Uranium in Fluorite, a Case Study: The La Azul Fluorspar Deposit, Taxco, Guerrero, Mexico

Round 1

Reviewer 1 Report

This MS has given readers a new insight for the uranium in fluorite in the La Azul fluorite deposit. Methods of ICP-MS, EDS/WDS, Micro-Raman Spectroscopy, X-ray diffraction, and Alpha-autoradiography were used to discuss the form, distribution, and genetic mechanism of uranium minerals in the Fluorite. Generally, it was a significant work to explore the mechanism of uranium mineralization in Fluorite deposits. However, many questions are still existing before publishment as followings:

1. In the Introduction, authors have stated that there are a few works to be done to invest uranium mineralization in fluorite. However, the former works were noted clearly. As a result, the significance of this work was not clear enough for readers.

2. Based on many experiments, authors tried to describe or discuss uranium mineral morphology and structure, and the mechanism of uranium mineralization. But I am confused about these conclusions. (1) uranium minerals have spread in fluorites proved by the Alpha-autoradiography and EDS/WDS. Did they spread in crystals of fluorite or along fractures? How about the mineral morphology and U element distribution? Analysis of scanning electron microscope and mappings by EPMA or LA-ICP-MS can give more detail and convincing evidences. (2) In conclusions, it was a hydrothermal origin for the uranium-rich inclusions in fluorite and for the fluorite itself. However, few hydrothermal altered minerals were mentioned in the MS. Is the Uranium and Fluorite co-generated by the same hydrothermal fluid or different fluids? (3) It was mentioned that uranium concentrated because of existing of organic matters. Few evidences were provided in the MS.

3. In the conclusion, rhyolitic rocks were regarded as the provenance of leachable uranium. Reasonable evidences were also lack.

4. In the MS, authors have cited the (U-Th)/He ages to discuss the mineralization ages. However, (U-Th)/He ages were commonly used to discuss the regional tectono-thermal events. Authors also presented they were hydrothermal origin. In my views, the temperature of mineralization would be higher than the closure temperature of (U-Th)/He system. Authors should be cited these (U-Th)/He ages carefully and discuss the mineralization ages. For the uranium mineralization age, authors tried to constrained by the chemical ages. However, in-situ U-Pb dating of uranium minerals have been used in the granitic or unconformity-type uranium deposits. So, this method was suggested to be used in the new MS which would be more convincing.

5. The conclusion were suggested to be re-organized. Some papers should be cited, which have been published about the uranium in the Minerals.

Author Response

Please, see attached document.

Author Response File: Author Response.pdf

Reviewer 2 Report

Teresa Pi Puig et al. provide a detailed study to introduce the uranium forms in fluorite by a case study in the La Azul fluorspar deposit in Mexico. Bulk uranium concentrations, uranium distribution patterns, and mineral occurrences have been systematically illustrated, providing interesting and useful information for the understanding of the uranium features in fluorite. The manuscript is also well-written with clear structures. However, the major contents in the abstract, context and conclusions seems not consistent with each other, and the significance of this manuscript is not fully discussed, other than simply fact introduction and very limited in-depth discussion. Therefore, I suggest that the manuscript should be substantially modified before been accepted to better demonstrate the significance of this paper and add necessary discussions in the context.

The quality of English is generally okay but still needs improvement.

Author Response

Please, see attached document.

Author Response File: Author Response.pdf

Reviewer 3 Report

- In the Materials and Methods section (3.1): "U, Th, Sm contents [...] were determined [...] using 200mg aliquots." Please provide more detail on how the aliquots (or geological samples) were prepared. 
- Section 3.1: Provide more detail on what international reference materials were used as external standards.

- Section 3.2: "Particles emitted from inside the geological sample are stopped within a very short range, [...]". Please specify what particles you are referring to.

- Table 1: Please include uncertainties on concentration measurements.

- Table 1: Provide a reference to the text on how age was determined.

- Table 2: Add percentage as a unit to the table.

- Table 2: Based on the text on line 145, these are semi-quantitative measurements and therefore a measurement of 4 significant numbers (for example, 2.042%) does not seem meaningful. Please update the table to reflect that these are estimates at the percentage-level.

- Section 3.4: Typo in "The analyzes [...]"

- Section 5.4: It is unclear how the age determination results are to be interpreted in this context, since the authors seem to use the concentration measurements from the microprobe, but then later in the paragraph state that the measurements from the microprobe are not accurate enough to corroborate the range of the isotopic ages.

-Above Section 5.5: Line space missing

- Conclusion: The conclusions seem to focus on the applicability of autoradiography and there is little connection with the statements in the abstract.

Author Response

Please, see attached document.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

According to the comments, the authors have made a good work to improve the MS. The new MS was more fluent and reasonable for readers’ understanding. The MS have provided a significant understanding for uranium in fluorite from the La Azul fluorspar deposit. Multi-methods were used in the MS to discuss the uranium occurrence and its relationship with the Fluorite. Generally, it was a very good work. But at present, some problems or suggestions were needed to be considered in the new MS before the acceptance. The main problems of the MS are listed as followings. 

Specific comments: 

1. In the MS, it was stated that two stages of fluorite were determined and the F1 was considered to be related with uranium ore-forming process. However, it was unclear for me what the differences were between the fluids of F1and F2. From the Fig.2, it was recognized that the uranium minerals were developed at the end of the F1 and the beginning of the F2. However in the text, it was stated that there was no relationship with the F2. I am confused for this. 

2. For the X-ray diffraction, there are no significant meaning in the MS, which is suggested to be deleted in the new MS. 

3. In line 252-253, uranium is deposited along the growth zones or to the peripheral parts. However, it was unclear in the Fig. 3, and should be outlined in the photos. By the way, in the text, the citing of Figures was also unclear, such as Fig.3-A or Fig.3-B? 

4. In line 264-265, some ages of deposits were cited. But I am confused that these dated deposits were also spread in the La Azul area or other locations. 

5. In line 358-359, we can get that the Morelos formation with carbonates has high values of fluorite. In Line 430-431, it was gotten that calcite clasts were free from uranium. But the topic of MS is the uranium in Fluorite. So, I am confused these descriptions. 

6. In section 4.7, how to separate the ore-forming fluid inclusions and other fluid inclusions? Which kinds of fluid inclusions were related with the uranium? 

7. Form line 499, all texts described the uranium ore-forming process, which was suggested to be a new section with title. 

8. In line 192, the abbreviations should follow with the full text at the first time. 

9. For Fig.3, I did not find the differences between F1 and F2 clearly. Furthermore, the figure was not artistic. E and F should have the same size.

For Fig.4, more detail information should be added in the figures. Some descriptions can be shown in the figures.

For Fig.7, there was no information in the photos, no size information. 

10. The format of references should be uniform.

There is no comments on the quality of English.

Author Response

Please, see attached docuemnt.

Author Response File: Author Response.pdf

Reviewer 2 Report

The revised manuscript is significantly improved, and I suggest acceptance after minor revision.

The English language is significantly improved.

Author Response

We appreciate the reviewer's comments. In this new version the format has been revised again, figures 2, 3, 4 and 7 have been improved and the English language has been edited again.