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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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    Tungsten skarn potential of the Yukon-Tanana Upland, eastern Alaska, USA—A mineral resource assessment

    Case G.N.D.Labay K.A.Graham G.E.Marsh E.E....
    21页
    查看更多>>摘要：? 2020Tungsten (W) is used in a variety of industrial and technological applications and has been identified as a critical mineral for the United States, India, the European Union, and other countries. These countries rely on W imports mostly from China, which leaves them vulnerable to supply disruption. Consequently, the U.S. government has a current initiative to understand domestic resource potential. The eastern Alaska portion of the Yukon-Tanana Upland (YTU), is prospective for W skarn deposits, the major source of global W supply. The regional geology consists of juxtaposed Paleozoic lithotectonic packages that were reaccreted to North America in the Mesozoic. Multiple subsequent episodes of arc-related magmatism intruded the lithotectonic packages, accompanied by W skarn formation mostly associated with 100–90 Ma intrusions; major W skarn deposits in Canada are part of the same metallogenic event (e.g., Mactung, Cantung). In this paper, we present an assessment for undiscovered W skarn resources for parts of the lesser-explored western (Alaskan) portion of the YTU. We used GIS proximity analysis to map the intersection of pluton and carbonate-bearing rocks to define three permissive tracts for W skarn deposits. The permissive tracts were qualitatively assessed by mineral potential mapping using region-wide sediment geochemistry and mineral concentrate datasets. This analysis showed that much of the western YTU has high potential for undiscovered W skarn deposits, whereas the eastern and southern YTU had only isolated areas of medium to high potential. Historical production and the quality of the geochemistry data of the western YTU tract (ca. 9200 km2) permitted a quantitative assessment of undiscovered W resources. Probabilistic estimates by a panel of 20 experts predicted a 70% chance of one to three undiscovered W skarn deposits in the western YTU tract. The rationale for favorability employed by the expert panel included favorable lithology, previous production, clustering of previously mined deposits, W placers in the area, lack of recent exploration, pan concentrates containing W minerals, and W geochemical anomalies. Estimates were combined with a global grade and tonnage model for W skarns in a Monte Carlo simulation and provided a median estimate of undiscovered resources of 94 kt WO3. If the undiscovered W skarn deposits are located close to infrastructure (e.g., near Fairbanks, or close to roads and/or power grid), application of an economic filter indicates that the median total economically recoverable WO3 is 63 kt with a net present value (NPV) of $330 million USD (2008 dollars). Whereas if deposits are far from infrastructure, median recoverable WO3 is only 30 kt and the NPV is $44 million. Our models for contained WO3 resources and NPV estimates for the western YTU tract are considerably lower than the known resources in skarns in adjacent areas in Canada. Estimates for the western YTU are also lower than preliminary estimates for undiscovered W skarn deposits in areas of the western conterminous United States. We speculate that lower permeability and continuity of favorable carbonate rock horizons in the relatively higher-grade metamorphic country rocks in the Alaska portion of the YTU may explain some of the differences in prospectivity. More detailed geologic mapping, modern geochemistry, and geophysical surveys are needed to refine the resource potential of the whole YTU. Regardless, quantitative mineral resource assessment provides a useful tool for making first-order regional estimates of undiscovered resources, identifying target areas for new data acquisition, and guiding research on the fundamental controls of district-scale metallogenic endowments.
      原文链接:
    • NSTL
    • Elsevier

    Distribution of mantle-melt interaction zone: A petrological exploration tool for podiform chromitite deposits in the Kalaymyo ophiolite, Myanmar

