Metallogenesis of Wrangellia Terrane, Eastern Alaska Range, Alaska: ABSTRACT

Abstract

The Wrangellia terrane contains seven principal types of mineral deposits, each of which formed at a specific stage in the history of the terrane. They are from oldest to youngest: (1) small vein deposits of Cu-, Pb-, Zn-, Ag-, and Au-sulfides in fracture zones up to a few meters wide and as disseminations in hydrothermally altered late Paleozoic volcanic rocks; (2) Cu-, Ag-, and Au-sulfides in massive lenses and as disseminations End_Page 673------------------------------ in skarn deposits hosted in late Paleozoic marble and in hydrothermally altered volcanic rock adjacent to Permian dacite porphyries; (3) local Cu-, Pb-, Zn-, and Ag-sulfides, as disseminations in hypabyssal Permian dacite porphyries, often propylitically altered; (4) disseminated grains and lenses of Ni-bearing chromite hosted in extensive sills of Late Triassic(?) cumulate mafic and ultramafic rocks; (5) Au- and Ag-sulfide skarn deposits hosted in late Paleozoic and Upper Triassic marble adjacent to granitic plutons of Late Jurassic through Late Cretaceous age; (6) disseminated Cu-, Ag-, and Au-sulfides hosted in a few hydrothermally altered granitic plutons of the same age; and (7) Cu-, Ag-, and Au-sulfides in quartz veins and in associated altered Nikolai greenstone and older metav lcanic rocks. The following tectonic model is postulated. Deposit types 1-3 formed during building of a late Paleozoic island-arc. Type 4 formed during subsequent Late Triassic rifting and extrusion of mafic magma that formed the Nikolai greenstone and coeval emplacement of mafic and ultramafic sills. Types 5 and 6 formed during subsequent subduction and formation of a Late Jurassic through Late Cretaceous island arc along the leading edge of Wrangellia during migration toward North America, and type 7 formed during accretion of Wrangellia to the North American continent during Middle or Late Cretaceous time, resulting in regional greenschist facies metamorphism and in formation of quartz sweat veins. End_of_Article - Last_Page 674------------