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Volume 31 Issue 3
Jul.  2020
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Esra Yildirim, Nail Yildirim, Cahit Dönmez, Kurtuluş Günay, Taner Korkmaz, Mustafa Akyildiz, Burcu Gören. Composition of Pancarli Magmatic Ni-Cu±(PGE) Sulfide Deposit in the Cadomian-Avalonian Belt, Eastern Turkey. Journal of Earth Science, 2020, 31(3): 536-550. doi: 10.1007/s12583-020-1299-5
Citation: Esra Yildirim, Nail Yildirim, Cahit Dönmez, Kurtuluş Günay, Taner Korkmaz, Mustafa Akyildiz, Burcu Gören. Composition of Pancarli Magmatic Ni-Cu±(PGE) Sulfide Deposit in the Cadomian-Avalonian Belt, Eastern Turkey. Journal of Earth Science, 2020, 31(3): 536-550. doi: 10.1007/s12583-020-1299-5

Composition of Pancarli Magmatic Ni-Cu±(PGE) Sulfide Deposit in the Cadomian-Avalonian Belt, Eastern Turkey

doi: 10.1007/s12583-020-1299-5
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  • Pancarli Ni-Cu±(PGE) sulfide deposit occurs in the Neoproterozoic basement complex of the Bitlis massif, which is one of the Andean-type active continental margin fragments with arc-type assemblages represented by the Cadomian orogenic belt. Pancarli sulfides are associated with quartzo-feldspathic gneisses (country rock) and mafic intrusions (host rock). Composed of only semi-massive ore, the Ni-Cu±(PGE) sulfide deposit is a small-scale deposit, and it does not contain net-textured and disseminated ore. The mineral assemblage comprises pyrrhotite, pentlandite, and chalcopyrite. The semi-massive ore samples contain 2.2 wt.%-2.9 wt.% Ni, 0.8 wt.%-2.2 wt.% Cu (Cu/(Cu+Ni)=0.2-0.5) and 0.13 wt.%-0.17 wt.% Co. The Cu/Ni ratios (average 0.57) are consistent with the segregation of sulfides from a basaltic magma. Low Pt+Pd100%S values of 0.08 ppm-0.89 ppm, relatively low Pt/Pd ratios of 0.2-1.4, and Pd/Ir ratios of 4.5-39 have also been revealed. These values demonstrate that the magma reached S saturation before its emplacement and the mineralization with high Cu/Pd ratios formed by sulfides segregated from a PGE-depleted magma. δ34S isotope values (average -3.1‰) of Pancarli sulfides are lower than mantle source. Negative δ34S value indicates contamination from surrounding rocks. Concerning the composition, remobilization style and magma type, the Pancarli Ni-Cu±(PGE) sulfide deposit is similar to the deposits associated with Andean-type magmatic arcs located in the convergent plate margin settings.
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    Yildirim, N., Gö ren, B., Dö nmez, C., et al., 2016. Magmatic Ni-Sulfide Mineralization in the Precambrian Massif, Eastern Turkey (Bitlis- Pancarli). 69th Geological Congress of Turkey, MTA Ankara
    Yilmaz, O., Michel, R., Vialette, Y., et al., 1981. Réinterprétation des Données Isotopiques Rb-Sr Obtenues Sur Les Métamorphites de La Partie Méridionale Du Massif de Bitlis (Turquie). Sciences Géologiques Bulletin, 34(1):59-73. https://doi.org/10.3406/sgeol.1981.1590 doi:  10.3406/sgeol.1981.1590
    Yilmaz, Y., Yiğitbaş, E., Genç, Ş. C., 1993. Ophiolitic and Metamorphic Assemblages of Southeast Anatolia and Their Significance in the Geological Evolution of the Orogenic Belt. Tectonics, 12(5):1280-1297. https://doi.org/10.1029/93tc00597 doi:  10.1029/93TC00597
    Zientek, M. L., Likhachev, A. P., Kunilov, V. E., et al., 1994. Cumulus Processes and the Composition of Magmatic Ore Deposits: Examples from the Talnakh District, Russia. Ontario Geological Survey Special Publication, Ontario. 5: 373-392
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Composition of Pancarli Magmatic Ni-Cu±(PGE) Sulfide Deposit in the Cadomian-Avalonian Belt, Eastern Turkey

doi: 10.1007/s12583-020-1299-5

Abstract: Pancarli Ni-Cu±(PGE) sulfide deposit occurs in the Neoproterozoic basement complex of the Bitlis massif, which is one of the Andean-type active continental margin fragments with arc-type assemblages represented by the Cadomian orogenic belt. Pancarli sulfides are associated with quartzo-feldspathic gneisses (country rock) and mafic intrusions (host rock). Composed of only semi-massive ore, the Ni-Cu±(PGE) sulfide deposit is a small-scale deposit, and it does not contain net-textured and disseminated ore. The mineral assemblage comprises pyrrhotite, pentlandite, and chalcopyrite. The semi-massive ore samples contain 2.2 wt.%-2.9 wt.% Ni, 0.8 wt.%-2.2 wt.% Cu (Cu/(Cu+Ni)=0.2-0.5) and 0.13 wt.%-0.17 wt.% Co. The Cu/Ni ratios (average 0.57) are consistent with the segregation of sulfides from a basaltic magma. Low Pt+Pd100%S values of 0.08 ppm-0.89 ppm, relatively low Pt/Pd ratios of 0.2-1.4, and Pd/Ir ratios of 4.5-39 have also been revealed. These values demonstrate that the magma reached S saturation before its emplacement and the mineralization with high Cu/Pd ratios formed by sulfides segregated from a PGE-depleted magma. δ34S isotope values (average -3.1‰) of Pancarli sulfides are lower than mantle source. Negative δ34S value indicates contamination from surrounding rocks. Concerning the composition, remobilization style and magma type, the Pancarli Ni-Cu±(PGE) sulfide deposit is similar to the deposits associated with Andean-type magmatic arcs located in the convergent plate margin settings.

Esra Yildirim, Nail Yildirim, Cahit Dönmez, Kurtuluş Günay, Taner Korkmaz, Mustafa Akyildiz, Burcu Gören. Composition of Pancarli Magmatic Ni-Cu±(PGE) Sulfide Deposit in the Cadomian-Avalonian Belt, Eastern Turkey. Journal of Earth Science, 2020, 31(3): 536-550. doi: 10.1007/s12583-020-1299-5
Citation: Esra Yildirim, Nail Yildirim, Cahit Dönmez, Kurtuluş Günay, Taner Korkmaz, Mustafa Akyildiz, Burcu Gören. Composition of Pancarli Magmatic Ni-Cu±(PGE) Sulfide Deposit in the Cadomian-Avalonian Belt, Eastern Turkey. Journal of Earth Science, 2020, 31(3): 536-550. doi: 10.1007/s12583-020-1299-5
  • There are numerous magmatic Ni-Cu-PGE (platinum group element) deposits discovered worldwide. These deposits usually occur in extensional tectonic settings (Barnes and Lightfoot, 2005; Barnes and Francis, 1995), but they are locally associated with compressional settings, as orogenic belts (Thompson and Naldrett, 1984) and magmatic arcs (Piña et al., 2006; Tornos et al., 2006, 2001; Casquet et al., 2001).

