Interpretations and implications of preliminary LA ICP-MS analysis of chert for the origin of geochemical signatures in banded iron-formations (BIFs) from the Meadowbank gold deposit, Western Churchill Province, Nunavut

Abstract

This project is designed to establish if there is a distinctive geochemical signature for the types of banded iron-formations (BIF) that contain gold mineralization and whether a hydrothermal footprint for the mineralization can be detected. Herein are reported the preliminary geochemistry results of a LA ICP-MS study of 39 chert samples for BIFs from the Meadowbank deposit in the Rae Domain of western Churchill Province where gold mineralization is associated with several Algoma-type BIFs within the Neoarchean Woodburn Lake Group. The main deposit is located in the Central BIF, which has been in production since 2010 with 24.5 Mt proven/probable ore reserves grading 2.8 g/t (2011). Recently, mineralization has also been identified associated with BIFs in the Far West, West, East and Grizzly zones. The geochemistry of the cherts from these five BIFs, as determined from line traverses of chert using the in situ LA ICP-MS method, has identified an ambient seawater signature (characterized by enrichment in HREE relative to LREE, positive La, Gd, and Y anomalies) and a hydrothermal signature (characterized by a positive Eu anomaly), with some influence of crustal contamination.

Interpretations and implications of LA ICP-MS analysis of chert for the origin of geochemical signatures in banded iron formations (BIFs) from the Meadowbank gold deposit, Western Churchill Province, Nunavut

“…The results of the study presented here represent the first in a series of sub-projects on the geochemistry of BIFs to address how lithogeochemistry of chert may be used to better understand the nature and origin of this gold deposit type. A preliminary account of this work is found in Gourcerol et al (2014). Moreover, the study seeks to identify similarities and/or differences between mineralized (i.e.…”

Depositional setting of Algoma-type banded iron formation

“…Numerous units of oxide-, silicate-and locally sulfide-faciesAlgoma-type BIF have been identified, which include the West IF, Central BIF and East BIF; all of the BIFs are generally interlayered with ultramafic to felsic volcanic rocks and locally with a quartzite unit (Gourcerol et al, 2015a;Sherlock et al, 2001aSherlock et al, , b, 2004. The BIF display cm-to mm-thick, laminated magnetite and white-to grey chert with associated layers (0.2 to 5 cm thick) of grunerite/biotite, cummingtonite/biotite or garnet/biotite combinations that are related to metamorphic variation on the property (e.g., Gourcerol et al, 2015a). Moreover, minor chlorite, sericite, ankerite, siderite, stilpnomelane and apatite grains are observed either as layers interbedded with chert and magnetite or as inclusions in chert bands (Armitage et al, 1996;Hrabi et al, 2003;Sherlock et al, 2004;Gourcerol et al, 2015a).…”

“…The BIF display cm-to mm-thick, laminated magnetite and white-to grey chert with associated layers (0.2 to 5 cm thick) of grunerite/biotite, cummingtonite/biotite or garnet/biotite combinations that are related to metamorphic variation on the property (e.g., Gourcerol et al, 2015a). Moreover, minor chlorite, sericite, ankerite, siderite, stilpnomelane and apatite grains are observed either as layers interbedded with chert and magnetite or as inclusions in chert bands (Armitage et al, 1996;Hrabi et al, 2003;Sherlock et al, 2004;Gourcerol et al, 2015a). These BIFs are described more in detail in Gourcerol et al (2015a).…”

“…Where metamorphosed, the Fe-rich assemblage may comprise more complex mineral assemblages that include a variety of silicate phases (e.g., amphibole, garnet, and plagioclase). The interbedded chert horizons are considered to reflect: (1) direct seawater precipitation (e.g., Bolhar et al, 2005;Thurston et al, 2012); (2) hydrothermal precipitation from vent fluids (Allwood et al, 2010;Thurston et al, 2012); and/or (3) the products of secondary replacement (Hanor and Duchac, 1990) as confirmed by their shalenormalized chemical signature (e.g., Thurston et al, 2011;Gourcerol et al, 2015a).…”

“…These four gold deposits were selected in order to validate the restricted-basin model (e.g., Barrett et al, 1988a) as a depositional setting for Algoma-type BIFs by using the geochemical signature of the chert bands as a proxy for the primary signature of ocean water chemistry and hydrothermal vent fluids.The chert chemistry was characterized by using in situ LA-ICP-MS analysis following the protocol outlined in our earlier contributions (Gourcerol et al, 2015a, b).…”