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TitlePyrite deformation and connections to gold mobility: insight from micro-structural analysis and trace element mapping
AuthorDubosq, R; Lawley, C J MORCID logo; Rogowitz, A; Schneider, D A; Jackson, SORCID logo
SourceLithos vol. 310-311, 2018 p. 86-104,
Alt SeriesNatural Resources Canada, Contribution Series 20170359
PublisherElsevier BV
Mediapaper; on-line; digital
File formatpdf
ProvinceOntario; Quebec
NTS32E/13; 32E/14; 32L/03; 32L/04
AreaDetour Lake
Lat/Long WENS -80.0000 -79.4167 50.2500 49.7500
Subjectseconomic geology; igneous and metamorphic petrology; geochemistry; mineralogy; mineral deposits; mineral exploration; gold; ore mineral genesis; mineralization; ore controls; pyrite; pyrrhotite; tectonic elements; metamorphism; deformation; mineral enrichment; strain; pressure-temperature conditions; fluid dynamics; crystallography; trace element analyses; modelling; mineral assemblages; bedrock geology; lithology; metamorphic rocks; amphibolite facies; electron diffraction analyses; mass spectrometer analysis; veins; paragenesis; sulphides; Archean; Detour Lake Deposit; Abitibi Subprovince; Superior Province; Sunday Lake Deformation Zone; Precambrian
Illustrationslocation maps; geoscientific sketch maps; models; tables; photographs; photomicrographs; stereonets
ProgramTargeted Geoscience Initiative (TGI-5) Gold systems
Released2018 04 06
AbstractThe metamorphic transition of pyrite to pyrrhotite results in the liberation of lattice-bound and nano-particulate metals initially hosted within early sulphide minerals. This process forms the basis for the metamorphic-driven Au-upgrading model applied to many orogenic Au deposits, however the role of syn-metamorphic pyrite deformation in controlling the retention and release of Au and related pathfinder elements is poorly understood. The lower amphibolite facies metamorphic mineral assemblage (Act-Bt-Pl-Ep-Alm±Cal±Qz±Ilm; 550 °C) of Canada's giant Detour Lake deposit falls within the range of pressure-temperature conditions (450 °C) for crystal plastic deformation of pyrite. We have applied a complementary approach of electron backscatter diffraction (EBSD) mapping and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) 2D element mapping on pyrite from the Detour Lake deposit. Chemical element maps document an early generation of Au-rich sieve textured pyrite domains and a later stage of syn-metamorphic oscillatory-zoned Au-poor pyrite. Both pyrite types are cut by Au-rich fractures as a consequence of remobilization of Au with trace element enrichment of first-row transition elements, post-transition metals, chalcogens and metalloids during a late brittle deformation stage. However, similar enrichment in trace elements and Au can be observed along low-angle grain boundaries within otherwise Au-poor pyrite, indicating that heterogeneous microstructural misorientation patterns and higher strain domains are also relatively Au-rich. We therefore propose that the close spatial relationship between pyrite and Au at the microscale, features typical of orogenic Au deposits, reflects the entrapment of Au within deformation-induced microstructures in pyrite rather than the release of Au during the metamorphic transition from pyrite to pyrrhotite. Moreover, mass balance calculations at the deposit scale suggest that only a small percentage of Au could have been sourced from pyrite and instead point to the role of substructures in pyrite as depositional traps for Au during syn-metamorphic deformation and fluid-assisted diffusion Au-upgrading.
Summary(Plain Language Summary, not published)
Research at the giant Detour gold deposit as part of the Targeted Geoscience Initiative program provides new insight into the relationship between pyrite and gold. Pyrite is an important guide to gold ore zones at many deposits and has possibly represents an important source for gold. New data, however, also documents pyrite as a important trap for gold as the gold-rich veins are deformed and buried. These findings improve our understanding of ore systems.

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