Paleocene diorite bodies, intruded into
late Cretaceous meta-sediments and
metavolcanics, hosted copper
mineralization in the Atlas Mines in
Cebu Island. The diorite bodies lie
along a northnortheasterly trend,
suggestive of intrusion along
The Atlas copper district lies within a
2-mile wide horst, bounded by two almost
parallel east-northeast treading
structures. Uplift of the horst resulted
in the denudation and erosion of the
OligoŚMiocene sedimentary cover and the
development of the present geomorphology
of the area.
The Lutopan and BigaŚBarot deposits are
the two maior ore bodies. They are
essentially large tonnage, low grade
disseminated copper deposits. Northeast
and northwest structures played major
roles in the localization of the ore. At
Biga, mineralization appears to be
related to breccia pipes.
Chalcopyrite is the principal ore
mineral. Bornite is minor. The precious
metals and molybdenite occur as traces.
Pyrite is ubiquitous. Magnetite is
fairly abundant, sometimes reaching 5
per cent. These minerals occur mainly as
fracture fillings with or without
quartz, and fine disseminations.
The most important alteration is
silicification, occuring chiefly as
quartz veinlets, stringers and massive
replacements. The mafic minerals in the
host rocks are altered to secondary
brown biotite and chlorite. Feldspar
transformed to clays. Sericitization and
pyritization accompanied silicification.
Chlorite with minus epidote occur in the
fringe zones and outside of the