IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

1P1_1E-O15

Room A3

Date/Time: July 21 15:00-15:15

Reconstructing the volcanological and paleoenvironmental setting of an Archean
Hollandaire Cu-Au volcanic hosted massive sulphide deposit, Murchison Domain,Yilgarn Craton, Western Australia
Raymond A.F. Cas1 , Patrick C. Hayman1 , Sarah Hull1 , Edward Summerhayes2 , David Price2
1

School of Geosciences, Monash University, Clayton, 3800, Australia, Australia, 2 Silver LakeResources, South Perth, Western Australia, 6951, Australia, Australia
E-mail: ray.cas@monash.edu

Discovered in late 2011, Hollandaire is a Cu-Au VMS deposit situated near the town of Cue within the Archean
Murchison Domain of the Youanmi Terrane, Western Australia, and occurs within the Greensleeves Formationof the Polelle Group (2820-2735 Ma). Host rocks are variably silicified, chloritised and sericitised, have been
metamorphosed to upper greenschist facies, and have a pervasive foliation (S1) that is crenulated (S2) in places.
As a result, primary textures are obscured. From stratigraphic logging of 31 diamond drill holes, geochemistry(major and trace elements), petrography and geochronology, we reconstruct the paleo volcano-sedimentary setting.
Host rocks consist dominantly of either quartz-chlorite-muscovite schists (andesitic to dacitic in composition) or
quartz-chlorite-muscovite schists with larger blue quartz crystals (rhyolitic). The former lithofacies, where least
deformed and altered, consists of thin interbedded fine and coarse layers up to 100 m thick, as well as intervals offine-grained carbonaceous black material. This lithofacies is interpreted as a metasedimentary, below wave-base,deep water, distal turbidite succession. The rhyolitic schist lithofacies, with evenly dispersed quartz crystals, ranges
up to 300 m thick, and even within less deformed domains is massive and uniform. Fragmentation is absent at
the margins of this lithofacies, indicating it is a high-level intrusion. The lone breccia interval ( 1 m), consistingof cobble-size clasts of coherent rhyolite in a metasedimentary matrix, is interpreted as reworked autoclastic
volcanic debris. Undeformed dacite porphyries cross-cut the stratigraphy and clearly post-date deformation, andbased on our preliminary geochronological work, are 2780 Ma. Sulphide mineralisation ranges from massiveintervals of mainly pyrite and chalcopyrite (up to 14 m thick) to stringers and disseminated styles. Massiveintervals are restricted to the metasedimentary lithofacies, while disseminated sulphides are found within boththe metasediments and high-level rhyolite intrusion and rarely within the younger dacite porphyries. We interpret
much of this as remobilisation but are uncertain to what extent the primary mineralisation reflected seafloorvs sub-seafloor emplacement. We interpret the setting as a rhyolitic cryptodome with VMS mineralisation ina deep-water setting that was pervasively deformed by both S1 and S2 and subsequently intruded by dacitic
porphyries. We know of no clear evidence for an arc, however, the tectonic setting remains unclear. Voluminous
volcanic events contemporaneous with Hollandaire include the nearby Eelya plutonic complex (2750 Ma), which
has similar geochemistry to the high-level rhyolitic intrusion, and the mafic-ultramafic Gnanagooragoo IgneousComplex. This study highlights some of the difficulties in working with Archean deposits and adds to the small
database of VMS deposits within the Yilgarn Craton.

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