Iraqi Bulletin of Geology and Mining

This is a review paper on the results of the extensive exploration for radioactive minerals in Iraq, based on previous reports and published papers. The radiometric, geological and geochemical surveys carried out by the Nuclear Geology Department in the Iraqi Atomic Energy Commission since 1966 and later continued by Iraq Geological Survey showed significant radioactivity related to uranium and partly to thorium in the Zagros Suture Zone, mostly related to acidic intrusions of igneous rocks (anorthosite) and associated metamorphic rocks (olivine marble). The Qalat Diza region is the most prominent in this part of Iraq. The Lower Miocene Euphrates Formation is found with remarkable radioactivity along the Hit – Abu Jir (Euphrates) Fault Zone and related to uranium hosted in carbonate rocks in the uppermost part of the formation. The most prominent in this region is Abu Skhair uraniferrous deposit. Numerous areas with anomalous radioactivity are found in the Western and Southern deserts related to Paleogene and Upper Cretaceous phosphorite exposures. Several theories have been postulated to explain the source of syngenetic uranium enrichment in the Euphrates Formation along the Euphrates River, but it is agreed that successive oxidizing and reducing conditions were effective in the epigenetic uranium concentration in these carbonate rocks. Detailed exploration in the Abu Skhair deposit led to the opening of an underground mine and to the development of an efficient uranium extraction process despite the poor grade of the deposit classified as a lean ore. The results obtained so far point to the absence of commercial uranium deposits in Iraq, but the potential of phosphorites, as uranium-bearing rocks, is very significant. Industrial experience at Al-Qaim fertilizers plant proved that uranium can be effectively and commercially extracted as a by-product during the production of phosphate fertilizers.

This is a review paper on zinc-lead deposits and occurrences in northern and northeastern Iraq. These deposits can be genetically classified as low-temperature hydrothermal strata-bound deposits composed of simple sulfide ores of Zn-Pb, commonly associated with barite in the Northern (Ora) Thrust Zone, and as volcano-sedimentary deposits, composed of Zn-Pb-Cu-Fe sulfide ores and Zn-Fe skarns in the Shalair Terrain, NE Iraq. The former deposits are hosted in carbonates of wide age range (Permian – Tertiary), whereas the later (Marabasta) is found in phyllites of the Triassic imbricates. The Zn-Pb mineralizations of Iraq form part of the Alpine Metallogenic Belt extending from the Atlantic Ocean in the west to Iran in the east. They are forming local metallogenic provenances in northern and northeastern Iraq, running parallel to the main fold and thrust belt direction in the north and the Zagros suture in the northeast. Most of them are classified as strata-bound deposits where structure and lithology were the main physical factors controlling the distribution of these deposits. Faults, joints, fractures and permeable strata acted as paths in the transportation of the ore-bearing solutions. Generally, the low-temperature strata-bound deposits of N Iraq are dominated by sphalerite, galena, barite and pyrite with smithsonite, cerussite and goethite as weathering products, while the ore mineralogy in the volcano-sedimentary and skarn deposits in NE Iraq is represented by galena, sphalerite, pyrrhotite, marcasite, arsenopyrite, pentlandite, magnetite, willemite, gahnite and garnet. Limonitic gossans are common phenomena in the oxidized zones of these deposits and occurrences. The mostly studied of these deposits are the Duri-Serguza deposit, described as epigenetic low-temperature strata-bound hydrothermal mineralization, and the Marabasta deposit which was described as a volcano-sedimentary strata-bound deposit, partly developed, by low-grade metamorphism, into a skarn deposit. The Iraqi Zn-Pb-barite deposits and occurrences have not yet been proved to be economic, but they may become a potential source for some metals after further exploration.

