X-ray Computed Tomography of PGE-Rich Anorthosite from the Main Reef of the Yoko–Dovyren Layered Massif
, Sergei N. Sobolev 1, Vasily O. Yapaskurt 2, Georgy S. Nikolaev 1 and Evgeny V. Kislov 3
Round 1
Reviewer 1 Report
1) The manuscript demonstrates detailed and consistent studies of computed tomography of anarthosites from a low-sulfide reef of the Yoko-Dovyrkna massif. As a result, the authors obtained data on the content of the sulfide phase and PGM in the studied samples and sulfide connectivity. One conclusion is that there is no correlation between these parameters. But the authors do not offer a logical explanation for this regularity, which differs from other ore associations of the same massif. What is the genetic meaning of this result?
2) The authors have identified precious metal minerals (moncheite and "electrum") but do not provide analyzes of these phases. The presence of Pb in moncheite is unusual and requires some interpretation. Add analyzes of minerals, especially since in the "Microprobe studies" are indicated in the analitical conditions.
3) in the conclusions, we would like to understand what new computed tomography has given in comparison with the previously known data that sulfides and PGMs in platinum-bearing reefs are unevenly distributed, and that they are associated primarily with the sulfide phase. Probably the main difference between these associations is the additional connection of platinoids with the fluid phase and the significant role of fluid transport of platinum metals.
4) It should be more clearly emphasized in the conclusions what gives a new revelation of the 3-D morphology of sulfide aggregates and platinum grains, in addition to the well-known evolution of the sulfide melt as a result of its crystallization in the intergranular space of plagioclase crystals?
Some comments and questions are given in the text of the reviewed manuscript.
Comments for author File: 
Comments.pdf
Author Response
1) The manuscript demonstrates detailed and consistent studies of computed tomography of anarthosites from a low-sulfide reef of the Yoko-Dovyrkna massif. As a result, the authors obtained data on the content of the sulfide phase and PGM in the studied samples and sulfide connectivity. One conclusion is that there is no correlation between these parameters. But the authors do not offer a logical explanation for this regularity, which differs from other ore associations of the same massif. What is the genetic meaning of this result?
Response: In fact, we argue that due to relatively small size of scanned mineralized samples and uneven distribution of sulfides, obtained estimates of the local sulfide connectivity cannot be used for any genetic speculations, including probable link with PGMs.
2) The authors have identified precious metal minerals (moncheite and "electrum") but do not provide analyzes of these phases. The presence of Pb in moncheite is unusual and requires some interpretation. Add analyzes of minerals, especially since in the "Microprobe studies" are indicated in the analitical conditions.
Response: Table 3 has been added to the manuscript.
3) in the conclusions, we would like to understand what new computed tomography has given in comparison with the previously known data that sulfides and PGMs in platinum-bearing reefs are unevenly distributed, and that they are associated primarily with the sulfide phase. Probably the main difference between these associations is the additional connection of platinoids with the fluid phase and the significant role of fluid transport of platinum metals.
Response: In this paper, we simply demonstrate that regardless of the location of PGMs relative to original sulfides, they may associate with late hydrous minerals or occur without any signatures of fluid control processes.
4) It should be more clearly emphasized in the conclusions what gives a new revelation of the 3-D morphology of sulfide aggregates and platinum grains, in addition to the well-known evolution of the sulfide melt as a result of its crystallization in the intergranular space of plagioclase crystals?
Response: Herein, we do not discuss evolution of protosulfide melts, instead focusing on quantifying parameters of the spatial distribution of sulfides and PGMs in the PGE-rich anorthosite, using CT-examinations.
5) Provide a link to experimental data on the temperature conditions for the formation of "electrum"
Response: An additional reference has been added to the manuscript (No 26): Spiridonov, E.M. Review of the gold mineralogy in the main types of Au-mineralization. In Gold of the Kola Peninsula and adjacent regions; Yu. A., Voitekhovsky, Ed.; K&M: Apatity, Russia, 2010; pp. 143-171.
Other minor changes are added to the text.
Reviewer 2 Report
X-ray computed tomography is a method that allows the registration and analysis of the internal structure of an object without disturbing its structure, and integrity. Over the last decades, microfocus fluoroscopy and computed tomography technologies have rapidly developed and gained metrological status. Industrial X-ray computed tomography systems provide high accuracy and the ability to measure the internal and external dimensions of the specimen under study without destroying it. The new and rapidly developing technology quickly proved its value for geological research. The processing of X-ray computed tomography data in the field of geology is a complex task in terms of the choice of approach, which directly affects the quality of the output information. Therefore, the results of a detailed study of ore anorthosites by X-ray computed tomography presented in the manuscript by I.V. Pshenitsyn et al. can serve as an additional source of knowledge for creating a methodology for 3d studies of geological samples.
