origin of the boron in the gas hure salt lake of the northwestern … · 2019. 10. 10. · 1 / 19...

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Origin of the Boron in the Gas Hure Salt Lake of the Northwestern

Qaidam Basin, China: Evidence from Hydrochemistry and Boron

Isotopes

HAN Jibin1, 2, *

, XU Jianxin1,2

, Syed Asim Hussain1,2

, JIANG Hongchen1, 2, 3

, MA Yunqi1, 2

, XU Kai1, 2

,

and MA Haizhou1, 2

1Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources, Qinghai Institute of

Salt Lakes, Chinese Academy of Sciences, Xining, 810008, China.

2 Qinghai Provincial Key Laboratory of Geology and Environment of Salt Lakes, Xining, 810008, China.

3 State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan,

430074, China.

Abstract: Gas Hure salt lake (GHSL) in the northwestern Qaidam Basin is rich in boron (B) resources, but its B

resource origin is rarely known. This study presents hydrochemical compositions and B isotope characteristics of

different waters collected around the GHSL, including the river water, stream water, spring water, salt lake brine,

intercrystalline brine, well water, drilling brine, and solar pond brine. The hydrochemical signatures suggested that

silicates, carbonates and evaporates are the mainly B-bearing rocks during the water dynamic. The reservoir

estimation of B resources shows that the Kulamulekesay River (KLMR) and Atekan River (ATKR) annually

contribute 18.3 tons and 22.84 tons of B, respectively, with a total amount of 11.72×104 tons of B during the past

5.7 ka. In comparison with the known B reservoir (32.96×104 tons) in the GHSL, a significant amount of B in the

GHSL should be recharged from deep fluids and sediments around the GHSL. The B concentration and B

enrichment degree are shaped by the evaporation process, and they are highly elevated at the carnallite and

bischofite stages.

Keywords: Boron; Sources; B-bearing rock; Weathering; Evaporation process

E-mail: [email protected]

1 Introduction

Boron (B) is an indispensable element in modern life, such as chemical industry, medicine, aviation industry, and construction business. More than 30% B is storedin salt lakebrine and sediments in the Qaidam Basin, China (Sun et al., 2014).Thus, it is of great significance to identify B sources and to explore B resources in salt lakes in the Qaidam Basin.

Up to date, only a few works have been aimed to identify the origins B in some salt lakes of the

* Corresponding author at: Han Jibin, No.18, Xinning Road, 810008Xining, China. Tel.: +8618997051664.

E-mail addresses: [email protected] (J. Han)

This article is protected by copyright. All rights reserved.

This article has been accepted for publication and undergone full peer review but has not been

through the copyediting, typesetting, pagination and proofreading process, which may lead to

differences between this version and the Version of Record. Please cite this article as doi:

10.1111/1755-6724.14377.

mailto:[email protected]


https://doi.org/10.1111/1755-6724.14377

https://doi.org/10.1111/1755-6724.14377

https://doi.org/10.1111/1755-6724.14377

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Qaidam Basin, such as the Qarhan salt lake (Duan and Yuan, 1988; Li and He, 1993; Wei et al., 2014; Chen et al., 2015), Dongtai salt lake (Tan et al., 2012; Yu et al., 2013), and Da Qaidam salt lake (Gao et al., 2015), one of the most important B deposit areas in the Qaidam Basin. Gas Hure salt lake (GHSL) is located in northwestern Qaidam Basin and possesses high-level B concentration. The B content in the drilling brine of GHSL is as high as 100 mg/L, which reaches the industrial mining grade. Previous studies have ever investigated the contents of B, potassium (K), and uranium (U) (Zhang, 1987; Li et al., 2013) and the source of K (Han et al., 2017) and U (Han et al., 2018) in the GHSL brine. They showed that K and U in the GHSL were mainly originated from K/U-bearing rock weathering and deep fluids. The GHSL brine consisted of three end-member water (EMW) systems: i.e. EMW1 consisting of waters from Kulamulekesay River (KLMR), Atekan River (ATKR), and Aler River (ALER), springs, streams and wells, EMW2 consisting of deep fluids, and EMW3 consisting of GHSL brine and drilling brine (Fig.1). Extensive hydraulic connections existed among waters from these three EMWs (Han et al., 2018). However, limited is known about the source as well as the recharging rate of B from the above mentioned different end-member waters. Such information is essential to exploit B resource in GHSL brine. Therefore, the purpose of this study is to quantitatively identify the origin and recharging rate of B in GHSL brine by studying the

11B values and chemical compositions of the water samples

in the groundwater flow system of GHSL.

