Pathfinder Elements Research Articles

Tree ferns and tea trees in biogeochemical exploration for epithermal Au and Ag in New Zealand

Biogeochemical orientation surveys were undertaken at low sulphidation epithermal Au–Ag occurrences in the Hauraki Goldfield–Coromandel Volcanic Zone and the Taupo Volcanic Zone, and at the Waiotapu active geothermal area in the Taupo Volcanic Zone. Several plant species were sampled, including the foliage of tree ferns and tea trees. The ferns – silver fern ( ponga ), rough tree fern ( wheki ) and black tree fern ( mamaku ) – were ubiquitous and were the easiest species to sample, although tea tree was the dominant genus at Waiotapu. At the Waiotapu geothermal area, significantly higher concentrations of Ag, Au, Sb, As, Cs and Rb were present in samples close to Champagne Pool than elsewhere, confirming its location as the main outflow source of Au, Ag and their pathfinder elements. The fern survey areas at Luck at Last mine, Pine Sinter and Ohui in the Coromandel Volcanic Zone each exhibited biogeochemical anomalies, which successfully highlighted most of the known quartz veins and provided additional anomalies for further investigation. Rough tree fern was the most common species at Goldmine Hill, Puhipuhi (Taupo Volcanic Zone). Although this species absorbs lower concentrations of many elements than the silver fern, the spatial distribution of elements is of greater significance than their absolute concentrations. The highest Au, Ag, As and Al concentrations occurred in samples from a ridge extending WNW from Goldmine Hill. Sb and Bi were at anomalous levels in an area peripheral to the precious metal anomalies, indicating the potential zonation of elements distal from the Au and Ag deposits. Supplementary material: The full datasets on the fern and tea tree chemistry, including quality assurance/quality control and multi-element plots, are available free of charge through the GNS Science website (search for Dunn) at http://shop.gns.cri.nz/publications/science-reports/ .

Gold distribution and lithogeochemical discrimination of residual regolith and transported overburden, Minotaur gold deposit, Lake Lefroy, Western Australia

The Yilgarn Craton of Western Australia hosts a number of Cenozoic paleochannels, which have been incised into the underlying Paleozoic and Precambrian rocks, filled with sediments and subsequently weathered. The paleochannels are of particular interest in mineral exploration as they may not only host placer-type deposits but also overlie significant supergene and primary mineralisation. Paleochannels also pose particular challenges during exploration as they mask underlying geochemical anomalies, including gold and pathfinder elements. This study investigates a method of distinguishing transported overburden from residual regolith utilising a combination of field and laboratory-based techniques. At the Minotaur deposit, the residual regolith and transported overburden are mineralogically similar, although the presence of biotite, chlorite and muscovite is more characteristic of the residual regolith. Geochemically, Zr, Ti, Co and Sc ratios form distinct groupings allowing more confident discrimination of transported overburden from the underlying residual regolith units. The presence of a distinct gold depletion zone at the redox front was also identified to be a feature of the Minotaur deposit, with Au enrichment occurring above (within transported overburden) and below (within saprolite) the redox front, similar to other gold deposits on Lake Lefroy. The lithological, stratigraphic and Au-enrichment characteristics at Minotaur have also been compared with regional studies and suggest the long-lived impact of paleovalleys on the depositional systems and Au distribution of Lake Lefroy. This work provides a basis for future studies of the region in particular the variation of depositional sequences within regional paleochannel networks.

Spatial distribution and trace element geochemistry of laterites in Kunche area: Implication for gold exploration targets in NW, Ghana

