Vein Deposits Research Articles

Ore dilution control when mining low-thickness ore bodies using a system of sublevel drifts

Purpose. The research is aimed at substantiating the optimal parameters of blast-hole ore breaking to reduce the rock mass destruction when mining low-thickness vein deposits using the mining system of sublevel drifts (SD). The focus is on analyzing the impact of blasting on the out-contour rock mass during the blast-hole breaking process. Methods. The three-dimensional block model is constructed using rating classifications of rocks based on studying their strength properties and structural peculiarities. The inelastic deformation zones around the stoping extraction are determined by numerical analysis using the finite element method in 2D formulation. Experimental blasts are assessed by varying the blast-hole drilling scheme depending on the stability rating. Findings. During the experimental-industrial tests, rational blast-hole drilling schemes have been substantiated, contributing to maintaining the stability of the host rocks when mining low-thickness veins. Originality. Effective methods for reducing the ore dilution have been substantiated, which take into account not only the strength properties and structural peculiarities of rocks, but also their seismic impact from blasting on the out-contour rock mass stability when mining low-thickness deposits using a system of sublevel drifts. Practical implications. Practical significance is in the possibility of minimizing the percentage of mineral dilution when mining low-thickness ore bodies using a system of sublevel drifts, which can significantly reduce the cost of mined minerals by reducing ore losses caused by the rock mass destruction during mining operations.

Cassiterite trace element discrimination diagrams to facilitate critical mineral exploration

Cassiterite is a weathering-resistant mineral, which can incorporate a variety of trace elements. Trace elements in cassiterite samples collected from twelve deposits in the Herberton Mineral Field, Australia, were measured with the use of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The results were combined with published data from other tin fields, including the Andean Sn belt in South America; the Karagwe Ankole belt in Rwanda; and, from China, the Kangxiwa-Dahongliutan pegmatite field, the Youjiang basin, the Nanling belt and the Da Hinggan Range belt. Tin deposits in the dataset can be subdivided into four deposit types: 1) greisen and veins; 2) skarns; 3) Li-Cs-Ta pegmatites; and 4) polymetallic veins. The cassiterite dataset was analyzed using basic descriptive statistics, principal component analysis (PCA), and cluster analysis. Cassiterite grains from greisen and vein deposits are characterized by high concentrations of Ti (avg. 1751 ppm) and moderate concentrations of Al (avg. 97 ppm), whereas cassiterite grains from skarn deposits generally contain lower concentrations of Ti and Al. Chemical compositional boundaries in cassiterite from different deposits were recognized with cluster analysis. The relative enrichment of Al and Ti in cassiterite grains from greisen and vein deposits is likely due to greisenization reactions. The Ti vs. Al diagram can be used to differentiate between cassiterite grains derived from greisen and vein deposits, as compared to cassiterite grains derived from skarn deposits, whereas Sb vs. V diagram can be used to differentiate between cassiterite grains from polymetallic vein deposits. Zirconium and Nb concentrations are useful in identifying cassiterite grains sourced from LCT pegmatite deposits. The discrimination diagrams developed in this study through cluster analysis indicate that cassiterite grains sourced from different deposit types can be differentiated based on their trace element geochemistry and this can be a useful tool in critical mineral exploration. Therefore, these diagrams can be used effectively to understand metal association and deposit types in a region with detrital cassiterite from stream sediments, till and heavy mineral placer deposits.

Determination of structural lineaments of the mafic-ultramafic belt of the Southern Argentine Precordillera

In central-western Argentina, an Early Paleozoic belt including mafic-ultramafic bodies and marine metasedimentary rocks occurs along the western margin of the Precordillera and in the eastern Frontal Cordillera. In this paper, we present the analysis of aeromagnetic data and its processing focused on mapping geological limits, structures and the relation at depth of the southern Precordillera. With this main objective were applied filtering algorithms, reduction to the pole, tilt derivative, analytic signal, and particularly, the use of Improved Logistic Function (IL) as a new method of edge detection, in combination with the inversion map obtained from the Magnetization Vector Inversion (MVI) method. The results allow us to describe at depth the main trend of the Southern Precordillera Mafic Ultramafic Belt as two separated bocks, one in Peñasco and another in Cerro (Co.) Cortaderas, passing through Cerro (Co.) Pozos with a possible NNE-SSW direction. The combination of this techniques also can be used as prospecting guide to Pb–Zn–Ag vein deposits and High sulfidation Au-Epitermal deposits.

