Pub Date : 2024-05-07DOI: 10.1016/j.gexplo.2024.107497
Peng Xia , Yifu Zhao , Xianjun Xie , Junxia Li , Kun Qian , Haoyu You , Jingxian Zhang , Weili Ge , Hongjie Pan , Yanxin Wang
Geogenic contaminated groundwater (GCG), characterized by elevated arsenic, fluoride, and iodine levels, present a significant challenge to public health and government management. Conventional survey-based approaches of collecting groundwater samples, conducting physicochemical tests, and performing spatial interpolation to obtain regional groundwater chemical component maps are inefficient and costly. More importantly, it does not take into account the actual hydrogeological conditions or the characteristics of pollutant transport and enrichment. To address this issue, we utilized Support Vector Machine (SVM), Random Forest (RF), Adaptive Boosting (AdaBoost), and Extreme Gradient Boosting (XGBoost) to analyze the likelihood of occurrence of arsenic, fluoride, and iodine as well as their spatial distribution in shallow groundwater from the Hetao Basin. Our study incorporated 20 indicators related to meteorology, soil physicochemical properties, and groundwater conditions, along with 1505 labeled samples consisting of groundwater arsenic, fluoride, and iodine concentrations and their corresponding coordinates. Subsequently, the study automatically analyzed the meteorological, soil physicochemical properties and groundwater conditions by constructing a machine learning model using the available data. In order to optimise and select the best prediction model, this paper presents a quantitative evaluation of the prediction performance of various machine learning models. The accuracy (AC), area under curve (AUC) and mean squared error (MSE) were calculated to predict the spatial distribution of CGC. Subsequently, the optimized model for predicting the spatial distribution of GCG was selected. The results showed that the XGBoost algorithm provided optimal predictions for groundwater with arsenic concentrations above 10 μg/L and fluoride concentrations exceeding 1.5 mg/L, whereas the RF model provided the best predictions for groundwater with arsenic concentrations surpassing 50 μg/L and iodine concentrations exceeding 100 μg/L. Subsequently, groundwater health risk zones were delineated based on an optimal prediction model, and demographic analysis was conducted in both the direct and potential groundwater risk zones. Model predictions indicated that hundreds of thousands of people in the Hetao Basin were facing a public health crisis caused by high concentrations of arsenic, fluoride and iodine in groundwater. These findings underscore the significant health challenge in the study area. Considering the agricultural development and increasing groundwater use in the area, our findings can guide local governments in managing the extent of groundwater development, establishing control zones, and enhancing protection measures for populations at risk from groundwater contamination.
{"title":"Machine learning prediction of health risk and spatial dependence of geogenic contaminated groundwater from the Hetao Basin, China","authors":"Peng Xia , Yifu Zhao , Xianjun Xie , Junxia Li , Kun Qian , Haoyu You , Jingxian Zhang , Weili Ge , Hongjie Pan , Yanxin Wang","doi":"10.1016/j.gexplo.2024.107497","DOIUrl":"https://doi.org/10.1016/j.gexplo.2024.107497","url":null,"abstract":"<div><p>Geogenic contaminated groundwater (GCG), characterized by elevated arsenic, fluoride, and iodine levels, present a significant challenge to public health and government management. Conventional survey-based approaches of collecting groundwater samples, conducting physicochemical tests, and performing spatial interpolation to obtain regional groundwater chemical component maps are inefficient and costly. More importantly, it does not take into account the actual hydrogeological conditions or the characteristics of pollutant transport and enrichment. To address this issue, we utilized Support Vector Machine (SVM), Random Forest (RF), Adaptive Boosting (AdaBoost), and Extreme Gradient Boosting (XGBoost) to analyze the likelihood of occurrence of arsenic, fluoride, and iodine as well as their spatial distribution in shallow groundwater from the Hetao Basin. Our study incorporated 20 indicators related to meteorology, soil physicochemical properties, and groundwater conditions, along with 1505 labeled samples consisting of groundwater arsenic, fluoride, and iodine concentrations and their corresponding coordinates. Subsequently, the study automatically analyzed the meteorological, soil physicochemical properties and groundwater conditions by constructing a machine learning model using the available data. In order to optimise and select the best prediction model, this paper presents a quantitative evaluation of the prediction performance of various machine learning models. The accuracy (AC), area under curve (AUC) and mean squared error (MSE) were calculated to predict the spatial distribution of CGC. Subsequently, the optimized model for predicting the spatial distribution of GCG was selected. The results showed that the XGBoost algorithm provided optimal predictions for groundwater with arsenic concentrations above 10 μg/L and fluoride concentrations exceeding 1.5 mg/L, whereas the RF model provided the best predictions for groundwater with arsenic concentrations surpassing 50 μg/L and iodine concentrations exceeding 100 μg/L. Subsequently, groundwater health risk zones were delineated based on an optimal prediction model, and demographic analysis was conducted in both the direct and potential groundwater risk zones. Model predictions indicated that hundreds of thousands of people in the Hetao Basin were facing a public health crisis caused by high concentrations of arsenic, fluoride and iodine in groundwater. These findings underscore the significant health challenge in the study area. Considering the agricultural development and increasing groundwater use in the area, our findings can guide local governments in managing the extent of groundwater development, establishing control zones, and enhancing protection measures for populations at risk from groundwater contamination.</p></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":"262 ","pages":"Article 107497"},"PeriodicalIF":3.9,"publicationDate":"2024-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140905421","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}
Pub Date : 2024-05-07DOI: 10.1016/j.gexplo.2024.107500
Cheng Chang , Keyan Xiao , Guanhong Feng , Li Sun , Junsheng Yang
The Haopinggou Ag-Au-Pb-Zn deposit is the only deposit that simultaneously contains Au and Ag-Pb-Zn vein-type ores at the Xianyu ore field in Xiong'ershan District, Henan Province, China. The early-stage gold-bearing pyrite-quartz veins are cut or surrounded by late-stage silver-bearing Pb-Zn-sulfide veins. However, there is controversy whether these two-stage veins were formed from distinct fluid systems associated with discrete mineralization events or via hydrothermal evolution processes of individual mineralization events. To study the metallogenic dynamics of how the Au and Ag-Zn-Pb veins were formed at the same depth in the Haopinggou deposit under these two distinct metallogenic models, we established a series of reactive transport numerical models. We studied the influence of the temperature of the hydrothermal fluid, fault permeability, and HS−, Au+, and Ag+ concentrations on the mineralization of Au, Ag, Pb, and Zn. Based on the model results, two distinct mechanisms causing Au and Ag to precipitate at the same depth has been established: (1) Under the assumption of the single hydrothermal fluid metallogenic model, the deep part of the early Au precipitation will be overlapped by the shallow part of the late Ag precipitation due to temperature and permeability decreases, causing Au and Ag to precipitate at the same deep depth; (2) Under the assumption of the distinct hydrothermal fluids metallogenic model, the shallow part of the early Au precipitation will be overlapped by the late Ag precipitation due to high concentration of HS−, causing Au and Ag to precipitate at the same shallow depth. The metallogenic mechanisms behind these two controversial understandings indicate that the deeper parts of the Haopinggou deposit have a high metallogenic potential for gold or silver.