Copper mineralization in Iraq stretches along the northeast of Kurdistan Region, hosted by various rock units of the Mawat Ophiolites Complex and the Qandil Series. The mineralization in the Mawat Ophiolite is hosted by mafic igneous and associated quartz veins; meanwhile they are hosted in phyllite and marble in the Sharosh area. Two types of copper mineralization have been recognized by ore microscopy in the previous studies: disseminated and vein filling. Textural relationships among the minerals suggest three stages of mineralization: syngenetic, epigenetic and supergene enrichment. The dominant primary mineralization assemblage is represented by chalcopyrite, sphalerite, galena, pyrite, magnetite, and ilmenite. On the other hand, covellite, hematite, limonite goethite, tenorite, azurite, and malachite represent the supergene enrichment products. The Cu mineralization at the Mawat Ophiolite was formed from magmatic segregation and hydrothermal solution generated from tectonomagmatic activity. Mesothermal fluid system, with low to medium density and dilute NaCl-type, is the source of the mineralization at the Sharosh area. There is a promising potential to locate underground economic concentrations of copper in the Kurdistan Region based upon the evaluation of the wide spread copper supergene minerals at surface which indicate transportation of copper from subsurface sulfide mineralization to the supergene enrichment zone.

The podiform chromitite ore-fields of the Iraqi Kurdistan Region have been investigated by various authors in Mawat, Penjween, Qalander and Rayat localities; all of which are situated in the Iraqi Zagros Suture Zone (NE of Kurdistan Region). They are found in a serpentinized dunite halo hosted within peridotite units that represent the remains of the obducted ophiolite complexes of Iraq. Their original sites of crystallization imply ocean spreading and plate convergence, followed by subsequent re-emplacement by thrusting. Tectonically, the chromitite of Mawat and Penjween ophiolite complexes as well as those of N-Shitna area are considered as supra-subduction type, whereas the chromitites at N-Qalander and Rayat can be interpreted as the products of MORB-like melts. Chromite forms small lensoidal ore bodies in the northeastern part of the ophiolite sequences, surrounded by dunite envelops of variable thickness and dimensions and show transitional boundaries to harzburgite. The chromite occurrences in the Iraqi Zagros Suture Zone resemble the world Cretaceous and Tertiary ophiolite ores with respect to their peridotite host rocks, geochemical characters and podiform shape. The composition of ore-forming chromites in depleted mantle rocks of Kurdistan Region are rather uniform, showing high Cr-number [Cr/ (Cr+Al)]; mostly (0.7 – 0.8), while the values of Mg-number [Mg/ (Mg+Fe2+)] are more variable (0.44 – 0.73). Two textural types of inclusions are distinguished in the chromite: 1) Silicate minerals (mainly serpentine chlorite, amphibole, olivine and clinopyroxene) and 2) Platinum group minerals (mainly laurite RuS2). The perfect euhedral shape and sharp boundaries of the laurite crystals suggest early precipitation from a primitive magma, free growth at high temperature and later entrapment, as laurite inclusions, in the chromian-spinel. The presence of Os-rich inclusion in the chromites of Qalander and Mawat ophiolite complexes suggests that sulfide-undersaturated parent magma was involved in the formation of the chromitites.

The Benavi ironstone deposit is a stratiform iron mineralization within the Jurassic – Cretaceous sequence of the Imbricate Zone (N Iraq). It is composed of several mineral assemblages including iron oxides/ hydroxides (hematite, goethite, limonite and magnetite), sulfides (pyrite and arsenopyrite), carbonates (calcite, siderite and ankerite), silicates (kaolinite, chamosite, and glauconite), quartz and apatite. The main iron minerals are hematite and goethite. Goethite formed as a result of oxidation processes of pyrite, siderite and chamosite under surface weathering. Calcite is the main non-iron mineral in the Benavi ironstones, mostly containing Mg+2 and Fe+2, while siderite and ankerite are minor. Kaolinite and chamosite are the main clay minerals in the ironstone whereas glauconite is trace. Arsenopyrite is found restricted at the base of the Benavi ironstone outcrop, having dark grey color in the field, associated with chamosite, pyrite, apatite and glauconite. Chemical analyses showed that Fe2O3 ranges between 3.28 – 33.9 wt.% with an average of 20.44 wt.%, which is considered as a low-grade ironstone deposit. Replacement of calcareous components by iron minerals is indicated by the very strong negative correlation between CaO and Fe2O3, suggesting epigenetic ore formation by the diagenetic replacements of carbonate rocks. The significant role of diagenetic processes is supported by the negative correlation of CaO with SiO2, Al2O3, P2O5, Co, Ni and Zn.

