Inhaltszusammenfassung

The influx of a H2O-CO2-dominated fluid into actinolite-bearing metabasic rocks during greenschist facies metamorphism in the Kalgoorlie area of Western Australia resulted in a zoned alteration halo around inferred fluid conduits that contain gold mineralisation. The alteration halo is divided into two outer zones, the chlorite zone and the carbonate zone, and an inner pyrite zone adjacent to the inferred fluid conduits. Reaction between the fluid and the protolith resulted in the breakdown o...The influx of a H2O-CO2-dominated fluid into actinolite-bearing metabasic rocks during greenschist facies metamorphism in the Kalgoorlie area of Western Australia resulted in a zoned alteration halo around inferred fluid conduits that contain gold mineralisation. The alteration halo is divided into two outer zones, the chlorite zone and the carbonate zone, and an inner pyrite zone adjacent to the inferred fluid conduits. Reaction between the fluid and the protolith resulted in the breakdown of actinolite and the development of chlorite, dolomite, calcite and siderite. In addition, rocks in the pyrite zone developed muscovite-bearing assemblages as a consequence of the introduction of potassium by the fluid. Mineral equilibria calculations undertaken using the computer software thermocalc in the model system Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-CO2 show that mineral assemblages in the outer zones of the alteration halo are consistent with equilibrium of the protoliths with a fluid of composition X-CO2 = CO2/(CO2 + H2O) = 0.1-0.25 for temperatures of 315-320 degreesC. The inner zone of the alteration halo reflect equilibrium with a fluid of composition X-CO2 approximate to 0.25. Fluid-rock buffering calculations show that the alteration halo is consistent with interaction with a single fluid composition and that the zoned structure of the halo reflects the volume of this fluid with which the rocks reacted. This fluid is likely to have also been the one responsible for the gold mineralisation at Kalgoorlie. » weiterlesen» einklappen

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Klassifikation

DFG Fachgebiet:
Mineralogie, Petrologie und Geochemie

DDC Sachgruppe:
Geowissenschaften