Copper mineralization and alterations in Gercus Basalt within the Gercus Formation, northern Iraq

Ore Geology Reviews 111 (2019) 102974

Contents lists available at ScienceDirect

Ore Geology Reviews journal homepage: www.elsevier.com/locate/oregeorev

Copper mineralization and alterations in Gercus Basalt within the Gercus Formation, northern Iraq Yawooz A. Kettanaha,b, a b

T

⁎

Department of Applied Geosciences, Faculty of Spatial Planning & Geosciences, University of Duhok, Duhok, Iraq Department of Earth Sciences, Faculty of Graduate Studies, Dalhousie University, Halifax, Canada

ARTICLE INFO

ABSTRACT

Keywords: Gercus Basalt Gercus Formation Copper mineralization Late magmatic hydrothermal alterations

The Gercus Basalt is a recently discovered body within the Gercus Formation, which is exposed on both limbs of the large, double-plunging, NW/SE-trending Bekhair Anticline to the north of Duhok city, northern Iraq. The basalt is mostly basanitic and alkaline in nature, greenish to grayish black in color, and very fine-grained, vesicular, amygdaloidal and microscopically porphyritic in texture. It consists of anorthoclase, diopside, forsterite and accessory titaniferous magnetite, ilmenite and apatite as well as their alteration products. The primary minerals are pervasively altered by calcitization, zeolitization, serpentinization, chloritization, silicification, iddingsitization, martitization, and possibly anorthoclasization. Copper mineralization has taken place as veins and fracture/joint-filling which is mostly observed near the northwestern plunge of the anticline where the basalt attains its maximum thickness of about 16 m. Twelve copper minerals were found within veins and fractures, including primary minerals (bornite, chalcopyrite and an unidentified sulfide – Cu2.3FeS3) and their secondary alteration and replacement products represented by sulfides (covellite, digenite, and chalcocite), native copper, cuprite, carbonates (malachite and azurite), silicate (chrysocolla) and possibly sulfates. The copper minerals are in many cases zonally arranged as spherules where the primary minerals acted as cores, surrounded outward by secondary minerals. Primary copper mineralization is of late magmatic hydrothermal origin, postdating the emplacement, consolidation, deuteric alterations, and fracturing/jointing of the Gercus Basalt; followed by the formation of secondary supergene copper minerals as a result of alteration and replacement of the primary copper sulfides along mineralized veins and fractures/joints due to chemical weathering by meteoric and/or groundwater during Eocene time.

1. Introduction The Gercus Basalt, the host of copper mineralization discussed in this paper, is the first volcanic body of its kind recently discovered in the Middle-Late Eocene Gercus Formation within a large, double-plunging Bekhair Anticlinal Mountain to the north of Duhok city, northern Iraq (Kettanah and Bamarni, 2018) (Figs. 1, 2). This basalt is an exceptional and rare volcanic occurrence within the High Folded Tectonic Zone of Iraq (Fig. 1a). Volcanic bodies have not been previously identified within the Gercus Formation, a widely exposed and well-studied formation in northern Iraq, southeastern Turkey and northwestern Iran. The studied area includes sedimentary formations ranging in age from Late Campanian to Recent (Figs. 1b, 2a). The Gercus Basalt hosting copper mineralization is pervasively altered by processes such as anorthoclasization, calcitization, zeolitization, serpentinization, chloritization, silicification, iddingsitization, martitization, and iron oxidation.

⁎

Metallic mineral occurrences in Iraq are restricted to the northeastern Zagros Suture Zone near the border with Iran, and the northern Thrust Zone near the border with Turkey. Mineralization in the Iraqi Zagros Suture Zone includes Cu, Fe, Cr, Ni, and Mn, and rarely Pb and Zn; meanwhile, those of the Northern Thrust Zone are mostly Pb, Zn, barite, pyrite, siderite and rarely copper (Al-Bassam and Hak, 2006). Most copper mineralization is concentrated within the ophiolitic complexes. Many occurrences are located within the Mawat ophiolite, some 300 kms northeast of the currently studied copper mineralization of the Gercus Basalt. For this reason, the copper mineralization of the Mawat ophiolite has been the focus of many studies since 1948. Previous studies on copper and related base-metal mineralization in Mawat and other nearby ophiolites of N/NE Iraq include those of Williams (1948), Smirnov and Nelidov (1962), Al-Hashimi and Al-Mehaidi (1975), AlBassam (1984, 2013), Kettanah (1991), Al-Bassam and Hak (2006), Musa (2007), Hadi et al. (2010), Yassin et al. (2015), Mirza et al. (2017,

Address: Department of Applied Geosciences, Faculty of Spatial Planning & Geosciences, University of Duhok, Duhok, Iraq. E-mail addresses: [email protected], [email protected].

https://doi.org/10.1016/j.oregeorev.2019.102974 Received 3 November 2018; Received in revised form 4 June 2019; Accepted 11 June 2019 Available online 12 June 2019 0169-1368/ Crown Copyright © 2019 Published by Elsevier B.V. All rights reserved.

Ore Geology Reviews 111 (2019) 102974

Y.A. Kettanah

Fig. 1. (a) Tectonic map of Iraq (compiled by Fouad, 2015); the names in the map were transferred from the source legend by the author, the location of study area is also shown; (b) Geologic map of the study area (the map is simplified from Abdulla, 2013; the inset google map is of the same area; (c) Field view of the Gercus Basalt within the Gercus Formation, exposed in the northeastern limb of the Bekhair Anticline to the north of Duhok City, northern Iraq.

both limbs of the Bekhair Anticlinal Mountain, a prominent, asymmetrical; double plunging dominant structure in the area (Figs. 1b, c; 2a–e). The Bekhair Anticline is not consistent in its characteristics: the eastern part is wider, trending NW/SE, with an eroded core, and surrounded by high dolomitic limestone ridges of the Pila Spi Formation, whereas the western part trends E/W where the dolomitic limestone ridges on both limbs unite, producing a continuous mountain extending westward to the Syrian border near the Dayrabon village (Fig. 1b). Similarly, the dolomitic limestone ridges on both limbs of the eroded core of the southeastern part of Bekhair Anticline unite to produce a single ridge and continue as a mountain terminating southeast of Lalish village (Fig. 1b). The total length of the Bekhair Anticline is about 90 kms. The exposed formations in the eroded core of the anticline are the Bekhme and/or Aqra, Shiranish, Kolosh, Khurmala, Gercus, Avanah, and the Pila Spi formations (Figs. 1b, 2a). The complementary formations exposed on the surrounding synclines are the Fatha, Injana, Mukdadiya, and Bai Hassan formations, as well as Quaternary and Recent sediments (Fig. 1b). The Gercus Formation hosting the Gercus Basalt is one of the most widely exposed formations in northern Iraq and in surrounding parts of Turkey and Iran. It is known as the Gercüş Formation in Turkey (Maxon, 1936; Bolgi, 1961) and as the Kashkan Formation in Iran (Homke et al., 2009). It is of Middle-Late Eocene age (Jassim and Buday, 2006) and characterized by a distinctly reddish color surrounded by other gray- and white-colored formations consisting of clastic rocks dominated by thick clayey siltstone and mudstone beds interbedded with less common, more resistant sandstones and fewer limestone, gypsum and conglomerate beds. The average thickness of the Gercus Formation in the study area is about 560 m (Al-Azzawi and AlHubiti, 2009). The depositional environment of the Gercus Formation is debatable, fluctuating between fluvial to coastal marine interpretations, although it is viewed to be fluvial by most previous studies. According to Jassim and Buday (2006), the red clastics of the Gercus Formation were deposited as molasse sediments in a narrow intermontane basin within a strongly subsiding trough.

2018), Sissakian (2018), and Yara and Mohammad (2018). Many of these studies and others are documented as internal reports of the Iraq Geological Survey (GEPSURV). None of these studies have described economic copper ore bodies in the region. Most of the surface and subsurface copper mineralization is sporadic in nature, occurring as disseminations in mafic (gabbro and basalt) and ultramafic igneous rocks and less commonly in metamorphic rocks, or in hydrothermal quartz veins. According to these studies, chalcopyrite is the main copper mineral in Mawat and other occurrences, in addition to bornite, covellite, chalcocite, malachite, azurite, and chrysocolla. Other associated minerals include pyrite, magnetite, and goethite. A 270 m deep exploration well (Waraz-1), drilled by GEOSURV in the Mawat area and studied by Kettanah (1991), showed that chalcopyrite is the predominant copper mineral filling amygdules in the spilitic basalts. Copper is a transitional chalcophile element with the affinity to unite with sulfur, oxygen and many other elements to form minerals in almost all known mineral classes and can originate from many geological processes, such as magmatic, volcanic, hydrothermal, sedimentary and metamorphic processes. Copper has also been an important metal since historic times for its multiple uses. This article is complementary to a recently published paper by Kettanah and Bamarni (2018) who studied the petrology, mineralogy, geochemistry, and tectonics of the Gercus Basalt. The aim of the current research work is to report on copper mineralization and alterations in the Gercus Basalt, using detailed transmitted- and reflected-light microscopy and electron probe microanalyzer (EPMA), supported by geochemical analyses. The mineral chemistry of primary and secondary minerals, the origin of alterations and copper mineralization, and the mineral paragenesis of the Gercus Basalt are determined and discussed. 2. Geological setting The Gercus Basalt is located within the lower part of the High Folded Zone, a part of the Western Zagros Fold-Thrust Tectonic Zone of Iraq (Fig. 1a). It is exposed in the middle of the Gercus Formation, on 2

Ore Geology Reviews 111 (2019) 102974

Y.A. Kettanah

Fig. 2. (a) Google map of the Bekhair Anticline showing the exposed formations in the eroded core, and also the outline of the Gercus Basalt indicated by numbered placemarks at the northwestern plunge of the anticline; (b) Google map of the Bekhair Anticline showing the placemarks of sampled sections and the outline of Gercus Basalt exposed within the Gercus Formation on both limbs of the anticline and also showing the studied sites of copper mineralization; (c) Field image taken from the southwestern limb looking towards the northeastern limb of the Bekhair Anticline where the Gercus Basalt is well exposed within the red-colored Gercus Formation, and also showing the sites of copper mineralization; (d, e) Field images of the thickest parts of the Cercus Basalt where copper mineralization is best seen and sampled for the current study. P = Pila Spi Fm; A = Avanah Fm; G = Gercus Fm; Kh = Khurmala Fm; K = Kolosh Fm; S = Shiranish Fm; A-B = Aqra or Bekme Fm; See Fig. 1b for details.

