Page 197 - Introduction to Mineral Exploration

180 C.J. MOON & M.K.G. WHATELEY

Fault
Structural
reading
Inclined (dip)
drillhole
Vertical
drillhole

Lithological
Sample unit
location (polygon)
FIG. 9.1 Typical geological objects
with differing dimensions.

TABLE 9.1 Typical geological features and their representation and quality.
Relationship Typical attributes Geometry Typical quality
Geological unit Contacts Lithology, age, name Polygon ±25 m
Fault Contacts Type, name Line ±25 m
Structural reading Type, orientations Point ±5m
Sample location Number, lithology, assay Point ±5m
Inclined drillhole Number, date, driller Line ±0.1 m
Vertical drillhole Number, date, driller Point ±0.1 m
Drillhole sample Depth, lithology, assay Point or line ±0.5 m
(interval)

key factors in deciding on a format are resolu- In a simple (two-dimensional) vector model,
tion and amount of storage required. Figure 9.2 points are represented by x and y coordinates,
shows a simple geological map in vector and lines as a series of connected points (known as
raster format. The raster method is commonly vertices), and polygons as a series of connected
used for remote sensing and discussed in sec- lines or strings. This simple model for polygons
tion 6.2.2, whereas the vector method is used is known as a spaghetti model and is that
for drillholes and geological mapping. Most adopted by computer aided drawing (CAD)
modern systems allow for integration of the packages. For more complex querying and
two different types as well as conversion from modeling of polygons, the relationship between
one model to another, although raster to vector adjoining polygons must be established and
conversion is much more difficult than that the entire space of the study area subdivided.
from vector to raster. This is known as the topological model. In this