Mineral. Deposita 19, 289 297 (1984) MINERALIUM DEPOSITA

© Springer-Verlag 1984

Sulfides Associated with Podiform Bodies of Chromite at Tsangli, Eretria, Greece M. I. Economou i and A. d. Naldrett 2 1 Institute of Mineralogy and Petrology, National University of Athens, Panepistimiopolis, Ano Ilissia, Athens 261, Greece, and 2 Department of Geology, University of Toronto, Toronto M5S 1A1, Canada

Abstract. Small bodies of pyrrhotite, chalcopyrite, minor pentlandite, and magnetite occur at the peripheries of podiform bodies of chromite in ultramafic ophiolitic rocks at Tsangli, Eretria, central Greece. Banding of magnetite and sulfide within the bodies is reminiscent of magmatic banding. A magmatic origin has been proposed for similar sulfide masses in the Troodos ophiolite (Panayiotou, 1980). The compositions of the host rocks, chromite, and of the sulfides have been investigated. On average, the sulfide mineralization, recalculated to metal content in 100% sulfide, contains 0.55% Ni, 5.15% Cu, 0.29% Co, 9 ppb Pd, 179 ppb Pt, 16ppb Rh, 112 ppb Ru, 31 ppb Ir, 58ppb Os, and 212 ppb Au. These metal contents, particularly the high Cu/ (Cu+ Ni) ratio of 0.78 and the Pt/(Pd + Pt) ratio of 0.95, are inconsistent with the sulfides having reached equilibrium with their Ni rich host rocks at magmatic temperatures and accordingly it is concluded that they are not of magmatic origin. The average d 34S value of the sulfide bodies is + 2 while that of a sample of pyrite from country-rock schist is -15.6. These values are inconclusive as to the origin of the sulfur. It is suggested that the sulfides have been precipitated by hydrothermal fluids, possibly those responsible for the serpentinization of the host rocks. The source of the metals may have been the host rocks themselves.

Introduction

Amongst the largest chromite deposits in Central Greece are those in the Eretria (Tsangli) area, at the northern part of the Othris ophiolite complex (Fig. 1). The village of Tsangli lies 20 km east of the town of Farsala and 30 km southwest of the city of Volos. The Tsangli mine has been known as a producer of massive chromite since 1870. The chromite occurs as spherical, lenticular, or irregular pods, ranging in size from a few to 40,000 tonnes within ser- pentinite which is the prevalent rock type in the area. The pods are randomly distributed within the host rock, al- though an unusually large concentration is present around Tsangli.

Recently, diamond drilling and underground develop- ment have disclosed an association of sulfides and magne- tite with chromite at the peripheries of some of the pods. Banding between the sulfides and the spinels is suggestive of a magmatic origin for these ores. A description of this

unusual association and some analytical data have been given by Economou (1982). In this study the host rocks and sulfides were analysed by electron microprobe, XRD, XRF, and instrumental neutron activation to see if their compositions were compatible with the hypothesis that the sulfides had coexisted with their ultramafic host rocks at magmatic temperatures.

Geological Setting

The ophiolite complex of the Othris belongs to the sub- pelagonian zone, west of the Pelagonian massif. This zone is characterized by Mesozoic ophiolites and limestone- radiolarian chert sequences overlain uncomformably by Upper Cretaceous limestones (Aubouin, 1959; Brunn, 1960; Hynes, 1972; Marinos, 1975; Mastoris, 1979).

The Othris mountains consist of a stack of thrust sheets. The upper sheets contain the rocks of the ophiolite suite, peridotites, gabbros, diabase dykes, and pillow lavas (Menzies, 1973). The lower sheets each contain a succes- sion of varied igneous rocks, in some cases underlain by lightly metamorphosed clastic sediments of Permian and possibly Lower Triassic age, and overlain by a limestone- chert-shale sequence extending into the Upper Jurassic and possibly Middle Cretaceous (Hynes, 1972). There is dispute amongst previous workers concerning the origin of the ophiolites themselves. It is maintained by some that these rocks preserve the facies of the continental margin of a Jurassic ocean basin (Brunn, 1956), while Aubouin (1959) and Smith (1977) suggest that the thrust sheets were derived from an ocean basin, the Pindos basin of the Othrys ocean. However, other interpretations are possible. Bernouli and Laubscher (1972), and Dewey et al. (1973) suggest that the ophiolites west of the Pelagonian zone were derived from the Axios basin, in particular from the Almopias subzone, and were thrust westward across the Pelagonian massif.

