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Review

The Role of Organic Matter and Hydrocarbons in the Genesis of the Pb-Zn-Fe (Ba-Sr) Ore Deposits in the Diapirs Zone, Northern Tunisia

by
Larbi Rddad
1,*,
Nejib Jemmali
2,3 and
Samar Jaballah
4
1
Earth and Planetary Science Division, Department of Physical Sciences, Kingsborough Community College, City University of New York, 2001 Oriental Boulevard, Brooklyn, New York, NY 11235-2398, USA
2
Faculty of Sciences of Gafsa, Department of Geology, University of Gafsa, Sidi Ahmed Zarrouk, Gafsa 2112, Tunisia
3
Laboratory of Useful Materials, National Institute of Research and Physicochemical Analysis, Technopole Sidi Thabet, Ariana 2026, Tunisia
4
Laboratory of Geodynamic, Geonumeric and Geomaterials, Faculty of Sciences of Tunis, University of Tunis EL Manar, Tunis 2092, Tunisia
*
Author to whom correspondence should be addressed.
Minerals 2024, 14(9), 932; https://doi.org/10.3390/min14090932
Submission received: 14 August 2024 / Revised: 6 September 2024 / Accepted: 9 September 2024 / Published: 12 September 2024
(This article belongs to the Special Issue The Role of Hydrocarbons in the Genesis of Mineral Deposits)
Browse Figures
Versions Notes

Abstract

:
Extensional tectonics along NE-trending faults, coupled with diapirism, created paleo-highs and subsiding basins, providing the structural framework for subsequent mineralization processes. The preservation of organic matter within the Fahdene and Bahloul Cretaceous formations during the Anoxic Oceanic Events (AOE-1 and AOQ-2) facilitated the extraction of metals from seawater. The association of metals with organic matter, Fe-Mg oxides, and pyrite is revealed by principal component analysis (PCA). The subsequent maturation of organic matter generated hydrocarbons, with thermal cracking leading to the incorporation of organo-metallic ligands into mobile hydrocarbons. Oilfield brines form as a byproduct of this catagenesis. The metal-rich hydrocarbons and basinal brines invaded SO4−2-rich fluids from Triassic evaporites, resulting in the precipitation of sulfates (barite and celestite) and the bacteriogenic (BSR) and/or thermal (TSR) reduction of sulfate to reduced sulfur, which combined with metals to form sulfide ores. This study examines the role of hydrocarbons in the genesis of ore deposits within the diapiric zone, drawing upon a synthesis of literature and geological data. It highlights the interplay between basinal evolution, the organic matter-rich Cretaceous formations (Fahdene and Bahloul), diapiric paleo-highs, and the Alpine orogeny, which are identified as crucial factors in ore genesis in the diapiric zone.

1. Introduction

Organic matter and hydrocarbons play crucial roles in the genesis of ore deposits, particularly in sedimentary environments. The organic matter-rich facies were deposited during global Oceanic Anoxic Events that occurred in the Cretaceous period, such as OAE-1 and OAE-2 [1,2]. These facies are often associated with abnormally high concentrations of metals like lead (Pb), zinc (Zn), copper (Cu), and iron (Fe) compared with average crustal rocks. The presence of organic matter-rich sedimentary formations has drawn significant attention from researchers globally, as these formations are frequently targeted for ore exploration. Studies spanning various countries have highlighted the common occurrence of organic matter-rich formations alongside mineral deposits, particularly Zn-Pb Mississippi Valley-type (MVT) deposits [3,4,5,6,7,8,9,10,11,12,13,14,15]
The association between organic matter-rich formations and ore deposits suggests a potential link between organic material and metal concentration. Organic matter in marine environments is known to extract metals either through bioconcentration (e.g., [16,17] and/or the removal of metals from solution [6,10,18,19], leading to the enrichment of OM in metals. Salt diapiric structures associated with these formations are recognized as crucial factors in the emplacement of ore deposits globally [14,20,21,22,23,24,25,26].
The proximity of organic matter-rich formations to ore deposits may suggest their role as a source of metals and hydrocarbons for ore genesis in the diapiric zone in Tunisia. Understanding the importance of organic matter and hydrocarbons and the associated oilfield brines in ore genesis involves exploring their roles in metal concentration, ore transport, and the formation of mineral deposits within sedimentary environments. A comprehensive review of pertinent papers on the role of hydrocarbons in the genesis of MVT ores, along with PCA of trace elements, allow us to highlight the pivotal role of hydrocarbons and accompanying basinal brines in the genesis of Mississippi Valley-type (MVT) ore deposits within the Tunisian diapiric zone. The involvement of deep-seated metalliferous fluids emanating from the pre-Triassic basement is beyond the scope of this study.

