Elucidating Pathfinding Elements from the Kubi Gold Mine in Ghana
Round 1
Reviewer 1 Report
Very interested contributions about gold mineralisation in Africa.
Author Response
Reviewer’s comment: Very interested contributions about gold mineralisation in Africa.
Author’s reply: We thank the reviewer for this observation.
Reviewer 2 Report
This is a good and very interesting paper including a complete study of XPS and also of EDX developed over a gold ore. However, some questions need to be improved. You find here enclosed some comments and suggestions.
- Keywords: The terms "qualitative and quantitative analysis" should be removed.
- Lines 225-227: The Au powder concentrate weighed 80 g, but once separated you mention two fractions: 0,85 g coarse and 1,20 g fine-grained. You should revise this statement.
- Figure 3a is not indicated in the text.
- Lines 231-232: it appears 0,05-0,2 cm size, but Figure 3b seems to indicate 2 cm x 1,60 cm. It should be clarified.
- Line 370: Detected you pure elemental iron in the studied sample? I think that pure iron only can be detected as meteoric iron; but here?
- Lines 380, 382, 385: subscripts
- Tables 1 and 2: And sulfur? It not appeared in your analysis? This elements not appeared as sulfide?
- Page 17: Detected the authors FeO in these samples? This is not common in minerals
- Table 3: If these results are quantitative, then three significant digits (not decimals) should be used: 11.7 / 9.50 / 23.3 / 7.44 / 14.4 and so on. If these analyses are semiqunatitative then only two significant digits: 12 / 9,5 / 23 / and so on
- Table 3: sulfur not appears?, but in line 460 you mention pyrite, pyrrothite and so on.
- Line 465: subscript. On the other hand appears the term pure iron; it should be clarified. Is it pure elemental iron?
- Conclusions, line 500: X-ray
- References: This item needs to be revised. The year of publication is sometimes listed in parentheses and sometimes without parentheses. On the other hand, subscripts must be introduced in bibliographic citations 19, 21, 25, and 71.
- I think that a detailed and final reading of the work by the authors will result in an improvement of it.
Author Response
Reviewer’s comment:
This is a good and very interesting paper including a complete study of XPS and also of EDX developed over a gold ore. However, some questions need to be improved. You find here enclosed some comments and suggestions.
Reviewer’s comment: Keywords: The terms "qualitative and quantitative analysis" should be removed.
Author’s reply: Implemented
Reviewer’s comment: Lines 225-227: The Au powder concentrate weighed 80 g, but once separated you mention two fractions: 0,85 g coarse and 1,20 g fine-grained. You should revise this statement.
Author’s reply: on line 228 we added for clarity: “(the residual 77.95g containing sand and gravel was disposed)”
Reviewer’s comment: Figure 3a is not indicated in the text.
Author’s reply: This was added on line 222: “as shown in Figure 3a”, on line 224: “in Figure 3c” and on line 226: “Figure 3d”.
Reviewer’s comment: Lines 231-232: it appears 0,05-0,2 cm size, but Figure 3b seems to indicate 2 cm x 1,60 cm. It should be clarified.
Author’s reply: 0,05-0,2 cm size represents the grain/particle size while 2 cm x 1,60 cm is the image size or coverage area of sample.
Reviewer’s comment: Line 370: Detected you pure elemental iron in the studied sample? I think that pure iron only can be detected as meteoric iron; but here?
Author’s reply: Telluric iron, also called native iron, is iron that originated on Earth is found in a metallic form rather than as an ore is extremely rare, with only one known major deposit in the world, located in Greenland. On line 390 we added: “As telluric iron is extremely rare, we anticipate that the pure metallic Fe observed by our XPS measurements originates from iron oxides are readily reduced in the argon monomer sputter cleaning process”.
Reviewer’s comment: Lines 380, 382, 385: subscripts
Author’s reply: Changes done
Reviewer’s comment: Tables 1 and 2: And sulfur? It not appeared in your analysis? This elements not appeared as sulfide?
Author’s reply: In Table 1 we added sulfur which was ignored because of the negligible content that was below the detection limit in both XPS and EDX. During panning and washing the sulfide minerals get washed away since they are much lighter than the Fe and Au metals that settle at the bottom of the pan.
Reviewer’s comment: Page 17: Detected the authors FeO in these samples? This is not common in minerals.