    Less attention has been drawn to compressive orogenic areas for the relatively small host prospecting (e.g., Vammala in Finland, Makkonen, 2015; Peltonen, 2005; St. Stephen in North America, Paktunc, 1990; Bruvann in Norway, Boyd and Mathiesen, 1979). But, in recent years, arc settings have become more promising due to sulfide ore potential (e.g., Tati and Selebi-Phikwe in Botswana, Maier et al., 2008; Aguablanca in Spain, Piña et al., 2006; Sally Malay in Australia, Hoatson and Blake, 2000). To define the large magmatic Ni-Cu deposits as a growing number, which are situated in orogenic settings, most of the orogenic belts must be examined again. The Pancarli Ni-Cu±(PGE) mineral deposits occur in the basement complex of the Neoproterozoic Bitlis massif in the Cadomian-Avalonian belt in eastern Turkey (Fig. 1a). The mineralization is mostly hosted in quartzo-feldspathic-gneiss (Yildirim et al., 2016; Çağatay, 1987; Hirano and Boyali, 1980). Their magmatic origin is indicated by the association of sulfides with small-scale gabbro intrusions. The Pancarli mineral deposit is exceptional because no other magmatic Ni-Cu sulfide deposits have been documented in Southwest Asia. Pancarli mineralization is a small Ni-Cu sulfide deposit, which contains 2.65 wt.% Ni, 1.49 wt.% Cu and 15 490 tons proved reserve (e.g., Hirano and Boyali, 1980). This study (Fig. 1a) emphasizes the significance of potential developed for Ni-Cu±(PGE) with the definition of small mafic-ultramafic bodies (Fig. 1b). The objective of this paper is to determine certain exploration areas in SW Asia for new Ni-Cu sulfide ores which are associated with small mafic intrusions within convergent margin settings.

    Figure 1.  (a) Tectonic map showing the locations of the Cadomian-Avalonian basement units in Europe and the eastern Metiterranean area. Suture zones of Turkey are indicated. The Cadomian orogenie belt includes an Andean-type margin along the peri-Gondwana margin. This crust was later dispersed as exotic terranes throughout Paleozoic-Cenozoic orogenic belts (simplified after Ustaomer et al, 2012 and references therein). The red box (larger rectangle) indicates the location of Fig. 2 and the blue box (smaller rectangle) indicates the study area. GTZ. Gavrovo-Tripolitza-lonian zone; MP. Moesian Platform; P. Pindos zone; PZ. Pelagonian zone; SMZ. Serbo-Macedonian zone; SZ. Srednegora zone; VA. Vardar-Axios zone; WT. western Taurides. (b) Simpified geological ma 2002). (C) Geological map of the Pancati nickel-copper deposit area (modified from Hirano and Boyali, 1980).

    The authors intend to develop a new point of view for the Pancarli Ni-Cu±(PGE) mineral deposit using whole-rock, PGE, and δ34S isotope data. Based on the data, the paleotectonic environment of the intrusions, the composition of the magma, factors leading to sulfide saturation, field relations, textures and the degree of the modification of the ore during regional metamorphism and deformation are reconsidered.

  • The Bitlis massif is a part of the eastern Taurids in the Alpine Himalayan Mountain Range. The massif lies within the probable suture zone between the Arabian-African and the Anatolian plates. Its geology is important for understanding the Tethyan evolution. The Bitlis massif is a metamorphic terrain covering a large area (~300 km in length, 40 km in width) in the southeastern part of Anatolia (Fig. 1b). It is a regional-scale allochthon that was emplaced on the Arabian continental margin with a southernly movement in the Early Miocene (Ustaömer et al., 2012; Yilmaz et al., 1993). The massif is underlain by a southernly fold and a thrust belt, which contains Upper Cretaceous fragmented ophiolites, melanges, and high-pressure/low-temperature blueschist-facies rocks. These rocks provide evidences for the closure of the southern branch of the Mesozoic Tethys Ocean (Ustaömer et al., 2012; Yilmaz et al., 1993; Hall, 1976).

    The Bitlis massif includes a large outcrop of Precambrian continental crust, the closest counterpart of the Arabian-Nubian Shield, ~1 000 km to the south (Ustaömer et al., 2012). Many researchers have divided the metamorphic rocks in the Bitlis massif stratigraphically into two main groups (Fig. 1b) and different names have been given to different parts of the massif. An older basement rock complex (Yolcular Formation) is unconformably overlain by younger metasedimentary cover rocks (Kotum Group) with an angular unconformity. It is known that the basement complex is older than the Paleozoic and the cover units are younger. It has been suggested that the older rocks belong to the Precambrian Pan-African basement (Helvaci and Griffin, 1984; Yilmaz et al., 1981; Perinçek, 1980; Genç, 1977; Boray, 1973). The basement rock complex comprises moderate to high-grade metamorphic rocks, which mainly consist of amphibolite, eclogite, microcline gneiss, biotite gneiss/schist and muscovite gneiss/schist that are cut by biotite granite and hololeucocratic aplite-pegmatite (quartzo-feldspathic gneiss) veins (Ustaömer et al., 2012; Okay et al., 1985; Göncüoğlu and Turhan, 1984).

    Rb-Sr isotopic ages have been obtained for amphibolites (920±224 Ma), paragneisses (596±89 Ma) and granites (570 Ma) of the basement complex (Yilmaz et al., 1981). Detrital zircon grains from paragneiss have yielded U-Pb ages of 999–627 Ma and the granitic plutons, which have intruded into the highly metamorphosed basement, have given U-Pb zircon ages of 533–572 Ma (Ustaömer et al., 2012, 2009). The Late Neoproterozoic ages suggest the Bitlis massif is a Peri-Gondwanan terrane with a likely origin in Northeast Africa where similar Early Neoproterozoic (0.9–1.0 Ga) ages have been reported (Ustaömer et al., 2012). Neoproterozoic Bitlis massif, which belongs to the Peri-Gondwana's continental margins, is interpreted as the part of Andean type active continental margin, characterized by the Cadomian-Avalonian belt presenting Ediacaran-Cambrian arc-type assemblages (Ustaömer et al., 2012; Fig. 1a).

  • The Pancarli Deposit is located approximately 20 km southeast of Bitlis City where the dominant lithology is low-to high-grade metamorphic rocks. The area represents the base of a large thrust zone at the southeast of Bitlis (Fig. 1b). High-grade metamorphic rocks of the basement complex crop out in the core of a large E-W trending anticline, while low-grade metamorphic rocks of the cover unit are observed on its flanks (Şengün et al., 1991).

    The high-grade metamorphic basement complex (Yolcular Group of Şengün et al. (1991) or Hizan Group of Göncüoğlu and Turhan (1984)), includes metasedimentary rocks (paragneiss, mica schist and garnet-mica schist), metabasic rocks (amphibolite) and meta-silicic volcanic rocks (leptite gneiss; meta-rhyolite/rhyodacite) (Şengün, 1993; Şengün et al., 1991; Genç, 1990, 1985). In the mineralized area, the high-grade metamorphic basement complex mainly comprises quartzo-feldspathic gneiss, biotite gneiss, amphibolite, high-grade metagabbro, eclogite, meta-granites and augen gneiss (Fig. 1c).

    The mineralized area is characterized by the presence of thin (~10 m) amphibolite and biotite gneiss interlayers within quartzo-feldspathic gneisses (Fig. 1c). However, in the southeastern parts of the area, there are rather thick (~125 m) amphibolite and biotite-gneiss layers. There are also augen gneisses which dispersed continuously in the southeastern edge of the area (Fig. 1c). In the study area, meta-granitic plutons, sills and dykes cut high-grade metasedimentary and meta-igneous rocks (Fig. 1c). These meta-granitic rocks were affected by metamorphism, which might have occurred at a very low grade. Except meta-granites, all basement rocks show amphibolite-facies metamorphism.

