Studio 3 Geological Modeling User Guide.pdf

Geological Modeling Studio 3 User Guide

Studio 3 Geological Modeling Concepts and Processes TTR-MUG-ST3-0003

Datamine Software Limited 2, St Cuthbert Street Wells, Somerset, United Kingdom Tel: +44 (0) 1749 679299 Fax: +44 (0) (0) 1749 670290

Author: James Newland Technical Author Datamine Software Limited

This documentation is confidential and may not be reproduced or shown to third parties without the prior written permission of Datamine Corporate Limited. © Datamine Corporate Limited

Contents 1

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Overview

1

Purpose of this document Prerequisites Acronyms and Abbreviations More information

1 1 1 1

Introduction

2

Cell Size Filling plane Defining the Model

2 3 4

Modeling Techniques

6

Unconstrained Modeling Constrained Modeling Modeling Using Wireframes

6 6 8

Structure Modelling

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Surface Topography Seams Massive Deposits Intrusive Features Open Surfaces such as Faults and Supergene Horizons.

11 11 12 13 13

Combining Models

14

Model Requirements Attribute Fields Combining Cells Combining Individual Models Optimizing a Model

14 14 14 15 16

Grade Estimation

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EXECUTIVE SUMMARY This User Guide outlines the processes and concepts that underpin geological modelling routines in Studio 3. The core aspect of this process, and the most significant single component required to undertake this task, is the Block Model. This data type, a key component of Studio 3 software, is described in detail, from its initial composition in the form of a prototype model, to a full resolved block model mass comprising parent and sub-cells. This guide explains each aspect of geological modelling in detail, from both a Studio 3 perspective and a real-world basis.

OVERVIEW

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Purpose of this document This document aims to provide: !

An understanding of the basic concepts behind geological modelling.

!

An explanation of the block model data type, parent cells and sub-cells.

!

Details of the files and fields associated with block modelling processes.

!

!

An overview of the different techniques used for manipulating the block modelling processes. A brief foray into the area of Grade Estimation. This is intended as a precursor to the ‘Studio 3 Grade Estimation User Guide ’

Prerequisites Although this document explains the concepts of geological modelling, you should have at least a basic understanding of real-world geological modelling processes.

Acronyms and Abbreviations The following Acronyms and Abbreviations are used throughout this document: Acronym

Description

DTM

Digital Terrain Model

More information !

Studio 3 Grade Estimation User Guide

Studio Geological Modeling User Guide

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INTRODUCTION

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 Datamine geological model is composed of rectangular blocks, or cells, each of which has attributes such as grades, rock types, oxidization codes, etc. 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 deposits there can be elegant solutions to the problem of representing grades and geological boundaries. A comprehensive modelling 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

Cross-section through a geological model

Cell Size A Parent cell is the largest cell allowed in a model. The size of these cells is defined by the user and should be based on several factors such as the drillhole spacing, mining method, and the geological structures hosting the ore. Where the model needs greater definition, such as within thin seams or at the edges of boundaries, it is possible to subdivide the parent cells into smaller sub-cells. The degree of parent cell splitting is controlled by the user. A significant advantage of Datamine 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.


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Filling plane Cell splitting can be done along any axis in the model. When using a constraining boundary, such as a perimeter or wireframe, it is necessary to define a filling plane to control the direction of the cell splitting. For example, if the filling plane is set to 'XY' then the process will create the specified number of sub-cells 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. Careful selection of the filling plane is therefore important in providing the best possible modelling of geological boundaries.


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Studio 3 stores the exact length of each cell in the X, Y and Z directions in 3 separate fields. This approach allows cells to be created with no cell dimension restrictions.

Defining the Model Before creating a model it is necessary to define the region it will represent and the size of the parent cells it will contain. This information is stored in a model prototype file. This prototype can be an existing model or a new file created using the process PROTOM (Models | Create Model | Define Prototype). A model prototype can also be described as an empty model. The Model Fields Studio 3 requires the following numeric fields in every model file. Note that instead of east, north and elevation Studio 3 uses the generic names 'X', 'Y' and 'Z'. This is because it is possible to align models to a local grid instead of the true coordinate grid. These fields are all created by the PROTOM process. Field Name

Explicit or Implicit

Description

XMORIG

Implicit

Easting coordinate model origin

of the

YMORIG

Implicit

Northing coordinate model origin

of the

ZMORIG

Implicit

RL coordinate origin

NX

Implicit

Number of parent cells in the X direction

NY

Implicit

Number of parent cells in the Y direction

NZ

Implicit

Number of parent cells in the Z direction

XINC


X axis cell dimension

YINC


Y axis cell dimension


of the model

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ZINC


Z axis cell dimension

XC

Explicit

X coordinate of cell centre

YC

Explicit

Y coordinate of cell centre

ZC

Explicit

Z coordinate of cell centre

Explicit

Used by Datamine to position parent cells within the model. Each Parent cell will have a unique IJK value. Sub-cells that lie within the same parent cell will have the same IJK value.

