An independent report commissioned by Chatham Rock Phosphate has estimated the company's stock could be worth between $1.87 and $2.29 a share.
Edison Research says the valuation depends on Chatham Rock Phosphate attracting $US10 million of investment it is seeking.
The company's share price was three cents higher at 26 cents at midday on Thursday.
Edison says the drivers of the valuation are the rock price, foreign exchange movements and mining costs.
The research house says doubts over the technical viability of the project have reduced significantly with major global dredging company Royal Boskalis taking a cornerstone 20% stake in Chatham Rock.
Chatham Rock, which wants to mine phosphate on the seafloor on the Chatham Rise for use as a fertiliser, is also seeking to list on the Toronto Stock Exchange.