A cold war of ideas centred on the possible origins of one of the world’s richest base metals deposits is entering into its fourth decade with fresh troops carrying the standard into battle.

The point of contention is simple enough. How did the Mount Isa deposit form? At issue are the assumptions drawn to mine its riches and discover the next deposit. 

There was abundant evidence to challenge decades-old truisms said University of  Adelaide Embedded Research Fellow Dr Richard Lilly.

Dr Lilly has worked with Mount Isa Mines for more than ten years and has been supported by the company to examine a theory that questions orthodox beliefs.

He asks did the world-class stratiform lead-zinc come first 1.6 billion years ago when the sediments were still muds, followed by the world-class copper system at a later date, which is the widely held view, or did the whole copper-lead-zinc system form at a later date, well after the sediments were originally formed?

“The implications for this are huge, because of course, if you were looking for lead-zinc that was formed only in that particular rock type you look for that particular rock type,” Dr Lilly said.

“If all of the economic mineralisation came during a later event then your exploration opportunities open up and you’d possibly be looking in some non-traditional rock types.”

When the ‘late’ timing of mineralisation alternative was first postulated in the 80’s and 90s, it was often hailed down said Dr Lilly. 

“… it normally stays pretty civil, but I think the emotions and the pride people put into their work, means sometimes it doesn’t. 

“I’ve experienced it myself because ironically, more than 20 years after the idea was published, I went back to university and I’ve come to the same conclusions as previous MIM geologists, who I think nailed it in the mid-90s’

“My work challenges the widely held view. I’ve been heckled at talks by people who say, ‘well, you know, we had all this discussion in the 80s and 90s and you were wrong then and you’re wrong now’. I think some of that community liken us to a noise that they wish would go away so as to retain the status quo.”

Mt Isa was one of the most famous and charismatic examples of where geoscience professionals held different views on the origin of ore deposit, said Dr Lilly. 

“Geology is a young discipline and our actual understanding of these deposits is always growing as we collect more data. Almost every ore has some pretty big question marks about how it formed.

“The bigger the ore deposit, the bigger the question marks and the bigger the potential prize for the team who unravel the story and discover the next deposit. 

“It’s these questions which drive me to continue to study ore deposits. Unfortunately, with most research, you might go in with the idea to answer one of these questions, but invariably you uncover even more questions that you then need to follow up.

“In my mind, in situations when you have two polarized arguments, the results are often that the answer lies somewhere in between.

“Because the evidence people quote is normally valid it is just that we’re maybe not finding that last missing piece to put the whole story together.”