Plants growing in abandoned mines of Portugal are useful for biogeochemical exploration of arsenic,antimony, tungsten and mine reclamation

Several plants across taxonomic hierarchy have evolved heavy metal tolerance strategies and detoxification mechanisms that enable them to survive, grow and reproduce in metal contaminated and polluted sites. Plants growing on the abandoned Portuguese mines, highly contaminated with arsenic (As), antimony (Sb) and tungsten (W), have been studied for their biogeochemical prospecting and mine stabilization potential. The results of soil analysis show relevant anomalies of As, Sb and W. We have observed that the plant species accumulating tungsten are Digitalis purpurea, Chamaespartium tridentatum, Cistus ladanifer, Pinus pinaster, Erica umbellata, and Quercus ilex subsp. ballota. Accumulators of antimony are D. purpurea, E. umbellata, Calluna vulgaris and C. ladanifer. Accumulations of arsenic are found in the old needles of P. pinaster, Calluna vulgaris and C. tridentatum and leaves of C. ladanifer, E. umbellate and Q. ilex subsp. ballota. These are the key stone species allowing biogeochemical delineation of areas of anomalous soil composition.     

Biogeochemical characteristics of the Hetai goldfield, Guangdong Province, China

In the Hetai goldfield, Guangdong Province, China, samples including rocks, soils and leaves of four plants (Pinus massoniana, Rhodomyrms tomenlosa, D. linearis var. dichotoma and Embelia laeta) collected from the gold mineralization zone and the background area were analyzed for Au, Ag, Cu, Pb, Zn, Hg, As and physiological parameters. The objective of this investigation is to study the geochemical and biogeochemical characteristics of studied plants, aiming at biogeochemical methods in Au exploration. The goldfield region shows geochemical and biogeochemical anomalies. Abundances of Au in rocks, soils, plants and the leaf pigments in the mineralized area are much higher than those in the surrounding region. The plants display unhealthy physiological and ecological characteristics in the Hetai goldfield area. The cell structures of the goldfield plants were anomalous and aberrant, and there were many nano-metal particles diffused in mitochondria and chloroplasts. Macro- and microscopic evidences of the vegetation in the goldfield areas are distinctly different from the background regions. The strongly anomalies in responses to Au are profound in further geochemical and botanic exploration studies.     

Biogeochemical prospecting for uranium in Nova Scotia

Ashed twigs of Picea rubens (red spruce) collected over an area of uranium mineralization in central Nova Scotia were analyzed for uranium in the course of biogeochemical prospecting for this element. Uranium levels in background samples were significantly lower than in those collected from areas with mineralization either at depth or on the surface. Scintillometric data were useful only to differentiate background and surface mineralization. Uranium levels in soils showed no correlation whatsoever with mineralization or with radiometry. There was a very high degree of correlation between the scintillometric data and uranium concentrations in ashed twigs and it is considered that twigs of Picea rubens might be successfully used for biogeochemical prospecting for uranium in this area.     

Biogeochemical studies of areas of sulphide mineralization in Northern Greece

Biogeochemical and geobotanical studies have been carried out in several areas of sulphide mineralization in northern Greece. In porphyry copper areas, mineralized zones can be delineated by mapping the distribution of Minuartia verna, or by measuring the copper content of Rumex acetosella and Thymus sibthorpii. Elevated levels of molybdenum in the soil are indicated by higher concentrations of this element in T. sibthorpii. In an area of barite mineralization, biogeochemical methods were not useful in showing the barium distribution, but did provide an indication of the associated lead mineralization. The appearance of the nickel accumulator Alyssum murale near a zone of antimonite mineralization seems to be related to sporadic occurrences of ultrabasic rocks nearby.     

