Acta Geochimica最新文献

The Baidi Au-Sb deposit, which contains 8 t of Au and 10,979 Mt of Sb, is a typical and rare paragenetic deposit located in southwestern Guizhou Province, China. Previous studies have focused on individual ores, but have not combined them to identify their paragenetic mechanism or metallogenic regularity. Therefore, we used field investigations, microscopic observations, and in situ analyses to identify the spatial distribution, mineral paragenesis, compositional evolution, and metallogenic material sources of the ore bodies. We also determined the Au and Sb paragenetic characteristics and the metallogenesis of the deposit. The main Au-bearing minerals in the deposit were early (Apy1–2) and late (Apy3) stage arsenopyrites, as well as pre-mineralization (Py1), mineralization (Py2–5), and late mineralization (Py6–7) stage pyrites. The main Sb-bearing minerals were stibnite (Snt), skinnerite, bournonite, and valentinite. The minerals formed in the order of Py1, Py2–3 + Apy1, Py4–5 + Apy2, Snt, and Py6–7 + Apy3. The δ³⁴S values of the arsenopyrites and pyrites ranged from − 5 to 5‰, while those of stibnite were mostly less than − 5‰ in the later mineralization stages. Sulfur was provided by deep magmatic hydrothermal fluids, but sedimentary sulfur was added in the later stages. Moreover, the trace elemental contents fluctuated and eventually became similar to those of the sedimentary strata. By comprehensively considering the ores along with the geological characteristics of the deposit, we determined that deep magma provided the Au during ore formation. Later tectonic changes provided Sb from the sedimentary strata, which precipitated along fault expansion areas and produced Au and Sb paragenesis.

The sandstones of the Late miocene–Pliocene Dibdibba Formation in the Najaf–Karbala Plateau and Basra were examined to determine their source rocks and origin. The rare earth elements (REE) and trace elements (Sc, Co, V, and Th) concentrations in these sandstones revealed that they likely derived from a single source. The steep light rare earth elements (LREE) and flat, heavy rare earth element (HREE) patterns, negative Eu anomaly, and high ΣREE contents in sandstones suggest its derivation from a suggests that a passive continental margin environment and originated from felsic source rocks. The average concentration of ΣREE is 93.5 ppm, which is lower than that of the average crustal compositions like Upper Continental Crust and Post Archean Australian Shale. The higher proportion of LREE compared to HREE implies that these sandstones were recycled and derived from a distal source. The Th/Co, Th/Sc, La/Sc, La/Co, Eu/Eu* and (La/Lu)cn elemental ratios indicated that these Late Miocene–Pliocene sandstones were derived from felsic rocks located in the marginal region of the Arabian Shield.

The Ain El Bey abandoned mine, in North-West Tunisia, fits into the geodynamic context of the European and African plate boundary. Ore deposit corresponds to veins and breccia of multiphase Cu–Fe-rich mineralization related to various hydrothermal fluid circulations. Petro-mineralogical studies indicate a rich mineral paragenesis with a minimum of seven mineralization phases and, at least, six pyrite generations. As is also the case for galena and native silver, native gold is observed for the first time as inclusion in quartz which opens up, thus, new perspectives for prospecting and evaluating the potential for noble metals associated with the mineralization. Scanning Electron Microscope—Energy Dispersive Spectroscopy and Transmission electron microscopy analyses show, in addition, a large incorporation of trace elements, including Ag and Au, in mineral structures such as fahlores (tetrahedrite-tennantite) and chalcopyrite ones. The mineral/mineral associations, used as geothermometers, gave estimated temperatures for the mineralizing fluids varying from 254 to 330 °C for phase III, from 254 to 350 °C for phase IV, and from 200 to 300 °C for phases V and VI. The seventh and last identified mineralization phase, marked by a deposit of native gold, reflects a drop in the mineralizing fluid’s temperature (< 200 °C) compatible with boiling conditions. Such results open up perspectives for the development of precious metal research and the revaluation of the Cu–Fe ore deposit at the Ain El Bey abandoned mine, as well as at the surrounding areas fitting in the geodynamic framework of the Africa-Europe plate boundary.

