Geoscience Reference
In-Depth Information
little interaction. Most major mining software packages
allow for interactive geological and engineering work in
three dimensions, and also visualization and presentation of
the results. The required basic elements of geologic and en-
gineering plots vary with the objective of the work, but some
elements are essential and common to most of them.
types; and (c) considerations about legibility; for example, it
is very difficult to read numbers plotted using yellow; shades
of brown can be used for different surfaces, but they should
plot in a distinct way; the point size of the numbers and let-
ters chosen should be such that they do not overprint or abut
against each other.
Although it may seem that some of these details are obvi-
ous and common-sense, a well-thought out plotting scheme
can save significant time and effort, lead to better modeling
and validating practices, and should be considered an impor-
tant part of the work plan.
3.3.1
Scale
Showing data at appropriate scales is a fundamental attribute
of any plot. Accurate information on locations, distances,
and volumes should reflect the level of detail and accura-
cy desired. Scales of 1:2.5 million may be appropriate for
metallogenic maps of entire continents, but will not show
individual deposits. Regional geologic maps at 1:500,000
up to 1:100,000 are typically used in mineral reconnaissance
work. Large, open pit mines may use scales of 1:1,000 to
1:500 for the geologic cross sections and plan views used
for interpretation. Smaller underground mines will generally
require larger scales, and may work on 1:200 or 1:100 scales
for better definition of smaller orebodies and mine stopes.
There are no fixed rules about the appropriate scale to use
in each circumstance, but the scale should allow for the best
accuracy that is practical.
3.4
Block Model Setup and Geometry
3.4.1
Coordinate Systems
Spatial data, block models and other mineral resource es-
timation data require the use of coordinate systems to lo-
cate relevant attributes. Appropriate coordinates have to be
defined based on the available sources of information. The
largest scales of work for mapping and map projections are
dealt within the field of cartography, and are outside the
scope of this topic. Geographic coordinates are measured in
terms of
longitude and latitude.
Longitudes are referenced to
meridians defined by a line joining the North and South Pole
and latitude are parallels that result from planes that intercept
the idealized spherical earth. Latitude measures the angle be-
tween any point in the earth's surface and the Equator. Longi-
tude measures the corresponding angle between the meridian
that passes through that same point and the central meridian,
arbitrarily defined as that which passes through Greenwich,
England. For further discussion on the subject, see Maling
(
1992
); Snyder (
1987
); and Bonham-Carter (
1994
).
Geographic coordinates (latitudes and longitudes) are con-
verted for use at smaller scales into planar coordinates, based
on projection transformations from a quasi-spherical globe
(the earth) onto a plane. These projections introduce some
geometric distortion. The type of distortion is used to classify
the projections into equal angle, equal area, or equal distance,
depending upon whether the projection preserves angular,
area, or distance relationships between features of interest.
The most commonly used system is the Universal Trans-
verse Mercator (UTM) system that is an equal angle system
established in 1936 by the International Union of Geodesy
and Geophysics (Snyder
1987
). The UTM system is widely
used by national geographic surveys and offices of countries
around the world as well as mining companies. The popu-
larity of the UTM system is mostly because regional-scale
maps available from geological surveys and governmental
offices around the world are UTM-based, generally at a
1:250,000 scale or larger. The world is divided into 60 UTM
zones, numbered from west to east and starting with 1º at
180º west.
3.3.2
Data
Virtually all work involved in developing geologic models
and mineral resource estimations require geologic and assay
data from drill hole data, surface trenching or underground
stope sampling. It is necessary to plot all relevant informa-
tion for analysis, interpretation, and checking. Drill hole
names and traces (in three dimensions or represented in a
two-dimensional section), down-the-hole geologic codes
and assays, topography, underground workings, and other
relevant surfaces and volumes should be included in plots
used for model development and engineering. These may be
cross sections, longitudinal sections, or plan maps.
In the case of model-checking, the data presented needs
to be relevant, legible, and accurate, and, in the case of block
models, for example, should include estimated grades, as-
signed rock types, assigned resource classification codes,
and metallurgical properties. Additional specifics related to
model-checking are described in Chap. 11.
Color-coding is used as an aid to visualization, interpre-
tation and engineering work. Suggestions for color-coding
include: (a) standardization to common practice, whereby
warm colors (yellow, orange, red, magenta) indicate high
values, and colder colors (grey, blue, green) indicate lower
values; (b) consistency in the definition of the set of color
codes (legends) to be used for the different attributes, always
applying the same codes to the same attributes and data
