Cohiba finding answers to surprising results in pursuit of potential Zambian-style deposit

This is the first in a two-part feature series.

This article is a sponsored feature from Mining.com.au partner Cohiba Minerals Ltd. It is not financial advice. Talk to a registered financial expert before making investment decisions.

For many junior exploration companies, the main question they often need to ask is around where funding might come from for their planned drilling activities.

For Cohiba Minerals (ASX:CHK), which has assets located in South Australia, Western Australia, and Queensland with a key focus on its Olympic Domain tenements in South Australia, the company is pondering something more profound.

Within the Olympic Domain tenements, Cohiba holds a ‘highly strategic’ tenement package in the world-class Gawler Craton comprising 8 exploration licences within the Horse Well (Pernatty B), Pernatty C, and Andamooka-Peninsula (Lake Torrens) areas.

The Gawler Craton is well-known to be prospective for iron oxide-copper-gold (IOCG) deposits.

Within Pernatty C, however, in its pursuit of a potential Zambian‐style deposit, Cohiba was somewhat caught off guard when the company encountered substantial intersections of zinc, lead, and silver. 

As such, for Cohiba, the main question it has been considering ever since is – What does this all mean?

As Chief Executive Officer (CEO) Andrew Graham explains, initially, the team was surprised by the assay results. Zambian Copper Belt (ZCB) style deposits are generally known for high-grade copper (Cu) and cobalt (Co) with lesser lead (Pb), zinc (Zn) and silver (Ag). 

Cohiba had no indication that the area where Pernatty C is situated might be so abundant for zinc, lead, and silver as at the time it was not targeting these important commodities.

“Our encounter with zinc, lead, and silver at our Pernatty C project was not from an attempt to make an IOCG discovery but rather to pursue the proposition that Pernatty C represents the best ZCB style play in Australia”

“Our encounter with zinc, lead, and silver at our Pernatty C project was not from an attempt to make an IOCG discovery but rather to pursue the aforementioned proposition that the Pernatty C area represents the best ZCB style play in Australia. Our original intent was to look for ZCB style mineralisation closer to surface but with no visual evidence of Cu-Co mineralisation it was decided to continue drilling to determine the source of the geophysical target. 

Whilst there is a lot of exploration being conducted in the Gawler Craton in relation to IOCG deposit styles we need to be reminded that this vast and complex structure contains a myriad of deposit styles such as intrusion-related Au, orogenic Au, supergene Fe, volcanogenic Pd-Zn-Ag, sedimentary-hosted Pb-Zn, epithermal, metasomatic deposits and more. To this end, nothing is unusual and nothing should be discounted from future investigation.”

Cohiba Map

A worthwhile pursuit

With many years of skin in the game in mining, the CEO says from a geologist’s perspective, Pernatty C in particular is presenting the company with an interesting opportunity. Any zinc-lead-silver discovery is worthwhile pursuing, however further investigation of the area is needed.

Graham explains: “Initially, I was surprised by the assay results as we had no indication that this area may be prospective for zinc, lead, and silver and we were not targeting these. In terms of what it could mean I would state that it is early days and 2 drillholes does not provide us with enough information to make definitive statements. 

“Initially, I was surprised by the assay results as we had no indication that this area may be prospective for zinc, lead, and silver”

We are in the process of reviewing all of the drill core in detail to extract as much information as possible before making any further exploration decisions. The outlook for zinc is good over the next few years and with the emergence of new zinc metal batteries its contribution to the green energy sector is looking very robust. The outlook for lead is also good with demand strengthening and prices looking like they will remain high. 

To this end any zinc-lead-silver discovery is worthwhile pursuing but with the understanding that we have encountered mineralisation at depth (>700m) and as such the grades and tonnage would need to support ongoing investigations at these depths.”

As the CEO notes, while this discovery looks interesting to be potentially prospective for zinc, lead, and silver, there are already some well-known zinc-lead deposits within the Gawler Craton and other emerging exploration targets, so it is not entirely unusual. 

“So, it is not unique but it is certainly interesting. The key issue for the company is to gain a solid understanding of the exact mineralisation style and what the implications of this will be for future investigations.”

Building an understanding of geology & structure 

Earlier in December, Cohiba announced significant zinc results from in-fill, follow-up assays for PSDDH01 at the Pernatty C project. The drill program (conducted from December 2021 to March 2022) tested the Tapley Hill Formation for ZCB sediment-hosted mineralisation, and to continue to drill to the Wallaroo Group basement for Copper Skarn or distal IOCG mineralisation. Geophysical magnetic and electrical conductivity anomalies were used to plan the drillholes.

Graham says the original target of high temperature chalcopyrite vein and IOCG related alteration and/or mineralisation was not encountered but significant mineralisation and assay results were obtained from low temperature calcite-sphalerite veins with zinc-lead silver association. 

