Host Rock Minerals Research Articles

Processes controlling magma fertility at buenavista del cobre porphyry copper deposit (cananea, méxico): A new petrogenetic model based on zircon u-pb dating and apatite geochemistry

The Buenavista del Cobre is a world-class porphyry Cu-Mo deposit located in the Cananea Mining District, northern Sonora, México. Using zircon U-Pb dating, we show that the Proterozoic Cananea Granite, unconformably overlain regionally by Paleozoic limestones hosting skarn deposits underlies the present-day pit. We also present new crystallization ages for host rocks of copper mineralization in the District, dating for the first time a volcanic rock of the Henrietta Formation at 186.8 ± 1.1/3.0 Ma and the El Torre Syenite at 176.3 ± 1.1/2.9 Ma. Zircon U-Pb dating of the different porphyritic bodies reveals that the magmatic activity at Buenavista del Cobre lasted at least 4 Myr, from 59.7 ± 0.5/1.1 Ma to 56.1 ± 0.2/0.9 Ma. The deposit is composed by several porphyry intrusions referred to as “ore-rich” and “ore-poor” based on their individual metal contributions, which provides the opportunity to study the origin and processes enhancing magma fertility in an individual deposit. Combining our new geochronological dataset with geochemistry of apatite from the different porphyries allows us to propose a new petrogenetic model for the Buenavista del Cobre deposit. As the apatite Eu and Ce anomalies overlap with no clear difference between the ore-rich and ore-poor intrusions, we propose that the magmatic oxidation states of the magmas were similar. However, differences in apatite REE signatures, as well as variations in apatite Sr compositions between the two groups suggest that fractional crystallization processes in the parental magma influence the fertility of the porphyries. Additionally, apatite Cl contents of ore-rich porphyry intrusions are higher (>0.4 wt%) than the ore-poor intrusions (<0.2 wt%), suggesting an important role of the initial Cl content of the magmas in the mineralization process. These observations give new insights on the petrogenetic processes at origin of porphyry magma fertility. We propose that the evolution of the parental melt by fractional crystallization of hydrous minerals (hornblende) at upper crustal levels induced low H2O content of the residual magma, resulting in the formation of ore-poor porphyries. In contrast, we suggest that fractionation of anhydrous minerals (plagioclase) increased the H2O content in the residual melt, leading to the formation of ore-rich porphyries. Our new data allow us to propose an original genetic model for the Buenavista del Cobre deposit, which involves two cycles of supply, cooling and partial crystallization. This contribution shows that petrogenetic processes controlling porphyry copper magmas fertility are recorded in the composition of apatite at the deposit scale and highlights the importance of considering apatite geochemistry as an exploration tool.

Revealing Yukon’s hidden treasure: an atomic-scale investigation of Carlin-type gold mineralization in the Nadaleen Trend, Canada

AbstractThe invisible-gold deposits known as Carlin-type are becoming more important as easier to find deposits are progressively depleted. The combination of the invisible nature of the Au in these deposits, as well as the limited surface indicators of these deposits, makes exploration to find new Carlin-type deposits extremely difficult. Comprehensive mineralization models are essential to find new Carlin-type deposits in similar geologic settings. The Nadaleen Trend of Yukon, Canada, is one such district where an improved understanding of this deposit type has led to new discoveries. Previous studies compared and contrasted the tectonic setting, host rock depositional setting, structural preparation, and mineralization style of the Nadaleen Trend with those in Carlin-type localities, Nevada. However, the comparisons at an atomic scale, between Carlin-type Au deposits in the Nadaleen Trend and those in Nevada, has yet to be investigated. This study fills this knowledge gap by combining high resolution microanalytical techniques with atom probe tomography to examine the distribution of Au and other trace elements in the Nadaleen Trend, compare them to a representative Carlin-type deposit in Nevada (Turquoise Ridge), and determine how widespread the mineralization model is. Our findings show that in the Nadaleen Trend, as in Nevada, Au is generally directly linked with As at the macro to atomic scale, and is incorporated into As/Au rich overgrowths on sedimentary/diagenetic pyrite. Gold-rich pyrite rims in the Nadaleen Trend are generally smaller than those found in Nevada (0.5–2 µm vs &gt; 10 µm), although the ore grades appear comparable. We find that the Au in the pyrite of the Nadaleen Trend is homogenously distributed (i.e. lattice bound) at the atomic scale, but that there is a notable enrichment of As surrounding individual Au atoms. These findings are in agreement with those from previous work on a representative deposit in Nevada, and support the assertation that As is the key ingredient in facilitating the incorporation of Au into the pyrite lattice. Arsenic as an essential component in the trapping mechanisms of Au in CTG deposits, is something that has been as to yet underappreciated in the current models of CTG deposit formation.