2. Regional Geology and Tectonics

The diapiric zone corresponds to the Atlasic foreland, comprising rock sequences overlying the Precambrian-Paleozoic rocks of the African substratum. The latter consists of Precambrian granite and metamorphic rocks, covered by Paleozoic sandstone, shale, and arkose [27]. Located within the Tunisian Atlas, the diapiric zone extends approximately 300 kilometers in length and 100 kilometers in width (Figure 1) [28,29,30].
This region is characterized by numerous NE-SW-trending diapirs that contain Triassic evaporite intrusions penetrating Jurassic and Early Cretaceous sedimentary formations [31,32]. The rock units of the diapiric zone have experienced several tectonic events, spanning from the Triassic to the Miocene time. From the Triassic until the Aptian Cretaceous time, the diapiric zone underwent extensional tectonics related to the opening of the Tethys and Central Atlantic oceans. This tectonic event is marked by the development of half-graben basins bordered by NE-SW-trending faults under a general NW-SE extensional regime [33]. Diapirism was facilitated by these NE-trending deep-seated faults inherited from N-S major basement faults during Aptian time. The fault-bounded subsiding basins were filled with around 1000 m of alternating evaporitic and siliciclastic Triassic sediments. This sequence predominantly comprises gypsum and halite with layers of silt, clay, and dolostone [31,34,35] lying unconformably over the Precambrian-Paleozoic basement [27].
Tectonic and halokinetic events influenced the sedimentation and resulted in variations in facies and thicknesses of the Cretaceous and Tertiary. Reactivation of NE-SW-trending extensional faults during the Early Cretaceous (Late Aptian–Albian) period resulted in two episodes of halokinesis: salt flow and dome formation. Diapirism initially occurred during the Late Aptian [36] and later during the Middle Albian [31]. Early halokinetic activities formed paleo-highs hosting shallow marine Aptian reefs and platforms of the Serdj Formation (e.g., Slata, Bou Jabeur, Jerissa, and Ouenza) [37,38,39]. In the fault-bounded basins, organic matter-rich facies of the Albian–Vraconian (alternating marl and limestone) (Fahdene Formation) and the Cenomanian–Early Turonian (platy limestone and black shale) (Bahloul Formation) were deposited. They are succeeded by a 2000-m-thick sequence of Turonian–Paleocene marls and limestone.
The collision of the African and European plates led to the inversion of the North Tunisian Tethyan margin [40] This tectonic activity, marked by compressional and extensional events, began during the Middle Eocene and continued through the Oligocene-early Miocene and the Middle Miocene [41,42,43,44]. Salt diapirism occurred during these periods of compression [31], alongside igneous activity during the Eocene and Middle Miocene at the Nappes zone [45]. In this zone, a subsequent extension phase in the Late Miocene led to the deposition of molasse and lacustrine limestone [46].
According to Hammami [47], structural analysis has identified several faults: N-S, E-W, NW-SE, and NE-SW. The N-S faults are observed at the periclinal ends of the main structures of, e.g., Jebel El Akhouat, Jebel Mourra, Fedj-el-Adoum, and Jebel Bou Grine. The general arrangement of the diapir may have arisen from the deformation of the original NNE-SSW structure due to compressive forces oriented in the N-S direction [48,49]. The NE-SW-to-NNE-SSW direction is the most prominent. The E-W dextral strike-slip faults are related to E-W discontinuities in the basement [49] and outcrop at Jebel El Akhouat (the Borj fault) [50], which are thought to have developed subsequent to the NNE-SSW-to-NE-SW directions. The NW-SE faults were reactivated in both extensional and compressional periods [49,51]. From the Oligo-Aquitanian to the Tortonian period, these faults functioned primarily as extensional faults, opening the grabens. However, starting from the upper Tortonian period, a compressive regime dominated, affecting this fault system. The NE-SW-trending faults, which outcrop mainly at Jebel Ech Chehid and Jebel Mourra, form the deformation of the primitive NNE-SSW structure by compression forces oriented NW-SE, which is that of the Tunisian Grabens zone. The folds in this direction are the result of an ENE-WSW compressive phase while the faults would be generated by an extensional phase.

3. Ore Distribution in the Diapiric Zone

Mineralized sites (Pb-Zn-Fe ± Ba-Sr-F) are distributed across the salt diapiric zone and are associated with the Zn-Pb province of the Circum-Mediterranean Sea and Alpine Europe [23]. Tunisian diapir-related ores are found where diapirs intersect Cretaceous organic-rich formations (Fahdene and Bahloul Formations) and within marls and limestones of the Late Cretaceous.
The Tunisian diapiric zone contains numerous Pb-Zn-Fe-Ba-Sr ore deposits associated with NE-SW-trending Triassic salt diapirs that intrude the Cretaceous cover (Figure 1 and Figure 2).
The ore bodies are preferentially distributed in carbonate rocks, regardless of the morphology of the bodies and the age of the host. Mineralization always develops in favor of secondary discontinuities and at the base of transgressive series.
The descriptive analyses of the various ore bodies in the Diapirs zone led to distinguishing three groups: (i) strata-bound Pb-Zn-Fe-Sr ores in the transition zone, (ii) peridiapiric Pb-Zn ores, and (iii) vein-type unconformity ore within the peridiapiric:
(i)
The first group constitutes one of the traditional and potential ore-bearing formations within the entire Diapiric zone. The host rock consists of brecciated formations known as the “transition zone” [56], the “X limestone or zebra facies” (B.R.G.M.–BulgarGeomine, 1977–1986), the “cortical or peripheral formations” [35], or Type 1 or F1 [22]. This transition zone is situated at the reactive edges of the complex Triassic contact with its Cretaceous or Tertiary carbonate cover rocks. In this zone, breccias develop as a result of halite dissolution and accumulation of anhydrite and gypsum residue, forming the cortical zone of the diapiric evaporite [4,23,26,27,35]. These ore bodies typically occur as lenses of varying dimensions (ranging from 10 to 150 m in length and 3 to 10 m in thickness). The paragenesis is simple, with sphalerite, galena, and pyrite, and is characterized by a sulfate gangue containing celestine. The ore is sealed by the organic matter-rich Fahdene and/or Bahloul Formations. The ore occurs primarily as open-space fillings in dissolution breccias. Three sub-groups can be distinguished: (1) F1a with Pb-Zn-rich ores containing galena and sphalerite associated with pyrite/marcasite and celestite-barite (examples: Fedj-el-Adoum, Guarn–Halfaya, Oued Jebs, Zag Ettir, and Sakiet-Koucha; Figure 2); and (2) F1b with iron sulfide (pyrite/marcasite)-rich ores associated with galena, sphalerite, and celestite-barite (examples: Bou Grine and Kebbouch South; Figure 2). The oil seeps were identified within the transition zone of Fedj-el-Adoum, El Akhouat mine, Boukhil, Zag Ettir, and Kebbouch [57]. The calcite caprock exhibits a zebra texture, characterizing this category, and is only identified in Fedj-el-Adoum, Kebbouch, and Sakiet-Koucha. Fedj-el-Adoum is a representative example of category F1a, with a maximum mineralization width of 45 m (0.5 Mt of Pb+Zn metals [7,23,58]. (3) F1c, an economic target for strontium, is represented by the Bou Khil and Doghra mines [59,60].
(ii)
The second group comprises the peridiapiric Pb-Zn ores called Type 2 or F2 [22] Figure 3). It is situated within clayey limestone formations known as black shales or laminites, notable for their high organic content [61,62,63]. These limestone deposits belong to the Bahloul Formation identified by [64], marking the transition from the upper Cenomanian to the lower Turonian [29]. F2 corresponds to stratiform mineralization with predominant fine crystalline sphalerite and accessory galena, pyrite, and marcasite [4,36]. A representative ore deposit in this category is Bou Grine, hosted in the Bahloul Formation with a maximum mineralization width of 20 m (1 Mt Zn metal, [4]; Figure 4), and, to a lesser extent, Kebbouch South. The oil seeps were recognized in the core drilled in Bou Grine; they consist of bituminous impregnation within the Cenomanian–Turonian Bahloul located in the non-mineralized Pb-Zn zone [57].
(iii)
The third group consists of vein-type unconformity ore within the peridiapiric cover and sub-unconformity concentrations. This mineralization is the most prevalent and has been historically exploited in nearly all deposits and mines, accounting for about 70% of the extracted potential [47]. Two sub-groups can be distinguished: (1) ore within the peridiapiric cover and (2) unconformity-related vein ore. The first subgroup consists of mineralized ore bodies in the peridiapiric cover, which differ in size and form (e.g., stockworks, veins, columns, and clusters), are located within transgressive carbonate sequences and are found across various stratigraphic levels. There are three main directional preferences for the occurrence of intersecting ore bodies [47]: N-S to N20° (e.g., El Akhouat and Bou Grine), N80° to 100° (e.g., El Akhouat, Fedj-el-Adoum, and Oued Jebs), and N130° to 140° (e.g., El Akhouat). These ore bodies exhibit a diverse range of dimensions, from small veins to larger stockworks, columns, and mega-fissures. A notable example is the roof cluster of Bou Grine (referred to as type F3; [22], containing an average of nearly 1 Mt with 27% zinc and lead content. The filling materials may include Pb-Zn sulfides (e.g., Bou Grine, Fedj-el-Adoum, Sakiet-Koucha, Kebbouch South, Bou Khil, Lorbeus, Oued Jebs, and El Akhouat deposits). The mineralization consists of galena, sphalerite, and lesser marcasite/pyrite [4,7,35,36,50,59] (Figure 5).
The second sub-group sub-unconformity concentrations are found within the Aptian reef limestones (Serdj Formation). They typically occur within fractures and karstic cavities. The paragenesis of these deposits includes galena, sphalerite, Fe-carbonates and oxides, fluorite, and barite (Figure 6J,K,L). Notable representatives of this group include Bou Jabeur and Jebel Slata ore deposits ([38,40,41]. These ore bodies are sealed by transgressive series ranging from the upper Albian to the Vraconian, indicating a regional unconformity. Oil seeps were identified within the intensely fractured upper Albian series of Fedj-el-Adoum, the Abiod Formation limestones of Bou Khil (Figure 7), the Oligo-Miocene sands and lumachelles of Zag Ettir, and the Aptian carbonate microporosities of the Bou Jabeur mine [57].

