Fluid Evolution and Ore Genesis of the Juyuan Tungsten Deposit, Beishan, NW China

Round 1

Reviewer 1 Report

General comments

The manuscript presents a fluid inclusion, stable isotopes and and Pb and Ar-Ar isotopes study of the Juyuan tungsten deposit with the aim to investigate the nature of ore-forming fluids and deposited metals, the evolution of the fluids, and the mechanism of ore deposition and to determinate the age of the deposit.

The manuscript is very interesting, very complete and well written. However major modifications should be necessary.  I suggest some major and other minor modifications.

Specific comments

Line 43. This is the tungsten resources in China, not worldwide.

Line 114. I suggest to replace the word “strata”, because not all are sedimentary rocks.

You talk about “Juyuan deposit” and “Juyaan ore distrit”. From line 114 to 117 you describe the ore deposit and later the ore district. It is necessary to describe first the ore district and later the ore deposit.

Figur2 2. This map has no scale!!

Figure 4 c and e. Could you add a scale?.

It is difficult to read the scale bar of Figure 4 g, I, k and l; the figure would be improved if you draw a new scale bar.

 

Line 150. “the metallic minerals in the veins appear mainly as oxides (e.g., wolframite and scheelite)” These minerals are not oxides but wolframates (classification from Strunz).

Line 152. It is not gelenite, replace this name by “galena”.

Line 416. From which minerals did you analyse the O,D isotopes’ were these minerals in equilibrium with quartz?. Did you measure some Oxygen isotopes in quartz?.

 You need to use the fractionation equations for the mineral-water pair. The equation of Clayton et al [42] is only for the quartz-fluid pair. This can be considerably different (see e.g. Vho et al, 2019; Journal of Petrology, 60(11), 2101–2130 doi: 10.1093/petrology/egaa001).

You cannot do a graph with oxygen from water and D from mineral.

Caption of Figure 9. " Plot of δ¹³C_PDB versus δ¹⁸O_SMOW for the quartz from the Juyuan tungsten deposit....this should be " Plot of δ¹³C_PDB versus δ¹⁸O_SMOW for fluids from IF in quartz from the Juyuan tungsten deposit...."

Figure 10. needs references

Line 467-468 " Sulfides from the intermediate stage have reasonably homogeneous δ34S values 467 (+3.7‰ to +6.3‰), suggesting that the ore-forming fluids were derived mainly from crustal rocks."

The homogenous values cannot be related to the source. This may be because of one of two things (or both): (1) there are few samples, non-representative of all the deposit, and (2) a metamorphic episode could homogenize the values.

You say that pyrite and galena are in equilibrium, but do you analysed both one together? I assumed these mineral pairs: 

  D1936-3 py=6.2, same number of sample Gn= 4.0 

D1936-4 py=6.2, same number of sample Gn= 3.7 

D1936-1 py=6.3, same number of sample Gn= 3.7 

If this is like that, you can calculate the equilibrium temperature and you can comment the results (T= 350 – 400 ºC).

In the discussion section a plot of Homogenization temperature vs Salinity should be very useful to identify the processes that occurred in the mineralizing fluid. This would greatly facilitate to readers the understanding of the fluid evolution.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

 

 

Review of the paper “Fluid evolution and ore genesis of the Juyuan tungsten deposit, Beishan, NW China“ authored by Yan et al., submitted to Minerals

 

This paper combines geological, mineralogical, fluid inclusion and stable isotope data to develop a genetic model for a recently discovered W deposit in NW China. Based on this, the paper would be within the scope of Minerals, and would raise interest of a broad audience, both in the science and in the industry.

Albeit the merit of publication of this study, the following items are required to be addressed.

