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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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    Evaluation of strontium isotope tracers of produced water sources from multiple stacked reservoirs in Appalachian, Williston and Permian basins

    Marza M.Ferguson G.McIntosh J.Mowat A....
    12页
    查看更多>>摘要：? 2021Both unconventional and conventional oil and gas production have led to instances of brine contamination of near-surface environments from spills of saline produced waters. Strontium isotope ratios (87Sr/86Sr) have been used as a sensitive tracer of sources of brine contamination in surface waters and shallow aquifers in areas where oil and gas production are limited to only a few reservoirs and produced water sources are well-defined. Recent expansion of conventional and unconventional oil and gas production to additional tight formations within sedimentary basins has resulted in production of formation waters from multiple oil and gas reservoirs that may have similar chemical and isotopic ratios, including 87Sr/86Sr. This study evaluates the utility of 87Sr/86Sr, the most widely available tracer dataset beyond major ion chemistry and water stable isotopes, as a tracer of brine contamination related to conventional and unconventional oil and gas production in the Williston, Appalachian and Permian basins. Multiple stacked oil and gas reservoirs within each basin have overlapping formation water 87Sr/86Sr, based on a non-parametric statistical test. For example, in the Appalachian Basin, produced waters from unconventional gas production in the Middle Devonian Marcellus and Upper Ordovician Utica shales have overlapping 87Sr/86Sr. In the Permian Basin, produced waters from the unconventional Pennsylvanian-Permian Wolfcamp Shale and conventional and unconventional Pennsylvanian Cisco/Canyon/Strawn formations have similar 87Sr/86Sr. In the Williston Basin produced waters from Late Devonian to Early Mississippian Bakken Formation unconventional oil production have overlapping 87Sr/86Sr with produced waters associated with minor production of conventional oil from the Middle Devonian Winnipegosis. Improved spatial characterization of 87Sr/86Sr and other isotopic signatures of produced waters from various oil/gas reservoirs are needed to constrain geographic and depth variability of produced waters in hydrocarbon producing regions. This is particularly important, as unconventional oil and gas production expands in areas of existing conventional oil and gas production, where delineating sources of saline produced waters in cases of accidental surface spills or subsurface leakage will become a greater challenge. Sr isotopes alone may not be able to distinguish produced waters in areas with overlapping production from reservoirs with similar isotopic signatures.
      原文链接:
    • NSTL
    • Elsevier

    Geological mapping of basalt using stream sediment geochemical data: Case study of covered areas in Jining, Inner Mongolia, China

    Ge Y.-Z.Zhang Z.-J.Cheng Q.-M.Wu G.-P....
    11页
    查看更多>>摘要：? 2021 Elsevier B.V.Multidisciplinary exploration data have been widely and successfully applied when using machine learning methods to conduct geological mapping. However, in covered areas such as Jining, Inner Mongolia, China, where remote sensing and geophysical data are unavailable or difficult to obtain, geochemical data become more important. In addition, previous studies have often selected data labels based on geological maps, which are generally obtained by interpolation or extrapolation of field lithological points and so are inherently uncertain. This study collected seven types of 2341 field lithological points and evaluated the errors of each lithological unit, based on a confusion matrix. Using these field lithological points, we applied the random forest (RF) and support vector machine (SVM) methods to delineate basalt in the Jining region by integrating 1:50,000 stream sediment geochemical data. The evaluation indexes of accuracy, precision, recall, and the receiver operating characteristic curve (ROC) all indicated that RF outperformed SVM. Based on the predictions of RF, five types of target areas were generated, which were further verified using Sentinel-2 images. This research highlights that using lithological points as data labels and trace-element stream sediment data as a training dataset can provide encouraging results when conducting lithological mapping in covered areas.
      原文链接:
    • NSTL
    • Elsevier

    Geology, alteration geochemistry, and exploration geochemical mapping of the Ertsberg Cu-Au-Mo district in Papua, Indonesia

