Large Deposits Research Articles

Research on Sustainable Mining and Water Prevention in Large Open-Pit Water Deposits

Due to the impacts on the ecological environment, production safety and the economic benefits of large open-pit water deposits, there is no longer a single drainage method within the pit that can be used to meet the need for further deep mining. Therefore, curtain grouting technology is proposed for use in the prevention and control of mine water. The flow control equation of slurry in vertical fissures under the influence of self-weight stress was derived, and a three-dimensional visualized laminated jointed rock grouting model was developed independently to study the slurry transport mechanism, diffusion pattern, and sealing mechanism, which verified the correctness of the control equation. Field trials of industrial curtain grouting were also carried out at the mines, and the effectiveness of curtain water blockage was tested using visual analysis, inspection hole detection, and geophysical exploration methods. The results showed that after grouting the curtain, water-conducting cracks in the formation can be filled well and sealed, and the curtain has a good water-blocking effect. A complete set of diversified value-taking grouting systems is obtained, which can ensure the development of a green, safe and sustainable mine in the future.

Soil Environmental Study Analysis of Mining Areas in the Yangshan Gold Belt,Gansu

The Yangshan gold deposit in Gansu province is a super large gold deposit in the West Qinling metallogenic belt, with a cumulative gold accumulation of 400 tons. The soil environment conditions in Anba- Getiaowan ore section were investigated and analyzed to provide a reference basis for mine construction, development and treatment. A total of 120 samples (95 horizontal profile samples and 25 vertical profile samples) were collected, taking into account the topography, cover type, soil use type and soil type in the study area, and the distribution characteristics and change patterns of soil heavy metals As, Cd, Hg and Pb in the study area were evaluated sterically from both horizontal and vertical dimensions. Meanwhile, the distribution characteristics of F and Se elements in soil were compared and analyzed. The results of the study showed that: (1) the value of heavy metal elements As exceeded the standard, and the rest of the heavy metal elements were above the second grade of soil quality, among which the exceedance rate of heavy metal elements As in Anba area was 15%, and that in Getiaowan area was 84%; (2) the average value of As, F and Se content was higher than the background value of Longnan City, which was speculated to be significantly related to the presence of high arsenic and high fluorine water in the evaluation of poor quality water in the study area; (3) the excessive content of As element in the soil in the mining area is related to the occurrence of arsenic-containing minerals in gold, and As element pollution problem should be emphasized in the later construction and development of the mine.

A Review of the Metallogenic Mechanisms of Sandstone-Type Uranium Deposits in Hydrocarbon-Bearing Basins in China

As a valuable mineral resource, uranium is extensively utilized in nuclear power generation, radiation therapy, isotope labeling, and tracing. In order to achieve energy structure diversification, reduce dependence on traditional fossil fuels, and promote the sustainable development of energy production and consumption, research on the metallogenic mechanisms and related development technologies of uranium resources has been one of the focuses of China’s energy development. Sandstone-type uranium deposits make up approximately 43% of all deposits in China, making them the most prevalent form of uranium deposit there. Sandstone-type uranium deposits and hydrocarbon resources frequently coexist in the same basin in China. Therefore, this study summarizes the spatial and chronological distribution, as well as the geological characteristics, of typical sandstone-type uranium deposits in China’s hydrocarbon-bearing basins. From the perspectives of fluid action, geological structure, and sedimentary environment, the metallogenic mechanisms of sandstone-type uranium deposits in hydrocarbon-bearing basins are explored. According to the research, the rapid reduction effect of oil and gas in the same basin is a major factor in the generation of relatively large uranium deposits. Additionally, ions such as CO32− and HCO3− in hydrothermal fluids of hydrocarbon-bearing basins, which typically originate from dispersed oil and gas, are more conducive to uranium enrichment and sedimentation. This study provides guidance for efficient sandstone-type uranium deposit exploration and production in hydrocarbon-bearing basins and helps to achieve significant improvements in uranium resource exploitation efficiency.

