Today is

 

 

PRELIMINARY STUDIES ON HYDROTHERMAL
ALTERATION IN PHILIPPINE PORPHYRY COPPER
DEPOSITS IN RELATION TO TECTONIC ENVIRONMENT

Jose S. Portacio, Jr.
 

 

 

 

ABSTRACT



On the basis of extensive petrographic studies of wallrock samples gathered and collected from major porphyry copper-producing mines and prospects, some definitive pattern regarding hydrothermal alteration and mineralization of porphyry deposits in intra-oceanic island-arc environment such as the Philippines has been observed.

Typical products of hydrothermal alteration such as sericite, K (potash) feldspar, secondary biotite, silica, clay, anhydrite, epidote, calcite, chlorite, zeolite, uralite and pyrite are present. These are grouped into mineral suites following Lowell and Guilbert’s (1970) model namely:
potassic (quartz, secondary biotite, +/- Kfeldspar, +/- chlorite, +/- sericite, +/- anhydrite); phyllic (quartz, sericite, pyrite, +/- chlorite, +/- secondary biotite, +/- anhydrite); argillic (clay, sericite, pyrite, +/- quartz, ichlorite and +/- gypsum) and propylitic (epidote, chlorite, calcite, pyrite, zeolite, uralite).

Ore is commonly observed to occur within the potassic or the phyllic zones and, less commonly, within the argillic and propylitic zones. In many instances, the ore is enveloped by a thick pyrite halo. In some deposits containing copper mineralization within the propylitic zone, non·commercial tonnage may occur along narrow shear zones, accompanied locally by biotitization, silicifcation, and sericitization. Magnetite content is usually weak within the potassic and phyllic zones, progressively increasing towards the propylitic zone.

Finally, although the generalized model of alteration zoning of S. W. USA porphyry copper deposits (Lowell and Guilbert, 1970) is also recognizable in the Philippine deposits, overlapping of the various alteration zones is commonly observed in the latter type copper deposits.

 

 

 

Geological Society of the Philippines

Unit 250, 2nd Floor, Cityland Pioneer, 128 Pioneer Street, Mandaluyong City, Philippines

Tel: +(63-2) 633-9025