The application of biogeochemistry for gold exploration in the Masjed–Daghi, Julfa, NW Iran

The aims of present study are investigation of endemic plants at Masjed–Daghi area introducing hyperaccumulator and indicator plants for Au, Ag, As, Cu, Mo, Hg, Re, Sb, and Te mineralization and also describe the biogeochemical response pattern over a known Au–Cu mineralized site. The Masjed–Daghi prospecting area is covered by Eocene flysch, andesite, trachyandesite, dacite, rhyodacite, Oligocene agglomerate, and Quaternary deposits. Previous researches reported copper porphyry mineralization and related epithermal gold veins in this area. This study presents that plants with high metal intake enabled us to obtain invaluable information about natural concentrations of chemical elements in the substrate and to recognize new potential areas for mineral prospecting. Stachys inflata has biological absorption coefficient mean exceeding or near hyperaccumulating criterion >1 for most of the elements investigated then could be as a hyperaccumulator. The indicator values belong to S. inflata, Artemisia sp., Salvia sp., Astragalus sp., Peganum harmala, Moltkia coerulea, and Cousinia sp.     

遥感生物地球化学找金矿方法研究进展

总结了金矿的生物地球化学性质、植物的生物地球化学效应特征以及其波谱和遥感影像特征，以及利用遥感图像处理提取生物地球化学效应引起的植被光谱异常信息的专题信息提取方法。研究表明，在金矿区上生长的植物对金及伴生元素有较强的吸收和聚积作用，植物明显受到生物地球化学效应的毒化作用；金及伴生元素的过量吸收，使植物叶片中的叶绿素、类胡萝卜素含量、水含量和叶面温度相应降低；植物叶片细胞结构发生变异，叶冠波谱反射率和波形等光谱特征明显变化；在遥感图像上，金矿区的植被表现出异常特征信息。这些信息可以作为在植被区寻找隐伏矿床的遥感生物地球化学找矿的标志。利用遥感生物地球化学的理论和技术方法，从遥感数据中分析金矿的植被图像特征，提取与金矿化有关的植被异常特征信息，可以优先出金矿化遥感异常区，并列举了几个应用实例。同时，指出了需加强该领域的理论和应用研究，为广大植被覆盖地区寻求一种快速有效的探矿方法。     

Hybrid outranking of geospatial data: Multi attributive ideal-real comparative analysis and combined compromise solution

Identifying mineralization areas with an acceptable level of reliability is a complex matter demanding the implementation of supervised methods for mapping mineralization exploration aims. In this study, further collecting all available exploratory information and data of the region of study, their good processing and analysis, and then integrating them with an appropriate method, multi-criteria decision-making (MCDM) approaches were utilized to outranking porphyry Cu mineralization areas. This paper describes an acceptable procedure for obtaining evidential layers for recognizing porphyry Cu mineralization, assigning weight to the layers, and combining them. For this aim, first, a data-driven multi-class index overlay (DMIO) approach is applied as it is a proven method with proper results in mineral prospectivity mapping (MPM) to integrate evidential layers (criteria and sub-criteria emanated from geoscience data including geological, geochemical, remote sensing, and geophysical datasets). After that, two recent MCDM models, combined compromise solution (CoCoSo) and multi attributive ideal-real comparative analysis (MAIRCA), were used to prioritize the porphyry Cu potential areas producing MPM. Concentration-area (C–A) fractal method and prediction-area (P–A) plots by considering the areas of occurrence of the known mineralization and normalized density (N_d) as traditional methods were applied for weighting and integration evidential layers and evaluation of the final maps in a data-driven manner. Consequently, verifying the verisimilitude of the MAIRCA prospectivity map (N_d = 3.17) is similar to the DMIO map in delimiting the priority areas. The results of the CoCoSo model (N_d = 2.7) show this methodology was also successfully applied in mapping the porphyry Cu mineralization areas in the study.     

