah. Can,Mineral. 29.561,-5&. L322 THECANADIAN MINERALOGIST

KsaNosrvar, B.L. & VERMA,V.P. (1976): Liquid-liquid WERNER,P.E. (1969): Refinementof unit cell. Arkiv Kemi distribution,spectrophotometric, thermal, IR and Raman 31,513-516. studieson seleniteuranylates. J. Inorg. NucI. Chem.38, 763-769.

MaNoanno, J.A. (1981):The Cladstone-Dalerelationship. IV. The compatibilityconcept and its application.Ccrz. Mineral.19.441450.

MoRRrs,R.E., HannrsoN,W.T.A., STUcKy,G.D. & CmETMAN,A.K. (1991):The synthesisand crystalstruc- ture of two novel aluminumselenites, Alr(SeOr)r.6H2O Received July 14, 1996, revised manuscript accepted andAIH(SeO3)2.2H2O. J. Solid State Cheru 94,227-235. October20, 1996.