When the deposits are deeper, they may design an underground mine. In the western United States, open pit mining is usually chosen whereas in South Africa, most mines are underground. The engineers use computers to help them determine the precise design and measurements of the eventual mine. Even for an open pit mine, the construction phase is complicated and can take well over a year. Roads have to be built.
Buildings have to be erected to house and maintain all the engineering and processing equipment.
Offices have to be built for the technical and administrative personnel. None of this construction can begin right away. First, to ensure the plans meet zoning regulations and adequately protect the environment, they must be submitted to the authorities - the federal, state and local agencies that govern mining operations. The mining company also must set aside adequate funds to pay for reclaiming the land after the mining is eventually finished. Only when all this is completed and all the necessary permits have been issued can construction begin.