Kunche area is located in NW Ghana within the Wa-Lawra greenstone Birimian belt and is composed mainly of volcaniclastics, metasediments and some intrusive granitoids. The area is covered with laterites making it difficult to identify exploration targets. In this study, we describe a new methodology based on statistical tools and trace element geochemistry to map the pathfinder elements of gold deposits in lateritic context. However, the results of this study are specific to a particular context and cannot be extrapolated without supplementary studies to all the lateritic areas. In this respect, a total of 67 lateritic samples were collected from residually weathered materials and their spatial distribution was determined by means of the GIS-based kriging interpolation method. The samples collected vary from detrital to residual laterites/duricrusts and are hosted in volcaniclastic rocks. ICP-MS and XRF techniques were used to determine the element concentrations of the samples. The trace element geochemical data were analyzed using bivariate and multivariate geostatistical analysis to establish relationships among elements. Fe-oxides such as goethite and hematite and clay minerals like kaolinite are the main secondary minerals of the concretionary reddish lateritic samples. All the analyzed elements showed asymmetrical distribution rather than normal distribution. Spearman correlation shows that Cu, Pb, S, As, and Ag have moderate to strong positive correlation with Au. From the multivariate geostatistical analysis, three element associations; a) Fe, Pb, S, Co, Cr; b) Ni, Y, Rb, Sr, Zn, and c) Ca, Cu, Mn, Ti, Zr, As, Au, Ag were observed. Threshold values of selected elements were determined using the median absolute deviation (MAD) method, which indicates possible anomalous concentrations in the laterites for Pb (≥48 ppm), Cu (≥46 ppm), As (≥134.2 ppm), and Ag (≥0.42 ppm). Multi-element mapping indicates that Pb + Cu + As + Ag is the most ideal association in the exploration of gold deposits. It reveals ellipsoidal anomalies comparable to the Au distribution map that suggest dispersion and accumulation of the pathfinder elements in the area. The geochemical anomalies are mainly restricted to the environment of the residual laterites in the Kunche area and we recommend that exploration programs should be focused in such areas.

Identification of geochemical anomaly and gold potential mapping in the Sonakhan Greenstone belt, Central India: An integrated concentration-area fractal and fuzzy AHP approach

The present work combines Concentration-Area (C-A) fractal model with the Fuzzy Analytical Hierarchy Process (FAHP) on a GIS platform for mapping gold potential in the Sonakhan Greenstone Belt, India. A set of stream sediment geochemical data obtained over a part of the study area was used to delineate potential regions of gold mineralisation. In order to develop a suitable predictive model, the gold exploration target was taken as target (dependent variable) and concentration of pathfinder elements of gold such as Au, As, Ag, Hg, Sb and Se in the stream sediments were used as predictors (independent variables). The C-A fractal model was applied to the geochemical data of each element to decompose anomaly and background components of the spatial dispersion of element concentration in the study area. AHP combined with fuzzy set theory (FAHP) was used to determine the priority or, the weight of each evidential geochemical anomaly map. The Gold exploration targets are delineated by multiplying the weights with the respective fuzzy normalised geochemical anomaly map of the gold pathfinder elements and integrating the weighted geochemical evidential layers using fuzzy Gamma operator. The reliability of the outcome was assured by the coincidence of known gold mineralisation with the potential regions delineated in the final gold potential map. The areas with high potential are good targets for detailed exploration of gold in the region. The results highlight that (a) application C-A fractal model can effectively separate geochemical anomalies as it considers the spatial variation of the data unlike the conventional statistical methods which account only the frequency of the data, (b) the FAHP allows more flexibility in judgements of multiple decision makers in a group and reduces the inconsistency of the result which is essentially required in the knowledge-driven predictive mapping of mineral prospectivity.

Geochemical signature of earthquake-induced surface flooding by mineralized groundwater over the buried Atlántida deposit, northern Chile

At the buried Atlántida deposit (Cu–Au–(Mo)) in the Atacama Desert of Chile, highly saline pockets of fine-grained material 10 cm–3 m in diameter were identified on the alluvial surface using remote sensing and detailed regolith mapping. The median salinity (NaCl dominant) of the saline pockets is 2.2% compared to background alluvial material with a median salinity of 0.01%. Their distribution along mapped fault structures and the highly saline nature of the material suggest they form as an expression of groundwater forced through fractures to the surface during seismic activity. A targeted geochemical survey, oriented parallel to the orientation of the structures (sample spacing 250 m along structural trend) specifically sampling saline pockets on relatively old surfaces, was performed over the deposit. Deionized water extraction of soluble salts and analysis by inductively coupled plasma mass spectrometry revealed strong correlations of increasing salinity and increasing concentrations of porphyry copper pathfinder elements. Elevated responses of Se, Mo, Re and Te normalized to a groundwater volume proxy are present directly over the Atlántida deposit. This suggests the rate of erosion and sedimentation is slow enough in the Atacama Desert to preserve surficial anomalies as saline pockets, formed by periodic seismically induced surface flooding of groundwater along faults extending to surface. Targeted sampling of saline pockets along structural trends using weak leach geochemistry in terrains dominated by transported cover can serve as a routine exploration method for the potential discovery of buried copper porphyries and other styles of mineralization in the Atacama Desert of Chile.