In the Tano River Basin, groundwater serves as a crucial resource; however, its quantity and quality with regard to trace elements and microbiological loadings remain poorly understood due to the lack of groundwater logs and limited water research. This study presents a comprehensive analysis of the Tano River Basin, focusing on three key objectives. First, it investigated the aquifer hydraulic parameters and the results showed significant spatial variations in borehole depths, yields, transmissivity, hydraulic conductivity, and specific capacity. Deeper boreholes were concentrated in the northeastern and southeastern zones, while geological formations, particularly the Apollonian Formation, exhibit a strong influence on borehole yields. The study identified areas with high transmissivity and hydraulic conductivity in the southern and eastern regions, suggesting good groundwater availability and suitability for sustainable water supply. Secondly, the research investigated the groundwater quality and observed that the majority of borehole samples fall within WHO (Guidelines for Drinking-water Quality, Environmental Health Criteria, Geneva, 2011, 2017. http://www.who.int) limit. However, some samples have pH levels below the standards, although the groundwater generally qualifies as freshwater. The study further explores hydrochemical facies and health risk assessment, highlighting the dominance of Ca–HCO₃ water type. Trace element analysis reveals minimal health risks from most elements, with chromium (Cr) as the primary contributor to chronic health risk. Overall, this study has provided a key insights into the Tano River Basin’s hydrogeology and associated health risks. The outcome of this research has contributed to the broader understanding of hydrogeological dynamics and the importance of managing groundwater resources sustainably in complex geological environments.

This study is the first attempt to assess the nature of the soil, especially on the western side of the Porali Plain in Balochistan; a new emerging agriculture hub, using weathering and pollution indices supplemented by multivariate analysis based on geochemical data. The outcomes of this study are expected to help farmers in soil management and selecting suitable crops for the region. Twenty-five soil samples were collected, mainly from the arable land of the Porali Plain. After drying and coning-quartering, soil samples were analyzed for major and trace elements using the XRF technique; sieving and hydrometric methods were employed for granulometric analysis. Estimated data were analyzed using Excel, SPSS, and Surfer software to calculate various indices, correlation matrix, and spatial distribution. The granulometric analysis showed that 76% of the samples belonged to loam types of soil, 12% to sand type, and 8% to silt type. Weathering indices: CIA, CIW, PIA, PWI, WIP, CIX, and ICV were calculated to infer the level of alteration. These indices reflect moderate to intense weathering; supported by K₂O/AI₂O₃, Rb/K₂O, Rb/Ti, and Rb/Sr ratios. Assessment of the geo-accumulation and Nemerow Pollution indices pinpoint relatively high concentrations of Pb, Ni, and Cr concentration in the soils. The correlation matrix and Principal Component Analysis show that the soil in this study area is mainly derived from the weathering of igneous rocks of Bela Ophiolite (Cretaceous age) and Jurassic sedimentary rocks of Mor Range having SEDEX/MVT type mineralization. Weathering may result in the undesirable accumulation of certain trace elements which adversely affects crops.

