PhosCo Ltd (ASX:PHO) is primarily known as a phosphate developer, so the headline from its wholly owned Simitu Project in northern Tunisia today deserves a second read. Rock chip samples from the King’s Eye prospect have returned copper grades up to 21.3%, silver grades up to 100g/t, and zinc grades that exceeded the 30% upper detection limit of the assay method across six samples. Those are not marginal exploration results.
The important context for investors is what these surface samples actually represent. Rock chip sampling is selective by nature, meaning the grades reflect the richest material visible at surface rather than a representative average across the system. PhosCo has been explicit about that caveat. The significance of these numbers is not that they define a resource, but that they confirm high-grade polymetallic mineralisation is present and warrant systematic follow-up work across a corridor the company describes as extending over 30 kilometres.
PhosCo picked up the Simitu project as a first-mover opportunity in an underexplored region of northern Tunisia, and King’s Eye is just one of numerous prospects within the permit. The company’s flagship Gasaat phosphate project remains the primary focus, but Simitu is emerging as a genuine secondary asset with its own exploration upside. Given the scale of the permit area and the historical mining evidence at surface, the investment question is now whether the geophysics at depth confirms a system worth drilling.
We recently published a research note on PhosCo and what the future could look like for the company.
Why the IP Anomaly Below 100 Metres Is More Significant Than the Surface Grades
The rock chip samples are eye-catching, but the more analytically important data point from this announcement is the induced polarisation survey result. IP is a geophysical technique that measures the capacity of the subsurface to store electrical charges, which makes it particularly sensitive to the presence of sulphide minerals even at concentrations too low to show up on resistivity surveys alone.
On Section 4 of the geophysical survey, the IP chargeability signal increases sharply below 100 metres depth and shows what the company describes as a hanging apophysis, meaning the anomaly is intensifying and opening outward at depth rather than closing off. Combined with the ERT resistivity profiles that successfully mapped the historical underground workings at a shallow depth of around 40 metres, this creates a picture of a copper sulphide system that has been mined only at its shallowest expression.
Historical production at King’s Eye ran from 1962 to 1970 and extracted material only to about 40 vertical metres. The IP signal pointing to mineralisation below 100 metres represents genuinely undrilled ground in a system that has already demonstrated it can carry high-grade copper, silver, and antimony. That is the exploration target PhosCo is now aiming to test.
Two Mineralisation Styles Across a 30km Corridor Add Scale to the Opportunity
PhosCo has identified two distinct styles of mineralisation at King’s Eye that appear to represent separate geological events. The copper-antimony-silver suite occurs as fracture-filling veins and replacement bodies in Aptian limestone, and is interpreted as an earlier high-temperature hydrothermal event potentially linked to deep-seated igneous activity. The zinc-lead oxide mineralisation is a separate system consistent with Mississippi Valley Type deposits, which form from lower-temperature brines migrating through carbonate units near tectonic disconformities.
The practical implication for investors is that Simitu is not a single-target project. The 396 square kilometre permit covers a mineralised corridor along the Medjerda Thrust Zone, a structural setting that hosts multiple polymetallic prospects across northern Tunisia, Algeria, and Morocco. King’s Eye is the most advanced prospect with the best current data, but PhosCo has flagged several other targets within the permit that have not yet been sampled systematically.
The Investors’ Takeaway for PhosCo
PhosCo is at a genuinely early stage with Simitu. No drillholes have been completed, no resource has been defined, and the assay results from this program are selective samples designed to characterise the mineralisation rather than define grade continuity. Investors should position this announcement as a successful first-pass result that justifies moving to the next stage of exploration, not as evidence of a defined deposit.
The milestones that matter from here are the design and execution of a follow-up drilling program targeting the IP anomaly below 100 metres at King’s Eye, further systematic sampling across the broader Simitu corridor to test whether King’s Eye-style mineralisation repeats at other prospects, and any resource definition work that follows positive drill results.
The risk profile is typical of early-stage exploration. Selective rock chip grades rarely translate directly into drillhole intersections of equivalent continuity, and the geophysical anomaly at depth could reflect clay-rich alteration rather than economic sulphide mineralisation. PhosCo carries its Gasaat phosphate project as the value anchor, which gives it a dual-asset structure that slightly de-risks the Simitu exploration spend. Investors can follow more coverage of ASX resources and mining names at stocksdownunder.
Pitt Street Research Directors owns shares in the company discussed. This article reflects personal views and is not financial advice.