The Gercus Basalt is an elongate, lenticular bed-like body located in the middle of Gercus Formation and exposed in both limbs of the Bekhair Anticline (Figs. 1b, c, 2), Its total outcrop length from one limb of the anticline to the other is about 4.5 kms (Fig. 2b). The thickness of basalt varies between 16 m near the northwestern plunge of the host

anticline on the road-cut, and gradually thins at both ends to about a meter before dying out within the northeastern and southwestern limbs of the Bekhair Anticline (Figs. 2b, c). It seems to be a concordant igneous body within the Gercus Formation, with dips and strikes similar to those of the clastic beds of Gercus Formation (Figs. 1b, c, 2). The 3

Ore Geology Reviews 111 (2019) 102974

Y.A. Kettanah

Fig. 3. (a) Field view showing few millimeter-thick, dark-colored, copper mineralized veins with multiple offshoots, all radiating upward from the lower contact of the hosting Gercus Basalt which is characterized by amygdaloidal texture; (b, c) Dark-colored fractures perpendicular to the lower contact of the Gercus Basalt, filled with primary copper sulfides, and joint surfaces stained by secondary supergene copper carbonates (malachite and azurite) and silicate (chrysocolla).

Gercus Basalt is grayish black to pale green in color, very fine-grained, massive, porphyiritic vesicular and amygdaloidal in texture, and pervasively altered and weathered (Figs. 2c–e, 3a, 4a–m). The Gercus Basalt consists essentially of pyroxene (diopside), olivine (forsterite) and feldspar (anorthoclase) as phenocrysts, embedded in a very fine- to fine-grained mixture of these minerals and interstitial volcanic glass as well as few accessory minerals including Ti-magentite, ilmenite, and apatite. These primary minerals are associated with their alteration products. This basalt is dissected by three perpendicular joint systems and is also cut by irregular fractures. Whitish, millimetric irregular fractures traversing the basalt are mostly filled by calcite veinlets, some of which contain copper mineralization (Figs. 3a–c). The amygdules are of various sizes and shapes, whitish in color, and are filled mostly by calcite, zeolite, and silica (Figs. 3a, b, 4a–m). Some of the amygdules

are filled with secondary copper minerals where they are in contact with veins and fractures/joints hosting copper mineralization. A few fractures contain small globules of jet (Fig. 4o). 3. Materials and methods Forty samples were collected from eighteen sampling sites covering the whole length and width of the Gercus Basalt exposed on both limbs of the Bekhair Anticline, in addition to twenty more samples taken from the mineralized veins, fractures/joints, and from the basalt in direct contact with these veins and fractures (Figs. 2, 3). The basalt samples were used in a publication about the petrology and geochemistry of Gercus Basalt (Kettanah and Bamarni, 2018), and were also used in this work to study the details of alterations of the basalt. The mineralized 4

Ore Geology Reviews 111 (2019) 102974

Y.A. Kettanah

samples were used for mineralization studies, including petrographic, mineral chemistry and paragenetic relations. Most mineralized samples were taken from thick sections of the Gercus Basalt near the northwestern plunge of the Bekhair Anticline, close to a paved road where most of the mineralization is visible (Figs. 2a–e, 3). Thin sections were prepared from the forty collected basaltic

samples and forty polished thin- and thick-sections from twenty mineralized samples. For detailed paragaentic studies, more than one polished thin/thick sections were prepared from mineralized samples, cut in different directions. The polished and polished thin-sections were studied by transmitted- and reflected-light microscopy and by electron microprobe analyses (EPMA). All thin- and thick-polished section

(caption on next page) 5

Ore Geology Reviews 111 (2019) 102974

Y.A. Kettanah

Fig. 4. Photomicrographs showing the deuteric alteration products of the primary minerals constituting the Gercus Basalt. (a) General appearance of the Gercus Basalt showings altered olivine (forsterite) and pyroxene (diopside) phenocrysts, and amygdules in a very fine-grained groundmass (TPL); (b) Partially serpentinized forsterite phenocrysts (TXN); (c) Altered euhedral, and zoned forsterite phenocrysts, with fresh center surrounded by serpentine, as well as relatively fresh twinned feldspar (anorthoclase), lath-shaped diopside, and Ti-magnetite in a very fine-grained groundmass (TXN); (d) Completely altered euhedral forsterite to serpentine in the center, surrounded by chlorite, embedded in fine grained groundmass (TPL); (e) Euhedral zoned forsterite phenocrysts, completely altered to iddingsite (center), rimmed by chlorite, and to goethite along a fracture (TPL); (f) Completely altered forsterite crystals to serpentine (center), surrounded by chlorite, and rimmed by goethite, together with many altered, lath-shaped feldspars in a very fine-grained groundmass (TPL); (g) Iddingsite as pseudomorph of forsterite crystal (RXN); (h) Relatively fresh, elongate, twinned diopside phenocryst surrounded by fine-grained groundmass (TXN); (i) Completely altered pyroxene to serpentine and goethite; tiny lath-shaped feldspar aggregates are also pervasively altered (TPL); (j) A pyroxene phenocryst altered to zeolite, calcite, and goethite; and a feldspar crystal altered to calcite within a very fine-grained groundmass (TXN); (k)) A fresh twinned anorthoclase feldspar, and an altered pyroxene in a very fine-grained groundmass (TXN); (l) Scattered pieces of volcanic glass containing tiny spherules of crystalline silica (chalcedony) as its alteration products, surrounded by a network of calcite crystal aggregates (TXN); (m) a Ti-magnetite crystals strongly martitized along their borders (RPL); (n) ilmenite crystals showing lamellar twining (RXN); (o) A piece of jet showing concentric conchoidal fractures. Abbreviations: ilm = ilmenite; RPL = reflected polarized light; RXN = reflected crossed nicols; TPL = transmitted polarized light; TXN = transmitted crossed nicols.

preparations, microscopic studies and EPMA analyses were done at the laboratories of the Department of Earth Sciences, Dalhousie University, Canada. The petrographic and mineralogical studies were conducted on polished thin- and thick-sections using an advanced transmitted-reflected polarized light research microscope (Olympus BX51) equipped with an advanced Olympus DP71-12.8MP digital color camera. Mineral chemistry studies were performed using a fully automated JEOL 8200 electron microprobe equipped with five wavelength spectrometers, operating under the following conditions in wavelength-dispersion mode: accelerating voltage of 15 kV, beam current of 20nA, beam diameter of 1 mm, peak count-time of 20 s and background count-time of 10 s. The standards used were PETJ sanidine (K), PETJ kanganui kaersutite (Ca), PETJ kanganui kaersutite (Ti), PETJ Cr-metal (Cr), TAPH jadeite (Na), TAPH almandine and TAPH kanganui kaersutite (Mg), TAP almandine and TAP sanidine (Al), TAP almandine and TAP sanidine (Si), LIFH pyrolusite (Mn). Chalcopyrite and copper metal standards were used for the analyses of native Cu, pyrrhotite and pyrite for Fe and S, and arsenopyrite for As and Ni.

pseudomorphosely replaced by their alteration products. Serpentine as a common alteration product of forsterite, usually surrounds the fresh remnants (Figs. 4b, c). Most serpentinized or iddingsitized forsterites are surrounded outward by a clinochlore alteration zone and/or rimmed by goethite (Figs. 4d-f); similar goethite is also seen along fractures and cracks (Fig. 4e). Diopside phenocrysts, rarely seen as fresh crystals (Figs. 4c, h), are also altered to serpentine (Figs. 4i-k). Pseudomorphism of forsterite and diopside by their alteration products is evident from the preservation of their perfect euhedral shaped crystals (Figs. 4b-i). EPMA analyses results indicated that serpentine consists of SiO2 (52.7%), MgO (24.9%), FeO (8.7%), CaO (0.4%), Al2O3 (0.1%), K2O (0.1%), and negligible amounts of the other oxides with a total of 87.1%; the remaining 12.9% is expected to be water (Table 1). Clinochlore Clinochlore (diabantite) is the alteration product of forsterite which forms the outer rim of the altered phenocrysts surrounding the serpentinized internal zone that is in turn rimmed by goethite (Figs. 4d–f). Clinochlore also forms the outer rim of many altered zoned forsterite phenocrysts surrounding iddingsitized internal zones (Fig. 4e). EPMA analyses results show that the clinochlore consists of SiO2 (36.9%), MgO (24.1%), FeO (18.1%), Al2O3 (5.8%), CaO (0.6%), TiO2 (0.3%), K2O (0.1%), Cr2O3 (0.1%), and Na2O (0.04%) for a total of 86.1%; the remaining 13.9% is expected to be water (Table 1).

4. Results 4.1. Primary minerals The primary minerals composing the Gercus Basalt are essentially feldspar, pyroxene, and olivine, and accessory minerals including Timagnetite (ulvospinel), ilmenite, and apatite, as well as volcanic glass. Based on EPMA analyses results, the feldspar is anorthoclase (Ab85An2Or13), the pyroxene is diopside (Wo49En40Fs11), whereas the olivine is forsterite (Fo87.2Fa12.6Tp0.2). The mineralogy of Gercus Basalt was studied in detail by Kettanah and Bamarni (2018). These minerals and their alteration products are shown in Figs. 4 and 5.

Iddingsite Iddingsite is generally found as an alteration product pseudomorph after forsterite. Iddingsite has a variable composition because it consists of a mixture of cryptocrystalline goethite with phyllosilicates such as smectite, chlorite, talc, and mica (Delvigne et al., 1979); amorphous phases may also be present (Sun, 1957; Wilshire, 1959). Most forsterite crystals in Gercus Basalt were pseudomorphosed by iddingsite (Figs. 4c–g). These iddingisitized crystals usually contain many alteration products including serpentine in the center, surrounded by chlorite and rimmed by goethite (Figs. 4d–g).

4.2. Alteration products Pervasive alteration of the Gercus Basalt by late magmatic hydrothermal solutions prior to its consolidation, followed by another implse of late magmatic hydrothermal fluids postdating consolidation and jointing/fracturing, and the subsequent chemical weathering by meteoric water, resulted in the formation of secondary minerals. The products of hydrothermal (deuteric) alterations and chemical weathering processes filled the interstices in the groundmass, vesicles, fractures and joints in the Gercus Basalt (Figs. 3a, 4). The mineral chemistry of the secondary minerals was determined by EPMA analyses, in support of the transmitted- and reflected-light microscopic results (Table 1). The characteristics and mineral chemistry of alteration products are described below.

