Open pit mining is safer for the workers than tunnel mining, however, it should never be done where there is a living ecosystem. I grew up in a mining town in the Atacama desert in Chile that did open pit. There weren't any trees, vegetation or animals to destroy up there, so the most it did was leave a manmade scar on the desert. It seems with all our engineering technology these days and expertise learned from tunneling for the rail roads, that we can figure out a safe way to tunnel and preserve the landscape and all those living things. I'm sure if there was ore they wanted under a city, they would figure out a safe way to tunnel.