Two main sedimentary ironstone deposits are investigated in the Western Desert of Iraq; the Ga\'ara and the Hussainiyat deposits. The former is found within the fining-upwards successions of the Ga\'ara Formation (Permocarboniferous) and the latter within the Clastic Unit of the Hussainiyat Formation (Lower Jurassic). Both deposits are continental, deposited in fluvial systems (meandering rivers represented by channels and floodplain deposits with lakes and marshes, with lateritic characteristics. They are mostly pisolitic-oolitic, concretionary, fragmentary and massive in texture and composed of goethite and hematite in association with kaolinite and quartz. The source rocks are highly weathered igneous, metamorphic and older sedimentary rocks of the Arabian Shield, transported by rivers to the depositional sites. The ironstone resources are limited (~80 m.t.) and the grade is low (<40% Fe2O3) with high contents of kaolinite and quartz impurities. Two open pit mines in the Ga\'ara and Hussainiyat deposits have been operating since the early nineties to supply the cement industry in Iraq.

The North Hussainiyat karst bauxite deposits in the Western Desert of Iraq are the only known bauxite resources in Iraq. They were discovered by Iraq Geological Survey in 1990 as few meters to 35 m thick lenses in fossil karsts of various sizes in the Ubaid Formation (early Lower Jurassic), associated with bauxitic kaolinite, kaolinite, flint-clay and quartz sandstone. Some strongly bauxitic profiles reach up to 100 m in thickness. They are pisolitic or massive in texture and composed of boehmite, gibbsite, kaolinite and accessory amounts of anatase. The bauxite lenses are sandwiched between the underlying bottom sandstone and kaolinitic mud rocks and the overlying top clay, which is dominated by kaolinite, quartz and goethite. Geochemical data suggest that the immobile elements such as Al2O3, TiO2, Cr, Zr, and Ni were enriched, while SiO2, Fe2O3, CaO, MgO, Zn, Co, Ba, Mn, Cu and Sr were depleted during the bauxitization process. The results of various studies strongly suggest that these karst bauxite deposits were derived from the kaolinitic clay deposits of the Hussainiyat Formation (late Lower Jurassic). The age of these bauxite deposits is controversial; some authors suggest they are of Early Cretaceous (Aptian – Albian) age whereas others believe they are of Lower – Middle Jurassic age and some authors suggested Paleocene – Eocene age based on their pollens and spores content. High grade bauxites are scarce and most of the deposits are kaolinitic bauxite or bauxitic clays. The reserves were estimated by about 1.28 m.t., distributed in various karst deposits, and have been used in alum production and refractories, with limited laboratory experiments in alumina extraction.

