Ore-Forming Fluid Evolution and Ore Genesis of the Cuyu Gold Deposit in Central Jilin Province, NE China: Constraints from Geology, Fluid Inclusions, and H–O–S–Pb Isotope Studies

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript presents a comprehensive study on the ore-forming fluid evolution and genesis of the Cuyu gold deposit in Central Jilin Province, NE China. While the work provides valuable insights into the geological, fluid inclusion, and isotopic characteristics of the deposit, several critical issues need to be addressed to strengthen the conclusions and align the interpretations with the data. Specific concerns are outlined below:

1. The manuscript extensively discusses mineralization stages, fluid evolution, and isotopic signatures but fails to clearly define the genetic type of the Cuyu gold deposit. While the authors propose a "mesothermal magmatic-hydrothermal lode gold deposit" in the conclusions, this classification is not sufficiently justified in the context of established deposit models.

The deposit is compared to the Jiapigou-Haigou Gold Belt (JHGB), but the genetic criteria distinguishing "magmatic-hydrothermal" from "orogenic" or other types are not rigorously addressed.

Explicitly classify the deposit using globally recognized schemes (e.g., Groves et al., 1998; Goldfarb et al., 2005; Deng et al., 2020; Qiu et al., 2024). Discuss how the Cuyu deposit aligns with or deviates from orogenic, epithermal, or intrusion-related, or even Jiaodong models, supported by structural, mineralogical, and isotopic evidence.

2. Contradictions Between Data and Magmatic-Hydrothermal Origin

The assertion of a magmatic-hydrothermal origin is not fully supported by the presented data. Key inconsistencies include:

The δ³⁴S values (-6.5‰ to -0.9‰) are significantly lower than typical magmatic-hydrothermal systems. This discrepancy suggests a possible contribution from non-magmatic sulfur sources (e.g., sedimentary or metamorphic reservoirs).

The homogenization temperatures (242–326°C in Stage I, declining to 106–188°C in Stage III) and salinities (4.69–9.73 wt.% NaCl eq. to 1.39–3.53 wt.% NaCl eq.) are consistent with epithermal or orogenic systems rather than purely magmatic-hydrothermal deposits, which often exhibit higher temperatures (>350°C) in early stages.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This study focuses on the Cuyu gold deposit in central Jilin Province. Through methods such as geology, fluid inclusion microthermometry, laser Raman spectroscopy, and H-O-S-Pb isotope analysis, the study systematically explores the evolution of ore-forming fluids and the genesis of the deposit. Additionally, it compares the findings with typical deposits in the Jiapigou-Haigou Gold Belt (JHGB). This paper holds significant academic value in the study of ore-forming fluid evolution and deposit genesis. The research data are comprehensive, the methodology is scientific, and the conclusions are reasonable. It provides important reference value for regional gold exploration. It is recommended that this paper be accepted for publication. Below are some suggestions for improvement:

1. The sections on Geological Background and Deposit Geology should be divided into two separate chapters.  
2. In Fig. 1-c, the symbols for gold deposits larger than 20 tonnes and those smaller than 20 tonnes are too similar in size, making them difficult to distinguish. 3. Neither Fig. 2-a nor Fig. 2-b includes directional indicators.  
4. In Fig. 5, the axis for homogenization temperatures lacks units.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The presented article is the result of a detailed study of the formation parameters and nature of ore material at the Cuyu gold deposit. The authors use a range of methods for a comprehensive study of the deposit. A study was conducted of the geological structure of the deposit, the mineral composition of the ores, the characteristics of the ore-forming fluids were determined, and isotopic characteristics were obtained, allowing the source of the fluid and ore substance to be established. In general, the article can be accepted for publication, taking into account several corrections.

