Introduction

Orogenic gold deposits in collisional or post-collisional tectonic settings form via a range of transpressional to compressional processes (Groves et al. 1998; Goldfarb et al. 2001). Such deposits commonly exhibit the following characteristics: (1) their host rocks are deformed and metamorphosed, although mineralization is structurally controlled by brittle faults or ductile shear zones that cross-cut metamorphic fabrics; (2) fluid inclusions indicate the presence of low-salinity ore-forming fluids that are primarily mixtures of H2O and CO2, with minor CH4 and N2, and a near-neutral pH; (3) associated metasomatic alteration assemblages contain quartz, sericite, sulfide, carbonate, and chlorite (Chen 2006; Goldfarb et al. 2001; Groves 1993; Groves et al. 1998; Pirajno 2009). Thermobarometry performed on these deposits indicates that the mineralized lodes formed at pressure–temperature (P–T) conditions of 1–5 kbar and 200–650 °C, representative of the upper and middle continental crust.

The Arabian-Nubian Shield (ANS) is a developing world-class area for gold assets where gold deposits are broadly linked to post-tectonic granitoid rocks (El-Gaby et al. 1988; Pohl 1988). Gold is common within Egypt’s Eastern Desert, with major deposits identified in El Sukkari, Hamash, and El-Barramiya. According to Goncharenko (1970) and Kuleshevich (1984), the term "listvenite" was first used by Soviet geologists in the Ural goldfields of Russia and is now commonly used throughout Europe and North America. It defines a mineralogical assemblage that emerges from the carbonatization of serpentinized ultramafic rocks and represents a peculiar alteration suite that is frequently connected to quartz-carbonate lode gold deposits. Listvenite forms when fluids rich in carbon dioxide permeate and bearing K alter the previously altered ultramafic rocks, usually serpentinites. Although listvenite has long been known to exist in Saudi Arabia's Neoproterozoic rocks, several of these occurrences have recently undergone fresh research due in large part to its close connection to gold mineralization (Gahlan et al. 2020a, 2022). Carbonation causes the destabilization of the silicates, minor oxides, and sulfides that make up serpentinized peridotites, affecting the redistribution of transitional elements between minerals and fluids. The carbonation of listvenite is accompanied by changing assemblages of Fe oxides and sulfides in Fanja (Decrausaz et al. 2023). An important geological process having significance for the production of ore deposits is carbonatization of mafic–ultramafic rocks (Gahlan et al. 2020a; Moussa et al. 2021). In addition to sulfides and other hematite, magnetite, cobalt minerals, and chromite remnants, listvenite frequently contain quartz, carbonate minerals (magnesite, ankerite, and dolomite), and/or fuchsite. According to Osman (2014), El-Barramiya is considered one of the deposits related to Mubarak-Hamash structural block. El Barramiya gold mine area is located at the intersection zone between two major shear zones trending E–W and NW–SE directions (Fig. 1C). The Intersection zones promoted gold mineralization of gold because this area becomes highly sheared due to the effect of brittle–ductile deformation and also the porphyry granite played an important role in hydrothermal solutions and listvenitization process (Zoheir and Lehmann 2011). Buisson and Leblanc 1986; Likhoidov et al. 2007 stated that granitic magmatism has a role in the development of the most fruitful listvenite-related gold resources. The area contains different types of structures such as faults, joints, and foliations (Fig. 1A, B, E).

Fig. 1
figure 1

Field relationships at the Barramiya mine area. A Xenoliths of Serpentenite in carbonate rocks, B foliation (N75° E–S255° W) best preserved in the actinolite–tremiloite schist adjacent to the tectonized serpentinites. C Highly sheared alteration zone for mineralization in the study area. D Foliation of talc carbonate and serpentinite in the E–W direction (E) Joints in listvenite rocks in the study area. F Highly shared serpentine with stockwork vienlets of carbonate

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El Barramiya gold mine area is located at the intersection zone between two major shear zones. The early shear zone trending E–W due to obduction of serpentinite on metasediments and metavolcanics and the later is Najd shear zone which trending NW–SE. The area has become highly sheared due to the effect of brittle–ductile deformation and also the porphyry granite played an important role listvenitization process, and this has resulted in deposition of gold in the intersection zones (Zoheir and Lehmann 2011). Buisson and Leblanc 1986; Likhoidov et al. 2007 stated that granitic magmatism has a role in the development of the most fruitful listvenite-related gold resources.

El-Barramiya area has been studied by many researchers in order to identify subsurface structures, such as faults, shear zones, and lithological contacts, which may affect ore deposit mineralization and allow effective prospecting via a range of geological and geophysical techniques (Mahmoud et al. 2013; Saleh et al. 2018; Mohamed et al. 2022; Abdelrady et al. 2023). Here, we present the results of field work (Fig. 1), petrography, fluid inclusion analysis, and geochemical analyses of mineralized rocks (listvenites, and gold-bearing quartz and carbonate veins) in the El-Barramiya area. From these new data, we interpret the source of the auriferous fluids that led to ore formation, constrain the physico-chemical conditions of mineralization, and identify the major structural controls on the mineralization of ore deposits. The present study covers the applications and importance of fluid inclusion technique, geochemical data for tracing origin of ore-forming fluids, the source of gold and transporting form of Au.