    Park G.Park J.-W.Kim J.Heo C.-H....
    14页
    查看更多>>摘要：? 2021 Elsevier B.V.Podiform chromitite deposits in the Kalaymyo ophiolite, Myanmar, are hosted by replacive dunites and harzburgites with varying degrees of mantle-melt interaction. Combining petrography and spinel and whole-rock compositions of harzburgites from the Bophi-Vum area, one of the ultramafic massifs of the Kalaymyo ophiolite, we investigated petrological and geochemical indicators of the mantle-melt interaction in the harzburgites and their spatial relationship with the location of chromitites. Two end-member types of mantle harzburgites with distinct textures and compositions are recognized in the study area. Low-Cr# (Cr-spinel Cr# < 30; Cr# = molar Cr/(Cr + Al) × 100) harzburgites represent residual mantle peridotites after low degree of partial melting. They are characterized by high whole-rock Al2O3, CaO, and TiO2 contents with a negative correlation between spinel Cr# and TiO2 contents, following the partial melting model trend of the depleted mid-ocean ridge basalt (MORB) mantle. The Cr-spinels from the low-Cr# harzburgites are lobate and vermicular and occur in association with orthopyroxenes, which is typical features of residual harzburgites. On the other hand, the high-Cr# (Cr-spinel Cr# > 30) harzburgites mostly have lower whole-rock Al2O3 (< ~1.4 wt%), CaO (< ~1.3 wt%), and TiO2 (< ~0.04 wt%) contents than the low-Cr# harzburgites, indicating lower modal abundances of pyroxenes. The positive correlation between spinel Cr# and TiO2 contents in the high-Cr# harzburgites suggests their metasomatic origin from the interaction between the low-Cr# harzburgite and island-arc tholeiitic or boninitic melts. The Cr-spinels from the high-Cr# harzburgites, recrystallized during the mantle-melt interaction, are mostly euhedral and associated with olivine. Geochemical maps of the spinel Cr#, whole-rock Al2O3, and CaO contents for the mantle harzburgites show that the distribution of the high-Cr# harzburgites, i.e., the mantle-melt interaction zone, is closely associated with the locations of the dunite and chromitite outcrops. This spatial relationship suggests the potential use of the distribution of mantle-melt interaction zone for podiform chromitite exploration in the study area.
      原文链接:
    • NSTL
    • Elsevier

    Potential contamination of stream waters by ultramafic mining sediments: Identification of geochemical makers (New Caledonia)

    Boula A.Laporte-Magoni C.Gunkel-Grillon P.Selmaoui-Folcher N....
    17页
    查看更多>>摘要：? 2021 Elsevier B.V.The ultramafic massifs of New Caledonia are mainly composed of regolites with lateritic soils rich in metals such as Co, Fe, Mg and Ni. The nickeliferous ore is exploited by opencast mines. After rainfalls, erosion and particle runoff cause the mobilization of metals and metalloids in surface waters. The objective of this study is (i) to determine the geochemical background of metals and metalloids in surface waters draining a mining ultramafic massif, (ii) to identify the geochemical markers influenced by the mining of nickeliferous ore (iii) and to define discriminant values of the mining impact. Hydrochemical monitoring was carried out on five streams draining the Koniambo massif over a 15-years period. Twenty-four elements were analyzed for their total concentration and 18 for their dissolved concentration (<0.45 μm). The descriptive analysis shows that one river has higher total concentrations of As, Co, Cr, Ni, Mn, Al, Fe, Si and Mg and higher dissolved concentrations of Al, Cr, Ni than the other 4 rivers. This difference results from an old mine whose erosion exacerbates sediment transport. These 5 rivers drain the same ultramafic massif of small surface area (21 km2). The description by the boxplot method of the 4 non-impacted rivers allowed us to define a geochemical background. The graphical comparison between the geochemical background with the median values of the river impacted, validated by the ANOVA one way, allowed us to identify markers of the mining anthropization. The use of a supervised classification as a decision tree ranks the markers according to their discriminating power. In addition, this method determines the range of threshold values that separate impacted from non-impacted rivers. The elements Cr, As, Si, Mg and Al are identified as discriminating markers for total concentrations. Only Cr has been identified as a discriminating metal for the dissolved fraction with an interval around 58 μg/l. This concentration is close to the limit defined by the WHO for drinking water which is 50 μg/l.
      原文链接:
    • NSTL
    • Elsevier

    Leaching of acid generating materials and elements from coarse- and fine-grained acid sulfate soil materials