    Ni-Cu sulfide mineralizations are commonly observed in quartzo-feldspathic gneisses and rarely in the high-grade metagabbros which are observed at the lower level of metamorphic basement complex (Fig. 1c). In the mineralized area, however, the only rock type that could be a source for nickel and copper among the sulfide minerals is high-grade metagabbros. These rocks, which are cut by isoclinally folded granitic and pegmatitic dikes, occur as numerous sills and massive bodies of various sizes that are concordant with gneissic foliation (Fig. 1c). High-grade metagabbros, which are traced as lenticular bodies within gneisses have occasionally preserved their primary lithology and gabbroic textures (e.g., metagabbro and amphibolitic transition rocks; Hirano and Boyali, 1980). High-grade metagabbros contain hornblende+augite+calcic plagioclase+biotite+garnet± magnetite±apatite and ilmenite. These high-grade metamorphic gabbros may include eclogites (e.g., Oberhänsli et al., 2013; Okay et al., 1985; Türkünal, 1980). The deformation associated with retrograde metamorphism has transformed the metagabbros into garnet amphibolite. Ustaömer et al. (2012) reported that the amphibolites have a basaltic-andesitic composition, tholeiitic affinity and mid-ocean ridge basalt and volcanic arc basalt characteristics.

  • The Pancarli Ni-Cu sulfide deposits crop out as small lenticular gossans in the quartzo-feldspathic gneisses, also crop out as high-grade metagabbros in the Neoproterozoic-aged high-grade metamorphic basement complex (Yolcular Group) of the Bitlis massif. Occurrences of Pancarli Ni-Cu sulfides are found in three different areas (Poav, Pokan and the northern orebodies; Fig. 1c) and they are rather distinct due to the presence of gossans on the surface (Fig. 1c). The mineralization type of Pancarli Deposit is in the form of semi-massive sulfides (including amphibole, garnet, biotite, chlorite and quartz). The mineralization occurs as semi-massive sulfide lenses which are aligned parallel to the distinct foliation of wall rocks and usually have narrow alteration margins (Figs. 2a, 2b, 2d, 2e). Structurally, the Poav and Pokav sulfide occurrences seem to be located on the limbs of a syncline, but the northern occurrences seem to have no direct connections with them (Fig. 1c). The Poav ore bodies, which are the most intensely mineralized, contain ore masses which are 0.1–2 m in thickness and distributed as lenses over a length of 500 m in the N-S direction (Figs. 1c, 2a, 2b). The presence of extensive foliation, folds, and faults in the wall rock made the mineralization complicated and caused lenticular arrangements in different areas (Fig. 1c). The ore bodies sometimes mobilize along shear zones as veins and veinlets, which could be traced in different orientations from the foliations and folds of the host rock (Fig. 2c). The shear zones are more common around ore masses due to the different behaviours of ore and wall rock during deformation. Ore bodies are usually oxidized forming gossans on the surface in which limonite-hematite-goethite-malachite mineralizations are prevalent (Figs. 2d, 2g, 2h). These zones are a product of weathering of shallow parts of the sulfide ore bodies. Ancient mine workings and excavations (Fig. 2h) are present in these mineralized zones, and slag is also observed on the western slopes of the Pokan Stream (Fig. 2i).

    Figure 2.  Outcrop images of Pancarli Ni-Cu deposit. (a), (b) Massive ore lenses that are parallel with foliation of paragneiss (Poav Stream). (c) Vein-like massive ore (mobilized along the shear zone) from the country rock foliation oriented in different directions. (d), (e) Massive ore, illustrating a narrow, oxidized alteration halo (~5–10 cm). (f) Close-up surface of massive ore. (g) Hematite, limonite and malachite observed in the oxidation zone. (h) Intense hematite and goethite observed in ancient mine workings. (i) Slag observed in restricted areas on the western side of the Pokan Stream.

    In brief, the Pancarli sulfide masses are syn-to late-tectonic and co-genetic with the basement units (quartzo-feldspathic gneisses and high-grade metagabbros). Sulfide minerals were mobilized and concentrated during tectonism (accompanied by shear). This situation formed thick sulfide-rich zones which were traced along long narrow fold limbs. The vertical and horizontal discontinuity of the sulfide masses has been derived from deformation and is also similar to the high-grade metagabbros which have the features of host rocks (Fig. 1c).

  • The main ore minerals of the Pancarli Ni-Cu sulfide ore bodies are pyrrhotite, pentlandite, chalcopyrite and pyrite, i.e., a typical magmatic Ni-Cu sulfide deposits mineral assemblage (e.g., Schulz et al., 2010; Barnes and Lightfoot, 2005; Naldrett, 1989). The accessory minerals are magnetite, ilmenite and rutile. In Pancarli sulfides metamorphic recrystallization, oxidation and supergene alteration proceeded after magmatic crystallization. Complete recrystallization of sulfides developed concerning prograde metamorphism, retrograde cooling and changes in temperature accompanied by deformation in some cases. The sulfide minerals in the upper parts of the ore bodies above the groundwater table have been transformed into hydrated ferric oxides and various carbonate and silica minerals under oxidative conditions (e.g., limonite, goethite, hematite, malachite) and crop out as gossans. Sulfide mineral oxidation begins with the transformation of pentlandite-pyrrhotite into violarite/ pyrite+marcasite, i.e., losing their base metals. In rocks where pyrrhotite-pentlandite have undergone supergene alteration, chalcopyrite and pyrite might have been still present (e.g., Schulz et al., 2010). Quartz, amphibole, garnet, chlorite, biotite are the main gangue minerals and are commonly intergrown with the ore minerals.

    Pyrrhotite is the most abundant ore mineral. Interlocked pyrrhotite crystals are generally larger than 0.1 mm. They are typically anhedral and show wavy lamellar texture. Pyrrhotite crystals, which are mostly crystallized in the hexagonal crystal system, are observed as parallel rod-shaped bouquets (Figs. 3b, 3d, 3e). In pyrrhotites, complete violarite pseudomorphs after pentlandite and tiny pentlandite flames and very fine-grained pyrite grains and clusters are observed (Figs. 3a, 3c, 3d). Banded hexagonal pyrrhotite shows a transformation into marcasite+pyrite (a transition mineral assemblage caused by the transformation of pyrrhotite into pyrite) along crystal boundaries, fractures and cleavage planes (Figs. 3e, 3g, 3i, 3k). Under crossed polarized light, pressure-twinned and twisted banded pyrrhotite grains are observed (Figs. 3e, 3f) which were formed as a result of metamorphism. Additionally, in some sections, euhedral almandine crystals are encapsulated in pyrrhotite (Figs. 3k, 3l).

