Multiple Generations of Wolframite Mineralization in the Echassieres District (Massif Central, France)

Round 1

Reviewer 1 Report

Overall a good contribution that reads well. My main comments suggest re-organising a part of the sections.

 

Abstract – the abstract reads well. The first sentence is catchy and the results are described clearly. I would however add a conclusion to it, summarising the new model (the sentence should also show that this study can be of general interest for people working outside of the study area).

 

Introduction – The first part of the introduction is very good: it sates the problem and why the study is important. I was less convinced by lines 55-78 – these are details that should be moved to the Geological setting section. The introduction should keep l. 79-82, then explain how this study will have general implications for our comprehension of W mineralisation. This will shorten the Introduction, which is good – an introduction needs to be short, catchy, to the point, and make us want to read more.

45 – tungsten; please use W throughout

 

Geological setting – this section has a good first part, and it will read better once l.55-78 are incorporated to it. Please make sure you classify the granite with the usual igneous petrology terminology (S-type, peraluminous, 2-micas granite) and that you refer to the deposits using the general terminology too (intrusion-related, magmatic-hydrothermal system, something like that).

Figure 1 – please defined ‘FMC’ in the legend / ‘mineralizated occurrence’ – use mineralised instead of mineralizated, or simply use ‘showing’

106 – the Pluton is …. (should give information about magma type) / to talk about mineralisation, use: the Beauvoir pluton is associated with World-class rare-metal deposits (not rare-metal granite, that is a type of magma I don’t know)

 

Methodo. – a few things to add to this section

118 – samples were collected by the authors (they were necessarily collected in the field) / add samples amount + GPS location (by referencing a table or supplementary material) 143 – that’s one way to do it but, as everybody hates to have to read another paper to understand the one he/she is reading, I would make sure that the protocol (including standards, QA-QC, detection limits, etc.) is summarised in supplementary material at least. What software was used to reduce the data?

 

Results – I would suggest re-organising the article to shorten and focus the Result section. The first part of this section is about petrology. This could be moved to a new section, added between Geological setting and Methodology, and that will be dedicated to sampling (sample nb and location) and sample description (including paragenesis). Then the methodology could talk about microprobe and laser ablation and will be followed by a Result section focused on the main results: 1) 3 generations of Wolf. identified; 2) mineral chemistry results.

149 – and, not plus 155-157 – some of this info could go in Geological Setting 166 – the rock is sericitized 167 – except 170 - greisenized (please provide mineral assemblage in brackets) 187 – greisen-stage muscovite 198-199 – a bit out of place. If ‘complex parageneses’ is something that comes from previous study, it should be mentioned in the previous sections and used to explain why the study focuses on topaz etc. The Result section is just a list of results, not an introduction nor discussion section 201 – stockworks say all that 220-235 – here and elsewhere in the Result section, work on the English (it is of lesser quality than English in the first part of the article) 365 – how many samples? Analyses? 368 – 4, 8 and 1

 

Discussion – Needs re-organising. The discussion should start with the data and built on them. These are the petrological observations, these is the mineral chemistry, this is what it tells us and, using that, this is the model we propose to explain how this mineralisation formed. I advise reworking the first part of the Discussion as such. Section 6.3 should be blend in the rest of the Discussion, not isolated in its own section. Section 6.4. should be presented much earlier in the Discussion (near it’s beginning, when Results are still explained) – the Discussion should end by presenting of the general metallogenic model.

Figure 13 – very good figure. Please add words on the grey and dark grey background (alteration halo I guess), so we have no doubt on what the color mean

453 – this hydrothermal event caused … (alteration is a consequence) 467 – first time I see ‘orthomagmatic’ – is it used in the literature? Otherwise, you could just say magmatic fluid 576 – CF of evolved magmas (because for earlier stage differentiation, CF causes increase of Fe-content) – or do you mean Mn/Fe ratio, not absolute Fe-content? 586 – least evolved MAGMA

 

Conclusions – avoid one-sentence paragraphs (or add bullet points). Also, add more interpretations – e.g. l. 604-608, state the origin of the fluids as it is done above by designated stage 1 porphyry-style. You could even go further with your interpretation: is one of the 3 steps more important than another to make the deposit? In the gold-deposits World, that I know better, there is a lot of work on multistage models (giant deposits are generally multistage = accumulation of individual sub-economic events ending-up making an economic deposits) – could the study area be understood along these lines? (please read Meffre et al. 2016 for inspiration)

596 – detailed, not careful

 

Author Response

Overall a good contribution that reads well. My main comments suggest re-organising a part of the sections.

