Again, I wish there had been an accompanying photo. This brief notice also did not include any speculation about the age or cultural period of the find. I did find references online to Tibetan funerary practices that said inhumation was the most common form of burial before Buddhism was introduced to Tibet, but after that sky burial became the most widely accepted funerary practice. Buddhism was first introduced in Tibet in 173 CE [Reference: Buddhism in Tibet] but supposedly had little impact at that time. I'm not sure what this website means by introduced because it goes on to say the appearance of the first Buddhist scripture did not occur until the 6th century CE and it goes on to say the scripture was not translated at that time. The first Buddhist monastery was erected in the ninth century after King Trisong Detsen officially declared Indian Buddhism and not Chinese Buddhism to be the religion of Tibet in 792 CE. If inhumation was abandoned somewhere between the 6th and 8th centuries, then the sarcophagus would predate that period at least.
I also found a fascinating discussion of ancient Tibetan royal burial practicies.
"... the funeral rituals of the tsenpos [early Tibetan kings] [are] closer to those of other Eurasian cultures - for example, the Scythians. We know quite a lot about the funerals of the Scythian kings because Herodotus wrote about them in the 5th century BC. Here’s what he wrote:
The tombs of their kings are in the land of the Gerrhi, who dwell at the point where the Borysthenes is first navigable. Here, when the king dies, they dig a grave, which is square in shape, and of great size. When it is ready, they take the king’s corpse, and, having opened the belly, and cleaned out the inside, fill the cavity with a preparation of chopped cypress, frankincense, parsley-seed, and anise-seed, after which they sew up the opening, enclose the body in wax, and, placing it on a wagon, carry it about through all the different tribes. On this procession each tribe, when it receives the corpse, imitates the example which is first set by the Royal Scythians; every man chops off a piece of his ear, crops his hair close, and makes a cut all round his arm, lacerates his forehead and his nose, and thrusts an arrow through his left hand.*
And as a commentator on Herodotus recently wrote: “The magnificent funerals of the Scythian kings have several parallels among Eurasian nomads of every age…” Indeed, restricting ourselves to the practices of cutting off the hair and self-laceration among mourners, we can easily pick out the following further examples. It was reported that at the funeral of Attila the Hun, mourners cut off their hair and made deep cuts in their faces. They kept the body in a ceremonial tent for a time before being buried. The Xiongnu (a nomadic empire that ruled northern China for a while in the 3rd and 4th centuries AD) buried their kings in large tombs, and plaits of hair have been found in some of those that have been excavated. The Khazars (around in the 7th-11th centuries) buried their dead in mausoleums near rivers, and at the funerals they beat drums, whistled and lacerated their faces. And so on
What we see again and again is the mourners cutting off their hair and lacerating their faces and bodies. This seems to me to be quite persuasive circumstantial evidence for rereading the Old Tibetan Chronicle in the same way. It also shows just how much the religion of the early Tibetan clans preserved the culture of their nomadic ancestors from the northern steppes. Other aspects of the tsenpo’s funerals which I haven’t mentioned here are also found among Eurasian nomadic peoples - like the long period elapsing between death and burial; the sacrifice of animals, especially white ones, and especially horses; and the killing and entombment of the king’s retainers.I think all this helps us to see the early Tibetan religion (at least the myths and rituals surrounding the tsenpos) in the wider Eurasian cultural matrix shared by Scythians, Huns, Khazars, Turks, Mongols, and many more people of nomadic origin. - More: Early Tibet
A sarcophagus carved from stone, has been unearthed in Dongga Town, Lang County, southeastern Tibet's Nyingchi Prefecture, the prefecture's Cultural Relics Survey Team said.
The coffin was discovered in the course of building a road in the area. The frame and top of the stone coffin were made of bluish schist. The sarcophagus was 1.4 m long, 0.7 m wide, and 0.5 m tall. The tomb chamber was filled with cobblestones, sand and stones. A skeleton was also found in the chamber.- Tibet.news.cn