Very large kaolin clay deposits are recorded at the Western Desert of Iraq, in the Ga'ara Formation (Permocarboniferous), Hussainiyat Formation (Lower Jurassic), and Amij Formation (Middle Jurassic) and as flint clay at the base of the Hussainiyat Formation in karsts developed in the Ubaid Formation carbonates. Other exposed formations, such as Zor Hauran Formation (Upper Triassic) incorporate some thick impure kaolinitic horizons. The investigated clays are sedimentary (transported) except the flint clay, which is from in situ alteration of kaolin during bauxitization. The Ga'ara and Hussainiyat kaolin clays are of fluvial origin, Amij kaolin clay of paralic origin and Zor Hauran kaolinitic clay of marine origin.
Kaolinite is the major clay mineral present in these deposits with minor proportions of illite and mixed-layer illite-smectite. The other main admixtures present are quartz, iron oxyhydroxides (mostly goethite) and anatase. Particle size of these deposits ranges from very fine to coarse and their plasticity ranges from super-plastic to moderately plastic, except the Hussainiyat flint clay is non-plastic. Tests on nature of slaking showed that the Ga'ara and Amij kaolin clays disintegrate within 2 – 4 minutes after immersion in water, whereas the Hussainiyat kaolin clays require longer time to disintegrate. Thermal behavior revealed that clays with little impurities sustain higher temperatures and hence physical properties of the test tiles level off at temperatures as high as 1200 °C. On the other hand, clays containing high impurities, such as alkalies and iron oxides, level off at temperatures ranging from 1050 to 1100 °C. Thermal behavior of the silty clay differs from the rest as the linear shrinkage and bulk density show gradual and very slight increase with rise of firing temperature, whereas its open porosity and water absorption decrease in a steeper gradient.
The kaolin clays are classified, for industrial purposes, into two classes: white kaolin clays (Al2O3≥20% and Fe2O3˂3%) and coloured kaolin clays (Al2O3 ≥20% and Fe2O3 ≥3%). Follow-up investigations were carried out on eighteen localities to estimate, verify and categorize the quantity and quality of the kaolin clay deposits. The investigations at the Ga'ara locality resulted in estimating about 960 million tons of white and coloured kaolin clay (categories A, C1 and C2), at the Hussainiyat locality about 311 million tons of white and coloured kaolin clays (categories C1 and C2), at Amij locality 32 million tons of coloured kaolin clays (category C2) and at Northeast Hussainiyat locality about 10 million tons of flint kaolin clay.

Bentonite (senso stricto) is reported in the Mukdadiya Formation (Upper Miocene – Pliocene) in several localities within the Low Folded Zone of Iraq. The bentonites are beleived to have resulted from the alteration of volcanic ash in a fluvial system (lakes) environment. The mineralogy is dominated by Ca-montorillonite and quartz. The major chemical oxides are SiO2, Al2O3, CaO and Fe2O3. The reserves were estimated by about 1.45 million tons, but the Na-activation processes showed little success and most of the reserves were exhausted in the native sulfur purification process at the Mishraq sulfur mines. On the other hand, the Late Maastrichtian – Danian phosphatic succession of the Iraqi Western Desert, include 5 to 6 smectite-rich shale beds, arranged in a transgressive cyclic sequences deposited in an open-subtidal reducing marine environment of the Maastrichtian Digma Formation (Safra Beds) and the Paleocene Akashat Formation (Traifawi Member, Danian). The mineralogy is dominated by smectites, rich in montmorillonite, with subordinate kaolinite, quartz, calcite, apatite, pyrite, palygorskite, chalcedony, opal-CT and organic matter. The dominant major chemical elements are Si, Al, Fe, Mg, Ti, Ca and P. Trace elements, normalized to average shale show high anomalies of Cd, Mo, Cr, Zn, V, U and Ni. The important factors controlling the mineral formation include intense chemical weathering in the source area, normal marine coupled with upwelling currents, precipitation of the authigenic phosphate-shale-silica facies association in a middle to outer system of shallow to deep marine environment within local inner to outer ramp semi-closed basin. Geochemical indices reflect the chemical weathering of the source rocks, which included metamorphic, felsic with a great influx of mafic rocks, and older sedimentary rocks of the Arabian Shield. Weathering, under warm and semi-humid climate, generated low lateritic pedogenic soils at the source area. The reserves were estimated by about 300 million tons in the Digma Formation deposits and about 23 million tons in the Traifawi Member deposits. The former is being mined for the past 25 years and used mainly as a drilling mud.

