The Passa Três Granite Intrusion-Related/Hosted Neoproterozoic Gold Deposit (Paraná State, Brazil): Mineralogical, Geochemical, Fluid Inclusion and Sulphur Isotope Constraints

Round 1

Reviewer 1 Report

interesting study on a gold deposit in Brasil. Unfortunately, the research question is not adapted to the deposit, check the litterature ! Therefore the conclusion is erroneous.

Some geological information lacking. Change the intro, the discussion and the conclusion.

Comments for author File: Comments.pdf

Author Response

Answer to reviewer 1

Comments on the paper by Dressel et al on the manuscript entitled: ‘’The Passa Três granite intrusion-related/hosted Neoproterozoic gold deposit (Paraná State, Brazil): Mineralogical, geochemical, fluid inclusion and sulphur isotope constraints’’ submitted to Minerals.

The manuscript has for object an interesting deposit that has been for long the only producer of gold in the Parana state. Gold veins are hosted by a red granitic intrusion that has been describe before as a syenite. The paper offers new data on the mineralogical association, the chronology of alteration, some detailed mineralogical, isotopic and fluid inclusion studies.

However, the paper has a major weakness. Its major question is confirming that the deposit belongs to the IRGD class of deposit… (with IRGD define as reduce intrusion). The answer of the author is YES…. But this answer is false because the Passa Très is an oxidised pluton!

Response:

• Regarding the syenite composition, indeed, there is some previous work that mentions a syenite composition for the Passa Três granite, like Piekarz (1992). However, the petrographic classification presented by Piekarz (1992), Picanço (2000) and Cury (2003) indicates a syenogranite composition for most of the thin sections analysed, based on the diagram of Streckeisen (1976). In terms of geochemistry, the samples anaysed by the same study present a SiO2 content between 62,65% and 70,70%, with an average of 68,4%, that the author stated as a quartz-syenite composition. Despite of these SiO2 contents and based on major and minor elements, the author compares the main facies of the Passa Três granite (that we called GEM in this study) with the high-potassium calc-alkaline granites, of shoshonitic affiliation. Because of the alteration, Turini Neto (2012) assumes a calcium-sodium classification for the Passa Três granite, considering a possible diorite composition. If plotted on a TAS diagram for plutonic rocks, our samples are placed on the granite field, near the border with syenites. Another point to consider is the strong intemperic alteration observed throughout the outcropping granite and the alteration related to the mineralization, that despite its weak intensity, may have affected the liability in a classification based on geochemistry analysis. Therefore, in this work we consider the classification based on petrography (granite).
• The oxidation state of the Passa Três’ granite is considered controversial, and a frequent posed question was the reason of its red colour, assumed by several local geologists as oxidation. In order to verify this matter, in the beginning of our study, we collected some samples to be analysed for the verification of the Fe²⁺/Fe³⁺ in order to determine its oxidation state, but based on the thin sections there was a suspicion of metasomatism and alteration, which could lead to false results. Nevertheless, according to Baker & Lang (2001), there are intrusion-related gold deposits in both kinds of granites (oxidized and reduced), so the oxidation state of the intrusion does not prevent a classification as IRGD.              

The major problem is that this is not a good question. This class of deposit was defined in the American cordillera and cannot be applied to this deposit. Basic data from previous works have shown that this deposit belong to the class of syenite-hosted gold deposit, with all the key parameters: hosted within an intrusion, oxidized pluton, magmatic connection, copper and fluorite abundance… This class of deposit have been described in numerous deposits all over the world: in the Archean (Beattie, Young Davidson in the Abitibi – see Robert, 2001, Bigot and Jébrak, 2015), the Proterozoic (Tulu Kapi, Ethiopia), the Paleozoic (Zarmitan, Uzbekistan) and even the Cenozoic (Allard Stock, La Plata, Colorado). Gold associated with alkaline rocks (primary or secondary) have been synthetized by the famous book of D. Müller and D.I. Groves (2019) Potassic igneous rocks and associated gold-copper mineralization, fifth edition. Mineral resource reviews, Springer, 398 p

Response: Previous works of the Passa Três deposits presented a common goal towards understanding the structural complexity of the orebodies and the origin of the mineralizing fluids as well of a comprehension of the Passa Três intrusion, reflected by the proposition of porphyry-type (Soares & Góis, 1987; Chiodi-Filho et al., 1989; Piekarz, 1991), “plutogenic” deposit (Piekarz, 1992 - including a comparison of the orebodies disposition with the Riedel system – Riedel (1929)) and filonean deposit associated with shear zones (Picanço, 2000). The Passa Três granite deposit shares some similarities with syenite-hosted gold deposits, like the mineralization hosted by an igneous stock, a major fault zone context, presence of fluorite in the orebodies, CO2-bearing fluids, and ankerite and calcite as alteration minerals. However, syenite-hosted gold deposits are also disseminated, with a mineralization associated with stockwork and breccia, and a characteristic alteration including K-feldspar, albite and commonly hematite, magnetite and biotite alteration (Robert, 2001; Bigot & Jebrak, 2015), which are not observed in the Passa Três deposit, where alteration is very weak.