The mineralized serpentinites in the Eretria (Tsangli) area are overlain by "upper schist" that is covered un- conformably by Cenomanian limestone, and underlain by "lower schist" (Fig. 2). Crystalline limestones are found interbedded within the schists (Mastoris, 1979). Ser- pentinite is the most abundant rock type in the Eretria area. Its thickness is variable; in the area of the mine it is about 100 m. Brittle and brecciated forms are very com- mon in the serpentinite. Its composition is fairly constant

290

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throughout the whole area, although close to contacts with the ore, a pale green alteration zone is present in which andradite, pyroxene ranging in composition from Di68Hed3~ to Di92Heds, and chlorite are common (Tables 1 and 2).

Both the upper and lower schist contain a nearly constant mineral assemblage: Chlorite + epidote+albite + quartz + white mica + calcite + / - Fe z +-oxide + / -py r i t e . They can, however be distinguished by their bulk chemical composition and the proportion of these minerals (Ta- ble 1). In addition, the chlorite and white mica have very different compositions in the two schists (Table 3). In the lower schist, the chlorite is richer in Mg and the co-existing mica is phengitic sericite whereas in the upper schist the chlorite is richer in Fe and the mica is less phengitic. Also the calcite in the upper schist is Mg and Fe-bearing. The pyrite in the lower schist is minor in amount but in the upper schist it is more abundant, forming veinlets and occurring as octahedra up to 2 mm in diameter, sur- rounded by quartz. The average thickness of the lower schist is 400 m while the upper schist has an average thick- ness of only 40 m.

Relation Between the Sulfides and the Chromite Bodies

A detailed description of the chromite bodies and the relationship of the sulfides to them has been given by Economou (1982). The chromite pods are small, varying from 0.1 to 5 m in width and from 2 to 30 m in length. Tectonized surfaces occur at the contacts with the sur- rounding serpentinite and within the pods themselves. Brecciated angular fragments of ore occur within the pods. The sulfides are found at the periphery of the pods, associated with chromite and magnetite, generally re- stricted to small zones a few centimetres to a few metres in dimensions. Sulfides occur as veins and irregular masses within zones of chromite and magnetite, and also inter- stitial to concentrations of chromite. In some samples, the proportions of chromite and magnetite vary in bands, so that the combination of interstitial sulfide and banding is very reminiscent of a magmatic fabric.

The magnetite occurs in masses separated from the sulfides, as individual grains dispersed within sulfide, as euhedral magnetite containing sulfide inclusions adjacent to massive magnetite, and as compact crystals and rims surrounding porous ferrit-chromite (Fig. 3 a), again close to bodies o~" massive magnetite. Contacts between bodies of massive magnetite and chromite are sharp, whereas magnetite-sulfide contacts are always gradational.

Mineralogy of the Sulfide-Bearing zones

Of the sulfide minerals, pyrrhotite is the most abundant. Cobalt pentlandite is a minor mineral, occurring as coarse, highly corroded grains dispersed throughout magnetite and/or as small inclusions within pyrrhotite. Chalcopyrite and other Cu-sulfides (geerite and spionkopite) occur in lesser amounts while sphalerite is rare.

Pyrrhotite has a hexagonal structure, as has been dem- onstrated by microscopic observation after the application of a thin film of magnetic colloid, and also by X-ray dif- fraction. Its chemical composition has been determined by

292

Table2. Electron microprobe analyses of silicates from Eretria area. Analyses 1-3: garnets from borehole No. 8492 (an. 1 & 2) and underground workings at level 254 (an. 3); Analyses 4 -9 : pyroxenes (Di68Hed32-Di92Heds) from borehole No. 8492 (an. 4-8) and from underground workings at the 254 level (an. 9); Analyses 10 and 11: serpentine from the 254 level. In all cases the associated ore minerals are magnetite and sulfides; accessory chromite grains are also present

