4.4.1. Platinum Group Elements
The PGE are highly conservative elements that may carry information on processes such as melting, sulfide precipitation, and sulfide addition via metasomatism in the upper mantle (see Alard et al. [
17]). Bulk lherzolite xenoliths from East Antarctica display non-fractionated PGE patterns with concentrations of the PGE that are mostly around 0.01 × CI chondrite [
53]. Such low PGE concentrations are consistent with studies by Kiseeva and Wood [
15], Griffin et al. [
18], Mitchell and Keays [
42], and many others who show that sulfides are the main host phases for the PGE in the upper mantle rocks.
The PGE from the studied sulfides can be grouped according to the distribution pattern styles (
Figure 7a–g): (a) subdued convex down I-PGE patterns followed by a deep trough at Pt; (b) convex up PGE patterns for the I-PGE followed by a deep trough at Pt and a peak at Pd; (c) almost unfractionated PGE patterns and ≥10 × CI chondrite PGE concentrations; (d) significantly fractionated PGE patterns often characterized by troughs at Ir and Pt and with PGE concentrations varying from chondritic to ≥10 × CI chondrite; (e) significantly fractionated PGE patterns often characterized by a trough at Ir; (f) “M“-shaped PGE patterns and strong enrichment in Pd with overall high PGE concentrations (up to ~1000 × CI chondrite)—this pattern is typical for the Cu-Ni mss; and (g) almost unfractionated and sometimes incomplete PGE patterns typical of m-type sulfides.
Overall, distinguishing different sulfide populations can be done on the basis of relations between the I-PGE and the P-PGE. The residual PGE signatures are evident from (Pd/Ir)
N ratio < 1, whereas (Pd/Ir)
N > 1 suggests metasomatic influence [
27]. Typically, the (Pd/Ir)
N ratios in the e-type sulfides are much lower, and Os and Ir abundances are higher than those for the i- and m-type sulfides. This records melting processes in the e-type sulfides, while the i- and m-type sulfides have PGE patterns suggesting precipitation from silicate melts or the introduction of other forms of metasomatism [
11,
15,
24,
27]. Additionally, the relationship between Pt and Pd in residual sulfides provides information re- equilibration with the initially depleted melt portion in Pd sulfides, (inducing [Pt/Pd]
N to be <1 [
27]). The time-resolved laser ablation signals on sulfides mostly did not show any irregularities for the PGE. This is strong evidence that most PGE are rather evenly distributed throughout the sulfide phase than grouped in individual clusters.
Only a few of the studied e-type sulfide grains in Cpx-poor Spl lherzolite displayed residual PGE signatures ((Pd/Ir)
N = 0.74–1.33, and 7.45 for Ccp) with insignificant secondary re-enrichment ([Pt/Pd]
N = 0.27–0.39 and 0.09 for Ccp). These sulfides are characterized by convex up PGE patterns with Ir
N over Os
N (
Figure 7b). On the contrary, the domination of the P-PGE over the I-PGE ((Pd/Ir)
N = 3–28) suggests that almost all i-type sulfides in Cpx-poor Spl lherzolites can be considered as precipitated from melts that have migrated through the lherzolite matrix. The PGE patterns for these sulfides vary from insignificantly fractionated and similar to those observed for the e-type sulfides, but with Os
N over Ir
N (
Figure 7d), to fractionated with the P-PGE strongly enriched over the I-PGE (
Figure 7e). Interesting features are displayed by the interstitial Cu-Ni mss. They are characterized by extremely high concentrations of the PGE (519–596 ppm) where Pd strongly prevails (304–422 ppm). Anomalously high concentrations of Ir (69–86 ppm) accompanied by low concentrations of Os (1.5–5.3 ppm) suggests a state of disequilibrium and rapid solidification of the Cu-Ni mss. High Ir concentrations that are inconsistent with low Os concentrations may also suggest that sulfide liquid of such composition could be parental to the Ir-bearing sulfides of the Bowieite–Kashinite series known as orogenic peridotite massives [
54]. Enrichment in Pd relative to Pt is consistent with overall metasomatic/melt origin of the Cu-Ni mss.