Geological setting

Depending on substantial contrasts in physiographic characteristics and exceptional variances in exposed lithologies, the Eastern Desert of Egypt can be divided into three main provinces; the Northern Eastern Desert (NED), the Central Eastern Desert (CED), and the Southern Eastern Desert (SED) (Abdel Khalek 1979; El-Gaby et al. 1988; Stern and Hedge 1985; Fowler and Osman 2009). The provinces are arranged in opposition to one other along two important structural elements: the Idfu-Mersa Alam Shear Zone separates CED from SED and the Qena-Safaga Shear Zone separates NED from CED. The El-Barramiya region is located in the western portion of the CED, near to its boundary with the SED. The area is located between longitudes 33° 45′ E and 33° 55′ E and latitudes 25° 00′ N and 25° 10′ N and covers about 65 km2 in surface area and is considered a part of the Arabian Nubian shield (Fig. 2C). The basement rocks of El-Barramiya is represented by dismembered ophiolite fragments obducted on metasediments and metavolcanic. During pan-African (Pre-Cambrian) serpentinites were obducted onto island arc metavolcanic and metasedimentary rocks, which themselves are intruded by deformed gabbro and diorite (Fig. 2A).

Fig. 2
figure 2

A Geological and structural map of the El-Barramiya area, B simplified geologic map of the El-Barramiya gold mine area after Zoheir and Lehmann (2011) and Zoheir and Weihed (2014). C Satellite image (ETM) showing the location map of the study area

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Later, subduction related to syn-continental, calc-alkaline, and syn-orogenic granitoids related post- continental collision intruded across this entire sequence, and post-orogenic granites (monzogranite and porphyry) occur in the northern and southern parts of the study area. The study area is also cross-cut by dykes of basic to acidic composition. These ophiolitic mélange rocks in El-Barramiya area are covered from the western part the Nubian Sandstone, which is Upper Cretaceous and Cambrian in age and this resulted in unconformity between basement rocks and sedimentary rocks (Fig. 2A).

Along the thrust zones, talc, magnesite and chromite form veinlets, nodules or irregular pockets are occupied in the sheared ultramafic rocks (Fig. 1D, C, F). Tectonized serpentinites (Fig. 1D, C) such as talc-actinolite schist and talc carbonate rocks are altered to listvenite as near steeply dipping transpressive faults, carbonatization intensifies. According to Zoheir and Lehmann (2011) listvenite is represented by a several hundred meters long and elongate body up to 100 m broad near the mine area (Fig. 2B).

Several gold provinces have regional metamorphic profiles that show moderate to strong geothermal gradients during gold mineralization. There has been discussion on the genesis of gold lodes and the connections between mineralization, metamorphism, and granitoid magmatic processes ever since the discovery of the Sukhoi lode gold–quartz–sulfide dispersed ore in 1961 (Buryak 1982). In El-Barramiya area, the coexistence of actinolite and chlorite in the peak assemblage, for example, suggests that the metamorphism only reached the greenschist-amphibolite facies transition, although Abu-Alam and Hamdy (2014) recommended upper greenschist facies (300–400 °C) for the ophiolitic rocks of the Arabian-Nubian Shield. The gold-bearing quartz and quartz-carbonate veins are geographically and chronologically connected to a dextral shear system that formed in the area during late phases of its deformation history (See Zoheir and Lehmann 2011). Petrographically, large and severely asymmetric and distorted microstructures, dynamic recrystallization, and slip on discrete carbonaceous laminae suggest that the mineralized quartz veins formed from a variety of compressional and tensional regimes (cf. Cox et al. 1987).

Methods

Petrographic studies

Petrographical study where more than 100 thin sections from different rock units include country rocks and quartz Veins have been investigated by the Zeiss optical polarizing microscope model Axioskop 40 for transmitted and reflected light to determine the textures and modal mineralogy of the samples in addition to Ore Microscopy for polished sections. Microscopic and scanning electron microscope (SEM) investigations of samples from mineralized quartz veins with visible areas of sulfide minerals helped to establish a paragenetic sequence of ore minerals. Samples with interesting microscopic features observed by optical microscopy at the geology department, faculty of science, University of Assiut.

Geochemical studies of listvenite and quartz vein rocks

Fourteen samples have been analyzed for major, trace and rare earth elements. Eight samples from listvenite rocks and six samples from hydrothermal quartz veins. These analysis were carried out using ICP-MS technique at ACME laboratories in Canada. SiO2 and LOI were analyzed using gravimetric method in the geochemistry lab, faculty of science, Assiut University. Bulk chemistry analysis have been done on selected samples using AQ250–Ultratrace by ICP Mass where the detection limit equal 1 ppm for 15/30 gm analysis for 37 elements. Double-polished wafers 200–300 µm thick were prepared from the samples.

Fluid inclusion studies of listvenites and quartz veins

Double-polished wafers 200–300 µm thick were prepared from the samples. The present study includes the genetic and non-genetic description of fluid inclusions as well as the phase transition (microthermometry). Microthermometric runs were carried out at the Geology Department, Faculty of Science, Assiut University using a Linkam THMS 600 heating/freezing stage. The stage was calibrated for temperatures between − 56.6 and + 400 °C using Merck chemical standards as well as according to the melting point of distilled water (0 °C) and phase transition in natural pure CO2 inclusions with triple point at (− 56.6 °C). From microthermometric results, the bulk composition and density of the fluids are calculated by using the equation of state of Zhang and Frantz (1987) for H2O–NaCl system and Brown and Lamb (1989) for volatile-rich system. Isochores for different fluid densities are calculated until a fit with the known homogenization temperature is achieved using FLINCOR computer program (Brown 1989). The minimum pressure of trapping is estimated from the constructed P–T diagrams.

