Mobility of Major and Trace Elements during the Bauxitization Processes in Ngaoundal Area (Adamawa Cameroon): Implication on Mining Perspectives

This study was focused to assess major and trace elements in bauxitic duricrusts from Ngaoundal and its surroundings in order to establish their mining interest. To this end, fieldworks, mineralogical and geochemical analyses were carried out. Four facies of duricrust were identified and characterized from the summit to the top of the slope of the Ngaoundal mountain: scoriaceous, pisolitic, nodular and massive. Mineralogical and geochemical analyses performed on 16 samples, revealed a significant concentration of Al2O3 mainly in the scoriaceous facies (over 45% in grade), moderate in Fe2O3 (averaging 23.69%) and SiO2 (averaging 21.7%). Trace elements were generally low, excluding Cr (421 ppm on average), Zr (327 ppm on average and V (213 ppm on average). In addition, the limited quantities of alkalis (Na2O, K2O) and alkaline earths metals (MgO, CaO) coupled with the very high values of Chemical Index of Alteration (CIA) and Mineralogical Index of Alteration (MIA), (more than 99%) attest to the intense weathering of the studied materials. Allitization and monosiallitization constituted the crystallochemical phenomena that have led to the development of bauxitic minerals. More than 90% of gibbsite in scoriaceous facies, 52.21% - 76.01% of kaolinite in pisolitic facies and more than 40% of hematite in nodular facies were quantified. The relationships between the constitutive components indicated their interdependency during the bauxitization phenomenon. The mineralogical and geochemical properties highlighted the mining interest of the studied duricrusts to be valorized.

Distribution of major and trace elements in surface sediments of Hangzhou Bay in China

The Inductively Coupled Plasma Optical Emission Spectrometer was used to analyze sediment samples collected from the Hangzhou Bay to determine major and trace elemental concentrations. Based on these concentrations, the study area can be classified into three geochemical provinces. Province I covers the northern Hangzhou Bay area and contains high concentrations of A120~, Fe203, MgO, Na20, K20, MnO, Cr, Cu, Ni, Pb, V, Co and Zn. Province III is located in the western Hangzhou Bay, near the Qiantang River mouth, and contains high concentrations of SiO~, Na20, P205~ TiO2, Cr, Sr, Zr. Province II is located in the middle and eastern Hangzhou Bay, with the medium concentrations of major and trace elements. The results also demonstrate that the grain size is the dominating factor controlling the spatial variations of elemental concentrations, and the Changjiang River （Yangtze River） and Qiantang River sediments play an important role in the distribution of these elements. Anthropogenic impact on heavy metal concentrations （especially Cr, Sr and Zr） can be detected in the surface sediments near the Qiantang River mouth.

Characteristics of major and trace elements in surface sediments of the Makran Accretionary Prism, Pakistan and their implications for natural gas hydrates

To accurately identify the natural gas hydrates(NGH)in the sea area of the Makran Accretionary Prism,Pakistan,this paper presents the testing and analysis of major and trace elements in sediment samples taken from two stations(S2 and S3)in the area by the China Geological Survey.As shown by testing results,all major elements are slightly different in content between the two stations except SiO2 and CaO.This also applies to the trace elements that include Sr and Ba primarily and Cr,Ni and Zn secondarily.It can be concluded in this study that the tectonic setting of the Makran Accretionary Prism is dominated by oceanic island arc and that provenance of the Makran Accretionary Prism is dominated by felsic igneous provenance,which is at the initial weathering stage and mainly consists of granodiorite.Besides terrigenous detritus,there are sediments possibly originating from Makran-Bela Ophiolite from the northwestern part and Murray Ridge igneous rocks from the southeastern part.The V/Cr,Ni/Co,and V/(V+Ni)ratios indicate that sediments of the two stations are in an oxidation-suboxidation environment.However,the authors infer that the sedimentary environment of the sediments 3.0 m below the seafloor tends to be gradually transformed into a reduction environment by comparison with the Qiongdongnan Basin in the South China Sea where NGH has been discovered.The sediments in the Makran Accretionary Prism are rich in organic matter,with total organic carbon(TOC)content greater than 1%.According to comprehensive research,the organic matter in the sediments mainly originates from marine algae and has high TOC content,which is favorable for the formation of NGH.