    Figure 3.  Reflected-light photomicrographs of massive ores in the Pancarli area. (a) Violarite grains as pentlandite pseudomorphs showing well-developed cleavage within interlocked pyrrhotite crystals. Chalcopyrite, seen as various-sized grains and veins, fills the spaces and fractures of ore minerals (pyrrhotite-violarite) and gangue minerals. (b) Pyrite, filled by chalcopyrite and pyrrhotite along its fractures and cleavages. (c) Pyrite grain clusters and relicts in pyrrhotite and chalcopyrite. (d) Pentlandite disjunction exsolution flames and anhedral chalcopyrite within pyrrhotite. (e) Anhedral chalcopyrite between banded (and twisted) structured hexagonal pyrrhotite crystals. Pyrite+marcasite observed along the edges and cleavages of pyrrhotite. (f) Pressure-twinned pyrrhotite formed as a result of metamorphism. (g) Euhedral magnetite (mag) surrounded by chalcopyrite, pyrite+marcasite, pyrrhotite, and violarite. (h) Magnetite grains within pyrrhotite and chalcopyrite. Limonite observed along the fractures. (i) Violarite, with well-developed cleavage, within pyrrhotite, changed into pyrite+marcasite along its edges and cleavages. Chalcopyrite filling the spaces between pyrrhotite and violarite and biotite platelets (gangue). (j) Biotite surrounded by pyrrhotite, chalcopyrite, and violarite. Limonite developed along the fractures and cleavages of biotite and ore minerals. (k) Violarite surrounding euhedral almandine crystal, and pyrrhotite transforming mid-product. (l) Garnet (almandine) surrounded by pyrrhotite and chalcopyrite, and limonite along fractures. alm. Almandine; bt. biotite; cp. chalcopyrite; lm. limonite; mag. magnetite; mrc. marcasite; pn. pentlandite; po. pyrrhotite; py. pyrite; vl. violarite.

    Most of the pentlandites have turned into violarite, while some were preserved. Pentlandite occurs as various-sized grains inside pyrrhotite. Generally, pentlandite grains have a well-developed cleavage and show cataclastic fractures with chalcopyrite/pyrrhotite infillings. Pentlandite is also present as small flame-like or skeletal exsolutions parallel to the pressure twins of the host pyrrhotite (Fig. 3d).

    Chalcopyrite is another abundant ore mineral. It occurs as anhedral grains with variable size. Chalcopyrite forms intergrowth textures with pyrrhotite and pentlandite. Chalcopyrite is between pyrrhotite and violarite crystals and is located in violarite fractures and cleavages. It is also traced along the boundaries of ore and gangue minerals (Figs. 3a3e, 3h3j, 3l). Chalcopyrite grains sometimes contain early pyrrhotite inclusions (Fig. 3c).

    Pyrite occurs in fewer quantities. Small-sized grains (the largest pyrites are only 140–150 μm) are observed in the form of grain clusters and relicts in pyrrhotite. Pyrite is clearly replaced by pyrrhotite, and that replacement causes the formation of relict pyrite grains. The fractures and cleavages of the pyrite are filled by chalcopyrite and pyrrhotite (Figs. 3b, 3c).

    Magnetite and ilmenite are observed in very small amounts. Magnetite is observed as euhedral, subhedral crystals in gangue minerals and is usually fractured and fragmented due to post-formational processes. The largest magnetite crystals observed are 0.2 mm in size. Magnetite is usually found in pyrrhotite or is localized by chalcopyrite, pentlandite, and violarite (Figs. 3g, 3h). Ilmenite grains are rod-shaped and less common. The largest ilmenite crystal observed is 0.4 mm×0.075 mm in size.

    Secondary mineral assemblages are formed by the supergene replacement of Pancarli sulfides. Pyrrhotite is altered to a mixture of submicroscopic marcasite+pyrite. Violarite is a common product of supergene alteration and does not contain pentlandite relicts (Figs. 3a, 3g, 3i, 3j, 3k). Furthermore, magnetite is oxidized to hematite. These replacements are associated with the loss of metal, leading to a distinct decrease in modal abundance of pentlandite and pyrrhotite. The supergene alteration of Pancarli sulfide ores, resulting in the local formation of goethite (and limonite; Figs. 3h, 3l) and gossans, is observed in most of the magmatic Ni-sulfide deposits.

    Very small amounts of gangue minerals such as biotite, amphibole, quartz, garnet, and chlorite are observed among ore minerals (Figs. 3i3l). Gangue minerals are replaced by ore minerals and their fractures and cleavages are filled by these minerals.

  • In the present study, PGE, Cu, Ni, S, Fe and some other elements in 12 samples (8 semi-massive ore samples and 4 gossan samples) representing the Pancarli Ni-Cu±(PGE) deposit were analyzed. The PGE and Au were determined by instrumental neutron activation analysis (INAA) after fire assay preconcentration in a Ni sulfide bead (see Bédard and Barnes, 2002, for analytical details) and sample irradiation at the ACME Analytical Labs, Canada. Copper, Ni, S, Fe and some other elements were dissolved in aqua regia, and the solution was injected into an inductively coupled plasma mass spectrometer (ICP-MS) for analysis at the ACME Analytical Labs, Canada. Lower detection limits are 20 ppm for S; 0.1 ppm for Se, Ni and Co; and 0.01 ppm for Cu. For the noble metals, the lower detection limits are 1 ppb for Au, Ir, Os, Rh, Ru, Pd and Pt.

    Sulfur isotope analyses were performed on pyrrhotite grains, which had been separated from the semi-massive ore samples using a magnetic separator. The sulfur isotope ratios of the purified SO2-gas were measured with a VG Micromass MM602 dual inlet mass spectrometer at the Activation Laboratories (Actlabs) in Ontario, Canada. Quantitative combustion to SO2 was achieved by mixing 5 mg of the sample with 100 mg of V2O5 and SiO2 mixture (1 : 1). The reaction was carried out at 950 ℃ for 7 min in a quartz glass reaction tube. Pure copper turnings were used as a catalyst to ensure the conversion of SO3 to SO2. All results were reported in per mil notation related to the international Canyon Diablo Troilite (CDT) standard.

  • The Pancarli Deposit has high values of Cu, Ni, and Co, whereas PGE seems to be insignificant. The semi-massive ore has average values of 9.24 wt.% S, 1.49 wt.% Cu, 2.65 wt.% Ni, 0.14 wt.% Co and 24 ppb–194 ppb Au, and 34 ppb–251 ppb total PGE (Table 1). Most of the PGE components are composed of Pt (7 ppb–101 ppb) and Pd (12 ppb–118 ppb). Rh (< 1 ppb–10 ppb), Ru (2 ppb–14 ppb), Os (< 1 ppb–6 ppb) and Ir (< 1 ppb–8 ppb) contents are quite low (Table 1). The gossan samples have average values of 0.45 wt.% S, 0.23 wt.% Cu, 0.03 wt.% Ni, 0.003 wt.% Co, 60 ppb–116 ppb Au, and 48 ppb–301 ppb total PGE (Table 1).

