Mineralogy and Pretreatment of a Refractory Gold Deposit in Zambia

Round 1

Reviewer 1 Report

I am not sure that XRF could be trusted for assay below 15 g/t.Results should be validated by pyro-assay.  We have tried using an XRF for gold and found error of +/- 20 g/t. I am surprised to see that oxygen (Table 2) can be measured by XRF...

Page 9 : alena instead of galena

Usually a gold ore is labelled refractory when a standard cyanide leaching test yields recovery below 70%.  I have not found results of any leaching tests in the paper.  On which basis the authors have decided to label the ore as refractory gold? It is not because the ore contains pyrite that it is refractory. About 68% of the gold is in native form and 18% in py+ArsPy, so leaching in oxidizing conditions should give acceptable recovery. WIth a head grade of 16 g/t.  I don't see the advantage of doing a pre-concentration.  Is it  to reduce the size of the downstream equipments?

It is not clear of how the authors intend to process the gravity and flotation concentrate to recover the gold. What do the authors mean by «needs further treatment by metallurgy to obtain the corresponding products»? Is the  corresponding product is gold??

Author Response

Dear Reviewer,

We would like to deeply thank you all for your carefully reviewing our manuscript (Title: Mineralogy and pretreatment of a refractory gold deposit in Zambia, Manuscript number: Minerals-531101). We also thank you for your careful read and thoughtful comments which would help us both in English and in depth to improve the quality of the paper. Based on your comment and request, we have made extensive modification on the original manuscript. We hope that you find our responses satisfactory and that the manuscript is now acceptable for publication.

The following is a point-to-point response to your comments.

 

1、I am not sure that XRF could be trusted for assay below 15 g/t. Results should be validated by pyro-assay. We have tried using an XRF for gold and found error of +/- 20 g/t. I am surprised to see that oxygen (Table 2) can be measured by XRF.

Reply: Thank you for your valuable suggestions .We carefully reviewed and revised the article based on your comments. The grade of gold in the article was based on chemical analysis and had been noted in the text. Please check it.

The oxygen content will displayed when XRF is used for element content detection. After careful analysis and research, we found that the determination of oxygen content by XRF is extremely inaccurate. We have removed it in Table2 according to your comments. Please check it.

2、Page 9 : alena instead of galena

Reply: Thank you for your valuable comment. Based on your suggestion, we have revised it in the revised manuscript. Please check it.

3、Usually a gold ore is labelled refractory when a standard cyanide leaching test yields recovery below 70%.  I have not found results of any leaching tests in the paper.  On which basis the authors have decided to label the ore as refractory gold? It is not because the ore contains pyrite that it is refractory. About 68% of the gold is in native form and 18% in py+ArsPy, so leaching in oxidizing conditions should give acceptable recovery. WIth a head grade of 16 g/t.  I don't see the advantage of doing a pre-concentration.  Is it to reduce the size of the downstream equipments?

Reply: Thank you for your valuable comment. We carefully reviewed and revised the article based on your comments. After carefully reviewing the information, we found that the word "refractory" has several meanings. We want to express that this gold mine is relatively diff cult to separate, not difficult to smelt. In order to give readers a more accurate understanding of the intent of this article, we have made a deletion in the article "refractory". Please check it.

Compared with most domestic gold mines, the gold content of the Zambia gold mine is high. However, due to limited local conditions, the gold mine will eventually be shipped back to China for metallurgical treatment. In order to reduce the transportation cost and reduce the load of the subsequent treatment process, the gold ore is pre-enriched by means of beneficiation. We have revised and explained in the introduction. Please check it.

4、It is not clear of how the authors intend to process the gravity and flotation concentrate to recover the gold. What do the authors mean by «needs further treatment by metallurgy to obtain the corresponding products»? Is the  corresponding product is gold??

Reply: Thank you for your valuable suggestion. We are so sorry that we have not expressed any clear on this issue. The purpose of this study is to pre-enrich the gold mine by means of beneficiation in order to reduce subsequent transportation costs and metallurgical costs. The gold concentrates will eventually be shipped back to China for metallurgical processing to obtain gold. We have further explained this issue in the introduction and conclusions. Please check it.

Author Response File: Author Response.docx

Reviewer 2 Report

The article provides a detailed mineralogical description of the research object, but there are questions and comments.

1. The paragraph “2.2.2.Gravity separation and flotation” gives very brief information about grinding. It does not say what the balls load, what the grinding mode, etc. It is also not said to what size grinding continues and how much time it takes.

More complete information should be given.

2. The text of the article should provide information on the liberation of intergrowths at the grinding stage and the particle-size characteristics of grinded products.

