The Australian Mining Review - - FRONT PAGE - TONY BELPERIO

Minotaur Ex­plo­ration has al­ready had sig­nif­i­cant suc­cess at its Eloise joint-ven­ture with OZ Min­er­als 60km south­east of Clon­curry in QLD thanks to its tar­get­ing of a rel­a­tively un­known style of de­posit called Iron Sul­phide Cop­per Gold (ISCG). As drilling con­tin­ued into the Jeri­cho cop­per-gold sys­tem at the end of 2018, Amy Blom spoke with Minotaur ex­ec­u­tive di­rec­tor busi­ness devel­op­ment Tony Belperio about the ben­e­fits of tar­get­ing ISCG de­posits, re­cent re­sults from Jeri­cho, and plans to roll out the ex­plo­ration model else­where. Q. Minotaur Ex­plo­ration has achieved a break­through based on a new de­posit style called ISCG. What led to Minotaur’s de­ci­sion to tar­get this par­tic­u­lar style of de­posit?

His­tor­i­cally, Minotaur has been ex­plor­ing for Iron Ox­ide Cop­per-Gold (IOCG) de­posits, as ex­em­pli­fied by Prom­i­nent Hill in South Aus­tralia and Ernest Henry in the Clon­curry district, for more than 20 years.

IOCG is a cop­per-gold de­posit style in which the dom­i­nant host gangue is iron in the ox­ide form – mag­netite and/or haematite.

About 10 years ago, as part of our ex­plo­ration ef­fort north of Ernest Henry, our ge­ol­o­gists be­gan en­coun­ter­ing high iron sul­phide (pyrite-pyrrhotite) ver­sions in and around its IOCG tar­gets.

Tri­alling of var­i­ous elec­tri­cal geo­phys­i­cal method­olo­gies al­lowed us to track this iron sul­phide – bear­ing vari­ant (named Cor­morant) for many kilo­me­tres – more than 10km – un­der cover.

It was the re­al­i­sa­tion that this ISCG sys­tem could be as large as, and con­tain as much iron as, a typ­i­cal IOCG sys­tem, al­beit stretched over many kilo­me­tres and re­spond­ing dif­fer­ently to the ex­plo­ration tolls be­ing utilised, that lead to the de­ci­sion to fur­ther tar­get this style di­rectly.

Q. What are the pro­cesses in­volved in tar­get­ing ISCG and how do they dif­fer from the pro­cesses used to tar­get the more com­monly known IOCG style of de­posit?

The key ac­cepted tools for IOCG ex­plo­ration un­der cover are grav­ity and mag­net­ics.

These re­spond to the den­sity con­trast caused by a large mass of haematite and/or mag­netite to its mag­netic prop­er­ties.

The ISCG style is char­ac­terised by sim­i­larly large quan­ti­ties of iron, but with the iron in a re­duced sul­phide form, prin­ci­pally as pyrrhotite.

A key char­ac­ter­is­tic of pyrrhotite is that it is one of the most elec­tri­cally con­duc­tive of min­er­als, so that elec­tri­cal geo­physics be­comes a key tar­get­ing method­ol­ogy.

In ad­di­tion, the ISCG style of min­er­al­i­sa­tion ap­pears to be less mag­netic – even non-mag­netic – and more tab­u­lar, fol­low­ing lin­ear struc­tural weak­nesses in the crust com­pared to di­a­treme, like brec­cia bod­ies of IOCG de­posits.

This makes ISCG de­posits less likely to be de­tectable by re­gional grav­ity and mag­netic meth­ods.

Con­versely, the high con­duc­tiv­ity of the mas­sive pyrrhotite host makes elec­tri­cal meth­ods a pre­ferred tool.

In this re­gard, re­cent tech­no­log­i­cal ad­vances in elec­tri­cal geo­phys­i­cal meth­ods, in­clud­ing air­borne EM, VTEM, B field EM and Squid EM are an added in­cen­tive, par­tic­u­larly where ex­plor­ing un­der con­duc­tive cover.