Fig.1 Sketch showing hydraulic connections among different waters (Han et al., 2018)

2 Regional hydrogeology

The study area spans northwestern Qinghai Province and southeastern Xinjiang Province (37

o35’00” and 38

o19’00” N, 87

o58’00” and 91

o07’00” E) (Fig.2a). This area is surrounded by the

Altun Mountains (ALTM) to the north with an average elevation of 4790 meters above sea level (m.a.s.l.), the Yousha Mountains (YSM) to the northeast with an average elevation of 3500 m a.s.l., the QimanTage Mountains (QMTGM) of the Kunlun Mountains (KLM) to the south with an average elevation of 4500 m a.s.l. Around the study areathere are two major sinistral fault systems: the Altun deep fault to the north and the Kunlun deep fault to the south (Cheng et al., 2015; Zhang et al., 2016). To the east of GHSL, NW- or NNW-direction faults (i.e. Ganchaigou, Xiaohongshan, Qigequan, Hongliuquan, Youshashan) and NWW- and NEE-direction Aler overfaults are widely developed (Rong et al., 2003; Cheng et al., 2015; Zhang et al., 2016) (Fig.2c). The GHSL lies at the east end of the basin with an average elevation of 2860 m a.s.l., which is the discharge area of different waters (Fig.2b).

The KLMR and ATKR are the largest rivers consisting of snow and ice melt water in the study


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area. These two rivers disappear in the front of alluvial fan and recharge groundwater with runoff 1.22×10

8 m

3/a and 9.93×10

7 m

3/a, respectively (Rong et al., 2003). Due to the change of lithology

along the alluvial fan, groundwater is exposed to the surface in the form of springs, streams and spring-set rivers. As one spring-set river, the Aler River (Fig.2b) has water all the year round (average water flow of 3.754 m/s) and supplies the GHSL directly in the form of surface runoff (Rong et al., 2003). In contrast, the other streams are seasonal rivers (mainly recharged during the period from June to August), which can supply salt lakes directly during high water periods but dry up in flat and dry periods. The sampling cruise of this study is performed in flat water period. Therefore, the stream flow is so small that it has dried up not far away and is unable to directly supply the GHSL. The atmospheric precipitation decreases from the mountain area to the salt lake plain, with annual mean precipitation of 300.0 mm/a, 137.1 mm/a and 55.3 mm/a in the mountain area, overflowing area, and plain area, respectively. By contrast, along these corresponding areas, the annual mean evaporation increases with 25.34 mm/a, 1208.5 mm/a and 2856.9 mm/a, respectively (Rong et al., 2003).

In the mountain area the dominant types of rocks are generally granodiorite, plagioclase granite and quartz diorite(Rong et al., 2003; Ye et al., 2014b); at the alluvial fan (overflowing area) the main rocks consist of pluvial sands, gravels and sandy clay; while at the salt lake plain, the lithology is mainly composed of clay, salts, and gypsum-dominated evaporites (Zhang, 1987; Rong et al., 2003; Ye et al., 2012).


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Fig. 2 Maps showing the studying area: Panel a. locations of sampling sites; Panel b. salt lake and salt lake field; c.

tectonic map of the studying area (Rong et al., 2003; Zhang et al., 2015).

