A Mine Closure Risk Rating System for South Africa

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors' article is devoted to an important and topical issue related to the development of a comprehensive risk assessment system for the closure of mining mines.

Rising environmental expectations, the desire to reduce health risks, the competitive attractiveness of land and the increasing value of the environment as a recreational resource are significant drivers for improvements in the mining sector. This type of pressure has led to significant improvements in mining regulations and practices in many countries. Indeed, in response to social and regulatory pressure, many mining companies and authorities around the world have adopted technologies, as well as policies and management practices, that have significantly reduced the negative environmental impacts of the mining industry.

Mine rehabilitation is an ongoing program designed to restore the physical, chemical and biological qualities or potential of the air, water and soil regimes (disturbed by mining) to a condition acceptable to regulatory authorities and subsequent users of the land. The objective of mine closure is to prevent or minimize long-term negative impacts on the environment and to create a self-sustaining natural ecosystem or alternative use of the land in accordance with an agreed set of priorities. The process of operating and closing mines must take into account the expectations and concerns of the public, government requirements, the profitability of the project, and also minimize the impact on the environment.

Moreover, operation and closure must be carried out in a manner that avoids compromises to human health and future safety; protect the environment and resources from physical and chemical destruction; the subsequent use of the territory was profitable and sustainable in the long term.

The research presented in the work will undoubtedly be of interest to readers in the field under consideration.

 

However, it would be necessary to clarify a number of comments that are available to the article:

1. The introduction should pay more attention to the closure of coal mines, which constitute a large proportion of all mines in Africa. Categories of environmental risks for the mining industry and specific examples for coal mines should be provided. In particular, consider the issues of greenhouse gas emissions (active ventilation of methane from mines, chronic seepage of methane from mines), emissions from burning rock dumps, and aerological risks. The following works could be analyzed: https://doi.org/10.3390/fire6030095, https://doi.org/10.21177/1998-4502-2023-15-2-234-245.

2. A comparative analysis of the historical mine closure areas in South Africa shown in Figure 1 should be undertaken with similar areas in other regions of the world. This is necessary to form a more holistic systemic concept for assessing the risks of mine closure.

3. In sections “1.2. Mine Closure", "1.3. Mine Closure Risk”, the presented theoretical aspects could be confirmed with specific practical examples.

4. It is not entirely clear whether the methods of expert assessments and cluster analysis are used when considering various factors influencing the risks of mine closures. What does expertise consist of? (Figure 2).

5. The presented methodology should include the equipment and software that will be used to achieve the goals set in the work.

6. On the data presented in tables 1-6, a correlation analysis should be carried out between the provinces under consideration, the mines being closed, various risks, population, etc. and present the corresponding correlation coefficients, which can be used as the basis for the developed concept of possible risks when closing mines.

7. In the presented work, it is necessary to present the forecast values of the various parameters under consideration for short-term and long-term periods of time. The most effective way to do this is to use machine learning methods based on artificial neural networks (https://doi.org/10.3390/en15238919).

8. The work does not provide prospects for further research on specific objects and specific practical results.

9. A generalized methodology for conducting research related to the development of a risk assessment strategy for mine closures using the methodology used in the work should be provided, so that it can be used by other authors when conducting similar studies.

10. The work must be supplemented with scientific and practical results.

Author Response

Response to Reviewer 1

1. The importance of coal mine closure is highlighted in the paper in the Introduction, Results and Conclusion. I do not believe that a detailed analysis of environmental issues for coal mining is appropriate for the paper, which is focused on the development of a national rating system for all mines and all aspects of mine closure risk. The influencing factors and indicators used in the environmental risk rating capture the hazards posed by coal mining to biodiversity, water resources and agriculture.
2. I believe that a comparative analysis of historic mine closure is beyond the scope of this paper and is not necessary to inform a South African mine closure risk rating system.
3. Practical examples from South Africa have been added to section 1.2 and 1.3.
4. Clarification on the experts has been provided in subsection 2.4 which has been renamed Expert review to correlate with Figure 2.
5. The only software used for the study was ArcGIS Pro and Microsoft Excel and this has been added to the Methodology section.
6. Correlation analysis between provinces, regions and commodities would be very interesting but unfortunately was beyond the scope of this project. It has been included in the Discussion section 4.2 under future research.
7. The paper presents a first attempt at a national mine closure risk rating system and recognizes that it could be improved in certain ways. It uses current data on operating mines to calculate the ratings and not future forecasts, which are beyond the scope of this paper.
8. The discussion section has a subsection titled Data gaps and future research.
9. I am not sure if I have understood this comment properly, but the methodology summarized in Figure 2 and described in the subsections of section 2 are meant to provide sufficient details on the methods so that others can perform similar studies in other countries. Figure 2 has been modified to illustrate the process flow in determining the risk ratings.
10. The results section provides risk ratings based on practical and scientific data for 230 mines in South Africa. This paper is not merely a framework and a methodology but it also shows the results from years of work on data collection and analysis, enabling actual figures to be calculated and plotted. The underlying data will be published as supplementary information.