Calcite Calcite is a common mineral filling joints/fractures in Gercus Basalt, mostly < 1 cm in width, which is seen as a three-dimensional network in outcrop. Calcite also occurs within phenocrysts and groundmass and as euhedral crystals associated with analcime, chalcedony, and opaline silica in amygdules. Anorthoclase feldspar, rarely seen in the fresh state (Figs. 4c, k), is mostly altered to calcite (Fig. 4j). Calcite is also an alteration product of diopside (Fig. 4j) and form the matrix of volcanic glass in some cases (Fig. 4l). Calcite is a common mineral in the Gercus Formation hosting the Gercus Basalt which contains few limestone beds and is the common cementing material in the sandstone beds. Chemically, calcite consists of CaO (57%), together with minor amounts of MnO (0.7%) and MgO (0.5%) (Table 1).

Serpentine The Gercus Basalt consists of phenocrysts and amygdules embedded in a very fine-grained groundmass (Figs. 3a, 4a). Most of the forsterite and diopside crystals in the Gercus Basalt are pervasively altered and 6

Ore Geology Reviews 111 (2019) 102974

Y.A. Kettanah

Fig. 5. Photomicrographs of the secondary, amygdule-forming minerals in the Gercus Basalt: (a-b) Ellipsoidal amygdule filled by chalcedony (center) surrounded by opaline silica (or glass) and analcime (middle) and rimmed by an unidentified silicate (zeolite?); (c-d) Kidney-shaped amygdule filled by analcime and tiny spherules of an unidentified silicate (zeolite?); (e-f) Ellipsoidal amygdule filled by analcime (center) and surrounded by an unidentified silicate (zeolite?); (g-h) Spheroidal amygdule filled by radiated, needle-shaped aggregates of an unidentified silicate (zeolite?); (i-j) Ellipsoidal amygdule filled by analcime (center), surrounded by opaline silica (or glass), calcite, and rimmed by an unidentified silicate (zeolite?); (k-l) Ellipsoidal amygdule filled by calcite and surrounded by euhedral analcime crystals, and rimmed by clay?. Photomicrographs a,b,c,g,h,i are taken under transmitted polarized light; Photomicrographs d,e,f,j,k,l are taken under transmitted crossed nicols.

Anorthoclase Unaltered feldspar is rare in the Gercus Basalt (Figs. 4c, k). EPMA analyses of fresh feldspars proved that it is anorthoclase with an endmember formula An1.7Ab85.0Or13.3 (Kettanah and Bamarni, 2018). Anorthoclase is mostly altered to calcite (Fig. 4j). Whether the feldspar was deposited originally as anorthoclase or as a calcic-plagioclase, and later altered to anorthoclase by a process similar to albititization (i.e., anorthoclasization) is difficult to determine. Unlike forsterite and diopside, anorthoclase crystals are commonly small in size and rarely form large phenocrysts.

color and has conchoidal fractures (Fig. 4o). It burns easily with an odor of coal/oil. Jet probably formed from organic material such as plant fragments which were possibly derived from the surrounding sediments to be trapped within joints/fractures, and later transformed to jet by the effect of pressure and heat during the cooling stages of the basaltic body. 4.3. Amygdule-forming minerals The Gercus Basalt is rich in amygdules filled by secondary alteration products (Figs. 3a, 5a-l). However, some of the minerals formed by deuteric alterations such as serpentine, chlorite, and iddingsite were not found in amygdules (Figs. 4, 5) The materials observed in amygdules are analcime, calcite, silica phases (chalcedony and opaline silica, and possibly volcanic glass) and clays as well as an unknown fibrous radiating mineral which is possibly a zeolite (Fig. 5).

Fe-oxides Goethite, an important alteration product of forsterite and diopside, is seen as thin fracture fillings (Fig. 4e), as rims around the altered forsterite and diopside phenocrysts (Figs. 4f, i), and within the iddingsitized crystals (Fig. 4g). EPMA analyses results indicate that goethite consists of FeO (82.6%), SiO2 (3.1%), MgO (1.3%) and minor amounts of other oxides, bringing the total to 88.14%. The remainder is assumed to be water (Table 1).

Analcime Analcime is a common zeolite, mostly filling amygdules associated with calcite, chalcedony, amorphous (opaline) silica, and an unidentified fibrous radiating silicate mineral (Figs. 5a-l). These minerals are mostly arranged zonally within the amygdules, with chalcedony in the center, followed outward by mixed opaline silica and/or calcite, and then the fibrous radiating silicate mineral (Figs. 5a, b). Analcime mostly forms euhedral polygonal crystals. EPMA analyses results show that it consist of SiO2 (59.5%), Al2O3 (22.5%), Na2O (9.2%) and probably water, with a formula of Na0.64Al0.96Si2.12O6.(H2O) (Table 1).

Martite Martite is a common alteration product of Ti-magnetite (ulvospinel), the most common accessory mineral in the Gercus Basalt. Martitization ranges from partial to pervasive (Fig. 4m). Ilmenite also occurs as scattered tiny accessory mineral in the Gercus Basalt (Fig. 4n). Both minerals are mostly < 100 µm in dimensions. Jet

Jet has been found as small globules, up to 2 cm in dimensions, filling pockets within fracture intersections in basalt. It is pitch black in

Unidentified silicate mineral (zeolite?) This mineral is common and consists of needle-shaped crystal 7

Ore Geology Reviews 111 (2019) 102974

Y.A. Kettanah

Table 1 Mineral chemistry of the secondary minerals formed by alteration of the Gercus Basalt. Mineral No. of analysis ► Oxide % ▾ SiO2 TiO2 Al2O3 Cr2O3 FeOt MnO MgO CaO Na2O K2O BaO SO3 SrO P2O5 TOTAL % # Oxygens Si Ti Al Cr Fe+2 Mn Mg Ca Na K Ba S Sr P TOTAL

Analcime

3.72

Unidentified silicate Clinochlore (Diabantite)

Serpentine

Calcite

Goethite

Barite

9

6

3

7

2

1

1

58.49 0.00 22.51 0.00 0.00 0.00 0.00 0.00 9.15 0.03 – – – – 90.20

45.81 0.00 6.09 0.00 3.08 0.00 23.51 1.49 0.05 0.17 – – – – 80.20

52.68 0.01 0.13 0.03 8.73 0.02 24.92 0.39 0.06 0.10 – – – – 87.09

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.99 0.00 0.00 63.16 33.51 2.34 – 100.00

0.3226 0.0000 0.0506 0.0000 0.0182 0.0000 0.2466 0.0112 0.0007 0.0016 – – – – 0.65

0.00 0.00 0.00 0.00 0.06 0.67 0.50 56.97 0.01 0.02 – – – – 58.22 4 0.1787 0.0408 0.0000 0.0000 3.5298 0.0008 0.0398 0.0047 0.0058 0.0068 – – – –

3.06 0.16 0.34 0.30 82.59 0.13 1.30 0.17 0.03 0.08 – – – – 88.14

2.1183 0.0000 0.9607 0.0000 0.0000 0.0000 0.0002 0.0000 0.6426 0.0012 – – – –

36.94 0.27 5.81 0.05 18.12 0.13 24.09 0.60 0.04 0.07 – – – – 86.13 28 7.5740 0.0420 1.4028 0.0084 3.1114 0.0235 7.3651 0.1310 0.0157 0.0190 – – – – 19.69

0.928 – – – – – – – – – – – – –

– – – – – – – – – – – – –

2.0990 0.0003 0.0063 0.0009 0.2904 0.0008 1.4783 0.0167 0.0046 0.0050 – – – –

aggregates, radially arranged as amygdules, or as an outer layer of the amygdules enveloping other minerals such as analcime, calcite, opaline silica and chalcedony (Figs. 5a-j). EPMA analyses showed that it consists of SiO2 (48.8%), MgO (23.1%), Al2O3 (6.1%), FeO (3.1%), CaO (1.5%), K2O (0.17%), and Na2O (0.05%), for a total of 80.2%; the rest (∼20%) is expected to be water (Table 1). Petrographically, it is colorless under plane polarized light, with grey, white and yellow interference colors under crossed polars, indicating an anisotropic behavior resembling chalcedony (Figs. 5g, h). This mineral has the appearance of fibrous radiating zeolite although it has different chemistry than the other common zeolites found in basaltic rocks.

4.4. Copper mineralization Copper mineralization in the Gercus Basalt is easily recognized from bluish green colors on exposed joint/fracture surfaces, representing azuritization and malachitization of black- to dark brown-colored primary copper minerals. (Figs. 3a–c). Transmitted- and reflected-light microscopic studies, complemented by EPMA analyses for forty thinand polished-thick sections of samples taken from the mineralized veins, joint/fracture, and their contact zones within the Gercus Basalts revealed the existence of twelve copper minerals (Figs. 6–10). These minerals include three primary sulfides (bornite, chalcopyrite, and an unknown mineral) (Figs. 6a–h), and nine secondary minerals (Figs. 7–10), The secondary supergene copper minerals, formed as a result of alteration and replacement of primary copper minerals, are composed of sulfides (chalcocite, digenite, and covellite), native copper, oxide (cuprite), carbonates (malachite and azurite), silicate (chrysocolla) and possibly a sulfate. Some of the secondary copper minerals can easily be seen on the surface of the exposed basalt along fractures and joints (Figs. 3b, c). The detailed microscopic features of these secondary minerals in relation to the associated primary minerals are shown in Figs. 6–10. These secondary minerals are mostly zonally arranged around the primary minerals or around themselves (Figs. 6–10). The detailed microscopic features of copper minerals and their mineral chemistry are given below.

Amorphous silica Amorphous opaline silica and chalcedony has been found within amygdules. Chalcedony forms the center of some amygdules (Figs. 5a, b), whereas opaline silica which could be the altered volcanic glass, is intergrown with analcime (Figs. 5i, j). Volcanic glass is found as interstitial material in the groundmass and occasionally as scattered pieces associated with calcite (Fig. 4l); the volcanic glass contains tiny spherules of silica, possibly as its alteration product. Other minerals Clay minerals also exist as deuteric and chemical weathering alteration products of the dominant minerals including anorthoclase and diopside. Some amygdules filled by calcite and analcime are surrounded by a thin rim which is possibly a clay mineral (Figs. 5k, l). Barite is rare and possibly secondary in origin; it has been detected only by EPMA analyses and is found to consists of BaO (63.2%), SO3 (33.5%), and SrO (2.3%) with a typical formula of BaSO4 (Table 1). Barite was probably formed with calcite by hydrothermal solutions.

