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Journal of Geochemical Exploration
Elsevier
Journal of Geochemical Exploration

Elsevier

0375-6742

Journal of Geochemical Exploration/Journal Journal of Geochemical ExplorationSCIISTPEIAHCI
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    Significance of ferruginous pisoliths and interface sampling for gold exploration in the covered terrains

    Salama W.Anand R.R.Schoneveld L.Noble R.R.P....
    27页
    查看更多>>摘要：? 2021The deeply weathered Yamarna Terrane is the easternmost, least explored Terrane of the Yilgarn Craton in Western Australia. Investigation of the landscape evolution, mineralogy and geochemistry of the transported cover showed that the near surface ferruginous regolith can provide a significant tool for exploration under cover. Three types of ferruginous materials were identified and examined in three gold prospects: Smokebush, Toppin Hill and Santana. The ferruginous materials include: 1) lateritic residuum and its detrital ferruginous clasts of underlying or nearby bedrock; 2) authigenic pisoliths and nodules of Permian glacial sediments (PPS); and 3) authigenic pisoliths of aeolian sand (PAS) overlying the other two. Our findings show that As is the main pathfinder element for Au mineralization. Arsenic and Au are elevated and form near surface anomalies in lateritic residuum, detrital ferruginous clasts, PAS, <75 μm and <2 μm soil size fractions at Smokebush. At Toppin Hill, Au migrated directly from the mineralization through the Permian cover and became enriched at the surface in the PPS above mineralization. Laser ablation ICP-MS mapping shows Au in the PPS as nano-grains, microcrystalline aggregates and veinlet fillings. This is supported by partial extraction analyses, where Au was extracted mainly by K-iodide and K-cyanide, indicating that it is dispersed in particulate and soluble forms. The absence of an As anomaly in transported cover over the Toppin Hill prospect compared to Smokebush is related to the absence of arsenopyrite in the Toppin Hill Au mineralization. Arsenic, which was extracted mainly by 0.1 M tetra?sodium pyrophosphates, is associated with organic compounds and has a different fractionation pathway from Au near surface. This is also shown by an As anomaly in the Eucalyptus foliage over the Smokebush Au mineralization. At the Santana prospect, there are no Au and/or As anomalies in the PPS over the mineralization. The PPS at Santana are reworked from barren Permian cover and could be deposited with ferruginous clasts from different sources, as shown by textural and mineralogical variations between the grains and matrix. Furthermore, there is no evidence of hydromorphic dispersion of Au and As from the underlying mineralization. Thus, the PPS at Santana cannot be used to vector towards the mineralization. However, sampling at the unconformity (interface sampling) is more effective in locating the mineralization at Santana. This study shows that ferruginous pisoliths and clasts in the cover are potential sampling media for Au exploration in the Yamarna Terrane. The exploration methods used in this study can be also applied in similar covered terrains not only in Australia but also in areas with complex weathering histories in the tropics and sub-tropics.
      原文链接:
    • NSTL
    • Elsevier

    Corrigendum to “Distances to compositional equilibrium” [J. Geochem. Explor. 227 (2021) 106793] (Journal of Geochemical Exploration (2021) 227, (S0375674221000716), (10.1016/j.gexplo.2021.106793))

