Journal of African Earth Sciences 101 (2015) 70–83

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Journal of African Earth Sciences

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Cu–Mn–Fe alloys and Mn-rich amphiboles in ancient copper slags from the Jabal Samran area, Saudi Arabia: With synopsis on chemistry of Fe–Mn(III) oxyhydroxides in alteration zones ⇑ Adel A. Surour

Department of Mineral Resources and Rocks, Faculty of Earth Sciences, King Abdulaziz University, P.O. Box 80206, Jeddah 21589, Saudi Arabia Department of Geology, Faculty of Science, Cairo University, Egypt article info abstract

Article history: In the Jabal Samran area (western Saudi Arabia), secondary copper mineralization in a NE-trending shear Received 15 July 2014 zone in which the arc metavolcanic host rocks (dacite–rhyodacite) show conjugate fractures and exten- Received in revised form 27 August 2014 sive hydrothermal alteration and bleaching. The zones contain frequent Fe–Mn(III) oxyhydroxides Accepted 2 September 2014 (FeOH–MnOH) that resulted from oxidation of pyrite and Mn-bearing silicates. In the bleached part, Available online 16 September 2014 the groundmass is represented by Fe-bearing interstratified illite–smectite with up to 4.02 wt% FeOt. FeOH–MnOH are pre-weathering phases formed by hydrothermal alteration in a submarine environment Keywords: prior to uplifting. Five varieties of FeOH are distinguished, four of them are exclusively hydrothermal Fe–Mn(III) oxyhydroxide with 20 wt% H O whereas the fifth contains 31–33 wt% H O and might represent reworking of earlier Synthetic Mn-rich amphiboles 2 2 Cu prills hydrothermal FeOH phases by weathering. FeOH fills thin fractures in the form of veinlets and crenulated Slags laminae or as a pseudomorph for pyrite, goethite and finally ferrihydrite, and this oxyhydroxide is char- acterized by positive correlation of Fe2O3 with SiO2 and Al2O3. On the other hand, MOH shows positive

correlation between MnO2 and Al2O3 whereas it is negative between Fe2O3 and SiO2. Paratacamite is the most common secondary copper mineral that fills fractures and post-dates FeOH and MnOH. It is believed that Cl in the structure of paratacamite represents inherited marine storage rather than from surfacial evaporates or meteoric water. The mineralogy of slags suggests a complicated mineral assemblage that includes native Cu prills, synthetic spinifixed Mn-rich amphiboles with 16.73 wt% MnO, brown glass and Ca–Mn–Fe phase close to the olivine structure. EMPA indicate that the some Cu prills have either grey discontinuous boarder zone of S-rich Mn–Cu alloy (with up to 21.95 wt% S and 19.45 wt% Mn) or grey Cu–Mn–Fe alloy (with up to 15.9 wt% Cu, 39. 12 wt% Mn and 61.64 wt% Fe). Mn in the Cu prills is expelled inward as Cu–Mn–Fe alloy inclusions whereas S is expelled outward as S-rich Mn–Cu alloy crust. Remains in the Samran smelter sites suggest the use of charcoal as a source of energy, quartzite as a flux and an air- cooling technique was used. Ó 2014 Elsevier Ltd. All rights reserved.

1. Introduction antique houses that were used as shelters for workers at the same sites of their primitive small-scale mines. Such wastes and ruins The Jabal Samran area is known for its secondary copper miner- are still kept partially in some localities, for example Samran, alization and heaps of ancient slags that belong to the Abbasid Kutam, Ash Shizm and Umm ad Damar that all include secondary Caliphate (750–1258 A.D.) in the Arabian Peninsula (Sabir, 1999; copper mineralization as a result of oxidation of hidden late Neo- Sahl et al., 1999). The miners and smelters of the Abbasid Caliphate proterozoic volcanic massive sulphides (VMS). Ore reserves in mined and extracted considerable amounts of copper that was the Kutam and Samran deposit are the highest and lowest (4.5 needed for coinage and manufacturing tableware, shields and and 0.9 million tons, respectively), and their grade averages 2% weapons. Their activities left behind several heaps of slags and Cu but it reaches up to 2.92 at the Ash Shizm deposit (Fadol, 2002). Generally, the Arabian Shield in western Saudi Arabia includes some hundreds of copper mineral deposits and occur- ⇑ Address: Department of Mineral Resources and Rocks, Faculty of Earth Sciences, King Abdulaziz University, P.O. Box 80206, Jeddah 21589, Saudi Arabia. Fax: +966 rences. Three copper districts are known in the shield, namely 126952095. northern, central and southern (Collenette and Grainger, 1994). E-mail address: [email protected] The Samran and the nearby Abu Mushut occurrences, in addition http://dx.doi.org/10.1016/j.jafrearsci.2014.09.005 1464-343X/Ó 2014 Elsevier Ltd. All rights reserved. A.A. Surour / Journal of African Earth Sciences 101 (2015) 70–83 71