The Contribution of Carbonaceous Material to Gold Mineralization in the Huangjindong Deposit, Central Jiangnan Orogen, China

The Huangjindong gold deposit in northeastern Hunan is one of the most representative gold deposits in the Jiangnan Orogenic Belt. The orebodies are mainly hosted in the Neoproterozoic Lengjiaxi Group, which comprises carbonaceous slates. Abundant carbonaceous material (CM) can be found in the host rocks and ore-bearing quartz veins, but its geological characteristics and genesis, as well as its association with gold mineralization, are still unclear. Systematic petrographic observation demonstrated two types of CM in host rocks and ores, i.e., CM1 and CM2. Among them, CM1 is the predominant type and mainly occurs in the layered carbonaceous slates, while CM2 is mostly present in quartz veins and mineralized host rocks. Laser Raman spectroscopic analyses of CM1 were performed at higher temperatures (376–504 °C), and CM2 was generated at similar temperatures (255–435 °C) to gold mineralization. Combined with previous studies, we can conclude that CM1 was produced by Neoproterozoic to early Paleozoic metamorphism before gold mineralization, while CM2 is of hydrothermal origin. Geochemical modeling indicates that CM1 could promote gold precipitation through reduction, as well as facilitate structure deformation and metal absorption as previously proposed. However, hydrothermal CM2 is favorable for gold mineralization because it triggers sulfidation, similar to other Fe-bearing minerals (such as siderite) in the host rocks. Consequently, both types of CM in the Huangjindong deposit are favorable for gold mineralization and carbonaceous slates could be important gold-bearing units for future ore prospecting in the Jiangnan Orogen as well as other places in South China.

Characteristics of Host Rocks Manganese of The Anabanua Village Barru District South Sulawesi Province, Indonesia

One of the prospects for a wealth of geological resources that can be utilized for the benefit of mankind is manganese metal mineral resources. In Anabanua Village, especially at the research location, there is an indication of manganese mineralization that the type of rock carrying the mineralization is not yet known. The purpose of this study was to determine the chemical elements of metallic minerals, mineralogy, and types of mineralization-carrying rocks, as many as three samples in the form of chunks, which were analyzed using megascopic analysis methods identifying the texture and structure of carrier rocks, XRD (X-Ray Diffraction) analysis minerals, and XRF (X-Ray Fluorescence). The characteristics of manganese mineralization carrier rocks consist of metallic elements Mn (0.046%-20.455%), Fe (1.555%-3.673%), and nonmetallic elements SiO2 (11.403%-48.165%), K2O (0.398%-4.177%). Mineralogy of manganese mineralization carrier rocks are roeblingite (Pb2Ca6Mn2+(Si3O9)2(SO4)2(OH)2·4H2O), rhodonite (CaMn3Mn[Si5O15]), diopside (CaMgSi2O6), calcite (CaCO3), kieserite (Al, Ga)2(GeO4)(OH)2), zeolite (Mn2O.Al2O3.xSiO .yH2O), and palygorskite ((Mg, Al)2 Si4O 10(OH)·4H2O). Manganese mineralization host rocks are determined by referring to the SiO2 (%weight) and K2O(%weight) diagrams to produce basalt igneous rock types.

Mineral chemistry of the Geyer SW tin skarn deposit: understanding variable fluid/rock ratios and metal fluxes

AbstractThe Geyer tin skarn in the Erzgebirge, Germany, comprises an early skarnoid stage (stage I, ~ 320 Ma) and a younger metasomatic stage (stage II, ~ 305 Ma), but yet, the source and distribution of Sn and the physicochemical conditions of skarn alteration were not constrained. Our results illustrate that contact metamorphic skarnoids of stage I contain only little Sn. REE patterns and elevated concentrations of HFSE indicate that garnet, titanite and vesuvianite of stage I formed under rock-buffered conditions (low fluid/rock ratios). Prograde assemblages of stage II, in contrast, contain two generations of stanniferous garnet, titanite-malayaite and vesuvianite. Oscillation between rock-buffered and fluid-buffered conditions are marked by variable concentrations of HFSE, W, In, and Sn in metasomatic garnet. Trace and REE element signatures of minerals formed under high fluid/rock ratios appear to mimic the signature of the magmatic-hydrothermal fluid which gave rise to metasomatic skarn alteration. Concomitantly with lower fluid-rock ratio, tin was remobilized from Sn-rich silicates and re-precipitated as malayaite. Ingress of meteoric water and decreasing temperatures towards the end of stage II led to the formation of cassiterite, low-Sn amphibole, chlorite, and sulfide minerals. Minor and trace element compositions of cassiterite do not show much variation, even if host rock and gangue minerals vary significantly, suggesting a predominance of a magmatic-hydrothermal fluid and high fluid/rock ratios. The mineral chemistry of major skarn-forming minerals, hence, records the change in the fluid/rock ratio, and the arrival, distribution, and remobilization of tin by magmatic fluids in polyphase tin skarn systems.

