The Balabag deposit contains gold mineralization typical of low-sulphidation epithermal vein-type deposits, and is characterized by quartz veining, which exhibit a en echelon pattern and silica replacement. The veins tend to develop within andesitic and dacitic volcanic and fine-grained laminated tuffs. Also, stockworks of quartz veins and veinlets are present in some areas, the mineralization is believed to be coeval with the intrusion of hypabyssal rocks consisting andesite and dacite porphyries.
The Balabag property has a total area of almost 4,800 hectares, and is located within the Municipalities of Bayog, Zamboanga Del Sur and Zamboanga Sibugay Province, Island of Mindanao, Philippines.
Zamboanga City, the most important urban center in the peninsula, is accessed from Manila by plane, after approximately an 80 minute flight. From there, access to the property is by a 5-hour drive via the all-weather Zamboanga–Dipolog national highway passing through a sealed road from Imelda town to Barangay Guinoman, Municipality of Diplahan in Zamboanga Sibugay Province. Balabag can be reached by an 2 hour-long ride from the paved road along the Depore river, including a trail that borders rice fields and also runs on an old logging road.
The topography is moderately rolling to semi-rugged. Towards the western section of the area, elevations range from 200 to 928 meters above mean sea level (AMSL). The area is drained by the southeasterly flowing headwaters of the Kabasalan and Palandoc Rivers. The higher elevations are vegetated with secondary forest growth, cogon and grasses while the lower elevations are cultivated for agricultural crops.
Geologically, the Mindanao peninsula is bounded to the west by the Eurasian Plate being subducted southeastward into the Sulu Trench, and on the east by the Philippine Sea Plate being subducted westward into the Philippine Trench
This complexity is increased in Zamboanga (West Mindanao) by the NE-subducting Cotabato trench that is expressed on-land as a collision zone along the Cotabato-Sindangan Fault, which is believed to connect northwestward to the Negros Trench (Acharya and Aggarwal, 1981). This tectonic setting has produced three distinct rock-stratigraphic assemblages in West Mindanao, namely: (a) “SW- Zamboanga Zone”, (b) “Cotabato-Sindangan Collision Zone and”, (c) “NE - Zamboanga Zone” (Flores, 1999).
The SW – Zamboanga Zone consists of a generally NE-trending and relatively older suite of rock-stratigraphic units. These include the pre-Tertiary basement complex consisting of Triassic Schists and other metamorphics, Jurassic Granites, Cretaceous Ultramafics and Ophiolitic Rocks, and Paleocene to Eocene Sediments. Oligocene to Miocene sediments and volcanics unconformably overlie the basement complex. Miocene intrusive and hypabyssal rocks intrude the pre-existing rocks. The youngest sequences comprise Quaternary volcanics and finally a young cover of Quaternary sediments, alluvium and terrace gravel.
The Cotabato-Sindangan Collision Zone is characterized mostly by NW-trending braided or anastomosing sinistral faults and similarly-trending litho-stratigraphic units. Rock suites comprise Cretaceous ultramafics and ophiolitic rocks, Paleocene-Eocene sediments and Oligocene to Miocene volcanics and sediments. Miocene intrusives and hypabyssal rocks, Quaternary igneous sequences (both intrusive and extrusive), and alluvium comprise the youngest sequences.
The NE-Zamboanga Zone is mostly covered with the Quaternary Malindang Volcanics and related lahar and alluvial deposits.
Balabag is a low sulphidation, quartz vein epithermal gold deposit with anomalous gold values in the apical part of the system. Vein systems appear to locally consist of closely-space individual veins varying from a few millimeters to tens of centimeters thick.
The most significant vein systems known to date are Miswi and Tinago. Warik-Warik corresponds to the Eastern extension of Tinago. On the other hand, hydrothermal brecciation and tectonic hydro-fracturing indicates depressurization accompanied by vigorous boiling and mineral precipitation.
The Tinago vein strikes generally ENE and dips 30°- 40° to the north and appears to be traceable through surface workings for several hundred meters. Neither the Tinago nor the Miswi veins have been closed off along strike. Occasional stringered to stockworked quartz veining has been observed in the immediate walls to the veins.
The veins exhibit a en echelon pattern and tend to develop within andesitic tuff and volcaniclastic units bordered to the north and south by NWSE running faults showing sinistral displacement.
The vein structures which develop braiding and typical pinch and swell within the andesites tend not to extend on either side of the faults, in the sediments. The vein systems appear to have been locally slightly displaced by N-S trending sub vertical faulting that would be post-mineralization.