Abstract – the abstract reads well. The first sentence is catchy and the results are described clearly. I would however add a conclusion to it, summarising the new model (the sentence should also show that this study can be of general interest for people working outside of the study area).

We have complied with the reviewer’s suggestion

 Introduction – The first part of the introduction is very good: it sates the problem and why the study is important. I was less convinced by lines 55-78 – these are details that should be moved to the Geological setting section. The introduction should keep l. 79-82, then explain how this study will have general implications for our comprehension of W mineralisation. This will shorten the Introduction, which is good – an introduction needs to be short, catchy, to the point, and make us want to read more.

We agree with the reviewer, and have removed lines 55-78 and added them to the Geological Setting section, and added a short sentence to provide general implications of this study.

45 – tungsten; please use W throughout

Done

Geological setting – this section has a good first part, and it will read better once l.55-78 are incorporated to it. Please make sure you classify the granite with the usual igneous petrology terminology (S-type, peraluminous, 2-micas granite) and that you refer to the deposits using the general terminology too (intrusion-related, magmatic-hydrothermal system, something like that).

Igneous petrology terminology has been used to describe the granites. As for the mineralization, it is hosted in stockwork, veins and greisen, and we specify that in all cases. We do not see how to generalize it, and such exercise risks misleading the reader, we feel.

Figure 1 – please defined ‘FMC’ in the legend / ‘mineralizated occurrence’ – use mineralised instead of mineralizated, or simply use ‘showing’

Both items were fixed as suggested.

106 – the Pluton is …. (should give information about magma type) / to talk about mineralisation, use: the Beauvoir pluton is associated with World-class rare-metal deposits (not rare-metal granite, that is a type of magma I don’t know)

This was done as requested. However, we left the term ‘rare-metal’ because this is widely used in the specialized literature.

Methodo. – a few things to add to this section

118 – samples were collected by the authors (they were necessarily collected in the field) / add samples amount + GPS location (by referencing a table or supplementary material) 143 – that’s one way to do it but, as everybody hates to have to read another paper to understand the one he/she is reading, I would make sure that the protocol (including standards, QA-QC, detection limits, etc.) is summarised in supplementary material at least. What software was used to reduce the data?

We added GPS locations in the supplementary material (Sup Table 1). As for the ICP-MS details, we added info on standards and software used to Table 1.

Results – I would suggest re-organising the article to shorten and focus the Result section. The first part of this section is about petrology. This could be moved to a new section, added between Geological setting and Methodology, and that will be dedicated to sampling (sample nb and location) and sample description (including paragenesis). Then the methodology could talk about microprobe and laser ablation and will be followed by a Result section focused on the main results: 1) 3 generations of Wolf. identified; 2) mineral chemistry results.

We thank the reviewer for this suggestion and understand the purpose. However, we wish to include the petrographic work after the Method part because this work is new and to us it is part of the results (we do not use a Results title to avoid making too many sub-headings).

149 – and, not plus 155-157 – some of this info could go in Geological Setting 166 – the rock is sericitized 167 – except 170 - greisenized (please provide mineral assemblage in brackets) 187 – greisen-stage muscovite 198-199 – a bit out of place. If ‘complex parageneses’ is something that comes from previous study, it should be mentioned in the previous sections and used to explain why the study focuses on topaz etc. The Result section is just a list of results, not an introduction nor discussion section 201 – stockworks say all that 220-235 – here and elsewhere in the Result section, work on the English (it is of lesser quality than English in the first part of the article) 365 – how many samples? Analyses? 368 – 4, 8 and 1

We applied most of the suggested edits, except moving 155-157, as we consider this to be information relating to petrography. We modified line 201, but left it because it introduces the description of the vein arrangements. As for the counting of the samples and analyses (line 365), we did not change it there, because these introductory lines group analyses for all minerals. However, we did add the relative info to the appropriate sub-sections (topaz, goethite, etc) as was done for wolframite.