The other major challenge with this manuscript is the lack of local geological information. There is no local geological map, the cross sections are not localized, and therefore the mineral information cannot be taken with confident.

Response: Ok, we included a map with the local geological information in Figure 1. Samples were collected from the drill holes and in the underground mine, in 5 different levels and in the galleries open and with access granted at the time of the study, in order to optimize representation. The depths of the samples are also indicated on the map by their levels. As we did not employ a cross-section approach, there is no cross-section to display.

I suggest therefore major corrections; you should

- Propose an adapted scientific question for the paper.

Response: Regarding the two above chapter and explanations on the Passa Tres granite type, and the parts added in the introduction, we assumed that the scientifc question is still valuable. This scientific question is developed within the last paragraph of the introduction and really correspond to the duslity between intrusion-related and intrusion-hosted mineralisation.

- Give local geological data

Response: Ok, we included a map with the local geological information in Figure 1.

- Organize a real discussion, i.e., the possible answers to the question of the paper

Response: As the question is not modified (see above, the discussion seems correct in our opinion and not changed.

- Conclude by answering the question

Response: Here also, the conclusion looks good for us. However, a sentence has been added in order to satisfy the reviewer comment (also in the abstract).

You did a great analytical job, and it could make a very good contribution to science. Some more work needed!

Hereafters are some detailed comments

1. 48 what is the importance and the economic value of the deposit? Is it exploited? For what? Since how many times?

                Response: Ok, we included this information in the text.

1. 67 not confirm. You should be open to another hypothesis! for instance, mesothermal gold, or alkaline gold….

Response: Ok, we included information about previous works (on session 2.1) and other models of formation considered for the deposits, as well, as included other kinds of models to broaden the discussion on the model types.

1. 78 it would be interesting to get some information about the composition of these terranes before reading their structural relationships

Response: We included information on the composition of the geological units on the regional map (Figure 1).  

Fig.1 the map is fine. However, most of the readers does not know the composition of all these units that appear very different, would it be possible to get a short description of the composition on these units: Sedimentary, Volcanic…

Response: We included information on the composition of the geological units on the regional map (Figure 1).  

1. 104 you name numerous units. Which one correspond to the pull apart detrital basin?

Response: The pull-apart basins are represented by the Castro Group, in the Apiaí Terrane. We included this information in the text.

1. 108 It is surprising not to see any reference of the Daniel Socoman work (2015) that was directed by one of the authors of this manuscript. His work offers interesting structural description of gold mineralization.

Response: Ok, we included some information provided by his study.

1. 110 references needed. What is the discussion?

Response: Ok, we included a paragraph with the previous studies, presenting other models of formation previously proposed for the Passa Três gold deposit.

1. 150 is there any evidence of crosscutting relationship between magmatism and mineralization?

Response: Ok, we did not observe cross-cutting relationship between magmatism and mineralisation, and we included this information on the text. However, the discussion about the structural characteristics of the deposit was presented by Dressel et al. (2081).

1. 236 a map of the local geology with the location of ore is absolutely needed. You should locate on this map where the drill section come from.

Response: We included a local geological map in Figure 1b. Schematic drill section is a composite of boreholes samples from several drill holes throughout the mine and available for description. Location of the mine was also included in the map.

2014. 278 nothing on the white granite? No granite geochemistry? Your granite presents strong analogies with high ba granite, typical from post orogenic intrusion, both in Archean terrane (sanukitoid clan), and Proterozoic and Phanerozoic environment. See Lara et al., 2017; Laurent et al. 2014. Is the white granite a greisen?

Response: No, it is impossible to suppose that this white granite can be a greisen…it is really a granite with no muscovite associated. As, we did not observe relationships between this white granite and the mineralization (the white granite has been observed only in cores), we focused on the red granite; therefore we did not have the geochemistry on this granite.

1. 307 the au bi association is well describe, especially as a marker of melting process in Maldon or Hemlo. But not the Bi pb + au association.

Response: This association Au-Bi-Pb was also observed by previous studies (Piekarz, 1992; Picanço, 2000) in the Passa Três deposit and on the San Juan de Chorunga Ag-Ag deposit (IRGD, Peru) by Crespo et al. (2020), despite the lack of explanation for this association.  We included the previous works and that Au-Bi is a classical association specifically in IRGD deposits.

1. 351 figure 8 is not a paragenetic diagram. All minerals occur at the same time. The diagram is therefore of limited interest. Use the same terminology than in the text (PQC…)

Response: We altered this figure (Figure 7), including the barren quartz veins and orebodies, that are related with alteration. We corrected the alteration for the same terminology as used in the text.

