Geosciences Journal最新文献

Abstract

Skarn and Fe-Zn-Pb mineralization at the Wondong deposit located in the Taebaeksan Basin of the central-eastern region of Korean Peninsula occurs along the contact between the Upper Cretaceous quartz-feldspar porphyry (QFP) and carbonate rocks of the Ordovician Makgol Formation. The QFP is relatively fresh and has a sharp contact with the garnet skarn. Skarn is dominant in the carbonate rocks but is rare in the QFP. It consists almost of grandite throughout the skarn but has mineralogical zonation of proximal garnet, intermediate pyroxene, and distal wollastonite with increasing distance from the contact between the QFP and garnet skarn. Garnet becomes Fe-rich, and pyroxene tends to be enriched in Fe and Mn toward the marble front. Massive Fe mineralization, replacing garnet skarn, is restricted proximal to the QFP. In contrast, although the Zn-Pb mineralization is found in all areas it mostly occurs in the carbonate rocks beyond the skarn. Zinc-Pb mineralization occurred as stockwork and vein in the QFP and the garnet skarn consists of sphalerite, galena, Al-rich garnet, and calcite with a minor quantity of arsenopyrite. In contrast, the carbonate replacement of the Zn-Pb mineralization beyond skarn consists of sphalerite, pyrrhotite, galena, diopsidic pyroxene, and calcite with minor minerals such as arsenopyrite, löellingite, and chalcopyrite. Sphalerite, principal ore mineral, becomes darker and Fe- (up to 34.4 mol% FeS) and Mn-rich (up to 1.5 mol% MnS) with increasing distance from the QFP. Arsenopyrite is closely associated with sphalerite tends to be decreased in As away from the QFP. All sulfide minerals from Zn-Pb mineralization in the Wondong deposit have δ³⁴S values ranging from 2.9 to 5.9‰, which are attributed to the magmatic source. In addition, the narrow range and subtle variation of the δ³⁴S values for all sulfides throughout the Wondong deposits are not interpreted to be involved in the mixing of multiple sulfur sources. Geological, petrographic, mineralogical, and isotopic geochemical investigations show that the early skarn was formed in an environment of high fluid: rock ratios at the contact between the QFP and Makgol Formation and it was dominated by grandite, indicating the oxidizing nature of the skarn-forming fluids. The ore deposition began after the formation of the main garnet dominated skarn. The ore-forming fluids responsible for Zn-Pb mineralization are characterized by a less oxidizing nature, as defined by comparatively Al-enriched garnet in vein type mineralization in and around the QFP. Farther, the fluids producing the carbonate replacement of the Zn-Pb mineralization are unlikely to be engaged in external effects such as mixing with multiple sulfur sources even though it travels over long distance.

Iron ores and iron bloom slags from two iron archaeological sites (Chilgeumdong: 300–600 AD, Wanori: ∼20th century) as well as iron ores from six iron deposits in Chungju, South Korea, were examined to assess the provenance of the raw iron ores. Different ore mineralogy proves to be a useful tool in interpreting the ore provenance of samples from the iron archaeological sites, although limited by the simplicity of the assemblage. The application of Ca + Al + Mn vs. Ti + V diagram for classifying the genetic type of magnetite suggests that the iron ores of the iron archaeological sites may have originated from multiple deposits. Comparing the chondrite-normalized REE patterns and the correlation between La_n and Ce_n in iron ores and iron bloom slags aids in determining the provenance of samples from the iron archaeological sites. Despite notable deviations, the use of Pb-Sr isotope ratios as a means of identifying the origin of unprocessed iron ores proves to be a meaningful approach. Based on our findings, it appears that the iron ores discovered at archaeological sites were typically sourced from nearby iron deposits like Changdong, Yeonsudong, Daekyo, and possibly Manjeong. This preference for local sources as opposed to more distant ones, such as Obok and Yusang, seems to have remained a constant throughout various historical epochs, spanning from the Baekjae to the Joseon period. Overall, this study demonstrates the effectiveness of integrated interpretation of various complementary approaches, including ore petrography, trace and rare earth element geochemistry, and Pb-Sr isotope analysis, in determining the provenance of raw iron ores excavated from iron archaeological sites.

Seismic attribute analysis, a method of highlighting important information in seismic data, has been used in various fields. Recently, several studies have used seismic attributes to interpret seismic anomalies associated with subsurface gas. In this study, we applied seismic attribute analysis to seismic data acquired in Yeongil Bay to identify the subsurface gas distribution. Before applying seismic attributes to the Yeongil Bay seismic data, we selected promising seismic attributes and applied them to F3 Block seismic data to analyze the relation between the seismic attributes and seismic anomalies caused by subsurface gas. Since there are previous studies on the subsurface gas in the F3 Block, we could identify the characteristics of the seismic attributes based on the F3 Block seismic data. Then, we applied the selected seismic attributes to the Yeongil Bay seismic data to define the subsurface gas distribution. Through seismic attribute analysis, a three-dimensional gas distribution model of Yeongil Bay was generated, and this model can provide quantitative information on the subsurface geology of Yeongil Bay.

