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Qarhan Salt Lake - Drying yard of the heavens

IN vast Qarhan Lake, the salt blossoms like flowers and takes the form of pillars, corals and pearls. The awesome crystalline landscape contains rich deposits of potassium and other minerals, and mining is a vital industry in Qinghai Province. Shan Zhiqiang reports.

From the shallow basin containing Qinghai Lake, we crossed the Qinghai Nanshan Mountains and entered the Qaidam Basin to the west. Both basins are endorheic, meaning they have no outlet - they are fed by rivers and rain, but do not allow water to flow to the sea due to their closed nature.

These adjacent basins have met with different fates: one holds the largest lake in China, while the other is a dry expanse of salt lakes.

As we began our venture into the heart of the Qaidam Basin in Qinghai Province, we could see trees growing on the mountain ridges. But there were no trees to be found on the flat expanse. This is because precipitation actually decreases as the elevation gets lower. Most of the trees are the Qilian cypress (Sabina przewalskii), which are among the oldest living trees in China.

Around 1,800 years old, they are an important record of climate change: Scientists can determine the ancient climate by analyzing the thickness of the tree rings.

Before long all the trees disappeared. All we could see were shrubs of camelthorn. Just then, a herd of two-humped Bactrian camels appeared; the landscape provided a fitting backdrop to their majestic stature. Out from the bushes popped two wild rabbits, which quickly hopped away.

As we moved on, all vegetation cover totally disappeared. We had reached the bottom of the vast Qaidam Basin.

We soon encountered our first salt lake - Caka Lake. As early as the Western Han Dynasty (206 BC-AD 25), the ancient Qiang people who lived here used to mine salt and trade it for other goods. A salt-trading bureau was established during the Qing Dynasty (1644-1911). However, the growing competition with sea salt has led to a drastic drop in demand for Caka salt. The salt mine at Caka was already closed when we got there.

It was a different scene at Qarhan Lake, some 300 kilometers to the west of Caka Lake. The next day we visited a mine owned by the Qinghai Salt Lake Potash Co. There, hundreds of workers were filling bags of potassium chloride destined for use as a chemical fertilizer. Qarhan Lake has one of the world's richest deposits of potassium salts, with reserves estimated at 274 million tons of potassium.

The Qaidam Basin measures 800 kilometers from east to west and 350 kilometers from north to south. It is bounded by the Altyn-Tagh (Aerjin) Mountains to the northwest, the Qilian Mountains to the northeast and the Kunlun Mountains to the south.

As our car sped along the highway from Nomhon to Golmud, we could see the undulating Kunlun Mountains to the south, and an endless flat expanse to the north.

It's a lonely world out here - not a blade of grass, not a single tree, no bird in the sky, no animals to be seen anywhere. The land is totally barren.

Salt lakes are formed when dissolved salts from rivers are concentrated in a lake that has no outlet. The rate of inflow relative to the rate of evaporation (the main way water leaves the lake) determines whether the lake ends up as a freshwater lake, saltwater lake or salt lake.

Water enters the lake through surface rivers, precipitation or groundwater. If the rate of evaporation and the rate of inflow are the same, the lake will remain in a state of equilibrium.

However, if the rate of evaporation exceeds the rate of inflow, the lake surface will shrink and the lake water becomes increasingly saturated with dissolved salts. Eventually the salts precipitate out as crystals, and the lake becomes a dry salt lake.

The impact of evaporation on a lake depends greatly on its surface area. In the flat and wide Qaidam Basin, the large and shallow lakes formed are easily dried by evaporation. It is this combination of climatic and topographic factors that has made the Qaidam Basin - and Qarhan Lake - the so-called "drying yard of the heavens."

This lake is indeed a treasure trove of minerals. The 5,856-square-kilometer lake contains more sodium chloride (table salt), potassium and magnesium than the Great Salt Lake in the United States, or the Dead Sea that straddles Jordan and Israel.

Qarhan Lake is the largest potash production base in China. In addition to the mine owned by the Qinghai Salt Lake Potash Co producing more than a million tons of potash a year, there are other smaller mines around the lake, each of which produces around 50,000 to 200,000 tons of potash a year.

