Journal of Geochemical Exploration最新文献

{"title":"Dissolution behavior of mixed calcium‑cobalt carbonates at 25 °C in contact with different gas phases","authors":"","doi":"10.1016/j.gexplo.2024.107558","DOIUrl":"10.1016/j.gexplo.2024.107558","url":null,"abstract":"<div><p>The potential immobilization of cobalt in various environments can be achieved through the incorporation of Co into carbonate minerals, forming solid solutions of (Ca_1-xCo_x)CO₃. However, the thermodynamic properties of these minerals are not well-understood due to conflicting data from natural observations and experiments. In this work, a series of mixed calcium‑cobalt carbonates were prepared and their interaction with aqueous solution was investigated. Depending on the Co/(Ca + Co) mol ratio (X_Co) of the mixed solution, ranging from 0.00 to 1.00, pure calcite, Co-bearing calcite, Co-bearing aragonite, Ca-bearing spherocobaltite and pure spherocobaltite were successively synthesized using a precipitation method. Upon dissolution of the Co-bearing solids (X_Co = 0.10–1.00) in N₂-degassed water (NW) and air-saturated water (AW), the Co concentration of the aqueous solutions increased gradually to a stable state of 0.017–0.191 and 0.018–0.186 mmol/L after 240–360 d dissolution, respectively. When the dissolution occurred in CO₂-saturated water (CW), the Co concentration initially spiked to 0.372–2.258 mmol/L within 6 h ∼ 15 d and then decreased to a stable range of 0.030–0.559 mmol/L after 240–360 d. The Co/(Ca + Co) mol ratio in the aqueous solution (X_Co2+,AS) was significantly lower than the Co/(Ca + Co) atomic ratio in the solids (X_Co,SS), particularly when dissolved in NW and AW. During these dissolution processes in NW, AW and CW at 25 °C, the average log IAP values at the final stable state were determined as follows: for calcite (CaCO₃), the values were −8.25 ± 0.03 in NW, −8.34 ± 0.11 in AW, and −8.10 ± 0.08 in CW; for spherocobaltite (CoCO₃), they were −9.24 ± 0.26 in NW, −9.39 ± 0.23 in AW, and −9.38 ± 0.09 in CW. Furthermore, the log IAP values increased from those typical for calcite to −7.89 ± 0.01 ∼ −7.84 ± 0.10 for the solid with X_Co,SS = 0.187 as X_Co,SS increased, eventually aligning with those typical of spherocobaltite. Lippmann diagrams, constructed using the Guggenheim parameters <em>a</em>₀ = 2.30 and <em>a</em>₁ = 0.265 for the “subregular” calcite-spherocobaltite solid solutions [(Ca_1-xCo_x)CO₃] with a miscibility gap ranging from X_Co,SS = 0.251 to 0.858, highlighted the “peritectic” point at X_Co₂₊_,AS = 0.0538 on the <em>solutus</em>. This analysis revealed that the solids dissolved non-stoichiometrically in water. Consequently, the Co-poor aqueous solution would reach equilibrium with the Co-rich calcite-structure phase at the solid surface.</p></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141936914","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Trace element signatures in scheelite associated with various deposit types: A tool for mineral targeting","authors":"","doi":"10.1016/j.gexplo.2024.107555","DOIUrl":"10.1016/j.gexplo.2024.107555","url":null,"abstract":"<div><p>Scheelite is a widespread mineral in several geological settings and its trace element composition provides valuable information about the source and composition of the hydrothermal fluids. In this study, scheelite from 22 magmatic-hydrothermal deposits and 2 orogenic Au deposits (Hangar Flats and Corcoesto) were analyzed by EPMA and LA-ICP-MS. Magmatic-hydrothermal scheelite, together with literature data are investigated using partial least square-discriminant analysis (PLS-DA) and Random Forest (RF) classifier, to evaluate the use of scheelite as a robust indicator mineral for W-bearing deposit targeting. Cathodoluminescence images show that scheelite is texturally homogeneous in reduced intrusion-related gold systems (RIRGS) and varies from homogeneous to heterogeneous in other magmatic-hydrothermal and orogenic Au deposits. Scheelite displays six REE chondrite-normalized patterns, which are a function of the source and composition (mainly salinity) of the mineralizing fluids and partitioning with co-genetic minerals (e.g., garnet, clinopyroxene). The PLS-DA highlights that scheelite trace element composition from magmatic-hydrothermal deposits varies following different deposit types (e.g., oxidized and reduced skarns, porphyry W<img>Mo, RIRGS, quartz-vein/greisen Sn<img>W), and that such compositional variation reflects mainly the difference of <em>f</em>O₂ and composition of mineralizing fluids. Additionally, scheelite from magmatic-hydrothermal deposits are chemically distinct to those formed dominantly by metamorphic fluids in orogenic settings as shown by their higher Mo, Nb and Mn, and lower Sr contents and predominantly negative Eu anomalies. Metamorphic