Phosphate Petrochronology of the Belcina REE Mineralization (Ditrău Alkaline Massif, Romania)

Round 1

Reviewer 1 Report

Dear authors,

This manuscript addresses important dating results through petrological observations of monazite and xenotime which were lacking in previous studies. However, there are some problems with data organization and representation, which makes the links between data and discussion unclear. Cited results in the discussion are only Figures 5, 6, and 7 although authors represent Figures 3-10, which appears to be a lack of discussion against represented data for readers. Some figure captions are too long and sometimes include explanations of the results, whereas the main text is insufficient to explain and/or discuss the figures. The order of the figure numbers does not match the order of the figure explanations in the main text. I strongly recommend revising the figures and manuscript for clarifying the relationship between the data and discussed topics.

Other comments are as follows:

Discussion

1) Discussion 5.1. lines 475-495 are not a discussion of data in this study but a sampling strategy for the study purpose. This should be moved to the Introduction part. 

2) 5.1.2., 5.1.3.

Authors should explain monazite before xenotime according to the order of the represented result.

3) Authors address the economic importance of REE mineralization in this region. I recommend adding some implications of the contribution to the REE resource demand or future exploration.

Figure 3

1) Annotation for abbreviated names for minerals is needed in Figure 3 Caption.

2 ) I cannot understand the sentence “All mineral data presented herein is from 1457-A” (lines 200-201) in Figure Caption. Figures 3c and d are not 1457-B but 1457-A?

Figure 4

1) No subheading in Figure 4.

2) Contents of Figure 4, Figure 5a, and Figure 6a are duplicated with each other. These figures should be summarized as one figure for the explanation of the microscopic occurrence of monazite and xenotime. Legend for each color also should be added instead of the annotations of minerals names with arrows. 

Figure 5

1) Subheading is too big. 

2) The letters on the scale in Figure 5e, f are unreadable.

3) Contents of Figure 5b are duplicated with that of Figure 7a. One of them should be eliminated. 

4) Legend of the colored circle for Figures 5c, d, e, and f is needed.

5) Figure 5c should be shown after the main geochronology data (Figures 9, 10)

6) It is better to reverse the order of Figures 5e and 5f if the authors would like to highlight the pseudo-linear trend in Figure 5f. 

7) Mark the two linear trends seen in the mnz1 data should be highlighted in the Figure with arrows or something.

8) Overall, the sentences in the figure caption are too many. Explanations for the result in the caption should be moved to the main text. 

9) In the main text, the authors explain in the order of Figure 5a (line 214) and Figure 6a (line 244) without explanation of Figure 5b-f. The order of the figure numbers should match the order of the figure explanations in the main text.

10) The sentence “Line 275 For a more detailed discussion see text” should be deleted.

Figure 6

1) Subheading is too big.

2) The letters on the scale in Figure 6e, f are unreadable.

3) Contents of Figure 6b are duplicated with that of Figure 7b. One of them should be eliminated. 

4) Legend of the colored circle for Figures 6c, d, e, and f is needed.

5) Figure 6c should be shown after the main geochronology data (Figures 9, 10)

6) As commented in Figure 5, the sentences in the figure caption are too many. Explanations for the result in the caption should be moved to the main text. 

7) In the main text, the authors return to the explanation of Figure 5b, c (line 286) after Figure 6a (line 253). Such disorder of the explanation in text and figure number makes readers confused.

8) The sentence “Line 275 For a more detailed discussion see text” should be deleted.

Other minor comments

1) I recommend adding photos of outcrops if the authors have them. It would help the understanding of readers in terms of sampling strategy for the geochronological work.

2) Line 278, “Tabs. 1, 2” -> “Tabs. S1, S2”

3) Line 78, “[12-19] and references therein)” -> “([12-19] and references therein)”

4) Line 108, “(equivalent to the” close parenthesis is missing

line 111, “(equivalent to the” close parenthesis is missing

line 113, “(formerly red syanite” close parenthesis is missing

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

General comments:

- Overall, a well-written paper.

- The English wordage and grammar are quite good.  See various comments below concerning minor changes that need to be made.

Abstract:

Line 21.  Replace "recommending" with "suggesting".

