Precambrian Metamorphic Rocks Research Articles

Anisotropic effect of shear zone on groundwater potentiality in crystalline hard rock terrain

Assessment of potential groundwater recharge sites and sustainable water resource management in semi-arid crystalline rock terrain is a challenging task. Globally, analysis of remote sensing satellite imagery data for delineation of groundwater potential zones over sheared crystalline hard rock terrains has been fairly successful. But there is no existing study present at our disposal which discusses the factors controlling the inconsistent groundwater potentiality that exits along the shear zones. This study attempts to analyse the major geological factors controlling the irregular groundwater potentiality of shear zones within older crystalline rock terrain. Therefore, the study area selected for this analysis is the Purulia district of West Bengal, NE India, composed mostly of Precambrian metamorphic rocks i.e., quartzite, granite gneisses, porphyroclastic granite-gneiss, quartzo-feldspathic-granite-gneiss, mylonitic granites, quartz-biotite-granite gneiss, quartzites, carbonatites and phyllites. Satellite imagery study of IRS-P6 LISS IV standard FCC image reveals the presence of two bifurcating shear zones namely North Purulia Shear Zone (NPSZ) and South Purulia Shear Zone (SPSZ) over the study area. Careful analysis of rock structure, different lithotypes, soil thickness, electrical resistivity tomography data and water table data with an emphasis on high water table fluctuation, shows a strong spatial relation between the potentially good groundwater recharge zones and the branching/confluence sites of shear zones present in the study area. The study constructs an attempt to demonstrate the relationship between shear zone conjunctions and significant groundwater recharge sites in Precambrian crystalline fractured-rock aquifer system.

Metallogenic Difference between the Late Aptian Nansu and Aishan Pluton in Jiaodong: Constraints from in Situ Apatite Elemental and Nd Isotopic Composition

A series of Mo-polymetallic deposits have been developed in the Jiaodong Peninsula. Notably, these Mo-dominant deposits formed essentially during the same period as the well-known world-class Au deposits in this area, hinting at a potentially unique geological correlation between them. Therefore, conducting thorough research on Mo deposits in Jiaodong holds significant importance in exploring the area’s controlling factors of Mesozoic metal endowments. To reveal the petrogenesis and metallogenic potentials of Mo-fertile and ore-barren granitoid, apatite grains from the Late Aptian Nansu granodiorite and Aishan monzogranite are investigated in this study. Detailed petrographical observations, combined with in situ analysis of electron probe micro-analyzer (EPMA) and Laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), have been conducted on apatite grains from the Nansu and Aishan plutons. This comprehensive analysis, encompassing both major and trace elements as well as isotopic characteristics of apatite, aims to elucidate the metallogenic differences within the late Early Cretaceous granitoids of Jiaodong. The results reveal that the apatite grains across all samples belong to fluorapatites, suggesting their magmatic origin. Additionally, chondrite-normalized rare earth element (REE) patterns of apatites in ore-fertile and ore-barren granitoids exhibit a “right-leaning” trend, characterized by relative enrichments in light REEs and depletions in heavy REEs. Both the Nansu and Aishan plutons exhibit moderately negative Eu anomalies (with averages δEu values of 0.44 and 0.51, respectively), along with slightly positive Ce anomalies (averaging δCe values of 1.08 and 1.11, respectively). A negative correlation is observed between their δEu and δCe values, indicating that the parental magmas of ore-fertile and ore-barren granitoids were formed in a relatively oxidizing environment. The calculated apatite OH contents for the Nansu pluton range from 0.26 to 1.38, while those for the Aishan pluton vary between 0.24 and 1.51, indicating comparable melt H2O abundances. Consequently, the results suggest that neither the oxygen fugacities nor the water contents of the parental magma can account for the metallogenic differences between Nansu and Aishan plutons. The apatite in the Nansu pluton exhibits a higher Ce/Pb ratio and a relatively lower Th/U ratio, indicating the involvement of a greater volume of fluids in the magmatic evolution process of this ore-bearing granitoid. Apatite grains sourced from the Nansu and Aishan plutons exhibit εNd(t) values ranging from −16.63 to −17.61 (t = 115.7 Ma) and −17.86 to −20.86 (t = 116.8 Ma), respectively. These results suggest that their parental magmas primarily originated from the partial melting of Precambrian metamorphic basement rocks within the North China Craton, with a minor contribution from mantle-derived materials. Additionally, the presence of mafic microgranular enclaves in both the Nansu and Aishan plutons indicates that both have undergone magma mixing processes. The binary diagrams plotting the ratios of Ba/Th, Sr/Th, and U/Th against La/Sm demonstrate that apatite grains of ore-fertile granitoid exhibit a distinct trend towards sediment melting. This suggests the potential incorporation of sedimentary materials, particularly those rich in molybdenum, into the magmatic source of the Nansu pluton, ultimately leading to the occurrence of molybdenum mineralization.

