Search Results (19)

Spodumene-bearing pegmatites are geochemically anomalous among crystalline rocks and important critical mineral resources in the green energy transition. However, prospecting is challenging due to their small size and the fact that they are often covered by soil and vegetation. This study demonstrates that, rather than being a hindrance, soil cover can enhance geochemical exploration, at least at the prospect scale. This study examines the dispersion pathways of lithium (Li) and its pathfinder elements (Rb, B, Ga, and Sn) from pegmatites (<10 m thick) into metamorphic host rocks and further into overlying undisturbed soils in heavily forested, postglaciated terrain of northeastern Wisconsin, USA. Soil-sample traverses over the world-renowned, lepidolite-type Animikie Red Ace pegmatite and two nearby dikes reveal pronounced <20 m anomalies with up to 1400 ppm of Li, 450 ppm of Rb, 3100 ppm of B, 40 ppm of Ga, and 60 ppm of Sn, greatly exceeding the control soil concentrations from nonmineralized granite and pegmatites. Soils mirror both the magmatic fractionation and alteration of pegmatite bedrock and metasomatic halos in parent host rocks. Metasomatized amphibolite revealed the presence of a holmquistite-ferro-holmquistite mineral. This greenfield pilot exploration led to lithium-rich pegmatite discoveries within the district and demonstrates the applicability of proximal sensors for soil exploration in Wisconsin and beyond. Full article

Characterizing alteration and its geochemical signature provides critical information relevant to ore-deposit genesis and its related footprint; for porphyry-type deposits, zoned potassic-phyllic-propylitic alteration and metal enrichment are critical features. Here we integrate earlier lithological and mineralogical studies of the (10+ Moz Au) Archean Côté Gold porphyry-type Au(-Cu) deposit (Ontario, Canada) with identified alteration types to provide exploration vectors. The ca. 2740 tonalite-quartz diorite-diorite intrusive complex and co-temporal Au(-Cu) mineralization as disseminations, breccias and veins are co-spatial with ore-related alteration types (amphibole, biotite, muscovite). An early, locally developed amphibole event coring the deposit is followed by emplacement of a Au(-Cu) mineralized biotite-rich magmatic-hydrothermal breccia body and broad halo of disseminated biotite and quartz veining. These rocks record gains via mass balance calculations of K, Fe, Mg, LILE, and LREE with Au, Cu, Mo, Ag, Se and Bi. Later muscovite alteration is enriched in K, Rb, Cs, Ba, CO₂, and LOI with varied Au, Cu, Mo, Te, As, and Bi values. A strong albite overprint records extreme Na gains with the loss of most other elements, including ore metals (i.e., Au, Cu). Together these data define an Au-Cu-Mo-Ag-Te-Bi-Se core co-spatial with biotite breccia versus a peripheral stockwork and sheeted vein zone with a Te-Se-Zn-Pb-As association. These features further support the posited porphyry-type model for the Côté Gold Au(-Cu) deposit. Full article

The Youjiang Basin in China is the world’s second-largest concentrated area of Carlin-type Au deposits after Nevada, USA, boasting cumulative Au reserves nearing 1000 t. This study examined the recently unearthed Lintan Carlin-type Au deposit within the Youjiang Basin. Factor analysis and association rule algorithms were used to identify exploration vectors and indicators essential for navigating this promising geological territory. In the Lintan mining area, the geological strata encompass the Triassic Bianyang, Niluo, and Xuman formations comprised clastic rocks, followed by the deeper Permian Wujiaping Formation with massive carbonate rocks. The orebodies are restricted to the F₁₄ inverse fault, cutting through the Xuman Formation, with an additional F₇ fault between the Wujiaping and Xuman formations. A total of 125 rock samples from the F₁₄ fault and a representative cross-section were analyzed for 15 elements (Au, Ag, As, Bi, Cd, Co, Cu, Hg, Mo, Ni, Pb, Sb, Tl, W, and Zn). The elements were divided into four groups based on cluster and factor analysis. Group 1 (Co, Cu, Zn, Ni, Tl, W, and Bi) was mainly enriched in the Xuman, Niluo, and Bianyang formations controlled by sedimentary diagenesis. Group 2 (Au, As, Hg, and Sb) was concentrated in the F₁₄ and F₇ faults, representing Au mineralization. Group 3 (Pb, Ag, and Mo) was mostly enriched near the F₁₄ and F₇ faults, displaying a peripheral halo of Au mineralization, and was probability controlled by ore-forming hydrothermal activities. Group 4 (Cd and Mo) exhibited extreme enrichment along the periphery of the F₇ fault. This pattern indicates the presence of a substantial hydrothermal alteration zone surrounding the fault, likely influenced by ore-forming hydrothermal processes. Additionally, Pb, Ag, Cd, Mo, and W are considered essential indicators for ore formation besides Au, As, Sb, Hg, and Tl. Twelve effective association rules were derived using the association rule algorithm, which can aid in discriminating Au mineralization. The spatial distributions of the 15 elements indicated that the F₁₄ fault is the main ore-bearing fracture zone, while the F₇ fault serves as the ore-conducting structure, channeling ore-forming fluids into the F₁₄ fault. Faults between the Wujiaping and Xuman formations, along with their associated reverse faults, present potential prospecting targets both within and outside the Lintan Au deposit in the Youjiang Basin. Exploration geochemical data can be fully utilized by combining factor analysis and association rule algorithms, offering key guidance for prospecting Carlin-type gold and similar deposits. Full article

