Review Reports

1. Summary

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions highlighted with red color in the re-submitted files.

2. Point-by-point response to Comments and Suggestions for Authors

Comments 1: I suggest to make the introduction more soundness for worldwide audience. Also, sandstone rich U-bearing minerals are largely used to decipher the orgin and the age of the sandstone itself (i.e., Sanità et al., 2025 - Scientific Reports; Pandolfi et al., 2026 -  Tectonoiphysics). I suggest the authors to outline briefly how this type of deposits can be used highlighting their importance. I suggest the auhtors to make a soundness introduction, remarking how specific techniques can give information on natural processes

Response 1: Thank you for pointing this out. In the paper, We have revised the introduction section. Specifically, we supplemented the geological significance of sandstone-type uranium deposits, the primary exploration type of uranium resources in China, the formation mechanism of sandstone-type uranium deposits, and element migration behaviors during mineralization. In addition, several new references have been added to support the updated content. Please refer to Page 1 Lines 37–40，Page 2 Lines 41–47,58-73.

Comments 2: Please, improve significantly the image from a scierntific and aestetihc point of view.

Response 2: We have redrawn Figure 1B. Please refer to Page2 Figure 1B.

Comments 3: meta-arenites?

Response 3: This section describes the basement of the Songliao Basin, and metasandstone occurs within the basement rock series.

Comments 4: Are these original data? if no, please provide the proper reference(s) in the figure caption. The latter  should be improved and detailed.

Response 4: These data are primary data obtained by the authors during field exploration. The location of Profile L1 is indicated in the figure caption. Please refer to Page 6 Figure 2.

Comments 5: I sueggst to use diagrams where the differences ddescribed by authors can be appreciated by readers.

Response 5: We have added Figure 3. Element content distribution curves for different sandstone types of the Sifangtai For-mation in the Daqing Placanticline area. Please refer to Page 9 Figure 3.

Comments 6: This is strongly different from other patterns. Can the authors explain this better?

Response 6: This sample has relatively high Cu, Co, and Ni contents and may contain Cu‑Co‑Ni heavy minerals..

Comments 7: How Fe₂O₃ has been estimated by authors?

Response 7: We have noted the estimation method for Fe₂O₃ below Table 1: Fe₂O₃ = TFe₂O₃ - 1.11 × FeO. Please refer to Page13.

Comments8: Please uniform tha table with at least two decimals after the point

Response 8: Please uniform tha table with at least two decimals after the point.

Comments9: this part is not clearly explained in the geological setting. The auhtors should add this part in the geological setting and discuss it in in depth in the current section.

Response 9: We have supplemented the hydrocarbon reservoir characteristics of the Quantou and Nenjiang Formations in the geological background section, which provides solid geological support for the subsequent discussion. Please refer to Page 4 Lines 132-136.

Comments10: I would try to use a different title for this paragraph..

Response 10: Thank you for pointing this out. After careful discussion, we have revised the title to “Mineralization model”, which is considered more appropriate for this study. Please refer to Page 19 Line 473.

Comments11: Conclusions are too long. Please reduce it in the revised version of the manuscript. Also, I retain that conclusions should be outline the main remarks of the paper. In the current form, conclusion are a summary of the discussion section awith no emphasis on what has been find by authors, that is very interesting.

Response 11: Thank you for pointing this out. We have streamlined the conclusions to highlight the key findings of this study. Please refer to Page 20 Lines 505-521. In addition, the abstract has been completely rewritten. Please refer to Page 1 Lines 11-32.

3. Additional clarifications

We have reorganised the reference list. Some less relevant Chinese references were removed, and several newly published English papers from recent years have been added.

1. Summary

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions highlighted with blue color in the re-submitted files.

2. Point-by-point response to Comments and Suggestions for Authors

Comments 1: Lines 236–250: The sampling strategy and analytical methods require substantially more detail.The manuscript states that 41 samples from 11 drill holes were analyzed, but the sampling depths, spatial distribution, criteria for selecting representative samples, and relationship between samples and individual ore zones are not provided. More importantly, the 232 additional geochemical-index measurements (TOC, total sulfur, pH, Eh, etc.) are only described as data collected during exploration work. The analytical methods, sample preservation, measurement conditions, detection limits, quality control, and whether these data are directly comparable with the 41 whole-rock samples must be reported. Without this information, an important part of the redox interpretation cannot be independently evaluated.