CHARACTERIZATION OF THE ZOOPLANKTON COMMUNITY OF A SHALLOW LAKE WITH ORGANIC-RICH SEDIMENT

In this research, the ecological quality of the lake Vēveru (Latvia, Rēzekne district) according to zooplankton was investigated. Lake Vēveru has a large sapropel deposit with rich reserves of sapropel. Removal of sapropel requires organization of spatio-temporal monitoring to control the state or disturbance of the existing ecosystems in the long term. Zooplankton samples were collected and analyzed using standard methods in the open pelagic and littoral zones of the lake in different seasons. Quantitative samples of zooplankton in each sampling site were collected from the surface water layer at the depth of 0.5 m by filtering 100 l of water through an Apstein-type plankton net (64 µ). Biodiversity of zooplankton taxa in Lake Vēveru shows that the food base of juvenile and planktophagous fish is sufficient. The Shannon index according to the diversity of zooplankton taxa ranges from 0.84 to 1.52 by abundance, from 1.52 to 2.21 by biomass.

ASSESSMENT BY MACROINVERTEBRATES OF THE ECOLOGICAL QUALITY OF SHALLOW LAKE WITH RICH SAPROPEL SEDIMENTS

In this research, the ecological quality of the Lake Vēveru (Latvia, Rēzekne district) according to macroinvertebrates was investigated. The Lake Vēveru has a large sapropel deposit. The Lake Vēveru is relatively little affected by human economic activity, the only moderate impact is sapropel mining in the lake in 2009-2012, it is planned to resume industrial sapropel mining in the lake. During the period of sapropel removal, a decrease in the transparency of water is noted due to the nutrient flow into the water mass, pH increases, the habitat of planktonic and benthic organisms is disturbed. Macroinvertebrates samples were collected and analyzed using standard methods in the open pelagic and littoral zones of the lake in different seasons. The ecological quality of the lake was assessed in accordance with the requirements of the European Water Framework Directive in Latvia. To characterize the ecological status of the lake the Latvian Lake Macroinvertebrate Multimetric Index was used. According to the Ecological Quality Ratio (EQR) the lake indicates a good ecological status of the water. However, a moderately low species diversity index indicates the dominance of certain taxa. In general, macroinvertebrates species that are often and widely found in Latvia and are environmentally tolerant have been found in the lake. Water temperature, pH, conductivity, dissolved oxygen, oxidation reduction potential, chlorophyll-α were measured with a HACH OTT DS5 Probe. Water transparency was measured using a Secchi disc.

Zircon U-Pb chronology and geochemistry of porphyritic granites: A case study of the Dalancun granites in Zhaoyuan, Shandong Province

The granite in Dalancun, Zhaoyuan, Shandong Province is mainly porphyry granite. In this paper, detailed field geology, petrology, isotopic chronology and whole-rock principal and microgeochemistry have been studied. LA-ICP-MS zircon U-Pb chronology shows that it was formed in the Early Cretaceous (129.7 ± 0.8 Ma), later than Linglong granite (160-150 Ma) and earlier than Laoshan granite (120-114 Ma). It is consistent with the main ore-forming age of Jiaodong large gold deposit and the diagenetic age of Guojialing granite (130-126 Ma). K2O+Na2O=7.41%~9.37%, K2O/Na2O=0.78~1.24; A/CNK=0.89~1.06, MgO=0.63%~1.01%, with high K, Al characteristics, belongs to the quasi-aluminum-peralumin high potassium calc-alkaline series. The strong differentiation of rare earth elements (La/Yb) N=68.24~93.96, weak positive Eu anomaly (δEu=1.26~1.769), enrichment of large ion lithophile elements Ba, Sr, high field strength elements Nb, Ta, Ti deficit, indicating the geochemical characteristics of continental lithosphere. In addition, high Sr (1817×10-6~2017×10-6), low Y (7.55×10-6~9.36×10-6), Sr/Y ratio between 199.89~262.29, Nb/Ta ratio between 14.67~16.73, consistent with continental crust ratio, It shows the characteristics of type I granite and Adakite. Combined with other geochemical indexes and regional geological studies, this paper suggests that the Dellancun porphyritic granite belongs to crust-mantle granite, which may have been formed in the arc environment of continental margin during the transition from compressive to extensional tectonic system in Jiaodong area, and is closely related to the subduction of the paleo-Pacific plate. This study not only helps to understand the Mesozoic tectonic evolution in eastern China, but also provides a basis for revealing the formation mechanism of Jiaodong gold deposit.

