REMOTE SENSING STRATEGIES IN MINERAL EXPLORATION AND DEVELOPMENT: THE
PRECIOUS METAL AND PORPHYRY DEPOSIT MODELS
David M. Spatz
BHP Minerals
Tucson, Arizona, U.S.A.
Commission VII, Working Group 4, ISPRS
KEY WORDS: Exploration, Gold, Copper, Porphyry Deposits, Remote Sensing, Multispectral, Resolution, Alteration,
ABSTRACT:
Modern exploration programs are based on well planned strategies that typically begin with an ore deposit model, the
characteristics of which constrain exploration techniques. Since ore deposit models are defined largely by physical geologic
features that relate conveniently to remote sensing, remote sensing is commonly applied in exploration. Exploration strategy
dictates scale, which in turn controls spatial resolution requirements. Scale correlates with the aerial extent of the program
andis generally ranked from small scale to large scale and categorized as reconnaissance, regional, district, or deposit scale,
Spatial resolution requirements for these categories are about 20-80m, 10-30m, 6-10m, and 3-7m, respectively. Both spatial
and spectral resolution requirements vary with ore deposit models and geologic features of interest. For these reasons, it
is important to outline exploration objectives and remote sensing strategies in order to assist prudent selection of remote
sensing instruments, imagery and image processing techniques.
1.0 INTRODUCTION
Since the launch of NASA's ERTS-1 (Landsat 1) satellite
in 1972, various applications of remote sensing systems
andimage processing techniques have been widely applied
to geologic mapping and mineral exploration. Geologists
have used remote sensing to improve alteration mapping
within known mining districts (e.g. Abrams et al., 1983),
identify alteration leading to new ore discoveries (e.g. Dick
et.al., 1993) and select areas with new discovery potential.
Applied research in remote sensing is vigorous and can be
divided into 1) spectral analysis of rocks, minerals, soil and
vegetation; 2) image processing which rides the wave of
advancing computer technology; 3) instrument engineer-
ing and technology; and 4) test studies or orientation
surveys. Advanced applications of remote sensing to min-
eral exploration and mineral property mapping depend on
research in these four areas. Image processing techniques
influence image interpretation. Remote sensing images are
computer enhanced, routinely, to improve contrast be-
tween surface cover and provide spectral information on
lithology, alteration types, and vegetation.
2.0 MINERAL EXPLORATION STRATEGIES
AND SPATIAL RESOLUTION
2.1 Strategies
Variations among ore deposit types as well as variations
between deposit subtypes influence choice of remote sens-
ing instruments as well as image processing techniques.
Based on the spectral characteristics of the geologic fea-
tures that define the various ore types or deposit models, a
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geologist can design a remote sensing strategy that is
compatible with an overall exploration or development
strategy developed for the project. Spectral and spatial
resolution are paramount in the decision process and
depend chiefly on the ore deposit models under consider-
ation andthe scale ofthe exploration program. The deposit
model is fundamental to the development of an effective
exploration strategy, and the scale of the program follows
closely. Deposit models are comprised of physical geologic
features which vary in relevance to remote sensing. The
size of deposit models and the dimensions of alteration
zones control requirements for spectral range and resolu-
tion and spatial resolution. The stage or phase of explora-
tion is another important control on scale and spatial
resolution.
2.1 Scale
Table 1 compares exploration stage with aerial coverage
and spatial resolution requirements. The most common
application of remote sensing in mineral exploration and
development has been at the reconnaissance stage from
satellite based instruments. Landsat TM, because of à
capability to detect hydrothermal alteration, intermediate
scale spatial resolution, near ubiquitous Earth coverage,
and nominal cost, has provided the most prolific remote
sensing imagery for earth science applications throughout
the 80's and 90's. Exploration scales correlate with the
aerial coverages planned for evaluation and are commonly
subdivided from large to small (small scale to large scale)
into reconnaissance, regional, district, and project Of
deposit scale. Spatial resolution requirements for these
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996