    Semi-massive sulfides Gossan
    Sample Tp-1 Tp-3 Tp-4 Tp-5 Tp-8 Tp-14 Tp-16 Tp-17 Tp-9 Tp-11 Tp-12 Tp-13
    S (wt.%) 8.86 6.22 9.74 11.44 7.39 8.68 11.22 10.36 0.81 0.36 0.37 0.26
    Fe 38.94 48.47 48.11 42.22 43.91 44.69 45.84 45.57 > 40.00 38.47 18.05 16.24
    Ni (ppm) 26 350 27 050 29 120 28 520 24 480 22 130 28 090 26 160 265 508 256 154
    Cu 8 050 16 830 12 850 14 250 11 600 19 210 14 190 22 120 2 610 2 999 2 608 850
    Co 1 407 1 280 1 669 1 548 1 272 1 250 1 507 1 588 27.6 61.4 16.7 12.8
    As 8.3 6.6 4.5 4.3 4.2 44.6 9.3 7.4 2.3 4.70 < 0.1 4.3
    Cr 77.0 38.7 39.4 43.7 75.5 25.7 64.5 40.0 129.4 142.3 51.3 17.5
    Pb 40.67 3.42 3.40 4.53 4.33 4.33 14.07 17.21 4.70 11.19 5.57 10.13
    Zn 68.7 26.3 22.8 31.8 46.3 66.4 43.3 20.8 15.3 31.7 19.9 11.6
    Sb 0.31 0.07 0.17 0.13 0.06 0.98 0.13 0.14 2.99 0.42 0.10 0.11
    Ag 3.63 5.99 3.76 3.36 2.10 4.79 4.53 3.50 8.14 1.48 0.52 3.71
    V 24 17 16 16 36 96 70 62 154 184 58 60
    Bi 5.14 4.28 5.46 5.94 5.42 8.21 10.12 9.51 21.92 17.95 3.46 6.48
    Th 0.2 < 0.1 < 0.1 < 0.1 < 0.1 0.6 < 0.1 0.3 1.5 1.6 5.8 1.4
    U 0.05 < 0.05 < 0.05 1.18 < 0.05 0.18 < 0.05 < 0.05 0.14 < 0.05 0.20 0.05
    Sr 5.9 < 0.5 < 0.5 0.5 0.9 1.0 1.9 2.1 < 0.5 1.0 3.0 5.5
    Cd 0.37 0.63 0.54 0.73 0.87 0.82 1.10 0.86 0.05 0.05 0.02 0.19
    Ba 2.8 4.1 6.5 8.4 15.0 13.1 10.9 9.5 4.6 1.9 27.1 33.3
    Sc 3.3 < 0.1 < 0.1 0.2 1.7 2.6 0.4 0.6 2.2 2.1 8.9 3.8
    Se 51.4 50.8 50.7 52.3 53.1 86.4 69.2 66.8 44.3 3.6 12.7 37.2
    Te 0.88 1.10 0.98 0.92 1.21 3.40 1.99 2.43 2.35 1.29 0.58 1.17
    Ga 5.4 1.7 0.5 1.6 2.2 2.8 2.3 3.3 5.5 9.8 14.7 4.8
    La 1.6 < 0.5 < 0.5 < 0.5 < 0.5 0.6 < 0.5 < 0.5 0.9 0.8 1.9 5.0
    Pr 0.32 < 0.02 < 0.02 < 0.02 0.02 0.16 0.02 0.11 0.26 0.18 0.42 0.97
    Nd 0.85 0.04 0.11 0.09 0.24 0.55 0.39 0.50 1.10 0.7 1.57 2.92
    Sm 0.23 0.03 0.02 0.03 0.09 0.25 0.09 0.15 0.31 0.13 0.32 0.68
    Eu 0.07 < 0.02 < 0.02 < 0.02 0.03 0.03 0.05 < 0.02 0.06 0.06 0.11 0.13
    Gd 0.39 0.08 0.03 0.06 0.15 0.23 0.14 0.03 0.18 0.19 0.33 0.73
    Tb 0.06 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 0.05
    Dy 0.47 0.10 0.06 0.09 0.32 0.22 0.10 0.11 0.12 0.18 0.27 0.59
    Ho 0.11 < 0.02 < 0.02 0.02 0.06 0.05 0.03 < 0.02 0.04 0.02 0.05 0.14
    Er 0.28 0.04 0.03 0.04 0.18 0.11 0.06 0.05 0.08 0.08 0.17 0.3
    Tm 0.05 < 0.02 < 0.02 < 0.02 < 0.02 0.03 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 0.05
    Yb 0.27 0.03 < 0.02 0.05 0.16 0.13 0.06 0.03 0.04 0.09 0.10 0.34
    Lu 0.05 < 0.02 < 0.02 < 0.02 0.04 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02 0.03 0.05
    Os (ppb) < 1 6 4 2 5 5 4 2 2 < 1 1 < 1
    Ir 2 8 < 1 4 3 3 4 2 9 < 1 1 < 1
    Ru 9 10 6 14 7 14 8 2 10 10 3 < 1
    Rh 3 5 4 9 2 10 4 < 1 6 < 1 1 < 1
    Pt 7 8 11 16 12 101 39 8 38 14 15 12
    Pd 12 47 12 18 35 118 28 23 236 64 35 32
    Au 24 28 35 27 28 194 69 78 116 91 60 76

    Table 1.  Compositional data of mineralized samples in the Pancarli Ni-Cu±(PGE) deposit

    The geochemistry of the gossan samples in the Pancarli Deposit shows that Ni is relatively more mobile and more depleted than Cu and Co compared to massive ore compositions. Gossans, which are formed by the weathering (atmospheric decomposition) of magmatic Ni-Cu±PGE hypogene ore minerals, are typically expected to retain immobile PGEs (e.g., Schulz et al., 2010), but the PGE content of gossan samples in the Pancarli Deposit is also very low. This can be explained by low PGE content of hypogene ore minerals.

    The concentrations of Ni, Cu, and PGE are important in determining the viability of Ni-Cu sulfide deposits.

    Semi-massive ore samples have high base metal/S ratios, while the gossan samples have lower base metal/S ratios (Figs. 4a, 4b). This is interpreted as the reflection of the mobility of Ni, Cu, and S in the oxidative environment. The PGE/S and Au/S contents of massive ore and gossan are similar, which suggests the PGEs and Au are immobile during weathering (Figs. 4e, 4f). Sulfur is quite compatible when Se is incompatible with silicates and oxides. Thus, there is a clear correlation between Se and S (Fig. 4c). The Ni, Cu, Se, Au, and PGE contents of the semi-massive ore samples are tightly clustered (Fig. 4).

    Figure 4.  Binary variation diagrams of S versus (a) Cu, (b) Ni, (c) Se, (d) Pt, (e) PGE and (f) Au. Compositional fields of gossan (green circle) and massive sulfide ore (red circle) belonging to the Pancarli Deposit. See text for further explanation.

    To compare and interpret the composition of the massive ore samples, their metal concentrations are recalculated to 100% sulfide by using the method of Naldrett et al. (2000) (see Table 2). The maximum PGE content (recalculated to 100% sulfide) of semi-massive ore in the Pancarli Deposit is 33 ppb Oss, 44 ppb Irs, 57 ppb Rus, 41 ppb Rhs, 410 ppb Pts and 479 ppb Pds. The Pt+Pd100%S ranges approximately from 0.08 ppm to 0.9 ppm, and the grade is very low (Table 2). Compared to most other magmatic sulfide ores, the Aus content is relatively high; in some samples, it is higher than the total PGE content. The average Aus content of all samples is 233 ppb and those of Pds and Pts are 152 ppb and 97 ppb, respectively (Table 2). Similarly, high Au/PGE ratios and low Pt+Pd100%S contents have been reported for some deposits in Sudbury, Canada (Hoffman et al., 1979), in Caraiba, Brazil (Maier and Barnes, 1999), in Rana, northern Norway (Boyd et al., 1987) and in O'okiep, South Africa (Maier et al., 2012).