1. 447 a lot of information is missing about the fault gouge: Where is it located on a map, what is its strike, thickness, cinematic, relations to pluton and alterations?

Response: Ok, we included this information in the text: structural data of the orebodies (N-S/60-75W; E-W/45-70S; normal fault planes, fault gouge thickness (0.2-3.0mm), it crosscuts pluton and alterations.

1. 458 this list is poorly organized. Some minerals do not belong to alteration but to magmatic events. Reorganize this section please.

Response: Ok, we changed the title of this session to “Mineral chemistry”, and of session 4.3 to “Mineral chemistry on ore minerals (EPMA and LA-ICP-MS analyses)” in order to avoid confusion.

1. 535 The assemblage is fluorine rich. In this context, the use of zirconium as a stable element could be problematic. Did you try other elements, not F-mobile such as Ti? You should better justify your choice.

Response: We have done the mass balance calculations with both Zr and Ti and results are pretty similar. Zircon stability is apparently not affected by the presence of minor F in the system, as it has been revealed by Qemscan analysis. We also corrected and substituted the figure (a minor error was verified and corrected).

1. 708 The discussion is not a real discussion. There is no question, no hypothesis to discuss with contrasting arguments. Your scientific methodology is therefore rather weak. I understand that it would be a hard work to rewrite completely this section but consider your primary hypothesis: Is this deposit an irgd type? So, discuss if it has all the parameters. Could it be an orogenic gold deposit? An alkaline gold deposits. What are the differences? Your “discussion” is only deductive, and no alternate hypothesis are even evocated.

Response: Several parameters regarding the classification of the deposit were discussed in a previous publication by Dressel et al. (2018), that was focused on structural and geochronological data, and the main goal of this paper was to provide further data on alteration, fluid inclusions and ³⁴S for this deposit. Nevertheless, we included some discussion considering other deposits types in the discussion and information on previous works on the Passa Três deposit in the session 2.1.

1. 736 please indicate where the gold is in this figure. Give a scale, even approximative.

Response: We added the location of the gold in figures 20 and 21. A scale is presented in the borehole (depth from 0 to 400 m) of the figure 20.

1. 753 why do you have carbonate in an acid, low ph environment?

Response: The carbonate minerals from the alteration assemblages described are not pure calcite, but rather have compositions between ankerite and more complex Fe-Mg-Mn carbonates, which can be stable at pH of 4-4.5, which is compatible with the stability of muscovite/sericite in the studied assemblages. This type of carbonates are very common alteration features for intrusion-related /orogenic gold deposits.

1. 773 try avoiding personal reference in a scientific paper (our…). The concept of exteriority is fundamental in natural sciences.

Response: Ok, we changed the text.

1. 807 you state several times the “pull apart” structural context, but you never demonstrate it, neither show it in a figure. Please delete these mentions or explain, demonstrate, give a reference…

Response: Yes, it is because the pull apart context was explained on the previously paper published (Dressel et al., 2018), that’s why structural data are lesser mentioned in this paper. In order to clarify this, we added the citation of Dressel et al., 2018 and Dressel, 2018.

1. 830 please show a geological local map showing where the cupola is.

Response: We inserted a local geological map in Figure 1b. We consider that the whole extent of the outcropping granite (5 km2) is the cupola zone. We included this information in the text.

This conclusion is the logical output of your scientific approach. You cannot discover anything new of general interest… and therefore refer to existing model. It is a pity because your data deserves a better conclusion.

Response: See above. We added a sentence but the conclusion answer to the question in our opinion.

Author Response File: Author Response.pdf

Reviewer 2 Report

Lines 41-47: need biography

Figure 1: need in the legend symbology for separation of terranes.

Lines 122-134: need biography

Line 154: which minerals for U/Pb, and which for Ar-Ar.

Lines 173-174: locations, depths of sampling. Need more information. Do you have a location map for the samples? What levels and what mine?

Lines 179-186: What was the counting time? What were the arrangement  of the crystals? What was the beam diameter? The crystal arrangement for elements in silicates would have been different for sulfides. What was the crystal arrangement for each case? How many samples do you prepared in the thin section laboratory?

What were the accelerating voltage, absorption current, working distance, spot size of SEM analysis?

Line 192: change pyrite for “sulfides and gold”.

Line 196: How was the instrument tuned?

Line 201: what standard do you use for gold to reduce the data?

What isotopes do you monitored? What was the dwell time? Why do you used 90 second for background?

Line 221: Are the X-ray maps quantitative or qualitative?

Line 222: Why do you use thin section for fluid inclusions. Are thin or thick sections?

Lines 228-235: The isotope analysis methods need more details.

Line 258: It is observed that the biotite is altering to chlorite. It is possibly part of the low temperature hydrothermal alteration. It is probably part of the system as a low-temperature alteration to the host rock.

