Base Metal Exploration Research Articles

Enhancing Mineral Exploration Programs Through Quantitative XRD: A Case Study from the Gumsberg Polymetallic Sulphide Deposits, Sweden

As challenges in precious and base metal exploration intensify due to the diminishing availability of high-grade ore deposits, rising demand, energy costs, and stricter regulations towards net-zero carbon activities, advanced techniques to enhance exploration efficiency are becoming increasingly critical. This study demonstrates the effectiveness of quantitative X-ray diffraction (QXRD) with Rietveld refinement, coupled with multivariate statistical analysis (including agglomerative hierarchical clustering, principal component analysis, and fuzzy analysis), in characterizing the complex mineralogy of strata-bound volcanic-associated limestone-skarn Zn-Pb-Ag-(Cu-Au)-type sulphide deposits (SVALS). Focusing on 113 coarse rejects from the Gumsberg project located in the Bergslagen mining district in central Sweden, the research identified five distinct mineralogical clusters corresponding to polymetallic base metal sulphide mineralization, its proximal alteration zones, and variably metamorphosed host rocks. The results reveal significant sulphide mineralization, ranging from disseminated to massive occurrences of sphalerite, pyrrhotite, pyrite, and galena, with trace amounts of secondary minerals like anglesite in certain samples indicating weathering processes. The study also identifies rare minerals such as armenite, often overlooked in traditional geological logging. These findings underscore the potential of QXRD to enhance resource estimation, optimize exploration strategies, and contribute to more efficient and sustainable mineral exploration programs. The accuracy of QXRD was cross-validated with geological logs and geochemical data, confirming its reliability as a mineralogical discrimination tool.

Base-metal exploration by using remote sensing, geological, geophysical, and geochemical datasets with clues from ancient mining: A comprehensive review on Aravalli-Delhi Fold Belt, Rajasthan, India

Base metal deposits are present in different continents with evidences of their mining activities during ancient times as mentioned in the historical literature. Aravalli – Delhi Fold Belt (ADFB) in Rajasthan, India is having numerous base metal prospects where ancient mining signages are recorded. Modern-day mining has commenced taking clues from these evidences. Present-day techniques such as remote sensing, geological mapping, geophysical survey, geochemical survey, and exploration/drilling are utilized for the identification of surficial ancient mining features and identification of the mineralized zones. These techniques utilize their unique criteria to get an idea of the mineral association. The integration of all the unique characteristics of modern techniques with the help of weighted overlay analysis, fuzzy logic, multi-criteria overlay analysis, etc. helps to identify the mineral potential zones from the ancient working sites. Their integrated results provide the surficial as well as sub-surficial information of the region that gives a better revelation about the region and helps in decision-making towards the mineralization status of the region. World-over surficial ancient features have been recorded in exploratory sites for base metals, and the case histories where integrated techniques were used for mineral exploration are discussed. Zawar – Dungarpur belt also has the potential for base metals therefore, the boolean approach, weighted overlay, and multi-criteria overlay analysis were performed using remote sensing, structural, and geochemical datasets. The integrated results showed that the head zone and southern broader part near Keekawat have the potential for base metals.

Geochemical Signatures of Mafic Volcanic Rocks in Modern Oceanic Settings and Implications for Archean Mafic Magmatism

