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Stream sediment surveying is a geochemical sampling method which is typically applied in the preliminary stages of mineral prospecting. Both continuous and discrete mapping approaches have been proposed to delineate geochemical anomalies at large scales using stream sediment samples. We aim to enhance the efficiency of a recent discrete mapping method called Weighted Drainage Catchment Basin (WDCB) which is independent of sampling sites and density, and has an advantage given that samples may not be uniformly distributed throughout the study area. The Enhanced WDCB (E-WDCB) method can be applied to calculate the weight of each catchment basin using different geochemical parameters such as factor scores. Our study focuses on the factor analysis of three datasets from the Bathurst region, New South Wales, Australia, with different numbers of samples. Different associations of the elements revealed by the factor analysis show that such analyses highly depend on the contributing samples and elements. We propose the Catchment Basin Score (CBS) index to delineate the suitability of sampling in each catchment basin. This index can also be applied to integrate the components resulting from several multivariate analyses on different datasets in a same area. The prediction-area plots show that our proposed method is able to predict a higher percentage of porphyry Cu Au occurrences in a smaller area compared to other canonical methods, e.g. the median of factor scores in each catchment basin. We demonstrate that prospective areas for porphyry Cu Au mineralization using the proposed discrete mapping method are also well correlated with volcanic and intrusive rocks.

The Dayingezhuang deposit is a representative large gold deposit within the Zhao-Ping fault zone in Jiaodong Peninsula, eastern China, and contains gold reserves of 170 t with an average grade of 3.10 g/t. The orebodies are hosted in the Late Jurassic Linglong granite intrusion and are Jiaojia-type (disseminated- or stockwork-style) ores. Mineralization and alteration are structurally controlled by the NE- to NNE-striking Linglong detachment fault located near the central section of the regional Zhao-Ping fault zone. Mineralization can be divided into primary and supergene periods. The primary period can be further divided into four hydrothermal stages: I) pyrite–(K-feldspar)–sericite–quartz; II) auriferous quartz–pyrite; III) quartz–gold–polymetallic sulfides; and IV) quartz–carbonate. Gold was mainly deposited in the second and third stages. Three types of fluid inclusion were observed (in decreasing order of abundance): AC-type (aqueous–carbonic), A-type (aqueous), and PC-type (pure carbonic). Based on petrographic, microthermometric, and laser Raman spectroscopic analyses of these fluid inclusions, three types of fluid inclusion assemblage (FIA) were identified in the quartz grains: FIA1 (AC- and PC-type), FIA2 (AC-, PC- and A-type), and FIA3 (A-type). First stage quartz grains contain mainly FIA1-type inclusions, with trapping temperatures of 305–388 °C and salinities of 4.28–8.51 wt% NaCl equivalent. Quartz grains that formed in the second and third mineralization stages contain all three types of FIA. Second stage inclusions homogenize completely at temperatures of 219–317 °C and have salinities of 1.56–11.12 wt% NaCl equivalent, while third stage inclusions homogenize completely at temperatures of 195–319 °C and have salinities of 2.73–13.33 wt% NaCl equivalent. In contrast, quartz grains that formed during the last mineralization stage contain mainly FIA3-type inclusions that yield homogenization temperatures of 126–233 °C and salinities of 0.48–6.72 wt% NaCl equivalent. The microthermometric data indicate that the ore-forming system evolved from a CO2-rich mesothermal fluid into a CO2-poor fluid. The existence and microthermometric characteristics of AC-, PC-, and A-type inclusion assemblages (FIA2) within a single thin section of grains that formed during the second and third stages show that ore fluids underwent unmixing during the syn-ore mineralization stages, due to pressure and temperature fluctuations. The microstructural deformation of auriferous samples indicates that both ductile and brittle deformation occurred during the syn-ore mineralization. Based on the inference that fluids were immiscible in FIA2, trapping pressures during ore formation are estimated at 127–276 MPa. Assuming a fluid pressure regime controlled by fault-valve activity, these pressures are equivalent to a mineralization depth of 9.2–14.0 km. The depth to which erosion occurred in the study area has been calculated as ~10.3 km since the formation of the deposit at 130 Ma, which suggests good prospecting potential for gold at depth in Dayingezhuang.

This paper investigates Xiyi Pb-Zn deposit in Yunnan Province, China, which has little mineralized outcrop and rare supergene enrichment. The deposit is overlain by transported cover with a thickness of ~0.2–50 m. The geoelectrochemical extraction method (GEM) was tested over well-characterized areas of the deposit (sections A–B, C–D), and in an unexplored region (area E). GEM results are compared with soil geochemical methods (SGM) in areas of known mineralization and show that the geoelectrochemical anomalies (Pb, Zn, Ge, As, Au) exhibit a positive response to the deep concealed ore body, and that GEM can be more effective for finding the concealed Pb-Zn ore in the study area compared to SGM. A geoelectrochemical prospecting index was created for this deposit type and tested in an area without known mineralization (area E). The index shows that anomalies can be identified where the contrast value (CV) is >1 for Pb and Zn, and where there is the Y1 factor score (y1) >0 (for Pb-Zn-Ge-As-Mo-Bi). Correlation and factor analysis identify two comprehensive anomaly zones (CAZ) in area E with good prospecting potential, which can be used as the focus of the next exploration. The strong surface geoelectrochemical and soil geochemical anomalies above the fracture belt, with weak to moderate anomalies over thick transported cover above the fracture belt extension, suggest that dilatancy pumping is a dominant migration mechanism in the formation of anomalies in areas of shallow transported cover.

Three dimensional (3D) geochemical modeling was used to identify deposit scale exploration targets combining the geological (110 boreholes and 6 tunnels with 709 assay borehole samples) dataset and 374 litho-geochemical samples in the Dashui Au deposit (China). The Dashui Au deposit, located in the Western Qinling orogenic belt, is a magmatic-hydrothermal type large Au deposit discovered in recent years. The methodologies are summarized as follows: (1) the 3D geological bodies (ore bodies, granitic stocks/dikes, fault fractures, and alteration zones) modeling using GOCAD software. (2) 3D deposit-scale geological modeling in mining zones combination the deposit-scale plane maps, cross sections, longitudinal sections, tunnel planes, borehole datasets, and the range of 3D model is 2.3 × 0.55 × 0.6 km3. (3) The ordinary kriging and discrete smooth interpolation (DSI) interpolation methods were used to analyze the distribution trend of Au grade features combined with borehole and the primary litho-geochemical halos dataset, and the Cu/Pb ratio model is analyzed and constructed by metallogenic model/rule using primary geochemical halos data with DSI interpolation method. (4) The concentration-volume (C–V) fractal method is used to analyze the anomaly classification of grade and Cu/Pb ratio in 3D space using GeoCube software. The results show as follows: (1) the high Au grade value zones are associated with ore-bearing intrusion and the NW- and NE-trending fault structures; (2) the high Au value blocks of Cu/Pb ratio can be used to delineate ore-bearing magmatic fluids channel and mineralization zones; (3) the integrated exploration criteria are Cu/Pb ratio, the NE- and NW-trending faults, and intrusions in the Dashui deposits, the potential targets at depth are located in the southwest and southeast zones under the mining levels of No. 2, No. 170, No. 20, and No. 35 Au orebodies, and the Au resource is >172 t (the depth is

The Jiaojia-type gold deposits, hosting >80% of gold resource in the Jiaodong Peninsula, Eastern China, are characterized by veinlet- and disseminated-style mineralization associated with the Mesozoic detachment faults. In this study, we performed multi-constraint geological modeling and spatial analysis involving 3D buffer analysis, shape analysis, and field analysis for the Dayingezhuang gold deposit to quantitatively assess the gold distribution and its association with geological features. The obtained spatial data were further integrated into three dimensional (3D) prospectivity modeling by fuzzy weights-of-evidence (WofE) and continuous WofE methods to evaluate mineral potential. Our results determine a quantitative correlation between phyllic alteration thickness and tectono-geochemical anomaly to construct the geometric models of alteration zone. The hydrothermal intensity extracted from the models shows a bimodal distribution and it is significantly high in the center of No. 2 orebodies, indicating an overprinting gold mineralization. The spatial analysis on the Zhaoping fault reveals that the most probable locations for gold deposition were determined to be in segments of the Zhaoping fault with a slope of 20° to 40°, dip angle changes of −5°, and undulation of near 0 m. All of the features likely result from structural controls on fluid flow and infiltration, as well as variations in the stability of Au-bearing complexes related to fault morphology. 3D prospectivity models generated by continuous transformed spatial evidence values with lower bias and uncertainty yielded a higher predictive efficiency than classified evidential layers. Our study not only highlights that gold enrichment of the Jiaojia-type deposit is essentially controlled by shape features of detachment faults, but also emphasizes the applicability of 3D prospectivity modeling in identifying potential gold mineralization at depth in the Jiaodong Peninsula.

The Bonaparte Lake area in southern part of the Quesnellia terrane of the Canadian Cordillera is proximal ( Au and Cu Mo deposits. This area has potential for finding more porphyry type Cu deposits, but is overlain by a thick and nearly continuous cover of glacial sediments, which adds difficulty in finding mineral deposits in underlying bedrocks. This study uses geochemical data following an aqua regia leach on the clay fraction (

Although the origin of the snow is atmospheric, heat and gasses coming from underlying soil affect the concentration of hydrocarbons and elements in snow. For testing the use of snow in geochemical exploration, a test campaign was carried out in three different mineralization types in northern Finland: Au-Co, P-REE and Cu mineralizations. The snow samples were collected from the bottom of snow cover in two consecutive years. Two methods for analysing geochemical signatures of mineralized bedrock were applied to these snow samples: Spatiotemporal Geochemical Hydrocarbons (SGH) and ultra-trace elements determination by single collector high resolution inductively coupled plasma mass spectrometry (SC-HR-ICP-MS). The SGH method is based on detection of the hydrocarbons that are decomposition products of bacteria that use specific mineralization in their growth phase. In the case of the inductively coupled mass spectrometry, the content of a wide range of elements was determined. The results of both methods showed that the traces inherited from the tested mineralization can be observed in snow. The SGH signature located the Au-Co mineralization using an Au template and the Cu mineralization using a Cu template, although low signal repeatability may be the weakness. The response to the P-REE mineralization with a Polymetallic template was unclear. An improvement was achieved by reinterpreting the result with a customized template for REE. In addition, the repeatability with reinterpreted results showed similarities in the results between the sampling rounds. In the case of the SC-HR-ICP-MS method, results for several elements (e.g. As, Cu, Fe) showed a clear response over the mineralized zones for all three mineralization types. Mineral exploration would benefit using of snow as sampling material: this activity leaves virtually no footprint. Further studies are needed to improve the confidence and reliability in the use of snow as a sampling medium in mineral exploration.

