عنوان
پدید آورنده
موضوع
رده
کتابخانه
محل استقرار
TLpq304274011
انگلیسی
Skarn formation and ore deposition at the Gunung Bijih Timur (Ertsberg East) complex, Irian Jaya, Indonesia
[Thesis]
J. N. Rubin
J. R. Kyle
The University of Texas at Austin
1996
311
Ph.D.
The University of Texas at Austin
1996
The Gunung Bijih Timur (GBT--"Ertsberg East") skarn complex, Gunung Bijih (Ertsberg) mining district, was formed within the Tertiary New Guinea Limestone Group and is adjacent to the 2.9-Ma Ertsberg intrusion. The complex consists of three vertically stacked orebodies (in descending order: GBT, Intermediate Ore Zone--IOZ, Deep Ore Zone--DOZ) which total 122 Mt of ore averaging 2.0 w% Cu, 0.8 g/t Au, and 10.6 g/t Ag. The contact between the calcareous Faumai and dolomitic Waripi Formations separates Ca Mg skarn (GBT and much of IOZ: together the upper skarn--US) from Mg Ca skarn (DOZ and lowermost IOZ: lower skarn--LS). The US is typified by monticellite and diopside forsterite. Garnet replaced earlier-formed calc-silicate minerals. The LS consists of forsterite + diopside. Retrograde phases include tremolite-actinolite, phlogopite, talc, serpentine, and chlorite. Anhydrite increases with depth. Minor quartz fills space. Bornite and subordinate chalcopyrite are the principal ore minerals, filling interstices in magnetite, particularly in the LS. Bornite and chalcopyrite occur in highly brecciated ore in the US. Native Au occurs as inclusions in bornite and less commonly in quartz veinlets. Fluid-inclusion and sulfur-isotope analyses indicate that the skarn and associated orebodies were formed from predominantly magmatic waters. Hot, prograde skarn-forming fluids cooled progressively. Salinities may have increased during skarn formation. Latest assemblages formed from substantially cooler and more dilute fluids. Sulfur isotopes yield magmatic signatures for sulfides. Anhydrite displays a bimodal distribution of S-values, indicating igneous and sedimentary sources. Shallow emplacement and crystallization of the Ertsberg intrusion created contact-metamorphic skarn and marble. Metasomatic calc-silicate-magnetite skarn, along with Cu-Au-Ag ore, were formed by hot, saline, hydrothermal fluids from a cupola of an underlying magma chamber. Volume loss resulting from lower skarn formation led to failure of overlying rocks and dip-slip motion along a pre-existing fault, brecciating the orebodies. GB-district Au displays generally high fineness typical of Au in porphyry/skarn systems. Native Au from the GBT complex has a wide fineness range: 920-990 and 340-820. Native Au (Pd) from Grasberg is usd\gequsd930 fine, averaging half as much Cu as GBT-complex Au. Fineness of Big Gossan Au ranges from 540 to 960, and is Cu-poor. Bornite contains most of the Ag and native Au in the GBT complex. Copper and silver correlate positively throughout the GBT complex, Grasberg, and Dom.
Earth sciences
Geochemistry
Geology
Geology
New Guinea
skarns
J. N. Rubin
J. R. Kyle
مطالعه متن کتاب p
[Thesis]
276903
a
Y