下坪沟银-金-铅-锌矿床是中国河南省熊耳山地区仙峪矿区唯一同时含有金矿和银-铅-锌脉型矿石的矿床。早期的含金黄铁矿石英脉被晚期的含银铅锌硫化物脉切割或包围。然而，对于这两段矿脉是由与独立成矿事件相关的不同流体系统形成的，还是由单个成矿事件的热液演化过程形成的，还存在争议。为了研究在这两种不同的成矿模式下，下坪沟矿床同一深度的金矿脉和银锌铅矿脉是如何形成的，我们建立了一系列反应运移数值模型。我们研究了热液温度、断层渗透率、HS-、Au+和Ag+浓度对Au、Ag、Pb和Zn成矿作用的影响。根据模型结果，建立了两种不同的机制，导致 Au 和 Ag 在同一深度沉淀：(1）在单一热液成矿模型假设下，由于温度和渗透率的降低，早期金沉淀的深部与晚期银沉淀的浅部重叠，导致金、银在同一深部沉淀；(2）在不同热液成矿模型假设下，由于高浓度的HS-，早期金沉淀的浅部将与晚期银沉淀的浅部重叠，导致金、银在同一浅部沉淀。这两种有争议的理解背后的成矿机制表明，下坪沟矿床深部具有很高的金或银成矿潜力。
{"title":"Reactive transport numerical modeling of intermediate sulfidation epithermal deposit: A case study of Haopinggou Ag-Au-Pb-Zn deposit, Henan province, China","authors":"Cheng Chang , Keyan Xiao , Guanhong Feng , Li Sun , Junsheng Yang","doi":"10.1016/j.gexplo.2024.107500","DOIUrl":"10.1016/j.gexplo.2024.107500","url":null,"abstract":"<div><p>The Haopinggou Ag-Au-Pb-Zn deposit is the only deposit that simultaneously contains Au and Ag-Pb-Zn vein-type ores at the Xianyu ore field in Xiong'ershan District, Henan Province, China. The early-stage gold-bearing pyrite-quartz veins are cut or surrounded by late-stage silver-bearing Pb-Zn-sulfide veins. However, there is controversy whether these two-stage veins were formed from distinct fluid systems associated with discrete mineralization events or via hydrothermal evolution processes of individual mineralization events. To study the metallogenic dynamics of how the Au and Ag-Zn-Pb veins were formed at the same depth in the Haopinggou deposit under these two distinct metallogenic models, we established a series of reactive transport numerical models. We studied the influence of the temperature of the hydrothermal fluid, fault permeability, and HS<sup>−</sup>, Au<sup>+</sup>, and Ag<sup>+</sup> concentrations on the mineralization of Au, Ag, Pb, and Zn. Based on the model results, two distinct mechanisms causing Au and Ag to precipitate at the same depth has been established: (1) Under the assumption of the single hydrothermal fluid metallogenic model, the deep part of the early Au precipitation will be overlapped by the shallow part of the late Ag precipitation due to temperature and permeability decreases, causing Au and Ag to precipitate at the same deep depth; (2) Under the assumption of the distinct hydrothermal fluids metallogenic model, the shallow part of the early Au precipitation will be overlapped by the late Ag precipitation due to high concentration of HS<sup>−</sup>, causing Au and Ag to precipitate at the same shallow depth. The metallogenic mechanisms behind these two controversial understandings indicate that the deeper parts of the Haopinggou deposit have a high metallogenic potential for gold or silver.</p></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":"263 ","pages":"Article 107500"},"PeriodicalIF":3.9,"publicationDate":"2024-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S037567422400116X/pdfft?md5=a45a35c1107dcbad39ac82c1ae58c9f7&pid=1-s2.0-S037567422400116X-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141027886","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}
Pub Date : 2024-05-07DOI: 10.1016/j.gexplo.2024.107498
Hakundwi Mandende , Themba Mothupi
The uppermost Upper Zone of the Bushveld Complex is known as a potential host of significant apatite-ilmenite resources. Recent exploration studies have delineated two apatite-rich zones representing a huge potential resource of phosphate. A detailed mineralogical and geochemical study of the two apatite-rich zones is undertaken to demonstrate that in addition to phosphate, apatite and ilmenite could be important saleable by-products for REE and Ti. In the Lower Apatite Zone (LAZ), the average concentrations of apatite, ilmenite, and titano-magnetite are 11%, 6%, and 18%, respectively. Grades of about 30 wt% combined apatite, ilmenite, and titano-magnetite can be recovered from the Upper Apatite Zone (UAZ), of which apatite and granular ilmenite constitute 9 and 10%, respectively. There is an association between diamagnetic (apatite), paramagnetic (mostly silicates and ilmenite), ferromagnetic (titano-magnetite) minerals and, to a lesser extent, sulphides. In addition, the majority of the targeted minerals; apatite, ilmenite, and titano-magnetite are relatively coarse, with a median value ranging between 270 μm and 931 μm. In-situ trace element data obtained on apatite demonstrate an increase in Light Rare Earth Elements (LREE) stratigraphically, grading from an average of 3180 ppm Total Rare Earth Elements (TREE+Y) in the LAZ to an average of 4068 ppm TREE+Y in the UAZ, indicating a sub-economic potential of REE that may be economically viable as by-product to phosphate. Preliminary resource estimations show that ~1,405,560 t and ~1,798,056 t of TREE can be exploited from the LAZ and UAZ, respectively. The discrete ilmenite grains are an attractive additional by-product considering their higher average >50% TiO2 and lower concentration of impurities such as <1.06% MgO, <1.21% MnO, <0.08% Al2O3, <0.02% V2O5 and <0.01% Cr2O3. These results suggest that apatite-rich layers in mafic layered intrusions are viable prospects for economic extraction of REE in conjunction with titanium as other by-products that can be recovered from phosphate rocks.