to the Khnaiguiyah are confined to the so-called ‘‘Samrah Belt’’. On (99.99 wt% Cr2O3), periclase for Mg, wollastonite for Ca, fayalite the other hand, the northern and southern districts contain high- for Fe, nickel oxide for Ni (99.99 wt% NiO), barite for Ba, KTiPO5 grade ore of marginally commercial sizes such as those of Jabal for K & Ti, jadeite for Na and manganosite for Mn. The ore minerals Sayid-Nuqrah and Kutam-Al Masane, respectively. (native Cu and metal alloys) in the slags were also analyzed by the In the framework of tectonism, the VMS mineralization in the electron microprobe for Fe, S, Cu, Au, Ag, Zn, Pb, Co, Ni and As. Ana- Arabian Peninsula and northeast Africa was developed in associa- lytical conditions were 20-kV accelerating voltage, 20-nA probe tion with calc-alkaline subaerial volcanism that characterizes current, 3 lm beam diameter and the counting time was 20 s for island-arc setting during the late Neoproterozoic (Johnson and each element except for Au and Ag which were 50 and 30 s, respec- Vranas, 1984; Roobol, 1989; Volesky et al., 2003; Al-Shanti, tively. The standards used were pyrite for Fe and S, pure metals for 2009; Johnson et al., 2011; Haldar, 2013; Legault et al., 2013). Cu, Au, Ag, Zn, Pb, Co and Ni, and gallium arsenide for As. The site of secondary copper mineralization at the Jabal Samran Some XRD analyses, mineral spectra and back-scattered elec- area overlies subsurface VMS (Liddicoat, 1966). The Cu-rich VMS tron (BSE) images were obtained. The latter were produced using of Jabal Samran and the gold-rich VMS of the Shayban prospect a (SEM–EDX) Philips XL 30 at the Central Laboratories of the Egyp- are the eastern extension of the famous Ariab deposit with tian General Authority of Mineral Resources in Dokki, Egypt. The economic cupriferous pyrite in northern Sudan. All of them show obtained data were in the form of spot semi-quantitative microa- confinement to the so-called ‘‘Ariab-Samran-Shayban’’ greenstone nalyses of some ore minerals and non-opaque minerals in the belt extends for a distance of almost 1000 km from the Nile Valley investigated samples. In Fe oxyhydroxide (FeOH), Mössbauer spec- in Sudan north-eastwards across the Red Sea to Mahd adh Dhahab tra were obtained to investigate accommodation of either Fe2+ or in Saudi Arabia (Dolbear, 2007). This VMS-rich greenstone belt has Fe3+ in the structure. In order to test crystallinity of the Fe–Mn oxy- an average width of about 50 km and many of them are capped by hydroxides (FeOH–MnOH) phases in the alteration zones, some gold-rich oxide-hydroxide ‘‘gossans’’ to depths of 20–50 m. XRD runs were carried out that help to decide whether they are The current work presents the detailed mineralogy and crystalline or amorphous. microchemical analysis of both slags and secondary copper miner- alization at the Jabal Samran area. A possible scenario for the extraction of copper from the ore is suggested based on mineralogy 3. General geology of Jabal Samran area and the anthropological relics found at the sites of smelting. Also, the current work presents some new mineralogical and The Jabal Samran area is an island-arc terrane that comprises a geochemical data about the Fe–Mn(III) oxyhydroxides in the variety of late Neoproterozoic rock assemblages that are domi- ‘‘bleached’’ intermediate to acidic metavolcanics at the Jabal nated by volcanics and volcaniclastic rocks (Figs. 1 and 2a) that Samran area where significant information about Fe–Mn(III) oxy- undergone regional metamorphism mostly in the greenschist hydroxides are lacking in the literature. A few mineralogical data facies condition (Nebert, 1969; Ba-battat, 1982; Ba-battat and about Fe–Mn(III) oxyhydroxides formed in soil and laterites or in Hussein, 1983). The metamorphosed volcanic association is inter- seamounts and mid-ocean ridges were presented (Varentsov rupted by some marble bands, and the entire succession is et al., 1991; Boughriet et al., 1996; Braun et al., 1998; Duzgoren- intruded by gabbro and granitoids. According to Ba-battat and Aydin and Aydin, 2009). Their origin is still a matter of ambiguity Hussein (1983), the metavolcanic–metavolcaniclastic succession but in general it is accepted that either hydrogenetic or hydrother- is of calc-alkaline to slightly tholeiitic composition and comprises mal (Bonatti, 1975). Some recent studies (Merinero et al., 2008; of three volcanic cycles in which the first two are metamorphosed Zeng et al., 2012) did not neglect the possible role of metal metatuffs of andesitic to rhyolitic composition whereas the third oxidizing bacteria and hydrocarbons in submarine chimneys in cycle is represented by non-metamorphosed flows of andesite. the formation of such hydrous phases in the proper marine From the lithostratigraphic point of view, the layered rocks environment. Whether it is hydrogenetic or hydrothermal, the (metavolcanic–metavolcaniclastic succession and the marble Fe–Mn(III) oxyhydroxides coating marine sediments are authigenic bands) at the Jabal Samran are believed to correlate with the Hul- (Bayon et al., 2004; Gutjahr et al., 2007; Charbonnier et al., 2012). ayfah Group of the Arabian Shield (Ba-battat and Hussein, 1983; In addition, an account about the formation condition of parataca- Johnson et al., 2011). The first nomenclature of the so-called ‘‘Sam- mite is given for natural geologic materials talking in consideration ran Series’’, was suggested by Nebert (1969) to assign an andesitic- that such phases are essential components of the so-called ‘‘bronze dominated volcanic section at the Jabal Samran area. Later on, disease’’ that forms as rust for copper tools, alloys and statues Skiba and Gilboy (1975) used ‘‘Samran Group’’ instead of ‘‘Samran (Scott, 2000; Frost et al., 2002; Zhang et al., 2013). Series’’. Schmidt et al. (1973) presented the stratigraphy of the Jed- dah Group in which its metabasalt to meta-andesite Qirshah For- 2. Methodology mation can be correlated with the ‘‘Samran Series’’. The ‘‘Samran Series’’ is also termed as the Samran Group (Smith and Kahr, The rock samples were systematically selected from secondary 1966; Skiba, 1980). The Jeddah Group itself represents a part of mineralization and slags area to represent mineralized veins, oxi- the early episode of mafic-intermediate volcanism and sedimenta- dation and alteration zones of Jabal Samran area. In order to study tion of the Hijaz tectonic cycle (Greenwood et al., 1973). The Jed- mineral composition and textures, twenty-four polished sections dah and Samran Groups are similar to the greenstone rocks in addition to sixteen polished mounts were prepared from the (metabasalt, meta-andesite and graphitic schists) of the Baish– selected rock samples. The sections were studied in both transmit- Bahah Groups that have been formed during the early Hijaz cycle, ted and reflected light for their silicates and ore mineralogy. and are believed to have accumulated in subareial to shallow mar- The quantitative electron microprobe analyses (EMPA–WDS) of ine environments and were metamorphosed to upper greenschist the oxyhydroxides and silicate phases both in secondary mineral- facies condition (Blodget and Brown, 1982). The age of the Jed- ization zones and slags were conducted using a Jeol JXA8200 dah–Samran–Baish–Bahah Groups is uncertain due to re-setting instrument. It is housed at the Faculty of Earth Sciences, King by the subsequent Ablah orogeny at 763 M.a. (Brown et al., Abdulaziz University in Jeddah, Saudi Arabia. Operating conditions 1989). Older ages of the Jeddah Group and its equivalents are were 15-kV accelerating voltage, 20 nA probe current, 3 lm beam obtained including 720–800 M.a. K–Ar ages of separated crys- diameter and 20 s counting time for each element. The following tals and a remarkably higher whole-rock age of 965–1025 M.a by standards were used: hornblende for Si and Al, eskolaite for Cr the Rb/Sr method (Aldrich et al., 1978). Johnson (2006) assumed 72 A.A. Surour / Journal of African Earth Sciences 101 (2015) 70–83