    Sample S Ni Cu Co Se Os Ir Rh Pt Pd Au Cu/Ni S/Se Pt/Pd Pd/Ir Pt+Pd δ34Spo
    (wt.%) (ppm) (ppb) (ppb) (‰)
    Semi-massive sulfides Tp-1 35.26 10.49 3.20 5 600 205 4 8 12 28 48 96 0.31 1 723 0.58 6.00 76 -3.10
    Tp-3 34.47 14.99 9.33 7 094 282 33 44 28 44 260 155 0.62 1 224 0.17 5.88 305 -3.50
    Tp-4 35.18 10.52 4.64 6 027 183 14 4 14 40 43 126 0.44 1 921 0.92 12.00 83
    Tp-5 35.38 8.82 4.41 4 787 162 6 12 28 49 56 84 0.50 2 187 0.89 4.50 105 -3.10
    Tp-8 35.03 11.60 5.50 6 028 252 24 14 9 57 166 133 0.47 1 392 0.34 11.67 223 -2.85
    Tp-14 35.20 8.97 7.79 5 071 350 20 12 41 410 479 787 0.87 1 005 0.86 39.33 888
    Tp-16 35.37 8.86 4.47 4 750 218 13 13 13 123 88 218 0.51 1 621 1.39 7.00 211
    Tp-17 35.22 8.89 7.52 5 399 227 7 7 3 27 78 265 0.85 1 551 0.35 11.50 105
    Metal concentrations are recalculated according to 100% sulfide following Naldrett et al. (2000); po. pyrrhotite.

    Table 2.  Metal contents of Pancarli Ni-Cu±(PGE) deposit

    The compositions of the semi-massive ore sulfide fractions (metal contents were recalculated to 100% sulfide) of the Pancarli Ni-Cu±(PGE) deposit were normalized to the primitive mantle to compare the relative amounts of these elements. In the diagram Fig. 5a, semi-massive ore samples show highly fractionated patterns with increasing metal contents from Ir to Cu. Primitive mantle-normalized patterns for Pancarli sulfides show a negative anomaly in Os, Ir, and Pt (excluding 2 samples) while Pd, Rh, Au and Cu show positive anomaly.

    Figure 5.  (a) Primitive mantle-normalized patterns of Ni, Cu, platinum group element (PGE), and Au contents recalculated to 100% sulfides for the massive sulfide ores of the Pancarli Deposit. Primitive mantle normalization values are from Barnes and Maier (1999) and McDonough and Sun (1995). (b) Cu/Ni vs. S, (c) Pd/Ir vs. S. Fields of Cu/Ni and Pd/Ir ores in basalts, picrites and komatiites are from Barnes and Maier (1999), Barnes and Lightfoot (2005) and Naldrett (2004); after Maier et al. (2008). (d) Cu/Pd vs. Pd values of samples containing massive sulfides in the Pancarli Deposit. Tie lines are drawn for model sulfides crystallizing from metal-undepleted island arc magma (45 ppm Cu, 7.5 ppb Pd; Barnes et al., 1993; after Maier et al., 2008) at variable R factors. The remainder of the Pancarli samples have high Cu/Pd ratios, indicating sulfide segregation from strongly metal depleted magma. See text for further explanation.

  • Sulfur isotope ratios were determined for pyrrhotite samples (or separates) from the Pancarli Ni-Cu sulfide ores. Their δ34S values range from -2.9‰ to -3.5‰ (Table 2). Magmas resulting from the partial melting of mantle should have δ34S values of ~0 to 2‰ (Ripley, 1999). The negative δ34S values (average -3.1‰) of the Pancarli semi-massive ore samples are clearly outside the mantle range. This negativity of δ34S values may be explained by the δ34S-depleted mantle or maybe the result of secondary fractionation processes such as assimilation (e.g., Voisey's Bay; Ripley et al., 2002), oxidation, hydrothermal alteration (e.g., Jinchuan Deposit; Ripley et al., 2005) and sulfur devolatilization (e.g., O'okiep Deposit; Boer et al., 1994; Ohmoto, 1986).

  • The magmatic origin of Pancarli Ni-Cu sulfide ores is indicated by the association of sulfides with small mafic intrusions. These mafic intrusions which belong to the basal complex of Neoproterozoic Bitlis massif are high-grade metagabbros. Previous studies (e.g., see Ustaömer et al., 2012 for analyses; Genç, 1990; Çağatay, 1987) suggested that these rocks crystallized from tholeiitic basalt which contains approximately 8 wt.% MgO and 15 wt.% Al2O3.

    Primitive mantle-normalized chalcophile element diagram of the Pancarli sulfide ores (Fig. 5a) is similar to those shown normally by gabbronorite-hosted sulfides (average Pd/IrMN value is 10) and differs from more horizontal patterns of picrite or komatiite-hosted sulfides (e.g., Barnes and Lightfoot, 2005). Pancarli sulfides differ from the komatiitic sulfides due to being poor in IPGE (Os, Ir, Ru) and PPGE (Rh, Pt, Pd). The Cu/PdMN values of Pancarli samples are high with an average value of 81, suggesting that the Pancarli sulfides are predominantly fractionated from the PGE-depleted magmas (e.g., Selebi-Phikwe, Maier et al., 2008). All Ni/IrMN values are much higher than 1 (19 on average). These values are derived from the higher bulk partition coefficients of Ir relative to Ni during the fractionation of basaltic magmas (Maier et al., 2008; Crocket, 2002).

    Sulfide orebodies commonly consist of Fe- and Cu-rich sulfides (e.g., Barnes et al., 1997a), the formation of which is attributed to the fractionation of Fe-rich mss (monosulfide solid solition) from the sulfide liquid (Zientek et al., 1994; Distler et al., 1977). Based on experimental data (e.g., Li et al., 1996; Fleet et al., 1993), Fe-rich mss enriched in Os, Ir, Ru, and Rh is the first phase to crystallize, whereas the remaining liquid (Cu-rich portion) is enriched in elements that are incompatible with the mss, including Cu, Pt, Pd, and Au. There is no significant variation in Ni partition coefficients between the Fe- and Cu-rich phases (Barnes and Maier, 1999). Primitive mantle-normalized patterns for Pancarli sulfides (Fig. 5a) show a negative anomaly in Os, Ir, and Pt (excluding 2 samples) while Pd, Rh, Au and Cu show positive anomaly. Strong preferential partitioning of IPGE into mss and subsequent early fractionation of mss from the sulfide liquid explain the IPGE-depleted mantle-normalized patterns in the Pancarli sulfides (e.g., Manor, 2014; Mungall et al., 2006; Barnes and Lightfoot, 2005; Barnes and Maier, 1999; Barnes et al., 1988). Negative Pt anomalies are characteristic of sulfides representing the crystallization of mss (Barnes et al., 1997b), Pt-bearing alloys crystallized directly from the silicate magma before sulfide liquid segregation and were fractionated at depth (e.g., Thakurta et al., 2014). It can be the cause of negative Pt anomaly in Pancarli sulfides (Fig. 5a). Au also shows positive anomalies due to its mobility in fluids (Fig. 5a).