Relationship between gold mineralization and metamorphism

Several gold provinces have regional metamorphic profiles that show moderate to strong geothermal gradients during gold mineralization. There has been discussion on the genesis of gold lodes and the connections between mineralization, metamorphism, and granitoid magmatic processes ever since the discovery of the Sukhoi lode gold–quartz–sulfide dispersed ore in 1961 (Buryak 1982). In El-Barramiya area, the coexistence of actinolite and chlorite in the peak assemblage, for example, suggests that the metamorphism only reached the greenschist-amphibolite facies transition, although Abu-Alam and Hamdy (2014) recommended upper greenschist facies (300–400 °C) for the ophiolitic rocks of the Arabian-Nubian Shield. The gold-bearing quartz and quartz-carbonate veins are geographically and chronologically connected to a dextral shear system that formed in the area during late phases of its deformation history (See Zoheir and Lehmann 2011). Petrographically, large and severely asymmetric and distorted microstructures, dynamic recrystallization, and slip on discrete carbonaceous laminae suggest that the mineralized quartz veins formed from a variety of compressional and tensional regimes (cf. Cox et al. 1987).

Hydrothermal alteration processes

According to Hansen et al. (2005), serpentine minerals decompose into magnesite and talc due to carbonization, producing water. As alteration progresses, the silica content increases at the expense of carbonate and produces listvenite, which is a silica- and carbonate-rich mineral. The following petrographic descriptions document hydrothermally altered serpentinites samples from the El-Barramiya area.

Listvenite

Listvenite is a fine-to medium-grained rock that has reddish or yellowish-brown colors in hand sample. In the El-Barramiya area, samples either have a mylonitic schistose texture created by shearing, while others are porous. Petrographically, listvenite is mostly made up of magnesite (40–60 vol%), quartz (30–50 vol%), dolomite (5–10 vol%), and fuchsite (chromian muscovite), with minor serpentine, Cr–spinel remnants, and sulfide minerals. Reactions (1, 2) produce different generations of magnesite (M1, M2 and M3) (Hansen et al. 2005):

$$\begin{array}{*{20}c} {2{\text{ Mg}}_{48} {\text{Si}}_{34} {\text{O}}_{85} \left( {{\text{OH}}} \right)_{62} + \, 45{\text{ CO}}_{2} \to } & {45{\text{ MgCO}}_{3} + \, 17{\text{ Mg}}_{3} {\text{Si}}_{4} {\text{O}}_{10} \left( {{\text{OH}}} \right)_{2} + \, 45{\text{ H}}_{2} {\text{O}}} \\ {{\text{Antigorite}}} & {\text{Magnesite + Talc + Water}} \\ \end{array} ,$$
(1)
$$\begin{array}{*{20}c} {{\text{Mg}}_{3} {\text{Si}}_{4} {\text{O}}_{10} \left( {{\text{OH}}} \right)_{2} + \, 3{\text{ CO}}_{2} \to } & {3{\text{ MgCO}}_{3} + \, 4{\text{ SiO}}_{2} + {\text{ H}}_{2} {\text{O}}} \\ {{\text{Talc}}} & {{\text{Magnesite }} + {\text{ Quartz }} + {\text{ Water}}} \\ \end{array} .$$
(2)

Quartz in weakly deformed listvenite appears as strongly deformed amorphous crystals with a colloformal structure and as coarse isolated wedges. Amorphous microbands of quartz (chalcedony) also occur. Fuchsite in weakly deformed listvenite occurs as fine flakes of green color associated with carbonates, thin bands and cavity fillings (Fig. 3F–H).

Fig. 3
figure 3

Photomicrographs show: A Mafic microlithon bands (quartz and chlorite), reddish brown carbonate-quartz bands in sheared mylonitic listvenite, an augen shape of coarse grained magnesite crystals and asymmetric microstructure C/S. M1 is characterized by euhedral outline of early formed magnesite. B S-shape sigmoidal tension and gashes form along ductile shear indicating extensional deformation. Arrows show the direction of movement. C Carbonate stylolitic texture indicates ductile deformation of quartz of V1 stage. D Carbonates stylolitic structure (St), C/S and C' asymmetric fabrics and intrafolial asymmetric folds (IF) as well as recrystallized quartz (Q2) as indication to ductile shear deformation. E Enlargement of intrafolial asymmetric folds in D. F–H Photomicrographs of ore minerals associated with listvenite, quartz and quartz –carbonate veins. G Banded and brecciated talc carbonate, and the early appearances of amorphous quartz (Ch). H Carbonate rich listvenite, cavity filling quartz (Qz) and fushsite (Fs). F Alternate bands of carbonate (Car) and amorphous quartz (Ch). The latter is also present as filling microfractures in the carbonate bands. Bar 200 µm

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Highly sheared mylonitized listvenite

Strongly sheared listvenite consists of distinct greenish grey, reddish-brown carbonate-quartz bands with foliated mafic–ultramafic microlithon bands (fuchsite, quartz, and chlorite) (Fig. 3A). Altered asymmetric C/S, C’ fabrics, and S-style (winged) magnesite porphyroclasts bounded by fuchsite veinlets are also present. Increased shear strain is manifested by bended flakes of the mica fish elongated parallel to the direction of lineation. Asymmetric S-style quartz–carbonate veinlets are recorded. Common hydrothermal veins of quartz and quartz–carbonate with gold and sulfides mineralization fill these micro-cracks and fractures. Listvenite shows evidence of both brittle and ductile deformation. The change from compression to extensional deformation in the listvenite is manifested by S-shape sigmoidal tension gashes that formed along ductile shear zone (Fig. 3B). The early generation M1 exhibits a euhedral outline with respect to serpentine relics. It is often stained with iron oxides and variably deformed. With shearing progress, M1 is overgrown by dark color M2 magnesite associated with talc (Fig. 3G). The dark color may be due to higher in the Fe. The latest generation of magnesite M3 is represented by carbonates veinlets and veins filling the fractures in the highly sheared mylonitic listvenite. The M3 Magnesite associated with quartz, dolomite and calcite.

