Dabuxum Lake, Qaidam Basin, China

Dabuxum

Lakes of the Dabuxum region, on the downside of the Golmud fan delta, Qarhan Playa, China

The QaidamBasin covers an area of 120,000 km2, with elevations around 2800 m across the basin floor, and a catchment of about 250,000 km2. The present climate is hyper-arid, with average annual rainfall of 26 mm, mean annual evaporation of 3000–3200 mm, and mean annual temperature 2–4 °C in the central basin. The basin is surrounded by aeolian deposits, gobi, desert, sand dunes, and wind-erosion landforms (yardangs). Winds are dominated by strong northwesterlies, which in Spring transport and deposit large quantities of dust, especially in the southeast of the basin. During the stronger wind regimes of Pleistocene glacial and stadial episodes, the same winds even deposited large volumes of dust on the Loess Plateau of central China. 

The Qarhan Playa sump or salt flat occupies the southern part of the Qaidam Basin entrains nine perennial salt lakes: Seni, Dabiele, Xiaobiele, Daxi, Dabuxun (Dabsan Hu), Tuanjie, Xiezuo and Fubuxum north and south lakes (Figure). Dabuxum, which occupies the central part of the Qarhan Playa, is the largest of the perennial lakes (~184 km2). Lake water depths vary seasonally from 20cm to 1m and are never deeper than a metre, even when flooded. Salt contents vary from 165 to 360 g/l, with pH ranging between 5.4 and 7.85. +Today, the salt plains and pans of the Qahan playa are fed mostly from runoff from the Kunlun Mountains (Kunlun Shan), with a number of saline groundwater springs concentrated along the fault that defines an area of salt karst along the northern edge of the sump, especially north of Xiezuo Lake. 

Bedded and displacive salts began to accumulate in the Qarhan Playa depression some 50,000 years ago. Today, the surface salt crust consists of a chaotic mixture of fine-grained halite crystals and mud, with a rugged, pitted upper surface. Vadose diagenetic features, such as dissolution pits, cavities and pendant cement, form where the salt crust lies above the watertable. Interbedded salts and siliciclastic sediments underlie the crust to reach thicknesses of up to 75m.

Bedded potash, as carnallite, precipitates naturally in transient volumetrically-minor lake strandzone (stratoid) beds about the northeastern margin of Lake Dabuxum and as a cement in Late Pleistocene bedded deposits in nearby Lake Tanje. Ongoing freshened sheetflow from the updip fans means the proportion of carnallite versus halite in the unit increases with distance from the Golmud Fan in both the layered (bedded) and stratoid (cement) modes of occurrence.

At times in the past, when the watertable was lower, the meteoric inflow was also the driver for the brine cycling that created the karst cavities hosting the halite and carnallite cements. Solid potash salts are not present in sufficient amounts to be quarried, and most of the exploited potash resource resides in interstitial brines that are pumped and processed using solar ponds (see Warren, 2016; Chapter 12 for detailed literature compilation).

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Geology of carnallite in Lake Dabuxum area of the Qahan playa, Qaidam Basin. A) Distribution of surficial sediment types also showing the position of enlarged region seen in B - see Figure for regional location. B) Strandline geology of the northern shore of Lake Dabuxum showing position of coring traverse as shown in inset in A. C) Cross section showing how the process of brine cooling forms carnallite cement in the karstic voids in shallow subsurface halite crusts and creates karst-filling cement textures (after Casas et al., 1992).

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Tanje (MOP) pans, China, with a carnallite dredge in the left midground and the processing plant in the right background of image.

Today the Qinghai Salt Lake Potash Company Limited is the largest potash production base in China. It works a 120-square-kilometre salt lake area in the vicinity of Golmud, Qinghai. The company was established and listed on the Shenzhen Stock Exchange in 1997 and specialises in the manufacture and sale of potassium chloride, distributed under the brand name of "Yanqiao."


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