A Bayesian Approach to End-Member Mixing Estimations in a Geological Nuclear Waste Repository in Sweden

The Swedish Nuclear Fuel and Waste Management Co. (SKB) has been searching for a site to construct a deep geological repository for spent nuclear fuel in Sweden. In 2012, Forsmark was selected as the location for the nuclear fuel repository and construction will start in 2027. An understanding of the chemical composition and evolution of the groundwaters at the site is an integral part of the long-term safety case. SKB’s traditional approach to describe a site has been to use M3 mixing of end-members as the main process controlling the groundwater composition. We propose a new approach using a Bayesian mixing model. Similarly to the traditional mixing approach, the fraction of each end-member for all samples in the dataset is calculated, with the exception of the deep saline end-member. Given the slow movement of the deep groundwaters, it is likely that they have reached equilibrium with the host rock and fracture minerals. Therefore, we introduce an additional step, consisting of a Phreeqc model to construct the theoretical composition of groundwater with an increasing Cl concentration in equilibrium with the mineralogy of the host rock. This is a way of introducing a geochemical explanation to deep saline waters found in the geosphere of the Forsmark site. The results indicated a higher fraction of glacial meltwater in deep groundwaters in Forsmark compared to previous models. This approach could be directly applied to other groundwater systems, with different mineralogy of the host rock, assuming slow moving groundwater in equilibrium.

Gagates in Crimean middle jurassic sediments (Sudak): coal petrography, paleobotany, formation conditions

Background. The coal-bearing deposits of the Kopsel formation of the Bathonian-Callovian age of the Middle Jurassic near the city of Sudak (Crimea) are studied. The conducted lithological and mineralogical analysis of rocks, mainly sandstones and siltstones, with shell detritus, plant residues and coal lenses (gagates), made it possible to determine the coastal-marine and lagoon sedimentation conditions. The studied gagates are represented by structural vitrinite and belong to the humus group. Secondary minerals in coal seams and host rocks indicate the stage of early catagenesis. The botanical analysis revealed the coal-forming plants, belonging to a group of conifers of the araucaria family.Aim. To identify the facies-climatic and landscape conditions for the formation of gagates of the Kopsel formation, along with their composition, structure, and secondary changes. To demonstrate that the material composition of coals is the wood of gymnosperms, mainly conifers, rather than algal thalli.Materials and methods. The natural outcrops of the coal-bearing deposits of the Middle Jurassic of the Bathonian-Callovian stage of the Kopsel formation in the valley of the Kopsel River near the city of Sudak (Crimea) were studied. The lenses and interlayers of brown coal — gagate — present in these deposits were of particular interest. Gagate samples were studied both macroscopically (forms and occurrence conditions in the section) and microscopically (by coal petrography methods). To this end, double-sided polished sections were examined using a polarizing microscope and a Vega3 Tescan scanning microscope. The microanalysis of chemical elements was performed using an ULTM Max (GIN) microscope attachment. Paleobotanical studies of carbonified plant residues were carried out. The structure, texture and mineral composition of the rocks were studied in thin sections using a microscope. A mineralogical analysis was carried out using a D8 Advace X-ray diffractometer (gross composition in a powder diffractogram and composition of clays in a fraction of &lt;0.001 mm) and a Vega3 Tescan (GIN) scanning microscope.Results. The comprehensive studies conducted in the new, unique location of coals in the Kopsel Formation of the Middle Jurassic (Bathonian-Callovian stage) in the valley of the Kopsel River determined the paleobotanical composition of coal-forming plants (with the predominance of conifers of the Araucariaceae type), the climatic and paleolandscape conditions for the formation of these coals on the northern outskirts of Tethys. The lithological and mineralogical features of rocks, mainly sandstones and siltstones, with shell detritus, plant residues and lenses of coals (gagates), make it possible to determine the facies conditions of sedimentation as coastal-marine and lagoonal, with fragments of avantdelta and proluvial, landslide deposits. The established secondary changes in the host rocks and the coals indicate the stage of early catagenesis, to which the stratum was subjected at the next stages of geological history.Conclusion. Peat accumulation and subsequent coal formation most likely occurred in shallow lagoons. The type of peat accumulation is paralytic, paragenetically related to the studied sediments. Post-sedimentation transformations of the rocks correspond to early catagenesis. These transformations were established by the presence of secondary calcite (by rock cracks and in the form of nodule formations), the abundance of authigenic gypsum, and the widespread replacement of pyrite framboids with iron oxide minerals. The interlayers of gagates have also undergone changes. In those places where organic matter is impregnated with carbonate solutions, the coal substance is exposed to heat, thus becoming optically opaque.