Figure 2. What is the location of the samples? Underground mine? Borehole?

Figures 3 B-H needs bar scale.

Lines 279: Does exist pyrite 1?

Line 287: Is homogenous pyrite or massive pyrite?

Line 303: Is native gold or electrum?

Line 307: See this article where Bi-bearing minerals related to Au mineralization in IRGD are identified. “Crespo, J., Holley, E., Pfaff, K., Guillen, M., & Huamani, R. (2020). Ore Mineralogy, Trace Element Geochemistry and Geochronological Constraints at the Mollehuaca and San Juan de Chorunga Au-Ag Vein Deposits in the Nazca-Ocoña Metallogenic Belt, Arequipa, Peru. Minerals, 10(12), 1112.”

Figure 5. There is a negative linear tendency in the gold grains to incorporate Ag, that is, the more Au they have, the less silver they incorporate, and vice versa. See figure 8 in Crespo et al., 2020.

Line 318: Co vs Ni  diagrams have been widely used to discriminate pyrites geochemically. You could explore that possibility. You can review Reich et al., 2016 TRACE ELEMENT SIGNATURE OF PYRITE FROM THE LOS COLORADOS IRON OXIDE-APATITE (IOA) DEPOSIT, CHILE: A MISSING LINK BETWEEN ANDEAN IOA AND IRON OXIDE COPPER-GOLD SYSTEMS?

Figure 6A: Better results would be seen in boxplots

Figure 8: In the paragenetic sequence where does gold appear?

Figure 9: Where are located the carbonates in the figure?

Line 426. You mention that in figure 13 the biotite is being altered to sericite, but the above is not observed or mentioned in the figure.

Line 453. Biography?

Lines 483-485: Could you put the calculations in a table?

Fluid inclusions: Did you see wispy textures in fluid inclusions? if it is an IRGD type deposit, therefore deep, you should not have hydrothermal type inclusions, rather inclusions with high contents of H2O-CO2. With a wispy texture array, with lots of implosion and explosion textures, but not an array of primary or secondary inclusions. In orogenic and IRGD deposits, it is difficult to choose what type of fluid inclusions to measure salinity and temperature, since they present implosion and explosion textures, which means that they underwent large changes in lithostatic or hydrostatic pressure during their formation.

Figure 18 B-C-D-E-G and H, are typical wispy texture.

Line 764. Is the magmatic quartz, bull quartz? What type of quartz is magmatic quartz? Are all types of fluid inclusion in all types of quartz?

Line 771: this is a huge range of temperatures.

Line 789: Are all deposits IRGD? If not, Why you compare your deposits with other type of deposits? Also, IRGD are characteristic for rich CO2 contents (5-30 mole%CO2), because requires great pressure to keep CO2 of that amount dissolved in the water.

Lines 794-801: the evidence of sulfur isotopes only indicates its magmatic origin and I agree. Since pyrite is associated with gold mineralization events, and your sulfur is of magmatic origin, why is there supposed to be a hydrothermal-magmatic transition? What is the solid evidence for this statement?

Lines 803-809: What you mentions is the formation of epithermal or porphyry type deposits. Do you mean that the IRGD have an origin like porphyry type deposits? This paragraph is confusing for me. Explain more please.

Line 817: phase separation = boiling. That's what you want to say?

Line 823: When there is a decompression, the fluid inclusions experience a tremendous pressure differential inside the inclusion and explode (decrepit) giving implosion textures. Do you have evidence of these textures in your fluid inclusions?

If the deposit had a hydrothermal magmatic transition, different generations of pyrite would exist, and the sulfur delta values would also yield hydrothermal values. The term magmatic-hydrothermal is sometimes used for a wide range of deposits.

Line 858: I think is a huge range of temperatures.

Author Response

Answer to reviewer 2:

Lines 41-47: need biography

Response: Ok, we added references.

Figure 1: need in the legend symbology for separation of terranes.

Response: We highlighted the different terranes in Figure 1a with thick grey lines.

Lines 122-134: need biography

Response: The names of the facies are the same as the ones used in the Tabiporã mine. We included this information in the text. The other information was acquired during this study, previously published by Dressel (2018) and Dressel et al. (2018) (citation was already in the text).

Line 154: which minerals for U/Pb, and which for Ar-Ar.

Response: Ok, we included this information in the text (U/Pb: zircon; Ar/Ar: muscovite).  

Lines 173-174: locations, depths of sampling. Need more information. Do you have a location map for the samples? What levels and what mine?

Response: Ok, we included a map with the local geological information in Figure 1b, including location of the samples, location of the mine developed by Tabiporã mining company and the levels of the mine. Level’s depth was included in the text (materials and methods).

