Short answers, pulled from the story.
Pliny the Elder watched Roman miners work in Hispania Terraconensis during the 70s AD. He described these operations in his Natural History, which was published in the first century AD.
Judge Lorenzo Sawyer decided in favor of the farmers on the 7th of January 1884. He declared that hydraulic mining was a public and private nuisance and enjoined operation in areas tributary to navigable streams and rivers.
By the mid-1880s, an estimated 11 million ounces of gold were recovered from hydraulic mining. These ounces were worth approximately US$7.5 billion at mid-2006 prices.
The remains at Las Médulas show badland scenery on a gigantic scale today. At least seven large aqueducts fed supplies into this site with some reaching lengths of up to ten miles.
East Rand Gold and Uranium Company has operated since 1977 on the South African Rand. The facility processes nearly two million tons of tailings each month at a cost below US$3.00 per ton.