Distribution of Co, Se, Cd, In, Re and other critical metals in sulfide ores from a porphyry-skarn system: A case study of Chengmenshan Cu deposit, Jiangxi, China

Chengmenshan Cu deposit is a large porphyry-skarn copper deposit, located in the Jiutui ore district, Middle–Lower Yangtze River metallogenic belt, Eastern China. The deposit is enriched in tellurium, selenium, rhenium and cadmium; however, the occurrence and distribution of these metals are unclear. In this study, we report cobalt, selenium, cadmium, indium, rhenium and other critical metals in pyrite, chalcopyrite, and sphalerite from sulfide ores of Chengmenshan deposit. In-situ LA-ICP-MS trace element analysis and mapping of minerals were conducted to determine their trace element concentrations and reveal the distribution and occurrence of critical metals in different sulfides. Three ore types have been identified in Chengmenshan deposit, named: porphyry ore, skarn ore and strata-bound ore. Based on mineral assemblages, ore fabrics, and crosscutting relationships between the veins, Chengmenshan deposit is divided into three mineralization stages: pre-ore stage of skarn mineralization, syn-ore stage of sulfide mineralization, and post-ore stage of carbonation. The pyrite and sphalerite can be divided into two generations: Py1, Py2, and Sp1, Sp2, respectively. The critical metals exhibited an uneven distribution and closely related to sulfide minerals. Telluride minerals in the deposit mainly include hessite, tetradymite, joseite. Rhenium is mainly enriched in molybdenite (128 to 496 ppm, average 276 ppm); cobalt is mainly enriched in pyrite, and the value of the three types of ore in the early stage (Py1) higher late stage (Py2); Se in chalcopyrite is slightly higher than pyrite and sphalerite; Cadmium is mainly enriched in sphalerite (up to 3000–6000 ppm), and is relatively low in pyrite and chalcopyrite; Indium is distributed in chalcopyrite and sphalerite, and the values of sphalerite are higher than chalcopyrite; the Ga distribution was sphalerite > chalcopyrite > pyrite. The enrichment and distribution of Co, Cd, In in Chengmenshan porphyry-skarn deposit system were mainly control by the fluid temperature. The Cu-Mo (Re), Cu-Fe (Co, Se) and Cu-Pb-Zn-Ag (Te, Cd, In, Tl) mineralizations constitute Chengmenshan porphyry-skarn mineralization system, and show a Mo-Re to Cu-Co-Se-Te-Ga to Cu-Pb-Zn-Ag-Te-Cd-In pattern from granite to distal stratum in space.

Sociodemographic Disparities in Mercury Exposure from United States Coal-Fired Power Plants.

Hazardous air pollutants emitted by United States (U.S) coal-fired power plants have been controlled by the Mercury and Air Toxics Standards (MATS) since 2012. Sociodemographic disparities in traditional air pollutant exposures from U.S. power plants are known to occur but have not been evaluated for mercury (Hg), a neurotoxicant that bioaccumulates in food webs. Atmospheric Hg deposition from domestic power plants decreased by 91% across the contiguous U.S. from 6.4 Mg in 2010 to 0.55 Mg in 2020. Prior to MATS, populations living within 5 km of power plants (n = 507) included greater proportions of frequent fish consumers, individuals with low annual income and less than a high school education, and limited English-proficiency households compared to the US general population. These results reinforce a lack of distributional justice in plant siting found in prior work. Significantly greater proportions of low-income individuals lived within 5 km of active facilities in 2020 (n = 277) compared to plants that retired after 2010, suggesting that socioeconomic status may have played a role in retirement. Despite large deposition declines, an end-member scenario for remaining exposures from the largest active power plants for individuals consuming self-caught fish suggests they could still exceed the U.S. Environmental Protection Agency reference dose for methylmercury.