Abstract Greenstone belts are dominated by mafic volcanic rocks with geochemical characteristics that indicate a range of possible geodynamic influences. Many analogies with modern tectonic settings have been suggested. Increasing exploration of the modern oceans and comprehensive sampling of volcanic rocks from the sea floor are now providing unique opportunities to characterize different melt sources and petrogenesis that can be more closely compared to greenstone belts. In this study, we have compiled high-quality geochemical analyses of more than 2,850 unique samples of submarine mafic volcanic rocks (<60 wt % SiO2) from a wide range of settings, including mid-ocean ridges, ridge-hotspot intersections, intraoceanic arc and back-arc spreading centers, and ocean islands. The compiled data show significant geochemical variability spanning the full range of compositions of basalts found in greenstone belts. This diversity is interpreted to be due to variable crustal thickness, dry melting versus wet melting conditions, mantle mixing, and contamination. In particular, different melting conditions have been linked to mantle heterogeneity, complex mantle flow regimes, and short-lived tectonic domains, such as those associated with diffuse spreading, overlapping spreading centers, and triple junctions. These are well documented in the microplate mosaics of the Western Pacific. Systematic differences in mafic volcanic rock compositions in modern oceanic settings are revealed by a combination of principal components analysis and unsupervised hierarchical clustering of the compiled data. Mafic volcanic rocks from most arc-back arc systems have strongly depleted mantle signatures and well-known subduction-related chemistry such as large ion lithophile element (LILE) enrichment in combination with strong negative Nb-Ta anomalies and low heavy rare earth elements (HREEs). This contrasts with mafic volcanic rocks in Archean greenstone belts, which show no, or at least weaker, subduction-related chemistry, a less depleted mantle, less wet melting, and variable crustal contamination. The differences are interpreted to be the result of the lower mantle temperatures, thinner crust, and subduction-related processes of present-day settings. However, mafic rocks that are geochemically identical to those in Archean greenstone belts occur in many modern back-arc basins, including the Lau basin, East Scotia ridge, Bransfield Strait, and Manus basin, which are characterized by fertile mantle sources, high heat flow, and complex spreading regimes typical of small-scale microplate mosaics. These types of settings are recognized as favorable for volcanogenic massive sulfide (VMS) deposits in modern and ancient greenstone belts, and therefore the particular geochemical signatures of the mafic volcanic rocks are potentially important for area selection in base metal exploration.

Shallow base metal exploration in northern New Brunswick, Canada

This research paper explores the effective utilization of 2-D Resistivity and Induced Polarization (IP) techniques for identifying sulfide deposits in complex geological settings. To enhance the accuracy of the findings, the geophysical data were complemented with geological information, petrophysical data, Digital Elevation Model (DEM), and Electromagnetic data Versatile Time Domain Electro-Magnetics (VTEM) and Total Magnetic Intensity (TMI) Reduced-To-Pole (RTP).The analysis of DEM, magnetic susceptibility, and magnetic intensity revealed a lack of correlation with the DEM, indicating that these parameters alone were insufficient to confirm the presence of sulfide deposits. Consequently, five regions exhibiting high to moderate conductivity were chosen for conducting six survey lines using the Wenner array with a 10 m electrode spacing. The objective was to map sulfide zones in Restigouche County, located in northeast New Brunswick.Geophysical measurements were acquired using a RESECS instrument, and the field data were processed using the Res2Dinv software after removing erroneous data points. Since the study area was characterized by thick overburdened glacial sediments and lacked surface exposure, information from numerous boreholes and core samples from the western part of the study area were utilized.The study achieved successful mapping of the shallow alteration zone containing pyrite mineralization in most of the survey lines. Specifically, resistivity responses below 50 Ω⋅m, coupled with high chargeability, likely corresponded to the alteration zone containing pyrite. Additionally, resistivity responses above 50 Ω⋅m, combined with chargeability and RTP readings, were indicative of the alteration zone with pyrite.

Megashears and hydrothermalism at the Martian crustal dichotomy in Valles Marineris

Observations of ancient deep deformation systems on Mars are important for constraining planetary dynamics, as well as to identify potential mineral resources. However, such systems were thought to be unexposed and inaccessible to analysis. Here, we apply structural and hyperspectral analyses, and correlate results with magnetic anomaly patterns, to investigate two large right-lateral brittle-ductile shear zones and fault megabreccia exposed in the deepest parts of Valles Marineris. The shear zones follow the trace of the edge of the Borealis impact basin, thought to represent the planetary dichotomy boundary. We identify hydrothermally altered mafic igneous rocks in the sheared basement. We suggest that the shear system was initiated as basin ring fault system in the pre-Noachian, with further reactivation up until the Hesperian, and may still be a potential source of marsquakes. Hydrothermal circulation through the shear zones may have initiated primary mineralizations which are promising for base and rare metal exploration.