IJK

Defining The Model Origin Datamine sets the origin with respect to the corner of the first parent cell and NOT its centroid. Defining The Extent Of The Model The extent of the model in the X, Y, and Z directions is defined by the number of cells allowed in each direction (NX,NY,NZ) in combination with the parent cell dimensions and the model origin. As an example, if a model had the following XMORIG, XINC, and NX values: !

XMORIG = 45000

!

XINC = 10

!

NX = 100

The range of easting (X) values covered would be 45000 (XMORIG) to 46000 (XMORIG+XINC*NX) Other Fields In addition to the standard Datamine model fields, the model will contain any extra fields necessary to define the deposit. These fields are generally made up of a mixture of grade, lithology, and density fields. Other common field types include dollar fields for polymetalic deposits and grade estimation fields recording values such as kriging variance.


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MODELING TECHNIQUES

Several techniques can be used to create models in Datamine. The choice depends on the complexity of the geology, the degree of precision required and the amount of time and resources available for the modeling.

Unconstrained Modeling The quickest way to build a model is to create the cells using an interpolation process. For interpolation it is necessary to define an empty model prototype, provide some assay data and a set of suitable interpolation parameters. As the interpolation process runs, it scans the centroid of each potential cell to ascertain the number of valid assays occurring within the search radius. If the assays do not satisfy the interpolation conditions, the process moves on to the next cell position without creating a cell. When enough assays that satisfy the interpolation constraints are present the process creates a cell at that position in the model and assigns it the interpolated value. The main disadvantage of this technique is that it is not possible to accurately model geological contacts. This approach is typically used when modeling high tonnage, low grade, disseminated deposits such as Porphyry Copper style mineralization.

Constrained Modeling For better control over the shape and position of structures it is necessary to include a geological interpretation. This interpretation can take the form of perimeters which define various boundaries of interest, or if more precision is required, a series of wireframed surfaces. Modeling Using Perimeters A geological interpretation consists of section or plan drawings showing structure and mineral boundaries. These can be created within Datamine using interactive graphics in the Design Window, or by hand over hardcopy plots which can be digitized at a later date. As the strings are digitized codes or attributes should be assigned to distinguish the different zones and or rock types. Datamine can later assign these to the cells created in the block model. Examples of attribute fields include COLOUR, ROCKTYPE , ZONE , WEATHER and OXIDE . Using the interactive graphics in the Design Window, perimeter points can be snapped at the precise three-dimensional coordinates of selected drillhole intervals. For Datamine to fill the strings with cells they must form closed areas or perimeters. Ensure that adjacent boundaries abut up against each other with no gaps or overlaps. The string editing utilities under the Design menu can be used to automatically generate outlines from open overlapping strings. This means that common boundaries need to be digitized only once. Note that perimeters can be digitized in a clockwise or anticlockwise manner. Once the strings are loaded into the Design Window they can be easily viewed and edited. Verifying the string positions and coding is critical because any incorrect values at this point


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may significantly influence the validity of the final model. Some techniques used for verification include; !

Generating statistics on the strings using the STATS and PROPER processes.

!

Plotting the string position and attributes.

!

Viewing the data in three-dimensions in the Visualizer Window.

Filling Perimeters with cells Building block models with strings is completed using the PERFIL command (in the Design window, select Models | Create Model | Fill Perimeters with cells ). This process requires that the perimeters be planar and lie in the 'XY', 'XZ' or 'YZ' plane. If the perimeters do not meet any of these conditions, it will be necessary to create a wireframe and fill the wireframe with cells. As well as filling perimeters with cells PERFIL creates cells perpendicular to the perimeters. The projection distance defined is generally set to half the section spacing. Care must be taken to ensure that the values used do not create gaps or overlapping cells between the sections. This method works best when the geological structure lies approximately along the orthogonal axis and the sections are closely spaced. Checking the Model Once the model is created it should be checked to ensure that the cell filling has gone as expected. This can be done visually by viewing various sections through the model at different orientations interactively in the Design Window. Load the drillhole data set into the Design Window and then view it in section. Colors or filters can be used to identify the assay and lithology codes for each sample interval.