4.4.1. Primary (hypogene) copper minerals Bornite, chalcopyrite, and an unknown mineral (Cu2.3FeS3) are coeval primary copper sulfides (Figs. 6b–h). Bornite and chalcopyrite are commonly associated and/or intergrown together (Figs. 6c–g) without having contact with the unknown sulfide mineral (Fig. 6h). The coeval deposition of bornite and chalcopyrite is indicated from their lamellar intergrowth; in some cases, late chalcopyrite and covellite partially replaced bornite (Figs. 6d–g). Chalcopyrite was subsequently 8

Ore Geology Reviews 111 (2019) 102974

Y.A. Kettanah

Fig. 6. Hand specimen view (a) and photomicrographs (b to h) taken under reflected polarized light for the primary and some associated secondary supergene copper minerals in Gercus Basalt. (a) Photograph of a hand specimen taken from the mineralized fractures showing primary minerals (bornite and chalcopyrite) surrounded by secondary minerals (malachite, azurite, and chrysocolla); (b) Primary chalcopyrite and its secondary replacement products (covellite and digenite) introduced to basalt along fractures surrounding the associated gangue minerals, mostly calcite; (c) Primary chalcopyrite and bornite and their alteration product (covellite) scattered within the gangue minerals along a fracture cutting the basalt; (d to f) Cogenetic intergrowth of chalcopyrite and bornite where bornite is also partially replaced by chalcopyrite and covellite; (g) The unidentified copper sulfide (Cu2.3FeS3), surrounded and partially replaced along microfracture network by its alteration products, covellite and digenite; (h) The unidentified copper sulfide (Cu2.3FeS3), surrounded and replaced along microfracture network by cuprite, goethite, and covellite. Abbreviations: cp = chalcopyrite; bn = bornite; cv = covellite; dig = digenite; mal = malachite; az = azurite; chry = chrysocolla; ca = calcite.

altered and replaced by secondary supergene copper sulfides, including digenite (Figs. 7a–d, 8a, b), covellite (Figs. 7e, 8a, b, 9a), and chalcocite (Fig. 7h), and by native copper (Figs. 8a, b). EPMA analyses showed that bornite contains 63.3% Cu, 11.0% Fe, 25.3% S and traces of Pb, whereas chalcopyrite consists of 34.1% Cu, 28.7% Fe, 33.2% S and trace amounts of Pb (Table 2). An unknown copper sulfide forms the center of many zonally arranged secondary supergene copper minerals (Figs. 6h, 10a, b). This mineral is different from chalcopyrite optically as it has paler whitish color rather than the normal yellow color of chalcopyrite under reflected polarized light. It is cracked and replaced along cracks and is also rimmed by digenite or covellite (Fig. 6h). Chemically, it consists of 48.5% Cu, 18.4% Fe and 31.2% S, corresponding to a formula of C2.3FeS3 or Cu7Fe3S9 (Table 2).

4.4.2. Secondary (supergene) copper minerals Sulfides. Covellite, digenite and chalcocite are common secondary supergene copper minerals closely associated with each other as alteration and replacement products of the primary sulfides (Figs. 6–10; Table 2). They were formed coevally and show replacement relation among themselves. Covellite replaces bornite (Figs. 6d–f, 7b), the unknown sulfide (Cu2.3FeS3) (Fig. 6h), chalcopyrite (Figs. 6b, 7a, d, e, 8a, b, 9a), and digenite (Figs. 6h, 7d, e, 8a, b), and is replaced by cuprite (Figs. 7e, g, 9a, 10a, b). Covellite is closely associated with native copper, suggesting their coeval formation (Figs. 8c, d). Covellite contains 70.3% Cu and 29.8% S (Table 2). Digenite replaces the unidentified sulfide (Figs. 6h, 10), bornite (Fig. 7b), chalcopyrite (Figs. 7a, c, d, e, 8a, b), and covellite (Figs. 7d, f). 9

Ore Geology Reviews 111 (2019) 102974

Y.A. Kettanah

Fig. 7. Photomicrographs showing alteration and replacement of primary chalcopyrite and bornite by secondary supergene copper minerals. (a) Chalcopyrite introduced to Gercus Basalt along fractures and spread as veinlets surrounding calcite crystals, which was later altered and replaced by secondary minerals such as covellite, digenite, and native copper (RPL); (b) Bornite altered and replaced by covellite and digenite (RPL); (c) Chalcopyrite replaced along micro-fractures and rimmed by digenite, surrounded by malachite and calcite (RPL); (d) chalcopyrite altered and replaced by digenite, covellite, and a black-colored mineral, surrounded by malachite and calcite (RPL); (e) pervasively altered chalcopyrite and replaced by covellite which was in turn replaced inward by digenite and outward by cuprite (RPL); (f) Chalcopyrite pervasively replaced by chalcocite and digenite, surrounded by calcite (RPL); (g) Covellite altered and replaced by digenite, surrounded by malachite (RXN); (h) Covellite altered and replaced inward by cuprite and surrounded by malachite (RXN); (i) Chalcocite replacing covellite and is replaced by cuprite, surrounded by malachite; few tiny primary Ti-magnetite crystals are scattered as accessory minerals in the groundmass of basalt. (RPL). Abbreviations: cp = chalcopyrite; bn = bornite; cv = covellite; dig = digenite; cc = chalcocite; Cu = native copper; cup = cuprite; mal = malachite; cal = calcite; Ti-mg = titaniferous magnetite; RPL = reflected polarized light; RXN = reflected crossed nicols.

It contains 77.3% Cu, 22% S and traces of Pb (Table 2). Chalcocite replaces chalcopyrite and digenite (Fig. 7h) and covellite (Fig. 7i) and is replaced by cuprite (Fig. 7i). It contains 80.5% Cu, 20.3% S, and traces of Fe and Cd (Table 2).

(Figs. 9b, c). EPMA analyses results showed that it contains 85.8% Cu (Table 2). Carbonates. Malachite and azurite are two common minerals which stain basalt outcrops (Figs. 3b, c) and coexist together (Figs. 9c, f). Malachite, with its distinct green color, exists in massive forms, as zoned spheroids (Fig. 9d), as amygdule (Fig. 9h), and as needle-shaped radiating crystalline aggregates around spheroids; it also replaces calcite along cleavage planes (Fig. 9e). Azurite, with its distinct deepblue color, coexists with malachite (Figs. 6a, b, 9c, f) and occasionally form perfect prismatic crystals (Fig. 9g). EPMA analyses results show that the copper contents of malachite and azurite are 58.7% and 50.1%, respectively (Table 2).

Native copper. Native copper is common as small scattered grains, occasionally associated with chalcopyrite, covellite, and digenite. It seems to be an alteration product of chalcopyrite (Figs. 8a, b), and formed coevally with covellite (Figs. 8c, d) and digenite (Figs. 8a, b). However, native copper commonly exists as a group of tiny, closely separated specks, isolated from the primary copper minerals, and mostly surrounded by a rim of cuprite as its oxidation product (Figs. 8c–f). The native copper specks are either partially or completely cupritized. EPMA analyses results showed that the native copper contains 96.7% Cu, with traces of Pb, Au, and Cd (Table 2).

Silicate and sulfate?. Chrysocolla, the only copper silicate associated with copper carbonates (Figs. 6a, 9f), takes the shape of flower-like spheroids (Fig. 9i); it contains 28.6% Cu. An unknown mineral, possibly another copper sulfate, containing 56.4% Cu and 21.7% S, was also detected by EPMA (Table 2); this mineral contains the same amount of copper as brochantite, a hydrous copper sulfate with a formula of Cu4(SO4)(OH)6, but with a different sulfur content.

Oxide. Cuprite, the only copper oxide found is characterized by its distinct deep red internal reflections masking the original color under reflected crossed nicols. It is the oxidation product of primary sulfides, replacing and forming a rim around native copper (Figs. 8c–f) and secondary copper sulfides (Figs. 7e, g–i). Cuprite is also closely associated with malachite and/or azurite in the form of spheroids 10

Ore Geology Reviews 111 (2019) 102974

Y.A. Kettanah

Fig. 8. Photomicrographs showing the relationship between native copper and the other supergene alteration products of chalcopyrite; (a, b) Chalcopyrite extensively altered and replaced by covellite, digenite and native copper, surrounded by malachite and calcite (RPL); (c, d) Native copper altered and replaced by cuprite, closely associated with covellite, and surrounded by malachite (RPL; RXN); (e) Native copper, partially altered and replaced by cuprite, and surrounded by calcite and malachite; (f) Native copper, partially replaced by cuprite, and surrounded by malachite and azurite (RPL). Abbreviations: cp = chalcopyrite; cv = covellite; dig = digenite; Cu = native copper; cup = cuprite; mal = malachite; az = azurite; cal = calcite; RPL = reflected polarized light; RXN = reflected crossed nicols.

5. Discussion

Olivine, pyroxene, feldspar, and volcanic glass constituting the Gercus Basalt are pervasively altered, most probably under the effect of two late magmatic hydrothermal alterations, prior to and after the consolidation of the lava flow. The deuteric secondary minerals most probably formed by such hydrothermal processes include iddingsite, chlorite, serpentine, calcite, zeolite, goethite, martite, anorthoclase, amorphous silica, and clay minerals which are described below (Figs. 4, 5). According to Hekinian (1982), the best criteria for recognizing deuterically altered minerals is the pseudomorphism of primary minerals which is clearly the case in Gercus Basalt. Chemical weathering played an important role in the overall pervasive alteration of the Gercus Basalt. Olivine can easily alter under both hydrothermal conditions and during chemical weathering (Smith et al., 1987). Pyroxene is the other mineral which can be altered under both conditions. Volcanic glass alters and decomposes by weathering, diagenesis, and hydrothermally, more readily than nearly all associated mineral phases in pyroclastic rocks, because it is thermodynamically unstable (Fisher and Schmincke, 1984). The order of susceptibility of primary phases in basalts during chemical weathering is olivine > glass > plagioclase > clinopyroxene > Ti-Fe oxide (Nesbitt and Wilson, 1992). Olivine is the most rapidly weathered primary mineral to iddingsite, followed by glass to allophane and smectite, plagioclase to kaolinite, and clinopyroxene to clay, chlorite, and limonite (Nesbitt and Wilson, 1992). Zeolite and bentonite deposits largely form by reaction of pyroclastic material with pore water (Grim and Giiven, 1978). The zeolites detected in the Gercus Basalt were probably formed by the

5.1. Origin of alterations Following the extrusion of the basaltic flow and prior to its final consolidation and jointing/fracturing, the hydrothermal magmatic solutions left over from the consolidating lava, caused alteration of the primary basalt-forming minerals including olivine, pyroxene, feldspar and the accessory minerals. These late magmatic hydrothermal alterations can also be considered deuteric alterations. Deuteric alteration is defined as a low-temperature magmatic alteration related to the solidification of a melt which is restricted to reactions involving changes in primary mineral phases during magmatic crystallization process (Hekinian, 1982). The early-formed minerals by this process in the presence of gas, water, and heat could react with the residual magmatic melt and form low-temperature phases. After the complete solidification of the Gercus Basalt, followed by jointing and fracturing during the cooling stage of the lava, another magmatic impulse took place introducing late residual magmatic hydrothermal solutions, most probably from the same magma source which previously created the Gercus Basalt. These late hydrothermal solutions introduced primary copper mineralization filling veins and fractures, and causing further hydrothermal alterations to the Gercus Basalt. Chemical weathering by meteoric and/or groundwaters succeeded these late hydrothermal magmatic events causing pervasive alteration of the whole body of the Gercus Basalt. 11

