Acta Geochimica最新文献

Recovered samples of Jilin H5 chondrite experimentally shocked to 12–133 GPa were studied to explore the behavior of opaque minerals under shock loading using SEM–EDS, Raman spectroscopy, and TIMA. The following results were obtained. Firstly, at pressures lower than 53 GPa, the opaque minerals still keep the unmelted state, while at 78 GPa and higher, FeNi metal and troilite form eutectic intergrowths occurring as disorderly fine veinlets filling the shock-induced fractures in silicate minerals. Secondly, single kamacite grains still maintain their contour at 12 GPa, but a part of brittle troilite grains was fragmented and squeezed into the shock-induced fractures within kamacite grains. At 53 and 133 GPa, many more troilite fragments are poured in the kamacite interior to form disordered hybrid aggregates or to form squiggly strips, respectively. Similar phenomena are observed within single troilite grains, but the mineral squeezed into troilite grains is kamacite. Thirdly, chromite is a hard and refractory oxide mineral. When the shock pressure rises step by step from 12 to 133 GPa, the shock effect of chromite is only fragmentation. Its grain size decreases from tens of µm at 53 GPa to a few µm at 133 GPa. And, fourthly, native copper exhibits distinct redistribution behavior at high temperature. In Jilin samples shock-loaded to 12 GPa, copper initially located at troilite–kamacite interfaces partially transferred into small troilite grains containing fine FeNi particles. At 53 and 133 GPa, native copper preferentially transferred into larger troilite grains containing more particles of eutectic FeNi metal.

The giant impact hypothesis for the Moon’s origin has had difficulty explaining the nearly identical isotopic compositions of Moon rocks and rocks from Earth’s silicate mantle and crust. These similarities are instead more compatible with the Darwin-Wise hypothesis that the Moon arose by fission of a rapidly spinning Earth. To overcome problems with the fission model concerning structural stability and angular momentum conservation, some authors suggested that lunar fission was feasible on a more slowly rotating Earth if assisted by a nuclear explosion near the core-mantle boundary. In this light we consider the possible roles of the large low-velocity provinces (LLVPs). These long-lived structures have been implicated in diverse geophysical processes ranging from deep mantle plumes to continental breakup and mass extinction events. While the LLVPs have been seen as possible remnants of the giant impactor, we propose that one of them was the site of lunar ejection. Internal heating of the liquid core is suggested to have given rise to an equatorial belt just under the core-mantle boundary analogous to the one recently detected by Ma and Tkalčić [Sci Adv 10(35):eadn5562, 2024]. Upwellings of heat and volatiles from this belt then generated two antipodal, equatorial bulges: the precursors of the Pacific and African LLVPs. Prior to the emergence of plate tectonics, core heat was mainly dissipated by networks of deep mantle plumes extending above the proto-LLVPs. These plume networks represent conduits of weakened mantle through which proto-lunar materials could later rise in a focused ejection. Continuing heat buildup in the core eventually triggered a cataclysmic explosion in the Pacific proto-LLVP, possibly analogous to a planetary-scale kimberlite eruption. This explosion launched LLVP and overlying mantle material into a low Earth orbit, where it coalesced to form the Moon. Some possible sources of additional energy to power the explosion are considered, including nuclear fission, bolide impacts and a hypothetical gravitational decay process culminating in a ‘Ʌ event’.

Nanophase iron particles (np-Fe⁰) have multiple formation mechanisms in lunar soil, which are mostly related to meteorite and micrometeorite impacts. Thermal modification of the impact is critical. Metal oxides have unique chemical and physical properties that allow np-Fe⁰ to form at a lower initial reaction temperature. Through the in-situ heating experiment of ilmenite in the Chang’e-5 sample, it was found that ilmenite can form np-Fe⁰ at 400 °C under high vacuum (10^–6 Pa). This fills in the missing information on the lowest measured temperature at which ilmenite forms np-Fe⁰. At 400–800 °C, only np-Fe⁰ and vesicles were formed without new Ti-rich minerals. At the same time, thermodynamic calculations showed that decomposition of ilmenite occurs in two stages. The experiments correspond to the initial stage of ilmenite thermal decomposition under high vacuum. The study explains the thermal decomposition reaction of ilmenite in a vacuum environment, provides a reference for the minimum measured temperature required for the formation of np-Fe⁰, and further improves the formation mechanism of np-Fe⁰.

