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TitleLarge igneous provinces and SEDEX deposits: the example of the Mesoproterozoic Sullivan deposit
AuthorLydon, J W
SourceProspectors and Developers Association of Canada Convention 2013, abstracts; 2013.
Alt SeriesEarth Sciences Sector, Contribution Series 20120358
PublisherProspectors and Developers Association of Canada
MeetingProspectors and Developers Association of Canada Convention 2013; Toronto; CA; March 2013
ProvinceBritish Columbia
NTS82F/01; 82F/02; 82F/07; 82F/08; 82F/09; 82F/10; 82F/15; 82F/16; 82G/04; 82G/05; 82G/12; 82G/13
Lat/Long WENS-117.0000 -115.0000 50.0000 49.0000
Subjectsigneous and metamorphic petrology; structural geology; metallic minerals; mineral deposits; sedimentary ore deposits; modelling; metallogeny; boron; tourmaline; pyrrhotite; Sullivan Mine; Moyie LIP; Belt-Purcell basin
ProgramTargeted Geoscience Initiative (TGI-4) Sedimentary Exhalative Ore Systems
Released2013 01 01
AbstractSEDEX ore systems consist of the cross-stratal expulsion of formational brines from sedimentary basins and typically form deposits in the sag sequence of epicontinental or intracontinental rifts. Both the geological environment and the Zn-Pb metal association of SEDEX deposits do not intuitively link them to igneous activity. However, some high tonnage, high grade, Pb- and Ag-rich deposits such as Broken Hill (Australia), Cannington (Australia) and Sullivan (Canada) occur in the rift-fill sequence where they are associated with rift-related igneous activity. The Mesoproterozoic Sullivan deposit is hosted by the Aldridge Formation which consists of intercalated turbidites and tholeiitic sills (Moyie sills) and forms the rift-fill sequence of the Belt-Purcell intracontinental rift. The volume of tholeiitic magma emplaced into the unconsolidated turbidites is likely in excess of 100,000 km3, qualifying the Belt-Purcell rift as a Large Igneous Province (LIP). Sullivan produced 149 million tonnes averaging 5.33% Zn, 5.64% Pb and 62 g/t Ag, which puts it among the top ten SEDEX deposits of the world in terms of amount of contained ore metal. Several lines of evidence link the formation of Sullivan to the tholeiitic igneous activity:
a) The Sullivan ore system was coeval with the emplacement of the Moyie sills during the period 1468±3 Ma;
b) Sullivan formed in the crater of a large mud volcano. On a regional scale, mud volcanoes in the Aldridge Formation are co-extensive the Moyie sills;
c) The association of a large quantity of tourmaline with the Sullivan deposit is consistent with boron release by the thermal metamorphism of young sediments and the concomitant high temperature phase separation of their pore fluids, as would accompany the emplacement of tholeiitic magma into unconsolidated marine sediment.
d) The dominant iron sulphide in the Sullivan deposit is pyrrhotite, as opposed to pyrite of SEDEX deposits of the rift sag sequence. The very low pO2 required to stabilize pyrrhotite in the sulphur-rich environment of a SEDEX deposit requires the ore fluids to have equilibrated with a ferrous mineral buffer such as the pyroxene-magnetite-quartz mineral assemblage of the Moyie sills.
LIPs can therefore be viewed as a potential catalyst for the formation of SEDEX deposits in that the emplacement of a large quantity of magma into a large volume of unconsolidated sediment can accelerate diagenetic, compactional and cross-stratal dewatering processes to form SEDEX deposits earlier in a basin's history (i.e., rift-fill sequence) than is normally the case (i.e., sag-fill sequence).

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