1975 Volume 25 Issue 132 Pages 303-320
The Mamut mine, located in northwestern Sabah, about 65 kilometers east of Kota Kinabalu, is the first porphyry copper mine in Borneo.
The ore deposit had been discovered by the geochemical reconnaissance under the United Nations Labuku Valley Project. Commercial operation commenced in May, 1975 under the management of Overseas Mineral Resources Development. Sabah Bhd. Ore reserves are estimated at some 178 million metric tons of 0.476 percent copper.
The area is occupied by the Upper Cretaceous and Tertiary flysch type sediments and igneous rocks of the Northwest Borneo Geosyncline, extending over a distance of 800 kilometers in NE-SW direction. In the mineralized area, sedimentary rocks consist mainly of sandstone and siltstone of Palaeocene to Eocene in age, and are emplaced by serpentinized ultrabasic rocks. These rocks are intruded by adamellite porphyry and its small associates. These stocks may be apophyses of a large batholith underlying the area, represented by Mt. Kinabalu. Several data of potassium-argon age determinations indicated that the intrusives are very young, namely Upper Miocene to Lower Pliocene in age.
The size of main adamellite porphyry intrusive is approximately 800 meters long and 300 meters wide. This intrusive body is cut by later stage granodiorite porphyry dike.
The shape of ore zone or "ore-shell" is alike a upside down short jar and it has a maximan width of 450 meters and 800 meters in length with a depth of 200 meters. The extent of the ore-shell generally includes the boundary of the main porphyry intrusive, and within the ore-shell the copper grade is roughly constant slthough the host rocks are different such as adamellite porphyry, siltstone and even serpentinite.
The alteration zoning is somewhat dissimilar to LOWELL'S (1968) model although it is not yet elucidated in detail as his model. It is formed by quartz-biotite zone, tremolite-actinolite zone and hornblende (or fresh) zone from margin to centre of mineralized body. Secondary K-feldsper also occurs in this body. The ore-shell overlaps the quartz-biotite zone and "low grade cone" located in the hornblend zone.
