Petrology and Geochemistry of Ophiolitic Host Rocks of Copper Mineralization in Dowlat Abad-Tang e Hana Area ( Neyriz-Iran )

Dowlat Abad-Tang e Hana area is a part of Neyriz ophiolite zone, parallel to the Zagros thrust, SW of Iran. It is also a part of obduction thrusting belt over the edge of the Arabian continent during the late Cretaceous. Petrographic investigation indicates the main host rocks are harzburgite, dunite, pyroxenite, basalt, gabbro and pelagic marine sediments. The main magma type of this ophiolite complex is sub-alkaline. The geochemical data of analysed samples show depletion of Na and K, and enrichment in Ca. Copper mineralization in Dowlat Abad-Tang e Hana is hosted mainly in peridotite rocks. The mineralizations are vein type and are associated as copper carbonate (malachite and less azurite). The average of Cu grade is 2.3 wt%. The geochemical and mineralogical data show that the primary source of copper is ortho-magmatic (from ultra-basic rocks and ferro magnesium minerals), which later influenced by hydrothermal processes.


Introduction
Many researches show that ophiolite complexes are formed in different geotectonic positions [1] [2].The Te-thyan ophiolites in the Alpine-Himalayan orogenic system are exposed along curvilinear suture zones, bounding a series of continental fragments of Gondowana [3].The Jurassic ophiolites in the Alpine-Apennine mountain belt in the west (Figure 1) commonly display MORB geochemistry [4] [5], while that Late Jurassic-Cretaceous ophiolites in the Taurid-Pontide (Turkey), Zagros (Iran), and the Himalayan mountain belts to the east show geochemical affinities characteristic of suprasubduction zone (SSZ) environments [3] [6]- [16].The ophiolitic complexes along Bitlis-Zagros Suture Zone include: Baer-Bassit (Syria), Hataya, Kizildag, and Cilo (Turkey); Kermanshah, Neyriz and Esphandagheh (Iran) [17]- [19].The ophiolites from Iran may be classified into two groups, the less abundant Paleozoic and the more abundant Mesozoic ophiolites [20].Stöcklin (1974) [21] divided Iranian ophiolites into four groups: i) ophiolites of the Zagros; ii) ophiolites (coloured melanges) of north-west Iran; iii) ophiolites and coloured mélanges that mark the boundaries of the Central and Eastern Iranian microcontinent [23]; and iv) ophiolites at the northern foot of the Alborz range [22] [23].Alavi(1991) used information from field relations to classify the Iranian ophiolites into three groups: i) the Proterozoic, which are present as isolated outcrops on the western edge of the central Iranian microcontinent (CIM), ii) the pre Jurassic, which are located within the Alborz Range to the north, and iii) the post-Jurassic, which are the most abundant.Neyriz ophiolite is located in western part of Zagros thrust zone which separates Sanandaj-Sirjan crystalline complexes and Zagros thrust belt [24].The Zagros fold-and-thrust belt extends in a NW-SE direction from the Iranian-Turkish border to Gulf of Oman (Figure 1) [25] [26].This still-active belt results from the collision of the Arabian and Eurasian plates during Cenozoic times and is one of the youngest continental collision belts within the Alpine-Himalayan orogenic system [27] [28].The geodynamic evolution of the Zagros Belt is mainly related to the opening and closure of the Neo-Tethys Oceanic basin.A Late Permian rift episode led to the opening of the Neo-Tethyan Ocean between the Arabian and Iranian plates.The NE-dipping subduction of this oceanic branch beneath the Iranian continental margin [29], started in the Late Jurassic [30].The obduction of the oceanic crust began in the Late Cretaceous and was accompanied by a diachronous emplacement of ophiolites on to the southern.Tethyan passive margin, which occurred during Santonian in Oman and Maastrichtian in NW Zagros [31].The consumption of the Neo-Tethys and the associated continental collision are recorded by the southern Iranian ophiolites (Kermanshah, Neyriz) (Figure 1), which surface along the Main Zagros Thrust Zone [29] [32] [33].In general ophiolite belt along the south-western Zagros main Zagros thrust divided into two parts as ophioliteradiolarites of Kermanshah [34] and Neyriz [35] in the Fars [36].According to spectrometry from biotite-bearing layers in garnet of amphibolite, related to mafic and ultramafic rocks of Neyriz ophiolite, primitive age of ophiolite replacement is middle Jurassic (170 Ma) and metamorphic stage was in last Cretaceous [37].In this paper, we present results on petrology and geochemistry of the Neyriz ophiolite(Dowlat Abad-Tang e Hana).The goal of this paper is to use field data, petrographic analyses and geochemical data, to i) identify different lithologic units of this complex, ii) shed light on the geochemistry and petrogenetic processes of formation, and iii) suggest a possible tectonic environment of formation for this ophiolite.

