18 Jan 2001


Treasure in the Clouds - Geology of the Grasberg-Ertsberg Porphyry Copper
System, Irian Jaya, Indonesia

Dr. Kurt Friehauf, Kutztown University

The Grasberg-Ertsberg porphyry copper district is one of the largest known
copper-gold deposits in the world.  The size and grade of the deposits make
them economic to mine, in spite of the extremely remote and rugged terrain
in which they occur.  Mineralization is related to circa 3 Ma intermediate
composition igneous rocks that intrude 10 Ma limestones of the New Guinea
Group and Cretaceous clastic rocks.  There are two main centers of
mineralization:  the Grasberg deposit and deposits surrounding the Ertsberg
pluton.  Mineralization in the Grasberg deposit is characterized by early
potassium metasomatism, followed by intense hydrolytic alteration styles and
sulfur-rich mineral assemblages.  Mineralization in the smaller Ertsberg
deposit, on the other hand, is characterized by early potassium metasomatism
and well-developed skarns, but a much weaker hydrolytic stage.  Differences
in the styles of mineralization in these two closely-spaced, nearly
contemporaneous porphyry centers are the focus of ongoing research.