METAL ZONATION AND THE TIMING OF GOLD MINERALISATION ASSOCIATED WITH THE BIG GOSSAN CU-AU DEPOSIT, ERTSBERG DISTRICT, IRIAN JAYA, INDONESIA
Several generations of brecciation in the Big Gossan skarn are associated with infill and alteration by pyroxene, garnet, magnetite, amphibole, and chalcopyrite-pyrite with a Cu-Au-Ag element association, whereas sphalerite, galena and minor pyrite postdate the Cu-Au mineralisation. Breccia zones occur in the Big Gossan Fault above the skarn and in the hanging wall adjacent to the skarn. The major hanging wall breccia contains infill and alteration composed of amphibole, calcite, magnetite and talc and is crosscut by fractures and faults containing gold associated with massive pyrite, sphalerite, galena and localised Bi-Pb sulphides (Rae et al., 1994). Gold in the minor fault breccias above the skarn is associated with massive banded sphalerite, pyrite, galena and minor arsenopyrite.
One or more late stage galena-sphalerite-pyrite-gold events overprints the main Cu-Au-Ag orebody, and the apparent vertical and lateral zonation is not the result of a single-stage evolving fluid.
References: Meinert, L.D. 1997. Econ. Geol. v92, pp509-533. Rae, A.J., Allen, J.M. and Powell, N.G., 1994. Unpublished internal report for PT Freeport Indonesia.