Boron isotope geochemistry of Bangor Co Salt Lake(central Tibet):implications for boron origin and uneven mixing of lake water

Boron is an essential,widely used,micronutrient element and is abundant in salt lakes on the Qinghai-Tibet Plateau.The origin and distribution of boron brine deposits on the Qinghai-Tibet Plateau is an important foundation for B resource formation,evolution,and enrichment,which have long been the subject of debate.The boron isotope system is a sensitive geochemical tracer,making it useful for eff ectively and precisely tracking a wide range of geological processes and sources.This study investigates the major cations,[B],andδB values of samples(lake brine,river waters,and cold spring water)from the Bangor Co Lake which is a typical salt lake rich in boron in Tibet,China.There are magnitude-scale diff erences in[B]among diff erent sample types:river samples<cold spring water<<brine lakes.[B]values vary from 0.73 to~1113 mg/L.Similar to[B],theδB values of the samples exhibit magnitude-scale variations as[B],ranging from-7.35‰to+7.66‰.There are also magnitude-scale diff erences inδB among diff erent sample types.TheδB values of cold spring water are relatively low,and the values range from-1.26‰to-7.75‰.However,the river water samples and saline lakes have higher values,from 0.38‰to 4.62‰,and theδB values of river water samples are basically in the distribution range of those of Bangor Co Lake.This indicates that the sources of boron in Bangor Co Lake are mainly the recharge water with higherδB values and spring water with lowerδB values,and the boron sources and the uneven mixing of lake water are two reasons that account for the large change in theδB value of Bangor Co Lake.

Chronology and Genesis of S-type Granites in Hetai District, Guangdong Province: Constraints from LA-ICP-MS Zircon U-Pb Dating and Tourmaline Boron Isotope In-situ Analyses

1 Introduction Hetai district,which is a mountainous area,situated on Guangning and Zhaoqing city,west Guangdong Province.Hetai district is generally located on southwest of South China Caledonian fold belt,east margin of Yunkai post-Caledonian uplift.Multiple type granites are widely distributed in Hetai district,including Caledonian,Indosinian and Yanshanian granites.Based on different

Geochemical study of boron isotopes in the process of loess weathering

In this paper the boron contents and boron isotopic composition of acid-soluble phases in loess and paleosol samples are determined for the first time. The boron contents of acid-soluble phases in the Luochuan loess section (S0 S2) vary within the range of (0.8—2.7)?0-6 and their d 11B values vary from 1.8?to +18.6? mostly within the range of 0—+10? The boron contents and d 11B values of paleosol layers are higher than those of loess layers, especially in the loess layer S1. Varying chemical weathering intensity and loess adsorption capability are the main fac-tors leading to the variations of boron contents and d 11B values of acid-soluble phases in the loess section. The variation of chemical weathering intensity in response to the variation of climatic con-ditions seems to be the main factor leading to the variations of boron contents andδ11B values of acid-soluble phases in the loess section.

Problems of Lithium Isotope Research in Salt Lake Study

Lithium in nature mainly exists in the forms of solid minerals and ionic liquid.More than 150 lithium minerals exist,which are mainly pegmatite mineral including triphane,lithionite and petalite.Liquid lithium mainly

Boron isotopic variations in tourmaline from metacarbonates and associated calc-silicate rocks from the Bohemian Massif: Constraints on boron recycling in the Variscan orogen

