Pathfinder Elements Research Articles

The use of property-scale portable X-ray fluorescence data in gold exploration: advantages and limitations

This study examines field portable X-ray fluorescence (pXRF) data for unsieved B- and C-horizon soil samples from two contrasting Au exploration programs in northern Canada and compares them to laboratory results from sieved samples to determine if a minimalist approach to sample preparation, equipment calibration and analysis produces results that are adequate for exploration purposes. The collection of 14 651 residual soil samples on detailed grids at the Whiskey Au project in the Black Hills of the Yukon Territory, Canada during the 2011 field season allows a comparison of pXRF data from unsieved samples with inductively-coupled plasma mass spectrometry (ICP-MS) data from the <100-µm grain size fraction digested in aqua regia. XRF data were generated on two devices: an Innov-X Delta handheld and a Niton FXL desk-top unit. Data for selected elements from the pXRF units show trends in gridded percentile plots comparable to the ICP-MS data, although the continuity of these trends reflects the degree to which the pathfinder element concentrations exceed the lower orders of detection. Acceptable merged gridded images for As and Cu from the two devices were generated without data levelling, whereas the Pb, Mo and Ni data require leveling prior to gridding in order to provide a reasonable fit to the laboratory data. Data for elements that occur in concentrations close to the lower limit of detection by pXRF, such as Sb, may provide some useful information but must be used with caution. Data for Fe also show a poor correlation, possibly due to heterogeneity of Fe in the samples, as well as due to incomplete digestion of all Fe-bearing minerals in some samples using an aqua regia digestion. A total of 680 till samples collected from regional and detailed sampling grids on the Kiyuk Lake Au property in southern Nunavut, Canada during the 2012 field season were analysed by pXRF and also by ICP-MS following an aqua regia digestion. pXRF data were generated on an Innov-X Delta using unsieved samples for comparison with ICP-MS data from the <70-µm grain size fraction. The pathfinder element As shows good agreement with the laboratory data, whereas Ni, Mo and Sb data give poor matches due to proximity of the data to the lower orders of detection by pXRF. The use of pXRF data on soil samples with no sample preparation other than drying and no instrument calibration is a robust approach for Au exploration using particular elements, such As and Cu, provided the data are monitored for consistency. Even greater compatibility between pXRF and laboratory data would be expected where sample preparation and site-specific calibrations are implemented. Other pathfinder elements for Au, including W, Sb, Bi, Ag and Te, as well as Au itself, typically occur at levels in soil either close to or below the lower order of detection of the current generation of field-portable analytical devices. The use of pXRF in Au exploration allows for quick decision-making and provides near-real time sampling guidance in the field where ‘fit for purpose’ data for suitable pathfinder and lithologically-controlled elements can be obtained.

Pre-concentration of molybdenum in water samples using coconut husk

Molybdenum accompanies uranium in various types of deposits and plays an important role as a pathfinder element in the hydrogeochemical survey for uranium. In the present study, coconut husk was used for the pre-concentration of molybdenum in hydrogeochemical samples, prior to its analysis by ICP-OES. Quantitative sorption of molybdenum was observed at pH 2 and desorption was achieved by 8M HNO3. Enrichment factor obtained by this procedure was 50. Molybdenum concentrations up to 1.0 ng/ml can be determined easily after pre-concentration using this method. This pre-concentration technique was applied for the determination of molybdenum in hydrogeochemical samples.

Use of surficial geochemical methods to locate areas of buried uranium mineralization in the Jacque’s Lake area of the Central Mineral Belt, Labrador, Canada

