The MetalNRG tie-up was agreed in April and it envisaged that the parties would have entered in a transaction agreement on or before 30 June.
A recent £1.1mln injection of capital, from the exercise of share warrants, has led Mkango to proceed with plans to carry-out a programme at Thambani.
The miner retains 100% ownership of the project and said the new exploration programme aims to add value.
The company highlighted that Thambani features: “multiple zones of high-grade uranium, tantalum and niobium, with a number of extensive uranium radiometric anomalies.”
It also noted that effort will continue to evaluate partnership opportunities for the project.
In parallel, the company continues on the feasibility study for the Songwe Hill Rare Earths project, fully funded by strategic partner Noble Group.