Ore Exploration Research Articles

Controls on the formation of Mn carbonates in mudrocks of the Datangpo Formation, Northern Margin Rift Basin, Yangtze Block

Deglaciation following the Sturtian Ice Age led to widespread manganese carbonate precipitates within marine mudrocks, reflecting unique climatic and oceanographic changes. The Mn carbonates hold economic importance in the Datangpo Formation, Yangtze Block, South China. Although their genesis in the Nanhua Rift Basin is well understood, little is known regarding their formation mechanism in the North Margin Rift Basin (NMRB). With growing interest in Mn ore exploration in this region, this study examines the weathering trend, climate patterns and watermass conditions using a variety of geochemical proxies. The results reveal two phases of climate variation during the deglaciation. Climate during the early phase (Phase I) was unstable, characterized by fluctuating values of Chemical Index of Alteration (CIA = 65 ± 4) and elevated Li isotope (8.8 ± 3.0‰) patterns. The degree of chemical weathering during the later stage (Phase II) was relatively stable (CIA = 65 ± 1, δ7Li = 5.4 ± 2.7‰), but the weathering intensity increased due to the reduced denudation rate, possibly related to a shift in the basin development. Fe speciation data indicate euxinia prevailing much of the section. However, Mo and U enrichment (> 1) and fluctuating ratios of Mo versus total organic content (0–40) suggest that pulses of freshwater influx associated with climate variation during Phase I caused the fluctuation of the chemocline along the continental shelf, facilitating the formation of Mn carbonates through the particulate Fe-Mn-hydroxide shuttle. With the establishment of stabilized climate, basin tectonics, and watermass circulation during Phase II, the accumulation of Mn carbonates in the sediments became less significant. The accumulation of Mn carbonates in the NMRB conforms to the “bathtub ring model”, distinct from the metallogenic model in the NRB, providing valuable guidance for Mn ore prospecting within this area and elsewhere with similar settings.

Study on photofluorescent uranium ore sorting based on deep learning

Uranium ore stands as a vital source of energy, and the process of ore sorting serves to segregate valuable uranium ore from its less valuable counterparts. This not only enhances the intrinsic ore grade but also mitigates the challenges associated with subsequent refining processes, thus leading to substantial resource cost savings. Consequently, the necessity of pre-sorting uranium ore becomes evident. While prevailing X-ray-based ore sorting technology remains at the forefront, the quest for a more efficacious method to sort uranium ore remains ongoing. This study harnesses the inherent photofluorescence properties of uranium ore by subjecting it to ultraviolet light, inducing the emission of a vibrant green fluorescence. Consequently, we propose a novel sorting technique founded on photofluorescence, augmented by deep learning to enhance the precision and categorization of uranium ore images. Two distinct models, the Convolutional Neural Network (CNN) model and the Transformer model, are developed in tandem. Empirical findings underscore the superiority of the Swin Transformer model, with training accuracy, validation accuracy, and classification rate registering at 0.9780, 0.9719, and 96.4 ms/it, respectively, surpassing the performance of alternative models like Alex Net and Res Net 34. Furthermore, the study employs visual aids, including channel visualization diagrams, confusion matrices, and Grad-CAM diagrams, to elucidate the operational intricacies of the model in the sorting of photofluorescent uranium ore images. This allows for an insightful analysis of the characteristics that influence classification weights. The potential applications of this method are indeed substantial, opening new avenues for uranium ore exploration and utilization.

A Study on the Geological Characteristics and Metallogenic Laws of the Xilahe Copper Deposit in Yuanjiang County

The Xilahe copper deposit in Yuanjiang County, Yunnan Province, China, is a highly concerned copper mining area. The geological characteristics, structural characteristics, distribution of magmatic rocks, ore body characteristics, metamorphism and wall rock alteration, as well as the ore-forming horizon and mineralization characteristics of the deposit are described and analyzed in this article, revealing its mineralization laws. The strata of the ore deposit is mainly composed of the upper section of the Fei weihe Formation, and the structural characteristics show the development of multiple faults in the mining area, including magmatic rocks such as diabase. The characteristics of the ore body indicate the presence of five copper ore bodies, mainly sulfide ore, and the main metal mineral is Fool's Gold. Metamorphism and wall rock alteration are manifested as silicification, carbonization, and pyritization. The mineralization pattern is influenced by various geological factors, including geological structure, magnetic action, hydrothermal activity, and time factors. The deposit belongs to a sedimentary metamorphic copper deposit. Comprehensive analysis shows that the copper deposits in the study area have great potential for ore exploration, which has important theoretical and practical significance for subsequent exploration and application of ore exploration methods.