The Baiyun gold deposit is located in the Qingchengzi orefield, NE China. The gold mineralization occurs mainly as auriferous quartz veins and auriferous altered rock. Wall-rock alteration includes silicification and potassic alteration along with minor sericitization, carbonatization, and chloritization. Three stages of mineralization are recognized: an early quartz and coarse-grained pyrite stage (Stage I), a middle quartz–gold and fine-grained pyrite–polymetallic sulfide stage (Stage II), and a late quartz–carbonate stage (Stage III). Four types of inclusions are recognized in the quartz veins: two-phase liquid-rich fluid inclusions (Type I), CO2 three-phase aqueous fluid inclusions (Type II), two-phase vapor-rich fluid inclusions (Type III), and pure liquid fluid inclusions (Type IV). The early stage quartz contains Type I–III fluid inclusions that yield low–medium homogenization temperatures (162 °C–350 °C), low salinities (1.57–10.33 wt% NaClequiv.), and belong to a NaCl–H2O–CH4–CO2 ± H2S hydrothermal fluid system. The middle-stage quartz also contains Type I–III fluid inclusions that yield low–moderate homogenization temperatures (148 °C–290 °C), variable salinities (1.02–16.43 wt% NaClequiv.), and belong to a NaCl–H2O–CO2–H2S ± N2 system. The late-stage quartz contains Type I, II, and IV fluid inclusions that yield homogenization temperatures and salinities of 150 °C–183 °C and 6.30–13.29 wt% NaClequiv, respectively, and belong to a NaCl–H2O–CO2 ± N2 system. Therefore, the ore-forming fluids of the Baiyun gold deposit are generally characterized by low–moderate homogenization temperatures and low–medium salinities, and belong to a NaCl–H2O–CO2–H2S ± N2 system. The coexisting Type I and II inclusions of the early and middle stages have similar Th ranges but weakly contrasting salinities, indicating that fluid boiling occurred. The H-O isotopic values (δ18OH2O = −0.7‰ to 5.6‰; δD = −108.3‰ to −74.0‰) and composition of the fluids suggest that the ore-forming fluids consisted mainly of magmatic water with a small amount of meteoric water and metamorphic fluids. Fluid inclusions in hydrothermal pyrite yield 3He/4He ratios of 0.43–0.52 Ra and 40Ar/36Ar ratios of 4648.7–7685.9, indicating the mixing of fluids with mantle and crustal components, which were mainly crust-derived. The δ34SV-CDT values of pyrite are between −12.5‰ and 1.9‰ (average −5.0‰), while δ34SV-CDT values of wall-rocks are between 7.0‰ and 18.7‰ (average 12.6‰). The 206Pb/204Pb, 207Pb/204Pb, and 207Pb/204Pb values of the pyrites are 17.416–18.908, 15.511–15.714, and 35.541–40.032, respectively, indicating that the ore-forming metals may came from Triassic magma and Gaixian Formation. Based on geological, fluid inclusion, and isotopic data, as well as data from previous studies, we propose that the Baiyun gold deposit is a magmatic–hydrothermal ore deposit.

The Zefreh porphyry Cu-Mo deposit is located in the central part of the Cenozoic Urumieh-Dokhtar Magmatic Arc (UDMA), 75 km NE of Isfahan city, central Iran. The Zefreh rocks, ranging from diorite to granodiorite in composition, formed in a subduction-related arc setting, and likely in a pre-plate collisional environment. They are enriched in Th, U, Rb, Pb, light rare earth elements (LREE), but depleted in Ti, Nb, Ta, Ba, Sr, and P. Negative to slightly positive Eu anomalies (0.5–1.1), low to moderate Sr contents, (189–567 ppm), low to moderate Sr/Y ratios (5–23), and low La/Yb ratios (3–8) in the Zefreh magmatic suite rule out considerable amounts of fractionated amphibole from a hydrous magma in the lower crust. Arc crustal thickness in the Zefreh area was probably

Tellurium-bearing, base and precious metal sulfides from the Au-Ag-Te mineralization at Panormos Bay, Tinos Island, Cyclades, preceded and followed the main telluride-forming event. Ore petrography and chemistry of the sulfides suggest that they have precipitated under supersaturation conditions, i.e., grown with hopper habit, enriched in Zn, Fe, Ag, Cd and Pb, and Te in stage II, III and VI sulfides and incorporate nanoparticles with variable Ag/(Pb + Ag + Cu + Fe + Zn)% values. The noble gas, i.e., He, Ar and Ne isotope compositions obtained from these sulfides form two distinct populations, the “Liquids” and “Vapors”. All these features constitute overwhelming evidence that favors vapor transport for the base and precious metals by the vapor-like Panormos ore fluid. The widespread occurrence of CO2-effervescence and boiling at the Panormos Bay Au-Ag-Te ores provoked degassing of the CO2, HCl(g), H2S(g), H2Te(g), Te2(g), light noble gas isotopes (3He, 36Ar, 20Ne, and 21Ne), base- and precious-bearing laden vapors from the mineralizing fluid and transported a fraction of the base and precious metals to vapor. Geochemical simulation suggests that supersaturation in the vapor phase, rapid up-vapor transport, and subsequent condensation in the Panormos Bay ore solution of H2Te(g), Te2(g), and base and precious-bearing vapors led to the precipitation of sulfide (stages II, III and VI) and telluride (stage V) mineral assemblages.

This paper presents a novel gradient model for exploration of blind mineralization. The concentration gradient coefficient techniques have been proved to be very well-suited for typical mining geochemistry applications. Gradient concentration corresponds to concentration variations. Large concentration changes due to geochemical data distribution correspond to surfacing anomaly, and less concentration variations are more likely to be related to the deeper geochemical anomalies. The introduced technique is capable to distinguish the difference between the blind mineralization and zone dispersed mineralization, computationally and without exploration drilling. In this research, deep geochemical anomalies are investigated using the gradient concentration values for the porphyry–Cu deposits of the Jebal-Barez region in Iran. Based on the results obtained from the proposed gradient model, values >1.0 in G(Vz) reveal the existence of blind mineralization in the study zone. The findings based on this method suggest that SW of Jebal-Barez is a highly favourable zone for exploration of blind mineralization. The value for G(Vz) in this zone is equal to 5.04. The results obtained in this research were consistent well with the findings of the previous research in the area and the detected Kerver as the main blind mineralization in Jebal-Barez. A local exploration was carried out in this zone in four areas of Kerver using the gradient model.

The East Kunlun Orogenic Belt experienced two periods of mantle-derived magmatic activity during its post-collisional stages. One occurred during the Late Silurian-Early Devonian, and the other occurred during the Middle-Late Triassic. The Late Silurian-Early Devonian Xiarihamu mafic-ultramafic intrusions were found to be associated with a giant magmatic sulfide Ni-Co deposit discovered in 2012. The U-Pb age of websterite in the Kaimuqi mafic-ultramafic intrusion is 221.1 ± 2.3 Ma. None of the Middle-Late Triassic mafic-ultramafic intrusions in the East Kunlun Orogenic Belt contain Cu-Ni mineralization. Based on simulations by the software MELTS, we found that the crystallization process leads to a drop in the sulfur content at sulfide saturation. The mineralized Late Silurian-Early Devonian mafic-ultramafic intrusions exhibit both a broader range of m/f values and higher m/f values than the non-mineralized intrusions in the East Kunlun Orogenic Belt, which means that the mineralized intrusions experienced a long process of crystallization differentiation. This process is probably responsible for Cu-Ni mineralization in the Early Devonian Xiarihamu mafic-ultramafic intrusion. Compared to the olivine and clinopyroxene in the Xiarihamu giant Cu-Ni deposit, the Late Triassic Kaimuqi olivine contains significantly lower MgO, Fo and SiO2 contents and higher CaO and FeO contents, and the Kaimuqi clinopyroxene contains higher FeO and CaO contents. Therefore, we infer that the Kaimuqi intrusion formed from a melt with higher FeO and CaO contents and a lower SiO2 content. This melt required more sulfur to achieve sulfide saturation. This characteristic most likely hindered mineralization in the Kaimuqi mafic-ultramafic intrusion. All of the mafic-ultramafic intrusions that host Cu-Ni deposits in the East Kunlun Orogenic Belt contain lherzolite, harzburgite, and orthopyroxenite, indicating that the pyroxene in these intrusions is mainly the orthopyroxene. If an intrusion contains more clinopyroxene, it indicates that its magma contains more calcium. The magma with higher calcium content will need a higher sulfur content to achieve sulfide saturation. Although websterite occurred in the Kaimuqi intrusion, the clinopyroxene and orthopyroxene content in the websterite is 75% and 20%, respectively, and the peridotite lithofacies is wehrlite. Therefore, orthopyroxene is rare in the Kaimuqi mafic-ultramafic intrusions. Thus, the Kaimuqi mafic-ultramafic intrusion may not have had the potential to form Cu-Ni ore deposits. Finally, this paper summarizes some geological and geochemical indicators for Cu-Ni mineralization in the mafic-ultramafic intrusions in the East Kunlun Orogenic Belt. These indicators provide some enlightenment to the exploration of Cu-Ni deposits in mafic-ultramafic intrusions, especially for the geological exploration bureaus or companies, which do not have the budget for large numbers of geological dating, isotopes, major elements, and platinum group elements during the exploration evaluation process in the current global mining recession situation.

The Xiaotongchang Cu deposit is located in the south Ailaoshan and at the contact between Yunnan province of China and Vietnam. Four Cu ore bodies are distributed parallel to each other in an interlayer fracture zone in the Permian Emeishan basalt. The major ore mineral in the deposit is chalcopyrite, and the main gangue minerals are quartz and calcite. New Re-Os data for chalcopyrite from the Xiaotongchang Cu deposit show tens of ppb Re abundances (1–86 ppb) and contain essentially no common Os. All the samples have extremely high 187Re/188Os (up to 2.3 × 104), and the dominance of radiogenic Os and high 187Re/188Os are diagnostic features of “LLHR” (low-level, highly radiogenic) sulfides. The Re-Os isochrone age for the No. 1 and No. 3 Cu bodies show that the phase of Cu mineralization predominantly occurred in the Middle Triassic, with an age of 230.6 ± 1.1 Ma. Thus, the mineralization occurred much later than the periods of major eruption of the Emeishan large igneous provinces, indicating a closer relationship with the late collisional processes in the Ailaoshan orogenic belt. Combined with REEs patterns and consistently positive δ34S values (7.4–9.2‰), it can be concluded that the ore-forming materials of the Cu deposit are derived from a mixture of mantle and crust components.

