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Papers by D. Layton-matthews

Journal of Analytical Atomic Spectrometry, 2006

The goal of this study was to develop an accessible method for the determination of selenium isot... more The goal of this study was to develop an accessible method for the determination of selenium isotopes within selenium-rich geological samples and examine the inﬂuence of sample introduction, instrumental parameters, column separation and the application of standard-sample bracketing for mass bias and drift correction. Quantitative selenium separation and enrichment of samples was achieved by a column separation using 0.2 g thioglycollic impregnated cotton ﬁber prior to introduction of the sample to an ICP-DRC-MS. 0.6 ml min À1 premixed Ar (95%) þ H 2 (5%) was favored over CH 4 and NH 4 as a reaction cell gas and was used within the DRC coupled with optimized DRC rejection parameters RPa (0) and RPq (0.65) to eﬀectively reduce the signal to background ratio of all measured selenium isotopes (m/z 76, 77, 78, 80 and 82). Ion signal intensity of all measured selenium isotopes were increased 100 fold over classic nebulization by mixing of 1% NaBH 4 and acidiﬁed sample digestions in a membrane-less computer-controlled continuous hydride generator. Transient hydride ion signals were time-averaged for ﬁve readings and three replicates to produce an in-run precision (2s) of Æ0.45% d 82/76 Se Merck (relative to a Merck titrosol ICP-MS standard) and Æ0.85% d 82/76 Se Merck over an 18 month period. In the absence of a selenium isotopic standard, the accuracy of the method was determined using four interlaboratory solutions and ﬁve geological standard reference materials covering 0 to À4.5% d 82 /76 Se Merck . Our results indicate excellent reproducibility within method precision. The minimum mass of Se required for isotopic ratio determination was 3 mg (4100 000 cps at m/z 82 and 76).

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

Geochimica et Cosmochimica Acta, 2006

Primary massive sulﬁde gossans (MSG) in the Bathurst Mining Camp (BMC), New Brunswick, Canada, ar... more 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 (LnSO 4 + , Ln(SO 4 ) 2 À ). 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 Eu 2+ 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.

Ontario Geological Survey Open File Report 6258, 2011

Geological Survey of Canada Open File 6550, 2010

2010 Recommended citation Chapman, J.B., Peter, J.M., and Layton-Matthews, D., 2010. Geochemistry... more 2010 Recommended citation Chapman, J.B., Peter, J.M., and Layton-Matthews, D., 2010. Geochemistry database for carbonaceous and sulphidic metasediment horizons of the western Neoarchean Kidd-Munro assemblage, Abitibi Subprovince, Ontario; Geological Survey of Canada, Open File 6550, 1 DVD.

Metalliferous black shale horizons are a common but minor component of many subaqueous volcanic s... more Metalliferous black shale horizons are a common but minor component of many subaqueous volcanic successions. These horizons are commonly drilled during volcanogenic massive sulfide (VMS) deposit exploration programs. Although ore metal enrichment can be identified by conventional assay methods, matrix dilution and post-burial hydrothermal and metamorphic activity may obscure information on the type and mechanism of metal addition to the shale. We used a combination of geochemical investigations at a variety of scales to discriminate between VMS-prospective and VMS-barren horizons. In addition, element signatures associated with hydrothermal plume fallout were identified and used and to determine relative direction to the palaeo-venting centre. Portable x-ray fluorescence (pXRF) analysers were used to identify and correlate prospective horizons within exploration drill cores. pXRF is a rapid and relatively inexpensive method of analysis that can deliver quantitative geochemical infor...

INTERNATIONAL …, 2009

... Portable x-ray fluorescence (pXRF) analysers were used to identify and correlate prospective ... more ... Portable x-ray fluorescence (pXRF) analysers were used to identify and correlate prospective mineralized horizons within exploration drill cores. pXRF is a rapid and relatively inexpensive method of analysis that can deliver ...

Magnetite is a common mineral found in a wide range of mineral deposits and in different geologic... more Magnetite is a common mineral found in a wide range of mineral deposits and in different geological environments. The study of surface textures and morphology of magnetite can provide information that is useful to 1) discriminate different types of magnetite such as that attributed to magmatic, metamorphic and supergene environments, 2) identify host bedrocks, 3) sediment provenance, and 4) recognize chemical and mechanical processes affecting grains during erosion, transport, and after deposition in sedimentary environments. In this study, magnetite grains from the Izok Lake volcanogenic massive sulfide deposit (Nunavut, Canada) and from till covering the area have been investigated using scanning electron microscopy, mineral liberation analysis, and optical microscopy to document their mineral associations, surface textures, grain shape and size distribution. Evidences such as 1) contact relations between magnetite and sphalerite, 2) sphalerite and chalcopyrite inclusions in magnetite, and 3) intergrowths of magnetite with actinolite and gahnite suggest that in Izok Lake deposit and related gahnite-rich stringer zone, magnetite formed by replacement of sulfide minerals during regional, upper greenschist to amphibolite facies metamorphism. Magnetite from iron formation also formed as a result of oxidation-dissolution of almandine, or breakdown of Fe-bearing minerals during metamorphism. Euhedral, fine-grained magmatic magnetite in association with ilmenite, plagioclase and hornblende was identified in bedrock gabbro. Magnetite overgrowths on the surface of existing magnetite and other metamorphic minerals fingerprinted the supergene processes affecting bedrocks and sediments after metamorphism. Magnetite in till around the Izok Lake deposit is mostly imprinted by mechanical microtextures such as crescentic gouges, deep grooves, arc-shaped steps, and troughs that are diagnostic of transportation by thick continental ice sheets. A small proportion of magnetite grains characterized by V-shaped percussion cracks also indicate transportation by fluvial and/or glaciofluvial environments. Shape, grain-size distribution, and mineral association of magnetite in till suggest that in vicinity of the Izok Lake deposit, till has mainly been fed by the deposit and related alteration zones, though, a high proportion of grains have been derived from iron formations, bedrock gabbro, and Mackenzie dikes.

Journal of Analytical Atomic Spectrometry, 2006

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

Geochimica et Cosmochimica Acta, 2006

Ontario Geological Survey Open File Report 6258, 2011

Geological Survey of Canada Open File 6550, 2010

INTERNATIONAL …, 2009