Despite countless advances in recent years, exploration for volcanogenic massive sulfide (VMS) deposits remains challenging. This is particularly the case in the Yilgarn Craton of Western Australia, where outcrop is limited, weathering is deep and extensive, and metamorphism is variable. At Erayinia in the southern Kurnalpi terrane, intercepts of VMS-style mineralization occur along ~35 km strike length of stratigraphy, and a small Zn (-Cu) deposit has been defined at King (2.15 Mt at 3.47% Zn). An extensive aircore and reverse circulation drilling campaign on the regional stratigraphy identified additional VMS targets, including the King North prospect. Through a combination of detailed rock chip logging, petrography (inc. SEM imaging), and lithogeochemistry, we have reconstructed the volcanic stratigraphy and alteration halos associated with the King North prospect. Hydrothermal alteration assemblages and geochemical characteristics at King North (Mg-Si-K enrichment, Na depletion, and high Sb, Tl, Eu/Eu*, alteration index, CCPI, and normative corundum abundance values) are consistent with an overturned VMS system. The overturned footwall stratigraphy at King North is dominated by metamorphosed volcanic rocks, namely the following: garnet amphibolite (tholeiitic, basaltic), biotite amphibolite (andesitic, calc-alkaline), chlorite–quartz schist (dacitic), and narrow horizons of muscovite–quartz schist (dacitic to rhyolitic, HFSE-enriched). The hanging-wall to the Zn-bearing sequence is characterized by quartz–albite schists (metasedimentary rocks) and thick sequences of amphibolite (calc-alkaline, basaltic andesite). An iron-rich unit (>25% Fe₂O₃) of chlorite–actinolite–quartz schist, interpreted as a meta-exhalite, is associated with significant Cu-Au mineralization, adjacent to a likely syn-volcanic fault. Extensive Mg metasomatism of the immediate felsic footwall is represented by muscovite–chlorite schist. Diamond drilling into the deep hanging-wall stratigraphy at both King North and King has also revealed the potential for additional, stacked VMS prospective horizons in the greenstone belt stratigraphy. The discovery of HFSE-enriched rhyolites, zones of muscovite–chlorite schist, presence of abundant sulfide-rich argillaceous metasedimentary rocks, and a second upper meta-exhalite horizon further expand the exploration potential of the King–King North region. Our combined petrographic and lithogeochemical approach demonstrates that complex volcanic lithologies and VMS alteration signatures can be established across variably metamorphosed greenstone belts. This has wider implications for more cost-effective exploration across the Yilgarn Craton, utilizing RC drilling to reconstruct the local geology and identify proximal halos, and limiting more costly diamond drilling to key areas of complex geology and deeper EM targets. Full article