The World’s Largest Bauxite-Bearing Province, Fouta Djallon–Mandingo (West Africa). Part 4: a Zoning Mechanism in Laterite Bauxite-Bearing Weathering Crust

The results of detailed exploration and year-round observations of the hydrogeological regime at large deposits, as well as special hydrochemical studies of various types of water and changes in the gas composition of the underground atmosphere in the lateritic weathering crust, of the very large bauxite-bearing province, Fouta Djallon–Mandingo, thanks to a reliable factual base, made it possible for the first time to draw a number of important conclusions about the conditions and features of zoning formation in the lateritic weathering profile. The weathering profile consists of two metasomatic columns spatially combined in plan, but vertically separated: an upper one, consisting of hydroxides and oxides of iron and aluminum, and a lower one, composed of clayey eluvium and products of hydration and decomposition of aluminosilicates—polymineral clays and kaolinite. In both columns, the processes of change begin with the same rainwater, but differ in the hydrodynamic parameters in each of the columns. Changes in the weathering profile occur in accordance with the main patterns of low-temperature infiltration metasomatism. The modern hydrogeological and gas regime in bauxite-bearing lateritic covers controls the mineralogical and geochemical zoning. Features of biological and soil processes and hydrodynamics and hydrochemistry in the weathering profile lead to a threshold nature of the change in physicochemical and biochemical conditions, providing the action of geochemical (oxidation, reduction, gley, adsorption) barriers, which is the main mechanism of zonal distribution of matter in lateritic weathering crusts.

НОВЫЕ ДАННЫЕ О ВОЗВРАТЕ ДРЕВНЕГО ОРОШАЕМОГО ЗЕМЛЕДЕЛИЯ В ТУВЕ

According to the conducted research, the Republic of Tuva is an area of ancient agriculture, which was facilitated by the geographical location and natural conditions, first of all, the mountainous terrain and the abundance of rivers in this territory. Practically in all river valleys of the region there are various irrigation systems corresponding to the capabilities of technology and the organization of social labor of certain historical periods. Here you can observe all the stages of irrigation development. According to В.А. Latynin’s classification, it is the stage of early irrigated agriculture, the stage of the simplest types of irrigation channels that turn into complex fan irrigation systems. The presence of the rudiments of agriculture in the Neolithic is evidenced by the finds of pollen of cultivated barley aged 6–5 thousand years in the valley of the Small Yenisei, made by S.B. Potakhin. Mining and ore production contributed to the development of agriculture in the Bronze Age — there are large copper deposits in the bowels of Tuva. According to the conducted research, developed irrigated agriculture existed in this territory in the Xiongnu period (Ubsunur basin, SOAN-9199; East Tuva Highlands, SOAN-9201). In 2022, radiocarbon dating was obtained for the first time, confirming the presence of irrigated agriculture in Tuva in the 1st millennium BC, Scythian-Saka time.

Sources of Metals for the Rudny Altai VMS Deposits: Results of High-Precision MC-ICP-MS Lead Isotope Study