{"title":"Apatite-rich zones in the Uppermost Upper Zone, Northern Limb, Bushveld Complex: Possible non-conventional source of REE and TiO2","authors":"Hakundwi Mandende , Themba Mothupi","doi":"10.1016/j.gexplo.2024.107498","DOIUrl":"10.1016/j.gexplo.2024.107498","url":null,"abstract":"<div><p>The uppermost Upper Zone of the Bushveld Complex is known as a potential host of significant apatite-ilmenite resources. Recent exploration studies have delineated two apatite-rich zones representing a huge potential resource of phosphate. A detailed mineralogical and geochemical study of the two apatite-rich zones is undertaken to demonstrate that in addition to phosphate, apatite and ilmenite could be important saleable by-products for REE and Ti. In the Lower Apatite Zone (LAZ), the average concentrations of apatite, ilmenite, and titano-magnetite are 11%, 6%, and 18%, respectively. Grades of about 30 wt% combined apatite, ilmenite, and titano-magnetite can be recovered from the Upper Apatite Zone (UAZ), of which apatite and granular ilmenite constitute 9 and 10%, respectively. There is an association between diamagnetic (apatite), paramagnetic (mostly silicates and ilmenite), ferromagnetic (titano-magnetite) minerals and, to a lesser extent, sulphides. In addition, the majority of the targeted minerals; apatite, ilmenite, and titano-magnetite are relatively coarse, with a median value ranging between 270 μm and 931 μm. In-situ trace element data obtained on apatite demonstrate an increase in Light Rare Earth Elements (LREE) stratigraphically, grading from an average of 3180 ppm Total Rare Earth Elements (TREE+Y) in the LAZ to an average of 4068 ppm TREE+Y in the UAZ, indicating a sub-economic potential of REE that may be economically viable as by-product to phosphate. Preliminary resource estimations show that ~1,405,560 t and ~1,798,056 t of TREE can be exploited from the LAZ and UAZ, respectively. The discrete ilmenite grains are an attractive additional by-product considering their higher average >50% TiO<sub>2</sub> and lower concentration of impurities such as <1.06% MgO, <1.21% MnO, <0.08% Al<sub>2</sub>O<sub>3</sub>, <0.02% V<sub>2</sub>O<sub>5</sub> and <0.01% Cr<sub>2</sub>O<sub>3</sub>. These results suggest that apatite-rich layers in mafic layered intrusions are viable prospects for economic extraction of REE in conjunction with titanium as other by-products that can be recovered from phosphate rocks.</p></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":"263 ","pages":"Article 107498"},"PeriodicalIF":3.9,"publicationDate":"2024-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141057424","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}
Pub Date : 2024-05-07DOI: 10.1016/j.gexplo.2024.107496
Jialin Wang , Xuexiang Gu , Jingchi Xu , Yongmei Zhang , Yiwei Peng , Liangtao Lu
The Haerdaban PbZn deposit (with an ore reserve of 10.93 Mt. at 1.0–25.65 % Zn and 0.7–12.29 % Pb) is hosted in weakly metamorphosed clastic‑carbonate rocks from the Proterozoic Haerdaban Group. It represents a significant addition of the sediment-hosted PbZn deposits in the Yili block, Chinese western Tianshan. Currently, there are ongoing debates regarding its genesis, with a particular focus on the crucial metallogenic mechanism (syngenetic sedimentary exhalation or epigenetic reworking) responsible for the primary sulfide mineralization. Mineralization at Haerdaban primarily occurs as banded to stratiform ore layers or lenses conformably sandwiched in their host rocks. Vein and stockwork ores occur locally below the stratiform ore layers. A syn-sedimentary fault trending SN was identified based on abrupt lateral changes in lithofacies and thickness of the stratigraphic units. The ore mineralogy is dominated by sphalerite, galena, quartz, and dolomite, with a small amount of pyrite, barite, and organic matter. Detrital zircon LA-ICP-MS UPb dating of the Haerdaban siltstones obtained a maximum depositional age of about 604 Ma. Their geochemical composition similar to the passive continental margin signatures, with rare earth element (REE) patterns enriched in LREE and negative Eu anomalies (Eu/Eu* = 0.50–1.14). Stratiform beds of chert that host disseminated ores have relatively high contents of hydrothermal components (e.g., Ba, Zn), with apparent positive Eu anomalies (Eu/Eu* = 7.38–49.34) and negligible negative Ce anomalies (Ce/Ce* = 0.85–0.98). They are thus interpreted to be hydrothermal sedimentary rocks (exhalites) deposited in a suboxic-anoxic environment proximal to the hydrothermal vents. Integrated geological and geochemical evidence indicates that the Haerdaban PbZn deposit is a typical vent-proximal sedimentary exhalative (SEDEX) deposit formed in a Neoproterozoic Sinian (Ediacaran) passive continental margin rift basin. Post-depositional metamorphism and deformation in the Paleozoic may have caused partial remobilization of primary ores but did not significantly alter the morphology of the orebodies. Furthermore, establishing a genetic model for the Haerdaban deposit has important implications for the exploration of similar deposits preserved in the equivalent stratigraphy within the Chinese western Tianshan region.