Discussion – Needs re-organising. The discussion should start with the data and built on them. These are the petrological observations, these is the mineral chemistry, this is what it tells us and, using that, this is the model we propose to explain how this mineralisation formed. I advise reworking the first part of the Discussion as such. Section 6.3 should be blend in the rest of the Discussion, not isolated in its own section. Section 6.4. should be presented much earlier in the Discussion (near it’s beginning, when Results are still explained) – the Discussion should end by presenting of the general metallogenic model.

We thank the reviewer for his suggestion and agree that what he suggests is one way of organizing the discussion. However, we chose to keep our outline for it, which starts with providing the paragenetic sequence of mineralization, which derives directly from the preceding section. We then discuss on the possible sources for W in the three episodes (for which we need to have already presented the paragenesis). These two parts present the model for the W mineralization. At this point we go on in comparing our model with the literature and propose a feedback on the Fe/Mn ratio in wolframite as a proxy of magmatic evolution and fingerprint of fluid source, as proposed in a recent study.

Figure 13 – very good figure. Please add words on the grey and dark grey background (alteration halo I guess), so we have no doubt on what the color mean

Changes were done

453 – this hydrothermal event caused … (alteration is a consequence) 467 – first time I see ‘orthomagmatic’ – is it used in the literature? Otherwise, you could just say magmatic fluid 576 – CF of evolved magmas (because for earlier stage differentiation, CF causes increase of Fe-content) – or do you mean Mn/Fe ratio, not absolute Fe-content? 586 – least evolved MAGMA

 We have done the changes suggested. ‘Orthomagmatic’ is a relatively common term used to refer to something derived, originated, from a magma. Thus, orthomagmatic fluid refers to a fluid exsolved from a crystallizing melt. However, we did change the term to simply ‘magmatic fluid’ for sake of clarity.

Conclusions –

avoid one-sentence paragraphs (or add bullet points).

We had bullets in the submitted version, apparently, they have been removed during editorial handling. We have reorganized and partly rewritten the conclusion and this time we avoided point-form style.

Also, add more interpretations – e.g. l. 604-608, state the origin of the fluids as it is done above by designated stage 1 porphyry-style. You could even go further with your interpretation: is one of the 3 steps more important than another to make the deposit? In the gold-deposits World, that I know better, there is a lot of work on multistage models (giant deposits are generally multistage = accumulation of individual sub-economic events ending-up making an economic deposits) – could the study area be understood along these lines? (please read Meffre et al. 2016 for inspiration)

The conclusion has been reworked following the above suggestions.

 

596 – detailed, not careful

Changed

Reviewer 2 Report

All comments are in uploaded PDF file.

Comments for author File: Comments.pdf

Author Response

This reviewer’s comments are keyed to the annotated pdf. We have followed all of this reviewer’s suggestions, except:

Line 46, Yes, we acknowledge that there is one conference abstract that mentions an origin of W mineralization other than from greisen. However, this does not take anything away from our statement; we only say that numerous studies point to greisen as the origin of the fluids.

Line 171. We did not use abbreviation for most minerals for sake of clarity, given that many of these are relatively rare, this also keeps reader from having to find the abbreviation list.

 

Reviewer 3 Report

This study describes three episodes of wolframite mineralization which evolved through about 60 Ma in the area of Echassieres.  All episodes evolved not only in one area, but also within the identical structures which is very unusual. In addition, both the second and third episodes were similar in chemical composition being enriched in F and Li forming topaz and lepidolite as gangue minerals. The whole story is unlikely in terms of statistic, but, probably, possible.

I spend several days studying the manuscript and related publications to assess the credibility of the data and their interpretation. Finally, I support publication of this manuscript, because it will be a good base for further discussion about timing of different types of mineralization within Variscan Europe.