Main results of the diamond, precious metal, and base metal mineral resource base reproduction using the declarative principle of licensing

The article presents the results of geological exploration for diamonds, precious metals, and base metals, conducted in the Russian Federation in consistence with licenses granted based on the declarative principle, beginning from the moment this mechanism was introduced. Key aspects of changes in the legislative regulation of this mechanism are represented. The information on the planned and factual financing of these works, on the number of the issued licenses, and on the respective increase in the resources and reserves of precious metals is provided. Specific (unit) indicators of the mineral reserve increase and of the respective costs were proposed, based on which the effectiveness of geological exploration was determined for projects performed in administrative subjects of the Russian Federation in consistence with the licenses granted by the declarative principle. Problems in implementation of the mechanism were identified. Recommendations for elimination of these problems are proposed.

Reflection seismic imaging to unravel subsurface geological structures of the Zinkgruvan mining area, central Sweden

The Zinkgruvan mining area is located on the south-eastern part of the Bergslagen district, one of the three major mineral producing regions in Sweden. In this study, we present the results from three (P1, P2 and P8) reflection seismic profiles each approximately 3000 m-long crossing the Zinkgruvan Zn-Pb-Ag-(Cu) mining area. P1 was acquired using cabled geophones with 10 m receiver and source interval and crossed major geological features. The other two profiles (P2 and P8) were acquired by wireless recorders with 20 m receiver and 10 m source interval and ran perpendicular to P1. Through a special data processing workflow adapted to this dataset, good quality seismic sections were obtained along these profiles, although a high noise level due to high voltage electric power lines was present. The interpretations were constrained by (1) seismic P-wave velocity and density data from a series of downhole logging measurements, (2) 3D forward reflection traveltime modelling in both pre- and post-stack domains, and (3) other geophysical and geological observations available from the site. Despite the notably complex geology, the processed seismic sections clearly reveal a series of horizontal to gently dipping reflections associated with known geological formations. Results indicate that most structures and lithological contacts dip or plunge to the northeast, including the targeted Zinkgruvan Formation. The results from this seismic survey are encouraging regarding the potential of the seismic method for base-metal exploration in Sweden and in particular in the Bergslagen district. It shows the high resolving power of the reflection seismic methods for imaging complex geological structures in a cost-effective and environmentally-friendly way.

Metallogenesis of the Rhyacian Lavra Velha gold-rich IOCG deposit in the São Francisco Craton, Brazil

• The Lavra Velha deposit represents a new gold-rich IOCG mineralization at the São Francisco Craton . • The gold mineralization is associated with a hydrothermal breccia system with co-existing iron oxides and sulfides. • IOCG mineralization is related to the Rhyacian period of the northern São Francisco Craton. • Mineralization is marked by decreasing temperatures from the bottom to the top of the deposit. Lavra Velha is a newly discovered Rhyacian IOCG deposit in the northern portion of the São Francisco Craton, in the Bahia state of NE Brazil. Gold and copper mineralization is hosted by epigenetic hydrothermal breccia with large amounts of iron oxide. Multiple phases of breccia formation and hydrothermal alteration caused zoning from the base to the top of the deposit. The alteration is mainly characterized by hydrothermal calcite-epidote-magnetite, tourmaline-chlorite-magnetite, and sericite-hematite hydrothermal alteration styles. Tourmaline and chlorite chemistry indicates that low temperature alkaline fluids had variable Fe 2+ , Mg, Al, and Na contents throughout the evolution of the breccia complex. Magnetite and hematite display low vanadium content (≤0.24 wt%) and very low titanium content (≤0.06 wt%). The sulfide minerals are pyrite (with up to ~ 3 wt% Co), chalcopyrite, bornite, arsenopyrite, and covellite, in decreasing order of abundance. Coarse muscovite that is related to the latest stages of breccia displays a high barium content with an average of ≥ 1.27 wt%. Isotopic compositions of carbon and oxygen in calcite from the calcic breccia indicate that early mineralizing fluids were derived from a mixed magmatic/non-magmatic reservoir (δ 13 C ~ −2‰ and δ 18 O from 9.95 to 13.09‰ in calcite). The sulfur isotopic compositions of chalcopyrite and pyrite demonstrate that sulfur in the mineralized breccia was derived from cooling magmas that underwent weak contamination from oxidized fluids or host rocks (δ 34 S from 2.22 to 3.89‰). New U-Pb zircon ages indicate that mineralization occurred at approximately 2100 Ma, coeval with tourmaline-bearing porphyritic granite dikes that yield ages of 2098 ± 8 and 2112 ± 12 Ma respectively. Despite being considered a small deposit in relation to known reserves, Lavra Velha may be the first IOCG deposit recognized in the São Francisco Craton, particularly in the Gavião Block. Thus, it represents an important indicator for future precious and base metal exploration in the São Francisco Craton.

