Genesis of the Tangshang Au Deposit in Southeast Yunnan Province, China: Constraints from In Situ Chemical and S-Sr Isotope Analyses

Round 1

Reviewer 1 Report

GENERAL COMMENT

Some rewriting is required. First, a better general description of the Tangshang Au deposit with a clear summary of its features that are characteristic of Carlin-type deposits is required.  Second, the formation of Carlin-type deposits, in general, should be described in the introduction or Discussion.  Third, how the Tangshang deposit differs from typical Carlin-type deposit should be discussed.  Is a metamorphic fluid source as proposed for the Tangshang deposit typical of Carlin-type deposit?

Finally, the fluid source is said to be the Proterozoic basement schists and gneisses.  This seems unlikely as these rocks would have yielded their main pulses of metamorphic fluids in the Proterozoic and the deposit is Triassic in age.  Is there at least some evidence that those schists and gneisses underwent a prograde fluid-releasing metamorphic event during the Triassic?

 

 MINOR COMMENTS

Abstract: Use present tense. For example, “ PY1 contained…” should be “PY1 contains” because it does contains these elements now in the present.

Line 35-36: “The sulfides produced similar S isotope ratios, and integration of these and elemental composition data indicate that all pyrites (Py1, Py2, Py3, and Py4) formed during the ore stage.”

This is an open-ended statement. You need to give a reason why.

Figure 2-3:  Codes are used on map and sections that are explained in the legend or figure caption.

Line 174-175: “Hydrothermal alteration omit identified in the area include sulfidation, silicification, kaolinization, illitization, and carbonatization.”

 Sentence is incomplete or incorrect.  See bolded.

 Line 183-184: “….extensive Fe-bearing mineral dissolution, and silicification occurred to form early stage sulfides with high brightness, smooth surfaces, and high Au content.”

 This is stated without supporting evidence.  What is the evidence for extensive Fe-bearing mineral dissolution? How does silicification results in the formation of sulfides? The same questions applies to the rest of the paragraph.  What is the evidence supporting this paragenesis?

Lines 311-332:  You have to present the errors associated with those analyses.

 Line 399-402: “The concentrations of Au and As in pyrite associated with hydrothermal alteration exhibit a strong positive correlation, which suggests that the precipitation of Au and As was concurrent with the crystallization of pyrite (Fig. 7A).”

 This conclusion, although not uncommon in many deposits, is not supported by the data presentation in Fig. 7A, which do not show a “strong” correlation between Au and As. Need basic statistics to justify this claim such as R2 correlation factors.

 Line 452-455: “Therefore, metamorphic–hydrothermal fluids characterized by high S and Sr isotope ratios, which were derived from these basement rocks, are proposed as sources of the Au mineralization in Tangshang.”

The basement rocks are Proterozoic schists and gneisses.  How can they be the source of metamorphic fluids for Triassic deposits?  They should already have lost most of the fluids through metamorphic devolatilization when they were metamorphosed in the Proterozoic.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript deals with the very interesting subject of Au-bearing Carlin-type deposits. The manuscript is very well written, with clear structure and methodology. The results are also well presented and the discussion section is clearly developed.

Minor grammar and spelling mistakes need to be addressed. The authors should address the issues denoted in the revised version of the manuscript in order to be solid enough for publication (e.g. data in Tables 1 and 2, Fig. 5, choose between Apy or Asp for the arsenopyrite types, etc).

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.pdf