Application of High-Precision Magnetic Measurement in the Exploration of Deep Fluorite Deposits in Ore Concentrations

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have worked on exploring fluorite using aeromagnetic data. The work seems legible, but the application of only aeromagnetic data is not good enough to justify the findings.

Fluorite is present mainly in veins or crystal forms. Aeromagnetic data alone may give a signature, but why not other geophysical data such as SP, resistivity, IP, or even EM data? 

Are there any other geophysical data from the present location that will help to constrain the present results?

How is the subsurface model developed without the subsurface model development from aeromagnetic data?

Any borehole in the present location will give an idea about the presence of fluorite deposits.

Comments on the Quality of English Language

English needs to be improved.

Author Response

Dear Reviewer ,

Thank you for your meticulous review and constructive feedback, which have significantly improved the manuscript. We have addressed all concerns with targeted revisions (tracked in the uploaded file) and provide this point-by-point response for your convenience:

1. “Application of only aeromagnetic data is insufficient” (Data Diversity)

Response:
- Rationale for Aeromagnetic Priority (P.2 Abstract, P.12 5.4):
“Aeromagnetic survey was prioritized for its 100% coverage of 280 km² rugged terrain (Fig. 2), cost-effectively mapping fault-controlled fluorite systems (Smith et al., 2023, added as Ref. [22]). This aligns with industry standards for regional-scale exploration in complex terrains dominated by fault structures.*
Scientific Basis: Fluorite mineralization here is strictly controlled by faults and concealed intrusions (Fig. 7). Aeromagnetics excels in detecting these targets:
- The fault identified through magnetic gradients shows a high degree of consistency with known geological data. ( Fig. 7).
- Indirect Constraints from Lithological Contrast (P.6 2.5, Table 1):
”Fluorite’s low magnetism (15.57×10⁻⁵ SI) and density (2.42 g/cm³) contrast sharply with host Yanshanian granite (2612×10⁻⁵ SI, 2.58 g/cm³), validated by ZK4043 borehole (412 m ore, Fig. 9) at L-C-3 low-magnetic anomaly (-150 nT). This contrast provides a robust geophysical basis for anomaly interpretation.”*
- Future Multi-Method Plan (P.12 5.4):
“3D MT surveys (scheduled Q3 2025) will differentiate fluorite from non-mineralized alteration zones. While resistivity methods could directly sense fluorite veins, local conditions limit their efficacy:
- High-resistivity granite background masks subtle contrasts (Δρ < 200 Ω·m).
- Rugged topography induces unstable grounding resistances.
Planned 3D MT will instead be combined with seismic data in future work, beyond this paper’s scope on ‘aeromagnetic validation.’ Results will be reported in a follow-up study due to ongoing data acquisition.”

2. “No other geophysical data to constrain results” (Data Validation)

Response:
- Borehole Validation (P.10 4.3, Fig. 8–9):
“Four boreholes (Y2-ZK4041–4043, red stars in Fig. 8) in Y-2 target:
- ZK4043: 2.3 m fluorite at 412 m (Fig. 9), coinciding with F10–F2 fault intersection (Fig. 7) and -150 nT anomaly.
- 100% ore discovery rate (4/4 boreholes) validates the magnetic model without additional datasets.
- Residual anomalies (Fig. 6) correlate with concealed granite boundaries (L-C-1–L-C-4), confirmed by borehole lithology (monzogranite host rocks at 380–520 m, Fig. 9).
- Geological Constraints (P.7 2.3, P.11 5.2):
“NW/NE fault-controlled mineralization (Fig. 7) aligns with regional fluorite genesis , providing geological context for magnetic interpretations of hydrothermal fissure-filling deposits.”

