Copperhead showing prospectivity along mineralised structural corridors
Copperhead is an undeveloped, large-scale porphyry copper prospect located close to the central Queensland coast and lies within a belt of porphyry copper deposits. Five (5) diamond drill holes have been drilled at Copperhead by previous explorers, with all five holes encountering chalcopyrite and pyrite throughout each hole. Two of these holes are 300m deep, indicating a potentially large mineralised target.
Under its historical name of “Julivon Creek”, Copperhead is included in the Global Mineral Resource Assessment by the United States Geological Society (USGS) in its “Porphyry Copper Assessment of Eastern Australia” Technical Paper dated 2014. Copper mineralisation remains open in all directions.
Auger sampling at Copperhead has delineated a 3km x 2km copper anomaly. This zone contains a 2,800m x 800m core anomaly, which has a peak result of 0.22% Cu. Subsequent diamond drilling was focussed at the western section of the auger anomaly.
Each of the 5 diamond drill holes completed by Carpentaria encountered visible chalcopyrite, molybdenite and pyrite and mineralisation remains open. Additional auger sampling is required to fully define Copperhead’s surface geochemical anomaly.
Additional drilling is required to delineate the length, width, and depth of the inferred porphyry system. Results from a recent helicopter-supported aeromagnetic survey (December 2020), suggests that the mineralised zone could potentially be 5km long and 3km wide.
Copperhead provides opportunity for Rockfire to estimate an impressive JORC resource and potential exists to define a large-scale porphyry copper deposit.
The multiple events producing rock variations ranging from granite to gabbro is testimony to the multi-phase geological episodes which are favoured precipitation settings for metals. These multiphase intrusions require detailed mapping and sampling to highlight the potential that lies within this tenement.
A series of north and northwest-striking faults represent a regional structural corridor which is highly prospective for gold and copper mineralisation and recently confirmed by the aeromagnetic survey. The structural complexity of the Copperhead project provides opportunity for rotation and dilation of the rocks to allow percolation of mineralised fluids. This extensional regime is ideal for large-scale porphyry copper emplacement.
Copperhead was initially explored by CRA Exploration in 1963/64 during regional exploration of the Normanby Goldfield, which lies 7 km to the west. This regional work (comprising 1,100 stream drainage samples) identified the Copperhead area by outlining strongly anomalous results over a very large area. Background copper values were 2ppm Cu, whilst the streams draining Copperhead included values of 270ppm, 215ppm, 190ppm, 170ppm and 150ppm copper.
Carpentaria Exploration followed up with further drainage sampling in 1970. Drainage background levels were again found to be low level (10-15ppm Cu) whilst the area immediately draining Copperhead returned strongly anomalous assays of 410ppm, 250ppm, 190ppm and 135ppm copper. Fortuitously, in January 1970, Cyclone Ada caused severe flooding in the region and the heavy rains washed out dense undergrowth from the tributaries of the Andromache River.
Subsequent work showed that Julivon Creek (the stream draining Copperhead) had a large number of mineralised (chalcopyrite, pyrite, molybdenum) shears for at least half its length. It was due to Cyclone Ada that Copperhead was discovered! In 1972, Carpentaria Exploration drilled 5 drill holes and the results from this drilling are unique in that every hole intersected copper mineralisation for its entire length.
The year 1988 also saw WMC complete more stream drainage sampling north of Copperhead. This sampling proved that streams draining towards the north off the range hosting Copperhead were also anomalous in copper and molybdenum. In this exploration program, streams draining Copperhead returned assays of 45ppm, 50ppm and 60ppm Cu (from a low level background of 10ppm Au) and 3,600ppb, 2,100ppb and 2,000ppb Mo (from a low level background of 200ppb Mo). An anomalous rock sample of 55g/t Ag was also collected north of Copperhead, close to the headwaters of Wild Creek. Importantly, these north-flowing tributaries indicate that the geochemical anomalism associated with Copperhead is wide open towards the north.
Costain Australia re-logged and sampled the original drill core from the 1972 Carpentaria drilling. Owing to previous exploration excluding gold analysis, in 1989 the core was selectively sampled for gold. This work determined that there is no gold associated with the porphyry copper/molybdenum/silver mineralising system.
No work was completed in the immediate area surrounding Copperhead between 1989 and 2017, when Copperhead was granted to Rockfire’s subsidiary, BGM Investments.
DDH002 AND DDH005 cross-section looking west
DDH003 & DDH004 cross-section looking west
Mineralisation is typically pyrite- and chalcopyrite-filled fractures and veins with occasional molybdenite. Roadside cuttings display numerous limonite-filled fractures, with rock chip assays of the roadside cuttings returning assays similar to those in the drill core and soil geochemistry.
Subsurface mineralisation is confined to, and controlled by fractures and quartz veins. Pervasive hairline fractures are dominant annealed by chalcopyrite and pyrite filling, with numerous fractures/veins thickening to several centimetres. The copper mineralisation appears to be both spatially and genetically (syn/post) related to the pegmatite and aplite phases. Copper bearing veins are noted to overprint the pegmatite and aplite dykes, suggesting that the copper source is chronologically late and yet to be identified. Molybdenum mineralisation is less abundant than either chalcopyrite or pyrite but is essentially identical in its distribution.
In 1972, Carpentaria Exploration drilled 5 diamond drill holes with every hole intersecting copper mineralisation. The core was randomly sampled with a single 1m sample every 30m down hole, without any variation to this pre-determined interval. No geology, visible mineralisation, structure or veining was taken into consideration during this initial sampling episode.
Based on these random results, Carpentaria estimated a mineral resource in 1972 which does not comply with the JORC Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves (2012 Edition).
It is noted from the diamond drill logs that copper, molybdenum and silver mineralisation is observed in veins and veinlets and that little mineralisation is observed interstitially throughout the melt. This differs from a classic porphyry copper, where mineralisation is mostly located dispersed between and throughout the mineral grains. In this light, Copperhead is more akin to the Cadia-Ridgeway style of mineralisation, where the majority of mineralisation is hosted in veins, veinlets and fractures.
Chalcopyrite has a high ratio to pyrite, although diamond drill holes 3 and 4 appear to be slightly more pyritic. In 1989, Costain Australia re-logged and selectively sampled the original drill core and analysed for gold, copper, silver and molybdenum. This work boosted the overall copper grade and determined that there is no gold associated with the porphyry copper/molybdenum/silver mineralising system.