The Importance of Mineralogical Knowledge in the Sustainability of Artisanal Gold Mining: A Mid-South Peru Case

Round  1

Reviewer 1 Report

The authors present a survey of the mineralogy in a gold mining region in mid-south Peru. This area is an active region for artisanal gold mining, which supports the local economy. Because these miners have limited knowledge of the local geochemistry, the methods for gold extraction are rarely optimised. The survey includes analysis of the geology, minerology of gold-rich regions and veins, and details of the mineral processing. The photographs, SEM and elemental analyses are valuable information in characterising the ore samples. The analysis of tailings in several sites also provides information about the gold recovery efficiency and the amount of gold lost in tailings. Supporting ASM is important in developing economies and surveys such as those reported here are valuable to the mining advocates. The study should be published after taking into account the following minor comments. The authors might consider adding another section at the end of the paper and issue some recommendations to miners, their advocates, or NGOs operating in this region. It would be good to combine the knowledge of the ore types, the common mining practices, known losses in gold recovery, and suggest methods that can improve gold recovery based on this information. It might also be good to make some recommendations that can help improve gold recovery, minimise the use and release of mercury, and point out specific ways in which current practice falls short and ways to improve these methods. The authors might consider noting that moving toward clean mining will be a global priority as the Minamata Convention comes into force. The authors can cite relevant references for this aspect of mercury and ASGM. The authors rightfully note the environmental impact of using mercury amalgamation in ASM.  The following review should be cited in which the mercury problem is detailed: The Mercury Problem in Artisanal and Small-Scale Gold Mining, Chem. Eur. J. 2018, 24, 6905-6916 Other minor changes: In the first sentence of the main text, please revise the abbreviation for ASM – It should be Artisanal and small-scale gold mining (ASGM) or Artisanal and small-scale mining (ASM). Some of the scale bars and labels in the micrographs are difficult to see (for instance the SEM image in Figure 6i, Figure 7a, and the optical microscopic images in Figure 8a, 8b, 9a and 9b) – please check the units for these images as well – the μ looks closer to a u in some places – please check for all images.

Author Response

Dear reviewer

Many thanks for your revision, that sure will improve our manuscript. --We read and added the reference that you suggested.

-A subsection of final recommendations was added.

-The suggested reference on mercury pollution was read and included. Also reference to the Minamata convention was included. We don’t extent more about the specific problematic of mercury because we are working in another paper related to this topic. The present paper tries to highlight the important role of mineralogy to plan the strategy of gold recovery.

The complete name of the ASM acronym was corrected in the first sentence.

The scale bars of figures were drawn again.

Author Response File: Author Response.pdf

Reviewer 2 Report

The article seems to be a mineralogical review of different gold deposits in Mid-South Peru, which are currently being mined at artisanal scale. However, the title promises to stablish some relationship among mineralogical knowdege and sustainability at that artisanal scale, and that promise is not acomplished in the paper. No reference is made on how we can understand "sustainability" at artisanal scale, and what is worse, which role can play the mineralogical knowledge.

But the problem it is not only the lack of accuracy in the title (which could be solved with a minor revision). Along the manuscript, some details show clearly a lack of soundness (apart from the terrible translation). For instance:

In the Introduction or in the very Abstract can be found references to several cities with no mention to the figure 1, as if that cities must be well known by the reader.

Also, in line 56 it is mentioned "degree of recovery", which is commonly named as "recovery" in the technical literature.

Again, in line 122 it is mentioned a "Fairmined certification" without reference to the certifying entity.

In several opportunities along the manuscript it is mentioned that amalgamation is not used nowadays, but without reference to sources who could verify that extent. Moreover, in line 202 assumes that in some mines amalgamation is still the processing methodology.

Minind and mineral processing technologies description (paragraph 2.3) is very poor.

Materials and methods section is really lack of relevant information, for instance regarding sampling process to ensure representativeness, both in mineral sample and in tailings)

Results section has a good description of a mineralogical study, which is State of the Art. Nevertheless, line 294-294 has no sense.

Paragraph 4.4 has low credibility without a sound description os the sampling process.

In Discussion, line 376 is really meaningless for gold artisanal miners; regarding paragraph 5.1.2, there is a poor description of the available technologies in the case of gold refractory ores; special mention must be made at line 420-421, where reference to HF treatment is made (a very hazardous acid to be handled by artisanal miners?...)

Line 434 to 442: discussion on the advantages of cyanidation is obvious, unless related with the condition of artinsanal miners; 

Paragraph 5.2 is really out of place; it seems to be a revisiting of posible techniques but not linked to the artisanal mining  reality (phytoextraction? direct smelting? chlorination??)