Deep-seated mineralization prediction is an important scientific problem in the area of mineral resources exploration. The 3D metallogenic information extraction of geology and geochemistry can be of great help. This study uses 3D modeling technology to intuitively depict the spatial distribution of orebodies, fractures, and intrusive rocks. In particular, the geochemical models of 12 elements are established for geochemical metallogenic information extraction. Subsequently, the front halo element association of As-Sb-Hg, the near-ore halo element association of Au-Ag-Cu-Pb-Zn, and the tail halo element association of W-Mo-Bi are identified. Upon this foundation, the 3D convolutional neural network model is built and used for deep-seated mineralization prediction, which expresses a high performance (AUC = 0.99). Associated with the metallogenic regularity, two mineral exploration targets are delineated, which might be able to serve as beneficial achievements for deep exploration in the Zaozigou gold deposit. Full article

The exploration of buried mineral deposits is required to generate innovative approaches and the integration of multi-source geoscientific datasets. Mining geochemistry methods have been generated based on the theory of multi-formational geochemical dispersion haloes. Satellite remote sensing data is a form of surficial geoscience datasets and can be considered as big data in terms of veracity and volume. The different alteration zones extracted using remote sensing methods have not been yet categorized based on the mineralogical and geochemical types (MGT) of anomalies and cannot discriminate blind mineralization (BM) from zone dispersed mineralization (ZDM). In this research, an innovative approach was developed to optimize remote sensing-based evidential variables using some constructed mining geochemistry models for a machine learning (ML)-based copper prospectivity mapping. Accordingly, several main steps were implemented and analyzed. Initially, the MGT model was executed by studying the distribution of indicator elements of lithogeochemical data extracted from 50 copper deposits from Commonwealth of Independent States (CIS) countries to identify the MGT of geochemical anomalies associated with copper mineralization. Then, the geochemical zonality model was constructed using the database of the porphyry copper deposits of Iran and Kazakhstan to evaluate the geochemical anomalies related to porphyry copper mineralization (e.g., the Saghari deposit located around the Chah-Musa deposit, Toroud-Chah Shirin belt, central north Iran). Subsequently, the results of mining geochemistry models were used to produce the geochemical evidential variable by vertical geochemical zonality (Vz) (Pb × Zn/Cu × Mo) and to optimize the remote sensing-based evidential variables. Finally, a random forest algorithm was applied to integrate the evidential variables for generating a provincial-scale prospectivity mapping of porphyry copper deposits in the Toroud-Chah Shirin belt. The results of this investigation substantiated that the machine learning (ML)-based integration of multi-source geoscientific datasets, such as mining geochemistry techniques and satellite remote sensing data, is an innovative and applicable approach for copper mineralization prospectivity mapping in metallogenic provinces. Full article

The Qulong porphyry copper deposit in Tibet is located in the Tethis–Himalaya metallogenic domain, one of the three major porphyry metallogenic domains in the world. At present, the mining area is mainly used for surface mining. The depth revealed by the drilling project is less than 2 km. The potential for deep resources is unknown. Based on an analysis of the geochemical characteristics of the primary halos around the No. 16 prospecting line, deep extension is discussed in this paper. Studies show that the metallogenic elements are Cu and Mo; the near-ore halo elements are Co, Au, Ag, and W; the supra-ore halo elements are Pb, Zn, Mn, and As; and the sub-ore halo elements are Sn and Bi. According to Gregorian’s zoning index and the barycenter method, the primary halo zoning of the No. 16 exploration line from shallow to deep is Mn–P–Pb–Ni–Zn–V–As–Hg–Co–Au–Cu–W–Ag–Mo–Sb–Sr–Cd–Sn–Ti–Bi. This sequence has a distinct “reverse” zoning feature, indicating that there may be a blind ore body deep in the mine. The geochemical parameter evaluation index based on the element content contrast coefficient suggests that there may be a hidden ore body in the deep. The relative hydrothermal mineralization in the center position of the section may be located deep below the north side of borehole ZK1601-1 in the middle of the section. The ore body erosion parameter model shows that the bottom of the drilling engineering control is the middle tail of the ore body, and there is a certain amount of extension in the deep part. The ideal superimposed model of the primary halo reflects the ore body trend of the 16th line section. The ore body is inclined to the north as a whole; the ore fluid flows from the deep to the southern side of the north side, and the deep part of the northern side of the ore body has a downward trend. Full article