The manuscript is original and the evidence supports the conclusions presented. The abstract is sufficiently informative. Overall, the manuscript is of scientific interest and may be published in a special issue of Minerals.
As comments:
1. Unfortunately, the literature review on the use of computed tomography in geology did not include a number of advanced publications of recent years (e.g., Maier, W.D., Barnes, S.J., Godel, B.M. et al. Petrogenesis of thick, high-grade PGE mineralisation in the Flatreef, northern Bushveld Complex. Miner Deposita 58, 881–902 (2023). https://doi.org/10.1007/s00126-022-01156-6; Sittner J., Brovchenko V., Siddique A., Buyse F., Boone M., Renno A.D., Cnudde V., Merkulova M., Sluzhenikin S.F. Three-Dimensional Distribution of Platinum Group Minerals in Natural MSS-ISS Ores From the Norilsk One Deposit, Russia // Frontiers in Earth Science, 2022, 10. DOI=10.3389/feart.2022.860751).
2. Some of the figures (1a, 7b and 8b) are not of very high quality. Maybe the authors should use the map, from the paper by Ariska et al, 2018. It is of very good quality.
3. In the title and in the text of the manuscript, the low-sulfide reef is called Main, while in the abstract it is called Reef-1. If the authors stick to their title, it is necessary to bring the text in the abstract into conformity.
Other minor comments are made in the text file of the manuscript.
Comments for author File: Comments.pdf
No comments.
Author Response
1) Unfortunately, the literature review on the use of computed tomography in geology did not include a number of advanced publications of recent years …
Response: There was no purpose to present a more extensive review of CT-studies in geology. Instead we focused on the most important results obtained for reef-style deposits in layered intrusions, in which more cited references on the topic have been presented.
2) Some of the figures (1a, 7b and 8b) are not of very high quality.
Response: Some changes have been done in Figures 3 to 8. To escape of copying the map of Dovyren from other publications, Figure 1 was left without changes.
3) In the title and in the text of the manuscript, the low-sulfide reef is called Main, while in the abstract it is called Reef-1. If the authors stick to their title, it is necessary to bring the text in the abstract into conformity.
Response: Done.
Other minor changes are added to the text.
Reviewer 3 Report
The manuscript reports a study of sulfides and PGM associated with a layer of anorthosite of the Yoko-Dovyren massif, Siberia, using CT and SEM data. Based on the obtained data, the Authors to provide a model to explain the formation of PGM and associated sulfides and electrum, from relatively high to low temperature. The manuscript is well organized and, although I am not a native speaker, for me English is fully understandable. Therefore, for me it is suitable for publication in Minerals after minor corrections. The only general comment I have is related to the results of CT. It will be important if the Authors can provide more information how they are sure about the presence of PGM , using this technique that, if I am correct, is mainly based to the density of the investigated phases and is not providing chemical composition. For example, vysotskite, a common PGM, has the same or similar density of several sulfides, including cubanite. Is, therefore, possible that PGM like vysotskyte with low density cannot be identified using CT? In my opinion this analytical uncertainty should be mentioned in the paper. Here are few specific suggestions that I hope will help the Authors to improve their manuscript.
Along the text, please change the word object with mineral or phase.
Caption fig.1. Specify the abbreviations Qtz and Pig.
Caption fig.2. Specify all the abbreviations used in both the figures and in the captions.
Figure 3a. Indicate what are the grey and the green portions.
Table 1. How did you identify plagioclase and PGM using CT?
Table 2 and Figure 6. Please explain how do you classify PGM based on CT. Furthermore, there are several PGM characterized by complex composition.
Figure 7. Specify all the abbreviations used.
Figure 8 a. Is a PGM or electrum? Specify all the abbreviations used.
Best regards
Author Response
1) The only general comment I have is related to the results of CT. It will be important if the Authors can provide more information how they are sure about the presence of PGM , using this technique that, if I am correct, is mainly based to the density of the investigated phases and is not providing chemical composition.
Response: The attenuation of the X-ray signal depends on the density and composition of the studied materials. This effect is described by the Lambert–Beer law, which determines the attenuation of a monochromatic light beam as it propagates in an absorbing medium. This explains why initially we use the term “objects” instead of “minerals”. In addition, we write “potential PGMs”, based on our experience in previous detailed SEM studies of the PGE-rich anorthosites.
2) Caption fig.1. Specify the abbreviations Qtz and Pig.
Response: Done
4) Caption fig.2. Specify all the abbreviations used in both the figures and in the captions.
Response: Done
5) Figure 3a. Indicate what are the grey and the green portions.
Response: Corrected in the figure
6) Figure 8 a. Is a PGM or electrum? Specify all the abbreviations used.
Response: Corrected in the figure
