geo Essay

Chapter One


1.1. Preface

Chromite is one of the spinel group minerals, general formula is [(Mg, Fe+2) (Cr, Al, Fe+3)2O4], in generally chromite is a sensitive indicator mineral and used to constrain the petrogenesis of mantle Peridotite (Dick & Bullen, 1984; Arai, 1992; Kapsiotis, 2013). Chromite is the only economic Chromium mineral, different compositional types of chromite will be seen in the nature, such as High-chromium Chromite, High-Iron Chromite and High-Aluminum Chromite. Chromite ore is deposited as Load chromite ore deposit ( Stratiform and Podiform), and Secondary chromite ore deposit (Laterite and placer) (Pedrotti, 2012).

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The rocks that contain more than 90% of chromite with olivine and/or pyroxene are called Chromitite (Al-Chalabi, 2004).

According to (Craig & Vaughan, 1994) Chromium ore that associated with mafic and ultramafic rocks have two modes of occurrence as following:

Stratiform chromite: This type contains over 90% of chromite resources. These deposits consist of lower layers of layered intrusions (lapolites) of Bushweld and Stillwater type, the wall rock of this type varies from Dunite, predotite, Pyroxinite and variety of others, less commonly Gabbroic rock.

The chromite layer thicknesses is started vary from millimeters to more than meters and, extended tens of Kilometer with a rich of Iron. Stratiform chromite is linked with large, mafic – ultramafic layered intrusions will be seen in the continental crust, such as the Bushweld in South Africa (Hatton and Von Gruenewaldt, 1987), Stillwater in Montana (Schulte, et al., 2010) and Great Dyke Zimbabve.

Podiform chromite: These deposits are small magmatic bodies of chromite formed in the Mafic and ultramafic section of ophiolite complex in the oceanic crust. Most podiform chromite deposits are found in dunite or peridotite near the contact of the cumulate and tectonite zones in ophiolites (Mosier, et al., 2012) This type of chromite deposit is formed at the ridge of ophiolitic basin (upper part of mantle) and the alpine type peridotites are frequently more serpentinized than stratiform types (Coleman, 1977).

Most ophiolites peridotite of Alpine type has a chromite podiform that is first time was referred by (Thayer, 1960). Ophiolite peridotite is remaining particle or fragment of Oceanic ridge, that’s the fundamental source of ophiolite group is a mantle predotite and most of the mantle ophiolite are serpentinized by metamorphic foliation (Shirdasht Zadeh, et al., 2017).

Typical stratigraphy of an ophiolite sequence includes upper part of deep-ocean sediments, pillow lavas, sheeted dykes, gabbros, mafic – ultramafic cumulates, and ultramafic tectonites (Duke, 1983).

Podiform ore bodies affected by plastic deformation during forming of pods and also by different degree of tectonic deformation during and after emplacement. (Billor & Gibb, 2002)

Laterite chromite deposits contains (1 – 2 %) of chromite mineral that is derived from the weathering and leaching peridotite host rocks. This type is not commonly of ore grade and it mined in Indonesia and Vietnam (Pedrotti, 2012).

Placer chromite formed from erosion of peridotite host rock. The chromite mineral is relatively dense concentrated as lag deposited on beaches and streams. This type is not economic important and not mined currently worldwide (Pedrotti, 2012).

Chromites can be oversaturated in Mafic and Ultramafic magmas by several petrogenetic processes: magma mixing, assimilation of country rocks and pressure decrease, and crystallized as a secondary mineral or concentrated lenses (Pedrotti, 2012; Al-Chalabi, 2004).

Zagros Suture zone in Northern Iraqi Kurdistan is consist of many overriding nappes composed of ophiolite complexes. The zone is a part of Alpain – Himalaya belt what was formed by collision of Arabian plate with Eurasian plate and closure Tythes sea (Buday, 1980; Jassim & Goff, 2006).

