RENDlCO!'

290 M. TRISCARI

Ore Microscopy. Microhardness was mea-sured using a Vickers diamond pyramidindenter employing a load of 100 gr.

Field occurrence

This occurrence of gersdorflitc lies in asmall group of discordant veins, mainlyquartzitic in composition, that form pan ofa vein system cutting Hercynian phyllites ofthe so-alled Mandanici Unit. This unit isIcgarded as part of the Calabro-Pe1oritanarc, considered a complex ovenhrustingstructure; has a medium-Iow metamorphicgrade and it chiefly consists of phyllites,garnet and/or chloritoid phyllites, quartzites,metabasites and cristalline limestones (AMo-DlO MORELLI et al., 1976; BoNUDI et al.,1982; FERLA. 1982 a, b). The deposits ofthe Peloritani Mu were on~ considered tobe late magmatic in nature, but nowadaysare generally considered as suata bound ores{FERLA, 1982 b}, which have been secon-darily mobilized by relatively recent hydro-thermal activity. On the Peloritani Mts thetectonic sedimentary character of some ofthese deposits is stiJI recognizable in a fewareas, where small primary Pb, Cu, Zndeposits of simple composition were workedover the last few decades. The genesis ofthe sulphide ores locally appears to bespatially and temporally bound to thepresence of basic metavolcanics ID thehercynian phyllites of the Mandanaci Unit(ATZORI et al., 1973; FERLA, 1982 a, b).These primary strata-bound deposits, havebeen reworked by late tectonic events, thatin the investigated area involved hydro-thermal activity by which discordant veinsore bodies were deposited. The veins arebetween 5 and 30 cm wide, chiefly quartziticin composition, with ankerite-siderite gangue.The average strike is NNE-SSW; these veinsoutcrop at an height of about 250 m abovesea level in the Zilll area, south of thevillage of Fiumedinisi some 25 Km southof Messina.

Mineralogy

The main vein system consists of gersdorf-fite and associated tetrahedrite; gangueminerals are quartz, siderite and ankerite.Next to the surface, secondary alteration

products arc observed: limonite, malachiteand azurite. Gersdorffiitc in reflccted lightis seen as cubic idiomorphic masses andeuhedral crystals with typical (100) cleavageobservable as characteristic triangular pits.All sections studied showed evidence ofintense cataclastic deformation. In somesections very rare calcopyrite was observed,always well rounded, quite often borderedby an encircling rim of covelline, and alwaysconrained within the quartz. The earlyformed phase is gersdorffite and a secondepisode of mineralization has brought thetetrahedrite which in part replaces thegersdorffite. It seems that the tetrahedrite isalso associated with intense cataclasticphenomena; the substituting tetrahedrite ismainly present in the mylonitic zones. Bothphases occur togheter and sometimes thetetrahedrite contains distinct euhedral cubesof gersdoffite (6g. 1 and fig. 2).

The gersdorffite has been affected byrepeated episodes of clastic deformation:

Euhcdral cryslals of gersdorffite showfracturing and penetration by tetrahedriteveinlets. Following the characteristic (100)c1eavage,·the mechanical stresses have rcdun.-Jthe gersdorffite to an aggregate of irregularlyshaped grains; late quarlz with unduloseextinction fills the main veins. Only tetra-hedrite has been affected by an intensealteration to covelline; where covcllinc isobserved within gersdorffite it occurs onlyas an alterarion of tetrahcdrite. Some partsof the veins show an abundllnce of chaleo-pyrite with tiny euhedral crystals of pyritediffusely scattered, also in the form of stringsand curved lines. Tetrahcdrite shows a grey-white colour and takes a good polish,sometimes with a very light brownish tint:it is completely dark under crossed nicols.

Gersdorflite also polishes well: it is whitein colour, sometimes with a very lightyellowish tint. Zoning has not been observedin this locality. All sections studied areclearly isotropic. Although RAMDOHR (1980)reports that slight compositional variationsin gersdorflite can be ascrived to submicro-scopic intergrowth with chloantite, Ihismineral has not been observed optically orin XRD analysis.

