Yangbajain Hot Spring
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The Yangbajain Geothermal Field (羊八井地热田) is a geothermal field near the town of
Yangbajain Yangbajain (also spelled Yangbajing; ) is a town approximately north-west of Lhasa, halfway to Damxung in the Tibet Autonomous Region of China. The town lies just south of the Nyainqêntanglha Mountains, in an upland lush green valley surrounde ...
in Damxung County, Tibet Autonomous Region, China. The fluid is heated by
magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...
tic activity not far below the surface. It is a tourist attraction and also supplies steam to a major power plant with 25 MW capacity.


Location

The Yangbajain geothermal field is in a plateau basin on the southern slopes of the Nyainqentanglha Mountains, near to the Qinghai–Tibet Highway ( China National Highway 318) in Damxung County. The Qinghai–Tibet Railway, which terminates in Lhasa, also passes through Yangbajain. The field covers . It delivers natural thermal energy at the ground surface of up to 107,000 kilocalories per second. Yangbajain Geothermal Field is currently the largest proven geothermal field of its nature in China. It has an estimated power generation potential of 150,000 kW.


Geology

The Yangbajing Basin lies between the Nyainquentanglha Range to the northwest and the Yarlu-Zangbo suture to the south. The geothermal field is in the central part of a semi-graben fault-depression basin caused by the foremontane fault zone of the Nyainqentanglha Mountains. The SE-dipping detachment fault began to form about 8 Ma. Most of the outcropped rocks are metamorphosed lower
Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...
rocks,
Paleogene The Paleogene ( ; British English, also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period, geologic period and system that spans 43 million years from the end of the Cretaceous Period million yea ...
volcano-clastic rock series,
Neogene The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period Mya. ...
conglomerates and loose sediment accumulations from the
Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...
. The fault structures in the region run NE, NW, and nearly N-S. The NE faults are the largest and oldest, and usually have been cut by later fractures and faults. Although there still seems to be frequent magmatic activity, the main stages of magmatic intrusion were the Yanshanian granitic intrusion (88.7 Ma), the Yanshanian dioritic intrusion (88.0 Ma), and the Later Himalayan granitic intrusion (29.7 Ma). The field is part of the
Himalayan Geothermal Belt The Himalayan Geothermal Belt (HGB) is a region that extends for through India, Tibet, Yunnan, Myanmar and Thailand, and that contains many geothermal fields. Location The Himalayan Geothermal Belt was formed as a result of the collision of the ...
in the Lhasa-Gangdise terrane. The geothermal reservoir is basically a Quaternary basin underlaid by a large granite
batholith A batholith () is a large mass of intrusive igneous rock (also called plutonic rock), larger than in area, that forms from cooled magma deep in Earth's crust. Batholiths are almost always made mostly of felsic or intermediate rock types, such ...
. The basin has been filled with glacial deposits from the north and alluvial-pluvial sediments from the south. Fluid flows horizontally into the reservoir through the faults around the basin. A drill hole in the northern part of the field with a final depth of found thermal fluid with a maximum temperature of . Chemical analysis of the thermal fluid indicate that there is shallow-seated magmatic activity not far below the geothermal field. Other evidence, however, indicates that if there is a magmatic heat source vertically below the field, it must be over below. A 1996 paper proposed that the magmatic heat source lies to the southeast of the field at a depth of . In the area north of the highway, thermal fluids from this depth rises through a deep fault to the surface. In the area south of the highway, thermal fluid in the surface zone is heated by mixing with fluids that in turn are heated by deep circulation near the magmatic heat source. Carbon dioxide in the hot spring gases is probably largely organic, from the sedimentary rocks of the field. A 2000 paper presented evidence for a shallow reservoir with temperatures up to , and a deep reservoir with temperatures up to . The deep reservoir included an upper section between deep and a lower and hotter section below . Both the upper and lower reservoirs contained
sodium chloride Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g ...
thermal water. The shallow reservoir covers and is mostly hosted in porous Quaternary alluvium. Its basement is Himalayan granite and tuff. The water is a mixture of cold groundwater and deep thermal water. The deep reservoir was thought to have an area of below , contained in fractured bedrock. The thermal water is held in tectonic fissures and fracture zones. The isotopic composition of the thermal waters indicates local meteoric origin (rain and snow), including run-off from the Nyainquentanglha Range. The water runs down through the fractured rock, and is gradually warmed, with the warmer water rising towards the surface.


Recreational use

Yangbajing has been called "the highest-altitude hot springs in the world." It includes hot springs and boiling springs, geysers and hot water lakes. Various facilities for tourists have been developed in the field. A resort developed by government agencies in 1998 has hot spring baths that are reputed to have curative powers. There are two warm indoor pools and an outdoor pool where tourists can relax in spectacular mountain surroundings. A hot water lake lies to the east of the geothermal ground, from which steam rises high in the air on a clear day. The lake is deep, with water temperatures of . The local people have made pools for bathing in the west of the lake. The geothermal field is also used to operate greenhouses.


Power plant

The Yangbajain Geothermal Station was established in 1977. It is the first geothermal power station to be built in Tibet and is the largest geothermal steam power plant in China. 4,000 kW of electricity from Yangbajain began to be delivered to Lhasa in 1981 along a transmission line that runs southeast along the
Duilong River The Duilong River, or Duilong Qu (Tibetan: Toelung; ), is a right tributary of the Lhasa River, which it enters just below the city of Lhasa, Tibet, China. The river is about in length. Water quality may be compromised by dissolved substances incl ...
. It was the main source of power for
Lhasa Lhasa (; Lhasa dialect: ; bo, text=ལྷ་ས, translation=Place of Gods) is the urban center of the prefecture-level city, prefecture-level Lhasa (prefecture-level city), Lhasa City and the administrative capital of Tibet Autonomous Regio ...
until the Yamdrok Hydropower Station came into operation in 1998. The highest temperature inside the drilling hole is . By the end of 2000 eight steam turbo generators had been installed at the Yangbajain Geothermal Station, each with capacity of 3 MW, giving a total of 25 MW. The geothermal field delivers 25.181 MW, or 100 GWh annually, to the city of Lhasa to the south. As of 2000 the Yangbajing power plants were using 1,200 tons per day of water from the shallow reservoir, but pressure was falling fast and the turbines could not operate at full capacity. Deeper wells were being drilled to tap into lower-lying thermal fluid.


Pollution

Although rivers in Tibet are generally considered to be clean, the water of the
Duilong River The Duilong River, or Duilong Qu (Tibetan: Toelung; ), is a right tributary of the Lhasa River, which it enters just below the city of Lhasa, Tibet, China. The river is about in length. Water quality may be compromised by dissolved substances incl ...
is not. A 2015 study reported that during the non-monsoon season the levels of
arsenic Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, but ...
in the river, at 205.6 μg/L were higher than the WHO guideline of 10 μg/L for drinking water. The source of the pollution seems to be untreated water from the Yangbajain Geothermal Field power station. It can be detected downstream from this site.


References


Sources

* * * * * * * * * * * * {{refend Geothermal power stations in China