Fig. 1. Geological map of the Jabal Samran area (Ramsay, 1986). a 825–745 M.a. for the Samran Group and added that the strati- northwestern slope of Jabal Samran. The ancient workings at Jabal graphic relationships within the group is uncertain. Lateral and Samran are aligned in a NNE–SSW direction and extend for 500 m vertical variations around paleo-volcanic centers led Roobol along the western flank. These working follow mineralized - (1989) to divide the Samran Group into five formations (Nida, vines within a zone of shearing and brecciation. The country rocks Shayban, Madrakah, Fayidah and Amudan). The Madrakah and in mostly are metadacite–metarhyodacite with remarkable quartz Fayidah formations are similar to those reported in the Wadi augens due to extensive deformation. The secondary copper min- Fatima area (Moore and Ar-Rehaili, 1989). Precise SHRIMP ages eralization occurs in a number of quartz veins and stringers as an of the Shayban Formation and the youngest Amudan Formation expression of fracture filling and contains green and bluish green are 825–771 M.a. and 753–746 M.a., respectively (Hargrove, 2006). secondary Cu minerals such as paratacamite, brochantite, chryso- colla and azurite (Ramsay, 1986; Qadhi, 2008). The oxidation zone extends for a depth 30 m which was previously documented by 4. Local geology of mineralized zones and site of smelters drilling (Liddicoat, 1966, 1971). Below the oxidation zone, there are discontinuous lenses and stringers of quartz that bear pyrite, The observed secondary Cu and Fe mineralization in the form of chalcopyrite and native gold. There is a remarkable positive corre- ‘‘gossans’’ at the surface outcrops of Jabal Samran area (Fig. 2b) is lation between the concentrations of base and precious metals confined either to the sheared arc metavolcanics that range in with the degree of wallrock alteration (Ba-battat, 1982). composition from dacite to rhyodacite, or along its contact with The two sites of secondary mineralization at the Jabal Samran the metandesite tuffs. The most intensive mineralization is directly area were mined during the time of the Abbasid Caliphate which related to zones of faulting and brecciation. The wallrock alteration was left behind antique incomplete smelters and considerable is mostly represented by hematitization and silicification which heaps of slags (Fig. 2f) that are characterized by rope-like surface affected the country rocks for a distance of 300–400 m on each side texture (Fig. 2g). Also, there are still ruins of ancient shelters or of the veins. This is followed inwards by chloritization and finally houses of labors (Fig. 2h) and possible furnaces that were used by kaolinization and sericitization in the actual mineralized-zone. for metal extraction, in addition to massive fragmented slags in It appears that the hydrothermal alterations are older than the the region. These slags contain few fragments of charcoal that intrusion of microdiorite (Fig. 2c) because this diorite is completely may have been used as a fuel source, and were also found as fresh. As a sense of shear effect, the alteration zones possess a com- remains in the ancient ruins. mon ‘‘conjugate’’ fracture system (Fig. 2d). In some instances, the mineralized metavolcanics are ‘‘bleached’’ with common occur- rence of Fe–Mn(III) oxyhydroxides along fractures (Fig. 2e). This 5. Mineralogy and ore microscopy observation goes in harmony with Ramsay (1986) who stated that the mineralization lies in large areas of weathered, Fe-stained viv- The microscopic investigation of the secondary alteration zones idly colored or bleached rocks as gossans; where the bleached that contain Cu-bearing minerals revealed that the abundance of rocks are pervasively silicified and the vividly colored gossans FeOH–MnOH is much higher than secondary copper minerals. are distributed in linear belts parallel to the regional tectonic The latter occurs in the form of sub-parallel thin veinlets that often fabric. According to the current observations, the secondary miner- obey the major direction of shearing (Fig. 3a). This figure also alization is encountered in two mineral occurrences down the shows the presence of some pyrite cubes that are now transformed A.A. Surour / Journal of African Earth Sciences 101 (2015) 70–83 73

Fig. 2. (a) General view of the Jabal Samran stratified metavolcanics, (b) vivid-colored supergene alteration zone dominated by secondary Cu mineralization, (c) extensive hydrothermal alteration of metavolcanics and freshness of late microdiorite, (d) conjugate fracture system in hydrothermally altered meta-rhyodacite, (e) Fe–Mn(III) oxyhydroxides (FeOH–MnOH) filling fractures I ‘‘bleached’’ meta-rhyodacite, (f) dark dumps of Cu slags, (g) close-up view of Cu slag showing ropy-like surface, and (h) ruins of ancient houses at site of smelters. into the oxyhydroxide phases totally. The veins in the alteration chemistry data are presented in the next section of the paper. In zones commonly associate clay minerals in the ‘‘bleached’’ parts some instances, there is a brighter variety of FeOH–MnOH and these minerals are represented by interstratified illite/smectite (Fig. 3g) and the light grey domain show distinct concave outlines (Fig. 3b). These bleached metavolcanics are Al-rich and contain (Fig. 3h). abundant kaolinite and other clay minerals (Qadhi, 2008). As Microscopically, the copper slags of the Jabal Samran area are another evidence of shear effect, some of the pre-existing pyrite rich in sub-rounded to rounded Cu prills (Fig. 4a). These prills show shows perfect strain shadow (Fig. 3c). Pargenetically, it is clear that distinct variation in their size where the largest one is character- the secondary copper veinlets post-dates the formation of earlier ized by discontinuous border zone or incomplete crust of S-rich veinlets of FeOH (Fig. 3d). The width of the secondary copper vein- Mn–Cu alloy (Fig. 4a). The slags still preserve few relics of the lets (as green paratacamite) is obviously greater than the much secondary ore (paratacamite with inclusions of FeOH–MnOH) thinner oxyhydroxide veinlets (Fig. 3e) and because of time differ- inside the Cu prills (Fig. 4b). In the majority of cases, both glass ence, the former may contain the latter (Fig. 3f). In polished-sec- and quartz clusters (Fig. 4c) represents about 25–40% of the slag’s tions, the FeOH–MnOH occur in the form of thin veinlets or volume. The latter figure also documents the occurrence of radiat- colloform-like thin crenulated laminae with distinct zonation in ing Mn-rich silicate. The silicate formed in the slag during extrac- which two grey shades are observed (Fig. 3g). Sometimes, the cren- tion of copper is amphibole-like with radial structure grows at a ulated laminae display concave–convex geometric relationship. base of amorphous material, most probably glass (Fig. 4d). The The lighter grey phase shows better polishing whereas the darker Mn-rich amphibole is spinifixed and its length amounts 160– one is more or less spongy. The nature of such two domains with 200 lm, and some crystals show fine hollow structure due to its different grey shades is discussed later on when their mineral skeletal nature which results from quenching (Fig. 4e). Fig. 4f 74 A.A. Surour / Journal of African Earth Sciences 101 (2015) 70–83

