Bio-Geochemical Processes: Insights from Fe-Mn Mineralization in the Aegean Sea (Greece)
, Evdokia E. Kampouroglou, Ifigeneia Megremi and Maria Economou-EliopoulosRound 1
Reviewer 1 Report
My major comment concern the field occurrence of studied Mn-Fe deposits. As a field geologist interested in Fe-oxide mineralization, I would like to see in the figures some pictures showing the real occurrence of studied mineralization. With some more details about their size, shape (nodules, tabular, elongate concretions, irregular bodies, etc...), their spatial distribution, and relation with anisotropy (bedding planes, fractures, faults...) - if any.
I've provided a few comments in the attached PDF.
Comments for author File: 
Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
Dear Editor and authors,
the manuscript on “Bio-Geochemical Processes: Insights from Fe-Mn-Mineralization in the Aegean Sea (Greece)” reports the mineralogical and the geochemical characteristics of Fe-Mn deposits (oxides and hydroxides) collected in 4 sites located at the South Aegean Volcanic Arc. Data are based on SEM-EDS and bulk geochemical analyses (oxides and a few trace elements). Although XRD is also mentioned in the methods, no data is provided.
The reported data is interesting and important for the global knowledge of the oxide-hydroxide deposits, but I was expecting to read a clearer scientific explanation on the role of bio-geochemical processes (stated in the title) on the formation of these deposits. On the contrary, I found conclusions more based on assumptions. Although, I believe that some of the presented textures could have a biological mediation, this must be based in clear evidence/data and not in speculation. Also, I would like to highlight that this paper, while presenting additional data, is very similar (including the conclusions) to another paper written by the same authors: Minerals 2018, 8(3), 107; https://0-doi-org.brum.beds.ac.uk/10.3390/min8030107
Additional points to consider:
- the authors should consider substituting Fe-Mn Ores by Fe-Mn Deposits, once ore deposits are earth materials containing elements in sufficient concentration and quantity that can be extracted economically.
Introduction:
- please provide the correct depth and location of the different sites where samples were collected. Also, in figure 1 the sample’s location is not very clear.
Results:
L. 173 – Table 1 - please provide the detection limit for each element.
L. 249 – “Fossilized bacteriomorphic Mn-Fe oxides/hydroxides (Figure 6c, d) coated by a film composed by Na and Cl in a proportion close to that of sodium chloride (NaCl) “- How do you know that these structures are covered by a NaCl film? Did you conclude this from the chemical analyses? Can’t the Na and Cl detected being a consequence of the evaporation of water from seawater that was covering the samples when they were collected (the same for line 62 and 355). What were the methods used to treat samples to guarantee that seawater-derived Na and Cl were completely removed?
L. 434 - please substitute ore by deposits and rephrase.
- I suggest using discriminatory diagrams to distinguish between an hydrothermal and an hydrogenetic origin for these deposits
- in Figures 4, 5, 6: several arrows are shown, however, the caption does not explain their meaning. I can understand that they are pointing for the biological derived textures but this must be explained.
Discussion
L. 317 - the author said that "Such element (Mn in magnetite) deposition and subsequently redistribution may be facilitated by the action of microorganisms. " Why? This conclusion is based on what? justify
L. 331 - "A consortium of micro-organism fossils (white and black arrows) including rods, sphere or coccus, filament-type exhibiting a variation in their chemical composition were found in Fe-Mn ores from Varnavas, Grammatiko, Legrena and Milos (Figures 2, 4, 5, 7; 333 Table 1), suggesting that bio-geochemical processes may be a driving force for bio-mineralization." - this assumption is not based in any clear results. Although those textures could probably indicate the presence of microorganisms, similar textures like spherical structures, acicular, globular micro-aggregates and botryoidal are commonly observed in oxides / hydroxides phases. - Interpretation/conclusions cannot be based on assumptions, clear evidence must be provided!
L. 388 - I do not understand the relevance of section "5.6. Environmental Implications" to the objectives and conclusions of this work.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