Various metacarbonate and associated calc-silicate rocks form minor but genetically significant components of the lithological units in the Bohemian Massif of the Variscan orogen in Central Europe.These rocks vary in terms of their lithostratigraphy,chemical composition and mineral assemblage(dolomite/calcite ratio,silicate abundance).Tourmaline is present in five paragenetic settings within the metacarbonate and calc-silicate units.TypeⅠcomprises individual,euhedral,prismatic grains and grain aggregates in a carbonate-dominant(calcite±dolomite)matrix poor in silicates.TypeⅡis characterized by euhedral to subhedral grains and coarse-to fine-grained aggregates in silicate-rich layers/nests within metacarbonate bodies whereas typeⅢoccurs as prismatic grains and aggregates at the contact zones between carbonate and associated silicate host rocks.TypeⅣis in veins crosscutting metacarbonate bodies,and typeⅣtourmaline occurs at the exocontacts of elbaite-subtype granitic pegmatite.Tourmaline from the different settings shows distinctive compositional features.Typical for typeⅠare Mg-rich compositions,with fluor-uvite>dravite>>magnesio-lucchesiite.Tourmalines from typeⅡsilicate-rich layers/nests are highly variable,corresponding to oxy-schorl,magnesio-foitite,Al-rich dravite and fluor-uvite.Typical for typeⅢtourmalines are Ca,Ti-bearing oxy-dravite compositions.The typeⅣveins feature dravite and fluor-uvite tourmaline compositions whereas typeⅤtourmaline is Li,F-rich dravite.Tourmaline is the only Bbearing phase in paragenetic typesⅠ-Ⅳ,where it is characterised by two principal ranges of B-isotope composition(δ^11B=-13‰to-9‰and-18‰to-14‰).These ranges correspond to regionally different units of the Moldanubian Zone.Thus,the Svratka Unit(Moldanubian Zone s.l.)contains only isotopically lighter tourmaline(δ^11B=-18‰to-14‰),whereas metacarbonates in the Poli?ka unit(Teplá-Barrandian Zone)and Olesnice unit(Moravicum of the Moravo-Silesian Zone)has exclusively isotopically heavier tourmaline(δ^11B=-9‰to-13‰).Tourmalines from metacarbonates in the Variegated Unit cover both ranges of isotope composition.The isotopically light end of the B isotope range may indicate the presence of continental evaporites within individual investigated areas.On the other hand,variations in the range of~8δ-units is consistent with the reported shift in B isotopic composition of metasedimentary rocks of the Bohemian Massif due to the prograde metamorphism from very-low grade to eclogite facies.In contrast to the metacarbonate-hosted settings,tourmaline of paragenetic type V from the exocontact of granitic pegmatites displays a significantly heavier range ofδ^11B(as low as-7.7‰to-0.6‰),which is attributed to partitioning of 10 B to cogenetic axinite and/or different B-signature of the source pegmatite containing tourmaline with heavyδ^11B signature.

Geochemical and Boron Isotopic Evidence that Tourmaline Records Country Rock Assimilation of Leucogranites in the Himalayan Orogen

Tourmaline geochemical and boron(B)isotopic compositions in two-mica granites(TMG),tourmaline-bearing leucogranites(Tou-LG),tourmalites and metapelites from the Gyirong-Malashan areas of the Himalayan orogen provide evidence for country rock assimilation during the intrusion of Himalayan leucogranite.The schorls in Gyirong leucogranitic plutons show low contents of MgO(0.238%-1.160%)and δ^(11)B values(-12.1‰--11.2‰),while dravites gathered in the contact zone between the leucogranitic veins and metapelites show high contents of MgO(4.815%-6.755%)and δ^(11)B values(-10.7‰--9.3‰).This geochemical and isotopic variation of tourmalines can also be identified in the Malashan gneiss dome.As a result,three types of tourmaline were identified in the Himalayan orogen:(1)Tou-Ⅰ in the TMG and Tou-LG,which is the most common tourmaline type of schorl;(2)Tou-Ⅱ(dravite and high-Mg schorl)in the Tou-LG and tourmalite at the margins of the leucogranite;and(3)Tou-Ⅲ(mainly dravite,with minor high-Mg schorl)in metapelites of the High Himalayan Crystalline Sequence.The lenses and veins of Tou-LG may have experienced metasomatism and assimilation as a result of interaction with the High Himalayan Crystalline Sequence metasedimentary country rocks,which can be traced by the geochemical and isotopic characteristics of the tourmaline therein.

Metallogenic Chronology of Boron Deposits in the Eastern Liaoning Paleoproterozoic Rift Zone