Geological Setting
Iranian ophiolites are part of the Tethyan ophiolite belt of the Middle East.They join the Middle Eastern and Mediterranean Hellenides-Dinarides ophiolites (such as Turkish, Troodos, Greek and East European) to more easterly Asian ophiolites (such as Pakistani and Tibetan) [33].The Neyriz ophiolite, found in a semi-arid environment along the Zargos thrust Zone, SW Iran, is a well-preserved part of the Tethyan oceanic lithosphere [39].Neyriz ophiolite complex; is located in the north of the Neyriz city; it limits to the eastern Sanandaj-Sirjan zone, and the Bakhtegan Lake to west and the Zagros thrust to south.As structural division, studied area is a part of the high Zagros or crushed zone.An important feature of Zagros crushed zone is severity of deformation and also exposed ophiolite sequence.In the scope of the subject of this study (Dowlat Abad-Tang e Hana) (Figure 2), a series of Neyriz ophiolites observed; Three main ophiolite sections can be seen in this row: frequency of dunite and harzburgite and little chromite which forms the base of this Periodicity.Periodicity of webstrite, lherzolite, clinopyroxenite, olivine-webstrite and a little bit chromite in the middle part of the sequence, and in some articles referred to as the transition region.Section of gabbro is composed of and feldspar-bearing peridotites, from melagabro and norite gabbro, troctolite and anorthosite, respectively in the bottom part and in the middle section ferrogabbros, locogabros and finally in the end is composed of quartz and quartzdiorite and ferodiorite [40]- [43].

Analytical Methods
To evaluate the Eastern range part of Neyriz ophiolite complex (Dowlat Abad-Tang e Hana), after field surveying, the 84 samples selected from host rocks, trenches and wells logs.Thin sections of different rock-types were studied, achieving more information about the petrographic characteristics of the Dowlat Abad-Tang e Hana area.The sections gathered from harzburgite, dunite, chromitite, pyroxenite rock-types.Whole rock major elements of ultramafics and trace elements were determined by X-ray fluorescence (XRF) spectrometer.Also, these samples were analyzed by ICP-OES for REE and minor elements.The measurement results are presented in Table 1 and Table 2.

Petrography
The main host rocks, according to their composition divided into several groups: peridotite, pyroxenite, gabbro, diabase dikes, basaltic rocks, radiolarites, serpentinite [44], small masses of metamorphic rocks, lumps of chromite and magnetite veinlets.The most extensive rocks in Neyriz ophiolite are dunite, harzburgite, pyroxenite, little lherzolite and with norite, gabbro, serpentinite and chromitites often with dunite host rocks and some harzburgite host rocks [45].Serpentinite alteration of peridotite rocks with varying degrees (10% to 90% serpentine) has been made.The most abundant rock in the ophiolite complex of Dowlat Abad-Tang e Hana region is harzburgite [46].Based on abundance of pyroxene, rocks can be divided into two main groups wich are harzburgite (homogeneous) and depleted harzburgite.Harzburgites composed of olivine (55% -75%), orthopyroxene (30% -35%), clinopyroxene (3% -5%) and chrome-bearing spinel (3% -5%).Depleted harzburgite also contain olivine (60% -80%), orthopyroxene (15% -20%), clinopyroxene (1% -3%) and chrome-bearing spinel (less than 2%).It is believed that harzburgite is the result of increasing in degrees of partial melting in the upper mantle and by evolution of rock lherzolite is formed [47].In the course of the deep zones to the upper part of ophiolite column, depleted harzburgite the rocks and metamorphic foliation intensity increased and the mineral alteration in the rocks decreases (Figure 3).In this rocks, spinel often forms amorphous to hypidiomorphic and can be seen both the crystalline and the inclusion in olivine crystals (Figure 4 and Figure 5).Amount of olivine in dunites increases to more than 90%.Orthopyroxene changes between 1-8% and chrome spinel between 1% -2%.Clinopyroxene has been completely removed from this rock.Amorphous olivine crystals, sometimes they are hypidiomorphic and crystallized as aggregation and accumulation (Figure 6(a)).Intensity of serpentinized rocks are often very high and usually less altered olivine crystals settled in the field of lizardite (Figure 6(b)).
Orthopyroxenite rock composed of from 0% -3% olivine, more than 95% orthopyroxene, 0% -2% clinopyroxene and 1% -2% chrome bearing spinel.Orthopyroxene crystal size in orthopyroxenites is much larger than lherzolite and harzburgite and some of them also extend to 3 mm (Figure 7(a)).However, such as the covering rocks, severe deformation can be seen in this rock as perceived texture in orthopyroxene crystal bar orthopyroxene, yet the minerals are in the same shape and size and the boundaries between crystals, have contact with three 120-degree angle which is an indication that orthopyroxenite units have produced from magma [48].Orthopyroxenite is almost weathered and contain serpentine group minerals (not sepentinized).Gabbro is Mainly formed of calcium-rich plagioclase feldspar and augite clinopyroxene.Small amounts of olivine and orthopyroxene may also exist in these rocks.Plagioclase in a gabbro has poly synthetic.Plagioclase crystals can be seen as amorphous to hypidiomorphic, also clinopyroxene can be seen as large and semicrystalline crystals in large scale (Figure 7(b)).

