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The Cabalian hydrothermal system is centered within the Hugpa Kaipohan and Amagusan cold altered grounds. Hence, 
hydrothermal fluid outflows were inferred to migrate WSW by faults trending NNE to NE towards Tabunan thermal 
area and Hitunlob springs (Figure 5). 
The Cantodoc system harbors the Liptong and Manigaong kaipohan which in turn outflows NE accommodated by faults 
trending ENE towards the Mainit-Mahalo and Kapakuhan thermal areas (Figure 5). 
The Tamar system is manifested by the ground-truthed Ilaya kaipohan. This kaipohan indicate the upwelling portion of 
the Tamar hydrothermal system that is inferred to be associated with predominant sets of NE- and ENE-trending faults 
dissecting this relatively older Quaternary volcanic unit. Further N and NNW of Ilaya kaipohan, suspected group of 
altered grounds and springs (i.e. Ilaya-1 and Ilaya-2 springs) also follow a NE-trending structural grain which could 
have favored outflow of hydrothermal fluids (Figure 5). 
The overlapping hydrothermal system boundaries of Cabalian, Cantodoc and Tamar are possible at Mainit-Mahalo 
thermal area. This assumption is based initially on the available thermoluminescence data of Ramos et al. (1998). The 
thermoluminescence data implied that the Cantodoc system has an age of 5-6 ka. for its latest hydrothermal event. It 
was also noted that the Cantodoc volcanic system —— (510 ka.) is relatively older than the Cabalian volcanic system (17 
ka.). Tamar volcanic system has an age range of 490-670 ka. 
' The use of the PCA and NDVI methods has manifested clearly the approximate locations and spatial distribution of 
probable altered grounds and springs within the study area. The results based on these methods imply probable 
communication between primary (i.e., lithologic units/contacts) and secondary (i.e. faults) sources of permeability. 
4 GEOSCIENTIFIC MODELS 
4.1 Post-1996 Model 
Previous geological, petrological, geochemical and geophysical data support a single hydrothermal system for SLGP 
(Leynes et al, 1996; Rosell and Zaide-Delfin, 1997; Bayon, 1996; Los Baños, 1998; Catane and Apuada, 1998). 
Geology data points only to Quaternary Cabalian and Cantodoc volcanoes as probable heat source thereby 
representing the Cabalian- Cantodoc system (Leynes et al., 1996). While petrology data of well SL-1D indicate 
passage of geothermal brine at shallow levels (depths 200 to 400 mBSL) believed to be associated with the 
Cabalian-Cantodoc system along channels of Mahalo Fault Splay (Rosell and Zaide-Delfin, 1997). These 
affirmed the assumptions based on the Na-K-Mg (for water chemistry data) and N;-He-Ar (for gas chemistry 
data) ternary plots of SLGP thermal manifestations (Bayon, 1996). Also, two-dimensional representations of 
the « 5 ohm-meter anomalies at Hugpa and Mainit-Mahalo vicinities were delineated WSW and NE, 
respectively, of Mt. Cabalian through magnetotelluric survey results (Los Baños, 1998; Catane and Apuada, 
1998). 
These previous studies deduce a single Cabalian-Cantodoc system which channels hydrothermal fluid flow 
towards the WSW at Tabunan/Hitunlob thermal areas and to the NE at Mainit-Mahalo thermal areas. This 
initial geothermal model is consistent with their findings that fluid flows are evident along lithologic contacts, 
faults and permeable hostrocks (i.e. Tertiary volcanics). 
4.0 1999 Model 
Review of the post-1996 geoscientific data, especially geological (this study) and geophysical (Apuada, in prep.) data, 
delineated significant findings favoring a three-system geothermal model for SLGP. Based on the spatial distribution of 
thermal springs and kaipohans (ground-truthed and remotely-sensed data); clustering of these thermal features along 
associated NE to ENE (for the Ilaya kaipohan and Mainit-Mahalo thermal areas) and NNE to NW (for Hugpa kaipohan, 
Nava, Hitunlob and Tabunan thermal areas) fault sets suggest the probable influence of three geothermal systems. 
Moreover, isolated NE fault sets (i.e. Anislag and Hitunlob faults), located west of Mt. Cabalian, possibly extend 
towards the NE. These observations were similarly duplicated in the refined interpretation of the geophysical data by 
Apuada (pers. comm.). Using the same MT result of Los Baños (1998), a shallow Mainit-Mahalo anomaly was instead 
interpreted to exist only until 350 mBSL. 
Broad anomalies (< 10 ohm-meters) covering the NW part of Mt. Cantodoc and SE of Mt. Tamar extends down to 
depth 1000 mBSL. This anomaly (called "Ilaya" anomaly) is associated with Mt. Tamar (termed in this report as 
"Tamar system") through the predominant NE/ENE structures that dissect the area. The Hugpa anomaly (< 10 ohm- 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part B7. Amsterdam 2000. 225