Origin of the Pd-Rich Pentlandite in the Massive Sulfide Ores of the Talnakh Deposit, Norilsk Region, Russia

Round 1

Reviewer 1 Report

The manuscript "Origin of the Pd-rich pentlandite in the massive sulfide ores of the Talnakh deposit, Norilsk region, Russia" dedicated to actual and interesting problem. Pd-rich pentlandite occurs irregularly within sulfide Cu-Ni ores and requires a special formation condition. The work is provided with sufficient graphical data. Conclusions convincingly showed that the existing models do not fully satisfy the observed features of Pd-pentlandite. An original mechanism of Pd-rich pentlandite formation is proposed, which assumes the participation of a Pd-bearing fluid. However, the source of this fluid was not revealed.

Specific comments:

Title: I would recommend excluding "Origin" from the title and confining ourselves to "Pd-rich pentlandite in the massive sulfide ores of the Talnakh deposit, Norilsk region, Russia" because the source of the substance has not been identified;

Lines 46-47: add ref;

Line 54: Pentlandite is not necessarily exsoluted from mss and iss, it can crystallize from residual Ni-rich sulfide liquid, including after the chalcopyrite [Mungall, 2007], this is not considered at all in the work;

Figure 1: a mark for the location of the Kharaelakh intrusion is needed, only Norilsk is shown, but the text does not specify in which direction the object is located about Norilsk;

Lines 239, 242: no right angles of intersection of pentlandite lamellae are visible in Figs 4d and 4f;

Line 248: maybe 4e instead 4f;

Figure 6a: it would be worthwhile to show the site with the Pd-richest pentlandite in detail (for example, in Fig. 4) or, if there is one, to denote it more clearly in the text;

Line 353: 8e and 8f is it appropriate here?

Line 551: as noted above, you are not considering the possibility of pentlandite formation from the residual liquid;

Page 25: line numbering has been reset!;

Line 49: maybe "enrichment of pentlandite in palladium"?;

Discussion: it seems that the crystallization of the own Pd minerals is energetically more favorable for the system than the displacement of Ni from pentlandite, and where did the substituted Ni go?

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Row 50: I don't see the necessity of the abbreviations tss and bnss as these are not used in the text furthermore.

Chapter 2: Description of the geology is inadequate. Could the authors be more explicit: what kind of rocks form intrusions (peridotitie, gabbro or else), what do we know about the tectonic setting of the Kharaelakh trough (Permo-Triassic rifting or else), about the deposit type (magmatic or else) etc? These might be obvious for the authors but not for the reader. "Chronostratigraphically speaking" can be omitted.

Row 92 and Figure 1: Geological data are incomplete without exact reference to the location. Please give coordinates of the EM-7 drillhole! It would be also informative to indicate the hole on the map and to add some northing and easting data (latitudes and longitudes).

Row 351: "8e and 8f" - 8d and 8e, I think
Figure 8: Please give explanation to the colour scales!
Row 356: Explanations in the text are at the end of the Discussions, please refer to chapter 4.3!

Figure 9: Why do You not show Fe as well? The vertical scale could be further manipulated not to interfere with Ni.

Table 4 and Supplementary table: It would be more straigthforward to use <0.04, <0.06 or other numbers like that to indicate measurements below detection limit instead of zeros and hyphens.

Chapter 4: I miss that authors hardly use the documented textural relationships in the discussion. E.g. when discussing if PGM could be the source of Pd for Pdpn, it's only a possibility if PGM represent an older phase than Pdpn - however, as Pdpn lamellae are relict and partly replaced, maybe the sequence is the opposite.

Figure 10: Please indicate if data are in wt%!

Row 441: Do You mean by "visible" that microinclusions should be large, or clustered (distributed unevenly) enough to appear on BSE images? Or simply that you should have seen the chemical trace of further elements (e.g. Bi, As etc.) in the spectra?

Table 6 and rows 457-470: The (Pearson) linear correlation coefficient is not meaningful in this dataset. The variables are obviously neither independent nor linearly dependent as they sum up to a fixed value of 100% (i.e. 9+8 apfu now), being proportions of the total chemical composition. (In case of trace element compositions this problem is not arising as the sums are far below 100%, but here you have few variables, of which Ni, Fe and S have high percentages.) A safer choice would be to use rank correlations (e.g. spearman rho). For more complex approach, see e.g. https://statweb.stanford.edu/~gwalther/composition.pdf

Principal component analysis: Did You try to calculate with less than 6 assumed factor too? According to the previous problems, I doubt the relevance of this calculation.