Ore Geology Reviews 111 (2019) 102974

Y.A. Kettanah

Fig. 9. Photomicrographs of the secondary supergene copper minerals in the Gercus Basalt. (a) Chalcopyrite zonally surrounded and replaced by its alteration products covellite, cuprite and malachite (RXN); (b) A spheroid filled by covellite in the center and surrounded by malachite, and cuprite (RXN); (c) A spheroid filled by coevally deposited cuprite, malachite and azurite (RXN); (d) A zonally grown malachite spheroid (RXN); (e) Malachite replacing calcite along cleavage planes (RPL); (f) Intergrown malachite, azurite, and chrysocolla (RPL); (g) A perfect, euhedral prismatic crystal of azurite (RPL); (h) An amygdule filled by malachite, surrounded by calcite and rimmed by goethite (RXN); (i) A spheroid of chrysocolla grown in flower-like pattern where the central mass is radially sounded by smaller crystals (BSE). Abbreviations: cp = chalcopyrite; cv = covellite; cup = cuprite; mal = malachite; az = azurite; chry = chrysocolla; go = goethite; cal = calcite; RPL = reflected polarized light; RXN = reflected crossed nicols; BSE = back-scattered electron microprobe image.

alteration of volcanic glass (Figs. 4l, 5). The effect of chemical weathering is distinc at the upper part of the Gercus Basalt and within few internal horizons, as well as at both ends where the thickness of the basaltic body diminishes before dying out. The extremely weathered rocks of the Gercus Basalt have turned to crumbled material which can be crushed by bare hand. The effect of both hydrothermal actions and that of chemical weathering was so intense which resulted in pervasive alteration of the Gercus Basalt. Both the phenocrysts and the groundmass materials were altered and replaced to various extents by the newly formed secondary minerals including serpentine, chlorite, iddingsite, goethite, zeolites, silica phases and clays. Many of these alteration products filled the vesicles and produced amygdules, an important characteristic of the Gercus Basalt (Figs. 3a, 5a–l). The minerals or the amorphous compounds formed at the end of crystallization of basaltic lava flows as a result of hydrothermal alteration processes are located in the interstices of the groundmass, in amygdules, vugs, vesicles, or lining the walls of veins and/or cavities (Hekinian, 1982; Mas et al., 2006; Markusson and Stefansson, 2011). However, the minerals formed by hydrothermal deuteric alterations of olivine and pyroxene, including serpentine, chlorite, and iddingsite were not found in the amygdules of the Gercus Basalt (Fig. 5). This mean that serpentine, chlorite, and iddingsite which were formed as pseudomorphs of olivine and pyroxene, possibly remained structurally intact and have not been remobilized to move and fill the vesicles. The other possible explanation is that most of the

amygdules were formed as a result of chemical weathering rather than the hydrothermal deuteric alterations of the primary basaltic minerals. The minerals found in the amygdules of Gercus Basalt are analcime, calcite, silica phases (chalcedony, opaline silica, and volcanic glass) and clays (possibly kaolinite and smectite) as well as an unknown fibrous radiating mineral, possibly a zeolite. The Gercus Formation hosting the Gercus Basalt contains few beds of limestone and evaporites (gypsum, anhydrite, and halite), as well as calcite-cemented sandstones and siltstones. A similar mineral assemblage has been reported in the North Mountain Basalt of Nova Scotia, eastern Canada, where a variety of zeolites occur as amygdules (PePiper, 2000). Most of the amygdules in Gercus Basalt contain calcite, analcime, and silica (opaline silica and/or chalcedony). Analcime, possibly the only zeolite in these amygdules, suggests that the late hydrothermal solutions had sufficient alkalinity to produce analcime and other associated minerals are the common amygdule-forming minerals in Gercus Basalt. 5.2. Origin of copper mineralization The common association of copper with basaltic rocks led Alexander and Thomas (2011) to state that wherever there is an occurrence of massive basaltic lavas, the possibility of finding an associated native copper deposit cannot be ruled out. The massive continental Deccan basalts in India (Alexander and Thomas, 2011), the Keweenaw basalts 12

Ore Geology Reviews 111 (2019) 102974

Y.A. Kettanah

Fig. 10. (a and b) Zonally arranged secondary supergene copper minerals grown around the unknown primary sulfide (Cu2.3FeS3) which was altered and partially replaced by digenite (dig), and concentrically surrounded outward by an unknown isotropic mineral ring (?), followed by malachite (mal), limonite (lim), covellite (cv), and cuprite (cup); these zoned minerals are embedded in a mixture of analcime (an), and malachite (mal)-azurite (az)-chrysocolla (chry) and calcite (cal). (a) Reflected polarized light; (b) Reflected crossed nicols.

of northern Michigan in USA (Bornhorst et al., 1988; Bornhorst and Barron, 2011; Bornhorst et al., 2013; Bornhorst and Mathur, 2017; Brown, 1965, 2006, 2008, 2014, 2018), and the Emeishan basalts in China (Li et al., 2005) are three important examples of flood basalts hosting native copper deposits, with less important associated copperbearing minerals such as sulfides, oxides and carbonates of copper. Important native copper mineralization associated with the Volhyn flood basalt province was reported in Belarus, Poland, Ukraine and Moldova (Emetz et al., 2004). Native copper also occurs in the Paraná

volcanic province of Brazil (Pinto et al., 2011; Arena et al., 2014; Baggio et al., 2018). Many copper-hosting basalts are characterized by red colorations attributed to oxidation of the subareally deposited basalt (e.g., Keweenaw basalt, USA) or to spilitization of submarine basalt (e.g., Mont Alexandre, Canada; Cabral and Beaudoin, 2007). The case of Keweenaw basalt has also been attributed to oxidation by deep circulating meteoric water combined with metamorphogenic leaching of copper from deeply buried basalts (Brown, 2006). The Gercus Basalt 13

CuS

Cu9S5

Cu2S

99.74 100 96.12 100 98.23 100 97.09 100 101.26 100 99.62 100 100.52 100 86.08 59.57 50.56 29.22 79.08

5.2.1. Primary (hypogene) copper mineralization Copper mineralization in the Gercus Basalt started with coeval deposition of primary sulfides comprising bornite, chalcopyrite and an unknown mineral Cu2.3FeS3. These primary minerals were emplaced within the lately formed veins and fracture systems (Figs. 3a–c). One of the following three possible origins can be suggested and discussed for the primary copper mineralization in Gercus Basalt: (1) direct magmatic, (2) late hydrothermal magmatic, and (3) remobilization from the host Gercus Basalt and/or the surrounding Gercus Formation.

0.04 0.017 0 0 0.06 0.024 0.03 0.016 0.16 0.075 0.03 0.015 0.05 0.021 0.05 0.01 0 0.04 0

(1) The direct magmatic origin for the primary copper mineralization in Gercus Basalt can be excluded because the WDS electron microprobe analyses and the EDS back-scattered images and elemental maps conducted on the essential and accessory minerals constituents of the Gercus Basalt, including their alteration products in both phenocrysts and the groundmass, did not show any copperbearing mineral inclusions or any detectable traces of copper in their crystal structures. Furthermore, the primary copper mineralization is restricted to some veins and fractures, and has not been observed within the basalt itself as accessory minerals with other basalt-forming minerals. (2) The late hydrothermal magmatic solutions injected into the Gercus Basalt postdating its solidification and jointing/fracturing is the most probable source for the primary hypogene copper mineralization. Indications in favor of the hydrothermal magmatic origin include the restricted presence of primary copper sulfides mostly in some veins and fractures, as well as what the geochemical characteristics of the Gercus Basalt shows (Kettanah and Bamarni, 2018) (Table 3). The mean water and volatile content of the Gercus Basalt is 7% (Table 3), indicating that the magma which produced the Gercus Basal was rich in hydrothermal solutions. This hydrothermal magmatic event succeeded the formation, consolidation and jointing/fracturing of the Gercus Basalt. The residual, volatile-rich, copper-bearing hyrothermal solutions, probably from the same magma source which earlierly created the Gercus Basalt, moved upward under its own building up pressure, to be injected into the lower part of the Gercus Basalt and deposited primary copper sulfides as veins and fracture-fillings (Figs. 3a–c). Most of copper

6 1 2 2 1

Table 3 Summary of the geochemistry of Gercus Basalt (from Kettanah and Bamarni, 2018).

Silicates Sulfate?

Cuprite Malachite Azurite Chrysocolla Unknown Oxide Carbonates

10 Covellite

9 Digenite

3 Chalcocite Sulfides

4 Native

SECONDARY (SUPERGENE) COPPER MINERALS

3

Unknown (Cu2.3FeS3) Native Copper

Chalcopyrite

Bornite Sulfides

PRIMARY (HYPOGENE) COPPER MINERALS

3

wt. % % atoms wt. % % atoms wt. % % atoms wt. % % atoms wt. % % atoms wt. % % atoms wt. % % atoms wt. % wt. % wt. % wt. % wt. % 3

63.31 50.277 34.12 25.711 48.54 36.964 96.72 99.820 80.53 66.512 77.34 63.886 70.26 54.145 85.82 58.67 50.14 28.62 56.44

10.95 9.884 28.73 24.636 18.4 15.951 0.02 0.028 0.16 0.155 0.07 0.067 0.3 0.266 0.06 0.48 0.28 0.44 0.82

25.27 39.761 33.19 49.621 31.19 47.041 0.01 0.022 20.28 33.202 21.97 35.967 29.82 45.529 0.01 0.34 0.06 0.02 21.74

0.02 0.015 0.01 0.012 0.01 0.008 0.01 0.008 0.02 0.021 0.01 0.008 0.01 0.005 0 0 0.01 0 0.02

0 0 0 0 0 0 0.01 0.012 0 0 0 0 0 0 0.01 0 0.01 0 0

0 0 0 0 0 0 0 0 0 0 0 0.003 0 0.001 0 0 0 0 0

0 0 0 0 0 0.002 0 0 0 0 0 0.002 0 0 0 0 0 0 0

0.02 0.010 0 0 0 0.003 0 0 0.01 0.005 0 0.001 0 0.002 0 0 0 0.01 0.03

0 0 0 0 0 0 0 0 0 0 0 0 0.04 0.017 0 0 0 0 0

0 0.001 0.03 0.012 0 0 0.01 0.003 0.02 0.010 0.01 0.006 0.02 0.008 0.01 0 0.01 0.01 0

0.11 0.027 0.03 0.007 0 0.001 0.23 0.073 0.07 0.018 0.13 0.034 0.02 0.005 0.08 0.06 0.02 0.04 0

0.03 0.008 0.01 0.002 0.02 0.006 0.06 0.019 0.01 0.002 0.05 0.012 0.01 0.001 0.04 0 0.02 0.04 0.02

Cu

Cu5FeS4

Total Pb Cd Sn Ag As Zn Ni Co Mn S Fe Cu Unit No. of analysis Mineral Mineral Class Genesis↓

Table 2 Chemical composition of copper minerals in Gercus Basalt based on EPMA analyses.