{"title":"New insights into the origin and depositional setting of the Haerdaban PbZn deposit, Chinese western Tianshan: Evidence from geology, chert geochemistry, and detrital zircon UPb geochronology","authors":"Jialin Wang , Xuexiang Gu , Jingchi Xu , Yongmei Zhang , Yiwei Peng , Liangtao Lu","doi":"10.1016/j.gexplo.2024.107496","DOIUrl":"https://doi.org/10.1016/j.gexplo.2024.107496","url":null,"abstract":"<div><p>The Haerdaban Pb<img>Zn deposit (with an ore reserve of 10.93 Mt. at 1.0–25.65 % Zn and 0.7–12.29 % Pb) is hosted in weakly metamorphosed clastic‑carbonate rocks from the Proterozoic Haerdaban Group. It represents a significant addition of the sediment-hosted Pb<img>Zn deposits in the Yili block, Chinese western Tianshan. Currently, there are ongoing debates regarding its genesis, with a particular focus on the crucial metallogenic mechanism (syngenetic sedimentary exhalation or epigenetic reworking) responsible for the primary sulfide mineralization. Mineralization at Haerdaban primarily occurs as banded to stratiform ore layers or lenses conformably sandwiched in their host rocks. Vein and stockwork ores occur locally below the stratiform ore layers. A <em>syn</em>-sedimentary fault trending S<img>N was identified based on abrupt lateral changes in lithofacies and thickness of the stratigraphic units. The ore mineralogy is dominated by sphalerite, galena, quartz, and dolomite, with a small amount of pyrite, barite, and organic matter. Detrital zircon LA-ICP-MS U<img>Pb dating of the Haerdaban siltstones obtained a maximum depositional age of about 604 Ma. Their geochemical composition similar to the passive continental margin signatures, with rare earth element (REE) patterns enriched in LREE and negative Eu anomalies (Eu/Eu* = 0.50–1.14). Stratiform beds of chert that host disseminated ores have relatively high contents of hydrothermal components (e.g., Ba, Zn), with apparent positive Eu anomalies (Eu/Eu* = 7.38–49.34) and negligible negative Ce anomalies (Ce/Ce* = 0.85–0.98). They are thus interpreted to be hydrothermal sedimentary rocks (exhalites) deposited in a suboxic-anoxic environment proximal to the hydrothermal vents. Integrated geological and geochemical evidence indicates that the Haerdaban Pb<img>Zn deposit is a typical vent-proximal sedimentary exhalative (SEDEX) deposit formed in a Neoproterozoic Sinian (Ediacaran) passive continental margin rift basin. Post-depositional metamorphism and deformation in the Paleozoic may have caused partial remobilization of primary ores but did not significantly alter the morphology of the orebodies. Furthermore, establishing a genetic model for the Haerdaban deposit has important implications for the exploration of similar deposits preserved in the equivalent stratigraphy within the Chinese western Tianshan region.</p></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":"263 ","pages":"Article 107496"},"PeriodicalIF":3.9,"publicationDate":"2024-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140950911","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}
The study presented a high-resolution regional mapping of a significant Brazilian watershed, which is heavily influenced by mining, agriculture, and domestic/industrial effluents. Upper São Francisco Basin encompasses the largest karst area in the country and includes three important Brazilian biomes: Cerrado, Atlantic Forest, and Caatinga. Surface water (1418 samples) was collected during the dry season and was analyzed for physical-chemical parameters, cations, anions, and some metals. The spatial distribution and abundance of variables were assessed, and the processes controlling the sources of dissolved loads in surface waters were discussed. The results indicate that rock weathering is the primary factor controlling water chemistry, with a strong influence of carbonate and silicate minerals. Anthropogenic activities, particularly agriculture, play a key role in the chemical composition of the microbasins. Soil erosion and leaching processes also contribute significantly to the region, driven by land use practices and mineral extraction, which intensify erosion processes. The northern sector of the Upper São Francisco Basin, characterized by an arid climate and Caatinga vegetation, experiences low precipitation and high evapotranspiration rates. The VG stands out due to the presence of the karst zone and for the mixture of natural to anthropogenic sources.
{"title":"High-resolution mapping and multivariate technique (factor analysis) to support hydrogeochemical analysis and identification of surface water contamination","authors":"Daniela Vasconcelos Machado , Eduardo Duarte Marques , Eduardo Paim Viglio , Everton Assunção Martins dos Santos , Rafael Tarantino Amarante , Gerson Cardoso da Silva Júnior , Emmanoel Vieira Silva-Filho","doi":"10.1016/j.gexplo.2024.107495","DOIUrl":"https://doi.org/10.1016/j.gexplo.2024.107495","url":null,"abstract":"<div><p>The study presented a high-resolution regional mapping of a significant Brazilian watershed, which is heavily influenced by mining, agriculture, and domestic/industrial effluents. Upper São Francisco Basin encompasses the largest karst area in the country and includes three important Brazilian biomes: Cerrado, Atlantic Forest, and Caatinga. Surface water (1418 samples) was collected during the dry season and was analyzed for physical-chemical parameters, cations, anions, and some metals. The spatial distribution and abundance of variables were assessed, and the processes controlling the sources of dissolved loads in surface waters were discussed. The results indicate that rock weathering is the primary factor controlling water chemistry, with a strong influence of carbonate and silicate minerals. Anthropogenic activities, particularly agriculture, play a key role in the chemical composition of the microbasins. Soil erosion and leaching processes also contribute significantly to the region, driven by land use practices and mineral extraction, which intensify erosion processes. The northern sector of the Upper São Francisco Basin, characterized by an arid climate and Caatinga vegetation, experiences low precipitation and high evapotranspiration rates. The VG stands out due to the presence of the karst zone and for the mixture of natural to anthropogenic sources.</p></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":"263 ","pages":"Article 107495"},"PeriodicalIF":3.9,"publicationDate":"2024-05-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140950517","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}