3. “Subsurface model development unclear” (Model Methodology)

Response:
- Technical Details Added (P.8 3.1, Fig. 2 caption):
3D Euler deconvolution (geomagnetic parameters: inclination 43°, declination 3°; flight altitude 100 m) constrained by:
① Surface-mapped faults (F1–F5, Fig. 7);
② Borehole depths (300–500 m) matching 1000 m upward continuation (Fig. 4).
- Model Validation (P.11 5.1):
“Residual magnetic anomalies (Fig. 6) correlate with concealed granite boundaries (L-C-1–L-C-4), confirmed by borehole lithology (monzogranite host rocks at 380–520 m, Fig. 9).”

4. “No borehole data mentioned” (Empirical Evidence)

Response:
- Borehole-Magnetic Correlation (P.10 4.3, Fig. 8–9):
All boreholes positioned at:
 Low-magnetic anomalies (ΔT -100–-200 nT, Fig. 2)
 Fault intersections (e.g., ZK4043 at F10×F2, Fig. 7)
Ore characteristics: thickness 1.2–2.3 m, depth 380–520 m (Fig. 9 profile).”

5. “English language needs improvement”

Response:
 Revisions Completed (Full Manuscript):
 Hyphens: “ore-concentrated” standardized (100% corrected, tracked).
 Grammar: Tense consistency (e.g., Abstract revised to “has provided” for completed actions).
 Our paper proposal requests the editorial department's assistance in improving the quality of the English writing.

6．Final Note

We emphasize the study’s innovation: the first aeromagnetic model for fault-controlled fluorite deposits in Heyu, validated by 4 boreholes with 100% ore discovery.

Thank you again for your guidance. We welcome any further suggestions and stand ready to provide additional clarifications.

Sincerely,

Zhuo Zhang

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Please remove the spaces while using hyphens: ore-concentrated, not ore – concentrated.

 

I think that for the reader which is not familiar with the fluorite, it would be useful in the Introduction to provide some information on the mineral composition and applications.

 

There is a major flaw in section 2.5 Geophysical characteristics as there is no information on the magnetic remanence in Table 1.

 

You mention several times the gravity results, but you don’t show any data. It would be appropriate to at least show one gravity map.

 

I disprove the use of a paragraph title. I don’t find this appropriate for a scientific paper. One example of what I mean is the paragraph starting with: Overall characteristics of the residual magnetic anomaly: The … Another is: Results of Engineering Verification: During 2023-2024, a certain mining company newly completed 4 boreholes (ZK4043-ZK4041,Figure 9 ) within …

 

In the Abstract, I recommend: The Heyu ore-concentrated area in western Henan within the East Qinling metallogenic belt is a strategic area for fluorite mineral resources facing severe challenges of resource depletion. For this reason, this study focuses …

 

In the Abstract, I recommend: The establishment of this model not only provided strong support for identifying and delineating potential areas for deep-seated ore prospecting, but also supplied geophysical indications for the deep-seated exploration and development of fluorite mines in the ore-concentrated area.

 

In the Introduction, I recommend: Fluorite is an important strategic non-metallic mineral. Consequently, the application of high-precision magnetic methods in its exploration and development in this paper is of great significance for guiding ore prospecting, rational resource utilization, etc. [1].

 

With the rapid rise of industries … which industries?

 

The rapid depletion of shallow-exposed ore resources has made the replacement of mining areas of fluorite resources face severe challenges [2-3].

 

Section 2.5 Geophysical characteristics: Among the ores in the area, fluorite has the lowest magnetic susceptibility, …

 

This sentence is confusing: Given that fluorite mines in the Heyu area were mainly formed in the Early Cretaceous of the Yanshanian period and are mostly medium-low-temperature hydrothermal fissure-filling types, when the aeromagnetic anomaly area coincides with the geological structure of this period and the adjacent stratigraphic rock characteristics also meet the necessary conditions for fluorite mineralization, the probability of the existence of fluorite deposits in this area is significantly increased [34].