Surficial geochemical methods were applied to delineate zones of anomalous uranium and related element concentrations in areas overlain by an extensive blanket of glacial sediments and dense vegetation cover in the Jacque’s Lake area of the Central Mineral Belt, Labrador, Canada. The study involved sampling and analyses of vegetation including black spruce twigs and bark, Labrador tea shoots, and humus. Ash derived from the vegetation samples was analyzed using inductively coupled plasma – mass spectrometry (ICP–MS) following ignition at 450 °C, and humus was analyzed with delayed neutron counting (DNC) for a suite of 35 elements. B-horizon soil was analyzed using aqua regia digestion to investigate potential chemical signatures of bedrock mineralization at the surface. Uranium concentration in humus varied from 0.05 to 885 ppm. Zones exhibiting anomalous U responses were associated with areas proximal to anoxic peat and sphagnum bogs where mobile U species were sequestered. Uranium and pathfinder element (e.g., Pb, V, Sr, and Mo) concentrations were low in the <250 μm fraction of B-horizon soils. The soil geochemistry delineated bedrock U mineralization in areas with <15 cm of overburden and U concentration varied from 50 to 405 ppm. Biogeochemical signatures of the bedrock mineralization in black spruce twigs produced greater anomaly to background contrasts for U and pathfinder elements (e.g., Be, Ag, Pb, Ca, and Sb) and correlated more precisely with the detected radiometric U/Th anomaly than did those of soil and humus. Principal component analysis of spruce twig data discriminated three major components, including plant nutrients, ore-related elements, and a mobile species. Uranium concentration varied from below detection limit to 23 ppm U in black spruce bark and from below detection limit in ∼40% of samples to 18 ppm in Labrador tea stem.

Mineralogical and Geochemical Evolution of the Unconformity-Related McArthur River Zone 4 Orebody in the Athabasca Basin, Canada: Implications of a Silicified Zone

The McArthur River unconformity-related uranium deposit, located near the southeastern margin of the Proterozoic Athabasca basin in northern Saskatchewan, Canada, contains both basement-hosted and sandstone-hosted orebodies, one of which is the sandstone-hosted Zone 4 orebody and its alteration system. Early pre-ore quartz cementation forming immediately above Zone 4 produced a 200-m-thick silicified zone within the lower Manitou Falls Formation. Late pre-ore oxidizing basinal fluids ( δ 18 O = 1.1–8.9‰, δ 2 H = −70 to −34‰) formed zones of dickite, magnesiofoitite, and sudoite-rich alteration in the Manitou Falls Formation above the deposit. These zones were overprinted by an outer halo of illite and illite-chlorite mixed-layer clay that coincided with illite and clinochlore alteration of the Wollaston Group basement rocks. Circulation of basinal fluids into the fault zone, promoted by fault reactivation, created a reducing fluid ( δ 18 O = 3.9–7.8‰, δ 2 H= −62 to −25‰) through basement interaction, which formed a narrow sudoite alteration halo near the faulted unconformity. Mixing of these two contrasting fluids initiated uranium mineralization at ca. 1600 Ma. Post-ore alteration caused isotopic resetting of primary uraninite, broadly coincident with the intrusion of the Mackenzie dikes into the basin, followed by alteration of uraninite to coffinite, poorly crystalline uraninite, and gummite during the Neoproterozoic. Cool (ca. 10°C), oxidizing, meteoric waters ( δ 18 O = −15.7 to −13.2‰, δ 2 H = −120 to −93‰) later infiltrated fractures, produced post-ore kaolinite, and caused partial oxidation of uraninite to uranophane. The silicified zone at Zone 4 functioned as a physical barrier to fluid flow, creating favorable conditions for uranium mineralization by focusing basinal fluids into the fault zone, localizing reducing basement-modified basinal fluids, and enhancing ore preservation. However, the silicified zone limited the spatial extent of late pre-ore sudoite alteration and obstructed the post-ore mobilization of components such as radiogenic Pb and other pathfinder elements into the overlying strata.

Geochemistry and Petrogenesis of Acid Volcano-plutonic Rocks of the Siner Area, Siwana Ring Complex, Northwestern Peninsular India

Abstract Petrochemical studies on acid plutonic (granite, microgranite) and volcanic (rhyolite, trachyte) rocks occurring in the Siner area of the Siwana Ring Complex, Malani Igneous Suite have been carried out. These rocks are characterized by high concentrations of SiO2, Na2O, K2O, Zr, Nb, Y and REE (except Eu) but low in MgO, Fe2O3(t), CaO, Cr, Ni, Sr; indicating their A-type affinity. Field studies in conjunction with the geochemical characteristic indicate that the magmatism in the Siner area is generally represented by peralkaline suite of rocks which are formed due to rift tectonics. It is also suggested that these acidic rocks could have been derived by low degree partial melting of crustal material. Characteristics of certain pathfinder elements such as Rb, Ba, Sr, K, Zr, Nb, REE and the ratios of K/Rb, Zr/Rb, Ba/Rb along with the multi elemental primitive mantle normalized spidergrams suggest that the Siner peralkaline granites and microgranites have the potential for rare metal and rare earth mineralizations.

