The Chinese bank whose delegation stood on the lip of the Kimkan pit is in advanced negotiations for a $400 million loan to enable the developer, the Petropavlovsk mining company, to begin excavating ore. The reserves Mr. Ryabov spoke of are in Kimkan and a sister mine to the north, and would require 100 years or so to extract.

Petropavlovsk, whose shares trade on the London Stock Exchange, plans to transport ore directly south from the Kimkan mine by train to Chinese steel mills that now import iron ore from as far away as Brazil. Mine managers say they will have no trouble beating the Brazilians on price  although pricing of commodities may prove one of the sticking points in this emerging transborder trade, some analysts predict.

Skeptics of further economic development between the countries also point to deep mistrust dating to border skirmishes fought on Damansky Island in the Ussuri River in 1969 that put the Soviet Union in a defensive crouch along the border and froze all development for decades.

It was not until 1987 that Aleksandr A. Vinnikov, then the local communist party chief and now the governor of the Jewish Autonomous Region, a province in Siberia with a peculiar history, persuaded Moscow to allow a ferry crossing at a riverside village on the Amur.

Mr. Vinnikov has today become a staunch supporter of the biggest modern trade venture across the Amur  a planned railway bridge at Nizhneleninskoye village that is intended primarily to carry Kimkan iron ore to Chinese mills.

The bridge, whose construction is to be paid for by Petropavlovsk and the two governments, is another emblem of the new prospects in the region, as well as the deep freeze that came before. It would become the lone year-round border crossing along a 2,038-mile stretch of the Russian-Chinese frontier  stretching from Grodekovo, near Vladivostok, and Zabaikalsk, near Lake Baikal.

For comparison, the United States’ border with Mexico spans 1,969 miles and has 42 border crossings.