J.P. Morgan Asset Management Inc., a division of international banking and financial services giant J.P. Morgan Chase & Co., has boosted its stake in Augusta Resource Corp., parent company of Rosemont Copper, by buying 54,789 shares of the mining company's stock.

The J.P. Morgan firm now owns 10.763 million Augusta shares, or 7.45 percent of all of Augusta's common stock. The purchased, announced Thursday, was made on Wednesday, J.P. Morgan said in a news release.

The purchase came three days after Toronto-based Hudbay Minerals announced it had made an unsolicited offer to buy all of Augusta's stock besides the 16 percent that Hudbay already controls.

On Wednesday, Augusta announced it had hired two investment firms and two law firms to help it evaluate the Hudbay offer. It amounted to the equivalent of Hudbay stock that would be valued at $2.96 per share of Augusta stock.

On its website, J.P. Morgan Asset Management Holdings describes itself as "one of the largest asset and wealth managers in the world, with assets under management of $1.5 trillion," as of Sept. 30, 2013.

Rosemont Copper is proposing to build the U.S.' third largest copper mine at the Rosemont Mine site in the Santa Rita Mountains, about 30 miles southeast of Tucson.