Initial Report on the Geologic Quadrangle Mapping for Lakewood Quadrangle

The Mines and Geoscience Bureau Regional Office IX (MGB, R-IX) conducted systematic geological mapping in Lakewood Quadrangle (Sheet No. 3646-IV) in Zamboanga Peninsula last May 23 to June 20, 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, south of Sindangan River Quadrangle. It covers sections of the Municipality of Kumalarang and Pagadian city; and a large portion of the Municipalities of Bayog, Lakewood and Tigbao. 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.

Lakewood 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 .

Lakewood Quadrangle covers the latitude N 7° 50’ 0” to 8° 0’ 0”, and longitude E 123° 0’ 0” to 123° 15’ 0” is approximately centered in the Municipality of Lakewood. From Zamboanga International Airport, the target municipalities covered by Lakewood 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).

Potassic feldspar-rich coarse-grained intrusive rock (Quartz Diorite) outcrop exposed along the upstream tributary of the Sibuguey River which exhibit systematic fractures observed in Barangay Dimalinao, Bayog, ZDS.
Potassic feldspar-rich coarse-grained intrusive rock (Quartz Diorite) outcrop exposed along the upstream tributary of the Sibuguey River observed in Barangay Pulang Bato, Bayog, ZDS. This intrusive plutons produced the mineralizing body along the volcaniclastic carapace of the TVI Balabag Gold Project.
Thinly bedded to laminated quartz-rich sandstone-mudstone sequence having a strike orientation of E-W and dipping 30 N, this sedimentary unit is capped by the younger volcanic sequence of the Zamboanga Volcanic Complex observed in barangay Matalang, Lakewood, ZDS.
Another river exposure of the Midsalip Diorite observed along the upstream section of the Labangan River in barangay Gasa, Lakewood, ZDS.
Several prominent volcanic peaks where observed in the Lizon area in Pagadian City which is part of the younger Zamboanga Volcanic Complex, this rock unit intruded the Late Miocene dioritic plutons in the area.
A road exposure of a highly fracture silicified volcaniclastic rock which overlain the Sibugay Formation that was observed in barangay Liba, Bayog, ZDS.
Road cut exposure of a pinkish volcanic rock showing a trachytic texture of acicular hornblende laths, observed in barangay Bagong kahayagan, Lakewood, ZDS. Most of the volcanic peaks in the area are derived from silica-rich magma producing a viscous composition.

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