Geochemical and pathfinder elements assessment in some mineralised regolith profiles in Bole-Nangodi gold belt in north-eastern Ghana

This study presents gold mineralisation and pathfinder elements characteristics in five surficial regolith profiles, with the aim of enhancing exploration strategies in the north-eastern Bole-Nangodi Gold Belt in Ghana. Samples were collected from mature soils and bedrocks in exploration pits and prepared for chemical and soil particle size analysis. 13 major elements, mineral forms and fifty-one trace elements were analysed using XRF, XRD and ICP-MS devices, respectively. SiO2, Fe2O3–MnO and Al2O3 are elevated in the A, B and C horizons, respectively, while Na2O–K2O–MgO–CaO–P2O5 systems dominate the bedrocks. Gold pathfinder element suites of As–Mo–Ag–Sn–Sb–Te–W–Hg–Bi are above Primitive Mantle values by a factor of > 5, while the mean chemical index of alteration (CIA) values are above 80%. Profiles contain > 70% quartz with stable mineral concentrations of 53, 18 and 29% in the A, B and C, horizons, respectively. The B horizon is the most altered horizon based on CIA, loss on ignition and Fe/Al ratios; the horizon accounts for 52% of the material and 76% of elements in the > 2 mm particle size. Mass balance and principal component analysis shows that Au exploration targets and the associated pathfinder element suites are the following: (1) horizon A with Sr–Ca–Ge–Sn–Th in the amphibolite and biotite gneiss profiles (2) horizons A and B with S–K–Zr–Tl–Ge in the volcaniclastic and (3) the bedrocks with Cu–Pb–Sb–Ag–Mo and Mn–Cr–Ba–V–Ce–Bi–Fe–Co–Sb–As–Se of the metavolcanic and phyllite profiles, respectively. The regolith models summarise the mineralogical and structural framework of the profiles and may largely influence exploration designs.

Modelling ore-forming processes through a cosine similarity measure: Improved targeting of porphyry copper deposits in the Manzhouli belt, China

Recognizing distribution patterns of ore-related pathfinder elements requires an understanding of the corresponding ore-forming systems and may lead to the definition of more reliable exploration targets. Given that complex ore-forming processes in complex geological terrains can result in either enrichment or depletion of ore elements, simultaneous consideration of both processes in geochemical anomaly modelling would be advantageous for defining exploration targets. Here, we adapted the “cosine similarity measure” method for pattern recognition of ore-related geochemical anomalism to facilitate simultaneous modelling of element enrichment and depletion. We tested the performance of this new method on porphyry copper exploration data from the Manzhouli belt, China, and demonstrated that our method is highly efficient with respect to recognizing ore-related geochemical signatures and, thus, useful for “vectoring” towards porphyry copper deposits and defining more reliable geochemical exploration targets.

Effect of shifting ice flow and basal topography in shaping three-dimensional dispersal patterns, Lac de Gras region, Northwest Territories, Canada

Tracing indicator minerals and geochemical pathfinders in glacial sediments back to their up-ice source is a common mineral exploration approach in prospective, formerly glaciated regions. In this study, we utilize surface and subsurface data from the Lac de Gras area of the Northwest Territories to develop a three-dimensional understanding of till compositional anomalies emanating from two known kimberlite pipes, DO-18 and DO-27. Specifically, this study examines the three-dimensional shape of dispersal trains as defined by geochemical pathfinder elements and kimberlite indicator minerals shed from a pair of kimberlite pipes within a till cover of variable thickness. From our ninety-four reverse circulation boreholes (n = 251 till samples), and other publicly-available geologic datasets, we have reconstructed bedrock topography, till thickness, and the subsurface geometry of two dispersal trains. Utilizing our three-dimensional dataset, we have documented the role of basal topography in creating dispersal patterns with contrasting geometries from two adjacent kimberlites, as well as in the preferential preservation of older till units. The combination of field observations of ice-flow indicators and till compositional data demonstrates that features produced by multiple ice flows are preserved in both the erosional and depositional records in this region. Three-dimensional dispersion patterns of kimberlite indicators reflect the effect of shifting ice-flow direction with respect to slope aspect of bedrock topography in governing compositional variability within glacial drift. Our findings suggest that surficial data do not capture the full extent of dispersion patterns even in areas of relatively thin and discontinuous till cover.