Quartz and quartz–carbonate veins

Three generations (V1, V2 and V3) (Fig. 4A–C) of quartz and quartz–carbonate veins can be recognized in the area of study. Their length ranges from 70 to 300 m, and their widths range from 10 cm to 1 m. The first and pre-mineralization stage (V1) is generally milky white, lacks Au- and sulfides, and developed along regional schistosity (ENE–WSW). An assemblage of carbonate, graphite, fuchsite ± chlorite minerals occupy the serrate planes separating bent quartz crystals, producing a distinctive stylolitic texture (Fig. 3C). Mineralized veins (stage V2), contain Au and sulfides, and have thicknesses up to 15–20 cm. They are connected to E–W shear zones, related fractures and anastomosing zones. Asymmetric structures (e.g. C/S or C' shear bands) as well as intrafolial asymmetric folds document the V2-stage (Fig. 3D), indicating that V2-stage quartz veins are related to low-grade mylonitic shear zones. In certain veins, magnesite–siderite ± calcite aggregates and fibres fill the open vugs as replacement phases and are connected to comb quartz. Post-mineralization stage (V3) veins in sharply sloping NW–SE extensional cracks are barren, contain milky white quartz, and are aligned parallel to the Najd fault system.

Fig. 4
figure 4

Field photographs show the characteristics of different types of quartz veins in El-Barammiya gold mine area. A Stage V1 pre-mineralization highly deformed, boudinaged and cataclsites quartz veins parallel to the main foliation trend of the study area. B Fissure filling mineralized quartz–carbonate veins (stage V2). These veins are micro-brecciated, slip and bounded by carbonatized graphite- actinolite schist and listvenite. C Post mineralization veins (stage V3) intersected the brecciated V2 and F3 folds

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Ore minerals

The ore mineral concentrations in the El Barramiya gold mine area ranges from 1.6 to 7.5% of the rock volume (Abdel-Karim et al. 2017). They are represented by sulfides, chromite, magnetite, hematite and gold. Both gold and sulfides ore minerals occur scattered throughout the quartz, quartz carbonate veins and adjacent wall rocks. They are most prominently represented by arsenopyrite, pyrite and trace amounts of chalcopyrite, sphalerite, tetrahedrite, galena, pyrrhotite, gersdorffite and gold. Secondary minerals include covellite and goethite. According to Zoheir and Lehmann (2011) sulfides are typically less than 2% of the vein volume, but their abundance varies along the vein's breadth. In listvenite and schist adjacent to the veins, sulfides occur as scatter disseminations (Fig. 5H). In quartz and quartz carbonate veins, gold and sulfides mineralization are restricted to the stylolitic planes in recrystallized quartz veins, where disseminated sulfides are associated with a carbonaceous material (Fig. 5I). The early generation granulated and brecciated quartz are enclosed in a network of carbonate. Arsenopyrite and pyrite are the principal hosts of submicroscopic gold, where very fine-grained inclusions (~ 10 μm) of gold are detected within margins of pyrite and arsenopyrite crystals. It also occurs as minute crystals (up to 20 μm) either disseminated in the carbonates (Fig. 5I) or distributed along healing microfractures of quartz crystals (Fig. 5G). Under reflected light microscope, arsenopyrite is characterized fine- to medium-grained (30–500 μm), silvery-white to steel gray. Arsenopyrite is characterized by weak pleochroism from white or bluish tint, faint reddish yellow and strong anisotropism (red-violet). Crystals of arsenopyrite with common twinning on (100) are detected (Fig. 5C). It is easily oxidizing to slightly iridescent colors of pink, brown, or copper (Fig. 5D). Very fine-grained inclusions (~ 10 µm) of gold is detected in or within marginal to pyrite and arsenopyrite crystals (Fig. 5B). Gold is characterized by yellow color, non-pleochroic and none internal reflections. Marcasite is commonly recorded as pseudomorphism of cracked and cataclasites large pyrite crystals in association with chalcopyrite and digenite (Fig. 5E, F). Marcasite does not have the same brassy yellow color of pyrite. Instead, it is a pale brass color. Chemical analysis of pyrite after Zoheir and lehmann (2011) using electron microprobe proved the presence of traces of Ni (up to 0.69 wt%), As (up to 0.67 wt%), Cu (up to 0.61 wt%) and occasional hundreds of ppm Au.