3 Sampling and analysis

3.1 Field sampling

39 water samples were collected in this groundwater flow system on May 2015 (Fig.2a,b). Among them, four samples were collected from KLMR, two from ATKR, one from ALER, four from spring water, two from stream water, two from shallow well (2-5 m), three from GHSL, and three from shallow aquifer (intercrystalline brine, 3-5 m), five solar pond brine samples (GYT15-1 sampled from initial brine, GYT15-2 sampled from sodium salt pool,GYT15-3 sampled from regulation pool, GYT15-4 sampled from carnallite pool, GYT15-5 sampled from the bittern pool), 13 borehole waters including 2 from S1(S1-17.74 m, S1-28.45 m), 3 from S2 (S2-15.13 m, S2-29.10 m, S2-45.20 m), 3 from S3 (S3-9.55 m, S3-17.64 m, S3-24.89 m), and 5 from S4 (S4-3.67 m, S4-19.7 m, S4-31.7 m, S4-55.5 m, S4-61.0 m), respectively. The pH values of the waters were determined on site using YSI probe (Professional Plus 6050000, USA). After measurements, all collected water samples were filtered through 0.45 m membranes on site. Each sample was stored in two new 500 mL polyethylene bottles that had been rinsed three times with deionized water: one for the measurement of major elements and boron concentration, and the other for the measurement of B isotopes.


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3.2 Chemical analyses

All the collected water samples were measured at the Qinghai Institute of Salt Lakes, Chinese Academy of Sciences. The contents of Ca

2+, Mg

2+, Na

+, K

+ and B

3+ were determined by inductively

coupled plasma optical emission spectrometry (ICP-OES) (IRIS Intrepid II XSP, Thermo Elemental, Madison, WI, USA) (error<±1%), and concentrations of SO4

2- and Cl

- were tested by ion

chromatography (IC) (Dionex 120, Dionex, Sunnyvale, CA, USA) (error<±5%). The contents of HCO3

- and CO3

2- were analyzed by the methods of hydrochloric acid titration with phenolphthalein and

mixed solution of methylene blue and methyl red as indicators(error<±1%).

3.3. Isotope analyses

Boron separation and isotopic ratio measurement were conducted at the Qinghai Institute of Salt Lakes, Chinese Academy of Sciences. For determination of

11B/

10B ratios, the water samples containing

about 10 g B (pH at 8~9) were passed through a 0.8 mL Amberlite resin column (120 to 200 mesh) using 2 M NH4OH to remove the cations, followed by elution with 12 mL of 0.1 M HCl. The resulting eluents were dried by evaporation at 75

oC. An equal amount of mannitol was employed to suppress

volatilization of B during evaporation. Boron isotope ratios were determined by using positive the thermal ionization mass spectrometry and expressed conventionally in relation to the NIST SRM 951 boric acid reference material (4.0500±0.0002, with an analytical uncertainty of 0.3‰). The B isotope composition was expressed as the

11B value according to the following formula:

11B(‰)={[(

11B/

10B)

sample-(11

B/10

B)standard]/(11

B/10

B)standard}×1000 (Xiao et al., 2013; 2001; Wei et al., 2014; Fan et al., 2015).

4 Results

4.1 Hydrochemistry

The pH values of the sampled waters differ among different EMWs: waters from the EMW1, EMW2 and EMW3 showed pH of >8.0, 7.01–7.4 and 7.79–6.48, respectively (Table 1 and 2). The average of TDS in the waters from the EMW1, EMW2 and EMW3 ranges 1.50 g/L, 253.88 g/L and 339.61 g/L, respectively.

The chemical composition analysis (Table 1 and 2) shows that the hydrochemical type of the waters collected from EMW1 is Ca–Na·HCO3–Cl, with HCO3

-, Cl

- and Ca

2+/Na

+ being dominant anions

and cations; the hydrochemical type of the waters from the EMW2 is Na·Cl, with Cl- and Na

+ being

major anion and cation; and the hydrochemical type of the waters collected from the EMW3 is Na–Mg·Cl type, with Cl

- and Na

+/Mg

2+ being major ions (Fig. 3). For the solar pond samples, the

contents of cations and anions are changed as evaporation proceeds, with its hydrochemical type changing from Na·Cl to Mg·Cl (Fig. 3).


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Fig. 3 The piper plot showing different chemistry of the water samples analyzed in this study.


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4.2 Boron and boron isotope

The B concentration varies from 0.02 to 198.61 mg/L, with an average of 0.60 mg/L (n=15), 19.84 mg/L (n=3), and 99.82 mg/L (n=16) for the waters from the EMW1, EMW2, and EMW3, respectively. The

11B values vary among the waters from the EMW1, EMW2, and EMW3, ranging +6.23‰ to +17.14‰ (n=15), +34.49‰ to +36.25‰

(n=3), and +19.22‰ to +27.48‰ (n=15), respectively (Table 1, 2).The intercrystalline brine has the highest B isotopic values, but the lowest B concentration; while the drilling brine has lower B isotopic values, but the highest B concentration (Table 1, 2).