The In-Ga-Sb association of the post-Variscan Zn-Pb-Ag vein deposit at Lautenthal, Upper Harz Mountains, Germany: sphalerite mineral chemistry

The Lautenthal sphalerite-galena vein deposit is part of the world-class Upper Harz Pb-Zn-Ag district in the Harz uplift block of the Paleozoic Variscan fold belt in Germany. Its sphalerite-dominated mineral association was studied using bulk-ore chemistry, electron probe microanalysis, and laser ablation-ICP-mass spectrometry. Gallium and locally In are the main high-tech-relevant trace elements hosted by sphalerite, with up to 150 ppm Ga and up to 380 ppm In in hand-picked sphalerite samples (mean In/Zn, 0.70 × 10−3). Ore concentrates (≤ 50 kg) contain up to 65 ppm Ga and up to 109 ppm In (mean In/Zn, 0.36 × 10−3). Accessory Fe-Co-rich gersdorffite-1 occurs in the earlier quartz-sulfide ore stage and Sb-rich gersdorffite-2 in the later carbonate-sulfide stage. Enrichment patterns of In are either defined by overprinting textures in the Fe-richer sphalerite-1 of the earlier stage, or relate to primary growth zoning in Fe-poor sphalerite-2 of the later stage. Using the sphalerite geothermometer GGIMFis, formation temperatures (median) of sphalerite-1 were estimated at ~ 230 °C for the Lautenthal orebody and at ~ 175 °C for the Bromberg orebody, which may indicate lateral T-zonation for the earlier ore stage. Sphalerite-2 data indicate formation temperatures of ~ 185 °C (median). Copper-bearing brines of the carbonate-sulfide stage with assumed temperatures of ~ 250 °C initiated replacement of In-poor sphalerite-1 by chalcopyrite and remobilization of Zn and trace elements. Indium-rich sphalerite-2 occurs associated with calcite and fine-grained galena. A direct spatial or temporal link of ore formation to a magmatic-hydrothermal system is unlikely, which contrasts to In-rich epithermal and tin-polymetallic vein deposits worldwide.

Precipitation of Ag-Pb-Zn ores of the Poshan vein deposit in the Qinling orogen (central China) by dilution of magmatic hydrothermal fluids

Abstract Constraints on the source, nature, and evolution of ore-forming fluids are crucial for better understanding the ore genesis and mechanisms that lead to metal precipitation. Here, we present results of in situ analysis for quartz oxygen isotopes and sulfide sulfur isotopes, combined with apatite U-Pb age and fluid inclusion data, to provide insights into the source and evolution of ore fluids of the Poshan Ag-Pb-Zn vein deposit in the Qinling orogen, central China. Quartz-carbonate-sulfide veins at Poshan are hosted in lower Paleozoic metavolcanic-sedimentary rocks and structurally controlled by fracture zones associated with the Heqianzhuang anticline. The Ag-Pb-Zn mineralization consists of three stages, which are represented by quartz-pyrite-arsenopyrite (stage I), quartz-carbonate-sulfide-silver minerals (stage II), and quartz-calcite ± native silver (stage III). Apatite texturally associated with galena from stage II has a U-Pb age of 125 ± 14 Ma (2σ; mean square of weighted deviates [MSWD] = 0.9), which suggests that the Poshan deposit formed in the Early Cretaceous and thus significantly postdated the Paleozoic and early Mesozoic orogenic deformation of the Qinling orogen. Aqueous-carbonic fluid inclusions from stages I and II have similar total homogenization temperatures of 263–347 °C and calculated salinities of 1.2–5.1 wt% NaCl equivalent, whereas the values for liquid-dominated aqueous inclusions from stage III are 211–245 °C and 0.5–3.0 wt% NaCl equivalent. Five quartz generations are recognized from the three paragenetic stages, including Qz-1 and Qz-2 from stage I, Qz-3 and Qz-4 from stage II, and Qz-5 from stage III. Based on in situ secondary ion mass spectrometry oxygen isotopic analysis of the five quartz generations (Qz-1 to Qz-5), the calculated δ18Ofluid values for the ore fluids are 7.8‰ to 9.2‰ (mean 8.3‰), −3.2‰ to 8.7‰ (mean 5.6‰), −3.5‰ to 7.4‰ (mean 4.6‰), −4.5‰ to 7.6‰ (mean −0.2‰), and −6.4‰ to 1.4‰ (mean −3.8‰). The oxygen isotopic data and trend among the five quartz generations are best interpreted to represent magmatically derived ore fluid being diluted by modified meteoric water to cause mineralization. Fluid mixing is considered to be the principal mechanism that led to Ag-Pb-Zn precipitation at Poshan. Sulfides coexisting with the quartz generations have δ34SV-CDT values of −1.7‰ to 4.4‰, with no systematic variations among different paragenetic stages. These data, combined with apatite U-Pb age and geologic relations, provide additional evidence for a magmatic origin of the Poshan Ag-Pb-Zn deposit, as inferred from the oxygen isotopes. This study highlights the role of fluid dilution in triggering Ag-Pb-Zn deposition, and sheds light on the origin of silver-polymetallic deposits in orogenic belts.

