Abnormal Enrichment Mechanism of Potassium-Rich Brine Deposit in Lop Nor Basin of Xinjiang
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摘要:
罗布泊是世界上最大的单体硫酸盐型液体钾盐矿床，对于其矿床成因一直存在争议. 基于大量盐泉、地下潜水及地表水的化学实测数据，从水文化学的角度探讨罗布泊富钾卤水矿床成因. 结果表明，矿区富钾卤水钠氯系数为0.76~1.24，钾氯系数为38.58~60.49，主体表现为溶滤型卤水特征，指示有其他来源卤水混合参与成矿；首次在罗布泊东部断裂带发现Ca-Cl型卤水，具有典型的富Na+、K+、Ca2+、Cl-，贫HCO3-、CO32-、SO42-特征，指示罗布泊有深部热液流体补给. 在成矿过程中，Ca-Cl型卤水通过“兑卤”效应，直接改变原有成矿卤水成分及结晶路线，使其矿化度升高，而且富K、Na. 改造后的富“钠”卤水与前期生成的石膏（CaSO4·2H2O）反应，生成钙芒硝（Na2Ca（SO4）2·2H2O），并赋存于多孔的钙芒硝晶间，形成超常高矿化度富钾卤水矿床.
Abstract:Lop Nor is the largest single sulfate-type liquid potash deposit in the world, and the genesis of the deposit has been controversial. In this paper, the genesis of potassium-rich brine deposits in Lop Nor is discussed from the perspective of hydrochemistry, based on a large number of measured chemical data of salt springs, underground phreatic water and surface water. The results show that the sodium-chlorine coefficient of potassium-rich brine is 0.76-1.24, and the potassium-chloride coefficient is 38.58-60.49. The main body of the brine shows the characteristics of dissolving-filtering brine, indicating the mixing of brine from other sources. It is the first time that Ca-Cl type brine is found in the eastern fault zone of Lop Nor basin and Dawadi, which shows typical characteristics of enrichment in Na+, K+, Ca2+, Cl- and depletion in HCO3-, CO32-, and SO42-, indicating deep hydrothermal supply in Lop Nor Basin. In the ore-forming process, the Ca-Cl type brine can change the composition and crystallization route of the original ore-forming brine directly through the effect of "mixing brine", so that its mineralization degree is increased, and it is rich in K and Na. The reformed "sodium-rich" brine reacted with gypsum (CaSO4·2H2O), and formed glauberite (Na2Ca(SO4)2·2H2O), which existed among the porous glauberite crystals, forming super-high salinity potassium-rich brine.
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Key words:
- Lop Nor /
- potash deposit /
- potassium-rich brine /
- enrichment mechanism /
- brine chemistry /
- mineral deposit
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图 1 新疆罗布泊地区地质简图(引自王凯等，2020）
Fig. 1. Simplified geological map of Lop Nor area in Xinjiang (from Wang et al., 2020)
图 5 塔里木河水EQL/EVP蒸发模拟
FC为浓缩蒸发因子，左侧坐标为盐类矿物析出量（毫摩尔取对数）；垂直粉色条带示意钙芒硝开始析出至石盐析出之前
Fig. 5. Simulation of evaporation of Tarim River by EQL/EVP
图 6 罗布泊盆地水化学SO4-Ca-ALK三角相图
Fig. 6. SO4-Ca-ALK triangular phase diagram of water chemistry in Lop Nor Basin
