Ni-Co Bearing Laterites from Halmahera Island (Indonesia)^†

Round 1

Reviewer 1 Report

This paper deals with lithology and nature of mineralization of Ni and Co  occurring in Halmehra laterites.  This paper has very limited scientific analysis but has considerable technical data on this deposit.  Since Ni and Co are very important Critical Metals, information given is very useful.

Author Response

Dear Reviewer,
Thank you very much for your valuable comments and suggestions for changes to the manuscript. All your suggestions have been incorporated into the revised text. I enclosed the revised manuscript with visible changes.
Thank you for your cooperation
authors

Author Response File: Author Response.docx

Reviewer 2 Report

 

The article “Ni-Co bearing Laterites from Halmahera Island(Indonesia)” reported chemical and mineral compositions of laterites samples from Halmahera Island, Indonesia. The authors recognized the Co and Ni occurrence and associations with minerals in profiles of laterite (limonite and saprolite). The data is abundant yet the whole data presentation and explanations need deep revision. The writing also needs great improvement since there are many grammar mistakes. The major problems are listed below and some detailed comments are marked in attached PDF. I suggest major revision before publication.

1.      The most major problem is a lack of data and interpretation about connection between Co-Ni enrichment with mineralogy which is an important part of this article. In the conclusion (line 377-394) and abstract (line 22-25) the authors emphasis the Co and Ni are bound to specific minerals (goethite, manganese minerals etc.) yet this is not explained in the manuscript and no direct evidences have been provided. For example, line 390-392 “the goethite from the lower part contains more Ni than goethite from the upper part”, there is no relevant data supporting this conclusion. The authors presented Ni content of the zone (line 224-227) and get the conclusion that the Ni content is lowest in the upper horizon. But it should be noted that the Ni content of the zone didn’t equal to the Ni content of the mineral(goethite).

2.      Table 3 listed mineral compositions of the samples, but the authors didn’t show how they get those data, maybe XRD? There is no description of related experiment method in part 3.

3.      Data in table 3 can’t prove that statement in line 222-223 (The occurrence of nickel is associated with goethite less frequently with hematite.). How did the author confirm that Ni is associated with goethite instead of other minerals? Please add solid evidence to support this.

4.      please add some current research progress of the laterite Co-Ni deposit type in the introduction part.

5.      I suggest the authors add some microscopic pictures of the mineral assemblages in different horizons of the profile in part 4.

6.      Some of the figures are confusing, such as figure 11 and 12. Please see attached PDF for advices.

 

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,
Thank you very much for your valuable comments and suggestions for changes to the manuscript. All comments have been taken into account. Thank you for your help in improving the article. Authors.

 

1. New data and information on chemical composition variability have been added to the text of the article. In Section 4.2 Geochemical variability of the laterite profile, new text and Table 5 i 6 were added with the chemical composition of geothite and limonite.
2. New information about XRD analysis was added in part - 3.2.2.X-ray Powder Diffraction (XRD).
3. Data are presented in table 5 - concern chemical composition of limonite horizon
4. We add some information in Introduction - Indonesia is one of the world's major suppliers of nickel from laterite deposits and most of the resources are located in the Molucca and Sulawesi regions. Despite numerous discov-eries of laterite deposits in Indonesia, few investigations have been made into the geo-chemical characteristics of these deposits [11-14]. New research of Indonesian laterites have focused on the remobilisation/recrystallization and enrichment of critical raw mate-rials (i.a.i.e. Co, REE, Pt, Pd) in the laterite profile based on mass-balance [15]. Under-standing the geochemical processes leading to metal enrichment in different zones of the profile may contribute to more effective exploration of deposit and subsequent metallur-gical processes.  
5. The microscopic photos were added
6. The explanations to these fugures are added.

 

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The article “Ni-Co bearing Laterites from Halmahera Island(Indonesia)” reported chemical and mineral compositions of laterites samples from Halmahera Island, Indonesia. The revised version has met most of my suggestions. The writing has been greatly improved, and the data which would illustrate the connection between Co-Ni enrichment with mineralogy is added in this version. The current version is generally acceptable expected for a few questions listed below:

 

1.      There is a lack of XRF data of the chemical compositions of different horizons.

 

2.      The authors only listed chemical compositions of goethite in the limonite horizon(Table 5) but those data are absent for the transition and saprolite horizon. Please improve table 5 to give a full set of data.

 

3.      The figure caption is missing at line 360. Table and figure numbering should be corrected in line 371 and hereafter.

 

4.      Please explain how the Fe2O3 data were acquired in table 5, because normally the EMPA analysis can only provide Fe2+ but not Fe3+.

Author Response

Thank you very much to the reviewer for your extremely valuable comments and suggestions. I also provide responses to the 4 comments made by the reviewer in the second round of reviewing. 

Comment nr 1. There is a lack of XRF data of the chemical compositions of different horizons.

Answer: XRF data on the chemical composition of the different horizons are added in the appendix 1.

Comment nr 2. The authors only listed chemical compositions of goethite in the limonite horizon(Table 5) but those data are absent for the transition and saprolite horizon. Please improve table 5 to give a full set of data.

Answer: Detailed studies have focused on the limonite horizon, which has the greatest reservoir significance. The transitional and saprolite horizons were recognized mineralogically. Dr. Konopka (lead author) died and did not have time to complete further detailed studies. Thus, we have no detailed geochemistry of these horizons.

Comment 3. The figure caption is missing at line 360. Table and figure numbering should be corrected in line 371 and hereafter.

Answer: Untitled figure - should have the following title.: Enrichment/depletion in selected oxides and elements relative to the bedrock (fresh harzburgite).

Comment 4. Please explain how the Fe2O3 data were acquired in table 5, because normally the EMPA analysis can only provide Fe2+ but not Fe3+.

Answer: 

EMPA analysis only identifies chemical elements, so it identifies iron but without indicating its degree of oxidation.  The software supporting EMPA analysis allows the calculation of iron content in oxide form as FeO or Fe2O3. Then, according to the results of the XRD analysis identifying the mineral phases in the sample, chemical stoichiometric calculations are made that match the results of the chemical analysis with the qualitative phase analysis (also semi-quantitative).