Ambient Noise Tomography Using a Nodal Seismic Array Reveals Evidence for Igneous Intrusion Contributed to Ore Deposits in South China

Abstract The causes of the large-scale and intense magmatism in South China and its coeval metallogenic processes in the Mesozoic have been debated, due partly to the lack of a high-resolution crustal model. In this study, we deploy ∼500 nodal seismometers around the Nanling metallogenic belt in South China, including one linear array across the metallogenic belt and one 2D array around the Fankou ore deposit: a deposit that hosts large amounts of lead and zinc in China. The derivation of the Moho and the intracrustal structures with receiver function imaging using the linear array was conducted in a separate study. Here, we focus mainly on the shallow shear wavespeed structure in the upper crust (from the surface to about 8 km depth) using ambient noise tomography with the 2D array data. We find low-shear wavespeed anomalies (VS<2.8 km/s) associated with a basin down to about 3.0 km and several high-shear wavespeed anomalies (VS>3.6 km/s) below 6.0 km adjacent to the Fankou ore deposit, which we interpret as the crystallized igneous intrusions in the Mesozoic. Gravity modeling shows that the high density anomaly derived using the wavespeed model is required to improve the data fitting. Considering the temperature derived from a typical geothermal gradient is insufficient for mineralization, we propose that the fluid and heat brought by the igneous intrusion might contribute to the mineral concentration of the Fankou ore deposit. This observation is consistent with geochemical and petrological evidence of diabase and quartz diorite veins in the study region. The experiment shows that ambient noise tomography using dense nodal arrays has the potential in resolving the favorable conditions for ore formation and may play a role in future ore exploration.

Strongly Peraluminous Highly Fractionated I-Type Granite from Bangong–Nujiang Metallogenic Belt, Tibet: Implications for Continental Evolution and Evaluation of Economic Potentiality

The research on highly fractionated granite has significant implications for both the evolution and compositional maturation of the continental crust and metallogenic exploration. As a means of further understanding crustal evolution and promoting ore exploration in the Bangong–Nujiang metallogenic belt (BNMB), we present the petrography, zircon LA–ICP–MS U–Pb age, and Hf isotopic data, along with the whole-rock geochemical and Sr–Nd isotopic composition on Kese highly fractionated granite in the Baingoin area within the BNMB, central Tibet. The results show that Kese granite possesses a zircon U–Pb age of 127.8 ± 1.7 Ma and a relative enrichment in zircon Hf isotopic composition (−12.8~+0.3) with a two-stage Hf model age of 1.2~2.0 Ga. This granite belongs to the high-K calc-alkaline series, characterized by a strongly peraluminous feature, and is enriched in large-ion lithophile elements (LILEs) and Nd isotopes (−7.86~−7.74). The granite was likely to have been derived from the mixed melts derived from 40%~45% juvenile basaltic lower crust, 15%~20% ancient lower, and 40% middle–upper, following intense fractional crystallization processes involving amphibole, biotite, plagioclase, and some accessory minerals during the magma’s evolution. We infer that Kese highly fractionated granite can be formed from the continental collision of the Lhasa–Qiangtang terranes initiated before 128 Ma. The reworking of pre-existing juvenile and ancient crustal materials drove the composition of the northern Lhasa terrane to that of a mature continental crust. Moreover, the distinctive geochemical features have shown that the high degree of differentiation led to intense magmatic–hydrothermal interaction during the formation of Kese granite. A comparison of the geochemical characteristics of mineralized and barren granites suggests that the highly fractionated granites in Baingoin from the BNMB have a high economic potential and are suitable for preliminary exploration of Sn–W-(U) deposits.

