SYN-AMPHIBOLITE FACIES ARCHEAN LODE GOLD MINERALIZATION IN THE MT-YORK DISTRICT, PILBARA BLOCK, WESTERN-AUSTRALIA

The Archaean lode gold deposits in the Mt. York District, Pilbara Bloc k, Western Australia are hosted in banded iron formation (Main Hill/Br eccia Hill prospect) of the ca. 3.33 Ga Gorge Creek Group and in amphi bolites (Zakanaka prospect) of the ca. 3.46 Ga Warrawoona Group. Gold mineralisation at the Main Hill/Breccia Hill prospect is associated wi th breccias comprising quartz clasts in a quartz-pyrrhotite matrix, an d quartz-amphibole veins, with lollingite being the major host for gol d. Minimum temperatures for gold mineralisation at the prospect are co nstrained as 455-degrees-C to 550-degrees-C by arsenopyrite thermometr y. Gold mineralisation at the Zakanaka prospect is spatially associate d with -clinopyroxene-calcite-microcline-calcic-amphibole veins and bi otite altered wallrock adjacent to the veins. Temperatures for vein em placement are estimated as 480-degrees-C to 570-degrees-C using both p lagioclase-amphibole thermometry and mineral equilibria with respect t o T and X(CO2). The timing of gold mineralisation relative to the peak of metamorphism is constrained by mineral textures and the relative t emperatures of hydrothermal alteration and metamorphism. Gold minerali sation at both deposits was broadly synchronous with the peak of regio nal amphibolite facies metamorphism, which reached temperatures of 520 -degrees-C to 640-degrees-C based on amphibole-plagioclase and garnet- biotite thermometry. In this respect, the deposits are similar to othe r well documented syn-amphibolite facies lode gold deposits from the A rchaean Southern Cross greenstone belt in the Yilgarn Block, and repre sent the deeper section of a crustal continuum of lode gold deposits t hat includes mesothermal deposits such as those at Kalgoorlie at highe r crustal levels.