Survivor Isa Muhammad said many people are wounded and about 20 are missing. He said more than 50 gunmen invaded the informal mining site at Gidan Ardo yesterday afternoon and seized people's belongings.
He said no security forces had arrived by today morning and residents fear another attack.
Police deputy superintendent Shehu Muhammad said soldiers and an anti-terrorism squad are on their way.
Zamfara state Gov. Abdulaziz Yari Abubakar promised to hunt down the perpetrators of the "act of terrorism."
Nigeria is suffering an Islamic uprising in the northeast, militants attacking oil installations in the south, deadly conflict between nomadic herders and farmers in the center, cattle rustling, kidnappings and banditry.