Table 1: Geochemistry and isotope data cited from Han et al. (2018a, b). Note: KLMR means Kulamulekesay River water; ATKR means Aateatekan River water; ALER means Alaer River water; GQ means spring

water; GX means stream water; GJ means shallow well water; GJJ means intercrystalline brine; GHSL means Gas Hure salt lake brine; S4 means number 4 borehole brine; and GYT indicates salt lake field brine

Sample ID Latitude Longitude pH TDS g/L CO32-

mg/L HCO3- g/L SO4

2- g/L Cl

- g/L Ca

2+ g/L Mg

2+ g/L Na

+ g/L K

+ g/L B

3+ mg/L

11B ‰

KLMR15-1 37°48′49.7″ 88°01′15.0″ 8.93 0.62 0.00 0.11 0.15 0.18 0.07 0.03 0.09 0.00 0.04 6.25

KLMR15-2 37°50′28.7″ 88°16′54.3″ 8.28 0.35 0.00 0.11 0.07 0.08 0.04 0.02 0.04 0.00 0.02 6.23

KLMR15-3 38°00′37.8″ 88°52′42.6″ 8.23 0.33 0.00 0.12 0.05 0.06 0.04 0.02 0.02 0.00 0.12 7.38

KLMR15-4 38°04′29.4″ 89°46′42.5″ 8.01 1.05 0.00 0.37 0.22 0.17 0.09 0.05 0.14 0.01 0.43 8.03

ATKR15-1 37°41′11.3″ 90°13′06.2″ 8.25 0.45 0.00 0.11 0.08 0.13 0.05 0.02 0.06 0.00 0.08 8.01

ATKR15-2 37°58′18.0″ 89°54′48.6″ 8.23 0.64 0.00 0.15 0.11 0.18 0.06 0.03 0.10 0.01 0.28 7.89

ALER15-1 38°12′08.6″ 90°33′38.8″ 8.32 0.87 0.00 0.27 0.16 0.18 0.07 0.03 0.15 0.01 0.34 17.14

GQ15-1 38°05′09.0″ 90°23′57.5″ 8.01 3.20 0.00 0.32 1.08 0.78 0.29 0.10 0.59 0.05 1.54 9.45

GQ15-2 38°11′05.5″ 90°22′38.2″ 8.09 0.62 0.00 0.24 0.09 0.11 0.06 0.03 0.09 0.01 0.31 9.18

GQ15-3 38°12′54.0″ 90°19′40.1″ 7.99 6.49 0.00 0.28 2.90 1.30 0.29 0.35 1.30 0.07 2.27 9.56

GQ15-4 38°18′30.1″ 90°14′38.2″ 8.41 0.90 0.00 0.30 0.20 0.15 0.04 0.04 0.16 0.01 0.39 9.15

GX15-1 38°7′45.2″ 90°33′41.2″ 8.23 4.68 0.00 0.33 1.30 1.52 0.26 0.21 1.00 0.05 1.42 16.23

GX15-2 38°10′15.3″ 90°34′02.3″ 8.36 1.34 0.00 0.35 0.22 0.36 0.09 0.06 0.25 0.01 0.55 15.85

GJ15-1 38°16′44.0″ 90°16′59.2″ 8.30 0.70 0.00 0.23 0.14 0.13 0.04 0.03 0.12 0.01 0.33 9.08


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GJ15-2 38°01′16.9″ 90°48′51.5″ 8.20 0.30 0.00 0.11 0.06 0.05 0.02 0.02 0.05 0.00 0.91 9.05

