Oxygen isotope mapping in the Panorama VMS district, Pilbara Craton, Western Australia

Applications to estimating temperatures of alternation and to exploration

C. W. Brauhart, D. L. Huston*, A. S. Andrew

*Corresponding author for this work

Research output: Contribution to journalArticle

32 Citations (Scopus)

Abstract

Whole rock oxygen isotope data are presented for the Panorama district, in the Archean Pilbara Craton of Western Australia, where near-perfect exposure reveals a cross section through a complete volcanogenic massive sulfide (VMS) hydrothermal alteration system. The δ 18O values decrease with depth in the volcanic pile, across semi-conformable alteration zones, to values below 6‰ immediately above a large (180 km 2) subvolcanic intrusion. Altered rocks in the upper parts of the subvolcanic intrusion have lower δ 18O values (6-8‰) than least altered granite (8‰), apart from sericite-quartz altered zones, which are slightly higher (8-10‰). Corridors of low δ 18O values crosscut this regional zonation, and are coincident with transgressive feldspardestructive alteration zones, which underlie VMS mineralization. The whole rock oxygen isotope distribution patterns are interpreted to represent alteration temperature, where high δ 18O values correspond to low temperature alteration and low δ 18O values correspond to high temperature alteration. Alteration temperatures, which were calculated using modal alteration mineral abundances and an assumed fluid δ 18O, are consistent with this interpretation. Increasing temperatures with depth in the volcanic pile and high temperatures in transgressive corridors leading up to VMS deposits, are consistent with a convective hydrothermal model, in which heat from the subvolcanic intrusion drove seawater through the volcanic pile. Granite-hosted sericite-quartz alteration zones are 18O-enriched, and are tentatively interpreted to have formed from a mixed magmatic-evolved seawater fluid.

Original languageEnglish
Pages (from-to)727-740
Number of pages14
JournalMineralium Deposita
Volume35
Issue number8
DOIs
Publication statusPublished - 2000
Externally publishedYes

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