Mobile Forms of Gold and Pathfinder Elements in Surface Sediments at the Novye Peski Gold Deposit and in the Piilola Prospecting Area (Karelia Region)

The success of prospecting for gold deposit in overburdened areas based on the using of secondary dispersion haloes mostly depends on the chosen method of geochemical survey (sampling horizon, sample preparation for analysis, etc.). At the same time, the geochemistry of gold in the supergene zone is insufficiently studied, especially it’s migration and concentration in association with other elements in surface sediments due to weathering of gold-bearing ore. The main aim of the study presented in this paper is the determination of mobile forms of gold and pathfinder elements (As, Cu, Ni, Ag, Zn, Pb, Se, Sb, Mo, Bi, and Te) in podzol soil and moraine in the areas of Karelia region with known gold mineralization. As a result of conducted experiments it was determined that the main mobile forms of gold are water-soluble and bound to organic matter, while pathfinder elements bound preferably to Fe and Mn(hydr)oxides and to organic matter. As gold and some pathfinders bind with organic matter, this form was considered in more detail, and the elements’ interaction with humic and fulvic acids was investigated. In addition, it was determined that the studied elements are quite “mobile” because the percentage of the mobile form in their total content was mostly more than 50%. The main features of the elements’ migration and concentration were identified in surface sediments of the study areas.

Geochemical Mapping of Iron Quadrangle region by active stream sediments, State of Minas Gerais, Brazil

The geochemical survey of Iron Quadrangle was performed by the Geological Survey of Brazil - CPRM involving geochemical data from the area between 42o30´W and 45oWand 19o30´S and 21oS, totalling 45.000 km2. Active stream sediment was analyzed. Fine fractions (< 80# or 0.175 mm) were pulverized to –150# fraction (~ 0.100 mm), digested by hot acqua regia and analyzed for 53 elements by ICPMS. Maps of raw and manipulated data (element concentrations and multi-elemental scores) were made. Stream sediment (< 80# fraction) is an effective sampling medium for regional geochemical surveys. Geochemical structures, lithological units and mineralization processes were recognized with the sample density of 1 sample per 12 km2. Sample density has a key role in the quality of the geochemical maps produced. Caution must be taken when interpreting the results because of its nature; these data do not necessarily pinpoint specific geochemical anomalies or single ore deposits. The interpretation of stream sediment samples is not straightforward and must take into account secondary processes involved in the evolution of sampling media. These data may be used in mineral exploration to delineate favorable targets for more detailed studies. Mineral deposits often occur in geochemical provinces characterized by elevated concentration of elements of economic interest and pathfinder elements. Ore deposits tend to cluster along specific stratigraphic units and/or structural trends over large areas. These geochemical data can be used in environmental studies, support decision makers in the definition of public policies and in the management of sustainable land use.

Geochemical characterization of soil samples from gold mining areas using PIXE spectroscopy.

Particle-induced x-ray emission (PIXE) spectroscopy has been used to characterize soil samples from two relatively old gold mine sites (Iperindo and Itagunmodi) in the Ilesha schist belt of Southwestern Nigeria. This is with a view to identifying the indicator or pathfinder elements of gold for fingerprinting and toxicity potential assessment purposes. Average elemental concentrations of 19 major, minor, and trace elements were determined, and the geochemical data of Mn, Ni, Cu, Zn, Ag, As, Pb, and Au together with multivariate factor and cluster statistical analyses allowed to identify As and Ag as the pathfinder elements of gold. The high concentration of the determined pathfinder elements (As and Ag) as well as other toxic metals (Pb and Cu) implies a relatively high metal contamination risk to the miners and the ecosystem. The major hazard is represented by the abandoned mining wastes, pits, and ponds, already serving as fish ponds.