Distribution of indium and gallium in sphalerite from skarn and hydrothermal vein deposits in the Hwanggangri mineralized district, South Korea

The geochemistry of sphalerite from seven metallic ore deposits in the Hwanggangri mineralized district in South Korea was studied, with a special focus on the concentrations of In and Ga. The chemical compositions were analyzed using laser ablation-inductively coupled plasma-mass spectroscopy and compared based on deposit type (skarn and hydrothermal vein) and ore species (W, Mo, Zn–Pb, and W–Zn–Pb). In hydrothermal W and W–Zn–Pb vein deposits, In was highly concentrated, with averages of up to 696 ppm, whereas Mo and Zn–Pb skarn deposits produced low concentrations below 43 ppm on average. In contrast, the Ga concentrations were quite low throughout the deposits and did not exceed 16 ppm on average. Indium showed a clear positive correlation with Cu and was strongly associated with the development of chalcopyrite-disease, with Ag and Sn potentially playing subordinate roles in the substitution. The binary correlations between trace elements suggested that principal coupled substitutions, such as 3Zn2+ ↔ 2(Cu, Ag)+ + Sn4+ and 2Zn2+ ↔ Cu+ + In3+, prevailed in In-bearing sphalerite. A discernable weak positive correlation is observed between In and Cd, mostly in the W-bearing deposits, implying that Cd, a common constituent in sphalerite, could be used as an exploration proxy in some cases. The general tendency of high In and low Ga concentrations in the sphalerites from the Hwanggangri mineralized district indicates relatively high temperature of mineralizing fluids, generally above 250 °C, which favored the prevalence of In-chloride complexes over Ga-hydroxide complexes. Additionally, the In enrichment in the hydrothermal vein ores rather than the skarn ores emphasizes the importance of the direct contribution of magmatic fluids to ore mineralization under high temperature conditions with little influence from the host rock.

In situ illite Rb-Sr dating indicates the coevality of Carlin-type gold deposits inside and around the isolated carbonate platform in western Guangxi, China

The western Guangxi is a crucial component of the Guizhou–Yunnan–Guangxi “Golden Triangle”(hereafter referred to as the Golden Triangle) of South China. The most discovered Carlin-type gold deposits in this region are primarily situated at the periphery of isolated carbonate platforms. The ore bodies are vein-like in form controlled by faults, and the wall rock are Triassic carbonate-bearing terrigenous clastic rocks. Recently, some gold deposits have been discovered in the interior of isolated carbonate platforms. The ore bodies are primarily stratiform hosted in sedimentary unconformities. The mineralized strata span from the Cambrian to the Permian, and the host rock include sandy and muddy dolostones, as well as a combination of sandstone, mudstone, tuff, and chert. The geological and geochemical characteristics suggest that these stratiform deposits in the interior of isolated carbonate platforms share common characteristic with Carlin-type gold deposits in China and USA. However, it remains uncertain whether these deposits are products of the one mineralization system and are coeval with those vein deposits at the periphery of the isolated platforms. To address this question, we conducted geological and isotopic dating studies on the Longhuo gold deposit and the De'e gold occurrence in the interior of isolated platforms. The Longhuo stratiform gold deposit occurs along a parallel unconformity in the Carboniferous/Devonian composed of sandstone, shale, tuff, and chert. Hydrothermal illite, quartz and auriferous pyrite fill along joints and fissures, implying that illite formed during the main ore-forming stage and its age could represent the age of gold mineralization. The stratiform orebodies of De'e gold occurrence are hosted in Cambrian sandy and muddy dolostones. Gold occurs as invisible Au in zoned pyrite and arsenopyrite, with a dominant alteration assemblage of silicification, carbonate alteration, and illitization. Hydrothermal quartz, illite and dolomite often aggregate with zoned auriferous pyrite and arsenopyrite in the most intensely altered zones, suggesting that illite formed during the main ore-forming stage and its age could also represent the age of gold mineralization. Illite LA-ICP-MS Rb-Sr dating was performed on both deposits, yielding ages of 184.16 ± 3.14 Ma for the Longhuo gold deposit and 191.21 ± 6.76 Ma for the De’e gold occurrence.Previous studies have indicated that Carlin-type gold deposits in the Golden Triangle exhibits two distinct age clusters, one ranging from 184 to 235 Ma and the other from 134 to 148.4 Ma. These dual age clusters suggest the potential occurrence of two mineralization events. The obtained ∼ 190 Ma mineralization ages for the Longhuo and De'e gold deposits in this study indicate that the Carlin-type gold mineralization within the isolated platform took place during the Early Jurassic. This aligns with the early mineralization event of gold deposits along the platform's edge, implying that gold deposits inside and around the isolated carbonate platform are products of the same mineralization system, influenced by post-Indosinian extensional events. The interior of the isolated carbonate platform holds substantial exploration potential, making it a novel direction for prospecting Carlin-type gold deposits in western Guangxi.