Numerous palygorskite deposits and showings have been recorded and studied in Iraq. They range in age from Maastrichtian to Holocene, and are found in about 10 different formations. The Iraqi deposits are of sedimentary origin, deposited in marine, lagoonal, lacustrine, fluvial, and pedogenic environments as well as epigenetic fillings of fractures and veins. The majority was formed by the alteration of precursor minerals and to a lesser extent by direct precipitation from solution. The marine black shale deposits of the Upper Cretaceous Safra Beds of the Digma Formation and Lower Paleocene Traifawi Member of the Akashat Formation represent important palygorskite resources in the Western Desert of Iraq. Moreover, palygorskite is the dominant clay mineral in the lagoonal facies of the Tayarat Formation (Upper Cretaceous) in the Southern Desert. Other occurrences in the desert include thin palygorskite-rich claystone horizons in the lagoonal deposits of the Nfayil Formation, (Middle Miocene), and thin lenses of palygorskite-rich claystones in the fluvial deposits of the Zahra Formation (Pliocene – Pleistocene). In the Najaf – Karbala region, palygorskite is the dominant clay mineral in the fluvial and lacustrine mudstones of the Injana Formation (Upper Miocene), and in the sandy claystone lenses in the fluvial deposits of the Dibdibba Formation (Pliocene – Pleistocene). In the northern parts of Iraq, palygorskite veins and fracture-fill deposits are recorded in the sandstones of the Injana Formation, near Jabal Maqlub area, forming one of the most peculiar palygorskite showings in Iraq. In the Shikhan area, another interesting showing was recorded within the fluvial deposits of the Gercus Formation (Eocene). Furthermore, palygorskite forms the main clay mineral in the Holocene deposits of the Ahwar region of the Mesopotamia, as well as in the Recent soils of Iraq in general.

Very large silica sand deposits are documented at the Western Desert of Iraq. These deposits are found in the Ga'ara (Lower Permian), Hussainiyat (Lower Jurassic), Najmah (Upper Jurassic), Nahr Umr (Lower Cretaceous) and Rutbah (Upper Cretaceous) formations. Other exposed formations, such as the Amij Formation (Lower Jurassic) incorporates some thick silica sand horizons but not yet investigated for economic potentiality. Petrographic studies revealed that these silica sands are mostly weakly-cemented quartz-arenite, consisting predominantly of quartz and traces of alkali feldspars, heavy minerals and clay mineral. Some of these deposits are associated with kaolin clays, such as the Ga'ara, Hussainiyat and Amij formations. The Ga'ara and Hussainiyat deposits are of fluvial origin, whereas the Amij, Najmah, Nahr Umr and Rutbah deposits are of fluvio-paralic origin. The X-ray diffractograms revealed that the main associated clay mineral is kaolinite with minor proportions of illite and mixed-layer illite-smectite. The other main admixtures present, beside quartz, are iron oxyhydroxides (mostly goethite) and anatase. Particle size of the silica sand deposits ranges from very fine to coarse but the most common are fine to medium grain size. The shape of the grains is sub-angular to sub-rounded and the Fe2O3 ranges between (0.01 – 1.5) %. Follow-up investigations were carried out on five localities to estimate, verify and categorize the quantity and quality of the silica sand deposits. The investigations resulted in estimating 15.9 million m3 of silica sand on category B, 2.2 million m3 on category C1 and 4456.9 million m3 on category C2.

Gypsum deposits in Iraq are either primary or secondary in origin. The primary deposits were deposited in different geological periods in semi restricted basins, of which, only the gypsum and anhydrite deposits of the Fatha and occasionally the Dhiban formations are exposed on the surface in the areas of Nineva, Kirkuk, Erbil, Sulaimaniyah, Diyala, Wasit and Anbar governorates, forming important resources for cement and plaster industries. The total reserve of the primary gypsum is estimated to be 142 million tons. The secondary gypsum deposits, present as gypcrete or gypsiferous soil, are developed in the upper few meters of the soil cover by different processes leading to enrichment of calcium sulfate in the soil, mainly by the upward migration of the sulfate-rich water by capillary action. The gypsiferous soil is of low gypsum content in the depth of (0 – 25) cm and covers about 39% of Iraqi soil; while at the depth (25 – 150) cm it is of medium gypsum content and covers about 53% of the Iraqi soil. The reserve of the gypsiferous soil is estimated to be 6 million tons. Primary gypsum and gypsiferous soil have produced many problems in Iraq and are potential hazard to the constructions due to possible settlement of the foundations, as well as degrading the agricultural lands in reducing the productivity of the soils and limit the crop types.