    Mattback S.Sandfalt A.Osterholm P.Boman A....
    13页
    查看更多>>摘要：? 2021 The AuthorsIn Finland, acid sulfate (AS) soils are regarded as a serious environmental threat towards the Baltic Sea and watersheds situated in land areas that have emerged from the sea since the last glaciation due to glacial isostasy. The aim of this study is to compare the behavior of coarse-grained AS soil materials to the behavior of fine-grained AS soils and coarse-grained non-AS soils in order to (1) assess the potential environmental threat of coarse-grained AS soils and (2) to assess the need to distinguish coarse-grained AS soils from fine-grained AS soils in future risk assessment of AS soils. The hypotheses are that (1) a coarser grain size enhances the rate of oxidation and pH decrease due to larger inherited pore size, enabling better initial aeration and less efficient buffering processes due to lower particle surface areas and different mineralogy (more weathering resistant quartz and feldspars), and that (2) the leaching of acid generating materials and elements from coarse grained AS soils is significantly lower as compared to fine-grained AS soils but significantly higher as compared to coarse grained non-AS soils. The study used an incubation based “let the soil speak for itself”-approach, which means that parameters such as pH, acidity, amount of elements leached, and the electric conductivity of the leachates were measured on arrays of sample aliquots before, during, and after a 16 week incubation (oxidation) period. Even though the coarse-grained AS soil materials contained one order of magnitude less sulfide than the fine-grained AS soil materials, a S mass fraction as low as 0.01%, the pH dropped well below 4.0 upon oxidation, thus being classified as AS soils. The amount of acid generating materials and elements leached from coarse-grained AS soil materials were at least one order of magnitude less, as compared to the fine-grained AS soil materials, except for Fe, which leached in similar or greater quantities from coarse-grained AS soil materials. The differences in the leaching of acid generating materials and elements suggest it would be beneficial to divide coarse-grained and fine-grained AS soils into separate subgroups for risk management purposes.
      原文链接:
    • NSTL
    • Elsevier

    Regolith characterization and landscape evolution for geochemical exploration of the covered Yamarna Terrane, Western Australia

    Salama W.Anand R.R.Tunmer W.Aspandiar M....
    21页
    查看更多>>摘要：? 2021The easternmost Archaean Yamarna Terrane is the least explored terrane under transported cover in the Yilgarn Craton of Western Australia. Our aims are to understand the evolution of the paleolandscape, determine the weathering history and depositional processes, and the provenance, mineralogy and geochemistry of the Permian to Quaternary transported cover. This is a necessary step for selecting the appropriate sample media to vector towards buried mineral deposits in this terrane. The Permian cover was deposited in broad, structurally controlled valleys that were carved into and partly to completely truncate the previously weathered Archaean rocks. U[sbnd]Pb dating of zircon grains indicates that the main provenance of the Permian cover on the Yamarna Terrane is the Albany-Fraser Orogen, with limited contribution from the Yilgarn Craton, Musgrave Province and Antarctica. The Permian cover of the paleovalleys wedges out laterally towards pre-existing, weathered basement paleohighs, capped by lateritic residuum. The Permian cover is deeply weathered, and consists of upper ferruginous (mottled, brecciated, pisolitic and nodular) and lower kaolinitic, poorly lithified sandstones and mudstones with a basal gravel at the bottom. Above the basal unconformity between the Permian and weathered Archaean, the Rb/Zr ratio decreases sharply and the Permian cover shows negative Eu anomalies (Eu/Eu*) compared to positive Eu/Eu* in the underlying weathered and fresh mafic Archaean rocks, suggesting distal felsic source rocks for the Permian cover. In places, where Au increases, the base of the Permian cover still shows positive Eu/Eu* anomalies, suggesting physical dispersion from proximal mineralized mafic rocks. The Post-Permian weathering and erosion processes produced an extensive layer of Au-bearing detrital ferruginous clasts derived from lateritic residuum and ferruginous pisoliths and nodules from the Permian cover. These ferruginous grains occur as loose or cemented by Fe oxides forming ferricrete. Ferricrete is not necessarily related to the underlying weathered dolerite compared to the lateritic residuum. This is shown, in some places, by a sharp decrease in the Ti/Zr ratio, high HFSE, negative Eu/Eu*, high LREE/HREE compared to the underlying weathered dolerite suggest an unconformity and physical dispersion from weathered felsic source rocks. The Au-enrichment in the ferricrete derived from the felsic rocks occurred after deposition as a result of hydromorphic dispersion by groundwater. The weathered Permian cover and Archaean rock are covered by aeolian sand within which Au is concentrated in authigenic pisoliths. These pisoliths were formed by periodical water saturation during seasonal water table fluctuation. The unconformities and the ferruginous regolith materials are relevant to Au exploration through cover in the Yamarna Terrane and are highly recommended for regional-scale systematic sampling.
      原文链接:
    • NSTL
    • Elsevier

