Fenitization at the Lovozero Alkaline Massif, NW Russia: Composition and Evolution of Fluids
Wu-Bin Yang
Round 1
Reviewer 1 Report
This paper presents petrological, geochemical and fluid inclusion studies across the contact of the Lovozero alkaline massif, to reveal the post-magmatic alteration and fluid evolution of the fenitizing fluids. The field work is reliable and clear, data is huge and high quality, and the interpretation is sound. While the paper is overall well-written, there is still room for improvement. It would be better to conduct in-situ LA-ICPMS analysis on mineral chemistry and individual fluid inclusion, if possible in future after this work. The behaviors of the ore-forming elements, i.e., Zr-Nb-REE, should be constrained during this fenitization processes. This is exactly what we are expecting for. Overall, I recommend minor revision for the present form of this paper. Numerous comments and suggestions were marked in the attached PDF file.
Comments for author File: 
Comments.pdf
Need to improve
Author Response
This paper presents petrological, geochemical and fluid inclusion studies across the contact of the Lovozero alkaline massif, to reveal the post-magmatic alteration and fluid evolution of the fenitizing fluids. The field work is reliable and clear, data is huge and high quality, and the interpretation is sound. While the paper is overall well-written, there is still room for improvement. It would be better to conduct in-situ LA-ICPMS analysis on mineral chemistry and individual fluid inclusion, if possible in future after this work. The behaviors of the ore-forming elements, i.e., Zr-Nb-REE, should be constrained during this fenitization processes. This is exactly what we are expecting for. Overall, I recommend minor revision for the present form of this paper. Numerous comments and suggestions were marked in the attached PDF file.
Thank you very much for taking the time to review this manuscript. In the future, we plan to conduct in-situ LA-ICP MS analysis on mineral chemistry and individual fluid inclusion.
Please find the detailed responses in the attached PDF file and the corresponding corrections in the re-submitted manuscript.
Author Response File: Author Response.pdf
Reviewer 2 Report
The authors suggest that the narrow thickness of the fenitized zone was due to two-fold reasons: (1) intense autometasomatic alterations of alkaline rocks and (2) a decrease in the permeability of country rocks due to fluid immiscibility between coexisting CH4 and H2O.
The authors have not calculated the mass of the fluid separated out as a result of crystallization of the mother magma. If we assume water and other volatiles comprised 4-5 wt% of the Lovozero alkaline magma, then the volume of volatile degassed from a large massif (650 square km outcrop size and a depth of at least 5 km) would be enormous. Therefore, it would be hard to understand why the fenitized zone is only less than 4 m thick.
The authors may support or refute the possibility of an upward migration of volatiles in the Lovozero laccolithic massif.
Author Response
The authors suggest that the narrow thickness of the fenitized zone was due to two-fold reasons: (1) intense autometasomatic alterations of alkaline rocks and (2) a decrease in the permeability of country rocks due to fluid immiscibility between coexisting CH4 and H2O.
Thank you very much for taking the time to review this manuscript. Please find the responses below and the corresponding corrections in the re-submitted file.
Comments 1: The authors have not calculated the mass of the fluid separated out as a result of crystallization of the mother magma. If we assume water and other volatiles comprised 4-5 wt% of the Lovozero alkaline magma, then the volume of volatile degassed from a large massif (650 square km outcrop size and a depth of at least 5 km) would be enormous. Therefore, it would be hard to understand why the fenitized zone is only less than 4 m thick.
Response 1: Thank you for pointing this out. We roughly estimated the volume of fluid that could have been released during the crystallization of the Lovozero massif. According to Arzamastsev and colleagues (Arzamastsev, A.A.; Bea, F.; Glaznev, V.N.; Arzamastseva, L.V.; Montero, P. Kola Alkaline Province in the Paleozoic: Evaluation of Primary Mantle Magma Composition and Magma Generation Conditions. Russian Journal of Earth Sciences 2001, 3, 1–32), the calculated volume of the Lovozero massif is 1600±250 km3. Depending on the initial water content in the melt (4-6 wt%), the volume of water fluid released during crystallization of the massif could reach 100 km3. Considering such a huge volume of fluid, one should assume the presence of a wide fenite aureole. We have added this information to the manuscript (lines 59-63).
Comments 2: The authors may support or refute the possibility of an upward migration of volatiles in the Lovozero laccolithic massif.
Response 2: We assume that the upward migration of volatiles in the Lovozero massif was insignificant. Lovozero is a layered pluton; in the vertical cross-section of the Layered complex, intensely autometasomatically altered urtite and relatively weakly altered lujavrite alternate with each other.