scheelite can be discriminated from that of orogenic Au deposits by their lower Pb, As and REE contents and LREE/HREE ratios, which are related to local host rock composition and metamorphic grade. Using Na, Mg, Mn, As, Sr, Y, Nb, Mo, Pb, ΣREE concentrations and Eu anomaly as predictors, the RF model yields an overall prediction accuracy of 97 % for test data as function of deposit types (89.2 % for RIRGS, 100 % for porphyry W<img>Mo, 97.8 % for quartz-vein/greisen Sn<img>W, 96.9 % for oxidized skarn, 98.1 % for reduced skarn and 99.3 % for orogenic Au deposits). Application of RF classifier to scheelite composition from orogenic Au and skarn- and greisen-type W deposits from literature yields an overall prediction of ∼79 % (91 % for oxidized skarn, 71.4 % for quartz-vein/greisen Sn<img>W and 74.2 % for orogenic Au deposits) showing that scheelite is an efficient indicator mineral for Au and W deposits targeting. Metamorphic scheelite is predicted mostly as orogenic Au scheelite (83 %), reflecting the genesis of metamorphic fluids and similar geological setting, suggesting that RF classifier can be also used to predict the fluid sources.</p></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0375674224001717/pdfft?md5=4ac787e7aeccc4b9dadebc23cbf3656b&pid=1-s2.0-S0375674224001717-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141978564","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Numerical simulation-based targeting of the Au mineralization within the Hongbu Altered Rock type gold deposit, Eastern Shandong Peninsula, China","authors":"","doi":"10.1016/j.gexplo.2024.107557","DOIUrl":"10.1016/j.gexplo.2024.107557","url":null,"abstract":"<div><p>Altered rock type deposits are significant gold deposits widely distributed throughout the world, having important economic and industrial value. The Eastern Shandong Peninsula is the third largest gold mining camps in the world with known gold reserves of more than 5300 tons. The majority of the gold deposits here are located in three main orefields, namely the northwest Jiaodong (Laizhou-Zhaoyuan), the Qixia-Penglai-Fushan, and the Muping-Rushan orefields. The Hongbu deposit is a medium-sized altered rock type deposit within the northwest Jiaodong orefield. With decades of mining, the Hongbu deposit faces the dilemma of resource depletion and loss of undigitized data. Therefore, prospecting and exploration have to focus on deep and peripheral areas of known Au mineralization. This study built a three-dimensional model of the Hongbu deposit and sliced it to obtain nine cross-sections to conduct multi-field coupled numerical simulation (including heat conduction, fluid migration, chemical reaction, and material migration). Locations with relatively developed Au mineralization (the top 15 % within the concentration range of Au) are defined as having metallogenic potential, which are highlighted and projected to the geological map of the Hongbu district. The results also show that the spatial distributions of Au mineralization within these nine sections are different, indicating that the formation of Au mineralization is controlled by the morphology of the Hexi fault (other simulation parameters of these nine sections are the same) and the pyrite sericite cataclasite. This research proves that numerical simulation methods is effective in mineral exploration, especially for those areas with insufficient data to use data-driven prospectivity modeling approaches. Future development into both mathematical geosciences and computational science will provide more detailed answers for remaining hot issues related to mineral exploration.</p></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141844748","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Characterization and stable isotopic fingerprinting of mine seepage in hyperarid environments: An example of the Namib Lead & Zinc mine, Namibia","authors":"","doi":"10.1016/j.gexplo.2024.107554","DOIUrl":"10.1016/j.gexplo.2024.107554","url":null,"abstract":"<div><p>Mine drainage at the Namib Lead &amp; Zinc mine in the hyperarid environment of the Namib Desert close to Swakopmund, Namibia, has been investigated using mineralogical, hydrochemical, and isotopic methods. The principal ore minerals are galena and sphalerite. Mine drainage is neutral due to the reactions with the marble gangue rock. Mine water seepage is of the Na-Ca-Cl-SO₄ type and sources of dissolved ions are likely halite and gypsum in the unsaturated zone above the mine. Concentrations of dissolved metals are relatively low, and the principal attenuation mechanism of metals is probably their adsorption on ferric minerals because equilibrium of the seepage water with secondary minerals that host the metals is not attained. Based on strongly enriched δ²H (up to 13.27 ‰) and δ¹⁸O (up to 4.5 ‰) values, seepage water originates from advective fog and is strongly evaporated after the fog deposition. The high δ¹³C(DIC) values indicate equilibrium with carbonates and CO₂ de-gassing. The δ³⁴S(SO₄) values are enriched in shallower depths, probably because of pedogenic gypsum dissolution and then the δ³⁴S values decrease with depth, probably due to the increasing input of sulfur from sulfides. Mine drainage at the Namib Lead &amp; Zinc mine does not represent any risk for the environment due to its neutral character and relatively low seepage water volumes caused by high degree of aridity.