    Rumbiak U.Al Furqan R.Rosana M.Yuningsih E....
    21页
    查看更多>>摘要：? 2021 Elsevier B.V.The Ertsberg-Grasberg district hosts the world's largest Cu-Au([sbnd]Mo) skarn system. The mineralization is related to the Pliocene Ertsberg- and Grasberg intrusive complexes, which intruded the Jurassic-Cretaceous Kembelangan Group siliciclastics and Cenozoic New Guinea Limestone Group. Despite previous studies, elemental migration across the porphyry-skarn system and across the different ore stages is still unclear. Here, we attempt to tackle this issue by integrating ore deposit geology, alteration/mineralization paragenesis, whole-rock geochemistry of the Ertsberg granitoids and carbonate wallrocks, together with spatial mapping of hydrothermal minerals and target/pathfinder trace elements at the Deep Mill Level Zone of Ertsberg. Ores at Ertsberg are mainly skarn-hosted, whose formation comprises five stages: (I) prograde skarn; (II) retrograde alteration; (III) massive anhydrite replacement; (IV) late hydrothermal veining; (V) supergene alteration. Massive magnetite and main Cu[sbnd]Au mineralization occurred in Stage II and III, respectively, although minor Cu mineralization persisted to Stage IV. The Ertsberg granitoids have medium SiO2 and high Al2O3 contents, and consist mainly of (quartz-)monzonite and minor (monzo)diorite. Least-altered samples have upper crust-normalized enrichments in certain large ion lithophile elements (LILEs, e.g., U and K) and depletions in all high field strength elements (HFSEs, e.g., Ti, Y, and Yb). The samples are fresh to moderately-altered, featured by garnet-diopside skarn and/or porphyry-style (potassic, propylitic, phyllic) alterations and anhydrite replacement. Elemental mass balance calculation indicates that the porphyry-style alteration zones are featured by feldspar destruction and the accompanying alkali depletions, although the loss of K[sbnd]Rb (in potassic and phyllic zones) and Ca-Ba-Sr (in propylitic zone) are balanced by their respective capturing in secondary K-feldspar-mica and actinolite-epidote-anhydrite. Decarbonation of the dolomitic wallrocks likely released Mg-Ca-Sr, which facilitated the subsequent forsterite-diopside exoskarn and anhydrite alteration. The enrichments of various ore-related target/pathfinder elements in these altered samples are consistent with their mineralized nature, e.g., Fe[sbnd]Mn (magnetite), Cu-Fe-Bi-Se-Te (bornite), Mo[sbnd]Re (molybdenite), Au-Ag-As-Bi-Te (auriferous pyrite/arsenopyrite), Zn-Fe-Mn-Sn-In (sphalerite), and Pb-Ag-Bi (galena). Alteration mineral and target/pathfinder elemental distribution patterns show that the ore fluids were likely originated from the porphyry hydrothermal (potassic) centers near the Ertsberg pluton margin. The fluids then spread out from the potassic centers, forming the surrounding propylitic zone, and migrated along the largely NW-SE-oriented intrusive contact and fault zones. This formed the endoskarn in the Ertsberg pluton, the forsterite-diopside exoskarn in the Waripi Formation dolomite, and the garnet-diopside exoskarn in the Ekmai Formation limestone/calcareous sandstone-siltstone. As the hydrothermal system started to wane, the prograde skarn formation is partially overprinted/enveloped by retrograde serpentine and actinolite/tremolite-epidote-chlorite alterations, and then by magnetite mineralization and massive anhydrite replacement in the carbonate wallrocks. The texturally-destructive skarn formation, and the dissolution of carbonate wallrocks and hydrothermal anhydrite were likely pivotal in creating the highly-fractured Broken Zone, which served as a structural trap for the high-grade Cu-Au-Mo ore deposition.
      原文链接:
    • NSTL
    • Elsevier

    Multivariate analysis of dilution-corrected residuals to improve the interpretation of geochemical anomalies and determine their potential sources: The Mingardo River case study (Southern Italy)