The Rudny Altai metallogenic province, which is concordant to the structures of the eponymous terrane and located in the Central Asian orogenic belt (CAOB), is one of the largest volcanic massive sulfide (VMS) provinces in the world. Lead isotopic composition of galena (61 samples in total) was measured for the first time with high accuracy (±0.02%, SD) for 20 sulfide base metal deposits representing the dominant Kuroko type in the Rudny Altai. They are enclosed in the Early–Middle Devonian volcano-sedimentary sequence in association with volcanic rocks of the bimodal basalt-rhyolite series. We studied the large and superlarge deposits of this type: Ridder-Sokol’noe, Tishinskoe, Novo-Leninogorskoe, Zyryanovskoe, Zmeinogorskoe, and Korbalikha. In the province, the isotope ratios 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb vary within narrow limits. At average values of 206Pb/204Pb = 17.820, 207Pb/204Pb = 15.517 and 208Pb/204Pb = 37.669, the root mean square variations (variation coefficient, %) are 0.22, 0.038 and 0.063% respectively. Even more homogeneous composition is observed within ore districts of the province (0.054, 0.012 and 0.020%) and especially within deposits (0.025, 0.010 and 0.013%), where the scale of variations of lead isotope ratios reaches their measurement error (±0.02%). The lead isotopic composition in the province shows no isotopic “signatures” of juvenile (asthenospheric) origin. The evolutionary characteristics of the lead source (its depletion in uranium, the old model Pb-Pb age, and moderate values of the µ2 parameter) together with the persistent isotopic composition allow us to regard the lithospheric mantle consisting of metasomatized and recycled rocks as its source. This source was of regional significance, chemically (U-Th-Pb) and isotopically (Pb-Pb) homogeneous, and common for all deposits. Among other CAOB terranes, including the Chinese Altai, the 206Pb, 207Pb and 208Pb isotopes in the ore lead of the Rudny Altai terrane have the least radiogenic composition. The previously noted (Chiaradia et al., 2006) systematic decrease of radiogenic isotope content in the lead of ores and rocks of the CAOB terranes from the southwest to the northeast correlates with a decrease in the lower crustal contribution in the same direction in their composition, where fragments and blocks of Precambrian crust are also involved. The peculiarity of the Pb isotopic composition of the Rudny Altai terrane is largely determined by the absence of Precambrian crustal blocks in its composition.

The Violation of Human Rights during the Bakassi Peninsula Conflict from 1965 to 2013

The military skirmishes over the Bakassi peninsula between Cameroon and Nigeria was as a result of the vestiges of colonialism and the discovery of large deposits of natural resources in the area. This study explores the violations of human rights in the Bakassi peninsula during the Bakassi conflict. The study mainly explores how, when and where these human rights abuses were committed, and to a lesser extent why and who committed these abuses. The study adopts the qualitative research method and from it, historical consolidation and content analyses in terms of data collection. The use of secondary data, applied with the thematic approach in this study brings to the fore that there were lots of human rights violations during the Bakassi conflict in the Bakassi peninsula. This study could be utilised by researchers and policy makers to understand human rights trends in the Bakassi peninsula area.
 Keywords: Cameroon, Nigeria, Violations, Human Rights, Bakassi Peninsula Conflict

Laser induced crystallization of sputtered MoS2 thin films

The integration of transition metal dichalcogenides (TMDs) thin films into Si CMOS-based devices requires the development of new bottom-up material growth approaches producing high crystallinity films without affecting the SiO2/Si substrate. For this purpose, sputtering is a suitable deposition method due to its simplicity, jointly with high reliability and large area deposition capabilities. However, sputtered layers are amorphous and require a post-deposition thermal treatment to obtain a highly crystalline film. Nanosecond pulsed laser annealing (PLA) has recently emerged as promising route to achieve large-scale crystalline TMDs films without significantly heating or affecting the underlying substrate. The aim of this work is to explore the possibility to produce crystalline 2H–MoS2 on large areas directly on a SiO2-on-Si substrate. The film structure, composition and morphology were monitored as a function of the laser pulse energy density by Raman spectroscopy, X-rays diffraction, Rutherford backscattered spectroscopy (RBS), scanning transmission electron microscopy (STEM) and atomic force microscopy (AFM). The electrical properties of the film with optimized crystallinity were finally investigated through deposition of Cr/Au contacts using shadow masks. This approach can be scaled to other TMDs materials and substrates, also paving the way for the fabrication of heterostructures and electrical devices on the top of a single substrate.