4. Methods

In this review, we relied on pertinent works on the diapiric zone, focusing on organic matter (TOC and maturity) and ore deposits. We conducted a comprehensive literature search using reliable databases. The selection criteria for the included studies were based on their relevance to the topic, the robustness of their methodology, and the significance of their findings. We particularly included peer-reviewed articles published on the diapiric zone as well as papers published worldwide dealing with the role of hydrocarbons in the genesis of ore.
Principal component analysis (PCA) was performed using SPSS version 27, a statistical software package from IBM, Armonk, NY, USA. PCA is employed as a robust technique in geoscience research (see [65] and references therein). Datasets consisting of trace elements, major elements, and TOC of the whole rocks as well as of the Fe oxides/pyrite [14] were used for this purpose. The primary objective of PCA in this study was to identify the specific mineral and organic phases in the organic matter-rich formations of Bahloul and Fahdene that trace elements, particularly Pb and Zn, are associated with. For this analysis, three principal components (PC1, PC2, and PC3) were extracted and utilized, with Varimax normalized rotation applied to obtain the loading values for each variable (e.g., trace elements) within these components. Each principal component consists of a set of correlated parameters with both positive and negative loadings, aiding in the interpretation of the primary geochemical processes affecting the dataset. PCA is effective in identifying clusters of related elements. The variance (%) and cumulative variance (%) are reported in the Supplementary Datasets (Tables S1–S4).

5. Organic Matter-Rich Formations: TOC and Maturity of OM in the Diapiric Zone

Two formations that serve as source rocks for hydrocarbons are the Fahdene and Bahloul Cretaceous formations. The Fahdene Formation (Albian–Vraconian) consists primarily of intercalated black limestone and black to gray marls rich in OM with a total organic carbon (TOC) reaching up to ~4% (e.g., [14,66,67,68]). This formation was deposited during an Anoxic Oceanic Event (AOE-1) [1,2] (1, 2). The organic matter-rich Fahdene Formation exhibits fair to good hydrocarbon potential, primarily characterized by the predominance of Type II kerogen (oil and gas prone), with a lesser presence of Type III kerogen [14,66,67]. The Bahloul Formation, of the Cenomanian–Turonian age, consists of finely laminated carbonates interbedded with marls [64]. This formation, rich in organic matter, was deposited during an Anoxic Oceanic Event (AOE-2) [2]. The organic matter preserved within this formation is of marine planktonic origin (Type II kerogen) potential [14,63]. The organic matter in both the Fahdene and Bahloul Formations exhibits varying levels of maturity related to their hydrocarbon generation potential [63], as evidenced by Tmax values spanning 424 to 453 °C [66] and vitrinite reflectance ranging from 0.72% to 0.87% [69]. Here, Tmax is defined as the Rock Eval maximum pyrolysis temperature or the peak temperature of the S2 maximum, which measures the potential hydrocarbons (mg HC.g−1 rock) released after kerogen undergoes thermal cracking between 300 and 650 °C.
In the diapiric paleo-highs, where sediment burial is insufficient, the OM is immature, whereas in the fault-bounded basins, sufficient burial depth allowed the organic matter to reach thermal maturity and generate hydrocarbons (e.g., [14,66,67,68]).

6. Principal Component Analysis (PCA)

The result of the PCA conducted on trace elements, major elements, and total organic carbon of the immature organic matter-rich Baloul Formation of Guarn–Halfaya and the mature organic matter Fahdene Formation of Slata are reported in Figure 8 and Figure 9 and Supplementary Tables S1–S4.

