The sum will fully fund the project's bankable feasibility study and be invested in three tranches, with the first £2 million to be paid once regulatory approval is received from the TSX.
The next £3 million will be given 45 days after the approval and the final £7 million will be invested after the two parties complete a definitive joint venture agreement.
Noble has the option to acquire another 26% interest in Songwe Hill if it arranges funding for the project's development.
Mkango has also agreed that Noble can acquire up to a 49% interest in its new venture focusing on neodymium alloy powders, magnet and other technologies by investing £2 million in two equal tranches.
The two companies have also agreed to be each other's preferred partner for any rare earths' projects globally, with Noble granted right of first offer to finance any of Mkango's activities and Mkango being entitled to an offer of a 50/50 share on an economic basis in any Noble opportunities.
Noble was intitially announced as a strategic shareholder of Mkango at the end of 2016 and, in late October, invested £500,000 for a 14.5% interest in the company with the option to exercise its 12 million common share purchase warrants and give it a 20% share.
Mkango CEO William Dawes said the agreement will strengthen the company's balance sheet and ensure Songwe Hill progresses.
"It also comes at a pivotal time in the rare earth market with a very strong demand outlook for rare earths such as neodymium and praseodymium used in permanent magnets for electric vehicles, wind turbines and other clean technology applications," he said.
If Noble arranges financing for the project, it will own 75% of Songwe Hill in addition to its stake in Mkango.
Mkango, meanwhile, will have a 25% interest in Songwe Hill and a 51% interest in the new venture, which includes its research collaboration with Metalysis.
Mkango's shares were at £0.08 in early-morning trade, up 106% from yesterday's close.