Well-preserved epithermal Cu-Zn-Au mineralization is rare in the Precambrian. The NW-trending Mesoproterozoic Minjhari-Bamhani deposit in the Bastar Craton in central India represents the first documented example of a vertically zoned porphyry-linked epithermal system in the Indian Shield. The Minjhari-Bamhani deposit transitions from a porphyry-proximal system at Minjhari to an intermediate-sulfidation (IS) system at Bamhani-Denwari. The Minjhari sector exhibits phyllic alteration (quartz-sericite) associated with quartz veins and breccias that host pyrite, chalcopyrite, tennantite, and gold. Fluid inclusion data indicate boiling of high-salinity (up to 33 wt% NaCl equivalent), CO2-CH4-bearing magmatic-hydrothermal fluids at temperatures up to 315 degrees C. The adjacent Bamhani area displays classic IS textures such as colloform banding and comb quartz, together with significant Zn-Pb enrichment, likely precipitated from low-temperature (as low as 125 degrees C) and moderately saline fluids resulting from mixing of magmatic and meteoric waters. Sulfur isotope values from both regions (delta 34S: -2.57%o to +4.14%o Vienna Canyon Diablo Troilite) are consistent with a dominant magmatic sulfur source, with minor crustal input observed in the distal regions. Downhole increases in copper grades, spatially and genetically linked to potassic alteration (K-feldspar-biotite-chalcopyrite), point to a deeper, concealed copper-rich source at Minjhari. The Minjhari-Bamhani system exemplifies a preserved Mesoproterozoic magmatic-hydrothermal continuum, highlighting significant exploration potential for concealed, deep-seated porphyry Cu-Au roots and structurally controlled epithermal base-metal (Pb-Zn) mineralization within the Bastar Craton.
The hydrographic architecture of an aqueous basin is strongly influenced by thermal and salinity-induced stratification that can lead to isolation of a deep anoxic watermass. Salinity is, therefore, a crucial factor shaping Earth's marine systems, but despite its significance, it is relatively understudied in deep time, particularly in tandem with redox conditions. This study focuses on the Upper Devonian black shale succession of the Illinois Basin, North America (i.e., the New Albany and Chattanooga shales), presenting a novel temporal and spatial reconstruction of the redox, salinity, and productivity conditions that focuses on the hydrodynamics of this epeiric sea. Our findings indicate that the basin was highly heterogeneous in space and time with respect to redox and salinity conditions, with strong redox and salinity gradients existing over relatively short lateral and depth transects, as well as the basin experiencing a fundamental hydro graphic reorganization across the Frasnian-Famennian boundary. During the Frasnian, transiently oxygenated conditions existed in the basin center outside of a discrete anoxic pulse associated with the Rhinestreet Event, whereas strong anoxia persisted in shallow water environments along the Cumberland Sill, with shallow-water anoxia likely driven by enhanced nutrient loading and eutrophication. The basin was highly restricted in the Frasnian, leading to higher-than-marine salinities in the basin center. In the Famennian, however, the basin developed strong vertical salinity stratification driven by enhanced freshwater runoff, which may have resulted from an increase in land plant abundance or a shift in the latitudinal position of the basin toward the Intertropical Convergence Zone. The development of salinity-driven stratification led to a major expansion of euxinia in the Illinois Basin across the Frasnian-Famennian boundary, coincident with the Upper Kellwasser Event. This study highlights that salinity-related processes and evolving basin hydrography can control redox and productivity changes within epicratonic basins, influencing the expression of major biological transitions in Earth's history.
