Today is

 

 

GEOLOGY OF SOME ALPINE-TYPE CHROMITE DEPOSITS IN THE PHILIPPINES

GEORGE C. BACUTA, JR.
Geologist
PHILIPPINE BUREAU OF MINES

 

 

 

 

ABSTRACT



The Philippines is the major source of chromium ore in Southeast Asia. Chromite production from 1946 to 1976 amounted to 2,756,072 DMT of metallurgical grade ore and 12,425,200 DMT of refractory grade ore. Principal producers are the Coto and Acoje Mines in the rich
Zambales Chromite District in Luzon which respectively produce refractory and metallurgical
grade chromite. Total ore reserves of chromite as of 1976 is estimated at 4 million tons of metallurgical grade and 7.8 million tons of refractory grade.

Chromite occurs in most of the peridotite outcrops in the Philippines. The deposits treated in this report are those of the Zambales Ultramafic Complex and the Central Palawan Ultramafic Complex both in the form of peridotite-dunite-gabbro complexes typically occurring as portions of ophiolite sequences They belong to the alpine- or podiform-type chromite deposits according to Thayer's classification. Chromites in Zambales display a wide range of Cr:Al ratio, a confined Fe-2:Mg ratio, and a bimodal relationship concentrating into AI2O3 rich spinels and AI2O3 poor spinels. The chromites in Central Palawan are generally AI2O3 poor spinels and are quite similar to the Sabah chromites. The AI2O3 rich chromites in the Coto Ultramafic Belt and the Cabangan Massif in Zambales occur in peridotite associated with troctolite and olivine gabbro while AI2O3 poor chromites in Central Palawan and the Acoje Ultramajic Belt in Zambales occur in peridotite associated with pyroxenite and norite. Chromtte is disseminated. nodular, massive and brecciated in either a troctolitic or serpentinized dunitic gangue. The deposits are irregular in form and structure occurring as layers, lenses, schlieren and pods and are characterized by metamorphic features

The Zambales Ophiollte may be a remnant of the Mesozoic oceanic crust that underlies the China Sea and may have been emplaced by subduction/obductlon probably at pre·upper Eocene. The Central Palawan Ophiolite may originate from the oceanic crust underlying either the China Sea or the Sulu Sea and may comprise the Cretaceous (?) ophiolitic event described by Hutchison (1975) for the Darvel Bay-Labuk-Palawan Ophiolite Belt. The origin for the podiform chromlte deposlts ln Zambales and Central Palawan is described in the sense of Dickey (1975) for podiform deposits associated with normal oceanic crust.

 

 

 

Geological Society of the Philippines

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

Tel: +(63-2) 633-9025