Variations in lunar elastic thickness from admittance spectral analysis

We infer the elastic thickness of regions of the Moon by performing an admittance analysis on GRAIL gravity and LOLA topography data. Reliable results are generally confined to the lunar farside, away from large mare deposits. We find that elastic thickness varies between 13 km and 72 km, with a mean elastic thickness (Te) of 29 km. The highest reliable elastic thicknesses are found to the northwest of South Pole-Aitken (SPA) basin while the lowest elastic thicknesses are found in the equatorial farside and within SPA. Our findings suggest that much of the loading on the Moon must have taken place within the first 200 Myr after lunar magma ocean solidification, though some areas (Te > 40 km) may be recording events as late at 3.5 Ga. We find no correlation between elastic thickness and crater density, crustal thickness, or mean elevation in areas where reliable estimates of elastic thickness can be made, though we do note that regions with the highest crustal thickness and mean elevation are associated with lower elastic thickness values. We also demonstrate that smaller localization windows can lead to systematically lower elastic thickness estimates.

Geology, alteration system and uranium mineralization of Tamusu large uranium deposit, China

Tamusu uranium deposit is located in Yingejing sag in the Bayingobi basin. A rift type structural slope zone developed northwest of the sag. Based on the study of the lithology, lithofacies, whole rock geochemistry, and fluid inclusion characteristics of the deposit, a paragenetic association sequence of altered minerals in the deposit was established, and the characteristics of the source, temperature, salinity, and evolution of the ore-forming fluid in the deposit were discussed. The stratigraphic assemblage structure of the lower member of the Bayingobi Formation (falling-stage system tract, lowstand system tract, and transgressive system tract) laid the foundation for uranium mineralization. The uranium mineralization period of ore deposit can be divided into three stages. The altered mineral assemblages of Stage 1 are mainly composed of hematite, dolomite, iron-bearing dolomite, ankerite, fluorite, euhedral pyrite, and metal sulfide. Stage 2 altered mineral assemblages are dominated by limonite, euhedral-subhedral pyrite, and gypsum. The altered mineral assemblages of Stage 3 are mainly composed of layered gypsum, celestite, and barite. The early uranium ore-forming fluid mainly originated from the deep basin and percolated along the fault and sand body of the lowstand system tract to form uranium orebodies. The fluid inclusion temperature of ore-forming fluid was 211–140 ℃, and the salinity was 4.49%–16.24%. The temperature gradually decreased as the ore-forming fluid evolved, and CO2 was released, causing dolomite, calcite, fluorite, and other minerals to precipitate in the sandstone pores. The late ore-forming fluid mainly originated from supergene oxygen water, which migrated into the basin along the erosion window at the edge of the sag. The fluid inclusion temperature of ore-forming fluid was 100–130 ℃, the salinity was 2.24%–7.02%, and the average was 4.49%. In the late stage of the supergene fluid, the fluid inclusion temperature was 55–79 ℃, and the salinity was 4.96%–5.11%. The ore-forming fluid of the deposit gradually decreased in temperature from the early stage to the late stage of mineralization. In addition, the salinity gradually evolved from high in the early stage to low and evolved to high in the late stage. Sulfophile, lithophile, and rare earth elements precipitated first in the process of fluid action, followed by U, and Sc increased with the U content. A uranium metallogenic model of the deposit was established based on the relationship between the structural, lithology, mineralization alteration, fluid evolution, and uranium mineralization of the basin.