Origin of lithium in oilfield brines in continental petroliferous basin: Insights from Li and Sr isotopes in the Jianghan Basin, central China

Oilfield brines are a significant alternative lithium resource to meet the global demand in the next decades. However, their metallogenic characteristics and mechanism remain unclear. To constrain the source and enrichment process, this study presents chemical and multi-isotope data for oilfield brines from the Middle Eocene to Lower Oligocene Qianjiang Formation of the Jianghan Basin, central China. These formation water samples collected from 159 oil wells have salinities of 47–355 g/L and lithium contents of 5.36–150.00 mg/L. The good linear relationship between δD and δ18O values indicates that the salinities are achieved by dilution of the primary brine by meteoric water. Waters from the lower of the Qianjiang Formation have higher δD and δ18O values and 87Sr/86Sr ratios than those from the upper, in conjunction with the low correlation between the δD and δ18O value and the salinity and between the Sr content and the 87Sr/86Sr ratio, indicating the impact of associated water-rock interactions. Moreover, contributions from diagenetic processes of dolomitization, dissolution of evaporites and albitization are also indicated by the high Cl/Br mass and Na/Cl molar ratios and the Ca excess and Na deficit. Chemical geothermometers give reservoir temperature values of 118 °C and 138 °C on average for the oilfield brines from the upper and lower formation, respectively. The binary linear relationships between Li contents and TDS values and Br contents imply specific enrichment processes in addition to evapo-concentration. Variations in δ7Li values (+10.6‰–+21.3%) and 87Sr/86Sr ratios (0.709479–0.711516) were used to trace the process of Li enrichment in oilfield brines. The lower δ7Li values with more enriched Li in comparison to Na indicate a significant lithium input from clastic host rocks, which is also confirmed by the fact that more radiogenic waters have relatively lower δ7Li values. Overall, these results suggest that Li enrichment in the Qianjiang oilfield brines was generated by the interaction of Li-bearing minerals in the clastic host rocks with water formed by original evaporitic brines diluted by meteoric water. This work represents a significant role of lithium and strontium isotopic systematics in elucidating the Li origins of deep-seated oilfield brines in continental petroliferous basins.

Au-Bi-Te(-Cu) Mineralization in the Wawa Gold Corridor (Ontario, Canada): Implications for the Role of Bi-Rich Polymetallic Melts in Orogenic Au Systems

The Wawa Gold Corridor, a series of Archean orogenic Au deposits in the Michipicoten greenstone belt, Canada, comprises two styles of Au mineralization: (1) syn-deformation gold associated with pyrite and arsenopyrite; and (2) late- to post-deformation gold associated with chalcopyrite and Bi-Te(-S) phases. Through petrographic and mineral–chemical analysis, it was determined that gold in the latter assemblages precipitated from Bi-rich polymetallic melts during hydrothermal overprinting of the earlier Au-As-S mineralization; this event was likely driven by the emplacement of Archean lamprophyres. The formation and evolution of these melts was governed by fluid–pyrite reaction interfaces, where the bulk composition of the melts was broadly controlled by the trace-element chemistry of the sulphide minerals in the local host rocks. This suggests that the melt-formation event involved mobilization of existing metal endowments related to early Au events, rather than addition of new Au, Bi, and Te. Thus, the deposition of high-grade Au by Bi-rich melts was dependent on pre-existing sulphide mineralization, both as a source of metals and as micro-environments that stabilized the melts. The paragenesis documented in the Wawa Gold Corridor (i.e., early hydrothermal Au-As-S mineralization and late melt-related Au-Bi-Te mineralization) has been previously recognized in numerous other orogenic and non-orogenic Au deposits. Herein, it is suggested that this apparent consistency in the timing of melt events across multiple systems probably reflects the physicochemical conditions (i.e., fO2-aH2S) of orogenic fluids being incompatible with molten Bi. Bi-rich polymetallic melts are hence unlikely to form primary Au mineralization in orogenic systems but can, however, have a significant impact on the ultimate deposit-scale distribution of Au via secondary mobilization and enrichment.