Tectonic position of the Ukrainian shield

Statement of the general problem. The analysis of the geological structure of Europe indicates a wide development of Laramian (post-Cretaceous - pre-Cenozoic) deformations in non-Alpine regions. They are traced by the regional angular unconformity between the folded Mesozoic and non-folded Cenozoic from the Caspian Sea to Great Britain. The area of development of the Laramie folding of Europe also covers the Ukrainian shield. An unsolved part of the overall problem. The Ukrainian crystalline shield is described as "uplift of the crystalline foundation of the East European platform", where Precambrian rocks come to the surface. But the same rocks can also be traced far beyond its borders. The question arises - what structural position does the Ukrainian shield occupy in the structure of the Laramie folded region? Analysis of recent research and publications. On the geological maps of the pre-Cenozoic formations of Ukraine, the northern border of the Laramie folded region can be traced along the Chernihiv-Lysychansk line. Mesozoic folds and an angular unconformity in the Cenozoic basement disappear further north. To the south, the Laramie deformations intensify, but unevenly. The purpose of the article is identification of modern structural position of Ukrainian crystalline shield. Research materials and methods. Were involved more than 120 geological maps of Ukrainian regions and author's digital geological model of East Ukraine. Presentation of the main research material. A band of Mesozoic folds and NW vergence thrusts tens to hundreds of kilometers long is developed immediately south of the border of the folded region. The amplitude of the folds is 1.5–2 km. The band of development of these folds and thrusts with a width of about 100 km limits the Ukrainian shield from the northeast. To the south of the Ukrainian Shield, on the shelves of the Black and Azov Seas and in Northern Crimea, a sub-latitude band of Laramie thrusts and folds with a width of 150–200 kilometers has been established. Amplitudes of thrust folds reach 1–2 km, amplitudes of separate thrusts reach 8–10 km. This band of folds and thrusts limits the southern slope of the Ukrainian shield from the south. These Laramie folds and thrusts are overlain by Cenozoic sediments. To the south, in the Mountainous Crimea, the deformations are still intensifying. Folds and thrusts are replaced by wide and extended mélange zones of northwestern vergence. The Ukrainian shield is bypassed by the development of folds and thrusts from the northeast, east, and south. On the slopes of the Ukrainian shield, Mesozoic fold deformations subside, and the Mesozoic there lies gently sloping and monoclinally. Such poorly deformed blocks within folded regions are called middle massifs. This middle massif of the Laramie fold region within Ukraine has an anteclise structure. In the core of the anteclise, Precambrian metamorphic and igneous rocks emerge from under the sedimentary cover. The western wing of the anteclise is overlain by younger thrusts of the Carpathian folded structure of Attic (post-Miocene) age. Scientific novelty. In the modern geological structure, the Ukrainian shield is the core of the anteclise of the middle massif in the Laramie folded region. Conclusions. As a tectonic uplift, shield was formed in the Paleocene. In the Late Cretaceous, it was still buried under shelf carbonate deposits. Erosion of this uplift formed the Cenozoic deposits of Ukraine with a specific mineragenic specialization. Taking into account the Laramian folding allows us to reconcile the diverse geological phenomena of the region into a single system without contradictions.

Geochronology of the Shenjiayao gold deposit in the southern North China Craton: Constraints from in situ monazite U-Pb and mica Rb-Sr dating

The Shenjiayao gold deposit (8.59 t Au @ 3.01 g/t) is located in the northern Xiaoshan region on the southern margin of the North China Craton. However, the absolute gold mineralization age is not well constrained due to the lack of datable gold ore-related minerals. In this study, in situ monazite U–Pb and mica Rb-Sr dating were performed to constrain the mineralization timing. The Shenjiayao gold ores occur as massive auriferous pyrite veins in Precambrian metamorphic rocks. Four hydrothermal veining stages can be recognized: (I) milky quartz-pyrite veins, (II) gray quartz-pyrite veins, (III) quartz-polymetallic sulfides veins, (IV) quartz-carbonate-pyrite veins. Textural relationships between the vein minerals suggest that the gold-bearing minerals (pyrite, sphalerite, and chalcopyrite), monazite, and mica were simultaneously formed in the main-ore stages II and III. Hydrothermal monazite and mica yielded LA-ICP-MS 206Pb/238U ages of 129.9 ± 1.0 Ma (1δ, MSWD = 1.01) and Rb-Sr isochron age of 128.1 ± 1.9 Ma (1δ, MSWD = 0.58), respectively. The gold mineralization in the Xiaoshan region is related to an extensional setting associated with Early Cretaceous Paleo-Pacific rollback.