GJJ15-1 38°07′00.1″ 90°54′39.1″ 7.40 330.94 0.00 0.66 32.35 178.13 5.05 13.86 97.50 3.39 33.95 34.89

GJJ15-2 38°02′44.1″ 90°56′31.3″ 7.01 304.31 0.00 0.14 1.11 196.48 4.73 24.39 75.42 2.02 20.94 34.49

GJJ15-3 38°02′28.4″ 90°59′03.5″ 7.73 126.38 0.00 0.14 11.22 71.33 6.82 8.12 28.27 0.48 4.64 36.25

GHSL15-1 38°09′38.0″ 90°48′38.0″ 7.72 238.81 0.00 0.50 56.47 98.24 3.79 8.62 69.45 1.74 24.22 21.30

GHSL15-2 38°08′58.9″ 90°50′18.5″ 7.68 235.81 0.00 0.49 56.80 96.87 0.95 10.41 68.57 1.72 23.54 22.50

GHSL15-3 38°06′42.8″ 90°47′23.6″ 7.79 226.90 0.00 0.51 52.03 95.24 1.14 9.69 66.40 1.69 22.07 22.10

S4-3.67 38°04′3.32″ 90°56′28.64″ 6.95 381.02 0.00 0.88 59.35 182.30 0.10 50.06 48.37 6.39 119.63 22.30

S4-19.7 38°04′3.32″ 90°56′28.64″ 6.48 395.57 0.00 0.92 20.79 250.96 0.05 85.39 7.42 6.81 101.18 20.35

S4-31.7 38°04′3.32″ 90°56′28.64″ 6.90 374.65 0.00 0.88 41.08 199.14 0.09 57.76 35.64 6.99 126.83 20.89

S4-55.5 38°04′3.32″ 90°56′28.64″ 6.96 375.21 0.00 0.89 68.41 185.20 0.09 56.57 42.15 6.59 116.89 23.10

S4-61.0 38°04′3.32″ 90°56′28.64″ 7.09 371.43 0.00 0.87 70.47 179.93 0.10 53.94 44.97 6.12 112.42 21.83

Table 2 Chemical compositions and isotope values of the water samples in study area S1, S2, S3 and GYT. Note: the samples from S1, S2, and S3 are intercrystalline brine, while the GYT samples are salt

lake field brine; “-“ means not measured.(data cited from Han (2018a, b))

Sample ID Latitude Longitude pH TDS g/L CO32-

mg/L HCO3- g/L SO4

2- g/L Cl

- g/L Ca

2+ g/L Mg

2+ g/L Na

+ g/L K

+ g/L B

3+ mg/L

11B ‰

S1-17.74 38°07′19.4″ 90°53′25.2″ 6.92 386.87 0.00 1.32 22.60 259.38 0.08 88.68 7.11 7.72 198.61 --

S1-28.45 38°07′19.4″ 90°53′25.2″ 6.83 353.35 0.00 1.01 30.54 223.60 0.11 72.43 18.82 6.83 187.37 19.22

S2-15.13 38°05′37.3″ 90°53′25.2″ 6.85 370.15 0.00 0.99 30.17 234.12 0.03 73.24 22.93 8.66 114.97 21.86

S2-29.10 38°05′37.3″ 90°53′25.2″ 6.79 310.32 0.00 0.20 18.48 191.77 0.14 39.21 56.69 3.84 38.05 27.48


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S2-45.20 38°05′37.3″ 90°53′25.2″ 6.93 338.38 0.00 0.78 37.17 202.03 0.04 60.13 31.08 7.16 131.56 20.72

S3-9.55 38°05′41.5″ 90°58′06.9″ 6.70 388.00 0.00 0.85 35.03 237.28 0.14 65.72 42.87 6.11 91.52 23.42

S3-17.64 38°05′41.5″ 90°58′06.9″ 6.92 353.18 0.00 1.26 24.37 231.76 0.08 76.97 13.79 4.96 134.33 23.06

S3-24.89 38°05′41.5″ 90°58′06.9″ 6.86 334.08 0.00 0.44 27.74 208.08 0.20 59.20 32.87 5.54 53.90 27.10

GYT15-1 38°04′28.9″ 90°57′27.5″ 6.89 311.14 0.00 0.63 27.82 181.67 0.50 36.80 58.38 5.33 103.41 --

GYT15-2 38°04′21.9″ 91°01′34.6″ 6.65 581.01 0.00 0.87 52.27 325.80 0.44 42.27 152.58 6.76 135.72 --

GYT15-3 38°03′59.8″ 90°59′13.6″ 6.13 379.64 0.00 1.43 48.24 218.59 0.50 66.66 32.79 11.41 136.22 --

GYT15-4 38°03′39.3″ 90°58′17.1″ 6.09 387.68 0.00 1.45 53.10 220.05 0.63 68.58 31.81 12.07 170.42 21.42

GYT15-5 38°03′56.9″ 91°02′48.3″ 4.90 507.22 0.00 1.82 41.74 325.80 0.53 107.21 29.42 0.71 184.52 --


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5 Discussion

5.1 Boron bearing rock

Gibbs plot (Gibbs, 1970) can indicate three important natural mechanisms controlling major ion chemistry of the groundwater including water-rock interaction, evaporation and atmospheric precipitation. The TDS concentrations were plotted against the weight ratios of Na

