Composition and Structure of Zircon from Hydrothermal Uranium Occurrences of the Litsa Ore Area (Kola Region, Russia)

Round 1

Reviewer 1 Report

Much improved ms with only a few minor changes recommended. 

Comments for author File: Comments.pdf

Author Response

Dear reviewer,

Thank you very much for your comments and correction of our mistakes!

We corrected the manuscript according to your comments (as we understood them;)).

Line 145 - there was “’squid’ signal smoothing device”; I did not really understand what was wrong with it, that is why I just deleted the sentence.

In the section “REE composition of zircon” I added numerical data ((Sm/La)n, (Lu/Gd)n and order of magnitude of normalized values to describe “enrichment” and “depletion” in HREE or LREE.

The section “Temperature of zircon crystallization” has been completely removed. There are practically no titanium phases in the rocks (neither rutile nor titanite), and in general, it did not make sense to calculate the temperature from the very beginning.

To the DISCUSSION the reference Belousova et al., 2002 about zircon source was added. Mistakes were corrected and repetitions deleted.

All corrections, made according to your comments, are colored in magenta.

Sincerely yours,

Tatiana Kaulina

Reviewer 2 Report

Again, I think this manuscript writing is improved. With some rigorous spell check and further clarity editing, the writing of the manuscript is publishable.

There are instances where the language is either vague, confusing, and/or implies an interpretation where it should be describing observations.

The main weakness that remains is the presentation of the U-Pb LA-ICP-MS data. The presented errors of ~± 4–10 Ma on ~2800 Ma dates are absolutely not acceptable. Uncertainty of 10 Ma on 2800 Ma is 0.35% (from abstract), which the authors state is 2-sigma unc. on a weighted average from concordia.  The best one can do with that technique is 2% (2-sigma). Although the methods are better described, presenting data better than the worldwide accepted uncertainty requires a robust explanation of how errors were propagated. Alternatively the uncertainties need to be recalculated and presented according to the community standards (≥ 2% 2-sigma). This inflated sense of precision also leads to geologic interpretations that overstep the data.

The interpretation of the different REE patterns seems reasonable, but the choices for the 4+ cation thermometry seem strange without substantiating data. That is then the basis for some interpretations about the thermal history which causes some pause.

 

 

Comments for author File: Comments.pdf

Author Response

The answer is in the attached file

Author Response File: Author Response.pdf

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

I believe the paper is near ready for publication. Beyond then grammatical issues (see below), a general comment is that it would help many readers if the introduction contained more information about zircon alteration in general and its relation to CL and BSE imaging. For example, that high U zones are typically dark because U absorbs the luminescence wavelengths and these dark zones reflect growth during times of increased mobility of U as it is oxidized to +6. This mobility is also commonly reflected in low Th/U ratios, e.g., <0.1, in hydrothermal zircon. When you have altered zircons such as those described and are relating their ages to specific alteration processes, concordia plots are not always the best way to depict the age relationships. In this context, it might be helpful to make a few plots of age (207/206) vs. Th/U or total REE so the figures tie more directly to the discussion. As it is, figure 3a is pretty hard to decipher.

 

I have provided an annotated copy of the text with highlight ed suggestions for changes as described by the line numbers below:

 

33. disturbance?
34. not too sure that easily is a fair description. Many readers will likely misunderstand this.
35. studies
36. by
37. more strongly

62.with intercalated amphibole gneisses

69. to varying extents
70. sm = ?, sample shows
71. what is RAS?
72. what is 3c?
73. minerals
74. shapes
75. what is the age? Best to mention it here
76. is
77. what does this temperature refer to? What kind of errors are reported, 1 sigma, 2 sigma, ?
78. not sure metasomatite is a common word for these types of rocks, maybe metasomites?
79. REE contained in what?
80. not sure why you feel dissolution is the most likely explanation. If so, good to explain why you believe this to be the case.
81. exhibits
82. uranium-rich rim
83. more common expressions are: alteration or distortion
84. as above
    210. Increases
85. Delete? Not sure what this refers to.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

Thank you very much for your Comments and Suggestions!

We have expanded an Introduction and added information about zircon alteration and hydrothermal zircon.

We have corrected all mistakes (thank you for noticing them) and made English editing as well.

Thank you for your suggestion to add (207/206) vs. Th/U (or total REE) plot. It would be good, but the problem is that we have LA-ICPMS U-Pb data only for low-U plagiogranites and gneisses, where intensive metasomatic reworking of zircons were not obtained. The most interesting metasomatic zircon alteration is in high-U rocks: monzogranite KT-3 (only three LA-ICPMS data-points); metasomatic rocks and pegmatoid veins for which we have only ID-TIMS data for monazite and uraninite. So we don’t have enough 207/206 data to compare and can mainly operate with an overall age of rock. But in any case we tried to clarify zircon alteration in Discussion and to discuss Th-U ratios with hydrothermal processes.

