ASX-listed Sunstone continues to hold about 71 million shares in Copperstone after the recent divestment totalling 82.5 million shares.
That equates of a circa 6.4% shareholder in Copperstone, with its original stake being about 30% when it sold a copper project in Sweden to the Stockholm-listed company in late 2018.
Sunstone's focus on Ecuador dates back to about the same period.
Earlier this month Sunstone said a ground magnetic survey at El Palmar "has identified an outstanding drill target with a classic porphyry signature".
A 2000m diamond core program was flagged to start this quarter.
Sunstone is led by well-credentialed exploration geologist Malcom Norris, previously associated with the world class Tujuh Bukit copper-gold discovery in Indonesia.
Sunstone started the current quarter with about $2.75 million cash.
Shares in Sunstone were unchanged at 1.9c in morning trade, capitalising the company at $42 million.
The stock is up about 200% over the past 12 months.
