Porphyry Cu-Au Mineralization in the Ertsberg Intrusion, West
Papua, Indonesia: Style, Timing, and Sources of Hydrothermal Fluids
Gibbins, Stacie L., Titley, Spencer, and Friehauf, Kurt*, Geoscience,
University of Arizona, Gould-Simpson Building, Tucson, AZ 85721,
*Physical Sciences, Kutztown University, Kutztown, PA 19530
The Ertsberg Intrusion (EI) is located approximately 1.5 km southeast
of the Grasberg super-porphyry Cu-Au deposit (GIC), in the Gunung Bijih
(Ertsberg) Mining District, West Papua, Indonesia. Intrusion- and
carbonate-hosted mineralization is associated with the
3.28-2.97±0.54 Ma multi-phase Ertsberg Intrusion. The
orientation of the mineralized zone is parallel to the direction of
porphyry dike emplacement and regional structures.
Potassic, phyllic, propylitic and endoskarn alteration types are
recognized in the EI, distributed over 7 vein types. Two vein types
initiate pre-porphyry dike emplacement, and mineralization occurs pre
and post-dike emplacement. Cu-Au mineralization is associated with
pre-dike biotite-bornite-anhydrite veinlets, and post-dike
quartz-anhydrite-bornite+chalcopyrite//green sericite veins. Cu
mineralization is not associated with late quartz-pyrite//white
sericite mineralization; however, Au (in electrum and tellurides) has
been recognized in each alteration type except the endoskarn.
Sulfides associated with each alteration type in the EI have δ34S
values that range between -3.0 to 3.6‰. Sulfate δ34S values are
variable between different alteration types: potassic (9.6-11.1‰) and
hydrolytic (10.2-16.6‰). The bulk isotopic values associated with the
porphyry-style mineralization remained consistent throughout the life
of the hydrothermal, suggesting a common, magmatic source (Porter,
2004). Sulfide-sulfate equilibrium temperatures for potassic alteration
in the EI average 574°C, approximately 125°C cooler than
sulfide-sulfate equilibrium temperatures in the GIC. Preliminary oxygen
isotope data from potassic alteration in the EI give δ18O values
between 9.2-10.1‰ for quartz; >1‰ higher than δ18O values for quartz
in potassic alteration in the GIC.
Initial mass balance calculations using the EI volume estimate, and the
known mineralization associated with the EI show that the EI has an
insufficient volume of H2O to account for the known volume of
hydrothermal alteration and mineralization. Coupled with preliminary
sulfur and oxygen isotope data, and Re-Os isotope source data, this
suggests additional input of hydrothermal fluids from deeper magmatic
and sedimentary sources.
2005 Salt Lake City Annual Meeting (October 16–19, 2005)
Session No. 138
Sources of Porphyry Copper Deposits: Magmas, Metals, and Fluids II
Salt Palace Convention Center: Ballroom H
8:00 AM-12:00 PM, Tuesday, 18 October 2005
Geological
Society
of America Abstracts with
Programs, Vol. 37, No. 7, p. 314