This area in Choman district has not been studied in detail because of complexity of the geology and security problems. Except Choman District Zagroz Suture Zone has been studied in detail by many researchers. In Zagros suture zone, Chromite occurs within ultra-mafic rocks or serpentinized ultramafics , such as Bard izard from Choman and is studied by (Hajialioghli & Moazzen, 2014) Piranshahir closer to choman distrct in the Iranian part; Shetna shekhan from Mergasor (Al-Chalabi, 2004) Mawat and penjwin (Aswad, et al., 2011; Aziz, et al., 2011.a; Mohammad, 2011) in Iranian part such as Kirmanshah (Allahyari, et al., 2010; Saccani, et al., 2013) Sarve-Abad (Allahyari, et al., 2014) and Piranshahr (Ismail, et al., 2009; Hajialioghli & Moazzen, 2014).

Chromite ore are the primary source for both high-chromium, low-aluminum ore, used in metallurgical applications, and refractoriness (Thayer, 1946; Thayer, 1963; Dickey, 1975)

1.2. Location

The studied area is located North East of Iraqi Kurdistan Region / Erbil governorate about 90 km faraway from city center, exactly located between Choman district and Hajiomaran village close to Iranian border (Figure 1). The UTM coordinate from the study area are {(491448; 4056648), (490874; 4065242), (500411; 4063568), (500089; 4059028)}

Figure 1 – 1 Tectonic map of Iraq showing the location of main cities, district and studied area (Sissakian, et al., 2014)

1.3. Aim of Study

This study was carried out to determine and analyze features of chromite formations and host rocks of Choman District. For these; field studies, reflected and transmitted light microscopic investigations and geochemical analysis (XRF, ICP, SEM) were employed.

All the available data were analyzed and discussed to conclude the type and characteristics of chromite and petrogenesis of host rocks.

1.4. Previous studies

1- (Bolton, 1958): He was the first to describe the geology of the area and draws the geological map indicating an extend of distribution of ultramafic bodies and mentioned the podiform chromite in the study area.

2- (Vasiliev & Pentelikov, 1962) A group of Russian geologists published more comprehensive report about the geology of Bard izard hill from Rayat village, their work oriented to an exploration of chromite and sulfides, they modified the earlier map of (Bolton, 1958) by adding detailed structure and stratigraphy description.

3- (Buda & Al-Hashimi, 1977): they studied mineralogy, chemistry and genetic interpretation of chromite podiforms of the Iraqi Zagrous mountain ophiolitic complex, in detail.

4- (Al-Jawadi, 1980): mentioned to the chromite lenses and their chemistry in his study of petrography and geochemistry of serpentine of Bard-i-Zard hill in Rayat, East of Choman district and on the basis of the distribution of major and trace elements, he concluded that the peridotite and associated chromite are of Alpine type.

5- (Ismail, et al., 2009): They studied petrological and geochemical aspects of Chromite and peridotite from the Rayat area / Choman district, Northeastern Iraq. mentioned They concluded that the rocks consist of the Fragments of a Tethyan Ophiolite from the mantle section of ohiolitic complex in the Zagros thrust belt.

6- (Hajialioghli & Moazzen, 2014): Studied Supra-subduction and mid-ocean ridge peridotites from the Piranshahr area, NW Iran. They also mentioned geochemistry and petrology of the ultramafic rocks from the Iranian part in Study area.

7- (Othman & Gloaguen, 2017): Studied the area and mapped, mentioned Serpentine body in the study area by remote sensing methods.

1.4. Geology

The Study area located in the northeastern part of the Arabian plate. Tectonically Iraq is divided into three main tectonic zones (Buday, 1980): the Unfolded, Folded and the Thrust zones. The studied area was located within thrust zone (Figure 2).

Figure 1 – 2 Regional tectonic map of the Kurdistan region in NE Iraq, showing distribution of ophiolites along Zagros Suture Zone. Major tectonic subdivisions after (Aswad, et al., 2014; Fouad, 2015 ).

