Mobility and fractionation of rare earth elements during supergene weathering and gossan formation and chemical modification of massive sulfide gossan

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doi: 10.1016/j.gca.2005.11.003
Authors:Leybourne, Matthew I.; Peter, Jan M.; Layton-Matthews, Daniel; Volesky, John; Boyle, Dan R.
Author Affiliations:Primary:
University of Texas at Dallas, Department of Geosciences, Richardson, TX, United States
Other:
Geological Survey of Canada, Canada
University of Toronto, Canada
Volume Title:Geochimica et Cosmochimica Acta
Source:Geochimica et Cosmochimica Acta, 70(5), p.1097-1112. Publisher: Elsevier, New York, NY, International. ISSN: 0016-7037
Publication Date:2006
Note:In English. Includes appendices. 82 refs.; illus., incl. 1 plate, 1 table, geol. sketch map
Summary:Primary massive sulfide gossans (MSG) in the Bathurst Mining Camp (BMC), New Brunswick, Canada, are characterized by relative enrichment of Au, Sb, and As, formation of jarosite group minerals (jarosite, plumbojarosite, and argentojarosite) and little or no fractionation in the rare earth elements (REE), including preservation of large positive Eu anomalies (average [Eu/Eu*]NASC=4.14 in MSG; 6.61 in massive sulfide mineralization; 0.60 in host rocks). The chemical and mineralogical characteristics of MSG (e.g., Halfmile Lake deposit) imply low pH (<3) and relatively oxidizing conditions during gossan formation; oxidation of a volcanogenic massive sulfide body (comprising pyrite, pyrrhotite, sphalerite, galena, and chalcopyrite) with a falling water table. The lack of light REE or heavy REE fractionation and preservation of positive Eu anomalies characteristic of the original (465 Ma) hydrothermal fluid is consistent with relatively large water-rock ratios during massive sulfide mineralization oxidation, and removal of the REE predominantly as sulfate complexes (LnSO4+, Ln(SO4)2-). Low pH groundwaters recovered from past producing mines in the BMC display REE patterns reflecting those inferred to have occurred during gossan formation. Gossan at the Restigouche deposit, in contrast to the Halfmile Lake deposit, displays mineralogical and chemical evidence for having been chemically reworked since primary gossan formation. Evidence for chemical reworking includes loss of primary massive sulfide mineralization textures, replacement of plumbojarosite with anglesite, almost complete removal of jarosite minerals, loss of Au, Sb, and As and apparent preferential removal of Eu, resulting in loss of positive Eu anomalies for most samples (average [Eu/Eu*]NASC=1.21 in the gossan, with many displaying strong negative anomalies; 3.65 in massive sulfide mineralization; 0.54 in host rocks). Based on geochemical modeling, conditions inferred for the chemical reworking of the Restigouche deposit include near neutral conditions and either relatively oxidizing conditions with Eu2+ hosted in a preferentially weathered mineral host (possibly through substitution for Pb in plumbojarosite and beudantite) or cycling between reduced and oxidized conditions during gossan reworking. Abstract Copyright (2006) Elsevier, B.V.
Sections:Geochemistry
Subsections:Petrology; weathering; soils
Subjects:Alteration; Chemical composition; Chemical fractionation; Chemical ratios; Enrichment; Europium; Geochemistry; Gossan; ICP mass spectra; Igneous rocks; Jarosite; Mass spectra; Massive deposits; Massive sulfide deposits; Metal ores; Metals; Mineral assemblages; Mineral deposits, genesis; Mineral exploration; Mobilization; Ordovician; Oxidation; Paleozoic; Rare earths; Spectra; Sulfates; Sulfides; Supergene processes; Tetagouche Group; Trace elements; Volcanic rocks; Weathering; X-ray fluorescence spectra; Bathurst mining district; Canada; Eastern Canada; Gloucester County New Brunswick; Maritime Provinces; New Brunswick; Restigouche County New Brunswick; Halfmile Lake Deposit
Coordinates:N472000 N480000 W0643000 W0661500
Abstract Numbers:06M/1735
Record ID:2007058234
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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