Uranium Mineralization of Fossil Wood
Round 1
Reviewer 1 Report
The manuscript by George Mustoe on uranium mineralogy in fossilized wood is very interesting and a very good read. As the author mentions in the conclusions: "Specimens in collections commonly lack detailed provenance information. This report suffers from those limitations, and in many instances a uranium claim is represented by only a single specimen." however, because very limited information is available on the mineralogy of uranium within fossilized wood, I think this manuscript deserves publication, not least because I think this manuscript once published will provide a lot of questions for further research, both observational and experimental to provide further evidence on the mechanisms of uranium mineralization within fossilized wood, but also with respect to the mechanisms of uranium mobility within modern environments.
In my opinion this manuscript can be published with minor corrections as noted below.
Overall, I think the manuscript is well written, though the author should go through the manuscript to correct several typos and possibly references to incorrect figures (of which i will highlight a couple below). Additionally, and specifically because the mineralogy described in the manuscript is quite "obscure"/uncommon, I think that the manuscript could benefit of a table with the chemical formulae of all minerals described within the document and the chemical formula in brackets when first mentioning specific minerals. This would prevent readers to move away from the manuscript to continuously search for minerals online when these are introduced.
Specific comments:
L13-14, I would include that these are uranyl vanadate & sulfate minerals.
L35-38 "Under oxidizing conditions, uranium has relatively high solubility, and sedimentary ore deposits typically occur where uranium dissolved in groundwater encounters reducing conditions, causing the element to precipitate as “pitchblende” (uraninite, UO2).":
To note: the author is correct that U(VI) is highly soluble, but it also complexes heavily to natural organic matter.
L45-51: "The abundance of abundant wood and organic debris in Mesozoic uranium deposits in the Colorado Plateau can be explained by the nature of the mineralization process, which was initiated when uranium-bearing groundwater permeated the porous sediments of ancient river channels, a paleoenvironment that was likely to contain driftwood logs and woody debris. Uranium precipitation occurred in direct response to reducing agents produced by decomposition of the plant tissue, and compounds released by anaerobic microbes that benefited from nutrients released from the decaying wood [5,6]."
As U(VI) complexes heavily to natural organic matter, this process could provide an initial accumulation of uranium, following that microbial activity could induce the formation of reduced uranium precipates.
Figure 3: It's unclear whether these are BSE or SE SEM images. If these are BSE images, why does uraninite appear darker then chalcopyrite?
L66-67: "My studies reveal that in oxidized ores the uranium mineralization of fossil wood is very different from fossil wood in the primary ore zones.": Doesn't this need a reference, or is the author referring to the presented manuscript (in which case this should be clarified)?
Figure 14: To me these look like SE SEM images.
L238: a typo in "aluminum"
L257-258: "This mode of mineralization from the early descriptions of uraninite-mineralized wood (Figure 3)": This sentence does not look finished.
L263-264: "The latter mode of occurrence is perhaps analogous to the “vanadium clays” that have been reported from other mines in the American Southwest [13].": please briefly describe this "vanadium clays" mode, I haven't a clue what this means.
L315-323: "SEM/EDS spectral data (Figure 18, Table 2) provide clues for identifying the vanadium mineral. The major constituent elements are Fe, V, Ca, and O. The Fe:V ratio is close to 1:1, suggesting five possibilities (Table 3). Monument #2 Mine is the type locality for navajoite (Weeks et al. 1954); the mineral is commonly present in sandstone in the uranium ore zone (Figure 22). Montroseite and fervanite are important vanadium ores of the Uravan mining district in Colorado; both minerals have been informally reported from the Monument #2 Mine by mineral collectors, but the justifications for the identifications are not reported. Navajoite seems like the most likely correct identification for this sample. The presence of ~6 atom% Ca can be explained by the affinity of this element for vanadium, as evidenced by the presence of hewettite, CaV6O16.9H2O, at the Monument #2 Mine [13].": I think this needs to be Figure 22 instead of 18.
L335: "The relationships between mineralization and wood cell anatomy are unclear.": Is this a general statement, or about a specific sample? I assume this is about a specific sample, but I don't know why or where to look for this...
L354-356: "Distinctive characteristics of ore from this district [8] include mineralization of carbonaceous material with low-vanadium coffinite, abundance of calcite, and geometric fractures filled with amber- colored barite (Figure 25).": I think this might need to be a reference to figure 24 instead of 25.
Figure 26: The silicon & sulfur peaks in A & B appear very small for coffinite & zippeite, respectively.. Can the author elaborate on this?
