Keywords: AirSAR, lineaments, alteration zones
Abstract
The Airborne Synthetic Aperture Radar (AirSAR) system developed by the National
Aeronautics and Space Administration-Jet Propulsions Laboratories (NASA-JPL) is a tool for
a multidisciplinary approach in remote sensing. The AirSAR is presently used in many
applications. One such application is for geologic mapping and mineral exploration. This
paper presents some results of using AirSAR data as a tool for geologic mapping and mineral
exploration in the Philippines. This paper is part of the research study within the framework
of the Philippines-NASA AirSAR Project.
The study area is a mineral claim in Dumara, Antique, known as the Dumara Gold
Prospect by the Philex Gold, Inc. The gold prospect is mapped within the Lumbuyan
Formation.
The available AirSAR images of the study area are in 3 wavelength bands, namely:
C-band (3.75-7.5 cm), L-band (15-30cm), and P-band (30-100cm). The single band (C-band
VV) was enhanced and analyzed for geologic and structural data. Field verifications were
conducted to verify the features observed.
New lineaments were identified near and southeast of the prospect area. Also near the prospect site,
three alteration zones were identified. Field investigation shows that mineralization is along the Tigotay fault
trending N 75 0 E. The alterations along this fault are evident. However, no intrusive body was found. It
seems that the mineralization is transported through the fracture system rather than emplaced due to the low
dipping of the alteration zone. The extension of this mineralization must be searched. The thrust faults
mapped in the field are correlated with previously mapped structures. Further study of the data and the area is
necessary to delineate other probable mineralization areas.
1.0 Introduction
This report is the initial synthesis of the available field reports, field investigation and initial image
processing of the AirSAR data over Dumara, Antique, Philippines. The field investigation was carried out in
Antique last April 06 to 13, 1999. The said investigation is meant to verify features observed in the AirSAR
image and aerial photographs of the study area. It is also meant to gather field data for analysis and to
document the features observed in the images.
This report is part of the sub-project under the major project entitled “Analysis of AirSAR and
TopSAR Datasets for Resource Management and Development Planning Activities”. The major project’s
developmental objective is to “promote the use of remote sensing technology for various applications relating to
resource management and developmental planning activities. In this case, the application for the sub-project is
geologic studies and mineral exploration.
Remote sensing provides data for preparing and improving geologic maps which are
fundamental tools for exploration (Sabins, 1987). In addition, enhanced images, such as radar,
help to locate fracture intersections, which are possible mineral target areas.
In Antique, the rugged terrain and the long wet season from May to November inhibit detailed
exploration surveys. The available geological data are few. They include the 1987 BMG reconnaissance
geological map (1:50,000) and the working base map of Philex (1:125,000). Many parts of the area still have to
be mapped effectively. The AirSAR data provided an additional input to the geological mapping and mineral
prospecting in Antique.
2.0 The Study Area
2.1 Location and Physiography
The study area is within the Philex claim at Dumara, Antique. (fig.1, index map).
The study area is generally rugged and mountainous. It has a high relief and
v-shaped ravines and gullies. The ridges and spurs are sharp. The highest elevations in the
area are from 700m to 2,000m. These high points are along the eastern side of the study area
in a roughly N-S pattern. The prominent peaks are the Mt. Baloy and Mt. Nangtud which are
1900m and 2080m above mean sea level, respectively. Mt. Dumara has an elevation of
1370m and located on the NW side of the study area. To the west, the elevation is moderate
in the range of 700m to 1000m.
The major river system draining the area is the Paliuan River and its tributaries. This
river system has developed a wide flood plain with braided channels. It exits to the Sulu Sea.
The headwater tributaries have a sub-dendritic, sub-trellis to angulate patterns. The complex
patterns and arrangements of the drainage system can be explained by a combination of
lithological and secondary structural controls.
Vegetation growths are varied at the eastern portion of the study area. Cogon grasses,
undergrowth, secondary growths and shrubs are observed covering the spurs, ravines and
slopes. Forest, which includes pine forest, grows at high elevations.
2.2 Geology
Geologically, the Dumara area consist dominantly of red to purple mudstones and
siltstones, turbidites, volcanic wackes and some conglomerates belonging to the Lumbuyan
Formation (fig.1). The Mt. Baloy Volcanics, made up of pillow and brecciated basalt, minor
turbidites, boulder conglomerate beds, conformably overlies the Lumbuyan Formation. The
volcanics are found along peaks and ridges at the west portion of the study area (Geology of
the Philippines, 1996).
The other rock formations in the area are the Igsawa Pyroclastics and Maliao Wackes.
Both formations are in fault-contact with the underlying Lumbuyan Formation. However, in
some areas, they are found to be uncorformably overlying the Lumbuyan formation. The
Igsawa Pyroclastics is composed of the andesite flow breccia, buff wacke conglomerate and
calcirudite, calcarenite and marl. The Maliao Wackes, on the other hand, consist of turbidite
wackes, thin siltstones, minor conglomerate and andesite flow breccia (Geology of the
Philippines, 1996). Both formations are mapped along peaks, spurs and headwater tributaries.
They trend in the NE direction. However, the exact relationship of the Igsawa Pyroclastics
with the Maliao Wackes is unknown.
2.3 Structures
In the study area, two thrust faults trending NE-SW are observed to be the contact of
the wackes and the pyroclastics to the mudstone-siltstone turbidite of the Lumbuyan
formation -- a fault-contact (fig.1). New lineaments traced from aerial photos and the
AirSAR image are oriented NE-SW and NW-SE. They are complimentary structures to each
other. Streams usually follow these lineaments which are natural lines of weaknesses.
Anticlinal and synclinal fold structures trending NE-SW were mapped along the main
Paliuan River. Other fold structures can be traced in the adjoining area.