Line 27.  Replace "what" with "that".

1. Introduction:

Line 36.  Add reference(s) for text in Lines 34-36.

Line 40.  Replace "at Belcina regions" with "in the Belcina region".

Line 51.  Do not use "ore"  -->  replace with "mineralization".

Line 55.  What is the Lazarea Suite ??  Please add some words to say what it is (nepheline syenite ...).

Line 58.  Remove "of".

Line 72.  "through secondary processes".  Please provide one or more examples of these secondary processes.

Lines 83-86.  "We show that the vein formation follows a distinctive three-stage evolutionary pattern ... the DAM (at ca. 225 Ma)."  -->  This text sentence is actually a conclusion and it should be removed from the introduction.

2. Geological background:

Lines 91-93.  "It has the potential ... major geological interest."  -->  This text sentence is not 'geological background' and it should be moved to somewhere in the Introduction.

Line 104.  Add "joining" to this text "East of a line Jolotca ..."  -->  "East of a line joining Jolotca ...".

Line 124. Change "in which" to "within which".

3. Analytical methods

Line 132.  Provide the model of the NIKON microscope.

Line 137.  Add the acronym for 'backscatter electron imaging'  -->  "backscatter electron imaging (BEI)".  (Note that BEI is a more-accurate acronym than BSE.)

Line142.  Change "Mineral chemistry" to "Mineral chemical".

Lines 152-156.  Please provide some references for these natural and synthetic standards.

Line 158.  Change "U Mb" to "U Mβ".

Line 162.  Change "on PET" to "using PET".

Line 165.  Change "U+Th-total Pb" to "(U+Th)-total Pb".  Do the same in Lines 171 and 177.

4. Results

Line 182.  Remove the unneeded period.

Line 187.  Change "comparably" to "relatively".

Line 190.  "The fabric is magmatic ..."  -->  perhaps change to "The fabric is magmatic-hydrothermal ..." and then briefly describe what this fabric looks like.

Line 198.  Change "divided in a" to "divided into a".

Line 217.  Change "towards" to "with".  Also in Lines 248 and 254.

Line 220.  Change "backscattered electron images of ..." to "BEI of ...". 

Lines 225 & 226.  Use "BEI" instead of "BSE images".  Also in Lines 258 and 259.

Line 231.  Change "diverse" to "distinctly different".

Line 234.  Change "THO2+UO2" to "ThO2+UO2". 

Line 237.  Change "Mark the two linear trends ..." to "Note that there are two linear trends ...".  These trends should also be illustrated in Figure 5e.

Line 240.  Change "easily demonstrated" to "well illustrated".

Line 248.  As for Line 217.

Line 254.  As for Line 217.

Line 255.  Remove "the".

Lines 258 & 259.  As for Line 225.

Line 277.  Change section title from "Phosphates chemistry" to "Phosphate mineral chemistry".

Line 290.  Change "vertical on" to "perpendicular to".

Lines 291-292.  Provide the literature references for the average metamorphic and hydrothermal monazite compositions.

Line 301.  Change "aking" to "akin".

Line 308.  Change "Notably" to "Notable".

Line 322.  Change "Dim1 and Dim2" to Factor1 and Factor2".  Please also change "Dim" to "Factor" in Lines 332, 334, 339, and 340, as well as Lines 348, 352 and 355.  Also do this in Lines 387, 389, 392, 393, 395, 396, 398, 400, 402, 404, and 405.

Line 333.  Change "correlation" to "association".  Also Line 337.  (No correlation analysis has been performed on these data, so do not use the word 'correlation'.)

Line 334.  Change "correlated" to "associated".  Also Line 335.

Line 337.  Change "Notable" to "Notably".

Line 360.  Change "values are" to "weight% values are".  Also for Lines 366 and 372.

Lines 361- 363.  Provide the literature references for the average metamorphic and hydrothermal xenotime compositions.

Line 376.  Change "correlation" to "relationship".  Also in Line 378.  (No correlation analysis has been performed on these data, so do not use the word 'correlation'.)

Line 388.  As for Line 333.  Also in Lines 391, 392, and 394.

Line 389.  As for Line 334.

Line 399.  Change "correlations" to "relationships".