+/(Na

++Ca

2+) for

cations and weight ratios of Cl-/(Cl

-+HCO3

-) for anions. In this case, the waters from the EMW1

observed with low TDS values, which is controlled rock leaching; while the waters from the EMW2 and EMW3 are mainly influenced by evaporation (Fig.4).

Fig. 4 Gibbs plot of different waters (modified from Gibbs, 1970)

The plots of HCO3- vs. Ca

2++Mg

2+ (Fig.5), Na

+/Ca

2+ vs. Mg

2+/Ca

2+ (Fig.6), HCO3

-/Na

+ vs.

Ca2+

/Na+ (Fig.7) used for confirming the types of weathering rocks popularity (Gaillardet et al., 1999;

Han et al., 2004; Ryu et al., 2008).The Fig.5 indicates carbonate weathering also contributes, while the water samples from the EMW2 and EMW3 are deviated from the 1:1 line, suggesting that other weathering rocks participate in this leaching process. It is noticeable that the Mg

2+/Ca

2+ ratios of the

water from the EMW1 are below the Mg2+

/Ca2+

=0.8 line in Fig.6, indicating that calcite and dolomite contributed in the EMW1. The EMW1 samples were clustered near the silicate end-member, whereas those from the salt lake plain samples (EMW2, 3) were closed the evaporites, indicating that silicates and evporites were the major weathering rocks (Fig.7).The saturation index (SI) indicated by PHREEQC calculation suggested that carbonates (e.g., calcite, dolomite, magnesite) and evporites (e.g., gypsum, mirabilite, halite) were dissolved in the high mountain area, and saturated in the salt lake plain gradually (Table 3). Previous study reveals the B concentration (B2O3) of clays in the salt lake plain measured 161×10

-6 to 309×10

-6 mg/L (Shen et al., 1985), which was not only higher than 64.4×10

-6

mg/L (standard clay) (Turekian et al., 1961), but also higher than the clay, which is rich in B2O3 (126×10

-6) in eastern China (Yan et al., 2005). The concentration of B2O3 in the silicates distributed

around the basin varied from 236×10-6

to 338×10-6

mg/L (Fu et al., 2002), which is higher than standard material (GBW07103=77.3126×10

-6 mg/L). The concentration of B2O3 in the carbonate and evaporites

ranged 0.024%-0.306% and 0.013%-0.030%, respectively (Liu, 1999; Wei et al., 2014).Therefore, it is highly possible that the B is leached from carbonate, silicates and evaporites around the GHSL.

It is notable that the B isotope values of the EMW1 waters are similar to that (-20‰ to +10‰) of


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granite (Jiang, 1998; Wei et al., 2014) and are within the range of the 11

B values of carbonates and evaporites (ranging -17.35‰–0.52‰ and-6.5‰–2‰, respectively) (Wei et al., 2014). While the

11B

values differ between the waters from EMW2 and EMW3 (+19.22‰ to +27.48‰, +22.1‰ to +36.25‰, respectively), which are also different from that of sediments (+12.1‰) (Liu et al., 1999). In fact, the

11B values of sediments are often affected by pH (Fig.8) and Ca

2+concentration (Fig.9). The

B(OH)30 and B(OH)4

- types are the mainly forms of B in the solution, and the forms are controlled by

the pH values. When the pH<7, the dominant type is B(OH)30; while the pH>10, the dominant type is

B(OH)4-. The

11B is accumulated and stayed in the solution, while

10B is accumulated and entered into

the sediments (Liu et al., 1999; Xiao et al., 2001; Du et al., 2019). Meanwhile, the clay adsorption is highly effected in the B isotopic fractionation, the

10B is preferential adsorption by the clay, and

promoted the 11

B in the solution (Xiao et al., 2001). For the two reasons, the 11

B values should be increased in the EMW2 and EMW3. Liu (1999) indicated that when the Ca

2+ concentration is higher in

the recharging water, the 11

B values is increased, because of the 10

B is preferential entered in the lattice of CaCO3 by the forms of B(OH)4

- or the

10B is coprecipitated with CaCO3 (Vengosh et al.,1991;

1992).

