Initial Report on the Geologic Quadrangle Mapping for Sindangan River Quadrangle

The Mines and Geoscience Bureau Regional Office IX (MGB, R-IX) conducted systematic geological mapping in Sindangan River Quadrangle (Sheet No. 3644-III) in Zamboanga Peninsula last April 23 to May 19, 2019 as part of the 2019 Quadrangle Geological Mapping Project. The purpose of the mapping program is to produce and update the 1:50,000 scale quadrangle maps in Region IX which is one of the least mapped area in the Mindanao. Four quadrangles are targeted for the year 2019 with no published maps, all of which are within Zamboanga Peninsula. It is located in the north central portion of Zamboanga Peninsula, east of the Palandok Quadrangle. It covers sections of the Municipalities of Leon B. Postigo, Sindangan and Bayog and a large portion of the Municipalities of Siayan, Dumingag and Midsalip. The Geological Quadrangle Mapping Team is composed of Lawrence Zamoras, Ph. D., as the team leader and two other geologists Kris Elvis Alferez and Glen Ford Gamelo.

Field activities consisted of examination of rock exposures along accessible tracks and in coastal areas, physical and megascopic description of outcrops and rock samples, sampling of representative rock units and favorable units that contain fossils, structural feature measurements of prevalent deformation and sedimentary structures, and photograph documentation. The mapping utilized 1:50,000 topographic base map of NAMRIA furnished through their website. The locations were obtained using the Global Positioning System (Garmin GPSMAP 64s), while the data gathered were plotted on a 1:10,000 topographic map generated from the Interferometric Synthetic Aperture Radar (IFSAR) 2015 of NAMRIA.

This report presents the information gathered during the implementation of the Quadrangle mapping in Central Zamboanga Peninsula and describes the rock units within the study area. It is also intended to supplement the quadrangle map as the final output of the program which is a technical report and GIS-based geologic maps that are expected to be extremely useful for many practical applications such as in mineral exploration, groundwater resource and vulnerability assessment, geohazard mapping, solid waste disposal site selection, land use planning, and other applications.

Sindangan River Quadrangle (red box), one of the 4 targets for 2019 Quadrangle Geologic Mapping in Region IX, is located within the north-central portion of Zamboanga Peninsula and covers six municipalities.

Sindangan River Quadrangle covers the latitude N8° 0’ 0” to 8° 10’ 0”, and longitude E123° 0’ 0” to 123° 15’ 0” is approximately centered in the Municipality of Siayan. From Zamboanga International Airport, the target municipalities covered by Sindangan River Quadrangle are easily accessible via all-weathered national road which serves as the main access throughout the entire peninsula. Far-flung areas can be accessed using a motorbike (locally known as habal-habal).

A pink diorite intrusive is exposed along the barangay road in Barangay Duellic, Midsalip.
A limestone forming a hill in Barangay Balonai, Midsalip.
A volcanic sequence (Zamboanga Volcanic Complex) exposed along the proposed national road in Barangay Pisompongan, Midsalip.
A calcareous sequence (Timonan Formation) showing calcarenite beds exposed along the road in Barangay New Katipunan, Midsalip.
An ultramafic rock block exposed in a quarry area in Barangay Makasing, Dumingag.
A gabbro exposed in Barangay Macasing along the road to Barangay Dulian, Dumingag.
A bedded sandstone exposed along the steep upper slope beside the barangay road in Barangay Datu Tutukan, Dumingag.
A pillow basalt exposed in Barangay Datagan along barangay road to Bgry Macasing, Siayan.
A bedded sandstone exposed along the steep upper slope beside the barangay road in Barangay Macasing, Siayan.
A limestone forming a hill in Barangay Macasing, Siayan.
A volcanic sequence (Zamboanga Volcanic Complex) showing highly vesiculous basalt flow deposit exposed along the road in Barangay Diongan, Siayan.
A volcanic sequence (Zamboanga Volcanic Complex) showing tuffaceous mudstone-sandstone interbeds exposed along the road in Barangay Guibo, Siayan.
A massive sandstone exposed in Barangay Bato, Sindangan.
A volcanic sequence (Zamboanga Volcanic Complex) showing a columnar basalt exposed along the river in Barangay Bucana, Sindangan.
A volcanic sequence (Zamboanga Volcanic Complex) showing a volcaniclastic sequence with coal lenses exposed along the currently constructed National Road in Barangay Bucana, Sindangan.
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