Reflectance measurements on tetrahedritefall in the range 30.3-32.5 % at 589 nm.

A FIRST OCCURRENCE OF GERSOOII.FFITI; IN THE PELORITANI MTS. 291

-:-( .• "<

'J

.A'..

.,

Fig. I. - ChaloopyrilC: (brithl wblft'J in alc:trahc:drilC: mnlel ltrt'y), crossinc gersdorffilC:(whild. P.P.L. 400 x.

Reflectance measurements on gersdorRltefall in the range 44.8-47.0 % at 589 nm.

These values, while in good agreementwith data from GALOPIN et al. (1972) (Te-trnhedrite 30.7 - Ger,dorflite 47.5), VAU-GHAN et al. (1978) (Tetrahedrite 30-30.5 -Gersdorffite 46.3-53.8), PICOT et al. (1982)(Tetrahedrite 32.6 • Gersdocffite 45.4), showsignilicamly lower values for gersdorffiteIhan the IMAjCOM data, perhaps becauseof measurement of material of differentcomposition. In 6g. 3 are shown the spectralreflectance curves (air) for tetrahedrite andfor gersdorffite. VHN values vary in therange 275-322 for tetrnhedrite and 634-717for gersdorffiites, both at 100 gr load.Published data are: GALOPIN et al. (1972)(Tetrahedrite 328-367 and gersdorflite 665-743), VAUGHAN et al. (1978) (Tetrahedrile285·322 and gersdorffite 520·907). TheCOM data for gersdorffite. refer 10 syntheticmaterial {rhe material reported also in}.c.P.D.S.. card 12·705 and the values (782.

Fig. 2. - EuhednJ gc:ndorffile crystals lwbiu)with 5UbslilUling lelrlhedrite. P.P.L. 400 x.

835) are slightly different to those observedin Ihis work. Several X-ray powder dif-fraction patterns were run for tetrahedriteand for gersdorflite. The results are givenin table I and 2. From the observed dvalues, cell parameters were calculated fol-lowing the cell refinement program ofPREWlrT modi6ed by CoPLEY (1975).

The unit cell edge measured was a. =10.377 A for tetrahedrite and ao = 5.694 Afor gersdorffite.

Gangue minerals are quartz and thecarbonates siderite and ankerite; quartzveins often show included fragments of thehost rock (phyllite).

Secondary alteration products observedare malachite, azurite and limonite. In thenearby locality of « S. Carlo It' a much biggervein system with the same strike directionsand gangue minerals, studied by DoNATI eta1. (1978) and TRISCARI et al. (1982), showthe following assemblage (in order ofdecreasing abundance): tetrahedrite. chalco-

291 M. TRlSCARI

for synthetic stOichiometric NiAsS (YUNO,1962): it is noticeable that previous litera-ture reports show that the parameter ofnatural gersdorffites range from 5.60 A(PEACOCK et al., 1940) 10 5.731 A (OLS-HAUSEN, 1925). The crystal structures knownfor gersdorffiles (Pa3, P213, PI) were welldescribed by BAYLlSS et a1. (1967, 1968)and BAYLISS (19669, 1982 b) and the readeris referred to the work of YUND (1962)and BAYUSS 0982 b) for relevant literature.In his study, BAYUSS (1969) of more thana dozen gersdorffites and related minerals,noticed that gersdorffite with small cd1 sizescommonly occurs with calcite and sulphidessuch as pyrite and pyrrothite, while gersdorf-

TA,BLE 1Values 0/ cl ohs. and cl CIlJc.; cetl edgeparameUrs /0' th, eXQmined tetrahedrite

~, tll. ._. d C&tc.~ • ..~ !>.1118.n " 3.e7tl 3.1569'" '00 ,.- 2.5l95'" " 2.77e 2.773- " 2.5M 2.!>95= n 2 .....9 ,.-~. • 2.:123 ,.~n. • 2.119 2.11',~ • ,.= ,.=,,, • L_ ,.-~ M L= ,.-ro. • t.781 L",- , L_ L~HO • ,.- L_= , 1.&&5 L~,,, n L_ ,.-n' I..M 1..91... 1. &611 1..67'" • 1.&11 1.412- • I.n7 L",n' • L", L",,~ • 1.2.02 1.2.0,,, • 1.111 1.111= • L_ 1.0i3- • 1.057 L~UIH', t,~.t& ". • 10.377

A

B

-- .-

, , ,

. ..........

