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TitleTrace metal and isotopic depth profiles through the Abitibi cratonic mantle
AuthorLawley, C; Kjarsgaard, B; Jackson, S; Yang, Z; Petts, D; Roots, E
SourceLithos vol. 314-315, 2018 p. 520-533, https://doi.org/10.1016/j.lithos.2018.06.026
Year2018
Alt SeriesNatural Resources Canada, Contribution Series 20170370
PublisherElsevier BV
Documentserial
Lang.English
Mediapaper; on-line; digital
RelatedThis publication is related to the following publications
File formatpdf; html; docx
ProvinceQuebec; Ontario
NTS31M; 31N; 31O/04; 31O/05; 31O/12; 31O/13; 32B/04; 32B/05; 32B/12; 32B/13; 32C; 32D; 32E; 32F; 41P; 42A; 42H
AreaLarder Lake; Kirkland Lake; Rouyn-Noranda
Lat/Long WENS -82.0000 -75.6667 49.6667 47.1667
Subjectseconomic geology; geochemistry; geophysics; mineral deposits; metals; ore mineral genesis; structural controls; crustal studies; craton; mantle; lithosphere; electron probe analyses; mass spectrometer analysis; clinopyroxene; olivine; silicates; sulphides; peridotites; garnet; trace element analyses; statistical analyses; pressure-temperature conditions; alteration; emplacement; metasomatism; kimberlites; fluid flow; volcanism; geophysical surveys; seismic surveys; seismic velocities; anomalies; isotopic studies; lead isotope ratios; Archean; Canadian Shield; Abitibi Greenstone Belt; Kirkland Lake Kimberlite Field; Buffonta Dyke; Diamond Lake Pipe; xenocrysts; principal component analysis (PCA); geochemical signatures; geothermobarometry; Precambrian
Illustrationsgeoscientific sketch maps; profiles; photomicrographs; plots; models
ProgramGold systems, Targeted Geoscience Initiative (TGI-5)
Released2018 06 28
AbstractGeophysical imaging of trans-lithospheric structures provide a spatial link between ore deposits in the crust and the underlying cratonic mantle. However, the deep lithosphere's role in ore deposit genesis remains poorly understood because remotely acquired datasets do not provide any direct constraints on the behaviour of ore elements within these mantle-roots. The abundance and behaviour of ore elements governs the metallic endowment of the cratonic mantle and the economic potential of mantle-derived magmas. Herein we present in situ electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) geochemical datasets for clinopyroxene and olivine mantle xenocrysts from the Jurassic Kirkland Lake kimberlite field, Abitibi greenstone belt, Canada. We specifically focus on unconventional trace elements, including ore elements with chalcophile and/or siderophile affinities (Ag-As-Au-Bi-Cu-Mo-Pb-Pt-Pd-Sb-Se-Sn-Te-W-Zn). Robust principal component analysis suggests that low-T, large-ion lithophile element alteration (Ba-Sr), which likely occurred during kimberlite emplacement, represents the largest source of variance for the xenocrysts dataset. PT-dependent element partitioning during sub-solidus equilibration represents the second most important control on olivine and clinopyroxene chemistry. We demonstrate that least-altered, high-PT mantle silicates are, in fact, a significant mineral host for a range of ore elements (Cu-Zn ± Ag ± As ± Se ± Sn ± Mo) within equilibrated, garnet peridotite at depth (70-190 km). Statistical analysis of the raw, individual mass sweeps for each LA-ICP-MS signal suggest that the most abundant ore elements (Cu-Zn) occur predominantly as PT-dependent substitution reactions with the dominant mineral-forming elements, rather than as inclusions. A subset of high-PT olivine (160-180 km) yields Fe-Ni-S-poor and Na (Au ± Pt ± Pd)-rich compositions, which may reflect metasomatism, sulphide segregation and trapping of precious metal-bearing fluids at the base of the lithosphere. These anomalous mantle fragments possibly represent the first, direct sampling of precious metal-modified mantle peridotite beneath the Abitibi. Mid-PT olivine xenocrysts (70-120 km), which yield Mg-rich and high field-strength element-poor compositions, document a highly melt-depleted segment of mantle peridotite coincident with and below a shallow-dipping, low-seismic-velocity anomaly and conductive feature of the Kirkland Lake mid-lithosphere at 70-100 km. We speculate that the trace element signature of mid-PT xenocrysts documents the re-distribution of high-charge and incompatible elements from refractory garnet peridotite to phlogopite- and/or amphibole-bearing peridotite with conductive metasomatic up-flow zones. The rapid, sub-solidus diffusion of elements at high-T suggest that these processes likely occurred during, and/or immediately preceding, kimberlite volcanism. New in situ Pb isotope analyses of clinopyroxene xenocrysts sampled from metasomatized, low-Al garnet peridotite, however, also document ancient metasomatic events that likely pre-date Jurassic kimberlitic volcanism by at least one billion years.
Summary(Plain Language Summary, not published)
The Targeted Geoscience Initiative (TGI) is a collaborative federal geoscience program that provides industry with the next generation of geoscience knowledge and innovative techniques to better detect buried mineral deposits, thereby reducing some of the risks of exploration. Factors that influence the metal endowment within the source regions of ore deposits, however, remain poorly understood. This study addresses that knowledge gap by documenting the distribution of metals of economic interest within mantle minerals.
GEOSCAN ID306645