395

The Carndian M ineralo g ist Vol. 36, pp. 395-397 (1998)

MITRIDATITEFROM THE SAN LUISGRANITIC PEGMATITE, LA FLORIDA.ARGENTINA

MIGUELA. GALLISKII AN'DM. FLORENCIAMARQUEZ ZAV/J-LA

IANIGI-4,-CONICET, CC 330 (5500) Mendoza, Argentina, and Deparxnent of Geology, University of San Luis, Ejdrcito de lps Andes 950, (5700) San Luis, Argentina

IRENE LOMNICZI de UPTON

Depamnent of Chemistry, University of Salta, Buenos Aires 177, (4400) Salta, Argentina

JT]LIOC. OYARZABAL

Department of Geology, University of San Luis, Ejdrcito de Los Andes 950, (5700) San Luis, Argentina

ABSTRACT

An unusual coarse-grained sample of mitridatite from a granitic pegmatite is described. The mineral was found in three pieces of a fragmented nodule -10-20 cm, in the dumps of the San Luis mine, I-a Florida, Argentina. Similar nodules of primary triphylite-lithiophilite altered to ferrisicklerite and dufr6nite are included in quartz from the core-margin association ofthe rare-element-enriched,spodumene-bearing granitic pegmatite. Mitridatite is very dark green, almost black, has a dull pale green streak and deep ruby red internal reflections. It has very good { 100} cleavage, vitreous luste!, a density of 3.221 g/cm3 and a Mohs hardness of 5 to 5.5. The three strongest X-ray powder-diffraction lines [d in A(IXftftl)] are: 8.70(100)(200), 2.901(80)(6^00),and 2.176(60)(800).The refined unit-cell parametersare: d 17.505(1),b 19.327(3),c11.261(6) A, p 96.05(1)", y 3788(1) A:. Optically, mitridatite is transparent, with X pale green, almost colorless, )z= Z dark reddish brown, biaxial (-), 2V -lO', a I.775(5), p 1.843(5),^1 1.8aap), and very strong dispersion.The chemicalcomposition gives: CaO 17.16,Mn2O3 I.34,FerOr35.26,PzO532.26,HzO* 8.41, H2O 0.56, Rem. 4.51, which gives Cau.o,(II,0)6fFe3*8.6?Mno.33O6.r5(PO4)8.e1.3.17H2O. The mitridatite is considered to have formed by hydrothermal replacement of primary triphylite.

Keywords: mitridatite, nodule, granitic pegmatite, San Luis, Argentina.

Sonnrrene

Nous avons ddcouvert un nodule 6clat6 en trois morceaux, de diambtre -lU2O cm, contenant la mitridatite en gros grains, ce qui est assezrare dans une pegmatite. Ce nodule se trouvait dans une pegmatite granitique d la mine de San Luis, i La Florida, en Argentine. Des nodules semblablesde triphylite-lithiophilite primaires alteresa ferrisicklerite et dufrdnite sont inclus dans le quartz en bordure du coeur de la pegmatite granitique, enrichie en 6l6mentsrares et cristallisant le spodumbne.La mitridatite est vert trbs fonc6, presque noire, et possbdeune rayue vert p0le morne et des reflets intemes rouge rubis fonc6. Le clivage {100J est trds bon, l'6clat est vitreux, la densit6, 3.221, et la duret6 de Mohs, entre 5 et 5.5. Les trois raies les plus intenses du spectre de diffraction X (m6thode des poudres) ld en A(I)(hkDl sont: 8.70(100)(200), ?.901(80X600) et 2. 176(60[800). Nor:s avons affin6 les parambtresr6ticulaires: a 17.5O5(l), b 19.327(3), c 11.261(6) A, B 96.05(1)', y 3788(1) A3. La mitridatite est transparente,avec with X vert pdle, presqu'incolore, I = Z brun rougeAtre fonc6, -10', biaxe n6gatif, 2V a 1.775(5), p 1.843(5), T 1.844(5), et une ffbs forte dispersion. Une analyse chimique a donn6 CaO 17.16, MnrO. 1.34, FerOr35.26,P2Os32.26, H2O- 8.41, H2O- 0.56, Rem. 4.51, ce qui mdne I la formule empirique Ca6.q1(H2O)6[Fe3*rurMn633Ou.'r(PO4)s.e2].3.17H2O.La mitridatite se serait form6e par remplacement hydrothermal de la triphylite, primaire.

Mots-cMs: mitddatite, nodule, pegmatite granitique, San Luis, Argentine.