Adjust the view so that the screen lies at a selected section position. Set the clipping distances for both sides of the section plane to remove holes that lie outside the influence of this section. The clipping distances are typically halfway to the next section.


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Using the color coded samples digitize the geological interpretation on the screen. If the region is to be filled with model cells the strings must be closed. Multiple zones on the same section can be defined by coding them using color or any other attribute.

Once the section is complete; move the screen position to the next section and digitize another set of strings. Continue this procedure until all the sections are completed.

Fill the planar strings with cells using the PERFIL process. View the model in plan or section to ensure that the filling has produced the expected result.

Modeling Using Wireframes The most precise way to define a geological boundary in three-dimensions is with a wireframed surface or wireframed solid. Both are essentially the same except that wireframe solids enclose a volume while a wireframe surface is open. They may also differ in the techniques employed to create them. The use of wireframes, while giving more precision than perimeters, will require a thorough knowledge of how the deposit behaves in threedimensions.


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The starting point for solid wireframe modeling is usually a series of perimeters outlining the geology. These perimeters need not be planar and may lie at any orientation. They must not however overlap in three dimensions with themselves (forming a knot or 'twisted bowtie' shape) or with adjacent perimeters. Checking The Wireframes Once perimeters have been created, the string linking commands available under the Wireframes menu can be used to create the wireframe. The resulting wireframe must be checked carefully to ensure that all the links are valid and they represent the desired surface. This can be done by viewing slices through the wireframe at various orientations or by viewing the complete wireframe in the Visualizer Window. Another technique is to use the wireframe intersections function to find wireframe overlaps. A valid wireframe will not generate any intersection lines. The wireframe can be filled with cells using the process TRIFIL (in the Design window, select Models | Create Model | Fill Wireframe with Cells). An appropriate filling plane and sub-cell size based on the shape of the wireframe should be defined. The main advantages of this method over perimeters include. !

!

!

The resultant models are more precise in that they more accurately reflect geological structures and zones. The wireframe can be sliced at any orientation. The wireframe slices can be converted to strings allowing the creation of a new set of perimeters in a new orientation.

!

Wireframe volumes can be calculated quickly and easily.

!

Wireframes offer the clearest and most graphic way to display designs

Use the string linking commands under the Wireframes menu to create links between sections.


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Once completed, it is important to check the wireframe. This can be done by viewing it from several directions with hidden lines deleted or slicing the wireframe to produce various section profiles.

Fill the wireframe with cells using the TRIFIL process. Viewed in section the model is checked to ensure that the filling has produced the expected result.

Wireframe surfaces can be built and updated far more quickly than wireframe solids and can be generated from hanging wall and foot wall contacts.


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STRUCTURE MODELLING

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Complex geological models often contain separate structures such as different lithology, intrusives and surface topography. Managing all these and building them into the model simultaneously can be both difficult and time-consuming. In addition, if a change is made to one boundary position it may be necessary to repeat the whole modelling process. To overcome this problem, create a separate model for each of the different structures. For example, build separate models for the dyke and the host rock through which it has intruded. Construct the final model by adding them so that the dyke is superimposed over the host rock. Should it be necessary to refine the position of the dyke, build a new dyke model and add it again over the original host rock model.

Surface Topography Topography wireframe surfaces are built using the Wireframes | Interactive DTM creation | Make DTM (md) command. It is possible to create a DTM from contour strings, point data, closed boundary perimeters or any combination of the three. Once built the TRIFIL process is used to fill a model below the surface with cells

Seams Modeling of seams is similar to that of the surface topography. A topographic surface can actually be considered as a seam of air overlying the rock. For this reason the techniques used for modeling are similar to those given in the previous section. The main difference is that now there are tw o or more surfaces to consider. As with surface topography the technique u sed for creating the seam model depends primarily on the nature of the data available and the complexity of the seam. Two techniques and the conditions for their use a re outlined as follows;

Technique 1; Make DTM Build a surface using the Wireframes | Interactive DTM creation | Make DTM (md) command and then use TRIFIL (Models | Create Model | Fill Wireframe with Cells) to fill wireframe with cells This method should be used when: !

Point and/or string data (drillhole intersections, surface contours)

!

Information extends over the full model

!

Simple surfaces (no overhangs)

Technique 2; String Linking Build a surface using the string linking commands under the Wireframes menu (Wireframes | Linking) menu and then use TRIFIL to fill wireframe with cells This technique should be used when: !

String data (interpolated sections)


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!

Information extends over the full model

!

Complex surfaces (any orientation, overhangs)

Whatever technique is used if there are multiple seams each must be modelled separately and assigned the desired attributes and grades. Add the individual models using ADDMOD (Models | Manipulate Models | Add Two Block Models) to produce the final combined model.