    Consequently, sulfides that are formed from fractionated magmas tend to present higher Cu/Ni (and Pd/Ir) ratios (Maier et al., 2008). The Cu/Ni ratios of the Pancarli massive sulfide samples range from 0.3 to 0.9 (Fig. 5b; Table 2), while their Pd/Ir ratios range from 4.5 to 39 (Fig. 5c; Table 2). Relatively higher Cu/Ni ratios are similar to the sulfides which have differentiated from fractionated magma (e.g., Maier et al., 2008). These ratios are within the limits of the typical sulfide ores originating from basaltic magmas (Barnes and Lightfoot, 2005; Naldrett, 1989; Barnes et al., 1985), consistent with the basaltic origin of the Pancarli gabbroic intrusions. The Pancarli sulfide deposit shows significantly high Cu and Ni grades but also shows low PGE contents (Table 2). Pd/Ir ratios (average 12.2) for Pancarli samples are lower than Cu-rich ores (western East O'okiep, South Africa, Maier et al., 2012; Caraiba-Brazil, Maier and Barnes, 1999) whether they are similar to Ni-Cu rich ores (Hondekloof, Eezelsfentein, South Africa; Maier et al., 2012). The Pancarli sulfides are depleted in PGE relative to Ni and Cu. This is probably caused by sulfide differentiation before emplacement, thus depleting the magma in PGE. Consequently, sulfides segregated from PGE-depleted magmas formed the Pancarli sulfides.

    Cu/Pd-Pd diagrams can be used in modeling sulfide liquid compositions. As, Cu and Pd have similar partition coefficients into mss, the fractionation of mss does not change Cu/Pd ratios significantly, so it is possible that semi-massive sulfide samples formed from depleted or fertile magma (e.g., Barnes and Lightfoot, 2005). The Pancarli sulfide ore is an exception with the high Cu/Pd ratios (Fig. 5d). This feature is probably caused by early sulfide segregation and the removal of Pd (Huang and Wang, 2019; Barnes et al., 1993). The Pancarli samples have high Cu/Pd ratios that cannot be modeled by the segregation of depleted island-arc tholeiites. To model the Pancarli samples, advanced depleted magma is required (Fig. 5d).

    The Ni/Cu versus Pd/Ir (Fig. 6a) and Cu/Ir versus Ni/Pd (Fig. 6b) plots are also significant for determining the relationship between sulfides and the host rocks. In the Ni/Cu versus Pd/Ir diagram (Fig. 6a), Pancarli sulfide samples are clustered in the field of layered intrusions. These sulfide samples with relatively low Pd/Ir ratios are rich in Fe and are clustered along the mss bulk vector.

    Figure 6.  Ratio plots of (a) Ni/Cu vs. Pd/Ir, and (b) Ni/Pd vs. Cu/Ir for common rock types (Barnes and Lightfoot, 2005). (c) The plot of S/Se vs. δ34S for the magmatic Ni-Cu-PGE sulfide deposits and their associated contaminants (Queffurus and Barnes, 2015 and references therein). Abbreviations: Pech (Int). Pechenga intrusions; Pech (F). Pechenga flows; CR. country rocks; VCDT. Vienna Cañon Diablo troilite (International Standard). Orange squares indicate Pancarli massive ores. CHR. Chromite; OL. olivine; mss. monosulfide solid solition; SUL. sulfide; L.I. layered intrusion; OPH. ophiolites; PGM. platinium-group minerals.

    Variations in Ni/Pd and Cu/Ir are important in determining the effects of sulfide liquid separation. The separation of sulfide liquid from silicate magma will deplete the magma more in PGE than Cu and Ni (Barnes and Lightfoot, 2005). Therefore, sulfides segregated from depleted magmas will have higher Ni/Pd and Cu/Ir ratios than primary magmas. The Pancarli sulfides plot in the field of layered intrusions with high ratios of Ni/Pd and Cu/Ir (Fig. 6b). The depletion of the Pancarli sulfides is interpreted as there are some more PGE-rich sulfides at depth or as the magma was formed as a result of a low degree partial melting and retained some sulfides in the mantle (e.g., Barnes and Lightfoot, 2005).

  • The majority of magmatic Ni-Cu sulfide deposits are hosted within sulfide-bearing country rocks (Barnes and Lightfoot, 2005; Naldrett, 2004), which are inferred to have been assimilated or devolatilized by parental magmas (e.g., Arndt et al., 2005; Ripley et al., 2002; Li and Naldrett, 1999), thereby extracting sulfur and triggering sulfide saturation (Seat et al., 2009).

    In many magmatic Ni-Cu sulfide deposits, the addition of external sulfur from country-rock plays an important role in sulfide saturation (Su et al., 2012; Ripley et al., 2003, 2002, 1999; Mavrogenes and O'Neill, 1999). The best way to evaluate the source of sulfur is sulfur isotope data analysis (e.g., Ripley and Li, 2013). Comparing the sulfur isotopes and S/Se ratios in the major magmatic Ni-Cu deposits suggests that the S/Se (average 1 578) and δ34S isotope data (average -3.1‰) of Pancarli are lower than mantle-derived sulfur.

    Pancarli sulfide deposit is associated with the small mafic intrusions (high-grade metagabbros) within the basement complex of Bitlis massif and the country rocks (paragneiss). There is no study about country rock-derived assimilation and contamination of mafic intrusion magma. But, it is the country- rock which could provide an external sulfur contribution in the Pancarli area and was thought to be a principal mechanism for sulfide saturation. Although it has not been defined to date, if sulfide minerals are present in paragneisses, it will be reasonable to assume the δ34S values of sulfide minerals in a wide range in these paragneisses.

    The low δ34S values (-2.9‰ to -3.5‰; Table 2) of Pancarli sulfides indicate the addition of external sulfur and the contamination which country rock-derived sulfur (e.g., O'okiep Deposit, Maier et al., 2012; Voisey's Bay Deposit, Ripley et al., 2002). Besides, the low sulfur contents of ore samples may also reflect the assimilation of crustal material (e.g., Vaara Deposit; Konnunaho et al., 2013).

  • The basement rock complex of the Bitlis massif, where the Pancarli Ni-Cu sulfide deposit is observed, records at least three metamorphic processes. These are eclogite-facies metamorphism, epidote-amphibolite-facies metamorphism, and subsequent cataclastic metamorphism. Çağatay (1987) reported that the remains of early eclogite-facies metamorphism were observed in some of the amphibolite samples in the field. It is also known that there are eclogites in the high-grade basic complex in the west (e.g., Gabor Hill; Okay et al., 1985) and the east (e.g., Kesandere; Oberhänsli et al., 2013) of mineralization area. These eclogites are associated with augen gneiss and their protoliths are mainly gabbros (e.g., Oberhänsli et al., 2013; Okay et al., 1985; Türkünal, 1980).

    The development of the sulfide and silicate magma phases that form the Pancarli Ni-Cu deposit took place in a tectonically active environment. Multiple processes, such as metamorphic recrystallization, supergene alteration and oxidation, occurred after magmatic crystallization in the mineralizations. The effects of regional metamorphism on the pyrrhotite+pentlandite+ chalcopyrite paragenesis, which forms the Pancarli massive sulfide mineral assemblage, are apparent (e.g., Çağatay, 1987). Almost all the textures and structures of the Pancarli ores are of metamorphic origin and the effects of epidote-amphibolite and dynamic metamorphism can be clearly defined (Figs. 3e, 3f).

    Under conditions of the epidote-amphibolite facies (550 ℃, 5 kb) the Pancarli ores must have largely been a mss with low mechanical strength (e.g., Çağatay, 1987). During this metamorphic-tectonic event, the mechanically weak ores were easily deformed independently of the surrounding host rocks, incorporating blocks of country rocks, and plastically flowing around them. The evidence of this metamorphic event is the intergrowth of ore minerals with garnet, biotite, amphibole and chlorite (Figs. 3i3l). During the retrograde cooling period, pyrrhotite, pentlandite and chalcopyrite exsolved from mss. In the Pancarli ores, the absence of pyrite indicates a low sulfur content, and it emphasizes the supersaturation of pentlandite in the mss during metamorphic recrystallization (e.g., Çağatay, 1987; Durazzo and Taylor, 1982).

