It had the potential to be another Afghanistan Buddha disaster, recalling the Taliban’s destruction of two ancient statues that had stood for centuries in this country’s west: A buried Buddhist city lost to time was about to be obliterated by what promised to be one of the largest copper mines in the world.

Now, however, thanks to delays in construction of the massive mine and a hefty influx of cash from the World Bank, the 1.5-square-mile Mes Aynak complex is an archaeological triumph – though bittersweet.

An international team of archaeologists and more than 550 local laborers are now frantically excavating what turns out to be a unique window into Afghanistan’s role on the ancient Silk Road connecting China and India with the Mediterranean.

With its Buddhist city, a ring of perhaps a half-dozen monasteries and a striking complex of workshops and mine shafts built into a high mountain ridgeline at an altitude of 8,200 feet, the site shows the interplay of Buddhism, mining and trade during the years it was in operation, now thought to be from the fifth to the late eighth centuries....