Concerning scientific contents, I have following remarks and/or recommendations:

1. EMPA of wolframite: only one analyzed sample of the wolframite “C” may give only random data, not representing all post-Beauvoir wolframite. It is a pity, that authors analyzed Nb as only minor element. Recent mineralogical studies usually offer more complex analyses…

2. The “topazification” stage of the evolution is, according to my opinion, the most problematical. The combination of Toz1+ Li-mica is classical product of greisen-stage metasomatose in rare-metal granites. Where is the source of this matter? It is really impossible that these minerals postdated the Colettes granite? In the other hand, the assemblage Toz2+Ms+Wolframite “c” indicates late and relative low-temperature hydrothermal, not greisen stage, formation. The Toz1 and Toz2 may represent only two stages of the same hydrothermal event (?).

3. Three types of wolframite crystallized at different p-T and structural conditions. I will expect that we found three types of veins with appropriate mineral composition that sometimes cross each other’s and locally the younger metasomatized the older. Acc. the text, all wolframite types were found only together in the same structures. This is really strange for me.

4. Authors found wolframites with different Fe/Mn ratio and interpret, that these wolframites should have different sources. But, according to greisen deposit in Erzgebirge, the greisen-stage crystallization starts with relative Mn-poor wolframite, while hubnerite appears as product of late alteration or redeposition.

5. Authors interpreted the first W-bearing episode as a “porphyry type”. It is consistent with global evolution of the Massif Central at -360 Ma? Exist any porphyry-type granitoids of similar age through the France?

 

Some remarks to the formal aspect of the manuscript:

1. Mica names: authors used the IMA terminology in its pure form. OK, but the term “lepidolite-biotite solid solution” covers to different compositions like Lpd₉₅Bt₀₅ or Lpd₀₅Bt₉₅. The readers need information about real composition of particular mica type, this is important for understanding of the relation between mineralization and potential fluid source.

2. Please define better the rock types termed as “K-feldspar aplitic dyke” and “albite dyke”.

3. Term “greisen” originated in the Erzgebirge and labeled granite metasomatically enriched in secondary generation of quartz, mica and topaz (locally apatite, tourmaline etc.). Greisen stage is the first, high-temperature metasomatic stage following the solidification of the rock. In this study, authors used term “greisen” and “greisen fluid” for rocks without any enrichment in Li and F. Such metasomatites are in the Erzgebirge supposed to be post-greisen lower-temperature metasomatism (mainly muscovitisation).  For clarity of the text, several words about greisen and greisenising fluid in the author’s opinion will be for readers useful.

4. Authors document rock and mineral textures on 61 microphotographs. This huge amount of photos represents perfect primary documentation, but for readers it is rather difficult to orientate. Perhaps smaller amount of snaps arranged according to individual minerals (for example showing difference between typical examples of three types of wolframite) will be better. The whole photo series may be published as an appendix.

5. I will appreciate to add a figure with simple crossection through the Echassieres district showing relation among particular granites, dykes and veins.

 

Some detail comments are included in the annotated pdf.

Comments for author File: Comments.pdf

Author Response

R3

This study describes three episodes of wolframite mineralization which evolved through about 60 Ma in the area of Echassieres.  All episodes evolved not only in one area, but also within the identical structures which is very unusual. In addition, both the second and third episodes were similar in chemical composition being enriched in F and Li forming topaz and lepidolite as gangue minerals. The whole story is unlikely in terms of statistic, but, probably, possible.

I spend several days studying the manuscript and related publications to assess the credibility of the data and their interpretation. Finally, I support publication of this manuscript, because it will be a good base for further discussion about timing of different types of mineralization within Variscan Europe.

 

We thank this reviewer for the effort and in-depth of his review.

 

Concerning scientific contents, I have following remarks and/or recommendations:

EMPA of wolframite: only one analyzed sample of the wolframite “C” may give only random data, not representing all post-Beauvoir wolframite.