Thin-section Petrography and Heavy Mineral Study of sandstones of the Barail Group of rocks occuring around Sonapur area of Jaintia Hills, Meghalaya, India

The study area represents a part of the South Shillong Shelf, Meghalaya, where sandstones belonging to the Barail Group (Eocene-Oligocene) are well exposed. Thin section petrography and heavy mineral investigations have been undertaken to assess the geological significance of the sandstones. Framework grains of the Barail sediments comprise of quartz (56.98 to 71.91%), feldspar (1.87 to 7.35%), mica (1.07 to 9.72%), lithic fragments (2.20 to 8.41%) and matrix (9.20 to 20.43%). The detrital composition of the sandstones comprises primarily of quartz grains, angular to sub-rounded, fine to medium grained and moderately sorted in nature. The sandstones are classified as subarkose, feldspathic graywacke and lithic graywacke. Provenance discrimination triangular plots of QFL and QmFLt reflect that the detritus were mostly derived from cratonic interior sources. The Diamond diagram indicates that the Barail sandstones were derived from middle and upper rank metamorphic source. Heavy mineral study of these sandstones indicates the presence of zircon, tourmaline, rutile, sillimanite, kyanite, staurolite, garnet, epidote, sphene, hypersthene, hornblende, chlorite, chloritoid, andalusite, apatite and opaque minerals. The percentages of most stable heavy minerals zircon, tourmaline and rutile vary from 6.11to 21.61, 2.60 to 6.56 and 2.42 to 7.57 respectively. The ZTR maturity index varies from 15.15 to 34.37, which reflects that the sandstones are mineralogically immature. The petrographic and heavy mineral study of the sandstones suggest that the detritus was probably derived from Shillong Massif where Precambrian metamorphic rocks of pelitic and arenaceous composition with plutonic bodies were exposed around the shelf margin. As the Shillong Massif comprises of Precambrian metamorphic rocks of pelitic and semitic (arenaceous) composition with intrusive plutonic bodies.

Provenance identification and source-to-sink studies from an intrabasinal subaqueous uplift in the Eocene western Bohai Bay Basin, eastern north China

Intrabasinal subaqueous uplifts around small positive structural units are important targets of high-quality reservoirs in the Eocene Bohai Bay Basin (BBB). The western BBB was filled with sediments from northern and southern source regions. The southern sources are the Paleozoic rocks deposited in marine and costal settings, which are widely exposed along the Chengzikou uplift and stacked with Mesozoic igneous rocks. The northern sources are pre-Cambrian metamorphic rocks from the western Shaleitian uplift. To determine the origin of the Eocene sediments in the intrabasinal subaqueous uplift, eight sediment samples were collected from drill cores in the Shaxinan structural belt of Shanan sag, western BBB for detrital zircon U–Pb dating. We conduct detrital zircon U–Pb dating to shed new light on Eocene provenance evolution and analyze sediment dispersal characteristics of the lacustrine beach-bar sandstones by integrating lithology, wire-line logs and 3-D seismic data in the Shaxinan structural belt. The obtained ages vary between the Archaeological and Mesozoic (2692 ± 42 Ma to 79.8 ± 1.0 Ma). Dominant provenance for the Shahejie Formation has evolved temporally, that is, from the early Shaleitian uplift to the late Chengzikou uplift. The beach-bar sand bodies developed on the subaqueous uplift in the Shahejie Formation (from base to top: member 3 of the Shahejie Formation, Es3, and members 1 and 2 of the Shahejie Formation, Es12), while the gravel-rich fan delta-beach bar sand bodies mainly from the northern Shaleitian uplift in the Es3 transitions to the mixed sand-mud braided delta-beach bar sand bodies mainly influenced by southern Chengzikou uplift in the Es12. Types of intrabasinal subaqueous uplift (gentle palaeoslope), strong hydrodynamic environment, abundant multiple sediment provenance and the Eocene-Oligocene evolution collectively control beach bar sediment dispersal patterns in the deposit area.

The Formation of the Jiaodong Gold Province

AbstractGold deposits in Jiaodong, termed Jiaodong‐type, are tectonically located in the southeastern margin of the North China Craton. Their major features are reviewed in this paper to highlight the differences between Jiaodong deposits and other genetic types of gold deposits. The mineralization was synchronized with asthenosphere upwelling indicated by syn‐ore OIB‐like mafic dike and large‐scale crustal thinning suggested by decrease of Sr/Y from pre‐ore to syn‐ore granites. Asthenosphere upwelling induced by the roll‐back of Paleo‐Pacific Plate drove partial melting of lithospheric mantle and devolatilization, which induced the release of the ore‐forming fluids. In concomitant with magmatic records, mineralization migrated from the western Jiaobei terrane (133–127 Ma) to the eastern Sulu orogenic belt (114–108 Ma), corresponding to the eastward roll‐back of Paleo‐Pacific Plate. Gold mineralization in Jiaodong formed in the transitions of ductile to brittle deformation, rapid to slow crustal uplift, and regional compression to extension. In the regional‐scale, the gold deposits in the Jiaobei terrane are mostly situated at intersections between NE‐trending faults and EW‐trending basement faults, and gold orebodies dominantly controlled by the lithologic contacts between Precambrian metamorphic rocks and Mesozoic granites. The mineralization was dominated by the disseminated‐veinlet ores related to quartz–sericite alteration in strong cataclasite‐breccia zone, with subsidiary thick quartz‐sulfide veins developed in secondary fault zones. The ore‐forming fluids belong to a H2O–CO2–NaCl±CH4system and show minor variations in salinity among different types of ore. Structure‐fluid feedback involving fluid‐rock reaction and hydrofracturing triggered the fluid phase separation and resultant gold deposition. The Jiaodong gold deposits are distinct from orogenic and intrusion‐related gold deposits in terms of tectonic setting, origin of ore‐forming fluids, and mechanism of gold deposition.