1 2 3 4 5 6 7 8 9 10 11

SiO2 35.17 36.20 34.43 53.12 52.80 53.82 53.29 54.54 54.80 41.06 39.09 A1203 nd nd nd nd nd nd nd nd nd 0.00 3.29 Cr20~ nd nd nd nd nd nd nd nd nd nd nd FeO 31.63 a 31.03 a 3 1 . 6 6 ~ 10.00 11.25 9.12 6.98 5.87 2.74 3.68 3.18 TiO2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 MgO nd nd nd 12.09 11.22 12.60 1 5 . 9 5 14.80 16.70 38.80 39.72 CaO 32.75 32.97 33.12 24.43 24.75 24.56 24.65 24.95 25.78 nd nd

99.55 100.20 99.21 99.64 100.02 100.10 100.87 100.16 100.02 83.54 85.28

" Total i roninthe case ofgarnetsis expressed as Fe~O3. nd=no t determined

Table 3. Electron microprobe analyses of chlorites and white mica from schists of Eretria area. Analyses 1-6: coexisting white mica and chlorite in upper schist from boreholes No. 8099 (an. 1 & 2). 6687 (an. 3 & 4), 7701 (an. 5 & 6). Analyses 7-18: coexisting white mica and chlorite in lower schist from boreholes No. 8100 (an. 7-10), 7900 (an. 11 - 14), 6487 (an. 15-18)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

SiO2 51.09 52.28 52.01 25.65 54.12 26.83 51.88 48.98 28.28 27.59 52.58 50.26 28.81 29.63 51.87 49.81 27.84 27.90 A1203 26.61 26.53 29.78 18.44 22.05 16.48 22.91 23.67 17.58 18.07 22.62 22.80 15.87 16.30 22.69 23.12 16.62 16.55 FeO 3.48 3.92 2.65 24.41 5.20 24.41 5.11 5.27 15.42 14.98 5.98 6.70 15.89 15.43 5.99 6.51 17.33 16.96 IiO2 0.14 0.00 0.00 0.00 0.19 0.00 0.16 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 MnO 0.00 0.00 0.00 1.17 0.00 0.25 0.00 0.00 0.16 0.21 0.00 0.00 0.29 0.29 0.00 0.00 0.22 0.23 MgO 2.67 3.04 2.28 16.31 2.70 14.65 4.63 4.79 23.49 24.10 4.20 4.30 22.89 23.10 4.42 3.84 21.38 21.91 CaO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Na20 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 K20 9.52 9.74 9.09 0.00 9.16 0.00 8.97 9.28 0.11 0.00 9.06 9.50 0.11 0.11 8 . 9 1 8.10 0.00 0.00

93.51 95.51 95.81 85.98 93.42 82.63 93.66 91.99 85.04 84.95 94.44 93.56 83.86 84.68 93.88 91.38 83.39 83.55

Table 4. Electron microprobe analyses of sulfides from Eretria area. Analyses 1 & 2: pyrrhotite associated with chromite and magnetite; Analyses 3 & 4: chalcopyrite; Analysis 5: geerite; Analysis 6: spionkopite associated with chromite and magnetite; Analyses 7-9 : Co-pent- landite associated with chromite; Analyses I0 & 11: Co-pentlandite associated with magnetite; Analyses 12 & 13: Co-pentlandite associat- ed with pyrrhotite; Analysis 13: pyrite in upper schist; and Analysis 14: pyrite in lower schist

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Fe 62.8 63.9 30.6 30.1 7.8 0.1 24.2 24.8 15.9 15.4 15.7 32.7 31.7 46.5 46.2 Cu 0.2 0.0 35.0 34.4 67.2 78.6 0.2 0.2 0.3 0.2 0.2 0.3 0.2 0.3 0.0 Ni 0.0 0.0 0.0 0.0 0.0 0.0 22.6 23.5 25.1 25.0 24.9 31.5 31.8 0.0 0.0 Co 0.0 0.0 0.0 0.0 0.0 0.0 20.8 19.3 26.5 28.0 27.2 2.8 3.2 0.0 0.0 Zn 0.0 0.0 0.0 0.0 0.7 1.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 S 36.4 36.4 35.0 34.8 24.5 21.0 33.2 33.5 33.3 32.2 33.7 33.0 32.6 53.4 54.0

99.4 100.3 100.6 99.3 100.2 100.7 101.0 1 0 1 . 3 1 0 1 . 3 101.8 101.7 100.3 99.5 102.2 100.2

Fig. 3a and b. Photomicrographs of porous ferritchromite from the zone surrounding chromite core, a within magnetite ore, and b within sulfude ore. Polished sections Eretria (Tsangli) area

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both microprobe analysis and X-ray diffraction (Table 4). The Fe/S ratio is fairly constant, corresponding to NFeS = 0.997 (as determined from the d102 vs composition of Toulmin and Barton, 1964). The pyrrhotite contained less than detectable amounts of Ni, Co, Cu, and Zn.