Determination of anomalies associated with Sb mineralization in soil geochemistry: A case study in Turhal (northern Turkey)

In this study, a soil geochemistry survey was conducted and most suitable pathfinder elements for the exploration of Sb deposits and anomaly distribution models of these elements were studied. In this regard, 138 samples taken from the A (top soil) and B horizons of the soil were analyzed for concentrations of Ag, Al, As, Au, Co, Cu, Fe, Hg, Mn, Ni, Pb, Sb, and Zn. All elements had asymmetrical rather than normal distributions. In soil samples from the A horizon, concentrations of Sb, As, Ag, Au and Hg are 0.42–2000mg/kg, 2.10–5470.40mg/kg, 10–348μg/kg, 0.80–66.40μg/kg and 22–1714μg/kg, respectively. Concentrations of the same elements in the B horizon were 0.36–2000mg/kg, 4.10–4019mg/kg, 2–217μg/kg, 0.20–53.70μg/kg and 20–1853μg/kg, respectively. Cluster analysis indicated that Ag, As, Au, and Hg are strongly correlated with Sb, and therefore, they are the most suitable pathfinder elements for the exploration of Sb deposits. Threshold values of these elements were determined with the use of median absolute deviation (MAD) method. In addition, an anomaly map of each element and the element groups yielding the most ideal results for the exploration of Sb deposits were also ascertained using multi-element mapping. Results indicate that As+Au and Ag+As+Au are the most ideal multi-elements in the exploration of Sb deposits. In this method, some elements that yield weak anomalies when solely used were found to be effective when combined with other elements. These element associations can be successfully used in future Sb geochemical exploration works.According to enrichment factor (EF) and integrated pollution index (IPI) calculations, both A and B horizons of the soil are enriched in all examined elements. Element enrichment in A horizon is in the rank of Sb>As>Au>Ni>Hg>Co>Mn>Cu>Fe>Zn>Pb>Ag, while the rank of elements in B horizon is Sb>As>Ni>Hg>Au>Co>Cu>Fe>Mn>Zn>Pb and Ag. The A horizon hosts extremely high Sb and As enrichment; very high Au and Ni enrichment; and significant Co, Cu, Fe, Hg, Mn, Pb and Zn enrichment. B horizon is characterized by extremely high Sb and As enrichment; very high Ni enrichment; and significant Au, Co, Cu, Fe, Hg, Mn, Pb and Zn enrichment. According to integrated pollution index calculations, 44.9% of samples from the A horizon and 44.11% from the B horizon exhibit an extremely high level of pollution.

Multiple methods for regional- to mine-scale targeting, Pataz gold field, northern Peru