Fig.5 Correlation between HCO3- and Ca2++Mg2+ contents in different waters (modified from Ryu et al., 2008)


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Fig.6 Plot showing the correlation between the Mg2+/Ca2+and Na+/Ca2+ ratio among different waters (modified

from Han et al., 2004).

Fig.1 Plot showing the correlation between HCO3-/Na+ and Ca2+/Na+ for the different waters, indicating that

elements were weathered from silicate and evaporates (modified from Ryu et al., 2008).


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Fig.8 Plot showing the correlation between the 11B values and pH values among the different waters.

Fig.9 Plot showing the correlation between the 11B values and Ca2+ concentration among the different waters.

Table 3 The saturation indices (SI) of the waters from mountain area, alluvial fan and salt lake plain

Minerals mountain area SI alluvial fan SI salt lake plain SI

calcite 0.29 0.94 1.30

dolomite 0.00 1.90 3.84

magnesite -0.33 0.94 2.51

gypsum -1.77 -1.02 0.64


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mirabilite -7.28 -4.31 -0.71

halite -6.72 -4.45 -0.46

Previous studies suggested that Ca-Cl brines are characteristic of larger element ratio of Ca2+

(meq/L) than that of SO4

2-+HCO3

-+CO3

2-, suggesting its origin from deep subsurface (Lowenstein et al.,

1989, 1994; Zhang et al., 1993; Lowenstein and Risacher, 2009). Thus in this study, the geochemical property of the GJJ15-2 and GJJ15-3 (larger element ratio of Ca

2+ than that of SO4

2-+HCO3

-+CO3

2-)

suggests they may be recharged from deep fluids (Table 1). In addition, these water samples are distributed near one big fault (Fig.2c), which may be their upwelling recharge path. The oilfield brine around the GHSL is proved to be Ca-Cl type water, and recharges the GHSL (Han et al., 2018; Tan et al., 2012). Huang and Han (2009) proved that the volcano were distributed around the Qaidam Basin. Li (2013) used Sr isotopes (high Sr concentration, low

87Sr/

86Sr ratios) to prove the mantle origin of the

water. Therefore, with the low pH and rich Ca2+

, it is enough to boron isotope fractionation.

Previous research showed that the major minerals at the ALTG and QMTG mountains are granite from the Paleozoic group, sandstone from the Mesozoic group(Tan et al., 2012; Ye et al., 2014; Han et al., 2017), and abundant clay minerals deposited at the alluvial fan and salt lake plain, such as carbonaceous mudstone, carbonate clay, and mudstone from the Tertiary and Quaternary systems(Li et al., 2013; Zhang et al., 2016). These rocks were the potential B sources in this study.

5.2 Calculating the boron recharge

The B isotopic ratio can be used to distinguish water flow path and to evaluate recharge rate from different water sources (Vengosh et al., 1991; Gill et al., 2013; Coleman et al., 2015; Lehr et al., 2015; Long et al., 2015). According to the principle of water-salt balance, the total amount of B input to the GHSL from the KLMR and ATKR water can be calculated. The formulae (5-1, 5-2) below were used to calculate the B amount, where the AB is the annual total amount of B input into the GHSL from the rivers in tons; Q is the average annual runoff (m

3/a) for 20 years; CB is the annual concentration of B,

mg/L; and TB is the total recharge during the recharge time (a) in tons (Table 4).