Fig. 3. (a) FeOH in the form of veinlets and pseudomorph after pyrite, P.P.L., (b) sub-parallel veinlets of FeOH–MnOH in smectite/illite-rich groundmass, C.N., (c) pre-existing pyrite showing strain shadow, C.N., (d) BSE image showing the formation of paratacamite (white, right) followed by FeOH–MnOH (grey, left), (e) relatively thicker paratacamite veinlet (green) than artery-like thin FeOH–MnOH, P.P.L., (f) details of green paratacamite veinlet with earlier fringes of FeOH–MnOH (black), P.P.L., (g) light whitish grey colloform, spongy and dark grey FeOH, Polarized Reflected Light, and (h) details of fine polished light grey colloform FeOH, Polarized Reflected Light. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) shows different synthetic silicate phases which are represented by microanalyses of Fe–Mn(III) oxyhydroxide are given in Tables 1 Mn-rich skeletal amphiboles, Fe-silicate skeletal mush room-like and 2. The FeO–MnOH phases of Jabal Samran are amorphous as crystals and Fe-silicate fine dendrites. In few cases, the Mn-rich indicated by XRD (Fig. 5a) whereas the Mössbauer spectrum indi- amphibole phases in the form of needle-like clusters fill some vugs cates that the iron is typically ferric (Fe3+)(Fig. 5b). Because water in glass (Fig. 4g). The slags possess common quartz clusters that cannot be determined by the electron microprobe, these tables are occasionally idiomblastic and fractured (Fig. 4h). assumes 20 wt% H2O content which is the most acceptable water in similar hydrothermal b-Fe(III) oxyhydroxide (Pichler and 6. Mineral chemistry of natural and synthetic phases Veizer, 1999). In order to justify such a content, L.O.I. was deter- mined for two almost pure FeOH–MnOH samples from Samran 6.1. Fe–Mn(III) oxyhydroxide and the content was in the range of 17.5–23 wt% H2O which is almost the average of 20 wt%. This section is devoted to the microchemistry of minerals in the The EMPA analyses of different varieties of FeOH are given in investigated ore samples (secondary mineralization) and some Table 1. The grouping enabled the author to distinguish five dis- samples of slags. For this purpose several spots are analyzed by tinct varieties of FeOH, namely (1) well-polished colloform-like, the electron microprobe in both natural and synthetic minerals. (2) spongy colloform, (3) spongy phase pseudomorphing pyrite A special emphasis is given on the chemistry of Fe–Mn(III) cubes, (4) light grey veinlets, and (5) dark grey veinlets. The EMPA oxyhydroxide (FeOH and MnOH) because there are only few infor- analyses show that the two colloform varieties and the two veinlet mation available about the mineral chemistry in literature. Thirty varieties are Mn-free. The only Mn-bearing variety is the spongy A.A. Surour / Journal of African Earth Sciences 101 (2015) 70–83 75

Fig. 4. (a) Different sizes of Cu prills. Note a discontinuous S-rich Mn–Cu crust outside the largest prill, BSE image, (b) Cu prill with relict green paratacamite ore and black FeOH–MnOH, P.P.L., (c) light and dark brown glass with shattered quartz fragments from quartzite flux, P.P.L., (d) Mn-rich amphibole-like phase in the form of a rosette, P.P.L., (e) long spinifixed lathes of Mn-rich amphibole-like phase, P.P.L., (f) Mn-rich amphibole-like (dark) and Fe–Mn silicate dendrites and mushroom-like crystals (light), BSE image, (g) Mn-rich amphibole-like fine lathes filling cavity in brown glass, P.P.L., and (h) sub-idioblastic fractured quartz from the quartzite in the slag, C.N. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

phase after pre-existing pyrite. The Fe2O3 content in well-polished substitution and this appears more distinct from the contents of colloform FeOH lies in the range 76.45–78.96 wt% which is higher Fe2O3 (37.52–57.13 wt%), Al2O3 (10.22–14.69 wt%) and SiO2 than the range is spongy colloform-like FeOH (60.68–71.68 wt%). (11.27–17.82 wt%) if they are compared to the same contents in

Generally, Fe2O3 is negatively correlated with SiO2 (Fig. 6a), and the light grey FeOH veinlets (71.06–77.08 wt%, 0.05–2.99 wt% it is expected that Fe3+ occupancy in the tetrahedral for Si4+ in and 0.33–2.54 wt%, respectively). Four varieties of FeOH are almost the spongy colloform-like FeOH is very minor particularly when Mn-free except for the one that pseudomorph the pyrite cubes the range of SiO2 is 3.47–11.31 wt%. Structural formulae of amor- which are occasionally Mn-bearing with up to 6.82 wt% MnO2. This phous phases are not recommended because they lack ordered can be seen in Fig. 6c which shows also that some spongy collo- atomic structure. Nevertheless, the charge difference and contents form-like FeOH bears MnO2 (0.9–2.67 wt%). Mn is brought into of Ca and MgO may suggest possible erratic ionic substitution cou- pyrite by the decomposition of Mn-rich silicates in the alteration pled with silica for ferric oxide. Al2O3 content reaches up to zones. It is worth to notice here that some analyses of dark grey 2.98 wt% in both varieties of colloform FeOH and Table 1 shows FeOH veinlets with the lowest iron content have low totals 87– that in some spongy colloform FeOH, Fe3+ is replaced considerably 89 wt% which may indicate that their water content is much higher 3+ by Al where the Al2O3 content reaches up to 8.58 wt% and Fe2O3 and possibly amounts up to 33 wt%. This is normal for banded or content becomes as low as 60.68 wt%, and hence a negative corre- laminated amorphous phases that might show variation in H2O lation of Fe2O3 with Al2O3 is obtained (Fig. 6b). Similarly, the latest content in each ban or laminae, e.g. the cases of goethite and lep- phase of FeOH which are the dark grey veinlets have both types of idocrocite. In addition, it seems that little but not negligible Al3+ 76 A.A. Surour / Journal of African Earth Sciences 101 (2015) 70–83

Table 1 EMPA of Fe(III)-oxyhydroxide (FeOH). Oxides are in wt%.

Variety A A A A A A A A B B B B B Analysis # T14-1 T14-2 T14-3 T14-4 T14-8 T14-10 T14-6 T14-7 T13-6 T13-7 T14-5 T18-14 T18-16

SiO2 1.49 1.6 1.78 1.81 1.48 1.18 1.21 1.35 3.47 3.27 4.01 10.88 11.31

TiO2 0.05 0 0 0.01 0 0.02 0 0 0 0 0 0.03 0

Al2O3 1.39 1.27 1.47 1.63 1.01 0.6 1.28 1.34 0.15 0.02 2.98 8.58 7.88

Cr2O3 0 0 0 0 0.01 0 0 0.01 0 0 0 0 0.01

Fe2O3 78.72 78.44 77.83 76.63 77.88 78.96 77.3 76.45 73.6 74.11 71.68 60.68 61.07

MnO2 0 0 0 0 0 0 0 0 2.67 0 0 0.9 0 MgO 0.03 0 0.1 0.02 0.03 0 0.03 0.06 0.25 0.62 0.05 0.17 0.32 CaO 0.12 0.13 0.2 0.23 0.03 0 0.01 0.03 0.66 0.19 0.07 0.6 0.53

Na2O 0.06 0.01 0 0.06 0 0.02 0.06 0.07 0.05 0 0.06 0.06 0.07

K2O 0.02 0.02 0.01 0.01 0.01 0.03 0 0.01 0.02 0.01 0.04 0.05 0.04 NiO 0 0 0 0 0 0 0 0 0 0 0.04 0 0

H2O 20202020202020202020202020 Total 101.88 101.47 101.39 100.4 100.45 100.81 99.89 99.32 100.87 98.22 98.93 101.95 101.23 CCCCDDDDE E E E T13-1 T13-4 T13-5 T18-15 T14-11 T14-12 T14-13 T14-17 T14-14 T14-15 T14-16 T14-18

SiO2 2.36 1.94 0.33 2.54 1.96 1.33 1.71 1.71 12.67 17.82 11.27 11.58

TiO2 0.01 0.02 0 0 0 0 0 0.03 0.01 0.04 0 0

Al2O3 0.3 0.05 0.06 1.42 1.52 1.01 2.07 2.99 10.22 14.19 14.69 10.61

Cr2O3 0 0 0 0 0.01 0.01 0 0 0 0.03 0 0

Fe2O3 74.2 71.06 72.64 74.79 75.77 77.08 74.87 74.59 57.13 48.75 37.52 44.2

MnO2 2.23 6.49 6.82 0 0 0 0 0 0 0 0 0 MgO 0.32 0.16 0.24 0.19 0.05 0.01 0.08 0.03 0.04 0.01 0.38 0.38 CaO 0.69 0.59 0.54 0.65 0.06 0.08 0.06 0.15 0.08 0.05 2.04 1.4

