Genesis of the Mamut Porphyry Copper Deposit, Sabah, East Malaysia

Abstract

: The Mamut deposit of Sabah, East Malaysia, is a porphyry type Cu‐Au deposit genetically related to a quartz monzonite (“adamellite”) porphyry stock associated with upper Miocene Mount Kinabalu plutonism. The genesis of the Mamut deposit is discussed based on petrology of the intrusives in the Mount Kinabalu area combined with ore– and alteration–petrography, fluid inclusion and sulfur isotope studies. Groundmass of the adamellite porphyry at Mamut is rich in K which suggests vapor transport of alkaline elements during the mineralizing magmatic process, while the groundmass of the post‐ore “granodiorite” porphyry at Mamut contains small amounts of normative corundum suggesting depletion in alkaline elements at the root zone of the magma column. Sub‐dendritic tremolitic amphibole rims on hornblende phenocrysts in the Mamut adamellite porphyry suggest interaction between the mineralizing magma and the exsolved fluids. Occurrences of clinopyroxene microphenocrysts and pseudomor‐phic aggregates of shredded biotite and clinopyroxene after hornblende phenocrysts in the barren intrusives imply lower water fugacity and decreasing in water fugacity, respectively. Compositional gap between the core of hornblende phenocrysts and the tremolitic amphibole rims and those in the groundmass of the Mamut adamellite porphyry suggests a decrease in pressure. Higher XMg (=Mg/(Mg+Fe) atomic ratio) in the tremolitic amphibole rims in the Mamut adamellite porphyry compared to those of the barren intrusions suggests high oxygen fugacity. High halogen contents of igneous hydrous minerals such as amphiboles, biotite and apatite in the Mamut adamellite porphyry suggest the existence of highly saline fluids during the intrusion and solidification of the mineralizing magma. Fluid inclusions found in quartz veinlet stockworks are characterized by abundant hypersaline polyphase inclusions associated with subordinate amounts of immiscible gaseous vapor. Both Cu and Au are dispersed in disseminated and quartz stockwork ores. Chalcopyrite and pyrrhotite as well as magnetite are the principal ore minerals in the biotitized disseminated ores. Primary assemblage of intermediate solid solution (iss) and pyrrhotite converted to the present assemblage of chalcopyrite and pyrrhotite during cooling. Subsequent to biotitization, quartz veinlet stockworks formed associated with retrograde chlorite alteration. The Cu‐Fe sul–fides associated with stockwork quartz veinlet are chalcopyrite and pyrite. Overlapping Pb and Zn and subsequent Sb mineralizations were spatially controlled by NNE‐trending fractures accompanying the phyllic and advanced argillic alteration envelope. Sulfur isotopic composition of ore sulfides are homogeneous (about +2%) throughout the mineralization stages. These are identical to those of the magmatic sulfides of Mount Kinabalu adamellitic rocks.

Porphyry copper assessment of Southeast Asia and Melanesia: Chapter D in <i>Global mineral resource assessment</i>

“…The cumulative frequency plot shows the estimated resource volumes associated with cumulative probabilities of occurrence, as well as the mean, for each commodity and for total mineralized rock. Geological Research and Development Centre, 1987-2000, Systematic Geologic Map, Indonesia, map nos. 2010, 2013, 2014, 2015, 2016, 2109, 2110, 2111, 2112, 2113, 2114, 2115, 2116, 2117 (Berger and others, 2008;John and others, 2010), Porphyry copper-gold Cooke and others, 1998) Grade and tonnage model: Porphyry copper, Cu-Au subtype (Singer and others, 2008) …”

“…Nund, s, and Cv% are calculated using a regression equation Geological Research and Development Centre, 1987-2000, Systematic geologic map, Indonesia, map nos. 1108, 1109, 1110, 1208, 1209, 1210, 1308, 1309, 1407, 1408, 1409, 1507, 1508, 1509, 1607, 1608, 1609, 1707, 1708, 1707, 1807, 1907, 2107, 2207, 2307, 2407, 2408 (Berger and others, 2008;John and others, 2010); Porphyry copper-gold Cooke and others, 1998) Grade and tonnage model: Porphyry copper, Cu-Au subtype (Singer and others, 2008) Table G1 summarizes selected assessment results.…”

Environmental geochemistry of the abandoned Mamut Copper Mine (Sabah) Malaysia

“…The Cu minerals in the ore body are associated with adamellite porphyry (47 %), serpentinite (29 %), siltstone/hornfels (21 %) and granodiorite porphyry (3 %) (Akiyama 1984). The distinctive feature of the Mamut deposit compared to other porphyry Cu deposits in the region was the existence of ultramafic rocks as a wall rock in a large portion of the ore body (Imai 2000). This has environmental implications in the current post-mining landscape, for example the occurence of alkaline and acid drainage leading to the formation of floc.…”

“…The Mamut deposit is a porphyry-type Cu-Au deposit genetically associated with a quartz monzonite (or adamellite) porphyry stock, which is one of satellite facies of the K-rich Upper Miocene Mount Kinabalu batholith (Imai 2000). The Mamut porphyry is separated by a north-south fault into an east body and a west body, and both are mineralised (Kosaka and Wakita 1978).…”

“…1) was the largest metallic mine in the country at the time of operation. The mine site is an unusual derelict Cu-Au mine on account of its geological setting; a porphyry intrusion wedged between serpentinite rocks (Imai 2000), and its location surrounded by the biodiversity-rich nature reserve Kinabalu Park. The environmental legacy of the MCM site is significant and includes the presence of a large pit lake filled with polluted acid water surrounded by unstable pit walls, as evidenced by extensive cracks in the walls, and large amounts of acid-producing minerals waste.…”