Source: Sharecast
BHP's offer would create the world's biggest copper miner as companies compete for commodities to supply the growing electric car and battery market. The metal makes up 30% of Anglo's production.
However, it is conditional on spinning off Anglo’s platinum and iron ore businesses in South Africa, which are independently listed.
Legal & General Investment Management, one of Anglo's largest investors, also shared the board's concerns over valuation.
"The BHP proposal is opportunistic and fails to value Anglo American's prospects, while significantly diluting the relative value upside participation of Anglo American's shareholders relative to BHP's shareholders," Anglo said in a statement on Friday.
"The proposed structure is also highly unattractive, creating substantial uncertainty and execution risk borne almost entirely by Anglo American, its shareholders and its other stakeholders."
Under UK takeover rules, BHP has until May 22 to make a firm offer.
Reporting by Frank Prenesti for Sharecast.com