Na2O 0.01 0.05 0.19 0.03 0 0 0.03 0 0.04 0.02 0.41 0.28

K2O 0.01 0.02 0.12 0.02 0.03 0.01 0.01 0.03 0 0.01 0.57 0.49 NiO 0 0 0.04 0 0 0 0 0 0 0.01 0.01 0

H2O 202020202020202020202020 Total 100.13 100.38 100.98 99.64 99.4 99.53 98.83 99.53 100.19 100.93 86.89 88.94

A: Fine-polished light gry colloform FOH. B: Spongy colloform-like FOH. C: Mn-bearing FOH pseudomorphing pyrite cubes. D: Light grey Mn-free FOH veinlets. E: Dark grey Mn-free FOH veinlets.

replaces Fe3+ in the Samran FeOH in the same way like Al-saturated Table 2 goethite and hematite do (Amarasiriwardena et al., 1986). EMPA of Mn(III)-oxyhydroxide (MnOH). Oxides are in wt%. Table 2 shows that MnOH might also contain higher water con- Analysis # T13-2 T13-3 T18-11 T18-12 T18-13 tent up to 30 wt% with MnO2 content as low as 62 wt%. On the SiO2 0.43 0.53 0.33 0.35 0.28 other hand, analyses for spots with normal water content around TiO2 0 0 0.02 0.02 0 20 wt% show higher MnO2 content (70.03–76.87 wt%) either in Al2O3 0.13 0.27 0.66 0.8 0.57 the form of thin veinlets in the groundmass or as pseudomorph Cr2O3 000 0 0 Fe2O3 3.08 6.13 0.81 0.93 1.01 for pyrite. In the Mn(III) oxyhydroxide structure, Fe2O3 is positively MnO2 76.87 70.03 73.01 62.06 74.21 correlated with SiO2 (Fig. 6d) whereas it is negative correlation MgO 0.04 0.12 0.37 0.93 0.19 between MnO2 and Al2O3 (Fig. 6e). The plot of Fe2O3 vs. MnO2 does CaO 0.33 3.36 0.83 1.26 0.67 not show a clear trend and this suggest that there is almost negli- Na2O 0 0.06 1.57 1.46 1.03 gible substitution for manganese by iron in the MnOH (Fig. 6f). K2O 0.02 0.03 2.43 1.99 2.87 NiO 0.02 0 0.03 0.01 0.03

H2O2020202020 6.2. Silicate minerals Total 100.92 100.53 100.06 89.81 100.86

EDX spectral analysis of paratacamite by Qadhi (2008) and by Ca-bearing Fe-rich olivine-like phase from the Roman copper slags the present study confirms the composition of the ore. Hydrother- in Egypt was recently reported by Abd El-Rahman et al. (2013). mally altered feldspars are now represented by interstratified Hence, this olivine-like phase in the Samran slags can be consid- illite/smectite with considerable K2O content (6.45–8.51 wt%). ered as a phase that lies tentatively in the series kirschsteinite The given analyses in Table 3 suggest that they can be considered (CaFeSiO4)–glaucochroite (CaMnSiO4). The Samran’s olivine-like as Fe-smectite similar to those of Desprairies et al. (1989). The phase contains much higher Al2O3 (5.16 wt%) than in any natural smectite/illite structure contains considerable K atoms (1.132– analogue. The investigated olivine-like phase in the Samran slags 1.6) and a remarkably wide range of Aliv (0.601–1.805). Whether is relatively enriched in Si and the end-members of the analyzed it is formed by weathering or hydrothermal alteration, smectite/ phase are calculated as follows: Te19.73 Fo2.13 Fa58.98 Ca–Ol19.16. illite (mostly illite) can bear Fe2O3 about 1.04 wt% and low K2O Compositionally, the analyzed Mn-rich amphibole-like phases are about 4.86 wt% (Duzgoren-Ayden et al., 2002). close, but not identical, to mangnogrunerite and ferro–actinolite In the Jabal Samran slag samples, it was possible to analyze following the modern classification of Hawthorne et al. (2012) occasional synthetic silicate close to olivine and common synthetic and recommendations for precise nomenclature by Oberti et al. Mn-rich amphibole-like phases (Table 3). This olivine-like phase is (2012). The composition of such a synthetic Mn-rich amphibole- Fe-rich with 28.67 wt% FeO and considerable contents of both like phase and two spectral EDX analyses are given in Fig. 7. This CaO and MnO (7.27 wt% and 9.47 wt%, respectively). A similar amphibole (fine groundmass lath, long spinifixed lath and A.A. Surour / Journal of African Earth Sciences 101 (2015) 70–83 77

dendrite) show high MnO (8.97–16.73 wt%). It is evident that long spinifixed lathes bear lesser manganese which is negatively corre- lated with iron (Fig. 8). In the dendritic amphibole-like variety, MnO reaches up to 21 wt% and almost all amphibole-like varie- ties bear some barium where BaO amounts (2.9–3.7 wt%) (Fig. 7). According to the distribution of cations in the Samran synthetic amphiboles, the following structural formulae can be fitted: Chemical formula of mangnogrunerite:

2þ ðFe2:15Mg0:25Mn1:71Ca0:94Na0:24K0:11ÞR5:4ðSi7:98Al0:04ÞR8:02O22ðOHÞ2 Chemical formula of manganoan ferro–actinolite: Ã 2þ 0:39ðCa1:36Na0:17K0:08ÞR1:91ðFe2:29Mg0:16Mn1:39Al0:94ÞR4:78

ðSi8:10Al0ÞR8:10O22ðOHÞ2

What is important to mention here that the given structural formu- lae are close to structure of amphibole but not identical to formulae of natural and artificial amphiboles. Of course artificial amphibole is prepared in the laboratory under well-determined physico- chemical conditions and the ingredients are blended accurately which was not the case of Samran amphiboles because the latter were produced by ancient primitive metallurgy in open-air with haphazard ingredients and high possibility of contamination. Thus, if we compared the structural formulae of Samran amphiboles with the natural and artificial analogues, two important information will Fig. 5. (a) XRD chart of FeOH–MnOH phase showing amorphous to nano-crystalline nature. (b) Characteristic ferric iron in the same phase as appeared on the be noted. First, the Samran amphibole has remarkable deficiency at Mössbauer spectrum. the B-site (1.2–1.5 Ca apfu and 0.2–0.4 Na apfu), in addition to

Fig. 6. Binary plots of oxides in FeOH (a, b and c) and in MnOH (d, e and f). 78 A.A. Surour / Journal of African Earth Sciences 101 (2015) 70–83

Table 3 EMPA of silicate minerals from ‘‘bleached’’ hydrothermally altered metadacite and Cu slags. Oxides are in wt%.