Gold production in the Pataz district, northern Peru, is derived from mesothermal veins hosted by the Pataz batholith and basement-hosted epithermal and carbonate–base metal veins. At the regional scale, processing of Advanced Spaceborne Thermal Emission and Reflection Radiometer data can be used to delineate district-scale argillic alteration. One such area extends for tens of kilometres NNW of Vijus in the Maranon Valley. At the southern end of this area, basement-hosted quartz–carbonate–sulfide veins in faults support artisanal gold-mining operations. SEM analyses show that the alteration envelopes around these faults are dominated by illitic clays. These artisanal gold workings highlight the economic potential of the largely unexplored parts of the district-scale argillic alteration zone, further north. At the district scale, paleostress modelling maps areas of low minimum stress during Carboniferous ENE–WSW shortening, based on a new 1:25 000 geological map of the Pataz district. The resulting distribution of low minimum stress is used to predict sites of rock fracture under high fluid pressure, and consequent vein formation. These areas of low minimum stress occupy 11% of the modelled area but contain 50% of the known veins in the Pataz district. Some areas of low minimum stress contain no known veins, and where these are poorly explored or poorly exposed, they are proposed as potential targets for gold exploration. In combination with SEM microanalysis, ASD hyperspectral reflectance analysis of drill core samples shows that visible proximal sericitic alteration around batholith-hosted auriferous veins is predominantly phengitic illite. Automated software interpretation of ASD reflectance spectra using The Spectral Assistant shows that sericite in cryptic alteration distal from auriferous veins varies from mainly illite adjacent to the phengitic illite zone, to more distal muscovite. Reactivation of faults and mineralised vein contacts during the largely Cenozoic Andean orogeny produced chlorite alteration that locally overprints proximal phengitic illite alteration. ASD spectrometry identifies relict phengitic illite in some chloritic alteration zones and thus indicates proximity to mineralised veins at the deposit scale. Elevated pathfinder element concentrations within proximal phengitic illite alteration zones around batholith-hosted veins do not extend more than a few metres beyond the visible alteration envelope. The alkali alteration index [(Rb + Cs)/Th]N is elevated above background levels for up to 15 m beyond the visible sericite alteration zone in one of two holes investigated. In the other hole, both [(Rb + Cs)/Th]N and 3K/Al can be used as a lode-scale vector to gold-bearing veins within broad intersections of visible sericite alteration.

Riparian eucalypt biogeochemical expression of groundwater salinity, Murray River, South Australia

Salinisation of floodplains along the Murray River is a significant environmental and social problem in south-eastern Australia that can be expensive and time-consuming to monitor. The potential of plant biogeochemistry as an environmental monitoring tool, specifically its innovative application to groundwater salinity detection, is explored in this paper. Major and trace element biogeochemical data were compared to data from three geophysical surveys in the study area as well as field observations of the underlying stratigraphy. The result is an understanding of how groundwater chemistry can be characterised by plants, specifically river red gum ( Eucalyptus camaldulensis ) and black box ( Eucalyptus largiflorens ) leaves. From the survey it is evident that E. camaldulensis and E. largiflorens were both successful in expressing high salinity levels in the subsurface. Molybdenum was the most suitable pathfinder element for high salinity groundwater. The study has important implications for interpreting biogeochemical mineral exploration results; anomalous element concentrations need to be interpreted in relation to salinity levels.

Solid sampling ETV-ICP-OES to study the distribution of elements in clay and soil samples for mineral exploration

A simple and fast method, using solid sampling electrothermal vapourization inductively coupled plasma optical emission spectrometry (ETV-ICP-OES), was developed to determine the distribution of elements in clay separates and soil samples from across the Talbot Lake VMS Cu-Zn prospect, in the Flin Flon-Snow Lake terrane, Manitoba, Canada in order to locate the undercover ore deposit, which is buried under Palaeozoic dolomites and Quaternary till. In the development of the method, the mass of sample, the mass of carrier agent (polytetrafluoroethylene, PTFE) or flow rate of reactant gas (dichlorodifluoromethane (R12)), the carrier and bypass gas flow rates and the temperature program were optimised. Under optimal conditions and with a four-step ETV temperature program, the distribution of the pathfinder elements (Zn, P, S and I) in clay separates and soils showed clear anomalies at 400 and 650 m. The results for Zn and P are in very good agreement with results obtained, following aqua regia (AR) digestion, by ICP mass spectrometry (ICP-MS) by Anglo American Exploration Division (AA-ED). Moreover, the distributions of S and I could be precisely determined (these elements were not reported in the AA-ED study). Using 0–4 mg of AA-ED S5 standard mixed with 2 mg PTFE or with 4.1 ml/min R12 as reactant gas, and using internal standardisation with an argon emission line, calibration curves were obtained that, when applied to Talbot clay separates and soil samples, yielded Zn, S and P concentrations in agreement with AR-ICP-MS results previously obtained by AA-ED. Hence, ETV-ICP-OES completely eliminates the need for clay separation and for extraction or digestion of samples prior to analysis, which significantly simplifies the analysis of geochemical exploration samples.