We changed and expanded the Discussion.

We have added about 1 and 2 sigma errors and described all methods in more details.

We have added about the temperature of zircon crystallization to the Analytical methods, Results and Discussion.

About “metasomatite”, I think it is a common word, but we changed it to “metasomatic rocks”, probably it is better.

All corrected parts of the text are marked in red, but since there we a lot of comments from other reviewers, there a lot of red parts in the text. All changes according to other reviewers are fully consistent with your comments.

 

Thank you once again for your work with our manuscript!

Sincerely yours,

Tatiana Kaulina

Reviewer 2 Report

This manuscript describes U-Pb ages, REE concentrations and patterns and Raman spectrum for zircons included in various rock types in the U occurrences in Kola peninsula, Russia. However, the analytical methods and data are not properly presented. For example, each age datum shows analytical error, but readers do not understand what does it mean (1 sigma, 2 sigma, or others). This makes difficult to evaluate the results, and there is no discussion about the validity of the results. The duscussion is quite poor and no explanation about the characteristics of the magmatic, metamict  and hydrothermal zircons. Some discussions are included in the chapter of the result presentation.

Abstract does not provide clear results, discussion and conclusion. And finally this manuscript needs extensive editing of English. In conclusion, this manuscript is hard to be recommended for minerals.  

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

Thank you very much for your Comments and Suggestions!

We made all necessary corrections according to your comments.

 

You wrote “If this is the main aim of the research, this introduction should review the difference of magmatic and hydrothermal zircon instead of U-Pb geochronology. There are a lot of papers related to this topic.”

We added some information on magmatic and hydrothermal zircon to the Introduction (more to the Discussion) and add more References. But in the text we also explained, that the main purpose of the investigations in the area was to study and date uranium mineralization, but in the paper we presents most interesting data for zircons which we obtained during study of uranium mineralization.

 

The section Analytical methods was expanded, methods were described in more details, as well as we added about 1 and 2 sigma errors.

 

You wrote, that “The discussion is quite poor and no explanation about the characteristics of the magmatic, metamict and hydrothermal zircons. Some discussions are included in the chapter of the result presentation”.

We expanded the Discussion; add more information and references about the characteristics of different type zircons, and separated Results and Discussion correctly

 

You wrote, that “Abstract does not provide clear results, discussion and conclusion”.

Abstract was changed and made more informative.

 

Extensive English editing was also made, it was shown by “Track Changes" function.

 

The figure 1 redone, it became larger and we hope the text is clearly seen now. Abbreviations were explained in the Caption. Group names were added. The style of scales became uniformed. Coordinates of maps were added.

 

All corrected parts of the text are marked in red, also according to other reviewers comments, but all reviewers had similar comments, so therefore, corrections do not contradict each other.

 

Thank you for your work with our manuscript!

Sincerely yours,

Tatiana Kaulina

 

Reviewer 3 Report

Hello,

I have reviewed the manuscript and highlighted some of the necessary changes (see attached file with track changes). This study seems interesting, but requires significant revision to communicate the significance, methods, and data accurately. Overall, there is not enough information to assess the authors conclusions and interpretations from the data. The entire manuscript does not contain enough citations to assess what the authors contributed and what they gleaned from other authors and studies.

Additionally, many instances of problems with the English language made the paper difficult or impossible to follow.

The results are discussed, but every other section of the paper is generally lacking in depth of information.

The topic is interesting and could be published with significant work to improve the type and amount of information presented.

 

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

Thank you very much for your Comments and Suggestions!

We made all necessary corrections according to your comments.

 

First of all we made extensive English editing. Hope now it is easier to read the text.

We changed all parts of the manuscript to make the text more informative. All corrections are marked in red. We added references and discussed literature widely.

 

Below are your comments in the text and our answers:

 

Your comment - What are these tectonic zones and why are they important?

We added in the text: “The Litsa uranium ore area is located in the northwestern part of the Kola Region at the intersection of Titovka-Uraguba and Litsa-Araguba tectonic zones restricted by N-S and E-W striking faults, which determined a mosaic-block structure of the area.”

These are zones of deep faults and shear zones and it is written in the text below that they are more permeable for hydrothermal solutions and fluids.

 

Your comment - What does orthrometamorphic mean in this context and is it redundant with the term granite-gneiss? TTG = tonalite trondhjemite granite association? This needs to be explained.

You are right. We deleted “orthometamorphic” and explained TTG.

 

Your comment about Fig 1. – The largest scale map (a) does not contain enough information to locate this for a global audience. Some latitude and longitude or global position map would be useful. Much of the text is too small to read. What should the reader take away from this figure? This figure caption should be expanded to give some context.