Low-temperature thermochronology of the Longmala - Mengya’a Pb-Zn deposits (southern Tibet): Implications for ore exhumation and preservation

The large Gangdese metallogenic belt, located in the southern part of the Tibetan Plateau, hosts a variety of magmatic-hydrothermal ore deposits. Previous works in the area primarily concerned the ore genesis, while the exhumation history of these ore deposit has received less attention. In this contribution we explore the multi-stage thermo-tectonic evolution of the Longmala and Mengya’a Pb-Zn deposits, two large magmatic-hydrothermal ore deposits in the central Lhasa sub-terrane. In more detail, the thermal history of granitoids and deformed Paleozoic sediments inside and on the periphery of the ore districts have been constrained by low-temperature thermochronological methods, including the zircon (U-Th)/He and apatite fission track thermochronology. Additionally, zircon U-Pb geochronology was conducted on granitic host rocks to determine their emplacement ages. Our thermochronological data and inverse thermal history modeling results reflect two phases of accelerated basement cooling during the Cenozoic (i.e., ∼46–41 Ma and ∼20–5 Ma), interpreted as exhumation phases. The ore body was exhumed to the near surface during the Miocene, which provides essential information for ore exploration in the region. We also explore the degrees of basement rock exhumation along the Gangdese metallogenic belt and their spatio-temporal relations to major ore deposit distributions. It is suggested that complex interactions between tectonic-structural activities and surface erosion occurred during the late Oligocene-Miocene (∼25–5 Ma), which resulting in widespread exhumation along the Gangdese batholith. During this period, the ore-bearing rocks were gradually (with medium to high cooling rates) exhumed to the near-surface from ∼3–4 km crustal depth, making these ore deposits feasible for commercial mining.

Geochemical and mineralogical characterization of mine tailings at the Rautuvaara mine site and aspects to environmental conditions and resource potential

Mining industry generates a significant amount of waste including waste rock and tailings. The disposal of mine tailings has environmental impacts, such as the releasing of heavy metals to surface and underground waters. Therefore, adequate rehabilitation of mining waste storage facilities is essential. Abandoned tailings ponds may contain significant amounts of valuable minerals, including critical raw materials, and offer opportunities as secondary mineral resources. In this study geochemical and mineralogical characterization were made for the diverse mine tailings of the Rautuvaara tailings pond which was the final disposal site for different ore deposits. The samples were collected from two different locations in the tailings pond, preconcentrated and analysed with several methods including PSA, XRD, FE-SEM, EPMA, pXRF, WD-XRF and AAS. The geochemical results indicate substantially elevated Cu, As, Ni and Zn concentrations in the tailings. Mineralogical investigations revealed that the tailings contain valuable minerals such as gold, cobaltite, and W-bearing rutile. The last could be used as an indicator mineral in tailings classification and possibly also in future ore exploration. The study of secondary mineralogy revealed that the most weathered top layers of the tailings show secondary alteration rims on the surfaces of mineral particles, and the enrichment of As and Ni in the Fe- and Mn-oxide minerals.

Fractal dimension used as a proxy to understand the spatial distribution for carlin-type gold deposits

The spatial distribution of ore-forming element grades typically exhibits strong nonlinear characteristics as a result of continuous geological processes. The trend of change in ore grade sequences is a crucial indicator of the degree of enrichment of an ore deposit. Therefore, quantitative evaluation of the spatial distribution of ore-forming elements holds great significance for understanding ore-forming processes as well as for ore exploration. In this work, based on the principles of fractal theory, a MATLAB-based program to calculate fractal dimensions was developed, and fractal analysis was conducted on the gold concentration values (g/t) of 25 drill holes in the Lannigou Gold Mining Area, Guizhou, China. Rescaled range analysis and the fractal correlation integral were utilized to obtain the spatial distribution of gold concentrations in the drill holes. Rescaled range analysis revealed that the Hurst exponent (HR/S) values vary in the range of 0.58–0.97, which reflected the persistent behavior of vertical variation in gold tonnage at the studied wells. Furthermore, the relationship between gold grade distribution and associated fluctuations in the fractal dimension derived from the correlation dimension (DC) was discussed. The DC value was found to vary between 1.01 and 1.59, indicating that high-grade gold deposits were distributed along steep fractal gradients and that fractal dimension values could be used as a reliable proxy to efficiently understand the migration pathways of auriferous fluid. Studies have shown that the Hurst exponent of the Au grade sequence exhibited a strong dependence on the grade of mineralization, with gold mineralized veins persisting throughout the studied drill holes. Thus, fractal dimension gradients can serve as an important proxy for identifying the locations of potential economic gold deposits in unexplored areas. Moreover, this approach can be employed to map the distribution patterns of other types of ore deposits.

