General comments

I have read with interest the article “Development of an integrated analytical platform of clay minerals separation, characterization and 40K/40Ar dating”. The K-Ar dating of clays, particularly illite, has been used for sixty years but has had a renaissance in the last two decades. Its application to diagenesis and structural processes (faults, tectonic uplift, low-grade deformation, water circulation, and others) has promoted its use. The K-Ar method is particularly well-suited to the dating of clays, as the 40Ar-39Ar method, although more powerful, is analytically and interpretatively difficult in this case. It should be added that the closure of several Ar-Ar laboratories worldwide makes establishing a new K-Ar laboratory good news.

After a few detailed readings, I have not found any major problems in this contribution, which seems well-detailed and structured. However, some minor points need to be adressed, so I suggest it be published with minor revisions.

Since there are a few points to discuss, I have listed them below by line number, regardless of whether they are minor typographical errors or points that need better discussion. I am not a native English speaker, but I believe the manuscript is well-written. There are some minor language details that I have marked and perhaps some others that I have not detected.

Specific comments

Title. I propose three minor changes: “Development of an integrated analytical platform for clay mineral separation, characterization, and K-Ar dating.” The first two changes are grammatical, and the last is a suggestion to standardize the title with the main text where the term K-Ar is always used.

Line 27. Change to: “... detailed by Schaeffer and Zähringer (1966) and by ...”

Line 31. Point (1) is not strictly true. There is evidence that electron capture is affected by pressure, but this does not affect any "real" dating by the K-Ar method.

Line 32. Point (2) is erroneous. The 40K/K ratio decreases over time; this is the basis of the K-Ar geochronometer. The authors mean that it is constant for all samples at present, which is also strictly false, but within the margins of error currently achievable, it can be considered true.

Line 32. Point (3) needs to be worded a little differently, as stating that all 40Ar comes from the decay of 40K does not exclude 40Ar trapped during the rock's formation and originating from the decay of 40K before the system closed. The later point (5) also does not eliminate this case. Saying that 40Ar comes from the decay of 40K within the mineral will solve the problem.

Line 33. Point (4) we know is false, but we must assume it for atmospheric correction. In any case, most of the air in the extraction lines has a modern atmospheric composition. A different case occurs when measuring very old samples with trapped air bubbles (fluid inclusions) that could give values different from modern air (and that have been studied for this reason).

Line 34. As mentioned, point (5) does not exclude radiogenic argon trapped during rock formation.

Line 35. “The latter might be hypothetical ...” I would say it is typically false in these cases, which is why K-Ar (Ar-Ar) can be used to obtain data on the thermal history, as detailed already in the manuscript.

Line 39. “This age is then related to ...” I would modify this sentence as follows: “This age is related to the crystallization event in the case of fast cooling (e.g., unaltered volcanic rocks), the closure time for slow cooling rocks (e.g., plutonic, metamorphic) or ...”

Line 53. “One of the main concerns ...”

Line 61. The word “desorption” introduced here and used later raises some doubts. The Merriam-Webster dictionary defines it as “to remove (a sorbed substance) by the reverse of adsorption or absorption.” But this is not what happened with argon; argon was not absorbed. It would be better to name it ‘the extraction line,’ but I will leave it to the authors' discretion.

Line 68. “... (40Ar*, radiogenic daughter) ...”

Line 72. “... depends on the age and the argon content ...” It would be better to say “... depends on the argon content, i.e., potassium concentration and age ...”

Line 76. “... of argon ...”

Table 1. The lambda-beta value of Steiger and Jäger is 4.962. Where do the errors come from? They are not specified in the Steiger and Jäger publication.

Line 85. From here to the end of the article, including the tables, it is unclear whether the errors are expressed as one or two standard deviations. If the deviations differ, they should be stated now or noted on each occasion.

Line 102. “... released during sample melting ...”

Line 102. Add carbon dioxide to the list; it is quite common.

Lines 114-116. “To compare one analysis to another ... and a charcoal trap.” Is there a lot of volume change in the complete line? I assume the problem is the furnace.

Line 117. According to the published graphs by physicists, the highest cross-section of electronic impact ionization for argon is 80-100 eV, so why is the source regulated at 60 eV? To diminish the background?

Line 125. The sensitivity of the spectrometer also depends on the transmission, typically controlled by the slit widths and the quality of the focus given by the ion source, the magnet, and additional electrical filters, if any.

Line 139. Figure 4 and equation (2). The Y-axis value of Figure 2 is given in pA, but equation (2) seems to provide the values in fA. This should be stated in the text or Figure 2 modified accordingly. What is the relationship between the 40Ar intensity of -644 fA when DE=0 (i.e., no gas) deduced from equation (2) and the values of the analytical blank in Table 2, discussed below? The correlation in Figure 2 is very good, but I would expect the intersection to be positive, implying a positive analytical blank (atmospheric or otherwise). Is there any correction somewhere in the calculation?

Line 150, Figure 5. It seems to me there is some error in the equations under the figure. Perhaps it needs to be explained better how the equations are derived, particularly (3); see the comment below.

Line 153. “The number of 40Ar* atoms released per gram of sample is then:”

Line 153, equation (3). It should be better explained what DEs and DEp are, and it should also be stated that m is the mass in grams.

Lines 163-164. Is the oxygen peak sufficient to know that there is not still too much water, hydrogen, carbon dioxide, or hydrocarbons in the line? If the spectrometer is used to scan, it means the sample has already been introduced; does this not delay the first argon reading too much from time zero? Wouldn't it be better to have a "pipette" with a gas quadrupole in some section of the line to sample a small (but constant) volume of the gas before introduction? The information these instruments provide about the vacuum quality is very significant. Once you have tried one, you cannot work without it.