1. The paper needs massive English editing, ideally by an English native speaker. For example, “the quartz-oxide veins early, quartz-polymetallic sulfide veinlets middle, and carbonate-quartz veinlets late stages” (lines 14-15; replace with “the early stage of quartz veins with scheelite and wolframite, the middle stage of quartz veinlets with sulfides, and the late stage of carbonate-quartz veinlets”), “the host rocks within Triassic granite” (line 26; what is this ?), “in the mine” (line 29; did you mean “at the deposit” ?), “plate” (line 32; should be “plates”), “deposit” (line 106; should be “deposits”), “sediment” (line 109; should be “sediments”), “are mainly distributed” (line 110; better “occur mainly”), “gelenite” (line 152; should be “galena” ?), and so on.
2. Lines 75-77: how the Southern Tien Shan and Solonker sutures, generally east-west-trending faults, can border the area to the west and to the east, respectively ? Please label these at Fig. 1.
3. Lines 121-122: you stated “monzogranite, granite, and numerous dikes” – this is a mixture of compositions and shapes. Please indicates shapes (plutons, stocks, etc.) of “monzogranite, granite” and composition of the “dikes”.
4. Lines 122-136: description of igneous rocks is weak. What accessory minerals, besides zircon, are present ? Specifically, what about magnetite and ilmenite, which would define the respective granitoid types ? What is quartz porphyry, which was not mentioned before ? Does it form dikes or larger intrusives (plutons, stocks) ? What are the mineral compositions of diabase and diorite including accessory minerals ?
5. Line 139: you stated “The tungsten grade 0.065 ~0.14%”. What is this, variations of the grades ? What is the average deposit grade ? It is common to indicate W grades as WO3, thus, are these numbers WO3 grades in fact ? By the way, what is the deposit tonnage ? It is common to indicate deposit tonnages, while dealing with deposit characteristics.
6. Lines 143-145: you stated “…..scheelite occurs in two forms: (1) euhedral …. and (2) distributed in fissures…..”. This is again inconsistent description.
7. Lines 149-150: “mineral veins” – did you mean “mineralized veins”, or “ore veins” ? Wolframite and scheelite are not oxides but are tungstates (or wolframates). Please avoid using the term “metallogenic” (“post-metallogenic”, “metallogenic period”) in this context, better “post-mineralization” and “intermediate ore-bearing hydrothermal stage”, or so.
8. All these deficiencies appear to be quite minor as compared to those observed in the fluid inclusion data presentation and interpretation.

• In particular, you refer to some “ice-melting temperature” (line 188). In fact, there are two ice-melting temperatures usually measured in fluid inclusion studies, namely, (1) first ice melting temperature (or eutectic melting temperature), and (2) final ice melting temperature. According to the numbers in Table 1, you reported final ice melting temperatures. But what about eutectic melting temperatures, which are absolutely critical for determining salt compositions (NaCl, KCl, CaCl2, etc.) of fluid inclusions (see, for example, Crawford et al., 1981) ? Furthermore, how have you assigned your fluid inclusions to the systems containing NaCl – without these eutectic temperature measurements ? Please note that, if other salts are present (particularly CaCl2 that is well expected due to the presence of scheelite and calcite), other (than NaCl-H2O) equations of state should be explored. By the way, what would be a source of CaCl2, if detected ?
• You used tables/charts from Collins (1979) for determining salinities by clathrate melting temperatures, which are outdated; instead, newer tables/charts from Darling (1991: Geochim. Cosmochim. Acta 55: 3869-3871) must be used.
• Some of your carbonic phase melting temperatures are very low (up to -69.6^oC) indicating a significant methane (CH4) content. You briefly mentioned this fact in the Discussion section, however, the importance of this was not highlighted sufficiently. You can use the data (charts, etc.) from the paper by Thiery et al., 1994 (Europ. J. Mineral., no. 6, p. 753-771) to determine CO2/CH4 ratio, for example. Furthermore, you have to outline and discuss the respective limitations that the presence of CH4 would cause (in contrast to the pure CO2, CO2-H2O, etc., systems).
• Please re-word the term “daughter-mineral inclusions” (line 275) to “fluid inclusions with daughter minerals”. How did you determine that these solid phases are specifically “daughter” minerals ? Are they present consistently and in comparable volume ratios ? Also, you distinguished fluid inclusions with solid phases (S-type) and with CO2 as separate types but what if some inclusions contain both solid phases and CO2 ?

9. Your assumption on carbonatite melts (line 533) is totally irrelevant and makes no sense considering the type of mineral deposit under consideration and the low (<350^oC) temperatures of mineral formation. Please delete this.

10. Hydrothermal alteration types at the deposit are not really described and discussed. This should be done before you proceeded with FI studies.

11. Figures:

• Figure 2: Please add scale bar and a north arrow. What are “acidic vein” and “diorite vein” ? Did you mean “granitic dike” and “diorite dike”, respectively ? Where are quartz porphyries mentioned in the text ? Add rock symbols (crosses, etc.) to the legend bars.
• Figure 3: Why no geology and hydrothermal alteration are shown ? “Monogranite” – did you mean “monzogranite” ? What is the difference between “mineralized bodies” and “orebodies” ?
• Figure 4: Please add scale bares to ALL plates (e.g., a, b, e, h, i, k, l). Plate “a” – did you mean “monzogranite” ?

 

Based on the above observations, the paper requires a major revision before it can be considered for publication.

 

Sincerely yours,

Author Response

Please see the attachment

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The authors returned a significantly revised manuscript, taking on board most of the comments of the reviewer concise and to the point. Although some spell-check may be warranted, this can be done in the course of the typesetting and production of the paper. Based on this, I can now recommend the paper for publication. 

Sincerely yours,