Consolidated Gold Fields PLC, acting as a white knight to try to keep Newmont Mining Corp. out of the hands of corporate raider T. Boone Pickens Jr., bought millions of shares of Newmont stock yesterday in a "market sweep" -- less than a week after the Securities and Exchange Commission said it was considering outlawing such practices.

Huge blocks of stock of Newmont -- one as large as 5 million shares -- changed hands as Consolidated swooped into the market to buy enough shares to make Pickens' bid for control of Newmont all but impossible. The shares were purchased on Consolidated's behalf by First Boston Corp., the company's investment banker.

It could not be determined just how many shares Consolidated purchased, but a source close to Consolidated said, "we accounted for a very meaningful proportion of the volume today."

In all, 18.9 million shares of Newmont changed hands yesterday, more than a quarter of the company's outstanding stock. It was one of the busiest trading days ever for a single issue. Trading in Newmont accounted for more than 9 percent of the New York Stock Exchange's total volume yesterday of 210 million shares.

Newmont stock closed at $95.62 1/2, up $1.62 1/2.

A source in the Consolidated camp said the company, which began the day with 26.2 percent of Newmont's shares, did quite not reach its previously stated goal of a 49.9 percent holding in the company. But he said Consolidated now owned "clearly more than 40 percent" of Newmont. "We're much, much higher than that," he said.

The purchases came even as Pickens' investment group, Ivanhoe Partners, was in state court in Delaware challenging Consolidated's interest in Newmont. Ivanhoe asked the court to enjoin Consolidated from buying additional shares of Newmont and to void an agreement reached earlier this week between Consolidated and Newmont under which Consolidated was allowed to raise its stake to 49.9 percent. Ivanhoe contended that the agreement was a "lockout scheme" that would hurt Newmont shareholders by preventing Ivanhoe's offer.

The court said it would rule on the request today, but the Consolidated source said the delay was positive for his side. "Whether {the judge} grants an injunction or not, it's not going to make any difference," he said. "How's he going to unwind all those trades?"

Ivanhoe, which owns 9.9 percent of Newmont, or 6.6 million shares, has been seeking an additional 28 million shares in order to gain control. Ivanhoe, which had been offering $105 a share -- $2.9 billion in all -- for the stock, yesterday reduced its offer to $72 a share to take into account a $33-a-share special dividend announced by Newmont on Monday as a defensive measure.

But analysts said the Ivanhoe offer was doomed if Consolidated substantially increased its stake, and a source close to Pickens said, "as soon as they get up to about 40 percent, our offer is dead."

The Consolidated source said that after yesterday's developments, Pickens's bid "has got very severe problems. ... I think it's all over."

Speaking to reporters in Houston after a speech there yesterday, Pickens called Consolidated's action "a clear-cut street sweep," according to Dow Jones News Service. "This is the most flagrant situation we've seen," he said.

Sweeps of the market have been growing in popularity as a tactic in takeover battles in recent years, both as offensive and as defensive weapons. In perhaps the best-known instance of a sweep, Campeau Corp. last year bought 48 percent of Allied Stores Corp. in the open market within a half hour after Campeau dropped a formal takeover bid for Allied. And Carter Hawley Hale used a sweep as a defensive tactic in 1984, buying huge amounts of its stock to ward off a hostile takeover attempt by Limited Inc.

Consolidated's purchases of Newmont stock yesterday appeared to represent one of the first times that a sweep has been used by a third-party white knight to prevent a company from an unwanted takeover.

Last week, the SEC said it was considering banning all types of market sweeps, on the grounds that they act as illegal tender offers, forcing shareholders to sell their stock without giving them time to evaluate the price being offered or to seek other offers. Laws governing tender offers allow shareholders 20 days to consider a bid before deciding whether to accept it