Geochemical controls on the distribution of radio-trace
elements in groundwater resources of Shir-Kuh granitoid
aquifer, central Iran
Bahareh Yazdizadeh, Hadi Jafari and Rahim Bagheri
ABSTRACT
Granitic groundwaters are important resources in arid regions. However, they are not always pure
due to having appreciable amounts of trace elements. The present study was conducted to
investigate chemical compositions for finding controls on distribution of heavy metals and natural
radioelements (U and Th) in groundwater resources of Shir-Kuh granitoid aquifer (SGA), central Iran.
Thirty water samples were collected and analyzed for major and trace elements. The average values
of electrical conductivity (EC) and pH are 624 μs/cm and 7.5, respectively. The dominant groundwater
type is Ca-HCO
3
, as a result of the calcite dissolution and biotite weathering. Principal component
analysis in support of mass balance studies recognizes dissolution of fracture-filling sediments and
rock mineral weathering as the main factors enhancing major ions in SGA. These processes also
release trace elements in decreasing order of Sr > Ba > Sn > W > Cu > U > Zn > Th. Weathering of
biotite enclosing accessory minerals of monazite and zircon is introduced as the main source of
radio-trace elements in SGA. Health concerns are currently related to U in drinking groundwater, as
the maximum concentration (13.6 μg/L) approaches the Iranian drinking standard of 15 μg/L, in
response to the oxidizing nature of the groundwater, calcite dissolution-related mobilization, and the
degree of the water–rock interactions.
Bahareh Yazdizadeh
Hadi Jafari (corresponding author)
Rahim Bagheri
Faculty of Earth Sciences,
Shahrood University of Technology,
Shahrood,
Iran
E-mail: h_jafari@shahroodut.ac.ir
Key words | heavy metal, silicate weathering, thorium, uranium, Yazd
INTRODUCTION
Granitoid is a preliminary term used for plutonic rocks which
essentially contain quartz and feldspars, tentatively identified
as granite, granodiorite, or tonalite (Le Maitre et al. ).
These rocks have appreciable amounts of quartz, alkali feld-
spar, and/or plagioclase and other aluminosilicate minerals
such as micas. Quartz has very low solubility under existing
pH and temperature; however, incongruent dissolution of
aluminosilicates releases common cations (Ca
2þ
, Mg
2þ
,
Na
þ
, and K
þ
) into groundwater (Singhal & Gupta ).
Very low weatherability of silicate minerals in addition to
the low residence time of groundwater mainly through the
fissures and fractures result in the total dissolved solids
(TDS) of granitic groundwater to be usually less than
300 mg/L. As a result of the silicates weathering, the general
groundwater type from granitoids is Ca-HCO
3
and the silica
content ranges from 10 to 30 mg/L. High concentrations of
trace elements such as Pb, Cr, Fe, and Mn are also possible
to detect (Singhal & Gupta ). For example, high values
of Pb (about 0.19 mg/L) and Cr (around 2.6 mg/L) were
reported in acidic granitic groundwater in Ghana (Pelig-Ba
et al. ). Analysis results of the water samples collected
around granitic rocks in Turkey (Yuce et al. ) revealed
high concentrations of trace elements, including Al, Ba, Fe,
and Cr, over the drinking water norms.
974 © IWA Publishing 2019 Hydrology Research | 50.3 | 2019
doi: 10.2166/nh.2019.129
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