VANCOUVER, British Columbia ( TheStreet) -- The development-stage gold miner Rubicon Minerals ( RBY) spooked investors Monday morning when it announced that Canadian securities regulators had asked the company to amend a technical report that describes its most important project.

The report, filed with the British Columbia Securities Commission, is intended to provide geologic data in support of the estimated reserves and ore grades that companies say their deposits contain.

Rubicon offered no further information in its press release. The uncertainty fueled speculation that Rubicon may have to cut back previous estimates on the amount of metal contained in the deposit, called the Phoenix Gold Project, in western Ontario. Rubicon has said that it wants to begin production at the mine by the fourth-quarter of 2012.

In November, Rubicon said the Phoenix deposit contains as much as 4 million ounces of gold, based on the conclusions of Peter George, an independent geological consultant hired by the company to study the deposit. In its press release on Monday, the company said it would "make a timely announcement if any material changes to the estimates result from an amended report."

"We presume that the stock drop is as result of the news today, and we hope to clarify that in due course," Bill Cavalluzzo, Rubicon's vice president of investor relations, told TheStreet Monday afternoon.

The BC securities commission, in reviewing the report, must address its questions directly to the consultant, Cavalluzzo said. For that reason, he couldn't "put a timeline" on when Rubicon would be able to announce the results of the amended report.

Mining experts say that on most occasions, the amendments requested by regulators amount to relatively trivial checklist items, rather than wholesale revisions to reserve estimates.

Meanwhile, Rubicon shares were declining sharply Monday afternoon, trading recently at $5.07, down 9.3%. Volume reached nearly 4.7 million shares, more than double the daily average.

-- Written by Scott Eden in New York

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