Paper No. 6
Presentation Time: 3:00 PM
ISOTOPIC STRATIGRAPHY AND FLUID TRACING IN THE GUNUNG BIJIH SKARN, ERTSBERG DISTRICT, PAPUA, INDONESIA
HANSON, Cory M., Jackson School of Geosciences, University of Texas at Austin, Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, 1 University Station, C1100, Austin, TX 78712, KYLE, J. Richard, Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX 78712 and LASSITER, John C., Department of Geological Sciences, University of Texas at Austin, 1 University Station C1100, Austin, TX 78712, chanson@utexas.edu
The Ertsberg (Gunung Bijih) Skarn is a roof pendant of variably replaced and metamorphosed Cenozoic New Guinea Limestone within the 2.6-Ma Ertsberg Intrusive Complex. Highest Cu-Au ore grades are hosted in magnetite skarn which generally includes pyroxene with chalcopyrite and bornite. Magnetite skarn is enveloped by and grades into calc-silicate assemblages. Most calc-silicate skarn is replaced carbonate strata; however, a small portion of adjacent igneous material is variably replaced by calc-silicate minerals. When present, this endoskarn is invariably adjacent to exoskarn, but contacts between unaltered igneous material and replaced strata are also observed.
A pilot strontium isotope study of four marbles adjacent to the Ertsberg Skarn indicates 87Sr/86Sr values between 0.7078 and 0.7081, allowing comparison with those of the sedimentary units exposed elsewhere in the district and with the Cenozoic seawater strontium isotope curve (87Sr/86Sr values between 0.7075 to 0.7091). These values for marbles are consistent with a limestone protolith deposited at 30 to 35 Ma. An analysis of the strontium isotope composition of a monticellite-dominant calc-silicate assemblage replacing sedimentary units (87Sr/86Sr value of 0.7071) within the pendant suggests interaction with fluids exsolved from a magmatic source. Two previous analyses determined that the Ertsberg Igneous Complex has 87Sr/86Sr values of 0.7063 and 0.7065.