1.5. Thrust Zone:

This unit is over thrusted on the Arabian plate. It has highly folded and faulted. The thrust zone is composed of metamorphic and igneous rocks at Iraqi Kurdistan, Turkish and Iranian borders. The southwestern and western boundaries of the Suture zone with the Imbricated and High folded zones passes from southeast of Sulaimaniyah (Saisadiq and Nalparez area) to the east (Mawat and Chwarta area) through Qaladize, Qandil, Choman and Mergasor areas.

More recently (Buday, 1987; Jassim & Goff, 2006), proposed the new main tectonic sub-divisions of Thrust zone was divided into three subzones:,

a) Qulqula-Khuakurk zone: It is consisting of deep-water passive margin sediment and southern New-Tethys volcanic (Late Tithonian-Cenomanian), (Jassim & Goff, 2006).

b) Shalair zone: it is a part of Sanandaj- Sirjan zone that is consist of pre-Cretaceous metamorphic basement, metamorphic of volcanic arc and for-arc sequence (Jassim & Goff, 2006).

c) Penjwin-walash zone: It’s a part of main Zagros thrust zone from the north and northeastern of Iraqi Kurdistan border, characterized by allochthonous Thrust sheet (Aswad, 1999; Aziz, 2008; Ali, 2012). The studied area is located within this zone and represents the oceanic domain the central part of the Neo-Tethys and comprise metamorphosed volcanic and sediments of Cretaceous age. Unmetamorphosed Palaeogene fore-arc and volcanic arc rocks that formed during the final closure of Neo-Tethys. Walash volcanic rocks characterized by alkaline magmatism (Ali, 2012).

(Bolton, 1958; Buday, 1980) describe walash volcanic series enclosed in sedimentary rocks lithologically from base to top:

a- Lower Red Bed: Its consist of (Red Mudstone, Cherty Siltstone and Shale).

b- Lower Volcanic: Its consist of (mainly Basic less frequently acidic, lava and frequently pillow lava, and associated pyroclastics. These volcanic occur in the shape of cone.

c- Middle Red Bed: Its consist of (Tuffaceous rock, red Mudstone, Red-Gray Shale, Sandstone, conglomerate, Lenticular and brown Limestone with Paleocen – Eocene fossils.

d- Upper Volcanic: its consist of (Basalt, Sandstone flow, pyroclastic and associated sediments with Eocene fossils), the volcanic are in the shape of cone.

e- Upper red Beds: Its consist of (Red Mudstone, Conglomerate, brown-red siltstone and grey wakes).

According to (Bolton, 1958) the age of walash series is Paleocene – Eocene which is lie over red bed series (Early – Middle Miocene). And it’s the site of basic Laramid intrusion (Buday & Jassim, 1987) with a small mafic and ultramafic dyke of small size intruded in linear shear zone. In generals the study area is effected by regional metamorphism and contact metamorphism found near the intrusive body. Ultramafic intrusions occur in the study area and Chromite bodies occur in the Serpentinized peredotite in the lower part of walash Nappe close to the thrust line over Red Bed series. (Al-Jawadi, 1980) refers that this serpentinized ultramafic body is an Alpine type from the study area.

1.6. Methodology

After preliminary office work and preparation 50 rock and 60? Chromite ore samples were collected in Choman and …. Areas. Geological mapping was not possible due to security problems. However, coordinates and geological features of the sample collection sites were defined. Thin sections and polished sections had been prepared in different laboratories. The sections were investigated by employing both reflected and transmitted light microscopy methods at F?rat University, Geology Department laboratories. On the basis of microscopic studies 13 polished samples were chosen for Scanning Electronic Microscopic (SEM) studies to determine the minerals and inclusions and their compositions in chromite ore. SEM analysis were carried out at F?rat University, Main Laboratories. ( Model ZEISS, EVO, MA10, EHT = 15.00kV,)

For geochemical studies two analyzing methods were employed. X-Ray Florence (XRF) methods are used and 25 samples analyzed at Kurdistan University in Erbil –UKH to determine Major and trace element contents. 25 samples were analyzed using Inductively coupled plasma mass spectrometry (ICP-MS) methods at ACME Canada labs. to determine Major, Trace and rare earth element (REE) contents of the samples.

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