By Salini Krishnan
Lodestar Minerals has reported copper, gold, cobalt and molybdenum mineralisation in its first diamond hole at the Three Saints project in northern Chile, saying the results support an iron oxide-copper-gold (IOCG)-style interpretation of the undercover system.
Hole L3SRD003 returned peak assay values of 0.77% copper, 0.38 grams per tonne gold, 449 parts per million cobalt and 190 parts per million molybdenum, according to the company’s ASX announcement.
The results provide geological support for further exploration, but they do not establish a mineral resource or demonstrate that the system is economically viable. Lodestar said the reported intervals are downhole lengths, with true widths not yet known.
First hole tests a covered Chilean target
Three Saints is located about 75 kilometres southwest of Copiapó in Chile’s Region III, within the Coastal Cordillera’s major copper-producing belt. Lodestar describes the project as a fully undercover target, with sand and gravel concealing the bedrock.
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The company holds the project through its subsidiary Tesoro Andes. Its Three Saints project page says the area lies within a broader IOCG province that includes major deposits such as Candelaria and Mantoverde.
L3SRD003 was drilled to a depth of 600 metres. Lodestar said anomalous copper and gold were identified from approximately 197 metres through to the end of the hole, where drilling finished in mineralisation.
The hole was designed to test an annular magnetic “negative” anomaly, or demagnetisation zone. The company said this type of geophysical response can be associated with both porphyry copper and IOCG-style systems where hydrothermal alteration has destroyed magnetite originally present in the host intrusive rocks.
Company-reported peak results
| Metal | Peak result reported by Lodestar | Reported context |
|---|---|---|
| Copper | 0.77% Cu | 0.42 metres from 373.27 metres |
| Gold | 0.38 g/t Au | Same 0.42-metre interval |
| Cobalt | 449 ppm Co | 1.69 metres from 410.37 metres |
| Molybdenum | 190 ppm Mo | 0.32 metres from 468 metres |
The peak copper and gold values occurred together in a silica-rich vein containing chalcopyrite, according to the company. The cobalt and molybdenum peaks occurred in separate intervals and should not be read as a single combined grade.
What the assays indicate
Lodestar said the drill core contains several mineralisation styles. These include copper, gold and iron associated with chalcopyrite, pyrite and magnetite; copper and molybdenum in quartz-rich veins; and later gold-bearing quartz veins.
The company interprets the copper-gold-iron association as consistent with IOCG-style mineralisation. It also described the mineralisation as structurally controlled, occurring in narrow corridors, veins, veinlets and hydrothermal breccias within tonalitic rocks.
The reported peak copper-gold interval was:
- 0.42 metres at 0.77% copper and 0.38 g/t gold from 373.27 metres
Other reported intervals included:
- 0.61 metres at 0.40% copper and 0.15 g/t gold within a broader mineralised corridor.
- 1.69 metres at 449 ppm cobalt, with only trace copper reported in that interval.
- 0.32 metres at 190 ppm molybdenum, accompanied by low copper and gold values.
- 2 metres at 623 ppm copper and 103 ppm cobalt from 596 metres near the end of the hole.
The results show that the metals are distributed across different parts of the hole and across several hydrothermal events. That pattern is relevant to geological interpretation, but it is different from demonstrating a continuous, mineable ore zone.
Copper-bearing drill core is examined during geological logging.
Why IOCG classification matters
IOCG deposits are generally defined by hydrothermal copper and gold mineralisation associated with abundant magnetite or hematite. They can also contain pathfinder elements such as cobalt, molybdenum, uranium, rare earth elements, nickel and arsenic.
In Chile’s Coastal Cordillera, IOCG systems commonly occur in Jurassic to Early Cretaceous volcanic, volcano-sedimentary and intrusive rocks. Mineralisation may be hosted by veins, breccias, mantos or broader replacement zones.
The combination reported at Three Saints : copper, gold, cobalt, molybdenum and iron-related alteration : is therefore compatible with the regional exploration model. Magnetite, biotite and actinolite alteration, together with chalcopyrite and pyrite, can provide additional support for an IOCG interpretation.
However, IOCG is a broad deposit classification rather than a grade threshold. No single copper, gold, cobalt or molybdenum value proves that a project contains an IOCG deposit.
The geological setting, mineralogy, alteration, structural controls, geophysics and distribution of metals must be considered together. Cobalt can be a useful pathfinder in some IOCG systems, while molybdenum may occur in IOCG-related or metasomatic events but is also common in porphyry copper-molybdenum environments.
That distinction is important at Three Saints because the company has identified more than one mineralising event. The presence of molybdenum in a quartz vein does not, on its own, determine whether the system is IOCG, porphyry-related or part of a broader hydrothermal system.
The limits of a first-pass drill result
The L3SRD003 assays are significant as a first test of a previously covered target. They confirm that the magnetic anomaly corresponds to a mineralised hydrothermal system at depth, rather than only a geophysical feature without confirmed metal content.
The evidence remains preliminary for several reasons.
First, the peak grades are narrow. The strongest copper-gold result covers 0.42 metres downhole. The reported peak cobalt and molybdenum values occur in separate intervals. The company has not yet established the true thickness of any mineralised zone because the drill hole was not oriented and the geometry of the structures remains uncertain.
Second, the reported results are not a resource estimate. Lodestar’s JORC disclosure states that the spacing and distribution of the drilling are insufficient to establish geological and grade continuity for a mineral resource.
Third, no metallurgical test work has been completed at Three Saints. Lodestar used recoveries from comparable Chilean deposits to calculate copper-equivalent values in its announcement, but those assumptions are not a substitute for project-specific recovery, mineralogy or processing studies.
Finally, the results come from one completed hole. A single hole can demonstrate mineralisation and help refine a geological model, but it cannot establish the size, continuity, orientation or economic value of a deposit.
Geophysical surveys help refine drill targeting across the covered exploration area.
Next steps focus on the system’s core
Lodestar said the broader geophysical anomaly extends more than 1.6 kilometres across and remains open laterally and at depth. The company interprets L3SRD003 as having tested an outer portion of the system rather than its potential core.
The next phase will involve detailed geological relogging of the hole, integration of assays from the second hole, L3SDD004, and reprocessing of the magnetic survey. Lodestar said the new drilling data will be used to calibrate the geophysical interpretation and identify higher-priority targets.
The company’s immediate exploration questions are:
- Can the narrow mineralised corridors be traced laterally and vertically?
- Does the magnetic and alteration pattern identify a stronger copper-gold zone at depth?
- Are the separate copper-gold, cobalt and molybdenum events part of one connected system?
- Can future drilling establish true widths and grade continuity?
Results from L3SDD004 are expected to provide another test of the target. Further drilling will be required before the project can be assessed through resource modelling, metallurgical work or development studies.
For the Chilean copper exploration sector, Three Saints is an example of how undercover IOCG targets are evaluated: geophysics identifies a possible system, drilling confirms mineralisation, and successive holes determine whether the geological model can support a coherent deposit.
Lodestar’s current results strengthen the case for continued exploration at Three Saints. They do not yet establish an economic discovery.
Iron-oxide alteration and copper sulfides are important features in IOCG exploration models.
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Sources
- Lodestar Minerals ASX announcement: Three Saints drilling confirms IOCG mineralising system
- Lodestar Minerals: Three Saints project
- Lodestar Minerals: Chile projects
- Andean IOCG research and geological context
- Skillings Mining Intelligence copper exploration coverage
- Skillings Mining Intelligence copper market coverage