Major and trace element geochemistry of the mid-Bay of Bengal surface sediments: implications for provenance

The major and trace elements in 110 surface sediment samples collected from the middle of the Bay of Bengal（mid-Bay of Bengal） are analyzed to investigate provenance. Si levels are highest, followed by Al, and the distributions of these two elements are identical. The average CIA＊（chemical index of alteration） value is 72.07,indicating that the degree of weathering of the sediments in the study area is intermediate between those of sediments of the Himalayan and Indian rivers. Factor analyses and discrimination function analyses imply that the two main provenances are the Himalayan and the Indian continent. The inverse model calculation of the Tinormalized element ratios of the Bay of Bengal sediments indicate an estimated average contribution of 83.5%and 16.5% from the Himalayan and peninsular Indian rivers to the study area, respectively. The Himalayan source contributes more sediment to the eastern part of the study area, whereas the western part receives more sediment from the Indian Peninsula than did the eastern part. The primary mechanisms for deposition of sediments in the study area are the transport of Himalayan matter by turbidity currents and river-diluted water and the transport of Indian matter to the study area by a surface circulation in the Bay of Bengal, particularly the East India Coastal Current.

The distribution and variation of elements in sediments off the Huanghe (Yellow) River mouth

Surface sediment samples collected off the Huanghe （Yellow） River mouth during the period 2007-2009 were analyzed for major and trace element concentrations. Concentrations of 16 elements were measured using X-ray fluorescence spectrometry. Results demonstrate that sediment grain size is the dominant factor controlling the spatial variations of elemental concentrations. Correlation and cluster analyses allowed classification of the study area into four geochemical regions： Regions Ⅰ and Ⅲare characterized by high concentrations ofAl2O3, Fe2O3, MgO, Na2O, K2O, Cr, Cu, Mn, Ni, Pb, V, and Zn, and contain fine-grained sediments with mean grain size （Mz）〈22 μm; and; Regions Ⅱ and Ⅳcontain mostly coarse-grained sediments, and are characterized by high concentrations of SiO2, Na2O, and Zr. The sediment entering the sea from the Huanghe River and its tributaries is enriched in Ca. Thus, the Ca/Al ratio was used as an indicator of the proportion of sediments in the study area that originated from the Huanghe River. Ca/Al ratios decrease from Regions Ⅰ and Ⅱ（located in the nearshore zone of the Huanghe River delta） to Regions Ⅲand Ⅳ（distributed in the offshore zone of the northern Huanghe River delta, southern and southeastern Laizhou Bay area）.

Mineralogy and geochemistry of sands of the lower course of the Sanaga River, Cameroon: implications for weathering,provenance, and tectonic setting

This study focuses on the mineralogy and bulk chemical composition of 19 sediment samples,collected from the Sanaga River bed,between Nanga-Eboko and the Atlantic Ocean in Cameroon,to infer provenance,weathering,and tectonic setting.The textural analysis revealed that these sediments are mainly coarse-grained sands.X-ray diffraction and heavy mineral analyses show that these sands are made of quartz,microcline,plagioclase,muscovite,ilmenite,anatase,magnetite,opaques,and epidote.The Index of Chemical Variability values(1.07–2.68)indicates that the sands are immature.The Chemical Index of Alteration(53–66%),Plagioclase Index of Alteration(PIA;57–75%),and Mafic Index of Alteration(54–67%)values revealed a moderate intensity of weathering for these sediments.According to the compositional maturity diagram,the sands are mainly litharenites.The studied sands show enrichment in light rare earth elements relative to heavy rare earth elements and a negative anomaly in Eu(Eu/Eu*=0.32–0.83).These sands were derived from felsic metamorphic rocks dated Meso to Neoproterozoic from the Pan-African(700–1000 Ma)domain of south Cameroon.Th/U ratios(mean=5.40;n=19)reveal that these sands originating from felsic source rocks and are low to moderately recycled.On the tectonic discrimination diagrams,all the samples are plotted in the rift and passive margin domains,which is consistent with the tectonic history of Pan African in southern Cameroon.

Paleosalinity and Its Association with Organic Matter: A Case Study from the Eocene Shahejie Formation, Laizhou Bay Sag, Bohai Bay Basin (China)

Paleosalinity is vital for the paleoenvironmental reconstruction and affects the formation of source rock.The lower-middle sections of the third member of Eocene Shahejie formation(Es3M-L)constitute the most important source rock layer in Laizhou Bay Sag.However,the paleosalinity of the depositional water in which Es3M-L submembers are deposited remains unclear.A series of integrated experiments,including major and trace elements,X-ray diffraction,total organic carbon,and Rock-Eval,was performed to reveal the paleosalinity and its relationship with organic matter(OM).Various inorganic proxies(Sr/Ba,Rb/K,B/Ga,Walker’s paleosalimeter,Adam’s paleosalimeter,and Couch’s paleosalimeter)were employed to determine the paleosalinity of samples.Prominent differences existed in the proxies.Couch’s paleosalimeter is the most reliable and qualitative approach for Laizhou Bay Sag.Samples from the lake center(depocenter)and margin showed paleosalinities from 4.92 wt‰to 9.73 wt‰,suggesting a ubiquitous brackish(oligohaline-mesohaline)water body in the paleolake.Molybdenum enrichment in samples indicates an oxygen-depleted(suboxic or anoxic)condition.The increase in salinity has a certain but non-significant positive correlation with oxygen reduction.This condition may be attributed to the weak stratification of the water column in brackish water bodies.Moreover,paleosalinity has a weak and indirect relationship with OM accumulation during the deposition of Es3M-L submembers in Laizhou Bay Sag.

