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TitleThe gold content of volcanogenic massive sulfide deposits
AuthorMercier-Langevin, P; Hannington, M; Dubé, B; Bécu, V
SourceConference of Metallurgists 2011, World Gold 2011 meeting, abstracts; 2011 p. 47
LinksOnline - En ligne
Alt SeriesEarth Sciences Sector, Contribution Series 20130576
MeetingConference of Metallurgists 2011, World Gold 2011 meeting; Montreal; CA; October 2011
Mediaon-line; digital
File formatpdf
Subjectseconomic geology; mineral deposits; mineral occurrences; mineralization; gold; sulphides; sulphide deposits; volcanogenic deposits
ProgramTargeted Geoscience Initiative (TGI-4), Gold Ore Systems
AbstractVMS deposits contain variable amounts of gold, both in terms of average grade and total contents. The analysis of gold grades and tonnages of 513 VMS deposits worldwide revealed that a large proportion of deposits are characterized by a relatively low gold grade (<2 g/t), with a gradual decrease in frequency towards maximum grades. The geometric mean and geometric standard deviation appear to be the simplest metric for identifying subclasses of VMS deposits based on gold grade. The geometric mean gold grade is 0.76 g/t; the geometric standard deviation is +2.70 g/t Au. Deposits with more than 3.46 g/t Au (geometric mean plus one geometric standard deviation) are considered auriferous. The geometric mean gold content is 4.7 t Au, with a geometric standard deviation of +26.3 t Au. Deposits containing 31 t Au or more are considered to be anomalous in terms of gold content, irrespective of the gold grade. Deposits with more than 3.46 g/t Au and 31 t Au are considered gold-rich VMS. A large proportion of the total gold hosted in VMS worldwide is found in a relatively small number of such deposits. The identification of these truly anomalous systems helps shed light on the geological parameters that control unusual enrichment of gold in VMS. At the district scale, the gold-rich deposits occupy a stratigraphic position and volcanic setting that commonly differs from other deposits of the district possibly due to a step change in the geodynamic and magmatic evolution of local volcanic complexes. The gold-rich VMS are commonly associated with transitional to calc-alkaline intermediate to felsic volcanic rocks, which may reflect a particularly fertile geodynamic setting and/or timing (e.g, early arc rifting). At the deposit scale, uncommon alteration assemblages (e.g., advanced argillic) and trace element signatures are present, suggesting a direct magmatic input in some systems.