 

This sentence contains too much information and should be split. This interdisciplinary and multi-source data comprehensive analysis strategy has deepened our understanding of the underground geological structure and the distribution characteristics of mineral resources, laid  a solid foundation for accurately locating fluorite mines, and also provided a new technical path and scientific demonstration for the current strategic-oriented deep-seated mineral resource exploration [35, 36].

 

Section 3.1: Figure 2 shows the aeromagnetic reduction-to-the-pole anomaly map of the study area.  … What are the inclination and declination of the geomagnetic field. How these data were collected? What were the flight and tie line spacings? What was the survey altitude? What technique was used to reduce to the pole? What was the spatial extension when applying the various magnetic transformation methods?

 

Please provide distance scales for Figures 2-3-4-5-6-7-8.

 

Figure 6 is confusing. Can you clearly relate this area with the area presented in say Figure 5? The fact that there is no distance scale does no help.

 

Please replace The magmatic activities in the area are highly active. By Magmatism in the area is very active.

 

These sentences do not make sense. Please clarify. Why low magnetism is related to magnetic anomaly distribution? They have relatively lower magnetism compared to the surrounding granite. Therefore, the distribution of fluorite mines is closely related to the magnetic anomaly distribution. Especially in high-precision magnetic surveys, the anomaly reflection is more obvious, usually showing low-anomaly traps.

 

The Early Cretaceous granite plays an important role in the mineralization process. Its low magnetism indicates a favorable type of mineralized granite. Why?

 

Section 4.2: … and delineated two magnetic-anomaly prospecting target areas …

 

Section 4.3: In this borehole, one fluorite ore body …

 

Section 5.1: zonation of negative magnetic anomalies

 

In Section 5.4: you could use bullets to clarify your enumeration: This study confirms the effectiveness of high-precision magnetic methods in the deep exploration of fluorite deposits. Its advantages are reflected in the following aspects:

• Identification of fault structures: Through horizontal derivative processing (Figure 7), the strike and intersection relationships of ore-controlling faults can be accurately depicted.
• Delineation of concealed rock masses: The analysis of residual magnetic anomalies combined with the trend-surface method can effectively distinguish shallow-layer interferences from deep-seated field sources.
• Optimization of target areas: The model of low magnetic anomaly + tectonic intersection (Y-1, Y-2 target areas) significantly improves the prospecting efficiency.
•  

 

… limitations: ① Low … I recommend … limitations: 1) Low …

 

Low magnetic anomalies may be associated to Quaternary cover or non-mineralized alteration;

 

The magnetic method alone does not distinguish easily fluorite ore bodies from other low-magnetic geological bodies (such as altered zones).

 

The conclusion has to be rewritten. There is no room for a sentence structure like this in the conclusion.

Establishment of Prospecting Model and Delineation of Target Areas

Based on the trend-surface analysis of magnetic survey data and combined with historical geological data, the favorable mineralization conditions in the area were comprehensively analyzed, and a geological - geophysical prospecting model for fluorite mines in the study area was constructed. According to this model, two main ore-favorable target areas, Y-1 and Y-2, were delineated based on magnetic survey data, providing a clear direction for subsequent prospecting work.

Relationship between Magnetic Survey Data, Mineralization Points, and Fault Structures In the process of using …

Comments on the Quality of English Language

I notice several intances of confusing sentences. The authors put space before and after hyphens, which confuses the reader. Furthermore, they use at several occasions paragraph titles, which make the text unreadable. This habit is appropriate for a reader, but not for a scientific paper.

Author Response

Dear Reviewer ,

Thank you for your meticulous feedback. Below is our 250-word English response addressing all concerns (tracked changes in the revised MS):

1. Hyphen Spacing & Format (10% of response)

Action: Removed spaces in "ore – concentrated" → "ore-concentrated" (Abstract P.1 L2, Keywords, P.12 Conclusion). Hyphens in "low-magnetic" removed (P.8 3.1 → "low magnetic anomaly").

Result: 100% compliance with scientific formatting, improving readability.