Table 4 Calculated amounts of B resources recharged from the KLMR and ATKR to the GHSL

River Q (m3/y) CB (mg/L) AB (ton) TB (ton)

KLMR 1.22×108 0.15 18.3

ATKR 9.93×107 0.23 22.84

23.45×104

Proved reservoirs (Rong et al., 2003) 32.96×104

Accumulation time (a) 5.7 ka

B BA Q C (5-1)

B BT Q C t (5-2)

The calculation shows that the total annual recharge of B into the GHSL from the KLMR and ATKR waters is 18.3 tons and 22.84 tons, respectively. OSL dating of late Quaternary river terrace sequences indicate bottom ages of 5.7±1.34 ka and 6.84±0.44 ka, and 9.9±1.7 ka and 12.58±0.87 ka for the T2 terraces of the KLMR and ATKR, respectively (Wang et al., 2009). Assuming that there is no


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significant change in the recharge of the KLMR and ATKR to the Qaidam Basin salt lakes at least in the past 5.7 ka and the B inputs from the KLMR and ATKR are lost due to clay mineral adsorption and or co-precipitation in evaporates, a total amount of 11.72×10

4 tons of B inputs have been accumulated

in the GHSL during the past 5700 years, which is much less than the proved B reservoir (32.96×104

tons) in the GHSL. Therefore, a significant amount of B resource is recharged from deep fluids, or much more B is redistributed in the sedimentary deposits around the GHSL.

5.3 Boron enrichment during the evaporation process

Solar ponds accept inappreciable precipitation and have negligible hydraulic connections with other waters around the GHSL, therefore, solar ponds are suitable for studying element enrichment processes under evaporation according to the natural evaporation process of carnallite extracted from the solar ponds of the GHSL (Fig.10). The original brine (mixed by the intercrystalline brine and drilling brine) is firstly collected into the salt pond (GYT15-2) with NaCl precipitation, and then inflow to the regulating reservoir (GYT15-3) and receive further evaporation with precipitation of NaCl and MgSO4. At the third stage (GYT15-4) NaCl and KCl·MgCl2 are precipitated; and then the resulting brine leftover is discharged into the bischofite pond (GYT15-5).

Fig.10 The solar ponds for the carnallite production using the brine from the GHSL.

Table 5 indicates that the enrichment degree is higher than once, suggesting that the B concentration is increased during the carnallite extraction process. In addition, in contrast with the original brine, the enrichment degree up to 1.648 and 1.784 at the carnallite and bischofite stages, respectively. Wang (2011) reported that the enrichment degree in the solar ponds is influenced by the eolian sediments, which can adsorb B on their surface, leading to B concentration decrease in aqueous phase. Previous evaporation experiments suggested that the enrichment degree of major elements (K, Ca, Na, Mg) at the bischofite stagecan be up to 16.474 times larger than its initial brine (Wang et al., 2011). Thus, it is reasonable to observe the high concentration of B and B enrichment degree in the GHSL but low concentration of B in its inflowing river water.


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Table 5 The enrichment times of B and evaporation stages

Samples B (mgL-1

) Enrichment degree Evaporation stages

GYT15-1 103.41 Original brine

GYT15-2 135.72 1.300 NaCl

GYT15-3 136.22 1.003 Mg(H2O)7(SO4)

GYT15-4 170.42 1.251 KCl

GYT15-5 184.52 1.083 MgCl2

6. Conclusions

The B in the GHSL is mainly originated from weathering of B-bearing rocks such as silicates, carbonates and evaporates transported with the KLMR and ATKR water and from the recharge of deep fluids.

The KLMR and ATKR waters annually contributed 18.3 tons and 22.84 tons of B to the GHSL, respectively, with a total amount of 11.72×10

4 tons of B stored in the GHSL during the past 5.7 ka. A

significant amount of the B resources in the GHSL is recharged from deep fluids, or much more B is redistributed in the sedimentary deposit around the GHSL.

The evaporation process plays important roles in shaping B concentration distribution in different waters and the enrichment degree is highly elevated at the carnallite and bischofite stages during the evaporation processing.

Acknowledgments

Financial support for this research was provided by the Western Light Fund of Chinese Academy of Science Foundation (Y910061016) and Funds for the Natural Science Foundation of Qinghai Province (No. 2019-ZJ-7028). The authors are grateful to Dr. Peng Zhangkuang for the help of B isotopic measurement.

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About the first author (corresponding author)

HAN Jibin, male, born in 1985 in Xining City, Qinghai Province; Ph.D; graduated from China university of Geosciences; research assistant of Qinghai Institute of Salt Lakes, Chinese Academy of Sciences. He is now interested in study on hydrology process of salt lake area and hydrochemistry of salt lake. Email: [email protected]; phone: 18997051664



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