By CLAYTON PARK

Northgate Mall owner Simon Property Group has found a potential buyer for another large chunk of the Northgate South Lot, but it won't say who it is or what the buyer plans to use the site for.

The one thing for certain is that the buyer ISN'T Security Properties, the Seattle-based housing developer that had spent more than a year working on a plan to build a mixed-use complex that would have included daylighting a portion of Thornton Creek that currently flows in an underground culvert beneath the South Lot.

"As it stands right now, Security Properties is out of it," said the developer's spokeswoman, Jeanne Muir, of the company's bid to buy the South Lot from Simon. "They'd still love to be part of the development of this site, but they're not in current negotiations with Simon."

Muir said, however, that Security Properties hasn't given up on trying to find a site in the Northgate area to build a multifamily housing development. She said the developer is currently considering a possible site elsewhere in the area.

Simon announced at a meeting in late March with City officials and community activists that it had optioned a portion of the South Lot just under six acres to a potential unnamed buyer.

The mystery buyer is not thought to be interested in building a mixed-use project and because it would only buy a portion of the 12.8-acre South Lot, it is unlikely that daylighting Thornton Creek would be part of its plans.

Simon has already sold a 3.9-acre portion of the South Lot earlier this year to King County, which plans to use its portion of the site as a Metro Park-N-Ride lot.

With the pending sale of the nearly six-acre portion of the South Lot to the mystery buyer, that would leave just over three acres of the property left to sell. Because the remaining portion of the lot is mostly where Thornton Creek is located underneath, it is unlikely that Simon would be able to find a willing bidder for that property, at least anyone interested in developing a commercial project on that site.

Two community groups, the Thornton Creek Legal Defense Fund and Citizens for a Liveable Northgate, have been waging a several-year legal battle to try to require that Thornton Creek at the Northgate South Lot be daylighted.