    Trace element geochemistry of sphalerite and chalcopyrite in arc-hosted VMS deposits

    Torro L.Benites D.Vallance J.Ortiz-Benavente B.A....
    21页
    查看更多>>摘要：? 2021 Elsevier B.V.Trace element compositions of sphalerite and chalcopyrite have been investigated for four arc-hosted Cretaceous VMS deposits (María Teresa, Perubar, and Palma in Peru, and Cerro de Maimón in the Dominican Republic) using laser ablation inductively-coupled plasma mass spectrometry. In sphalerite, Fe, Mn, Cd, Hg, Ag, Sb, Se, In, Ge, and Ga are lattice-bound, whereas Sn, Tl, Bi, and Pb occur at least partly as mineral microinclusions. Significant variations in the contents of minor and trace elements are observed in sphalerite grains from individual deposits. A strong negative correlation between Fe (Inter-Quartile Range [IQR] 44,009–18,168 ppm) and Zn indicates a dominant Fe2+ ? Zn2+ simple isovalent substitution. Regarding potential high-tech by-products, the contents of In (IQR 42–1.6 ppm, up to 415 ppm) and Ga (IQR 31–5.9 ppm, up to 96 ppm) in the studied sphalerite are normally much higher than those of Ge (IQR 0.85–0.16 ppm, up to 9.3 ppm). Correlation trends suggest Cu+ + In3+ ? 2Zn2+, Cu+ + Ga3+ ? 2Zn2+, and more complex substitution mechanisms of Zn involving combinations of monovalent (Cu+, Ag+), divalent (Ge2+?), trivalent (In3+, Ga3+, [Sn3+?]), and quadrivalent (Ge4+, Sn4+) cations. As for chalcopyrite, Zn, Ag, Sn, Cd, Se, In, Ga, and Ge are interpreted to be lattice-bound, whereas Mo, Au, Tl, Sb, Pb, and Bi probably occur as microinclusions. Relative to sphalerite, chalcopyrite is depleted in In (IQR 28–8.4 ppm, up to 49 ppm) and Ga (IQR 8.3–2.9 ppm, up to 24 ppm) and enriched in Ge (IQR 5.9–0.70 ppm, up to 80 ppm). Of the other trace elements, Zn (IQR 426–190 ppm) is the most highly concentrated in the studied chalcopyrite, followed by Ag (IQR 136–23 ppm), Se (IQR 64–22 ppm), Sn (IQR 53–1.3 ppm), and Cd (IQR 12–6.0 ppm). General positive correlation trends between Zn, Cd, In, Ge, and Ga in chalcopyrite suggest varied coupled substitution mechanisms of Fe and Cu with fluctuating valences due to covalent bonding. Trace-element distribution patterns in sphalerite and chalcopyrite were studied for the zone-refined Sofía-D massive sulfide body in the María Teresa deposit, which comprises a lower lower portion of dominant pyrite sheathed upward by zones of chalcopyrite (Cu zone), sphalerite (Zn zone) and galena + sphalerite ± fahlore ± barite (Pb – Zn – Ag zone). Bottom to top of the sulfide body, sphalerite records progressive depletion in In, Cu, Mn, and Se, and enrichment in Ge. This distribution pattern agrees with increasing crystallization temperatures and/or volatile magmatic influx towards the lower portion of the massive mineralization. Distribution of trace elements in chalcopyrite is rather uneven except for a sustained enrichment in Se towards the basal portion of the sulfide body. The fact that such trends are preserved in spite of extensive recrystallization during thermal metamorphism in parts of the Sofía-D massive sulfide mineralization suggests i) a closed metamorphic system and ii) that element interdiffusion was prominently local. Accordingly, we propose that sphalerite lattice-bound trace elements distribution patterns described in this article can help determine the polarity of massive sulfide bodies in VMS districts in metamorphosed and tectonized terranes.
      原文链接:
    • NSTL
    • Elsevier