1. Line 27, “microscopic temperature measurement” should be replaced by “microthermometry”. It is more common term.
2. Lines 260-263, the sentence “Mineralizition quartz and calcite samples that represent the three mineralization stages for studies of petrography, microthermometry and Laser Raman spectra analyses of fluid inclusions at the Laboratory of Geological Fluid of the Key Laboratory of Mineral Resources Evaluation in Northeast Asia, Ministry of Natural Resources of China, Changchun, Jilin Province, China.” should be simplified and divided into two. For example: “The samples of quartz and calcite from the three mineralization stages were selected for studies of petrography, microthermometry and Laser Raman spectra analyses of fluid inclusions. The studies were carried out at the Laboratory of Geological Fluid of the Key Laboratory of Mineral Resources Evaluation in Northeast Asia, Ministry of Natural Resources of China, Changchun, Jilin Province, China.”
3. Some fluid inclusions look like pseudosecondary or even secondary in the Figure 4. A clearer separation of fluid generations could provide more information about the evolution of the fluid ore-forming system.
4. Please add the explanation on how the δ18OH2O values were calculated. What equation was used?
5. Figure 9. Usually, negative values ​​of sulfur isotopes are placed to the left of zero, and positive values ​​to the right. Please correct.
6. Lines 576-578. The sulfur isotope composition of pyrite characterizes the substance itself, not the sulfur isotope composition of the fluid. Yes, sulfur isotope composition can indicate changes in oxidation-reduction conditions during formation. These processes are described in the article, and this phrase “Thus, the sulfur isotopic composition of pyrite in this deposit serves as a proxy for the total sulfur isotopic composition of the mineralizing fluid” should be removed.
7. Line 742. “Its mineralization process can be divided into four stages” – Seems like this is a typo, tree stages were reported in the article.

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

Dear Respected Editor,

Many thanks for assigning me as a reviewer for the submitted manuscript entitled "Ore-forming fluid evolution and ore genesis of the Cuyu Gold Deposit in Central Jilin Province, NE China: Constraints from Geology, Fluid Inclusions, and H–O–S–Pb Isotope Studies."

I have thoroughly reviewed the manuscript and found that the authors present a comprehensive investigation of the Cuyu Gold Deposit in Central Jilin Province, NE China, using geological, fluid inclusion, and H–O–S–Pb isotope methods. While the English language requires revision for clarity and readability, the results and conclusions appear to be correctly interpreted.

Before the manuscript is accepted for publication in Minerals, I suggest the authors address the following comments to improve the overall quality of the work:

 

Lines 80 to 81- Please provide more details regarding the existing controversies.

Additionally, it is essential to include comprehensive information covering lines 78 to 84. If there is any background information on the geodynamic setting of the ore-forming minerals, please incorporate it into the main text.

Lines 110–113: Please provide detailed information regarding the "multi-system tectonic evolution." Since readers may not be familiar with this region, it is important to offer sufficient context and explanation.

 

Lines 115–116: Please specify the rock types of the intrusive bodies mentioned in this section.

 

Lines 117–119: Please provide the by-products associated with each deposit—for example, Mo ± Cu or Au ± Cu ± Mo.

Lines 229 to 234- K-feldspathization should be clearly distinguished from silicification, and milky quartz is a textural rather than compositional term—it could be clearer. My suggestion is that clarify that milky quartz forms during silicification and may reflect fluid inclusions or microcrystalline growth.

 

Lines 235 to 248- The sentence: "The intrusion of potassium-rich hydrothermal fluids triggered sericitization...” could be misinterpreted. Sericitization is often related to acidic fluids, which leach K from feldspar or introduce it via muscovite/sericite formation.

The reference to chloritization of feldspar is questionable—feldspar usually alters to clay or sericite; pyroxene and amphibole are more likely precursors for chlorite.

My suggestion is that replace “feldspar underwent chloritization” with “mafic minerals such as pyroxene and amphibole underwent chloritization; feldspar alteration mainly produced sericite or clay.”

Lines 249 to 254- The phrase "carbonatization became the dominant alteration" is fine but could be more precise: carbonatization is not always pervasive—it often occurs along fractures or in veins.

My suggestion is that specify whether carbonatization was pervasive or restricted to late-stage vein infill.

 

Line 346- Native-crystal” is not a standard term in fluid inclusion or crystal morphology literature. I would like to suggest “euhedral,” “well-formed,” or “isolated” if you meant inclusion morphology or spatial occurrence.

Line 362-At 25°C, CO2 exists as a supercritical fluid, not as a stable liquid. The phrase “pure-liquid CO2” is misleading. I would like to suggest “CO2-dominated inclusions” or clarify the conditions under which the CO2 exists in liquid form (e.g., during cooling below critical temperature: ~31.1°C).

Moreover, this is awkward; the correct term is “homogenize to...”. The authors can use:

L-type: “...homogenize to a liquid phase.”

V-type: “...homogenize to a vapor phase.”

C-type subtypes: “...homogenize to liquid CO2 / aqueous solution phase.”