Pub Date : 2024-05-03DOI: 10.1016/j.gexplo.2024.107491
Janne Hokka , Hanna Leväniemi , Tuomas Leskelä
<div><p>The Paleoproterozoic Metsämonttu Zn–Pb–Cu–Ag–Au deposit (1.5 Mt at 3.5 wt% Zn, 0.8 wt% Pb, 0.3 wt% Cu, 13.2 wt% S, 25 g/t Ag, and 1.4 g/t Au, production 1952–1974) is the largest past-producing mine in the Aijala–Orijärvi area (Orijärvi formation, Aijala member) within the Uusimaa belt, southern Finland. The Aijala member is characterized by 1.9–1.88 Ga felsic-dominated volcanic-sedimentary supracrustal rocks with intercalated sedimentary carbonates and iron formations. The area is underexplored, and little deposit-scale research has been carried out, despite the lateral continuum to the world-class ore district of Bergslagen in south-central Sweden. To better understand the Metsämonttu VMS-related alteration system, we reassessed the previously described metamorphic mineral assemblages and their protolith rock compositions by using mobile and immobile element geochemistry. This resulted in the definition of four metamorphosed alteration mineral assemblages and eight chemostratigraphic rock units. The chemostratigraphic results suggest that the lithological and/or structural setting of the Metsämonttu succession is more complex than previously considered. The stratigraphic footwall is mainly characterized by an extensive cordierite + anthophyllite ± biotite ± phlogopite + pyrite ± pyrrhotite (Mg–Fe–S) assemblage dominated by mafic rocks, designated Mafic B1 and Mafic B2, and Andesite A1. The main sulfide mineralization is hosted by tremolite + diopside ± biotite ± phlogopite ± chlorite skarn (Ca–Mg–K). A sericite-bearing muscovite + quartz ± biotite ± phlogopite + pyrite (K–Si–S) assemblage is composed of felsic to mafic protoliths (Mafic B1–B2, Andesite A1, Dacite A1, Dacite B1, Dacite C1) and extends several tens of meters into the stratigraphic hanging-wall. A quartz + pyrite ± muscovite (Si–S) assemblage represents the immediate ore-proximal alteration and is derived from rocks with a rhyolitic composition (Rhyolite A1).</p><p>Limited drill core samples near Metsämonttu mineralization, along with restricted surface alteration, pose challenges in studying geochemical variations from distal to ore proximal areas and limits the ability to model the shape and size of the alteration zone. Large mass changes suggest that the alteration was hydrothermal, and due to several protolith compositions, the alteration is interpreted to be predominantly discordant to stratigraphy. A 60-m-wide alteration halo surrounds the Metsämonttu deposit. Major and trace elements, namely MgO, Na<sub>2</sub>O, K<sub>2</sub>O, SiO<sub>2</sub>, Fe<sub>2</sub>O<sub>3</sub>, Cu, Zn, Pb, S, Ag, Tl, Hg, Se, Te, Sn, Sb, Rb, and Sr, and the indices modified alteration index (MAI), Ishikawa alteration index (AI), chlorite‑carbonate-pyrite index (CCPI), S/Na<sub>2</sub>O can be used for chemical vectoring, which can assist regional or near-mine exploration. Elements MnO, Ba, Cd, Bi, As, Ni, Co, W, Ga, Mo, and indices Hashigushi index and advance argillic alteration index (
{"title":"Hydrothermal alteration and geochemical proximity indicators to ore at the Metsämonttu Zn–Pb–Cu–Au–Ag deposit, Uusimaa belt, southern Finland","authors":"Janne Hokka , Hanna Leväniemi , Tuomas Leskelä","doi":"10.1016/j.gexplo.2024.107491","DOIUrl":"https://doi.org/10.1016/j.gexplo.2024.107491","url":null,"abstract":"<div><p>The Paleoproterozoic Metsämonttu Zn–Pb–Cu–Ag–Au deposit (1.5 Mt at 3.5 wt% Zn, 0.8 wt% Pb, 0.3 wt% Cu, 13.2 wt% S, 25 g/t Ag, and 1.4 g/t Au, production 1952–1974) is the largest past-producing mine in the Aijala–Orijärvi area (Orijärvi formation, Aijala member) within the Uusimaa belt, southern Finland. The Aijala member is characterized by 1.9–1.88 Ga felsic-dominated volcanic-sedimentary supracrustal rocks with intercalated sedimentary carbonates and iron formations. The area is underexplored, and little deposit-scale research has been carried out, despite the lateral continuum to the world-class ore district of Bergslagen in south-central Sweden. To better understand the Metsämonttu VMS-related alteration system, we reassessed the previously described metamorphic mineral assemblages and their protolith rock compositions by using mobile and immobile element geochemistry. This resulted in the definition of four metamorphosed alteration mineral assemblages and eight chemostratigraphic rock units. The chemostratigraphic results suggest that the lithological and/or structural setting of the Metsämonttu succession is more complex than previously considered. The stratigraphic footwall is mainly characterized by an extensive cordierite + anthophyllite ± biotite ± phlogopite + pyrite ± pyrrhotite (Mg–Fe–S) assemblage dominated by mafic rocks, designated Mafic B1 and Mafic B2, and Andesite A1. The main sulfide mineralization is hosted by tremolite + diopside ± biotite ± phlogopite ± chlorite skarn (Ca–Mg–K). A sericite-bearing muscovite + quartz ± biotite ± phlogopite + pyrite (K–Si–S) assemblage is composed of felsic to mafic protoliths (Mafic B1–B2, Andesite A1, Dacite A1, Dacite B1, Dacite C1) and extends several tens of meters into the stratigraphic hanging-wall. A quartz + pyrite ± muscovite (Si–S) assemblage represents the immediate ore-proximal alteration and is derived from rocks with a rhyolitic composition (Rhyolite A1).</p><p>Limited drill core samples near Metsämonttu mineralization, along with restricted surface alteration, pose challenges in studying geochemical variations from distal to ore proximal areas and limits the ability to model the shape and size of the alteration zone. Large mass changes suggest that the alteration was hydrothermal, and due to several protolith compositions, the alteration is interpreted to be predominantly discordant to stratigraphy. A 60-m-wide alteration halo surrounds the Metsämonttu deposit. Major and trace elements, namely MgO, Na<sub>2</sub>O, K<sub>2</sub>O, SiO<sub>2</sub>, Fe<sub>2</sub>O<sub>3</sub>, Cu, Zn, Pb, S, Ag, Tl, Hg, Se, Te, Sn, Sb, Rb, and Sr, and the indices modified alteration index (MAI), Ishikawa alteration index (AI), chlorite‑carbonate-pyrite index (CCPI), S/Na<sub>2</sub>O can be used for chemical vectoring, which can assist regional or near-mine exploration. Elements MnO, Ba, Cd, Bi, As, Ni, Co, W, Ga, Mo, and indices Hashigushi index and advance argillic alteration index (","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":"262 ","pages":"Article 107491"},"PeriodicalIF":3.9,"publicationDate":"2024-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0375674224001079/pdfft?md5=f083ca07038338944e239cc134f06160&pid=1-s2.0-S0375674224001079-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140906051","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}
