Answer:
No, they do not contain fake gold but they might not be pure gold. The purity is measured can be measured by karats. 18 karat gold which is used for jewelry for example is 18 parts gold and 6 parts other metal such as nickel, copper etc....Such metal mixes are called alloys.
Suisse gold bars on the other hand which are bought as investments for example are 24 karat solid gold.