| Title | Tracing the transition of gold from source to sponge to sink |
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| Author | Lawley, C J M; Jackson, S ; Yang, Z; Davis, W; Eglington, B |
| Source | Economic geology and the bulletin of the Society of Economic Geologists vol. 112, no. 1, 2017 p. 169-183, https://doi.org/10.2113/econgeo.112.1.169 |
| Image |  |
| Year | 2017 |
| Alt Series | Earth Sciences Sector, Contribution Series 20160072 |
| Publisher | Society of Economic Geologists |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Province | Nunavut |
| NTS | 55J/12; 55J/13; 55K/09; 55K/16; 55K/10; 55K/15; 55N/01; 55N/02; 55O/03; 55O/04 |
| Area | Meliadine gold district |
| Lat/Long WENS | -94.0000 -90.0000 64.0000 62.0000 |
| Subjects | geochemistry; gold; mineral deposits; pyrite; metamorphic rocks; lead isotope ratios; lead geochemistry; isotopic studies |
| Illustrations | location maps; geological sketch maps; photomicrographs; tables; diagrams; graphs |
| Program | Targeted Geoscience Initiative (TGI-4) Gold Ore Systems |
| Released | 2017 01 09 |
| Abstract | The late timing of gold is a characteristic feature of orogenic gold deposits. For many of these deposits, gold and other metals were liberated from the host greenstone belt and/or early sulfides
concomitant with the syndeformational and fluid-assisted metamorphic transition of pyrite to pyrrhotite and remobilized into late, high-grade ore shoots. However, this metamorphic-driven gold-upgrading model is usually inferred, at least in part,
from mineral textures, which can be equivocal in the absence of geochemical and/or isotopic constraints. Herein, we report new bulk mineral separate and in situ Pb isotope results for minerals in key textures in the Paleoproterozoic
Meliadine gold
district. Arsenopyrite and pyrite porphyroblasts occur in Paleoproterozoic quartz ± ankerite veins and are enveloped by remobilized pyrrhotite, chalcopyrite, and galena crystals that accompany gold in late, microtextural sites, a texture that forms
the basis for the gold-upgrading model. Early, sievetextured arsenopyrite and pyrite are gold rich and tend to yield the least radiogenic Pb isotope compositions (high 207Pb/206Pb and 208Pb/206Pb ratios), suggesting these relict domains escaped
complete recrystallization
during later reworking. Late, inclusion-free arsenopyrite and pyrite overgrowths scatter to more radiogenic Pb isotope compositions (low 207Pb/206Pb and 208Pb/206Pb ratios) and are typically gold poor, which we attribute
to reworking and precipitation from a younger and more radiogenic fluid prior to and/or during the precipitation of free gold in variably plunging high-grade ore shoots at 1.90 to 1.85 Ga. Remobilized sulfides are the youngest sulfide phases, but
locally yield low 206Pb/204Pb and 207Pb/204Pb ratios and, thus spurious old model "ages" which overlap with the least radiogenic, sieve-textured arsenopyrite/pyrite domains. The isotopic signature of these remobilized sulfides was likely inherited
from Pb liberated during reworking of early arsenopyrite and pyrite and a second, crustal Pb source that was introduced during late remobilization. Our results highlight the importance of element recycling from early sulfides and/or the Neoarchean
deposit host rocks during significantly younger Paleoproterozoic reworking and gold remobilization. The in situ Pb isotope results of early and remobilized sulfides document the transition of gold from source to sponge to sink, which is likely a
feature that
occurred during the formation of other orogenic-style gold deposits. |
| Summary | (Plain Language Summary, not published)
Many of the world's largest gold deposits are often conceptualized in terms of a simple transition from source to sink. In this contribution, we present
Pb isotopic analyses for a variety of sulphide minerals that accompany gold at the Meliadine gold district. Our results suggest that some sulphide minerals act as transient, gold-rich reservoirs that can release metals prior to the precipitation of
gold during younger metamorphic events. This intermediary step to the classic source-to-sink mineral exploration paradigm is likely a key feature of other world-class gold deposits. |
| GEOSCAN ID | 298813 |
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