Комплексное геомеханическое моделирование разработки жильных месторождений блочного строения

Mining of vein deposits formed in block structures requires consideration of the impact from the deformation processes occurring as a result of changes in the natural and man-induced state of the rock mass. Information on the magnitude and directions of stresses acting in the block mass are the boundary conditions taken into account in further calculations of the stressandstrain state and stability of structural elements of underground geotechnology. For an efficient assessment of the natural stressed state of a tectonically disturbed rock mass, associated with the need for numerical simulation of the geomechanical state of tectonic structures, spread over large areas, the PRESS 3D URAL dedicated software suite (Polygor LLC, St. Petersburg) was adopted for 3D settings. At the same time, due to the occurrence elements and morphology of the ore veins it is advisable to use the CAE Fidesys software suite (Fidesys LLC, Moscow) in 2D settings for local assessment of the stress concentrations in vicinity of mine workings and pillars formed as the result of mining operations.

Indosinian W–Sn mineralization in the Dupangling area, Western Nanling: Cassiterite U–Pb dating and trace element data for the Maoershi Sn polymetallic deposit

Nanling is located in central South China and contains the most important area of W–Sn polymetallic deposits worldwide. However, a lack of geochronological data hinders our understanding of the timing and mechanisms of W–Sn mineralization in the Dupangling area of western Nanling. The Maoershi Sn polymetallic deposit is located in the western body of Dupangling complex pluton, and is a significant hydrothermal vein deposit. Cassiterite U–Pb dating shows that the Maoershi Sn mineralization occurred during the Late Triassic (206.2 ± 2.6 Ma). This age is different from the age of granite in the western Dupangling pluton and similar to the age of the eastern Dupangling pluton. The cassiterite is enriched in Sc (4.5105–18.4049 ppm), V (37.2267–88.9671 ppm), Nb (62.0104–194.1846 ppm), Ta (11.1965–85.6881 ppm), Hf (22.0511–30.7650 ppm), U (2.8870–17.9187 ppm), Th (0.0005–0.0908 ppm), Ti (3873–6170 ppm), and other high-field-strength elements. Based on Nb/Ta and Y/Ho ratios, and the W–Fe discriminant diagram, Sn and the other mineralizing materials were mainly derived from hidden Indosinian granitic rocks. Tungsten–Sn mineralization in the Dupangling pluton exhibits a clear spatial–temporal relationship with Indosinian granitic magmatism, and occurred in an extensional setting after the continent–continent collision that marked the late Indosinian Orogeny.

Sulfide Mineralization of Carbonate–Silicate Veins in Early Proterozoic Metabasites of North Karelia: Mineral Assemblages, Mineral Forms of Silver, and Fluid Inclusions

The work presents the first data on sulfide mineralization in carbonate–silicate veins, which are widespread on the islands and coast of the White Sea (North Karelia), associating with Early Proterozoic metamorphosed gabbroid bodies. The veins with Fe–Cu sulfide mineralization up to ore occurrences are localized within metabasite bodies and along their contacts with host gneisses. During the study of the mineral composition of the veins, the main assemblages of sulfide minerals were identified: chalcopyrite –bornite ± chlorite ± selenides and Pb–Ag tellurides (B1); digenite–bornite ± selenides and Pb, Ag, and Pd tellurides (B2); pyrite–bornite ± chalcopyrite (B3); marcasite–pyrite–bornite–chalcopyrite (B4); and siegenite–chalcopyrite ± acanthite ± chlorargyrite. The development of sulfide associations, as well as quartz–chlorite aggregates, was related to the late stage of vein formation. Inductively coupled plasma and laser ablation mass spectrometry analyses showed that bornite from association B1 has the highest silver content (up to 675 ppm) and, in terms of Ag, Se, and Bi contents, is closest to bornite from low-temperature epithermal, skarn, and high-temperature vein deposits. In general, bornite is the main Ag carrier in the studied associations, while digenite containing up to 1000 ppm Ag, as well as discrete silver minerals (selenides, tellurides, acanthite, and chlorargyrite), occur in subordinate quantities. Fluid inclusions in quartz from sulfide associations, as well as from a sulfide-free carbonate–silicate vein, were studied by cryo- and thermometric methods. It is established that mineralization at the late stages of vein formation was related to heterogeneous CO2–H2O–NaCl metamorphic fluid. Carbon dioxide fluid inclusions were captured by vein quartz at temperature of 253–314°C and pressure of 2 ± 1 kbar. Water–salt inclusions were captured in a wider temperature range of 100–500°С. The highest temperature fluid inclusions with temperatures of homogenization 300°С are characteristic of quartz veinlets of the siegenite–chalcopyrite association with Ag sulfide and chlorargyrite.