6.1. PCA for Total Organic Carbon and Trace Elements

In the Bahloul Formation, PCA revealed that the first principal component (PC1) showed positive correlations among the trace elements Zn (0.942), Pb (0.953), Cu (0.968), Ni (0.902), and TOC (0.925) Figure 8A,B indicates an association between these trace elements and organic matter. The second principal component (PC2) had a strong positive loading for Co (0.851) and a negative loading for Cr (−0.508), while the third principal component (PC3) showed positive loadings for Sr (0.880) and Co (0.366) and a negative loading for Cd (−0.229). These findings suggest that Zn, Pb, Cu, and Ni are influenced by the presence of organic matter, whereas Co, Sr, and Cd exhibit distinct geochemical behaviors. Trace elements such as Pb and Zn are adsorbed and/or incorporated onto/in organic matter and clay minerals during diagenesis, as suggested by other researchers [14,70]. The carbonate fraction also contains Pb and Zn [14].
In the Fahdene Formation, PC1 indicated positive correlations among the trace elements Cr (0.942) and Cu (0.910), but these elements were not linked to TOC (0.283) (Figure 8C,D). The second principal component (PC2) showed positive loadings for Co (0.780) and Ni (0.470) and negative loadings for Sr (−0.813) and TOC (−0.412), while PC3 had positive loadings for TOC (0.697) and Cd (0.465) and negative loadings for Pb (−0.879). This indicates that unlike in Guarn–Halfaya, there is no clear association between organic matter (TOC) and the trace elements Zn, Pb, Cu, and Ni in the Fahdene Formation. The geochemical behaviors of Co, Sr, and Cd are distinct and vary between the two formations.

6.2. PCA for Trace Elements, Fe Oxides/Pyrites

In the Bahloul Formation, PCA analysis revealed that Pb (0.763), Cu (0.891), and Zn (0.060) in PC1 are positively associated with P2O5 (0.629) and Fe2O3 (0.499) (Figure 9A,B), suggesting a link between these trace elements and phosphate and iron oxides, although the correlation with Zn is insignificant. Pb and Zn are also associated with framboidal pyrite and pyrite [14]. Ba (−0.151) showed a weak negative association, indicating that it might not be strongly linked with these oxides. In PC2, Zn (0.448), Cu (0.391), and Pb (0.529) showed positive loadings with Fe2O3 (0.841) and MgO (0.892), suggesting an association with iron and magnesium oxides. Ba (−0.199) again showed a weak negative correlation.
In the mature Fahdene Formation, PC1 indicated that Cu (0.925) and Ni (0.876) are strongly associated with P2O5 (0.466) and Al2O3 (0.358) (Figure 9C,D), suggesting a link with phosphate and aluminum oxides. Zn (−0.146) and Pb (0.235) showed weaker associations, indicating that the correlations are less significant. In PC2, Fe2O3 (−0.969) exhibited a strong negative loading, with Zn (−0.165) and Cu (−0.115) also showing negative loadings. This suggests that Fe oxides are not strongly associated with these trace elements in the Fahdene Formation, likely due to the organic matter’s maturity, which altered such an association as the one observed for Guarn–Halfaya. In PC3, Zn (0.813) and Ba (0.959) showed strong positive loadings, indicating a potential association with Na2O (0.384).

7. Ore-Forming Processes and the Role of Organic Matter/Hydrocarbons in the Genesis of the Ore

7.1. Source and Transport of Metals

The Paleozoic basement is considered a potential metal source for ores found in diapir-related ore deposits [27,36,50,58,71]. Alternative perspectives have been presented, suggesting that organic-rich Cretaceous formations could also contribute metals. The Pb isotopic data of galena samples from different ore deposits in the diapiric zone [27,36,50,72] exhibit a linear array and fall near the orogenic curve (Figure 10A) and Upper crust curve (Figure 10B) of plombotectonic model of Zartman and Doe [73]. The Pb istopic data also fall between the Paleozoic-related Miocene magmatic rocks Pb fields of Nefza and the Galite Archipelago [45] and the Pb field of the unmineralized Cretaceous rocks [72] (Figure 10). This suggests that besides the Paleozoic rocks, the organic matter-Cretaceous rocks are also a source of metals. The organic matter-rich rocks have long been known to be enriched in a variety of metals such as Mo, Zn, Ni, Cu, Cr, V, Co, Pb, U, and Ag (e.g., [70,74]. The organic matter-rich dark rocks of the Fahdene and Bahloul Formations are enriched in trace metals disseminated in the organic matter phase [14,50]. After conducting a comprehensive analysis of trace elements and organic matter in the Slata-Guarn Halfaya area, Rddad et al. [14] and Rddad and Belayouni [75] concluded that the trace elements were extracted from seawater during the Cretaceous time and became integrated into organic matter and clay minerals. The association of trace elements with organic matter, particularly Pb and Zn is revealed by the principal component analysis for the immature organic matter persevered in the Bahloul Formation of Guarn–Halfaya (Figure 8). Clay minerals associated with organic matter are also favorable sites for trace element fixation [14,70]. In the locations where organic matter is mature, such as the Fahdene Formation of Slata, this OM-trace association is altered, which is reflected in the lack of correlation between TOC and trace elements (Figure 9). As organic matter matures, a portion of the initially concentrated endowment within the organic matter fraction, likely composed mainly of nitrogen-, sulfur-, and oxygen-rich compounds (NSO), undergoes dissociation and the release of metals [14,75].
A fraction of the released metals was incorporated into mobile hydrocarbons and specifically the polar fractions (resins and asphaltenes or NSO compounds) sourced from the thermal cracking of organic matter [76,77,78,79,80]. Hydrocarbons, including crude oils, contain dissolved metals to varying degrees [81,82,83,84]. The metal-rich hydrocarbons led [82,84,85,86] to suggest that petroleum might have played an important role in ore metal transport. The organometallic complexes, which include (i) compounds in which metallic cations are bonded to heteroatoms (including N, S, and O) in a variety of structures and (ii) poly-complexes associated with electrostatically polar functional groups, such as carboxyl radicals, are important transporting agents of ore metals (e.g., [85]). The presence of NSO compounds is notably pronounced in the OM preserved in the Fahdene and Bahloul Formations in the diapiric zone [66]. The oil seeps found in numerous diapiric-related ore deposits were also rich in NSO compounds [57], which suggests that metals carried by NSO migrated from the source rocks (Fahdene and Bahloul) to the sites of ore deposition. Organic-rich Cretaceous formations were also proposed as a contributor of metals to, e.g., Bou Grine deposits [4,50,61,72,87,88]. Demange et al. [89] and Banks et al. [90] investigated the hydrocarbon fluid inclusions from ore deposits of Bou Jabeur in Tunisia and showed that these hydrocarbons-rich fluid inclusions contain high metal concentrations (e.g., Pb, Zn, and Fe) reaching up 1000 s of ppm. This observation indicates that hydrocarbons are possible metal carriers [90].
During organic matter catagenesis of both the Fahdene and Bahloul Formations, oil field/basinal brines could be also released. Various studies have found that certain metals, including V, Ni, Mo, U, Cu, Pb, Zn, Au, Ag, As, Sb, and Hg, can be present in crude oil and oil field brine at concentrations comparable to or even surpassing those found in ores [81,85,91]. These brines are also capable of transporting significant amounts of metal [82]. The migration of hydrocarbons and accompanying basinal brines from subsiding basins where the organic matter is mature toward the diapiric paleo-high where the OM is immature occurred generally from SE to NW or from SW to NE [92], with local predominance of the SE-SW direction [27,34]. The metal expulsion from the basin and their subsequent migration was also proposed by other researchers (e.g., [23]).
The importance of hydrocarbons and associated oilfield brines as a source and carrier of metals is highlighted by several authors (e.g., [14,80,82,83,84]). Although hydrothermal brines are also potential sources of metals, our focus in this contribution is on the role of hydrocarbons as carriers of metals. Nevertheless, the hydrothermal fluids may have leached metals from the organic matter-rich rocks (e.g., Bahloul Formation) that host some ore deposits (e.g., Bou Grine and Fedj-el-Adoum).
The proposed Cretaceous dark facies as a source of metals were also proposed in other ore deposits in the diapiric zone [8,14,72]. According to Montacer et al. [8], the genetic model for the Bou Grine deposit involves the Bahloul Formation acting as a source for migrated oil and necessary metals due to its richness in organic matter and metals (e.g., Zn and Pb).