This paper focuses on researching the scientific problem of deep extraction and inference of favorable geological and geochemical information about mineralization at depth, based on which a deep mineral resources prediction model is established and machine learning approaches are used to carry out deep quantitative mineral resources prediction. The main contents include: (i) discussing the method of 3D geochemical anomaly extraction under the multi-fractal content-volume (C-V) models, extracting the 12 element anomalies and constructing a 3D geochemical anomaly data volume model for laying the data foundation for researching geochemical element distribution and association; (ii) extracting the element association characteristics of primary geochemical halos and inferring deep metallogenic factors based on compositional data analysis (CoDA), including quantitatively extracting the geochemical element associations corresponding to ore-bearing structures (Sb-Hg) based on a data-driven CoDA framework, quantitatively identifying the front halo element association (As-Sb-Hg), near-ore halo element association (Au-Ag-Cu-Pb-Zn) and tail halo element association (W-Mo-Co-Bi), which provide quantitative indicators for the primary haloes’ structural analysis at depth; (iii) establishing a deep geological and geochemical mineral resources prediction model, which is constructed by five quantitative mineralization indicators as input variables: fracture buffer zone, element association (Sb-Hg) of ore-bearing structures, metallogenic element Au anomaly, near-ore halo element association Au-Ag-Cu-Pb-Zn and the ratio of front halo to tail halo (As-Sb-Hg)/(W-Mo-Bi); and (iv) three-dimensional MPM based on the maximum entropy model (MaxEnt) and Gaussian mixture model (GMM), and delineating exploration targets at depth. The results show that the C-V model can identify the geological element distribution and the CoDA method can extract geochemical element associations in 3D space reliably, and the machine learning methods of MaxEnt and GMM have high performance in 3D MPM. Full article

The Segura mining field, the easternmost segment of the Góis–Panasqueira–Segura tin–tungsten metallogenic belt (north–central Portugal), includes Sn-W quartz veins and Li-Sn aplite-pegmatites, which are believed to be genetically related to Variscan Granites. Sediment geochemistry indicates granite-related Ti-enrichments, locally disturbed by mineralization, suggesting magmatic and metamorphic/metasomatic titaniferous phases. Therefore, Segura alluvial samples and the geochemistry of their TiO₂ polymorphs (rutile, anatase, and brookite) were investigated, and their potential as exploration tools for Sn and W deposits was evaluated. The heavy-mineral assemblages proved to be good proxies for bedrock geology, and TiO₂ polymorph abundances were found to be suitable indicators of magmatic and/or metasomatic hydrothermal processes. The trace element geochemistry of Segura’s alluvial rutile, anatase, and brookite is highly variable, implying multiple sources and a diversity of mineral-forming processes. The main compositional differences between TiO₂ polymorphs are related to intrinsic (structural) factors, and to the P-T-X extrinsic parameters of their forming environments. Anomalous enrichments, up to 9% Nb, 6% Sn and W, 3% Fe, 2% Ta, and 1% V in rutile, and up to 1.8% Fe, 1.7% Ta, 1.2% Nb, 1.1% W 0.5% Sn and V in anatase, were registered. Brookite usually has low trace element content (<0.5%), except for Fe (~1%). HFSE-rich and granitophile-rich rutile is most likely magmatic, forming in extremely differentiated melts, with Sn and W contents enabling the discrimination between Sn-dominant and W-dominant systems. Trace element geochemical distribution maps show pronounced negative Sn (rutile+anatase) and W (rutile) anomalies linked to hydrothermal cassiterite precipitation, as opposed to their hydrothermal alteration halos and to W-dominant cassiterite-free mineralized areas, where primary hydrothermal rutile shows enrichments similar to magmatic rutile. This contribution recognizes that trace element geochemistry of alluvial TiO₂ polymorphs can be a robust, cost- and time-effective, exploration tool for Sn(W) and W(Sn) ore deposit systems. Full article