Landscape evolution and geochemical dispersion of the DeGrussa Cu-Au deposit, Western Australia

Sedimentary systems associated with ore deposits may act as mechanical dispersion agents of pathfinder elements at local and regional scales. The DeGrussa Cu-Au Volcanogenic Massive Sulfide (VMS) deposit (12.4 Mt @ 4.7% Cu and 1.8 g/t Au) was discovered in a deeply weathered landscape in Western Australia. The DeGrussa deposit is geochemically characterized as being enriched in Cu, Zn, Au and Ag, as well as significant enrichments in In, Mo, Se, Te, Bi, As, Cd and Co, and depletions in Nb, Hf, Th, REE, Cr, Ni, V, Sc and Ba. The Cenozoic palaeochannel sedimentary package that overlies the DeGrussa deposit displays elevated Cu, Zn, Au, and Ag concentrations, as well as significant enrichments in Cr, Ni, V, Sc, In, Mo, Se, Te, Bi, As, Cd and Co, and a remarkable depletion in REE.The palaeochannel sedimentary package shows similarities in its chemical signature to the DeGrussa deposit and associated basement rocks. However, due to the complexity of the landscape evolution and weathering impacts, there is uncertainty regarding the source(s) of this anomalous signature. It may represent (1) the geochemical signature of the immediately underlying basement rocks and/or the DeGrussa deposit; (2) concentration related to the weathering intensity experienced by the sediments, (3) concentration related to the cannibalistic nature of the sedimentary system, resulting in the reworking of previous deposits, or (4) a combination of the above. The Cenozoic channel clay deposits display strikingly depleted values of total REE (TREE) content, which has been interpreted to indicate that the palaeochannel clay units were mostly derived from weathering of proximal dolerite, with no mixing with other weathering products. This, in combination with high Mo, In and Se, and elevated Cu, Zn, Au, and Ag concentrations, may represent the relics of the DeGrussa footprint. Chromium Ni, V, and Sc are interpreted as being sourced mainly from the mafic basement units.Despite the geochemical signatures reported, this study has discovered that the metal geochemical footprint observed in the palaeochannel sedimentary package represents the footprint of the DeGrussa deposit. Hence the geochemistry of the transported cover can be used as an efficient tool for mineral exploration in specific landscape contexts, since the cover can preserve key elemental vectors of the mineral deposit and the geochemical signature of the basement rocks.

VHMS mineralisation at Erayinia in the Eastern Goldfields Superterrane: Geology and geochemistry of the metamorphosed King Zn deposit

Despite having been a target for volcanic-hosted massive sulfide (VHMS) deposits since the 1960s, few resources have been defined in the Archean Yilgarn Craton of Western Australia. Exploration challenges associated with regolith and deep cover exacerbate the already-difficult task of exploring for small, deformed deposits in stratigraphically complex, metamorphosed volcanic terranes. We present results of drill-core logging, petrography, whole-rock geochemistry and portable X-ray Fluorescence data from the King Zn deposit, to help refine mineralogical and geochemical halos associated with VHMS mineralisation in amphibolite-facies greenstone sequences of the Yilgarn Craton. The King Zn deposit (2.15 Mt at 3.47 wt% Zn) occurs as a 1–7 m-thick stratiform lens dominated by iron sulfides, in an overturned, metamorphosed volcanic rock-dominated sequence located ∼140 km east of Kalgoorlie. The local stratigraphy is characterised by garnet-amphibolite and strongly banded intermediate to felsic schists, with rare horizons of graphitic schist and talc schist. Massive sulfide mineralisation is characterised by stratiform pyrite–pyrrhotite–sphalerite at the contact between quartz–muscovite schists (‘the footwall dacite’), and banded quartz–biotite and amphibole ± garnet schists of the stratigraphic hanging-wall. A zone of pyrite–(sphalerite) and pyrrhotite–pyrite–(chalcopyrite) veining extends throughout the stratigraphic footwall. Footwall garnet-amphibolites are of sub-alkaline basaltic affinity, with a central zone dominated by chlorite ± magnetite interpreted to represent the Cu-bearing feeder zone. SiO2, CaO, Fe2O3T, MgO and Cu concentrations are highly variable, reflecting quartz–epidote ± chlorite ± magnetite ± sulfide alteration. Hydrothermal alteration in stratigraphically overlying intermediate to felsic rocks is characterised by a mineral assemblage of quartz–muscovite ± chlorite ± albite ± carbonate. Cordierite and anthophyllite are locally significant and indicative of zones of Mg-metasomatism prior to metamorphism. Increases in SiO2, Fe2O3T, pathfinder elements (e.g. As, Sb, Tl), and depletions of Na2O, CaO, Sr and MgO occur in quartz–muscovite schists approaching massive sulfide mineralisation. Within all strata (including the immediate hanging-wall), the following pathfinder elements are strongly correlated with Zn: Ag, As, Au, Bi, Cd, Eu/Eu*, Hg, In, Ni, Pb, Sb, Se and Tl. These geochemical halos resemble less metamorphosed VHMS deposits across the Yilgarn Craton and suggest that although metamorphism leads to element mobility and mineral segregation at the thin-section scale, assay samples of ∼20 cm length are sufficient to vector to mineralisation in amphibolite facies greenstone belts. Recognition of minerals such as Mg-chlorite, muscovite, cordierite, anthophyllite, biotite/phlogopite, and abundant garnet are significant, in addition to Al-rich phases (i.e. kyanite, sillimanite, andalusite and/or staurolite) not identified at King. Chemographic diagrams may be used to identify and distinguish different alteration trends, along with several alteration indices (e.g. Alteration Index, Carbonate–Chlorite–Pyrite Index, Silicification Index) and the abundance of normative corundum and quartz.