Lines 167. “... the absence of radiogenic argon in the system ...” But there could also be hydrocarbons, or HCl at mass 36, that modify the 36Ar reading, not just radiogenic argon.

Lines 170-172 and Table 2. In my opinion, the composition of the electronic blank can be problematic. The values are certainly much lower than those of the furnace blank in the case of 40Ar, but in the case of 36Ar, the negative signal value is very close to the 36Ar of the furnace blank. Since it is unclear how the 4.7 fA of the furnace blank has been measured, I cannot confirm. However, suppose the value of 4.7 fA is directly the reading of the multimeter (or the equivalent conversion of voltage to current). In that case, the "base" value of -1.0 fA should be subtracted, giving 5.7 fA, which is not an atmospheric blank (40Ar/36Ar = 1358.8/5.7 = 238.4). The furnace blank may have some atomic or molecular species at 36 Da that is not 36Ar. If the same calculation applies to the "1 DE" values, the 40/36 ratio would be 298.6, which is exactly the value of air. I think the AX amplifier should be adjusted; it surely has a circuit to adjust the zero (offset) with a potentiometer to leave it positive, not negative, to avoid possible confusion. These comments might seem exaggerated, but we must consider that the latest-generation spectrometers have very stable electronics and provide high-precision data, so these details are relevant. All this should be clarified in the manuscript.

Table 2. The furnace blank is quite high, approximately 0.1 V for 40Ar. In modern laser systems, the blank is much lower by two or three orders of magnitude. According to the text, I understand that this is compensated by the weight of the samples analyzed, which makes the signal, on average, about ten times larger than the analytical blank. Even so, reducing the furnace blank by an order of magnitude would be a good goal.

Line 177. “Three micas (or related) ...” It is better to say “Three phyllosilicates (muscovite and glauconite) ...”

Line 191. “... various illite polytypes ...”

Line 237. “... using a Bruker D2 ...”

Line 243. “... (Kübler, 1966) ...”

Lines 337-338. Another explanation is that, at atmospheric pressure, heating oxidizes the Fe+2 that may be present, and the weight increases slightly, causing the weight loss due to water loss not to be so great. This phenomenon often occurs when determining the loss on ignition (LOI) of rock samples.

Line 348-349, equation (5). What is the value of the sensitivity S? With the data provided in the article, I inverted the equation and obtained S=1.5e-11 pA/at. Is this correct?

References

The Charbit et al. citations in the bibliography and the text are 1984a and 1984b, but they have been repeated in the bibliography, and both references are the same.

In the main text, line 375, Eremin (2005) is cited, which is not in the bibliography.

The Kübler, B (1966) citation is misspelled (“Klübler”).

In line 238, Moore & Reynolds (1997) is cited but does not appear in the bibliography.

In line 334, Zimmermann & Odin (1979) are cited but do not appear in the bibliography.

I hope these comments are helpful to the authors and that I have not misunderstood anything.

Sincerely,

Jesús Solé

Does the paper address relevant scientific questions within the scope of GI?

1. Does the paper present novel concepts, ideas, tools, or data? YES
2. Are substantial conclusions reached? YES
3. Are the scientific methods and assumptions valid and clearly outlined? YES
4. Are the results sufficient to support the interpretations and conclusions? YES
5. Is the description of experiments and calculations sufficiently complete and precise to allow their reproduction by fellow scientists (traceability of results)? YES, with some comments.
6. Do the authors give proper credit to related work and clearly indicate their own new/original contribution? YES
7. Does the title clearly reflect the contents of the paper? YES
8. Does the abstract provide a concise and complete summary? YES
9. Is the overall presentation well-structured and clear? YES
10. Is the language fluent and precise? YES
11. Are mathematical formulae, symbols, abbreviations, and units correctly defined and used? YES, with some comments
12. Should any parts of the paper (text, formulae, figures, tables) be clarified, reduced, combined, or eliminated? NO
13. Are the number and quality of references appropriate? YES
14. Is the amount and quality of supplementary material appropriate? -

General comments

The manuscript by Gerardin et al. contributes to development of the K-Ar dating technique. This technique is known already for decades and numerous studies on various mineralogical phases  have proved its feasibility for conducting the material formation ages in time range from thousands to billions years. This method is also promising for in situ chronology applications and is of considerable interest for future landing planetary missions (e.g. on Mars). Though, the instrumentation used to analyze the abundances of K and Ar differs to the current method, the performance studies showed its applicability for in situ application. Among other interest clay material considered here is  important mineral phases in searches for extinct and extant life on the other planets. Thus, the current studies can be helpful for the currently important topic in planetary sciences.

The manuscript described  the studies conducted on illite which is isolated from clay phase by authors by using  isolation system specifically developed for this application.  The abundance analysis and dating  results are convincing and encouraging proving  feasibility of the current approach for delivering accurate and precise  analysis of even uneasy samples. The manuscript is well-structured and the experimental part sufficiently detailed so could be reproduced with an ease by others if necessary.

Overall this is well-written manuscript, well justified with respect to analyses of clays, important group of mineral phases and the results of analysis are of high quality. At this point, I do not see also any minor corrections to be added to the last version of manuscript. Thanks to first reviewer my job here is easier and  again, followed  the first reviewer I recommend publishing the manuscript after the last changes.