Pegmatitic deposits of critical metals (e.g., Li, Ta, Be) are becoming increasingly significant, with growing interest in understanding metal enrichment processes and potential vectors to aid the discovery of new resources. In southeast Ireland, the Leinster pegmatite belt comprises several largely concealed Li-Cs-Ta albite-spodumene-type pegmatites. We carried out detailed mineralogical characterization and whole-rock geochemical analyses of six drill cores intersecting pegmatite bodies and their country rocks. Exomorphic halos 2–6 m thick, enriched in Li, Rb, Be, B, Cs, Sn and Ta, are identified in both mica schists and granitic rocks adjacent to spodumene pegmatites. Metasomatism in wall rocks visible to the naked eye is restricted to a few tens of centimeters, suggesting country rock permeability plays a key role in the dispersion of these fluids. We propose that halos result from the discharge of rare element-rich residual fluids exsolved near the end of pegmatite crystallization. Halo geochemistry reflects the internal evolution of the crystallizing pegmatite system, with residual fluid rich in incompatible elements accumulated by geochemical fractionation (Be, B, Cs, Sn, Ta) and by auto-metasomatic resorption of spodumene and K-feldspar (Li, Rb). The possibility of identifying rare-element enrichment trends by analysis of bedrock, stream sediments and soils brings opportunities for mineral exploration strategies in Ireland and for similar albite-spodumene pegmatites worldwide. Full article

In this study, the zonality method has been used to separate geochemical anomalies and to calculate erosional levels in the regional scale for porphyry-Cu deposit, Abrisham-Rud (Semnan province, East of Iran). In geochemical maps of multiplicative haloes, the co-existence of both the supra-ore elements and sub-ore elements local maxima implied blind mineralization in the northwest of the study area. Moreover, considering the calculated zonality indices and two previously presented geochemical models, E and NW of the study have been introduced as ZDM and BM, respectively. For comparison, the geological layer has been created by combining rock units, faults, and alterations utilizing the K-nearest neighbor (KNN) algorithm. The rock units and faults have been identified from the geological map; moreover, alterations have been detected by using remote sensing and ASTER images. In the geological layer map related to E of the study area, many parts have been detected as high potential areas; in addition, both geochemical and geological layer maps only confirmed each other at the south of this area and suggested this part as high potential mineralization. Therefore, high potential areas in the geological layer map could be related to the mineralization or not. Due to the incapability of the geological layer in identifying erosional levels, mineralogy investigation could be used to recognize this level; however, because of the high cost, mineralogy is not recommended for application on a regional scale. The findings demonstrated that the zonality method has successfully distinguished geochemical anomalies including BM and ZDM without dependent on alteration and was able to predict erosional levels. Therefore, this method is more powerful than the geological layer. Full article

The Wulonggou Au district in the East Kunlun Orogen is one of the most important Au producing regions in China. The Yanjingou Au deposit occurs within a shear zone in the northeastern Wulonggou Au district. Based on detailed field investigations, geochemical data for the primary halo, and in situ thermoelectric data for pyrite, the following key results were obtained: (1) the Yanjingou Au deposit has the fractured-altered-rock type gold mineralization that is arsenopyrite-rich; (2) elemental correlations and cluster analysis show that Au and As are the most diagnostic elements; (3) geochemical data for the primary halo indicate the deposit is a shallow supra-ore halo ore body; and (4) in situ pyrite thermoelectric data show that the proportion of P-type pyrite is >80% and the detachment rate is 50%, which can be inferred that the location of the ore body is shallow. Based on our data, we present a mineralization prediction model for the ore body. The Yanjingou Au deposit has a good mineralization and high prospecting potential, with at least half of the ore body being concealed at depth, which has important scientific guiding significance for the breakthrough of prospecting and exploration. Full article

A suite of coal samples near a diabase dike were collected to investigate the petrographic, mineralogical, and geochemical characteristics of thermally altered coal in Datong Coalfield, China. Proximate analysis, vitrinite reflectance measurement, and petrographic analysis were applied to identify and characterize the alteration halo; optical microscope observation, qualitative X-ray diffractometry, and SEM-EDS were applied to study the phases, occurrence, and composition of minerals; XRF, ICP-MS, and AFS were applied to determine concentrations of major and trace elements; and the occurrence modes of elements were studied by correlation and hierarchical cluster analysis as well as SEM-EDS. The results demonstrated that the 3.6 m dike has caused an alteration halo of approximately 2 m in diameter. In addition, the thermally altered coals were characterized by high vitrinite reflectance, low volatile matter, and the occurrence of thermally altered organic particles. Dolomite and ankerite in the thermally altered coal may be derived from hydrothermal fluids, while muscovite and tobelite may be transformed from a kaolinite precursor. The average concentration of Sr in the Tashan thermally altered coal reached 1714 μg/g, which is over 12 times that of the Chinese coal; the phosphate minerals and Sr-bearing kaolinite account for this significant enrichment. The cluster analysis classified elements with geochemical associations into four groups: group 1 and 2 were associated with aluminosilicates, clays, and carbonates and exhibited enrichment in the coal/rock contact zone, indicating that the dike may be the source of the elements; group 3 included P₂O₅, Sr, Ba, and Be, which fluctuate in coals, suggesting that their concentrations were influenced by multiple-factors; group 4 did not manifest obvious variations in coals, implying that the coal itself was the source. Full article