Response 1: Thank you for pointing this out. In the paper, All samples in this study were collected from drill holes during field exploration, and the sampling horizon corresponds to sandstones in the lower member of the Sifangtai Formation. The drill hole numbers and sampling depths are newly supplemented in Table 1. Meanwhile, we have added detailed sampling criteria for three types of samples, including host rock, mineralized sandstone, and uranium ore. In addition, the testing institutions, analytical methods, and detection limits of each geochemical item for 109 exploration samples have been supplemented in the revised manuscript. The two types of samples were collected simultaneously during field work. The geochemical samples were obtained for production testing, while the whole-rock geochemical samples were used for scientific research, which guarantees the reliability and comparability of the comparative analysis in this study. Please refer to Pages 7 Lines 249-252, 264-272 and Table 1.

Comments 2: Lines 283–300: The interpretation of Eh values appears internally inconsistent and should be carefully re-evaluated.Table 5 shows average Eh values of 116.40 mV for wall rocks, 257.90 mV for uranium-mineralized sandstone, and 227.07 mV for uranium ore. The text nevertheless states that the higher Eh values of the mineralized rocks indicate more reducing conditions. In conventional usage, higher Eh generally reflects more oxidizing conditions. Please define exactly what ‘ΔEH’ represents, how it was measured or calculated, and what reference electrode or correction was used. The redox interpretation should then be revised accordingly. This issue is central because reducing conditions are used repeatedly to support the proposed mineralization mechanism.

Response 2: Thank you very much for identifying this issue. The authors have rechecked the analytical data of the original 232 samples, which were tested by two laboratories: CNNC Institute No.240 and CNNC Geological Party No.208. We found that the Eh values obtained from these two laboratories differ by one order of magnitude. To facilitate data comparison and analysis, we re-performed statistics using the 109 samples tested by CNNC Institute No.240. The statistical results show that the variation trends of total organic carbon, total sulfur (∑S), and pH remain consistent with previous results, although there are minor differences in absolute values, which have been corrected in the manuscript. The Eh values show little distinction among host rocks, mineralized sandstones and uranium ores. Accordingly, only the measured results are presented in the revised text without further interpretative inferences. Please refer to Page 9 Lines 308-313, Page 10 Lines 317-319,321-322,and Table 5.

Comments 3: Lines 258–282: The Fe₂O₃/FeO ratio and CaO contents are over-interpreted as direct evidence of mineralization processes.Whole-rock Fe₂O₃/FeO ratios can be affected by lithology, detrital mineral composition, diagenesis, and analytical procedures, and do not by themselves demonstrate Fe³⁺–Fe²⁺ transformation during uranium mineralization. Likewise, elevated CaO in some ore samples may reflect carbonate-rich lithologies or cement rather than a mineralization-related process. The authors should evaluate these effects using mineralogical or petrographic evidence and, where possible, compare samples of similar lithology. Statements regarding redox transformation and carbonate alteration should be moderated if direct mineral-scale evidence is unavailable.

Response 3: In this section, we only present the specific characteristics of major elements. Relevant discussions regarding redox transformation and carbonate alteration have been removed to weaken speculative conclusions.

Comments 4: Lines 385–405: The proposed transport of uranium as uranyl-carbonate complexes is insufficiently supported. The manuscript infers uranyl-carbonate transport mainly from the relatively high CaO content of uranium ores. Ca enrichment alone does not establish the aqueous uranium species present during mineralization. This interpretation requires stronger evidence, such as carbonate mineralogy, petrographic relationships, carbon–oxygen isotope data, fluid chemistry, or thermodynamic/speciation calculations. If such evidence is not available, the discussion should present uranyl-carbonate transport as a plausible mechanism rather than a demonstrated one.

Response 4: Since this study did not involve carbonate mineralogical analysis, carbon–oxygen isotope testing, or thermodynamic and speciation simulation calculations, we have revised the relevant statement to infer that uranium migration may have occurred in the form of uranyl-carbonate complexes. Please refer to Page 17 Lines 415-416,419-420,Page 18 Line 421.

Comments 5: Lines 361–381: The correlations between U and Mo, Pb, Y, Sc, and REE should be quantified statistically. The manuscript describes several relationships as ‘significant’ or ‘good’ based mainly on visual inspection of Figure 5. Please provide correlation coefficients, regression equations, significance levels, and sample numbers for the relevant relationships. The authors should also assess the influence of the few very high-U samples, which may dominate the apparent trends. In particular, the strong U–Pb relationship should be discussed carefully because Pb in high-U samples may include a radiogenic contribution rather than representing only co-transport by mineralizing fluids.