Formation of authigenic grey monazite: A palaeo-thermal anomaly marker in very-low grade metamorphic rocks?

Reassessment of France’s rare earth element (REE) potential led us to investigate REE behaviour in the black shales of the Middle Ordovician Angers-Traveusot Formation in central Brittany (France). This study focuses on the distribution of nodular grey monazite (up to 200 g/t) within the shales, which formed in response to the diagenetic and low-grade metamorphic evolution of the studied area. Whole rock geochemistry, rock–eval pyrolysis and evolution of clay mineral crystallinity were firstly used to determine temperature and mass transfer conditions in the black shales. Then, monazite texture, composition and U–Pb in-situ dates were determined, and correlated with the diagenetic/anchimetamorphic conditions. Nodular monazite appears in the Ordovician black shales at the transition between high-grade diagenesis and the anchizone metamorphic facies, in response to processes controlled by competing influences such as organic matter maturation, Fe oxide/hydroxide reduction and clay transformation with accompanying fluid release. Monazite occurs mainly as elongated nodules, up to 2 mm in diameter that are characterised by their grey colour caused by an abundance of host-rock mineral inclusions. Monazite nodule compositions are zoned with Nd and middle REE-rich cores surrounded by Ce-rich rims, with no evidence of inherited domains. Ce-monazite also occurs as a replacement of nodular monazite or in late-stage fractures. Zoned nodular grey monazites were dated at ca. 403.6 ± 2.9 Ma, which is proposed to record the high heat flux that led to the anchimetamorphic conditions found at the base of the Angers-Traveusot formation, prior to the Variscan deformation. Crystallisation of the metamorphic Ce-monazite occurred at two periods, dated at 382.6 ± 2.9 Ma and 349.6 ± 6 Ma, which correspond to pre-collisional and collisional tectono-metamorphic stages respectively. Nodular grey monazite constitutes an interesting alternative economic solution because of its very low content in both Th (X¯=2160 ppm) and U (X¯=145 ppm) and negligible radiological impact if mined. However, placers currently display a limited economical interest.

Frictional power dissipation in a seismic ancient fault

The frictional power per unit area Q˙ (product of frictional traction τ and slip rate u˙ in MW m−2) dissipated during earthquakes triggers fault dynamic weakening mechanisms that control rupture nucleation, propagation and arrest. Although of great relevance in earthquake mechanics, Q˙ cannot, with rare exceptions, be determined by geophysical methods. Here we exploit theoretical, experimental and geological constraints to estimate Q˙ dissipated on a fault patch exhumed from 7-9 km depth. According to theoretical models, in polymineralic, silicate rocks the amplitude (< 1 mm) of the grain-scale roughness of the boundary between frictional melt (pseudotachylyte) and host rock decreases with increasing Q˙. The dependence of grain-scale roughness with Q˙ is due to differential melt front migration in the host rock minerals. This dependence is confirmed by friction experiments reproducing seismic slip where pseudotachylytes were produced by shearing tonalite at Q˙ ranging from 5 to 25 MW m−2. In natural pseudotachylytes across tonalites, the grain-scale roughness broadly decreases from extensional to compressional fault domains where lower and higher Q˙ are expected, respectively. Analysis of the natural dataset calibrated by experiments yields Q˙ values in the range of 4-60 MW m−2 (16 MW m−2 average value). These values, estimated in small fault patches, are at the lower end of broad estimates of Q˙ (3-300 MW m−2) obtained from frictional tractions (30-300 MPa) and fault slip rates (0.1-1 m/s) assumed as typical of upper crustal earthquakes.

Implications of multiple fluids in the deposition of Pb-Zn-Ba deposits in the Alvand Mountain, Golpayegan, Iran: Evidence from fluid inclusions and O, C, S isotopes