Fig. 5
figure 5

A Chalcopyrite (Cp) crystal replaced by sphalerite (Sp) along the margins. B Large crystal of arsenopyrite (Ar) replaced by chalcopyrite (Cp), which altered to covellite (Cv). C Twinned arsenopyrite (001) in the listvenite from wall rock. D Iridescent colors (Ir) of the oxidized arsenopyrite crystal (Ar). E Highly deformed and cataclastic large crystals of pyrite (Py) in associated with arsenopyrite and marcasite. F Chalcopyrite (Cp) replacing large crystal of pyrite (Py), and associated with marcasite (Mr). G Iridescent colors (Ir) of the oxidized arsenopyrite crystal (Ar). H Disseminated arsenopyrite (Ar) and pyrite (Py) in listvenite country rocks. I Disseminated arsenopyrite and pyrite along stylolitic carbonate structure planes in quartz veins. J Fine-grained grains of gold (Au) arranged parallel to stylolitic carbonate plane. Bar 200 µm

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XRD identification of listvenite rocks and quartz veins rocks

Mineralogical identification of the collected samples was performed using XRD at the physics department in Assiut University, Assiut. XRD analysis illustrate quartz, magnesite, dolomite and calcite are the most common minerals in listvenite rocks where the principal peaks of quartz are indexed with their d-spacing and relative intensities, as follows: 20.671° 4.297 Å; 20.808° 4.269 Å; 26.582° 3.353 Å; 26.591° 3.352 Å; 54.88° 1.673 Å; 54.82° 1.675 Å; 59° 1.501 Å. Magnesite follows the quartz in abundance and is where the principal peaks appears 42.424° 2.131 Å; 42.28° 2.138 Å; 32.439° 2.76 Å; 44.56° 2.033 Å; 44.892° 2.019 Å; 54.892° 1.673 Å; 59° 1.501 Å. Dolomite is represented on the XRD charts by the characteristics lines at d-spacing and relative intensities 30.797° 2.903 Å; 30.878° 2.896 Å; 33.46° 2.678 Å; 35.868° 2.504 Å; 50.158° 1.819 Å; 51.018° 1.79 Å; 59° 1.501 Å. Calcite is represented on the XRD charts by the lines at d-spacing 3.137 Å, 2.418 Å, 2.335 Å and 3.037 Å and relative intensities 28.454°, 37.18°, 38.56° and 29.414°. Iron oxides are represented by chromite, hematite and magnetite (Fig. 6A, B). Chromite is represented on XRD charts by d-spacing 2.986 Å and 4.745 Å and relative intensity 30.88° and 18.7°. Hematite is represented on XRD charts by d-spacing 2.284 Å and 2.24 Å and relative intensity 39.451° and 40.254°. Magnetite also represented on XRD charts by d-spacing 2.61 Å and relative intensity 34.36°.

Fig. 6
figure 6

A, B Photomicrographs showing the XRD charts of Listvenite rocks

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XRD analysis indicate that quartz is the most abundant mineral in the studied rocks from d-spacings and relative intensities, as follows: 20.79° 4.272 Å; 26.555° 3.357 Å; 50.149° 1.819 Å; 36.515° 2.461 Å 20.732° 4.285 Å; 26.47° 3.367 Å. 36.448° 2.465 Å; 50.069° 1.822 Å 59.87° 1.545 Å.

Mineral association and paragenesis

The early oxide ore minerals in the studied area are represented mainly by chromite and magnetite. Chromite forms irregular to euhedral fractured crystals with silicate minerals filling the cracks. Moreover, cataclastic and brecciated chromites are recorded in talc‐carbonate and carbonate rich listvenite rocks. Magnetite is mostly common in talc‐carbonate, but also detected in listvenite rocks. It appears as anhedral crystals with peripheral granules of pyrite. Sulfides ore minerals disseminated in the quartz veins and adjacent wallrocks (listvenite and graphite schist) are mainly arsenopyrite, pyrite and smaller amounts of chalcopyrite, sphalerite, tetrahedrite, galena, pyrrhotite, gersdorffite and gold. Based on rock association alterations and textural relations (intergrowth and replacement), a two-stage mineralization paragenesis is suggested for the Barramiya deposit (Table 1). During the early mineralization stage, arsenopyrite, gersdorffite, pyrrhotite, pyrite ± refractory gold has been formed, followed by chalcopyrite, tetrahedrite, sphalerite, galena and free gold in the late mineralization stage. The bulk sulfide mineralization was overprinted by a late, variably pervasive secondary alteration which represented by marcasite, covellite, bornite goethite and hematite.

Table 1 Mineral association and paragenesis of ore minerals in El-Barramiya area
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Fluid inclusions

Various kinds of fluid inclusions were noted in quartz-filling cavities and fractures in listvenite (Table 2), which include type-1 H2O–CO2 ± CH4 inclusions, type-2a (H2O + CO2) inclusions (Fig. 7A, B), type-2b two-phase (L–V) aqueous inclusions and type-3 secondary aqueous inclusions, which are represented by two-phase (L–V), mono-phase liquid and mono-phase vapor inclusions. In type-1 inclusions, the melting temperature ranges between − 70.2 and − 58.6 °C indicating the presence of CH4-phase. Clathrate melting (Tmclat.) ranges between 9 and 12 °C, indicating very low salinity < 3 wt% NaCl eq. (Diamond 1992; Fall et al. 2011). The homogenization temperature of CO2 (ThCO2) was achieved between 26 and 29 °C, corresponding to CO2-density between 0.631 and 0.697 g/cm3. Due to decrepitation, bulk homogenization was recorded in few inclusions between 360 and 390 °C. In type-2a inclusions, TmCO2 was measured at temperatures between − 62 and − 57.2 °C, slightly below the triple point of CO2, indicating the existence of trace quantities of dissolved components like CH4, this was confirmed by laser Raman spectroscopy analysis (Zoheir and Lehmann 2011). CO2-phases were homogenized to liquid between 20 and 25 °C, corresponding to densities of CO2 (dCO2) between 0.71 and 0.77 g/cm3. The total homogenization temperatures were measured between 270 and 340 °C with a maximum peak at 300 °C (Fig. 7C). In type-2b inclusions, the total homogenization (Thtot) to liquid was measured at temperatures ranging from 210 to 330 °C, with a peak at 280 °C (Fig. 7C). The trapping conditions, which represent the mineralizing conditions for gold and sulfides (arsenopyrite, pyrite, chalcopyrite, sphalerite, tetrahedrite, galena, pyrrhotite and gersdorffite) mineralizations, were characterized by temperature between 280 and 340 °C, and pressure between 1.5 and 1.9 kbar (Fig. 7D), which is consistent with mesothermal conditions.

