Using Process Mineralogy as a Tool to Investigate Blending Potential of the Pentlandite-Bearing Ores at the Nkomati Ni Mine in South Africa
Round 1
Reviewer 1 Report
Dear authors,
enclosed please find informal comments/suggestions mostly refering to mineralogy and style of publication:
Issue of sequence of references in numerical order:
Line 85: Ref. 41 follows Ref. 19 (wrong sequence)
Line 87: Ref. 37,38 follow Ref. 41
Refs. 20 to 36 missing in between (Refs. 21,22 first mention line 148)
Line 104: Ref. 31, 34 follow Ref. 41
Line 105: Ref. 35 and Ref. 42 missing in between
Line 153 ff.: Ref. 53 missing in between 52 and 54
Line 172: Ref. 60 before 57.
Line 207: Possibly the term "mass pulls" should be explained in more detail to the non-metallurgist, such as "We therefore label Mass Pull as the % of the material (mass) sent to flotation a “pulled/floated” into the concentrate. This number needs to be as small as possible to consider the flotation to be selective. Mass pull, or the flowrate of solids reporting to the concentrate, is affected by changes in froth structure and stability which are in turn affected by changes in operating parameters such as air flowrate and froth depth." (Hadler et al., 2010)
Line 229: Bottom line of Table 1: "The chromite grains are often surrounded by, and enclosed in, a network of secondary fibrous chlorite and serpentine (Figure 1F-G)."
This is hard to see, rather refer to Fig. 3 D
Line 240: Fig. 4 A: What has been labelled as Cpx looks rather like a composite of alteration minerals such as serpentine and talc. Please correct accordingly.The same applies for the suilicates in figure 4.E
Lines 236 and 240: All abbreviations not explained previously in Fig.2 should be written out such as Hbl, Pl, Ox, Ol, Cpx. Additionally refer to abbreviations in Fig.2 caption.
abbreviations "Po, Py, fine-grained BMS" in Fig. 3B, 3C and possibly 3.D difficult to read, maybe chose different colour.
Lines after 235: High-grade bleb ore (Bleb_HG):"Composite sulphide blebs comprise chalcopyrite, pentlandite, pyrrhotite and pyrite, which are mainly located on silicate grain boundaries (Figure 2C)." In figure 2.C The ore minerals are called BMS and it is difficult
to see that they are positioned along grain boundaries. Maybe indicate grain boundaries with thin yellow line.
same for Medium grade bleb ore (Bleb_MG): Sulphide blebs consist of chalcopyrite, pentlandite, pyrrhotite and pyrite, and are located along silicate grain boundaries (Figure 2E-F).
Line 244: Difficult to find the albite abbreviations in one of the section photographs. Also, Fig. 4B, C, E and F difficult to read Opx, Cpx, Py and Chl, possibly chose other BG or colour.
Line 252: caption fig. 6: oxide (Ox), plagioclase (Pl) capital "O" and "P"
Line 254: caption fig. 7: explanation for "Gln" missing
Fig. 7 B and E: There is no fresh Cpx, and also Opx in Fig.7B looks almost entirely altered to amphibole. On what basis was Cpx determined (XRD-mode)? It looks to me as amphibole or in places serpentine.
Possibly call it Chl, Amp or srp after Opx, Cpx.
Line 275, Table 4, what are the "other minerals", alteration minerals such als "Gln" or oxides?
Line 308-310: "The liberation of pentlandite in the -75 + 38 micron sieve fraction of the mill product from the milling tests as per figure 10, is broadly similar (with the exception of the MCHR sample which shows very poor liberation of pentlandite compared to all of the other samples investigated)."
I could not realise this information from figure 10, it must be figure 11. Maybe put (Fig.11) at the end of this sentence.
Line 344: Fig.13J, wrong diagram same as Fig.12J, the x-axis must be labelled "cumulative Ni recovery (%)" and y-axis "cumulative Ni grade (%)
Line 350/351: "...correlates..."
Line 364: Does reference 63 DHZ give information about the relation of difference in ore texture and level of alteration w.r.t. milling times? Otherwise do not cite it. It is not clear whether an advanced level of alteration increases or decreases the milling time of the ore samples. According to Table 4 net-textured sulphide ores have a lesser amount of chlorite than Bleb_MG and Dis_MG sulphide ores but similar act., amp. and serp., does this mean chlorite abundance is increasing rock strength?
Line 365-367: Since the chemistry of the samples is discussed, why have the samples assys not been given, or are these in an data appendix?
Line 371: "...a mine based..." space between "a" and "mine"
Line 424: full stop missing
Line 436: one "grind" too much
Line 473: "Amine based depressants...", rather "Mine based depressants..."
General questions: I think the general issues such as below should be addressed, possibly in the discussion.
1. the occurrence of excessive pyrite, which is a fast floater, in MMZ samples as a problem for floatation should be mentioned; since during mapping of the PCZM in the open-pit this appeared to be an issue.
2. The excessive occurrence of alteration minerals such as serpentine (max. 2.67%), talc (not listed, maybe among "others", max. 12.88%), amphibole (max. 8.27%), actinolite (max. 2.27%), chlorite (max. 18.63% in Dis HG) and biotite, as listed in table 4, producing coatings on sulphide causing reporting to flotation tailings, should in my opinion be mentioned.
3. Why has the mineral talc not been reported, which occurs frequently in PCMZ ore, it should have been discovered? Authors should explain.
4. The problem of the loss of flame pentlandite with sizes of 5-20 microns to the pyrrhotite gangue is not mentioned at all and should be discussed. Are there any suggestions of how to recover this part of the Ni mineralisation by grinding down to 75 microns, do other mining operations also write this portion off? Is the use of an industrial hydroelectric liberator (Vero-type as used in Pt-processing) an option to liberate the Pn-flames or do exsolutions not behave the same way as grain boundaries?
I have only checked the metallurgical downstream effects of the concentrate compositions on the smelting rearding plausibility and not controlled the contents of each reference in detail, but only looking at the titles.
Line 504, space missing between Subhash and Jaireth
Line 520: "Geology of the ultrabasic to basic Uitkomst Complex, eastern Transvaal, South Africa: an overview." "to basic" missing
Line 525: space between Sulphide and Mineralisation
Line 530: spaces between Peridotitic, Chromitite, and Mineralised
Line 533: "...Mineralogical..."
Have not checked all references and their form in detail.
Interesting paper,
kind regards
Author Response
Please see the attachment
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The main conclusion of this paper is a recommendation, based on MLA quantitative mineralogy, to grind the MMZ ore slightly finer – P77 rather than P67 @ 75 μm), and that both ore types could be processed together at a grind of P80 @ 75 μm, which is the current grind for PCMZ ore. This conclusion is of interest to the mine management, but probably not of much wider significance.
p. 4, 4.3 Automated mineralogy: GXMAP and GXMAP_SPL procedures should be explained; citing references to the methods is not sufficient as the techniques are central to the paper.
The analytical method for Ni used by Genalysis should be stated, not just the detection limit.
p. 5, Figure 1: poor quality photographs. F and G are blurred on my copy.
pages 7 to 14, Figures 2 to 8: seven figures of photomicrographs are unnecessary. Three would be sufficient – one for each ore type.
There are too many references in the paper, and many have little relevance. Some standard texts are referenced (e.g. 21 – Craig and Vaughan; 63 – Deer, Howie and Zussman). Some references are incorrect, e.g. ref 61 should be 62, and 67 should be 68. Reference 10 appears to be wrong. I could find no mention of references 20, 26 to 30 and 60 in the text. Entire reference list should be reviewed.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
