Stratigraphy of Superior-type Iron-formation in the Schefferville - Knob Lake area, Quebec and Labrador

1966 ◽  
Author(s):  
I S Zajac
Keyword(s):  
Iron Formation ◽  
Lake Area ◽  
Superior Type

Palladium-bearing gold deposit hosted by Proterozoic lake superior-type iron-formation at the Caue iron mine, Itabira District, southern Sao Francisco Craton, Brazil; geologic and structural controls; reply

1995 ◽  
Vol 90 (8) ◽  
pp. 2372-2374
Author(s):  
Gema Ribeiro Olivo ◽  
Michel Gauthier ◽  
Marc Bardoux ◽  
Euripides Leao de Sa ◽  
Jose Teotonio F. Fonseca ◽  
...  
Keyword(s):  
Gold Deposit ◽  
Lake Superior ◽  
Iron Formation ◽  
Structural Controls ◽  
Iron Mine ◽  
Superior Type

U–Pb ages from the Nimish Formation and Montagnais glomeroporphyritic gabbro of the central New Québec Orogen, Canada

1995 ◽  
Vol 32 (8) ◽  
pp. 1208-1220 ◽  
Author(s):  
Jon M. Findlay ◽  
Randall R. Parrish ◽  
Tyson C. Birkett ◽  
Donald H. Watanabe
Keyword(s):  
Iron Formation ◽  
Lake Area ◽  
Quartz Syenite ◽  
Polymictic Conglomerate

Three U–Pb zircon dates were obtained from two igneous suites associated with cycle 2 sedimentation in the central New Québec Orogen (Labrador Trough). In the Dyke Lake area of the western part of the orogen (Schefferville zone), the Nimish Formation includes a polymictic conglomerate containing quartz syenite cobbles that crystallized at 1877.8 ± 1.3 Ma. These cobbles are petrographically and geochemically linked to the Nimish volcanics, which are intercalated with the Sokoman iron formation. Consequently, the syenite date gives an approximate age for both Nimish magmatism and ironstone deposition in the Schefferville zone. A date of ca. 2.65 Ga obtained from a Nimish trachyte in the same area indicates that zircons in the sample are xenocrysts. Farther east, at Howse Lake (Howse zone), a Montagnais plagioclase-glomeroporphyritic gabbro sill crystallized at 1884.0 ± 1.6 Ma. The Howse Lake sill, which intrudes turbidites of the Menihek Formation, is considered comagmatic with the basalts that cap the formation, and with the Willbob basalts to the east (Doublet Terrane). Consequently, the Menihek turbidites, as well as the underlying Sokoman Formation, were deposited prior to 1884 Ma in the Howse zone. In contrast, the syenite date indicates that deposition of the Menihek Formation in the Schefferville zone did not commence until after 1878 Ma. The 1884 Ma date from the Howse Lake sill also provides an estimate for the timing of cycle 2 tholeiitic volcanism in the eastern part of the orogen. The correlation between the upper Menihek and Willbob basalts suggests that the Murdoch and Thompson Lake formations, which underlie the Willbob basalts in the Doublet Terrane, are the stratigraphie equivalents of the lower and middle portions of the Menihek Formation, respectively.

The composition of hornblende, grunerite, and garnet in Archean iron formation of the Itchen Lake area, District of Mackenzie, Canada

1977 ◽  
Vol 14 (8) ◽  
pp. 1740-1752
Author(s):  
Hewitt H. Bostock
Keyword(s):  
Oxygen Fugacity ◽  
Electron Microprobe ◽  
Microprobe Analysis ◽  
Electron Microprobe Analysis ◽  
Metamorphic Grade ◽  
The Other ◽  
Alumina Content ◽  
Iron Formation ◽  
Lake Area ◽  
Factors Affecting

The compositions of seven pairs of coexisting hornblende and grunerite and five assemblages of coexisting hornblende, grunerite, and garnet from Archean silicate iron formation of low and medium metamorphic grade have been obtained by electron microprobe analysis. Important factors affecting the composition of the amphiboles are: (1) the Mg/Fe ratio of the iron-formation beds, which controls the gross Mg/Fe ratio of the amphiboles; (2) the alumina content of the beds, which affects the degree of alumina substitution in hornblende thereby altering the distribution of Mg and Fe in the coexisting amphiboles; and (3) the occurrence of iron-rich garnet, which produces higher Mg/Fe ratios in both amphiboles. A fourth potentially important factor, the oxygen fugacity, cannot be satisfactorily assessed with these data, but has not obscured the effects of the other three. Temperature of crystallization of the amphiboles was an important factor mainly insofar as it affected the crystallization of garnet in the alumina-rich rocks.Four coexisting hornblende–cummingtonite pairs from metatuffs show similar control of Mg–Fe fractionation by alumina substitution in hornblende.

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