An evolving MVT hydrothermal system: Insights from the Niujiaotang Cd-Zn ore field, SW China

• The carbonate rocks acted as a key role during sulfide mineralization . • The change of alkaline-oxidized to acid-reduced resulted in sulfide precipitation. • The fluids evolved from the SW to the NE ore deposits . • The MVT deposits are the coupled mineralization product of fluid–structure-lithology. The metallogenic characteristics of Mississippi Valley-type (MVT) deposits have been widely concerned, but the evolution of MVT hydrothermal systems still needs to be further explored. The Niujiaotang Cd-Zn ore field (5,300 t Cd @ 0.04–1.43 wt% and 0.35 Mt of 5.85–24.48 wt% Zn) is located along the southeastern margin of the Yangtze Block, SW China, and consists of seven ore deposits, i.e. Dongchong, Mapo, Daliang, 768, Caiyuanhe, Shuanglongquan and Duniu. The ore bodies occur as stratiform or lenticular and are hosted by dolostone of the early Cambrian Qingxudong Formation, and are structurally controlled by the NE-trending Mandong fault. The hydrothermal dolomite has δ 13 C values of −3.03 ‰ to + 2.94 ‰, with lower contents of ΣREE (6.76–53.5 ppm), negative Eu and weakly positive Ce anomalies, all of which are similar to those of wall rocks. This suggests that the early Cambrian carbonate rocks involved in sulfide mineralization through water/rock (W/R) interaction and provided part of ore-forming materials. The δ 18 O values (+17.14 ‰-+22.79 ‰) are within the range of metamorphic fluids (δ 18 O=+16 ‰-+25 ‰), implying the hydrothermal fluids were derived from the Precambrian basement metamorphic rocks. The sulfides are characterized by scattered sulfur isotopes (δ 34 S=+10.03 ‰-+32.82 ‰), implicating that the reduced sulfur was derived from a mixed source of metamorphic fluids and thermo-chemical sulfate reduction (TSR). In situ Pb isotopes indicate that both Precambrian metamorphic rocks and early Cambrian sedimentary rocks provided metals for the hydrothermal fluids. In addition, the increased δ 34 S Σ values and Pb isotopes from Dongchong (SW part of the Niujiaotang ore field) to 768, and then to Duniu (NE part of the Niujiaotang ore field), indicating the hydrothermal fluids likely evolved from the SW to NE ore deposition sites along the Mandong fault, which is also confirmed by other evidence. Hence, we propose an evolving MVT hydrothermal system and a fluid-tectonic-lithology combination coupled metallogenic model for the Niujiaotang ore field. The determination of such metallogenic model of this ore field is conducive to the research and exploration of the similar MVT deposits nearby and worldwide.

Seismic Imaging and 3D Architecture of Yongle Atoll of the Xisha Archipelago, South China Sea

AbstractYongle atoll in the Xisha (Paracel) Archipelago is an isolated carbonate platform developed on Precambrian metamorphic and Mesozoic volcanic rocks since the early Miocene. To identify the 3D stratigraphic architecture and evolution of this platform, 13 high‐resolution seismic profiles and shallow‐to‐deep water multi‐beam data were processed and analyzed to reveal seismic facies, sequence boundary reflectors, seismic units, and platform architecture. Nine types of seismic facies were recognized based on their geometry, which included seismic amplitude, continuity, and termination patterns; additionally, six reflections, i.e., Tg, T60, T50, T40, T30, and T20, were identified in the Cenozoic strata. Five seismic units, SQ1 (lower Miocene), SQ2 (middle Miocene), SQ3 (upper Miocene), SQ4 (Pliocene), and SQ5 (Quaternary), were identified from bottom to top across the platform. The platform grew rapidly in the middle Miocene and backstepped in the late Miocene–Pliocene. Here, we discuss the developmental characteristics and evolution of the Yongle Atoll, in combination with drilling wells, which can be divided into four stages: the initiation stage in the early Miocene, the flourishing stage in the middle Miocene, the partial‐drowning stage in the late Miocene–Pliocene, and modern atoll in the Quaternary.