Middle Cretaceous sedimentary carbonates of Alvand Mountain host Pb-Zn-Ba veins. This mineralization occurs mainly as veins, breccia fillings, and to a lesser extent disseminated and host rock replacements. Ore mineralogy is simple and consists of sphalerite, galena, and barite, with minor pyrite, rare chalcopyrite, and tetrahedrite. Host rock dolomitization and hydrothermal silicification are typically associated with ore. Two types of primary liquid–vapor fluid inclusions were distinguished in sphalerite, quartz, and barite. Type I (salinity, 17–23 wt% NaCl; Th, 130 ± 30 °C) is dominant in sphalerite, whereas type II (salinity, 4.5–10 wt% NaCl, Th, 190 ± 40 °C) is dominant in quartz and barite; these fluids have characteristics of basinal brines and show a negative mixing trend in an evolving process of sulfide and gangue saturation. The δ18O and δ13C values for host rock and altered minerals range from 22.0 to 12.9 ‰ and 3.8 to −3.2 ‰, respectively, which suggest the influence of increased temperature fluids, presence of organic carbon, and fluid mixing. The δ34S values of sulfides and barite varies from 2 to 17 ‰ and 23 to 24 ‰, respectively, suggesting that reduced sulfur could be derived by thermochemical reduction of Paleogene seawater sulfate in the presence of organic matter; however, the wide ranges of δ34S sulfide values (15 ‰) exhibits that reduction of sulfur probably originated by different sulfur reduction processes. The data present in this study suggest that during increased tectonic activity in the late Cretaceous-Paleogene, mixing of basinal brines and water–rock interaction resulted in Pb-Zn-Ba deposition in carbonate host rocks. Therefore, it may represent low-temperature mineralization, possibly analogous to MVT depositional systems.

Physical and chemical studies of finely-dispersed slurry tailings of the Donskoy Ore Mining and Processing Plant (DMPP) for chemical beneficiation to produce chromium concentrate

During the processing of chromium ores, chromite concentrate is obtained for the production of ferrochrome, and waste is also collected - tailings beneficiation. Fragment and sludge tailings depending on the beneficiation technology. Finely dispersed sludge tailings of the Donskoy MPP of Kazchrome JSC are stored at the Dubersay and Akzhar tailings, which are man-made deposits (MMD) or man-made mineral formations (MMF). To develop a technology for processing sludge tailings, which contain up to 30% chromium oxide, their physical and chemical studies were carried out. According to the chemical analysis of sludge tailings, it follows that research should be directed to the removal of magnesium and silicon oxides, thereby increasing the content of chromium oxide to a standard chromium concentrate. A very thin dissemination of chromite with minerals of host rocks necessitates additional grinding of intermediate products, which are intergrowths of chromite with waste rock. According to the results of fractional analysis and IR spectroscopy, the content of a large number of flocculants in the studied sludge tailings and a large number of particles with a particle size of less than 20 μm, which, in heavy liquid solutions, due to its small size, is in suspension and does not stratify, was revealed. According to the granulometric composition, it was determined that the sludge minus 0.071 mm must also be classified into 0.04 and 0.02 mm and enriched each class separately. It has been established that in order to obtain high technological performance, the traditional gravitational beneficiation scheme used at the DMPP is technologically cumbersome, because includes operations of flocculant disintegration, classification, grinding, beneficiation on concentration tables of each size class, regrinding of intermediate products. The results of the physicochemical study of chromium sludge tailings showed the need for a combined beneficiation scheme, including chemical enrichment with finishing of chromium concentrate by gravity beneficiation.

Mineralogy and paragenesis of the Meso-Proterozoic Rohil uranium deposit, North Delhi Fold Belt, Rajasthan, India

The Rohil uranium deposit, located about 70 km south of the Khetri copper deposit in the North Delhi Fold Belt, Rajasthan, India, is albitite-hosted. This deposit is associated with Na-metasomatism, mainly affecting the metasedimentary wall rocks. Quartzite, quartz biotite schist, quartz amphibole schist, and graphite schist underwent variable degrees of albitization, as documented by a wide range of altered wall rocks, including weakly altered metasediments to almost pure albitites. These host rocks consist of metamorphic mineral assemblages such as Ca plagioclase – quartz – biotite – Ca amphibole – graphite – garnet – sillimanite – corundum – ilmenite. The hydrothermal alteration assemblages contain variable amounts of albite, chlorite, biotite, sericite, orthoclase, sphene, rutile, allanite, actinolite, and calcite. The textural relationships between primary host rock minerals and hydrothermal alteration products suggest four main stages of metasomatism: (1) an early pre-albitization stage, (2) a Na-metasomatic stage, that are followed by (3) a Na‐Ca-Mg- and (4) K- metasomatic stage. Albites are of two types: albite-1 is subhedral to euhedral and equidimensional, formed by the alteration of metamorphic plagioclase during the Na-metasomatic stage. Albite-2 is feathery and formed in fractures/cavities by precipitation of alkali-rich fluid during Na-Mg-Ca metasomatic stages. Albitization is pervasive on a regional scale. The hydrothermal metasomatic fluids utilized structures such as shears and breccias in the metasediments as conduits and as the loci of uranium mineralization. Major uranium minerals are uraninite, U-silicate, and brannerite. Uranium-bearing minerals occur as disseminations, in veins and as minute inclusions in biotite and titanite within albitized metasediments. The petrographic studies suggest that the metasomatic alteration of host rocks is characterized by albitization, actinolitization, carbonatization, chloritization, sericitization, biotitization, sulfidation, and silicification. The close association of U, REE-bearing minerals, and albite-2 indicates that the main U-REE mineralization stage was coeval with the Na-Ca-Mg and K-metasomatic stages.

