A series of high-grade intersections gathered from over 50 years of exploration at the Oracle Ridge underground copper mine in Arizona have given current owner Eagle Mountain Mining (ASX: EM2) reason to further investigate the size and grade of the mineralisation.
The mine’s existing dataset includes 618 drill holes for a total 76,000m drilling and over 11,000 assays, which have delineated multiple zones of high-grade copper mineralisation, along with significant gold and silver.
Eagle Mountain said it sees “significant value” in defining the zones of higher-grade mineralisation to support future mining studies and will incorporate the results into a planned update of the project’s mineral resource estimate.
New exploration work will focus on an area of the mine informally known as Block 12, where copper grades are, on average, higher than the rest of the orebody.
Previous results from this block have included 7.7m at 5.11% copper, 0.72 grams per tonne gold and 55.83g/t silver; and 5.2m at 6.44% copper, 0.22g/t gold and 62.9g/t silver.
Eagle Mountain chief executive officer Tim Mason said Block 12 would be a priority drill target for potential extension of the mineralisation at Oracle Ridge.
“The geology in this area is less well-known and interpretation from previous operators at Oracle Ridge did not connect this high-grade intersection with other orebodies,” he said.
“Our technical team will also be working on a detailed structural and geological model as 2D maps were compiled by previous owners but no attempt was made to create a mine-scale structural model.”
He said the company would digitise additional information such as lithology and alteration for over 400 drill holes not included in the existing database.
The updated models will assist in understanding the geological controls of the mineralisation and the assessment of potential exploration targets.
The Oracle Ridge mine sits within Arizona’s highly-prospective Laramide belt, 26km from BHP’s (ASX: BHP) San Manuel mine which was once the largest underground mine in the US.
The project comprises five skarn zones believed to have been formed during the Laramide period when most of the region’s copper porphyry deposits were created.
An influx of solutions from a nearby intrusive is believed to have been responsible for altering the pre-existing limestone into skarn and then depositing copper, gold and silver minerals.
Mining at Oracle Ridge ceased in 1996 and there has been no modern exploration or drilling beyond the defined resource estimate of 11.7 million tonnes at 1.57% copper, 17.47g/t silver and 0.18g/t gold.
Eagle Mountain acquired 80% of the project last November for $765,000 cash upfront with another $9.79 million to be paid on delayed terms.
The project has been classed an “advanced stage opportunity”, with 18km of underground development and significant exploration upside.
At the time of the acquisition, Eagle Mountain said it planned to commence a significant resource expansion exploration program beginning with the consolidation of existing data.
It also aimed to locate the source of the existing skarn mineralisation.
“Copper skarn mineralisation is commonly associated with porphyry systems,” Mr Mason said.
“However the location of the potential porphyry system at Oracle Ridge is not known and will be a key focus for us over the coming months.”
At midday, shares in Eagle Mountain were up 14.81% to $0.155.