Uranium Concentrations in Private Wells of Potable Groundwater, Korea.

Uranium (U) is one of the typical naturally occurring radioactive elements enriched in groundwater through geological mechanisms, thereby bringing about adverse effects on human health. For this reason, some countries and the World Health Organization (WHO) regulate U with drinking water standards and monitor its status in groundwater. In Korea, there have been continuous investigations to monitor and manage U in groundwater, but they have targeted only public groundwater wells. However, the features of private wells differ from public ones, particularly in regard to the well’s depth and diameter, affecting the U distribution in private wells. This study was initiated to investigate U concentrations in private groundwater wells for potable use, and the significant factors controlling them were also elucidated through statistical methods. The results obtained from the analyses of 7036 groundwater samples from private wells showed that the highest, average, and median values of U concentrations were 1450, 0.4, and 4.0 μg/L, respectively, and 2.1% of the wells had U concentrations exceeding the Korean and WHO standard (30 μg/L). In addition, the U concentrations were highest in areas of the Jurassic granite, followed by Quaternary alluvium and Precambrian metamorphic rocks. A more detailed investigation of the relationship between U concentration and geology revealed that the Jurassic porphyritic granite, mainly composed of Daebo granite, showed the highest U contents, which indicated that U might originate from uraninite (UO2) and coffinite (USiO4). Consequently, significant caution should be exercised when using the groundwater in these geological areas for potable use. The results of this study might be applied to establish relevant management plans to protect human health from the detrimental effect of U in groundwater.

Hydrogeochemical factors controlling the occurrence of chronic kidney disease of unknown etiology (CKDu).

Chronic kidney disease of unknown etiology (CKDu) has posed a serious threat to human health around the world. The link between the prevalence of CKDu and groundwater geochemistry is not well understood. To identify the potential geogenic risk factors, we collected 52 groundwater samples related to CKDu (CKDu groundwater) and 18 groundwater samples related to non-CKDu (non-CKDu groundwater) from the typical CKDu prevailing areas in Sri Lanka. Results demonstrated that CKDu groundwater had significantly higher Si (average 30.1mg/L, p < 0.05) and F- (average 0.80mg/L, p < 0.05) concentrations than those of non-CKDu groundwater (average 21.0 and 0.45mg/L, respectively), indicating that Si and F- were the potential risk factors causing CKDu. The principal hydrogeochemical process controlling local groundwater chemistry was chemical weathering of silicates in Precambrian metamorphic rocks. Groundwater samples were mostly undersaturated with respect to amorphous silica and clay minerals such as talc and sepiolite, which was conducive to silicate weathering and elevated Si concentrations in groundwater. Decreased Ca2+ being facilitated by calcite precipitation and cation exchange between Ca2+ and Na+ favored fluorite dissolution and thus led to high groundwater F- concentrations. Competitive adsorption between [Formula: see text] and F- also enhanced the release of F- from solid surfaces. This study highlights the CKDu potential risk factors regarding groundwater geochemistry and their enrichment factors, which helps in preventing the prevalence of CKDu.

Geochronology and oxygen fugacity of the pelitic granulite from the Diwani hills, NE Gujarat (NW India)

AbstractThe Diwani hills are located SE of Balaram–Abu Road in the Banaskantha district of north Gujarat. The crystalline rocks of the Diwani hill area are a diverse assemblage of Precambrian metamorphic and igneous rocks. These rocks are petrologically more complex and date back to the Aravallis or earlier. The mineralogical assemblages such as grt–sp–opx–qz of these rocks indicate their origin in anhydrous or dry conditions, implying metamorphism under pyroxene granulite facies. These granulitic rocks were subjected to Delhi orogenic deformation and were later intruded by the Erinpura granite. Textural and microstructural relationships, mineral chemistry, P–T–X pseudosection modelling and the oxidation state of pelitic granulites from the Diwani hill area of north Gujarat are all part of the current approach. The winTWQ program and pseudosection modelling in the NCKFMASHTO model system utilizing Perple_X software were used to restrict the P–T evolution of these pelitic granulites. The unification of these estimates shows that the pelitic granulites reached their pressure and temperature maxima at 8.6 kbar and 770 °C, respectively. The oxygen fugacity (log fO2) versus temperature computations at 6.2 kbar revealed log fO2–T values of −13.0 and 765 °C, respectively. The electron microprobe dating of monazite grains separated from the granulites of the Diwani hills yields ages ranging from 769 Ma to 855 Ma. The electron microprobe dating presented here from the Diwani hills provides evidence for a Neoproterozoic (Tonian) metamorphic event in the Aravalli–Delhi Mobile Belt.

