Rotation Madness and estimation screw-ups

Creating a Mined Geology Model in Leapfrog Geo

I was asked the other day – can you filter the model for the mined / unmined material in Leapfrog. This got me thinking – the answer is yes but doing it once and only once is a lot of work to get a single result. If we flag a model as mined/unmined today, then tomorrow the result is wrong as we have mined some more. So I asked myself “Is there a way to create a mined model that is easily updated?” It has been a while since I did a ‘how to’ post so I figured this might be a good topic to cover.

In Leapfrog Geo the terminology of the geology modelling process and workflow can easily impose a straitjacket on your thinking – create a geology model using erosion, deposition and intrusion surfaces. What you are in fact creating is a domain model using cutting, covering and slicing surfaces. Remove the geology straitjacket and you will see the domaining process can be used for anything. In this case we can use the cutting (erosion) and covering (deposition) surfaces to cut in a mined/unmined model. Then we can evaluate this model against the drilling, geology models and resource models to flag out the mined material.

The main hurdle in creating a model you can update is that if you use an updated pit pickup surface mesh you can only access it once, you cannot refer to it again to build another separate surface and you can not edit the surface with another mesh. To get around this we create a new surface from points by extracting the vertices from the pit pickup surface mesh.

This gives you a point cloud you can access as many times as you wish.

Once we have the point cloud we create the geology model, it is always practical to create a template model that covers the mine site. I create a GM_Template model as below based on the resource model that covers the mine, then I simply copy the template and build the models from there – makes it easy. If you are starting from scratch then set up the model, calling it GM_Mined_Unimined as below. Make sure you select <None> for the base lithology, you also need a relatively fine resolution to ensure you can closely match the mined surface. It’s a bit of a balance of resolution against processing time but here I find 5m in our context to be pretty close.

Once the domain model has been created make sure you turn off the “Use Topography” option under the Boundary Tab, else you limit the model to below surface and can not create waste dumps.

Create the “lithologies” for mined, unminmed and fill material to cover the waste dumps.

Next we create two surfaces from the same as built vertices point cloud we extracted earlier. We use one surface (call it Mined) as the mined cutting surface, the second we call Fill (for the waste dumps). We can use the same point file to create each of these meshes which means the whole model can be built using the one as built surface.

Within the geology model we add 3 surfaces, two erosion contacts in order from bottom to top Unmined-Mined (using the mined asb mesh we created earlier) and Mined-Unknown (using the original topography mesh). We then add a deposit surface called Fill-Unknown so we can build the waste dumps using the Fill mesh created earlier.

Turn on all the surfaces in the surface chronology and make sure the stratigraphy is properly organised as shown below. If you get something weird – say the unmined sits in the sky or mined occupies the unmined material it is usually because you have the wrong order in the surface itself (say you have fill younger than unknown). You may have to play around with the younger to older relationships if it looks weird

And there we have it, a geological model of mined or unmined material!

A geology model based on mining surfaces that you can…

…flag drilling and composites as mined/unmined…

…flag the block model to create a mined flag within the model for queries, visualisation and filters…

…or filter the block model with Mined/unmined so you can filter out the mined blocks when assessing the composites and drilling against the model looking for those little wins that help carry the months production.

But wait you say – what happens when the end of month rolls around and the surveyors flick you a new pickup surface and you can see that the model is no longer accurate. How do you update the model without rebuilding the whole damn thing. Of course you could rebuild it – call the original GM_ASBIULT_EOM_APR for example and create a new one for May. I would prefer to save the model as a static copy with that date if I felt I wanted to keep it and update the GM model with the new as built surface.

So what you do is extract the vertices as earlier…

Then you edit both the fill and mined meshes by selecting Add… Points… and add the new as built vertices, then remove the old vertices.

 And then you Remove... the old one.

The model will then go away and process for as long as it takes based on all lovely things like resolution, size of the project and speed of your computer.

And just like magic your old model has updated to be a new model!

Best of all your filters and drillhole evaluations update too!

Hope you find this useful. Remember that the geology model is really a domain model and if you think outside the box you can use the models for all sorts of things!

Happy Modelling!

Ron Reid, is the Group Resource Geologist for Harmony Gold in Brisbane, and has been contributing posts for orefind.com/blog for the last several years. This post, and many more like this, can be found at www.Orefind.com/blog and on Ron’s Linkedin profile. Comments contained within are the authors alone and do not in any way represent the opinions of Harmony Gold.