    Egozcue J.J.Pawlowsky-Glahn V.Buccianti A.
    1页
    查看更多>>摘要：? 2021 Elsevier B.V.The authors regret that in Section 5, “Discovering stoichiometric equilibrium” (Egozcue et al., 2021), some misleading statements and notations were detected. These mistakes are placed in a paragraph referred to testing the hypothesis of equilibrium of the olivine data set used in Section 4.2. A corrected paragraph is here reproduced for easy reading. A final comment is also added. Corrected paragraph There are circumstances in which distances to a possible equilibrium may not be small enough to accept that the sample is in equilibrium. A statistical test on H0: E(δeq) = 0, where E denotes expectation, can be carried out. In fact, δeq is a real random variable. Maintaining δeq for denoting the sample values, both the sample mean [Formula presented] and standard deviation S(δeq) can be obtained from the sample. Moreover, the univariate distribution of [Formula presented] can be approximately normal if the sample size is large enough. The standard t-student test, or alternatively a Chi-square test, on the mean value is then appropriate. If the distribution of [Formula presented] cannot be assumed normal, bootstrap techniques are also available. This kind of testing equilibrium has been largely studied for Hardy-Weinberg equilibrium, in particular, in a compositional approach see (Graffelman and Egozcue, 2011). For instance, the olivine sample used in Section 4.2 can be checked for olivine equilibrium in Equation (8) using the t-student statistic for testing [Formula presented] where n = 8827 is the sample size. The test statistic is t = 4.4027 and the p-value is 1.082e?05. This suggests rejection of H0, indicating that the stoichiometric equilibrium of olivine in the sample can be rejected. The reasons for the rejection of equilibrium of the olivine data set are found in the fact that it is the result of collecting several data sets producing an heterogeneity in the samples. Also the test is referred to Mg-Fe olivine, excluding other possible substitutions beyond the Mg-Fe pair, which may produce outliers. The authors would like to apologise for any inconvenience caused.
      原文链接:
    • NSTL
    • Elsevier

    Incorporation of geological constraints and semivariogram scaling law into geostatistical modeling of metal contents in hydrothermal deposits for improved accuracy

    Kiriyama T.Koike K.Kubo T.Lu L....
    19页
    查看更多>>摘要：? 2021 Elsevier B.V.Detailed metal distributions in a deposit can be used to determine the generation mechanism and process of the deposit type and improve mining development efficiency. Two geostatistical methods were developed that incorporate geologic information and a semivariogram scaling law to improve the spatial estimation accuracy of metal contents at the fine scale. In the first method, a binary dataset is prepared by assigning 1 to the location of the targeted geologic category in each borehole column and 0 elsewhere. Principal component analysis is implemented to generate a geologic model using principal values and ordinary kriging (OK). By overlapping with a 3D geologic model, OK of the main metal contents is then performed by limiting the content data with the same geologic category as the calculation point. This method is termed kriging with a geological constraint (KGC) and focuses on the correlation between the geologic category and metal content. The next step downscales the KGC model using a semivariogram scaling law to obtain finer spatial resolution (KGC-DS). This law is experimentally derived by repeatedly thinning out the original sample data and approximating the relationship between the mean distance of the data pair and semivariogram parameters (range, nugget effect, and sill) using a power function. This approximation can produce semivariograms in a virtual scenario with more sample data than the original. These two methods were applied to two types of hydrothermal deposits: one of the largest kuroko (volcanogenic massive sulfide) deposits in northern Japan using 77 vertical or sub-vertical drilling data and one porphyry copper deposit in northern Sulawesi, Indonesia using 58 drilling data. In the first case study, the accuracy in the high-content zones increases and the metal content distribution becomes considerably more detailed than the OK result by reducing the smoothing effect. The superposition of the geologic model and high-content zones can be used to trace the ore solution flows and interpret the deposit formation process. For the second case study, oxidation, supergene, and hypogene mineralization zones with high copper contents are clearly detected and the relationship between high-content zones and hydrothermal alteration type is identified. The results of these two case studies therefore demonstrate the effectiveness of KGC and KGC-DS.
      原文链接:
    • NSTL
    • Elsevier

    The middle Permian pyrophyllite-rich ferruginous bauxite, northwestern Iran, Irano–Himalayan karst belt: Constraints on elemental fractionation and provenance