Line 409.  As for Line 165.  Change "U+Th-total Pb" to "(U+Th)-total Pb".  Also Lines 423, 428, and 433.

Line 415.  Change "range of" to "range between"

Line 443.  Remove "and)".

Line 450.  Please explain.  Also Line 471.

Line 451.  Remove the hyphen.

5. Discussion

Line 493.  As for Line 165.  Change "U+Th-total Pb" to "(U+Th)-total Pb".  

Line 537.  Change "As xenotime-(Y) shows ..." to "Xenotime-(Y) shows ...".

Line 539.  Change "correlation" to "association".  Also Line 541.  (No correlation analysis has been performed on these data, so do not use the word 'correlation'.)

Line 541.  Change "correlated with" to "related to".

Line 543.  Change "Dim" to "Factor".  Also Lines 544, 545, 546, 559, 560, 563, 564, and 571.

Line 565.  Change "that significantly" to "as well".

Line 566.  "A significant apatite (Ca5[(PO4)3]) component in mnz1 is not directly conceivable."  -->  please explain why you say this.

Line 570.  Change "correlations" to "relationships".

Lines 576-577.  Change "... the xenotime-(Y) component decreases from mnz1 to mnz2, but increase in mnz3 to even higher values as in mnz2 (Figure 5e, f)." to "... the xenotime-(Y) component decreases from mnz1 to mnz2, but increases in mnz3 to even higher values than in mnz1 (Figure 5e, f).".

Line 578.  Change "... from which the monazite-(Ce) crystallized had ..." to "... from which the various types of monazite-(Ce) crystallized had ...".

Line 599.  Change "Another interesting feature are ..." to "Other interesting features are ...".

Line 601.  Change "suggestion" to "suggesting".

Line 615-616.  Change "paragenesis indicative for" to "parageneses indicative of".

Line 638.  Change "... any PbCommon contribution ..." to "... any non-radiogenic PbCommon contribution ..."

Lines 641-643.  Perhaps rewrite these sentences "We judge the PbCommon contribution in our phosphate analyses to be insignificant. This is based on the argument that all CHIME ages show within analytical uncertainty a regression intercept at Pb (µg/g) = 0 [30,31,51].  Any undetected PbCommon would render the ages to be too old. Therefore, the true (PbCommon free) ages would be younger and thus the age difference to the intrusives even larger." to something like this "Any undetected PbCommon would render the ages to be too old, so the true (PbCommon-free) ages would be younger, making the age difference between the phosphate-bearing veins and the intrusives even larger.  However, we judge the PbCommon contribution in our phosphate analyses to be insignificant. This is based on the argument that all CHIME ages show within analytical uncertainty a regression intercept at Pb (µg/g) = 0 [30,31,51].  Thus, we feel that the 215.9 ± 1.3 Ma age for the phosphate-bearing veins is accurate.".

Line 647.  Change "Thereby hydrothermal fluids" to "Thereby, it is interpreted that hydrothermal fluids".

Line 652.  Change "mineralized carbonate veins" to "mineralized carbonate-phosphate veins".

Line 659.  Add Figure number.  Change "to ca. 225 Ma (Lower Norian) [2]." to "to ca. 225 Ma (Lower Norian) [2] (Figure 11).".

Line 662.  Change "from youngest the" to "from the youngest".

Lines 668-670.  Provide reference(s) for this sentence.

Line 695.  Change "cluster" to "clustered".

----------------------------------------------------------

Table S1. Monazite EMP data - ok

Table S2. Xenotime EMP data - ok

Figure 1.  Please revise the figure to also locate Romania within the context of greater Europe.

Figure 3.  Please provide mineral phase explanations at the end of the caption.  Such as: "Mnz - monazite, Dol - dolomite, ... et cetera".

Figure 5.  Part 5e: Change "THO2+UO2" to "ThO2+UO2" in the 5e plot label.

Figure 5.  Part 5e: the two linear trends seen in the mnz1 data points should be illustrated in this Figure by lines.

Figure 8.  You should change the labels from "Dim" to "Factor'.

The English wordage and grammar are quite good.  See various comments provided concerning the minor changes that need to be made. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf