Publication Type:

Journal Article

Authors:

Lafrance, Bruno

Source:

Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre, National Research Council of Canada, Ottawa, ON, Canada, Volume 52, Number 12, p.1093-1108 (2015)

ISBN:

0008-4077

Keywords:

Abitibi Belt, basalts, Canada, Canadian Shield, chemical composition, clastic rocks, deformation, eastern canada, gold ores, igneous rocks, KOMATIITE, Larder Lake District Ontario, major elements, metal ores, mineralization, North America, Ontario, orogeny, petrography, plutonic rocks, sandstone, Sedimentary rocks, superior province, syenites, tectonics, tholeiitic basalt, Trace elements, volcanic rocks

Abstract:

The Larder Lake-Cadillac deformation zone (LLCDZ) is one of two major, auriferous, deformation zones in the southern Abitibi subprovince of the Archean Superior Province. It hosts the Cheminis and the giant Kerr Addison-Chesterville deposits within a strongly deformed band of Fe-rich tholeiitic basalt and komatiite of the Larder Lake Group (ca. 2705 Ma). The latter is bounded on both sides by younger, less deformed, Timiskaming turbidites (2674-2670 Ma). The earliest deformation features are F1 folds affecting the Timiskaming rocks, which formed either during D1 extensional faulting or during early D2 north-south shortening related to the opening and closure, respectively, of the Timiskaming basin. Continued shortening during D2 imbricated the older volcanic rocks and turbidites and produced regional F2 folds with an axial planar S2 cleavage. D2 deformation was partitioned into the weaker band of volcanic rocks, producing the strong S2 foliation, L2 stretching lineation, and south-side-up shear sense indicators, which characterize the LLCDZ. Gold is present in quartz-carbonate veins in deformed fuchsitic komatiites (carbonate ore) and turbiditic sandstone (sandstone-hosted ore), and in association with disseminated pyrite in altered Fe-rich tholeiitic basalts (flow ore). All host rocks underwent strong mass gains in CO (sub 2) , S, K (sub 2) O, Ba, As, and W, during sericitization, carbonatization, and sulphidation of the host rocks, suggesting that they interacted with the same hydrothermal fluids. Textural relationships between alteration minerals and S (sub 2) cleavage indicate that mineralization is syn-cleavage. Thus, gold was deposited as hydrothermal fluids migrated upward along the LLCDZ during contractional, D2 south-side-up shearing. The gold zones were subsequently modified during D (sub 3) reactivation of the LLCDZ as a dextral transcurrent fault zone.

Notes:

GeoRef, Copyright 2018, American Geological Institute.<br/>2016-014740<br/>Cheminis Deposit<br/>Larder Lake-Cadillac deformation zone