The composition of cobalt pentlandite depends on its association. That associated with pyrrhotite has a constant cobalt content of close to 3 wt percent while that associ- ated with chromite and magnetite has 20-25 wt percent cobalt and much less nickel and iron (Table 4).

Where chromite is associated with bodies of magnetite or sulfide, it is replaced by a zone of porous ferritchromite (Fig. 3 a, b) and rimmed by magnetite (Fig. 3 a). Our data indicate that the chromites associated with sulfide are somewhat richer in Fe203 and FeO and, in some cases (analyses 10-12), somewhat poorer in A1203 and MgO than the typical chromite of the pod. Where chromite is associated with magnetite, the porous ferritchromite itself is distinctly depleted in Cr2Q and enriched in Fe203 and A12Q with respect to the grains from which it has been derived (Table 5).

In addition to occurring as rims on ferritchromite, magnetite occurs as individual grains or aggregates of grains dispersed throughout the host sulfides or serpen- tinite, but only adjacent to the massive chromite ore. This is pure magnetite with very little Cr203, A1203 or MgO in solid solution (Table 5).

293

C o m p o s i t i o n o f t h e O r e

The concentrations of major and trace elements in sulfide- rich samples from the Eretria area are given in Table 6 both as raw data and recalculated to metal content in 100 percent sulfide. It is seen that the average metal contents in 100% sulfide are 0.55% Ni, 5.15% Cu, 0.29% Co, 179 ppb Pt, 16ppbRh, l l 2 p p b R u , 31ppbI r , 58ppb ON, and 212ppbAu. The average Cu / (Cu+Ni ) ratio is 0.78. Sulfur isotope data are given in Table 7 from which it is seen that sulfur in the deposits under discussion has an average d ~4S value of +2.0 while that in one sample from the surrounding schist has a value of-15.6.

D i s c u s s i o n

Following the experiments of MacLean and Shimazaki (1976) and Rajamani and Naldrett (1978) on the partition coefficients to be expected between sulfide and silicate melts, a number of authors have discussed the composition of sulfide ores in relation to that of their assumed source magmas (Naldrett et al., 1979; Naldrett and Duke, 1980; Naldrett, 1981; Ross and Keays, 1979; Keays and Campbell, 1982) and in relation to the olivine that has either crystallized from the source magma (Boctor, 1981, 1982; Thompson and Naldrett, in press; Thompson et al., in press) or has equilibrated with the sulfide under metamorphic conditions (Binns and Groves, 1976).

It is agreed by most workers (but not all, cf. Fleet et al., 1977; Fleet and McRae, 1983) that a general equilibrium is established appropriate to the exchange partition coeffi- cient for the reaction

NiO(in magma) + FeN(in sulfide) = FeO(in magma) -I- NiNon sulfide) of about 44 and for the reaction

NiSi l /202 (in olivine) + FeN(in sulfide) = FeSi 1/202 (in olivine) + NiNon sulfide)

of from 5 to 15. Clark and Naldrett (1972) and Binns and Groves

(1976) suggested that the sulfide-olivine partition coeffi- cient increased with decreasing temperature, having a value of 30 at 800 to 900 °C.

The host rocks to the ores of the Eretria area contain an average of 0.26 wt percent Ni. These rocks are highly serpentinized and their modal content of olivine is not known from direct observation, but, from their chemical compositions (Table 1), it is reasonable to assume that this was between 60 and 80%. Since they are essentially devoid of sulfide, it is also reasonable to assume that most of their nickel was originally contained in the olivine. Thus this olivine would have contained at least 0.30 wt percent Ni. Again, from the analyses in Table 1 and also by analogy with other ophiolite complexes it is also reasonable to assume that the olivine originally contained about 10 mole percent fayalite.