Cu2.3FeS3

Formula

varies in color between pale green, dark grey to black, unlike the reddened basalts just cited. Copper mineralization in the Gercus Basalt has taken place in two stages described below.

CuFeS2

Ore Geology Reviews 111 (2019) 102974

Au

Y.A. Kettanah

14

Oxide wt%

Range

Mean

Median

SiO2 TiO2 Al2O3 Fe2O3t MnO MgO CaO Na2O K2O P2O5 LOI Total Trace elements (ppm) Cu Zn Pb SiO2 wt% on anhydrous basis Mg# = MgO/(MgO + FeOt)*100 An# = CaO/(CaO + Na2O + K2O)*100 Na2O/K2O

38.12–41.88 2.42–2.63 9.95–11.50 11.47–12.87 0.13–0.30 9.39–13.84 10.42–13.14 0.75–3.77 0.19–1.44 0.8–1.03 3.07–11.05 98.51–100.70

39.81 2.55 10.70 12.22 0.19 11.53 11.29 2.41 0.63 0.91 7.04 99.28

39.93 2.52 10.69 12.14 0.18 11.41 11.37 2.79 0.52 0.89 7.02 99.02

30–120 80–140 5–29 42.04–44.53 56.36–65.84 72.78–93.10 1.63–13.7

57.1 118.0 8.7 43.16 60.29 82.16 4.63

60 120 9 43.20 59.46 80.30 3.58

Ore Geology Reviews 111 (2019) 102974

Y.A. Kettanah

mineralization has been observed in the lower part of the Gercus Basalt near the northwestern plunge of the Bekhair Anticline where the basalt has maximum thickness (Figs. 2, 3). The relationship between copper mineralization and joints in basalts have been demonstrated by Baggio et al. (2018) in his study of Paraná volcanic province of Brazil, based on previous studies on Kilauea volcano by Peck and Minakami (1968) and Lore et al. (2000). According to Peck and Minakami (1968), surface cracking of basaltic flows starts at 900 °C, while the formation of cooling joints completes when the temperature of the bulk of volcanic flow reaches ∼ 750 °C during the consolidation and formation of the basaltic volcanic rocks (Lore et al., 2000). Baggio et al. (2018) suggested that native copper mineralization postdated the formation of cooling joints in the case of Paraná volcanics. Based on these three studies, it is quite possible that a somewhat similar senario took place in the Gercus Basalt where the primary copper sulfides were deposited filling the veins and fractures. (3) Remobilization from the host Gercus Basalt and/or the surrounding Gercus Formation: The copper content of the Gercus Basalt ranges between 30 and 120 ppm (57 ppm and 60 ppm as mean and median values, respectively) (Kettanah and Bamarni, 2018) (Table 3). The mean concentration of copper in world basalts varies between 87 and 116 ppm based on studies by Turekian and Wedepohl (1961), Vinogradov (1962), Wedepohl (1962), and Prinz (1967). Alexander and Thomas (2011) reviewed copper occurrences in major flood basalts of the world and reported that the concentrations of copper are: 148 ppm in the Columbia River basalts (Prinz, 1967), 125 ppm in the Keweenaw lavas of Michigan (Prinz, 1967), 126 ppm in the Aleutian volcanics of Alaska (Prinz, 1967), 125 ppm in the Karroo basalts (Alexander and Paul, 1977), 110 ppm in the Siberian Traps (Nesterenko et al., 1964), and 45 to 540 ppm in the Decan basalts of India (Alexander and Thomas, 2011). This review indicates that the mean content of copper in Gercus Basalt is lower than all reported worldwide averages for basalts and the major flood basalts. The copper content of the siliciclastic rocks forming the Gercus Formation hostings the Gercus Basalt ranges between < 10 and 40 ppm (author’s unpublished data). Furthermore, copper mineralization in the Gercus Formation has not been reported before, despite many previous studies on this widely distributed formation in Iraq, Turkey and Iran. Therefore, the remobilization of copper from the Gercus Basalt itself or from the surrounding Gercus Formation, as the first possible origin for copper mineralization can be ruled out because of its low overall copper content.

also show vein-like offshoots filled by primary copper minerals indicating forceful injection of copper-bearing magmatic hydrothermal solutions to the Gercus Basalt after its consolidation (Fig. 3a). Further supporting evidence is indicated by the fact that the mineralized veins and fractures are mostly located at the lower part of the Gercus Basalt, perpendicular to its lower contact with the Gercus Formation (Figs. 3a–c). Copper is the only metal deposited in the mineralized veins, joints/ fractures and in amygdules in direct contact with these fractures within the Gercus Basalt, raising questions as to why copper is alone without the other commonly associated base-metals such as lead and zinc. One possible reason, given by Xu et al. (2014) for similar cases, is that supercritical fluids released from the underplated basalts, were undergoing boiling during their ascent because of depressurization (Pirajno, 2009). Copper can effectively be separated during such boiling process from lead and zinc because of its strong partition into magmatic vapour phase (Williams-Jones and Heinrich, 2005), while elements such as lead and zinc remain in the fluid phase. Copper in the vapour phase can thus be separated and moves more rapidly than the lead and zinc which remain in fluid, to form copper mineralization in the overlying basalt and the surrounding formations (Xu et al., 2014). The absence of leadand zinc-bearing minerals with copper mineralization means that the hydrothermal solutions carrying copper from the hydrothermal magmatic source at depth did not contain sufficient amounts of these metals to form their own discrete minerals. This is indicated from the low content of lead and zinc in Gercus Basalts, averaging 9 ppm and 120 ppm, respectively (Kettanah and Bamarni, 2018) (Table 3); such concentrations are insufficient to form lead and zinc minerals. The copper of the Gercua Basalt shows significant positive correlations with Lu (0.69), Yb (0.60), Pb (0.59), and K2O (0.52), and negative correlations with Fe2O3 (−0.57), TiO2 (−0.16), and LOI (−0.20). 5.2.2. Secondary (Supergene) copper mineralization The Gercus Basalt was intensely weathered after its extrusion and solidification to such an extent that primary basalt-forming minerals (i.e., feldspar, pyroxene, and olivine) were rarely survived (Fig. 4). Weathering also affected the primary copper mineralization in mineralized fractures. The meteoric and/or groundwater reaction within the mineralized fractures created supergene conditions and resulted in the alteration and replacement of the primary copper sulfides (Figs. 6–10). The alteration and replacement products are native copper, supergene sulfides (digenite, covellite, chalcocite), cuprite, carbonates (malachite and azurite), chrysocolla, and sulfate (Figs. 7–10). These supergene copper minerals were produced within the same veins and fractures hosting the primary copper sulfides and spread over the adjacent joints (Figs. 3b, c), and some of them formed spherules and amygdules within basalt in direct contacts with the veins and fracture walls (Fig. 9). The primary hypogene copper sulfides and the secondary supergene copper minerals are telescoped within narrow veins and fractures which are only few meters in their vertical height. Some of the mineralized veins show radial arrangement with offshoots (Fig. 3a), are concentrated in the lower part of the Gercus Basalt, just above its contact with the underlying Gercus Formation (Figs. 2d, e, 3c). One possible reason for such telescoping of twelve copper minerals belonging to almost all copper mineral classes within narrow fractures of limited vertical dimention is the vertical fluctuation of the meteoric and/or groundwater level with time which created changing conditions between oxidation and reduction, and thus overlapping of minerals formed under these conditions. All the identified primary and secondary copper minerals sometimes can be found within a single specimen as evidence of the telescoped nature of the copper mineralization in Gercus Basalt.

Detailed geochemical studies by Kettanah and Bamarni (2018) on the Gercus Basalt hosting the copper mineralization (summarized in Table 3) showed that it is of basanitic and alkaline type: strongly deficient in silica (SiO2 = 39.8%), alkali-rich (Na2O + K2O = 3.04%), sodic (Na2O/K2O = 4.63), titania-rich (TiO2 = 2.55%), rich in CaO (11.3%), MgO (11.5%), Fe2O3T (12.2%), Al2O3 (10.7%), water, and volatiles (LOI = 7%), and poor in Cu (60 ppm), Zn (120 ppm) and Pb (9 ppm). The geochemistry suggests that the water-rich hydrothermal magmatic solutions injected into the Gercus Basalt after its formation, consolidation and jointing/fracturing, were rich in Cu, Fe, and S. These solutions ascended at a late stage resulted in additional alteration and vesicle filling to the previously altered basalt, and soon afterward, deposited primary copper minerals in veins and fractures/joints. The ascending solutions were alkaline and, while passing through the overlying sedimentary formations, probably gained more alkalinity and became enriched in calcium and sodium, necessary for the precipitation of analcime and calcite. The field relations suggest that the Gercus Basalt was formed by multiple lava pulses of the same type and from the same magmatic source, indicated by its bedded appearance and alternating amygdule-rich and poor horizons. This pulsic nature of the Gecus Basalt strengthen the idea of late introduction and deposition of primary copper-bearing minerals as veins and in fractures. Field evidences

5.2.3. Copper mineralization in Iraq Copper mineralization in Iraq is restricted to the ophiolites of the Iraqi Zagros Suture Zone (Fig. 1a). The related literature review, given in the introduction, indicates that most of the copper occurrences are 15

Ore Geology Reviews 111 (2019) 102974

Y.A. Kettanah

located within the Mawat ophiolitic igneous complex, some 300 kms from the copper mineralization of the Gercus Basalt currently described here. Previously published and unpublished studies have shown that copper mineralization is dominated by chalcopyrite accompanied by one or more other copper minerals such as bornite, covellite, chalcocite, malachite, azurite, and chrysocolla; occasionally associated with pyrite, magnetite, and goethite. According to these studies, copper mineralization is of igneous, hydrothermal and/or metamorphic origin. Most of the surface and subsurface copper occurrences are sporadic in nature as disseminations and/or amygdules in gabbroic, basaltic and ultramafic igneous rocks, and in lesser abundances in metamorphic rocks or as minor hydrothermal veins with quartz. Unlike these copper occurrences within the ophiolitic rocks of northeastern Iraq, the currently studied Gercus copper is located within the Gercus Formation which is part of a thick sequence of sedimentary formations constituting the High Folded Zone of northern Iraq (Fig. 1a). In addition to different tectonic settings, the Gercus copper occurs within the Gercus Basalt, which is alkaline, anorogenic, rift-related and not part of the ophiolites of Suture tectonic zone of northeastern Iraq. Other important differences are that the Gercus copper contains native copper in addition to eleven other copper-bearing minerals including sulfides, oxides, carbonates, and silicates, whereas copper occurrences of the Mawat and nearby ophiolites have simple mineralogies with no reports of native copper.

