Deep Copper at Blue Rose Needs Its Own Proof, Not the Shallow Grades

• Cobra Resources has completed diamond drilling at the Blue Rose prospect, and the chemistry recovered from that drilling indicates that the deep copper zone and the shallow skarn are two separate alteration systems.
• The shallow intercept of 86 meters (m) at 0.60% copper and 0.14 grams per metric ton (g/t) gold from 18 m groups with serpentine and chlorite, a retrograde assemblage.
• Readings taken through one diamond hole over an interval of 0 to 321 m group with phlogopite and albite, a prograde assemblage carrying only a minor retrograde overprint.
• Three porphyry indicators were logged in the core: more than 50 m of hydrothermal breccia, large anhydrite veining, and copper-potassic mineralization at depth.
• Diamond drill results and a September step-out drill program are the next two tests of the deeper zone, with results targeted for the third and fourth quarters of 2026.

What Has Happened

The chemistry Cobra Resources (LSE: COBR) recovered from its completed diamond drilling at Blue Rose describes the deep copper zone and the shallow skarn as two separate alteration systems. Blue Rose is one of the prospects in the Manna Hill copper project in South Australia, where drilling to date has concentrated on shallow, high-grade skarn material.

Portable X-ray fluorescence (pXRF) readings taken through one diamond hole over an interval of 0 to 321 meters (m) group with phlogopite and albite, a prograde assemblage formed as the system heated. The shallow intercept of 86 m at 0.60% copper and 0.14 grams per metric ton (g/t) gold from 18 m groups instead with serpentine and chlorite, a retrograde assemblage formed as it cooled. Copper mineralization at depth is associated with increasing potassic alteration, a change in chemical and geological control compared with the shallow calc-silicate-hosted mineralization. Assays from the diamond program have not been reported. 

Two Alteration Assemblages at Blue Rose

The two assemblages are separated by the proportions of potassium, aluminum, and magnesium in the sampled material, plotted against mineral fields that include potassium feldspar, muscovite, albite, phlogopite, and the serpentine-chlorite pair. Each plotted point is sized by its copper content, so the metal and the alteration chemistry hosting it are read from the same diagram. The shallow readings cluster in one part of that diagram and the deep readings in another, with chlorite and serpentine appearing in the deep set only as a minor overprint.

In the geological model built from this drilling, the deeper zone is a copper-potassium system and the shallower one a copper-magnesium system, with normal faulting between them acting as fluid pathways. Diorite and dacite porphyry intrusions occupy the center of the model as the interpreted heat source, with a copper-depleted potassium-rich zone above them, chalcopyrite and bornite enrichment in potassium-rich rock alongside them, and an outer alteration halo on the flanks. Multiple alteration overprints are recorded across the same section, and the model supports a preserved, scalable porphyry source. 

Managing Director and Chief Executive Officer of Cobra Resources, Rupert Verco, describes the mineral that changes as the drilling moves into the potassic zone:

"And in this potassic alteration halo, we see a change in that copper mineralization or speciation from chalcopyrite to bornite."

That shift from chalcopyrite to bornite was logged as bornite mineralization from 220 m to 257 m in one diamond hole, with coarse chalcopyrite in potassium-rich rock at 195 m in the same hole and calc-silicate rock with chalcopyrite at 186 m above it.

What the Shallow Grades Do and Do Not Predict

The shallow intercepts describe the skarn, and the chemistry now marks off that rock from the zone beneath it. Drilling at Blue Rose in January 2026 returned 86 m at 0.60% copper and 0.14 g/t gold from 18 m, 74 m at 1.02% copper and 0.25 g/t gold from 70 m, 62 m at 1.0% copper and 0.08 g/t gold from 62 m, 22 m at 0.8% copper from 20 m, and 56 m at 0.34% copper from 34 m, reported in March and April 2026 across an estimated width of around 70 m. That program supported extensions for primary mineralization at depth and along strike.