I E-mnil address:[email protected] 396 THE CANADIAN MINERALOGIST

INTRoDUCTToN nodule with external borders of quartz were found. The curvature of the external border of the fragments During the flust inspection of the San Luis granitic suggests that they belong to a nodule 10-20 cm pegmatite, located near La Florida" San Luis province, in diameter. Each fragment has 5-7 cm of mitridatite. Argentina, in the dumps of the main quarry, three The external border of the {iagments consistsof a layer pieces of a nodule of a cleavablephosphate were found. of brownish microcrystalline quartz, in places with According to the optical and physical properties, and crystal-linedvugs. the X-ray powder-diffraction pattern, the mineral was initially classified as belonging to the robertsite- PHvstcal ANDOP'IcAL PRoPERTIES mitridatite series. For its precise characterization,a chemical analysis and X-ray diffraction analysis were Mitridatite occurs in massive, very dark green, carried out. The data conespond to mitridatite. Because almost black aggregates.It has a dull pale green streak, of the infrequent occurrence of coarse-grained, and perfect { 100} cleavagein bladesradiating from the good-quality samples of this mineral, we document core of the nodule.The chips show deepruby red internal here some of its basic properties. reflections, visible to the naked eye. The measured Mohs hardnessis 5 to 5.5. The densiry, measuredwit}r Rrvrgw a Berman balanceusing single fragments, is 3,221.gl cm3, in good agreementwith3.24(2) g/cmr determined with Mitridatite is a basic calcium phosphatecommonly heavy liquids by Moore (19'74).The mineral has a few found as a thin crust or as colloidal nodular aggregates impurities of oxide minerals. In polished section, these in ferric oolitic deposits of the Kertch and Taman seem to be coatings of secondary Mn-oxides. The peninsulas,Russia, known since the beginning of the mitridatite contains some apatite, as is indicated by century (e.9., Chukhrov et a|.1958, and references some peaks in the X-ray-diffraction diagrams. The therein). It also is found as a product of weathering of mineral is not fluorescent under short or longwave primary ferric phosphates,mainly triphylite, in granitic ultraviolet light. The optical properties were deter- pegmatites;it commonly is visible as a yellowish gteen mined with a spindle stage and Cargille inmersion stain on dump samples.Owing to the cryptocrystalline liquids. The data obtainedare shown in Table 1. nature and the impurify of the aggregates,the determi- nation of the chemical composition and crystalline TABLE I. OPTICAL PROPERTIESOF MITRJDATITE FROM structure had to await the discovery of exceptionally THESANLIJISGRANITICPM-TTTE.ARGENTINA well-formed crystals,in the dumpsof theWhite Elephant pegmatite, Black Hills, South Dakota (Moore 1974). Its composition is Ca6(H2O)6Fe3*eOu(POo)r).3HrO;it is monoclinic (pseudotrigonal) in symmetry, and (-) Biaial (-) Biqial '1.785 crystallizes in space grotp Aa, Z= 4 (Moore & fuaki 1.775(s) p 1.843(s) l.r5 t977\. 1.844(5) l.t5

X vqy palsgm palegr@ish yellow Occunneucp Y=Z dryk reddirhbrcm d€tp gr@ish brcm 2V -10' 5'- l0' Mitridatite was found on the dumps of the San Luis DispqEim vqy strong granitic pegmatite.This deposit is located at latitude 32"59'20"5 and longitude 65'59'30"W 28 km to Smpl6: l. Thisp8pq,2. M@re (lta), qydds ftoo the whtoElerpho g@itic peeEdit€, Blac&Hixq souh Dakota the north of La Florida, Totoral district, Pringles department,San Luis province, Argentina. This deposit was mined intermittently for spodumenein the past,but is not presentlyexploited. It consistsof the juxtaposition of two different types of rare-element pegmatite: an X-Rav DrnnnecrloN albite-spodumene type that was synkinematically emplaced and folded, and a body of complex type, X-ray powder diagrams of mitridatite were recorded spodumenesubtype, called San Luis II, emplaced in using Cu radiation (30 kY 40 mA) with a Philips 1710 the core of folds of the former (Oyarz6bal & Galliski diffractometer at the Department of Geological 1993). The core-margin association of the San Luis II Sciences, University of Manitoba. Annealed CaF2 pegmatite contains phosphatenodules of triphylite- (a 5.46379 A) was used as an internal standard.Table 2 lithiophilite solid solution, generally up to 20 cm in shows the results obtained.The interplanar spacings diameter. The primary minerals are usually hydrother- were used for the unit-cell parameter calculations with mally altered to ferrisicklerite and dufr6nite. the CELREF program (Appleman & Evans 1973;. In the dumps of the mine workings of the San Luis Results are compared with those of Moore (1974) for II pegmatite, three triangular pieces of a phosphate the White Elephant material in Table 2. MITRIDMITE FROM THE SAN LUIS GRANITIC PEGMATTTE 397

