Comment on “E Re-examination of the Aïn
Allegua-Aguiba Celestite-Pb-Zn salt diapir-related
Mississippi Valley-Type Deposits (Nappes zone,
Northwestern Tunisia): New conceptual model”-A
discussion by Aroua Mzoughi, Hechmi Garnit, Salah
Bouhlel, Georges Beaudoin, Driss Khlifa, Anis Barkouti,
ZiedTabaibi (Ore Geology Reviews (2023) 105681 and
https://doi.org/10.1016/j.oregeorev.2023.105681)

Riadh Abidi, Christian Marignac, Étienne Deloule, Christian Hibsch, Dominique Gasquet, Christophe Renac, Alireza Somarin, Nouri Hatira, Najet Slim-Shimi

HAL Id: hal-04413172

https://hal.science/hal-04413172v1

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Comment on “E Re-examination of the Aïn Allegua-Aguiba Celestite-Pb-Zn salt diapir-related Mississippi Valley-Type Deposits (Nappes zone, Northwestern Tunisia): New conceptual model”-A discussion by Aroua Mzoughi, Hechmi Garnit, Salah Bouhlel, Georges Beaudoin, Driss Khlifa, Anis Barkouti, ZiedTabaibi (Ore Geology Reviews (2023) 105681 and https://doi.org/10.1016/j.oregeorev.2023.105681)

Riadh Abidi<sup>a</sup>, Christian Marignac<sup>b</sup>, Étienne Deloule<sup>c</sup>, Christian Hibsch<sup>d</sup>, Dominique Gasquet<sup>e</sup>, Christophe Renac<sup>f</sup>, Alireza K. Somarin<sup>g</sup>, Nouri Hatira<sup>h</sup>, Najet Slim-Shimi<sup>a</sup>

Recently, Mzoughi et al. (2023) published in Ore geology Reviews a paper, entitled « Re-examination of the Aïn Allegua-Aguiba celestite Pb-Zn salt diapir-related Mississippi Valley-Type deposits (Nappes zone, Northwestern Tunisia): New conceptual model », in which they claim to devise a better genetic model than the one proposed by our team in an earlier paper published in Mineralium Deposita (Abidi et al., 2022b).

We aim to demonstrate that the paper by Mzoughi et al. (2023) presents:

1. A biased introduction

2. Omission of results from our team

3. Technical errors, misused data and Scientific errors

4. Interpretation and modelling in contradiction to regional geology, mineralogy...

5. False conclusions based on misleading wording, biased handling of previous papers

## Depreciating presentation

### 1. A biased introduction

In their introduction, Mzoughi et al. (2023) assert that scant attention has been given to the geology, ore textures, and mineralogy of the deposits. However, they omit mentioning our team's dedicated works on these subjects (Abidi, 2011, Abidi et al., 2010, 2011, 2022a, b). Interestingly, these works are acknowledged later in the introduction, but the presentation implies a sole focus on fluid inclusion studies. There is an insinuation that these works are internally contradictory, branding them as "controversial" and supposedly necessitating a re-examination of the deposit. This presentation overlooks the crucial fact that our latest production (Abidi et al., 2022a; b) serves as the definitive stance of the team, rendering previous conclusions obsolete. Thus, there is no genuine controversy other than that initiated by Mzoughi et al. (2023).

At this point, Mzoughi et al. (2023) consider that these "contraversies" are "strange and enigmatic" in a province "where the MVT mineral system is widely accepted (Rouvier et al., 1985; Sheppard et al., 1996; Souissi et al., 2007; Bouhlel et al., 2016; Laouar et al., 2016)": again a quite biased presentation, since (i) the syn-genetic model advocated by Sheppard et al. (1996) is basically different of the syn-orogenic model proposed by the other workers; and (ii) this list conveniently forget the SEDEX model of Decrée et al. (2008); so that the stated

<footnote><sup>a</sup> Faculté des Sciences de Tunis, Département de Géologie, Laboratoire (3G): Géodynamique, Géonumérique et Géomatériaux, Université de Tunis El Manar, C.P. 2092 Tunis, Tunisia</footnote>

<footnote><sup>b</sup> Laboratoire GéoRessources UMR-CNRS 7359, École des Mines de Nancy, Campus ARTEM, CS14234, 54042 Nancy Cedex, France</footnote>