Mineral A B C C D D EEEE Analysis # T21-4 T13-10 T13-8 T18-17 T21-7 T21-8 T22-12 T22-13 T22-14 T22-15

SiO2 43.87 36.56 42.04 53.78 51.27 51.79 52.08 51.92 51.62 51.64

TiO2 0.12 0.07 0.52 0.15 0.14 0.14 0.24 0.21 0.1 0.07

Al2O3 5.16 18.85 30.49 25.52 5.05 5.26 6.21 8.74 6.69 5.93 FeOt 28.67 9.81a 4.02 1.5 20.77 17.49 17.95 14.71 15.18 14.31 MnO 9.47 28.59 0.14 0 8.97 10.47 13.35 12.59 13.65 16.73 MgO 0.58 0.12 0.65 0.49 0.78 0.67 1.02 0.77 0.99 1.93 CaO 7.27 3.89 0.22 0.06 6.66 8.13 4.62 5.35 5.73 6.08 BaO 0 0 0 0 3.72 3.17 1.34 2.12 2.78 1.77

Na2O 0.31 0 0.35 0.79 0.5 0.56 0.78 1.4 1.13 0.18

K2O 0.44 0.02 8.51 6.45 0.48 0.41 0.71 0.79 0.6 0.17 NiO 0 0 0 0 0.04 0 0 0.03 0.05 0.01 Total 95.89 97.91 86.94 88.74 98.38 98.09 98.3 98.63 98.52 98.82 Structural formulae Oxygens 4 12.5 22 22 23 23 23 23 23 23 Si 1.451 3.057 6.195 7.399 8.091 8.098 8.012 7.892 7.991 7.935 Al iv 0.201 1.858 1.805 0.601 0.000 0.000 0.000 0.108 0.009 0.065 Al vi 0 0 3.490 3.537 0.939 0.969 1.126 1.458 1.212 1.009 Ti 0.003 0.004 0.058 0.016 0.017 0.016 0.028 0.024 0.012 0.008 Fe2+ 0.793 1.002a 0.495 0.173 2.741 2.287 2.309 1.870 1.965 1.839 Mn 0.265 1.977 0.017 0 1.199 1.387 1.740 1.621 1.790 2.177 Mg 0.029 0.017 0.143 0.101 0.184 0.156 0.234 0.174 0.228 0.442 Ca 0.258 0.340 0.035 0.009 1.126 1.362 0.762 0.871 0.950 1.001 Ba 0.691 0.592 0.264 0.321 0.499 0.293 Na 0.018 0.000 0.100 0.211 0.153 0.170 0.233 0.413 0.339 0.054 K 0.019 0.000 1.600 1.132 0.097 0.082 0.139 0.153 0.118 0.033 OHa 2.000 2.000 2.000 2.000 2.000 2.000 Total 3.037 8.115 13.938 13.178 17.238 17.119 16.847 16.905 17.114 16.856 Ca + Na (B) 1.279 1.532 0.994 1.284 1.290 1.055 Na (B) 0.153 0.170 0.233 0.413 0.339 0.054 Na + K (A) 0.097 0.082 0.139 0.153 0.118 0.033 Mg/Mg+Fe2+ 0.063 0.064 0.092 0.085 0.104 0.194 Amphibole name Grunerite Ferro–actinolite Grunerite Grunerite Grunerite Grunerite

A: Olivine-like phase in slag. B: Mn-rich epidote in bleached metadacite host. C: Smectite/illite in bleached metadacite host. D: Mn-rich amphibole short lathes, mostly in groundmass and cavities in glass. E: Mn-rich amphibole long spinifixed lathes forming the majority of groundmass for Cu prills. a Total Fe as ferric.

Fig. 8. Variations of FeOt vs. MnO in two varieties of Mn-rich amphibole phases.

Fig. 7. SEM–EDX spectrum of a short spinifixed silicate phase and spectral analyses of that phase and Fe–Mn silicate dendrites. BSE image is the same as in Fig. 4f. 6.3. Cu prills and metal alloys almost sufficient Fe + Mg to fill the C-sites. Accordingly, the most acceptable analyses of Samran amphiboles that are analogous to Table 4 provides some EMPA of native almost native Cu prills natural or artificial amphiboles are spot analyses # T22-13 and (with 97–100 wt% Cu) and some metals alloys that occur as T21-8. If totally identical to the natural analogue, the Samran inclusions in the prill or as crusts in the border zone which were amphiboles should bear Ca in the B-site >1.5 apfu and the sum of shown before in the section of ore microscopy. Fig. 9 shows the dif- B + C cations should not be 5.4 but 7. ferent clusters of the analyzed metals. It seems that the both the Cu A.A. Surour / Journal of African Earth Sciences 101 (2015) 70–83 79 prills and inclusions contain very minor sulphur whereas the grey 2013) suggest that iodine-rich Cu-rich supergene zones are formed crust contains high S content amounting 20.78–21.95 wt% (Table 4 from marine waters rather than a meteoric and/or atmospheric and Fig. 9a). On the other hand, Cu is negatively correlated with source. This is strongly supported by the formation of atacamite both Fe and Mn in both varieties of alloys (Fig. 9b and c) suggesting and paratacamite from cuprous-chloride complexes in the MOR substitution of Fe2+ M Mn2+ as shown in Fig. 9d. Table 4 shows that seafloor hydrothermal fields. Such complexes migrate from the some Cu prills and inclusions in it have considerable Au content reaction zones and upon increasing Eh, Cu2Cl(OH)3 precipitates (0.08 wt% and 0.06 wt%, respectively) taking in consideration that (Dekov et al., 2011). Opposite to such a mechanism, Arcuri and lower detection limit of gold by the EMP was 0.057 wt%. Brimhall (2003) believed in a meteoritic origin of the fluids and excluded a non-magmatic origin based on high bromine content and low d37Cl. The potential sources of non-magmatic chloride 7. Discussion can be sweater or marine sediments including evaporates. In accordance, the present author favors the formation of Samran 7.1. Precambrian geology and ore genesis paratacamite from an inherited marine source which is supported by the presence of some barite and natrojarosite in the secondary The concealed Samran 825–745 Ma VMS ore is characterized by Cu supergene zone (Qadhi, 2008). The occurrence of barite was the presence of supergene copper mineralization that was used to responsible for the introduction of Ba2+ into the structure of extract the metal in antiquity (Nehlig et al., 1999; Johnson, 2006). synthetic Mn-rich amphibole-like phase in the slag (Fig. 7). The host arc metavolcanics undergone common deformation related to the tectonics of the late Neoproterozoic such as dextral and sinistral brittle-ductile shearing and isoclinal folding. The pres- 7.2. Fe–Mn(III) oxyhydroxides and their significance ent work documents the formation of hydrothermal pyrite in the wallrock alteration zones that is commonly transformed into a Generally, Fe and Mn tend to fractionate into distinct phases Fe–Mn(III) oxyhydroxides (FeOH–MnOH). The cross-cut depending on the redox conditions because of their different oxi- relationships suggest a younger age for the supergene Cu ore dation potentials (Hem, 1972; Braun et al., 1998). FeOH–MnOH (mostly paratacamite) than the FeOH–MnOH which indicates formed in deep marine sites and their origin can be either hydrog- hydrothermal alteration superimposed by supergene enrichment enous or hydrothermal (Bonatti, 1975; Varentsov et al., 1991; (Fig. 3d–f). The Jabal Samran subsurface VMS ore (Liddicoat, Boughriet et al., 1996) and sometimes anthropogenic (Holmström 1966, 1971; Rexworthy, 1972) might represent a keel zone of a and Öhlander, (2001). The present example of the Jabal Samran VMS deposit or a ‘‘Bonanza’’ near surface epithermal vein type FeOH–MnOH in ‘‘bleached’’ in metadacite–metarhyodacite host deposit (Ba-battat and Hussein, 1983). rocks represent products of submarine hydrothermal alteration