Lines 179-186: What was the counting time? What were the arrangement  of the crystals? What was the beam diameter? The crystal arrangement for elements in silicates would have been different for sulfides. What was the crystal arrangement for each case? How many samples do you prepared in the thin section laboratory?

Response: Ok, we added this information in the text.

What were the accelerating voltage, absorption current, working distance, spot size of SEM analysis?

Response: Ok, we included the following information in the text : accelerating voltage: 15 kV; working distance: 10 mm; spot size: 3.5 um. The information on the absorption current was not provided by the equipment.

Line 192: change pyrite for “sulfides and gold”.

Response: Ok, we made the alteration.

Line 196: How was the instrument tuned?

Response: Ok, we included more details in the text. (Prior to analyses, the instrument was tuned for maximum sensitivity and low oxide production (ThO/Th < 1%) using a NIST612 glass. This includes torch alignment and gas flow optimisation)

Line 201: what standard do you use for gold to reduce the data?

Response: The mentioned standard MASS-1 was utilized to reduce the data, including Au.

What isotopes do you monitored? What was the dwell time? Why do you used 90 second for background?

Response: Ok, we included this information in the text (Monitored isotopes: ⁵⁹Co, ⁶⁰Ni, ⁶⁵Cu, ⁶⁶Zn, ⁷⁵As, ¹⁰⁷Ag, ¹²¹Sb, ¹²⁵Te, ¹⁹⁷Au, ²⁰⁸Pb and ²⁰⁹Bi with a dwell time of 12ms.). Background duration of 90s was typically used to achieve a good statistics on most elements).

Line 221: Are the X-ray maps quantitative or qualitative?

Response: Yes, the X-ray maps are qualitative. We included this information in the text.

 Line 222: Why do you use thin section for fluid inclusions. Are thin or thick sections?

Response: Indeed, they are thick sections (200 µm thick). We corrected in the text.

Lines 228-235: The isotope analysis methods need more details.

Response: Ok, we included more details of the procedure in the text.

Line 258: It is observed that the biotite is altering to chlorite. It is possibly part of the low temperature hydrothermal alteration. It is probably part of the system as a low-temperature alteration to the host rock.

Response: We did not understand the relation with this paragraph, but chlorite alteration is mentioned in the session about the sericite-carbonate-chlorite alteration and on the session about mineral chemistry.

Figure 2. What is the location of the samples? Underground mine? Borehole?

Response: (A) underground mine and (B) borehole. The information is already in the legend of the figure that also included information on thin section (sample from underground mine).

Figures 3 B-H needs bar scale.

Response: Images from (a) to (h) present the same region (but in different views), therefore scale bar in (a) is the same for images from (b) to (h). In order to avoid visual pollution, we added a phrase in the legend of this figure. This figure was transferred to Supplementary Material A, Figure S1.

Lines 279: Does exist pyrite 1?

Response: No, it doesn’t, we observed only two pyrites: pyrite 2a and pyrite 2b. We named them like that to designate the phase in which they occur (hydrothermal phase 2), and we decide to adopt this nomenclature to remain consistent with the 1st publication (Dressel et al., 2018).

Line 287: Is homogenous pyrite or massive pyrite?

Response: We change to « massive » in the text.

Line 303: Is native gold or electrum?

Response: Native gold. We specified this in the text.

Line 307: See this article where Bi-bearing minerals related to Au mineralization in IRGD are identified. “Crespo, J., Holley, E., Pfaff, K., Guillen, M., & Huamani, R. (2020). Ore Mineralogy, Trace Element Geochemistry and Geochronological Constraints at the Mollehuaca and San Juan de Chorunga Au-Ag Vein Deposits in the Nazca-Ocoña Metallogenic Belt, Arequipa, Peru. Minerals, 10(12), 1112.”

Response: Very interesting. We cited this article in this paragraph.

Figure 5. There is a negative linear tendency in the gold grains to incorporate Ag, that is, the more Au they have, the less silver they incorporate, and vice versa. See figure 8 in Crespo et al., 2020. 

Response: Indeed, the linear trend is very similar. We cited this article.

Line 318: Co vs Ni  diagrams have been widely used to discriminate pyrites geochemically. You could explore that possibility. You can review Reich et al., 2016 TRACE ELEMENT SIGNATURE OF PYRITE FROM THE LOS COLORADOS IRON OXIDE-APATITE (IOA) DEPOSIT, CHILE: A MISSING LINK BETWEEN ANDEAN IOA AND IRON OXIDE COPPER-GOLD SYSTEMS?

Response: The Ni analyses are below detection limit, so impossible to construct any reasonably representative plot with this.

Figure 6A: Better results would be seen in boxplots

Response: We don’t agree because, for some elements, there are just a few points which are above limit of detection. If they were 100 points to be presented – then yes, box plots would be a better solution, but with the limited number of points analysed by LA-ICP-MS, plots with individual points are more informative. (This figure is now Figure 5)

Figure 8: In the paragenetic sequence where does gold appear?

