Block Modelling

Mining technology

Studio 3 Block Modelling Introduction

Block modeling is a very powerful technique which models deposits as a set of 3-D cells and sub-cells. Sub-cells are a unique Datamine concept, in which and cell may be split into any number of differently sized sub-cells to define any required level of local detail.

Models may represent geological structure, or grade distribution, or both. There is a choice of interpolation methods, statistical and geostatistical, and the model can be edited and examined interactively in plan or section.

Evaluations of reserves for the whole model or selected areas can be produced, and many different types of data can be processed at once.

Separate models representing different properties or zones can be combined and superimposed, and the models so created are used throughout the Datamine system. The cell/sub-cell structure is equally suitable for massive, layered, vein type or alluvial deposits.
Studio 3 block modelling
Reproduced with the Kind Permision of Ernest Henry Copper-Gold Mine

Cell models may be displayed over a wireframe surface, allowing for example the ore in the walls of a drive or an open pit to be shown, with user specified colours defined by filters.

Within a perimeter, cells may also be displayed at distances above or below the view plane, allowing for example selective examination of the model on the bench above or below the current plane without changing the view.

An evaluation method is also provided, in which a temporary wireframe model is constructed between any two user-defined three-dimensional perimeters and evaluated against the cell model

Studio 3 Block Modelling - Basic Principles

Geological Models

The purpose of a geological model is to accurately represent not just the grades of a deposit, but also its boundaries and internal structures. A Studio 3 geological model is composed of 3D 'rectangular' blocks, or cells, each of which has attributes such as grades, rocktypes, oxidization codes, etc.

Why use blocks?

Though many cell shapes, such as polygons, distorted cubes, mathematical surfaces and triangulations are possible none is completely general in application. The simplest form of three dimensional model consists of a rectangular grid in which each cell has the same dimensions. This is also the most commonly used type of model because it lends itself well to efficient handling in a computer. For some particular deposits there can be elegant solutions to the problem of representing grades and geological boundaries. A comprehensive modeling system such as Studio 3, however, requires a method that is applicable without modification to the widest possible range of deposits. The solution is to use a block model that allows rectangular cells of different dimensions.

Studio 3 Block Modelling - Defining the Model

Before creating a model you must define the region it will represent and the size of the parent cells it will contain. You store this information in a model prototype file, which contains the following components:

Model Fields - DATAMINE requires the following numeric fields in every model and prototype file. Note that instead of east, north and elevation, Studio 3 uses the generic names 'X', 'Y‘ and 'Z'. This is because you can align models to a local grid instead of the true coordinate grid.

XMORIG, YMORIG, ZMORIG - XYZ origin of the model. Studio 3 sets the origin with respect to the corner of the first parent cell (and not its centroid).

XINC, YINC, ZINC - XYZ cell dimensions. If the model is not to contain any subcells then these three fields can be implicit (not stored on every record). This will reduce the storage space required by the model.

NX, NY, NZ - Number of model parent cells in XYZ. Studio 3 allows a value of one for modeling seams. The number of cells, in combination with the cell dimensions, defines the extent of the model.

XC, YC, ZC - XYZ cell center coordinates.

IJK - Code generated and used by Studio 3 to uniquely identify each parent cell position within the model. Subcells that lie within the same parent cell will have the same IJK value.

Attributes - In addition the model can contain any extra attribute fields necessary

Studio 3 Block Modelling - Cells

Cell Size

A Parent cell is the largest cell allowed in a model. You set the size of these cells based on several factors such as the geostatistical properties, drillhole spacing, mining constraints, geology, topography.

Where your model needs greater definition, such as within thin seams or at the edges of boundaries, you can subdivide the parent cells into smaller subcells. You control the degree of parent cell splitting, and thus the size of the subcells.

A significant advantage of Studio 3 block modelling is that it is not necessary to create a cell in every position within the model. Only regions of interest, such as a mineralized zone, need be modelled. This can dramatically reduce both the computer power and disk storage you require.


Studio 3 Block Modelling - Parent Cell Splitting

Filling plane

Cell splitting can be done along any axis in the model. When you use a constraining boundary, such as a perimeter or wireframe, you also need to define a filling plane to control the direction of the cell splitting.

For example, if you set the filling plane to 'XY' then the process will create the specified number of subcells in both the X and Y directions. In the third axis the cell size will be calculated using seam filling. With seam filling the cell dimension is set automatically so that it precisely fits the perimeter or wireframe boundary. Thus, careful selection of the filling plane is important in providing the best possible modeling of geological boundaries.

Studio 3 Block Modelling - Rotated Block Models

A Rotated Model is one whose axes, and therefore cells, are rotated with respect to the coordinate system. It is particularly useful in the situation where you have a stratified orebody which is dipping and/or plunging. As you can see from the diagram Below the model cells provide a much better fit when the model Is rotated. Using a rotated model aligned to one or more of the major axes used to model the structure or shape of a deposit has the following advantages;

* a smaller number of subcells can be used
* the subcells provide a better fit to the boundary
* in particular circumstances there can be a small improvement in the grade evaluation.

Studio 3 Block Modelling - Combining Models

The ability to combine models is a powerful tool of Studio 3 geological modeling.

As well as allowing you to create complex models in simple stages, it also lets you later update and build upon your existing models. Understanding how Studio 3 combines models is therefore important.

For adding models the best option is to use the first model as a prototype for restructuring the second model.

Attribute fields

Any attribute fields such as lithology or grades are handled according to the following rules:

* If the fields are unique to each input model then all these fields are written to the output model. Those fields that do not get a value from either of the input models are set to undefined (-).
* If the same fields exist in both input models the 2nd model overwrites the common fields in the 1st model.

Combining cells

When models are added, the cells are first compared to find how they overlap.

* If cells do not overlap, or overlap exactly, then no cell splitting is done and only the cell attributes are updated.
* If the cells partially overlap then they are split along each cell boundary before updating the attribute fields. As the resulting cells must be rectangular the splitting will continue throughout the full length of a cell.