In light of the recent ‘lithium boom’, a screening study for Sn-W and Li-Cs-Ta deposits was carried out and located an early 1980s Bureau de Recherches Geologiques et Minieres (BRGM) geochemical survey with W anomalies of >50 ppm in the Sainte-Marie-aux-Mines area, NE France. These anomalous areas, along with historic mining of polymetallic veins in the area, led to the present investigation of the regional potential for Variscan vein-hosted Sn-W-Li-Cs-Ta and Mesozoic-Cenozoic Cu-Pb-Zn-As-Ag-Ni veins in the central Vosges Mountains. A total of 144 stream sediment samples were collected in the central Vosges Mountains covering an area of >200 km2. Multi-element pXRF and ICP-MS assays revealed previously undescribed W-Li-Cs-Ta geochemical anomalies related to major ENE-WSW trending fault zones and splay faults in the I-type Central Vosges Mg-K (‘CVMg-K’) granite. Field mapping evidence, previously published age data along with strong geochemical fractionation trends obtained from K/Rb, Zr/Hf and Nb/Ta ratios, imply that the CVMg-K granites were intruded by younger crustal melts derived from crustal anatexis of metasedimentary and metaigneous source rocks, that potentially exploited pre-existing fault control, and subsequently fractionated and enriched incompatible elements of economic interest. This study demonstrates that Sn-W-Li-Cs-Ta geochemical anomalies can occur in I-type granites, if later orogenic processes leading to crustal anatexis resulted in the production of peraluminous melts, strong magmatic fractionation and emplacement of mineralization along regional fault zones. Therefore, the presence of I-type granites in Variscan and other geological terrains should encourage regional Sn-W-Li-Cs-Ta exploration.

Sometimes geochemical anomalies linked with buried mineral deposits are too weak to be recognized by conventional methods. In this study, element concentration data from a stream sediment survey were subjected to a combined method of SWPCA (spatially-weighted principal components analysis) and WT (wavelet transformation) to derive a geochemical anomaly model for epithermal Au deposits in the Dashui ore-concentration district. The SWPCA was applied as a data integration method to extract information related to mineralization in the geochemical data. The WT was applied as a powerful tool for recognizing mineralization related anomalies in a complex geochemical field and for enhancing weak anomalies from background. The SWPCA–WT geochemical anomaly model indicated high favorability values for the known mineral occurrences and out-performed PCA–WT and SWPCA models. The SWPCA–WT geochemical model generated in this study provides a robust guide for further gold exploration in the Dashui ore-concentration district.

The Nanling belt (South China) is one of the most important metallogenic region in the world in regard to tungsten polymetallic resources. In this belt and surrounding area, the most important elements accompanying tungsten deposits are Sn, Bi, and Mo. Modelling the spatial variability and uncertainty of W, Sn, Bi, and Mo anomalies is critical for tungsten polymetallic exploration risk assessment. However, traditional interpolation methods (e.g., kriging, polynomial trend surface and inverse distance weighted method) for modelling continuous geochemical fields based on sparse sampling data provide smoothed representations of element concentrations, which often result in unreliable decisions. Here, uncertainty analysis of geochemical anomaly for tungsten polymetallic exploration targeting was investigated through combined sequential indicator simulation and local singularity analysis. Anomalous thresholds of E-type singularity indices for the selected elements (W, Sn, Mo and Bi) were determined by singularity-quantile plot analysis. The distribution pattern of probability of not exceeding a threshold singularity index was obtained from a series of equally probable representations of singularity indices of individual elements (W, Sn, Mo and Bi) based on local and spatial uncertainty algorithms. Based on the four probabilistic models, one per element, a synthetic probability map was produced for uncertainty assessment of geochemical anomaly for exploration targeting. The results indicate that zones with very high probabilities are significantly correlated with known tungsten polymetallic deposits and are closely associated with lithostratigraphic contacts. These results provide for important decision-making for risk evaluation of tungsten polymetallic exploration targeting based on spare stream sediment geochemical data in the Nanling belt.

The copper and zinc isotope ratios of massive sulfide and stockwork ores of Honghai volcanogenic massive sulfide (VMS) deposits in eastern Tianshan Orogen, NW China, were measured by multiple collector-inductively coupled plasma-mass spectrometry (MC-ICP-MS). The overall range of δ65Cu (where δ65Cu = [{(65Cu/63Cu)sample / (65Cu/63Cu)NIST976} − 1] × 1000) values of 16 mineral separates from Honghai deposit varies from −0.28 to 0.70‰, with near-surface massive Zn ores having isotopically heavy values compared to massive Cu ores from deeper levels. This suggests that a kinetic fractionation of copper isotopes could be encouraged during precipitation of chalcopyrite. However, the δ65Cu values of mineral separates from Massive Zn ores in drill hole ZK0302 are considerably higher than those of other mineral separates, which might be associated with the development of secondary mineralization. We also obtained zinc isotope data from 6 sphalerite-bearing samples. The range of δ66Zn (where δ66Zn = [(66Zn/64Zn)sample / (66Zn/64Zn)JMC 3-0749L − 1] × 1000) values varies from 0.05 to 0.17‰, with central parts of mineral separates having isotopically light values (δ66Zn = 0.05‰) compared with that from distal (δ66Zn = 0.12–0.17‰) of VMS system. The results suggest that Cu and Zn isotopes could provide a valuable tool for tracing flow paths toward the center of hydrothermal systems.

The Qiucun gold deposit, located in the central Fujian Province, is one of the most important gold producers at the Dehua prospecting region. The deposit is hosted in the Nanyuan Formation consisting of continental arc volcanic rocks, which belong to the Mesozoic coastal volcanic belt of south China. Gold ore bodies are controlled by a group of NE-NEE trending faults. Wall rock alteration shows that gold mineralization is closely associated with quartz (chalcedony)-illite-pyrite-calcite assemblages, in which pyrite is the dominate sulfides (>90%). Petrographic study of ore minerals shows that gold occurs as electrum grains of 2–65 μm in diameter, interstitially or in fractures within pyrite. EPMA analysis of electrum yielded compositions of 62–69 wt% Au and 28–33 wt% Ag. Fluid inclusions petrographic and microthermometric studies were carried out on auriferous quartz veins from three different elevations, i.e. 712 m, 742 m and 820 m above sea level. Two types of fluid inclusion were observed, namely two-phase liquid-rich (type I) and two-phase vapor-rich (type II) fluid inclusions. There inclusions are predominately aqueous inclusions but can sometimes contain minor CO2 and N2 as revealed by laser Raman analysis. Type I inclusions show homogenization temperatures (Th) of 181–248 °C, with salinities of 0.5–2.6 wt% NaCl equivalent. Type II inclusions display Th of 208–249 °C, with salinities of 0.5–0.9 wt% NaCl equivalent. The occurrence of platy calcite and hydrothermal breccias, together with coexisting type I and type II inclusions which shows similar homogenization temperatures but contrasting salinities, all indicate that fluid boiling is a crucial mechanism for ore deposition at the Qiucun gold deposit. Combining the geological settings, alteration, mineralization and fluid inclusion characteristics, we propose that the Qiucun gold deposit is a low-sulfidation epithermal deposit. The estimated pressure calculated by fluid inclusion boiling assemblages corresponds to a formation depth of 200 to 260 m below paleo-surface, which is slightly deeper than the current depth. Accordingly, the denudation thickness of the overlying Nanyuan volcanic rocks is supposed to be approximately 100 m since ore deposition, which is conductive to the preservation of epithermal ore deposit. It is therefore suggested that the large area of the Daiyunshan Volcanic Basin at Dehua district is of great potential for epithermal ore exploration.

The Xiwang uranium ore deposit is one large-scale granite-hosted U deposit in the Xiazhuang U orefield in South China. Uranium orebodies occur as thin veins along the fracture zones within the Maofeng granitic pluton. Pyrite is the main sulfide mineral in the ores. Textural observation suggested that formation of hydrothermal pyrite can be divided into three stages: pre-mineralization stage pyrite (Py I), mineralization stage pyrite (Py II) accompanying with U-minerals, post-mineralization stage pyrite (Py III). In this study, in-situ sulfur isotopic compositions and trace element contents of pyrite from different stages were analyzed by laser ablation (MC-) ICP-MS methods. The δ34S values of Py I vary from −28.5‰ to −12.0‰ with an average value of −18.4‰, Py II from −15.9‰ to −10.2‰ with an average value of −12.5‰ and Py III from −22.3‰ to −14.8‰ with an average value of −19.4‰. The variations of sulfur isotopic compositions of pyrites were caused by the changes of oxygen fugacity of hydrothermal fluids. The hydrothermal fluids at the pre-mineralization stage had relatively higher oxygen fugacity (ƒO2 > 10−34). The decreasing of oxygen fugacity (to 10−36–10−35) at the mineralization stage might promote the precipitation of uraninite. The mineralization was terminated as the increasing of oxygen fugacity of hydrothermal fluids back to 10−35. Pyrite from the Xiwang deposit generally contains high U contents (up to ten thousand ppm) and very low Th contents (mostly

The Dongyang gold deposit is a recently discovered large gold deposit located within the Dehua–Youxi–Yongtai mining camp in central–east Fujian Province, southeast China. The deposit contains two individual ore sections: the northwestern Jitou section and the southeastern Dadongkeng section. Most of the mineralization is hosted by rhyolite porphyry and volcanic rocks of the Nanyuan Formation. The locations of subvolcanic intrusions in this area are controlled by NE–SW and NW–SE trending faults that are also closely related to mineralization. Detailed drillhole logging and adit mapping indicates that the deposit contains massive, polymetallic quartz–sulfide veins, and cryptoexplosive breccia type ores. Ore minerals consist of gold, electrum, silver minerals, pyrite, marcasite, and arsenopyrite with lesser amounts of sphalerite and chalcopyrite. The mineralization is hosted by quartz, sericite, illite, chalcedony, and calcite gangue and is associated with sericite and argillic alteration as well as silicification. Fluid inclusion microthermometry indicates that the inclusions within quartz from auriferous quartz–sulfide veins formed during the main stage of mineralization and homogenize at temperatures (Th) of 172 °C–217 °C (average of 192 °C) and have salinities of 0.4–2.6 wt% NaCl equivalent. These low to moderate temperatures and low salinities suggest that the mineralization occurred in an epithermal environment. The precipitation of gold mineralization at Dongyang was most likely caused by the mixing of a large amount of meteoric fluid with a smaller amount of magmatic fluid. Quartz-hosted fluid inclusions have H and O isotope compositions (δDH2O = −63.1 to −54.2‰; δ18OH2O = −5.7‰ to −3.8‰) that are indicative of derivation from a predominantly meteoric source. The S isotope values of pyrite vary from a narrow range of −3.4‰ to 0.9‰, suggesting that the S within the deposit was derived from a homogeneous magmatic source. The mineralization and alteration, gangue and ore mineral assemblages, fluid inclusion and H–O–S isotope compositions indicate that the Dongyang gold deposit is a low-sulfidation epithermal-type deposit. The estimated ore formation depth of Donyang is nearly identical to its actual depth, indicating minor denudation in the region. These results imply a great prospecting potential for other epithermal mineralization at the Dehua–Youxi–Yongtai mining camp.