Wallrock alteration categories and their geochemical signatures in gold-bearing Neoproterozoic granitoids, Batouri gold district, southeastern Cameroon

Hydrothermally altered granitoids in the Batouri district host gold mineralization. Gold and associated metals occur as disseminated, stockwork and veins. The granitoids range from quartz-alkali granitoids sensu stricto to diorite with various types of wallrock alterations including K-feldspar alteration, sericitization, silicification, and sulphidation/ferruginization. Most gold-bearing samples are extensively brecciated. Gold mineralization is accompanied with sericitization, silicification, and sulphidation/ferruginization alterations. Gold concentrations reach a high of 103.7 ppm. The granitic rocks are sub-alkaline. They show enrichment in the LREE, a negative Eu anomaly and a depletion in the HREE reflecting the breakdown and mobility of the initial plagioclase feldspar bearing HREE during fluid-rock interaction. On multielement variation diagrams, spikes at K, Ba, Pb, and Th are depicted resulting from selective enrichment during alteration. Mass gains/losses during alteration calculated using the immobile element method indicate, amongst others, gains in SiO 2 (silicification), K 2 O (K-feldspar alteration), SO 3 and Fe 2 O 3 (sulphidation/ferruginization) with losses in Na 2 O linked to sericitization. The samples show Pd and Pt as high as 2 ppm. Gold mineralization is associated with wallrock alteration zones with elevated contents of As-Ba-Cu-Pb-Rb-Sr-Zn and Zr due to the neominerals developed during hydrothermal alteration. Au-Ag-Zn defines a potential pathfinder element cluster in the Batouri district.

Applied statistical functions and multivariate analysis of geochemical compositional data to evaluate mineralization in Glojeh polymetallic deposit, NW Iran

Various genesis of epithermal veins as well as host rock cause complication in the modeling process. Thus LINEST and controlling function were applied to improve the accuracy and the quality of the model. The LINEST is a model which is based on multiple linear regression and refers to a branch of applied statistics. This method concerns directly to the application of t-test (TINV and TDIST to analyses of variables in the model) and F-test (FDIST, F-statistic to compare different models) analysis. Backward elimination technique is applied to reduce the number of variables in the model through all the borehole data. After 18 steps, an optimized reduced model (ORM) was constructed and ranked in order of importance as Pb>Ag>P>Hg>Mn>Nb>U>Sr>Sn>As>Cu, with the lowest confidence level (CL) of 92% for Cu. According to the epigenetic vein genesis of Glojeh polymetallic deposit, determination of spatial patterns and elemental associations accompanied by anomaly separation were conducted by K-means cluster and robust factor analysis method based on centered log-ratio (clr) transformed data. Therefore, 12 samples (cluster 2) with the maximum distance from centroid, indicates the intensity of vein polymetallic mineralization in the deposit. In addition, an ORM for vein population was extracted for Sb>Al>As>Mg>Pb>Cu>Ag elements with the R2 up to 0.99. On the other hand, after 23 steps of optimization process at the host rock population, an ORM was conducted by Ag>Te>Hg>Pb>Mg>Al>Sb>As represented in descending order of t-values. It revealed that Te and Hg can be considered as pathfinder elements for Au at the host rock. Based on the ORMs at each population Ag, Pb, and As were often associated with Au mineralization. The concentration ratio of (tSb × tAl)vein/(tSb × tAl)background as an enrichment index can intensify the mineralization detection. Finally, Glojeh deposit was evaluated to be classified as a vein-style Au (Ag, Pb, As)-polymetallic mineralization.