Factor Analysis of Stream Sediment Geochemical Data from Onyami Drainage System, Southwestern Nigeria

An R-mode quartimax rotated factor matrix was applied to a statistical study of stream sediment geochemical data from Onyami drainage system within Igarra area in southwestern Nigeria. The area is underlain by the gneiss-migmatite complex, the low grade supracrustal schist belts and the Pan-African granitoids which intruded both the gneiss-migmatite complex and the supracrustal units. A four-factor model which accounts for 76.49% of the total variance of the stream sediment geochemical data was established. Factor 1 (Sc-Ga-V-La-Ni-Co-Ag-Bi-Sr-Pb-Hf-Nb-Cu-Cr) probably defines an underlying complex granitic lithology with contributions from mafic and ultramafic rocks. Factor 2 (Th-U) is attributable to a granitic lithology which reflects the parent rock as the influencing factor. Factor 3 (Mo-Nb-Zn) appears to define a minor sulphide mineralization associated with granitic rocks that intruded the schists and granite gneiss in the area. Factor 4 indicates the occurrence of gold and its pathfinder element, As, in the study area. This inference is consistent with the reported occurrence and mining of gold during the colonial era in Dagbala, which lies within the Onyami river catchment area.

Geology and Gold Mineralization around Kutcheri, northwestern Nigeria

The study area predominantly consists of metasediments, porphyritic granites with minor amphibolite dykes, quartz vein and quartzofeldspathic intrusions. The metasediments are fractured and folded in places. The dominant fold axes and quartz vein intrusions trend NNE-SSW parallel to the regional foliation of the rocks. Artisanal mining of placer gold mineralization were documented around the banks of Rivers in northwestern part of the study area. Panning of 40kg sediments from pits in the area around Gidan Boss and Dutsen Burka yields 0.28g Au. Grain morphology shows both eluvial and alluvial deposits occur. The eluvial gold are presumed to occur within steeply dipping (70° E and above) quartz veins. Geochemical analysis of 13 quartz vein samples to characterize samples enriched with target (Au) and some pathfinder elements (Pb, Hg, Cu, Ag and Zn) above background levels were carried out. The concentration in ppm had Au (< 1-4.8) and others, Pb (<1-28), Hg (<0.5), Cu (6.2 to 61.4), Ag (<0.5) and Zn (8.8 to 39). There is no significant difference between concentration of analytes in Dutsen Burka and Gidan Boss at α = 0.05. Also, strong positive correlation between Au and Cu, Au and Pb confirms they are indicator elements for Au in the area.

Geochemistry of shallow aquifers and soil gas surveys in a feasibility study at the Rivara natural gas storage site (Po Plain, Northern Italy)

A geochemical survey, in shallow aquifers and soils, has been carried out to evaluate the feasibility of natural gas (CH4) storage in a deep saline aquifer at Rivara (MO), Northern Italy. This paper discusses the areal distribution of CO2 and CH4 fluxes and CO2, CH4, Rn, He, H2 concentrations both in soils and shallow aquifers above the proposed storage reservoir. The distribution of pathfinder elements such as 222Rn, He and H2 has been studied in order to identify potential faults and/or fractures related to preferential migration pathways and the possible interactions between the reservoir and surface. A geochemical and isotopic characterization of the ground waters circulating in the first 200m has allowed to investigation of (i) the origin of the circulating fluids, (ii) the gas–water–rock interaction processes, (iii) the amount of dissolved gases and/or their saturation status. In the first 200m, the presence of CH4-rich reducing waters are probably related to organic matter (peat) bearing strata which generate shallow-derived CH4, as elsewhere in the Po Plain. On the basis of isotopic analysis, no hints of thermogenic CH4 gas leakage from a deeper reservoir have been shown. The δ13C(CO2) both in ground waters and free gases suggests a prevalent shallow origin of CO2 (i.e. organic and/or soil-derived). The acquisition of pre-injection data is strategic for the natural gas storage development project and as a baseline for future monitoring during the gas injection/withdrawing period. Such a geochemical approach is considered as a methodological reference model for future CO2/CH4 storage projects.

