GEOBAROMETRY IN ARCHEAN LODE-GOLD DEPOSITS

Citation
Sg. Hagemann et Pe. Brown, GEOBAROMETRY IN ARCHEAN LODE-GOLD DEPOSITS, European journal of mineralogy, 8(5), 1996, pp. 937-960
Citations number
119
Categorie Soggetti
Mineralogy
ISSN journal
09351221
Volume
8
Issue
5
Year of publication
1996
Pages
937 - 960
Database
ISI
SICI code
0935-1221(1996)8:5<937:GIALD>2.0.ZU;2-Y
Abstract
A compilation of geobarometric data from Archean lode-gold deposits wo rldwide suggests that these deposits display a continuum of formation pressures from < 50 MPa to 700 MPa. The calculated fluid pressures hav e been utilized, using the fluid-inclusion program MacFlinCor, to cons train crustal depths assuming litho- and hydrostatic-pressure gradient s. The inferred crustal depths of mineralization in lode-gold deposits from the Archean Yilgarn Craton of Western Australia, the Superior Pr ovince in Canada, and cratonic areas in South Africa and Brazil displa y a continuum of depths for the formation of these late-orogenic, epig enetic lode-gold deposits. Three major pressure ranges and related dep th-levels can be identified: (1) epizonal levels (at < 150 MPa corresp onding to < 6 km e.g., Wiluna and Racetrack), mesozonal levels (at > 1 50 to 300 MPa corresponding to > 6 to < 12 km, e.g., Golden Mile and H ollinger-McIntyre), and hypozonal deposits (at > 300 MPa corresponding to > 12 km e.g., Marvel Loch and Griffins Find). The large crustal ex tent of epigenetic Archean lode-gold deposits appears to be an importa nt characteristic when compared to other ore-deposit classes such as V olcanic Massive Sulfide (VMS) and Mississippi-Valley type (MVT) deposi ts that are constrained to have formed at upper crustal levels only. T he crustal depths of late-orogenic, epigenetic Archean lode-gold depos its from Western Australia display a continuum from shallow to deep, w hereas lode-gold deposits from the Superior Province in Canada show a distinct clustering of depths at the mesozonal level (> 6 km to < 12 k m). The geobarometric data for the Western Australian deposits are com patible with the model of Groves et al. (1991, 1992) that predicts a c rustal continuum for Archean lode-gold deposits in Western Australia. The limited number of known large epi- and hypozonal deposits in the C anadian Superior Province may be a result of a combination of a differ ent crustal make-up, scant fluid-inclusion studies, and/or lack of exp loration in terrains of high- and low-metamorphic grade.