The main results of an exploration venture on Balabac Island, Philippines are presented. The east-central portion of Balabac is underlain by a volcanic-chert associaticn intruded by ultramaflcs and contains copper mineralization. Isoclinal folding and thrusting have been important. The remainder of the island is mainly sandstone and mudstone. It apparently contains no economic mineralization.

Geophysical prospecting methods and the proving of an orebody by diamond drilling are described.

The Lorraine Orebody is a massive hypothermal cupriferous pyrite deposit, averaging over 4 percent copper. It is of some interest in that hydrothermal wallrock alteration is almost entirely absent, with contracts between ore and barren country rock generally knife-edged. Some secondary enrichment occurs. Controls of localization are structural and lithologic, and the presence of ultramafic intrusions probably has genetic significance.

Some comparisons of the general geology are made with mainland Palawan and North Borneo, and the ore environment is briefly compared with other areas.