<footnote><sup>c</sup> CRPG-CNRS, 15 Rue N-D des Pauvres, 54500 Vandoeuvre-lès-Nancy, France</footnote>

<footnote><sup>d</sup> Laboratoire GéoRessources UMR-CNRS 7359, Faculté des Sciences et des Technologies, Campus Aiguillettes, 54506 Vandoeuvre-lès-Nancy Cedex, France</footnote>

<footnote><sup>e</sup> Laboratoire EDYTEM UMR-CNRS 5204, Bâtiment "PôleMontagne", Université Savoie Mont Blanc, Campus Technolac Scientifique, F-73 376 Le-Bourget-du-Lac, France</footnote>

<footnote><sup>f</sup> CNRS, OCA, IRD, Géoazur, Université Côte d'Azur, 250 rue Albert Einstein, Sophia Antipolis, 06560 Valbonne, France</footnote>

<footnote><sup>g</sup> Department of Geology, Brandon University, Brandon, Manitoba R7A 6A9, Canada</footnote>

<footnote><sup>h</sup> Faculté des Sciences de Bizerte, Département de Géologie, Université de Carthage, 7021 Jarzouna, Bizerte, Tunisia</footnote>
consensus is more cosmetic than real.

Finally, Mzoughi et al. (2023) claim to have realised a “detailed field, mineralogical, petrographic, and geochemical study (fluid inclusion and stable isotopes)”: thus, implying that the works of our team were not. A quantitative examination will allow to judge about the respective degree of detail reached in Mzoughi et al. (2023) and Abidi et al. (2022b): 112 and 290 lines respectively devoted to ore description and paragenesis; 30 and 50 lines respectively for the stable isotope studies.

## 2. Omission of results from our team

It is as if Mzoughi et al. (2023) were pretending to believe that the results they were presenting were not only original but also innovative, having not been the subject of previous works. That is how they fail to cite the results:

- from Abidi et al. (2022b), when dealing with stable isotopes in carbonates (none of our results referred to) and, less obviously however, in sulphides: the SIMS results on sulphides from Abidi et al. (2022b), although cited in the text, are omitted in the Figure 15 of Mzoughi et al. (2023); and these apparently embarrassing SIMS data has been removed from the discussion of Mzoughi et al. (2023);

- from Abidi et al. (2012) when dealing with composition of celestite and barite; the latter omission may be readily understood, since, contrary to the assertion of Mzoughi et al. (2023) that are only present “the end-members of the barite-celestite solution”, the work of Abidi et al. (2012) (work taken up by Abidi et al., 2022b) clearly highlighted the presence of intermediate terms of the solid solution; Abidi et al. (2022b) discussed at length the reasons for this presence, and this was of course neglected by Mzoughi et al. (2023).

- from Abidi et al. (2022b), when dealing with lead isotopes.

They also did not say a word of the detailed description of the sphalerite micro textures, allowing Abidi et al. (2022a and b) to conclude that they represent bio-mineralizations, with important consequences for the ore genesis; while Mzoughi et al. (2023) content themselves by writing that “a low-temperature environment is indicated by the fine crystalline colloform and botryoidal texture of the sphalerite”.

## 3. Technical errors, misused data and Scientific errors

**Fluid inclusions:** In the first place, judging from what they write (their p. 14) about FIs in celestite: “stretching”, “partially decrepitated”, “vapour bubble disappears (...) and then reappears with an increase in volume” (all behaviours not encountered during the work of Abidi et al., 2022b), it may be suspected that the work of Mzoughi et al. (2023) did not met the precautions recommended by Ulrich and Bodnar (1988) concerning both the mounting of the samples and the measurement procedures, when delicate minerals (carbonates, sulphates) are implied.