latest paragentic event, the copper mineralization is indicated by copper-bearing minerals that were grown independently and do not share the same amygdules with other alteration products (Figs. 6, 9h); furthermore, they have not been observed within the altered primary basaltic minerals (Fig. 4). Copper mineralization started by coeval deposition of primary sulfides represented by bornite, chalcopyrite, and an unknown sulfide (Cu2.3FeS3) which were later altered to supergene copper minerals by meteoric and/or groundwater during their chemical weathering. These coevally deposited primary minerals, together with their associated alteration/replacement products form two groups not having shared contact even where they are found within the same slide (Figs. 6c–h). The bornite-chalcopyrite group is represented by lamellar intergrowth of these two minerals where bornite was later partially replaced by chalcopyrite, covellite, and digenite (Figs. 6c–g, 7a–e). The unknown sulfide (Cu2.3FeS3) is commonly zonally surrounded by its alteration products (Figs. 6h, 10a, b); such zonation starts from the center outward, by digenite, an isotropic mineral (possibly amorphous or opaline silica), malachite, azurite, limonite, covellite, and ends with cuprite. These zoned minerals are commonly surrounded by other secondary and supergene minerals such as analcime, malachite, azurite, and chrysocolla (Figs. 10a, b). The two primary copper mineral groups are mostly associated with and replaced by their secondary alteration products (Figs. 6–10). The other mineral mostly forming a distinct group detached from the other groups is native copper deposited as a supergene secondary mineral. Native copper consists mostly of many tiny, closely grouped specks, partially or completely replaced by cuprite and surrounded by copper carbonates and calcite (Figs. 8e, f). However, native copper has also been found in association with chalcopyrite, possibly as its alteration product (Figs. 8a, b), and with covellite and digenite which indicates their coeval deposition (Figs. 8a–d). The secondary supergene copper minerals formed as alteration products of the primary sulfides, were deposited in sequence starting with sulfides (digenite, covellite, and chalcocite) and native copper, followed by an oxide (cuprite) and carbonates (malachite and azurite), and culminated with silicate (chrysocolla) and possibly a sulfate (Fig. 11). Calcite, the dominant gangue mineral, accompanied most stages of mineralization. The source of calcite is probably the alteration products of feldspars and pyroxenes, as well as the carbonate minerals within the sedimentary rocks of the Gercus Formation hosting the Gercus Basalt. Calcite forms the cementing material of the sandstones and siltstones and exist as several minor limestone beds within the Gercus Formation. The hyrothermal solutions have apparently dissolved these sources of carbonates while emanating through the Gercus Formation and redeposited the carbonate as calcite in fractures traversing the Gercus Basalt. Copper carbonates were found replacing hydrothermal calcite along cleavage planes (Fig. 9e).

5.3. Paragenesis The successive crystallization of essential and accessary basaltforming minerals, in the order of olivine, Ti-magnetite, ilmenite, feldspar, pyroxene, and apatite, was followed by two hydrothermal magmatic events as well as weathering, These events intervened with three alterations stages, jointing/fracturing, and two copper mineralizations processes. Soon after the basaltic lava flow and before its complete consolidation, the remaining hot hydrothermal solutions caused partial to pervasive deuteric alteration and pseudomorphism of the essential and accessory minerals of the Gercus Basalt. Jointing and fracturing occurred after cooling and consolidation of the Gercus Basalt. A new hydrothermal fluid impulse probably originated from the same magmatic source which formed the Gercus Basalt at earlier stage, caused additional hydrothermal alterations and primary hypogene copper mineralization as veins and fracture-fillings, mostly concentrated at the lower part of the Gercus Basalt (Figs. 3a, 6), Chemical weathering by meteoric and/or groundwater affected the whole basalt and resulted in its additional alteration, as well as partial alteration and replacement of the primary copper minerals by supergene copper minerals within the same veins, fractures and adjacent joints. The vesicles were filled with the alteration products of the hydrothermal solutions and meteoric water during weathering, forming amygdules, a common feature of the Gercus Basalt (Fig. 3a). Deuteric and hydrothermal alterations of the primary basaltic minerals have taken place in the form of serpentinization, chloritization, iddingsitization and goethitization of olivine; serpentinization, silicification, goethitization, calcitization, and zeolitization of pyroxenes; anorthoclasization and calcitization of feldspars; partial crystallization of volcanic glass; as well as martitization of Timagnetite (Fig. 4). In addition to the alteration products of primary essential and accessory basaltic minerals, both the hydrothermal and meteoric fluids also created and introduced additional amygdule-filling minerals represented in the order of their zonal arrangement within amygdules by chalcedony and opaline silica, analcime, calcite, and an unknown radiating silicate mineral (zeolite?) (Fig. 5). The petrographic and geochemical characteristics of the primary basalt-forming minerals were given by Kettanah and Bamarni (2018). Primary copper mineralization followed by their alteration, leading to the formation of secondary supergene copper minerals occurred as the final paragenetic event, filling some veins, fractures/joints and the nearby vesicles in direct contact with these planes of weaknesses. As the

6. Conclusions 1. The Gercus Basalt, hosting the studied copper mineralization, occurs in the middle of the Gercus Formation within the High Folded Tectonic Zone of Iraq and is not related to the ophiolites of northeastern Iraq; such basaltic bodies have not been reported elsewhere in the Gercus Formation which is widely exposed in Iraq, Turkey, and Iran. 2. The basanitic and alkaline Gercus Basalt is anorogenic and rift-related in origin and is pervasively altered at available exposures to such an extent that fresh primary minerals are only rarely found. 3. Alteration of the Gercus Basalt started with deuteric alteration by the left over magmatic hydrothermal solutions producing secondary minerals as pseudomorphs of the basaltic minerals; succeeded by a new surge of magma from the same earlier source magma which produced the Gercus Basault causing additional hydrothermal alterations, followed by chemical weathering via meteoric and/or groundwater producing new secondary minerals. The product of 16

Ore Geology Reviews 111 (2019) 102974

Y.A. Kettanah

Fig. 11. Paragenesis of minerals constituting the Gercus Basalt and the associated copper mineralization.

both hydrothermal alterations and weathering filled fractures/ joints, vesicles and produced amygdules. 4. The alterations of the Gercus Basalt include calcitization, serpentinization, chloritization, iddingsitization, zeolitization, silicification, iron oxidation, martitization, and possibly anorthoclasization. 5. Copper mineralization started with late magmatic hydrothermal fluid injection, postdating the consolidation of the Gercus Basalt and fracturing/jointing which resulted in deposition of primary hypogene sulfides (bornite, chalcopyrite, and an unidentified sulfide – Cu2.3FeS3) along veins and fractures, followed by chemical weathering due to meteoric and/or groundwater action producing secondary supergene copper minerals in the same veins, fractures/ joints and the adjacent amygdules. 6. The paragenesis of the Gercus Basalt was as follows: crystallization of the essential and accessory minerals – deuteric alteration of the basaltic minerals – fracturing and jointing – renewed hydrothermal magmatic injection – primary hypogene copper mineralization in veins and fractures – weathering by meteoric and/or groundwater – formation of secondary minerals and supergene copper minerals –

fracture/joint/vesicle-filling – formation of amygdules – continued weathering and alteration. 7. The overall copper mineralization, primary and supergene, seems to be of local and minor occurrence, which minimizes its economic importance. 8. Unlike ophiolite-related copper occurrences of the Suture Zone of northeastern Iraq which contain very few copper minerals, the Gercus mineralization contains native copper as well as eleven other copper minerals in the same fractures. Acknowledgments Most of the work on this paper was performed at the Department of Earth Sciences, Dalhousie University, Canada. Among the persons working at this department, I am particularly thankful to Dr. Grant Wach for allowing the use of his research microscope, Danny MacDonald for his help in microprobe analysis, and Gordon Brown for preparing thin and polished-thick section. I am thankful to both reviewers for their constructive and critical comments and suggestions 17

Ore Geology Reviews 111 (2019) 102974

Y.A. Kettanah

which were very helpful in improving the revised version of this article. This research was self-supported and did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

