Tesla Motors has chosen Nevada as the site for a massive, $5 billion lithium-ion battery factory dubbed the "gigafactory," sources told CNBC. "That's a go, but they are still negotiating the specifics of the contract," a source within the Nevada's governor's office told CNBC Wednesday afternoon. The source noted that it could be a week before the deal is official. Gov. Brian Sandoval will hold a news conference Thursday in Carson City, Nevada, to make a "major economic development announcement,'' according to a media advisory from the state. Tesla spokesman Simon Sproule declined to give details but confirmed Tesla officials would be at the event. In July, the automaker announced that it had partnered with Japanese electronics firm Panasonic to build the factory. Tesla also considered California, New Mexico, Arizona and Texas as possible locations for the factory. Tesla has done site-preparation work at the Reno Tahoe Industrial Center but had not publicly committed to building in Nevada. CEO Elon Musk said he would prepare two sites, in case one falls through.