The Paleocene mudrocks in Ghana’s Tano Basin have received limited attention despite ongoing efforts to explore hydrocarbon resources. A thorough geochemical analysis is imperative to assess these mudrocks’ petroleum generation potential and formulate effective exploration strategies. In this study, a comprehensive geochemical analysis was carried out on ten Paleocene rock cuttings extracted from TP-1, a discovery well within the Tano Basin. Various analytical techniques, including total organic carbon (TOC) analysis, Rock–Eval pyrolysis, gas chromatography-mass spectrometry, and isotope ratio-mass spectrometry, were employed to elucidate their hydrocarbon potential and organic facies. The findings in this study were subsequently compared to existing geochemical data on Paleocene source rocks in the South Atlantic marginal basins. The results indicated that the Paleocene samples have TOC content ranging from 0.68 to 2.93 wt%. The prevalent kerogen types identified in these samples were Type II and Type III. Molecular and isotope data suggest that the organic matter found in the Paleocene mudrocks can be traced back to land plants and lower aquatic organisms. These mudrocks were deposited in a transitional environment with fluctuating water salinity, characterized by sub-oxic redox conditions. Maturity indices, both bulk and molecular, indicated a spectrum of maturity levels within the Paleocene mudrocks, spanning from immature to marginally mature, with increasing maturity observed with greater depth. In comparison, the organic composition and depositional environments of Paleocene source rocks in the Tano Basin closely resemble those found in the Niger Delta Basin, Douala, and Kribi-Campo Basins, the Kwanza Formation in Angola, and certain Brazilian marginal basins. However, it is worth noting that Paleocene source rocks in some of the basins, such as the Niger Delta and Brazilian marginal basins, exhibit relatively higher thermal maturity levels compared to those observed in the current Paleocene samples from the Tano Basin. In conclusion, the comprehensive geochemical analysis of Paleocene mudrocks within Ghana’s Tano Basin has unveiled their marginal hydrocarbon generation potential. The shared geochemical characteristics between the Paleocene mudrocks in the Tano Basin and those in the nearby South Atlantic marginal basins offer valuable insights into source rock quality, which is crucial for shaping future strategies in petroleum exploration in this region.

In this study, we report for the first time an Early Palaeozoic basement diorite from the drilled well Nirona-A in the Banni Half-Graben of the Kutch basin, western India. The ⁴⁰Ar–³⁹Ar dates provided a plateau age of 441.84 ± 2.66 Ma and another pseudo plateau of 441.28 ± 5.82 to 388.08 ± 16.65 Ma for the basement diorite. These ages constrain the basement formation age to the Late Ordovician-Early Silurian period. The obtained basement ages are correlatable with the later part of Cambro-Ordovician alkaline magmatism that has been reported from the Huqf area in Central Oman, whereas their lithological and petrographic correlativity with basement diorites occurring in the Dinsi Body of Nagar Parkar igneous complex in Pakistan can also be envisaged. The geochemical studies characterized the diorite with enrichment of LILE (Rb, Ba, and K) and LREE (La, Ce, Nd), strong depletion of HFSE (Nb, Sr, P, and Ti), along with weakly negative Eu anomalies. The geochemical signatures indicate their petrogenetic affiliation with mantle-derived magmas, as well as their tectonic setting to be arc-related, having post-collisional continental-arc type affinity. The ~ 440 Ma basement of Kutch, therefore, appears to represent the later thermal event associated with the reworked Neoproterozoic subduction-related suite from Greater India’s northwest edge, which has implications for Gondwana assembly in the northwest Indian subcontinent.

The Lichi volcanics are a suite of mafic-intermediate-felsic rocks and are considered coeval with the Abor volcanics (~132 Ma) of the Siang window in the Eastern Himalaya. Here, we present the first report of trachytic rocks from the Lichi volcanics, which are exposed in the Ranga valley, along the Kimin-Yazali road section in the Eastern Himalayan Region, Northeast India. The trachytes occur in close association with sandstones of the Gondwana Group of rocks and are characterised based on field, petrographical, and geochemical investigations. These fine-grained trachytes are composed of alkali feldspar, biotite, plagioclase, sodic-amphibole, apatite, illmenite, and titanite. The REE profiles of the evolved trachytic rocks (higher SiO₂ content) display fractionated trends. The fractionation of accessory mineral phases, like apatite and titanite, was possibly responsible for the strongly fractionated REE patterns of the evolved samples. The trachytic rocks demonstrate high apatite saturation temperatures of 988 ± 14 °C (1σ, n = 8). The Aluminium Saturation Index (< 1.1) and binary discrimination diagrams of these peralkaline trachytes define their affinity with A-type granitoids. Elemental ratios like Y/Nb, Nb/U, and Ce/Pb signify that the Lichi trachytes are differentiated products of mantle-derived ocean island basalts. Trace elemental discrimination diagrams Th/Yb versus Nb/Yb, Y versus Nb, and Y + Nb versus Rb reflect a within-plate tectonic regime for the trachytes. From the results presented in this work, we infer that the development of rifting events during the breakup of eastern Gondwana due to the onset of Kerguelen plume activity further led to underplating of basic magma in lower crustal levels. These parental basaltic magmas underwent fractionation processes forming differentiated trachyandesites and trachytes. Taking into consideration the similarities recorded between the Lichi volcanics and Abor volcanics, this study supports the idea that Kerguelen plume activities resulted in the emplacement of these volcanics in the Eastern Himalayas.