The world-class Jiaodong gold province in the North China Craton hosts over 5000 t of Au resource and is characterized by abundant visible gold mineralization. However, the critical processes controlling the formation of visible gold in this province remain poorly understood. To solve this problem, integrated microtextural, trace elemental, and sulfur isotopic analyses of pyrite from the high-grade Linglong gold deposit in the Jiaodong gold province were conducted in this study. Two distinct pyrite types were identified within auriferous quartz-sulfide veins: (1) Py1 aggregates in quartz-pyrite veins (hydrothermal stage II), and (2) euhedral to subhedral, coarse-grained Py2 crystals in quartz-polymetallic sulfide veins (hydrothermal stage III). Microtextural and elemental analyses revealed that visible gold predominantly occurs as intergranular particles between primary pyrite crystals within Py1 aggregates. The Py1 exhibits complex microtextures with abundant mineral inclusions of polymetallic sulfides and has low concentrations of Au (median: 0.032 ppm) with a narrow δ³⁴S range (4.86‰–6.75‰), indicative of rapid crystallization under unstable, disequilibrium conditions. By contrast, the Py2 is texturally homogeneous and contains higher Au concentrations (median: 0.304 ppm) with progressively increasing δ³⁴S values (5.25‰–10.14‰) over time, suggesting slow crystal growth under more stable, near-equilibrium conditions. Based on the microtextural and geochemical information, it is proposed that fluid boiling occurred only during the hydrothermal stage II, which resulted in the unstable physicochemical environment and rapid deposition of gold. During the boiling processes, gold colloids likely occurred and promoted the formation of visible gold.

This paper describes a method for estimating the continuation of ore bodies at depth based on concentration-volume (C-V) fractal modeling of the pyrite thermoelectric coefficient in the Pujon gold deposit, Democratic People’s Republic of Korea. The method is first established using data in the Kumjomdong area, a well-explored brownfield, and it is then applied to estimate the continuation of ore bodies at depth in the Pyongsandok area, a less-explored greenfield. The methodology consists of four steps: (1) 3D modeling of ore bodies using surface geological mapping, mining tunnels in different levels, and a borehole dataset; (2) 3D modeling of thermoelectricity coefficients from Au-bearing pyrites based on discrete smooth interpolation and C-V fractal techniques; (3) determination of levels used for calculation of the thermoelectric parameter of pyrite by C-V fractal modeling instead of traditional levels; and (4) determination of the thermoelectric parameter vertical gradient of pyrite reflecting the variation characteristics of pyrite thermoelectricity in the Pujon deposit. The results indicate that (1) pyrites in the Pujon deposit are dominantly P-type, and it is not reasonable to use traditional levels to calculate the thermoelectric parameter of pyrite; (2) thresholds determined by C-V fractal modeling can be used as levels to calculate the thermoelectric parameter of pyrite; (3) the thermoelectric parameter vertical gradient of pyrite ranges from 1 to 2 in the Pujon deposit; and (4) ore body Pyongsan No. 9 extends 85 m to 235 m downward from the current borehole location.

CM chondrites contain valuable insights into the formation and evolution of the solar nebula, as well as the secondary aqueous alteration processes that affected their parent bodies. Our study focuses on primary and secondary sulfides within the Aguas Zarcas (CM2) chondrite, investigating their formation mechanisms based on their morphology, textures, and compositions. Moreover, we infer the formation temperatures of the sulfides from 230 to 500 ℃ for primary and from 100 to 135 ℃ for secondary. We select representative grains and conduct Fe isotope measurements on them. The primary sulfides with δ^56/54Fe ranging from − 2.44‰ to + 0.69‰ are associated with sulfide–silicate melt segregation, while secondary sulfides with δ^56/54Fe values between − 1.83‰ and − 0.14‰ are linked to aqueous alteration. Overall, the Ni content of the grains is positively correlated with δ^56/54Fe. It might be related to the changes in crystal structure and chemical bond lengths due to the increase in nickel content. Fe isotopes provide a new perspective on sulfide formation and the evolution of a carbonaceous chondrite parent body.

The Martian core mainly contains iron, nickel and some light elements. However, controversies remain about the structure and chemical composition of the Martian core due to a lack of samples and marsquake data. Recently, the InSight lander collected long-term marsquake data, which improved the Martian interior structure model. Based on the preliminary analysis of marsquake data, Mars has a molten liquid core with a radius of around 1700 km. As the Martian core has a smaller density and lower temperature than pure iron at corresponding pressure and temperature conditions, some light elements are introduced to reduce the density and liquidus temperature. With various methods for seismic analysis, in-situ high-pressure and high-temperature experiments, and first-principal calculations, the Martian core composition and evolution models have been updated in the past few years. Here, we review those studies on the light elements in the Martian core from four aspects including (1) high-temperature and high-pressure experiments, (2) marsquake data, (3) mineral physics model with molecular dynamics simulations and (4) cosmochemistry investigation. We discussed the effect of different light elements on the Martian core’s density, sound velocity and liquidus temperature. Moreover, the review examines the varieties, abundances and forms of light elements in the Martian core.