Metal response in plants to sulfide mineralization in the Longobucco area (Calabria, southern Italy)

The results of a multielemental biogeochemical orientation survey carried out in Calabria, southern Italy, are reported in this paper. Five plant species: three herbaceous species, Oenanthe pimpinelloides, Anthemis triumphetti, and a stonecrop (Sedum tenuifolium), a leguminous shrub, spanish broom (Spartium junceum) and laricio pine (Pinus nigra ssp laricio) were studied to determine which species is the most responsive to sulfide mineralization and which are the best indicator elements. Si, Fe, Ti, Mn, Zn, Mo, Cu, and Pb were determined in ashed material by X-ray fluorescence analysis. All the data were treated statistically and classified into geometrically increasing intervals, in order to discriminate anomalous from background values. In addition, an R-mode factor analysis and a correlation analysis were performed to find out whether any specific metal association that could characterize both the lithology and mineralization existed for each plant species. The herbaceous plants, particularly Oenanthe, were much more effective as indicators of mineralization compared with laricio pine. The elements that gave the best indication of sulfide mineralization were Zn and Pb, confirming the usefulness of biogeochemical methods as an additional prospecting tool in Calabria, where such exploration has never been attempted before. R-mode factor analysis was found to be extremely promising as a supplemental tool in the interpretation of results from this biogeochemical survey. Each plant species is always characterized by a metal association (predominantly Pb-Zn-Mn) whose high factor loading scores constantly show a close relationship with proven sulfide mineralization.     

Bacillus cereus,gold and associated elements in soil and other regolith samples from Tomakin Park Gold Mine in southeastern New South Wales,Australia

Efficient exploration for new Au deposits is increasingly important as existing deposits become depleted. This is particularly relevant in Australia, where exploration can be difficult because of a thick regolith cover. New and effective methods of exploration need to be developed, and possibilities lie in geomicrobiological methods. For instance, Bacillus cereus, a common soil bacterium, has been shown to act as a biogeochemical indicator for concealed mineralisations, including vein-type Au deposits. We report the results of the first Australian case study of the association of B. cereus and Au at the Tomakin Park Gold Mine in southeastern New South Wales. Soil samples from the Ah horizon were analysed for B. cereus spores and 56 major and trace elements. The results show enrichment of Au, As, B. cereus spores and, to a lesser extent, Sb, Bi and Pb over the top of the Au deposit. Gold concentrations over the mineralisation range from 100 ppb to 1.1 ppm compared to a background of 2 ppb and As concentrations are enriched to 100 ppm from a background of 5 ppm. B. cereus spore counts were up to 10 times higher in soils with elevated concentrations of Au. Factor analysis indicates four main associations: TiO₂+lanthanides+actinides; CaO+MgO+Cs+Be+Ba(+Ga+Pb+Rb); B. cereus+Au+As+Sb+Bi(+Pb); Fe₂O₃+MnO+Co+Ni+Cu+Mo. Selective sequential leaching was used to study the fractionation of Au and As in soils, other regolith materials and Au-bearing vein quartz to infer their mobility and bioavailability. In unweathered quartz vein material, the majority of the Au was extracted only in the strongest, final step, with aqua regia. However, in soils from the Ah horizon, 50% of the Au was present in the water-, ammonium acetate- and sodium pyrophosphate- and hydroxylamine hydrochloride-extractable fractions. In contrast, As displays little change in fractionation with an increasing degree of weathering, and is predominantly associated with the operationally defined Mn- and Fe-oxides and oxyhydroxides. These results indicate that: (i) Au is mobilised during the weathering of the host rock; (ii) Au is bioavailable in these soils; and (iii) the increase in B. cereus spores is likely to be linked to elevated concentrations of bioavailable Au in these soils. The results indicate also that an effective biogeochemical exploration technique may be developed, where B. cereus spore counts are measured in the field and used as a pre-screening method to target areas useful for further sampling and complete geochemical analysis.     

Gold in vegetation and soil — three case studies from the goldfields of southern Western Australia

Biogeochemistry has not been widely used as an exploration technique for Au in Western Australia because (1) sampling of soils and other surficial materials have been reasonably effective in finding new mineral deposits, and (2) it has been difficult to identify a consistent and regionally typical vegetation sample type. The potential of the technique has been tested at three sites in the goldfields of southern Western Australia. Vegetation and soil were analysed for Au from the Bounty (Mt Hope), Panglo and Zuleika Au deposits in the southern Yilgarn Craton. Gold concentrations in vegetation were generally lower at Panglo and Zuleika compared with Bounty, and probably reflect the depth to mineralization which is considerably greater at Panglo (40 m) and Zuleika (20 m) than at Bounty, where it is close to the surface. At Bounty, Au concentrations in dried vegetation varied from < 0.5 ppb in background areas to a maximum of 11 ppb (the highest for any area) over mineralization. In general, the association between Au concentrations in vegetation and mineralization is only weak although, at Zuleika, Maireana (bluebush) seemed a slightly better sample medium than soil for predicting the location of underlying mineralization.As the emphasis in exploration changes to more difficult terrains, the suitability of biogeochemistry needs to be re-examined. These preliminary results from Western Australia suggest that biogeochemistry may have some role to play in the search for deeply buried mineral deposits.     