In the south Eastern Desert of Egypt, two contrasting types of magmatism (mafic and felsic) are recorded in the Wadi Kalalat area, and form the Gabal El Motaghiarat and Gabal Batuga intrusions, respectively. The two intrusions post-dates ophiolitic and arc associations represented by serpentinite and metagabbro-diorite, respectively. The mafic intrusion has a basal ultramafic member represented by fresh peridotite, which is followed upward by olivine gabbro and anorthositic or leucogabbro. This mafic intrusion pertains to the Alaskan-type mafic–ultramafic intrusions in the Arabian–Nubian Shield (ANS) being of tholeiitic nature and emplaced in a typical arc setting. On the other hand, the Gabal Batuga intrusion comprises three varieties of fresh A-type granites of high K-calc alkaline nature, which is peraluminous and garnet-bearing in parts. A narrow thermal aureole in the olivine gabbro of the mafic intrusion was developed due to the intrusion of the Batuga granites. This results in the development of a hornfelsic melagabbro variety in which the composition changed from tholeiitic to a calc-alkaline composition due to the addition of SiO₂, Al₂O₃, alkalis, lithosphile elements (LILEs) such as Rb (70 ppm) and Y (28 ppm) from the felsic intrusion. Outside the thermal aureole, Rb amounts 2–8 ppm and Y lies in the range < 2–6 ppm. It is believed that the Gabal Batuga felsic intrusion started to emplace during the waning stage of an arc system, with transition from the pre-collisional (i.e., arc setting) to post-collisional and within plate settings. Magma from which the Gabal Batuga granites were fractionated is high-K calc-alkaline giving rise to a typical post-collisional A-type granite (A₂-subtype) indicating an origin from an underplating crustal source. Accordingly, it is stressed here that the younger granites in the ANS are not exclusively post-collisional and within-plate but most likely they started to develop before closure of the arc system. The possible source(s) of mafic magmas that resulted in the formation of the two intrusions are discussed. Mineralogical and geochemical data of the post-intrusion dykes (mafic and felsic) suggest typical active continental rift/within-plate settings.

The mineralogical and geochemical characteristics of the K-rich granites from the Armoor granitic rocks in the northeastern portion of the Eastern Dharwar Craton (EDC) are presented. In order to understand its physicochemical conditions, the petrogenesis of the granitoid was explained from biotite chemistry and geochemical systematics. Studies of mineral chemistry expose that compositionally, K-feldspar and plagioclase in Armoor granite rocks range from An_0, Ab_3−5.9, Or_94−96.9 and An_{5−29, Ab71.9−94.9,} Or_0−1.5, respectively. The mineral chemistry of biotite crystals exhibits composition that varies from primary to re-equilibrated primary biotites. Although biotites from the Armoor granites generally exhibit an I-type trend, with calc-alkaline parental magma in a subduction setting. Biotite chemistry of granites displays magnetite (oxidized) series nature, which has oxygen fugacity (fO₂₎ = − 15.1 to − 16.7(log₁₀ bar), under high oxidizing conditions. Temperature and pressure estimates for the crystallization of Armoor granites based on biotite composition are T = 612–716 °C and 1.0−0.4 kbar, respectively. Geochemically, these rocks are metaluminous to slightly peraluminous and magnesian, with calc-alkaline potassium-rich granite. On the chondrite normalized REE diagram, the granites have positive europium anomalies; rich Sr/Y, (Dy/Yb)_N ratios and reduced Mg^#, Rb/Sr, Rb, Sr indicate that the melting of earlier rocks, crystal accumulation and residual garnet source formed at high pressures. The examined granites show that they are produced from the melting of crustal sources. Thus, the extensive analyses of the described Armoor granite suggest that they were produced by crust sources and developed under oxidizing conditions in subduction setting.