7.2. Hydrocarbon Migration, Source of Sulfur, and Ore Precipitation

The generation and migration of hydrocarbons reached their peak during the Eocene-Miocene period [57], coinciding with the phase of Alpine compression. The combined effect of the compaction of organic matter-rich Fahdene and Bahloul Formations due to the Cretaceous load in the subsiding basins and the Alpine compression caused the expulsion of the hydrocarbons and accompanying oilfield brines, which carry metals from the basins toward the margins of the diapiric paleo-highs [14,34]. Compaction in concert with compression serves as an effective mechanism for driving these fluids from depocenters to paleo-highs [93,94]. Numerous instances of oil seeps have been discovered within diapir-related ore deposits [57,95]. The analysis of oil seep-source rock correlations indicates that the oils entering the mines are sourced from the Fahdene and/or Bahloul Formations [59,95] (e.g., Bou Grine, Fedj-el-Adoum, and El Akhouat). The presence of oil seeps in the mines points to common pathways for the migration of the metal-rich hydrocarbons from subsiding basins toward the sites of ore deposition. The connection of deposition sites to the sources of hydrocarbons is one of the most crucial factors in ore mineralization related to salt diapirs and organic-rich source rocks formed during the Oceanic Anoxic Events (OAEs).
In diapiric paleo-highs, the Triassic evaporites had provided the necessary sulfur via bacterial sulfate reduction (BSR) of gypsum and oil degradation by sulfate-reducing bacteria under low-temperature conditions (Fej el-Adoum, [88,96]; Bou Grine, [4,87]) following this reaction:
Hydrocarbons + complexed metals + (CaSO4, 2H2O) → CaCO3 + CO2 + H2S + metals
At the sites of deposition, these metal-rich fluids (hydrocarbons and basinal brines) mixed with the generated H2S-rich fluid. This mixing led to the precipitation of Pb-Zn ore deposits [4,8,14,36,50,87]. The metals can also combine with unreduced sulfates to generate sulfate minerals (celestite and barite) [14,36]. Two significant observations that could support the role of hydrocarbons in the ore genesis are as follows. Firstly, all Pb-Zn ore deposits in the diapiric zone are found in the vicinity of biodegraded oil seeps [4,8,87]. Secondly, the presence of zebra calcite and/or dolomite (carbonates after gypsum) is observed [59]. Zebra calcite, also known as methanogenic calcite, is formed as a by-product when gypsum is reduced in the presence of hydrocarbons, such as methane:
CaSO4.2H2O (Gypsum) + Hydrocarbons→CaCO3 (Zebra calcite) + H2S (Hydrogen sulfide)
It is noteworthy that the reduced sulfur necessary for sulfide precipitation has also originated from dissolved Triassic sulfates via the thermochemical sulfate reduction (TSR) under high-temperature conditions [14,50,58,88].
The model proposed herein shows striking similarities with the one proposed for the salt diapir-related Pb-Zn ore deposits in North Africa and Southern Europe [23]. The authors suggested a model in which they emphasized the importance of halokinesis and basinal evolution in the emplacement of ore. The proposed model also bears similarities with the Devonian reef carbonate-hosted MVT deposits of the eastern Lennard Shelf, Canning Basin, Western Australia [97]. In these ore deposits, the authors suggested that the metals and hydrocarbons were expelled from the Devonian sedimentary sequence of the Fitzroy basin. The metals and hydrocarbons, subsequently, migrated to the Lennard carbonate shelf where metals combined with H2S to produce Zn-Pb ore deposits. Our proposed model also shows notable similarities with a range of ore deposits including unconformity-type Athabasca sandstone-bearing uranium (Canada), Witwatersrand gold–uranium (South Africa), Carlin gold, and Mississippi Valley-type lead–zinc deposits (see [83] and references therein). These genetic models emphasize the role of hydrocarbons as (i) immobile traps where metals precipitate through reduction processes and ii) carriers transporting metals to deposition sites (see [83] and references therein).