Structural mapping using PALSAR data in the Central Gold Belt,Peninsular Malaysia

The Central Gold Belt (CGB) of Peninsular Malaysia has been investigated to map structural elements associated with gold mineralization using the Phased Array type L-band Synthetic Aperture Radar (PALSAR) satellite remote sensing data. Gold mineralization in this belt is structurally controlled and associated with steeply dipping faults and fold hinges. Adaptive local sigma and directional filters were applied to PALSAR data for tracing structural elements associated with gold mineralization. Structural features along the Bentong–Raub Suture Zone have been identified as highly potential areas for gold prospecting. Four sets of lineaments trending N–S, NE–SW, NNW–SSE and ESE–WNW were identified. Results of this study demonstrate the applicability of PALSAR remote sensing data to assist gold exploration in the CGB particularly in reducing costs related to exploration for epithermal and polymetallic vein-type mineralization in tropical environments.     

遥感技术在黑龙江呼玛地区金矿找矿中的意义

提出了森林茂密,松散覆盖层较厚地区的遥感基础图象制作方法,利用热红外波段及生物地球化学遥感技术地植被覆盖区与金有关异常信息的提取;建立了植被覆盖区遥感构造解译标志,解译出４组线性构造,百余个环形构造和一个大型环块构造;将区域构造应力场的演化划分为３个阶段,ＮＥ－ＮＮＥ与ＮＷ,近ＥＷ向构造带相互交织成菱形格子状构造是本区构造的基本格架;大型环块构造及其周边环形构造和菱格状构造的各“角”区,往往是金矿     

Geology and Gold Mineralization in the Pan-African Rocks of the Adola Area, Southern Ethiopia

Primary and placer gold deposits are mined from the Pan-African Adola volcano-sedimentary sequence, in southern Ethiopia. Two major mineralized belts can be recognized: the Megado (‘Gold Belt’) and the Kenticha Belts. The Kenticha Belt is also known for its rare metal mineralization. Extensive exploration of the area resulted in two most important primary gold deposits of Lega Dembi and Sakaro. The primary gold deposits are classified into four classes based on their geological setting:

- auriferous veins, lodes, stockworks and silicified zones disseminated in schistose rocks

- gold associated with quartzite

- gold mineralization confined to conglomerates and meta-arkoses

- auriferous quartz veins in high grade gneiss rocks

This classification provides a useful guide for future exploration programme     

Spinifex biogeochemistry across arid Australia: Mineral exploration potential and chromium accumulation

Spinifex (Triodia spp.) grasslands cover vast areas of arid Australia, across a variety of soils and landscapes. These grasses are deep rooted and long lived, hence have great potential as a biogeochemical sampling medium for mineral exploration. This study discusses the results of analyses of Triodia pungens and Triodia scariosa from field sites over buried Au mineralisation (Coyote, Oberon and Tunkillia Prospects). At each site there is a multi-element anomaly in the vegetation over the projected mineralisation, the haloes are of different scales depending on the local landscape setting and dispersion potential of each element associated with mineralisation. The magnitude of the anomalies is similar for each site independent of underlying substrate. Overall, spinifex chemical composition has the potential to act as a point indicator of substrate geochemistry with very minimal dispersion (hundreds of metres only) that can delineate the extent of a potential ore deposit.This study also discusses the Cr accumulation potential of T. pungens and T. scariosa, discovered during the mineral exploration studies, from several field sites (Coyote, Oberon, Tunkillia and North Miitel Prospects). Triodia species are shown to be able to accumulate Cr up to potentially toxic levels independent of substrate concentration. This could be due to accumulation (active transport) or the lack of a barrier mechanism (passive uptake) within the plant.     