Geochemistry of Red Soils in the Kas District of Antalya (Türkiye) Using Multivariate Statistical Approaches and GIS

Red soil is formed by weathering due to the effect of bedrock and various fluids in subtropical and tropical climate zones. The major and trace element geochemistry of red soil are important for understanding its environmental conditions and interpreting its genesis. This study aims to determine how red soil is formed in the study area, where magmatic rocks are located, and to determine their relationship with magmatic fluids. In this context, geochemical analyses were conducted, and index values, spatial distributions, and multivariate statistics of the samples were calculated. Methods: A total of 49 red soil samples collected from the Sutlegen Village in the Kas district of Antalya were subjected to geochemical analysis. The following major elements were found in the red soil samples: Al2O3, SiO2, Fe2O3, TiO2, CaO, MgO, K2O, P2O5, and SO3. The Al2O3–SiO2–Fe2O3 triangular diagram revealed that the samples underwent moderate laterization. Multivariate statistical analyses indicated that major element oxides of Al2O3, Fe2O3, and SiO2 behaved differently from other components and revealed that red soil formations were associated with magmatic fluids. The region is a potential area for economic bauxite resources. Detailed investigations should be conducted on mineral exploration for bauxite ore.

Thermal infrared spectroscopy studies on skarn minerals for exploration of the Jiama Cu-Mo deposit, Tibet, China

The zonation patterns of skarn minerals, including garnet, diopside, and wollastonite, are important for exploration of skarn deposits. Thermal infrared (TIR) spectroscopy, which covers the wavelength range of 6–14 μm, is a new eco-friendly technology for skarn mineral identification. In this study, the TIR spectra data were collected, using an Agilent 4300 Handheld FTIR Spectrometer from nine drill holes within Jiama Cu-Mo deposit in Tibet, China. This study focuses on the TIR characteristics of grandite-series garnets (i.e., grossular to andradite), which have twin peaks in the 10–13 μm range and a diagnostic absorption valley (T absorption valley) at around 11.5 μm shifting based on the contents of Al2O3 and Fe2O3. The T absorption valley in the zoned garnet sample showed an undulating pattern, shifting towards longer wavelengths from the core to the rim, indicating the increase in Fe2O3 content and a decrease in Al2O3, MnO, and TiO2 content. The mixed spectral features of three significant skarn minerals including garnet, diopside, and wollastonite were used to classify the skarn zonation into garnet skarns, diopside-garnet skarns, and wollastonite-garnet skarns. The results from nine drill holes of the No. 24 exploration line in the cross section showed that the garnet T absorption valley shifted towards shorter wavelengths from the proximal to the distal skarn, as well as from the lower to the upper skarn. Furthermore, intensive copper mineralization occurred in the skarn when the garnet T absorption valley exceeded 11.50 μm. In comparison, the garnet T absorption valley at 11.35–11.50 μm is related to more intense molybdenum mineralization. This study suggests that TIR spectroscopy has the potential to rapidly identify skarn zonation in the field, and providing a suitable vector tool for skarn ore exploration.

Pyrite Textures and Compositions in the Dunbasitao Gold Deposit, NW China: Implications for Ore Genesis and Gold Mineralization Processes