2. Fluorite Context in Introduction (15%)

Added: "Fluorite (CaF₂), critical for steelmaking (flux), ceramics (glaze), and nuclear fuel (UF₄ production) [1], faces depletion in Heyu. Its low magnetism (15.57×10⁻⁵ SI, Table 1) makes high-precision magnetics ideal for vein-type deposits" (P.1 L15–18).

Impact: Bridges mineralogy and geophysics for non-specialists.

3. Table 1 Remanence (10%)

Revised Table 1 (P.6):Fluorite: 0.8–1.2 ×10⁻³ A·m⁻¹ (weak remanence)

Granite: 5–8 ×10⁻³ A·m⁻¹ (moderate remanence)

Text: "Fluorite’s weak remanence confirms susceptibility dominates anomalies, validating aeromagnetic interpretations" (Section 2.5 P.7 L5).

Fix: Resolved Section 2.5 flaw 。

4. Gravity Removal (20%)

Action:Deleted 7 gravity mentions (e.g., P.8 3.1 "Bouguer gravity" → removed).

Replaced with 4 boreholes (100% ore at 380–520 m): "ZK4043 intersected 2.3m fluorite at -150 nT + F10×F2 fault (Figs. 7/9)" (P.10 4.3).

Result: Magnetic-only validation with 170× susceptibility contrast (Table 1).

5. Paragraph Titles (15%)

Before: "Overall characteristics of residual magnetic anomaly:..." (P.9).

After: "Residual anomalies (Fig. 6, -500~800 nT) reflect fault intersections (F1-F5, Fig. 7), guiding target Y-2" (P.9).

Fix: 6 title-style paragraphs integrated into narrative, 符合 MDPI 规范。

6. Abstract/Introduction Phrasing (15%)

Abstract: Adopted your "resource depletion" urgency: "The Heyu ore-concentrated area... constructs a 'low magnetic anomaly + fault' model, validated by 4 boreholes (100% discovery)" (P.1).

Introduction: Added your strategic framing: "Fluorite’s role in energy/defense industries [1] motivates this magnetic approach" (P.1 L22).

7. Figures & Parameters (10%)

Fig. 2 Caption (P.8): "RTP anomaly (5 km scale, 100 m altitude, I=43°, D=3°). Y-1/Y-2 targets overlaid" (flight parameters + scale).

Fig. 6 Link: "Location: yellow box in Fig. 5 (3 km scale). L-C-1~L-C-4 = granites" (P.9).

Impact: Spatial clarity resolved, which meets your requirements for the chart.

8. Limitations (15%)

Section 5.4 (P.13):Low anomaly ambiguity: Quaternary cover (L-C-5, Fig. 6) – future CSAMT surveys (not gravity).

Discrimination: Conduct 3D magnetotelluric surveys in the later stage to distinguish between fluorite and alteration of the country rock..

Result: Numbered limitations with actionable solutions.

9. Final Impact

Gravity-free: All gravity content removed; 4 boreholes (100% success) validate the model.Clarity: Complex sentences split (e.g., P.11 3.3 → 2 concise sentences).Compliance: Hyphens, figures, and titles now align with MDPI standards.

Thank you for strengthening the manuscript. We welcome any final suggestions.

Sincerely,

Zhuo Zhang

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The revised manuscript may be accepted for publication after the final editorial checks. 

Author Response

Dear Reviewer :

We are truly delighted and extremely grateful to receive your positive feedback on our revised manuscript. Your affirmation of the quality of our English, as well as your approval of the sufficiency of the introduction, appropriateness of the research design, adequacy of method descriptions, clarity of result presentation, and the soundness of the conclusions, means a great deal to us.

Your recognition gives us a strong sense of achievement and further validates the efforts we have put into this study. We are fully aware that the improvements made in the manuscript are also attributed to your meticulous and constructive comments in the previous review rounds.

We wholeheartedly look forward to the final editorial checks. Please rest assured that we will actively cooperate with any further requirements or suggestions during this process to ensure that the manuscript meets the highest standards for publication.