8. Ore Controls, Ore Genetic Model, and Exploration

The discussion presented above shows that the key factors responsible for the genesis of ore in the diapiric zone are tectonics, halokinesis/diapirism, the development of anoxic conditions, and the generation of hydrocarbons [14,27,36]. Traps are commonly associated with particular paleogeography with positive structures, typically centered on Triassic extrusions guided by active paleo-faults during different geologic events. A schematic ore genetic model is illustrated in Figure 11 and Figure 12 with two major phases: (i) Early Cretaceous extensional tectonics and diapirism and (ii) Alpine orogeny with the migration of hydrocarbons and accompanying metals. Extensional tectonics created NE-SW-trending faults that delimited half-graben basins tilted SE under major tensional stress (σ1) roughly oriented NW-SE [34]. These faults, in conjunction with the overlying Cretaceous sedimentary load, facilitated the upward movement and emplacement of the Triassic evaporite, causing the formation of numerous NE-SW oriented diapirs (paleo-highs) (Figure 11A). The development of anoxic events (AOE-1, 2) in the adjacent basins led to the preservation and accumulation of organic matter in both the Fahdene and Bahloul Formations (Figure 11B). Trace elements, particularly Pb and Zn, are adsorbed on and/or into the inorganic (clay; Fe and P oxides) and organic fractions during sedimentation and early diagenesis (Figure 11C). This metal adsorption is revealed by the clustering of metals and organic/inorganic fractions in the PCA biplots (Figure 9A,B). These associations are absent in the mature Fahdene Formation (Figure 9A,B), likely due to thermal cracking. In this respect, the maturation of organic matter occurred during subsidence and the subsequent release of hydrocarbons and associated metals as well as the release of the basinal brines. The hydrocarbons not only contributed to carrying metals to the deposition sites during the Alpine orogeny (Figure 11D and Figure 12) [14,27,36,57] but also promoted the reduction of sulfates and the formation of reduced sulfur necessary for sulfide precipitation [14,27,36,38].
The impermeable Triassic clay–gypsum and marl/clay layers act as barriers, constraining the flow of metal-rich hydrocarbons around the margins of the diapir. The Triassic evaporites also act as a provider of dissolved sulfates required for the precipitation of sulfates (celestite and barite) and sulfide ores. In some ore deposits (e.g., Slata), the Albian–Vraconian series created a seal, constraining the metal-rich fluids to flow within the permeable Aptian Carbonates [14,27]. The faults, along with porous and permeable geological structures such as discontinuities, fractures, and breccias, act as conduits for the flow of these metal-rich hydrocarbons around the diapirs.
The exploration of mineral deposits related to salt diapirs necessitates the integration of various geological factors (see [14,27,34,36] and this study). These include structural features such as extensional-related normal faults, the formation of basins and diapiric paleo-highs, and the Alpine orogeny, which provide a geotectonic framework for fluid migration. Additionally, stratigraphic units rich in organic matter (Fahdene and Bahloul) deposited in these basins could have served as source rocks generating hydrocarbons and associated basinal brines, which are capable of transporting metals. Lithological controls, comprising (i) impermeable layers and evaporite diapirs that focused fluid flow and evaporite units that supplied sulfates and (ii) permeable features (e.g., discontinuities, breccias, and carbonates) played a crucial role. Identifying the structural, stratigraphic, and lithological controls guides the exploration of prospective areas, source rocks, fluid pathways, and physical and geochemical traps, thereby enhancing the likelihood of discovering economically viable ore deposits associated with salt diapir settings in the diapiric zone (e.g., [14,27,36]).

9. Concluding Remarks

The thorough analysis of literature along with the geologic data and principal component analysis led to the following conclusions regarding the role of hydrocarbons and accompanying basinal brines in the genesis of ore in the diapiric zone. Several authors have explored the significance of organic matter preserved in the Cretaceous formations, particularly the Bahloul Formation, in the formation of these ore deposits. According to isotopic studies of galena by Fedj-el-Adoum [88] the Fahdene and Bahloul Formations contributed to the source of metals. Through geochemical investigations, [8,14,22] have proposed that the Bahloul and/or Fahdene sediments could have served as a source of both hydrocarbons and metals. The importance of sulfate-reducing bacteria in the genesis is highlighted by the works of several researchers [4,14,36,88,98].
The sequential events that led to the formation of diapir-related ore deposits in which hydrocarbons play a role are summarized as follows:
  • Extensional tectonic along with diapirism created graben basins and diapiric paleohighs delimited by the NE-SW-trending faults.
  • The organic matter in both the Fahdene and the Bahloul formations, preserved due to the Anoxic Oceanic Events, facilitated the metal extraction from seawater, primally mediated by organic matter alongside clay minerals, Fe-Mg oxides, and pyrite. In the subsiding basin, the organic matter reached maturity, generating hydrocarbons while formational waters were expelled forming oil field brines. As a result, the organo-metallic ligands were destabilized and dissociated due the thermal cracking of the organic matter. The metals were expelled and incorporated into mobile hydrocarbons (polar fraction) and the related basinal brines.
  • The metalliferous fluids (hydrocarbons and related basinal brines) interacted with the SO42−-rich fluid derived from Triassic evaporites, leading to the precipitation of sulfates (barite and celestite). The reduced sulfates via thermochemical sulfate reduction (TSR) and/or bacterial sulfate reduction (BSR) generated sulfur which combined with the metals to precipitate the sulfide ores (e.g., sphalerite, galena).
  • Basinal evolution, organic matter-rich Cretaceous formations (Fahdene and Bahloul), diapiric paleohighs (halokinesis/diapirism), and the Alpine orogeny are key elements in the genesis of ore in the diapiric zone.
  • Structural (faults, diapiric paleohighs), lithological (juxtaposition of permeable and impermeable rocks), and stratigraphic (organic matter-rich formations) controls on ore formation are key elements that can assist in the identification of potential ore prospects in the diapiric zone.
To bolster the reliability and broader applicability of the findings, it is essential for future research to include a more extensive collection of samples for comprehensive trace element analysis, particularly in both mature and immature organic matter. Broadening the research to include additional geological contexts beyond the diapiric zone, such as the Nappes zone, would deepen our understanding of hydrocarbon involvement in ore genesis. Such an approach would not only support the validation of current conclusions but also uncover crucial factors that could enhance ore exploration strategies.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/min14090932/s1. Table S1. Principal components (PCs) with loading values for major and trace elements and total organic carbon (TOC) in the Bahloul Formation of Guarn–Halfaya, Diapir zone, Tunisia; Table S2. Principal components (PCs) with loading values for major and trace elements and total organic carbon (TOC) in the Fahdene Formation of Slata, Diapir zone, Tunisia; Table S3. Principal components (PCs) with loading values for major and trace elements in Fe oxides/sulfides in the Bahloul Formation of Guarn–Halfaya, Diapir zone, Tunisia; Table S4. Principal components (PCs) with loading values for major and trace elements in Fe oxides/sulfides in the Fahdene Formation of Slata, Diapir zone, Tunisia.

Author Contributions

Conceptualization, L.R.; Methodology, L.R.; Validation, L.R. and N.J.; Formal Analysis, L.R. Investigation, L.R. and N.J.; Writing—Original Draft Preparation, L.R.; Writing—Review and Editing, L.R. and N.J.; Visualization, L.R., N.J. and S.J. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The data used for PCA are available upon request from the first author (Larbi Rddad, email: [email protected]).