    Khosravi M.Mongelli G.Abedini A.
    19页
    查看更多>>摘要：? 2021The pyrophyllite-rich ferruginous (PRF) bauxites in northwestern Iran from the Irano–Himalayan karst belt are deposited on the paleokarst of the middle Permian carbonate sequence of the Ruteh Formation. They were selected from the lowermost part of weathered profiles from 9 karst bauxite deposits, belonging to different stratigraphic positions. These bauxite deposits share similar mineralogical and geochemical features. Powder-XRD analyses show that the bauxites consist of diaspore, hematite, and pyrophyllite, with lesser amounts of goethite, rutile, anatase, illite, and clinochlore. Among minor constituents, single crystals, such as monazite, florencite, and zircon, were detected by SEM–EDS analyses. The positive Ce anomaly of the PRF bauxites (1.0–2.2), the relevant depletion of mobile elements, and values of the La/Y ratio (1.0–3.2) indicate that the PRF bauxites formed in a well-drained environment, characterized by a prevailing alkaline environment, promoting the stability of Fe (oxyhydr)oxides. The mineralogical composition of the PRF bauxites affects the distribution of trace elements: the redox-sensitive trace elements Ni, Cr, Co, Ce, U, and V are probably controlled by Fe (oxyhydr)oxides, whereas most of high field strength elements, such as critical metals Hf and Nb, are hosted in the pool of resistant minerals. Gallium co-varies with Al2O3, indicating this critical trace metal is distributed by diaspore. Phosphate-bearing minerals probably played an efficient role in concentrating light (LREE: La–Sm) and heavy (HREE: Eu–Lu plus Y) rare earth elements during the generation of the PRF bauxites. The mineralogical control on the distribution of LREE and HREE, coupled with the preferential complexation of HREE in an alkaline environment clearly affect the (La/Yb)ch and (LREE/HREE)ch fractionation ratios. Based on the Th–Zr and TiO2–Zr binary diagrams, the concentration of trace elements Zr, Cr, and Ga, bivariate plots of Ta (ppm) versus Al2O3 (wt%) and TiO2 (wt%), and the discriminant function 3 against discriminant function 4 variation diagram, basalt rocks within carbonate bedrocks of the Ruteh Formation have considered to be a probable provenance for the PRF bauxites, similar to some bauxite deposits from the Mediterranean-type karst bauxite belt of different ages, especially northern and northwestern Iran and western India.
      原文链接:
    • NSTL
    • Elsevier

    Estimating natural background concentrations for dissolved constituents in groundwater: A methodological review and case studies for geogenic fluoride

    Humez P.Mayer B.Chaste E.Cloutier V....
    13页
    查看更多>>摘要：? 2021 Elsevier B.V.Knowledge of the natural background concentrations of groundwater constituents is important for the management of groundwater resources, particularly for the assessment of groundwater contamination and the establishment of clean-up goals and regulatory target levels. In recent years, an increasing number of studies have assessed the natural background concentrations of dissolved constituents in groundwater using a variety of different methods, each with its own assumptions, advantages and limitations. The objective of this paper is to provide a methodological basis for improving the estimation of natural background concentrations of groundwater constituents. To this end, this paper critically reviews the different approaches used to determine natural background concentrations of dissolved constituents in groundwater. In addition, two regional case studies of fluoride in Canadian groundwater are presented to illustrate the estimation of background concentrations for natural groundwater constituents. The review of existing methods shows that the use of pristine groundwater samples is not possible in many cases, due to the widespread influence of human activities. The widely used pre-selection method can provide misleading results because of inadequate selection criteria and poor statistical significance associated with the reduction of the dataset. A variety of model-based methods have been developed, but these methods are all based on assumptions that cannot be verified. Relying on the user's experience and previous knowledge of the groundwater system, exploratory data analysis has many advantages and can be applied for both anthropogenic and natural constituents. The case studies show that the exploratory data analysis approach provides critical information to determine the sources of groundwater constituents and to properly delineate groundwater bodies for which background values will be established. Natural background concentrations should always be considered as theoretical values due to their spatio-temporal variability and scale dependence, and thresholds as concentration values above which further investigation is required.
      原文链接:
    • NSTL
    • Elsevier