    The cataclastic textures (Figs. 3d, 3g, 3h, 3k, 3l) of the Pancarli semi-massive ores were probably developed during dynamo-metamorphic events. Cataclastic metamorphism could have been developed after emplacement and might redistribute sulfide ores or remobilize the sulfides in shear zones (e.g., Schulz et al., 2010). As a result, deformation might change the position of the deposit. Magmatic sulfides show variable ductile behaviours under stress regimes. Ductility decreases from chalcopyrite to pyrrhotite to pentlandite (Barrett et al., 1977). This causes the significant fragmentation of magnetite, ilmenite and pyrrhotite minerals, while chalcopyrite is plastically forced into fractures in the ore and the surrounding wall rocks. This mechanism resulted in the formation of shear zones and might have changed the shape and location of the Pancarli semi-massive ore masses (Figs. 1c, 2). Additionally, related to ores, the undeformed natures of the silicate host rocks are caused by their greater brittleness and durability compared to sulfides.

    The effects of deformation and metamorphism on magmatic sulfide deposits might be observed on many sides. Metamorphism is one of the most important post-magmatic processes to change the mineralogical and chemical composition of the primary magmatic ore and large S/Se variations which are associated with advanced metamorphic events (Queffurus and Barnes, 2015; Maier and Barnes, 1996; Cawthorn and Meyer, 1993). Eckstrand and Hulbert (1987) determined that the mantle has an S/Se ratio between 2 850 and 4 350. The Pancarli Ni-Cu sulfides which have undergone moderate to high-grade (eclogite facies/ epidote-amphibolite facies) metamorphism, have low S/Se ratios (average 1 578). Additionally, the δ34S values (from -2.9‰ to -3.5‰) of semi-massive ore are lower than those of the mantle source (Table 2). Plots of S/Se versus δ34S and their associated contaminants of magmatic Ni-Cu±(PGE) sulfide deposits are given in Fig. 6c. It is determined that the Pancarli samples are located in similar areas as deposits from O'okiep (South Africa), Vammala (Finland), Voisey's Bay (Canada) and they have S/Se and δ34S values that are lower than mantle values. Lower S/Se ratios have been reported in Cu-rich deposits at Curaçá Valley (Brazil) and O'okiep (South Africa) where the effect of high- grade metamorphism was determined (Curaçá Valley, Maier and Barnes, 1999; O'okiep, Cawthorn and Meyer, 1993). These deposits suggest the replacement of primary magmatic sulfide assemblages by metamorphic oxidation and desulfurization during metamorphism and are explained by the abundance of bornite and magnetite (Maier et al., 2012; Maier, 2000; Maier and Barnes, 1999, 1996; Cawthorn and Meyer, 1993). But, the magmatic sulfide assemblages (pyrrhotite+pentlandite+chalcopyrit+pyrite) of Pancarli sulfides did not reflect the destabilization of sulfides and S-loss and the restricted effect of metamorphism. Besides, it is known that some magmatic Ni-Cu-PGE sulfide occurrences in the Grenville Province, Canada which have also undergone high-pressure granulite-facies metamorphism, don't display a strong S-loss in comparison with Se (e.g., Thompson Nickel belt/upper amphibolite-facies metamorphism; Tati and Selebi- Phikwe belt/low amphibolite and granulite facies metamorphism; Queffurus and Barnes, 2015).

    Pancarli sulfides are similar to mss cumulates due to their low Se (average 60.1 ppm), Pt+Pd100%S (average 250 ppb) contents and low R factor. In spite of that, they differ from mss cumulates by having low S/Se ratios. S is moderately incompatible with sulfide minerals which were first crystallized from mss. This incompatibility can change the S/Se ratio between Cu-rich and Fe-rich zones in the Pancarli sulfide ores. The Pancarli sulfides which are rich in pyrrhotite, have lower S/Se values than mantle values. These low values can be derived from mss fractionation.

  • (1) The Pancarli sulfides show clear evidence for post- magmatic processes. All the textures and structures of the ores have metamorphic origins and were affected by moderate-high grade metamorphism and also cataclastic metamorphism. The mineralization subsequently formed various supergene assemblages through weathering. But, magmatic sulfide mineral assemblages (pyrrhotite+pentlandite+chalcopyrite±pyrite) are exempt from bornite and magnetite (e.g., Curaçá Valley, Brazil; O'okiep, South Africa), which were formed by metamorphic oxidation and desulfurization.

    (2) Cu/Ni ratios (0.3–0.9) of Pancarli sulfides contain pyrrhotite dominant Ni-Cu-rich ores and have lower Cu/Ni ratios than Cu-rich deposits.

    (3) Primitive mantle normalized patterns of Pancarli ores are similar to the gabbronorite-hosted sulfides. Strong preferential partitioning of IPGE into mss and subsequent early fractionation of mss from the sulfide liquid explain the IPGE-depleted mantle-normalized patterns.

    (4) The composition of Pancarli sulfide ores is similar to those found in associations with mafic intrusions with tholeiitic compositions due to their low Pt+Pd100%S (average 0.25 ppm) and low S/Se (average 1 578).

    (5) Very high Cu/Pd and high Ni/Pd and Cu/Ir ratios indicate that the Pancarli sulfides were formed by the segregation of sulfides from a magma that was depleted in PGE relative to Ni and Cu.

    (6) Sulfur isotope data suggest that Pancarli sulfide ores are contaminated by country-rock-derived sulfur and external sulfur plays a significant role in the genesis of deposits. The low S contents of the ores may be related to the assimilation of the crustal material.

    (7) Basaltic, relatively Cu-rich and PGE-poor magma was differentiated during the rising through the crust. Sulfide saturation was triggered by contamination and continued to ascent in magma leading to extensive fractionation of the sulfide liquid. Monosulfide solid solution fractionation produced relatively Ni-rich cumulates and Cu-rich residual liquid and formed Pancarli Ni-Cu sulfide ores (e.g., Hondekloof and Eezelsfontein, South Africa; Maier et al., 2012). In different parts of the area, the sulfides which were formed by solidification of Cu-rich residual liquid, have the high probability of occurrence in the veins of the country rocks.

    (8) The Pancarli Ni-Cu sulfide ores represent the only mineralization documented from the Andean magmatic arc setting in SW Asia. This deposit recorded in the region provides an alternative perspective for magmatic Ni-Cu±(PGE) explorations. Thus, it is essential to understand the genesis and mineralogical characteristics of the Pancarli prospect.

  • This study was supported by the General Directorate of Mineral Research and Exploration. We thank Serkan Özkümüş, Mahmut Eroğlu for their help in the field study, Yunus Sönmez for drawing of the figures and Drs. Neşe Oyal and Emin Çifçi for proofreading of this paper. We thank Michael Zientek and Eero Hanski for their constructive criticism and suggestions. We are also, grateful to Drs, Peter Lightfoot, Sarah-Jane Barnes, and Phil D. Sounders for their help on the geochemical calculations. The final publication is available at Springer via https://doi.org/10.1007/s12583-020-1299-5.

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