Reviewer 2 Report

Comments and Suggestions for Authors

This paper is well structured, and its subject matter is important for assessing the impact of mine closures on local communities in South Africa so that the necessary measures can be taken in high-risk areas. For the improvement of your work, I can only suggest a few minor changes:

• Delete unnecessary spaces in the entire text.
• Lines 40-53: Referring to which of the circled areas (in Figure 1) for the case studies mentioned in the text.
• Line 116: Replace …and application of a novel with …and proposition of a new.
• In the methodology section, The risk is a product of likelihood with the impact, so we may need to change the titles Social Risk and Environmental Risk to Social Impact and Environmental Impact, respectively. It is better to modify accordingly to generate one risk rating parameter instead of three separate ratings. I provide you with three relevant kinds of literature to help with your research; see If you found it appropriate to use in your citation list:

Amirshenava, S., & Osanloo, M. (2018). Mine closure risk management: An integration of 3D risk model and MCDM techniques. Journal of Cleaner Production, 184. https://doi.org/10.1016/j.jclepro.2018.01.186 

Siu, M. F. F., Leung, W. Y. J., & Chan, W. M. D. (2018). A data-driven approach to identify-quantify-analyze construction risk for Hong Kong NEC projects. Journal of Civil Engineering and Management, 24(8). https://doi.org/10.3846/jcem.2018.6483 

Galetakis, M., Deligiorgis, V., Steiakakis, E., Raka, S., & Alheib, M. (2022). Risk Assessment Methodology for Pit Lakes Instabilities. https://doi.org/10.3390/materproc2021005092 

• In section 2.1.1, you must refer to which two parameters are not used in the rating system and why.
• Reshape tables 1-2 to reduce column size for better representation.
• In Table 4, an orange underline appears in the Indicator title.
• In Table 6, you can add colour shadow to emphasize risk categories (red for high. Yellow for medium, and green for low impact and high likelihood).
• Need to enhance your conclusion section.

Author Response

Response to Reviewer 2

• Unnecessary spaces have been removed.
• Figure 1 has been updated to show the cases mentioned in the text.
• Text in Line 116 ‘…and application of a novel’ has been replaced with ‘… and proposition of a new’.
• The terms social risk and environmental risk were used as they incorporate both likelihood and impact within the factors and indicators. I believe that it is important to maintain separate parameters that highlight likelihood of closure, risk of social impact and risk of environmental impact as they are very different and require different policy and management responses. This approach was supported by experts during the study.
• The two parameters in section 2.1.1 that are not used are identified and explained.
• Tables 1 and 2 have been reshaped to align with the text and reduce column size.
• I do not see any orange line so I assume this was an error in the pdf document.
• Colours have been added to Table 6 to show risk categories.
• The conclusion has been enhanced.

Reviewer 3 Report

Comments and Suggestions for Authors

The article contains a very interesting analysis relating to the recent process of mining activity. Particularly worth mentioning are the risk ratings for likelihood, environmental and socio economic impacts of mine closure, which can be very helpful in assessing the resource base and planning future mining and ensuring continued work for mine workers. Below are some minor comments and suggestions:

1. In the subsection 1.1, please write what type of mining the process of closing mines applies to: open-pit or underground; in addition, please write what the annual increase in the depth of exploitation is;

2. In the subsection 1.2, please add information regarding the balance criteria for selected ore deposits: gold, platinum, zinc, lead and hard coal, for which exploitation is economically and technically profitable - please refer to the literature source;

3. In the subsection 2.1.1, please write the period in years for which the mine is designed: hard coal and ore (approximate value);

4. In the subsection 2.1.2, please write how many employees there are per one employee working in the mine - in other words, what is the multiplier (for example, if 500 employees work in a mine, then mining-related companies that provide services and materials are about 2,000 employees) - this is very important information showing the relationship between individual industries: of course, this is an indicative value;

5. In the subsection 2.1.3 it is worth mentioning that the extension of mine operations is very often done by transition from open-pit to underground methods (doi: 10.3390/en15228740 ; doi: 10.3390/en16010148), which is very often the case in ore mining;

6. In the subsection 2.2, please write clearly whether the rating scale is your own categorization or rather a borrowed one;

7. In the subsection 2.3, please add information on the depth of mining for the considered mines;

8. In the section 3.1, please add a simple formula by which probability is calculated;

9. In the fourth chapter, it is worth adding two/three sentences regarding the transformation of underground workings into other forms, for example underground hydroelectric power plants, tourist routes, energy storage facilities, which may constitute new jobs;

10. In the conclusions, please add one statement, how many mines are planned to be closed in the next 10 years and how many to be built - this will be a form for future research.

Author Response

Response to Reviewer 3

1. The type of mining (underground and open pit) has been added to subsection 1.1. The mining method for each mine is included in the risk rating system and the detailed data are provided later on in the paper. There is no complete dataset on depth of mining however it is taken into account on a mine-by-mine basis for the risk rating for mining method (e.g. deep level vs shallow underground). Often mines expand horizontally (for example, a new open pit is opened adjacent to the first one, or an underground mine opens a new section linking to the adjacent shaft) rather than vertically, so increase in depth is not aways a proxy for exploitation.
2. The balance criteria relate to delineating mineral resources and reserves at the start of a project. This subsection gives a general overview of mine closure for the industry as a whole, and therefore it is not clear why such criteria should be included. In addition, these criteria vary from mine to mine and cannot be summarized by commodity.
3. The designed life of mine is a key factor for the likelihood of closure rating. The data for each mine are included in the results.
4. An additional influencing factor ‘indirect mining jobs’ has been added to subsection 2.1.2 Social risk. This cannot be quantified at this stage due to lack of data.
5. This has been included in subsection 2.1.1 under the Life of Mine section. Lines 157-158.
6. This has been clarified in lines 404-405
7. Information of the mining type (open pit or underground) for each case study mine has been included in Table 6 which lists all the case study mines and their ratings.
8. A simple equation has been provided in the Methodology section in subsection 2.2
9. Three sentences have been added to subsection 4.3 to address this.
10. A sentence stating that 48 mines have a life of mine of 10 years or less has been added to the conclusion – line 631. I do not have data on all mines under construction.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have corrected the article according to my comments. The article may be published in my opinion.