Orebody Modelling for Exploration: The Western Mineralisation, Broken Hill, NSW

The Western Mineralisation in the Broken Hill deposit was studied to identify the zonation sequence of lithogeochemical haloes along and across the strike of the orebody. Samples used are from 77 drill holes and the samples were assayed for Pb, Zn, Fe, S, Cu, Ag, Cd, Sb, Bi and As. Variogram analyses were calculated for all the elements and kriging was used to construct the 3D block model. Analysis of cross sections along and across the strike of the orebody shows that Bi and Sb form broader halos around sulphide masses and this suggests that they are pathfinder elements for the Pb and Zn elements of this orebody. The threshold concentrations (minimum anomaly) of the 10 elements were determined using the concentration-area analysis. On east–west vertical cross sections, the values of linear productivity, variability gradient and zonality index were calculated for each element. Based on the maximum zonality index of each element, the sequence of geochemical zonation pattern was determined from top to bottom of the orebody. The result shows that S, Pb, Zn and Cd tend to concentrate in the upper part of the mineralisation whereas Ag, Cu, Bi and As have a tendency to concentrate in the lower part of the mineralised rocks. Also, an empirical product ratio index was developed based on the position of the elements in the zonation sequence. The methods and results of this research are applicable to exploration of similar Zn and Pb sulphide ore deposits.

Cluster and R-mode factor analyses on soil geochemical data of Masjed-Daghi exploration area, northwestern Iran

Masjed-Daghi is located in Julfa sheet (1:100,000 series) in the northwest of Iran. The area consists of a very likely gold mineralization bearing epithermal mineralization which appears to be associated with a porphyry Cu–Mo system at deeper levels. Ninety-three soil samples were collected and analyzed for 13 elements (Au, Mo, Cu, Pb, Sn, Ag, Zn, Cr, Mn, Ba, Be, Ni, Co) by using emission spectrometry and atomic absorption spectrophotometry. The data were processed and interpreted using univariate and multivariate statistical analyses. The distribution of the majority of variables is slightly to moderately positively skewed which can be interpreted by log-normal model. Only Ni, Be, and Mn show normal distribution. Based on cluster analysis, the variables can be classified into two main groups. The first group consists of the main ore forming elements such as Au, Ag, and Ba which belong to epithermal system and Mo, Sn, and Cu which have more affiliation to porphyry mineralization. The principal component analysis extracted three factors. These factors calculated using varimax rotated R-mode factor loading matrix account for more than 65 % of the total variance. The first factor represents the main constituents of the epithermal system (Au, Ag, Ba) and its geochemical halo at the northeast of the study area. The second factor represents the main constituents of the porphyry system (Cu, Mo, Sn) and its geochemical halo in the western part of the study area which is overlapped with the volcanic rocks affected by local intrusions with higher alteration overprint. The third factor, however with less significance, represents Pb and Zn which are not the main ore constituents but can be considered as pathfinder elements. The results have been used to locate hidden orebodies using presented factor score mapping.

Biogeochemical exploration using the Thola shrub in the Andean Altiplano, Bolivia

This study concerns the implementation of the most suitable geochemical prospecting methodology to explore for gold deposits in the Andean Altiplano, Bolivia. The main gold ore deposits in this area are associated with the ‘saddle reef antimony-gold type’ in low-grade metamorphic Ordovician–Silurian siliciclastic rocks, placer gold deposits of Miocene age and epithermal gold deposits related to acid volcanic rocks of Tertiary age. An orientation biogeochemical survey was carried out over these deposits by analysing a common plant (Thola shrub) for Au, Sb and pathfinder elements. Thola is widespread and abundant in this semi-arid highland terrain and includes different families such as Compositae ( Baccharis incarum/B. tola ) and Solanaceae ( Fabiana densa ) with deep roots (&gt;5 m) that are able to penetrate allochthonous rocks (acid tuffs) and mineralized zones. This orientation survey shows strong anomalies in gold and antimony over saddle reef antimony-gold deposits and anomalies over placer gold deposits where the bottom of the placer is exposed. High concentrations of Au and pathfinder elements were obtained in transects across acid volcanic rocks in the vicinity of abandoned mines. The Thola shrub therefore has the potential to be an excellent exploration medium throughout an area of 140 000 km 2 in the Bolivian Altiplano.