The high sedimentation rates in tidal flats are useful for paleomagnetic and paleoenvironmental reconstruction studies. However, the tidal flat sediments in the Korean Peninsula have received little or no attention for their sedimentary magnetism. Therefore, we aimed to investigate the acquisition and preservation of natural remanent magnetizations (NRMs) to explore the usability of tidal flat sediment as a recorder of Holocene paleomagnetic secular variation (PSV). Paleomagnetic and mineral magnetic analyses and dry density and X-ray fluorescence data from a tidal sediment core (QJS29 of 11 m in length in total) in the Dongjin River estuary revealed primary NRM acquisition and preservation depending on the depth and sample dry density in a 2-3.9 m depth interval. The major NRM carriers in the samples were mixtures of lowcoercivity ferrimagnetic minerals, probably detrital magnetite and greigite of diagenetic and biogenic origins. With increasing depth, NRM acquisition efficiency and remanence stability increased while sample dry density decreased. Well-defined stable characteristic remanence (ChRM) components were observed in the tidal muds below 3.075 m depth. The correlation of the stratigraphic record of the ChRM and relative paleointensity with the available local reference curves reflected a local PSV between ca. 4 kyr before present (B.P.) and ca. 2 kyr B.P., suggesting a temporal lag in remanence acquisition (lock-in) from sedimentation. Our results suggest that a postdepositional remanence acquisition mechanism could dominate PSV-related ChRMs even though the remanence carriers are a combination of detrital, diagenetic, and biogenic sources. Thus, this study improves the usability of muddy tidal sediments as PSV recorders.
The architecture of mature faults commonly reflects long-lasting, cumulative tectonic histories marked by multiple episodes of deformation localization, fluid inflow, and variable slip behaviors. Hence, reconstructing fault tectonic histories and associated seismotectonic patterns requires the integration of (micro)structural, geochemical, thermal, petrophysical, and mechanical data throughout the fault's lifespan. Using a multitechnique approach, we investigate the Carboneras fault (CF), a NE-SW-striking, similar to 140-km-long active strike-slip fault in the Betics of SE Spain that has accommodated up to similar to 40 km of displacement since the Miocene. To unravel the spatio-temporal-thermal evolution of the CF, we combine multiscale structural analysis, X-ray diffraction, and illite K-Ar geochronology of six fault gouge samples with previously published data. Our results reveal a >20 Myr-long polyphase thermotectonic evolution including (1) late Oligocene N-S orthogonal shortening leading to nappe stacking and E-W fabrics, (2) Middle-Late Miocene sinistral transpression along a NE-SW shear corridor with selective reactivation of earlier E-W fabrics, and (3) Early Pliocene-Middle Pleistocene reactivation of the inherited fabrics. Faulting occurred under progressively cooler conditions (from >275 degrees C to similar to 70 degrees C) and at progressively shallower structural levels during the evolution of the eastern Betic orogen of SE Spain. Although the CF is widely regarded as an archetypal strike-slip fault, our results reveal a significantly more complex structural evolution, resulting in the superposition of multiple deformation phases with distinct kinematics and deformation styles. These findings provide valuable insights into the growth and exhumation of crustal-scale faults recording complex thermotectonic histories and contribute to a better understanding of their seismotectonic behavior.
The Qaidam Basin of western China hosts numerous salt lakes, some of which are rich in boron (B) resources. These salt lakes are separated by a central uplift and receive inflow from the Kunlun Mountains to the south and from the Qilian Mountains to the north, defining the South and North systems, respectively. The B concentrations of river water in both systems are significantly higher than those of the world's major rivers; consequently, the salt lakes are expected to be enriched in B due to the discharge of high-B rivers. However, although the Da Qaidam and Xiao Qaidam salt lakes in the North System contain considerable solid borate resources, no solid borates are found in the South System despite its river water flux being much greater. In this study, samples from various water bodies-including river water, salt lake brines, and fault-related Ca-rich spring waters-were collected and analyzed for chemical compositions and delta 11B values. The results, combined with literature data, suggest that B-enrichment in river waters is primarily driven by hot-spring brines from mountainous areas (distinct from Ca-rich spring waters within the basin). In the South System, the input of Ca-rich brines reduces the B concentration relative to total dissolved solids (TDS), typically to <270 mg/L, which is unfavorable for B-enrichment and borate precipitation. Thermodynamic modeling and evaporation experiments indicate that salt lake brines from neither system can precipitate borates readily. Nonetheless, the dilution of highly concentrated brines in certain North System lakes can promote borate precipitation by increasing pH values, as supported by thermodynamic calculation. Ultimately, our results demonstrate how the coupling of tectonic hydrochemistry and hydrological fluctuations shapes the distribution of B resources in hyper-arid basins.