Sulfide inclusions in Cr-spinel and in silicate minerals comprise a population of the e-type sulfides in Cpx-rich Spl lherzolite. Sulfide that is included in Cr-spinel (
Figure 4c) has PGE characteristics and patterns similar to those observed for the e-type sulfides from Cpx-poor Spl lherzolite (
Figure 7b). Sulfide phases from the inner part of the inclusion (Pn + Ccp) were characterized by the residual to metasomatic PGE signatures ((Pd/Ir)
N = 0.36–6.39) with fingerprints of secondary re-enrichment ([Pt/Pd]
N = 0.05–0.69). However, the outer part of the inclusion that is represented by chalcopyrite, displayed almost no signatures of metasomatic influence ((Pd/Ir)
N = 0.82 and [Pt/Pd]
N = 1.51). Chalcopyrite from the outer part of the inclusion displays an almost unfractionated PGE pattern with PGE concentrations being ≤10 × CI chondrite (
Figure 7c). Chalcopyrite of this type is directly adjacent to the chain of tiny sulfide blebs healing a former crack in the spinel grain (
Figure 4c). This suggests that chalcopyrite originated as interstitial mss incorporated into spinel through the cracks (in liquid or semi liquid state) but not as a product of the mss break up. On the contrary, most e-type sulfides in silicates and i-type sulfides from the lherzolite matrix are characterized by the metasomatic/melt PGE signatures ((Pd/Ir)
N = 5.4–11.6) and show pronounced fingerprints of metasomatic Pd re-enrichment ([Pt/Pd]
N = 0.16–0.59). They display variably fractionated PGE patterns complicated by troughs at Ir and Pt and by sub- to suprachondritic PGE concentrations (
Figure 7d). This evidently precipitated from silicate melts migrating through the lherzolite matrix as it follows the strong domination of the P-PGE over the I-PGE reflected in ((Pd/Ir)
N = 1.5–51.6). In this process, the i-type sulfides from Cpx-rich Spl lherzolits are similar to the i-type sulfides from Cpx-poor Spl lherzolites. However, two occurrences of the i-type sulfides represented by big multi-phase grains can be interpreted as carrying residual PGE signatures ((Pd/Ir)
N = 0.16–0.51) with no or with only subtle evidence of the metasomatic re-introduction of Pd ([Pt/Pd]
N = 0.57–1.33). These sulfides are characterized by very specific PGE patterns with a convex down I-PGE pattern followed by a deep trough at Pt (
Figure 7a). Such distribution could be considered as typical for residual sulfides that are almost unaffected by enrichment processes (see Westner et al. [
27]). Additionally, one group of the i-type sulfides was characterized by almost unfractionated PGE patterns ((Pd/Ir)
N = 1.28–3.02; [Pt/Pd]
N = 0.38–0.64) with PGE concentrations of >10 × CI chondrite (
Figure 7c). In this case, such sulfides are similar to chalcopyrite from their inclusion in spinel. Such characteristics could be typical of sulfides directly precipitated from the melt (see Westner et al. [
27]).
Most analyzed sulfides in the Spl-Grt lherzolites were found inside kelyphite aggregates that replaced Grt. Since sulfides from kelyphite display obvious residual PGE signatures ((Pd/Ir)
N = 0.09–0.32) and were virtually unaffected by metasomatic Pd re-introduction ([Pt/Pd]
N = 0.55–1.05), it is likely that intrakelyphitic sulfides were initially included in garnet and therefore are associated with the e-type sulfides with typical residual PGE patterns (
Figure 7a). The absence of evidence of metasomatic influence is interesting because during kelyphite formation, some melting occurred, which resulted in metasomatizing liquid [
8]. Interstitial sulfides rarely observed in Spl-Grt lherzolites (
Figure 5c,d) are enriched in the P-PGE relative to the I-PGE ((Pd/Ir)
N = 1.2–44.6) and display fingerprints of metasomatic Pd re-introduction ([Pt/Pd]
N = 0.06–0.45), which is overall typical for most i-type sulfides from all of the considered lherzolite types. Distribution of the PGE for the i-type sulfides is characterized by the two pattern styles, i.e., almost unfractionated PGE patterns with ≥10 × CI chondrite PGE concentrations (
Figure 7d) and significantly fractionated PGE patterns often characterized by troughs at Ir and Pt and with PGE concentrations varying from just above chondritic to ≤100 × CI chondrite (
Figure 7e).