In summary, the objectives of the paper are not specifically declared, the Methodology and Results sections lack of soundness (specially when speaking about sampling), the Discussion is not really linked to the artisanal scale reality, and finally the Conclussions do not give the necessary answers to the Objectives.

So the final recomendation is that this paper is nor suitable for publication in Minerals under the present form.

Author Response

Dear reviewer

Many thanks for your revision, that sure will improve our manuscript.

Comments and Suggestions for Authors

The article seems to be a mineralogical review of different gold deposits in Mid-South Peru, which are currently being mined at artisanal scale. However, the title promises to stablish some relationship among mineralogical knowdege and sustainability at that artisanal scale, and that promise is not acomplished in the paper. No reference is made on how we can understand "sustainability" at artisanal scale, and what is worse, which role can play the mineralogical knowledge.

A reference of sustainalitily was now introduced.

But the problem it is not only the lack of accuracy in the title (which could be solved with a minor revision). Along the manuscript, some details show clearly a lack of soundness (apart from the terrible translation). For instance:

In the Introduction or in the very Abstract can be found references to several cities with no mention to the figure 1, as if that cities must be well known by the reader.

Now, we cite Figure 1 in the introduction, the first time that we mention artisanal locations.

Also, in line 56 it is mentioned "degree of recovery", which is commonly named as "recovery" in the technical literature.

We deleted “degree of” everywhere.

Again, in line 122 it is mentioned a "Fairmined certification" without reference to the certifying entity.

This was explained in line 109, where we indicated that this is obtained from Alliance for the Responsible Mining (ARM)

In several opportunities along the manuscript it is mentioned that amalgamation is not used nowadays, but without reference to sources who could verify that extent. Moreover, in line 202 assumes that in some mines amalgamation is still the processing methodology.

There are not references because we explain this respect to an area that we studied.

Line 219 we added “of the visited”. We don’t specify because continuously miners are reducing the use of mercury.

Minind and mineral processing technologies description (paragraph 2.3) is very poor.

We tried to improve this part, although this is not the objective of the article.

Materials and methods section is really lack of relevant information, for instance regarding sampling process to ensure representativeness, both in mineral sample and in tailings)

We explained the sampling more carefully.

Results section has a good description of a mineralogical study, which is State of the Art. Nevertheless, line 294-294 has no sense.

OK, we delete “yield”

Paragraph 4.4 has low credibility without a sound description os the sampling process.

We increased the explanation of the sampling process.

In Discussion, line 376 is really meaningless for gold artisanal miners;

Why not?, in some cases there is more that 1 wt.% Cu, this is important.

regarding paragraph 5.1.2, there is a poor description of the available technologies in the case of gold refractory ores; special mention must be made at line 420-421, where reference to HF treatment is made (a very hazardous acid to be handled by artisanal miners?...)

the only way to destroy quartz is with the dissolution in HF. We don’t say that it is the best option, in fact we said that cyanidation is not the best option.

Line 434 to 442: discussion on the advantages of cyanidation is obvious, unless related with the condition of artinsanal miners;

Paragraph 5.2 is really out of place; it seems to be a revisiting of posible techniques but not linked to the artisanal mining  reality (phytoextraction? direct smelting? chlorination??)

We increased this paragraph according to the indications of other reviewers and tried to link them with artisanal mining.

Author Response File: Author Response.pdf

Reviewer 3 Report

I thought this was a very well-written and interesting paper.  Really enjoyed the figures as well.  The only thing is that I would add more content towards the end: the section where you discuss alternatives, you need to state these and their shortcomings.  Please feel free to access that information in both: Zolnikov, T. R. (2012). Limitations in small artisanal gold mining addressed by educational components paired with alternative mining methods. Science of the Total Environment, 419, 1-6.  And Zolnikov, T. R., & Ortiz, D. R. (2018). A systematic review on the management and treatment of mercury in artisanal gold mining. Science of the Total Environment, 633, 816-824.

The final paragraph needs more content on future suggestions, solutions, ideas.  Research, implementation, intervention ideas?  Limitations, etc.  Just add more in that regard.

Author Response

Dear reviewer

Many thanks for your revision, that sure will improve our manuscript.

-We read and added the references that you suggested.

-According to your suggestions a subsection of final recommendations was added at the end of the discussion.

Author Response File: Author Response.pdf

Round  2

Reviewer 2 Report

The paper has been improved. English revision should be performed.

Author Response

Dear reviewer

The English was completely revised along all the document. Mistakes were corrected, Two repetitive paragraphs were deleted. The english style has changed to the American. 

Author Response File: Author Response.docx