Analytical methods
The chemical analyses were measured at the laboratory of Beijing
Research Institute of Uranium Geology (Table 1). K, Na, Mg and Ca were
measured by 22.2 ion chromatogram using 883 Basic IC pulse ion
chromatograph based on the Standard Test Method of Drinking Water-Metal
Indicator (GB/T 5750.6-2006). Cl, F, NO3 and
SO4 were analyzed by ion chromatogram using ICS-1100 ion
chromatograph based on the Test Method of the Quality of Groundwater
(DZ/T 0064.51-1993). HCO3 and CO3 were
analyzed by titration method using AT-510 automatic titration analysis
meter based on the Test Method of the Quality of Groundwater (DZ/T
0064.49-1993). Si were determined by plasma mass spectrometry using
NexION300D plasma mass spectrometer based on the Test Method of the
Quality of Groundwater (DZ/T 0064.80-1993).
H2SiO3 was measured by spectrophotometer
at the Laboratory of the Beijing Brigade of Hydrogeology and Engineering
Geology. The concentration of SiO2 was calculated
according to the concentration of Si and
H2SiO3. δ 2H andδ 18O were detected by zinc reduction method for
hydrogen isotopes (DZ/T 0184.19-1997) and carbon dioxide–water
equilibrium method for oxygen isotopes (DZ/T 0184.21-1997).
The saturation index (SI) value is the logarithm of the ratio of the ion
activity product (IAP) to the equilibrium solubility product (K) at
sample temperature is described as:
SI=log (IAP/K) (1)
The value of the saturation index (SI) indicates whether the solution is
in a state of undersaturation (negative SI), saturation (positive SI),
or at the state of equilibrium (SI=0) with respect to a mineral (Lorah
and Herman, 1988; Shen et al., 1993). The value of the saturation index
with respect to anhydrite, aragonite, calcite, dolomite, gypsum and
halite of the water samples were calculated with PHREEQC (Parkhurst and
Appelo, 1999) and using Aq•Qa carbonate equilibria database to obtain
their partial pressure of CO2 (PCO2).
The concentrations of the hydrochemical compositions of the water
samples were checked by charge balance error (Freeze and Cherry, 1979).
The absolute values of relative error calculated for all the water
samples from the balance between cations and anions range from 0.06% to
1.7%.
Table 1 Field data and chemical constituents of the hot water
samples