In summary, most analyzed e-type sulfides maintain the residual PGE signatures and were only affected by metasomatic re-enrichment insignificantly, if at all. On the contrary, the i-type sulfides (with a few exceptions) display evidence of precipitation from the migrating silicate melts (melt-sulfides after Westner et al. [
27]). Since sulfides with both residual and metasomatic PGE signatures coexist within a single xenolith sample, the PGE seem to be capable of effectively recording mantle processes related to mantle melting and intramantle melt migration (see Westner et al. [
27]). Based on the observed PGE features, we interpret the e-type sulfides as residues of melting processes and the i-type sulfides as the crystallization products of sulfide-bearing (metasomatic) fluids/liquids (see Foley et al. [
4], Kogarko et al. [
9], Solovova et al. [
11], Hughes et al. [
40]).
Pyrite from silicate-carbonate patches in Spl-Grt lherzolites displays very low I-PGE content (down to complete absence of both Os and Ir), with most PGE represented by the P-PGE. This is consistent with metasomatic origin of these sulfides. Although the PGE patterns for pyrite are incomplete, there is some evidence of an unfractionated style of such patterns (
Figure 7g). Co-violarite from metasomatic veinlets in both Cps-poor Spl and Spl-Grt lherzolites is characterized by unfractionated PGE patterns with suprachondritic concentrations of the elements at about 10 × CI chondrite (
Figure 7g). This suggests a very simple m-sulfides origin that does not record histories of either depletion or re-enrichment.
4.4.2. Other Trace Elements
A number of studies that have been conducted on non-PGE trace elements so trace elements have shown that at upper mantle conditions, the extent of element partitioning into sulfide liquid depends on pressure, temperature, oxygen fugacity, and host rock composition [
15,
55,
56,
57,
58,
59,
60]. Experimental studies have shown that at upper mantle conditions such as those suggested for the Jetty Peninsula lherzolite suite [
2,
4,
12], partial melting depletes the elements in rocks that strongly partition into sulfide melts (P-PGE, Cu, S, Se, Te, Ni, Co, Ag, Pb, Bi, ±Sn, Sb, and As), whereas elements such as the I-PGE, Mo, Zn, Mn, and V tend to be retained in mantle residue [
17,
58,
60,
61,
62]. The rest of the trace elements behave transitionally, either partitioning to sulfide melts or retaining in the residue. The behavior of most transitional elements depends especially strongly on the oxygen fugacity. Li and Audetat [
58] and Steenstra et al. [
60] showed that increasing
fO
2 typically decreases trace element partitioning into sulfide liquid; therefore, increasing their retention in mantle residue.
We studied the behavior of chalcophile (Cu, Zn, Ga, Ge, As, Se, Ag, Cd, In, Sn, Sb, Te, Pb, and Bi) and a few siderophile (Mn, Ni, Co, and Mo) and lithophile (Ti and Cr) trace elements in different sulfide phases. The observed features were compared with those acquired from experimental work for the system “mss–sulfide liquid–mafic silicate liquid” [
58]. The experiments were performed at 15–30 kb and 1175–1300 °C, i.e., at the conditions close to those suggested for the Cpx-rich Spl and Spl-Grt lherzolites from East Antarctica [
4].
Features of trace element distributions in the studied sulfides are depicted in CI chondrite-normalized spider-diagrams (
Figure 8a–g). Distribution patterns of non-PGE trace elements look very similar for all sulfide types except for the m-type sulfides. Generally, siderophile elements and a part of the chalcophile elements display almost unfractionated patterns (often complicated, however, by peaks at Cu and Ag), with concentrations varying from chondritic to ~10 × CI chondrite. The right part of all spider diagrams in
Figure 8 shows significant steady depletion in the chalcophile elements such as In, Sn, Ge, Ga, and often Zn and in lithophile Ti and Cr (down to ≥0.01 × CI chondrite).