    National-scale distribution and its influence factors of calcium concentrations in Chinese soils from the China Global Baselines project

    Wang X.Wang W.Liu X.
    11页
    查看更多>>摘要：? 2021The China Geochemical Baselines (CGB) project provides geochemical baselines for nearly all chemical elements, including Ca, by sampling transported soils at a density of 1 sample per approximately 3000 km2 across nearly all of China. A total of 3382 top samples (TS) were collected at depths of 0–25 cm and 3380 deep samples (DS) at depths >100 cm. The median (background) values of Ca in the TS and DS were 1.96% and 1.84%, respectively. On the spatial distribution maps, Ca concentrations generally decreased from northwestern to southeastern China. The natural climate, especially the aridity/humidity status, primarily influences this national-scale distribution. The median Ca values were ranked as follows: arid (4.61% in the TS and 4.15% in the DS) > semi-arid (2.73% in the TS and 2.55% in the DS) > sub-humid (1.37% in the TS and DS) > humid (0.56% in the TS and 0.52% in the DS) areas. In the arid areas of northwestern China, evaporite minerals can be deposited in soils, resulting in a regional high-Ca background. In the humid regions of southeastern China, soil water readily leaches Ca, leading to a regional low-Ca background. The highest Ca concentrations sparsely distributed in northwestern China (>90% quantile, Q90) and the higher Ca contents in the semi-arid and sub-humid areas (Q75–Q90) are linked to the parent Ca-bearing rocks. While no high Ca concentrations exist in both the TS and DS in southeastern China, although carbonate rocks are widely distributed. The lowest Ca concentrations distributed in southeastern China (<Q10) are predominately a result of continuous exposure to human-induced acid rainfall. Both natural and anthropogenic factors control the Ca concentrations and distribution in Chinese soils.
      原文链接:
    • NSTL
    • Elsevier

    Integration of self-organizing maps, statistical analysis, and hydrogeochemical modeling methods to identify spatio-seasonal variations in mine water quality

    Tran T.Q.Heinze T.Wohnlich S.Banning A....
    16页
    查看更多>>摘要：? 2021Monitoring the quality of mine drainage is an important task in the Ruhr coalfield in western Germany, especially after decommissioning all mining activities in 2018. In this study, seasonal and spatial variations in mine water quality of abandoned coal mines around the lower Ruhr river area were investigated. Statistical analysis, self-organizing maps (SOMs), and hydrogeochemical modeling were used to reveal changes in the water quality of 103 water samples collected between January 2018 and November 2019. An analysis of physical and chemical properties using SOM subdivided mine water samples into five groups: freshwater (groups 1, 2, 3, and 4) and brackish water (group 5) with different physical and chemical characteristics. Freshwater samples were mostly distributed in the southern and central parts, whereas brackish water samples were mostly distributed in the northeastern part of the study area. Approximately 18% of the sampling locations experienced significant seasonal changes during the study period, while 82% of the remaining locations showed only slight variations. Across all groups, seasonal variations in the water quality were less pronounced than differences between southern and northeastern sampling locations. A significant increase was observed in major ion concentrations, TDS, and EC values from southern to northern and northeastern sampling points during the monitoring period. A general trend of approaching saturation state from studied mineral phases was detected with increasing TDS concentrations from groups 1, 2, 3, and 4 to group 5. Trace element concentrations were relatively low, except for several streams with higher Fe and Mn concentrations, and varied between seasons. The SOM approach helped to identify the seasonal changes in mine water properties in the area. The evaluation of changes in mine water quality is useful for the management and protection of water resources, especially drinking water resources, in the densely populated Ruhr area.
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    • NSTL
    • Elsevier

    Principal component analysis and K-means clustering as tools during exploration for Zn skarn deposits and industrial carbonates, Sala area, Sweden