In the second place, although recognizing that most of the fluids trapped in the FIs from the Aïn Allegua and Aguiba sulphates and carbonates are representative of a bivalent cation-bearing brine, Mzoughi et al. (2023) were satisfied with measuring only the ice melting temperature (Tmice) and estimating the salinity in the H₂O-NaCl system (Te = -21.9 °C) known that The initial melting temperature (Tim) data mentioned in the text of Mzoughi et al. 2023, ranging from -64 to -54 °C (average -60 °C), clearly, this leads to erroneous results. It is well-known among all competent fluid inclusion (FI) researchers that, in the presence of divalent cations, it is necessary to measure not only the ice melting temperature (Tmice) but also the hydrohalite melting temperature (Tmhh). This additional step allows the use of the H₂O-NaCl-CaCl₂ model system (Te = 52 °C), which is necessary to apply in the study region in order to estimate true bulk salinity and the Ca/Na ratio. When applied at Aïn Allegua-Aguiba, it was found that two brines were present in the system, one Na-dominated and another exhibiting a Ca to Na exchange process (Abidi et al., 2022b).

Upon reviewing the salinity calculations conducted by Mzoughi et al. (2023) using the Bodnar equation for the NaCl-H₂O system and their melting temperature (Tm), which is an unsuitable aqueous system, as clarified in the preceding paragraph for the Aïn Allega-El Aguiba region, the reported salinity value is inaccurate.

Therefore, it is unsurprising that Mzoughi et al. (2023) did not identify the distinct anisothermal mixing trends obtained by Abidi et al. (2022b). A comparison of the figures in Mzoughi et al. (2023) and Abidi et al. (2022b) reveals this. Mzoughi et al. (2023) acknowledge the existence of fluid mixing processes, but without sufficient evidence. Mzoughi et al. (2023) did not acknowledge the existence of FIs with high homogenization temperatures in the late calcite. This discrepancy is crucial for the model proposed by Abidi et al. (2022b). It is surprising that Mzoughi et al. did not comment on this finding.

Finally, Mzoughi et al. (2023) did not attempt an estimation of the depth of formation by the construction of isochores, contenting themselves of the measured Th as temperature estimates for the mineral formation temperatures. It is therefore not surprising that the temperatures considered by Mzoughi et al. (2023) for constraining their model are somewhat different of that obtained by Abidi et al. (2022b), using an anisothermal mixing model in a context of pressure fluctuation.

In conclusion, it has to be said that, from the point of view of understanding the fluid system at Aïn Allega-Aguiba, the work of Mzoughi et al. (2023) represents more regression than progress, when compared with the work of our team.

**The paragenetic sequence:** The paragenetic sequence presented lacks coherence and contains numerous errors, making it nonsensical. During the Cretaceous period, specifically the Aptian, diapirism began, a crucial aspect omitted in the text and devoid of proper referencing. The deposition of celestine in the caprock during the Eocene is claimed without supporting arguments, observations, or dating. The introduction of thrust sheets and hydrothermal dolomite raises questions about their relationship and supporting evidence.

However, the text does not provide any arguments or answers to support this comparison. It is not possible to compare a thrust sheet on the scale of northern Tunisia with hydrothermal dolomite without further evidence. The process involves classic dolomitization, where a mineralizing fluid circulates and induces hydrothermal alteration of the host rock (gypsum), transforming it into dolomite. This concept has been extensively discussed in the works of Abidi (2011), Abidi et al. (2012), and Abidi et al. (2021).

The text mentions the transition to the third stage, but lacks explanations or demonstrations of the mechanical or chemical phenomena facilitating this transition. The text presents marcasite, sphalerite, barite 1, and calcite as cogenetic, which is incorrect. The mention of galena 2 lacks valid arguments, and the inclusion of supergene alteration minerals in the paragenesis lacks coherence. The text overlooks other studied minerals, such as chalcopyrite and jordanite, as well as cinnabar, realgar, and orpiment (Abidi, 2011; Abidi et al., 2023).

In summary, the figure does not accurately depict the mineral paragenesis described in the works of Abidi (2011), Abidi et al. (2010), Abidi et al. (2022), and Abidi et al. (2023).

## 4. Interpretation and modelling in contradiction to regional geology, mineralogy...

**Flaws in the approach of Mzoughi et al. (2023):** Mzoughi et al. (2023) did not consider the significance of the location of the Aïn Allega-Aguiba deposits along the major lithospheric Ghardimaou-Cap Serrat Fault Zone, which is associated with magmatism. Additionally, they did not mention the Ras Rajel rhyolite, which is close to the deposits and absent from the map in Fig. 2 of Mzoughi et al. (2023). Furthermore, they did not discuss the specific metal Hg, which is present in the El Arja deposit near the Ba-Sr-Pb-Zn deposits and was included in the work of Abidi et al. (2022b) for this reason.

