Geochemical Compositions and Detrital Minerals of Stream Sediments around the Zijinshan Copper-Gold Orefield and Their Implications

Round 1

Reviewer 1 Report

An interesting paper with lots of great data. I suggest a review of the text, nothing major, but I did note some minor edits on the manuscript and there are undoubtably more.

In detail:

• On lines 35 and 46, the authors mention “geological blocks”. I’m not sure what they mean, what is a “geological block”?
• On Line 129 the authors state that “thin sections” were prepared of the sediment samples. A thin section is a cut piece of cohesive rock, but the samples used in this study were stream sediments; so presumably the material was mounted in epoxy and polished? Typically sediments are actually mounted in epoxy moulds. How exactly were the samples prepared for analyses? The samples must also have been polished? More detail please.
• Line 152 – “conventional… methods; what are these methods? Provide a reference if they’re “conventional”.
• Lines 172 to 190 describe the Hf isotope analytical techniques and in section 3.3 Hf data are presented and then compared with U-Pb data. Presumably the zircon grains analysed for Hf are the same ones that were analysed for U-Pb? How did you map the zircons to make sure that each one yielded a U-Pb date and a Hf ratio? Presumably the white spots on zircons in Figure 5 are the analytical spots for either U-Pb or Hf or both? If both, please comment on how you could ablate enough material for both analyses in the same spot.
• Figure 5 caption – what are the round white spots on zircons? Presumably ablation points?
• Lines 245-256 – It’s not clear what you think the Fe-oxide is/does. You term it the “main carrier mineral for Cu and Cd”, but what exactly does this mean? Are you suggesting that the Fe oxide absorbs these elements from the stream water? Are do you think Cu and Cd are carried as detrital material in the stream? When you analysed the Fe-oxide grains by EMP it looks like there is variation across the oxide; is there a difference between core and rims? Table 4 LA-ICP-MS analyses, what do the samples listed mean? (i.e., ZJS02-1-1, 1-2 and 1-3 are from the same sample? How are they related?). Why are only Cu and Cd said to be concentrated in Fe oxide? For instance, on Table 4, Cd is only enriched in 4 analyses, and Zn-Sb-Mo-Pb-Bi actually have greater contents than Cd!!

Author Response

1. On lines 35 and 46, the authors mention “geological blocks”. I’m not sure what they mean, what is a “geological block”?

The concept of geochemical block was put forward by exploration geochemist Xuejin Xie based on spatial distribution characteristics and geochemical data of elements obtained from China's national geochemical mapping program [4]. It represent an area with high concentrations of metal elements in rocks, soils and stream sediments. Generally, it is associated with specific geological tectonic unit. We added relevant explanations in the manuscript.

2. On Line 129 the authors state that “thin sections” were prepared of the sediment samples. A thin section is a cut piece of cohesive rock, but the samples used in this study were stream sediments; so presumably the material was mounted in epoxy and polished? Typically sediments are actually mounted in epoxy moulds. How exactly were the samples prepared for analyses? The samples must also have been polished? More detail please.

Stream sediment samples were dried (60 ℃). After drying, the samples were placed on glass slides for epoxy drip infusion and set simultaneously. Then, the samples fully filled with epoxy resin were dried for approximately 24 hours (60 ℃). The samples were ground flat after drying. The sample were glued to the glass slides again and put into the drying oven until the glue dried. After grinding, thinning and polishing, the samples were made into thin sections.

We provided details in the manuscript.

3. Line 152 – “conventional… methods; what are these methods? Provide a reference if they’re “conventional”.

The stream sediments were sorted by the electromagnetic isodynamic heavy mineral methods. We replaced ‘conventional’ by ‘electromagnetic isodynamic’.

4. Lines 172 to 190 describe the Hf isotope analytical techniques and in section 3.3 Hf data are presented and then compared with U-Pb data. Presumably the zircon grains analysed for Hf are the same ones that were analysed for U-Pb? How did you map the zircons to make sure that each one yielded a U-Pb date and a Hf ratio? Presumably the white spots on zircons in Figure 5 are the analytical spots for either U-Pb or Hf or both? If both, please comment on how you could ablate enough material for both analyses in the same spot.

