Major copper and gold miner Freeport-McMoRan (FCX 0.52%) announced in a press release Wednesday that it will acquire  Plains Exploration and Production (NYSE: PXP) and McMoRan Exploration (NYSE: MMR) for $6.9 billion for the former and $3.4 billion for the latter. The actual cash amount to purchase McMoran Exploration will amount  to just over $2 billion because of Freeport-McMoRan's current 36% stake in the company.

In all, the acquisitions will cement Freeport's mineral assets and production capabilities, creating what the corporation expects to be "a premier U.S.-based natural resource company." The move adds oil and natural gas assets inside the U.S., including in locations such as Eagle Ford in Texas and in the Deepwater Gulf of Mexico sites. Freeport estimates 26% of future EBITDA to come from natural gas and oil with the purchases.

Freeport President and CEO Richard C. Adkerson pointed out the opportunities from the deal, saying, "The transaction will add a high quality portfolio of assets with strong current cash flows, significant growth options and complementary exposure to markets positioned for global growth in the developed and developing world."

Wall Street didn't think as highly of the deal, however. Shares of Freeport fell more than 15% after the announcement, with BlackRock managing director Evy Hambro saying, "I haven't heard anything ... that in any way justifies why these companies should be put together." Investors further seemed skeptical at burgeoning debt and share dilution from the deal's results, not to mention the company's strategic shift into natural gas and oil after long being a staple in copper and gold mining.

McMoRan shares jumped 85% on the news, while Plains Exploration's stock soared 24%.