Research SOLID MODELING

The application of solid modeling to mine design resulted from Curran’s initial interest in stress analysis as a tool for evaluating the stability of underground excavations. Realizing that the geometry of a mine posed the biggest obstacle to making practical, 3-dimensional stress analyses, he quickly focused on the technique of solid modeling.

The idea behind solid modeling is that a complex solid can be built up on a computer screen by combining a group of simpler solids. One model- building method is called Constructive Solid Geometry (CSG). Objects are constructed out of a combination of simpler, 3-dimensional shapes such as cubes, cylinders, wedges, spheres, cones and tori (doughnut shapes). The shapes are put together using basic Boolean operations of union, difference and intersection.

The processes of extrusion and revolution can also be applied to CSG. Extrusion refers to extruding a 2- dimensional surface in the direction normal to the surface. With revolution, a curve is revolved around an axis.

For example, take a wedge and cylinder, move the cylinder into the centre of the wedge and take the difference. You end up with a wedge with a hole in it. Mine openings can be easily modelled using this concept: by taking a block, putting a cylinder through it and taking the difference, one ends up with a tunnel.

A solid model of Block One ore at Hemlo Gold Mines’ Golden Giant operation, in Hemlo, Ont., was created by solid modeling. Using the mine level plans and longitudinal sections, plus the basic CSG method, the solid model of the mine was constructed. It was built up from the basic mine structures, rather than dealing with the mine as a whole.

The drift structures were constructed by digitizing the 2- dimensional sections of each of the level plans and extruding them. This was done for the 5000, 4975, 4950, 4925 and 4900 levels.

The stopes were created by grouping together blocks, along with the extruded section, to come up with the components for each of the different levels. Each of those components is 25 m high. The raises and the ramp were added as separate entities. The ramp was created by taking a torus, cutting it in half, rotating one half with respect to the other, and then repeating the process. The raises are composed of a number of blocks.

Solid modeling can be thought of as a data base for all the geometry of the mine, and the solid model as a display on the screen. The data stores co-ordinant information on virtually every surface, edge and vertex in the mine. The real power of solid modeling is that the data base can be used to quickly calculate volumes.

One of the tools available in solid modeling is called Group Operations. It was possible to construct the Golden Giant mine model from many components because of the Group Operation feature. It allows probing of the data base for information on any combination of components of the mine. For example, if one wants to calculate the total volume of mineable ore on a particular level, the individual stopes in the model can be highlighted and the volume of ore calculated from the data base. If the geometry of the orebody is updated, these values can be easily recalculated.

Solid modeling was also applied to Minnova’s Ansil property near Rouyn, Que., where the copper orebody is high-grade and odd-shaped, making it difficult to visualize. In the pre- mining stage now, the mine design and mining sequence are of prime consideration for the safe extraction of the deep, high-grade ore.

A solid model of the orebody was created by extruding 13 longitudinal drillhole sections and grouping them together. Three levels of drift structures were done by extrusion and two shafts made with cylinders.

The odd shape of the Ansil orebody makes it an interesting model to examine. The model serves as a good representation of the geometry of the orebody and mine development. As you walk, vicariously, around the developing mine in a clockwise direction, you can see the complexity of the cap near the top of the orebody. It becomes evident that there is a slight curve to it, that it thins out at the bottom. The ability to see this detail from different viewing points, on a computer screen, is a useful result of solid modeling.

Prof Curran is concentrating on developing a practical and affordable design tool that can be used in mine- planning offices. The software should be able to deal with the mine geometry in mining terms and be able to display the data needed by mine-planners.

Suppose you had ordered some exploratory drilling of two drifts. The assays for the holes were received and are stored in the data base. Ideally, that would be sufficient information to allow you, based on a particular cut-off ore grade, to determine (from the data base) where the concentration is sufficient to define it as ore. What Curran would ultimately like is to use this information to automatically create a solid model of the orebody. Joyce Musial is a Toronto-based geologist and freelance writer.

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