表 1 罗布泊盆地不同入流水源化学组分
Table 1. Chemical compositions of different inflow waters in Lop Nor Basin
水源类型 TDS(g/L) Na+(g/L) K+(g/L) Ca2+(g/L) Mg2+(g/L) HCO3‒(g/L) CO32‒(g/L) Cl‒(g/L) SO42‒(g/L) Li+(mg/L) B3+(mg/L) 盐泉 最大值 488.01 133.00 13.50 4.55 127.00 0.26 0.79 354.00 68.40 144.00 215.00 最小值 18.64 1.42 0.04 0.10 0.15 0.00 0.00 8.03 0.35 0.10 1.85 平均值 190.40 41.51 1.87 0.89 19.81 0.14 0.06 104.16 22.13 15.29 25.49 变异系数（%） 85.22 102.39 138.80 121.17 203.40 40.48 229.97 103.44 83.46 225.72 149.94 潜水 最大值 412.90 133.00 12.20 3.86 54.30 0.69 0.43 188.00 101.00 64.80 175.00 最小值 3.84 1.32 0.03 0.00 0.02 0.00 0.00 1.35 1.01 0.02 0.58 平均值 277.32 84.12 5.31 0.36 11.83 0.17 0.04 138.50 36.99 10.57 41.20 变异系数（%） 46.29 49.48 101.55 166.26 117.25 85.87 173.56 48.34 71.42 125.26 98.85 河水 最大值 1.00 0.20 0.02 0.09 0.04 0.23 0.00 0.27 0.34 0.06 0.31 最小值 0.57 0.07 0.01 0.05 0.02 0.13 0.00 0.09 0.16 0.01 0.09 平均值 0.69 0.10 0.01 0.06 0.03 0.17 0.00 0.12 0.20 0.03 0.18 变异系数（%） 18.65 34.19 35.68 18.92 21.27 17.33 / 38.09 23.68 59.33 42.77 
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表 2 罗布泊富钾卤水化学组分
Table 2. Chemical compositions of potassium-rich brine in Lop Nor Basin
矿区 TDS(g/L) Ca2+(g/L) Mg2+(g/L) Na+(g/L) Cl‒(g/L) SO4‒(g/L) K+(g/L) HCO3‒(g/L) Br‒(mg/L) B3+(mg/L) Li+(mg/L) 新庆矿区 最大值 356 0.8 20.1 101.7 186.1 5.9 8.8 0.2 35.2 724.5 18.1 最小值 256 0.0 6.3 48.4 130.5 0.3 6.7 0.1 2.1 293.9 3.4 平均值 332 0.2 11.2 80.9 167.9 2.3 7.2 0.2 15.1 478.5 11.2 变异系数（%） 31 83 31 15 8 75 13 31 48 24 29 罗北凹地 最大值 385 0.4 29.3 99.2 194.7 7.4 9.8 0.3 29.3 715 25.3 最小值 278 0.0 6.3 41.6 104.9 0.2 5.5 0.1 1.9 293.9 8.4 平均值 367 0.2 13.6 81.3 176.3 2.5 8.0 0.2 12.1 504.2 16.8 变异系数（%） 26 77 36 16 8 77 12 0 61 20 23 腾龙矿区 最大值 334 0.6 23.4 93.2 191.8 9.5 9.3 0.3 48.8 755.6 17.6 最小值 247 0.0 7.8 24.4 102.8 0.2 6.1 0.0 2.5 277.3 8.9 平均值 325 0.2 14.8 71.6 164.1 3.0 7.7 0.1 15.5 507.5 14.0 变异系数（%） 24 93 31 23 11 83 12 38 65 25 15
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表 3 罗布泊Ca-Cl型泉点卤水化学组分
Table 3. Chemical compositions of Ca-Cl brine in Lop Nor Basin
样品编号 Na(g/L) K(g/L) Ca(g/L) Mg(g/L) HCO3(mg/L) Cl(g/L) SO4(g/L) Li(mg/L) Sr(mg/L) SPW 1.52 1.11 4.55 125 263 354 1.35 141 71.3
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表 4 罗布泊Ca-Cl型泉点固相化学组分
Table 4. Chemical compositions of solid phase from Ca-Cl brine in Lop Nor Basin
样品编号 Na(%) K(%) Ca(%) Mg(%) HCO3(%) Cl(%) SO4(%) Li(ug/g) Sr(ug/g) SPG1 0.37 0.09 0.24 12.40 0.16 35.3 < 0.15 33.9 19.8 SPG2 7.84 10.00 0.53 6.31 0.15 40.1 1.0 11.7 138.0
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