The Laochang polymetallic deposit is located in the Sanjiang Tethyan metallogenic province of southwestern China. This deposit contains stratabound (and locally vein-type) Pb–Zn–Ag mineralization and underlying porphyry–skarn Mo mineralization. The stratabound Pb–Zn–Ag mineralization is characterized by massive sulfide ores composed mainly of pyrite, sphalerite, galena, and minor chalcopyrite, whereas the underlying porphyry–skarn Mo mineralization is characterized by quartz–sulfide veins comprising mainly pyrite, chalcopyrite, molybdenite, and minor sphalerite and galena. The age and origin of the stratabound Pb–Zn–Ag mineralization has long been debated, and its relationship to the porphyry–skarn Mo mineralization remains unknown. Integrated pyrite Re-Os isotope, sulfur isotope, and in situ trace element data are used here to constrain the age and origin of both types of mineralization and their genetic relationships. Pyrite related to porphyry–skarn Mo mineralization yields a Re-Os isochron age of 47.3 ± 4.8 Ma, which is consistent with a previous molybdenite Re-Os age of the quartz–sulfide ores and zircon U-Pb ages of the granite porphyry (~44–50 Ma). Pyrite from the stratabound Pb–Zn–Ag mineralization failed to yield a geologically meaningful age, but associated sphalerite and galena have a Re-Os isochron age of 308 ± 25 Ma (Liu et al., 2015), which is consistent with the Carboniferous age of the host basalts. Pyrite, sphalerite, galena, and chalcopyrite from the stratabound Pb–Zn–Ag mineralization have δ34S values (−2.1 to 0.5‰; average 0.48‰) indistinguishable from those of sulfides from the porphyry–skarn Mo mineralization (−4 to 1.9‰; average 0.52‰). Initial Os isotope ratios indicate a mainly crustal origin for both types of mineralization. The calculated (Se/S)fluid and Co/Ni values of pyrite from the stratabound Pb–Zn–Ag mineralization indicate a mixed sedimentary and hydrothermal origin, with a significant magmatic contribution. The identification of a magmatic component, Eocene sulfide mineralization, and phyllic and propylitization alteration in stratabound Pb–Zn–Ag ores indicates that the magmatic–hydrothermal component reflects the overprinting of Carboniferous volcanogenic massive sulfide mineralization by magmatic–hydrothermal fluids derived from an Eocene granite porphyry.

The carbonate-hosted Kuh-e-Surmeh deposit is located in the Zagros Simply Folded Belt, southwestern Iran. The semi-conformable tabular–like ore body lies within the northern flank of the NW–trending Kuh-e-Surmeh anticline. It is comprised of sulfide and non-sulfide base-metal ore types. The sulfide ore has a simple mineralogy and consists almost entirely of sphalerite, galena, and pyrite. Sphalerite is the main sulfide mineral having both crystalline and colloform texture. The Fe content of the sphalerite ranges between 0.04 and 8.9 wt% with the dark sphalerite zones containing higher (3.37–8.9 wt%) Fe values. Crystalline sphalerite is the main source of Ag in the sulfide ore. Galena formed simultaneously with and after sphalerite mineralization. The precipitation of pyrite occurred during the pre- to late sulfide ore mineralization phases. Anglesite is the most abundant non-sulfide mineral. Gray-colored, massive anglesite contains >100 ppm Ag, representing the main host of Ag mobilized during supergene events. On the basis geochemical data, in non-sulfide portion, there is an increase in Ag values with increasing Pb contents, independent of depth. The sulfur isotope enrichment factor (eSO 4 –primary sulfide minerals = 7.8‰) reflects the SO4−2 of the late stage gypsum formed by sulfate generated from the dissolution of primary sulfate minerals that mixed with sulfate originating from the oxidation and dissolution of sulfide minerals. Topographic relief, tectonic fracture systems, reactivation of the Surmeh Fault, and uplift related to the Zagros Orogeny all favored the establishment of arid climate conditions, providing an ideal environment for converting Zn-Pb sulfide ore to Pb-Zn-Ag non-sulfide ore.

Mineralization-related nonlinear geological processes result in the deposition of ore bodies. Consequently, the ensuing geochemical anomalies could be detected through techniques taking into account this complex processes. Power spectrum-area (S-A) method is an approach that can provide significant information for identifying geochemical anomalies associated with mineralization. In the present study, S-A was applied on soil geochemical analysis to generate favorable areas to Pb-Zn mineralization. To consider surface geochemical properties of Irankuh district, a total of 804 soil samples were collected in Gushfil-Tappeh Sorkh areas having few known deposits and the aim was to locate promising zones for further exploration activities. Samples were collected over an almost regular grid; however, there are irregularities and unsampled areas leaving holes in the sampling region. This method becomes a bit complicated and is influenced by edge effects in areas with irregular geometric shape. In order to reduce this phenomenon, radial basis function was used that has resulted in considerable improvement in final produced maps compared to other methods.

The Qixiashan Pb–Zn deposit, Jiangsu Province ( 1212011220678 ), is hosted in Huanglong Formation limestones and is one of the largest Pb–Zn deposits in the Lower Yangtze region, China, which is an important Cu–Pb–Zn metallogenic belt. Here we report in situ sulfur isotopic analyses of sulfides using LA-ICP-MS method, together with fluid inclusion data. Three types of pyrite mineralization were identified in the host rocks and ores, corresponding to three genetic stages: (1) fine-grained framboidal or colloform pyrite hosted in limestone (Py1); (2) fine-grained euhedral–subhedral pyrite (Py2) associated with brown sphalerite (Sph1), occurring as massive sulfide ores; and (3) coarse-grained euhedral–subhedral pyrite (Py3) associated with yellow–brown sphalerite (Sph2) in breccia-type or massive ores. Stages 2 and 3 constitute the main Pb–Zn-forming event. Depending on the stage in which they were formed, the sulfides exhibit different sulfur isotope values, implying different ore-forming processes. The Stage 1 Py1 was formed by bacterial sulfate reduction and yields extremely low δ34S values, in the range −14.39‰ to −3.08‰. Stage 2 Py2 and Sph1 have δ34S values ranging from 6.5‰ to 9.4‰ and from 5.0‰ to 8.3‰, respectively. Stage 3 Py3 and Sph2 have δ34S values of 1.3‰ to 3.2‰ and −0.05‰ to 2.5‰, respectively. The δ34S value of pyrite is greater than that of sphalerite for each coexisting pyrite–sphalerite pair, indicating that sulfur isotope equilibrium was reached between these minerals. The total δ34S values and formation temperatures of the ore fluids in Stages 2 and 3 were 9.4‰ and 173 °C–279 °C, and 2.3‰ and 195 °C–328 °C, respectively. The high total δ34S in Stage 2 ore fluids was a result of the interaction of magmatic fluids with marine sulfur, whereas the low total δ34S in Stage 3 ore fluids reveal that these fluids were derived from magmatic water only. Two-phase liquid-rich aqueous inclusions in Stage 2 sphalerite (Sph1) yield homogenization temperatures and salinities of 182 °C–284 °C and 0.9–8.8 wt% NaCl equivalent, respectively. Such inclusions in Stage 3 sphalerite (Sph2) yielded higher homogenization temperatures (207 °C–306 °C) and higher salinities (0.4–12.3 wt% NaCl equivalent), suggesting an increase in magmatic–hydrothermal activity from Stage 2 to 3. Such high-salinity fluids may be produced by magmatic water exsolving from a concealed intrusion beneath the Qixiashan ore district. On the basis of ore fluid temperatures and total δ34S values, sulfides in Stage 2 (δ34S = 9.4‰, T = ~250 °C) are inferred to have precipitated under conditions of pH 2–6 and log fO2 −38 to −33, and sulfides in Stage 3 (δ34S = 2.3‰, T = ~350 °C) are inferred to have precipitated under conditions of pH 2–6 and log fO2 −31 to −27. The textural, fluid inclusion, and sulfur isotopic evidence indicate that the Qixiashan Pb–Zn orebody is a hybrid deposit (rather than a SEDEX or magmatic–hydrothermal deposit) that formed by syngenetic sedimentary deposition and hydrothermal overprinting.

Exploration for mineral deposits is becoming increasingly difficult, requiring the use of novel approaches that are reliable and cost-effective. One such approach is the use of vein-hosted mineral chemistry. A number of studies have described the use of vein-hosted mineral chemistry as an exploration tool, but few have assessed a variety of factors that may have controlled the composition of these minerals. An understanding of why and how the composition of minerals varies, however, is critical to the development of robust exploration tools. This contribution combines detailed mineralogy using energy- and wavelength-dispersive spectroscopy, Raman spectroscopy, and μXRD with high-resolution laser ablation ICP-MS trace element analysis to characterize the controls on the chemistry of vein-hosted minerals, and the implications of these controls for the applicability of these minerals for mineral exploration. In and around the Marathon Cu-Pd deposit, veins consist of a complex mixture of phyllo and chain silicates, including chlorite, serpentine, saponite, and Ca-rich amphibole, whereas disseminated alteration consists predominantly of Ca-rich amphibole with lesser chlorite. The abundance of these veins is inversely correlated with the presence of mineralization. Minerals hosted in veins and patchy alteration crystallized from different fluids during temporally distinct events; the veins formed later than the disseminated alteration and from multiple stages of lower-temperature fluids. There is no correlation between the rock types that the veins are hosted by and the composition of the vein minerals, but on a very local scale, the mineral that a vein is hosted by does exhibit a compositional control. Vein minerals that are hosted by magnetite, and to a lesser extent, pyroxene, are enriched in Ti, V, and Cr compared to those hosted by plagioclase. In vein minerals that are hosted by plagioclase, the concentration of Co, Ni, and Zn increase systematically with distance from mineralization. The concentrations of Co, Ni, and Zn in vein minerals hosted by plagioclase also, however, increase systematically with distance from the contact between the mineralized pluton and the underlying Archean country rocks (i.e., the footwall contact). This suggests that the Co, Ni, and Zn in the fluids were likely derived by progressive leaching from pyroxene, olivine, and magnetite as the fluid migrated upwards through the pluton, rather than from the mineralization. Consequently, the correlation between vein-hosted mineral chemistry and sulfide mineralization are misleading. The only vein characteristic that can be used as an exploration tool at Marathon is the inverse correlation between vein density and zones of sulfide mineralization. This study demonstrates that the application of vein and mineral chemistry to mineral exploration needs to be carried out in the context of a careful assessment of the variations and controls on mineral chemistry from the scale of the deposit and its surrounding rocks down to the grain-scale.