Identifying Pathfinder Elements for Gold in Multi-Element Soil Geochemical Data from the Wa-Lawra Belt, Northwest Ghana: A Multivariate Statistical Approach

A multivariate statistical analysis was performed on multi-element soil geochemical data from the Koda Hill-Bulenga gold prospects in the Wa-Lawra gold belt, northwest Ghana. The objectives of the study were to define gold relationships with other trace elements to determine possible pathfinder elements for gold from the soil geochemical data. The study focused on seven elements, namely, Au, Fe, Pb, Mn, Ag, As and Cu. Factor analysis and hierarchical cluster analysis were performed on the analyzed samples. Factor analysis explained 79.093% of the total variance of the data through three factors. This had the gold factor being factor 3, having associations of copper, iron, lead and manganese and accounting for 20.903% of the total variance. From hierarchical clustering, gold was also observed to be clustering with lead, copper, arsenic and silver. There was further indication that, gold concentrations were lower than that of its associations. It can be inferred from the results that, the occurrence of gold and its associated elements can be linked to both primary dispersion from underlying rocks and secondary processes such as lateritization. This data shows that Fe and Mn strongly associated with gold, and alongside Pb, Ag, As and Cu, these elements can be used as pathfinders for gold in the area, with ferruginous zones as targets.

Soil geochemical prospection for gold deposit in the Arzular area (NE Turkey)

The Arzular gold mineralization is located at the southern part of the Black Sea Tectonic Unit in northern Turkey. This belt hosts several high-potential epithermal gold deposits and it is highly probable that there are a number of undiscovered occurrences in the region. The presence of intensely altered areas, suitable structural elements and acidic intrusions indicates that the region has an important potential for epithermal gold. Soil geochemistry surveys are widely used for the exploration of buried mineral deposits. In this work the applicability of soil geochemistry surveys for exploration of buried mineral deposits was tested using various statistical methods. In this respect, concentrations of 16 elements have been assayed in about 50 soil samples collected from the Arzular area. Soil samples were taken from the B horizon. The data revealed elevated concentrations for gold (0.20–259.2 μg/kg), silver (23–26,972 μg/kg), arsenic (1.7–301.8 mg/kg), copper (54.09–170.7 mg/kg), zinc (5.1–261.3 mg/kg) and lead (2.6–385.45 mg/kg). Gold is significantly correlated with elements such as Sb, Cd, Pb, Ag, As, Cu and Mo. Relatively high anomaly contrasts between Au, As, Ag and Sb and their coinciding anomalies along an E–W trending fault at the eastern part of the field might indicate that As, Ag and Sb could be used as a pathfinder element for exploration of gold deposits. Factor analysis was applied to elements in soil samples and then distribution diagrams were prepared using the factor scores obtained. In a distribution diagram for mineralization-associated factor score, two anomaly fields along the E–W trending fracture line and one anomaly field at the eastern part were distinguished. The largest anomaly in an ellipsoidal shape with long axis of 350 m was obtained from the southeast part of the area. Anomaly patterns show that factor scores might yield suitable and net results for the exploration. NE–SW trending fracture system is not related to mineralization and is younger than E–W trending fracture line. However, the E–W trending fault system controls the mineralization; therefore, the eastern extent of this fault zone needs to be investigated.

Quantifying Metasomatism in Epithermal Au-Ag Deposits: A Case Study from the Waitekauri Area, New Zealand