Response: Gold is associated with the SCC alteration. We included the barren quartz veins (associated to PQC alteration) and orebodies (associated to the SCC alteration) in this figure (now Figure 7).

Figure 9: Where are located the carbonates in the figure?

Response: Ok, we indicated the carbonate and replaced the figure (Figure 8).

Line 426. You mention that in figure 13 the biotite is being altered to sericite, but the above is not observed or mentioned in the figure.

Response: Yes, we corrected the text.

Line 453. Biography?

Response: The information about the fault gouge was acquired by this study, but we added the citation of a previously published paper and a thesis defended by the 1st author of this article (Dressel, 2018), Dressel et al.,2018).

Lines 483-485: Could you put the calculations in a table?

Response: Because the paper is too long, we decided to not show the calculations, but it is not necessary.

 Fluid inclusions: Did you see wispy textures in fluid inclusions? if it is an IRGD type deposit, therefore deep, you should not have hydrothermal type inclusions, rather inclusions with high contents of H2O-CO2. With a wispy texture array, with lots of implosion and explosion textures, but not an array of primary or secondary inclusions. In orogenic and IRGD deposits, it is difficult to choose what type of fluid inclusions to measure salinity and temperature, since they present implosion and explosion textures, which means that they underwent large changes in lithostatic or hydrostatic pressure during their formation.

Response: We didn’t observe such textures, and also the microthermometry is not supporting H₂O-CO₂ composition only. The salinity goes up to 12wt% NaCl, indicating a system H₂O-NaCl-CO₂.

Figure 18 B-C-D-E-G and H, are typical wispy texture.

Response: We don’t agree, because we observe fluid inclusions planes with well-defined inclusions.

Line 764. Is the magmatic quartz, bull quartz? What type of quartz is magmatic quartz? Are all types of fluid inclusion in all types of quartz?

Response: As shown in the figure 19 (Synthetic sketch on the fluid inclusions) (this figure is now Figure 13), the magmatic quartz is the one that integrates the granite (primary quartz), and we observed fluid inclusions types 1, 2 and 3 in the magmatic quartz; however types 2 and 3 only on the hydrothermal quartz  

Line 771: this is a huge range of temperatures.

Response: Yes, definitely, but this T range could also result from recrystallization of the quartz.

Line 789: Are all deposits IRGD? If not, Why you compare your deposits with other type of deposits? Also, IRGD are characteristic for rich CO2 contents (5-30 mole%CO2), because requires great pressure to keep CO2 of that amount dissolved in the water.

Response: Yes, all these deposits are classified as IRGD (Baker & Lang, 2001 - check). As for the CO₂ contents, we corrected the text (high CO₂ contents).

Lines 794-801: the evidence of sulfur isotopes only indicates its magmatic origin and I agree. Since pyrite is associated with gold mineralization events, and your sulfur is of magmatic origin, why is there supposed to be a hydrothermal-magmatic transition? What is the solid evidence for this statement?

Response: That is supported by the observation of the different stages: granite -> aplite -> pegmatite -> quartz veins with K-feldspar border -> mineralized veins. The magmatic-hydrothermal transition was the main subject of a previously published article (Dressel et al., 2018), we added this citation in the text.

Lines 803-809: What you mentions is the formation of epithermal or porphyry type deposits. Do you mean that the IRGD have an origin like porphyry type deposits? This paragraph is confusing for me. Explain more please.

Response: In this paragraph we explain that gold deposits associated with magmatic-hydrothermal transition may involve a combination of several different processes, and some similarities exist between different types of deposit. However, IRGD present a specific set of characteristics that are unique of this classification, as cited in the introduction of this paper.

Line 817: phase separation = boiling. That's what you want to say?

Response: Because the homogenisation temperature is variable among fluid inclusions in a same FIA, it is not possible to conclude that boiling occurred; nevertheless we can assume that a phase separation occurred because the fluid inclusions present different vapor/liquid ratios, which could be also caused by decompression of the system and the fault-valve model, as mentioned in the text.

Line 823: When there is a decompression, the fluid inclusions experience a tremendous pressure differential inside the inclusion and explode (decrepit) giving implosion textures. Do you have evidence of these textures in your fluid inclusions?

Response: No, we didn’t observe this kind of texture. The fluid inclusions selected for this study are well-defined inclusions and occur in planes.

If the deposit had a hydrothermal magmatic transition, different generations of pyrite would exist, and the sulfur delta values would also yield hydrothermal values. The term magmatic-hydrothermal is sometimes used for a wide range of deposits.

Response: Pyrite is not stable at magmatic temperature, so this mineral precipitates only from a fluid phase, not a melt. If the fluid has magmatic composition, then the pyrite and the other sulfides crystallizing synchronously will also show ³⁴S indicating magmatic origin for the sulfur.