Origin and geochemistry of surface sediments in the mud deposit area offshore the Shandong Peninsula,China

The waters offshore the Shandong Peninsula separate the North Yellow Sea from the South Yellow Sea,and receive a large amount of terrestrial material from Chinese and Korean rivers,making it an ideal area for studying land-sea interactions.However,little attention has been given to measuring sediment transportation in most previous studies.Based on an analysis in composition of major and trace elements and particle size characteristics from 62 surface sediment samples from the northeastern region off Shandong Peninsula,the type,element composition,and controlling factors of the surface sediments were investigated.In addition,the transportation of sediments from source to sink was described from measured thermohaline data.The results show two types of surface sediments:sandy silt and silt.The sediments were mainly terrestrial;and marine carbonate had little effect on sediment composition.Shown on a binary diagram of Rb/Sc to Co/Sc,the Huanghe(Yellow)and Changjiang(Yangtze)Rivers are the main sources of surface sediments in the study area.The component mixing model showed that the relative contribution of sediment from the Huanghe River was up to 92%,followed by the Changjiang River(8%).The Yellow Sea Warm Current and the North Shandong Peninsula Coastal Current met at∼37.7°N in the study area,and were the main forces carrying sediment from the two main river sources.However,there was a deficit of transported material into the study area in summer.The secondary distribution of sediment from the two river sources was controlled by tidal currents and waves.

Paleoenvironment evolution and organic matter enrichment mechanisms in the first member of the Qingshankou Formation,Songliao Basin,China

Organic matter is the basis for oil and gas generation,and the depositional environment controls its enrichment.The first member of the Qingshankou Formation(K_(2)qn^(1))in Songliao Basin has a thick organic-rich shale and so is an important target section for shale oil exploration and development.In the Gulong Sag,shale samples from this unit were collected over the full length of the section.The characterization of the environments of deposition(EOD)of K_(2)qn^(1)was improved by utilizing lithological characteristics,thin section observations,elemental compositions,and organic carbon concentrations.Combined with the normalization coefficients proposed in this paper,an organic matter correlation model was established to elucidate the factors that influence organic matter enrichment.From the bottom to the top of K2qn1,the lake depth gradually becomes shallower,the primary productivity first decreases and then increases,the reducing conditions become stronger and then weaker,the water salinity gradually decreases,the climate first becomes semi-humid and then warm and humid,and the input of terrigenous debris first decreases and then increases.A major marine transgression at the base of the K_(2)qn^(1)᾽s brought in nutrients to increase primary productivity,and the density-stratified reducing environment preserved and enriched organic matter.High primary productivity occurred during the middle of the deposition of the K_(2)qn^(1),while terrigenous input is low.Organic matter is preserved in reduced deep lake environments,resulting in organic matter-rich black shale.The lake became shallower,and the salinity decreased in the upper part of K_(2)qn^(1).Benthic organisms rapidly multiplied,consuming large amounts of oxygen and destroying the previously depositional environment,resulting in a reducing environment disturbed by benthic organisms with poor preservation conditions and the lowest organic matter content.

Petrologic and geochemical characteristics of high-quality saline lacustrine source rocks in western Qaidam Basin

The main oil source in western Qaidam Basin is the Paleogene saline lacustrine source rocks.Traditionally,it was considered that these source rocks were characterized by low abundance and poor type of organic matter as well as limited oil generation potential,but this poor source rock condition was very inconsistent with good hydrocarbon exploration results.A previous study has just confirmed that this area develops high-quality source rocks,which is of great significance for recognizing potential of hydrocarbon resource and consolidating confidence to search large and medium-sized oil and gas fields in western Qaidam Basin.Based on fine geochemical analysis of source rocks,petrology,element geochemistry and organic geochemistry are applied to discuss development conditions of high-quality source rocks in this area.The results showed that the saline lacustrine sediments in western Qaidam Basin were deposited in relatively shallow and quiet water with relatively high salinity and low nutrient content;influenced by the drought and cold climate,the terrigenous supply of fresh water was limited,and few aquatic organisms were developed.Good preservation condition is favorable for rapid preservation of oil generating biomass(such as aquatic organisms),to form source rocks rich in hydrogen element with high soluble organic matter content;but relatively lower paleo-productivity makes organic matter abundance lower than that in the eastern saline lacustrine basins.The semi-deep lake,with relatively low salinity and abundant nutrients,is the most favorable are for development of high-quality source rocks;the source rocks have large thickness in the sedimentary depression areas,but due to high water salinity and far away from the provenance area,the water stratification was obvious,so it have moderate to high organic matter abundance.