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Gossan in Lake Harbour Group psammite adjacent to a layered mafic-ultramafic sill, Meta Incognita Peninsula, Baffin Island, Nunavut; hammer is 35 cm long.
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This paper summarizes the 2014 field observations on a suite of mafic, ultramafic and layered mafic-ultramafic sills on Meta Incognita Peninsula, Baffin Island, Nunavut. The sills, several of which are up to hundreds of metres in thickness, are emplaced into the dominantly psammitic to pelitic sedimentary strata of the middle Paleoproterozoic Lake...
Context in source publication
Context 1
... of the intrusions contain disseminated sul- phide (pyrite and minor chalcopyrite); chromite and Summary of Activities 2014 13 pentlandite were not noted. Deep orange gossans ( Figure 6) were observed in psammite adjacent to the mafic-ultra- mafic bodies with ferricrete ( Figure 7) occurring at the base of some sills. The ferricrete comprises a medium to coarse clastic sediment cemented by an iron oxyhydroxide. ...
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Citations
... 1.93 Ga (corresponding to the youngest detrital zircon age, Scott et al. 2002). Sparse mafic/ultramafic sills up to 200 m thick and 5.6 km in maximum dimension intrude the LHG and were affected by peak granulitefacies metamorphism (St-Onge et al. 2015). The supracrustal rocks of the THO, including the LHG, were subject to multiple deformational and metamorphic events (see St-Onge et al. 2007). ...
Samples from 14 spinel occurrences in the Lake Harbour Group (LHG), Baffin Island, Nunavut, Canada, were studied using a combination of petrography, whole rock geochemistry, microprobe analysis, and, where possible, geochronology. Spinel at most occurrences is blue to violet and generally not of gem quality. Two spinel occurrences near Kimmirut contain vivid blue, cobalt-enriched (0.03-0.07 wt.% CoO) spinel. The spinel mostly occurs in metasedimentary (sensu stricto) rocks, with the exception of a few metasomatic occurrences. All spinel occurs in marble and calc-silicate/silicate-rich metacarbonate rocks. Minerals occurring with spinel as part of a stable assemblage include calcite, dolomite, phlogopite, pargasite, diopside, humite, forsterite, scapolite, anorthite, graphite, and pyrrhotite. The spinel formed under peak granulite facies metamorphic conditions. Metasedimentary (s.s.) spinel-bearing rocks in the LHG are interpreted to have the following protoliths: (1) impure dolomite-bearing and dolomitic limestone; (2) dolomitic marl; and (3) evaporitic magnesitic marl. Other significant gemstone occurrences in the LHG (sapphire and lapis lazuli) are interpreted to have similar protoliths. Factors that favor spinel genesis in Mg-bearing metacarbonates include: (1) a low abundance of Si relative to Al, which is a primary control on whether spinel forms in most calc-silicate rocks; (2) low K activity limiting the formation of phlogopite and thus leaving Al available for spinel formation; (3) low XCO2 in marbles; and (4) insufficient quantities of Mg or dolomite reactant in diopsidite limiting Al incorporation into phlogopite to form spinel. The spatial distribution of Co enrichment at the cobalt-blue spinel occurrences is indicative of highly localized enrichment. Cobalt and Ni are interpreted to have been enriched in the original sediment, or during diagenesis or low-grade metamorphism. Concentrations of Co (up to 29 lg/g) and Ni are anomalously high, while concentrations of Fe, Mn, V, Cr, and Cu are much lower than expected; this chemical signature speculatively could be caused by diagenetic processes prior to metamorphism. Pyrrhotite strongly partitions Fe relative to spinel, and therefore an abundance of sulfide is expected to improve the attractiveness (and commercial value) of spinel by decreasing the amount of Fe incorporated, thus preventing spinel from having an overly dark color. © 2019 Mineralogical Association of Canada. All rights reserved.
Archean and Paleoproterozoic cratonic rocks of Baffin Island define four stacked structural levels that are juxtaposed within the middle Paleoproterozoic Trans-Hudson Orogen. From north to south, and highest to lowest structural level, these comprise:1) the Archean Rae Craton, unconformably overlain along its southern margin by middle Paleoproterozoic supracrustal cover (Piling Group) and stratigraphically similar units of the Hoare Bay Group on Cumberland Peninsula; 2) Archean to middle Paleoproterozoic metaplutonic units and middle Paleoproterozoic metasedimentary cover (Lake Harbour Group), collectively termed the 'Meta Incognita microcontinent'; 3) middle Paleoproterozoic orthogneiss, interpreted as a deformed arc-magmatic terrane (Narsajuaq terrane) or alternatively as Narsajuaq-age intrusions emplaced in the Meta Incognita microcontinent; and 4) Archean orthogneiss, interpreted as the northern continuation of the lower-plate Superior Craton, and associated middle Paleoproterozoic continental-margin supracrustal cover (Povungnituk Group).