Geochemistry of gold deposits in West Hunan and East Guangxi,China

Six kinds of element association in the gold deposits in the studied region are distinguished: (1) tungsten-antimony-gold; (2) tungsten-gold; (3) antimonygold; (4) lead-zinc-silver-gold; (5) uranium-silver-gold; and (6) simple gold. The present paper deals with the distribution, source, mineralization, migration and accumulation of gold. The results show that all ore-controlling strata or source beds related to the gold deposits have high background levels of gold; the gold and other ore-forming elements associated are obviously derived from the country rocks. The mineralization of gold is related chiefly to regional metamorphism or alkali-metasomatism. In response to metamorphism of ore-controlling strata, gold was removed into solutions, and then transported and deposited in some parts of the ore-controlling strata. The main form of gold carried in the solutions was Na[Au(HS)₂]. Native gold or electrum were precipitated from the ore solutions and concentrated into ore deposits with the decrease ofT, pH andfo ₂.     

Distribution of gold in igneous granitoid complexes in the central and southwestern areas of eastern Transbaikalia

The distribution of gold in rocks from some igneous complexes of the central and southwestern areas of eastern Transbaikalia (Daurian, Aga, and Argun structure-formational zones) was studied by quantitative extraction–atomic-absorption analysis and mass spectrometry with inductively coupled plasma (Element-2 mass spectrometer). High gold concentrations (on average, 0.0043 ppm) are typical of the most widespread hornblende-biotite granodiorites and granites of the main phases of batholith intrusions in the Upper Paleozoic Unda complex in the east of the study area and in the Triassic–Middle Jurassic Kyra complex in the west. The rocks of the Early–Middle Jurassic (Sokhondo) and Middle–Upper Jurassic (Shakhtama, Kharalga, and Kukul’bei) complexes have much lower Au concentrations (mainly 0.0014–0.0030 ppm), with the minimum ones established in the Shakhtama complex. During the magmatic differentiation of granitoid intrusions, the concentrations of gold in the late leucogranite differentiates decreased.The Au concentrations in the studied complexes do not depend on the composition of the host terrigenous rocks of different ages, which evidences the endogenous nature of the revealed differences in Au concentrations in the regional granitoids. Abnormally high concentrations of gold in some studied samples are observed mainly in the regional hydrothermal mineralization occurrences.The classification R-type cluster analysis showed that all variables of the studied igneous rocks are subdivided into three groups by the degree of correlation. Gold shows a distinct tendency to the correlation with siderophile oxy- and sulfurophile groups of metals. The Q-type analysis generally confirmed the correctness of the known formational classification of the regional granitoids.     

遥感生物地球化学在找矿勘探中的应用及效果

以海南西部金成矿区为例,利用遥感生物地球化学的理论和技术方法,从遥感资料中分析金矿的图象特征,提取与金矿化有关的植被异常信息,成功地优选出金矿化遥感异常区,并进行了地面验证,取得了良好的应用效果     

Botanical and geochemical exploration studies at the seruwila copper-magnetite prospect in Sri Lanka

Geobotanical, biogeochemical and geochemical studies were carried out over the Seruwila copper-magnetite prospect near Trincomalee in Sri Lanka. Soil and plant samples were collected along a 180-m transect across the ore body near a gossanous outcrop at Kollan Kulam. Eighteen elements were determined in plant foliage and soil samples. The data showed that in the soils, the concentrations of the ore elements copper and iron and of the pathfinders Ca, Co, Mg, Mn, Mo, Ni and P, were highly indicative of the position of the ore body as determined by a drilling programme.Plant mapping showed that only two species (Glycosmis mauritiana and Pterospermum canescens) were sufficiently ubiquitous to be of use for biogeochemical prospecting in this area. Neither species had a foliar copper content related to Cu levels in the soils, but G. mauritiana had P levels which related well to the position of the ore body and to the concentrations of Fe, Cu and pathfinders in the soils.Principal components and factor analysis of the biogeochemical and geochemical data showed that most of the variance in the plant-soil system was accounted for by the concentrations of ore elements in the soils. It is concluded that the data will be of use for further geochemical and botanical exploration studies in the region or in other genetically similar ore occurrences in South Asia.     

