Page 89 - Introduction to Mineral Exploration

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

Leveling is the most accurate method of described in the book by Majoribanks (1997).
obtaining height differences between stations Although the regional environment of the pro-
and is used for example to obtain the eleva- spect is important, particular attention will fall
tion of each station when undertaking grav- on known mineralisation or any discovered
ity surveys. This method measures the height during the survey. The geological relationship
difference between a pair of stations using a of the mineralisation must be assessed in
surveyor’s level. Leveling is required in an detail, in particular whether it has any of the
underground mine to determine the minimum features of the geological model sought. For
slope required to drain an adit or drive and in a example, if the target is a volcanic-associated
surface mine the maximum gradient up which massive sulfide deposit then any sulfides
load, haul, dump (LHD) trucks can climb when should be carefully mapped to determine if
fully laden (usually <10%). they are concordant or cross cutting. If the
More exact ground surveys use a theodolite sulfides are cross cutting it should be estab-
as a substitute for a compass. It is simple lished whether the sulfides are in a stockwork
enough for geologists to learn to use. Numer- or a vein. Particular attention should be paid
ical triangulation is carried out using angles to mapping hydrothermal alteration, which is
measured by theodolite to calculate x and y described in detail by Pirajno (1992).
coordinates. By also recording the vertical Detailed guidance on geological mapping is
angles, the heights of points can be computed beyond the scope of this book but can be found
(Ritchie et al. 1977). Professional surveyors are in a series of handbooks published by the Geo-
readily available in most parts of the world and logical Society of London (Fry 1991, McClay
they should be contracted for more exact sur- 1991, Thorpe & Brown 1993, Tucker 2003), par-
veys. They will use a theodolite and electronic ticularly in the summary volume of Barnes and
distance measuring (EDM) equipment, often Lisle (2003).
combined in one instrument, and can produce One of the key elements of mapping is its
an immediate printout of the grid location of final presentation. Conventionally this was in
points measured. the form of a map drafted by Indian ink pen on
to transparent film. From film, multiple copies
either on film or on paper can be made using
5.1.3 Geological mapping
the dyeline process and the map can be overlaid
One of the key elements during the exploration on other maps of the same scale, allowing easy
of a prospect is the preparation of a geological comparison of features and selection of targets.
map. Its quality and scale will vary with the The conventional pen and paper approach
importance of the program and the finance has been superseded by computerized drafting
available. Initial investigation of a prospect that allows the storage of information in digital
may only require sketch mapping on an aerial form. Computer packages, such as AUTOCAD,
photograph, whereas detailed investigations a computer-aided drafting package, are widely
prior to drilling may necessitate mapping every used in industry (see section 9.2). Maps and
exposure. Mapping at the prospect scale is gen- plans can be produced to scale and different
erally undertaken at 1:10,000 to 1:2500. For features of the overall data set, held on differ-
detailed, accurate mapping a telescopic alidade ent layers in the computer, can be selected for
and plane table or differential GPS may be viewing on the computer screen or printed as
used. The principle of the alidade is the same as a hard copy. The data can also be transmitted
for a theodolite, except that the vertical and to more sophisticated Geographical Informa-
horizontal distances between each point are tion Systems (GIS), for example ArcGIS or
calculated in the field. The base of the alidade MapInfo, that allow the inquisition of data (see
is used to plot the position of the next point on section 9.2).
the waterproof drafting film covering the plane
table.
The process of geological mapping of mineral 5.1.4 Mapping and sampling of old mines
prospects is similar to that of general geolo- Many prospects contain or are based around
gical mapping, but is more focused, and is well old mines. They may become attractive as