Characteristics and variations of sinters in the Coromandel Volcanic Zone: application to epithermal exploration

ABSTRACTThe Hauraki Goldfield of the Coromandel Volcanic Zone, North Island, New Zealand, hosts up to 19 known siliceous hot spring deposits, or sinters, some directly associated with Au–Ag ore bodies, in a Miocene–Pliocene, sub-aerial, calc-alkaline volcanic arc overlying Jurassic meta-sedimentary basement. Sinters are surface expressions of predominately adularia-sericite epithermal systems, potentially linked to Au–Ag mineralised conduits at depth. They provide a paleosurface marker to determine the level of erosion, and help determine zones of thermal fluid upflow and/or lateral outflow. Mapped sinters of the Coromandel Volcanic Zone are mainly affiliated with rhyolite domes, occur along structural corridors of the volcanic arc, and contain characteristic textures, mineralogy and pathfinder elements typical of near-neutral pH alkali chloride fluid discharge derived from convectively circulating magmatic fluids diluted by meteoric waters. Textures and trace element compositions of the Coromandel sinters are similar to those of the Taupo Volcanic Zone, New Zealand, and the Jurassic Au–Ag mining districts of the Deseado Massif, Argentine Patagonia. Thus, detailed mapping, textural analysis and trace-element studies demonstrate the prospecting potential of siliceous hot spring deposits for locating ore deposits, and in particular to help define proximal to distal positions relative to vent zones at the paleo-surface.

Vertical distribution of major ore-forming elements and the speciation in the semiarid system above the concealed Baiyinnuoer Pb-Zn deposit in inner Mongolia, China

The concealed (&gt;80 m) Baiyinnuoer Pb-Zn deposit in Inner Mongolia is a typical skarn deposit in North China and has been studied to improve geochemical exploration within the area. Two vertical soil profiles were studied in order to evaluate the vertical geochemical distribution patterns within the residual soil associated with this deposit. Soil Profile #6 is located above the Pb-Zn orebody whereas Profile #8 is located away from this deposit. To determine the dynamics of the vertical geochemical distribution patterns, concentrations and species of nine elements in samples of six different size fractions were used. The distribution patterns of all the nine elements along Profile #6 display a similar trend of lower concentrations in both the topsoil and moderately-weathered bedrock layers but higher concentrations in the residual subsoil layer, showing an inverted ‘C-shape’. The normalized concentrations (using Fe) of elements and the normalized enrichment factors also follow the same distribution patterns. A sequential extraction study of the soil showed that ore-forming and pathfinder elements were dominantly related to humic acid, Fe-Mn oxides and residual fractions. Based on the results, the recommended soil sampling depth for detecting surficial geochemical anomalies in this and similar semi-arid and thickly covered area is 2–3 m. Furthermore, Hg, Sb, As, Cu, Pb, Zn, Mn and Bi appear to be important indicators for geochemical exploration of Pb-Zn deposits. The research approach and results of this study are useful for evaluating mineral resources in similar covered areas through surface geochemical soil surveys as well as for providing insights to the dynamics of vertical geochemical patterns in soil from concealed Pb-Zn deposits.

