Sulfur Isotope Ratios from VMS Deposits in the Penokean Volcanic Belt, Great Lakes Region, USA: Constraints on the Source of Sulfur in a Paleoproterozoic Intra-Arc Rift

Round 1

Reviewer 1 Report

The study reports δ34S values obtained from sulfide minerals collected from eight VMS deposits in the Penokean Volcanic Belt: Back Forty, Bend, Eisenbrey, Flambeau, Horseshoe, Lynne, Reef, and Schoolhouse. The average δ34S values from most of these deposits lie within the mantle-range between -2 and 2‰ (VCDT).

The article can be published with some corrections.

Geological setting. Information about occurrence geology seems insufficient. It need to add data about metamorphic alterations, ore structures and mineralogy.

Results. I think that tables 1-8 need to be placed in the application. Table 9 and pictures 5-6 contain enough information. In this case article will be more compact.

Since the range of values δ34S indicates that the source of sulfur was homogeneous fig. 7 is not needed. May by limited to one deposit.

Discussion. Part 4.1 is better to consider in the introduction. It is important to add more information about sulphur isotopy for Precambrian VMS deposits another regions

Figures 9 and 10 with regional distribution of δ34S can be combined 

Comments for author File: Comments.doc

Author Response

Review of manuscript minerals- 412610 (Nicholas Moleski, Anthony Boxleiter, Joyashish Thakurta) Sulfur-isotope ratios from VMS deposits in the Penokean Volcanic Belt,
Great Lakes Region, USA: Constraints on the source of sulfur in a
Paleoproterozoic intra-arc rift

The study reports δ34S values obtained from sulfide minerals collected from eight VMS deposits in the Penokean Volcanic Belt: Back Forty, Bend, Eisenbrey, Flambeau, Horseshoe, Lynne, Reef, and Schoolhouse. The average δ34S values from most of these deposits lie within the mantle-range between -2 and 2‰ (VCDT).

The article can be published with some corrections.

I have addressed all your suggestions, point by point in the following paragraphs. My responses are in blue.

Geological setting. Information about occurrence geology seems insufficient. It need to add data about metamorphic alterations, ore structures and mineralogy.

In section 1.1 Geological setting, I have added 2 paragraphs on the depositional environments in the region, types of host rocks, grade of metamorphism, hydrothermal alteration, ore textures and major ore minerals. Lines 102-116.

Results. I think that tables 1-8 need to be placed in the application.

I have combined table 1-8 in one table: Table 1.

Table 9 and pictures 5-6 contain enough information. In this case article will be more compact.

I have also moved Figure 5 to the appendix. This made the article more compact.

Since the range of values δ34S indicates that the source of sulfur was homogeneous fig. 7 is not needed. May by limited to one deposit.

I have moved the entire Figure 7 to the appendix.

Discussion. Part 4.1 is better to consider in the introduction. It is important to add more information about sulphur isotopy for Precambrian VMS deposits another regions

I have moved the first part of Section 4.1 to the introduction.

I have added more information about locations of VMS deposits in the Precambrian where sulfur isotope ratios have been used.

This paragraph was already there:

“Furthermore, numerous studies on Archean and Proterozoic VMS deposits by authors such as Sharpe and Gemmell [14], Wagner [35] and Bailie et al. [36] have demonstrated that sulfur-isotope ratios recorded in sulfide minerals within VMS deposits are not distorted by subsequent processes of structural deformation and regional metamorphism”. 

I have added a new paragraph based on your suggestion:

“Sulfur-isotope signatures have been used by several workers to model the geochemical characteristics of the mineralizing hydrothermal fluids of VMS deposits in the Archean and Proterozoic Eons. Apart from the studies mentioned above, there are more studies on sulfur isotope characteristics of VMS deposits in the Teutonic Bore Volcanic Complex, Western Australia [50], VMS deposits at Strelley, Pilbara craton, Western Australia [51], and the VMS district of Tierra del Fuego, Argentina [52]”.

