Chatham Rock Phosphate is on track to raise $1 million in new capital from shareholders.
The company plans to mine rock phosphate under the sea from the Chatham Rise.
The share purchase plan closes at 5pm today, and shares will be alloted early next week.
CRP chief executive Chris Castle said the $1m support reflected three years of strong progress and the board was pleased with the response from shareholders.
The company's shareholder base had also risen from 300 in September to 430 now.
CRP holds a prospecting permit to develop an undersea rock phosphate resource, about 450 kilometres east of Christchurch.
The company was granted its prospecting licence in 2010, and since then it has increased its market value from $2.5m to $48m and raised $21m from investors.
The company applied for a mining licence last year.
CRP has three cornersone shareholders; Boskalis, Subsea Investments and Odyssey Marine. Last year, international dredging giant Boskalis took a 20 per cent stake in CRP, mainly as a prepayment for services
CRP plans to file its marine consent application by the middle of the year. It also aims to list on an overseas sharemarket.