Start |Author Index | View Uploaded Presentations | Meeting Information

Northeastern Section - 51st Annual Meeting - 2016

Paper No. 31-1
Presentation Time: 8:00 AM

LA-MC-ICP-MS U/PB ZIRCON GEOCHRONOLOGY OF THE GRENVILLE-AGE IRON DEPOSITS OF NEW YORK


LUPULESCU, Marian V., Research and Collections, New York State Museum, Cultural Education Center, 260 Madison Avenue, Albany, NY 12230, CHIARENZELLI, Jeffrey R., Department of Geology, St. Lawrence University, Canton, NY 13617, SELLECK, Bruce, Department of Geology, Colgate University, Hamilton, NY 13346, MCLELLAND, James M., Geology, Colgate University, Dept. Geology, 13 Oak Drive, Caroga Lake, NY 12032 and REGAN, Sean P., Department of Geosciences, University of Massachusetts, Amherst, 611 North Pleasant Street, Amherst, MA 01003, Marian.Lupulescu@nysed.gov

The Grenville-age iron deposits of New York are related to three intrusive events which occurred at the end of the Shawinigan, Ottawan, and Rigolet orogenic activity, respectively: (a) Fe – Ti oxide associated with rocks of the AMCG suite (anorthosite, “cumberlandite”, hornblendite) at ca. 1155 Ma; (b) low Ti - Fe oxide - fluorapatite associated with the A-type Lyon Mountain Granite (LMG), low – Ti - Fe oxide - vonsenite associated with skarns, low Ti – Fe oxide - sillimanite with no certain spatial affiliation, all at ca. 1040 Ma; (c) Low Ti – Fe oxide associated with amphibole peridotite at ca. 1000 Ma (Hudson Highlands). The present contribution will focus on the still controversial low Ti-Fe oxide-fluorapatite ores (LowTiFe).

The LowTiFe ores from eastern Adirondacks consist of intrusive sills or dikes of magnetite, REE-rich fluorapatite, augitic pyroxenes, and minor quartz. Other mineral phases include ilmenite with hematite exsolution, vanadiferous titanite rimming magnetite, zircon, monazite-(Ce), stillwellite-(Ce), lanthanite-(Ce), allanite-(Ce), and thorite. Observations under transmitted light show polygonal and cumulate textures. The ore bodies, each with very sharp contacts, are closely associated in time and space with A-type leucogranites and granitic gneisses (ca. 1040 Ma). Zircon separates from the Cheever mine magnetite ore contain 632 -1432 ppm U, display a U/Th ratio of 2.5-22.2 and yield a Concordia age of 1043±11 Ma. Zircons from the Rutgers mine ore display cores and rims. The cores contain 99-1197 ppm U, show U/Th ratio of 2.6±1.0, and an age of 1142 ±20 Ma whereas rims have 295-2267 ppm U, U/Th ratio of 5.6±3.7 and an age of 1043±11.9 Ma. The cores are probably remnants from the AMCG suite and the igneous rims are contemporaneous with the LMG. Undeformed pegmatites cross-cutting Mineville magnetite-fluorapatite ore bodies yield U-Pb zircon ages of ca. 1039±11 at Barton Hill, 1022±13 Ma at Old Bed (rim at 949 ±10 Ma), and 1023+8.5 Ma at Bonanza Shaft indicate that the ore cannot be younger than ca. 1040 Ma.

Session No. 31

T14. The Grenville-Age Low Ti-Fe Oxide Deposits from New York State: Igneous or Hydrothermal?
Tuesday, 22 March 2016: 8:00 AM-12:00 PM
Meeting Room 3 (Empire State Plaza Convention Center)
Geological Society of America Abstracts with Programs. Vol. 48, No. 2
doi: 10.1130/abs/2016NE-272344
© Copyright 2016 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: T14. The Grenville-Age Low Ti-Fe Oxide Deposits from New York State: Igneous or Hydrothermal?
Previous Abstract | Next Abstract >>