You misunderstand.
The Chinese annexation of Mongolia is in response to U.S. chokehold on Chinese oil from the Middle East. We are way past sanctions. We are at the stage of war.
That's why I also highlighted Mongolia's mineral resources. Economic sanctions don't mean a thing. Who cares about little bits of pieces of paper money during a war? Only resources matter.
You are at a stage of war where sanctions with the involvement of other countries that can affect a country's ability to fight a war.