Rows 593-594: The last sentence of the paragraph is grammatically incorrect, please rewrite it as you meant it.

On Page 25 the row numbering starts again from 1.

Row 63: "areolas" - aureoles

Rows 71-76: The existence of fluid inclusions, even if nothing was measured on these, should be documented in Chapter 3. It is strange that some observed things come up at the end of the discussion only.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Comments on the manuscript:

 ‘Origin of the Pd-rich pentlandite in the massive sulfide ores of the Talnakh deposit, Norilsk region, Russia’

by Valery Kalugin et al.

General comments:

The authors undertook petrographical, petrological and mineral-chemical studies in order to investigate  Pd-rich pentlandite grains, in order to reveal the Pd distribution in individual grains and grain populations, and, in addition, to contribute to the discussion of the possible causes and processes for the Pd enrichment in certain pentlandite occurrences. The authors mainly used the electron microscope, EP microanalyzer (for element chemistry & mapping) and SEM for semiquantitative element analyses to obtain the pentlandite in situ mineral-chemistry.

This is a relatively well-written (with few semantical errors) and interesting manuscript since one of the main results of the petrographical, mineral-chemical and petrological study suggests that most of the proposed hypotheses concerning the origin of the Pd-rich pentlandite grains are unsuitable to explain the here observed characteristics. The present study rather indicates that the enrichment of palladium in pentlandite is neither related to the crystallization of a sulfide liquid or to subsolidus transformations of the base metal sulfides. Instead, the authors suggest that the Pd-enrichment is the result of a superimposed process that allowed for the replacement of nickel by palladium and the decrease in the Ni/Fe ratio in the respective pentlandite grains. Most likely, this process occurred at a lower sulfur fugacity compared to that which happened during the crystallization of the ore-forming pentlandite. These result are of interest for a wide international readership. Thus, in my opinion the manuscript deserves publication in an international journal such as Minerals. However, the present version of the manuscript has some few semantical and content-related shortcomings, for instance regarding the citation of up-to-date references. Therefore, in my opinion the manuscript needs some minor revisions before it can be published. The attached review addresses the major points of concern as well as some detailed minor points.

Detailed comments:

Line 10: ….. ore-forming pentlandite (Pn) has been found in the …..

Comment: I suggest: ……ore-forming pentlandite (Pn) occurs in the……

Line 14: …… palladium concentrations indicate sharp changes in palladium content both within a single grain and within group of grains. Palladium…….

Comment: I suggest: …..palladium concentrations indicate distinct variations in the palladium content within and between individual grains. The palladium…..

Lines 31-33: Several studies have demonstrated to a great extent that pentlandite is the only one of the three common sulfide minerals that concentrates Pd [1-7].

Comment: The authors cite here almost exclusively older literature (1-6) or review literature (7) despite detailed and commonly cited new standard-of-state (LA-ICPMS) data on the actual mineral-chemistry of sulfides such as pentlandite is available for example on the Bushveld and Stillwater mineralization (see detailed reconnaissance studies by Godel & Barnes 2008, Chem. Geol., Godel et al., 2007, JP; Osbahr et al. 2013, Min.Dep., v.48; Osbahr et al.  2014, Min Dep., v.49). Please add these references to the text in the manuscript.

Lines 39-41: …. Additionally up to thousands of ppm of Pd in pentlandite have also been reported in sulfide ores from the Platreef and Merensky Reef in the Bushveld Complex [12-14]. …

Comment: The latest with up-to-date references on the Merensky- and Platreef pentlandite compositions are Osbahr et al. 2013 (Min.Dep., v.48) and Klemd et al. 2016 (South African Journal of Geology, v.119), respectively. Please add these references to the text in the manuscript.

Lines 68-69: …. The aim of this work is to study the grains of Pd-rich pentlandite, to…

Comment: Should read:   …. The aim of this work is to study Pd-rich pentlandite grains, to…..

Line 86: …… locate …

Comment: Better: …..occur…...