Geochemical dispersion evaluation by criterion-based backward elimination at the Glojeh polymetallic Au (Ag–Cu–Pb–Zn) vein deposit, NW Iran

We applied the backward elimination method as a criterion-based iterative stepwise method to estimate the concentration of Au from the variables Ag, Cu, Pb and Zn. We optimized the quadratic polynomial model on various boreholes and trenches. The results indicate that the vertical zonation of Au is associated with Ag and Cu, along with their respective elemental functions Ag × Cu, Pb 2 , Pb × Zn and Zn 2 . On the other hand, the lateral dispersion of Au is determined by Pb and Zn, along with the essential functions Ag × Zn and Pb × Zn. Zonation is in-depth and is indicated primarily by Zn rather than Cu and minor Pb, with Cu–Pb–Zn gradually extending upward at the upper levels. The vertical zonation trend describes the Ag < Au < Cu < Pb < Zn sequence from proximal to distal veins, with the near-surface zone exhibiting enrichment in Zn. At the Glojeh site, the host rock value, Ag × Cu, Zn 2 and Pb × Zn were identified as strong indicators of the vertical occurrence of Au in the upper host rock, whereas Pb 2 proved more suitable for the deeper boreholes. Cu→Pb→Zn demonstrates the enrichment trend from depth to the surface. The lateral kriging surface estimation confirms the dispersion pattern of elements revealed in-depth at Glojeh. Our aims with this approach were to reduce the cost of fire-assay analysis due to high-precision estimation by associated variables and to determine elemental interactions and the lateral or vertical dependencies of elements.

Genesis of volcanic-hosted Cu vein deposits in the foreland fold-thrust belt, southeastern Tibetan Plateau: Insights from ore geology, C-O-S-Pb-Cu isotopes, and fluid inclusions at Wenyu

Copper deposits hosted by volcanic rocks can have different genetic types. Many copper vein deposits at the margin of the Cenozoic Lanping-Simao foreland fold-thrust belt in southwest China are controlled by thrust faults and hosted by Triassic volcanic rocks formed in association with the evolution of the Paleo-Tethys Ocean. The genesis of these copper deposits is poorly understood. Wenyu is a typical Cu deposit hosted in the Middle−Late Triassic basaltic-andesitic rocks and experienced three major hydrothermal stages characterized by mineral assemblages of calcite, anhydrite, and barite (Stage I); early quartz, chlorite, and epidote (Stage II); and Cu sulfides, galena, pyrite, hematite, and late quartz (Stage III). Consistency of the boiling temperature from fluid inclusions in the calcite and the temperature inferred from the C-O isotopes of the calcite, and the oxygen isotopes of the anhydrite and barite indicate that the stage I fluids probably have a δ13C value of ∼−4.5‰ and δ18O values in the range of ∼−3‰ to +4‰. Oxygen isotopes of the early quartz (δ18O = 15.1‰ to 17.4‰), D-O isotopes of chlorite and epidote, and the fluid inclusion data indicate that the stage II fluids have δ18O values of ∼2.4‰ to 5.0‰ and δ18D values of −68‰ to −53‰. Thus, the stage I and II fluids were inferred to be deep-seated brines with temperatures predominantly between 180 °C and 240 °C and salinities of 16−18 wt% NaCl eq. More significant meteoric water was involved during stage III based on the oxygen isotopes of the late quartz (δ18O = 6.2‰ to 9.5‰). The large variation in δ34S values (−21.3‰ to 1.6‰) in the sulfides, the sample- and grain-scale sulfur isotope fractionation, combined with the ore textural evidence that the sulfates and chlorite were replaced by Cu sulfides accompanied by hematite, indicate that the reduced sulfur responsible for sulfide precipitation was generated by inorganic reduction of the previously formed anhydrite and barite (δ34S = 6.3‰ to 8.6‰) or sulfates in the brines by oxidation of chlorite to hematite. Lead isotopes of galena (206Pb/204Pb = 18.67−18.87; 207Pb/204Pb = 15.68−15.72) and copper isotopes of Cu sulfides (δ65Cu = −0.34‰ to 0.51‰) indicate that the ore-forming metals (e.g., Cu and Pb) were derived from the ore-hosting Triassic volcanic rocks. The Wenyu copper deposit cannot be classified as a porphyry, epithermal, or volcanogenic massive sulfide deposit. It is believed that the deep-seated brines, such as the saline formation water in the Permian marine strata, migrated upward along the thrust faults into the Triassic basaltic-andesitic volcanic rocks, and leached metals from the volcanic rocks and precipitated Cu sulfides via inorganic sulfate reduction at Wenyu during the Cenozoic. Such mineralization processes may explain the genesis of the volcanic-hosted copper vein deposits in the Lanping-Simao foreland fold-thrust belt and other similar belts in the world.