Pub Date : 2024-05-03DOI: 10.1016/j.gexplo.2024.107490
Michele Arienzo , Sergio Bravi , Maria Toscanesi , Carlo Donadio , Giuseppe De Simone , Corrado Stanislao , Luciano Ferrara , Vincenzo Allocca , Antonella Giarra , Marco Trifuoggi
The study investigated the presence of heavy metals in the surface sediments of one of the most important wetlands in south Italy, Lake Patria, and the related environmental risk. Surface sediments were analyzed for particle size and shape, total organic carbon and As, Cd, Cr, Cu, Fe, Hg, Ni, Pb and Zn levels. Mean total organic carbon was high, 3.1 %, with a peak of 5.9 % near the input of freshwater channel whereas sediments appeared to be mainly composed of sand and/or gravel and significantly polluted by metals especially Cr, Cu and Zn. Data from heavy metals spatial distribution, Pearson correlation, principal component analysis and geochemical indices suggested dominant anthropogenic source for most metals. Mean Igeo values of Cr, Cu and Ni were in the range of 4.6–7.3 of strongly polluted class while their relative mean enrichment factors were largely exceeding the threshold of the anthropic pollution, 1.5. A very high pollution situation was also outlined when considering the Cf indices, with Cr, Cu and Ni possessing mean values from an order of magnitude of ten to hundred times higher the very high polluted class, 6 ≤ Cf. On the overall, the integrated indices of modified contamination degree, pollution load and ecological risk revealed a serious pollution scenario. The mean comprehensive ecological hazard index was fivefold the most critical limit, ≥600, in almost all the lagoon and especially in the locations close to channel.
{"title":"Heavy metals in surface sediments of Lake Patria wetland, southern Italy, and environmental risk","authors":"Michele Arienzo , Sergio Bravi , Maria Toscanesi , Carlo Donadio , Giuseppe De Simone , Corrado Stanislao , Luciano Ferrara , Vincenzo Allocca , Antonella Giarra , Marco Trifuoggi","doi":"10.1016/j.gexplo.2024.107490","DOIUrl":"10.1016/j.gexplo.2024.107490","url":null,"abstract":"<div><p>The study investigated the presence of heavy metals in the surface sediments of one of the most important wetlands in south Italy, Lake Patria, and the related environmental risk. Surface sediments were analyzed for particle size and shape, total organic carbon and As, Cd, Cr, Cu, Fe, Hg, Ni, Pb and Zn levels. Mean total organic carbon was high, 3.1 %, with a peak of 5.9 % near the input of freshwater channel whereas sediments appeared to be mainly composed of sand and/or gravel and significantly polluted by metals especially Cr, Cu and Zn. Data from heavy metals spatial distribution, Pearson correlation, principal component analysis and geochemical indices suggested dominant anthropogenic source for most metals. Mean I<sub>geo</sub> values of Cr, Cu and Ni were in the range of 4.6–7.3 of strongly polluted class while their relative mean enrichment factors were largely exceeding the threshold of the anthropic pollution, 1.5. A very high pollution situation was also outlined when considering the Cf indices, with Cr, Cu and Ni possessing mean values from an order of magnitude of ten to hundred times higher the very high polluted class, 6 ≤ Cf. On the overall, the integrated indices of modified contamination degree, pollution load and ecological risk revealed a serious pollution scenario. The mean comprehensive ecological hazard index was fivefold the most critical limit, ≥600, in almost all the lagoon and especially in the locations close to channel.</p></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":"263 ","pages":"Article 107490"},"PeriodicalIF":3.9,"publicationDate":"2024-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141038446","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}
Pub Date : 2024-05-02DOI: 10.1016/j.gexplo.2024.107492
Zhengan Wei , Shaopeng Huang , Chengshan Wang
Pearl River Delta (PRD) region of South China is abundant of geothermal water resources. However, the development and utilization level of geothermal resources in this region is relatively low, due in part to the lack of fundamental geochemical research. To access water-rock interaction processes of the PRD geothermal system, we analyzed the geochemistry of geothermal waters by combining trace elements (B, Sr, and Br) and isotopes (δ11B and 87Sr/86Sr) with conventional tracers (major elements) that had been reported. The Cl/Br ratios (from 31 to 639) confirm the multi-source salinity of marine origin, precipitation, and a minor dissolution of halite. Major ions chemistry highlights the influence of ions exchange, the dissolution of carbonate, silicate, and sulphate minerals as well as the contribution of seawater. The Cl/B ratios (61 to 22,583) suggest interactions with carbonate rock and felsic rock, input of seawater, and groundwater mixing. Boron isotopic compositions (δ11B) range between −9.22 and +39.78 ‰. Sr contents and 87Sr/86Sr ratios are more homogeneous, falling between 0.06 and 32.26 mg/L and between 0.71239 and 0.72121, respectively. The B and Sr isotopic signatures show that three processes contribute to geochemistry of geothermal waters: 1) water/rock interaction involving marine carbonate rock, evaporite, and granitoid or/and gneiss, 2) seawater intrusion, and 3) shallow groundwater mixing. Major-trace element chemistry and these isotope systematics on their own indicates essential information on the aspects of fluid origin or water-rock interaction processes, and however provide a more comprehensive understanding of the geothermal system in the PRD region, South China.
