TORONTO -- Ontario's governing Liberals are killing development of the Ring of Fire -- believed to have the economic potential of Alberta's oilsands -- by failing to stop a major player from pulling out of the project, critics charged Thursday.

Plans to mine the massive chromite deposit in northern Ontario suffered a major setback after U.S.-based Cliffs Natural Resources Inc. said it won't spend any more money on the project and was suspending its operations indefinitely.

The Liberals ignored the warning signs that Cliffs -- which was prepared to pour billions of dollars into the project -- might pull out as development stalled over a conflict over access to the site, said the opposition parties.

"Guys, you just blew a $10 billion-dollar deal of a lifetime and you're about to put more people out of work," fumed Progressive Conservative Vic Fedeli.

It's not just a blow to Ontario's future economic growth, it's also sending the message to other major mining companies that they can't do business in the province, said Tory Norm Miller.

"You sold hope to the people of northern Ontario and have failed to deliver," he said in the legislature.

"First Nation communities, cities like Thunder Bay and Sudbury are all waiting for the investment in jobs that this project would bring."

Late Wednesday, Cliffs said it was suspending operations, citing an uncertain timeline and risks associated with the development of necessary infrastructure to the project.

Technical project work, including feasibility study, development and exploration activities, are being halted and there is no restart date planned, Cliffs said.

The company wanted to build an all-weather road to the site, but junior mining company KWG (TSXV:KWG) had already staked the most viable corridor through very difficult wetland terrain for a potential railroad.

Cliffs suspended its environmental assessment activities in June and asked Ontario's Mining and Lands Commission for an easement over KWG's mining claims. The application was dismissed in September and Cliffs has appealed.

Last month, the company told The Canadian Press that if it couldn't build the road, it would have to consider shutting down operations.

A few weeks later, the Liberals announced a development corporation to bring together private and public partners, including First Nations and mining companies.

But it was too little, too late, critics said.

"Their bungling has snuffed out an amazing opportunity for northerners and for Ontarians overall in terms of jobs and resource development," said NDP Leader Andrea Horwath.

Northern Development and Mines Minister Michael Gravelle insists the project isn't dead and there are many other companies interested in developing the Ring of Fire.

"Yes, we're disappointed that indeed they've made this decision to suspend the project," he said. "But that does not mean that the work that we're doing to move the project forward will not continue."

Fedeli mocked Gravelle for trying to assure voters that the Ring of Fire is a "multigenerational opportunity."

"My question is, which generation did you have in mind to finally get around to doing something?"

Other mining companies involved in the Ring of Fire were more upbeat.

Cliffs' decision to stop work may not be all negative, said Alan Coutts, president and CEO of Noront Resources, which is developing the Eagle's Nest nickel-copper project.

"It certainly will get attention to the fact that timelines and uncertainties around resource development in this region can't extend forever," he said.

"There have to be some timing decisions made and I'm hoping that this will light a fire in the Ring of Fire."

There does need to be road infrastructure into the area, he said.

For years, the Liberals have been touting the Ring of Fire as a major mining project that will help boost the cash-strapped province's economic fortunes, create jobs and bring in revenue to struggling First Nations.

It's believed to contain the largest deposit of chromite -- a key ingredient in the making of stainless steel -- to be discovered in North America. The federal government has compared it to the Alberta oilsands in terms of its potential to create wealth and development.

The Ontario government has faced lawsuits from companies that can't reach agreements with First Nations in the area.

With files from Craig Wong in Ottawa