Trace element and S-Pb isotopic compositions of pyrite from the Precambrian metamorphic rocks and their derivative pegmatites in the Xiaoqinling district, southern North China Craton: Implications for possible gold source of the Early Cretaceous gold deposits

The North China Craton is well endowed with numerous Early Cretaceous gold deposits that are mainly hosted in Archean to early Paleoproterozoic metamorphic rocks and late Mesozoic granitoid intrusions intruding the former. Whether or not gold was sourced from those metamorphic rocks remains hotly debated. Here we present trace element and S-Pb isotope data of pyrite from the Neoarchean to early Paleoproterozoic metamorphic rocks in the Xiaoqinling district of southern North China Craton and late Paleoproterozoic pegmatites derived from the former rocks, in an attempt to provide new insights into the gold sources for Early Cretaceous gold lodes genesis in this district. Pyrite from the metamorphic rocks typically occurs as inclusions in rock-forming minerals or disseminated grains roughly distributed along the foliation of the rocks, whereas pyrite from the pegmatites usually occurs as disseminations closely associated with quartz and magnetite. The textural data suggest that pyrite in the metamorphic rocks and pegmatites are of metamorphogenic and magmatogenic origins, respectively. LA-ICP-MS spot analyses show that pyrite both from the metamorphic rocks and pegmatites has Au contents mostly below the detection limit, with minor analyses revealing Au marginally higher than the detection limit. Considering that Au is moderately incompatible and highly siderophile, the very low gold contents in pyrite allow us to infer that the metamorphic rocks contain negligible gold. Pyrite grains from the metamorphic rocks and pegmatites have broadly consistent δ34S values ranging from −2.7 to 31.5 (mean = 17.6) per mil and 6.3 to 17.9 (mean = 14.3) per mil, respectively. Similarly, they have comparable, highly radiogenic lead isotopes, which are 16.859–24.889 for 206Pb/204Pb, 15.355–15.694 for 207Pb/204Pb, and 37.480–43.848 for 208Pb/204Pb. The sulfur and lead isotopes of pyrites from the metamorphic rocks and pegmatites are distinct from those of Early Cretaceous gold deposits hosted by these rocks. Taken together, the pyrite trace element and S-Pb isotope data presented here preclude the Precambrian metamorphic basement rocks as an important gold source for the extensive Early Cretaceous gold mineralization in the Xiaoqinling district and, by inference, other major Early Cretaceous gold provinces across the North China Craton.

Mercury isotopic compositions of the Precambrian rocks and implications for tracing mercury cycling in Earth's interior

Mercury isotopes undergo unique mass-independent fractionation (MIF) during photochemical processes on Earth's surface. Studies have observed pronounced Hg-MIF signals in sedimentary and magmatic rocks, suggesting recycling of Hg from Earth's surface systems into the lithosphere via sedimentation and magmatism. However, the isotopic signature of Hg in metamorphic rocks and the geochemical fate of Hg during metamorphism remain unclear. Precambrian basements are important components of cratons or orogenic belts on Earth. Here, we study the Hg concentration and isotopic composition of Precambrian metamorphic and sedimentary rocks from the eastern Central Asian Orogenic Belt, and North and South China cratons. Metamorphic rocks show much lower Hg contents (0.21–7.8 ppb) than sedimentary rocks (2.6–694 ppb), indicating a substantial loss of Hg during metamorphism. The lack of correlation between δ202Hg values (–2.41 to 0.18‰) and metamorphic grades indicates no systematic mass-dependent fractionation (MDF) of Hg isotopes during metamorphism. The Δ199Hg/Δ201Hg ratios of ∼ 1.0 for both metamorphic and sedimentary rocks indicate Hg was sourced from Earth's surface systems. The coupling of Hg-MIF signals between the metasedimentary rocks and the sedimentary settings of their protolith suggests no Hg-MIF during metamorphism. The negative Δ199Hg values (–0.30 to –0.02‰) in the Precambrian coastal sedimentary rocks imply the input of Hg into coastal regions via soil erosion. The positive Δ199Hg values (0.06 to 0.31‰) in the Precambrian marine sedimentary rocks suggest deposition of atmospheric Hg(II) to open oceans via wet deposition. The lack of significant Hg-MIF during metamorphism and other underground geological processes shows that Hg-MIF signals can work as a reliable tracer for indicating material cycling in Earth's interior.

Mapping the spatial variability of subsurface resistivity by using vertical electrical sounding data and geostatistical analysis at Borena Area, Ethiopia

Vertical electrical sounding survey has been done to map and visualize resistivity distribution at Borena basin. The area is situated in Southern Main Ethiopian Rift, where Rirriba rift, Mega rift and associated fractures define the structural setting of the area. It is covered by Quaternary deposits, Quaternary and Tertiary basaltic rocks and Precambrian metamorphic rocks. Bullal basaltic formation outstretch in the Rirriba rift and it is thought to be potential groundwater aquifer. About 288 Vertical Electrical Sounding data were collected. Inflection and extreme points were used to identify characteristic points. Variograms are modeled and kriging interpolation is used to map distribution of resistivity, determined from characteristic points, in the area. Very low to low resistivity variations are mapped in northern end of the study area, whereas medium to moderately resistive ground are mapped in the middle and southern part of the area. The low resistivity horizon at the shallow subsurface could be due to salinity since the area occupy numerous saline craters and maars. Approximate mapping of large sets of Vertical Electrical Sounding data with geostatistical treatment has facilitated the interpretation and provided a sound picture of the subsurface.• Inflection and extreme points were extracted from smothed VES curves to identify characteristic points.• Variograms are modeled and kriging interpolation is used to map 3D distribution of resistivity data.

