Publication Type:

Book Chapter

Authors:

Gourcerol, Blandine; Thurston, Phillip C.; Kontak, Daniel J.; Cote-Mantha, Olivier; Biczok, John

Source:

Targeted Geoscience Initiative 4; contributions to the understanding of Precambrian lode gold deposits and implications for exploration, Geological Survey of Canada, Calgary, AB, Canada, p.55-68 (2015)

Keywords:

algoma-type deposits, banded iron formations, Canada, Canadian Shield, chemically precipitated rocks, chert, Churchill Province, eastern canada, epigene processes, geochemistry, gold ores, iron formations, metal ores, metals, mineral deposits, genesis, North America, Nunavut, Ontario, rare earths, Sedimentary rocks, superior province, yttrium

Abstract:

Algoma-type banded iron formations (BIFs) are chemical sedimentary rocks in Archean greenstone belts that comprise alternating layers of iron-rich minerals and chert and are generally interstratified with bimodal submarine volcanic rocks. However, the geological setting for Algoma-type BIF deposition remains equivocal due to the overprinting effects of post-depositional deformation and metamorphism, and the absence of modern analogues for comparative studies. Recent studies suggest the abundance of rare earth elements and yttrium (REE+Y) in chert bands may reflect the primary BIF geochemical signature and therefore may constrain geological settings favourable for BIF deposition. In this study, the results of LA-ICP-MS analysis of chert at three BIF-hosted gold deposits are presented to assess whether epigenetic gold mineralization is preferentially developed within a particular geochemical type of BIF. Three deposits were studied: 1) the Meadowbank deposit (Churchill Province); 2) the Meliadine gold district (Churchill Province); and 3) the Musselwhite deposit (Superior Province). The results of this study, which explores REE and yttrium as tracers of depositional processes for Algoma-type BIF, suggest that chert bands record either (1) interaction of seawater with Fe-oxyhydroxides, as suggested by heavy REE enrichment coupled with La and Y enrichment; (2) high-temperature (>250 degrees C) hydrothermal fluids, as suggested by positive Eu excursions; and/or (3) hydrogeneous contamination, which is suggested by relatively consistent REE concentrations and a chondritic Y/Ho ratio. Moreover, the pH conditions of the water column at the time of BIF deposition are evaluated using Ce/Ce* as a pH proxy, with acidic conditions associated with positive Ce/Ce* anomalies. This data set does not suggest there is a chemical preference of the studied BIF for epigenetic gold mineralization.

Notes:

GeoRef, Copyright 2018, American Geological Institute.<br/>2016-084454<br/>Ennadai-Rankin greenstone belt<br/>Meadowbank Deposit<br/>Meliadine Deposit<br/>Musselwhite Deposit<br/>North Caribou greenstone belt<br/>Woodburn Lake greenstone belt