Assuming exchange partition coefficients between olivine and sulfide of from 5 to 15, the Ni content of sul- fides that would have been in equilibrium with the ultramafic rocks of Eretria has been calculated to the be- tween 8 and 20 wt percent. To produce a sulfide with the Ni content that is observed, that is about 0.5 wt percent, the partition coefficient would have had to have been of

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Table 6 a. Concentrations of metals in sulfide ores from the Eretria area. All the samples consist of massive pyrrhotite with small amounts of chalcopyrite and/or Co-pentlandite, except samples EM-4, EM-6 and EM-10 which contain significant amounts of chromite, and sample EM-7 which contains a significant amount of magnetite. Blanks in the columns indicate elements present below the detection limits. Average=average of metals shown. Average * = average of metal tenors assuming that the concentration of elements not detected is one half the detection limit. All the samples are from various locations of the underground workings at the 254 level

Sample ppb ppb ppb ppb ppb ppb ppb wt % wt % wt % wt % Factor Palladium Platinum Rhodium Ruthenium Iridium Osmium Gold Nickel Copper Cobalt Sulphur

EM-1 72 6 1.4 3 0.36 5.48 0.239 37.5 1.18 EM-2 2 167 4 0.1 30 0.41 6.52 0.162 37.4 1.21 EM-3 32 6 17 2.9 5 0.13 3.48 0.052 13.0 3.81 EM-4 3 256 11 97 39 70 525 0.14 3.35 0.056 13.8 3.49 EM-5 25 8 43 3 9 5 0.34 0.99 0.221 23.9 1.68 EM-6 122 15 213 71 119 10 0.37 0.37 0.028 15.5 2.53 EM-7 7 1.5 3 0.20 0.93 0.177 17.0 2.40 EM-8 9 44 6 35 2 3 0.38 0.97 0.45 30.6 1.31 EM-9 5 40 10 1.7 6 0.37 5.19 0.316 35.2 1.25 EM-10 9 189 8 16 12 8 452 0.41 1.78 0.226 32.7 1.24 EM-11 54 7 68 3.3 20 15 0.46 1.54 0.177 29.2 1.39 EM-12 34 10 82 6 24 10 0.39 3.69 0.167 28.8 1.50

Table 6b. Concentration of metals recalculated to 100 percent sulfide

Sample ppb ppb ppb ppn ppb ppb ppb wt % wt % wt % Pd Tenor Pt Tenor Rh Tenor Ru Tenor Ir Tenor Os Tenor Au Tenor Ni Tenor Cu Tenor Co Tenor

EM-1 85 7 2 4 0.42 6.45 0.28 EM-2 2 202 5 0 36 0.50 7.88 0.19 EM-3 122 23 65 11 19 0.49 13.24 0.19 EM-4 10 894 38 339 136 245 1834 0.52 11.70 0.19 EM-5 42 13 72 5 15 8 0.57 1.66 0.37 EM-6 309 38 539 180 301 25 0.94 0.94 0.07 EM-7 17 4 7 0.48 2.23 0.42 EM-8 12 57 8 46 3 4 0.50 1.27 0.58 EM-9 6 50 13 2 8 0.46 6.51 0.39 EM-10 I1 235 10 20 15 10 563 0.51 2.22 0.28 EM-11 75 10 94 5 28 21 0.64 2.14 0.24 EM-12 51 15 123 9 36 15 0.59 5.54 0.25

Average 8 193 16 162 31 106 212 0.55 5.15 0.29 Average* 5 179 16 112 31 58 212

Table 7. Sulfur isotope ratios

Sample Mineralogy oa4s

EM-2 Po-Cp + 2.1 EM-2 Po-Cp + 2.2 EM-9 Po-Cp + 1.8 EM- 10 Po-Cp + 2.0 Pyrite Py 15.6

the order of 0.2. Whatever uncertainty may exist about partit ion coefficients, it is quite certain that they could not have been as low as this. Thus the Ni contents of the sulfides indicate that they are extremely unlikely to have been in equil ibr ium with the magma responsible for their host rocks.