TABLE 2. POWDER.DIFFRACTIONDATA FOR MITRIDATITE FROM ontcn. THESANLUIS.RAMTI.*BffMATTTE ARGENTTN^

The genesis of mitridatite has been principally rd d6 d* J6 de d& ascribed to alteration processes operating in low- temperature environments, such as weathering of l@ 8.70 2.215 2.215 533 8.70 2W | granitic 5.5E 5.5E 031 60 2.116 2.t76 800 primary iron phosphates in dumps of 50 4.35 4.35 400 | 2.1u2 2.tv2 J82 pegmatites, alteration of oolitic sedimentary iron ore I 3.46 3.459 242 I 2.061 2.@ deposits, or development of stains in femrginous soils l5 322 3.nl 060 t2 t.x1 l.x1 5t2 and rocks impregnatedwith organic remains (Moore I 3.t20 3.f20 260 | 1.740 t.74 L000 1973, Moore &Araki 19'77).Mitndadte also occurs as EO 2.Xt 2.Nl 6@ 13 r.614 t.6t4 w2 It 2.780 2.784 I 1.588 r.587 g7r a late-stageproduct of porous, altered triphylite. The 50 2.734 2.n4 162 t2 1.551 1.551 Tt rl massive, coarse-grainedappearance of the San Luis I 2.624 2.624 153 I t.475 1.475 II33 mitridatite suggeststhat it was formed by a late-stage 20 2.s70 2.569 I 1.451 1.450 lw hydrothermal replacement of primary triphylite. I 2AU 2.43 7rr I l.40t t.,l08 6120 Acrcqougocgtrlems Tbeuitsll pmnetm elorlrcl ftom the abovsag',s' a 17.505(l), b 19.32'l(3), c ll.2.6l(6) A, p 96.05(l)", I/ 3?88 /qP. Fu onpariro!, ths pmerm of The authors thank N. Menegatti for the first X-ray middabb froo the Wlite El€pbrd lFmitic pqEdite (lrmre 1974) re: a powder diagrams, E. Perino for the XRF data, and t7.ss3(2),b t935ap), c rr.24E(2)A p e5.84(lr. the University of San Luis for grants to support project 349001.Dr. W.B. Simmons and Mr. A. Falsterkindly Cruurcar Arqer-vsrs reviewed the manuscript, and R.F. Martin offered useful suggestions. According to a preliminary X-ray fluorescence spectrum,the major componentswere found to be Cq Fe REFERENCES and Mn, whereasSr, Zn, Cu and As are present at trace levels. A strong positive reaction was obtained with ArILEMAN, D.E. & EveNs, H.T., Jn. (1973): Job 9214: the ammonium molybdate test for phosphate.After the indexing and least-squares refinement of powder determination of H2O* and H2O-, the dehydrated diffraction data. U.S. Geol. Surv., Comput. Contrib.20 PB2-16188). sampleswere dissolvedin 1:3 HCI; the small insoluble fNTIS Doc. residue was mainly granular quartz, pale pink in color. CHUKHRoV,F.v., Mor-rvn, Y.A. & Eruvn-ove,L.P. (1958): New Ca, Fe, and Mn contents were establishedby atomic data concerning mitridatite. Dokl. Akad. Nauk SSSR,Sen absorption spectroscopy,with La addedin the first case Geol. 1958(8),16-26 (in Russ.). (Ca) to minimize the interference of phosphate,and using the addition of standardsolutions for the other Moonr, P.B. (1973): Pegmatite phosphates: descriptive Fwoelements to check the matrix effect. The proportion mineralogy and crystal chemistry. Mineral. Rec. 4, of phosphatewas determined by spectrophotometry 103-130. with molybdo-vanadate.The results are presentedin I. Jahnsite, segelerite, and robertsite, three Table 3. The following structural formulae, based on -(1974): new transition metal phosphatespecies. II. Redefinition of by Moore & Araki (1977), is the structure determined overite, an isotype of segelerite. IIL Isorypy ofrobertsite, Ca"6, (HrO)u[Fe3*s.67Mn6.3306.rs(PO4)8 e2].3.17 H2O. This mitridatite, and arseniosiderite. Am. Mineral. 59r 48-59 formula is more plausible than the one calculated (erratum: 640). according to Moore's earlier proposals (1914, 1976). (1976): Derivative structuresbased on the alunite octahedml sheet: mitridatite and englishite. Mineral. Mag. TABLE 3. CHEMICAL COMPOSIfiON OF MITRIDATffE 40, 863-866. SANLI,'III GRANITIC PEG{\4A,TTTqARGENTINA & Anerr, T. (1977): Mitridatite, Cau(HrO)fernOu (PO )r).3H20. A noteworthy octahedralsheet structure. Inorg. Chem. 16, 1096-1106.

CaO vto/o 17.16 t5.7 Asot OvenzArel, J.C. & Gar-r-rsrl M.A. (1993): Geologia del It4tr2o3 1.34 2.4 Ir2o" t 4I ll.5 yacimiento San Luis: un caso de yuxtaposici6n de FerO. 35.26 32.1 Hro- 0.56 tipologfas diferentesen pegmatitasde elementos raros.X11 PrO, 32.26 ?4.4 R@ 4.51 10.5 Cong. GeoI. Arg. y ll Cong. Expl. Hidrocarburos, Actas 1{, Total 99.50 100.6 167-174.

Received May 25, 1996, revised manuscript accepted r (sI-) Fl€ph'n (WE) Edqisl: JE Amlyss' Sd "ii mceial LL. tlo Upt4 Whit€ December 23, 1997. Ib.