Lead isotopic analytic data of 30 ores gathered from the Zhuanmiao boron deposit, Wengquangou boron (iron) deposit and its Dongtaizi Ore Member constitute three isochrons, the corresponding ages of which are 1902 ± 12 Ma, 1852 ± 9 Ma and 1917 ± 48 Ma. Lead isotopic analyses of marble from the Xiquegou Member of the Qingchenzi orefield yield a Pb-Pb isochron age of 1844 ± 27 Ma. 40Ar-39Ar quick neutron activation dating of phlogopites and microclines coexisting with ore minerals in the Wengquangou boron (iron) and Zhuanmiao boron deposits shows that: (1) the phlogopite from the Wengquangou has a plateau age of 1923 ± 1.5 Ma and an isochron age of 1924 ± 2.5 Ma; (2) the microcline from the Wengquangou has the plateau age of 1407 ± 5.4 Ma and 220 ± 12 Ma and an isochron age of 1403 ± 19 Ma; (3) the phlogopites from the Zhuanmiao yield a plateau age 1918 ± 1.3 Ma and an isochron age of 1918 ± 2.9 Ma; (4) the microclines from the Zhuanmiao yield the plateau age of 1420 ± 16 Ma and 250 ± 8 Ma and an isochron age of 1425 ± 19 Ma and 269 ± 16 Ma. These ages indicate that the eastern Liaoning area happened around 1900 Ma, an important tectonomagmatic event, which is consistent with the worldwide Mid-Proterozoic tectonomagmatic event. During this period, the Proterozoic Liaohe Group was folded and underwent strong normal metamorphism, and the (hydrothermal) sedimentary boron deposits (or source beds) formed earlier were strongly superimposed by mineralization, resulting in enrichment of boron; later regional geological processes made little contribution to the formation of the boron deposits. Lead isotopic components show that the U-Pb and Th-Pb isotopic system reached homogenization in the ores whereas only the U-Pb isotopic system reached homogenization in the marble from the Xiquegou district, which indicates that the boron deposits superimposed in the studied area endured a relatively strong process of hydrothermal migmatization during the end phase of early Proterozoic metamorphism.

Boron Isotopic Composition of Halite from 46-m-long Sediment Core in the Qarhan Salt Lake,Western China

Previous studies have investigated the boron isotopic composition of salt lake brines in the Qaidam Basin,western China.However,the research on boron isotopic composition of halite is very limited due to halite’s low

A Multi–fluid Constrain for the Forming of Potash Deposits in the Savannakhet Basin: Geochemical Evidence from Halite

The Khorat Plateau on the Indochina Terrane is known to have formed during the closure of the Tethys Ocean, although the origin of its potash mineral deposits is a topic of current debate. Data from a borehole on Savannakhet Basin is used in this study to re-define the evaporation processes of the study area. Geochemical analyses of halite from various borehole-derived evaporite strata have elucidated the fluid sources from which these ores formed. Measured δ11B indicated that ore deposits formed primarily due to evaporation of seawater, although non-marine fluids affected the later stages of the evaporation process. Fluctuations in B and Br concentrations in carnallite- and sylvite-rich strata indicate the influence of fresh water. Boron concentration in carnallite unit indicated the influence of hydrothermai fluids. From the relative timings of these various fluid influxes, the evolution of these evaporates can be divided into four stages： （1） an initial marine evaporation at the beginning of the deposit＇s formation, where seawater （and minor fresh water） trapped on the uplifted Khorat Plateau produced sediments and salts with Br contents lower than those of normal marine-derived evaporites; （2） a transgression stage, where seawater recharged the basin; （3） a hydrothermal infiltration stage, which was coeval with the late Yanshan movement; and （4） a stage of fresh water supply, as recorded by fluctuations in B and Br contents, inferring intermittent fresh water influx into the basin. Thus, although evaporites on the Savannakhet Basin primarily formed via marine evaporation, they were also influenced to a significant degree by the addition of non-marine fresh water and hydrothermal fluids.

Proto-Adamastor ocean crust(920 Ma)described in Brasiliano Orogen from coetaneous zircon and tourmaline

Proto-Adamastor ocean bathed Rodinia and successor continental fragments from 1.0-0.9 Ga up to0.75 Ga,and evolved into world Adamastor Ocean at 0.75-0.60 Ga.Mesoproterozoic oceanic crust is poorly preserved on continents,only indirect evidence registered in Brasiliano Orogen.We report first evidence of ophiolite originated in proto-Adamastor.We use multi-technique U-Pb-Hf zircon andδ^11B tourmaline isotopic and elemental compositions.The host tourmalinite is enclosed in metaserpentinite,both belonging to the Bossoroca ophiolite.Zircon is 920 Ma-old,εHf(920 Ma)=+12,HfTDM=1.0 Ga and has’oceanic’composition(e.g.,U/Yb<0.1).Tourmaline is dravite withδ^11B=+1.8‰(Tur 1),0‰(Tur 2),-8.5‰(Tur 3).These characteristics are a novel contribution to Rodinia and associated world ocean,because a fragment of proto-Adamastor oceanic crust and mantle evolved at the beginning of the Brasiliano Orogen.

