Indicator Minerals, Pathfinder Elements, and Portable Analytical Instruments in Mineral Exploration Studies

Round 1

Reviewer 1 Report

The authors present a fairly comprehensive panel of the different portable techniques for mining exploration studies and they are very well and clearly presented. Although there are already several review articles on this subject, this article has the advantage of focusing on mining exploration and emphasizing the elements of interest. They also show how to indirectly access certain elements that are difficult to analyze due to their low concentrations. In addition, the authors show the cross-over benefits of these portable techniques. Parts 9 and 10 on the development of these techniques for the analysis of extraterrestrial or deep-sea materials show the value of further development of these analytical techniques under challenging conditions.

Since this article is more of a review article and there are already some available, I suggest that some parts be completed:

Part (4.2) on FTIR spectrometry lacks examples and part (8) on core scanners only deals with LIBS sensors, it would be interesting to add examples with other sensors (XRF, hyperspectral IR…).

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

A review of field-portable and handheld instrumentation is important and will be very interesting for the readers of Minerals. This manuscript is a good manuscript summarizing the current status of field-portable and handheld instrumentation but it is not ready for publication. A major revision is suggested.

Reporting on a review paper is always difficult, since the organization of a review is often a matter of taste, and should not be questioned too much, provided the authors are expert in their field and the information is clear and complete.

 My comments:

1. My first comment is on the definition of the different instruments. Classifying the instrumentation as Portable is fine, to me. My only concern is the fact that handheld LIBS instrumentation is generally referred as hLIBS. Portable handheld XRF instruments are often defined as pXRF, therefore the analogy between pLIBS and pXRF cannot be exploited too much. At the end, most of the portable instruments described here can be considered handhelds since they're compact, lightweight, self-contained units that can be comfortably
used whilst being held in the hand of an operator. Even because the same authors have to take care also about consistency in their text. There are many inconsistencies between portable and handheld in the current version. 

2. It is highly recommended that the authors compile a summary Table listing all described portable instruments with their components, parameters, features, and applications they were used for. Such a table would be very useful for quick referencing, and then the Reader can make specific considerations about what instrument is suitable for a particular application.

3. There is no mention of a long history of instruments in the lab environment. There is almost no comparison of performances of field-portable or handheld instruments versus laboratory instruments. Presenting a relationship between handheld and laboratory instruments would be very important to the Minerals Reader. Figures of merit can be summarized (e.g., a Table) for portable handheld instruments, based on the information presented in the current review. Then the conclusions should be drawn by the authors.

4. Unusually, the Cremers book or other fundamental books on LIBS are not even cited in the section of pLIBS as also some strictly related review papers such as "Spectrochimica Acta Part B: Atomic Spectroscopy 175 (2021) 106013"  and "Applied Geochemistry 128 (2021) 104929". The same general comment is valid also for the other instrumentations.

5. The single sections describing the multiple handheld instruments somewhat unfortunately have repetitions about what instrument and what parameters were used.  Just few examples: row 464 vs  row 474; rows 465 vs 490-493.

6. The comparative data are rare, and thus it would be desirable to accurately compile and present it in a separate section. A summary table with LODs, RSDs and other figures of merit attained by handheld instruments is strongly suggested.

Some minor comments:

row 343: "Usually, pressed pellets of samples prepared in the field are used for analysis." Please explicit better this sentence. Do you make pellets in field?

row 455: "...high resolutiom imaging in the field" this sentence is quite risky more correct what you say few lines below at rows 508-509. Please reformulate.

row 461 : "...depending on the laser wavelength." This is absolutely not the only effect affecting it. These others should be considered wavelength and pulse duration of laser, chemical composition of the target material, matrix effects.

rows 480-481: add reference to this sentence.

Fig. 9: the caption of this figure is not appropriate. Please modify it.

These suggestions and comments are intended to help the authors making their paper better.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Dear authors
I am pleased with the corrections and new paragraphs on other techniques that you have made. Table 3 gives a good visibility on the choice and interest of the different techniques that can be used in the field of mineral exploration.

Sincerely,

Reviewer 2 Report

The manuscript has seen a substantial improvement by addressing most of the reviewers' criticisms.