Cocotohai No.3 Mine is one of the largest and most typical granite veins containing rare metal ores known in the world at present. It is a "holy place" for Chinese and foreign scientists studying granite pegmatite and rare metal ores to worship. It was once the gold exploration route of Beijing International Geological Congress. After 50 years of mining, the No.3 vein has been dug into 143 meters deep underground, 250 meters long and 240 meters wide from the towering gabbro mountain, which was hundreds of meters above the surface. It forms a circular ore-transporting lane and looks like the giant Colosseum of ancient Rome. There are 86 kinds of minerals coexisting in the pit, 7 of which are not found in the periodic table of elements, mainly lithium, beryllium, tantalum, niobium and other rare metal elements. this vein has abundant reserves, large scale, many kinds of minerals and high grade, and its belts are clearly unique in China and rare abroad. it is known as "museum of geology and mineral resources" at home and abroad and has become "mecca" in the eyes of Chinese and foreign geologists.