Line 87: …. one edge of the ore body can be located inside the intrusion, …..

Comment: I suggest: …. one edge of the ore body is located inside the intrusion,…..

Line 101: …….. 35 polished sections fixed…..

Comment:….. Thirty-five polished sections fixed…..

Line 105: …… 20 polished sections were…...

Comment: ……Twenty polished sections were…..

Lines 125-145: 3.2. Mapping of Pd distribution in pentlandite.

Comment: How was this done ? Please write what method you use. I guess it’s done by EP microanalyses ? But you also use EDS and SEM (semiquantitative ?) analyses ?

Line 136: …..sum….

Comment:  Should be:…..sums…..

Lines 180-181: ….The mineral association of the PGM and their compositions is consistent with previously published data [23-24] but it is not the aim of this paper.

Comment: Please be precise: What is not the aim of the paper ? What do you mean ?

Line 184: … (Figure 2).

Comment: Should be: ……(Figure 2):

Lines 203-204: The most remarkable feature of the layer is an important presence of pyrrhotite.

Comment: I suggest: The most remarkable feature of the layer is the presence of pyrrhotite.

Lines 207-208: ….. layer are distinguished by the disappearance …..

Comment: I suggest:…... layer are characterized by the disappearance…..

Lines 249-250: …. This indicates that the chalcopyrite lamellae are parallel to the edges of the cube. …

Comment: What do you mean with ‘cube’ ?. That the host mineral has a cubic shape ?

Line 254: ….allow….

Comment: …..allows….

Lines 283-284: ….. Concentration of Ni gradually increases to the top from 33.20 to 40.58 wt.%, whereas concentration….

Comment: I suggest: …..The concentration of Ni gradually increases to the top from 33.20 to 40.58 wt.%, whereas the concentration…..

Line 285:…. bottom are slightly out of the general trend…..

Comment: I suggest: …… bottom plot slightly off the general trend…..

Line 375:…..uneven….

Comment: I would use:…..inhomogeneous or heterogeneous…..

Line 422:….. Fe content in Pd-rich p…

Comment: The Fe content in Pd-rich p…….

Lines 439-441: Nonetheless, the studied Pd-rich pentlandites have high palladium concentrations at the weight percentage level. At such concentrations, microinclusions of Pd-bearing PGMs would be visible.

Comment: How do you know ? Are there any references available ?

Lines 531-534 (also abstract and throughout the discussion): Suggesting that, the crystallization of ore-forming pentlandite occurred under higher sulfur fugacity, giving as a result a higher Ni/Fe ratio. However, its transformation into Pd-rich pentlandite seems to have occurred at a lower sulfur fugacity, which caused a decrease in the Ni/Fe ratio due to the replacement of part of the nickel with iron.

Comment: This is a very interesting result seeing that Klemd et al. (2020, Minerals) suggested that the presence of pentlandite with variable Pd concentrations even on the thin section scale is related to variations in the S content at S-saturation, resulting in relatively diluted PGE concentrations during abundant formation of BMS at high sulphur saturation. Thus, the variations of pentlandite grain PGE concentrations on a thin section scale could be due to the presence of different generations of pentlandite. Please refer to this reference.

Line 526: …. However, Ni*/Fe ration turned…

Comment: …However, Ni*/Fe ratios turned….

Line 545: …different time.

Comment: …different times.

Line 549: … [1-7].

Comment: see comment above on these references.

Lines 624-627: In addition, high concentrations of palladium have been found in pentlandite lamellae within cubanite (Figure 8f), which excludes completely the formation of such pentlandite as a result of the peritectic reaction before described.

Comment: I suggest: In addition, high concentrations of palladium occur in the pentlandite lamellae within cubanite (Figure 8f), which completely excludes the formation of such pentlandite as a result of the peritectic reaction as described before.

Lines 73-75, page 26:…. Some of them are euhedral in shape (Figure 12b) and contain Pd-bearing daughter mineral phases (Figure 12a, 12b).

Comment: How do you know that these inclusions are true daughter minerals and not  accidently trapped solid inclusions ?

Lines 89, page 27: …ores form by crystallization…….

Comment: I suggest:….ores that formed by crystallization…….

Author Response

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Author Response File: Author Response.docx