Geobarometry in Archean lode-gold deposits
Hagemann, Steffen G.; Brown, Philip E.
European Journal of Mineralogy Volume 8 Number 5 (1996), p. 937 - 960
published: Oct 30, 1996
manuscript accepted: May 3, 1996
manuscript received: Sep 22, 1995
ArtNo. ESP147050805006, Price: 29.00 €
Abstract A compilation of geobarometric data from Archean lode-gold deposits worldwide suggests that these deposits display a continuum of formation pressures from < 50 mpa to 700 mpa. the calculated fluid pressures have been utilized, using the fluid-inclusion program macflincor, to constrain crustal depths assuming litho- and hydrostatic-pressure gradients. the inferred crustal depths of mineralization in lode-gold deposits from the archean yilgarn craton of western australia, the superior province in canada, and cratonic areas in south africa and brazil display a continuum of depths for the formation of these late-orogenic, epigenetic lode-gold deposits. three major pressure ranges and related depth-levels can be identified: (1) epizonal levels (at < 150 mpa corresponding to 150 to 300 MPa corresponding to > 6 to 300 MPa corresponding to > 12 km e.g., Marvel Loch and Griffins Find). The large crustal extent of epigenetic Archean lode-gold deposits appears to be an important characteristic when compared to other ore-deposit classes such as Volcanic Massive Sulfide (VMS) and Mississippi-Valley type (MVT) deposits that are constrained to have formed at upper crustal levels only. The crustal depths of late-orogenic, epigenetic Archean lode-gold deposits from Western Australia display a continuum from shallow to deep, whereas lode-gold deposits from the Superior Province in Canada show a distinct clustering of depths at the mesozonal level (> 6 km to < 12 km). The geobarometric data for the Western Australian deposits are compatible with the model of Groves et al. (1991, 1992) that predicts a crustal continuum for Archean lode-gold deposits in Western Australia. The limited number of known large epi- and hypozonal deposits in the Canadian Superior Province may be a result of a combination of a different crustal make-up, scant fluid-inclusion studies, and/or lack of exploration in terrains of high- and low-metamorphic grade.