Massive Deposits Massive deposits hosting disseminated mineralization often exhibit few clear contacts or boundaries defining the extent of the mineralization. Alternatively, the boundary (e.g. pluton) contact may lie outside the zone of interest. In such cases the model can be considered as unconstrained. Cells can be created using the interpolation process ESTIMA (Models | Interpolate Grade | Interpolate Grades into Model). A menu driven version of the process called ESTIMATE (Models | Interpolate Grade | Interpolate Grades from Menu) can be used as an alternative to starting the process from the Command line.

Empty Prototype Model

Prototype Model with Cells

Interpolation Process

Interpolation Process

Cells Created in Search Ellipse

No New Cells Created


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There are two approaches for building a model with an interpolation process; !

!

Fill the model prototype completely with cells using the PERFIL or TRIFIL processes. Use this model as the prototype for an interpolation process to assign grades to cells. Cells that do not satisfy the constraints for grade interpolation are left with undefined values. Use ESTIMA or ESTIMATE to interpolate grades into an empty prototype to create cells (unconstrained estimation).

Intrusive Features Generally, intrusive features have distinct boundaries that can be interpolated from the drillhole information. The first step is to digitize a set of sectional outlines then create a wireframe and fill it with cells.

Open Surfaces such as Faults and Supergene Horizons. Open surfaces are best represented using wireframes. As this is another case of surface modeling the techniques used for creating these wireframes are very similar to those used for topographic wireframes. While creating a fault plane wireframe is generally easy, including i t in the geological block model is a more involved procedure. Rather than filling a volume with cells the cells are created on one side of a wireframe. Use the TRIFIL process and select an east, west, north or south filling direction. Assign a unique zone code to the cells so that they can be identified later. Another way in which a fault wireframe can be used is to display it as a slice overlaying it on geological sections. This shows the precise three-dimensional position of the fault which can be used in the geological interpretation.


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COMBINING MODELS

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The ability to combine models is a powerful tool. As well as providing the ability to create complex models in simple stages, it also allows the updating and extension of existing models.

Model Requirements To combine two models using the process ADDMOD (Models | Manipulate Models | Add Two Block Models) both input models must have the same model definition (i.e. the same origin, parent cell dimensions and number of cells). They must also be sorted on the IJK field. If the two models do not have the same model definition it is necessary to change the definition of one of the models. The easiest way to do this is by using the process SLIMOD (Models | Manipulate Model | Put Model onto a New Prototype). It is necessary to supply this process with the model to be changed and a model prototype file describing the new model format. The model prototype is created using the process PROTOM or, more conveniently, use an existing model as the prototype.

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 absent data (-). 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 performed 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.


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Adding Cells Using ADDMOD Parent Cell

Combined

Parent Cell

Adding Cells Using ADDMOD

Combining Individual Models The following diagram demonstrates the processes involved in created a full geological model comprised of individual model data sets. Note that the direction of the black arrows denote the order in which the models are added (e.g. Seam 1 is added on top of Seam 2), and the white arrows follow the build-up of the combined model data set:

Seam 1

Seam 2

Weathered Zone

Intrusive Dyke

Surface Topography

Final Model


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Optimizing a Model When adding two models together the new output model may contain more cells than either of the input models. This is a result of the cells being split along smaller subcell boundaries. If the new model is becoming too large due to all the new cells the process PROMOD (Models | Manipulate Model | Optimise Block Model) can be used to combine model cells according to a set of constraints. It is also possible to minimize the creation of small cells during modeling. In the PERFIL and TRIFIL processes set the @RESOL parameter to define the smallest cell size allowed. This in effect forces the subcelling in the seam filling direction to be completed using subcell splitting by rounding the cell lengths to a minimum set fraction of the parent cell dimension. As an example for parent cell length of 10 in the Z direction and a RESOL value of 10, the minimum cell length in the Z direction allowed will be 1/10 i.e. 1 metre.


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GRADE ESTIMATION

Grade estimation is the process of estimating cell values (e.g. block mo del cells) based on a set of three-dimensional sample data. This information usually takes the form of drillholes, surface samples or underground grab samples. There are several mathematical techniques available for doing the interpolation. For more information on grade estimation refer to the Grade Estimation User Guide.


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Datamine Software Limited 2, St. Cuthbert Street Wells Somerset Tel: +44 (0) 1749 679299 Fax: +44 (0) 1749 670290 www.datamine.co.uk


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Studio 3 Geological Modeling User Guide.pdf

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