Buried Ice Deposits in Lunar Polar Cold Traps Were Disrupted by Ballistic Sedimentation

AbstractThe NASA Artemis program will send humans to the lunar south polar region, in part to investigate the availability of water ice and other in situ resources. While trace amounts of ice have been detected at the surface of polar permanently shadowed regions (PSRs), recent studies suggest that large ice deposits could be stable below cold traps in the PSRs over geologic time. A recent study modeling the rate of ice delivery, ejecta deposition and ice loss from cold traps predicted that gigatons of ice could be buried below 100s of meters of crater ejecta and regolith. However, crater ejecta vigorously mix the target on impact through ballistic sedimentation, which may disrupt buried ice deposits. Here, we developed a thermal model to predict ice stability during ballistic sedimentation events. We then modeled cold trap ice and ejecta stratigraphy over geologic time using Monte Carlo methods. We found that ballistic sedimentation disrupted large ice deposits in most cases, dispersing them into smaller layers. Ice retention decreased in most cases, but varied significantly with the sequence of ejecta delivery, particularly from basin‐forming events. Over many model runs, we found that south polar craters Amundsen, Cabeus, and Cabeus B were most likely to retain large deposits of ice at depths up to 100 m, shallow enough to be detectable with ground‐penetrating radar. We discuss these findings in the context of the imminent human exploration activities at the lunar south pole.

Acid modification of clays from the Kalzhat, Orta Tentek deposits and study their physical-chemical properties

This research work is an acid modification of Kalzhat and Orta Tentek clays. Kazakhstan is rich in large deposits, and the Kalzhat and Orta Tentek deposits are not fully explored, therefore, in this research work, these deposits were studied. The activation of clays Kalzhat and Orta Tentek deposits of the Republic Kazakhstan with 5% and 10% hydrochloric acid solutions was carried out. Using X-ray fluorescence analysis and scanning electron microscopy, the chemical composition and morphology of the initial and modified clay samples were established. Using the X-ray diffraction method, it was established that the main rock-forming mineral of the Kalzhat and Orta Tentek clays is montmorillonite. It has been established that modification with hydrochloric acid leads to a decrease and leaching of calcium, potassium, magnesium, barium, zinc, aluminum and molybdenum ions from samples of both clays and an increase in the content of iron ions. It is shown that the zeta potentials of the initial clays are negatively charged and acid modification leads to a decrease in the negative value of the zeta potential due to a decrease in alkali and alkaline earth metal ions in the clay.

THE WORLD’S LARGEST FOUTA DJALLON–MANDINGO BAUXITE PROVINCE (WEST AFRICA): PART 4. THE MECHANISM OF ZONING FORMATION IN LATERITE BOXITE-BEARING WEATHERING CRUSTS

Obtained as a result of detailed exploration and year-round observations of the hydrogeological regime at large deposits, as well as special hydrochemical studies of various types of water and changes in the gas composition of the underground atmosphere in the lateritic weathering crust of the largest bauxite-bearing province FDM, thanks to a reliable factual base, allowed us to draw a number of important conclusions on the conditions and features of the formation of zoning in the lateritic weathering profile for the first time. The weathering profile consists of two metasomatic columns spatially combined in plan, but vertically separated: the upper, lateritic cover, composed mainly of the products of the final hydrolysis of lateritic weathering, that is, hydroxides and oxides of iron and aluminum; the lower one, composed of clayey eluvium, products of hydration and decomposition of aluminosilicates - polymineral clays and kaolinite. In both columns, the processes of changing begin with the same rainwater, but differ in hydrodynamic parameters in each of the columns. Changes in the weathering profile occur in accordance with the main patterns of low-temperature infiltration metasomatism. The modern hydrogeological and gas regime in the bauxite-bearing lateritic covers controls the mineralogical and geochemical zoning. Peculiarities of biological and soil processes, hydrodynamics and hydrochemistry in the weathering profile lead to the threshold nature of the change in physicochemical and biochemical conditions, providing the action of geochemical (oxidative, reducing, gley, adsorption) barriers - the main mechanism of zonal distribution of matter in lateritic crusts.