Mountain topography can cause both pressure-gradient driven advective flow and temperature-gradient driven convective flow. Compared with the pressure-gradient driven advective flow, the temperature-gradient driven convective flow can last long enough to enable the hydrothermal ore-forming system to reach a steady state. This paper is focused on the numerical modeling of a hydrothermal ore-forming system, in which the temperature-gradient driven convective flow is the main driving force of orebody formation and mineralization. A generic model, which can be viewed as a generalized geological model, is used in the numerical modeling. To simulate the chemical aspects of the hydrothermal ore forming system, a simplified chemical process associated with the Broken Hill type Pb-Zn deposit is considered in this study. The related numerical results demonstrated that: (1) The mountain topography plays an important role in controlling Pb and Zn mineralization distribution patterns in a hydrothermal ore-forming system; (2) The mixing of the reactive sulfide and sulfate fluids can be enhanced by the temperature-gradient driven convective flow; (3) If the duration of mineralization time is known, then the computed mineral precipitation rate can be used to predict the average (weight) grade of a mineral in the hydrothermal ore-forming system. Similarly, if the average (weight) grade of a mineral is known from a mining site, then the computed mineral precipitation rate can be used to estimate the duration of mineralization time in the hydrothermal ore-forming system.

Magmatic and hydrothermal quartz populations related to the Late-Variscan Zinnwald/Cínovec Sn-W-Li greisen-type deposit in the Eastern Erzgebirge/Krušné Hory (German/Czech Republic) were studied in terms of trace element contents and growth structures visualized by cathodoluminescence. The sample suite represents different populations of hydrothermal greisen quartz and magmatic quartz of the granitic host collected at a 600-m long, lateral section crosscutting the northern part of the deposit at the 750-m level. The studied quartz populations are characterized by generally low concentrations and low variation of Al and Ti indicating relatively constant crystallization conditions (temperature, pressure and fluid chemistry) during ore precipitation. Magmatic and hydrothermal quartz are distinguished by their Al, Ti, Li and Ge concentrations and ratios. Magmatic quartz has commonly higher Al (>100 ppm) and Ti (>3 ppm) compared to hydrothermal quartz. The Ge/Al ratio in quartz increases systematically from high to low formation temperatures (664 to ~400 °C = temperature range including published data and our estimates) whereas Ti decreases. The Zinnwald albite granite (mineralization host), an albite-rich alkali granite, and massive quartz-zinnwaldite greisen contain both magmatic and hydrothermal quartz populations which are distinguishable by their Ge/Al weight ratio: magmatic quartz has a Ge/Al ratio of 0.008. Hydrothermal vein quartz related to the Sn-W mineralization (Flöze = flat veins and Morgengänge = steep veins) does not show systematic trace element variations along the sampling profile indicating that no significant chemical gradients (in lateral direction) in the ore forming fluid existed. The uptake of Li in the quartz lattice is limited by the incorporated Al although the Zinnwald/Cínovec magmatic-hydrothermal system was strongly enriched in Li. The calculated crystallization temperatures of quartz of the Sn-W mineralization applying the TitaniQ thermobarometer reveal crystallization temperatures ranging from 575 ± 48 °C (albite granite), 612 ± 12 °C (stockscheider), 610 ± 23 (massive greisen), 536 ± 77 °C (flat veins), to 516 ± 58 °C (steep veins) confirming in general early estimations based on fluid and melt inclusion studies. In economic terms, the hydrothermal quartz (flat and steep veins) with an average total trace element content of 128 ± 56 ppm has intermediate chemical quality and can serve as a by-product if colour sorting and other processing steps are applied. Rock-forming quartz of albite granite and massive greisen with an average total trace element content of 233 ± 127 ppm has medium quality and the disadvantage that quartz contains a high amount of contaminating mineral inclusion, which will be challenging to remove by processing.

The Hadamengou gold deposit, which is located in a high-grade metamorphic terrane at the northern margin of the North China Craton, is characterized by K-feldspar-quartz vein gold mineralization. The 40Ar/39Ar dating of hydrothermal K-feldspar indicates that the mineralization formed over 45 Ma commencing at 243.5 ± 1.3 Ma and ending at 199.0 ± 0.8 Ma. The Pb, C and O isotope compositions and the geochronology of the gold-bearing K-feldspar-quartz veins imply a close genetic association between the gold mineralization and alkaline magmatism, which are both products of the Indosinian alkaline magmatic event caused by the extensional tectonic setting that prevailed during the late Hercynian collisional orogeny. We propose an Indosinian phase of gold mineralization in addition to the abundant mineral deposits formed during the Yanshan Epoch.

The Zinkgruvan deposit is the largest stratiform Zn-Pb-Ag mineralization in Sweden. The most recent genetic model attributes ore formation to the discharge of oxidized, near-neutral pH, metallifero ...

In China, bauxite is mainly of the karst type. Karst bauxite deposits in Central Guizhou are widely distributed in the Qingzhen, Xiuwen, and Zunyi districts. The Xiaoshanba deposit is located in the Xiuwen district and is hosted in the Lower Carboniferous Jiujialu Formation. It shows parallel unconformity with the overlying and underlying strata. The main chemical contents of the bauxite ore in the Xiuwen district is Al2O3 (55.7 to 73.5 wt%), followed by SiO2, Fe2O3, TiO2, CaO, MgO, S, P, etc. There are obvious enrichments in rare earth elements (REEs) and immobile trace elements (such as Ti, Nb, Zr, Hf, Ta, and Th) in the Al-bearing rocks. The mass change calculation (MC) is an effective means of investigating the relative mobility of elements. Here we present the multiples of mass change calculation (MMC), which represents an improvement over the MC, and is effective for element mobile investigations. The MMC results for REEs of the Xiaohsanba Al-bearing rocks showed grouping phenomenon, in which REEs were divided into four groups (Group A: La–Ce–Pr–Nd; Group B: Pm–Sm–Eu–Gd; Group C: Gd–Tb–Dy–Ho, and Group D: Er–Tm–Yb–Lu) and showed different fractionation trends in the MMC curves. The tetrad characteristic of the REEs (tetrad effects) most likely induced the special grouping phenomenon. During bauxite mineralization, REE fractionations caused by mineral control, especially the widespread distribution of accessory minerals that are rich in REEs such as Ti-dioxide minerals (i.e., TiO2 such as rutile and anatase) and zircon, and water–rock interactions resulted in the REE grouping phenomenon in the Xiaoshanba profile. The majority of these immobile elements tend to concentrate in the accessory minerals of bauxite, and barely any elements (except Li and Ga) seem associated with the ore-forming minerals. For instance, Ti-dioxide minerals played an important role in the accumulation of some elements, such as Ti, V, Nb, and Ta. Another important mineral was zircon, which is rich in Zr, Hf, and Th, etc. In general, there were two main factors that influence the content of immobile elements in the karst bauxite profile: (a) the chemical composition of the precursor rock (the higher the content of immobile elements in the parent rock, the higher the content of accessory minerals and immobile elements in bauxite), and (b) the weathering degree of the precursor rock (the stronger the degree of weathering, the higher the content of accessory minerals and immobile elements in bauxite).

Background separation from anomalous populations in the polymetallic mineralization is a problematic issue in geochemical exploration. This study focuses on the applications of fractal modeling, correspondence analysis (CA), classical principal component analysis (PCA), and PCA method based on centred log-ratio (clr) transformation for the multi-elemental evaluation of geochemical data in Glojeh polymetallic mineralization, NW Iran. A Concentration-Number (C-N) multifractal modeling was applied to delineate individual self-similar patterns for elemental distributions simultaneously in terms of Au, Ag, Cu, Pb, and Zn. The differences between fractal dimensions and clockwise angle between fitted lines in the C-N Log-log plots could lead to evaluate mineralized rank corresponding to Au ≥ Ag ≥ Pb ≫ Cu ≈ Zn. A more comprehensive evaluation via CA and PCA of clr-transformed data could facilitate the vein structure identification in high-dimensional data. The PCA results of clr-transformed data revealed the potential intensification trend of (Pb, Ag, As, Te, Au) > (Mo, Zn, Be, Cu) > W > (S, Cd), that is more consistent with fractal and CA approaches. The closure effect problem was overcome by the clr transformation, and the total variance explained by the first factor increased from 28.2% in classical PCA to 43.7% in clr transformation. Accordingly, As, Sb and Cd were considered as potential pathfinder elements for Au in Glojeh deposit. The ability to handle zeros in the data matrix and determining an elemental eccentricity as a criterion are the advantages of CA method, while loading factors spread in a full circle and providing subcompositional coherence are the competitive advantages of PCA (calculated according to log-ratio transformation). However, the CA and PCA based on Log-Ratio transformation techniques showed significant potential to draw an inference in such deposits.

The ordinary singularity mapping (OSM) approach utilizing regular square window and ignoring the representativeness of geochemical samples may not characterize the anisotropic geochemical anomaly features. To overcome the abovementioned drawbacks, a spatially weighted singularity mapping (SWSM) method was developed. The SWSM approach focuses more on the spatial anisotropy and the representativeness of samples considering the ore-controlling factors in the mineralization process. In this case study, the stream sediment geochemical data of Ag, As, Pb and Zn, which are the main ore forming elements of epithermal Ag and Pb-Zn polymetallic mineralization in northwestern Zhejiang distinct, China, have been used to illustrate implementation of the SWSM method. Using the spatial weighting factor associated with NE-SW ore-controlling faults system, anisotropic singularity index values for each of the four elements were estimated. Principal component analysis (PCA) was then applied to the anisotropic singularity index to obtain a comprehensive geochemical anomaly. A strong spatial correlation between the integrated anomalies and the known Ag and Pb-Zn polymetallic deposits have been detected through weights-of-evidence modeling. Finally, a comparison of the hybrid geochemical anomaly identification methods including SWSM-PCA (PCA applied to the estimated anisotropic singularity index), OSM-SWPCA (spatially weighted PCA applied to the estimated ordinary singularity index), and OSM-PCA (PCA applied to the estimated ordinary singularity index), has been discussed. The main conclusions are: (1) the SWSM method is applicable for identifying the geochemical anomaly incorporating both singularity and anisotropy that are two significant properties inherent from a nonlinear mineralization system; and (2) compared with the other two hybrid methods, the SWSM-PCA approach provides a better tool to delineate geochemical anomalies for predicting locations of potential mineral deposits.

Recognition of weak geochemical anomalies from background is an overlooked issue in the interpretation of regional geochemical data used to define the exploration targets in the areas covered by deserts, regolith, or vegetation. In this study, the log-ratio transformation methods were used to account the compositional character of the geochemical data. A robust compositional factor analysis (CoDa-FA) was utilized to identify the ensembles of elements related to mineralization. Multifractal singularity analysis and the mean ± 2 standard deviation (mean ± 2STD) method were used to identify the Au mineralization-related geochemical anomalies in North Qaidam Gobi Desert landscape area. The results show that CoDa-FA for the centered logratio-transformed geochemical data can accurately recognize the geochemical compositional assemblages related to Au and Pb-Ag mineralization, representing the orogenic Au mineralization and hydrothermal-type Pb-Ag mineralization, respectively. The geochemical anomalies delineated by the mean ± 2STD method showed weak signals in SE Shuangkoushan. However, singularity mapping is efficient for enhancing and outlining the weak anomalies in a low background relative to the mean ± 2STD method. The anomaly maps determined by singularity mapping show good ore-potentiality in SE Shuangkoushan, and many Au and Pb-Ag ore bodies have been found in the anomalous areas. The results would not only be useful to guide anomaly verification and potential exploration targets in the North Qaidam metallogenic belt, but also raise the awareness of reanalyzing those weak anomalies in a covered area.