With new advances in rapid-acquisition geochemical and hyperspectral techniques, exploration companies are now able to detect subtle halos surrounding orebodies at minimal expense. The Nimbus Ag-Zn-(Au) deposit is unique in the Archean Yilgarn Craton of Western Australia. Due to its mineralogy, alteration assemblages, geochemical affinity, and tectonic setting, it is interpreted to represent a shallow water (~650 mbsl) and low-temperature (<250 °C) volcanogenic massive sulfide (VMS) deposit with epithermal characteristics (i.e., a hybrid bimodal felsic deposit). We present a detailed paragenetic account of the Nimbus deposit, and establish lithogeochemical and hyperspectral halos to mineralization to aid exploration. Mineralization at Nimbus is characterized by early units of barren massive pyrite that replace glassy dacitic lavas, and underlying zones of polymetallic sulfides that replace autoclastic monomict dacite breccias. The latter are dominated by pyrite-sphalerite-galena, a diverse suite of Ag-Sb ± Pb ± As ± (Cu)-bearing sulfosalts, minor pyrrhotite, arsenopyrite, and rare chalcopyrite. The main sulfosalt suite is characterized by pyrargyrite, and Ag-rich varieties of boulangerite, tetrahedrite, and bournonite. Zones of sulfide mineralization in quartz-sericite(±carbonate)-altered dacite are marked by significant mass gains in Fe, S, Zn, Pb, Sb, Ag, As, Cd, Ni, Cu, Ba, Co, Cr, Tl, Bi, and Au. Basaltic rocks show reduced mass gains in most elements, with zones of intense quartz-chlorite-carbonate±fuchsite alteration restricted to thick sequences of hyaloclastite, and near contacts with dacitic rocks. Broad zones of intense silica-sericite alteration surround mineralization in dacite, and are marked by high Alteration Index and Chlorite-Carbonate-Pyrite Index (CCPI) values, strong Na-Ca depletion, and an absence of feldspar (albite) in thermal infrared (TIR) data. White mica compositions are predominantly muscovitic in weakly altered sections of the dacitic footwall sequence. More paragonitic compositions are associated with zones of increased sericitization and high-grade polymetallic sulfide mineralization. Chlorite in dacitic rocks often occurs adjacent to zones of sulfide mineralization and is restricted to narrow intervals. Carbonate abundance is sporadic in dacite, but is most abundant outside the main zones of Na-Ca depletion. Basaltic rocks are characterized by strongly paragonitic white mica compositions, and abundant chlorite and carbonate. Shifts from Ca carbonates and Fe-rich chlorites to more Mg-rich compositions of both minerals occur in more intensely hydrothermally altered basaltic hyaloclastite, and near contacts with dacitic rocks. Hanging-wall polymict conglomerates are characterized by minor amounts of muscovitic to phengitic white mica (2205–2220 nm), and an absence of chlorite and carbonate alteration. Full article

Calcite-mineralized wood occurs in marine sedimentary rocks on Vancouver Island, British Columbia at sites that range in age from Early Cretaceous to Paleocene. These fossil woods commonly have excellent anatomical preservation that resulted from a permineralization process where calcite infiltrated buried wood under relatively gentle geochemical conditions. Wood specimens typically occur in calcareous concretions in feldspathic clastic sediment. Other concretions in the same outcrops that contain abundant mollusk and crustacea fossils are evidence that plant remains were fluvially transported into a marine basin. Fossiliferous concretions commonly show zoning, comprising an inner region of progressive precipitation where calcite cement developed as a concentric halo around the organic nucleus. An outer zone was produced by pervasive cementation, which was produced when calcite was simultaneously precipitated in pore spaces over the entire zone. Full article