proto–Zagros foreland basin, Lurestan Province, SW Iran. Geol. Soc. Am. Bull. 121, 963–978. Jassim, S.Z., Buday, T., 2006. Middle Palaeocene-Eocene megasequence AP10. In: Jassim, S.Z., Goff, J.V. (Eds.), Geology of Iraq. Dolin, Prague and Moravian Museum, Brno, Czech Republic, pp. 155–168. Kettanah, Y.A., 1991. Petrography, mineralization, and metamorphism of the spilitic basaltic rocks in Mawat area, northeastern Iraq: A case study on borehole number WZ-1. An internal report submitted to the General Establishment of Geological Survey and Metallurgy, Baghdad, Iraq, 45p. Kettanah, Y.A., Bamarni, A.H., 2018. Petrogenesis, geochemistry and tectonic setting of a basaltic body within the Gercus Formation of northern Iraq: first record for Eocene anorogenic volcanic activity in the region. Turk. J. Earth Sci. 27, 460–491. Li, H., Mao, J., Chen, Y., Wang, D., Zhang, C., Xu, H., 2005. Epigenetic hydrothermal features of the Emeishan basalt copper mineralization in NE Yunnan, SW China. In: Mao, J., Bierlein, F.P. (Eds.), Mineral Deposit Research: Meeting the Global Challenge. Springer, Berlin Heidelberg, Beijing, pp. 149–152. Lore, J., Gao, H., Aydin, A., 2000. Viscoelastic thermal stress in cooling basalt flows. J. Geophys. Res. 105, 695–709. Markusson, S.H., Stefansson, A., 2011. Geothermal surface alteration of basalts, Krýsuvk Iceland – alteration mineralogy, water chemistry and the effects of acid supply on the alteration process. J. Volcanol. Geoth. Res. 206, 46–59. Mas, A., Guisseau, D., Patrier Mas, P., Beaufort, D., Genter, A., Sanjuan, B., Girard, J.P., 2006. Clay minerals related to the hydrothermal activity of the Bouillante geothermal field (Guadeloupe). J. Volcanol. Geoth. Res. 158, 380–400. Maxon, J.H., 1936. Geology and Petroleum Possibilities of the Hermis Dome: MTA Derleme no. 255, 25 s., Ankara. Mirza, T.A., Kalaitzidis, S.P., Mohammed, S.H., Rashid, S.G., Petrou, X., 2017. Geochemistry and genesis of sulphide ore deposits in Sharosh Village, Qandil Series, Kurdistan Region, NE Iraq. Arab. J. Geosci. 10, 428–446. Mirza, T.A., Rashid, S.G., 2018. Mineralogy, Fluid inclusions and stable isotopes study constraints on genesis of sulfide ore mineral, Qaladiza area Qandil Series, Iraqi Kurdistan Region. Arab. J. Geosci. 11, 146–160. Musa, E.O., 2007. Petrography, Geochemistry and Genesis of Copper-iron Mineralization and Associated Rocks in Waraz Area, Sulaimanya, NE Iraq. Unpubl. M.Sc Thesis. University of Baghdad, Baghdad, pp. 155. Nesbitt, H.W., Wilson, R.E., 1992. Recent chemical weathering of basalts. Am. J. Sci. 292, 740–777. Nesterenko, G.V., Avilova, N.S., Smirnova, N.P., 1964. Rare elements in the Traps of the Siberian Platform. Geokhimiya 10, 1015–1021. Peck, D.L., Minakami, T., 1968. Formation of columnar joints in the upper part of Kilauean lava lakes, Hawaii. Bull. Geol. Soc. Am. 79, 1151–1166. Pe-Piper, G., 2000. Mode of occurrence, chemical variation and genesis of mordenite and associated zeolites from the Morden area, Nova Scotia, Canada. Can. Mineral. 38, 1215–1232. Pinto, V.M., Hartmann, L.A., Wildner, W., 2011. Epigenetic hydrothermal origin of native copper and supergene enrichment in the Vista Alegre district, Paraná basaltic province, southernmost Brazil. Int. Geol. Rev. 53, 1163–1179. Pirajno, F., 2009. Water and Hydrothermal Fluids on Earth, Hydrothermal Processes and Mineral Systems. Springer, Netherlands, pp. 1–71. Prinz, M., 1967. Geochemistry of the basaltic rocks: trace elements. In: Hess, H.H., Poldervaart, A. (Eds.), Basalts. Interscience Publication, New York, pp. 271–323. Sissakian, V.K., 2018. The mineral wealth in Kurdistan Region, Iraq: a critical review. UKH J. Sci. Eng. 2 (2), 23–36. Smirnov, V.A., Nelidov, V., 1962. Reoprt on 1:200,000 prospecting correlation of Sulaimaniya, Chwarta, Penjwin area, carried out on 1962. GEOSURV Internal Report No. 290. Smith, K.L., Milnes, Anthony R., Eggleton, R.A., 1987. Weathering of basalt: formation of iddingsite. Clay Clay Miner. 35 (6), 418–428. Sun, M.S., 1957. The nature of Iddingsite in some basaltic rocks of New Mexico. Amer. Miner 42, 525–533. Turekian, K.K., Wedepohl, K.H., 1961. Distribution of the elements in some major units of the Earth’s crust. Geol. Soc. Am. Bull. 72, 175–192. Vinogradov, A.P., 1962. Average contents of chemical elements in the principal types of igneous rocks of the Earth’s Crust. Geochemistry 9, 801–812. Wedepohl, K.H., 1962. Beitrage zur Geochemie des Kupfers. Geol. Rundsch. 52 (1), 492–504. Williams, W.R., 1948. Mineral survey of mountains of north Iraq. GEOSURV, Internal Report No. 133. Williams-Jones, A.E., Heinrich, C.A., 2005. 100th Anniversary Special Paper: vapor transport of metals and the formation of magmatic-hydrothermal ore deposits. Econ. Geol. 100 (7), 1287–1312. Wilshire, H.G., 1959. Deuteric alteration of volcanic rocks. J. Roy. Soc. N.S Wales 93, 105–120. Xu, Y., Huang, Z., Zhu, D., Luo, T., 2014. Origin of hydrothermal deposits related to the Emeishan magmatism. Ore Geol. Rev. 63, 1–8. Yara, I.O.M., Mohammad, Y.O., 2018. Iron-copper mineralization associated with metagabbro in Mirawa village, Kurdistan region, northeastern Iraq. J. Zankoy Sulaiman (Part-A: Art and Pure Sciences) 20 (2), 95–107. Yassin, A.T., Alabidi, A.J., Hussain, M.L., Al-Ansari, N., Knutsson, S., 2015. Copper ores in mawat ophiolite complex (Part of ZSZ) NE Iraq. Nat. Resour. 6, 514–526.

References Abdulla, H.H., 2013. Rock slope analysis in Duhok Governorate, Bekhair Anticline by using GIS technique. J. Al-Nahrain Univ. 16, 46–54. Al-Azzawi, N.K., Al-Hubiti, S.T., 2009. The fold style variations of Baikher Anticline – northern Iraq. Iraqi J. Earth Sci. 9, 1–20. Al-Bassam, K., 1984. Final Report on the Regional Geological Survey of Iraq, vol. 5 Economic Geology of Iraq Geological Survey Library Report No. 1449. Al-Bassam, K., 2013. Mineral resources in the Kurdistan region. Iraqi Bull. Geol. Mining 9 (3), 103–128. Al-Bassam, K.S., Hak, J., 2006. Metallic and industrial rocks and minerals. In: Jassim, S.Z., Goff, J.V. (Eds.), Geology of Iraq. Dolin, Prague and Moravian Museum, Brno, Czech Republic, pp. 288–302. Alexander, P.O., Paul, D.K., 1977. Geochemistry and strontium isotopic composition of basalts from the eastern Deccan volcanic province, India. Mineral Mag. 41, 165–172. Alexander, P.O., Thomas, H., 2011. Copper in Deccan basalts (India): review of the abundance and patterns of distribution. Boletín del Instituto de Fisiografía y Geología 79–81, 107–112. Al-Hashimi, A., Al-Mehaidi, H., 1975. Cu, Ni, Cr dispersion in Mawat ophiolite complex, NE Iraqi. J. Geol. Soc., Iraq Special Issue 37. Arena, K.R., Hartmann, L.A., Baggio, S.B., 2014. Geological controls of copper, gold and silver in the Serra Geral Group, Realeza region, Paraná, Brazil. Ore Geol. Rev. 63, 178–200. Baggio, S.B., Hartmann, L.A., Lazarov, M., Massonne, H.J., Opitz, J., Theye, T., Viefhaus, T., 2018. Origin of native copper in the Paraná volcanic province, Brazil, integrating Cu stable isotopes in a multi-analytical approach. Miner. Deposita 53, 417–434. Bolgi, T.V., 1961. Petrol Bölgesi seksiyon ölçmeleri AR/TPO/261 nolu saha ile ReşanDodan arasıbatısındaki sahanın strüktürel etüdleri: TPAO Arama Grubu, Rapor no. 162, 52 s., Ankara. Bornhorst, T.J., Barron, R.J., 2011. Copper deposits of the western Upper Peninsula of Michigan. The Geological Society of America Field Guide 24, pp. 83–99. Bornhorst, T.J., Barron, R.J., Whiteman, R.C., 2013. Caledonia Mine, Keweenaw Peninsula native copper district, Ontonagon County. Michigan. Inst. Lake Super. Geol. Proc. 59 (2), 43–57. Bornhorst, T.J., Mathur, R., 2017. Copper isotope constraints on the genesis of the Keweenaw Peninsula native copper district, Michigan, USA. Minerals 7 (10) 185, 20p. Bornhorst, T.J., Paces, J.B., Grant, N.K., Obradovich, J.D., Huber, N.K., 1988. Age of native copper mineralization, Keweenaw Peninsula, Michigan. Econ. Geol. 83, 619–625. Brown, A.C., 1965. Zoning in the White Pine copper deposit Ontanogon County, Michigan. Econ. Geol. 66, 543–573. Brown, A.C., 2006. Genesis of native copper lodes in the Keweenaw district, northern Michigan: A hybrid evolved meteoric and metamorphogenic model. Econ. Geol. 101, 1437–1444. Brown, A.C., 2008. District-scale concentration of native copper lodes from a tectonically induced thermal plume of ore fluids on the Keweenaw Peninsula, northern Michigan. Econ. Geol. 103, 1691–1694. Brown, A.C., 2014. Latent thermal effects from porcupine volcanics calderas underlying the White Pine-Presque Isle stratiform copper mineralization, Northern Michigan. Econ. Geol. 109, 2035–2050. Brown, A.C., 2018. Copper isotope constraints on the genesis of the Keweenaw Peninsula native copper District, Michigan, USA: A Comment. Minerals 8 506, 7p. Cabral, A.R., Beaudoin, G., 2007. Volcanic red-bed copper mineralisation related to submarine basalt alteration, Mont Alexandre, Quebec Appalachians, Canada. Miner. Deposita 42, 901–912. Delvigne, J., Bisdom, E.B.A., Sleeman, J., Stoops, G., 1979. Olivines, their pseudomorphs and secondary products. Pedologie XXIX 3, 247–309. Emetz, A., Piestrzynski, A., Zagnitko, V., 2004. Geological framework of the Volhyn copper fields with a review of the Volhyn flood basalt province (western margin of the east-European craton). Annales Sosietatis Geologorum Poloniae 74, 257–265. Fisher, Richard V., Schmincke, Hans-Ulrich (Eds.), 1984. Pyroclastic Rocks. Springer Berlin Heidelberg, Berlin, Heidelberg. Fouad, S.F., 2015. Tectonic map of Iraq scale 1:1,000,000, 3rd edition, 2102. Iraqi Bulletin of Geology and Mining 11, pp. 1–8. Grim, R.E., Giiven, N., 1978. Bentonites: Geology, Mineralogy, Properties and Use. Develop, in Sedim. 24. Elsevier, Amsterdam, pp. 1–256. Hadi, A., Musa, E.O., Al-Bassam, K., 2010. Genesis of copper-iron mineralization and the associated rocks in Waraz area, Northeast Iraq. Int. J. Sci. Technol. 5 (4), 27–47. Hekinian, R., 1982. Petrology of the Ocean Floor. Chapter 11 Deuteric Alteration Elsevier Oceanography Series, 33, pp. 329–331. Homke, S., Vergés, J., Serra-Kiel, J., Bernaola, G., Sharp, I., Garcés, M., Montero-Verdú, I., Karpuz, R., Goodarzi, M.H., 2009. Late Cretaceous-Paleocene formation of the

18