The Mine Grid—a seemingly innocent practice that lobotomises mine and resource geologists

Unbelievable as it may sound, the following account is something that really happened. Only the names have been changed to protect the innocent.  

A mysterious gold deposit

Between 2004 and 2012, I ran Leapfrog software workshops for clients who had leased Leapfrog software. This meant I travelled to mine sites all over the world, teaching Leapfrog to exploration and mine geologists. My way of teaching doesn’t emphasise teaching the software because I consider that a secondary issue; instead, I believe it is more important for participants to gain important structural geological insight about the deposits they’re working on, so this was the emphasis in my workshops.

To maximise the drilling data that companies acquire at great expense, I believe it is essential to understand the structural control of deposits at the deposit-scale. This can be all worked out from studying the assay data using the basic principles of structural analysis that any undergraduate can understand. In my workshops, the geologists worked on interpreting and modelling their own deposits, but also on modelling deposits from other parts of the world so that they can gain varied experience.

At a particular gold mine I was visiting, I challenged the geologists to interpret and model an extensively drilled high-grade Anoroc gold deposit—a gold deposit that had been recently discovered in Saudi Arabia.

The students were surprised as they had not heard of this mysterious Anoroc deposit, but I could disclose that the deposit was owned by private equity firm funded by Saudi oil tycoons and was not commonly known.

So, we loaded the data into Leapfrog software and step-by-step I taught the geologists my way of structurally interpreting the deposit from the assay and lithology data and then applying the interpreted structural model to model the deposit. This special interpretation and modelling process is what I refer to as the ‘Outside-In’ method that I detail in my recent paper on the Sigma-Lamaque gold deposit in Quebec.

In the ‘Outside-In’ method, it is important to zoom back and look at the overall geometry of the entire mineralisation and interpret the broad grade patterns in terms of a structural architecture. It’s the type of interpretation that we do when we examine regional magnetic data, for example, and make inferences about the regional structural controls, but I do this using the drilling data of entire deposits, or a cluster of deposits.

The students (all professional geologists) and I took an entire day to interpret and model the Anoroc gold deposit. We all marvelled at the model we’d created and spun it around on the Leapfrog screen. One of the students exclaimed: ‘Wow, this is amazing. What a fantastic deposit and such clear structural controls!’

Someone else sighed and said: ‘I wish I was working on a fantastic deposit like this…’

At which point I asked everyone in class: ‘Don’t you recognise this deposit?’

A puzzled look appeared on the students’ faces. Someone laughed and said: ‘That’s a silly question! This deposit is from Saudi Arabia—of course we haven’t seen this deposit before!’

I told them: ‘This isn’t a Saudi deposit. Just spell the name of the deposit backwards and you’ll find out its true identity.’

A N O R O C spelled backwards is C O R O N A

‘Corona’ was the mine site I was visiting and where the workshop was taking place. (Okay, this isn’t the real name of the deposit, because I won’t reveal the actual mine site, but bear with me…)

Just imagine being one of those 15 geologists when you suddenly learn that you’ve been working on your own deposit all day and you hadn’t even recognised it!

If you’re wondering how I managed to pull off this illusion, read on…

A trick of the mind

I kid you not—this actually happened. In fact, it happened at two completely separate mines, two different continents, operated by two different top-tier international gold producers.

So, how did I manage to fool all these educated geologists?

I used a trick of the mind. I took advantage of a shortcoming of the commonly accepted mining workflow that I knew affected the perception of geologists, but that the geologists weren’t aware of.

The trick is set up like this. In my extensive travelling to various mine sites, I had observed that at any one mine site there may be several other satellite deposits being mined, with each pit having its own ‘mine coordinate system’, commonly referred to as the ‘mine grid’.

I won’t go into the history of mine coordinates here, but basically local mine coordinates are specific to an individual mine and allow block models to be more optimally aligned with local grade continuities for mining purposes. This is a good thing for mining; however, mining engineers gain at the expense of geologists because this seemingly innocuous practice effectively limits the geologist into thinking local and not beyond the confines of the local grid system. In this insular and myopic view, the state of other satellite deposits isn’t something they ever think about. Sadly, many resource geologists operate in this way.

How I prepared the ‘Anoroc’ deposit

When I arrived at this ‘Corona’ mine, I noticed that six deposits were being mined, all with separate mine coordinate systems. A mine geologist might be responsible for several deposits, but not all of them; others would be responsible for other satellite deposits. Because my ‘Outside-in’ methodology examines all the drilling data together (including the grade control data from each pit) to gain an overall understanding of the mineralising system, I asked the database manager to export all the drilling data in the common UTM coordinates.

Then a mischievous thought crossed my mind.

I always thought the various mine coordinate systems were harmful to the geological interpretation process, but I’d never had the opportunity to demonstrate that to be the case. The situation at Corona was a perfect opportunity to test my hypothesis with a live audience to see if using multiple local coordinate systems is detrimental to the geological interpretation process and the overall understanding of site geology.

The night before the workshop, I swapped the X and Y values from the exported UTM data of the collar file so Y was now X. But in my haste, I forgot to save the swap so all I had was X and Y in the original UTM coordinates. When I loaded the data in class the next day, I realised my mistake and was sure I’d be found out. But to my surprise, every geologist in the class swallowed my Saudi gold deposit yarn—hook, line, and sinker!

The lesson—how not to get lobotomised

In mining, we routinely follow common industry-accepted practices; these are often habits that have developed over time, some of which have no real use in modern times. Collectively, we have no memory of how these methods evolved, yet we follow them. The mining grid is totally logical and understandable in the mining context, but it’s potentially harmful if the geologist doesn’t look regionally beyond the local grid.

Although seemingly innocuous, using the mine coordinate system is the most effective way to digitally lobotomise geologists, who are unaware that their brains have been effectively throttled by an unintended ‘interpretation limiter’

What’s so frustrating to me is that defining a mining grid from a UTM grid is one of the simplest computer operations—it’s translation and rotation, an operation a high school student can easily understand. That’s it, but it could well be the source of huge amounts of geological ignorance. This affects exploration geologists less, as they work in UTM coordinates most of the time, but potentially it could be impacting near-mine exploration and resource estimations.

For example, if you’re confused about how to model the resource envelope of deposit X, the answer may be found in the patterns seen in neighbouring deposit Y, which uses a different coordinate system that you’ve never examined

My preference is to work in UTM coordinates, which allows any satellite deposit to be viewed in relation to another. It also lets me easily drop data available in UTM coordinates (such as maps, geophysical data, field measurements) into my project. And there is less likelihood for making mistakes when transforming coordinates from UTM to local.

When I joined the mining industry twenty years’ ago, I thought that using the local mine grid was a crazy practice from an interpretation standpoint. Sadly, this practice has not changed over the last two decades. This means that geologists are forced to interpret individual deposits in local grid systems thereby disadvantaging them of ever seeing potentially helpful patterns in neighbouring satellite deposits. 

At Corona, the various mine grids the geologists were dealing with had such a strong psychological silo effect that they couldn’t recognise their own deposit when all the drilling data were combined!

I believe the UTM grid should always be the coordinate system used for interpretation as all satellite deposits can be unified into one view. If a mine grid is required for localised block modelling and mine planning, then this should be a simple software operation that can be done at the end of the interpretation process.

Fortunately for the Integra Gold Rush contest, Integra Gold used the UTM grid to save both Sigma and Lamaque deposits into a single UTM coordinate system. This is ideal for the ‘Outside-In’ interpretation approach that I favour.

If you are forever stuck in a mine grid, you might want to take a look around you. You’ll never know what you might discover!