Assessment of contamination level of watercourses and streambed sediments downstream the Capillitas Mine, Catamarca, Argentina

The present study constrain the degree of contamination by heavy metals and metalloids of streams impacted by mining activities in Capillitas Mine (Catamarca, Argentina), an epithermal precious- and base-metal vein deposit previously mined for copper along with gold and silver; and subsequently for rodhochrosite. Geochemical analyses of water of three streams (Ortíz, Acid and Capillitas) and a small pond depicting a very thin layer of turquoise-colored precipitates in its bottom were performed and the environmental risk factor was calculated. Moreover, the concentrations of potential toxic elements in sediments from the Ortíz and Capillitas streams were determined by ICP-OES and the Index of geoacumulation (Igeo) for As, Cd, Zn, Cu, Mn and Pb was computed.
 According to their major ions concentration the four water samples correspond to calcium SO4 waters. The Acid and Ortíz streams and the turquoise pond show concentrations of Al, Mn, Cd, Zn, Cu, Cr, Ni and Pb that largely exceed the limiting concentrations for protection of aquatic life, as well as for irrigation waters. The Capillitas stream has a lower content of heavy metal but shows concentrations of Mn, Zn, Cu and Pb exceeding the limiting values for protection of aquatic life. 
 According to the obtained Igeo the three streambed sediments from the Ortíz creek are extremely polluted for Cd, Zn and Pb, whereas they range from strongly to extremely polluted for Cu, As and Mn. The sediments from Capillitas creek depict lower contents of metals and metalloids; though it is strongly polluted for Cd, moderately polluted for Cu and unpolluted to moderately polluted for Pb and Zn.

Genesis of Tertiary Akçakışla vein-type Pb-Zn-Cu mineralisation (Central Anatolia, Turkey): Evidence from fluid inclusion and O, H, S, Pb-isotope compositions

The Akçakışla Pb–Zn–Cu vein type deposit is one of the active mining deposits located in the Akdağmadeni (Yozgat) metallogenic province in Turkey. The sulfide vein deposit, trending E-W, is hosted by calcschist of the Akçakışla and Topaktaş formations of Akdağmadeni metamorphites, which are intruded by the Central Anatolian granitoids and overlain by sedimentary and Tertiary volcanic rocks. Microthermometric measurements indicate that the Pb-Zn-Cu deposit formed by hydrothermal fluids containing dissolved CaCl2, MgCl2 and NaCl. A mixing of fluids with greatly varying salinities and temperatures is shown by the wide range of calculated salinity (0.2–10.4%) and temperature (170–400 °C) values. Isotope ratios of oxygen (δ18OH2O = −5.09 to +4.71‰) and hydrogen (δD = −67‰ and −82‰) suggest that water in hydrothermal fluid might be either mixing of meteoric and magmatic waters or meteoric water that oxygen isotope composition was modified by fluid-rock interaction. Sulphide minerals exhibit δ34S values ranging from 5.51‰ to 8.40‰, which assume a magmatic sulphur source modified by assimilation of upper crustal material (possibly the host metamorphites). In galena from the studied Akçakışla Pb–Zn–Cu deposit ratios of 206Pb/204Pb (18.783–18.821),207Pb/204Pb (15.654–15.700) and 208Pb/204Pb (38.874–39.039) suggest a mixture of lead sources from orogenic-upper crust materials. We assume that hydrothermal fluids dissolved the sulphur from the intruded granitoids and the lead from the host metamorphites. The galena Pb model ages values point out two different ore forming ages; suggesting initial formation in upper Cretaceous (87 Ma) and highly reworking in Eocene–Oligocene (23 and 39 Ma).

Triple-halogen (Cl-Br-I) fluid inclusion LA-ICP-MS microanalysis to unravel iodine behavior and sources during marine fluid infiltration into the basement in unconformity settings

Halogen signatures of hydrothermal fluids are a powerful tool for deciphering fluid provenance and reconstruction of key ore-forming mechanisms such as fluid mixing processes. Analytical protocols for LA-ICP-MS fluid inclusion analysis of Cl and Br concentrations have existed for over 10 years, but Br/Cl ratios alone do not provide unambiguous evidence of fluid provenance. However, recent methodological advances now allow also for quantification of I by LA-ICP-MS analysis in single fluid inclusions, significantly expanding the applicability of halogens for unambiguous fluid provenance analysis. However, owing to the novelty of the fluid inclusion triple-halogen LA-ICP-MS method, and due to the notorious difficulties caused by the generally low I concentrations in hydrothermal fluids, reference Cl-Br-I data of many crustal fluid types remains scarce, even when including data from bulk analytical techniques. Single fluid inclusion halogene analytics as are used here are vital due to the lack of sampling bias inherent to bulk analytical techniques that narrow the analyzed compositional range.The evaluation of Cl, Br and I systematics of fluid inclusions from unconformity-related hydrothermal veins in the Schwarzwald, Germany, provides new insight into the behavior of I and the evolution and source of the fluids involved in formation of unconformity-type vein deposits in central Europe during the Triassic to Cretaceous. While the variation in Br/Cl (molar ratio: 0.1 × 10−3–8.3 × 10−3) is consistent with previously established models of mixing processes between two fluids with a salinity source in seawater evaporation (modified bittern brine) and halite dissolution (modified halite dissolution brine), respectively, the large scattering of I/Cl (molar ratio: 1.4 × 10−6–330 × 10−6) cannot be attributed to the salinity source alone. Instead, I must have been derived from interaction with organic matter, which appears to have been more pronounced within the modified bittern brine fluid endmember. During fluid infiltration into the basement and associated fluid-rock interaction, I/Cl and Br/Cl acted conservatively on analytically detectable scales and large inhomogeneities in source I signatures remained intact. This finding also presents direct evidence of local fluid composition inhomogeneity and absence of internal mixing of basement reservoirs for long time periods (more than 100 Ma).