Feldspar traces mineralization processes in the Qongjiagang giant lithium ore district, Himalaya, Tibet

Recently, a large spodumene pegmatite deposit was discovered in the Higher Himalayan orogenic zone near Qongjiagang. The granites exposed on about 1500 vertical meters of the outcrop (with elevation varying from 4077 m to 5533 m) show an evolution from two-mica granite to tourmaline muscovite granite and tourmaline albite granite. Various types of pegmatites are dispersed throughout the granite, creating an opportunity to examine the evolutionary relationship between these rock types and their potential as ore deposits rich in lithium. This study collected feldspar samples from various granites and pegmatites along a vertical cross-section, and analyzed their structures using various techniques including Raman spectroscopy, and transmission electron microscopy. Elemental and isotopic compositions were determined using electron microprobe and laser ablation inductively coupled plasma mass spectrometry, providing valuable mineralogical information on the formation of widespread lithium deposits in the Qongjiagang area. The observed variations in feldspar composition suggest that changes in granite lithology and ore-bearing potential of pegmatites with increasing altitude result from upward fractional crystallization of magma formed by partial melting of Himalayan crystalline basement. This process is likely driven by decreasing temperature, resulting in a significant decrease in concentrations of alkaline earth metals (e.g., Ca, Sr, Ba), and gradual enrichment of trace elements including Rb, Cs, and Li. As a result, pegmatites attain a melt environment similar to that of the adjacent granite at similar elevations. Structural features of feldspar suggest that the decrease in Li concentration in K-feldspar and the formation of lithium-rich zonation of pegmatites are a result of simultaneous growth of spodumene and blocky orthoclase during the magmatic stage, as well as deuteric fluid extraction by syntectonic processes during the transition to the stable stage of microcline feldspar.

Formation of the Huayangchuan (Central China) carbonatite-associated REE-Nb-U polymetallic deposit constrained from monazite mineral chemistry and isotope systematics: HREE enrichment in late-stage monazite

The process of enrichment of middle and heavy rare earth elements (MREE and HREE = Sm-Lu plus Y) in magmatic-hydrothermal systems, especially the carbonatite system, remains unclear. Here, we performed in-situ monazite element and isotopic analysis to investigate the genesis of the Huayangchuan REE-Nb-U polymetallic deposit in central China and the enrichment process of MREE and HREE during the evolution of the magmatic hydrothermal system. The Huayangchuan deposit is spatially associated with HREE-rich calcite carbonatites, which exist as two mineralization stages: the ores of the first stage are hosted by carbonatite itself; in the second stage, the ores are present as veins, dominantly by wall rocks around the carbonatite. The results of secondary ion mass spectrometry (SIMS) monazite U-Pb dating on the thin sections yielded Tera-Wasserburg lower intercept ages of 207 ± 4 Ma and 206 ± 5 Ma for carbonatite-hosted monazite and vein-type monazite, respectively. However, some monazite analysis points provide a wide Yanshanian age range (112–182 Ma). The lower intercept age of 206–207 Ma is explained as the mineralization age of the deposit, whereas the wide younger age with higher 238U/206Pb and lower 208Pb/232Th ratios may be ascribed to the loss of radioactive Pb, as the varying degrees of reworking resulted from the later Yanshanian tectono-thermal event. The monazite laser-ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICPMS) Sr-Nd isotopes from both carbonatite-hosted and wall-rock-hosted vein-type ores indicate that the Huayangchuan deposit is closely related to enriched mantle-derived (EM1) calcite carbonatite but locally affected by late fluid activation. Combined with the integrated age spectra, such reworking processes associated with new weak mineralization widely exist in other carbonatite-related deposits in the Lesser Qinling, but are not important for carbonatite-related mineralization in this area. Controlled by element behaviors, MREE and HREE are more likely to dissolve in hydrothermal fluids, enabling their long-distance migration and deposition, than light REE (LREE) in some carbonatite systems, resulting in much higher MREE and HREE contents of the late monazite in the vein-type ores than those of the early carbonatite-hosted monazite. Therefore, it could be expected that there might be MREE and HREE enrichment and exploration potential in the periphery of some large carbonatite-related LREE-dominated deposits.