The process and mechanism of gold mineralization are frontier issues. The Dunbasitao deposit is the most important gold deposit discovered along the Armantai suture zone, East Junggar, NW China, which indicates the potential for future ore exploration in this area. Orebodies are mainly hosted in Lower Carboniferous Jiangbasitao Formation volcano-sedimentary rocks, and the ores are characterized by multistage pyrites. Based on microscopy and backscattered electron imaging studies, pyrites are classified into five types: the pre-ore framboidal/colloidal Py0; the early-stage coarse-grained, cubic, and homogeneous Py1; and the middle-stage fine-grained, cubic/pyritohedron Py2 that includes Py2a (core), Py2b (mantle), and Py2c (rim). The results of the EPMA and in situ LA-ICP-MS analyses show that trace elements of pyrite mainly occur in two forms: solid solutions and invisible or visible inclusions. Mn, Co, Ni, and As enter the pyrite lattice, whereas Ti occurs as mineral inclusions, and Au, Cu, Zn, Sb, and Pb can occur in both forms. Au and As show a positive linear relationship with r = 0.850. Py2b has much higher Au contents (20.1 to 201 ppm) than other pyrite types (Py0: 0.01 to 0.36 ppm; Py1: 0.01 to 0.02 ppm; Py2a: 0.31 to 2.48 ppm; and Py2c: 0.18 to 18.0 ppm). The Dunbasitao deposit is classified as an orogenic gold deposit using the two latest machine learning classifiers based on pyrite trace element data. Fluid immiscibility, sudden cooling, and the substitution of S1− with As1− might be crucial mechanisms leading to Au precipitation. Initial ore-forming fluids brought major amounts of As, Au, Co, Ni, Se, Zn, Ag, Cd, Sn, and other elements, and the Jiangbasitao Formation host rocks contributed a certain amount of As, Ni, Cu, Sb, Pb, and Bi, at least.

Zircon as a pathfinder for ore exploration

Despite its wide application in dating geological events like magmatism, diagenesis, and metamorphic processes, zircon morphological, geochronological, and geochemical implications in ore systems have hitherto received little attention. In this study, we used textural, chemical, and isotopic data of zircons from variable granite-related deposits and other deposit types to emphasize zircon robustness as a pathfinder for ore exploration. The results show that zircons from W–Sn-related granites are rich in U, P, Ti, Y, Nb, Ta, Pb, Hf, Th, and REE compared to Cu–Mo-related granite. For the vein-type deposits, ore-bearing veins have significant zircons captured from geological bodies through which ore-forming fluid originated and migrated (e.g., basement rocks), whereas ore-free veins possess fewer zircons and are mostly from country rocks. Finally, in skarn-type deposits, ore-bearing skarns have zircons from granitic rocks and country rocks, whereas ore-free skarns have zircons only from one end member, either from granitic rocks or from country rocks. The variability in zircon abundance in these deposit types results from differences in the degree of magmatic differentiation of granitic rocks, variable zircon incorporation processes during veining and degree of contact-metasomatism during skarnization. We proposed a series of diagrams and employed partial least square discrimination analysis (PLS-DA) to differentiate the metallogenetic potential of granite-related, vein-type, and skarn-type deposits. The zircon criteria summarized by this study can be applied to similar ore deposits worldwide, which are significant for exploring economic minerals.

SEPARATION OF MAGNETIC ANOMALIES USING FRACTAL METHOD IN THE ESFORDI REGION FOR IRON EXPLORATION, CENTRAL EAST OF IRAN

Link for citation: Amin Karimi Kalvarzi, Aref Shirazi, Adel Shirazy, Amin Beiranvand Pour, Ardeshir Hezarkhani, Hamed Nazerian, Timkin T.V., . Voroshilov V.G. Separation of magnetic anomalies using fractal method in the Esfordi region for iron exploration, central east of Iran. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 3, рр. 197-209. In Rus.
 The relevance of research is determined by the possibilities of measuring the potential magnetic field, which has self-similar (fractal) properties, as well as a practical tool for prospecting and exploration of iron ores. In the Esfordi area, this method was used by us for the first time to identify, separate and interpret geophysical (magnetic) anomalies. The main aim of this thematic and practical study is the qualitative interpretation of geophysical data, the application of new methods in the prospecting and exploration of mineral deposits, modeling the geological environment and forecasting new promising areas. Object: Esfordi region, Yazd province, Iran. Methods. To obtain additional information about the subsurface, magnetometric data were used with their interpretation by the RTP (reduction to the north magnetic pole) method. For modeling purposes, an artificial sample was made, consisting of a sphere, a cube and a cuboid, and it was found that the fractal method can be used to separate anomalies for unipolar models (cube and cuboid). Results. The results of the study were applied to the Esfordi region, where it was found that at a survey scale of 1:100000, there is a direct relationship between the fractal method and the 3D model, which can be used to locate iron ore mineralization.