Author’s reply: We thank the referee for this observation. We did not explicitly detect FeO but it was part of our assumption and analysis since it belongs to the oxide group of minerals. We removed FeO on page 17.
Reviewer’s comment: Table 3: If these results are quantitative, then three significant digits (not decimals) should be used: 11.7 / 9.50 / 23.3 / 7.44 / 14.4 and so on. If these analyses are semiqunatitative then only two significant digits: 12 / 9,5 / 23 / and so on
Author’s reply: This was implemented in table 3.
Reviewer’s comment: Table 3: sulfur not appears?, but in line 460 you mention pyrite, pyrrothite and so on.
Author’s reply: We thank the referee for this observation. The mineralization at the Kubi site is controlled by garnet and sulfur rich minerals. The XPS could not detect the sulfur content in samples since the intensities were below the detection limit. Our analysis was based the Fe content rather than the sulfur content. With the aid of binding energies in the literature as reference the possibilities are the aforementioned minerals.
On line 290-294 we added: “In the present experiment sulfur is very diluted in the samples due to the preparation method that make the detection of sulfur by XPS very challenging (low sensitivity). Only a very weak S 2p peak around 165 eV was observed in untreated powder while in the fine-grained sample it was hardly discernable. In the other samples it was below the signal-to-noise level. The S 2s cross-section 231 eV is even lower than for the S 2p signal”.
For clarity on line 479-483, we also added: “In our analysis we have prepared the samples (fine and coarse grained) from the untreated powder so that almost all sulfur containing grains were discarded. This is due to the fact that the sulfide minerals get washed away during panning and washing since they are much lighter than the Fe and Au metals that settle at the bottom of the pan”.
Reviewer’s comment: Line 465: subscript. On the other hand, appears the term pure iron; it should be clarified. Is it pure elemental iron?
Author’s reply: Yes, it is pure elemental iron. Corrected.
Reviewer’s comment: Conclusions, line 500: X-ray
Author’s reply: Corrected.
Reviewer’s comment: References: This item needs to be revised. The year of publication is sometimes listed in parentheses and sometimes without parentheses. On the other hand, subscripts must be introduced in bibliographic citations 19, 21, 25, and 71.
Author’s reply: Corrected.
Reviewer’s comment: I think that a detailed and final reading of the work by the authors will result in an improvement of it.
Author’s reply: We agree.
Reviewer 3 Report
Lines 45-50 - too long, please restructure
etc. could mean anything, indicate what you meant or remove
Lines 272 to 276 should be under sample preparation
Line 415 - The lower energy t2g orbitals do not favor sigma interactions with ligands. why? Please explain
Lines 488 - 493 - could please show how you arrived at 22 carats? If it has been written somewhere in the ms, please make it obvious
Author Response
Reviewer’s comment: Lines 45-50 - too long, please restructure etc. could mean anything, indicate what you meant or remove
Author’s reply: We have amended the text to the following:
“Indicator and pathfinder theories are deployed by geologists and explorers to gain information on the location of ore deposits, through methods such as; gold grain morphology, gold grain inclusion, composition studies, and geochemistry to test clues and patterns to locate ore-bodies for gold [4,5]. Gold grain morphology focuses on changes in Au surface shape via weathering and erosion as sediments are transported from far distances while gold grain inclusion focuses on the presence of other minerals in gold grains to provide information about the deposit type and mineralization associated. Composition studies on the other hand are used to gather and examine mineral samples for information on distances and direction of transport and finally geochemistry de-pends on identifying and analyzing minerals like silver, platinum, palladium, copper, lead, iron, telluride etc”.
Reviewer’s comment: Lines 272 to 276 should be under sample preparation
Author’s reply: These lines have been moved to lines 231 to 234 on section for sample preparation.
Reviewer’s comment: Line 415 - The lower energy t2g orbitals do not favor sigma interactions with ligands. why? Please explain
Author’s reply: For clarity, on line 436 we added the following: “Au has a face centered cubic (fcc) crystal structure, and its bonding is a mixture of covalent, ionic, and metallic bonds. Due to symmetry considerations, the covalent contribution consists of Au eg-ligand 2p (pd-σ), Au t2g-ligand 2p (pd-ℼ), and Au-Au t2g (dd-sigma) bond regions that can be observed in the valence band”.
