We tend to think of geometry as being all about triangles and squares and angles, circles and mathematics. However, the origins of the word from Latin and Greek, ‘geo’ and ‘metria’ literally mean earth measuring or earth craft. The ‘geo’ was probably related to both its use in astronomy and also its use in surveying plots of land (usually for taxation purposes).
Geometry is also a fundamental element of all that we do when modelling geology
and estimating mineral resource.
The vast majority of deposits contain direct or underlying structurally controls,
either as fluid pathways and traps or as hard boundaries. At the regional and deposit scale, these structures are often highly linear or planar in their geometry, or at least made up of numerous linear and planar features. However, we often don’t or can’t, collect and/or process sufficient structural data to define these features in the detail required for mineral resource estimation.
We almost always have vastly more, and more closely spaced, grade information
in the form of multi-element assays than geological information. We can use the grade to understand the geometry, then use the geology to refine the geometry and use both geometry and geology to guide the grade estimates. Grades approximate structural geometry – geometry approximates geology – geology provides the key understanding.
The thickness and shape of our domains is also a major driver of the estimation
methodology we choose and also impacts the estimation (and apparent estimation quality) that results.
The relationships between the drill spacing, block size, domain shape and variography are all about the relative geometries.
Most modelling and estimation software now allows us to use some sort of automated trend modelling features for both creation of surfaces and solids and for block estimation search orientations and variogram model orientations. These tools not only allow us to build more realistic models but they can also aid us in the initial interpretation and understanding of the controls on a deposit, particularly when the mineralisation is not aligned with the stratigraphy or lithology.