</p></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141936907","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Ore mineralization in the Mofete and San Vito geothermal fields, Campi Flegrei volcanic complex, Naples, Italy","authors":"","doi":"10.1016/j.gexplo.2024.107556","DOIUrl":"10.1016/j.gexplo.2024.107556","url":null,"abstract":"<div><p>The Mofete and San Vito geothermal fields, located west of Naples, Italy, are part of the Campi Flegrei volcanic complex. In the 1970s, exploratory wells were drilled to a depth of ~3000 m in an attempt to locate high-enthalpy fluids for potential power production. Drill core samples from Mofete wells (MF1, MF2, and MF5) and from San Vito wells (SV1 and SV3) contain authigenic ore mineralization. Pyrite, pyrrhotite, and galena are abundant. Less common are chalcopyrite, sphalerite, arsenopyrite, and scheelite; rare are millerite, violarite, native bismuth, tellurobismuthite, cassiterite, molybdenite, and acanthite. Mineral chemistry was determined by electron microprobe wavelength dispersive spectroscopy aided by a scanning electron microscope equipped with energy-dispersive spectroscopy. The mineral assemblage suggests a low sulfidation environment and the absence of pyrrhotite in the MF1 well and upper part of the SV1 well indicates variable sulfur activity. Both molybdenite and scheelite were identified in samples SV1–2860 and SV3–2353 and scheelite in the SV3 well is zoned with variable Mo⁶⁺ content; low Mo⁶⁺ zones show blue cathodoluminescence, whereas, zones with high Mo⁶⁺ content are yellow to brown. Zoned scheelite and the occurrence of both Mo-bearing minerals attest to the variability of ƒO₂ and ƒS₂ in the geothermal fluid.</p></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141853904","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Magmatic-hydrothermal evolution of the Dangba rare-metal granitic pegmatites in the Songpan–Ganzê orogenic belt, Eastern Tibet: Insights from muscovite and columbite-group minerals","authors":"","doi":"10.1016/j.gexplo.2024.107559","DOIUrl":"10.1016/j.gexplo.2024.107559","url":null,"abstract":"<div><p>Rare-metal granitic pegmatites are commonly considered to be the results of a combination of magmatic and hydrothermal processes. Although magmatic crystallization and fractionation, and magmatic-hydrothermal transition have been extensively investigated, the processes related economically valuable mineralization of rare-metals and strong fractionation of geochemical twins remain controversial. This study presents a comprehensive analysis of the geochemical evolution of rare-metal mineralized pegmatites, focusing on the mineral chemistry of muscovite and columbite-group minerals (CGM) from the Dangba rare-metal granitic pegmatites in the Songpan–Ganzê orogenic belt. Our findings suggest that the random orientation growth of spodumene crystals and widespread distribution of disordered columbite-group minerals crystals are indicative of lithium saturation in the initial melt at the Dangba No. VII dike. Magmatic fractionation is indicated by gradually increasing ratios of alkali metals (K/Rb ratios) and Ta# (Ta/(Ta + Nb)) in muscovite and CGM, and is proposed to be an important factor for enrichment of rare-metals. During the magmatic-hydrothermal transition, muscovite from metasomatism of spodumene exhibits similar or slightly higher levels of Li, Rb, and Cs, compared to primary muscovite, but shows strong depletion of Ta, Nb, Sn, and W. Alteration of primary minerals (e.g., spodumene, alkali feldspar, and columbite-group minerals) results in the release of these elements into the reactive media (melt/fluid) during the metasomatism. This process ultimately leads to the depletion of rare metals in the early crystallized minerals. However, this process is advantageous for the subsequent mineralization of Ta and Nb, as well as their fractionation. The chemical compositions of exsolved aqueous fluid are influenced by the mineralogy of pegmatites and the partitioning behavior between melt and fluid. Furthermore, pervasive albitization serves as an exploration criterion for Li–Ta–Nb in the Ke'eryin Orefield.