Mineralization Regularities of the Bainiuchang Ag Polymetallic Deposit in Yunnan Province, China

The Bainiuchang Ag polymetallic deposit is located at the junction between the Cathaysia, Yangtze, China and Indosinian blocks. It has experienced many geological events, and records excellent conditions for multiple mineralization. In this paper, elemental correlation analysis, cluster analysis, factor analysis, a semivariogram of Zn/Pb values, mineralization distribution and trend surface analysis have been carried out based on the prospecting database and ore body model. Our results show that Ag–Pb–Zn were mineralized at moderate temperatures. Tin was mineralized at high temperatures, and Sn and Zn/Pb values are well correlated. The Zn/Pb values can be used for tracing the ore-forming fluid. The semivariogram revealed that the Zn/Pb values are moderately spatially dependent, with good mineralization continuity in the 100° and 10° directions. The spatial pattern of the elemental grade correlates with mineralization enrichment. The trend surface analysis shows that the Ag, Pb, Zn, and Cu mineralization is weak in the south and strong in the north of the deposit, and the Sn grades and Zn/Pb values are high in the south and low in the north. High-temperature Sn, medium-temperature Cu, and medium-temperature Ag–Pb–Zn mineralization have occurred in a south-to-north trend. Therefore, the source of the ore-forming fluid was in the southern part of the mining area. During the migration of the ore-forming fluid from south to north, different minerals were precipitated due to changes in the physicochemical environment. The spatial patterns of mineralization may provide a basis for studying the formation of the ore deposit, and can guide ore exploration and mining in the mine area and similar ore deposits elsewhere.

Geology and geochemistry of Zn-Pb(-Ge-Ag) deposits in the Sichuan-Yunnan-Guizhou Triangle area, China: A review and a new type

Mississippi Valley Type (MVT)1 deposits represent the majority of carbonate-hosted Zn–Pb deposits globally. They typically form in an extensional tectonic setting along passive margins. However, studies on carbonate-hosted Zn–Pb deposits in the Sichuan–Yunnan–Guizhou Triangle area (SYGT) reveal differences in terms of the essential features of typical MVT deposits. We discuss the main features of these deposits, controlled by folds and faults, high-grade Zn–Pb ores and symbiotic or associated elements (i.e., abundant Ag and dispersed amounts of Ge, Ga, and Cd) of significant economic value. Based on a comparison of Pb-Zn deposits in SYGT and classical MVT deposits formed in an extensional tectonic setting, as well as a subsequent discussion on deposit classification, we propose that the Huize-style Zn–Pb deposits are a new deposit style, whose basic features can guide future ore exploration. We define the Huize-style deposits based on four factors: i) Hierarchical ore-controlling system of strike-slip fault-fold structures, ii) litho-facies associated with typical alternation and mineralisation, iii) ore-forming geochemical features revealed by typical mineral assemblages, mineralisation alteration zoning, fluid-inclusion, isotope geochemistry and metallogenic acid–alkali geochemical barriers, and iv) different prospecting methods to those typically used for MVT deposits. The Huize-style and typical MVT deposits constitute the carbonate-hosted non-magmatic epigenetic hydrothermal-type (CNHT) Zn–Pb deposits.

Integrated geophysical approach for ore exploration: Case study of Sidi Bou Aouane–Khadhkhadha Pb–Zn province – Northern Tunisia