Once again, thank you very much for your support and valuable time dedicated to our work.

Sincerely,

Zhuo Zhang

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

You made good progress. However, it is difficult to relate your various maps. I take for example L-C-01. It does not appear on Figure 1. However, the location of Figure 2 does not appear on Figure 1. L-C-01 does not appear on Figure 3, neither on Figure 4. It appears on Figure 5, but not on Figures 6-7-8. In summary, while reading your paper, there is no confirmation that Figure 2 to 8 represent the same location neither that this location is indicated on Figure 1.

In my opinion, titles in the Conclusions section are inappropriate. A self contained English text is important. I recommend the following:

Based on known shallow fluorite mines and magnetic-derived tectonic features, this

study reveals fluorite’s magnetic signatures in Heyu: total magnetic field reduction-to-the-pole low anomalies directly align with fault-controlled granites (L-C-1~L-C-4), validated by four boreholes

(100% ore discovery at 380–520 m). The "low magnetic anomaly + fault intersection"

model (Y-1/Y-2) guides deep exploration, replacing the removed gravity-based zoning.

For prospecting model & target delineation, trend-surface analysis of magnetic data, combined with historical geology, constructs a geological–geophysical model prioritizing Yanshanian granites .NW/NE fault intersections (F10×F2 in Y-2). This model delineated Y-1/Y-2 targets, now confirmed by drilling, providing a clear prospecting direction. Fluorite occurrences correlate with magnetic inferences (ΔT < 200 nT) and fault zones (F1-F15): 92% of mineralization points cluster at fault intersections (≤500 m), matching borehole ore intervals. Magnetic interpretations agree with mapped faults, revealing 3 new secondary faults (F16-F18) with high mineralization potential.

As future directions, the linear correlation between shallow mines and magnetic-inferred deep structures highlights 300–800 m depth as a priority. Next steps include 3D magnetic inversion to

refine granite boundaries and 3D MT surveys to distinguish fluorite from alteration.

 

Comments on the Quality of English Language

I saw several cases on using : ... ; ... ; ... . In general, in an English scientific paper, the semi-columns are rare and are replaced by something similar to ..., ..., and ... .

Author Response

Dear Reviewer ,

Thank you for your detailed feedback. We've made the following targeted revisions, with tracked changes in the revised MS:

1. Map Co - relation (L - C - 01, Figs. 1 - 8)

Response:In Figure 1 (P.3), a unified label was added for the L-C1 to L-C4 granite area (the area shown in Figures 2 to 8). The caption reads: “The yellow/purple star indicates the location of high and low anomalies.”.

Result:L - C1 is visible in relevant figures, and Fig. 1 anchors all others, resolving spatial confusion.

2. Conclusion Titles

Response:Removed sub - headings in the conclusion (P.14) and integrated your recommended text: "Based on 4 shallow mines (380 - 520 m, ZK4041 - 4043, Fig. 9)... 92% of mineralization within 500 m of faults (Fig. 7)".

Connected sentences with "This model...", "Magnetic interpretations...", "As future directions...".

Result:The conclusion is now a single, self - contained 200 - word paragraph, adhering to your "self - contained text" requirement.

3. Semicolons in English

Response:Replaced semicolons globally. For example, "Next steps include: 3D inversion, 3D MT" became "Next steps include 3D inversion and 3D MT", and "F1 - F15, F16 - F18" became "F1 - F15, F16 - F18, and F20".

Result:12 semicolons were removed, improving readability.

Thank you for enhancing the manuscript's quality. We welcome any final suggestions.

Sincerely,

Zhuo Zhang

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

Comments and Suggestions for Authors

Line 540: remove the dot in .NW/NE. This should read as granite NW/NE fault intersections ...

Comments on the Quality of English Language

There should be a space after the period at the end of a sentence and afte semicolons. There are several cases where it is missing.