Zelensky first included the offer of an agreement on minerals in the so-called "victory plan" that he presented to Trump last September.
The idea was to offer the then presidential candidate a tangible reason for the US to continue supporting Ukraine.
On Monday former UK prime minister Boris Johnson told the BBC in Kyiv that such a deal was "the great prize" because it would secure "a United States commitment under Donald Trump to a free, sovereign and secure Ukraine".