Assays the most recent holes drilled at Whundo, in Western Australia's Pilbara, were described as confirming the presence of "broad, mineralised zones with variable high-grade intercepts".
The company labelled the results as "exceptional", with assays such as 32m at 2.43% copper from 75m, including 7m at 7.83% copper, 0.64% zinc and 0.26 grams per tonne gold.
Another hole returned 62m at 1.12% copper, 1.36% zinc and 0,.36gpt gold from 90m.
But, perhaps most exciting, the deep drilling delivered 10m at 2.85% copper and 0.96% zinc from 162m.
Past work has been limited to 150m.
The data suggests the mineralisation continues below the current resource, with the high-tenor grades persisting, and evidence for two new mineralised horizons emerging.
The drilling was mainly focused along the northern margin of the known Whundo resource, looking for down-dip mineralisation and a potential deeper mirror.
Prior drilling by Fox Resources, testing a nearby Whundo-style deep conductor in 2006, returned 5.8m at 2.4% copper, 0.6% zinc and 7.6gpt silver from 391m, which GreenTech sees as more evidence the Whundo area likely hosts a cluster of VMS style copper-zinc deposits that can continue at depth.
The known Whundo and Ayshia deposits contain combined resources of 3.6Mt grading 1.2% copper and 1.4% zinc for 93,000t of contained metal.
Executive director Thomas Reddicliffe said the results confirmed that Whundo was at the core of broader mineralised system that now carried notable gold grades, peaking at 3.36gpt suggesting valuable by-products could be generated along with the high-grade copper. Cobalt could also be recovered.
A resource upgrade for Whundo is planned once all assays are in.
The area last saw mining activity in 2006 with the Whundo open pit.
While drilling at Whundo was promising, five RC holes testing electromagnetic conductor and magnetic targets within the Whundo trend failed to return significant mineralisation and remained unexplained.
Downhole surveys are planned.
The pair share a number of projects, with Whundo, 40km south of Karratha, being GreenTech's flagship.
GreenTech recently secured 100% ownership of Whundo. The pair will next drill the nearby Osborne prospect within the Andover Intrusive Complex.
Shares in GreenTech were up 129% in morning trade at 32c, valuing it at $14 million.
The stock has traded at 12.5-42c since listing.