The provisions of sections 57-101 to 57-105 shall not apply to any veins of coal or iron ore already discovered nor to any oil wells or gas wells already producing, nor shall the provisions of said sections apply to the discovery of the same vein of coal or iron ore, or oil pool or gas field already discovered, nor shall any reward specified under the terms of said sections be paid for a second discovery of the same veins, pools or fields within the limits of the same county.