|
Mankayan Dacitic Complex | |
|
Lithology |
Dacite, breccias, pyroclastic rocks |
|
Stratigraphic relations |
Intrudes older rocks |
|
Distribution |
Lepanto mine, Mankayan, Benguet; Baguio District |
|
Age |
Late Pliocene - Pleistocene |
|
Previous Name |
Imbaguila / BatoDacite Porphyry |
|
Named by |
Lepanto Consolidated Mining Company |
|
Renamed by |
Balce and others (1980) |
|
Synonymy |
Balatoc Dacite |
Dacitic rock units are represented by dacite porphyries in the Lepanto mine, Mankayan, Benguet and the Balatoc Dacite Plug in the Baguio District. Dacite domes, diatremebreccias and pyroclastics in the Lepanto area preceded and post-dated epithermal mineralization. These are known locally as Imbaguila Dacite Porphyry, and Bato Dacite Porphyryand their pyroclastic equivalents. The Imbaguila predates mineralization while the Bato postdates the mineralization.
The plug at the Balatoc Mine is roughly a vertical pipe measuring 980 m by 730 m in plan and tapers downward to a maximum known depth of 2,000 m (Mitchell and Leach, 1991). The pipe contains blocks of various rock types that include quartz diorite, andesite, metasediments, dacite and granodiorite. The matrix is made up of dacitic and andesitic material as well as an admixture of quartz, plagioclase and clayey material. Gold-bearing veins traverse the breccia. Later andesite dikes also cut across the breccia.
A similar type of breccia pipe is present in the Sto. Niño Mine. According to Balce (1978), it is 1,200 m by 500 m in plan and the bulk of the pipe is dacitic in composition.
Wolfe (1981) gives a K/Ar date of 1.7 Ma for a sample of dacite. Maleterre (1989) reports K/Ar dating of 1.5 Ma and 1.9 Ma for samples of dacite. MMAJ-JICA (1983) gives a dating of 0.8 Ma for the Balatoc Plug. These datings are equivalent to Pleistocene. In Lepanto, K/Ar dating of biiotite from the earlier dacite gave a value of 2.9 ± 0.4 Ma (Sillitoe and Angeles, 1985). On the other hand, K/Ardatings reported by Arribas and others (1994) for the later dacites (0.96 ± 0.29 Ma; 1.18 ± 0.08 Ma) are close to the dating for the Balatoc Plug (0.8 Ma).
Formation sequence[]
- Preceeded by - Balabac Andesite
- Succeeded by - Malaya Formation