Base metal sulfides of the e-type are characterized by higher concentrations of both Ti and Cr than the BMS of the i-type sulfides (
Table 5). This suggests “conservative” behavior of these lithophile elements during mantle melting and their preferable retention in the residue. Although Li and Audetat [
58] did not include Ti and Cr in their experimental compositions, they showed that V (a proxy for Cr) would preferably be retained in the residue. An interesting observation was made for chalcopyrite from the sulfide inclusion in Cr-spinel (
Figure 4c). Chalcopyrite developed along the edges of the inclusion displays strongly elevated concentrations of Cr (5659 ppm), whereas chalcopyrite from lamellae in the same inclusion does not show significant enrichment in Cr (823 ppm). Therefore, Cu-rich liquid incorporated into the Cr-spinel interior through the cracks and represented now by massive chalcopyrite around the Pn-Ccp core seems to interact with the host Cr-spinel. Very low concentrations of Mn are typical for all sulfides from Cpx-poor Spl lherzolites: these are below the detection limits in the e-type sulfides and are 3–24 ppm for the i-type sulfides. A different picture was observed for Cpx-rich Spl lherzolites and Spl-Grt lherzolites. Here, the e-type sulfides contain more Mn than i-type sulfides. It therefore seems that at higher P-T conditions, Mn is preferably retained in the residue. This is consistent with experimental data suggesting that Mn behaves as a siderophile element and is retained in mantle residue. However, pentlandite from the sulfide inclusion in Cr-spinel (Cpx-rich Spl lherzolite) displays low concentrations of Mn (32–49 ppm) that are comparable to those in sulfides of the i-type. However, chalcopyrite that is developed along the marginal parts of the sulfide inclusion in Cr-spinel displays strongly elevated concentrations of Mn (2122 ppm). Once again, as in the case of Cr, chalcopyrite from the exsolution lamellae in the same inclusion is much poorer in Mn (497 ppm). This observation points once more to the interaction of Cu-rich sulfide material with the host mineral. Cobalt is a dominant siderophile trace element in most studied sulfide types. Because Co behaves coherently with Ni, pentlandite is expectedly the main concentrator of Co (>5000 ppm). There is no significant difference between the Co concentrations in pentlandite from sulfides of the e- and i-types (
Table 5 and
Table S1). Sulfides of both types were characterized by low Mo concentrations (mostly 1–10 × CI chondrite). For two analyses that have very high Mo concentrations in interstital pentlandite (1541–1561 ppm;
Table 5 and
Table S1), Mo forms zones of enrichment within a pentlandite body (
Figure 9), probably due to the presence of molybdenite solid solution. Molybdenum is more concentrated in chalcopyrite from sulfides of the i-type than from sulfides of the e-type, whereas there are no differences in the concentration of the element in the pentlandite from sulfide of different types (
Table 5 and
Table S1). Thus, we suggest preferential partitioning of Mo to sulfide liquid relative to the residue. According to experimental studies, Mo mostly behaves as a transitional element with some tendencies to be retained in the residue. Therefore, the observed behavior of Mo in chalcopyrite could be due to certain P-T-
fO
2 conditions that are typical for each lherzolite type.
