Host-Rock and Structural Controls on the Nature and Timing of Gold Mineralization at the Holloway Mine, Abitibi Subprovince, Ontario

摘要

The Holloway mine, a mesothermal gold deposit, is located within the western Abitibi subprovince, Ontario. Mineralized zones that contain microscopic gold within pyrite are hosted by a sequence of metakomatiites, mafic to felsic metavolcanic, and metasedimentary rocks. There were two mineralization events, however the early one was the main event in terms of the amount of gold mineralization. This event was associated with albitization, silicification, chloritization, and sericitization in addition to pyritization. The later mineralization is associated with sericitization and pyritization. Carbonate and sericite alterations are associated with both mineralizing events. Results of U/Pb zircon age dating of rocks within the sequence constrains the main mineralization event to approx 2672 Ma. Ore lenses of the Holloway deposit are enveloped by 080 deg-striking, steeply south dipping zones of intense deformation and fabric development within the Porcupine-Destor deformation zone. The shear zones are characterized by a strong foliation and, locally, an associated extension lineation. The ore lenses are interpreted to represent lithons that were formed by boudinage of the more competent mineralized zones, which are pervasively albitized. Analysis of geochemical data demonstrates that the REE, Th, Nb, Hf, Ti, Fe, and Al were largely immobile with respect to the albite, quartz, chlorite, sericite, and hematite alterations. Locally preserved textures such as abundant varioles and spherulites indicate that the host metavolcanics were relatively evolved rocks. Geochemical data show they have an iron enrichment trend typical of tholeiitic mafic to felsic suites and that they were derived through fractional crystallization of parent basalt. Because of their high Fe/Mg ratios the rocks reacted with hydrothermal solutions carrying gold, presumably as thio complexes, to form pyrite, which scavenged the gold.