The shallow system is extensive along the same corridor. The drilled section runs for 1.6 kilometers, and the intervals recorded along it include 22 m at 0.5% copper, 6 m at 0.77% copper, 26.7 m at 0.43% copper, and 23.25 m at 0.22% copper. A remnant magnetized anomaly to the west of the drilling and a resistivity anomaly beneath its central holes are both mapped on that section. The diamond hole drilled beneath those intercepts tested their depth continuity, and sulfide mineralization in the zone is recorded to a depth of 300 m. None of this material supplies a grade for the zone that the chemistry has separated out. 

Verco puts a limit on what core logging can settle before the laboratory reports:

"Whilst I need to be cautiously optimistic on visual observations, we're pretty excited about what we'll see."

Assay results would give the deeper zone the grade record that the pXRF readings and the core photographs cannot supply.

The Structures Standing In for Assays  

Three structures were logged in the diamond core, and each indicates proximity to a source of mineralizing fluid without measuring any copper grade. More than 50 m of hydrothermal breccia was logged in one hole over an interval from 350 m to 402 m. Anhydrite veining was logged in a second hole from 190 m to 220 m. The third indicator is the copper-potassic mineralization at depth, and together the three form the basis for the current interpretation of a deeper porphyry core.

The anhydrite is indicative of the sulfate, oxidizing fluids of a porphyry system, so its place in the model is as a marker of what carried metal into the skarn rather than as a host of metal itself. 

Verco distinguishes the anhydrite's own metal content from what its presence indicates:

"Now these things are not generally mineralized, but they're very important because they are the source of mineralization that's coming into that skarn." 

None of the three structures yields a copper number, so the grades from this program still depend on the laboratory assays that are still outstanding. 

Broader Context 

Blue Rose is one prospect on a landholding in the Nackara Arc of South Australia, a known porphyry province. The state's copper deposits include Olympic Dam, Prominent Hill, Carrapateena, Oak Dam West, Kalkaroo, Hillside, and Kanmantoo, grouped by size into three bands: more than 1 million metric tons of copper, 500,000 metric tons to 1 million metric tons, and 100,000 to 500,000 metric tons. The Manna Hill project contains multiple underexplored prospects across several exploration licenses, and Cobra Resources is targeting large-scale copper discoveries there. 

Skarn-hosted copper at the surface and porphyry-style mineralization at depth are both present on that ground. Blue Rose and the adjacent Neptune Rose are classified together as skarn and porphyry, and together they hold an intersection of 47 m at 2.2% copper and 0.78 g/t gold from 11 m alongside a 132 m interval at 0.5% copper. The inventory for the two prospects also includes 41 m at 1.6% copper, 48 m at 0.8% copper with 1.01 g/t gold, and 78 m at 0.4% copper. Netley Hill and Anabama are classified as porphyry prospects: Netley Hill from a 350 m intersection at 0.1% copper, and Anabama from a 27 m intersection at 0.2% copper.

What to Watch Next

Two pieces of work would test the deep chemistry. Results from the diamond drilling are targeted for the third and fourth quarters of 2026, and a September step-out drill program to test the Blue Rose skarn and two other porphyry systems follows in the same period, with drilling at Anabama and Netley Hill in the fourth quarter of 2026. The step-out work is a reverse-circulation program.

Two further porphyry targets have been defined from state radiometric datasets and not from drilling. Welsh Prince is described by a non-coincident thorium-uranium anomaly, and Round Hill by a uranium anomaly with copper at the surface, with the anomalism interpreted to be associated with hydrothermal alteration. Drilling of regional targets is placed in the first quarter of 2027 and again in the third and fourth quarters of 2027, behind heritage clearance work in the fourth quarter of 2026 and a second phase in the second quarter of 2027, and a soils survey and geophysics program running from the fourth quarter of 2026 into the second quarter of 2027.    

FAQs (AI-Generated)