Location and geological
setting
The Heinitang hot spring is located some 6 km to the northwest of the
Houqiao town near Tengchong in western Yunnan. Tengchong is situated at
the border area of southwestern China (Fig. 1).
Fig. 1. The location of Yunnan and Tengchong (Adapted from
National Geomatics center of China)
The Tengchong area lies in the Tengchong Block (Fig. 2a), where the
magmatism and volcanic activities occurred frequently and many hot
springs exist.
The field site for this study lies in the northwest of Tengchong in
Yunnan, which is underlain by Paleogene, Triassic, Permian, Devonian and
Proterozoic rocks. Lithologically, the Paleogene rocks are composed of
moyites. The Triassic rocks appear mainly in the west of the area and
consist of monzonitic granite. The Permian rocks consist of slates,
sandstones and quart arenites. The Devonian rocks consist of argillic
and carbonaceous slates and high permeability limestones. The
Proterozoic rocks consist of mica schist, plagiogneiss, quartzites and
granulites of low permeability (Fig. 2b).
The Heinitang hot spring is located at the western edge of the Permian
rocks and it is structurally controlled by a NW-SE fault. The Heinitang
hot spring includes of 7 vents (S1, S2, S3, S4, S5, S6 and S7) (Fig. 3).
The temperature of the hot water ranges from 50.9 ℃ to 66.6 ℃. In
addition, there are several fossil travertine mounds and cones near the
hot spring vents. The travertine mounds and cones were weathered to some
degree. The travertine cones range in height from 0.3 m to 5.5 m (Fig.
3). Apparent change in morphologies from travertine mounds to travertine
cones indicate that the discharge of the Heinitang hot springs decreased
with time in the past. In recent decades, the hot water was used for
bathing by constructing pools near vents S2, S3 and S4. New travertine
deposits near these pools as a result of outflow of hot water from the
pools. The C8 travertine cone is relatively well preserved (Fig. 4a).
Travertine deposited near vent S2 in 2018 (Fig. 4c) are obviously larger
than that in 2013 (Fig. 4b). Small scales of travertine are depositing
near vent S1, but in 2013 no travertine was found to deposit near this
vent.
Fig 2. (a) Simplified tectonic map of the western Yunnan
(Adapted from Bureau of Geology and Mineral Resources of Yunnan
Province) and (b) the location of the Heinitang hot spring (Adapted from
Bureau of Geology and Mineral Resources of Yunnan Province, 1990) 1
Paleogene Moyites; 2 Triassic Monzonitic granit; 3 Sandstones of the
Permian; 4 Devonian Argillic and carbonaceous slates; 5 Proterozoic
Quartzites.
Fig. 3. Plan diagram and profile of the Heinitang hot springs
with 2 travertine mounds and 14 cones. (The number is the height of the
inactive travertine cone (m)).
Fig. 4. Field photographs of travertines: (a) The inactive
travertine cone (C8); (b) Travetines near vent S2 in 2013 and (c)
Travertines near S2 in 2018.