Discu8sion

Fig. J. _ Spectral Rellectance Curves (AIR) forgersdorffite (A) and tetrahedrite (8); StandardZc:in WTiC.•••.•• (lMA/COM)-- PICOT et al.. 1982-- This work.

pyrite, boumonite. stromeyerite, bismuthini-te, galena, pyrite, sphalerite, pentlandite,covelline, arsenopyrite. boulangerite, jameso-nite. argentite, digenite as well as secondaryproducts as malachite, azurite, goethite andIimonite.

The formula of gersdorffite is NiAsS, itis cubic P213. KLEMM (965) observed thatFe and Co can substitute for Ni, andPALACHE et al. (1944) noted that Sb canalso substitute for As giving the varietycorynite, ahough this has been recentlyproved to be only an Sb bearing gersdorffite(BAYLlSS, 1982 a) so that use of thisvarietal name is unnecessary. The cell sizeof gersdorffite from the examined localityis similar to the cell size of '.69 A

..

..

..

..

..

A FIRST OCCURRENCE OF GERSDORFFITE IN THE PELORITANI MTS. 293

TABLE 2Va/u~s 01 d ohs. and dca/c.; etU edgeparameters lor the examin~d g~rrdorff;te

TABLE 3RepresentatilJ~ electron microprobe ana/yses01 gersdorffite and tetrah~dr;te 0/ the

pusent study

..... • .. 1< ...... •••• .... 0_", •• " >0•• "

U... ..... ..... .... .... .... .... .....

(HAWLEY et al., 1961)· These two otherphases have not been observed in the as-semblages from the locality studied and arenot mentioned in othet paragenetic sequen·ces from the Peloritani Mls.

BAYLlSS (1982 b) also confirmed, throughchemical analyses on thirteen gersdorffitesamples, that Co content causes a decreasein the cubic unit cell, and As increases it.Furthermore as the (001) and (110) re-flections may be used in space group dif-ferentiation (BAYLlSS, 1969) the presencein this gersdorffite of the (11 0) reBection inall the examined specimens indicate a cubicP2 13 structure; the (001) was always lookedfor but never found.

Heating experiments at 500"C and 600"Ccarried out by the same author, indicate acrystal structure change with the loss of the(100) reflection first, and the (001) later.From these heating experiments it seemslikely that the P2 13 form is the low-tem-perature, ordered phase.

Chemical analyses (electron microprobe)are shown in table 3. Ag, Zo, Au, Cd, Pband Bi were also looked for in the gersdorf.fite and Au, Cd, Te, Pb, Bi in the tetrahedri·te, but nOt found. In the gersdorffite chemicalanalyses showed a substitution of Ni by Coand Fe; it is worth also noting that the highSb and Cu contents ate probably related tothe associate tetrahedrite. In the tetrahedriteparticularly high values are found for Sband Fe. The lesser commonly associatedmineral phase showed normal characteristicsand were quite similar to the mineralassemblages of the nearby deposits of«S. Carlo .. , the main difference consistingonly in the presence of gersdorffite and a

....,

....,

..

,.

....

..

......

...." .....,..

..

