The Gaden Tangkas are among the most common of all Tibetan coins.
Here is a reference to these coins:
Oriental Numismatic Society, The Gaden Tangka Of Tibet, N.G. Rhodes http://gorila.netlab.cz/coins/Tibet/ONS_TangkaTibet.pdf
In this reference, the OP (909windy) coin looks like a type "D-iii", made 1896-1899.
I have one myself:
Tibet Tangka, looks like type "F-vii" made 1912-1918.
I saw "Lost Horizon" on television too many times as a kid.