The middle-scale Heima zinnwaldite deposit is situated in the southeastern Tibetan Plateau, SW China. The NNW- to NS-trending orebodies are hosted in the Gaoligongshan metamorphic zone. To clarify the zinnwaldite genesis at Heima, this study presents an integrated investigation of the Heima pegmatites, combining precise geochronology, isotopic tracing, and detailed mineral chemistry to constrain its formation age, petrogenetic origin, and mineralization processes. Our robust geochronological framework, employing magmatic zircon (56.93 ± 0.53 Ma) and cassiterite (57.0 ± 4.2 Ma), establishes the pegmatite emplacement during the Late Paleocene to Early Eocene, representing the maximum age of lithium mineralization. Hf isotopic compositions (εHf_(t) =  −14.3 to −12.4) demonstrate that the Heima pegmatite originated from remelting of ancient sediments, distinguishing it from contemporaneous Eocene Gangdese–Tengchong granites (εHf_(t) =  −12.7 to +11.0) that show mantle contributions. This crustal signature aligns with the evolutionary trend of Hf isotopes in regional gneissic granites (600−420 Ma), supporting an anatectic origin from ancient continental crust rather than being derivatives of nearby Eocene granitic plutons. Detailed geochemical analysis of Li-micas reveals two distinct generations with contrasting formation mechanisms. The primary mica-Ia (53.45 ± 0.86 Ma, Rb–Sr age) exhibits extreme incompatible element enrichment (Li, Be, Rb, Cs) and remarkably low K/Rb ratios (3.98–4.37), characteristic of crystallization from highly fractionated granitic melts. In contrast, secondary mica-Ib and mica-II (17.9–16.0 Ma, Rb–Sr age) show significant Nb–Ta–W enrichment, reflecting precipitation from F–P-rich hydrothermal fluids during Miocene metamorphic–hydrothermal events. Principal component analysis (PCA) confirms the compositional disparity between these mica generations, with the later phases attributed to fluid-induced alteration and reworking. Regional correlation identifies two distinct lithium mineralization episodes in the Gongshan area, southeast Tibetan Plateau. The Eocene phase (~ 55 Ma) is zinnwaldite-dominant (e.g., Heima, Puladi), associated with crustal melting following Neo-Tethyan closure. The Miocene phase (~ 17 Ma) is spodumene-dominant (e.g., Danzhu, Peili), linked to Himalayan leucogranites formed as the rapid exhumation, denudation, and decompression partial melting of Himalayan Crystalline Complex.

The Jalilabad Cu (± Au) deposit lies in the central section of the Tarom-Hashjin Metallogenic Belt, in northern Zanjan Province, NW Iran. Mineralization predominantly occurs within quartz-sulfide veins, veinlets, and breccia zones, primarily hosted by the Eocene volcanic and volcaniclastic units of the Karaj Formation. The mineralization trends NW–SE and is influenced by several strike-slip faults. Chalcopyrite and bornite are the principal hypogene sulfides, with chalcocite and covellite representing the supergene stage. The post-ore stage is characterized by brecciated calcite and quartz. Geochemical analyses show that the monzonite intrusion contains SiO₂ levels ranging from 69.80 to 70.24 wt.%, K₂O+Na₂O values between 8.10 and 8.15 wt.%, and K₂O/Na₂O ratios of 1.36 to 1.61. The intrusion is enriched in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs) while being depleted in high-field-strength elements (HFSEs). A low Hf/Sm ratio indicates an orogenic-related magma, and a low Nb/La ratio points to a depleted mantle source. Microthermometric studies of three quartz types reveal moderate to high formation temperatures (195.4–322.7 °C) and salinities ranging from 8.10 to 11.82 wt.% NaCl_equiv. Oxygen isotope data (δ¹⁸O_H2OO) range from +4.8‰ to +8.1‰, suggesting a magmatic origin for the ore-forming fluids, later diluted by meteoric water. Sulfur isotope values (δ³⁴S_H2S) between −6.0‰ and −9.1‰ confirm a magmatic source. Fluid mixing and dilution are identified as the primary mechanisms for ore precipitation. Raman spectroscopy enables nondestructive identification of minerals through their unique vibrational peaks. Chalcopyrite (213, 280, 1304 cm⁻¹), hematite (214, 282, 469, 689, 1309 cm⁻¹), goethite (967 cm⁻¹), and quartz (125, 198, 458 cm⁻¹) show distinct spectral fingerprints indicating mineral differentiation, alteration tracking, and structural analysis in geological studies. Based on its geological context, the Jalilabad Cu (± Au) deposit is interpreted as resembling a high-sulfidation epithermal deposit.