    Allen R.L.Skogsmo G.Tavakoli S.Jansson N.F....
    26页
    查看更多>>摘要：? 2021 The AuthorsThis contribution presents an application of principal component analysis (PCA) and K-means clustering as tools for data dimension reduction and grouping of multivariate, whole-rock lithogeochemical data. The study dataset consists of 64 geochemical variables and measurements of spectrophotometric brightness determined from 181 dolomite marble samples, collected at various distance from two contrasting types of mineral deposits, 1) stratabound, dolomite marble- and skarn-hosted Zn-Pb-Ag sulphide deposits and 2) industrial dolomite deposits. Clustering and PCA outputs are assessed based on spatial distribution relative to known mineral deposits and interpretability using geological domain knowledge, to test if the methods can provide a non-biased classification of dolomite samples which is useful for exploration vectoring. The PCA illustrate that three principle components derived from centered log-ratio transformed data can account for 79.69% of the dataset variance. K-means clustering provide unsupervised division of samples into different groups reflecting relative contents of detrital (siliciclastic-volcaniclastic), biogenic and hydrothermal components in the marble protoliths. Spatial analysis of principal components and K-means clusters reveal systematic distribution patterns relative to known deposits, thus providing an exploration guide. The samples most prospective for Zn-Pb-Ag deposits are divided into groups of ‘halo dolomite’ exhibiting elevated Fe and Mn, and an ‘ore dolomite’ also showing elevated Zn, Pb, Ag, Sb, Hg. This can be reconciled with magnetite and Mn-bearing Mg-silicates and carbonates in hydrothermal alteration haloes, and proximal enrichment in hydrothermal sulphides (galena, pyrrhotite, pyrite, sphalerite). Samples in these groups returned low spectrophotometric brightness, resulting from sulphides and Fe oxides grinding to dark powders during sample preparation, significantly lowering the brightness of powdered dolomite marble, even when occurring in low concentrations. Conversely, a ‘clean dolomite’ group is characterized by low contents of the elements above, high contents of Ca, Mg, Sr and total carbon, low magnetic susceptibility and high spectrophotometric brightness, and spatially coincide with known industrial dolomite deposits. An additional group of ‘detrital-rich dolomite’ is distinct from the other groups in an elevated content of high field strength elements and Al, and intermediate spectrophotometric brightness. This variety represent samples containing a higher content of co-settled volcaniclastic-siliciclastic material in the marble precursor. Assessment of the clustered data in relation to magnetic susceptibility measurements from the same samples show that Halo and Ore dolomite can be differentiated from other dolomite types by geomagnetic methods, hence providing a proxy for their indirect detection during geophysical surveys.
      原文链接:
    • NSTL
    • Elsevier

    Uraninite chemistry of the Central Mineral Belt, Labrador, Canada: Application of grain-scale unsupervised machine-learning