Automated Indicator Mineral Analysis of Fine-Grained Till Associated with the Sisson W-Mo Deposit, New Brunswick, Canada

Exploration under thick glacial sediment cover is an important facet of modern mineral exploration in Canada and northern Europe. Till heavy mineral concentrate (HMC) indicator mineral methods are well established in exploration for diamonds, gold, and base metals in glaciated terrain. Traditional methods rely on visual examination of >250 µm HMC material. This study applies mineral liberation analysis (MLA) to investigate the finer (<250 µm) fraction of till HMC. Automated mineralogy (e.g., MLA) of finer material allows for the rapid collection of precise compositional and morphological data from a large number (10,000–100,000) of heavy mineral grains in a single sample. The Sisson W-Mo deposit has a previously documented dispersal train containing the ore minerals scheelite, wolframite, and molybdenite, along with sulfide and other accessory minerals, and was used as a test site for this study. Wolframite is identified in till samples up to 10 km down ice, whereas in previous work on the coarse fraction of till it was only identified directly overlying mineralization. Chalcopyrite and pyrite are found up to 10 km down ice, an increase over 2.5 and 5 km, respectively, achieved in previous work on the coarse fraction of the same HMC. Galena, sphalerite, arsenopyrite, and pyrrhotite are also found up to 10 km down ice after only being identified immediately overlying mineralization using the >250 µm fraction of HMC. Many of these sulfide grains are present only as inclusions in more chemically and robust minerals and would not be identified using optical methods. The extension of the wolframite dispersal train highlights the ability of MLA to identify minerals that lack distinguishing physical characteristics to aid visual identification.

Genesis of the Abbasabad epithermal base metal deposit, NW Iran: Evidences from ore geology, fluid inclusion and O–S isotopes

The Abbasabad epithermal Pb–Zn–Cu deposit is located in the Tarom–Hashtjin Metallogenic Belt (THMB), northwest Iran. Mineralization occurs as quartz-base metal sulfide veins and breccias mainly hosted by Eocene volcanic and volcaniclastic rocks of the Karaj Formation. Four mineralization stages are recognized: (1) quartz-chalcopyrite-pyrite veins and breccias, (2) quartz-calcite I-sphalerite-galena ± chalcopyrite ± pyrite veins and breccias, (3) late stage barite veins and veinlets, and (4) barren post-ore calcite II veinlets. The primary metallic minerals, in order of abundance, are galena, sphalerite, chalcopyrite, and pyrite; gangue minerals are mainly quartz, barite, calcite, sericite/illite, and chlorite. The main wall-rock alteration is silicification, intermediate argillic, carbonatization, and propylitic alteration. Microthermometric measurements of primary LV fluid inclusion assemblages in quartz, sphalerite and barite show that the ore-forming fluids belong to the low- to moderate-temperature (170–315 °C), moderate-salinity (3.6–7.1 wt% NaCl equiv.), low-density H2O–NaCl system. Estimated trapping hydrostatic pressures are 60 to 100 bars, corresponding to entrapment depths of 614 to 1022 m below the paleowater table. Oxygen isotopic data (δ18OH2O of + 7.6 to + 0.6‰) indicate that the ore-forming fluid was derived largely from magmatic fluid, with the addition of meteoric water in the later stage. δ34SH2S values of sulfides vary over a narrow range from –17.4‰ to –15.4‰, (averaging − 16.3‰), indicate that sulfur might be derived from a relatively homogeneous magmatic source which oxidized by meteoric water through fluid mixing. The Abbasabad deposit is interpreted as an intermediate-sulfidation epithermal mineralization derived from a mixed source during a phase change in temperature and pressure interpreted as being related to fluid mixing and boiling. Our data suggest that mineralization at Abbasabad and other epithermal deposits in the THMB are related to late Eocene (~40 to 36 Ma) post-collisional magmatism, which is a useful concept for local and regional epithermal base metal exploration targeting.