Yes, the figure 1 redone, it became larger and we hope the text is clearly seen now. Coordinates of maps were added. The caption is expanded.

 

Your question to the section “Rock samples” - Why were the samples presented here chosen for study? What about the spatial organization, rock type, etc.? Why does figure 1 matter in the context of the samples and geologic history sections?

We explained in the text above the section, that samples were collected with increased radioactive background to study and to date uranium mineralisation in the area. The paper presents the most interesting data obtained for zircons in the frame of the U mineralisation study.

 

Abbreviation of minerals are deleted in the text (we used full mineral names) and explained in figure captions.

 

The section “Analytical Methods” is expanded with more details and references.

 

The title “LA-ICP-MS age of zircon” was changed to “LA-ICPMS data” and we tried to clarify in the Discussion why we consider some data to reflect an age of rock or metamorphic event.

Your comments to the Figure 2 (CL images of Zrn) - If you are reporting 207Pb/206Pb dates, then the data should be shown in Tera-Wasserburg plots rather than Wetherill concordia plots. Commented [A19]: The figure captions should be expanded to highlight what the reader should take away from inspection.

You see, I prefer Wetherill Concordia plot, I more got used of it and we also commonly report 207Pb/206Pb ages for it. But thank you very much, I found out, that we reported isotopic ratios for Tera-Wasserburg plot in the Table 1, but now I changed them according to Wetherill Concordia.

We added to the figure caption “see text for explanation”. I thought, how to expand the caption, but instead expanded the text with zircon description and hope it will be enough to avoid repetition.

 

Your comments to Figure 3 (U-Pb data) - Commented [A20]: Much of this text is too small to read. I think these should be plotted in Tera-Wasserburg space.

Commented [A21]: The MSWDs are incredibly low. What went in to calculating the presented ages? Are they weighted averages of one ratio, discords? How was the uncertainty propagated? The standard in U-Pb geochronology is to present 2-sigma uncertainty? Why was 1-sigma chosen and reported here?

The figure was redone. It became larger and hope understandable. As for Tera-Vasserburg, I plotted it to see, what is better, when the data was just obtained. But I prefer Wetherill plot, as I have told already.

Low MSWD, I think, is due to rather large errors. We calculated Discordia lines in ISOPLOT program, now it is mentioned in “Analytical methods”. Why 1 sigma error for each measurement – I think, it is common practice, as far as I know for SHRIMP data they also report 1 sigma error, and 2 sigma for the calculated ages in ISOPLOT program.

 

About temperature of Zircon crystallization. It was Ti-in-zircon thermometer. We added about it in the Analytical methods, in Results and Discussion.

 

Figure 5 also was made larger, since there was small text.

 

We also expanded the Reference list with papers about REE in zircon and those that were listed in Analytical methods.

 

Thank you once again for your work with our manuscript!

Sincerely yours,

Tatiana Kaulina

 

 

Round 2

Reviewer 2 Report

The manuscript was slightly improved, but it lacks basic geological and petrographical description to support the mineral paragenesis and zircon modification history. Without detailed description of petrography of rocks and zircon grains, good interpretation of obtained data is very difficult. In addition, the amount of presented data is too small to lead definite conclusions. 

Reviewer 3 Report

This manuscript is significantly improved in almost every regard. The authors addressed my original comments. However, there are still significant improvements required to be high quality and publishable.

The main issues:

• The English is much improved, there are still some minor English style problems and spelling errors remaining. A thorough edit is required to catch all the spelling mistakes still present.
• The depth of detail in the Introduction, Methods, and Results are still lacking. There is not enough presentation of why these hydrothermal processes are significant. The Ti-in-zircon, which is now present (great), does not discuss the critical details for applying this thermometer. What is the TiO2 and SiO2 activities in the hydrothermal fluid? How were they determined? Some people think the thermometer is pressure dependent, what is the paleodepth of these rocks? Would it significantly affect the thermometry?
• The geochronology uncertainties do not make sense to me. The best you can do with LA-ICP-MS is 2% on a multi collector, single collectors ~3–5%. The spot dates in the figures are <<0.5% (1-sigma) and the weighted mean errors are <1% (2-sigma). The authors reply mentions the low MSWD being caused by large errors. This is paradoxical with the percentage uncertainties reported. Why mix 1-sigma and 2-sigma uncertainties? How were the uncertainties propagated? This must be explained.
• A sixth summary figure that synthesizes the data and processes of preferential hydrothermal dissolution and re-precipitation of zircon would be very useful to the reader.

Again, this manuscript is very much improved and if the author further explains the points above it will be a good paper.

Cheers,