Figures 9 and 10 with regional distribution of δ34S can be combined

I have combined Figures 9 and 10 to one figure, which is Figure 7 in the revised article.

Reviewer 2 Report

In general, the paper is well-written and contains new interesting material regarding sulphur isotope systematics in VMS deposits in the Great Lakes Region. Authors present extended new data and discuss it in terms of a possible source of sulphur. The paper can be recommended for publication in “Minerals”, but some minor corrections yet can be suggested.

First of all, I would suggest presenting the geological history of the Penokean Volcanic Belt (lines 61-72) with less degree of confidence. It is quite complex, and I can hardly imagine that such history for such old rocks is well established and substantiated. I believe that other models for the same belt also exist. I would at least mention other possible scenarios.

I think that the paper is too overloaded with tables and figures. Tables 1 to 8 are of the same type and can be easily merged into a single table. This will save at least half page. Figures 5A to 5G are too big. If authors wish to publish all these diagrams, I would suggest producing a single figure containing several panels. Finally, I do not see any reason to present all diagrams 7A to 7G. This can be easily done in an industrial report, but authors are not supposed to present all their initial data in a scientific publication. One or two typical examples should be enough, while the rest can be shown in the supplementary materials if the authors insist on presenting all their data.

Figures 9 and 10 are the most important results of the research presented by the authors. These two maps still can be merged into a single map. In the text (lines 317-319) authors mention that “this geographic distribution pattern and the inferred δ34S-contours (Figure 10) closely mimic the known orientation of the continental margin in the southernmost part of the Superior Craton”. It would be really good to see the location of the continental margin.

Author Response

Comments and Suggestions for Authors

In general, the paper is well-written and contains new interesting material regarding sulphur isotope systematics in VMS deposits in the Great Lakes Region. Authors present extended new data and discuss it in terms of a possible source of sulphur. The paper can be recommended for publication in “Minerals”, but some minor corrections yet can be suggested.

I have made all corrections as suggested. I have explained them point by point in the paragraphs below. My reposes are in blue.

First of all, I would suggest presenting the geological history of the Penokean Volcanic Belt (lines 61-72) with less degree of confidence. It is quite complex, and I can hardly imagine that such history for such old rocks is well established and substantiated. I believe that other models for the same belt also exist. I would at least mention other possible scenarios.

I have modified the presentation style, as can be seen in the revised manuscript under section: 1.1 Geological setting. I have added some uncertainty in the presented tectonic model. There are some discrepancies with respect to direction of subduction and the nature of accreted arcs. I did not go into the details of the debated issues because in that case it will turn out to be an extended discussion.

 I think that the paper is too overloaded with tables and figures. Tables 1 to 8 are of the same type and can be easily merged into a single table. This will save at least half page.

I have combined Tables 1 to 8 in a single table, named Table 1 in the revised manuscript.

Figures 5A to 5G are too big. If authors wish to publish all these diagrams, I would suggest producing a single figure containing several panels.

I have moved Figures 5A -5G to the appendix. The Figure 5 in the revised manuscript is a combination of all the information.

Finally, I do not see any reason to present all diagrams 7A to 7G. This can be easily done in an industrial report, but authors are not supposed to present all their initial data in a scientific publication. One or two typical examples should be enough, while the rest can be shown in the supplementary materials if the authors insist on presenting all their data.

I have moved Figures 7A – 7G to the appendix also.

 Figures 9 and 10 are the most important results of the research presented by the authors. These two maps still can be merged into a single map. In the text (lines 317-319) authors mention that “this geographic distribution pattern and the inferred δ34S-contours (Figure 10) closely mimic the known orientation of the continental margin in the southernmost part of the Superior Craton”. It would be really good to see the location of the continental margin.

I have merged Figures 9 and 10 into a single map, which is Figure 7 on the revised manuscript. In that figure, I have marked the Niagara Fault Zone which is regarded as the accretion margin of the PVB with the Superior Craton. This is the probable location of the continental margin according to many workers.