Table 2 Microthermometric results of fluid inclusions from the studied gold mineralization
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Fig. 7
figure 7

A, B Photomicrographs show types, distribution and description of fluid inclusions at room temperature. A Primary distribution of type 1 (H2O–CO2 ± CH4) inclusions, B primary distribution of type 2a (H2O–CO2) inclusions in the mineralized veins, C histogram shows the total homogenization temperatures (Th) for type 2a and type 2b inclusions, D P–T diagram shows isochores of aqueous inclusions as well as CO2-bearing inclusions

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Geochemistry

Major elements

Listvenite samples show wide variations in major oxide contents, which reflect the different degrees of metasomatic hydrothermal alteration of the precursor rocks in the study area. Two groups are distinguished based on their silica content: high-silica (SiO2 > 50 wt%) and low-silica listvenites (SiO2 < 50 wt%). All listvenites are enriched in As, Ni, Cr, V, and Co, but have relatively low lithophile and other trace element/rare earth element levels (Table 3).

Table 3 Major (%) and trace elements (ppm) and composition of the listvenite, serpentinites and quartz veins of El-Barramiya area
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To understand the evolution of El-Barramiya listvenite, Harker diagrams were used to investigate co-variations of MgO with other oxides (Fig. 8). The figures show positive correlations with Fe2O3, CaO, and MnO, and negative correlations with alkalis (Na2O and K2O), Al2O3, SiO2 and P2O5. Bivariate plots show negative correlations of SiO2 versus MgO + CaO and Fe2O3 (Fig. 9A, B). The positive correlation of the loss of ignition (LOI) with MgO and MgO + CaO as well as the negative correlation with SiO2 (Fig. 9C–E) infers that CO2 in Mg-rich carbonates dominates the volatile component of the listvenites (see Gahalan et al. 2020a; b).

Fig. 8
figure 8

Variation diagrams of MgO with some major oxides for the listvenite rocks

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Fig. 9
figure 9

Bivariate plots: A, B SiO2 versus MgO + CaO, and Fe2O3. C–E Loss of ignition (LOI) versus MgO, MgO + CaO, and SiO2 of listvenite

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On SiO2–Fe2O3–(MgO + CaO) ternary diagram, listvenite and average serpentinites from El-Barramiya plot along the SiO2–(MgO + CaO) join (Fig. 10A). While some samples plot along the SiO2–MgO solid line and others shift toward the SiO2–CaO join on a SiO2–CaO–MgO diagram (Fig. 10B). Therefore, the conversion of serpentinites to listvenite was accompanied by loss of MgO and gain of CaO and SiO2, with progressive metasomatic alterations causing more and more extreme carbonatization and silicification. The gain of SiO2 and loss of MgO with continued listvenitization of serpentinites also accounts for the negative correlation between SiO2 and MgO on a SiO2–MgO diagram (Fig. 10C).

Fig. 10
figure 10

A Fe2O3–SiO2–MgO + CaO ternary diagram with alteration trends of serpentinites and fields of altered rocks according to Akbulut et al. (2006). B MgO–SiO2–CaO ternary diagram. C SiO2 versus MgO binary diagram (wt%) shows chemical changes during alteration of serpentinites, according to Akbulut et al. (2006). Solid circles represent listvenite rocks and empty circle represents an average of serpentinites

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Trace elements

Enrichment in Sr (47–770 ppm) and depletion in Ba (3–38 ppm) in listvenite compared to the average serpentinite (Table 3) may be attributed to the gain and loss of such elements, respectively, during metasomatism. Notably, the lowest Ni, Co and Cr concentrations were measured in the high-silica listvenite samples (5, 6, 7 and 8), In addition, the listvenite rocks contain higher (Ni, Co, and Cr) compared with quartz veins samples (Fig. 6A) can prove the ultrabasic origin of listvenite (Fig. 11A) (Table 4). The elements of Au, Ag, Cu, Sb, As, Rb, Ba, and Zn elements (Fig. 11B) in listvenite as well as quartz veins show random distributions. This random distribution reflects the overprint of metasomatic hydrothermal fluids on such elements. Both gold-bearing listvenite and quartz veins show similar positive correlations of Au and Ag contents with As, Cu, Zn, Pb, Sb and Tl (Fig. 12A, B). By contrast, Co, Ni, and Ba show different behaviors between mineralized quartz veins and listvenites: they show positive correlations in mineralized quartz veins and negative correlation in listvenite. These relations are consistent with petrographic observations showing that Au and sulfide mineralization is more common in late-stage (high-silica) listvenite, whereas base metal elements in low-silica listvenite are mostly barren. On the other hand, Au mineralization as well as other sulfides are disseminated in stylolitic carbonate and carbonates filling healed microfractures, which allow incorporation of base metals in the quartz-carbonate veins. Both listvenite and Au-bearing veins were subjected to brittle–ductile deformation. It is noteworthy that both high-silica listvenite and Au-bearing veins experienced more ductile deformation than low-silica listvenite.