Multistage fluorite mineralization in the southern Black Forest, Germany: evidence from rare earth element (REE) geochemistry

Abstract. The Black Forest hosts a wide range of hydrothermal mineralization, including fluorite–barite vein deposits. In a detailed investigation of the Finstergrund and Tannenboden deposits in the Wieden mining district (southern Black Forest), the diversity, geochemical evolution and relative chronology of multistage fluorite precipitation is tracked on the basis of rare earth element (REE) geochemistry, geologic field relationships and crystal zoning. Geochemical discrimination and mathematical λ coefficients suggest a total of seven fluorite REE groups, at least three distinguishable post-Variscan fluid mobilization events and independent formation histories for the deposits despite their spatial proximity. Fluorite vein mineralization at the Finstergrund deposit evolved over three fluid generations, was derived from gneissic source aquifers and comprises five distinct fluorite REE groups: the first fluid generation is characterized by fluorite precipitation above 200 ∘C (“group III”), below 200 ∘C (“group I”) and after fractional crystallization (“group IV”); the second generation comprises remobilized fluorite (“group II”); and the third generation revealed fluorite precipitation by meteoric water mixing (“group V”). Fluorite vein formation at the Tannenboden deposit is associated with two distinct fluorite REE patterns derived from the same fluid generation: fluorite precipitation above 200 ∘C (“group VII”) and after cooling below 200 ∘C (“group VI”). Its fluid source aquifer lithology best matches migmatites contrary to previous models that suggest either gneissic or granitic aquifer rocks for fluorite vein precipitation in the Black Forest. The decoupled formation history between the deposits is tectonically controlled as suggested by a new genetic model for the Wieden mining district. The model argues for a change in the local fluid percolation network and the termination of hydrothermal activity at the Tannenboden deposit after the first fluid mobilization event. The geochemical evolution of multistage fluorite mineralization, as exemplified by the Tannenboden and Finstergrund deposits in combination with other fluorite mineralizations in the Black Forest, provides unique insights into the lithospheric origin and precipitation behaviour of fluorite by various fluid–rock interaction processes occurring in large hydrothermal systems. The local diversity of REE patterns emphasizes the need for detailed investigations of individual hydrothermal vein deposits.

Mineral chemistry and in-situ U-Pb geochronology of altered pegmatite from the vicinity of the Strashimir Pb-Zn vein deposit

The current study presents new mineralogical, geochemical and geochronological data for a pegmatite body hosted in gneisses and marbles from the vicinity of the Strashimir Pb-Zn vein deposit, Madan ore district, South Bulgaria. The mineral composition of the studied pegmatite is represented by oligoclase–andesine (An10.1–33.2) and albite (An0–7.6), which prevail over K-feldspar (Or87.9–92.4), and quartz. The established accessory minerals are allanite-(Ce), titanite, apatite and zircon. The pegmatite/marble contact is affected by later hydrothermal silicate-carbonate alteration without detected ore mineralization, despite the spatial proximity with the Strashimir Pb-Zn vein deposit. Epidote-group minerals in pegmatite are defined as members of the clinozoisite–epidote series. As a major constituent of the hydrothermal alteration zone, they are manifested in two well-distinguished generations along with chlorite, quartz and carbonates. The calculated temperature of chlorite mineralization yields T° of crystallization in the range of 223–266 °C. As a result of the hydrothermal fluid circulation, the accessory allanite-(Ce) is transformed to REE-rich epidote-clinozoisite, marked by depletion of REE and Fe and enrichment of Si, Al, and Ca. Due to the limited mobility of REE in fluids, after leaching these elements are incorporated in nearby crystallized epidotes. According to the occurrence, mineral association and chemical properties, three titanite populations are distinguished in the pegmatite. Two of them were in-situ dated by the LA-ICP-MS U-Pb method and reveal overlapping ages of 39.9±2.1 Ma and 39.5±2.2 Ma (39.3±1.2 Ma combining all titanite analyses). The ages are interpreted as titanite growth in a pegmatite body related to granitic melts in the Late Alpine high-metamorphic units (Madan Unit) of the Central Rhodopes. Hydrothermal fluids either did not affect the U-Pb isotope system of the titanites or were derived from the same fluid-rich melt.

