The detention of Pema Tseden sparks fears over habitual violence by Chinese police against Tibetans.
Chuchen county residents fear mining may resume after briefly being stopped, though.
Only women take part in the march in hopes of avoiding attack by police.
He had founded an association dedicated to promoting education among Tibetan nomad youth, a Tibetan source says.
Their talks are held behind closed doors and away from the press to minimize offense to China, which objected to the meeting.
Chinese security forces watch the crowd but do not interfere, local sources say.
Chinese authorities try again to reduce the population of Serthar county's Larung Gar Buddhist Academy.
Lobsang Tsering was enrolled in restive Kirti monastery, the scene of frequent protests against Chinese rule.
Villagers oppose Chinese gold-mining operations on a nearby sacred mountain.
Property owners had applied for permission to build, but were turned down after failing to pay bribes, sources say.
The assault follows other raids last year against 'illegal' structures financed and built by nomads on their own land.
Freed three years ago after serving a 21-year term, he is seized by police at midnight in Tibet's capital Lhasa.
They are told not to block construction of a road planned to support mining operations in the area.
They are taken away by police with no word given on their present whereabouts or charges made against them.
Dangerous roads and exposed power lines lead to injuries and deaths, a local source says.
He has six years left to serve of a 13-year sentence for calling for the Dalai Lama's return to Tibet.
Police also found a call for Tibetan freedom written on the wall of his room, sources with contacts in the region say.