Line 858: I think is a huge range of temperatures.

Response: Yes, definitely, but this T range could also result from recrystallization of the quartz.

Author Response File: Author Response.pdf

Reviewer 3 Report

Authors: Barbara Carolina Dressel , Alain Chauvet, Kalin Kouzmanov, Barbara Trzaskos, Olivier Bruguier, Patrick Monié, Sandro Notto Villanova, José Bazille

Section: Mineral Deposits

Comments for authors:

General comments:

The authors present the paper entitled: "The Passa Três granite intrusion-related/hosted neoproterozoic gold deposit (Paraná State, Brazil): Mineralogical, geochemical, fluid inclusion and sulphur isotope constraints".

In my opinion it is an interesting title whose results could serve as a guide for important geological and geochemical prospecting work.

The methods are rigorously described.

However, the work is excessively long (40 pages !!!). There is too much information which is sometimes repeated.

In my opinion, this work should be significantly compressed to 20-5 pages. No more. I would even go so far as to say that this work could give rise to more than one research paper.

The excess of argument makes it more like a geological report, rather than a scientific paper.

I invite the authors to work on the points made.

Good luck!

Specific comments:

Abstract: Authors should rewrite the abstract indicating what are the fundamental objectives pursued by this work. A paragraph should be added at the end of the abstract stating how and in what field the results obtained could be used. Check.

Abstract: Lines 17 to 19. The authors say: "Orebodies are hosted by the pluton roof zone...", but in lines 31 and 32 they say: "The specific location of the mineralisation in the core of the Passa Três granitic intrusion...". I ask: is the mineralisation in the roof or in the core? Please answer.

Introduction: Lines 37 to 62: The arguments given by the authors do not define the sense of the Introduction. In the introduction, a state of the art of the work carried out in the area over time should be presented, highlighting the main aspects and levels reached by this research. The approach taken by the authors is more typical of Geological Setting. Please rewrite.

Subsections 2.1 and 2.2 are too long and overshadow the methodological part. Authors are advised to compress these subsections as much as possible. Rewrite

At the same time, authors are encouraged to increase the number of references. This is a very extensive work, therefore, it needs much more references. Rewrite.

Section 3. This section should be renamed "Materials and methods".

Lines 173 and 174. At what depth were each of the samples taken? Answer.

Section 4. This section should be renamed simply "Results". Check.

Conclusions: The authors do not provide data on the possible applications of the data obtained. It is essential to add a paragraph at the end of the Conclusions giving this idea. Fix.

Author Response

Answer to Reviewer 3

General comments:

The authors present the paper entitled: "The Passa Três granite intrusion-related/hosted neoproterozoic gold deposit (Paraná State, Brazil): Mineralogical, geochemical, fluid inclusion and sulphur isotope constraints".

In my opinion it is an interesting title whose results could serve as a guide for important geological and geochemical prospecting work.

The methods are rigorously described.

However, the work is excessively long (40 pages !!!). There is too much information which is sometimes repeated.

In my opinion, this work should be significantly compressed to 20-5 pages. No more. I would even go so far as to say that this work could give rise to more than one research paper.

Response: In order to reduce the pages number, we shorten figures 4 and 11 (and made the necessary changes in the respective legends), and transferred figures 3, 10 and 13 to supplementary material A (Qemscan), and tables 1 and 2 to supplementary materials E (table 1 - mass balance) and F (table 2 – ³⁴S isotopes). Indeed, the alteration supplementary material E (RAMAN) changes to G. Due to these modifications and text changing, we were able to reduce to 36 pages. We just want to highlight that there is not limit of page in Minerals, thus justifying our choice for this journal.

The excess of argument makes it more like a geological report, rather than a scientific paper.

I invite the authors to work on the points made.

Good luck!

Specific comments:

Abstract: Authors should rewrite the abstract indicating what are the fundamental objectives pursued by this work. A paragraph should be added at the end of the abstract stating how and in what field the results obtained could be used. Check.

Response: Usually, the objectives of a publication are written in the introduction, not in the abstract. The abstract has to summarize the entire paper. However, we have included a phrase about how the results could be useful for other discoveries.

Abstract: Lines 17 to 19. The authors say: "Orebodies are hosted by the pluton roof zone...", but in lines 31 and 32 they say: "The specific location of the mineralisation in the core of the Passa Três granitic intrusion...". I ask: is the mineralisation in the roof or in the core? Please answer.

Response: Both, the mineralisation is in the core of the granite regarding its outcropping area, but positioned at the roof zone. We included this at line 31-32.

Introduction: Lines 37 to 62: The arguments given by the authors do not define the sense of the Introduction. In the introduction, a state of the art of the work carried out in the area over time should be presented, highlighting the main aspects and levels reached by this research. The approach taken by the authors is more typical of Geological Setting. Please rewrite.