Processes of Enrichment of Trace Metals for High-Tech Applications in Hydrothermal Veins of the Ruhr Basin and the Rhenish Massif, Germany

ABSTRACTThe increasing demand for high-tech trace elements supports the need for systematic investigations of their primary occurrences. Mineralogy and trace element characteristics of hydrothermal base-metal veins from the Ruhr Basin (Ruhrgebiet) and the Rhenish Massif (Bergisches Land) in Germany were studied by energy-dispersive X-ray fluorescence mapping, laser ablation-ICP-mass spectrometry, and electron microprobe analyses. Quantitative trace element analysis proves elevated concentrations of Ge and Ga in sphalerite from the Ruhrgebiet. In addition to about 6 Mt of sphalerite-dominated ore, a potential of about 10 t of Ge is indicated to be concentrated in the Auguste Victoria and Graf-Moltke base-metal deposits in the Ruhrgebiet. Assessments on physicochemical fluid properties and metal sources using vitrinite reflectance analysis and host rock investigation indicate a genetic link between the Carboniferous carbonaceous rocks (hosting a number of coal seams) and significant trace metal enrichment in the veins. Gallium enrichment, outlining primary growth zones in ore stage 1 sphalerite, is facilitated by the alteration of Al-bearing minerals in adjacent host rocks due to intense fluid/rock interaction. Reduced Ga and very low In concentrations in ore stage 2 may reflect sealed fluid pathways or changes in the fluid properties. The high level of organic matter in the system probably supported enrichment of Ge in the hydrothermal fluids. The constantly high levels of fixation of Ge in sector zoning patterns of the sphalerite during both ore stages indicate a continuous supply. Elevated contents of Sb together with Cu, As, and Pb in sectors of the sphalerite grains point to a local enrichment of nanometer-scale inclusions of sulfosalt-like phases. Sphalerite of both districts and even of the two ore stages in the Ruhrgebiet shows variations in δ34S isotope compositions due to varying sulfur sources. Both the host rock composition and the presence of organic matter contributed to the trace metal enrichment in the Ruhrgebiet base-metal sulfides as compared to the low contents typical of base-metal ore from the Bergisches Land.

The role of parent lithology in nanoscale clay-mineral transformations in a subtropical monsoonal climate

Abstract Clay minerals are among the most important reactive components of soil systems, acting as a bridge linking organic and inorganic components. Lithology is a key factor in clay-mineral genesis and transformation, yet it has received scant attention to date at the nanoscale. Inferences regarding pedogenic clay-mineral transformations based on X-ray diffraction (XRD) are sometimes speculative, whereas mineralogic relationships documented by high-resolution transmission electron microscopy (HRTEM) are more robust due to direct evidence from lattice-fringe observations. In this contribution, the mineralogical and geochemical characteristics of four soils derived from different parent rock types (a gneiss, an Fe-rich siltstone, a sandstone, and a dolostone) from subtropical China were determined using HRTEM, XRD, and geochemical elemental data. The predominance of 2:1 clay minerals and kaolinite in the investigated soils is typical of subtropical climatic settings. Lattice-fringe images suggest the prevalence of topotactic transformations during clay-mineral alteration. Two distinct alteration pathways were observed in the investigated soils, one starting with chlorite and the other with illite, with convergence of mineralogic compositions toward kaolinite and crystalline iron and aluminum (oxyhydr)oxides. In the early stages of weathering, chlorite transformed into expandable clays through a continuous, solid-state mechanism with corrensite and/or randomly interstratified chlorite-vermiculite/chlorite-smectite as intermediate products. Unlike chlorite, which tends to form a 1:1 regularly interstratified phase, the weathering of illite commonly starts at layer edges. Under subtropical monsoonal climates, the precursor minerals in host rocks and aeolian materials determine the starting composition and, to a certain extent, the trajectory of clay-mineral transformation over time. With advanced weathering, mineralogic convergence toward kaolinite and Fe/Al-(oxyhydr)oxides tends to obscure the initial substrate composition. This study advances our understanding of the role of parent lithology in clay-mineral evolution at the nanoscale.