 

Although we only have one sample containing worlframite c originating from the greisen within the Beauvoir granite, we did analyze 7 or 8 grains in this sample, for a total of 16 analyses. It should be noted that occurrence of wolframite c in the granite greisen is extremely rare. Indeed, previous workers only found this wolframite generation as replacement of previous wolframite b. Instead, we could analyze crystals formed directly from the fluid, which make them of particular interest. Also, wolframite c from Mazet is now recognized for being of the same generation (i.e., post-Beauvoir), thus those analyses comfort the data from the one sample in question.

 

It is a pity, that authors analyzed Nb as only minor element. Recent mineralogical studies usually offer more complex analyses…

 

For the purpose of our study, we found that it was more interesting to obtain abundant EMPA data on many wolframite crystals rather than a limited amount of trace data by LA-ICPMS. We found that the Fe/Mn ratio was sufficient to clearly distinguish the different generations. Nevertheless, some trace element data for wolframite b are provided in Harlaux et al., 2018, and we have referred to them in the text.

 

The “topazification” stage of the evolution is, according to my opinion, the most problematical. The combination of Toz1+ Li-mica is classical product of greisen-stage metasomatose in rare-metal granites. Where is the source of this matter? It is really impossible that these minerals postdated the Colettes granite? In the other hand, the assemblage Toz2+Ms+Wolframite “c” indicates late and relative low-temperature hydrothermal, not greisen stage, formation. The Toz1 and Toz2 may represent only two stages of the same hydrothermal event (?).

 

We agree that multiple generations of wolframite are surprising, and initially we also considered tying the different episodes. However, wolframite b was dated at 334Ma, while the Beauvoir and Colettes granites were dated at 310Ma. Furthermore, they clearly crosscut the topaz-1 veins. We also have unpublished material supporting this. In particular, new ages obtained on other minerals confirm the dating reported above. The Toz2+Ms+Wolframite “c”(+qtz) assemblage is not necessarily a low-T assemblage; many greisen occurrences show this assemblage at early stages of alteration, worldwide. We have fluid inclusion data indicating trapping temperature in excess of 400°C, which are not low, particularly considering the maximum solidus temperatures obtained for the Beauvoir granite (around 600°C; eg Cuney et al 1992; Monnier et al 2018).

 

Three types of wolframite crystallized at different p-T and structural conditions. I will expect that we found three types of veins with appropriate mineral composition that sometimes cross each other’s and locally the younger metasomatized the older. Acc. the text, all wolframite types were found only together in the same structures. This is really strange for me.

 

Indeed, all wolframite types can be found within the same structure (LaBosse stockwork quartz veins). However, wolframite-a only occurs within these veins, wolframite-b only occurs in these and in the Topaz-1 veins, and wolframite-c can be found everywhere as it occurs as an alteration of previous generations. We believe that this is clearly explained in the text.

 

Authors found wolframites with different Fe/Mn ratio and interpret, that these wolframites should have different sources. But, according to greisen deposit in Erzgebirge, the greisen-stage crystallization starts with relative Mn-poor wolframite, while hubnerite appears as product of late alteration or redeposition.

 

Yes, the Erzgebirge provides further evidence that the Fe/Mn ratio in wolframite is very sensitive to the fluid chemistry, as it is efficient in highlighting the occurrence of a late alteration and reworking of primary wolframite. Our discussion on the different sources is based on other evidence than the Fe/Mn ratio.

 

 

Authors interpreted the first W-bearing episode as a “porphyry type”. It is consistent with global evolution of the Massif Central at -360 Ma? Exist any porphyry-type granitoids of similar age through the France?

 

Yes, it is consistent. Occurrence of felsic intrusive rocks of porphyry affinity in the Echassieres region is documented in the literature, which is where we took the information (e.g., De Rosen 1966, Aubert 1969).  In addition, the numerous dykes (and their intercutting relationships) that occur in the stockwork region (mentioned in the text) are typical of porphyry style intrusions.  There is also evidence for subduction-related magmatism in the French Massif Central at around 380Ma (Faure et al., 2009), which is the typical setting of calc-alkaline melts that produce porphyries.