Figs. 11
figure 11

A Co, Ni, Cr element distributions in Listvenites: (1–8) and Quartz Veins (9–14), B trace element distributions in all listvenite samples (n = 8) and quartz vein samples (n = 6) for Au, As, Ba, Ag, Cu, Sb and Pb elements

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Table 4 Rare earth elements composition of the listvenite, serpentinites and quartz veins of El-Barramiya area (ppb)
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Fig. 12
figure 12figure 12

A Bivariate plots of Au versus other trace elements of the listvenite (solid circular samples) and quartz veins samples (triangular samples). B Bivariate plots of Ag versus other trace elements of the (solid circular samples) and quartz veins samples (triangular samples)

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The Spearman’s rank correlation shows that gold has a positive correlation with Ag, Pb, As and Zn in the listvenite samples (Table 5). In mineralized veins, Au shows a positive correlation with Ag, Fe, Ni, As, Cu, Pb and Zn (Table 6). This is consistent with the association of free-milling gold and the late base metal sulfides (galena–tetrahedrite–arsenopyrite–chalcopyrite and pyrite assemblage). The correlations were also carried out for elements: Au, Al, Ca, Fe, Ga, K, Mg and Mn in the lode gold deposit samples. The elements related to mineralization/alteration were chosen based on their geochemical association with carbonates and other alterations, such as chloritization and sericitization of the wall rocks. In listvenite samples, Au showed a positive correlation with K and Ca (Table 7), while in mineralized quartz veins, Au has positive correlation with Ca, Mg, Mn, Fe and Al (Table 8) (Fig. 13). These results are consistent with petrographic observation that the Au-mineralization is associated with the later phase of carbonate (dolomite, ankerite, and calcite), chlorite and fuchsite formation.

Table 5 Spearman’s correlation coefficients for listvenite samples from El-Barramiya lode-gold deposit
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Table 6 Spearman’s correlation coefficients for mineralized veins samples from El-Barramiya lode-gold deposit
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Table 7 Spearman’s correlation coefficients for listvenite samples from El-Barramiya lode-gold deposit
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Table 8 Spearman’s correlation coefficients for mineralized veins samples from El-Barramiya lode-gold deposit
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Fig. 13
figure 13

Histgram showing Speaman's rank correlation in lode gold deposits from El-Barramiya area

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Rare earth elements

In the high- and low-silica listvenites, REE-normalized patterns show minor enrichment in LREE relative to HREE compared to serpentinite, with a LREE/HREE ratio of 1.7–3.2, with an average of 2.34, and (La/Yb)N of 2.8–13.8, with average of 6.2 (Fig. 8A).

The REE normalized pattern of gold-bearing quartz vein displays a steep, negatively sloping LREE pattern, flat HREE pattern, and strongly negative Eu anomaly (Fig. 14A). In the lode gold mineralization of El-Barramiya area, highly fractionated LREE (LREE/HREE ratio = 10.7 and (La/Yb)N = 27.4) and depletion in HREE (Fig. 13A) relative to the serpentinite host rocks and listvenites may be due to the existence of phases other than quartz-bearing carbonates and wall rock material. Zoheir (2008) and Zoheir et al. (2013) suggest dominant metamorphic water, with possible contributions from a magmatic source. This may provide an internal fluid supply (dehydration of the metasedimentary and metavolcanic rocks) through the region's peak metamorphism in the area. The occurrence of strongly negative Eu anomaly in both listvenites and hydrothermal quartz vein (Fig. 14A) could be related to highly acid pH conditions and/or an increase in ƒO2 of the hydrothermal system (Sverjensky 1984; Bau 1991). The average primitive mantle-normalized trace element pattern (normalization values of McDonough and Sun 1995) of each rock variety studied is shown in (Fig. 14B). Generally, all the patterns show slight to moderate enrichment in large ion lithophile elements (Rb and Sr, Th) and relative depletion in high field strength elements (Zr and Pb) and REEs.

Fig. 14
figure 14

A Chondrite-normalized REE patterns for listvenite, quartz vein and an average of serpentinites (n = 3 samples) (Boynton 1984). B Primitive mantle-normalized spider diagrams for an average of listvenites and serpentinites, normalization values from McDonough and Sun (1995)

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Discussion

El-Barramiya lode gold mineralization is occupied in a zone of strongly sheared ophiolitic rocks trending ENE. It is hosted by an ophiolitic mélange consisting of allochthonous blocks of serpentinites and listvenite structurally intercalated with metasedimentary and volcano-sedimentary rocks. Quartz and quartz-carbonate veins as well as altered wall rocks (listvenite) make up the mineralization. Sulfide minerals associated with gold in the quartz-carbonate veins and adjacent listvenite are arsenopyrite, pyrite and trace amounts of chalcopyrite, sphalerite, tetrahedrite, pyrrhotite, galena and gersdorffite. The geologic characteristics of the Barramiya deposit; its structural control, host rocks, alteration mineralogy, mineralization style, timing of the mineralization with respect to the deformation history, along with the fluid and stable isotope data, are in accordance with the orogenic mesothermal lode-gold deposit style in the sense of Groves et al. (2003), analogous to other deposits in the Eastern Desert (e.g., Helmy et al. 2004; Zoheir 2008; Zoheir and Lehmann. 2011).

