MADISON, Wis. -

A new report says the sand mining and natural gas industries have given Wisconsin candidates nearly $758,000 dollars since 2007, with contributions spiking last year as sand mining took off in the state.

The Wisconsin Democracy Campaign study found the gas and sand mining industries gave candidates a total of $18,762 in 2007 when only five sand mines were operating in the state. Last year the industries gave candidates $413,642. About 100 mines and processing plants were running in Wisconsin that year. Demand for silica sand is grown because it's used in hydraulic fracturing, or "fracking," a process thta produces oil and gas.

Republican Gov. Scott Walker received the most money of any candidate over that six year period, accepting $520,266.