Page 203 - Introduction to Mineral Exploration

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

of the Internet using Google or a similar search to include data storage, its main function is to
engine to find up to date information. allow the easy integration of data and output,
usually in the form of maps (Longley et al.
1999, 2001). Its development has been designed
9.1.7 Coordinate systems and projections
for a wide range of applications involving
Geologists have in the past generally managed spatial data, including the design of optimum
to avoid dealing with different coordinate siting of pizza delivery sites and monitoring the
systems in any detail, as the areas they were spread of disease, but the generic commercial
dealing with were small. The advent of GPS systems are applicable (with limitations) to
and computerized data management has mineral exploration data. The dominant com-
changed this. The plotting of real world data on mercial systems, at the time of writing, are
a flat surface is known as projection and is the ArcView and ArcGIS (ESRI) with 35% of total
result of the need to visualize data as a flat market share and they have wide use in geo-
surface when the shape of the earth is best logical applications; MapInfo has a much
approximated by a spheroid, a flattened sphere. smaller overall market share but a wide follow-
For small areas the distortion is not important ing in the geological world, particularly in
but for larger areas there will be a compromise Australia as add-on programs have been devel-
between preserving area and distance relation- oped for mineral exploration. Current commer-
ships. For example, the well-known Mercator cial systems allow the display of both vector
projection emphasizes Europe at the expense of and raster data with varying degrees of querying
Africa. The scale of the data also governs the and modeling facilities. These systems are well
choice of projection. For maps of scales larger suited to 2D data but, at the time of writing,
than 1:250,000, either a national grid or a only partly usable for 3D drill data including
Universal Transverse Mercator (UTM) grid is drillholes and underground sampling.
generally used. In the latter projection, the In addition to the complex (and expensive)
earth is divided into segments of 6 degrees fullblown GIS systems there are a number of
longitude with a value of 500,000 m E given to simpler software packages, such as Oasis
the central meridian of longitude and a north- Montaj (Geosoft 2004), Interdex (Visidata 2004),
ing origin of 0 m at the equator, if north of the and Micromine (Micromine 2004), specifically
equator, or large number, often 10,000,000 m, designed for mineral exploration. Some have
if south of the equator. features not easily accessed in GIS packages,
There are a variety of different values in use such as the gridding facilities for geophysical
for the ellipsoid that approximates the shape data and integrated data management in Oasis
of the earth, known as the datum. The most Montaj.
commonly used datum for GPS work is World
Geodetic System (WGS 1984) but the datum
used on the map must be carefully checked, 9.2.1 Arrangement of data using layers
as the use of different datums can change coor- The basis for the integration of data in a GIS
dinates by up to 1500 m. The reader is advised is their use as a series of layers. This method
to read about the problems in more detail in is really an extension of the old light table
texts such as Longley et al. (2001) and Snyder method in which maps were overlaid and the
(1987). result viewed by shining a light through them.
Combining layers is much easier then splitting
them apart and a good rule is to build layers
9.2 DATA INTEGRATION AND GEOGRAPHICAL from the simplest components. For example,
INFORMATION SYSTEMS rather than having a topographical layer it is
better to have separate layers for roads, field
One of the major advances in technology at the boundaries, buildings, and rivers. In the case of
early exploration stage has been the ability to a conventional geological map separate layers
integrate data easily. This has been driven by would be generated for geological units (poly-
the development of Geographical Information gons), structural readings (points), and faults
Systems (GIS). Although GIS is usually defined (lines).