Zinc does not show any preference in partitioning into a sulfide of any particular type, and Zn amounts are more dependent on the xenolith type. Concentrations of Zn are much lower in sulfides from Cpx-poor Spl lherzolite than in sulfides from Cpx-rich Spl lherzolite and Spl-Grt lherzolite. Since Cpx-poor Spl lherzolite was subjected to intensive melting and depletion [
4], it seems that Zn was significantly removed from the rocks. The much higher concentrations of Zn in Cpx-rich Spl lherzolite and in Spl-Grt lherzolite could be due to metasomatic re-enrichment, which intensively affected these two lherzolite types [
4]. Concentrations of Ga, Ge, and In are typically low in the studied sulfides (often below the detection limit), and no overall partitioning tendencies could be revealed at such a low concentration of the elements. However, chalcopyrite is richer in Ga than in other BMS, and concentrations of Ga are higher in the chalcopyrite from the e-type sulfides than those from the mineral of the i-type sulfides (
Table 5 and
Table S1). Since chalcopyrite is often a product of mss breakup and since Ga (like Cu) accumulates mostly in chalcopyrite, the amount of Ga in chalcopyrite would reflect that amount in the parental mss. Therefore, Ga would rather be retained in mantle residue during partial melting. Concentrations of Ge in the studied BMS are generally similar for the both e-type and i-type sulfides, with no partitioning preferences observed. Concentrations of Cd in pyrrhotite are higher than in pentlandite, and pyrrhotite from the e-type sulfides is richer in Cd (5.4–7.1 ppm) than the mineral from sulfides of the e-type (<1 ppm). It therefore seems that Cd, similar to Ga, would preferably be retained in the residue during partial melting. In spite of very low concentrations (
Table 5 and
Table S1), Sn and Sb show signatures of more preferable accumulation in e-type sulfides. Arsenic displays a slight tendency to partition more preferably into sulfide liquid that is more enriched in the i-type sulfides than in e-type sulfides although experimental data suggest that As would rather be retained in residue during partial melting. Selenium in the BSM does not show any partitioning preferences for any sulfide type. Silver displays much higher concentrations in e-type sulfides than in i-type sulfides (
Table 5 and
Table S1) in Cpx-poor Spl lherzolites, suggesting Ag being retained in the mantle residue during partial melting. For other lherzolites, however, there is no difference in the Ag concentrations in different sulfide types. Since the redox state does not significantly differ between the types of the studied lherzolites [
4,
30], it seems that the behavior of Ag would be rather sensitive to P-T conditions. The element would preferably be retained in residue at lower P-T but would partition to sulfide liquid at a higher P-T. Such behavior of Ag seems to be consistent with experimental data. Lead displays very similar behavior, suggesting that the partitioning of the element strongly depends on the P-T conditions. Although experimental studies show that while Pb is preferably retained in the residue (which is, in part, consistent with our observations for lower P-T), overall, the behavior of Pb is more complicated than that of Ag and requires more detailed study. Concentrations of Te are low but are higher than those of Ga, Ge, Cd, In, Sn, and Sb (
Table 5 and
Table S1). The element displays a pronounced tendency to preferably partition into the e-type sulfides and is retained in the residue during partial melting. Typically, low concentrations of Bi are characteristic for the both e-type and i-type sulfides. No tendencies in the distribution of the element were observed, but that was most likely due to low Bi concentration in most of the studied sulfides.
Interstitial Cu-Ni mss from Cpx-poor Spl lherzolite displays overall high concentrations of most trace elements (from <10 up to ~1000 × CI chondrite). The mss was not analyzed for Ti and Cr, but it displays a significant range of Mn concentrations (
Table 5). Since Mn concentration directly correlates with the concentration of Fe, we suggest the presence of tiny Mn-Fe oxides within the mss matrix. Concentrations of Co (2560–3150 ppm) are lower in the Cu-Ni mss than those in pentlandite but are higher than in the BMS of the e- or i-types. This points to disequilibrium for the Cu-Ni mss that had not yet started to break up into the individual BMS. Concentrations of Mo are higher than in any other sulfide phase except for the i-type sulfides in Cpx-poor Spl lherzolite (
Table 5 and
Table S1). These observations are consistent with the suggestion that at the P-T-
fO
2 conditions typical for mantle rocks parental to the studied xenolith samples, Mo would rather partition to the sulfide liquid than be retained in the residue. The Cu-Ni mss contains very low amounts of Zn (below the detection limit), which is generally consistent with our observations that the BMS from Cpx-poor Spl lherzolites are significantly depleted in Zn. This can also suggest that the Cu-Ni mss was locally generated and did not migrate from a remote mantle domain. The concentration of elements such as Ge, Ga, As, Cd, In, Sb, Sn, and Bi are very low in the Cu-Ni mss (often below the detection limit), suggesting either their preferential retention in the mantle residue during partial melting or their low overall concentration in the host rock. Cu-Ni mss contains very high amounts of the elements such as Se, Ag, Te, and Pb (
Table 5), suggesting that they partition into sulfide liquid at certain P-T-
fO
2 conditions. Trace element CI chondrite-normalized patterns (
Figure 8f) are similar to those observed for the BMS (at higher trace element concentrations than for the Cu-Ni mss, however). If the Cu-Ni mss precipitated directly from the melt, then the primary trace element (other than the PGE) composition of the studied BMS (both e- and i-types) was significantly affected by the fractionation between sulfide phases due to the influence of melt fluids (as it can be judged from trace element chondrite-normalized patterns).