Geochemistry
According to Table 1, MgO content is variable between 17.48 wt% to 39.2 wt%.Al 2 O 3 content changes from 0.26 wt% to 0.58 wt% and CaO changes from 0.29 wt% to 0.99 wt% also CaO content decreases with the rise of serpentinization [49].P 2 O 5 content is subjected to CaO changes, because phosphorus in magma has a close relation to calcium.Fe 2 O 3 , MnO and TiO 2 content decreases in result of increasing the amount of SiO 2 ; this represents pyroxene and olivine crystallization from magma.Since the amount of mantle peridotites, Mg# is considered as an indicator to determine degree of partial melting or mantle depletion [50]; a high proportion of peridotites, Mg# in the region are expressing a high degree of partial melting [51] [52].Given that serpentinization cause MgO values increase and CaO decreases, it is concluded that Neyriz peridotites are similar to magnesium serpentinized peridotites in the Alpine type ophiolites.In the case of partial melting of incompatible elements such as Al, Na and Ti are depleted, while compliant elements such as Cr and Ni do not change to the source.Ti depletion in rocks of the area is environmental characteristics of subduction and boninite ophiolite [53] [54].Neyriz peridotites have lower Al 2 O 3 content than adjacent ophiolite in Turkey and Iraq [55].In addition to the low amount content of Al 2 O 3 , Neyriz ophiolites are also very poor in TiO 2 .One of the resource depleted reasons is forming magma in subduction zones [56].Looking at the chart Cr-Ni (Figure 8) can be concluded that the rocks chemical compositions of the area are within the tholeiitic and komatiietic basalts (rich in Mg).   9) presented the type of magmatic zone as sub-alkaline.Also, the Ti-Cr graph (Figure 10) indicates low-K tholeiite of this kind of magma in the region.Ca-K-Na graph (Figure 11) showing Na and K depletion in rocks and enrichment in Ca.
In this (Figure 11), basaltic rocks that contain calcium and sodium minerals are located in Ca-Na pole.This subject indicates that ophiolite complex is formed in a pre-arc subduction zone [59].In such an environment in the presence of volatile substances by high-grade partial melting, boninitic magnesium-rich magma has formed.The elements such as Mg, Ni and Cr are abundant in the rocks which have produced from this magma.In addition, they are saturated or supersaturated of silica.Being rich in magnesium, abundance of volatiles and satura-    tion of silica may be contributing factors in the spread of silica and chlorite alteration and the presence of abundant silica and quartz masses in the study area.Along with copper mineralization within Dowlat Abad-Tang e Hana, there are high dispersion masses of silica and silicification alteration (Figure 12).
Extention of silica masses of the area cause acidic nature of altered fluid and as a result of destruction condition of silicate and ferromagnesian minerals, listonits are formed.Also these solutions cause copper washed out of primary copper minerals such as chalcopyrite and pyrite or supergene minerals, soluble copper in oxidation zone in presence of carbonate minerals cause to form malachite and azurite, which has spread throughout the region; among metals, copper shows supergene enrichment more significant than the other metals.Based on the ICP-OES analysis (Table 1), average copper cutie in the Dowlat Abad-Tang e Hana range reaches up to 2.3 by weight percentage.
In the other hand, the study area is situated in Zagros fold and thrust belt.From tectonics point of view, it contains orogenic belt of Arabian plate.Based on previous work on the salt and mud diapirism [60]- [74] and neotectonic regime in Iran [75]- [80], Zagros is the most active zone [81]- [101].Then, Alborz [102]- [150] and Central Iran [151]- [168] have been situated in the next orders.

Conclusion
The rocks of the Neyriz ophiolite include both rocks of the mantle and of the crustal suite.The mantle rocks are peridotites (dunite and harzburgite) and serpentinite with minor chromitites.The crustal rocks are cumulate gabbros, diorites, pillow and massive basalts as well as asequence of fossiliferous pelagic sedimentary rocks including umber and radiolarian chert.Harzburgite is observed in the most part of the area (Dowlat Abad-Tang e Hana) and occasionally accompanied with small dunite lenses.The major and trace-element geochemical results indicate that Neyriz ophiolite formed from sub-alkaline magma, tholeiitic-komatiietic type and low in K, Na and Ca-Mg-rich.This type of magmas is typical for subduction zone.Ti depletion in rocks of the area is environmental characteristics of subduction and boninite ophiolite.These characteristics are similar to other Tethyan ophiolites along the seam suture zone-Zagros (Bitlis-Zagros suture zone) are exposed.Mg-rich magma and the abundance of volatiles and saturation of silica made pervasive serpentinization, silica and chlorite alteration in the region.The hydrothermal processes were destructed ferromagnesian minerals of ultramafic host rocks and make fair conditions for Cu-mineralization.Although the Cu-mineralization average is high but it does not seem economic deposit.

Figure 1 .
Figure 1.Simplified tectonic map of the eastern Mediterranean region showing the distribution of the Neotethyan ophiolites and suture zones [38].

Figure 8 .
Figure 8.The composition of the rocks of the studied area in the diagram Ni/Cr [Rock et al. 1990].

Figure 11 .
Figure 11.The ophiolite rocks in the study area in diagram of Na-K-Ca.

Table 2 .
XRF analysis results of Dowlat Abad-Tang e Hana samples.