Q. What were the re­sults of adopt­ing the ISCG model?

Minotaur made the con­scious de­ci­sion in 2013 to tar­get the Eloise area, sur­round­ing the pri­vately-owned Eloise cop­per-gold mine as this was the best known com­mer­cial ex­am­ple of an ISCG de­posit at that time.

The Eloise un­der­ground min­ing op­er­a­tion has ex­tracted more than 10 mil­lion tonnes (mt) to date at a grade of 2.2 per cent cop­per and 0.9 per cent gold.

The greater Eloise area, be­ing un­der al­most com­plete cover, al­lowed for both re­gional screen­ing us­ing air­borne EM tech­nolo­gies, where cover was less than 50m, and di­rect tar­get­ing of re­gional struc­tural con­duits us­ing deep pen­e­trat­ing ground EM, where cover thick­ness was greater.

Each of these tech­nolo­gies proved suc­cess­ful in their own right with suc­ces­sive cop­per-gold dis­cov­er­ies at Artemis in 2014, Iris in 2016 and Jeri­cho in 2017.

Q. Can you out­line the re­cent re­sults of drilling at Jeri­cho and what they mean for Minotaur?

Jeri­cho was dis­cov­ered 12 months ago un­der 50m of cover and just 3km to 5km from the Eloise mine.

With al­most no mag­netic ex­pres­sion to stim­u­late in­ter­est, the area had been ig­nored by pre­vi­ous ex­plor­ers de­spite its prox­im­ity to a well-en­dowed min­ing op­er­a­tion.

With 30 broadly sep­a­rated drill holes now com­pleted into the geo­phys­i­cally-de­fined tar­get, cop­per-gold min­er­al­i­sa­tion has been out­line along some 3.5km, J1, and 2km, JT, of strike ex­tent in two sub par­al­lel tab­u­lar bod­ies about 150km apart.

Of sig­nif­i­cance is that ev­ery drill hole to date into the con­duc­tive plate tar­gets mak­ing up J1 and J2 at Jeri­cho has in­ter­sected cop­per min­er­al­i­sa­tion.

An ac­cel­er­ated and more sys­tem­atic drill out is an­tic­i­pated in the new year, sub­ject to dis­cus­sion with joint ven­ture part­ner OZ Min­er­als, to more for­mally de­fine scale, grade, con­ti­nu­ity, and ex­tend of min­er­al­i­sa­tion.

Closer spaced track­ing of high grade in­ter­vals in each of J1 – for ex­am­ple 8.4m at 2.78 cop­per and 0.66 grams per tonne (g/t) gold, and J2 – 27m at 2.42 per cent cop­per and 07g/t gold – is an­tic­i­pated.

Q. How will Minotaur use its model to un­lock the po­ten­tial of other pro­ject ar­eas?

Jeri­cho, Iris, Artemis and Cor­morant are em­phatic proof of con­cept for the ISCG ex­plo­ration model.

They demon­strate that the ISCG style of min­er­al­i­sa­tion can be both large and high-grade, and the ISCG model should be con­sid­ered in par­al­lel with IOCG mod­els in ex­plo­ration/com­ple­men­tary ex­plo­ration tools need to be con­sid­ered and utilised.

Minotaur has been and con­tin­ues to eval­u­ate ar­eas with po­ten­tial for both styles, the High­lands pro­ject area re­cently ac­quired be­ing one such re­gion wor­thy of crit­i­cal in­ves­ti­ga­tion.

Like the Eloise area, High­lands con­sists of a known pyrrhotite cop­per-gold de­posit, Barbara, and wide­spread struc­turally con­trolled cop­per-gold oc­cur­rences.

Sys­tem­atic ex­plo­ration with an ap­pro­pri­ate ex­plo­ration tool box is re­quired.

Q. Any fi­nal thoughts?

It has been sug­gested that Jeri­cho may be the most sig­nif­i­cant cop­per-gold discovery in the Clon­curry re­gion since Ernest Henry in 1991.

Although I can’t pos­si­bly com­ment on size and grade, it is clear to me that the ISCG ex­plo­ration model has evolved rapidly and el­e­gantly, and is now de­liv­er­ing very tan­gi­ble re­sults, and we ex­pect many more.

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