Major element geochemical exploration for epithermal deposits can extend the range of traditional pathfinder elements to a 1- to 10-km scale, and with knowledge of protolith composition, mass changes associated with hydrothermal alteration can be quantified. In the Hauraki goldfield of New Zealand, altered andesites and dacites host epithermal Au-Ag deposits and prospects. The major element compositions of equivalent unaltered rocks correlate with whole-rock Zr/TiO 2 , an immobile element ratio that is preserved during K metasomatism. We used this feature to estimate the initial composition and calculate a mass balance for veinless altered rocks in the Waitekauri area along a 3-km-wide section that extends from the central Waitekauri fault to the periphery of the alteration zone. The total transferred mass is equal to approximately 11 percent of rock mass in illite-dominated altered rocks, and 24 percent of rock mass in adularia-dominated altered rocks. On average mass losses exceed gains. Potassium was gained in most altered rocks, which contain illite and/or adularia as K-bearing hydrothermal minerals. Silica was gained in adularia-quartz–rich rocks close to the Waitekauri fault. Other major elements are preferentially lost (Ca, Na, Fe, Mg) or effectively immobile (Al, Ti). The greatest K and Si gains occur in adularia-rich rocks that surround Au deposits along the Waitekauri fault, whereas K gains are progressively lower and Si gains are mostly insignificant in deposits and prospects farther east where illite or interstratified illite-smectite is the dominant K-bearing mineral. In contrast, Na and Ca losses do not increase significantly from the periphery to the core of the Waitekauri area, because losses are commonly complete and therefore limited by the initial concentration. However, the K and Si gains correlate with other measures of K metasomatism including K/Sr and Rb/Sr values and molar ( M ) K/(K + Na + 2Ca) values, and together these parameters vector from the barren periphery to the orebody-hosting center of the Waitekauri area. In contrast to major element trends, the pathfinder elements As, Sb, and Hg define more local hydrothermal alteration cells within the larger Waitekauri area, some of which surround Au deposits.

Geochemical and Environmental Evaluation of Um Shashoba Gold Mine Area, Southeastern Desert, Egypt

Abstract:A suite of elements (Ag, Au, Ba, Bi, Cd, Co, Cr, Cu, Ga, Hf, Hg, Mn, Mo, Ni, Pb, Rb, Sb, Se, Sr, Te and Zn), total organic carbon (TOC) and pH were analyzed in stream sediment and tailing samples from Um Shashoba area, in order to evaluate Au placer and the sediments being impacted by old mining activities. Analytical results were examined using statistical, graphical and mapping methods. In spite of the results revealing that Au and most of the elements in sediments were in general significantly lower than those in tailing, Au was concentrated in the NE and SW parts forming Au placer. It is remarkably a close association of Au with Hg and Sb; both are useful as pathfinder elements for Au placers. Values of pH could not control a fate of analyzed elements, whereas TOC and Mn oxides and hydroxides could uptake some elements Au, Ba, Co, Cr, Hg, Ni, and Sr. The results also indicated that the sediments were contaminated by anthropogenic factors causing moderate, strong to very strong pollution with respect to Bi, Se and Te, respectively. Additionally, geogenic factors could also contribute elemental enrichment to the drainage system and cause significant toxicity level.

Transpressional zones in ophiolitic mélange terranes: Potential exploration targets for gold in the South Eastern Desert, Egypt

Gold-bearing quartz ± carbonate veins at the El-Anbat mine area, in the South Eastern Desert of Egypt, are associated with pervasively silicified, highly sheared ophiolitic and island arc rocks. Structural analysis of the shear fabrics along the ore zones indicate that geometry of the mineralized quartz veins and alteration patterns are controlled by the regional, NNW-trending zone of transpression, known as the Wadi Kharit–Wadi Hodein shear system, which is related to the 655–540 Ma, Najd strike–slip fault system in the Eastern Desert of Egypt. Microscopic and electron microprobe studies reveal that gold is chemically bound in As-pyrite, arsenopyrite, and gersdorffite, while free-milling gold is rarely observed in the quartz veins and silicified host rocks. Hydrothermal alteration could have liberated additional traces of gold from early pyrrhotite disseminated in listvenite. Geochemical studies reveal that shear zones associated with lenticular masses of porphyritic granite in the middle of the transpression zone are heavily mineralized (ppm levels) compared with other parts of the alteration zone. Where no granite is observed, low-grade zones (ppb levels) of gold mineralization occur in the highly deformed serpentinite and metavolcaniclastic rocks. Mass balance calculations suggest that hydrothermal fluids infiltrated under brittle–ductile shear conditions led to addition of Au, As, Cu, Rb, and Sb, concurrent with silicification, carbonatization and sericitization of the host rocks. Dispersion of gold and associated pathfinder elements is reported in altered rocks beyond the lode zone, indicating the potential for extensive, low-grade zones outside the already known El-Anbat mine location.