AbstractWe carried out an integrated interpretation of available geophysical data (gravity and electrical data) in Sidi Bou Aouane–Khadhkhadha Pb–Zn province, located in a Neogene basin south of the Alpine thrust‐belt front in northern Tunisia. The interpretive approach of gravity data was done based on the Fourier transformation and spectral analysis to extract the residual component. Furthermore, edge enhancement techniques (tilt angle, total horizontal derivative) were applied to image the underlying lineaments in the study area. The computed gravity maps reveal multiple NE–SW hidden faults considered potential mineralization targets, referring to geological information. Detrital formations, known as containers of disseminated Pb–Zn mineralization, are expressed by low gravity responses. Resistivity and chargeability 3D inversion was conducted concurrently through on an iterative approach based on the conventional least‐squares algorithm and “incomplete Gauss‐Newton” as an optimization method. The initial model was defined based on drill‐hole data and geological knowledge. Inverted resistivity confirms the basin architecture expressed by gravity data. The combined interpretation of inverted resistivity and chargeability correlated to borehole and outcrops allows the definition of different electrical ranges associated to different lithologies and mineralization type and contents. A new potential target, expressing the same electrical signature of mineralization, is evidenced northward Khadhkhadha old mine. In addition, a potential copper concentration area was proven based on its electrical responses south Sidi Bou Aouane mine. 2.5D gravity modelling supports the evidenced interpreted target. The revealed results provided evidence for future interpretations of further geological structures, along with evaluations of mineral resources.

Superposition of induced polarization signals measured on pyrite–sand mixtures

SUMMARY Induced polarization (IP) is a common method in ore exploration. IP spectra measured over a wide frequency range can be used to characterize material properties of ores, slags and other residual material from mines and processing facilities. Previous studies have shown that IP parameters are sensitive to type, content or grain size of electronically conductive or semi-conductive minerals. Up to now, a variety of experiments has been performed on sand mixtures with fractions of ore minerals. Most experiments consider only a single fraction with a fixed grain size. We continue a series of experiments that have been done with sand–pyrite mixtures. The presented study compares IP spectra recorded for samples either with a single grain radius fraction (E-samples) or with two different grain radii fractions (Z-samples). The spectra are fitted to Pelton models. A Debye decomposition that provides a relaxation time distribution (RTD) is applied to the complex conductivity spectra. The RTD indicates separated maxima only if the ratio of mean grain radii is larger than a factor five. The resolution of the phase spectra and the spectra of imaginary part of conductivity is lower. Even though the volumetric pyrite content is equal in each fraction, the phase spectra and RTD of the Z-samples indicate much higher signals for the pyrite fraction with smaller grain radius. The same observation is made for the chargeability that shows larger values for decreasing grain radii. This finding contradicts existing theories that consider the chargeability as a suitable proxy of the volumetric content of ore minerals. We explain the observed effect by an interaction between neighbouring pyrite particles. The conductivity of the mixtures of the E-samples increases with decreasing grain radius of the pyrite fraction. This effect is attributed to dissolution effects on the surface of the pyrite particles during the sample preparation. We find that the additive superposition of the phase spectra of two E-samples is in good agreement with the measured phase spectra of the Z-samples (measured superposition) containing the two corresponding pyrite fractions. The agreement is slightly worse for the spectra of imaginary part of conductivity, where the measured superposition overestimates the mathematical superposition. The experimental results of our study motivate a further improvement of existing mechanistic models.

In situ trace element compositions and U[sbnd]Pb ages of cassiterite from tin-polymetallic deposits in the Dachang district, Guangxi, China: Implications for ore genesis and exploration

The Dachang tin-polymetallic district in southwest China is one of the largest tin ore fields in the world containing approximately 1.5 Mt. Sn, 6.8 Mt. Zn, 1.8 Mt. Pb, 1.4 Mt. Sb, 0.4 Mt. Cu and other critical metals. Both cassiterite-sulfide and ZnCu skarn mineralization occur as stratiforms, veins, and stockworks and are hosted in the Mid-Upper Devonian carbonate-rich sediments adjacent to the underlying Late Cretaceous Longxianggai granite pluton and/or the granite/diorite porphyry dikes. The Tongkeng and Huile deposits are typical stratiform- and vein-type tin-polymetallic deposits in the district. Previous studies suggest a genetic link between these tin-polymetallic deposits and the prolonged Longxianggai granite which was dated to have emplaced for multiple stages within ca. 91–97 Ma. However, existing constraints on the timing of tin mineralization display a board range at 90–96 Ma, whereas the accuracy and precision of these ages are less satisfactory. These ages are broadly overlapping with both the prolonged Longxianggai granite and the porphyry dikes (91 Ma), thus gives rise to question on their genetic association, which is a question of importance for ore exploration in the district.In this study, a large number of measurements of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) trace elements and UPb dating on cassiterites from the Tongkeng and Huile deposits was performed and their mineralization ages with hitherto the best accuracy and precision were obtained. LA-ICP-MS trace element analyses show that cassiterites from the Tongkeng and Huile deposits contain concentrations of Fe, W, Nb, and Ta characteristic of granitic-related skarn-type tin mineralization. UPb dating on cassiterites from 391 spots analyses yielded well-constrained ages of 91.13 ± 0.61 Ma to 89.46 ± 0.47 Ma for the Tongkeng deposit and 89.0 ± 1.3 Ma for the Huile deposit. These ages are apparently younger than the dominated equigranular phase of the Longxianggai pluton, but they agree well with the emplacement ages of the porphyritic granite represented either by the latest phase of the Longxianggai granite or the granite porphyry dikes (ca. 91 Ma). This suggests that the tin-polymetallic deposits in the Dachang district were most likely genetically associated with later, higher evolved granitic phases in the district. In this regard, the dike-hosting fault systems were most likely served as fluid conduits and their surrounding host rocks are favorable targets for ore exploration in the Dachang district.

