The company has given Viva shareholders until July 31 to execute the share transfers once due diligence concludes. However, Gold Mountain expects the acquisition to be completed prior to this date.
Viva has three exploration licences in Enga province, which are about 75km from Mt Hagen and 25km from the nearest commercial airfield with daily flights to Port Moresby.
These would boost Gold Mountain's PNG licence inventory, which includes its flagship Wabag Gold project, also in Enga province.
In addition to PNG, the company has gold tenements in New South Wales - Dalton, Grenfell and Cowarra, and Peru where it holds a minority interest in Goldsmith Resources SAC.
Earlier this month, it released positive stage two exploration results of the Crown Ridge prospect in PNG, where significant gold values were encountered in soil samples and stream sediment.
Exploration director Mathew Morgan said: "It is very encouraging to see that the Stage 2 follow up sampling results confirmed in the initial stage 1 highly anomalous assays and continue to support the current geological interpretation at Crown Ridge, with hydrothermal alteration and mineralisation associated with the eruption of a diatreme breccia."