Mineral explorer Manhattan Corporation (ASX: MHC) has returned the highest intervals of copper ever intersected at the large-scale Joshua project in Chile, during a 3000 metre drilling program to expand the known extent of the project’s copper-bearing porphyry system.
The intervals were returned from a newly-identified, strongly-altered hydrothermal breccia and demonstrate the grade potential and prospectivity of the Joshua system.
Best assays included 16 metres at 0.51% copper from 546m, within 30m at 0.36% copper from 544m, constituting the highest interval intersected on record.
The company said 56% of assays from that hole are still being processed.
Drilling also intersected over 100m of molybdenite-bearing quartz veins in strongly-silicified dacite porphyry, indicating a “hotter” part of the system and, for the first time, the presence of a molybdenum-mineralised porphyry intrusion.
Elsewhere during the program, Manhattan intersected broad zones of breccia-hosted copper mineralisation, with best assays of 262m at 0.15% copper from 46m, including 70m at 0.21% copper from 238m.
Large, high grade system
To date, the company has drilled 2500m of the total 3000m program designed to test high-priority geophysical and geological targets at Joshua, with a fifth hole currently in progress to test between the molybdenum-rich porphyry and hydrothermal breccia zones.
Manhattan said the program has proven Joshua to be subject to multiple mineralising porphyry events, with the overall system being significantly larger and higher-grade than the area drilled previously.
“Our understanding of the metal associations and metal zonation trends within the Joshua system have improved considerably throughout this program,” said Manhattan non-executive director Marcello Cardaci.
“This has led to a more robust geological model for targeting higher copper grades within a broader zone of sulphide mineralised breccia [and is] an important development for more effective planning of future drill holes.”
Heads of agreement
The Joshua greenfield porphyry copper project was discovered by Helix Resources (ASX: HLX) in 2011, after which only 16 holes – or less than 5% of the system – were drilled with intercepts including 352m at 0.27% copper, 240m at 0.22% copper and 400m at 0.25% copper.
In mid-2018, Manhattan entered into a three-stage heads of agreement with Helix to drill test the project and earn a staged equity.
Under the terms of the agreement, Manhattan can earn a total 80% equity in Joshua (split over two earn-ins) by carrying out a total 8000m of diamond drilling including a high-resolution aeromagnetic survey over the entire alteration system, and completing a bankable feasibility study for the project.
The current 3000m program is part of the first stage and minimum commitment, with Manhattan sole-funding the $1 million spend.
Stage 2 will give Manhattan the right to earn an initial 51% equity by funding an additional 5000m of drilling.
Stage 3 will comprise the BFS and give Manhattan an opportunity to earn the remaining 29% equity.
Helix will be free-carried through to BFS stage, and has committed to retaining its in-country exploration team to manage drilling.
In the event Helix chooses not to contribute to the joint venture after the completion of the BFS, it will dilute its interest in exchange for an uncapped 1.0% net smelter return royalty over the project.
Helix said the agreement with Manhattan allows it to focus on advancing the high-grade Collerina copper project in New South Wales, while retaining an exposure to a potentially-significant porphyry copper project at a time when the copper market is supply-constrained.
The broad alteration response at Joshua is believed to be similar to the Andacollo copper-gold mine located 45 kilometres to the north-northwest and operated by Canada’s Teck Resources.
The project’s porphyry complex consists of multiple intrusive events with andesite, diorite and dacite compositions identified in mapping and drilling to date.
Joshua is located on an east-northeast trending transfer zone on a northwest lineament, considered an “excellent structural setting” for porphyry-style systems in Chile.
A recent technical review of the project area identified “new and exciting” drill targets with potential higher-grade zones which, if discovered, could lead to a significant economic copper porphyry deposit discovery.
At mid-afternoon, shares in Manhattan Corporation were up 40% to $0.007, while shares in Helix Resources were trading 3.23% higher at $0.032.