Geophysical interpretation and tectonic synthesis of the Proterozoic southern McArthur Basin, northern Australia

The southern McArthur Basin is highly prospective for sediment-hosted Zn-Pb-Ag mineralisation, and hosts the McArthur River and Teena deposits within the Batten Fault Zone. The basin formed in response to widespread extension and thermal subsidence, and was subsequently deformed during crustal shortening events that affected the North Australian Craton during the Proterozoic. Mineralisation is hosted in structurally controlled sub-basins that formed during deposition of the middle McArthur Group. Recognition of structures controlling these sub-basins has traditionally been challenging because overprinting relationships from several extension and crustal shortening events created a complex fault and depositional architecture. In this work, we interpret and model newly acquired and existing gravity, magnetic and seismic data to better understand the regional structural architecture and evolution of the southern McArthur Basin. Important for base metal exploration, results from this study suggest that the prospective lower Barney Creek Formation was deposited during intermittent, and broadly north–south-directed extension at ca. 1645–1640 Ma. This caused strike-slip movement along major north-northwest-trending faults, and normal movement along east–west to east-northeast-trending faults. Faulting resulted in significant sub-basin deepening in some areas, and uplift and erosion in others. These sub-basins developed in transtensional segments of strike-slip faults, and adjacent to normal faults. Geophysical modelling also identified an anomalously thick pile of mafic volcanics within the early basin fill represented by the Tawallah Group. This is significant because mafic volcanics have previously been interpreted as the source of base metals within the region, and the thick volcanic pile we identified occurs in close proximity to the McArthur River and Teena deposits. Sub-basin bounding faults that were active during mineralization tap into this anomalously thick pile of volcanics, suggesting that they likely represented fluid pathways for ascending metalliferous brines.

Exploration Potential of Fine-Fraction Heavy Mineral Concentrates from Till Using Automated Mineralogy: A Case Study from the Izok Lake Cu–Zn–Pb–Ag VMS Deposit, Nunavut, Canada

Exploration under thick glacial sediment cover is an important facet of modern mineral exploration in Canada and northern Europe. Till heavy mineral concentrate (HMC) indicator mineral methods are well established in exploration for diamonds, gold, and base metals in glaciated terrain. Traditional methods rely on visual examination of >250 µm HMC material, however this study applies modern automated mineralogical methods (mineral liberation analysis (MLA)) to investigate the finer (<250 µm) fraction of till HMC. Automated mineralogy of finer material allows for rapid collection of precise compositional and morphological data from a large number (10,000–100,000) of heavy mineral grains in a single sample. The Izok Lake volcanogenic massive sulfide (VMS) deposit, one of the largest undeveloped Zn–Cu resources in North America, has a well-documented fan-shaped indicator mineral dispersal train and was used as a test site for this study. Axinite, a VMS indicator mineral difficult to identify optically in HMC, is identified in till samples up to 8 km down ice. Epidote and Fe-oxide minerals are identified, with concentrations peaking proximal to mineralization. Corundum and gahnite are intergrown in till samples immediately down ice of mineralization. Till samples also contain chalcopyrite and galena up to 8 km down ice of mineralization, an increase from 1.3 km for sulfide minerals in till previously reported for coarse HMC fractions. Some of these sulfide grains occur as inclusions within chemically and physically robust mineral grains and would not be identified visually in the coarse HMC visual counts. Best practices for epoxy mineral grain mounting and abundance reporting are presented along with the automated mineralogy of till samples down ice of the deposit.

Application of VLF-EM method for base metal exploration in Gwani area (Misau 107), Jigawa state, Nigeria

The Very Low Frequency (VLF) electromagnetic (EM) survey is a reliable technique for identifying network of fractures usually hidden by overburden materials that overlie the crystalline basement. The Gwaram area, Jigawa state of Nigeria is underlain by Older Granite of the basement complex of Nigeria, with predominant rock type being coarsely porphyritic biotite granite. The project is aimed at confirming the occurrence of sulphide mineralization within the study area, using both the geological information and VLF techniques. Measurements involving 10 profiles spaced 50 m interval were collected within the study area, using the transmitter of Le Blanc in France whose radio frequency is 18.3 kHz. Profiles 1-10 show the respective cross-over points (points of intersection) at 430, 460, 430, 470, 480, 500, 550, 560, 610, and 620 m with a positive in-phase response of 11.1, 7.3, 22.1, 23.7, 30.8, 36.2, 29.5, 17.6 and 20.8% respectively, the suspected fault occurred at respective depth of 45, 130, 150, 135, 150, 135, 140, 145, 145 and 125 m. The ratios of primary to secondary electromagnetic anomalies on the ten profiles are not constant and their profile shapes are never identical or consistent. Such anomalies at cross-over points have been used to infer the presence of fracture. All the profiles show one identical anomaly which is suspected to be a hydrothermal zone or mineralized fault. VLF-EM contour and 3D map were produced and indicate that there is high conductivity toward the southwest of the map. The results obtained in the survey inferred that the deposit is expected to be economically viable.