However, China still needs to import potash, as production is still not enough to meet domestic needs. The vast potassium resources in the Qaidam Basin were discovered almost by accident. In 1957, the renowned scientist Zheng Mianping was doing his fieldwork at Qarhan Lake, as a member of a research team from the Chinese Academy of Sciences studying the lakes in the Qaidam Basin.

At that time, Zheng did not harbor any hopes of finding the potassium that China so urgently needed.

On October 2, 1957, Zheng and his team leader Liu Dagang were taking a stroll at Qarhan Lake when they noticed something beside the road: depressions around 20 millimeters deep occurred every 10 meters or so. Zheng found the depressions filled with brine, in which there lay transparent, orthorhombic crystals the size of broad beans. He took a few crystals and tasted them - they gave a slight "burning sensation."

Liu analyzed the crystals and found them to be carnallite (KCl°?MgCl2°?6H2O), a mineral that contained potassium. Subsequent testing of drilled samples confirmed the presence of potassium in the lake, with a preliminary estimate of 150 million tons in reserves. This discovery marked the end of the "dry spell" of potassium resources in China.

Millions of years ago, activity on the Earth's crust led to the formation of mountains around an enclosed depression - the Qaidam Basin. The rivers from these mountains carried with them eroded sediment rich in minerals such as potassium, sodium, calcium and magnesium. These minerals became dissolved in the rivers and were brought down to the lakes in the Qaidam Basin.

As the basin was too vast and flat, and the rate of inflow could not exceed the rate of evaporation, the water in the basin eventually became supersaturated, leaving the dissolved salts to be precipitated out as crystals.

There is an order to this: The least soluble substances are the first to be crystallized. At the mouth of the river, where it enters the lake, insoluble substances such as sand and silt are the first to be deposited. Calcium carbonate is the first salt to be crystallized; it is followed by other carbonates and sulfates, and then common salt (sodium chloride).

However, the coveted - and highly soluble - potassium is still hidden in the briny solution, and only much later does it discreetly make its appearance among the sodium chloride crystals.

Our next stop was East Taijnar Lake, which lies to the west of Qarhan Lake. East Taijnar Lake is rich in lithium, which is in great demand. Just think of mobile phones, laptop computers and electric vehicles, all of which are powered by lithium batteries.

In order to extract the lithium in East Taijnar Lake, the Chinese Academy of Sciences has already set up a research facility there together with a few companies. A similar situation has occurred less than 100 kilometers away in West Taijnar Lake, where some large corporations from Beijing have already set up bases to tap this resource.

Here we could see an endless expanse of white, crystalline salt that stretched as far as the eye can see. According to Ma Haizhou, director of the research center at East Taijnar Lake, we were lucky to be able to witness such a rare sight. That's because this area is prone to sandstorms, which tend to cover the salt with a layer of sand; we just happened to be here during a brief lull in the sandstorms.

That night we stayed at a makeshift house beside East Taijnar Lake. The noise from the generators made sleep difficult. Accompanying us was Dr Shan Fashou, who described being stuck in this barren expanse for a few days. Our driver Song told us how a research team in the Altyn-Tagh met with flash floods and was trapped in the mountains for a few days. These stories helped us better appreciate the hardship that the early researchers survived in their efforts to explore western China.

Everyone else was asleep. I put on a coat and got out under the blanket of stars above me. The landscape was lonely and surreal - I felt as if I had been on Mars or the moon. I could not help but wonder: How could we use such a place ? For racing? A casino city like Las Vegas? Or a massive solar farm? Later I found it rather amusing that we humans just can't seem to leave nature alone. Why must we "use" this space for "something?"

When I got back to my room, I found my boots covered in a sticky layer of mud. Dr Shan said that was because the salt on the ground absorbs moisture from the air and then dissolves in it - a process known as deliquescence. This process also gives the ground a wet appearance. By noon the next day, the sun would heat up the land; the salt in the ground would lose water and crystallize again. In this way the landscape of salt undergoes a perpetual cycle that repeats itself every day.

The next morning we were on our way, and the salt highway gleamed in the morning sun. I knew that was the deliquescence that Shan had told me about the previous night. I gazed at both sides of the road. The white and dry expanse that we saw the day before now looked like freshly tilled fields from the plains of northern China.

These "fields" would soon turn white in just a matter of hours. In this never-ending cycle of crystallization and deliquescence, the flowers of salt that bloom in the Qaidam Basin take on a different look day after day.


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