Similarly, the authors did not include the N100°E fault in their map
(Fig. 2), which is largely concealed under Quaternary sediments. That borders to the North the Douglas diapir, and allow a fluid connection between the Ras Rajel rhyolite environment and the Aïn Allega-Aguiba deposits: an important part of the Abidi et al. (2023)' model.

There are real contradictions between some conclusions of Mzoughi et al. (2023) and Abidi et al. (2022b) and the former are wrong: The main

problem is raised by the interpretation of the paragenetic sequence by Mzoughi et al. (2023), and the ensuing conclusions concerning the age of emplacement of the main sulphate mineralization. It is worth noting that Mzoughi et al. (2023) never discussed the discrepancies between their conception and the one of our team, in line with their constant attitude of downplaying the work of Abidi et al. (2022b).

<figure><img src="image_5.png" /><figcaption>**Fig. 1.** Comparison of the paragenetic schemes of Abidi et al. (2022b) and Mzoughi et al. (2023). Mineral abbreviations conform to the IMA (2019) recommendations. A: the conception of Abidi et al. (2022b), including the El Arja Hg deposit; note that the supergene assemblages are omitted. B: the paragenetic sketch of Mzoughi et al. (2023) (redrawn from their Fig. 6): stand out (i) the fundamental differences when the early stages are concerned, and (ii) the poor treatment of the sulphides and sulphates in comparison with Abidi et al. (2022b).</figcaption></figure>
As readily seen in Fig. 1, the paragenetic sequence of Mzoughi et al. (2023) is simplified in comparison to that of Abidi et al. (2022b); in particular they failed to recognize the alternation of substages of sulphate and sulphide deposition, nor the alternation of sphalerite and galena deposition during the sulphide substages; and they apparently did not see pyrite. Indeed, where Mzoughi et al. (2023) believe to see “barite growth on sphalerite”, Abidi et al. (2023) demonstrates on a factual basis that, to the contrary, sphalerite grew at the expense of the sulphates (the former using, at least in part, the sulphur of the latter by BSR reduction). Although decisive for a detailed interpretation of the mineralizing processes, these differences remain minor compared to the place given to a so-called early deposition of the main celestite, leading to the conclusion that the mineralization was related to the final (Lutetian) ascent of the Douglas diapir.

This conclusion relies on three points:

- the celestite-dolomite relationships; Mzoughi et al. (2023) assert that dolomite was essentially later than the celestite, without giving detailed evidence: their Figure 9d represents a macroscopic feature, claimed to feature the crosscutting relationships, which would however demand a correlative microscopic demonstration of the time relationships; such evidence is presented in Abidi et al. (2022b), indeed demonstrating that dolomite was earlier than the sulphates (see their Figure 4c); as usual, Mzoughi et al. (2023) did not discuss the contradiction.

- the significance of the dolomite; Mzoughi et al. (2023) refer the dolomite to the so-called “Late Dolomite”, said by them to have been formed during the Lutetian diapirism event according to Perthuisot

et al. (1987); thus, the celestite would equally have been formed in this late diapirism context; unfortunately, we were unable to find such a demonstration in Perthuisot et al. (1987): in this paper devoted to a FI study in the diapirs, the authors never addressed the relative timing of the dolomite. In any case, Mzoughi et al. (2023) are not afraid by internal contradictions, since they write in another section of their paper that celestite formation was associated to the Pyrenean tectonic phase of the Late Eocene-Middle Oligocene age.

- the significance of the zebra textures; these textures are assigned by Mzoughi et al. (2023) “probably to a pervasive replacement of evaporate-rich beds as indicated by relicts of holokinetic folding characteristic of evaporites”; however, Abidi et al. (2022b) describe zebra structures as cracks with syntaxial infillings of sulphate prisms, shown to have been hydrothermally reworked by “fracturing associated with dissolution and open space filling, and local re-using of the earlier zebra fabric which formed “pseudo-zebra” texture”- the latter being what Mzoughi et al. (2023) interpreted as replaced evaporites (an error that a detailed microscopic and SEM study would have avoid committing). Importantly, the zebra are found to be flat-lying in steepened host-rocks: which is evidently incompatible with a syn-sedimentary origin, and demonstrate an origin related to the late Miocene NE-SW shortening (folding) event (the zebra being interpreted by Abidi et al. (2022b) as tension joints resulting from hydraulic fracturing).