Application of ultrafine fraction soil extraction and analysis for mineral exploration

The need to innovate to advance exploration success is ongoing and, while regional geochemical surveys are common, increasing the data we collect and improving survey results has stagnated. A new adaption of existing methods known as UltraFine+™ extracts the <2 µm fraction of soils and sediments, which is then analysed and combined with spectral mineralogy proxies and physicochemical properties to improve targeting for Au and base-metal exploration. We applied the UltraFine+™ workflow to three small orientation site studies in Western Australia, and reprocessed archived regional soil samples from the Geological Survey of Western Australia to test the method. The orientation programme ( c . 200 samples) involved samples from the Leonora and Sir Samuel 1:250 000 map sheets, an area that hosts known major Au and base-metal deposits. We then applied this approach to the Kingston 1:250 000 map sheet area, analysing a further 300 samples in a region on the Yilgarn Craton margins that is essentially greenfields, as there has been little exploration and the original geochemical survey data were heavily censored due to the abundance of transported regolith dominated by quartz-rich sand. The archived samples were specifically selected soils (sheetwash or sandplain) with a component of Quaternary–Tertiary transported cover. Results at the orientation test sites (Telfer West, Tooting Bec and DeGrussa) were promising. Importantly, the study revealed a marked decrease in censored results for Au (from 63% to 10% below detection limit). Geochemistry and some example indices for mineral exploration and lithology mapping, as well as example maps using the additional spectral mineralogy proxies or particle-size variation, are presented. The application of the <2 µm particle-size separation and the UltraFine+™ workflow importantly demonstrate the additional value from (re-)assaying regional soil and sediment samples to generate new targets and improve regional geochemical maps. This is an exercise that can be applied to new greenfields surveys and, when exploration budgets are lean, to archived samples.

Organic matter and metal contents within the Cretaceous rocks of the Slata-Guern Halfaya area, North-Central Tunisia: Implication for ore genesis

The proximity of ore deposits, in the Slata-Guern Halfaya area (north-central Tunisia), to the Cretaceous Fahdene and Bahloul Formations raises the question of the role that these formations played in the emplacement of the ore. These formations are rich in organic matter (OM) with total organic carbon (TOC) values in the range of 0.2–1.4% and 0.62–5.46%, respectively, for the Albian–Vraconian facies of the Fahdene Formation at Slata and the Cenomano–Turonian facies of the Bahloul Formation at Guern Halfaya. Rock-Eval pyrolysis data indicates that the OM in the Fahdene Formation at Slata is relatively mature (oil window, 431 °C < Tmax < 447 °C) and with variable Production Index (PI, %)). Conversely, the OM preserved in the Bahloul Formation at Guern-Halfaya is immature (423 °C < Tmax < 433 °C). The analysis of whole rocks and the LA-ICP-MS analysis of inorganic fraction reveal high concentrations of trace elements (e.g., Pb, Zn) in both formations. We infer that seawaters were enriched in trace elements during the deposition of both formations. These trace elements were then sequestered by both organic and inorganic matter. Given the similar OM-rich lithologies (carbonates and marls) of these formations, the difference in trace element concentrations can be due to their contrasting thermal maturities. Concentrations of trace elements (Pb, Zn, Cd, and Ni) moderately correlate with OM content (TOC, pyrolyzable hydrocarbons and residual OM) positively in the organically-immature Guern-Halfaya ore district and negatively in the organically-mature Slata mining district. Subsidence of the OM-rich Cretaceous Formations (Fahdene and Bahloul), located in the deep part of the basin, resulted in thermal cracking of kerogen in these formations. This catagenesis allowed the dissociation of organo-metal ligands and subsequent expulsion of metals in low viscosity hydrocarbons during the Alpine orogeny. Metals and hydrocarbons migrated together from the subsiding areas of the basin and ultimately encountered salt diapirs. The mixing between metal-rich hydrocarbons and ore-bearing associated fluids, on the one hand, and the Triassic-derived sulfate-rich fluids, on the other hand, led to the precipitation of sulfides and sulfates at different times. A potentially effective trilogy to be targeted for base metal exploration is the juxtaposition of (i) mature OM-rich formations – potential sources of metals and hydrocarbons – with (ii) diapiric evaporites that served as a source of sulfur and sulfate, and (iii) a permeable reservoir that acted as a suitable site for ore precipitation.