Campbell and Naldrett (1979) have shown that the metal tenor of an ore is a function of the proportion of silicate magma that has reacted with a given amount of sulfide or, in their terminology, the magma/sulf ide ratio

(R). They argue that at very low R values, low values of Ni, Cu and PGE tenor will occur in a magmatic sulfide ore. Naldrett et al. (1979) and Thompson and Naldrett (in press) give examples of deposits where this appears to have been the case. However, if the low Ni tenor of the Eretrian sulfides had resulted in this way, low Cu tenors and, because of their very high partit ion coefficients, particularly low (undetectable) tenors of the PGE would also have resulted. This is true of neither Cu nor the PGE. Especially noticeable are the C u / ( C u + N i ) ratios of 0.5 to 0.96 given in Table 6, which are much higher than would be expected for a magmatic ore in ultramafic host rocks.

For these reasons we conclude that, despite their textures, the sulfides are not magmatic and have not at- tained equil ibrium with their host rocks at elevated tem- peratures. The large variation in the Co content of pent- landite is an indication of the lack of widespread equilib- r ium amongst the sulfides themselves, and thus of the unlikelyhood that they have resulted from a process that would inevitably have been accompanied by widespread equilibration.

296

The actual origin o f the sulfides is less clear. In Figure 4 the average concentration of the 6 PGE plus Au in 100% sulfides in our samples have been normalized against chondritic concentrations (Naldrett et al., 1979; Naldrett and Duke, 1980) and are compared with typical ranges shown by flood basalt and komatiite related de- posits (Naldrett 1981). The concentrations of all o f the PGE are low, Pd being particularly low; Ru, Ir and Os are enriched relative to Pt and Pd in comparison with those deposits related to basaltic magmas, so that the overall pattern of the Eretrian samples is relatively flat, with the exception of a pronounced dip in Pd. Flat patterns char- acterize ophiolitic ultramafie rocks and mantle nodules (Barnes, 1983). Whatever has concentrated the PGE has done so in roughly the same relative proportions (except for Pd) as those in which they occur in their host rocks, thus providing some grounds for suggesting that they have been derived from these host rocks. (Au appears in figure 4 to be more highly concentrated with respect to chondritic abundances than the PGE, but reference to Table 6 shows that the apparent high concentration of Au is due to the inclusion of 2 atypically enriched samples in the mean. I f these had been omitted, the concentration of Au would have been reduced by a factor of 14.)

With regard to the low Pd values, Keays et al. (1982) have emphasized that Pd is much more mobile in many hydrothermal fluids than Ir, and have pointed out that PGE may become fractionated with respect to one another in the hydrothermal environment. Thus it is possible that Pd has remained in our postulated hydrothermal fluid, to be deposited elsewhere. An alternative explanation is sug- gested by the data of Page et al. (1982) who note that chromite concentrations within ophiolite successions are characterized by low Pd concentrations relative to other PGE. Thus it is possible that the source of the PGE in the Eretrian sulfide bodies was the chromite segregations themselves.

We draw attention to the association of the sulfides with magnetite. Some of the magnetite is clearly later than the chromite since it can be seen to rim it. We suspect that sulfides were concentrated in the rocks by aqueous fluids, possibly those responsible for serpentinization, and that the sulfide bodies, together with the associated bodies of magnetite, have originated in this way. The metal contents of the sulfides would thus be a function of the dissolution of the metals in and their precipitation from these fluids and not of their solubilities in sulfide melts.

The sulfur isotope data are inconclusive as to the original provenance of the sulfur. The + 2 6 34S average of the mineralized zones is compatible with it being derived from original magmatic sulfide, perhaps that widely and sparingly disseminated in the ophiolite. It would have preserved the near zero 6 34S value characteristic of mag- matic sulfur if it had been dissolved by a reduced solution and precipitated from the same reduced solution. Alter- natively, the sulfur could have been leached by an oxidized solution from the surrounding schist, which could prefer- entially have dissolved 34S to give rise, perhaps, to a sulfate-beating solution with a near zero value of 6 ~4S. Reduction of this solution during serpentinization as a result o f it losing 02 to magnetite, followed by precipita- tion of sulfide could have given rise to a near zero d 34S for the sulfide.

References

Auboin, J.: Contribution a l'ttude geologique de la Grhce septen- trionale. Les confins de l'Epire et de la Thessalie. Thhse, Univ. Paris. Ann. Geolog. Pays Hell. 10:1-485 (1959)

Barnes, Sarah-Jane: The origin of platinum group element frac- tionation in abitibi komatiites. Unpub. Ph.D. Thesis, Univer- sity of Toronto (1983)

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Received: May 10, 1983 Accepted: March 15, 1984