How much Sumitomo had to pay wasn't disclosed.
The original joint venture terms agreed to in November 2019 remain unchanged with A$6 million having to be spent by the end of March 2024 for Sumitomo to have a 60% interest.
Work will reportedly focus on the Trafalgar trend.
Recent drilling results from Trafalgar are pending.
As well as holding interests in about 2200sq.km of ground in the Mount Isa region, Hammer also holds ground near the Bronzewing gold project in Western Australia.
Hammer had about $10 million cash as of June 30, with fundraisings last quarter attracting $6 million at 9.5c per new share.
Shares in Hammer were trading this week at 7.7c, capitalising the company at $62.6 million.