{"title":"Geochemistry and sources of boron and strontium of geothermal waters from the Pearl River Delta region, South China: Implications for water-rock interactions","authors":"Zhengan Wei , Shaopeng Huang , Chengshan Wang","doi":"10.1016/j.gexplo.2024.107492","DOIUrl":"https://doi.org/10.1016/j.gexplo.2024.107492","url":null,"abstract":"<div><p>Pearl River Delta (PRD) region of South China is abundant of geothermal water resources. However, the development and utilization level of geothermal resources in this region is relatively low, due in part to the lack of fundamental geochemical research. To access water-rock interaction processes of the PRD geothermal system, we analyzed the geochemistry of geothermal waters by combining trace elements (B, Sr, and Br) and isotopes (δ<sup>11</sup>B and <sup>87</sup>Sr/<sup>86</sup>Sr) with conventional tracers (major elements) that had been reported. The Cl/Br ratios (from 31 to 639) confirm the multi-source salinity of marine origin, precipitation, and a minor dissolution of halite. Major ions chemistry highlights the influence of ions exchange, the dissolution of carbonate, silicate, and sulphate minerals as well as the contribution of seawater. The Cl/B ratios (61 to 22,583) suggest interactions with carbonate rock and felsic rock, input of seawater, and groundwater mixing. Boron isotopic compositions (δ<sup>11</sup>B) range between −9.22 and +39.78 ‰. Sr contents and <sup>87</sup>Sr/<sup>86</sup>Sr ratios are more homogeneous, falling between 0.06 and 32.26 mg/L and between 0.71239 and 0.72121, respectively. The B and Sr isotopic signatures show that three processes contribute to geochemistry of geothermal waters: 1) water/rock interaction involving marine carbonate rock, evaporite, and granitoid or/and gneiss, 2) seawater intrusion, and 3) shallow groundwater mixing. Major-trace element chemistry and these isotope systematics on their own indicates essential information on the aspects of fluid origin or water-rock interaction processes, and however provide a more comprehensive understanding of the geothermal system in the PRD region, South China.</p></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":"262 ","pages":"Article 107492"},"PeriodicalIF":3.9,"publicationDate":"2024-05-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140820164","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}
The recent depletion of mineral resources near the Earth's surface has led to a shift in mineral exploration toward concealed deposits in covered terrain. Consequently, significant attention has been directed toward metal-bearing nanoparticles in the soil above such deposits to gain insights into the composition of concealed ore bodies.
In this study, the characteristics (type, size, shape, chemical composition, and aggregation) of metal-bearing nanoparticles in ore samples of the Zhonghedi Ag-Pb-Zn polymetallic deposit and their overlying loess were systematically analyzed using transmission electron microscopy. Numerous nanoparticles containing Ag, Au, Cu, Pb, Zn, Fe, Mo, and other metallic elements were observed in the loess overlying the deposits as well as the ore samples. These nanoparticles exhibit a well-defined crystal shape, suggesting their primary particle nature. Moreover, the nanoparticles in the loess and ore samples share similarities in element distribution, size, and type, demonstrating their homologous nature. However, ore-related metal-bearing nanoparticles were not detected in samples collected from the background areas. Most metal-bearing nanoparticles in loess, excluding native particles, were oxides and sulfates, which may be attributed to oxidation of the native metal particles near the surface where oxygen fugacity increases. The elemental mapping of the nanoparticles showed that the ore-forming elements had the same distribution patterns and element assemblages to the ore material. These results indicate that metal-bearing nanoparticles in the loess have likely relationships with concealed ore bodies. Accordingly, the metal-bearing nanoparticles in the loess can provide information about concealed ore deposits, explain surface geochemical anomalies, and improve prospecting accuracy as a vector to mineralization.
Routinely finding nanoparticles in transported cover remains a challenge. However, this study shows it is viable and marks substantial progress in our knowledge and comprehension of metal-bearing nanoparticles in loess-covered terrain. Evidence of their presence and association with concealed ore bodies contributes significantly to our understanding of mineral exploration processes and offers new avenues for future research and practical applications.
{"title":"Characterization of metal-bearing nanoparticles observed in loess-covered terrain: Implications for prospecting","authors":"Yuexin Lu, Bimin Zhang, Xueqiu Wang, Hanliang Liu, Jian Zhou","doi":"10.1016/j.gexplo.2024.107488","DOIUrl":"https://doi.org/10.1016/j.gexplo.2024.107488","url":null,"abstract":"<div><p>The recent depletion of mineral resources near the Earth's surface has led to a shift in mineral exploration toward concealed deposits in covered terrain. Consequently, significant attention has been directed toward metal-bearing nanoparticles in the soil above such deposits to gain insights into the composition of concealed ore bodies.</p><p>In this study, the characteristics (type, size, shape, chemical composition, and aggregation) of metal-bearing nanoparticles in ore samples of the Zhonghedi Ag-Pb-Zn polymetallic deposit and their overlying loess were systematically analyzed using transmission electron microscopy. Numerous nanoparticles containing Ag, Au, Cu, Pb, Zn, Fe, Mo, and other metallic elements were observed in the loess overlying the deposits as well as the ore samples. These nanoparticles exhibit a well-defined crystal shape, suggesting their primary particle nature. Moreover, the nanoparticles in the loess and ore samples share similarities in element distribution, size, and type, demonstrating their homologous nature. However, ore-related metal-bearing nanoparticles were not detected in samples collected from the background areas. Most metal-bearing nanoparticles in loess, excluding native particles, were oxides and sulfates, which may be attributed to oxidation of the native metal particles near the surface where oxygen fugacity increases. The elemental mapping of the nanoparticles showed that the ore-forming elements had the same distribution patterns and element assemblages to the ore material. These results indicate that metal-bearing nanoparticles in the loess have likely relationships with concealed ore bodies. Accordingly, the metal-bearing nanoparticles in the loess can provide information about concealed ore deposits, explain surface geochemical anomalies, and improve prospecting accuracy as a vector to mineralization.</p><p>Routinely finding nanoparticles in transported cover remains a challenge. However, this study shows it is viable and marks substantial progress in our knowledge and comprehension of metal-bearing nanoparticles in loess-covered terrain. Evidence of their presence and association with concealed ore bodies contributes significantly to our understanding of mineral exploration processes and offers new avenues for future research and practical applications.</p></div>","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":"262 ","pages":"Article 107488"},"PeriodicalIF":3.9,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140824166","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}