</p></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141847803","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mapping geochemical domains using stream sediment geochemistry: An approach based on compositional indicators in the Volturno River basin (South Italy)","authors":"","doi":"10.1016/j.gexplo.2024.107545","DOIUrl":"10.1016/j.gexplo.2024.107545","url":null,"abstract":"<div><p>When dealing with environmental problems, it is of fundamental importance to establish reference values (geochemical baselines) against which to determine the presence or absence of active contamination processes.</p><p>In the effort to develop a method to assess the geochemical baselines for territories featuring complex geological settings and a well-established anthropic environmental pressure, we combined compositional data analysis (CoDA) with geolithological information to reduce the degree of uncertainty possibly affecting the results. The proposed approach comprises (1) a knowledge-driven step to select a number of sample subsets from a geochemical dataset each with a high probability of having its composition strongly influenced by only one of the lithologies outcropping in the study area; (2) a data-driven step to compute compositional principal balances and define geochemical indicators to be used to assign each of the observations in the dataset to one of the geochemical domains associated to a mayor lithologies outcropping in the study area; (3) the determination for each geochemical domain of baseline values based on the samples assigned to them by the data-driven step.</p><p>The method was tested using the geochemical data referring to 887 stream sediment samples collected across the Volturno River catchment basin (Southern Italy), featuring a relevant lithological heterogeneity.</p><p>The results obtained were easily interpretable as they fitted well with the geomorphological, geochemical, and geodynamic processes characterizing the study area.</p><p>Despite the use of stream sediments for the specific case study presented, the application principles of the method hold for any environmental media and for any territory for which there is a need to define baseline values. However, for a successful application of the method, it is crucial to have a fair knowledge of the geological settings of the study area.</p></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0375674224001614/pdfft?md5=dda7d46e32367e0d80fd8ce9cb049e90&pid=1-s2.0-S0375674224001614-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141700256","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geochemical and mineralogical characterization of acid sulfate soils in Luleå, northern Sweden","authors":"","doi":"10.1016/j.gexplo.2024.107541","DOIUrl":"10.1016/j.gexplo.2024.107541","url":null,"abstract":"<div><p>Acid sulfate soils (AS-soils) are a common feature along coastlines in many countries that can have significant environmental and economic impacts. AS-soils oxidation may cause soil and water acidification, the release and mobilization of metals and the formation of new precipitated phases. In northern Sweden, some soils are already oxidized and constitute an environmental concern. This study aimed to analyze the geochemistry and mineralogy of AS-soils profiles by identifying element depletion and accumulation zones, the parent material, minerals that contribute to acidity and their oxidation products as well as anomalous element content values that could be related to anthropogenic sources. Two soil profiles were drilled close to the Lule River in Södra Sunderbyn, Luleå. The profiles were characterized by an oxidized zone (OZ) with a declining trend in element content, a transition zone (TZ) where elements tended to accumulate and a reduced zone (RZ) where elements had their maximum content. The pH was a key determinant of the element distribution. Cadmium, Co, Ni and Zn were found to be typical elements released into the environment during AS-soils oxidation. After sample incubation, pH measurements showed a pronounced decrease in layers with higher S and total organic carbon (TOC) content. Both profiles developed a larger thickness of potential acid-risk sediments according to S, TOC and pH measurements during incubation. Iron sulfides were identified as the main acidity generators, represented by an abundance of framboidal pyrites with a Mn-rich rim formed under anoxic-euxinic conditions. Iron sulfates and iron oxyhydroxides (FeOOH, FeOH₃) were identified as the most common products of oxidation processes.