Application of geostatistical analyst methods in discovering concealed gold and pathfinder elements as geochemical anomalies related to ore mineralisation

Abstract The study area in the West Junggar Basin is known to be rich in hydrothermal gold deposits and occurrences, even though there has been minimum exploration in the area. It is here hypothesised that this area could host more gold deposits if mineral exploration methods were to be reinforced. This research is aimed at identifying geochemical anomalies of Au, and determining possible factors and conditions which facilitate the formation of anomalies by referring to As and Hg as gold pathfinders. Geostatistical analyst techniques have been applied to 9,852 stream sediments and bedrock data collected on a total surface of 1,280 km2 of West Junggar, Xinjiang (northwest China). The kriging interpolation and quantile-quantile plot methods, combined with statistical methods, successfully identified both Au and its pathfinders’ anomalies. In the present study, median was considered as background values (10.2 ppm for As, 9.13 ppb for Hg and 2.5 ppb for Au), whereas the 95th percentile were threshold values (28.03 ppm for As, 16.71 ppb for Hg and 8.2 ppb for Au) and values greater than thresholds are geochemical anomalies. Moreover, the high concentrations of these three discovered elements are caused primarily by hydrothermal ore mineralisation and are found to be controlled mainly by the Hatu and Sartohay faults of a northeast-southwesterly direction as well as their related secondary faults of variable orientation, which facilitate the easy flow of hydrothermal fluids towards the surface resulting in the formation of geochemical anomalies. Most of anomalies concentration of Au are found near the mining sites, which indicates that the formation of new Au anomalies is influenced by current or previous mining sites through geological or weathering processes. In addition, the low concentration of gold and its pathfinders found far from active gold mine or faults indicates that those anomalies are formed due to primary dispersion of hosting rock.

Intensification of the polymetallic vein exploration by multivariate analysis and staged LINEST function at Glojeh deposit, NW Iran

In the exploration of polymetallic mineralization, the anomalies should be identified and differentiated from background values, simultaneously for polymetallic elements. Therefore, multivariate analysis and LINEST function modeling have been applied to vein identification in Glojeh polymetallic deposit in NW of Iran. It would be accompanied by the determination of multiple-effect ratio of element concentration which will intensify the vein and veinlet detectability and provide a quantitative measure of mineralization. In this study, 31 insignificant elements and threshold value were eliminated during 18 steps of backward stepwise algorithm. Accordingly, an optimized model was established to predict Au concentration by the contribution of pathfinder elements which presented as tPb>tAg>tP>tHg>tMn>tNb>tU>tSr>tSn>tAs>tCu. The (Pb × Sn)/(La × Te), (Ag × Sn)/(Rb × Te), and (Pb × Hg)/(Ce × Ba) multiple-effect ratios were determined for (intensify) tracking Au mineralization and polymetallic vein, veinlet and brecciated mineralization zone at Glojeh deposit. They were determined by dividing the concentrated elements (with highest t-values) at an insignificant ones that eliminated in the early steps of staged LINEST modeling.

EVALUATION OF SOIL GEOCHEMISTRY DATA OF CANCA (GÜMÜŞHANE-NE TURKEY) BY PROCESSING INVERSE DISTANCE WEIGHTING AND KRIGING INTERPOLATION METHODS-FIRST FINDINGS

The purpose of this study is to assess soil geochemical data of the Canca alteration area (Gümüşhane- Turkey) using statistical methods and investigate potential gold mineralizations of the area. With this purpose, 288 soil samples were collected and analyzed for gold and associated pathfinder elements. The concentrations ranged (Au and Hg: in μg/kg, others in mg/kg) between 0,68-19,20; 0,02-28,97; 2-314; 7-857; 2,1-394; 4-199,5; 0,59-49,29; 5-89; 0,04-37; 0,52-16,30; 1,25-91,9 for Au, Ag, Cu, Pb, Zn, As, Sb, Bi, Mo, Sn and Hg respectively. According to Sperman’s rho correlation coefficients, although not very strong, correlation was observed between Cu and Au; Zn and Cu; Sb and Pb and As; Mo and Pb and As and Sb; Sn and As; Sb and Mo. The threshold values of the elements were obtained by median+2 the median absolute deviation. The prediction maps of the elements were formed by using the Inverse Distance Weighting and Kriging methods. According to prediction maps; especially in the western part of the study area and also related to tectonic lines, elemental enrichments, (gold and silver) were determined. Therefore, it is suggested to give importance to the west of the area in exploration drilling, geophysics, etc. Since the element prediction maps produced by the Inverse Distance Weighting method has higher resolution in anomaly contrast, it is suggested that maps produced with this method can preferably be used to give an idea at first sight in soil geochemistry studies.