Police in Brooklyn Center have arrested seven protesters at a conference on silica sand mining.
The protesters were arrested Wednesday after they climbed on top of a bus that was scheduled to carry conference participants to a tour of silica sand mines in Wisconsin.
The protesters unfurled banners that read "Stop frac sand mining" and "No right way to do something so wrong."
Minnesota Public Radio News reported that the seven were charged with unlawful assembly and released.
Western Wisconsin and southeastern Minnesota are rich in silica sand deposits. The sand is used in the hydraulic fracturing process to produce oil and natural gas.
Critics said mining the sand can produce harmful dust, increased truck traffic and lower property values.