Firstly, the U–Pb ages of 600 detrital zircons from six stream sediments were tested. Then, the detrital zircons with high concordance and consistency with the U–Pb ages of magmatic zircons in ore-bearing magmatic rocks from the Zijinshan Copper-Gold Orefield were selected for Hf isotope analysis at a total of 145 points. The Hf isotopic composition and U-Pb age are on the same zircon, but not at the same laser spot. Spots for Hf isotopic ratio and U-Pb age analysis have similar structures. Only the laser spots (white spots) of U-Pb ages are shown in Figure 5.

5. Figure 5 caption – what are the round white spots on zircons? Presumably ablation points?

The white circles represent the laser denudation spots of zircon U-Pb ages. We added an explanation in Figure 5.

6. Lines 245-256 – It’s not clear what you think the Fe-oxide is/does. You term it the “main carrier mineral for Cu and Cd”, but what exactly does this mean? Are you suggesting that the Fe oxide absorbs these elements from the stream water? Are do you think Cu and Cd are carried as detrital material in the stream? When you analysed the Fe-oxide grains by EMP it looks like there is variation across the oxide; is there a difference between core and rims? Table 4 LA-ICP-MS analyses, what do the samples listed mean? (i.e., ZJS02-1-1, 1-2 and 1-3 are from the same sample? How are they related?). Why are only Cu and Cd said to be concentrated in Fe oxide? For instance, on Table 4, Cd is only enriched in 4 analyses, and Zn-Sb-Mo-Pb-Bi actually have greater contents than Cd!!

Metal elements can not only be absorbed by Iron oxides and clay minerals but also be carried as detrital materials of Fe-bearing minerals. It is difficult to distinguish them by EMP and LA-ICP-MS analysis. There must be a difference in element contents between core and rims. We will pay more attention on it in the future research.

We modified table 4. ZJS02 is sample ID, 1-1,1-2 are survey points. CuO and CdO contents are detected by EMP. On table 4, trace elements of iron oxides have greater contents than average for stream sediments in the orefield. We modified the relevant description as ‘In addition, CuO and CdO are detected in iron oxides, suggesting that iron oxides are at least main carrier minerals for Cu and Cd (Table 3). Furthermore, the contents of ore-forming elements are extremely uneven in the iron oxides and are greater than the averages of ore-forming elements in stream sediments (Table 4)’.

Reviewer 2 Report

The authors corrected the text according to my comments. The paper is interesting. The paper is well written, the text is clear and easy to read. The conclusions are reasoned.

The paper can be published in present form.

Author Response

I have read the reviewer's comments and suggestions 

Reviewer 3 Report

Dear Authors,

I think that this paper and results presented here are interesting and themanuscript can be accepted for publication with minor revisions in an international journal as Minerals.

The necessary condition is the insertion of the U-Pb data (ages and standard).

Best regards

 

Comments for author File: Comments.pdf

Author Response

     1. I highly recommend adding a major number of international community scientific papers to the local literature concerning for example the characterization of internal pattern zoning of zircon crystals deserving more attention and detail (lines 271-279). Please refer to the paper:

- Corfu, F., Hanchar, J. M., Hoskin, P. W., & Kinny, P. (2003). Atlas of zircon textures. Reviews in mineralogy and geochemistry, 53(1), 469-500 - Rubatto, D. Zircon: The Metamorphic Mineral. Rev. Mineral. Geochem. 2017, 83, 261–295;

We added the documents as reviewer suggested.

