Structure and alteration related to Hercynian gold deposition, Cape Spencer, New Brunswick, Canada.

摘要

ocks associated with the Cape Spencer gold deposits near Saint John, New Brunswick were studied to determine the time constraints and the main controls on gold deposition. Aspects studied include regional and detailed structural relationships, geochemistry of the altered rocks, and various details of the gold ores.;The deposits occur in the Avalon Terrane of the Appalachian Orogen, within a largely allochthonous Hercynian fold and thrust belt that is related to dextral transcurrent movement on the adjacent Avalon-Meguma Terrane boundary. Rock units in the Cape Spencer area were juxtaposed by Hercynian faulting. They include Precambrian granitoid and volcanic rocks as well as three sedimentary formations, two of Carboniferous age and one of probable Carboniferous age.;Early effects of Hercynian deformation (D;Three distinct types of alteration affected rocks in the Cape Spencer area. The earliest (D;Gold deposits occur within pyrite-rich parts of the illitic alteration zones, both in mylonitized granitoid and sedimentary rocks. Ore grades are generally limited to the units richest in iron oxides prior to illitization. Timing of gold deposition is bracketed by the age of the youngest rocks affected by illitic alteration (Westphalian B) and by the