Mapping and target generation in poorly exposed sub-tropical terrains: the application of heliborne VTEM and magnetic survey data in base metal exploration in the Central African Copperbelt

SUMMARY This study presents the result of an interpretation of heliborne electromagnetic (VTEM) and magnetic data over a base metal exploration tenement in the Central African Copperbelt in Zambia. The interpretation was based on several processed VTEM and magnetic grids, regional scale geological maps, geochemical data on soils and Landsat imagery. The electromagnetic responses in the VTEM or magnetic anomalies could not be ascribed directly to mineralisation. As a result, the identification and ranking of targets was based on the recognition of suitable geological conditions for base metal mineralisation rather than direct geophysical targeting.

Assessment of pyrite composition by LA-ICP-MS techniques from massive sulfide deposits of the Bathurst Mining Camp, Canada: From textural and chemical evolution to its application as a vectoring tool for the exploration of VMS deposits

PYRITE is ubiquitous throughout the massive sulfide deposits of the Bathurst Mining Camp, Canada. Pyrite locally preserves primary, pseudo-primary textures, as well as secondary textures, that formed in response to the hydrothermal, metamorphic, and deformation processes to which the host sequence was exposed. In the Bathurst Mining Camp most forms of pyrite are arsenian (up to 3.13 wt% As), with considerable enrichment in Tl, Sb, Sn, Bi, Ag, Se, and to a lesser extent Cd, Ga, Te, Hg, Ge, In, and Au. LA-ICP-MS analyses of primary pyrite show significant enrichment in fluid-mobile elements, in particular, Tl, Sb, As, and Hg, as well as Bi, Pb, and Sn. In contrast, secondary pyrite (syn-to post-deformation varieties) is not enriched in these elements. Superimposed metamorphism typically causes loss of fluid-mobile elements to different degrees, except for Se.Pyrite chemical variations have the potential to monitor ore petrogenesis at inter- and intra-deposit scales. Pyrite from the Cu-zone is enriched in Se relative to pyrite from Zn-Pb zone, in which Tl is elevated. Throughout the host sequence fluid-mobile element concentrations of pyrite vary by several orders magnitude, with the highest fluid-mobile element abundances in footwall rocks immediately proximal to the deposit. Moreover, elevated fluid-mobile element concentrations of pyrite are recognized in footwall felsic volcanic and sedimentary rocks as much as several hundred metres away from the deposit. Hanging-wall zones contain pyrite with fluid-mobile element contents comparable to pyrite from sulfide horizon. The fluid-mobile element concentrations of pyrite are higher in exhalative sedimentary rocks than pyrite from the sulfide mineralization itself.The spatial variation in fluid-mobile element concentrations in pyrite as identified using LA-ICP-MS can be used to identify otherwise cryptic deposit-related haloes. Ultimately, this technique, when combined with traditional exploration tools, can be used to vector toward VMS mineralization in the Bathurst Mining Camp and possibly a useful indicator in a prospect-scale base metal exploration.

