Field sampling and measurements
Field works at Heinitang were carried out in August 2013 and March 2018.
Two water samples (S2* and S4*) were collected in 2013 and another six
water samples (S1, S2, S3, S4, S5 and S6) were collected in 2018. S7
could not be collected since it was surrounded by mud. The water samples
were collected as close to the vents as possible. Water samples for
chemical and isotopic analyses were collected in 550 ml glass bottles
which were water-rinsed at least 3 times prior to field sampling. The
water samples were sent to the laboratory as soon as possible.
In situ measurements of some physicochemical characteristics of hot
springs were completed at all the sampling points. Water samples were
measured for free carbon dioxide
(CO2),
temperature, pH and Eh in the field (Table 1). The temperatures of water
samples were determined with a MIK-TP101 thermometer. The values of pH
and Eh were determined in situ using a CT-6821 pH meter. The
concentrations of CO2 were measured by NaOH-HCl
titration in situ using digital titrator manufactured by the HACH
company immediately after samples collection (Table 1).