The Panasqueira Mine is a world-class W-Sn-Cu vein-type deposit, currently exploited by Beral Tin & Wolfram Portugal, which has promoted the sampling and analysis of a series of chip-rocks covering an approximate area of 8 × 3 km over the Mine prospect and adjacent areas, with the objective of identifying geochemical signatures related to the Panasqueira granite emplacement and thus targeting new areas with potential W-Sn mineralization of the same ore-system. The geometry of the Panasqueira granite is still unknown but some drill-cores and geophysical techniques provided indications of its extension and presence beyond the current mine exploitation permit. The opportunity of using whole-rock samples, jointly with the current knowledge of the complex mineralizing stages and related geochemical signatures, allowed the proposal of empirical elemental ratios and exploration indexes, which combined with multifractal models for anomaly characterization and singularity mapping, provided a fairly complete and coherent picture of different anomaly patterns for Sn, W, and Cu. These patterns not only target the current exploited areas over the Panasqueira Mine but, more importantly, sustain the occurrence of additional anomalies that can potentially increase the current reserve estimation and consequently extend the mine's life-span. Most elements showed a single anomaly threshold, as W at 1.8 ppm, but others showed two, including Sn at 2.3 and 13.6 ppm, the latter notably close to the empirically deduced one of 15 ppm. The evidence for the extension of the current anomalies also relies in the singularity and anomaly mapping based on the different thresholds using associated elements, such as Nb, Ta, and Ti for W, F, Li, element ratios, for Sn, and ISW and IBM indexes.

Garnierite represents a significant nickel ore in many lateritic Ni deposits worldwide. To gain a better understanding of its nature and origin, a well-developed garnierite-hosting transect from the Kolonodale area of East Sulawesi, Indonesia, has been investigated using field geology, mineralogy and geochemical data. Garnierite occurs mainly in veins in the lower saprolite of a serpentinite-derived regolith. Mineralogically, it can be determined as an intimate mixture of Ni-rich serpentine-like (lizardite-Nepouite) and talc-like (kerolite-pimelite) phases. Results of EMP analyses indicate that Ni is preferentially enriched in the talc-like phases rather than the serpentine-like phases. A sequential precipitation of mineral phases progressively enriched in Ni and Si to form garnierite during weathering is suggested. The Ni-lizardite (2.63–8.49 wt% Ni) with elevated Fe (4.02–6.44 wt%) may have been inherited from saprolite in a first instance and enriched in Ni by cation exchange processes. Newly precipitated minerals are kerolite-pimelite (7.84–23.54 wt% Ni) and then followed by Ni-free quartz. Minor amount of Nepouite (23.47–28.51 wt% Ni) occur in laths along shrinkage cracks of previously formed minerals, indicating a late stage paragenetic sequence. With emphasis on a hydrologic consideration, indicators of a preferential flow regime are identified in the garnierite-hosting regolith, including: (i) non-uniform pattern of the garnierite field occurrence, (ii) syn-weathering active nature of the garnierite-hosting structures, (iii) close relationship between the garnierite occurrence and vertical Fe Mn oxides pipes as well as Fe Mn oxides patched areas, and (iv) specific physico-chemical property of the garnierite location with higher organic matter concentrations but lower pH values compared to surroundings. It is proposed that the origin of garnierite is closely linked to a preferential flow of oversaturated solutions through accessible conduits in the regolith. Garnierite features as colloidal nature, high organic matter and low pH are key-parameters in metal transport and deposition.

The geochemical signatures associated with seafloor massive sulfide mineralization recorded in pumiceous sediments in the Iheya North Knoll, middle Okinawa Trough, are examined. The key purpose of this research is to establish a method for the geochemical exploration of massive sub-seafloor volcanogenic sulfide deposits. Presently, the discovery of sub-seafloor mineralized zones is strongly method-oriented, including direct sampling and observation of ores. The utilizing of conventional method is even more complicated in the case of buried ore bodies. The well-characterized sub-seafloor hydrothermal systems of the Iheya North Knoll, containing delineated recharge-discharge zones, provide an opportunity to both verify and develop geochemical exploration methods. In this study, whole-rock geochemical data are obtained from samples taken from recharge and discharge zones, and from migration zones between these two regions. The resulting geochemical signatures are difficult to interpret due to variations in mineralization as well as magmatic effects. Normalization of the compositions of samples obtained from the discharge and migration zones relative to the composition of the recharge zone reveals the relationship between the average normalized values of rare-earth and ore-related elements. This method successfully distinguishes enrichment due to magmatic differentiation and mineralization. The approach described herein also allows the location of the discharge zone to be inferred, even in the case of a thin covering of sediment above the seafloor. This technique could allow surveying via systematic or grid sampling using dredging and/or piston-coring methods, both of which are simpler and less expensive than conventional methods.

The chemical variation of white mica, in particular fluid-mobile elements typically associated with base-metal mineralization, in the host rock alteration haloes enveloping massive sulfide deposits of the Bathurst Mining Camp is constrained by LA-ICP-MS. White mica from examined deposits hosts Tl (up to 744 ppm), Sn (up to 1069 ppm), Hg (up to 524 ppm), Sb (up to 3650 ppm), As (up to 17100 ppm), and In (up to 524 ppm). The occurrence of Tl, Sn, Sb, and probably As is predominantly controlled by crystal-chemical substitution, although the occurrence of micro- to nano-scale inclusions of other phases cannot be disqualified. White mica immediately adjacent (within 50 m) to the massive sulfides in both the hanging wall and footwall is enriched in Tl, Sb, Hg, and variably enriched in As, Sn, In, Se, Bi, and Cd and can be used to vector toward mineralization. In distal zones up to several hundred meters distant, the variation of fluid-mobile elements in white mica is recognized in lower concentrations, but detectable up to several hundred meters away from the ore horizons. Here, variation in the ∑ Tl + Sb + Sn + Hg can serve as a vectoring tool. This methodology can potentially serve as a complementary tool to other geochemical and geophysical exploration methods in prospecting for buried volcanogenic massive sulfide mineralization.

The Athabasca Basin in northern Saskatchewan, Canada, hosts the world's largest high-grade U resources near the unconformity between sandstones and underlying crystalline basement rocks. Finding U deposits is difficult in the interior of the Athabasca Basin where the sandstone cover can reach 1400 m. This study uses the lithogeochemistry of sandstones obtained from drill cores to identify elements associated with U using principal component analysis (PCA) from three areas; samples directly above the Phoenix U deposit, those in Denison Mine's Wheeler River property and background areas in the basin. The sandstone data from the Wheeler River property shows that U is positively associated with Y-Cu-Zn-Na-W-Co-Ni-B-Mg-HREEs-Cr-Sc-Mo-V-LREEs due to uraniferous hydrothermal alteration. In contrast, the principal components derived from the lithogeochemistry of sandstones far from known mineralization in the basin shows that U is positively associated with Th-Ti-Zr-Hf, suggesting that U is hosted in refractory detrital minerals. Linear discriminant analysis (LDA) and random forest (RF) analysis based on principal components of elements associated with U show three classes of sandstones with clear discrimination between samples; those above the Phoenix ore (Class Phoenix), in the Wheeler River (Class Wheeler River), and regional background (Class Regional Background). The class Phoenix contains most of the sandstone samples overlying the Phoenix deposit and a few samples in the Wheeler River property. This study shows that PCA, LDA and RF are able to detect geochemical footprints of uraniferous hydrothermal alteration >500 m from the ore and differentiate sandstones spatially associated with the mineralization from those in barren areas. Based on the performance of the two discrimination methods, we suggest that RF is a preferred method as it better differentiates altered sandstones from regional background samples. The classification analysis used in this study may be useful in U exploration in Athabasca Basin and other sedimentary basins.

Fluid mixing is an important process in the formation of many hydrothermal vein-type deposits. Here, we present evidence from hydrothermal fluorite-barite-quartz veins with Pb-Zn-Cu-(Ag)-sulfides and associated mineralization, indicating that mineral precipitation was initiated by mixing of fluids derived from multiple sources, including mixing between more than two end-member fluid compositions. Based on our observations, we relate the diversity of the hydrothermal veins of the Schwarzwald mining district in terms of mineral assemblage and fluid inclusion chemistry to the disturbed and transient geological environment during ongoing rifting. Literature data on the regional geology, current groundwater reservoirs, formation processes and hydraulic features are augmented by new fluid inclusion analyses from post-Cretaceous, hydrothermal vein minerals including microthermometry, crush leach, Microraman and LA-ICP-MS analyses of individual fluid inclusions. Petrography and microthermometry of fluid inclusions show complex sequences of alternating fluid signatures within different growth zones of one crystal. High (20–26 wt% NaCl + CaCl2), moderate (5–20 wt% NaCl + CaCl2) and low salinity ( By defining end member fluids and their proportions, we show that nearly all fluid mixtures are saturated with respect to barite. By contrast, fluorite-saturated fluids can only be modelled by mixing of a basement brine with fluids from Triassic sandstones. All fluid mixtures are strongly undersaturated with respect to galena, chalcopyrite and sphalerite, the most commonly observed ore minerals in the hydrothermal veins. As the calculated fluid mixtures are typically relatively oxidized and contain high sulfate/sulfide ratios, precipitation of sulfides was probably related to short-lived reduction events caused by an influx of hydrocarbons, by reactions with graphitic wall rocks in fractures by sulfidation related to fluid-rock reaction with the surrounding host rocks or an external influx of hydrocarbon-bearing fluids. The multi-aquifer fluid mixing processes involving aquifers of different chemical and physical constitution were triggered by brittle deformation related to rifting of the Rhine graben. This appears to be essential for the formation of a large number of mineralogically diverse hydrothermal ore deposits.