Acknowledgments

We are grateful to the two reviewers, whose comments and suggestions improved the quality of this paper. We also appreciate the Editor-in-Chief for the handling of this manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Simplified geologic map of northern Tunisia (modified from [28,29,30]) with distribution of ore deposits, magmatic rocks, and deep-seated faults.
Figure 1. Simplified geologic map of northern Tunisia (modified from [28,29,30]) with distribution of ore deposits, magmatic rocks, and deep-seated faults.
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Figure 2. Cross section passing by Nappes Zone, Diapirs Zone, Northern Atlas, and Foreland basin, Tunisia (modified from [52,53,54,55]). The cross section passes along line A-B in Figure 1.
Figure 2. Cross section passing by Nappes Zone, Diapirs Zone, Northern Atlas, and Foreland basin, Tunisia (modified from [52,53,54,55]). The cross section passes along line A-B in Figure 1.
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Figure 3. Synthetic lithostratigraphic log showing the rocks series from the Triassic to the Late Cretaceous, Diapirs Zone, Tunisia (modified from [47]).
Figure 3. Synthetic lithostratigraphic log showing the rocks series from the Triassic to the Late Cretaceous, Diapirs Zone, Tunisia (modified from [47]).
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Figure 4. Representative selected ore Type 2 stratiform within the Bahloul Formation from the Diapirs zone Pb-Zn deposits. (A) and (B) Stratiform Zn-rich ore of Bou Grine cut by veinlets of sphalerite or veins of calcite; (C) stratiform sphalerite with pyrite of Bou Grine cut by veinlets of crystalline sphalerite and calcite; (D) banded Zn-rich ore of Kebbouch South within sphalerite and galena; (E,F) stratiform Zn-rich ore of Kebbouch South, with fine-grained sphalerite cut by crystalline sphalerite and galena. L: limestone; Gn: galena; Sp: sphalerite; Py: pyrite; Ca: calcite.
Figure 4. Representative selected ore Type 2 stratiform within the Bahloul Formation from the Diapirs zone Pb-Zn deposits. (A) and (B) Stratiform Zn-rich ore of Bou Grine cut by veinlets of sphalerite or veins of calcite; (C) stratiform sphalerite with pyrite of Bou Grine cut by veinlets of crystalline sphalerite and calcite; (D) banded Zn-rich ore of Kebbouch South within sphalerite and galena; (E,F) stratiform Zn-rich ore of Kebbouch South, with fine-grained sphalerite cut by crystalline sphalerite and galena. L: limestone; Gn: galena; Sp: sphalerite; Py: pyrite; Ca: calcite.
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Figure 5. Representative selected ore Group 1 hosted in the strata-bound transition zone from the Diapirs zone Pb-Zn deposits. (A) Banded Zn-rich sulfide with sphalerite and galena of Fedj-el-Adou; (B) vein Pb-rich sulfide with galena and minor sphalerite and nacrite of Fedj-el-Adoum; (C) massive Pb-rich sulfide with galena, a minor amount of sphalerite and calcite of Fedj-el-Adoum; (D) massive pyrite with galena and calcite of Kebbouch South; (E) massive pyrite with sphalerite of Kebbouch South; (F) drill core shows massive pyrite in breccia dolostone of Kebbouch South; (G) breccia dolostone with galena and calcite of Sakiet Koucha; (H,I) brecciated black dolostones with sphalerite, galena, calcite, and celestite of Sakiet Koucha (photo I). D: dolostone; Gn: galena; Sp: sphalerite; Py: pyrite; Ca: calcite; Cel: celestite.
Figure 5. Representative selected ore Group 1 hosted in the strata-bound transition zone from the Diapirs zone Pb-Zn deposits. (A) Banded Zn-rich sulfide with sphalerite and galena of Fedj-el-Adou; (B) vein Pb-rich sulfide with galena and minor sphalerite and nacrite of Fedj-el-Adoum; (C) massive Pb-rich sulfide with galena, a minor amount of sphalerite and calcite of Fedj-el-Adoum; (D) massive pyrite with galena and calcite of Kebbouch South; (E) massive pyrite with sphalerite of Kebbouch South; (F) drill core shows massive pyrite in breccia dolostone of Kebbouch South; (G) breccia dolostone with galena and calcite of Sakiet Koucha; (H,I) brecciated black dolostones with sphalerite, galena, calcite, and celestite of Sakiet Koucha (photo I). D: dolostone; Gn: galena; Sp: sphalerite; Py: pyrite; Ca: calcite; Cel: celestite.
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Figure 6. Representative selected ore of Group 3 hosted in Cretaceous rocks from the Diapirs zone Pb-Zn deposits. (A) Veins of galena and calcite crosscutting the Bahloul Formation limestones in Kebbouch South; (B) sphalerite, pyrite, and calcite in veins in the Bahloul Formation of Bou Grine; (C) stockwork mineralization with sphalerite, galena, and calcite in the Bahloul Formation of Sakiet-Koucha; (D,E) veinlets of galena and sphalerite and veins of calcite crosscutting the Bahloul Formation of El Akhouat; (F) disseminated galena and veins of calcite in the Bahloul Formation of Guarn–Halfaya; (G) dolomitized limestone of the Abiod Formation with mainly sphalerite of Boukhil; (H) limestone of the Abiod Formation with mainly veinlets of galena of Boukhil; (I) galena and sphalerite with clayey limestone of the Abiod Formation of Boukhil; (J) disseminated galena and in veins associated with barite in the in the Serdj Formation brecciated zone of Jebel Slata, Sidi Amor; (K) coarse-grained galena with barite in the Serdj Formation brecciated zone of Jebel Slata, Sidi Amor; (L) veins with galena and barite hosted in the Serdj Formation of Jebel Slata, Sidi Amor. DL: dolomitized limestone; L: limestone; CL: clayey limestone; Gn: galena; Sp: sphalerite; Py: pyrite; Ca: calcite; Ba: barite.