    Gramazio A.Albanese S.Dominech S.Yang S....
    11页
    查看更多>>摘要：? 2021 Elsevier B.V.Stream sediment geochemical prospecting is historically acknowledged as a reliable tool to investigate the influence of geology and to assess the presence of natural and/or anthropogenic anomalies within river catchment basins at different scales. Several methods have been developed during decades to seek for geochemical anomalies especially those considered with a high potential for mineral resources. In the last decades, the Sample Catchment Basin (SCB) method, based on the use of dilution-corrected residuals (DCRs), has been developed, improved, and extensively used in mineral exploration, mostly at regional scale. In this paper the method was applied to a small catchment basin in southern Italy (Mingardo River) with the purposes of testing its reliability and improving the interpretation of geochemical patterns. The SCBs method was performed by using as input both unprocessed (raw) and centered log-ratio (clr) transformed data, and the obtained DCRs were classified through the concentration-area (C-A) method. After verifying the inadequacy of raw data, Principal component analysis (PCA) and Hierarchical Cluster Analysis (HCA) on PCA loadings were used to address and improve the interpretation processes in a multivariate perspective. The method has proved to be effective in identifying anomalies associated with lithological layers that are often not reported on the medium scale and which, however, have the ability to condition the geochemical patterns of the basin to which they belong. The geochemical footprint of anthropic presence (road, villages, etc.) was also detected although its impact on the study area is limited.
      原文链接:
    • NSTL
    • Elsevier

    Geochemical characteristics of the Silurian-Devonian Kroh black shales, Peninsular Malaysia: An implication for hydrocarbon exploration

    Shoieb M.A.Gebretsadik H.T.Ismail M.S.Ibad S.M....
    14页
    查看更多>>摘要：? 2021 Elsevier B.V.In this study, the hydrocarbon potential of the Silurian-Devonian Kroh black shales in Peninsular Malaysia was investigated. To this aim, seventy-five samples from the Kroh black shales were analyzed to identify their geochemical and mineralogical composition using X-ray diffraction (XRD) and X-ray fluorescence (XRF), respectively. XRD results showed that the samples consist of two main components: kaolinite and quartz. From the XRF analysis, the most dominant oxides in the Kroh black shale samples were SiO2 (75.1 wt%) and Al2O3 (13.5 wt%). The ratio of Al2O3/TiO2 suggests that the black shales are originated from an intermediate to felsic igneous rock. The ratio of V/(V + Ni) varies from 0.8 to 1, and V/Ni ranges from 4.3 to 7.1. These values suggest suboxic to relatively anoxic depositional conditions and purely marine sources of organic matter (OM). However, a cross-plot of Ni vs. V indicated that depositional conditions of the Kroh black shales are terrestrial oxic to marine-terrestrial oxic-dysoxic. Also, Rock-Eval 6 pyrolysis was applied to assess the hydrocarbon potential of the Kroh black shales and acquire more information on the thermal maturity of organic matter (OM). Data from the Rock-Eval pyrolysis revealed that the total organic carbon (TOC) content of the seventy-five black shale samples from seven outcrops (i.e., KR-1 to KR-7) varies from 0.33 wt% to 8.56 wt%. The TOC values indicate that the Kroh black shale samples have preserved a fair to a good quantity of the OM richness. Moreover, Rock-Eval analysis affirmed that the samples predominantly fall within a weak version of Type III kerogen, as gas-prone window, and Type IV kerogen, as inert solid bitumen. Furthermore, the relationship between hydrogen index (HI) and production index (PI) with vitrinite reflectance (Ro) confirms an immature to overmature of the OM in the Kroh black shales. Those findings bring to light the Kroh black shale samples are at a minimal level of HC generation; hence, commercial considerations for the Kroh Formation might not be worthwhile. It also adds new insight into the peninsular depositional conditions, contributing to the region's paleogeography understanding.
      原文链接:
    • NSTL
    • Elsevier

    Mineral prospecting from biogeochemical and geological information using hyperspectral remote sensing - Feasibility and challenges