Fate and transport of strontium in groundwater from a layered sedimentary aquifer system

In this article, strontium distribution in sedimentary coastal aquifers of Eastern India was studied and its association with groundwater particles has been ascertained using hydrochemical and morphological tools. Groundwater contains Sr2+ in the range of 0.08–4.0 mg/L with higher concentrations in Cretaceous formation. The particle number in groundwater varies from 4.5 × 105 to 3.3 × 106 per liter and follows the power law distribution with respect to the particle diameter. The calculated β values (2.54 and 4.03) signify the abundance of smaller particles over larger ones. The particle concentration of size range 0.45–8 μm is found to be 0.64–2.6 mg/L. Elemental data of groundwater particles clearly suggest their origin from the host rock minerals. Zeta potential data indicates diverse nature of colloids suggesting prevalence of both positive and negative charged species in the groundwater. The hydrochemical interpretation along with speciation studies infers that high Sr2+ in groundwater is a result of incongruent dissolution of carbonate minerals and the dissolved Sr2+ partitions into both dissociated and un-dissociated forms. Based on the Sr2+/Ca2+ ratio and mineral saturation indices, it can be inferred that the Sr2+ is preferentially associated with colloids over large particles and the migration takes place through sorption of Sr2+ onto clay-bound (extrinsic) colloids in groundwater. This study describes the mechanism of strontium release into groundwater and provides insights into the role of groundwater particles in controlling the strontium migration to deep aquifers.

Morphological characteristics of main minerals in coal and host rocks from Heidaigou Mine, northeastern Ordos, China

Morphological characteristics of main minerals in coal and host rocks from Heidaigou Mine, northeastern Ordos, China

Fusion of Lineament Factor (LF) Map Analysis and Multifractal Technique for Massive Sulfide Copper Exploration: The Sahlabad Area, East Iran

Fault systems are characteristically one of the main factors controlling massive sulfide mineralization. The main objective of this study was to investigate the relationship between fault systems and host lithology with massive sulfide copper mineralization in the Sahlabad area, South Khorasan province, east of Iran. Subsequently, the rose diagram analysis, Fry analysis, lineament factor (LF) map analysis and multifractal technique were implemented for geological and geophysical data. Airborne geophysical analysis (aeromagnetometric data) was executed to determine the presence of intrusive and extrusive masses associated with structural systems. Accordingly, the relationship between the formation boundaries and the fault system was understood. Results indicate that the NW-SE fault systems are controlling the lithology of the host rock for copper mineralization in the Sahlabad area. Hence, the NW-SE fault systems are consistent with the main trend of lithological units related to massive sulfide copper mineralization in the area. Additionally, the distance of copper deposits, mines and indices in the Sahlabad area with fault systems was calculated and interpreted. Fieldwork results confirm that the NW-SE fault systems are entirely matched with several massive sulfide copper mineralizations in the area. This study demonstrates that the fusion of lineament factor (LF) map analysis and multifractal technique is a valuable and inexpensive approach for exploring massive sulfide mineralization in metallogenic provinces.

Insights into the Metallogenesis of the Felsic Volcanic Hosted Mundiyawas-Khera Cu Deposit, Alwar Basin, Western India

Copper and associated gold mineralization in the Mundiyawas-Khera area of western India is hosted by the Proterozoic felsic volcanic rocks of rhyo-dacite composition. Signatures of hydrothermal alteration represented by sericite, epidote, scapolite and carbonates are well observed around the ore mineralization zone. The felsic volcanic rocks with gently to flat sloping REE pattern, variable negative Eu anomaly, intermediate abundances of HFSE and moderate to low Zr/Y anomalies are suggested to be FII, FIIIa and FIV type rhyolite. The felsic volcanic host rock for copper mineralization has a depleted and flat HREE pattern and indicates the crustal source, which is garnet free. Negative Eu anomaly in the rock is probably because of the intracrustal partial melting formed in a rift related environment. The high temperature magmatic activities are probably evolved due to the partial melting of crust at shallow to moderate depths, suggesting an evolved continental crust. The δ13C values of the mineralized carbonate veins range between −10.4‰ and −0.9 ‰ (min = −10.6‰, n = 27), whereas the δ18O values show a range of 16.35‰ to 25.23‰ (min = 21.49‰, n = 27), ideally suggesting a mixed source for the ore bearing fluid. Geological, geochemical and stable isotope data of the Mundiyawas-Khera copper deposit suggest it to be a VMS/VHMS setup and these insights will lead to finding new deposits in the nearby areas, having same stratigraphic horizons and similar lithogeochemical assemblages.