    Sphalerite as a record of metallogenic information using multivariate statistical analysis: Constraints from trace element geochemistry

    Zhang J.Shao Y.Liu Z.Chen K....
    15页
    查看更多>>摘要：? 2021 Elsevier B.V.In this study, the dominant geological factor that influences the element distribution in sphalerite was determined and the behaviors of the elements under a single factor were investigated (e.g., temperature). To this end, two multivariate statistical analysis methods, namely, principal component analysis (PCA) and factor analysis (FA), were performed on a published sphalerite dataset containing 1336 analysis points from 52 deposits. The PCA produced five element clusters, which were each controlled by the five dominant factors identified by the FA (including magmatic-derived materials, temperature, pH, element remobilization, and dynamic recrystallization). Furthermore, the influence of temperature on the trace element composition of sphalerite was quantitatively expressed based on the corresponding homogenization temperature of fluid inclusions from 27 deposits, i.e., TFAS (°C) = (32.22 ± 1.88) × FAS + (245.49 ± 3.79) (Ra2 = 0.918). The above research was then applied to the sphalerite from the Baoshan Cu-Pb-Zn deposit to reveal its metallogenic conditions. The results indicate that from the central-western mining districts to the northern mining districts, the contributions of the magmatic-derived materials, temperature, and fO2 decrease, whereas the contributions of the basement-derived hydrothermal fluid and pH increase.
      原文链接:
    • NSTL
    • Elsevier

    Mine waste from carbonatite deposits as potential rare earth resource: Insight into the Phalaborwa (Palabora) Complex

    Gomez-Arias A.Castillo J.Vermeulen D.Yesares L....
    13页
    查看更多>>摘要：? 2021The Phalaborwa (Palabora) Igneous Complex (PIC), South Africa, has been mined for the last six decades for copper and phosphate, among others commodities. As a result, more than 4500 Mt. of mining wastes have been deposited in waste rock dumps (WRDs) and tailing impoundments. This study aims to investigate the potential of the PIC wastes (WRDs and tailings) as a secondary resource of rare earth elements (REE) and its possible processing options, by means of both mineralogical and geochemical determinations, using X-ray diffraction (XRD), petrographic and scanning electron microscope with energy dispersive spectroscopy (SEM–EDS) and electron probe micro-analyzer (EPMA). The samples were also submitted to a REE leachability assay based in a sequential extraction procedure. Phoscorites and carbonatites are major lithologies in the WRDs and contain a notable concentration of REE, of which 0.2 and 0.1 wt%, respectively, would be easily extractable. The mineralogical results show monazite as the main REE-mineral (∑REE 60 wt%), while fluorapatite and calcite are the most important REE-bearing minerals (∑REE 1 and 0.5 wt%, respectively) for their abundance. On the other hand, the tailings are comprised mostly by monomineralic particles of calcite, dolomite, pyroxene, fluorapatite, magnetite and phlogopite. Based on the geochemical results, the extraction of REE from monazite, fluorapatite, calcite and dolomite, from tailings produced by both the Cu and the phosphate mines, might produce up to 5.65 and 1.75 kg of REE per ton, respectively. Therefore, tailings from PIC have the potential to become an asset. An approach to circular economy by re-processing mining wastes would extend the lifetime of the PIC mines and their benefits, while reducing the waste of resources and their environmental impact.
      原文链接:
    • NSTL
    • Elsevier

    Unsupervised drill core pseudo-log generation in raw and filtered data, a case study in the Rio Salitre greenstone belt, S?o Francisco Craton, Brazil