M-type sulfides typically contain moderate amounts of Ti and Cr with Co-violarite from Spl-Grt lherzolite displaying higher amounts of these elements (
Table 6). On the contrary, Co-violarite from Cpx-poor Spl lherzolite contains the lowest amounts of Ti and Cr. Such differences suggest different Co-violarite origin conditions than those of the two xenolith types derived from different SCLM levels [
4].
Interestingly enough, although Mn is supposed to behave coherently with Fe, both the highest and the lowest Mn amounts were measured in Fe-rich sulfides such as pyrite (
Table 6). Among all sulfides, Co-violarite, by stoichiometry, is the richest in Co (up to 15 wt%), as it is a major element in this mineral. Pyrite contains only 1–113 ppm Co, which is consistent with Ni-poor nature of pyrite. Sulfides of the m-type typically contain Mo amounts that are similar to those of the i-type BMS. Concentrations of Zn are very variable in the m-type sulfides (
Table 6), likely due to the very mobile and volatile nature of the element. Concentrations of Ga are low in all m-type sulfides, with the highest concentrations measured in Co-violarite (0.84–3.59 ppm). Sulfides of the m-type display the highest overall concentrations of volatile elements such as Ge and As among all of the studied sulfides (
Table 6). This points to the potential participation of these two elements in the metasomatic re-enrichment of the BMS, probably at the crustal horizons. Among the m-type sulfides, pyrite contains the lowest amounts of Se (below 40 ppm), whereas Co-violarite displays elevated concentrations of Se (up to 273 ppm). Concentrations of Ag are low in pyrite and Co-violarite from Spl-Grt lherzolites (0.5–1.9 ppm), but they are high in Co-violarite from Cpx-poor Spl lherzolite (28–48 ppm). As shown for the BMS, Ag is very sensitive to P-T conditions. Therefore, different Ag concentrations suggest different conditions for the generation of metasomatic veinlets in Cpx-poor Spl lherzolites and in Spl-Grt lherzolites. Concentrations of Cd and Sb are generally low in most m-type sulfides except for Co-violarite from Cpx-poor lherzolite, which display non-typically high amounts of Cd (10–12 ppm) and Sb (1–8 ppm). Concentrations of In are often below or just slightly above the detection limit that is similar to the BMS from lherzolite matrix. Concentrations of Sn in m-type sulfides are generally similar to those observed in the BMS from the lherzolite matrix. Tellurium is unevenly distributed among the m-type sulfides, with concentrations varying from below the detection limit in some pyrite and Co-violarite from Spl-Grt lherzolite to 34 ppm in Co-volarite from Cpx-poor Spl lherzolite. Similarly, concentrations of Pb vary from being very low in pyrite and Co-violarite from Spl-Grt lherzolite (0.1–2.7 ppm) to being very high (>60 ppm) in Co-violarite from Cpx-poor Spl lherzolite. Such distributions of Te and Pb are supposed to be due to the P-T-(
fO
2) conditions for the generation of the certain m-type sulfides. Bismuth is very poor in all m-type sulfides, with concentrations similar to those for the studied BMS. Co-violarite is enriched in siderophile elements and depleted in lithophile elements (
Figure 8g). Trace element patterns for m-sulfides (
Figure 8g) are different from those for BSM, suggesting a different origin of the m-type sulfides.