Gold-bearing quartz and quartz-carbonate veins as well as listvenite from El-Barramiya area contain low salinity (~ 4 wt% NaCl eq.) aqueous (H2O) and mixed H2O–CO2 ± CH4 fluid inclusions. Petrographic investigation and microthermometry (total homogenization temperatures and the variable CO2 densities) suggest heterogeneous trapping of these fluids after phase separation. Metamorphism produces large quantities of CO2 and produces carbonate-rich sedimentary rocks (Goldfarb et al. 2017). Generally, carbonaceous shale is a suitable source rock for elements that are commonly enriched in orogenic gold deposits, such as S, Au, As, and Sb (Large et al. 2011; Lisitsin and Pitcairn 2016; Pitcairn 2011; Steadman et al. 2014). These may also account for the deposition of sulfides associated with gold mineralization in El-Barramiya area. El-Barramiya gold-bearing veins and wall rocks are situated in carbonaceous listvenite rocks and associated with arsenopyrite, pyrite and pyrrhotite, and to lesser extent sphalerite and galena mineralizations. This proves that gold was transported as gold bisulfide (Au(HS)2−) complexes. The fluid inclusions study indicates that the heterogeneous trapping of mineralized fluids were low salinity aqueous-carbonic. According to Naden and Shepherd (1989) and Shepherd et al. (1991) contamination of CO2-bearing fluids by reaction with rocks containing carbonaceous matter is widely invoked to explain the presence of CH4 and N2 in fluid inclusions from shear zone-hosted gold deposits. Decreasing in fO2 of the fluid may due to the addition of CH4 during fluid–rock carbon interaction and carbonate precipitation. Consequently, destabilized gold–sulfur complexes, with sulfur consumption by sulfidation can lead to gold deposition. Refractory gold in early sulfide assemblage was deposited from a low-salinity CO2 ± CH4–H2O–NaCl or H2O–NaCl–CO2 ± CH4 fluid concomitant with the arsenopyrite + pyrite + pyrrhotite ± gersdorffite assemblage, whereas, the free-milling gold could have been mobilized and redistributed during deformation (Zoheir and Lehmann 2011).

Vearncombe and Zelic (2015) evaluated the relationship between structural discontinuities (faults, shear zones, fold noses, competency contrasts) and the production of orogenic gold deposits. These discontinuities serve as conduits for fluid migration from the metamorphic dehydration zone below the transition from green schist to amphibolite to the precipitation site in the upper crust, which is frequently in the greenschist facies. A dextral shear system that formed in the area's late deformation history is geographically and temporally connected to the gold-bearing quartz (± carbonate) veins (Zoheir and Lehmann 2011). Petrographic study illustrated that El-Barramiya area was subjected to hydrothermal metasomatic alteration processes (carbonatization and silicification). Listvenite is the result of metasomatic alteration of serpentinites. Geochemical study of listvenite exhibited higher levels of As, Sb and Hg which suggests the contribution of granite-related hydrothermal fluids; whereas the presence of Cr, Ni, Co and Pt points to the ultramafic protolith (Likhoidov et al. 2007). In El-Barramiya area, low grade green schist metamorphic, petrographic observations, such as the co-existing of actinolite and chlorite in the peak assemblage, indicate that the metamorphism was reached at the greenschist–amphibolite facies transition. Abu-Alam and Hamdy (2014) suggest metamorphic conditions of upper greenschist facies (e.g. 300–400 °C) for the ophiolitic rocks of the Arabian–Nubian Shield.

The primitive mantle-normalized trace element patterns of an average serpentinites, high and low silica listvenites are shown in (Fig. 14B). In general, all the patterns exhibit a relative depletion of high field strength elements (Zr and Pb) and REEs and a modest to moderate enrichment in big ion lithophile elements (Rb and Sr). In the study area, there is a spatial association of gold-bearing quartz ± carbonate veins and listvenite along a transecting network of steeply dipping faults, shear zones and fractures adjacent to granodiorite.

Conclusions

Ophiolitic rocks in the El-Barramiya area of the Eastern Desert, Egypt, were subjected to carbonatization and silicification metasomatic alterations. Intense alteration allowed listvenite formation in gold-bearing shear zones. The gold-bearing quartz (± carbonate) veins are spatially and temporally linked to a dextral shear system developed in the late stages of the deformation history of the area. Presence of massive to heavily asymmetric and deformed microstructures, dynamic recrystallization and slip on discrete carbonaceous laminae indicate that formation of mineralized quartz veins under variable compressional and tensional regimes.

The frequent association of orogenic gold deposit with various sulfides (e.g. pyrite, arsenopyrite and pyrrhotite) suggests the role of sulfidation process in transportation and deposition of gold in the study area. Graphite schist and serpentinites are a suitable source rocks for elements that are commonly enriched in orogenic gold deposits such as S, Au, As and Sb. Fluid-graphite schist reactions and carbonate precipitation are likely resulted in destabilizing gold–sulfur complexes and the coexisting sulfidation process triggered gold deposition.

Fluid inclusions study suggests a heterogeneous trapping of low-salinity aqueous-carbonic fluid ± CH4 after phase separation. The minimum P–T conditions of fluid inclusions trapping as well as gold deposition were estimated between 280 and 340 °C, and pressure between 1.5 kbar and 1.9 kbar, which is consistent with the mesothermal conditions.

Geochemical study of listvenite and mineralized veins demonstrated that high trace element concentrations such as Co, Cr, Ni and V in listvenite confirm the ultramafic genesis. Also, the random distribution for the elements Au, Ag, Cu, Sb, As, Rb, Ba and Zn reflects the effect of the hydrothermal fluids. Highly, more fractionated LREE and depletion in HREE of gold-bearing quartz vein relative to the serpentinites host rocks and listvenite can be attributed to the presence of other phases affecting the formation of quartz carbonates veins and gold-bearing wall rocks. This phase may be considered as the contribution of granitic intrusions in the geochemical characterization.