ПЕРСПЕКТИВИ УРАНОВОГО ЗРУДЕНІННЯ ПІВДЕННО-ЗАХІДНОГО СХИЛУ УКРАЇНСЬКОГО ЩИТА.

The geological position, composition and genesis of uranium mineralization of ore occurrences on the southwestern slope of the Ukrainian Shield are considered. In the Precambrian basement metamorphic rocks of the Dniester-Bug, Bug and ultrametamorphic rocks of the Golovanev, Pobuzh, Berdichev and Kirovograd complexes were established. On the southwestern slope of the Ukrainian Shield, 4 uranium occurrences and 4 radioactive anomalies have been discovered, studied and prospected. The uranium occurrences are localized along the regional unconformity surface of the Precambrian basement and platform cover. They are often confined to the nodes of the intersection of faults. The uranium occurrences are installed simultaneously both in the rocks of the basement and in the platform cover. The ore deposits form stockwork and vein segregations among the tectonized rocks of the Precambrian. In the rocks of the sedimentary cover they are discontinuous lenticular, subconcordant with the bedding of rocks. The uranium mineralization is vein-disseminated, represented by uraninite, pitchblende, coffinite, uranium black, casolite, etc. The uranium mineralization was caused by both endogenous and exogenous processes; several stages of uranium concentration have been established. The main source of uranium and associated elements was the low-temperature hydrothermal fluids of the “unconformity zone” faults of the Precambrian basement and sedimentary cover. A comparison is given and the similarity of the uranium mineralization of these occurrences with the rich uranium ores of the "zones of unconformity" of the Canadian and North Australian shields is given, which determines the significant prospects for uranium mineralization of the southwestern slope of the Ukrainian shield for the development of the uranium resource base of Ukraine.

Controlling factors and impacts of river-borne neodymium isotope signatures and rare earth element concentrations supplied to the Canadian Arctic Archipelago

Determining the factors controlling the neodymium (Nd) isotopic compositions (expressed as εNd) and rare earth element (REE) concentrations of rivers is imperative to improve our understanding of the distribution of these water mass tracers in the ocean. Here we present the first measurements of <0.45 μm-filtrate REE concentrations (i.e., the concentration of truly dissolved, nano-particulate and colloidal REEs passing through a 0.45 μm filter, hereafter referred to as dissolved) and εNd in rivers draining into the Canadian Arctic Archipelago (CAA). Results show a large variation in both REE concentrations (Nd=[8;37,260] pmol/kg) and εNd ([−32.1;−15.1]) in the thirteen rivers sampled. Dissolved REE concentrations increase with increasing fractions of metamorphic rocks and ice cover in the rivers' watersheds, while εNd and PAAS-normalized REE patterns are inherited from the watershed's bedrock lithology. The four rivers draining watersheds composed of Precambrian metamorphic rocks exhibit the highest REE concentrations, the least radiogenic εNd, and shale-normalized patterns enriched in light REEs. The remaining nine rivers drain mainly or exclusively sedimentary bedrock and have lower REE concentrations, more radiogenic εNd and generally show heavy REE enrichment, with variable negative cerium (Ce) anomalies. The presence of ice sheets in the drainage area, and the ionic strength, pH, and dissolved organic carbon concentration of river water are the main factors determining riverine dissolved REE concentrations by controlling the formation and stabilization of colloids. We estimate a flow of dissolved Nd transported by Arctic rivers discharging into the CAA equivalent to the Nd flux of seawater entering the CAA. Depending on the percentage of Nd removal during mixing with seawater, the impact of river water on the εNd of seawater exiting the CAA could be modest (if 90% removal) or more significant (if ≪90% removal). This riverine contribution could potentially impart a climate-sensitive εNd signature to the seawater reaching Baffin Bay, with possible implications for the use of εNd in paleoceanographic reconstructions of water mass distribution.