Response: We included information about the previous works conducted in the Passa Três granite in the introduction. However, one more time, the state of the art is for the geological setting, not for the introduction, usually…

Subsections 2.1 and 2.2 are too long and overshadow the methodological part. Authors are advised to compress these subsections as much as possible. Rewrite

Response: We shorten the session 2.1 and 2.2 as possible and moved portions of the session 2.2 to the results and discussion part, and eliminated some repetition. However, the remaining text in session 2.2 is very important to set the context of the deposit to the reader, and presents a condensed text on the structural, geochronological and classification of the deposit conducted in this study and published in another paper (Dressel et al., 2018).

At the same time, authors are encouraged to increase the number of references. This is a very extensive work, therefore, it needs much more references. Rewrite.

Response: Ok, we added more references, mainly in the introduction and in the discussion sessions.

Section 3. This section should be renamed "Materials and methods".

Response: Ok, we made the change.

Lines 173 and 174. At what depth were each of the samples taken? Answer.

Response: Ok, we included this information in the text, and also the distribution of the samples by mine level can be observed in the new local geological map inserted in Figure 1 (now figure 1b).

Section 4. This section should be renamed simply "Results". Check.

Response: Ok, we made this change but we prefer “Petrology, mineralogy and texture”.

Conclusions: The authors do not provide data on the possible applications of the data obtained. It is essential to add a paragraph at the end of the Conclusions giving this idea. Fix.

Response: Done.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors consider seriously the comment and modify their manuscript with the good approach.

I still think that the research question could have been more accurate (numerous veins in syenite hosted gold deposits...) but it could be the topic of another paper.

I recommend therefore the publication

Author Response

No comments

Reviewer 2 Report

In the paragenetic sequence figure, where is located pyrite 2a and pyrite 2b?

Thank you for your good work with the reviews.
As you yourself mention in the text, the deposit suffered a great decompression of the Fault-valve model type, therefore, there should be fluid inclusions of the wispy type (implosion and explosion textures), which are indicating this same phenomenon. I understand that to do the work of fluid inclusions, they looked for FI families in planes, which is not bad, but the results are not conclusive, you have a wide temperature range, which, although it is true, is a product of the recrystallization of quartz, but you could not constrain at what temperature the quartz-gold association was formed, for example.

Author Response

In the paragenetic sequence figure, where is located pyrite 2a and pyrite 2b?

Ok, we indicated the location of Py2a and Py2b and replaced the figure.

As you yourself mention in the text, the deposit suffered a great decompression of the Fault-valve model type, therefore, there should be fluid inclusions of the wispy type (implosion and explosion textures), which are indicating this same phenomenon. I understand that to do the work of fluid inclusions, they looked for FI families in planes, which is not bad, but the results are not conclusive, you have a wide temperature range, which, although it is true, is a product of the recrystallization of quartz, but you could not constrain at what temperature the quartz-gold association was formed, for example.

We agree that our type 2 fluid inclusions present irregular shapes but there are not wispy fluid inclusions. We don’t observed wispy inclusions within our samples and moreover, we carefully selected valid inclusions for microthermometry that can present different vapor/liquid ratios and irregular shaped but there are not destroyed. We don’t observed typical wispy inclusions characterized by irregularly shaped relict inclusions surrounded by new-formed inclusions, as the ones observed by Diamond & Tarantola (2015). Irregular shaped fluid inclusions, similar to the type 2 studied in our work, were also encountered in the Jiaodong-type Xinli gold deposit (Deng et al., 2015), and were interpreted as formed by heterogeneous entrapment of immiscible fluids. Faleiros et al. (2014) also described fluid inclusions with similar shape but with random three-dimensional distributions that are considered as orogenic and associated with fault-valve process. In order to explain the variable V/L ratios, Faleiros et al. (2014) considered first two possibilities: (i) entrapment of two unmixed fluids from a parental homogeneous fluid (fluid immiscibility) or (ii) the entrapment of two mechanically mixed fluids. In the first case, cogenetic fluid inclusions may have Th(tot) in the same temperature range, and a wide range of salinity, which let assume that other processes like fluid mixing also occurred in addition to fluid immiscibility (one more primitive high salinity solution hot fluid and a slightly saline meteoric fluid). As we did not observe post-entrapment modifications in our measured fluid inclusions, such a process could thus explain the wide range of Th(tot) and salinities observed in the Passa Três deposit, possibly associated with fluid pressure fluctuation that can occur during subsequent phases of pull-apart infilling (i.e., the model of formation of the Passa Tres deposit published by Dressel et al., 2018), and possibly by the mixing of two different fluids (a high temperature magmatic one and a low temperature meteoric one).

In order to make the manuscript clearer for the reader, we made some changes in the text (underlined in yellow) that may help for the understanding.

Reviewer 3 Report

The authors have replied to all the Reviewer's questions.

Author Response

No comments