.. .~, 1ft. ._. ....Ic.m " ..= ..-u, • ,.~ ,.~~ " vs..) ,.~'" '00 ,.~ ,.-m ., 2.)2) 2.)2"~ " 2.013 2.013~ • L_ L_

'" • Lm L~m ., I. ne 1.716m , 1.6"3 I.U3,~ " 1. 57~ 1.579'" " I.~l 1.52.~ , 1."22 1."23'"

, •• 3111 1.311.'" • Lm Lm~ • 1.21' 1.2'73." • 1.2"'3 Lm,n • 1.21'" 1.21.~ • 1.162 1.162'"

, 1.116 1.116.u " L_ L_~ • L_ l.e1»' • L_ L_- • ,.~ ,.-

12 NiAsS + (As)

fite with large unit cell size commonly occurswith siderite lind arsenides such as skutteru-dite and saffiorite; the presence of cobaltand iron being ubiquitous in arsenic richenvironments. Of these accessory minerals,only siderite, wich decomposes at 500u C,indicates any limitation to formation tem-peratures. The presence of only gersdorffiterules cut temperatures higher than 700" C.Above that temperature it would be repre-sented by niccolite and maucherile followingthe reaction

NiAs + Ni llAs8 + 3 As + 12 S

M. TR1SCARI

lesser number of associated minernls. Bothdeposits have in common strike directionsmain minc=rnls and similar ganguc=s: chemicaland physical data, as well as microscopicobservations and the accessory phases obser-ved for this mineralization of the Zilli areanext to Fiumedioisi (Messina, Sicily), agr«:with the data of the previous workers: thisfirst observed gersdorffite in the Pe10ritani

Mts., proved to be a low-tempernture,ordered phase of space group P213.

Acknowledgemenls. - This work was arri!!d OUIat tne Dept. of Geolotlical Science: of tne Universityof Aston in Birmingham, with lne supporl of aNATO-Consiglio Nazmale delle: Ricc:rchc: fe:Uow-ship. I wish 10 thank Dr. D.}. VAUCHAN for hishdpfull critici5III of the: manuscript, the: above-mmtionc:d [)rc:pl. of Geology for the: kind assistanceprovided .nd Mn. C. BICK for tiping it.

REFERENCES

AMODIO MDRELLI L. et al. (1976) _ L'arco ca/abm·pe/oritano nei/'omgene appnminico-maghrebide.Mem. Soc. CeoJ. hal., 17, 1·60.

ARTINt E. (190}) . Note minera/ogicbe sullll VIII-sllssina. Atti Soc. hal. Se. Na!. Museo Civ. SI.Milano, 42, 101-117.

ATZOttt P., SASSI P. (1973) - The barometricsignipCllnu 0/ tbe SlIoonll pb)"/Jites (Al. Peiori·tani). Schwdz. Min. u. Petr. Mill., ,))/2, 24}-2')).

BAVLlSS P., STEPHENSQ.'l N.C. (1%7) - The crystalstructure 0/ g"sdorffitt. Min. Maa., 36, 38-42.

BAYLlSS P., STEPIiENSON N.C. (1%8) - The crystalstructure 0/ t.ersdorffite (Ill), 11 distorted IJnddisordered pyrite strlU'ture. Min. Maa., 36,940-'J47.

BAYLlSS P. (l%9j X·rll] dlltll, optical /J1fiSolropism,IInd lbtrmlll stlJbility 0/ coballite, gersdmffitea"d ulma"nite. Min. Maa., 37, 26.)).

BAVLlSS P. (1982 a) . A /urtbtr crystlll structurerepnrment 0/ cobllltile. Amer. Mine:r., 67, 1048-Ion

BAVLlSS P. (1982 b) - A /Uft!Nr crystlll structurefejinement 0/ g"sdorffite. Amc:r. Mi~r., 67,10'8-1064.

BoNUDI G., GIUNTA G., DE VIVO B., Lt MA A.,PEUONE V., ZUPPETTA A. (1982) • AlinerlllhUl'zioni dell'lIrco Clllabfo-ptlOfitllno. / potesi gl'nrti·chI' e quadro evolutivo. BoIl. Soc. Geol. Ital.,101, 141·1:55.

CoMMISSION ON OItE M1CltOSCOPY (1977) - IMAICOM QUlIntitative DIIIII File (Editor N.F.M.Henry). Applied Mineralogy Group. Mineralo-.l\icll Society, London.