Paratacamite [Cu2Cl(OH)3] is a common product of weathering along shear zones which is indicated by the conjugate fracturing in arid regions that possess some primary Cu-rich VMS and por- (Fig. 2a), introduction of hydrothermal pyrite (Fig. 3a) and its strain phyry Cu deposits (Le Roux, 2013). Paratacamite has two similar shadow effect (Fig. 3c). So, they represent pre-weathering alter- polymorphs, namely atacamite and botallackite (Pollard et al., ation history that involved deuteric and/or hydrothermal events. 1989). The formation of paratacamite as a supergene mineral In this respect, it should be emphasized here that the formation requires considerable amount of Cl that can be derived either of FeOH–MnOH by weathering in felsic igneous rocks if the condi- from surface evaporates or the inherited chlorine content of the tions were humid enough for bleaching, fixation and oxidation marine volcanic rocks (Arcuri and Brimhall, 2003). Recently, (Duzgoren-Aydin and Aydin, 2009) which is not the case of the Barnes and Cisneros (2012) measured altered oceanic crust with Jabal Samran area. In the Jabal Samran example, the oxyhydroxides <0.1–0.9 wt% chlorine which is about 3 times than in the mantle, precipitate mainly from hydrothermal fluids with limited seawater and the Cl content increases with the increase of temperature contamination similar to the recently studied ones in the oceanic and is more enhanced by the alteration of amphibole in the rock. PACMANUS hydrothermal field, particularly in a back-arc basin Atacamite and paratacamite as Cu hydroxychloride can be formed similar to that of Samran (Zeng et al., 2012). According to the latter in superarid climate that is responsible for evaporation and con- authors, they oxyhydroxides are formed in relatively low-temper- centration of chloride in meteoric waters as indicated by 18O iso- ature (up to 70 °C) and acidic environment (pH up to 3). Several topes (Cameron et al., 2007) or from saline groundwater recent studies documents the formation of FeOH–MnOH as authi- (Cameron et al., 2010). Some recent studies (e.g. Reich et al., genic phases that can be enhanced occasionally by hydrocarbons

Table 4 EMPA Cu prills and associated metal alloys. Oxides are in wt%.

Variety A A A A A A A B B B C C C Analysis # T-2314 T23-15 T23-16 T23-17 T23-20 T23-24 T23-25 T22-7 T22-8 T23-21 T22-10 T22-12 T23-13 As 0.05 0 0.03 0.02 0.04 0.04 0.01 0.02 0 0 0.07 0.05 0.02 Co 0 0.02 0.02 0 0.02 0 0.04 0 0 0 0.11 0.13 0.11 S 0.2 0.07 0.03 0.02 0.68 0.04 0.05 20.83 20.78 21.95 0.2 0.16 0.21 Ni 0 0 0 0.01 0 0 0 0 0.01 0 0 0.02 0.05 Cu 98.4 98.16 98.12 96.66 96.56 99.33 99.55 53.75 56.82 76.25 15.9 1.09 5.65 Au 0 0 0 0.08 0 0 0 0 0 0 0 0.04 0.06 Zn 0.18 0.09 0.03 0.16 0.06 0.11 0.07 0.09 0.12 0.02 0.09 0.05 0.01 Ag 0.01 0.02 0.03 0 0 0.01 0 0.03 0.02 0 0 0 0 Pb 0.09 0 0 0.01 0 0 0 0 0 0 0 0.05 0.05 Fe 0 0 0 0 0 0.02 0.42 5.77 4.13 0.38 43.97 61.64 58.06 Mn 0.71 0.35 0.82 1.99 2.15 0.11 0.09 19.54 18.89 1.23 39.12 34.88 35.17 Total 99.64 98.71 99.08 98.95 99.51 99.66 100.23 100.03 100.77 99.83 99.46 98.11 99.39

A: Almost native or pure Cu prill. B: S-rich Mn–Cu alloy inclusions in Cu prill. C: Cu–Mn–Fe alloy crust as a border zone of Cu prill. 80 A.A. Surour / Journal of African Earth Sciences 101 (2015) 70–83

Fig. 9. Binary plots of metals in the Cu prills with S-rich Mn–Cu and Cu–Mn–Fe alloys as crusts and inclusions, respectively. and biogenic activities, if any (Gutjahr et al., 2007; Merinero et al., Matsubara et al., 2002; Barkley et al., 2010) nor members of the 2008; Charbonnier et al., 2012). In the Jabal Samran occurrence and Fe–Mg–Mn amphibole group of Leake (1978), Lan (1993) and elsewhere in the world, alteration of pyrite-rich zones (either Leake et al. (1997, 2004). The Samran amphiboles contain 4.62– hydrothermally or by weathering) is resulted from the release of 8.13 wt% CaO which is similar to synthetic low-Ca actinolite of Fe3+ which is transported by low-pH waters with negligible buffer- Driscall et al. (2005) with 8.10–12.60 wt% CaO. The Samran Mn- ing capacity, and precipitates initially as ferrihydrite with subse- rich amphiboles are occasionally close to ferro–actinolite according quent conversion to goethite, lepidocrocite, groutite and finally to the nomenclatures of Deer et al. (1997) and Hawthorne et al. to FeOH–MnOH (Deyell et al., 2000; Taylor and Eggleton, 2001; (2012) as the content of FeOt reaches up to 20.77 wt%, and can Liu et al., 2007). Almost all phases in the series are amorphous or be comparable to manganoan ferro–actinolite in natural assem- poorly (nano-)crystalline (Cudennec and Lecerf, 2006; Michel blages (Kazachenko et al., 1981; Damman, 1989; Pan and Fleet, et al., 2007). Experimentally, the direction of transformation can 1992; Damman and Lustenhouwer, 1992; Vassileva and Bonev, be reversed where goethite and lepidocrocite are topotactically 2001). The olivine-like phase in the Jabal Samran slags has a tenta- transformed into hematite and maghemite which is totally lacking tive location in the kirschsteinite (CaFeSiO4)–glaucochroite (CaMn- in natural geological assemblages (Cudennec and Lecerf, 2005). SiO4) series with 7.27 wt% CaO and 9.47 wt% MnO and not Mg–Fe Normally, a phase like ferrihydrite is characterized by partial olivine like in other Cu slags (Piatak et al., 2003; Rozendaal and ordered structure with up to 9 wt% silica (Childs, 1992; Horn, 2012) which is a direct result of Mn-enrichment of the mined Cismasu et al., 2011) and this is the same case or more crystalline Samran secondary Cu ore with common occurrence of hydrother- FeOH phase at the Jabal Samran which contains up to 11.31 wt% mal MnOH. This results in high tephorite or Mn component