 

Some remarks to the formal aspect of the manuscript:

Mica names: authors used the IMA terminology in its pure form. OK, but the term “lepidolite-biotite solid solution” covers to different compositions like Lpd₉₅Bt₀₅or Lpd₀₅Bt₉₅. The readers need information about real composition of particular mica type, this is important for understanding of the relation between mineralization and potential fluid source.

 

We use the term lpd-bt solid solution as a general description in some occasions, but because the composition of the micas varies from sample to sample, when we describe a specific occurrence we use simply lepidolite, F-rich biotite, and biotite, to indicate a more specific composition. We do not feel that in this paper exact mica compositions should be necessary (as would be the case for other minerals, e.g., feldspars).

 

Please define better the rock types termed as “K-feldspar aplitic dyke” and “albite dyke”.

 

We thank the reviewer for suggesting this and have changed the terms into potassic feldspar-dominated aplite and albitite dykes.

 

Term “greisen” originated in the Erzgebirge and labeled granite metasomatically enriched in secondary generation of quartz, mica and topaz (locally apatite, tourmaline etc.). Greisen stage is the first, high-temperature metasomatic stage following the solidification of the rock. In this study, authors used term “greisen” and “greisen fluid” for rocks without any enrichment in Li and F. Such metasomatites are in the Erzgebirge supposed to be post-greisen lower-temperature metasomatism (mainly muscovitisation). For clarity of the text, several words about greisen and greisenising fluid in the author’s opinion will be for readers useful. 

 

We agree with the reviewer. To avoid confusion, we have added the following text in brackets next to the first occurrence of the term greisen in the Geological settings section: “assemblage of quartz plus muscovite, accompanied by varying amounts of other distinctive minerals such as fluorite, topaz and tourmaline” (Pirajno, 2009).  Also, preliminary fluid inclusion data indicate that our greisen alteration initiated at around 400°C, so it does not qualify for the post-greisen low temperature muscovitisation.

Authors document rock and mineral textures on 61 microphotographs. This huge amount of photos represents perfect primary documentation, but for readers it is rather difficult to orientate. Perhaps smaller amount of snaps arranged according to individual minerals (for example showing difference between typical examples of three types of wolframite) will be better. The whole photo series may be published as an appendix.

 

We realize that we have a relatively large number of photographs. However, these are arranged in photographic plates and we feel that each is important to illustrate the specific assemblage that is discussed in the text. Petrography is an important aspect of this paper and we needed to show compelling evidence for the existence of several wolframite generations and involvement of different fluids. We should also point out that to redo them as suggested (i.e., focus on individual minerals) would necessarily lead to reorganizing much of the text, which, at the review stage, would invariably result in a less careful outcome.

 

I will appreciate to add a figure with simple crossection through the Echassieres district showing relation among particular granites, dykes and veins.

 

At this stage (we have more work in progress) we don't feel ready to produce a graphical model for the mineralization because we still lack constraints on several key items. Nevertheless, a cross section showing simple crosscutting relationships among the Beauvoir and Colettes granites, stockwork, dykes, and veins can be found in our previous publication (Monnier et al. 2018). We have referred to that in the revised text (caption to Fig 1).

 

Some detail comments are included in the annotated pdf.

 

We have considered all of the comments highlighted in the annotated pdf and changed the revised text accordingly. Some comments:

 

Figure 10 has been redrafted according to the comment, cutting it at the 0.01 detection limits. However, we left the scale in wt% because the purpose of this diagram is to show relative amounts, thus we prefer presenting raw data. Atomic values (apfu) are more pertinent, thus used, in the next Figure, which is related to possible substitutions within minerals.

 

Line 432, we do not have any data for the magmatic dykes.

 

Line 478. We agree that those textures could have occurred from a substitution as mentioned in our text. We studied these occurrences optically and by SEM but did not observe anything like that. However, we did secondary fluid inclusions in topaz 1 which correspond to primary fluid inclusions occurring in topaz 2 (these are preliminary data).

 

Line 579. In our discussion of the Mn/Fe we refer to the work of Michaud and Pichavant 2019, who attribute changes in that ratio to magmatic features, not effects of temperature.

Author Response File: Author Response.pdf