2. Detrital Zircon Chronology:

In particular for the filtering of the U–Pb ages:

206Pb/238U age should be considered for zircons with ages younger than 1.4 Ga. Instead, for grains older than 1.4 Ga, the 206Pb/207Pb age is considered as the best age in dependence of minor error of this ratio linked to Pb loss in inherited zircons as indicated by

- Spencer, C.J.; Kirkland, C.L.; Taylor, R.J.M. Strategies towards statistically robust interpretations in situ U-Pb zircon geochronology. Geosci. Front. 2016, 7, 581–589.

- Gehrels, G. Detrital zircon U-Pb geochronology: Current methods and new opportunities. In Tectonics of Sedimentary Basins: Recent Advances; Busby, C., Azor, A., Eds.; Blackwell Publishing: Oxford, UK, 2014; pp. 45–62.

 We added the documents as reviewer suggested.

3. Kernel density plots are preferable to Isoplot function for the treatment and representation of detrital zircon ages following.

- Vermeesch, P. On the visualization of detrital age distributions. Chem. Geol. 2012, 312, 190–194 as in

- Fornelli, A., Gallicchio, S., Micheletti, F., & Langone, A. (2021). U–Pb detrital zircon ages from Gorgoglione

Flysch sandstones in Southern Apennines (Italy) as provenance indicators. Geological Magazine, 158(5), 859-874.

- Fornelli, A., Gallicchio, S., Micheletti, F., & Langone, A. (2020). Preliminary U-Pb Detrital Zircon Ages from Tufiti di Tusa Formation (Lucanian Apennines, Southern Italy): Evidence of Rupelian Volcaniclastic Supply. Minerals, 10(9), 786.

We added the documents as reviewer suggested.

4. U-Pb data Tables are missing in the submitted version! It is not possible to publish a scientiphic paper without analytical detailed results!!! Please, follow the recent paper published in Minerals (see supplementary material files):

 - Fornelli, A., Festa, V., Micheletti, F., Spiess, R., & Tursi, F. (2020). Building an Orogen: Review of U-Pb Zircon Ages from the Calabria–Peloritani Terrane to Constrain the Timing of the Southern Variscan Belt. Minerals, 10(11), 944.

We provide the table U-Pb ages of detrital zircons from stream sediments.

5. Typos:

- reference 19 and not 190!!!

- line 51: 10-16 instead 10-156

- lines 445 and 456: magmatic

We modified them.

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

Review of “Geochemical compositions of detrital minerals in stream sediments of the Zijinshan Orefield and their implications”

This is a most interesting paper that attempts to solve some important questions concerning the use of stream sediment surveys in the exploration for mineral deposits. It is a “big picture” type of scientific analysis that is missing in most applied geochemical studies. I was most impressed with the extended trace element plots which showed definitive derivation form specific granitoids. The paper is well written.

I recommend acceptance with minor revisions.

Points of note:

• On Figure 1, since there is no room for topography, the authors should add some symbols defining stream flow direction.
• Line 72 – I don’t agree with the term “rare”
• Line 87 – what do you mean by the term “metallogenic age”?
• Line 114 – there should be more information on the samples – how heavy were they? In what part of stream were they collected? What was grain size range?
• Line 150 – what was analysed, the whole stream sediment sample? What were crushed sample weights?
• Figure 7 – there are two groups in the orefield granite zircons, why? The detrital zircons overlap both orefield fields, but also link the two fields together, why?

Reviewer 2 Report

Li et. at., discuss the elemental abundance, zircon U/Pb and Hf composition of zircons from stream sediments which pass through the Zijinshan Orefield area. The data looks robust and of good quality and the interpretations are sound. I have only a few comments below. However, I feel the English needs to be improved before the manuscript can be accepted (especially the introduction).
Line 34: More information on what anomalies you are speaking of needs to be given in this first paragraph. You mention regional anomalies in line 35 without giving any example of what this could be. 
Line 114: Can you give more information on the way the samples were taken/selected. Was it a blind dredge of the silt? So only the samples used for elemental analysis were sized. Is there a reason?
Line 180: You mention table 1 here but it doesn’t show up in the manuscript for another couple of pages. It may be better to move table 1 before figures 2 and 3 as you mention them in the main body of the text before table 1.
Line 204: I understand what you are saying but I think this sentence needs to be made clearer.
Line 237: Can you put a numerical limit/range on the migration distance of the ore-forming elements from your data. Fine if you can’t.
Line 461: As previous comment re. numerical range
Line 476: Aren’t the iron oxides from the stream sediments? So the iron oxides are relatively enriched in these ore-forming elements compared to the other phases present in the stream sediment with the exception of the clay minerals. In the text you state that the iron oxides are enriched relative to the stream sediments. I think this sentence needs to be rephrased.
Figures are good
Again with the tables I am unsure why you have gone down the route of 10-9 and 10-6 rather than ppb and ppm.