Sphalerite in the Daliangzai Pb-Zn deposit, one of the hundreds of Pb-Zn deposits in South China, was chosen as an case study for geochemical research using in situ laser-ablation inductively coupled mass spectroscopy analysis. Many kinds of minor and trace elements were investigated and subsequently treated by multivariate statistical analysis, especially principal component analysis (PCA). These research works indicate that the enrichments of Cu, Ga, As, Cd, Ge, Ag, Sb, Pb, Ni in sphalerite from different depths of the super-large No. I orebogy mutually imply a lower-temperature hydrothermal process dominating the mineralization in Daliangzi Pb-Zn deposit. A small temperature gradient controls the almost similar element distribution patterns indicated by the sphalerite samples which were enriched in Fe, Mn, Co, Cu, Ge, Ag, and Cd in the lower orebody whereas those in the upper orebody were enriched in Fe, Mn, Co, Cu, Ge, Ag, Cd, plus Ga and In. The enrichment of Fe in sphalerite matrix assists the incorporation of many metals, for example, Mn, Co, Ge, and (Ag + Sb). Some important coupled substitutions are discovered: 4Zn2 + ↔ 2Fe2 + + Ge4 + + □ (where □ denotes a vacancy), 2Zn2 + ↔ Ag+ (Cu+) + Sb3 +, and 3Zn2 + ↔ 2Ag+ (Cu+) + Ge4 +. Moreover, tetrahedrite–tennantite and jordanite–geocronite solid solution series distinctly feature the sphalerite formed in Daliangzi Pb-Zn deposit which differentiates it from other metallogenic types, especially those related to magmatic activities. Results of PCA work to the selected sphalerite samples from deposits of skarn, syngenetic massive sulfide, MVT, special Jinding and Daliangzi reveal that significant differences, which are mainly defined by the concentration of Fe, Mn, Co, and depleted In, exist in the composition of sphalerite from different deposit types and lie along a single dimension of PC2*. Such a conclusion bases a framework established by PCA and proposed to study the base-metal deposit types and the relevant metallogenic process that are typical for deposits located in South China.

The Central Mineral Belt (CMB) in Labrador hosts several enigmatic U ± base ± precious metal showings, prospects, and deposits. Multiple mineralization styles occur within different host rocks, which has led to a variety of ore system models to be proposed. Here, unsupervised machine-learning (principal component (PCA) and targeted cluster analyses) applied to quantitative LA-ICP-MS trace element maps of uraninite were used to understand genesis the U systems in the CMB. Trace element mapping, PCA and cluster analysis indicate that: i) the largest source of data variance in uraninite from the occurrences is related to Th, REE, Zr, Hf, As, V and Ba contents, and ii) there are distinct uraninite compositions at the Two-Time deposit, Near Miss and Anomaly No. 7 mineral occurrences, not recognized from petrographic studies or major element chemistry. Trace element chemistry indicates that uraninite precipitated from fluids under (1) high-temperature magmatic and/or metasomatic conditions (> 350 °C; Dandy prospect; U/Th = 107 and ΣREE = 0.9 wt%), (2) low-temperature ( In addition to the genetic constraints, PCA results and normalized REE patterns also show that the CMB uraninites have distinct geochemical signatures. Combining petrographic studies, trace element mapping, and unsupervised machine-learning unravelled cryptic chemical variations in key minerals that can guide future mineral exploration in the district. In the CMB, these chemical signatures provide insights on the evolution of U-rich fluids, in particular the presence of multiple fluid sources that evolved through a complex tectono-magmatic history.

In this study, the styles, types, and degrees of hydrothermal alteration associated with Pb-Zn-Cu-Ag-Au epithermal deposit systems in the Tarom-Hashtjin metallogenic province are evaluated using petrographic studies, as well as mass changes and molar elements ratios (MER), in order to examine regional exploration implications. The MER plots show that the hydrothermally altered rocks were most affected by various types of K-metasomatism, mainly characterized by K gains and Na and Ca losses. The intensity of K-metasomatism is related to precious and base-metal mineralization, showing increasing K trends toward the ore veins. The alteration index (AI) and chlorite-carbonate-pyrite index (CCPI) reveal that argillic, sericitic, and propylitic alteration types are the main zones of alteration surrounding ore veins indicating that AI increases and CCPI decreases toward more proximal to the structures linked to these ore systems. Determination of mass changes in altered rocks surrounding selected epithermal deposits suggest Si, K, and Al gains and Na and Ca losses increasing in intensity toward ore veins, consistent with alteration zoning from the silicic and K-metasomatic (sericite and argillic) inner zones to the propylitic (Fe-rich chlorite alteration) outer zone typical of epithermal ore systems. Data from this study show that the intensity of K-metasomatism in the acidic rocks is greater than in the intermediate and mafic rocks, where it is related to high to intermediate sulfidation epithermal systems. We suggest that exploration can be focused on highly altered volcanic rocks (especially andesite-dacite) with both high intensity of K-metasomatism and higher Pb, Zn, Ag, Au, Ba and Rb and lower Sr.

The Ertsberg-Grasberg district hosts the world's largest Cu-Au( Mo) skarn system. The mineralization is related to the Pliocene Ertsberg- and Grasberg intrusive complexes, which intruded the Jurassic-Cretaceous Kembelangan Group siliciclastics and Cenozoic New Guinea Limestone Group. Despite previous studies, elemental migration across the porphyry-skarn system and across the different ore stages is still unclear. Here, we attempt to tackle this issue by integrating ore deposit geology, alteration/mineralization paragenesis, whole-rock geochemistry of the Ertsberg granitoids and carbonate wallrocks, together with spatial mapping of hydrothermal minerals and target/pathfinder trace elements at the Deep Mill Level Zone of Ertsberg. Ores at Ertsberg are mainly skarn-hosted, whose formation comprises five stages: (I) prograde skarn; (II) retrograde alteration; (III) massive anhydrite replacement; (IV) late hydrothermal veining; (V) supergene alteration. Massive magnetite and main Cu Au mineralization occurred in Stage II and III, respectively, although minor Cu mineralization persisted to Stage IV. The Ertsberg granitoids have medium SiO2 and high Al2O3 contents, and consist mainly of (quartz-)monzonite and minor (monzo)diorite. Least-altered samples have upper crust-normalized enrichments in certain large ion lithophile elements (LILEs, e.g., U and K) and depletions in all high field strength elements (HFSEs, e.g., Ti, Y, and Yb). The samples are fresh to moderately-altered, featured by garnet-diopside skarn and/or porphyry-style (potassic, propylitic, phyllic) alterations and anhydrite replacement. Elemental mass balance calculation indicates that the porphyry-style alteration zones are featured by feldspar destruction and the accompanying alkali depletions, although the loss of K Rb (in potassic and phyllic zones) and Ca-Ba-Sr (in propylitic zone) are balanced by their respective capturing in secondary K-feldspar-mica and actinolite-epidote-anhydrite. Decarbonation of the dolomitic wallrocks likely released Mg-Ca-Sr, which facilitated the subsequent forsterite-diopside exoskarn and anhydrite alteration. The enrichments of various ore-related target/pathfinder elements in these altered samples are consistent with their mineralized nature, e.g., Fe Mn (magnetite), Cu-Fe-Bi-Se-Te (bornite), Mo Re (molybdenite), Au-Ag-As-Bi-Te (auriferous pyrite/arsenopyrite), Zn-Fe-Mn-Sn-In (sphalerite), and Pb-Ag-Bi (galena). Alteration mineral and target/pathfinder elemental distribution patterns show that the ore fluids were likely originated from the porphyry hydrothermal (potassic) centers near the Ertsberg pluton margin. The fluids then spread out from the potassic centers, forming the surrounding propylitic zone, and migrated along the largely NW-SE-oriented intrusive contact and fault zones. This formed the endoskarn in the Ertsberg pluton, the forsterite-diopside exoskarn in the Waripi Formation dolomite, and the garnet-diopside exoskarn in the Ekmai Formation limestone/calcareous sandstone-siltstone. As the hydrothermal system started to wane, the prograde skarn formation is partially overprinted/enveloped by retrograde serpentine and actinolite/tremolite-epidote-chlorite alterations, and then by magnetite mineralization and massive anhydrite replacement in the carbonate wallrocks. The texturally-destructive skarn formation, and the dissolution of carbonate wallrocks and hydrothermal anhydrite were likely pivotal in creating the highly-fractured Broken Zone, which served as a structural trap for the high-grade Cu-Au-Mo ore deposition.

The Zarshuran gold deposit as sediment-hosted Carlin-type has a total reserve of 120 million metric tonnes and an average grade of 3.5 g/t Au. The dominant hydrothermal alterations associated with gold mineralization are argillic and silicic as well as decalcification of the carbonate host rocks. The exploration geochemistry was applied to characterize the mineralization in the subsurface and peripheries of the open-pit mine at Zarshuran in order to enhance the proved reserves of the gold ores. A sampling network of a 10 × 10 m grid (n = 1720) was applied to almost unweathered surface outcrops to determine the primary geochemical haloes in the study area. Initially, the cut-off grades utilized in the exploratory data analysis were applied to identify the threshold values of the trace elements with lognormal distribution. Then, the central log ratio transformation was used to determine the robustness against outliers to characterize the closure problems with compositional data during Principle Component Analysis (PCA). The supra-ore and near-ore geochemical haloes are recognized by the indicator elements like As-Sb-Hg-Te-Au-Ag-Fe-Mn-Ba-F which are associated with mineral assemblages such as arsenical pyrite, orpiment, realgar, cinnabar, barite, and fluorite. The sub-ore geochemical haloes are characterized by index element association like Cu-Mo-Bi-W-Sn-Co-Ni-V-Cr. The ores at Zarshuran are enriched in Au, As, Sb, Ag, Te, Tl, Zn, Pb, and F but depleted in Cu, W, and Sn, as were observed in many other Carlin-type gold deposits. The enrichment factor of indicator elements (except S, Ag, and Sb) gradually decreases in value from the highly altered and mineralized zones (in proximity of the mine) toward the zones with least alteration and mineralization (in the distal parts of the mine). According to PCA analysis, two main types of ore mineralization occurred at Zarshuran, (1) Au mineralization associated with As, Sb, and Hg, and (2) Cu-Zn-Pb base-metal mineralization related to Ag. The ore-forming index was used to determine the primary axial haloes in both shallow ( −120 m) levels. The results of this study show that the main ore body may extend eastwardly and downwardly to greater depths, as was verified by the data obtained from diamond drill cores in the eastern part of the mine.

Gallium (Ga) is known as the backbone of the electronics industry, but its independent mineralization is rarely found in nature. The discovery of large Ga-bearing coal deposits suggests that the coal-bearing series can be used as the main source for the future development and utilization of Ga, and the organic matter of coal may play an important role in the aggregation of Ga. Based on the analysis of geological prospecting and study of coal samples, this paper discussed the distribution, occurrence, and enrichment of Ga in the Middle Jurassic coals of the Muli coalfield. The results demonstrate that coals from eastern mines are enriched in Ga, where the Ga concentration reaches the propositional cut-off grade (30 μg/g). The Ga concentration increases along with an increasing distance from the sediment source; the areas with the highest Ga concentration are the deposit-center and the location with the highest content of mudstone. Sediments were derived from the acid and intermediate magmatic rocks of the Tuolai Mountain in the northeastern Muli coalfield, partly from the crust weathering of the Upper Triassic formation. Ga was first transported in the form of colloids or solutions and finally deposited in authigenic kaolinite. In addition, the positive correlation between the Ga concentration and the inertinite constituents of coal indicates that fibrous tissue might be the dominant component absorbing Ga and that organic matter had a positive impact on the migration of Ga to peat swamps. Ga is prone to deposition in partially oxidized, acidic coal-forming environments with strong hydrodynamic forces. Hydrothermal activity might also stimulate the enrichment of Ga in coal.

