CEO Luis Tondo said the latest results exceeded expectations "on many fronts", including the above-mentioned longest intersect yet in Phase II and the highest grade intercept from Phase II of 20m at 3.7% copper.
"And finally, most satisfying of all, we can report an estimated 44% increase in the area of the mineralised zone to an enlarged 1,200m northwest to southeast strike length and 600m northeast southwest width, and it still remains open to the north and south," he said.
"The average depth of the oxidation zone is also believed to have increased from 100 to 130m."
The fully-funded Phase II drilling is targeting a resource update in the third quarter.
After finishing drilling at Atahualpa, the company plans to test the historic underground workings at Sorpresa 2km away, where Coro said sampling last month confirmed a new discovery.
The company sold its mothballed Berta mining operation in Chile last month to hone its focus on Marimaca's potential, which it describes as having an initial 76 million tonne resource at 0.51% copper.
Coro said it had US$15.5 million in cash at the start of December.
Its shares rose 11.76% yesterday to C9.5c, towards the upper end of its 52-week range of 4.5-12.5c, capitalising it at $138.3 million.