ClAlG ].R., VAUGHAN D.]. (1981) - Ofe miaoseopyand Qre petrogfapby. j. Wile)' 11< Sons, New York.

DoNATI G., STAGNO F., TltlSCAltI M. (1978) • Ri·cercbe IUlle mllni/estllvoni metaUi/efe dei M. Pe-10fitlllli. Ill) Gilldmenti delle C.de S. CIINO,Montllgne e lIidniori, pfesso Fiumedinisi (Mn·sinll). Ani Ace. Pdoritanl Pericollnri, a. Se.MII. rlS. Nal., 56, 177·238.

DuNCOMI P., jONES E.M. (1%9) - Electron PfObe1ttiUOllnalysis: IIn ellSY to IIse computer Pf0t.fll1ttfor COffectint. qlUlntitlJtive dllt•. Reporl n. 260,Tube InYC5tigation Research Lab., Hinxlon,Saffron, England.

FEItLA P. (1982 aj - Aspeni stfutlufali e composi-ziona/i delle sequenu aistalline pfealpine neiM. PeJoritani. In «Guida alia Geologia dellaSicili~ OccidentalelO, Ed. Catalano R. e D'Ar!,.nio B., Socicta Goologia haliana, Guidc Geo 0-githe: Regionali.

FUL\ P. (1982 b) - Inquadrllmento geologico-petro-graftro delle minefllliZUlvoni metlllli/ert nei M.Pe(ofitllni (Sidlill). Rc:ndk. Soc. hal. Min. Pell.,38, I07S·I091.

GALOPIN R., HENIV N.FM. (1972) - Microuopicstudy 0/ o/Nlqlle minerals. W. Hdler .. Son5 Lld.,Cambridge, England.

HAWLEY jE., STAHTON' R.L., SMITH A.V. (1%1) -Pselld~utectic inlegfowths in IIrsenical ores /fomSudbury. Canad. Mina., 6, '5,..5'7'.

JOINT CoMMITTEE ON PoWDEtt DIFFRACTION STAN-DAIDS (1974) - Selected powder diffraction dlltllfor min""ls. SWlnhrnore, USA.

Kf.El,tM DD. (196') - Syntbesen und Analyse" inden Drejeck dillgrammen FeAsS£oAsS-NiAsS undFdrCoSTNiS•. Neucs jahr. Abh., 103, 20.5-2".

OLSHAUSEN S.K.V. (192') - S"ukturuntersuchun~ennaek der Debye-Schefftf Method. Zc:ir. KlISI.,61, 463-'14.

P"LACHE C., BElMAN H., FttONOf.L C. (l944) - Tbesystem 0/ mineralogy - Vol. I. Wilcy Sons,New York.

PEACOCK M.A., BEItRY L.G. (1940) - R6ntgeno-grapbic observations on Ofe mineTa!s. ToronloUniv. Studies, Cool. ser., 44, 47-69.

PICOT P., IOHAN Z. (1982) - A/IllS 0/ ore minerals.B.R.G.M. EIsc:vier Pub!., Amslerdam.

PREWITT C.T. (1974) - A cell rejinement pfORrllm.Opt. Hc:arth .nd Space SciencC5, New YorkState Univcnity. Venion of august 197.5 mo-difi!!d by PA. Cuplcy Cambridge, England.

RAMDOHJ. P. (1980) - The ore minerllls lI"d lheifintergrowlhs. 2nd !!d. Pcrgamon Press, Oxford.

TltlSCAl1 M., SACcA C. (1982) - Scheelite lit the«S. CllrlO" Sb-Cu·At Mine, Fiumedinisi, Messi-nil, Italy. Mina. Pctr. Acta, 26, 1.59-168.

VAUGHAN D.j., WIG j.R. (1978) - Mit.eral cM-",ist'1 0/ metal sulphides. Cambridge UnivenityPlCS$, Cambridgc, England.