</p></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0375674224001572/pdfft?md5=cd20b375d2cf722defbe895ee72e33f6&pid=1-s2.0-S0375674224001572-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141694682","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Insights into the indium enrichment of the Ashele VMS Cu-Zn deposit, Altay, NW China","authors":"Guotao Sun ,&nbsp;Yunlin An ,&nbsp;Shuai Gao","doi":"10.1016/j.gexplo.2024.107544","DOIUrl":"https://doi.org/10.1016/j.gexplo.2024.107544","url":null,"abstract":"<div><p>Indium (In) is a critical metal used in the photovoltaic and semiconductor industries, which have exhibited extraordinary growth in demand. Indium is produced as a by-product of mining from different ore deposits (e.g., epithermal, sediment-hosted, and skarn). Volcanogenic massive sulfide (VMS) deposits are an important source of In; however, the mechanism of In enrichment is not fully understood. Here, we combine mineralogy with in situ trace element and S-Pb isotope geochemistry to reveal the enrichment of indium in the Ashele VMS Cu-Zn deposit (1.08 Mt. Cu, 0.43 Mt. Zn) located in Altay, NW China. The Ashele deposit is hosted in the metamorphosed Devonian felsic-bimodal volcanic rocks. This deposit consists of seafloor hydrothermal, metamorphic hydrothermal, and supergene stages. The seafloor hydrothermal stage comprises macro-scale Cu-rich bands (chalcopyrite, pyrite, and minor sphalerite) and Zn-rich bands (sphalerite, pyrite, and minor chalcopyrite). Indium is mainly hosted by chalcopyrite (mean 178 ppm) and sphalerite (mean 214 ppm) and occurs in the lattice. Mineral assemblages and trace element geochemistry suggest that the Cu-rich bands were deposited under high temperatures (&gt; 300–350 °C) and sulfur fugacity (−7.2 to −4.9), whereas the Zn-rich bands were formed under lower temperatures (180–220 °C) and sulfur fugacity (−15.7 to −11.5). The interlayered Cu-rich and Zn-rich bands may reflect the oscillating temperature and sulfur fugacity variations. In situ S isotopic compositions of sulfides cluster within two ranges: 1–3 ‰ and 3–6 ‰, suggesting two endmembers: volcanic origin and reduced seawater sulfate. Pb isotopic ratios are similar to those of the host volcanic rocks, indicating that the metals may be derived from the felsic volcanic system. During metamorphism, the indium may be retained, but Cu contents of sphalerite become more homogeneous. Most In-rich VMS deposits worldwide are hosted by the felsic-dominant system in island arc and back-arc settings. These tectonic settings are conducive to the production of felsic volcanic systems, which are more likely to contain In mineralization. This study highlights the enrichment mechanism of indium in VMS deposits and suggests that the South Altay could become an important source of In.</p></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141540482","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"How do non-deposit sites influence the performance of machine learning-based gold prospectivity mapping? A study case in the Pitangui Greenstone Belt, Brazil","authors":"Brener Otávio Luiz Ribeiro ,&nbsp;Danilo Barbuena ,&nbsp;Gustavo Henrique Coelho de Melo ,&nbsp;João Gabriel Motta ,&nbsp;Eduardo Duarte Marques ,&nbsp;Marcelo de Souza Marinho","doi":"10.1016/j.gexplo.2024.107543","DOIUrl":"https://doi.org/10.1016/j.gexplo.2024.107543","url":null,"abstract":"<div><p>One of the greatest challenges in mineral prospectivity mapping (MPM) research nowadays is to find a solid methodology that ensures the reliability of the prospectivity model during the learning and prediction procedures. Multiple uncertainties such as the location of non-deposit sites or the type of machine learning algorithm (MLA) can bias the MPM. To investigate these effects, we used multiple training datasets with different non-deposits locations, randomly created, and MLAs such as Artificial Neural Network (ANN), Random Forests (RF) and Support Vector Machine (SVM), to model orogenic-Au prospectivity in the Pitangui Greenstone Belt (PGB, Brazil). Regarding the implications in the methodology for MPM, there are great differences between the models' performances in mapping prospective zones when there is a slightly change in the location of negative samples. These changes can be observed by using the Shapley additive explanation metrics (SHAP values), which can help mitigate such effects by choosing an optimal model among all randomly created datasets. The SHAP values of non-deposit sites also showed that ANN and SVM present overfitting problems despite the use of balanced data. RF on the other hand outperformed in all ten datasets and showed great recognition and adjustment to the negative samples. The results presented in this research are also promising to the prospective studies in the PGB, as it shows a map capable to correctly predict 97 % of the known deposits and occurrences in 3 % of the total area and points the new frontiers for gold exploration in the PGB.</p></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141539549","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}