Structural controls on the gold mineralization at the eastern margin of the North China Craton: Constraints from gravity and magnetic data from the Liaodong and Jiaodong Peninsulae

The eastern block of the North China Craton (NCC) has been completely decratonized and it hosts numerous early Cretaceous gold deposits dated at about 130–120 Ma. The Jiaodong Peninsula in the easternmost NCC is the largest gold producing district in China, and it hosts more than 150 gold deposits with known gold resources of over 5000 tonnes (t). Also located at the eastern margin of NCC, the Liaodong Peninsula is poorly explored at depths greater than 800 m, with no large concealed gold deposit being discovered yet. In this paper, we carefully analyzed the gravity and magnetic characteristics of the ore-controlling structures in both provinces, including faults, Precambrian basement metamorphic rocks and the Mesozoic granitic intrusions. The deep regional faults are characterized by linear gravity gradient zones or elongated positive magnetic anomalies. The Precambrian basement metamorphic rocks usually have large-amplitude gravity and magnetic highs, while the lithological contacts of Mesozoic granite intrusions are commonly defined by gravity lows or narrow magnetic high anomalies. Interpretations from gravity and magnetic signatures predict two concealed lithological contacts between Mesozoic granites and Precambrian metamorphic rocks beneath Liaodong and Jiaodong.The spatial locations of known gold deposits are then correlated with the concealed structures inferred from the gravity and magnetic data in our paper. Their spatial relationship suggests that the gold mineralization is mainly controlled by oblique regional faults along the structural and lithological contacts between Mesozoic granites and Precambrian metamorphic rocks. Additionally, the structural intersections of different ore-controlling faults, especially the hydrothermal alteration zones at the contacts between Precambrian basement metamorphic rocks and the Mesozoic granites, are most favorable for the gold mineralization in the Liaodong and Jiaodong areas. Many large gold deposits are documented along a deep-seated, but concealed, structure beneath the Jiaodong gold district, while the Qingchengzi ore field and its vicinity in the Liaodong Peninsula still remain underexplored, despite of having a very similar structural setting, and deserve further investigation.

Alteration and elements migration of detrital zircons from the Daying uranium deposit in the Ordos Basin, China

To study the alteration and elements migration characteristics of detrital zircon in sandstone-hosted uranium deposits, we analyzed three groups of zircon samples from the Jurassic Zhiluo Formation of the Daying uranium deposit in the northern Ordos Basin, China. One group of zircons was selected from the uranium metallogenic belt, while the other two groups were obtained from the non-metallogenic belt. According to the back-scattered electron (BSE) images and energy dispersive spectrometer (EDS) elemental maps, zircon can be divided into altered and unaltered zircon, and alteration types include oscillatory zoning alteration and rim alteration. The rare earth element (REE) pattern of unaltered zircon is characterized by positive Ce anomalies and negative Eu anomalies, similar with those of the Early Precambrian metamorphic rocks of the Khondalite Belt in the North China Craton. The results of the trace element analysis showed that REEs, uranium, and non-formula elements (e.g., Al, Fe, and Ca) are abundant in the altered area, specifically observable in the BSE images, and along with the EDS elemental maps of altered zircon in the uranium metallogenic belt, exhibited higher uranium concentrations and more developed cracks. Interaction of fluids with the radiation-damaged zircon lattice can provide a favorable conditions for fluid infiltration and element migration. The action of uranium-bearing fluids and the radiation of uranium minerals can induce zircon alteration and crack formation, which is instructive in uranium prospecting.

Regional variations of sulfur isotope compositions for metallic deposits in South Korea

AbstractSouthern Korean peninsula comprises five major geotectonic provinces, throughout which various metallic deposits are distributed. We reviewed sulfur isotope data (n = 1,574) of sulfide minerals collected from previous works for 177 metallic deposits in the provinces to interpret the sulfur isotope characteristics of each province, comprising different wall rocks and geologic settings. The averaged δ34S values of each metallic deposit associated with Precambrian metamorphic rocks and Jurassic granitoids in the Gyeonggi massif and Yeongnam massif range from −7.1 to +10.3‰ (av. +4.5‰) and from −3.6 to +7.8‰ (av. +3.5‰), respectively. The Taebaeksan basin produced the highest δ34S value among the five, −0.4 to +13.2‰ (av. +6.1‰). This was influenced by sulfate sulfur derived from marine carbonate host rock. The Okcheon metamorphic belt, comprising metasedimentary and metavolcanics rocks, shows an isotope range from +1.9 to +8.3‰ (av. +5.7‰). The sulfur isotope distribution of the Gyeongsang basin with a range from −1.2 to +11.7‰ (av. +5.2‰) can be divided into two zones: higher δ34S values from the inner zone related to the volcanic rocks and magnetite‐series Cretaceous granitoids, and lower δ34S values from the outer zone related to the organic‐rich sedimentary rocks. Sulfur isotope variations of metallic deposits in each geotectonic province were mainly influenced by igneous sulfur and inherent wall rock sulfur sources, 32S‐enriched sedimentary sulfur (e.g., Precambrian metasedimentary rocks and biogenic sulfur‐rich sedimentary rocks), and 34S‐enriched seawater sulfur (e.g., carbonates and acid to intermediate volcanic rocks). These wall rocks also contributed to the changes in δ34S values for granitoid rocks and metallic deposits by time, ore genetic type, and ore species in South Korea.