## 6 Conclusions  
Here, we found a typical skarn profile of the Ningzhen mining district in the MLYRB, which is highly consistent with the typical skarn model. Our detailed whole rock and mineral geochemical analysis comes to the following conclusions:  
1. During the skarn formation process, inner skarn is enriched in Ca and Mn, accompanied by the loss of K, Rb and Ba. Compared to the marble zone, the outer skarn shows a large-scale enrichment of elements and certain dilutions of Ca, Sr and Cs. The element contents fluctuate more significantly at the contact zone between the rock body and the surrounding rocks, and the migration and transformation of Th and U are most significant. 2. Garnet REEs are coupled with Fe in the inner skarn but with Al in the outer skarn following the YAG-type substitution mechanism. Garnets from the outer skarn show a significant variation in the Y/Ho ratio, indicating a large-scale water-rock interaction process in the external outer skarn zone. The U content in garnets may be greatly influenced by \(f\)O\({}_{2}\) and fluid activity, while the Eu anomaly is not only controlled by \(f\)O\({}_{2}\) changes in the system but is mainly restricted by various factors such as water-rock ratio, crystal structure and \(f\)O\({}_{2}\), especially the change in the crystal structure, which is the main controlling factor. 3. Whole-rock in Na, Al, Ti, and Sr elements between inner and outer skarn, particularly in chondrite-normalized diagrams of trace elements Lu, Dy and Y versus Al\({}_{2}\)O\({}_{3}\) can effectively distinguish inner and outer skarn, except for samples located at the boundary. Fe, In, Al, Mn, Ni, Ti, Zr and Nb contents of garnets can also tell the boundary between inner and outer skarn. However, garnets in skarn are not fully developed, and multi-stage garnet features often occur, which may bring some interference. Whole-rock and mineral geochemistry each have their own advantages and disadvantages. It is more effective to determine the contact boundary of a rock body by combining the two methods for comprehensive analysis. The hand specimens, microscopic observations, whole-rock chemistry and mineral chemistry of the Tongshan skarn profile display typical skarn characteristics. Because the properties of magmatic rocks and surrounding rocks in which skarns develop vary considerably, more classic skarn profiles are still needed to carry out similar research to further the understanding of skarn formation and expand the research scope. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app1348118/s1](https://www.mdpi.com/article/10.3390/app1348118/s1)]([https://www.mdpi.com/article/10.3390/app1348118/s1](https://www.mdpi.com/article/10.3390/app1348118/s1)), Table S1. Whole-rock major and trace elements in TS-10 profile. Table S2. Major and trace element of the garnets in TS-10 profile. Table S3a. Whole-rock data and processing results of granite and inner skarn in TS-10 profile. Table S3b. Whole-rock data and processing results of marble and outer skarn in TS-10 profile. Methodology, F.W. ; Formal analysis, W.Z. and R.B. ; Investigation, W.Z. and R.B. ; Resources, F.W. ; Writing-original draft, R.B., W.Z., F.W. ; Writing-review & editing, F.W. ; Supervision, F.W. All authors have read and agreed to the published version of the manuscript. Figure 18: Andradite end member (And) vs. Ti, Zr, Nb diagrams. (**a**) And vs. Ti diagram, (**b**) And vs. Zr diagram, (**c**) And vs. Nb diagram. **Funding:** This research is jointly supported by the National Natural Science Foundation of China (Grants Nos. 91962218, 42273065) and the National Key Research and Development Program of China (Grant No. 2022 YFC2903503). **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** The original contributions presented in the study are included in the article and Supplementary Materials. Further inquiries can be directed to the corresponding author.