Reviewer 3 Report

The manuscript contains a lot of interesting data, which is very poorly analyzed, so the conclusions drawn seemed to be rather weak. You basically compare your sediment to the rocks of the ore field without drawing any conclusions about other sources of sediments. You declare in the Introduction that stream sediments provide information about geochemical anomalies, and sedimentary zircon - about crust-forming processes in the region. But you did not discuss your results in this direction. You promise to study the "genetic relationship" and "enrichment mechanism", but your conclusions are limited to description of your observations that there is a lot of ore-field material in the stream sediments near the ore-field, and little in the distance. You write about the increased or decreased LREE and HREE content and the europium anomaly, but do not explain the reason of it. You need to analyze the material obtained more seriously and to make more specific conclusions.

Comments

The Title

I think you need to add “Geochemical composition of stream sediments and detrital minerals” since the most of your geochemical data (trace elements and REE) were obtained for sediments (rocks) and not for minerals.

Introduction and Orefield description are well written. The only recommendation is to move the geological map to the section 2.1 (Orefield description).

2.2. Sample collection and analysis

I would be better to add subheadings, it will be easier to read. Something like: 2.2.1. Geochemical analysis of sediments (it should be the first, since it is the first in the Results); 2.2.2. Isotope analysis of zircon; 2.2.3. EMP analysis of iron oxides.

Results

Lines 190, 204-207 and 219-242 (together with the Fig. 4) should be moved to the Discussion.

3.3. Detrital zircon Hf isotope composition

I think it would be better to make Figure 7 with all concordant U-Pb ages (not only similar to ore-field granites) as well as with CHUR, and DM evolutionary lines.

Discussion

Add here 4.1. Elementary sediments composition (lines from Results). Discuss why they have increased or reduced REE content (probably because of mineral composition?).

Lines 378-379 - write the exact distance, starting from how many km? the same for Lines 396-397.

Move Lines 412-440 from the Discussion to the Results. They must be in the Results. And I think it is better to put them before Zircon data.

Conclusions

Lines 460-461 – how far in km?

Lines 471-473 – you don’t need it in the conclusions, since you did not study it. Your make this guess in the Discussion and that's enough

Reviewer 4 Report

The manuscript deals with the interesting topic of provenance involved in the mining exploration.

This is an extremely interesting topic that can potentially reach out a large crowd. Unfortunately (in my humble opinion), the paper must be improved to be considered for publication; as it is now it comes with too many flaws (methodological and logical).

PROs: the paper yields large databases and the results are mostly adherent to the database

CONs:

• abstracts are fundamental in a manuscript, most of the readers stick to abstract and figures before considering reading the paper and both needs a deep polish in this manuscript (figure style [fig 1, 7 above all] is not adequate for publication, and it took me few times before I could understand what you wanted to do).
• english, is seems that some sections have been looked over & corrected by some editor, while others are (I apologize for the term) a bit of a gibberish.
• methodologies: this is probably the worst issue of the manuscript. The methodology section can be corrected easily once you know where the issue is. However, as it is now, this section cannot get into publication
• there are some issue with the logic behind upscaling the discoveries the authors found in the study area to a global model 
• some other comments are in the attached pdf  

Comments for author File: Comments.pdf