Petrogenesis of granitic pegmatite veins:Perspectives from major element and B isotope in tourmalines,Chakabeishan,Northern Tibetan Plateau

The petrogenesis of regionally zoned granitic pegmatite veins remains debated.Because of the economic significance,we carried out a study on the Chakabeishan(CKBS)pegmatite-type Li-Be deposit,eastern North Qaidam Tectonic Belt,Northern Tibetan Plateau,by means of in-situ major element and B isotope compositions of tourmalines in the beryl-bearing and spodumene-bearing pegmatite veins.Tourmalines(Tur-Be)from the beryl-bearing pegmatite are homogeneous schorl with low Mg/(Mg+Fe),high Na/(Na+Ca)and Y Al,suggesting that they are of magmatic origin.Two generations of tourmalines(TurLi)from the spodumene-bearing pegmatite are identified:(i)the crystal cores(mostly elbaite and Lirich schorl with subordinate schorl)are consistent with being of magmatic origin crystallized at the magmatic stage;(ii)the crystal rims(schorl)are best understood as the overgrowth at the later hydrothermal stage.Tur-Be and Tur-Li show an obvious difference in core-to-rim B isotopic variation trend with d11B decrease in Tur-Be and increase in Tur-Li.The core-to-rim d11B decrease in Tur-Be results from degassing during its host pegmatitic melt evolution,whereas the core-to-rim d11B increase in Tur-Li is related to fluid exsolution.The estimated d11B values for the initial melts of the beryl-bearing and spodumenebearing pegmatites are10.46‰and10.78‰,respectively,indicating that they most likely originate from protracted fractional crystallization/differentiation of granitic intrusions rather than partial melting of metapelite.Both Mg/(Mg+Fe)ratios and Li abundances in the cores of Tur-Be are lower than those of Tur-Li,suggesting that Tur-Li crystallizes from chemically more evolved melts.

A preliminary experimental study of the boron concentration in vapor and the isotopic fractionation of boron between seawater and vapor during evaporation of seawater

A laboratory experiment was undertaken to investigate the behaviour of boron at the seawater-air interface under air flow conditions. Dried air at 25 and 35℃ was passed over or bubbled through seawater at the same temperature. A combination of ice-chilled condensers and KOH impregnated cellulose fibre filters was used to collect boron from the reacted air. When air stripped of boron was passed over the seawater, boron was found in the reacted air, and its concentration was higher in the higher temperature test. In the tests where air was bubbled through seawater the concentration of boron in the reacted air was directly proportional to the air flow rate. In this situation the boron in the reacted air was mainly introduced as a spray of microdroplets. Isotopic analysis of the collected boron in the non-bubbled tests yields fractionation factors which demonstrate that the lighter isotope, 10B, is enriched in the reacted air. The size of the fractionation changes with temperature, ruling out a purely kinetic

Two-neutron halo state of ^(15)B around 3.48 MeV by a three-body model

We investigate low-lying bound states of the neutron-rich nucleus ^15B by assuming it is a three-body system made of an inert core 13 B and two valence neutrons. The three-body wave functions are obtained using the Faddeev formalism. Special attention is paid to the excited state at 3.48（6） MeV observed in the 13 C（14 C,12 N）15 B reaction, whose properties are less clear theoretically. In our three-body model, besides the ground state 3/21, a second 3/22^-state is discovered at around 3.61 MeV, which might be identified with the excited state observed at3.48（6） MeV. We study this 3/22^-state in detail. It turns out to be a two-neutron halo state with a large matter radius rm≈4.770 fm. ＆nbsp

The neutron halo structure of ^(17)B studied with the relativistic Hartree-Bogoliubov theory

The properties of neutron-rich boron isotopes are studied in the relativistic continuum Hartree-Bogoliubov theory in coordinate space with NL-SH,PK1 and TM2 effective interactions.Pairing corrections are taken into account by a density dependent force of zero range.The binding energies calculated for these nuclei agree with the experimental data quite well.The neutron-rich nucleus 17 B has been predicted to have a two-neutron halo structure in its ground state.The halo structure of 17 B is reproduced in a self-consistent way,and this halo is shown to be formed by the valence neutron level 2s 1/2.