Start |Author Index | View Uploaded Presentations | Meeting Information
Paper No. 25
Presentation Time: 3:00 PM

BULK COMPOSITIONAL CONTROLS ON MINERAL ASSEMBLAGES IN METAMORPHOSED ORE DEPOSITS: AN EXAMPLE FROM THE LARONDE-PENNA AU-RICH VHMS DEPOSIT, QUEBEC, CANADA


THOMAS, Helen R.1, KELLY, Nigel M.2, MONECKE, Thomas1, MERCIER-LANGEVIN, Patrick3 and PITRE, David4, (1)Department of Geology and Geological Engineering, Colorado School of Mines, 1516 Illinois Street, Golden, CO 80401, (2)Geology and Geological Engineering, Colorado School of Mines, 1516 Illinois Street, Golden, CO 80401, (3)Geologic Survey of Canada, Natural Resources Canada, 490 De la Couronne Street, Quebec, QC G1K 9A9, Canada, (4)Angico-Eagle, Division LaRonde, 20, rte 395, Cadillac, QC J0Y 1C0, Canada, helenrthomas@gmail.com

Exploration for volcanic-hosted massive sulfide deposits is challenging in metamorphosed and deformed terranes due to modification of the mineralogy and geometry of the original alteration halos enveloping mineralized domains. Our current understanding of the effects of metamorphism on massive sulfide deposits is limited by the lack of a clear correlation between protolith bulk composition, P-T conditions of metamorphism, and the resultant mineral assemblages of metamorphosed alteration halo rocks.

Current work is targeting the LaRonde-Penna Au-rich massive sulfide deposit, which occurs in the late Archean Abitibi greenstone belt, Quebec, Canada. The deposit is hosted in felsic metavolcanic rocks (predominantly rhyodacite to rhyolite), which are now intensely deformed into a steeply-dipping homoclinal sequence, and is interpreted to have been metamorphosed at ~400-500ºC and at pressures <9 kbars. The now-metamorphosed altered footwall to the deposit shows mineralogical zoning with proximity to the deposit, and also along strike. The focus here is the footwall transition in the “20North (20N) lens” (massive chalcopyrite, galena, sphalerite, and pyrite), which hosts garnet-bearing assemblages that are absent in weakly- and un-altered rocks. The abundance and grain-size of Mn-bearing garnet increases with proximity to the ore lens, and the distribution of garnet has been linked to elevated Mn in the alteration halo.

P-T and T-X pseudosections generated in the phase equilibria modeling software THERMOCALC are being used to characterize bulk compositional controls on the appearance of key assemblages in the deposit footwall. In addition, data are being used to robustly relate assemblage domains in metamorphosed deposits to alteration halo compositions from unmetamorphosed deposits with the ultimate goal of developing predictive tools for mineral exploration of similar deposit types. Outcomes from this research are also being used place tighter P-T constraints on the evolution of the eastern Abitibi greenstone belt

Session No. 250

T186. STAMP: Structure, Tectonics, and Metamorphic Petrology (Posters)
Tuesday, 29 October 2013: 9:00 AM-6:30 PM
Hall D (Colorado Convention Center)
Geological Society of America Abstracts with Programs. Vol. 45, No. 7, p.601
© Copyright 2013 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.
Back to: T186. STAMP: Structure, Tectonics, and Metamorphic Petrology (Posters)
<< Previous Abstract | Next Abstract >>