HIGHLY METAMORPHOSED IRON-FORMATION ON ARCEDECKNE ISLAND, BOOTHIA PENINSULA, ARCTIC CANADA, AND THE PARAGENESIS OF HARRISONITE, Ca(Fe,Mg)6(SiO4)2(PO4)2

Abstract

Summary A layered quartz-iron silicate body, ca. 700 m x 200 m, bordered concordantly by Paleoproterozoic, granulite facies, supracrustal gneisses, outcrops on Arcedeckne Island, off northern Boothia Peninsula, Nunavut and is the type locality of the rare silico-phosphate mineral harrisonite (Roberts et al. 1993; Grice and Roberts 1993). Layers and lenses, up to 0.7 m thick, of massive garnetite are intercalated with microscopically layered quartz-orthopyroxene (or, rarely, olivine)-garnet granofels and subordinate, graphitic biotite-orthopyroxene-garnet metapelite. Contacts among the three rock types are commonly gradational. Apatite is a near-ubiqitous constituent of the rocks, which are anomalously rich in phosphorus. Garnet has mol % almandine of 84-92 in garnetite and granofels and 76-80 in metapelite. Orthopyroxene composition is Fs71-83 in garnetite and granofels, Fs59-63 in metapelite. In the two most iron-rich rocks analyzed, olivine Fo5-7 has crystallized in place of orthopyroxene. Although variable in composition, biotite is consistently rich in iron and titanium. Ilmenite is the sole oxide phase identified throughout the Arcedeckne body; pyrrhotite is a sparse accessory mineral in garnetite.