Figure 6. Representative selected ore of Group 3 hosted in Cretaceous rocks from the Diapirs zone Pb-Zn deposits. (A) Veins of galena and calcite crosscutting the Bahloul Formation limestones in Kebbouch South; (B) sphalerite, pyrite, and calcite in veins in the Bahloul Formation of Bou Grine; (C) stockwork mineralization with sphalerite, galena, and calcite in the Bahloul Formation of Sakiet-Koucha; (D,E) veinlets of galena and sphalerite and veins of calcite crosscutting the Bahloul Formation of El Akhouat; (F) disseminated galena and veins of calcite in the Bahloul Formation of Guarn–Halfaya; (G) dolomitized limestone of the Abiod Formation with mainly sphalerite of Boukhil; (H) limestone of the Abiod Formation with mainly veinlets of galena of Boukhil; (I) galena and sphalerite with clayey limestone of the Abiod Formation of Boukhil; (J) disseminated galena and in veins associated with barite in the in the Serdj Formation brecciated zone of Jebel Slata, Sidi Amor; (K) coarse-grained galena with barite in the Serdj Formation brecciated zone of Jebel Slata, Sidi Amor; (L) veins with galena and barite hosted in the Serdj Formation of Jebel Slata, Sidi Amor. DL: dolomitized limestone; L: limestone; CL: clayey limestone; Gn: galena; Sp: sphalerite; Py: pyrite; Ca: calcite; Ba: barite.
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Figure 7. Oil seeps in the dolomitized limestone (DL) of the Abiod Formation encountered in an underground mine in Boukhil.
Figure 7. Oil seeps in the dolomitized limestone (DL) of the Abiod Formation encountered in an underground mine in Boukhil.
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Figure 8. Biplot graphs displaying loading values for total organic carbon and trace elements in the Bahloul Formation of Guarn–Halfaya and the Fahdene Formation of Slata from the dataset of Rddad et al. [14]. PC1 vs. PC2 (A) and PC1 vs. PC3 (B) for the Bahloul Formation; PC1 vs. PC2 (C) and PC1 vs. PC3 (D) for the Fahdene Formation. The blue arrow is used to indicate whether trace elements are associated with organic matter or not.
Figure 8. Biplot graphs displaying loading values for total organic carbon and trace elements in the Bahloul Formation of Guarn–Halfaya and the Fahdene Formation of Slata from the dataset of Rddad et al. [14]. PC1 vs. PC2 (A) and PC1 vs. PC3 (B) for the Bahloul Formation; PC1 vs. PC2 (C) and PC1 vs. PC3 (D) for the Fahdene Formation. The blue arrow is used to indicate whether trace elements are associated with organic matter or not.
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Figure 9. Biplot graphs displaying loading values for total major and trace elements in the Bahloul Formation of Guarn–Halfaya and Fahdene Formation of Slata from the dataset of Rddad et al. [14]. PC1 vs PC2 (A) and PC1 vs PC3 (B) for the Bahloul Formation and PC1 vs PC2 (C) and PC1 vs PC3 (D) for the Fahdene Formation. The arrows are used to indicate the oxide phase(s) to which trace elements are associated.
Figure 9. Biplot graphs displaying loading values for total major and trace elements in the Bahloul Formation of Guarn–Halfaya and Fahdene Formation of Slata from the dataset of Rddad et al. [14]. PC1 vs PC2 (A) and PC1 vs PC3 (B) for the Bahloul Formation and PC1 vs PC2 (C) and PC1 vs PC3 (D) for the Fahdene Formation. The arrows are used to indicate the oxide phase(s) to which trace elements are associated.
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Figure 10. Plots of 208Pb/204Pb vs. 206Pb/204Pb (A) and 207Pb/204Pb vs. 206Pb/204Pb (B) for galena samples of Groups 1, 2, and 3 from selected diapiric-related ore deposits [27,36,50], as well as for Cretaceous rocks [72] and Miocene igneous rocks [45]. The curves depicting growth trends for Pb isotope ratios are from the plumbotectonic model of [73].
Figure 10. Plots of 208Pb/204Pb vs. 206Pb/204Pb (A) and 207Pb/204Pb vs. 206Pb/204Pb (B) for galena samples of Groups 1, 2, and 3 from selected diapiric-related ore deposits [27,36,50], as well as for Cretaceous rocks [72] and Miocene igneous rocks [45]. The curves depicting growth trends for Pb isotope ratios are from the plumbotectonic model of [73].
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Figure 11. A schematic conceptual model illustrating the ore genesis in the diapiric zone. (A) Jurassic extension and the formation of the fault-bounded graben basins; (B) Cretaceous tectonics with diapirism along the major faults and the accumulation of organic matter-rich Cretaceous formations (Fahdene and Bahloul); (C) close-up schematic model showing trace element fixation by the inorganic and organic fractions in organic matter-rich formations during the Cretaceous; (D) alpine orogeny with the migration of metal-rich hydrocarbons and the accompanying basinal brines to the loci of deposition in the diapiric paleo-highs.
Figure 11. A schematic conceptual model illustrating the ore genesis in the diapiric zone. (A) Jurassic extension and the formation of the fault-bounded graben basins; (B) Cretaceous tectonics with diapirism along the major faults and the accumulation of organic matter-rich Cretaceous formations (Fahdene and Bahloul); (C) close-up schematic model showing trace element fixation by the inorganic and organic fractions in organic matter-rich formations during the Cretaceous; (D) alpine orogeny with the migration of metal-rich hydrocarbons and the accompanying basinal brines to the loci of deposition in the diapiric paleo-highs.
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Figure 12. Schematic model illustrating the migration of metal-rich hydrocarbons and associated basinal brines towards diapiric paleo-highs, with ore precipitation primarily occurring along the SE side of the diapir.
Figure 12. Schematic model illustrating the migration of metal-rich hydrocarbons and associated basinal brines towards diapiric paleo-highs, with ore precipitation primarily occurring along the SE side of the diapir.
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Rddad, L.; Jemmali, N.; Jaballah, S. The Role of Organic Matter and Hydrocarbons in the Genesis of the Pb-Zn-Fe (Ba-Sr) Ore Deposits in the Diapirs Zone, Northern Tunisia. Minerals 2024, 14, 932. https://doi.org/10.3390/min14090932

AMA Style

Rddad L, Jemmali N, Jaballah S. The Role of Organic Matter and Hydrocarbons in the Genesis of the Pb-Zn-Fe (Ba-Sr) Ore Deposits in the Diapirs Zone, Northern Tunisia. Minerals. 2024; 14(9):932. https://doi.org/10.3390/min14090932

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Rddad, Larbi, Nejib Jemmali, and Samar Jaballah. 2024. "The Role of Organic Matter and Hydrocarbons in the Genesis of the Pb-Zn-Fe (Ba-Sr) Ore Deposits in the Diapirs Zone, Northern Tunisia" Minerals 14, no. 9: 932. https://doi.org/10.3390/min14090932

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