    Chakraborty R.Kereszturi G.Anderson C.Pullanagari R....
    15页
    查看更多>>摘要：? 2021 Elsevier B.V.Biogeochemistry is an effective and fast approach for orientation studies in mineral exploration. Vegetative cover has been used in a range of geological environments to gain insight into the composition of sub-surface soils and bedrock found at depth; however, there is little to no records of biogeochemistry being coupled within a remote sensing and spectroscopy framework in the domain of mineral exploration. The study uses lab- and airborne hyperspectral remote sensing to localize gold mineralisation using the concept of biogeochemistry. This pilot study uses plant species, Pinus radiata in close proximity to a mineralised shear zone. This study used a 2 m spatial resolution airborne hyperspectral data, captured by AisaFENIX sensor and was complimented with lab-based hyperspectral data of the sampled vegetation and soil/rock exposed along the Hyde-Macraes Shear Zone, within the Otago schist belt in the South Island, New Zealand. The hyperspectral data, and the biogeochemistry data was explored using several statistical approaches to determine significant relationships between the underlying soil and rock substrate and biogeochemistry of the sampled vegetation with a focus on pathfinder elements to gold-mineralisation. Three commonly used multivariate predictive regression models, were tested, including partial least squares regression (PLSR), kernel based PLSR (kPLSR) and random forest regression (RFR) modelling. The results suggest that hyperspectral scanning can discriminate samples from a mineralised zone spectrally. Furthermore, the lab-based hyperspectral data outcompetes the airborne hyperspectral data for vegetation to identify areas of potential mineralisation. The model performances vary depending on the part of the plant analysed, and bark samples are found to be promising to explore underlying geological resources in the future. The regression model that show up to R2cv > 0.7 using bark samples decreases to R2cv ~ 0.2 when trained with needle samples. The airborne data is significantly more complex, which is observed in poorer model performances with R2cv ranging from 0.2 to 0.5.
      原文链接:
    • NSTL
    • Elsevier

    Petrogenesis and U–Pb (titanite) age of Cu–Ag skarn mineralization in the McKenzie Gulch area, northern New Brunswick, Canada

    Massawe R.J.R.Lentz D.R.
    20页
    查看更多>>摘要：? 2021Copper–silver skarn occurrences in the McKenzie Gulch (MG) area are spatially associated with Middle Devonian (386.3 ± 2.3 Ma; U–Pb zircon) intermediate to felsic dyke swarms. Mineralization occurs as veins and stockwork veinlets, disseminations, patches, and locally as replacement of calc-silicate skarns in argillaceous limestone. Fluid inclusion data from the MG deposit suggest that hydrothermal systems associated with skarn formation evolved from an early magmatic-dominated stage to a late formation water and/or meteoric water-dominated stage. An early prograde endoskarn and exoskarn formed from high temperature (444–865 °C) and high salinity (36–40 wt% CaCl2 + NaCl) fluids, whereas retrograde skarn formed from low temperature (97–257 °C) and low salinity (1–15 wt% NaCl equiv.) fluids. The salinity gap between prograde and retrograde fluids (~ 4-fold dilution) may be due to throttling in the magmatic-hydrothermal system resulting in a pressure regime that alternated between dominantly lithostatic and hydrostatic. The δ34S values of sulfides from the skarn deposit range from +4.6 to +9.1‰. These values are lower than the corresponding δ34S values from the adjacent gold-bearing quartz-calcite-sulfide veins whose values range from +7.9 to +10.0‰. These high positive values suggest that magmatic hydrothermal fluids interacted with and incorporated significant amount of sulfides from sedimentary rocks, which typically have higher δ34S values in the region. Hydrothermal titanites from retrograde skarn ores were successfully dated by laser ablation-inductively coupled plasma-mass spectrometry (LA–ICP–MS) in an effort to constrain the timing of mineralization. These analyses yield weighted mean 206Pb/238U age of 387.2 ± 3.6 Ma, in agreement with 206Pb/238U age of 386.3 ± 2.3 Ma of zircon from associated porphyry dykes. The felsic porphyry dykes spatially associated with Cu–Ag skarn at MG, coupled with fluid inclusion data, provide evidence for magmatic activity coincident with the mineralizing events. In addition, Pb isotope compositions of galena and other sulfides (chalcopyrite, pyrite and pyrrhotite) are compatible with a model linking the skarns with Early to Middle Devonian magmatic activity at depth that eventually interacted with and incorporated significant volumes of sedimentary host rocks. Consequently, the MG Cu–Ag skarn mineralization occurred contemporaneously with the intrusion of porphyry dyke swarms.
      原文链接:
    • NSTL
    • Elsevier