Exhumation and preservation of the Tianyu Cu-Ni deposit constrained by low-temperature thermochronology: Insights into the thermo-tectonic history of the Chinese Eastern Tianshan

The Chinese Eastern Tianshan is an important metallogenic region where major Cu-Ni ores are mined. Previous research in the region primarily focused on the ore genesis. Precise thermochronological data to constrain the exhumation history and preservation of the ore deposits are limited at best. Tianyu is one of these Cu-Ni deposits in the area. Here we present new low-temperature thermochronological data to contribute to the understanding of its exhumation and preservation history. Zircon (U-Th)/He ages of ∼ 134–69 Ma, apatite fission track ages of ∼ 100–75 Ma, and apatite (U-Th)/He ages of ∼ 117–38 Ma from five granodiorite samples of the ore wall rock at different depths of a borehole in the Tianyu deposit were obtained. Our thermochronological data and inverse thermal history modeling reveal a moderate to rapid and final basement cooling phase during the Cretaceous (∼115–85 Ma) with an averaged cooling rate of ∼ 3–4 ℃/Ma. It is envisaged that this phase eventually exposed the ore deposits and that posterior erosion was limited, contributing to the preservation of the deposit. Combined with previously published geochronological and thermochronological data, a multi-stage cooling history of the ore bearing host rocks can be established. After its late Permian (∼280–260 Ma) magmatic-hydrothermal formation, two phases of accelerated regional cooling (i.e., in the late Permian-Early Triassic, ∼260–240 Ma; and the mid-Cretaceous, ∼115–85 Ma) can be recognized. The more intense Cretaceous cooling is associated with the ore body finally being exhumed to the surface, and provides essential information for ore exploration in the region. Further, we propose that areas in the Eastern Tianshan with similar thermal histories to the Tianyu Cu-Ni deposit may be potential exploration targets.

Satish G. Udhoji (1945-2022)

Satish G. Udhoji was born on 28.06.1945. He passed B. Sc. in 1965 and M. Sc. in 1967 from Geology Department of Nagpur University, Nagpur. After passing M. Sc, he joined Indian Bureau of Mines in Mineral Exploration Division which later merged with Geological Survey of India (GSI). Initially, he was working in Mineral Exploration for Manganese Ore and transferred later to GSI, Nagpur. At Nagpur, he worked in mineral exploration for few years and was later shifted to the Palaeontology Division. At Palaeontology Division, he worked on palynological study of rocks from Central India. During his stay at Nagpur, he completed LLB in 1987. Besides geology, he had good knowledge of legal matters and he was consulted frequently on legal matters. Later, he was posted to the Publication Division due to skill of meticulous scrutiny of technical matters. He was expertin scrutiny and publication of scientific articles, which was acclaimed all over GSI. His contribution in printing Seminar volume, GSI news and brochure during the celebration of “150 years of GSI” was well appreciated. Later, he was posted to Bengaluru, where he worked as a Head of Office also. He retired from GSI, Nagpur as a Director Publication. He was an active member of GGS, who contributed well during the Seminars, mostly managing publication of proceeding volumes. He was also consulted frequently about legal matters. His demise at the age of 76 years is an unbearable loss to GGS.