3. According to the results of mineralogical studies, it is clear that there is a presence of gravitational-extractable gold in the ore, but in the text of the article little attention is paid to the gravity processes. Nothing is said about the operation mode of the concentration table, nor is it said about research on other gravitational concentrators (for example, Knelson centrifugal concentrator). No data are presented on the final results of gravitational research and the choice of a gravity beneficiation scheme.

4. It is not clear whether the design of experiment was conducted when choosing the flotation mode. What is the reason for choosing these reagents?

5. In conclusion, it is said that the proposed scheme is economically advantageous, but the article does not include economic calculations, even preliminary ones. A brief justification of this conclusion should be given.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

This is a good original research paper dealing with the gravity–flotation combined beneficiation process to pretreat the refractory gold deposit according to the results of processing mineralogy study.

 

1- Page2, last sentence before Section 2.2; the statement was “According to the results of process mineralogy, the reasons for the low efficiency of beneficiation and the possibility of removing arsenic from gold concentrate are analyzed, and a suitable pretreatment process is proposed to recover the refractory gold ore reasonably and efficiently.” Were gravity and flotation separations used as pretreatment methods before cyanidation of gold in this study? How the authors define the refractory gold ores in this manuscript for readers since it can be defined as “Gold ores are classified as highly refractory when at least 80% of the gold cannot be extracted by conventional cyanidation leaching even after fine grinding” in the literature?

2-Why some recent centrifugal separators like MGS, Kelsey jig or Knelson separator did not used for such a fine liberated ores since these are effective down to 50 µm?

3-Page 3; Section 2.2.2; is there any other grinding conditions for conical ball milling?

4- Table 1 caption; no need to write multi-element

5-What were the operating conditions of shaking table?

6- Since this is a poor organized manuscript, some statements like “The sample was ground to the particle size of 70% passing 74μm for phase analysis” should be replaced to appropriate Section like Section 2.2.2

7-Figure 9; What the term Final means? Tailing or concentrate? Please correct the terms of concentrate for gravity and flotation in the flowchart

8-Figure 10; x axis should be grinding fineness or particle size (m)?

9-please discuss the experimental result with the previously published literature if similar works are present?

10-Figure 12; which one is true? feed size -0.074µm 73% or 70% passing 74μm for phase analysis. 

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

First of all, I would like to apologise for taking so long to finalise my review.

The authors present a method for the treatment of a complex gold or which includes gravity and flotation recovery. The methods applied are well-known laboratory techniques and suit this form of analysis. It is also very pleasing to see mineralogical work was done in advance to gain insights into what the ore delivered, before embarking on a test program. 

I have only minor comments on the manuscript:

The Au feed grade in Table 1, is this correct? This is a very high gold feed grade at 15.96g/t.

Is the As grade 6.5% or should that be 6.5g/t? The same with Table 2. Where is As mainly hosted?

There is no mention of the modal mineralogy of the feed? What are the key minerals in the feed?

Why was a ball mill used instead of a rod mill? Will this not potentially over-estimate liberation and therefore concentrate grades and recoveries?

There is mention of a range of flotation feed densities i.e. 25-40%. Was this tested and what was the best result? Or does this reflect the difference between rougher/scavenger and cleaner flotation feed densities?

Check the spelling of concentrate in figure 9.

On the flotation optimisation side, why was a proper factorial experimental program not followed? This will allow for all reagent dosages to be optimised and considers the possible interactions between them. The approach presented takes a step-by-step approach where the dosage rate of a reagent is optimised in isolation from the other.

As grade in concentrate should be in g/t?

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Taking into account the changes and responses to the comments, the article can be recommended for publication. But it should be noted that a clearance check is necessary (in some places there are missing spaces, etc.)

Author Response

Manuscript Number: Minerals-531101

Title: Mineralogy and pretreatment of a refractory gold deposit in Zambia

Dear Reviewer,

We would like to deeply thank you all for your carefully reviewing our manuscript (Title: Mineralogy and pretreatment of a refractory gold deposit in Zambia, Manuscript number: Minerals-531101). We also thank you for your careful read and thoughtful comments which would help us both in English and in depth to improve the quality of the paper. Based on your comment and request, we have made extensive modification on the original manuscript. We hope that you find our responses satisfactory and that the manuscript is now acceptable for publication.

 

Taking into account the changes and responses to the comments, the article can be recommended for publication. But it should be noted that a clearance check is necessary (in some places there are missing spaces, etc.)

 

Reply: Thank you for your valuable comments. We have made the best efforts to correct the spelling mistakes, grammatical errors, etc. in the article according to your suggestions, and marked them in the manuscript. Please check it.