Further, the company is now drilling a pegmatite area 1.2km along strike.
A resource update is due next quarter.
Manna currently has an inferred resource of 9.9 million tonnes grading 1.14% lithium oxide.
Global Lithium believes the diamond core drilling allows it to "potentially add significant tonnes to the existing resource".
The project is 80% owned by Global Lithium, with gold explorer Breaker having a 20% free carried interest.
Global Lithium had A$33 million at the end of June.
The company's other project, Marble Bar, currently has 10.5Mt at 1% lithium oxide.
Shares in Global Lithium were up 1.6% to $2.49 in morning trade, capitalising the company at $500 million.