Lines 369 to 374- The text strongly implies fluid immiscibility during stage II, which is scientifically significant. You might consider reinforcing this point by stating: “The coexistence of L-type, V-type, and C-type fluid inclusions in quartz from stage II provides strong evidence for phase separation (fluid immiscibility), a key process in ore-forming hydrothermal systems.”

 

Line 400- Please correct the text to “...homogenized to a single-phase aqueous solution”.

Line 405- It is the case that temperatures below –56.6°C indicate gaseous impurities, but be careful how you frame this. CO₂ triple point is for pure CO₂. If melting occurs below this, it’s not just temperature error. It implies mixed gases, which you state, but the phrasing needs tightening. I would like to suggest rewording as follows; “Melting temperatures of solid CO₂ below –56.6°C suggest the presence of volatile impurities (e.g., CH₄, H₂S, N₂), which depress the CO₂ triple point.”

 

Line 451- Contradicts the earlier range given (144–222°C). Check your numbers: should this be “mainly between 166 and 188°C”? Or was 106 a typo?

 

Section 4.1.3. Laser Raman spectroscopy

You could briefly mention Raman peak positions (e.g., CO₂ at ~1285 and ~1388 cm⁻¹; CH₄ at ~2917 cm⁻¹, etc.) or refer to peaks visually if they’re labeled in your Figure 6. Even just noting them improves technical clarity (e.g., CO₂ was identified by its characteristic peaks near 1285 and 1388 cm⁻¹, while CH₄ was detected at ~2917 cm⁻¹.”).

 

Lines 519 to 520- Slight contradiction here. "neither purely magmatic nor purely metamorphic..." but later state that the data plot near magmatic fields, so make sure that early sentence doesn't confuse readers. I would like to suggest to rewrite as follows; “...indicate that the fluids were not purely magmatic or metamorphic in composition; however, their isotopic signatures closely resemble those of magmatic fluids.”

 

Figure 7 and Table 5 – It would be helpful to include the literature data used for Figure 7 in Table 5, along with their corresponding references.

 

Lines 585 to 586- based on your data, I agree with comparing Cuyu values (~–4.1‰ avg.) to others (3.7‰–9.0‰ avg.) — which is fine — but you imply this is somehow “different” even though all still fall within the magmatic-hydrothermal range. Thus, I would like to rewrite it as follows;

“Although Cuyu values are lower, they still fall within the same isotopic regime and may reflect variation in sulfur source contributions (e.g., mantle vs. crustal magma) or fluid evolution (e.g., degassing, fractionation).”

 

Line 583- “May be mixed with mantle material” is a vague sentence for the readers. What do you mean by "mantle material"? Mantle-derived magmas? Mantle sulfur? The phrase lacks clarity.

 

Lines 596 to 611- The authors stated the conclusion three times in different ways:

"...ore-forming material... mainly comes from the Middle Jurassic diorite porphyrite veins.”
“Pb was derived from the mantle, with notable involvement of local crustal components...”
“...origin of ore-forming fluids and materials... originated from the diorite porphyrite veins.”

It is not reader-friendly to use a conclusion three times with different sentences. Thus, I recommend to avoid using repetitive sentences throughout the text during the revision.

 

Section “5.3. Ore Genesis and Exploration Indicate”

Some sentences are too long, repetitive, or have minor awkward phrasing that can be streamlined, e.g., “...the origin of ore-forming fluids and materials of the Cuyu gold deposit originated from the diorite porphyrite veins.” could be rewrite as: “...ore-forming fluids and metals were derived from diorite porphyrite intrusions.”

Comments on the Quality of English Language

The English could be improved to more clearly express the research.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 4 Report

Comments and Suggestions for Authors

Hereby, I confirm that the revised version meets the criteria for publication in Minerals. The English could be improved to more clearly express the research.

Comments on the Quality of English Language

The English could be improved to more clearly express the research.

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files.

Comments 1: Hereby, I confirm that the revised version meets the criteria for publication in Minerals. The English could be improved to more clearly express the research.

Response 1: Thank you for pointing this out. We agree with this comment. Therefore, we have been uploaded the article to the website you provided for polishing services. For the polished parts of the article, we marked them in red to highlight them.

Response to Comments on the Quality of English Language

Point 1: The English could be improved to more clearly express the research.

Response 1: We adopted your suggestions. We have sent the manuscript to MDPI Author Services for further English editing and polished the English Language of the article.

Author Response File: Author Response.pdf