Abstract

The valorization of Lake Maga for agricultural purposes has not only contributed to the socio-economic development of the study area, but has also modified the surface water (SW) and groundwater (GW) flow regimes. Understanding the interaction between the SW and the shallow Quaternary aquifer, under land use change and soil structure modification, is still a challenge, especially in the semi-arid area. In this study, GW level, hydrogeochemical characterization, and geological features are used to understand, locally, the influence of Lake Maga, its associated hydraulic components, and the other SW bodies on the GW behaviour. GW levels were measured in 51 wells in December 2012 and monitored in February 2013, and in 15 wells (beyond the 51) in June 2017 and December 2018. Physicochemical parameters of SWs and GWs were measured in the field, and 15 water samples were collected for major ion characterization. The GW levels were close (mean value ≈5 m) to the land surface, with zero to very low (< 1 m) water level fluctuations near SW bodies. The GW levels (< 2 m) are influenced more by their proximity to irrigation canals, ponds, and streams than Lake Maga (mean ≈3.5 m). The analysis of electrical conductivity (EC) values and GW levels showed that the weakly mineralized (< 200 µS.cm⁻¹) GW were associated with the shallower GW table level. The moderate GW mineralization (200 < EC < 700 µS.cm⁻¹) were more influenced by the geological texture of the shallow aquifer. The analysis of the geological characteristics of the sub-shallow aquifer structure in the locality of Pouss is mainly sandy, while in the localities of Maga and Guirvidig, clay, clayey-sand and sandy-clay materials dominate. There are no trends in GW chemical evolution from Lake Maga waters towards the shallow groundwater table (SGWT). The mixing-ratios values showed that the SW contributed for more than 65% (mean) to the sub-shallow aquifer in the study area, and the highest SWs (80%) contribution occurred in the locality of Pouss, close to Lake Maga, pond, Logone River, irrigation canal, and seasonal stream, associated with the shallowest GW levels (< 1.5 m). The proximity to SW bodies and the texture of the fluvio-lacustrine deposit of the shallow aquifer strongly influenced GW table levels and their hydrogeochemical characteristics. This work could be a prerequisite to understand how the physicochemical and chemical properties of GW in the shallow aquifer evolve and respond under the influence of SW bodies.

This study aims to determine the depositional setting and deposit type of the Ereen deposit in the Bayanjargalan soum of Dundgovi province and the Dartsagt deposit in the Dalanjargalan soum of Dornogovi province, Mongolia. Both deposits are hosted within the sediments of the Neoproterozoic Oortsog Formation. The ore-hosted Oortsog Formation consists of shale with muscovite-sericite-magnetite-quartz and marbled limestone. The former is characterzid by gray to black shaly texture. Major, minor and trace elements composition of 16 ore samples of these two deposits were analyzed by XRF, ICP-MS and ICP-OES. The total iron (TFe) contents of the ore samples from the Ereen deposit range from 28.83 to 51.09 wt% with an average of 41.92 wt% whereas the TFe contents of the Dartsagt deposit from 37.61 to 49.78 wt% with an average of 43.15 wt%. In the Post-Archean Australian Shale (PAAS)-normalized REY diagram, the samples from the Ereen and the Dartsagt deposits show a weakly LREE depleted and HREE weakly enriched trend. Also, in the chondrite-normalized REY diagram, negative Eu anomaly Y-enriched trend are observed. The Eu/Eu*_SN values of the Ereen deposit (0.93 to 1.25, average 1.08) and the Dartsagt deposit range from 0.93 to 1.25 (avg. 1.08) and from 1.05 to 1.61 (avg. 1.22), respectively. These trace elements characteristics indicate that these two deposits belong to the Superior-type BIF deposit formed on the passive continental margin and are not likely to be associated with volcanogenic rocks.

Diatom assemblages from ARA2B-1A taken in the Chukchi Sea shelf were analyzed to reconstruct paleoenvironmental changes during the last 10 ka BP. The main factors controlling the distribution of diatom in the Chukchi Sea are the relatively warm and nutrient-rich Pacific water inflow after the opening of the Bering Strait. Based on the selected diatoms, three diatom assemblage zones are identified. The diatom assemblage zone I shows a rare or very low abundance, which corresponds to the early Holocene (10–8 ka BP). The diatom assemblage zone II corresponds to the mid-to-late Holocene (8–2 ka BP). It is a seasonal sea-ice environment with relatively abundant diatom valves and Chaetoceors resting spores, as well as sea-ice species, cold-water species, coastal species, and upwelling species. The diatom assemblage zone III corresponds to the late Holocene (2–0 ka BP), and the the sea-ice species generally decreased compared to zone II, while the coastal species Paralia sulcata occurred abundantly. In particular, the Thalassiosira antarctica, a cold-water species, increased distinctly during this time interval. After ∼2 ka BP, T. antarctica rapidly increased while sea-ice species rarely appeared, indicating limited open-marine environments. In particular, after 1 ka BP, T. antarctica decreased while the sea-ice species increased, suggesting that the sea-ice increased again before the recent global warming of the Arctic, the late Holocene.