Modeling induced polarization effects in helicopter time-domain electromagnetic data: Field case studies

Induced polarization (IP) effects are becoming more evident in time-domain helicopter airborne electromagnetic (AEM) data thanks to advances in instrumentation, mainly due to improvements in the signal-to-noise ratio and hence better data quality. Although the IP effects are often manifested as negative receiver voltage values, which are easy to detect, in some cases, IP effects can distort recovered transients in other ways so they may be less obvious and require careful data analysis and processing. These effects represent a challenge for modeling and inversion of the AEM data. For proper modeling of electromagnetic transients, the chargeability of the subsurface and other parameters describing the dispersion also need to be taken into consideration. We use the Cole-Cole model to characterize the dispersion and for modeling of the IP effects in field AEM data, collected by different airborne systems over different geologies and exploration targets, including examples from diamond, gold, and base metal exploration. We determined how multiparametric inversion techniques can simultaneously recover all four Cole-Cole parameters, including resistivity [Formula: see text], chargeability [Formula: see text], relaxation time [Formula: see text], and frequency parameter [Formula: see text]. The results obtained are in good agreement with the ancillary information available. Interpretation of the IP effects in AEM data is therefore seen by the authors as providing corrected electrical resistivity distributions, as well as additional information that could assist in mineral exploration.

Practical geological mapping under cover using electromagnetic data Minerals keynote paper

As the world's 'easy' mineral deposits on surface are increasingly discovered, it becomes more and more necessary for geo-scientists to explore under cover. Southern Africa has vast expanses of young cover in the form of Kalahari sands and the Karoo sequence, and this cover is ignored at one's peril. The big challenge is to map the geology beneath these young sequences, using a variety of techniques to increase the validity of the interpretation. Instead of relying purely on magnetics and gravity, various electromagnetic (EM) techniques are discussed, ranging from airborne EM surveys to 2.5D audio magneto-telluric (AMT) surveys and high-temperature SQUID EM surveys. Datasets are presented from current base metal exploration projects in Botswana, South Africa and Zambia, and the innovative use of these in some cases is demonstrated. The emphasis is on interpreting the general structure and geology, using all available datasets, in ways that benefit the overall exploration strategy. The important role of understanding physical rock properties by using downhole geophysical logging (petrophysics) is also discussed, and related to the geological interpretation. The varying levels of success of some of these methods at a prospect scale are highlighted.

A Comprehensive View from Geophysical Signatures over Chitradurga Schist Belt, Karnataka

Abstract Geology of Chitradurga Schist Belt (CSB) from Gadag to Srirangapatna, as inferred from the gravity and magnetic data analysis and supportive evidences from digitized Airborne Total count map is presented in this paper. Significant inferences have emerged from the integrated geophysical analysis coupled with geological information. Pattern, continuity and intensity of anomalies indicate that CSB can be viewed as three sectors; northern (Gadag), central (Chitdradurga) and southern (Nagamangala). Qualitatively geophysical signatures are diagnostic for the purpose of broad classification of the area into different geological domains such as granite-gneissic (gravity lows, fluctuating magnetic values and moderate radiometric counts), metavolcanic (gravity highs, magnetic highs and radiometric lows), metasedimentary (moderate gravity low, low magnetic values and moderate radiometric values) and granitic (gravity low, magnetic high and radiometric high) regions. Images prepared from gravity, magnetic and radiometric values indicated possibility of an additional arm of the schist belt from Huliyar to Hosdurga between the known Kibbanahalli and Chitradurga arms of CSB. From the gravity image it appears that the eastern margin of CSB may be encompassing Bukkapatna granite in the central sector of CSB. Gravity low closures and gravity high gradient between the granites of Chitradurga and those near Jagalur suggest different nature of geological continuity. Structural features, particularly the sheared contacts of metavolanics with metasedimentaries are demarcated based on gravity gradients. Based on these inferred features coupled with known geological controls of mineralization, a few target areas for gold / base metal exploration are identified. A major structural feature affecting the strike of arms of CSB may be the possible regions for emplacement of ultramafic bodies as observed near Sasival and Ghattishosalli. This in turn is significant for mineral exploration in Chitradurga Schist belt. Gravity and magnetic profiles drawn across CSB for every 15’ latitude indicated crustal architecture beneath CSB. Significant rise is noticed in the background gravity field from the arms of CSB to the main schist belt suggesting that the Bababudan volcanics have generated from different depths compared to the Chitradurga volcanics. Further, long wavelength magnetic anomaly coinciding with the eastern margin of schist belt suggests the differences in nature of crust on either side. Frequency analysis of gravity and magnetic anomalies and the modeling indicated the depth persistence of geological units.