Based on the third point, we maintain that the ore deposits at Aïn Allega-Aguiba, including the sulphates, were formed coevally with the late Miocene tectonic events, long after the diapiric ascent ending in the

<figure><img src="image_6.png" /><figcaption>**Fig. 2.** Comparison of the conceptual models proposed (A) by Abidi et al. (2022) and (B) by Mzoughi et al. (2023). The latter has been redrawn, with the symbols having been homogenized with the first model as far as possible.</figcaption></figure>
Lutetian.

*Final conceptual model and conclusion:* When comparing the two models of Mzoughi et al. (2023) and Abidi et al. (2022b), there are obvious similarities (Fig. 2) (we are ready to admit that this is pure coincidence). But the differences are indeed striking. They are numerous and concern both the geologic details and the design of the hydrothermal systems; and we think that they are not to the advantage of Mzoughi et al. (2023). In particular:

- In the first place, the depth to the basement boundary (at the time of ore body formation) is given to 15 km in Mzoughi et al. (2023), and to 8 km in Abidi et al. (2022b); the latter is based on published seismic data (Khomsiet al., 2006, 2009), not referred to by Mzoughi et al. (2023): what data did they use?

- In the second place, the key role played by the deep-seated Ghardimaou-Cap Serrat fault zone is overlooked, and the demonstrated fact that the diapir was deformed in a post-nappe folding event is not shown in the section of Mzoughi et al. (2023).

- In the third place, we find very light-hearted the fact of drawing the Triassic salt mass as it is in the model of Mzoughi et al. (2023): represented as largely outcropping at the present-day level of erosion, while the cap-rock would have been nearly completely eroded: which is exactly the contrary of the reality, Sainfeld (1952) having already clearly shown that only cap-rocks are present at the outcrop, the presence of salt at depth having to be inferred (as indeed done in the model of Abidi et al., 2022a; b).

- In the fourth place, the depth of formation of the deposits is not justified by Mzoughi et al. (2023), allusively writing that deposition occurred "probably at a significant burial depth, more than several hundred meters" (which, incidentally, would have justified a correction of the measured homogenization temperatures, that the authors neglected to do): why in truth take into account the work of Abidi et al. (2022b), who estimated a $1.8 \pm 0.5$ km depth of formation for the deposits? What is more, what allows Mzoughi et al. (2023) to place the two Aïn Allega and Aguiba deposits at different formation depths, whereas indeed the geologic map demonstrates the contrary??

- Finally, while the proposed fluid trajectories in the Abidi et al. (2022b) model are constrained by the factual evidence derived from FI studies and lead isotopes data, the ones in the Mzoughi et al. (2023) appear based less on precise data than on a vague intuition. In particular, they call to two surprisingly symmetrical faults as fluid drains: it is a pity that there is no sign of these faults on the geologic maps. And we are unable to understand on what factual data (heat source? Confining reservoirs?) are based the convective cells affecting the brines in the Mzoughi et al. (2023) model.

We emphasize that nothing can be found in the model presented in the Figure 18 of Mzoughi et al. (2023) to justify the final conclusion that the Pb-Zn mineral system was "a result of a gravity-driven fluid circulation event related to late Alpine convergence and thrust sheet formation", although Mzoughi et al. (2023) themselves concluded from their FI study that most of the saline brines found in the deposits came from halite dissolution from the Douglas Triassic salt diapir: a local origin, then, which is not really the same as a basinalbrine. The call for a gravity-driven event is indeed in conformity with the general model of Bradley and Leach (2003), imported into the Tunisian context by Bouhlel (2005). For the specific Aïn Allega-Aguiba context, this conclusion appears purely gratuitous and indeed based on circular thinking: from an introduction asserting that in the Tunisian Pb-Zn province "the MVT mineral system is widely accepted" to a conclusion stipulating the same.