    Lithogeochemistry of various hydrothermal alteration types associated with precious and base metal epithermal deposits in the Tarom-Hashtjin metallogenic province, NW Iran: Implications for regional exploration

    Ghasemi Siani M.Lentz D.R.
    19页
    查看更多>>摘要：? 2021 Elsevier B.V.In this study, the styles, types, and degrees of hydrothermal alteration associated with Pb-Zn-Cu-Ag-Au epithermal deposit systems in the Tarom-Hashtjin metallogenic province are evaluated using petrographic studies, as well as mass changes and molar elements ratios (MER), in order to examine regional exploration implications. The MER plots show that the hydrothermally altered rocks were most affected by various types of K-metasomatism, mainly characterized by K gains and Na and Ca losses. The intensity of K-metasomatism is related to precious and base-metal mineralization, showing increasing K trends toward the ore veins. The alteration index (AI) and chlorite-carbonate-pyrite index (CCPI) reveal that argillic, sericitic, and propylitic alteration types are the main zones of alteration surrounding ore veins indicating that AI increases and CCPI decreases toward more proximal to the structures linked to these ore systems. Determination of mass changes in altered rocks surrounding selected epithermal deposits suggest Si, K, and Al gains and Na and Ca losses increasing in intensity toward ore veins, consistent with alteration zoning from the silicic and K-metasomatic (sericite and argillic) inner zones to the propylitic (Fe-rich chlorite alteration) outer zone typical of epithermal ore systems. Data from this study show that the intensity of K-metasomatism in the acidic rocks is greater than in the intermediate and mafic rocks, where it is related to high to intermediate sulfidation epithermal systems. We suggest that exploration can be focused on highly altered volcanic rocks (especially andesite-dacite) with both high intensity of K-metasomatism and higher Pb, Zn, Ag, Au, Ba and Rb and lower Sr.
      原文链接:
    • NSTL
    • Elsevier

    Transfer learning and siamese neural network based identification of geochemical anomalies for mineral exploration: A case study from the Cu[sbnd]Au deposit in the NW Junggar area of northern Xinjiang Province, China

    Wu B.Li X.Yuan F.Li H....
    9页
    查看更多>>摘要：? 2021 Elsevier B.V.The identification of geochemical anomaly plays an important role in mineral exploration. The division of geochemical background and anomaly can be treated as a binary classification problem. Deep learning has shown encouraging performance in various fields of classification and prediction, and research has shown that geochemical anomalies can be effectively identified on the base of spatial characteristics and internal relations in geochemical data. However, deep learning models are often limited by the number of training samples, so new improved algorithms are needed to improve the accuracy of the model in anomaly recognition. Considering that the spatial patterns of geochemical usually have nested or hierarchical multi-scale characteristics, it is possible to improve model performance by integrating local and regional geochemical information. In this study, a combination of transfer learning and siamese neural network was used to improve the ability to extract multi-element geochemical anomalies, and multi-scale geochemical data was tried to improve model performance. The model accuracy of using both transfer learning and siamese neural network reached 85%, which showed that the improved deep learning method can greatly improve the ability of anomaly recognition of the model. The integration of multi-scale geochemical data made the model accuracy to 88%, which showed that the deep learning model also had a certain ability to recognize the information of the scale. Therefore, deep learning can effectively depict complex geochemical spatial patterns and implicit anomalies, which can be better applied to the recognition of geochemical anomalies through continuous improvement.
      原文链接:
    • NSTL
    • Elsevier