The buried Daxing Uplift connects the Beijing Sag and Dachang Sag, which is the critical tectonic unit for understanding the structural evolution of the Beijing Sub-plain and its linkages to regional tectonics. This study combines paleomagnetic, ²⁶Al-¹⁰Be isochron dates and sedimentary analyses from a new borehole (Yx02) in the northeastern Beijing Sub-plain to shed fresh light on regional tectonic processes and the sedimentary history since the Pliocene. The main findings are as follows: (1) the Daxing Uplift had formed three depositional episodes: alluvial-fan, lacustrine-delta, and alluvial-fan sedimentation since the Cenozoic; (2) The borehole records the Brunhes, Gauss normal chron, and the Matuyama, Gilbert reversed chron in the Daxing Uplift, the corresponding depths are 0–148.9 m, 148.9–315.0 m, 315.0–520.5 m and 520.5–650 m; (3) An important tectonic event started in ~4.3 Ma, disintegrated NE-trending basin and range terrain, reactivated the NW-trending Nankou-Sunhe fault, and formed Shunyi fault in Beijing Sub-plain. Sedimentation occurs exclusively in the Beijing Sag and the northeastern Daxing Uplift during ~4.3–1.77 Ma; (4) During ~1.77–1.07 Ma, a transition from an extension to a strike-slip occurred, and is described not only in a progressively higher increase of the overall deposition rate, but also in a decrease of the relative deposition disparity between sags and uplifts. Since then, the Beijing Sub-plain has been shaped, associated with an overall subsidence depression in the Bohai Bay Basin. This work enhances our understanding of the formation and evolution of the Beijing Sub-plain, the division of tectonic episodes, and the initiation time of the latest tectonic movement in the break-up region, North China Craton, since the Neogene.

The Songjianghe gold deposit is located in the southeastern part of the Jiapigou–Haigou metallogenic belt, north of the North China Craton. The distribution of the ore body is governed by ductile shear zones and fractures oriented in the SN direction. The gold ore body consists of lenticular gold-bearing quartz veins. Mineralization can be divided into five stages: the quartz-oxidation stage (I), the pyrite-magnetite-quartz stage (II), the quartz-polymetallic sulfide stage (III), the telluride stage (IV), and the carbonate stage (V), with the main mineralization stages being III and IV. On the basis of lithological characteristics, three types of fluid inclusions were identified in the vein mineral assemblage: NaCl-H₂O (W-type), CO₂-H₂O (C-type), and a minor amount of pure CO₂ (pc-type). W-type and C-type inclusions coexist randomly around natural gold minerals in the same quartz grain, indicating that the mineralizing fluid is heterogeneous. The mineralizing fluids had a medium temperature and low to medium salinity based on micro temperature measurements of various inclusions. During the main mineralization phase, H-O isotope tests indicate that the mineralizing fluids are mantle-driven and mixed with atmospheric precipitation during mineralization. δ³⁴S data indicate that the mineralizing material originated from the mantle. The aforementioned characteristics suggest that Songjianghe is an orogenic gold deposit based on its dynamical background, with fluid immiscibility and sulfidation being the primary mechanisms of gold precipitation and enrichment.

Regolith-hosted Ni-Cr prospects in the Nkonko serpentinized massif are located near Kananga city in the Democratic Republic of Congo (DRC). This serpentinized massif displays an underground regolith profile divided into three main layers: (1) unweathered serpentinite bedrock, (2) saprolite serpentinites, and (3) the pedozone top layer. The bedrock serpentinites consist of serpentine (including lizardite and antigorite “garnierite”) as a major phase, with Cr-spinel and magnetite as a subsidiary phase. The rock contains rare pseudo-olivine relicts. Saprolite serpentinites contain serpentines (e.g., lizardite, chrysotile, antigorite “garnierite”) and subordinate ferrochromite and Cr-magnetite. These saprolite serpentinites are crosscut by veins of “garnierite” phase, talc, brucite, magnetite, magnesite, and chlorite. The pedozone primarily consists of lateritic soils with red and yellow limonite. Saprolite serpentinites exhibit relatively higher Al₂O₃, FeO, Fe₂O₃, and volatiles (LOI: loss on ignition) compared to bedrock serpentinites, while maintaining similar SiO₂ contents. For trace elements, saprolite serpentinites contain elevated Cr (up to 5.4 wt%) and Ni (up to 2.0 wt%) compared to bedrock samples (Cr up to 0.9 and Ni up to 0.3 wt%). The REE concentrations are low (total REE of about 2.0 ppm) and remain unchanged between the saprolites and bedrocks. Spinel is identified as the main host mineral for Cr, while secondary serpentine “garnierite” is the primary host phase for Ni. Plots of Al₂O₃/SiO₂ versus MgO/SiO₂ for bedrock and saprolite serpentinites, along with the REE patterns, suggest that the serpentine regolith originated from the alteration and weathering of harzburgite.