Reviewer’s comment: Lines 488 - 493 - could please show how you arrived at 22 carats? If it has been written somewhere in the ms, please make it obvious
Author’s reply: We have added on line 513: “Au bulk nugget (22 carats measured with a digital electronic Au purity Analyzer DH 300 K from VTSYIQ)”. Also in Figure 3.
Reviewer 4 Report
The study elucidates sediments from artinasal (Au) mining sites to quantify the content of Au and other elements/minerals to infer the original indicator host minerals in the area. Particular attention is paid also to chemical bonding by means of XPS and EDX spectroscopy. The paper presents interesting experimental data and provides a great potential for practical use. Therefore, there is a need to publish it (after minor revision as suggested below).
Specific comments and suggestions
The title is good, as well as the abstract and keywords.
Introduction properly summarizes the current research and knowledge gaps that are well connected with the objective of the study. Perhaps, information on line 141 (that identifiable elements were inferred to the pathfinder minerals hosting Au mineralization in the study areas) could be more specific - as it relates exactly to the results of the manuscript.
Introduction should be revised in terms of usage of the references. Firstly, please avoid using multiple (lumped) references and mention the contribution of each reference individually (e.g., line 98 - [25-32], line 125 - [35-44], etc. ) Secondly, if there is no special reason for it, there is no need to mention the year of the publication in the text; instead, the number of the reference should be placed next to the name(s): e.g., line 139: "Nude et al. [47] used a ..... of Ghana" should be used instead of "Nude et al. (2012) used a ..... of Ghana [47]". Please check the whole manuscript for such corrections (as they will be abundant).
Section 2.3. Sample preparation. Please add more details on the collection of the "composite concentrate sample" of 1.90 kg (line 222). Further procedure (after the collection of this sample) is sufficiently described.
There are two sections 3.2.
I appreciate the detailed literature search (95 references) - these references were used during the description of current state of knowledge and also for the comparison with measured results. Nevertheless, list of references at the end of manuscript needs revision as the format does not meet the journal reccomended style.
Author Response
The study elucidates sediments from artisanal (Au) mining sites to quantify the content of Au and other elements/minerals to infer the original indicator host minerals in the area. Particular attention is paid also to chemical bonding by means of XPS and EDX spectroscopy. The paper presents interesting experimental data and provides a great potential for practical use. Therefore, there is a need to publish it (after minor revision as suggested below).
Specific comments and suggestions:
Reviewer’s comment: The title is good, as well as the abstract and keywords.
Author’s reply: We agree with this statement.
Reviewer’s comment: Introduction properly summarizes the current research and knowledge gaps that are well connected with the objective of the study. Perhaps, information on line 141 (that identifiable elements were inferred to the pathfinder minerals hosting Au mineralization in the study areas) could be more specific - as it relates exactly to the results of the manuscript.
Author’s reply: we thank the reviewer for this observation and amended this sentence to the following: “In both cases the trace elements such as Fe, Mn, Ag, As, Cu, Zn, Ni, Pb, etc. were identified and appeared to be associated with Au and suitable as pathfinder elements of Au in the study areas”.
Reviewer’s comment: Introduction should be revised in terms of usage of the references. Firstly, please avoid using multiple (lumped) references and mention the contribution of each reference individually (e.g., line 98 - [25-32], line 125 - [35-44], etc. ) Secondly, if there is no special reason for it, there is no need to mention the year of the publication in the text; instead, the number of the reference should be placed next to the name(s): e.g., line 139: "Nude et al. [47] used a ..... of Ghana" should be used instead of "Nude et al. (2012) used a ..... of Ghana [47]". Please check the whole manuscript for such corrections (as they will be abundant).
Author’s reply: This has been implemented.
Reviewer’s comment: Section 2.3. Sample preparation. Please add more details on the collection of the "composite concentrate sample" of 1.90 kg (line 222). Further procedure (after the collection of this sample) is sufficiently described.
Author’s reply: For clarity we added following sentence on line 222: “The sample was collected by one of the authors (G.K.N) with the aid of a geological hammer into a sample collection bag”.
Reviewer’s comment: There are two sections 3.2.
Author’s reply: Corrected.
Reviewer’s comment: I appreciate the detailed literature search (95 references) - these references were used during the description of current state of knowledge and also for the comparison with measured results. Nevertheless, list of references at the end of manuscript needs revision as the format does not meet the journal recommended style.
Author’s reply: The references style has been adjusted to the recommended style of the journal.
