The Iron Gate breaks up the mountains between Samarkand and a province which is 20 kilometers northwest of what provincial capital?
Iron Gate (Central Asia):  It breaks up the mountains which extend from the Hisar range south towards the Amu Darya. Balkh: Balkh ( ; Persian/Pashto: بلخ‎ "Balkh"; Bactrian: βαχλο, "ẞaxlɔ") is a town in the Balkh Province of Afghanistan, about 20 kilometers northwest of the provincial capital, Mazar-e Sharif, and some 74 km south of the Amu Darya river.
Mazar-e Sharif