Introducing a new approach of geochemical anomaly intensity index (GAII) for increasing the probability of exploration of shear zone gold mineralization

Increasing the prediction rate in the identification of mineralization zones using the stream sediment geochemical data is an essential issue in the regional exploration stage. The various univariate (such as fractal and probability plot (PP) methods) and multivariate methods (such as principal component analysis (PCA)) have been performed for interpreting the geochemical data and detecting the mineralization areas. In this study, a new geochemical criterion named geochemical anomaly intensity index (GAII) was proposed for geochemical anomaly mapping. This approach was developed based on the PCA method and the catchment basin coefficient (CBC). The GAII as a weighted geochemical index is calculated using the mineralization principal component (MPC) scores and CBC. GAII can be mapped and utilized for geochemical anomaly mapping and detecting the mineralization areas. Besides, GAII can identify paragenesis elements better than the current methods. In this research, GAII was successfully used to generate geochemical anomaly maps on shear zone gold mineralization in the southwest of Saqqez, NW Iran. The geochemical data have been divided into three groups based on catchment basins and the host rock type. Then the MPCs and paragenesis elements of Au mineralization have been obtained individually using PCA. Three mineralization paragenesis groups consisting of (Au, Sn), (Au, W), and (Au, As, Sb and Ba) have been recognized for different catchment basins of the southwest of Saqqez district using PCA. GAII was calculated and mapped based on the CBC_{(Au, Sn)}, CBC_{(Au, W)}, CBC_{(Au, As, Sb, Ba)}, and their MPC scores. GAII accurately detected the Au mineralization zones and improved the geochemical anomaly map in this area compared to the PP method, concentration-area fractal model, and U-spatial statistics method. The results demonstrated that GAII was successfully used for (a) identifying the mineralization paragenesis elements, (b) intensifying the geochemical anomaly, and (c) increasing the prediction rate of mineralization zones. The shear zone gold mineralization areas in the southwest of Saqqez district were effectively detected using this new data analysis approach. GAII has provided better results than the current PP method, concentration-area fractal model, and U-spatial statistics method.     

Environmental biogeochemical characteristics of rare earth elements in soil and soil-grown plants of the Hetai goldfield,Guangdong Province,China

Very few studies deal with the biogeochemical behaviors of rare earth elements (REEs) in goldfields. This paper presents the geochemical and biogeochemical characteristics of REEs within the soil–plant system in the Hetai goldfield, Guangdong, China. The samples from the goldfield region show anomalies in distribution patterns and behavioral characteristics of REES as compared with those from the background areas. The REEs in rocks, soils, and plants prove to be much higher than those in the surrounding regions. The distribution patterns of REEs are characterized by LREE-enrichment and HREE-depletion, with the REE concentrations in Layer A being the highest. Differentiations between LREEs and HREEs may lead to some extent of negative Eu anomaly in the soils. Research results demonstrate that the REEs in a soil profile can be transferred and accumulated during the mineral formation and supergenic geochemical processes, and the anomalies are obviously related to the geological settings for the REE-bearing ore-forming processes and to the geochemical characteristics of the habitats for the REE-bearing plants. For Dicranopteris dichotoma, the total amount of REEs in the tissues shows an order of leaf > root > stem, while for Pinus massoniana the order becomes root > leaf > stem. The distribution patterns of REEs in Pinus massoniana leaves are similar to those in soils where the plants grow up in the mineralization area. However, in the background areas the REE distribution patterns for Pinus massoniana stems are similar to those for soils where the plants grow up. Parameters such as biological absorption coefficients and biological transfer coefficients show the differences in REE absorption features among plants and indicate that REEs can be transferred among plant organs. The two coefficients can reveal the different survival mechanisms for the two plant species, which are subject to long-term REE-affected stress conditions in the gold mineralization zone.