Sodium chloride salt deposits in Iraq are found in many forms. It is found as beds of rock salt and in the Quaternary inland salterns and sabkhas. The rock salt layers were deposited in closed basins in various geological times and found in Kurra Chine, Butmah, Adaiyah, Alan, Gotnia, Dhiban and Fatha formations. Another form of the rock salt is the salt plug at Jabal Sanam in southern Iraq, derived from the evaporites of the Hormuz Series and formed by the upward movement of the salt due to pressure of the overlying sediments and low density of the salt. On the other hand, the inland salterns are of Quaternary (Holocene) age and formed by the accumulation of salt derived from salt-bearing beds at depth, such as those in the Fatha formation, seeping upward through fault planes or washed from surrounding salt-bearing formations or saline soils and precipitated by evaporation in local depressions. The main inland salterns are those found in Bowara, Albu-Gharis, Snaisla, Ashgar, Umm Dhiyaba, Al-Tawila and Gzaiz in the Jazera area; Hawija Saltern NE of the Fatha gorge; Shari Saltern near Samarra Khalifa Saltern near Hemrin Mountain, Douz Saltern north of Duz Khurmatu town, Samawa and Umm Al-Tigan salterns in southern Iraq. Sea water of the Arabian Gulf represents another source of sodium chloride in Iraq. The Basrah salt plant is constructed to produce sodium salts from seawater and includes a number of artificial basins, some of them are for increasing the salt concentration by solar evaporation of the seawater and the others for salt precipitation. Sodium chloride is produced by the Ministry of Industry and Minerals for industrial and domestic uses mainly from the Samawa Saltern and from the Basra salt plant. In addition, numerous small-scale salterns are being exploited for this purpose by the private sector. The total reserves of sodium chloride have been estimated in the inland salterns by about 50 m.t., but the potential resources are much larger, especially in the rock-salt deposits.

Sodium sulfate is an evaporate minerals that precipitates from sulfate-rich water and brines mainly in the inland salterns or sabkhas and found naturally as economic deposits in many places in the world. It is used in detergent, glass, paper, sodium silicate and some pharmaceutical industries. In Iraq, the only economic sodium sulfate deposit is found in the Shari Saltern near Samarra City. The sodium sulfate reserve in the Shari Saltern was estimated by about 22 Million tons. Other potential resources of sodium sulfate are found in the salterns of the Jazera area, but they need detailed work to estimate their economic potential. The Shari Saltern is a longitudinal closed basin originated in a subsiding N – S graben, filled with different types of sediments and solutes supplied by the ephemeral streams and seepages. The evaporite minerals found in the Shari Saltern are gypsum, glauberite, thenardite, mirabilite (in winter at low temperatures) and halite with trace amounts of bassanite, natron, trona, huntite, dʼansite and hydrated magnesium bromide. The sequential precipitation of the evaporite minerals in the Shari Saltern starts with gypsum and clay; mirabilite (in winter); gypsum, glauberite and clay; glauberite and clay; glauberite, thenardite and clay then glauberite, thenardite, halite as salt crust over the black mud slurry towards the center of the saltern and the uppermost part of the sediments column. Mirabilite crystalizes as almost pure sodium sulfate with long transparent crystals at low temperatures in winter. While glauberite precipitates by the effect of organic matter and anaerobic bacteria present in the black mud slurry which occupies the lowest part of the saltern. The mineral facies are concentric horizontally and vertically in the Shari Saltern so that the clay and gypsum facies lies below the clay and glauberite layer at depth and around it at the surface. Upward movement of groundwater from the underlying Mukdadiya Formation aquifer, formed seepages through the graben faults. These seepages feed the saltern with sulfate-rich water and precipitate gypsum, which results in a change of water composition to become suitable for glauberite precipitation. The isoconcentration maps of the Shari Saltern show the highest concentration of sodium sulfate is in the lowest part which is occupied by glauberite.