The company will use these encouraging results to continue building its understanding of the geology and structure of this area with the intention of targeting further zinc-lead-silver mineralisation through a follow up program of work.

Graham adds: “These results showed zones of persistent low-grade zinc and silver with some shorter intersections of higher-grade zinc up to 5.28% and silver up to 13.3 ppm (g/t) similar to the previous results. PSDDH01 encountered zinc, lead and silver mineralisation at 735.2m and was variably mineralised to 1,088m which means the potential for mineralisation over a substantial stratigraphic width is very good. 

A number of the higher-grade mineralised veins were shown to exist as tension veins along bedding planes (strata-bound) which implies geological control to cluster veins, providing continuity and a target for further exploration which is definitely part of the company’s ongoing program of work.”

Zambian Copper Belt postulation gaining momentum

The Zambian Copper Belt (ZCB) accounts for close to half of the reserves of the Central African Copper Belt (CACB), which is the largest sediment-hosted, stratiform copper province in the world. As previously mentioned, ZCB-style deposits are generally known for ‘high-grade’ copper and cobalt, although there are lesser lead, zinc, and silver.

Graham says it is worth noting that just to the north-west of the ZCB (and within the CACB) the Kipushi deposit contains very high Zn, Cu, and Ag values.

“There has been considerable discussion amongst industry experts that the area around Pernatty C shares some strong similarities with Zambian Copper Belt style mineralisation”

“So, we know those metals can occur within this style of deposit. There has been considerable discussion amongst industry experts that the area around where Cohiba’s Pernatty C tenements are located shares some strong similarities with Zambian Copper Belt (ZCB) style mineralisation and could be considered the best ZCB-style play in Australia. 

The implications for Cohiba are considerable given that the basin setting around the Pernatty area has many similarities with the edges of the Katangan Basin which hosts world-class mines like the Chambishi Mine which according to its owners, China Non-Ferrous Metals has a remaining resource of 228 Mt @ 2.0% Cu.”

As the CEO notes, to have exposure to a Zambian‐style deposit means Cohiba would be in good company. He says groups such as the CSIRO and the Geological Survey of SA have done some excellent work in relation to sediment-hosted stratabound copper deposits in the Stuart Shelf, which he says has been most helpful. 

“I also think that DGO Gold (now acquired by Gold Road Resources) conducted some excellent work in this arena and had the foresight to engage ZCB experts such as Dr Stuart Bull (from CODES Key Centre, Tasmania) to assist them in their exploration efforts through a review of the historic data and drill core in the Stuart Shelf. No major discoveries have been made as yet but it is early days and the ZCB postulation is really just starting to gain momentum.”

Pernatty C worth the wait 

Two drillholes were drilled at Cohiba’s Pernatty C tenement from December 2021 to March 2022 but assay results were not received until the September quarter. The drillholes were co-funded by the Department for Energy and Mining in South Australia as part of the Accelerated Discovery Initiative (ADI) program. 

Wallaroo

The target of the drillholes was to test the Tapley Hill Formation for ZCB sediment-hosted mineralisation, and to continue to drill to the Wallaroo Group basement for Copper Skarn or distal IOCG mineralisation. Geophysical magnetic and electrical conductivity anomalies were used to plan the drillholes.

The project is located in an area of current and historical mineralisation 40km south of Oz Mineral’s (ASX:OZL) Carrapateena IOCG copper mine, 13 south-east of the historic Mt Gunson copper mine with mineralisation located at the base of the Whyalla Formation cover sequence, and 24km north-west of the Punt Hill copper skarn area. 

The nearest drillhole to basement is located 4.8km away to the south-east. 

The CEO says Cohiba recognises the challenges of the depth to basement and will further review the target with respect to a model with potential economic viability and feasibility to successfully explore the target. Given the strong metal grades, an increase in vein stockwork intensity and continuity over thickness and strike length would be sufficient to create a significant deposit, he adds.

In part two of this series, Graham explains that while understanding the abundance of zinc, lead, and silver Cohiba seems to be finding at the Pernatty C tenement, there are also knowns within its overall portfolio.

He says questions over Zambian-style deposits are being asked by the company, but what is already known is that Cohiba’s Olympic Domain tenements in the Gawler Craton are in a region well-known to be prospective for IOCG deposits.

With questions being asked, and answers being found, the outlook for 2023 is looking clearer by the assay for Cohiba.

Write to Adam Orlando at Mining.com.au

Images: Cohiba Minerals Ltd & iStock
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Written By Adam Orlando
Mining.com.au Editor-in-Chief Adam Orlando has more than 20 years’ experience in the media having held senior roles at various publications, including as Asia-Pacific Sector Head (Mining) at global newswire Acuris (formerly Mergermarket). Orlando has worked in newsrooms around the world including Hong Kong, Singapore, London, and Sydney.