SiO2. It is worth to mention here the late dark veinlets FeOH at (Te = 19.73%). the Jabal Samran samples could represent re-working of the early grey FeOH (Fig. 3g and h) and both phases are formed by hydro- 7.4. Ancient metallurgical extraction of Samran copper thermal alteration and weathering, respectively. The reworked FeOH and MnOH are more amorphous and contain much higher The recorded copper slags from the time of Abbasid Caliphate at H2O > 20 wt% (31–33 wt%) as given in Tables 1 and 2. the Jabal Samran area are mineralogically similar to other histori- cal Cu slags elsewhere in the world (e.g. Ryndina et al., 1999; 7.3. Formation of synthetic minerals in slags Manasse et al., 2001; Manasse and Mellini, 2002; Piatak et al., 2003; Rozendaal and Horn, 2012; Dill et al., 2013; Krismer et al., The slags at ancient sites of the Jabal Samran area have a pecu- 2013; Abd El-Rahman et al., 2013) in their native Cu remains that liar mineralogy that is characterized by common occurrence of are left behind after metal extraction from secondary Cu minerals, long spinifixed lathes of Mn-rich silicates that are close in their suphides, cupriferous and tennantite fahlore ores. The chemistry to some amphiboles like grunerite and ferro–actinolite composition of synthetic Mn-rich amphiboles and the complete (Fig. 4e) alongside with other similar silicates (Fe–Mn-rich den- absence of any spinel phase suggest temperature of furnace during drites) and glass, in addition to Cu prills with distinct composition smelting not exceeding about 600 °C, and can be as low as 220 °C of metals. Amphiboles in the slags of Samran are Mn-rich with which is the melting point of the paratacamite ore (Piatak et al., MnO up to 16.73 wt% (Table 3) and although of this percentage 2003; Rozendaal and Horn, 2012). It is believed that silica was used they are neither Mn-rich alkali amphiboles (Chang et al., 1991; as a flux to lower temperature in the Samran furnaces and this is A.A. Surour / Journal of African Earth Sciences 101 (2015) 70–83 81 indicated by the common occurrence of quartzite fragments and Ba-battat, M.A., Hussein, A.A., 1983. Geology and mineralization of the Jabal fractured crystals (Fig. 4h). Silica flux is proven to be very effective Samran-Jabal Abu Mushut area. J. King Abdulaziz Univ., Earth Sci. Section 6, 571–578. in the metallurgical reactions for extraction of copper from its ore Barkley, M.C., Yang, H., Downs, R.T., 2010. Kôzulite, an Mn-rich amphibole. Acta minerals (Schoniwelle et al., 1993). Finally, it is suggested Mn is Chrystallogr. 66, Section E, Part 12, i33. expelled from the Cu prill’s structure and nucleated inward Barnes, J.D., Cisneros, M., 2012. Mineralogical control on the chlorine isotope composition of altered oceanic crust. Chem. Geol. 326–327, 51–60. as Cu–Mn–Fe alloy inclusions whereas S is expelled outwards as Bayon, G., German, C.R., Burton, K.W., Nesbitt, R.W., Rogers, N., 2004. Sedimentary S-rich Mn–Cu alloy discontinuous crust (Fig. 4a). Fe–Mn oxyhydroxides as paleoceanographic archives and role of Aeolian flux in regulating oceanic dissolved REE. Earth Planet. Sci. Lett. 224, 477–492. Blodget, H.W., Brown, G.F., 1982. Geological Mapping by Use of Computer- Enhanced Imagery in Western Saudi Arabia. U.S. Geological Survey 8. Conclusions Professional Paper 1153, 10p. Bonatti, E., 1975. Metallogenesis at oceanic spreading centers. Annu. Rev. Earth The Jabal Samran secondary Cu mineralization is formed at the Planet. Sci. 3, 401–431. Boughriet, A., Ouddane, B., Wartel, M., Lalouj, C., Cordier, C., Genembre, L., expense of concealed late Neoproterozoic VMS ore bodies that Sanchez, J.P., 1996. On the oxidation state of Mn and Fe in polymetallic practiced chemical weathering in a supergene alteration zone. oxide/oxyhydroxide crusts from the . Deep Sea Res. Part I 43, The common Cu secondary mineral is paratacamite that fills frac- 321–343. Braun, J.J., Viers, J., Dupre, B., Polve, M., Ndam, J., Müller, J.J., 1998. Solid/liquid REE tures and post-dates FeOH and MnOH. Paratacamite incorporated fractionation in lateritic system of Goyoum, East Cameroon: the implication for Cl in its structure from an inherited marine source rather than the present dynamics of soil covers of the humid tropical regions. Geochim. from surfacial evaporates or meteoric water. Nevertheless, the role Cosmochim. Acta 62, 273–279. of meteoric water cannot be ruled out totally which still needs Brown, G.F., Schmidt, D.L., Huffman, A.C., Jr., 1989. Geology of the Arabian Peninsula, Shield Area of Western Saudi Arabia. U.S. Geological Survey Professional Paper some stable isotopic evidence in the future. The FeOH and MnOH 560-A, 188p. are pre-weathering phases that are formed prior to uplifting during Cameron, E.M., Leybourne, M.I., Palacios, C., 2007. Atacamite in the oxide zone of hydrothermal alteration in a submarine environment. They are copper deposits in northern Chile: involvement of deep formation waters? Minerallium Deposita 42, 205–218. associated with intrastratified Fe-bearing smectite/illite in Cameron, E.M., Leybourne, M.I., Reich, M., Palacios, C., 2010. Geochemical anomalies bleached siliceous metavolcanic host rocks. Four varieties of FeOH in northern Chile as a surface expression of the extended supergene metallogenesis of buried copper deposits. Geochem.: Explor., Environ. Anal. (with 20 wt% H2O) are exclusively hydrothermal whereas the late 10, 157–169. dark FeOH veinlets only and few MnOH (with 31–33 wt% H2O) Chang, W.O.H., Liou, J.G., Maruyama, S., 1991. Low-temperature eclogites and represent reworking of earlier hydrothermal FeOH–MnOH phases eclogitic schists in Mn-rich metabasites in Ward Creek, California; Mn and Fe by weathering. In the Samran slags, the most common silicate effects on the transition between blueschist and eclogite. J. Petrol. 32, 275–302. Charbonnier, G., Pucéat, E., Bayon, G., Desmares, D., Dera, G., Durlet, C., Deconinck, phase a Mn-rich amphibole-like phase that crystallizes in the form J.-F., Amédro, F., Gourlan, A.T., Pellenard, P., Bmou, B., 2012. 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