What is more, as far as the sulphate deposits are considered, this conclusion is internally contradictory on the basis of the results of Mzoughi et al. (2023) themselves, since they propose that the celestite deposits were formed no later than the Early Oligocene. It is true that

they believe the Pyrenean tectonic phase to have been associated to the Tell thrusting event: which is not, the Pyrenean phase being only marked by the inversion of earlier normal faults in the Tell Atlas. The present-day fold-and-thrust belt and the emplacement of thrust sheet did not occur before the Late Burigalian, and consequently, the celestite deposition would have occurred, in the Mzoughi et al. (2023) conception, before the inception of the postulated gravity-driven flow. The gravity-driven model would thus only apply to the minor Pb-Zn mineralization: the latter is indeed thought by Mzoughi et al. (2023), without any factual evidence, to have been late Tertiary; in a very confuse way, however, since in the Figure 6 of Mzoughi et al. (2023), Pb-Zn deposition is presented both as occurring in the Langhian-Serravallian interval (Late Serravallian-Early Tortonian in the text...), and being related to "post-nappe Messinian rifting and diapirism" (to what work do the authors refer to for this weird Messinian diapiric event remains a mystery).

Finally, we think that science does not consist in the servile repetition of ready-made models. There is no question about the role of the Douglas salt diapir in the genesis of the Aïn Allega-Aguiba deposits, nor on the assignment of these deposits to the generalized MVT class of deposits formed into carbonates from rather low-temperature brines. However, as demonstrated by the detailed multi-method work of Abidi et al. (2022b), the relation with the diapir is not the only (nor the more important) control in the genesis of the Aïn Allega-Aguiba deposits, which constitute an original model where the Tertiary magmatism took a significant part in the constitution of the hydrothermal system. When compared with this model, the contribution of Mzoughi et al. (2023) does not appear as a progress, contrary to the declared intentions; and at the very least to call it a new scientific contribution is indeed rather problematic.

**5. False conclusions based on misleading wording, biased handling of previous papers**

Contrary to the assertion of Mzoughi et al. (2023), writing that "temperatures measured in fluid inclusions hosted by dolomite and celestite (100° to 185 °C) are not caused by (...) the presence of a concealed sill below the deposit (Abidi et al., 2022b)", we have never envisaged the role of a magmatic heat source for the heating of the brine components in the hydrothermal system. In fact, Abidi et al. (2023) write that "temperatures as high as 210 to 245 °C would have been reached at 7 to 8 km depth, i.e. at the expected penetration depth of the L2b brine [the Ca-Na exchanged brine, see below]. There is thus no problem to obtain the L2 brine at ~200°-210 °C postulated by the model, by mixing of L2a [shallower Na-brine] and L2b before their arrival in the ore traps". We emphasize that to reach this result it was only necessary to consider a moderate geothermal gradient of 35 °C·km⁻¹, a typical post-collisional gradient. The 40° to 60 °C·km⁻¹ referred to by Mzoughi et al. (2023) are likely excessive; they are based on the pioneer FI study of Perthuisot et al. (1987), which, despite its undeniable value, was hampered by the poor knowledge of model systems at the time, and the P-T reconstruction they have proposed cannot longer be considered valid.

In reality, if Abidi et al. (2023) call on an additional heat source, it is only to explain the high temperature attained by the surficial meteoric fluids involved in the system; they write "a problem appears when looking at L1, because this meteoric water, which is weakly exchanged and therefore could not penetrate deeply, is credited with a temperature of ~235-245 °C in the same model: an additional source of heat is therefore required near to the surface" (a problem that Mzoughi et al. 2023 failed to identify, see below). To solve the problem, Abidi et al. (2022b) call not on the concealed sill, but on the visible Ras Rajel rhyolite intrusion: "the Ras Rajel rhyodacite intrusive complex is the most likely source of heat for the L1 fluid: heated in the vicinity of the intrusion, ambient water could have been channelized towards the mineralized sites through the E-W fault in the north of the diapir". Thus, Abidi et al. (2022b) never call for the concealed sill as a heat source,
contrary to what was written by Mzoughi et al. (2023) in their intro-
duction, pretending to cite the former: “shallow concealed magma sill
and felsic magmatism are involved as a heat source for the ore fluids” is a
sentence which cannot be found in Abidi et al. (2022b).