L387-389: "Uranium levels are low in both the barite and calcite, but high magnification SEM images show that small amounts of uranium occurs in some calcite crystals (Figure 27D).": Does the author have EDS evidence that in fact these bright-ish inclusions in calcite are uranium bearing minerals (and not e.g. barium bearing minerals)?
L453: typo in "mineral"
L500: This is the first mention of autunite in the manuscript. Did the author mean zippeite?
L504-508: "other modern analytical methods potentially offer additional possbilities for studying mineralization of carbonaceos maaterials in uranium deposits. In recent years, uranium ore minerals have been studied in using micro X-ray fluorescence (μXRF), inductively coupled plasma mass spectrometry (ICP-MS), and isotopic analysis. (For comprehensive references, see [29]). ": typos in "possibilities", "carbonaceous" and "materials". To note: there are several other analytical techniques not mentioned here (specifically techniques that could help understand the occurrence of uranium in opal), like: luminescence spectroscopy, (micro)X-ray absorption spectroscopy, and microXRD.
Author Response
Please see attached document
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This paper is focused on doing some very basic characterization (basic petrographic analysis followed by EDS elemental characterization) of a collection of uranium ore samples. I think there is room for this kind of study in the community, but because there are a lot of recent works focused on understanding uranium mineralogy utilizing much more advanced approaches (e.g. with XRD, TEM, Raman, Neutron Scattering, etc), the paper needs to emphasize right away that the goal is really to characterize a suite of natural samples at a basic level. The interest from the community would be in the fact that many of these samples are from mines that are no longer accessible for sampling etc. However, the paper in its current conception does not really rise to the level at which uranium mineralogical studies are being conducted (e.g. the tools utilized are rudimentary (SEM and EDS); there is no phase modeling to support the mineralogical conclusions). Another major issue is that there are a lot of unsupported statements (e.g. more references are needed, especially for recent studies in this field). The introduction provides a historical narrative of uranium prospecting in the American southwest, however, many of the statements need better referencing (especially those about uranium behavior under different redox conditions). There is a lot of literature out there at the moment about uranium mineralogy (see the recent publications coming from Peter Burns and Tony Simonetti at Notre Dame). If the paper can be fine-tuned for what it is (a descriptive study of samples that are no longer accessible, with some hypotheses about mineralization processes), than I think it is publishable.
Some of the graphics need serious improvement (e.g. figure 5) as well.
Minor comments:
Line 20-21- The statement about Uranium tinted glass from 79AD seems a little out of place- do you mean to use this statement to support the initial statement that uranium had little use for most of human history? Please clarify.
Line 30: It would be good to add a reference for the IAEA classification scheme.
Line 38: Some references about uranium mineralization under various redox conditions would be useful here.
Line 43: Boon or Boom?
Lines 45-48: Reference needed.
Line 66: ‘My studies reveal’; is this is a mistake?
Lines 72-73: These two statements seem out of place. Unless you can link them to processes taking place during/after uranium mineral precipitation.
Line 76: Reference?
Figure 5: This graphic can be greatly improved. Perhaps a geologic map underlay that includes the different mining district outlines, with the precise sample locations shown? If the precise locations cannot be shown, there is probably little value in showing a map like this.
Line 133: There has to be more information about the specimen localities- the map basically shows no useful information. Maybe this does not matter for the study, in which case the map can be done away with.
Lines 493-496: This information should probably go up in the section where the sampling strategy is discussed. It is understandable that not much information about the sample locations is available, but this should really be conveyed more clearly earlier in the paper to avoid readers thinking that there is a critical piece of available information lacking from the study.
Lines 503 – 508: This statement does not add any value. It is generally understood within the community that people study uranium minerals with tools like XRD, Raman, TEM, and other more advanced techniques. If more references were to be added citing some of the recent work in this field, the paper could be much improved.
Author Response
Please see attached document
Author Response File: Author Response.pdf
Reviewer 3 Report
Please see attached some comments re language and grammar. Introduction covers too much of the actual topic and should be more focused on the aims of this study and how this study fits with the existing body of work on the broader topic and deposit style.
Comments for author File: Comments.pdf
Author Response
Thanks for the encouraging review. I have made the changes you have suggested. These are:
- Add references for IAEA list of uranium deposit types.
- Fix several small wording errors
- Add inset map for Figure 1
Thanks for the help.
Round 2
Reviewer 2 Report
The author has made a good faith effort to address my concerns; I believe the paper is now ready to be accepted.