Pub Date : 2024-05-01DOI: 10.1016/j.gexplo.2024.107494
Ana Carolina de Faria Duarte , Claudio Gerheim Porto , Artur Cezar Bastos Neto , Reiner Neumann , Lucy Takehara , João Pedro Proença Bento
<div><p>The carbonatite rocks present at the Seis Lagos Carbonatite Complex (SLCC) are siderite carbonatites, and constitute the source of the titano-niobian mineralization hosted in the lateritic crusts that cover the complex. This study is based on the geochemical data from 6 drill holes conducted by the Geological Survey of Brazil (CPRM) in the 1980s plus the mineralogical descriptions and analyzes performed on these cores. The quality of the geochemical data was evaluated in order to select the most reliable elements for statistical treatment. Given the compositional character of the geochemical data, these were transformed into Centered Log Ratio (CLR) and submitted to principal component analysis. These data enabled definition of geochemical association of 4 types of carbonatite rock: (i) C1, siderite carbonatite; (ii) C2, friable siderite carbonatite; (iii) C3, light siderite carbonatite; and (iv) B1, carbonatite breccia. B1 is more phosphatic and enriched in Al, P, La, Ce, Ba, Sr, Zr, S, Be, U and REE minerals like bastnaesite-(Ce), monazite-(Ce), as well as those belonging to the plumbogummite group (such as florencite-(Ce)) — which were formed during a later carbohydrothermal stage. C3 is also enriched in the same suite of metals as a result of hydrothermal alteration after C1. The transition from C1 to its friable equivalent, C2, is more abrupt, suggesting that the weathering took place with well-defined limits in depth and was possibly delimited by structures. C2 is characterized by its enrichment in Th, Zn, Sn, Co, and Sb, with some influence from both Mn and Fe, and the leaching of Ce, Ba, La, and Sr. C2 contains goethite, rutile, brookite and gibbsite, evidencing the impact of weathering. Lateritic crusts are distinguished into 5 types: (i) L1, a fragmented cavernous crust; (ii) L2, a reddish-brown crust; (iii) L3, a manganese crust; (iv) L4, a gray crust; and (v) L5, a compact, grayish crust. The L1 crusts are richer in Al, P, Zr, La and U due to the residual enrichment of their immobile elements and to the formation of secondary aluminum phosphates, mainly florencite-(Ce). The L3 manganese crusts are characterized by a suite of metals, composed of Mn, Ba, Mo, Co and Ce. The contrasting compositions between segments of the upper and lower crusts it is more likely due to compositional differences in the siderite carbonatite, rather than reflecting the depth and hence intensity of weathering. A specific type of crust to which the Nb<img>Ti mineralization might be associated with was not identified. No specific geochemical association was identified for the deeper crusts, such as L4 and L5; however, the occurrence of Ce-rich pyrochlore, cerianite and carbonates in them, coupled with their absence in the upper crusts, suggests that the aforementioned ones are less evolved and therefore, closer to the carbonatite protolith. Our results indicate that despite intense weathering the composition of the primary siderite carbonatite exerts a
{"title":"Geochemical associations between the lateritic crusts and carbonatitic rocks of the Carbonatitic Complex at Morro dos Seis Lagos, AM, Brazil","authors":"Ana Carolina de Faria Duarte , Claudio Gerheim Porto , Artur Cezar Bastos Neto , Reiner Neumann , Lucy Takehara , João Pedro Proença Bento","doi":"10.1016/j.gexplo.2024.107494","DOIUrl":"https://doi.org/10.1016/j.gexplo.2024.107494","url":null,"abstract":"<div><p>The carbonatite rocks present at the Seis Lagos Carbonatite Complex (SLCC) are siderite carbonatites, and constitute the source of the titano-niobian mineralization hosted in the lateritic crusts that cover the complex. This study is based on the geochemical data from 6 drill holes conducted by the Geological Survey of Brazil (CPRM) in the 1980s plus the mineralogical descriptions and analyzes performed on these cores. The quality of the geochemical data was evaluated in order to select the most reliable elements for statistical treatment. Given the compositional character of the geochemical data, these were transformed into Centered Log Ratio (CLR) and submitted to principal component analysis. These data enabled definition of geochemical association of 4 types of carbonatite rock: (i) C1, siderite carbonatite; (ii) C2, friable siderite carbonatite; (iii) C3, light siderite carbonatite; and (iv) B1, carbonatite breccia. B1 is more phosphatic and enriched in Al, P, La, Ce, Ba, Sr, Zr, S, Be, U and REE minerals like bastnaesite-(Ce), monazite-(Ce), as well as those belonging to the plumbogummite group (such as florencite-(Ce)) — which were formed during a later carbohydrothermal stage. C3 is also enriched in the same suite of metals as a result of hydrothermal alteration after C1. The transition from C1 to its friable equivalent, C2, is more abrupt, suggesting that the weathering took place with well-defined limits in depth and was possibly delimited by structures. C2 is characterized by its enrichment in Th, Zn, Sn, Co, and Sb, with some influence from both Mn and Fe, and the leaching of Ce, Ba, La, and Sr. C2 contains goethite, rutile, brookite and gibbsite, evidencing the impact of weathering. Lateritic crusts are distinguished into 5 types: (i) L1, a fragmented cavernous crust; (ii) L2, a reddish-brown crust; (iii) L3, a manganese crust; (iv) L4, a gray crust; and (v) L5, a compact, grayish crust. The L1 crusts are richer in Al, P, Zr, La and U due to the residual enrichment of their immobile elements and to the formation of secondary aluminum phosphates, mainly florencite-(Ce). The L3 manganese crusts are characterized by a suite of metals, composed of Mn, Ba, Mo, Co and Ce. The contrasting compositions between segments of the upper and lower crusts it is more likely due to compositional differences in the siderite carbonatite, rather than reflecting the depth and hence intensity of weathering. A specific type of crust to which the Nb<img>Ti mineralization might be associated with was not identified. No specific geochemical association was identified for the deeper crusts, such as L4 and L5; however, the occurrence of Ce-rich pyrochlore, cerianite and carbonates in them, coupled with their absence in the upper crusts, suggests that the aforementioned ones are less evolved and therefore, closer to the carbonatite protolith. Our results indicate that despite intense weathering the composition of the primary siderite carbonatite exerts a","PeriodicalId":16336,"journal":{"name":"Journal of Geochemical Exploration","volume":"262 ","pages":"Article 107494"},"PeriodicalIF":3.9,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140843232","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}
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