Camit, Rex
Leynes et al. (1996) identified high occurrences of NE to ENE fault sets within the SE block (Quaternary Cabalian and
Cantodoc volcanics) based on aerial photo and later field ground-truthing. This is validated in this study using the NW-
directed hill-shading interpretation (Figure 3a and 3b). These structures could have been passageways of hot,
hydrothermal fluids outflowing towards the ENE at Mainit thermal area (i.e. Mahalo Fault Splay).
Well SL-1D encountered partial and total circulation losses at depths 788-999 m along Mahalo Fault Splay (Rosell and
Zaide-Delfin, 1997). In relation to this, well SL-1D intersected veneers of hematized/goethized, weathered volcanics
down to 241 m of the upper member of the Quaternary volcanics. Partial circulation losses were encountered within
these depths which are indicative of either an aquifer or paleosol (Leynes and Bien, 1998). Shallow permeability
probably exist along the NE portion of Mt. Cabalian and extends towards the Mainit thermal area through
interconnected primary (i.e., lithologic contacts between the Tertiary volcanics and underlying Tertiary clastics and
limestones) and secondary (i.e., Mahalo fault splay) sources of permeability (Rosell and Zaide-Delfin, 1997).
Despite the regional scale of lineaments delineated from the 30-m resolution Landsat TM imagery, a distinct younging
pattern (through crosscutting relationships) of NW-trending structures relative to the NE and ENE-trending lineaments
can still be observed. This suggests that these NW-trending lineaments have possible direct connection with
hydrothermal fluids beneath Mts. Cabalian and Cantodoc and are probably deep-seated like the Philippine Fault. Its
intersections with NE to ENE-trending fault sets could have localized fluid flow at shallow levels (i.e., Mainit thermal
area to the NE, Tabunan thermal area to the west). In addition, localized structures drawn from aerial photographs and
ground-checked lineaments (Leynes et al., 1996) show a variety of fault sets at the Cabalian-Cantodoc-Tamar volcanic
edifices which are not visible from the structurally-interpreted Landsat TM imagery (Figure 3a). This is probably due to
the Landsat imagery's 30-m spatial resolution. Structural lineaments extracted from the radar imagery confirmed the
occurrence of these localized structures (Figure 3a). This advantage of radar is due to its « 10-m spatial resolution and
its ability to penetrate cloud-covers.
32 ALTERATION MAPPING RESULT
Ground-mapped major altered grounds and springs (e.g. Mainit thermal area, Ilaya kaipohan and Tabunan thermal area)
are all located in proximity to the interpreted alteration zones (Figures 4 and 5). It is worthy to note the occurrence of
springs and altered grounds (e.g. Liptong altered grounds, Tabunan thermal area and Hitunlob springs) along faults and
fractures and lithologic contacts. Their occurrence and distribution seem to suggest three- (3) probable geothermal
systems: Cabalian, Cantodoc and Tamar systems.
PCA ANALYSIS
(PC3) Image
exp = d je
N ; FEES,
Dr &
T 3 ;
Ë : |
= 3
E ut "n
Ro Mains Mahalo
Location of B “ani iiid
hydroxyl-bearing 4 S
minerals t E i ; uc
irem = LE loi. ‚Mahal
Y. fern area
an ;
ares |
Ba /
a à " es Í
se exe SES E A Sus Ain
ume com A Ea A Easting ji nseberg) qUUE O-—- —B—
Figure 4. Alteration mapping of SLGP using Normalized : : cdi
Difference Vegetation Index (NDVI) and Principal Figure 5. SLGP Inter preted composite geophysical
Component Analysis (PCA). anomaly showing current and proposed drilling
pad locations.
224 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000.