    Larizzatti J.H.da Silva A.D.R.Lopes C.G.Klein E.L....
    16页
    查看更多>>摘要：? 2021 Elsevier B.V.The goal of this work is to emulate a situation where an analyst with none or little previous geological knowledge of the samples must deal with an unsupervised approach to gain some insights about drill core samples and compare the results of two main unsupervised algorithms with and without filtering methods. We used in situ portable X-ray Fluorescence data acquired in sawn drill core samples of rocks from the Sabiá prospect, at the Rio Salitre greenstone belt, S?o Francisco Craton Brazil, for pseudo-log automatic generation through running Unsupervised Learning models to group distinct lithotypes. We tested the K-means and Model-Based Cluster (MBC) algorithms and compared their performance in the raw and filtered data with a manual macroscopic log description. From the initial 47 available elements, 20 variables were selected for modeling following the criteria of presenting at least 95% of uncensored values. Additionally, we performed a Shapiro-Wilk test that confirmed a non-parametric distribution by verifying the P-value attribute less than the 5% significance level. We also checked if the dataset's distribution was statistically equivalent to the duplicates with the assistance of a Kruskal–Wallis test, which would confirm the representativity power of the measurements at the same 5% significance level. After this step, the pseudo-log models were created based on reduced dimension data, compressed by a centered Principal Component Analysis with data rescaled by its range. Concerning reducing the high-frequency noise in the selected features, we employed an exponential weighted moving average filter with a window of five samples. By the analysis of the Average Silhouette Width on sample space, the optimum number for K-means was fixed in two, and then the first models were generated for raw and filtered data. From the MBC perspective, the sample space is interpreted as a finite mixture of groups with distinct Gaussian probability distribution. The number of clusters is defined by the analysis of the Bayesian Information Criteria (BIC), where several models are tested, and the one in the first local maximum defines the number of groups and the type of probabilistic model in the simulation. For the data used in this work, the optimum group number for MBC is four, and the probabilistic model type determined by the BIC is elliptical with equal volume, shape, and orientation. Thus, Model-Based Cluster has detected four different cluster groups with almost the same representativity for the two drill cores' samples. All K-means and MBC models were able to detect changes in lithotypes not described in the manual log. On the other hand, one lithotype described by the experts was not detected by this methodology in any attempt. It was needed a detailed investigation with thin section descriptions to determine the cause of this response. Finally, compared with the manual log description, it is notable that the models built on filtered data have better performance than those generated on raw data, and the MBC filtered model had better performance than the others. Hence, this multivariate approach allied to filtering the data with a moving average transformation can be a tool of great help during several stages of mineral exploration, either in the creation of pseudo-log models prior the description of the drill core samples or in the data validation stage, when it is necessary to standardize several descriptions made by different professionals.
      原文链接:
    • NSTL
    • Elsevier

    Mercury distribution around the Siele Hg mine (Mt. Amiata district, Italy) twenty years after reclamation: Spatial and temporal variability in soil, stream sediments, and air

    Fornasaro S.Rimondi V.Costagliola P.Morelli G....
    12页
    查看更多>>摘要：? 2021 Elsevier B.V.The Siele mine and its smelting plant are part of the world class Monte Amiata Hg district (southern Tuscany, Italy). After closure in 1981, the area was subjected to the first reclamation in the district, completed in 2001. However, stream sediments in the Siele creek downstream of the mine still present highly anomalous Hg values (up to 5400 mg/kg). Gaseous elemental mercury (GEM) concentrations in air near the former metallurgical buildings, and immediately downstream of the mining area, are also high (up to 16,233 ng/m3), although lower than before reclamation, when values up to 237,000 ng/m3 had been measured. On the other hand, Hg mobility, determined by leaching tests, is mostly below the limits defined by pending regulations (1 μg/L), and methyl-Hg concentrations are mostly below 1 ng/kg (with a single value of 6 ng/kg). Therefore, the actual risk to environment and health is deemed low. In summary, reclamation reduced, but did not stop, the release of Hg from the Siele mining area. Results show that the Siele system has a low resilience and natural recovery will take many years (probably decades), during which the area will remain an important source of Hg for the Paglia and Tiber River systems, and eventually for the Mediterranean Sea.
      原文链接:
    • NSTL
    • Elsevier