Geochemical Characteristics and Metallogenic Significance of the X03 Vein Tourmaline in the Jiajika Rare Metal Deposit, West Sichuan

The Jiajika rare metal deposit contains the largest area of granitic pegmatite-type rare metal deposits in China. The X03 vein is an immense rare metal deposit dominated by lithium, which was found in the deposit in recent years. The contact metamorphic belt of tourmalinization and petrochemistry is widely developed in its wall rocks, and the altered rocks formed contain Li and other rare metal mineralization. In this paper, the tourmaline found in the different rocks of the Jiajika X03 vein is divided into four types: two-mica quartz schist (Tur-Ⅰ), tourmaline hornfels (Tur-Ⅱ), tourmaline-bearing granite pegmatite (Tur-Ⅲ) and spodumene-bearing granite pegmatite (Tur-Ⅳ); their in situ major element, trace element and boron isotope data are systematically studied. The results show that all tourmalines in the Jiajika X03 vein deposit belong to the alkali group, and are schorl–Oxy/Fluor–schorl, dravite–Hydroxy-dravite and foitite–Oxy foitite solid solutions, among which Tur-Ⅰ are dravite, Tur-Ⅱ are foitite of hydrothermal origin and Tur-Ⅲ and Tur-Ⅳ are schorl of magmatic origin. The boron isotope values show that the boron involved the formation process of tourmaline mainly originates from the Majingzi S-type granite, and the boron isotope variations in tourmaline are controlled by melt fluid and Rayleigh fractionation. Moreover, there is a clear correlation between the B isotope value of tourmaline and the Li, Mn, Zn, Mg, and V contents, showing that these contents in tourmaline are good indicators of the mineralization type of pegmatite.

Structural controls on the Co and Ni-bearing arsenides from the Bou Azzer mine (Case of Aït Ahmane F53 vein deposit): Implications for mineral exploration

The mining district of Bou Azzer is located in the central part of the Anti-Atlas, which is on the northern margin of the West African craton. Located about hundred kilometers southwest of the Ouarzazate city, the Bou Azzer inlier crops out along the major fault of the Anti-Atlas. In the eastern part of the Bou Azzer mining district, the "F53 vein deposit", in the Aït Ahmane area, represents one of the richest cobalt ore deposit; with production of more than 200 tons of cobalt per month. This study aims to define the different faults controlling the mineralization in the F53 vein deposit. In this work, we use the ArcPad mobile application to map faults, veins and geological formations and the digital collection of geological data (e.g., alterations, structural measurements, etc.) in the field. Then, we use the Win-Tensor software for structural analysis and reconstruction of paleostress. The results of this study indicate that the mineralization in the F53 vein deposit is structurally controlled by two main types of faults. The first one corresponds to overlapping faults with sinistral strike-slip component oriented N110° to N120° formed during the Pan-African orogenic event with a NNE-SSW to NE-SW of a maximum subhorizontal stress (σ1), and with N00 to N40° tension gashes. These faults control the mineralization located along the contact between the serpentinized peridotites and the quartz diorite. This type of mineralization named "Contact mineralization”, has massive to brecciated texture and are rich in Co–Ni–Fe arsenides. The second type correspond to a reactivation of tension gashes oriented N00° to N40° as reverse faults during a shortening phase, probably of Variscan age, with horizontal NW-SE trending maximum stress (σ1) and subvertical minimum stress (σ3). These faults oriented N00° to N40° control the vein-type mineralization, which has a banded texture and appears in the form of mineralized quartz-carbonate veins intersecting the quartz diorite. These mineralized faults N00° to N40° directions are transverse to the N120° fault contact between the serpentinized peridotites and the quartz diorite.

Nanoscale distribution of Ge in Cu-rich sphalerite

A large proportion of the critical elements resources Ge, Ga, and In are associated with sphalerite in Pb-Zn ore deposits. Germanium in sphalerite has been proposed to be structurally bound in the crystal lattice. Using a combination of microstructural, geochemical and nanoscale observations, we show that Ge can be hosted in sphalerite crystal structure as well as nanoparticles of briartite (Cu2(Zn,Fe)GeS4). The structurally-bound Ge was preserved in undeformed sphalerite grains from the Saint-Salvy Pb-Zn vein deposit (France), whereas the briartite nanoparticles were observed in metamorphosed sphalerite from Arre. The briartite nanoparticles likely exsolved from sphalerite during the Pyrenean-Alpine metamorphism and deformation. The presence of nanoparticles may harden the sphalerite during crystal-plastic deformation and help to preserve the critical elements resources of Pb-Zn deposits during metamorphism.