    Acosta-Gongora P.Potter E.G.Lawley C.J.M.Petts D....
    27页
    查看更多>>摘要：? 2021The Central Mineral Belt (CMB) in Labrador hosts several enigmatic U ± base ± precious metal showings, prospects, and deposits. Multiple mineralization styles occur within different host rocks, which has led to a variety of ore system models to be proposed. Here, unsupervised machine-learning (principal component (PCA) and targeted cluster analyses) applied to quantitative LA-ICP-MS trace element maps of uraninite were used to understand genesis the U systems in the CMB. Trace element mapping, PCA and cluster analysis indicate that: i) the largest source of data variance in uraninite from the occurrences is related to Th, REE, Zr, Hf, As, V and Ba contents, and ii) there are distinct uraninite compositions at the Two-Time deposit, Near Miss and Anomaly No. 7 mineral occurrences, not recognized from petrographic studies or major element chemistry. Trace element chemistry indicates that uraninite precipitated from fluids under (1) high-temperature magmatic and/or metasomatic conditions (> 350 °C; Dandy prospect; U/Th = 107 and ΣREE = 0.9 wt%), (2) low-temperature (< 350 °C) and locally oxidizing hydrothermal vein-type environments (e.g., Two-Time and Anomaly No. 7; U/Th ≥104 and ΣREE ≤0.1 to 3.6 wt%), and (3) complex environments were precursor uraninite was overprinted by presumably lower temperature hydrothermal fluids (e.g., Jacques Lake and Nash deposits; U/Th = 102 to 105 and ΣREE ≤0.1 to 1.4 wt%). Hydrothermal alteration caused LREE enrichment and/or increased U/Th ratios of the primary uraninite and locally, U remobilization into microfractures. Recognizing high- and low-temperature uraninite from the same mineral occurrences provides new evidence for multiple stages of hydrothermal fluid influx. Therefore, our results further support previous studies indicating significant variation in the trace element contents of uraninite due to hydrothermal alteration. In addition to the genetic constraints, PCA results and normalized REE patterns also show that the CMB uraninites have distinct geochemical signatures. Combining petrographic studies, trace element mapping, and unsupervised machine-learning unravelled cryptic chemical variations in key minerals that can guide future mineral exploration in the district. In the CMB, these chemical signatures provide insights on the evolution of U-rich fluids, in particular the presence of multiple fluid sources that evolved through a complex tectono-magmatic history.
      原文链接:
    • NSTL
    • Elsevier

    Petrogenesis of the Permian Luotuoshan sulfide-bearing mafic-ultramafic intrusion, Beishan Orogenic Belt, NW China: evidence from whole-rock Sr–Nd–Pb and zircon Hf isotopic geochemistry

    Ma B.Qian Z.Xu G.Duan J....
    17页
    查看更多>>摘要：? 2021The Permian Luotuoshan mafic-ultramafic intrusion is one of the ~280 Ma mafic-ultramafic complexes located in the Beishan Orogenic Belt at the southern margin of the Central Asian Orogenic Belt, NW China. The intrusion is predominantly composed of wehrlite, olivine clinopyroxenite, troctolite, olivine gabbro, and gabbro. Disseminated sulfides occur in wehrlite and olivine clinopyroxenite at the center of the intrusion. SHRIMP zircon U–Pb dating of a gabbro sample yielded a concordia age of 282.6 ± 2.6 Ma. The Luotuoshan mafic-ultramafic rocks are characterized by elevated εNd (282.6Ma) values from +0.42 to +6.10 and εHf (282.6Ma) values from +7.9 to +14.1, relatively low initial 87Sr/86Sr (0.703919–0.705272) and Pb isotope composition, and low ratios of TiO2/Yb, Nb/Yb, etc., suggesting the Luotuoshan magma was derived from a depleted asthenosphere mantle source. Some arc-like geochemical characteristics such as enrichment of light rare earth elements and large ion lithophile elements (Ba, Sr, Rb, etc.), pronounced negative Nb–Ta–Zr–Hf anomalies, and La/Nb, Ce/Pb, and Th/Yb ratios indicate that the mantle source was previously modified by subduction-related metasomatism. Petrographic features and mixing calculations of Sr–Nd–Hf isotopes suggest that the parental magma of the Luotuoshan intrusion underwent a moderate degree of crustal contamination (5–15%) followed by fractional crystallization process. Petrological modeling reveals that both fractional crystallization and crustal contamination may have played the important role in triggering the sulfide saturation in the Luotuoshan magma. The comparable formation age, petrographic and mineralogical characteristics, geochemistry of the parental magma and evolution process compared with intrusions in the Pobei area, indicate that the Luotuoshan intrusion may also have similar mineralization potential. This also suggests that the mineralization prospection of Permian mafic-ultramafic intrusions in the Gansu Beishan area should not be neglected, and it is worth considering that whether further exploration is worthy of being implemented in this region.
      原文链接:
    • NSTL
    • Elsevier