Not all the conclusions presented by Mzoughi et al. (2023) are new: In fact, a systematic observation of various sections of the work by Mzoughi et al. (2023) reveals that while Abidi et al. (2022b) extensively discusses a significant amount of data, Mzoughi et al. (2023) confine themselves to loose interpretations and speculative models, generally contributing nothing substantial to the dossier. Numerous examples illustrate this, such as:

- *Lead isotopes:* In their study, Mzoughi et al. (2023) base their conclusions on the only two data points obtained by Bouhlel et al. (2013) and assert that the lead is derived from upper crustal rocks without providing further details. However, Abidi et al. (2022b), relying on a more extensive dataset of 45 Secondary Ion Mass Spectrometry (SIMS) data, had already deduced a significant contribution from a basement source. Notably, Abidi et al. reached a more refined conclusion, indicating the presence of two distinct basement sources (two separate basement compartments divided by the Ghardimaou-Cap Serrat Fault zone), along with additional contributions from the sedimentary cover and Tertiary magmatism.

- *C-O isotopes in calcite:* Based on their own data and a larger data base from the literature (including data from Bouhlel et al., 2009), Abidi et al. (2022b), following the conclusions reached by Al-Assam and Abdallah (2006) highlight “the contribution of an organic source mixed with the Triassic carbon”. Thus, when they concluded, from only one negative $\overset{\circ}{\mathrm{S}}^{13}\mathrm{C}$ in a calcite, that “it likely reflects the interaction of the hydrothermal fluid with hydrocarbon water” without citing previous authors, Mzoughi et al. (2023) have not only found nothing really new, but have also shown a lack of interest in previous works. We add that introduce “organic matter” as “migrated hydrocarbons” in the paragenetic sequence, as done in Figure 6 of Mzoughi et al. (2023) is a real lie, in so far as no other evidence than the negative $\overset{\circ}{\mathrm{S}}^{13}\mathrm{C}$ has ever be found (no hydrocarbons in the Fls in particular).

- *Sulfur isotopes:*

Sulphates: the Triassic origin of the sulphur in Aïn Allega and Aguiba deposits is not a discovery of Mzoughi et al. (2023), having been already proposed by Abidi et al. (2022). Also, the problem of the heavy $\overset{\circ}{\mathrm{S}}^{34}\mathrm{S}$ in some celestite was already discussed at length by Abidi et al. (2022a and b); we acknowledge that Mzoughi et al. (2023) proposed a solution not considered by the former (i.e., a Middle Triassic source, however unlikely given the Late Triassic age usually assigned to the salt diapirs in northern Africa); but they conversely neglected to discuss the two more likely explanations proposed by Abidi et al. (2022a and b), a Rayleigh fractionation process (starting from typical sulphate compositions) or the simultaneous reduction of the sulphate resulting in $\overset{\circ}{\mathrm{S}}^{34}\mathrm{S}$ enrichment in the residual solution (a process proposed by Hanor 2000). Then, Mzoughi et al. (2023) cite Bouhlel et al., 2016 in reference to sulfur isotopic analysis in anhydrite. Nevertheless, it is important to highlight that Bouhlel did not perform any sulfur isotopic analysis on anhydrite in their paper (Bouhlel et al., 2016).

Sulphides: having (without any discussion) discarded the SIMS data of Abidi et al. (2022b), Mzoughi et al. (2023) deduce from the narrow range of $\overset{\circ}{\mathrm{S}}^{34}\mathrm{S}$ in sphalerite and galena that bacterial sulphate reduction (BSR) could not have been active at Aïn Allega-Aguiba, and, after a short discussion, conclude to a thermal reduction process (TSR) using local hydrocarbons, active in the cap rock environment prior to the influx of the metal-bearing brines. By contrast, having discussed at length the data in comparison with the observed ore textures (an exercise which was apparently beyond the reach of Mzoughi et al., 2023), Abidi et al. (2022b) comes to the conclusion that BSR in a closed system was the source of sulphur for the

sphalerite (explaining the large +1.6 to +26.5 ‰ range of the $\overset{\circ}{\mathrm{S}}^{34}\mathrm{S}$ values), whereas the sulphur for galena was for a large part issued from a TSR process. Refusing to accept a fact that we believe to be firmly established and which places severe constraints on fluctuations in temperature in the system, Mzoughi et al. (2023) necessarily invent a distorted and unconvincing version of the hydrothermal evolution.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

No data was used for the research described in the article.

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