Response 5: We quantitatively analyzed the correlations between U and other elements, including Mo, Pb, Y, Sc, and rare earth elements (REEs). The corresponding regression equations and correlation coefficients were supplemented to provide quantitative statistical evidence. In addition, we have re-discussed the elemental correlations based on the graphical results. Please refer to Page 16 Lines 386-396, Page 17 Lines 397-402,and Figure 6.

Comments 6: Lines 324–457: The interpretation of HREE enrichment as evidence for late-stage hydrothermal reworking needs stronger support. The manuscript acknowledges that REE contents are strongly affected by lithology, yet later attributes higher HREE contents in high-grade ores to late-stage fluid reworking. Several high-U samples have different lithologies and major-element compositions, making it difficult to separate fluid effects from host-rock control. The proposed ~500 μg/g U threshold also appears empirical and is not statistically justified. I suggest comparing lithology-matched samples, normalizing REE data to relatively immobile elements where appropriate, and providing quantitative tests before invoking hydrothermal reworking. Otherwise, the conclusion should be expressed more cautiously.

Response 6: We have thoroughly revised this discussion section. The previously proposed uranium threshold of 500 μg/g has been removed. We now focus on the HREE enrichment characteristics of several high‑uranium ore samples (ZKMX02-ST3, ZKMX02-ST2). Combined with the previous data, we only speculate that these high‑uranium ore samples may have experienced later ore‑forming fluid modification, and the conclusion of low‑temperature fluid alteration has been abandoned. Please refer to Pages 18–19 Lines 466-472.

Comments 7: Lines 458–516: The two-stage mineralization model involving deep hydrocarbon-bearing reducing fluids is presently too speculative. The proposed model combines supergene oxidized fluids with later deep hydrocarbon-bearing reducing fluids migrating along faults. However, the present study provides no direct geochemical tracer of hydrocarbons or deep fluids, such as organic biomarkers, carbon isotopes, fluid inclusions, sulfur isotopes, or mineral-scale paragenetic evidence. Regional hydrocarbon occurrence and fault development alone do not demonstrate that such fluids participated in uranium mineralization. The authors should clearly distinguish observations from regional inference, provide additional direct evidence if available, and substantially moderate the genetic model and Conclusions if it cannot be independently verified.

Response 7: We have supplemented previous published evidence, including carbon and oxygen isotope data of carbonate cements in sandstones of the Sifangtai Formation, hydrocarbon generation and expulsion timing of the basin, and fault development characteristics. Based on these additional data, the metallogenic model has been reformulated and revised. Please refer to Page 19 Lines 489-501.

Comments8: Figures 3 and 4 should be redesigned to improve readability and geological interpretation. Both figures contain many overlapping sample curves, making individual patterns difficult to distinguish. In Figure 3, the normalization values for ‘Chinese sedimentary rocks’ should be explicitly tabulated or clearly cited, and the element order and units should be checked. In Figure 4, the samples responsible for the proposed HREE enrichment cannot be readily identified. I suggest plotting group medians or means with ranges, or highlighting the high-grade samples discussed in the text. The captions should also clearly state the normalization scheme and sample categories.

Response 8: We have redrawn Figures 3 and 4. Mean values together with variation ranges are used to illustrate the geochemical features of each sample group, and the two high‑uranium samples (ZKMX02-ST3, ZKMX02-ST2) are highlighted. Meanwhile, we have added the normalized values of “Chinese sedimentary rocks” and chondrite-normalized values as well as corresponding references to Tables 2 and 3. The sample size for each group has also been marked. Please refer to Page 11 Figure 4, Page 11 Figure 5, Page 13 Table 3, Page 14 Table4.

Comments9: Figure 5 does not adequately support the stated correlation conclusions in its current form. The nine log–log plots are relatively small, and no regression lines, correlation coefficients, equations, confidence intervals, or p-values are shown. Because these plots underpin the identification of Mo and Pb as indicator elements and the proposed relationships between U and REE, the figure should be revised to include quantitative statistical information. Please also use consistent symbols and clearly indicate the number of samples in each group.

Response 9: Figure 5 has been redrawn, with supplementary quantitative statistical information, including regression equations and correlation coefficients, fully added. Please refer to Page 17 Figure 6.

3. Additional clarifications

No additional clarification.