All things considered, we can say that unlike in the case of the PGE, only a few other trace elements (Ti, Cr, Cd, ±Mo) in the BMS from lherzolite xenoliths display pronounced preferences to either partition to the sulfide liquid or to be retained in the residue during partial melting. Observed partitioning is mostly consistent with experimental studies [
58,
60] and PGE features. Most analyzed trace elements (other than the PGE) however, display dual behavior, i.e., in some lherzolites they preferably partition to sulfide liquid, while in others they would be retained in the residue. Such dual behavior seems to depend strongly on the P-T-
fO
2 conditions during partial melting, which is consistent with the features observed during the experimental runs [
58,
60]. Mostly similar trace element (other than the PGE) composition of the e-type and i-type sulfides accompanied by the dual behavior of most analyzed trace elements in the studied lherzolite xenoliths could point to the remobilization of interstitial sulfides and their aggressive influence on the sulfides enclosed in minerals. The presence of the chains of tiny sulfide droplets along existing or healed fractures in primary xenolith minerals (
Figure 4b,c) might be the result of such remobilization. Unlike most other trace elements, the PGE show different concentrations in sulfides of the e- and i-types, likely due to much more conservative behavior of the PGE preserving their primary features from being affected by later metasomatic processes. Sulfides of the e-type display residual PGE characteristics, whereas the i-type sulfides mainly display fingerprints of the secondary metasomatic re-enrichment. The i-type sulfides carry residual PGE signatures in only a few cases. All of the conducted observations show that the suggestion of Dromgoole and Pasteris [
19] regarding the lack of the compositional differences between the e- and i-type sulfides because of the incorporation of postmetasomatic S-bearing and CO
2-rich melts is close to reality. Such a lack of compositional differences was due to the later metasomatic re-enrichment of the e-type sulfides by the melts/fluids responsible for the generation of i-type sulfides. The few inconsistencies that exist between the experimental data and features observed in natural systems (lherzolite xenoliths) can be related to difficulties in precisely modeling the natural systems while preparing the experimental runs. Therefore, a complex approach including both the study of the natural systems and the experimental work at the upper mantle P-T-
fO
2 conditions is necessary in order to have a comprehensive view of the features of trace element behavior in silicate-sulfide systems.
Among the m-type sulfides, the trace element characteristics of the Co-violarite from two different lherzolite types, i.e., from Cpx-poor Spl lherzolite (32601-9b) and Spl-Grt lherzolite (DN-4), provided an opportunity to compare features of the metasomatic fluids/melts affecting the SCLM rocks derived from different upper mantle levels. It is notable that Co-violarite from Cpx-poor Spl lherzolite has much higher concentrations of most trace elements (other than the PGE) than the mineral from Spl-Grt lherzolite (
Table 6). While a sample (xenolith) of Cpx-poor Spl lherzolite was most likely trapped from the shallowest upper mantle horizons bordering the crust (as we can judge from the low ambient temperature (852 °C) and the composition of the xenolith), a sample of Spl-Grt lherzolite was trapped from much deeper upper mantle horizons (T = 1125 °C; P = 21.5 kb; [
4]). Since all of the studied xenoliths were collected from the same magmatic body and because they were delivered to the surface relatively quickly, it is unlikely that there was much variability in the interaction of the individual xenoliths with the transporting melt. Since the Cpx-poor Spl lherzolite xenolith 32601-9b might have been trapped from the uppermost mantle horizons bordering the lower crust, the influence of crustal fluids that are rich in elements such as Te, Pb, Ag, Se, and Zn might have been strong at those horizons. On the other hand, the metasomatic alteration experienced by the Spl-Grt lherzolite xenolith DN-4 might have been due to the migration of the intramantle fluids (silicate melt-related?) which were relatively depleted in “crustal” trace elements and instead enriched in elements such as As, Ge, Sn, and Sb.