Geochemical exploration plays a significant role in mineral exploration because it can help lead to the discovery of various types of mineral deposits. For a given geochemical exploration dataset, a number of elements are typically measured synchronously. Of these elements, several are associated with mineralization that can guide exploration, and the remaining elements may reflect other geological processes or events. How to identify elemental associations that are spatially correlated with locations of mineralization using spatial statistics, was addressed in this study. To do so, a hybrid method that combines the multifractal spectrum and the receiver operating characteristic (ROC) curve was applied. The spatial distribution characteristics of geochemical patterns were first investigated through multifractal analysis, in which enriched elements can be identified with a symmetry index R of > 1. These enriched elements were further examined using ROC to evaluate the spatial correlations between geochemical patterns and locations of mineral deposits. The elements with areas under curve (AUC) and ZAUC values obtained from the ROC curve > 0.5 and 1.96, respectively, which represent strong positive spatial relationships with mineralization, comprise the identified elemental association for locating mineralization. This hybrid method provides objective selection criteria for elemental associations related to mineralization based on spatial statistics. A case study was conducted in southwestern Fujian Province, China to demonstrate the capability of the proposed method. An integrated geochemical map based on the identified elemental association related to skarn-type Fe mineralization was produced and can be employed as a reference in further mineral exploration in the study area. However, the geological environment for the formation of mineralization should be considered in conjunction with the proposed approach.

The giant Zijinshan Cu-Au deposit in the Zijinshan orefield, Fujian Province, southeastern China, is the first high-sulfidation epithermal deposit identified in mainland China. The Cu and Au orebodies occur as veins and pods in the NW-trending faults and breccias zones. Intensive and pervasive alteration is characterized by downward and outward zoning from intensively leached silicic alteration (or vuggy quartz, Q), through alunite-quartz-pyrite alteration (advanced aragillic alteration, Q-Alu) and the quartz-alunite alteration overprinting the sericite alteration (Q-Alu-Di-Srt), to sericite (or phyllic) alteration zone. Gold mineralization mainly occurs in the silicic alteration zone, while the copper mineralization is confined in the alunite-quartz alteration zone. On the basis of detailed petrographic study, an early porphyry type mineralization stage, characterized by chalcopyrite-bornite-molybdenite-pyrite-sericite assemblage is recognized at Zijinshan, which is subsequently and strongly overprinted by the sulfate alteration and high-sulfidation Cu-Au mineralization stages. A supergene stage is also identified at shallow depth of the deposit, with gold largely enriched but copper commonly leached. The ore-forming fluids related to the early sericite alteration and possibly porphyry type mineralization are high-temperature, high-salinity magmatic water, characterized by the presence of the halite-bearing inclusions. The CO 2 -H 2 O (C-type) inclusions are mostly vapor-rich and abundantly identified in the samples with advance argillic alteration (alunite alteration). They are regarded to be the buoyant vapor phase by fluid boiling of a single-phase, low- to moderate-salinity magmatic fluid at depth, where a separated saline phase and related porphyry mineralization might be expected. A group of secondary inclusions coexisting with enargite grains are recognized in the samples with alunite alteration and suggested to be trapped from the ore-forming fluids of the Cu-Au mineralization stage. The total homogenization temperatures and salinities of the secondary inclusions are below 300 °C (peaking at 260–280 °C) and under 10 wt% NaCl eqv., respectively. Intensive fluid boiling is the major mechanism for the formation of the giant high-sulfidation Cu (covellite-, digenite-dominated) orebodies in the Zijinshan deposit. It is a deep-seated high-sulfidation epithermal deposit according to the estimated depth of 1.4–2.1 km from the C-type inclusions in quartz grains from the alunite alteration zone. By fluid inclusion mapping of a nearly NW-trending cross section profile, the isotherms are extrapolated using the average total homogenization temperatures and the possible heat source is suggested. It is indicated that the heat source and possible concealed porphyry mineralization nearly coeval to the high-sulfidation Cu-Au mineralization at Zijinshan might be located at the southeastern Zijinshan deposit or the northern area between the Zijinshan and Wuziqilong deposits, where deep drilling is encouraged.

Mississippi Valley-type (MVT) Zn-Pb mineralization in the U.S. mid-continent has formed in numerous widely dispersed trace occurrences and in a few large ore deposits that have been mined. Based on similarly high fluid inclusion salinities and high homogenization temperatures relative to inferred burial depth, the trace MVT occurrences and MVT ore deposits may be genetically related by having precipitated from the same regional groundwater flow system mobilized by Pennsylvanian-Permian tectonism. The purpose of the present study was to test the robustness of this inferred genetic relationship by characterizing the Pb and S isotope composition of trace MVT occurrences in light of the much more thoroughly studied MVT ore deposits. Lead and sulfur isotope compositions have been obtained for trace MVT occurrences from three broad regions of the U.S. mid-continent: the Forest City basin (FCB), the Illinois basin (ILB), and the Greater Upper Mississippi Valley (GUMV) region. Lead isotope compositions of trace MVT occurrences from each of these three areas define discrete linear trends that are similarly oriented but not strictly collinear with one another or with the Pb isotope trends of MVT ore deposits, suggesting that trace MVT occurrences in each of these three regions derived their Pb from separate pairs of end-member Pb sources. An exception is the GUMV trace MVT occurrences and the Upper Mississippi (UMV) district ores, which appear to have collinear Pb isotope trends and thus may be the most closely related genetically with respect to sources of Pb. All of the trace MVT occurrences have radiogenic Pb suggesting derivation from Precambrian igneous basement rocks and not from the formations that host trace MVT mineralization. Trace MVT occurrences tend to have less radiogenic Pb than the MVT ore deposits, although trace MVT occurrences from the GUMV region are the most heterogeneous and can have Pb that is as radiogenic as the MVT ore deposits. Regionally, Pb isotope compositions of trace MVT occurrences tend to become less radiogenic southwestward and southward, but do not correlate with host rock age, and by proxy, distance from the Precambrian basement. The sulfur isotope compositions of sphalerite and galena from the trace MVT occurrences are light compared to the MVT ore deposits and likely reflect incomplete reduction of marine sulfate reservoirs or derivation from organic matter. The Pb and S isotope compositions of the trace MVT occurrences do not correlate well, suggesting that Pb and S were not transported together in the same fluid.

Traditional metallogenic models posit that porphyry–skarn Cu systems form in subduction and collision zones. However, in eastern China, many important Late Mesozoic porphyry–skarn deposits have formed in intracontinental settings related to lithospheric break-up during the celebrated tectonothermal, Yanshanian event. The Xiaohekou Cu skarn deposit in the southern Qinling Orogen presents an ideal case study to describe such ore deposit geology, using mineral and fluid inclusion analysis, in addition to sulfide and granitoid S Pb isotope studies. A detailed metallogenic process model for the intracontinental skarn Cu deposit is proposed. The authors recognize four main paragenetic stages: (I) anhydrous skarn, (II) hydrous skarn–Fe oxide, (III) quartz–polymetallic sulfide, and (IV) carbonate–quartz. Stage I is characterized by high temperatures (346–547 °C), high to moderate salinities (6.74–49.2 wt% NaCleqv), together with acidic and oxidizing H2O-NaCl fluids. From early to late anhydrous skarn stage, un-zoned grossular (Adr24–31Gr68–74), a grossular–andradite alternation series with wide zones (Adr26–68Gr31–72) and diopside (Di73–91Hd8–24)–pure andradite with dense oscillation zones (Adr68–100Gr0–30) crystallized sequentially, representing a gradual shift toward higher fO2 conditions. Diopside-hosted fluid inclusions (FIs) contain halite-bearing three phase (H-type), liquid-rich two-phase (L-type), and vapor-rich two-phase (V-type) inclusions, suggesting such fluids were sourced from a silicate melt and stage I & II boiling of magmatic-hydrothermal fluids at lithostatic depths of 1.1–3.3 km.. The FIs in actinolite (stage II) are characterized by homogenization temperatures (Th) of 273–502 °C and salinities of 4.34–42.8 wt% NaCleqv. Cooling and dilution of the ore-forming hydrothermal fluid, as well as the high fO2 conditions were responsible for the hydrous skarn alteration in addition to magnetite and specularite deposition. Stage III constitutes the principal Cu mineralizing event. Quartz from this stage contains distinctive liquid-rich inclusions, with Th of 143–423 °C and salinity of 2.07–17.8 wt% NaCleqv. Their Th values include two populations (210–270 °C and 303–359 °C) suggesting a commingling of hot magmatic-hydrothermal fluid and meteoric water accompanied by a significant fO2 decrease and pH increase was a principal factor behind chalcopyrite-pyrite-pyrrhotite deposition. The fluids in stage IV (81–218 °C and 0.18–14.1 wt% NaCleqv) are likely be the chilled equivalent of fluid from the Cu mineralization stage which equilibrated with marble. S Pb isotopes reveal that the metals were derived from the granitic rocks and produced by hybrid (mantle+crust)-derived magmas. We propose hydrothermal fluids exsolved from the cooling granitic magma contributed the majority ore-forming materials. Whereas ore-forming fluids clearly interacted with country rocks affecting ore precipitation, skarn development and deposit geometry and emplacement. Devonian host rocks donated little if any of either sulfur or base metals to the mineralization process.

China has the largest antimony (Sb) resources, products and consumption in the world, which plays an important role in the global antimony trade. Chinese Sb deposits are characterized by large resources, concentrated distributions, primary deposits dominating, and associating with numerous valuable elements and minerals. In China, most of Sb deposits are located at the edges of various geotectonic units and are constrained by plate suture zones or large deep fault belts. There are 5 Sb metallogenic belts were distinguished in this paper including the Tianshan-Xingmeng Sb ore belt, Qin-Qi-Kun Sb ore belt, Qiangtang-Sanjiang Sb ore belt, South China Sb ore belt and South Tibet Sb ore belt. Sb deposits are hosted in Mesoproterozoic to Quaternary formations, but most of them were occurred in Precambrian, Devonian and Triassic strata. The ages of mineralization of Sb deposits in China are mainly concentrated in the Indosinian, Yanshanian and Himalayan, while the large-scale mineralization is restricted within the Jurassic to Cretaceous of the Yanshanian. Antimony deposits have multiple sources of ore-forming metals and fluids, of which Precambrian basement strata may be one of the most important. The magmatic activity caused by asthenosphere upwelling may be the main evocator for driving the circulation of groundwater to extract mineralized elements. According to the results of China National Mineral Resources Potential Assessment Project (NMRP), China delineated 94 Sb prospect areas, in which, 15.43 million tons of unproven Sb metal were predicted within 2 km below the surface. Among the 5 Sb ore belts, the South China Sb Ore Belt has the largest number of deposits, identified resources and resources potential, showing strongest mineralization intensity. The Qiangtang-Sanjiang Sb Ore Belt followed, where may become the future antimony resource-base of China.