Framboidal diagenetic pyrite occurs in low-grade turbidites on the northeast margin of the Otago Schist. Laser ablation inductively coupled plasma mass spectrometry (ICP-MS) analyses of these framboids show that the main metals present, in addition to Fe, are As, Pb, Zn, Te, Ag and Mo; Au is present at between 0.5 and 2 ppm. Minor Au and As anomalies also occur sporadically in the turbidite matrix. Porphyroblastic pyrite at the nearby Macraes mine contains micron-scale native gold and solid solution gold up to 30 ppm. These pyrite porphyroblasts are also enriched in As, W, Ni, Co and Bi. Lead, Zn, Te and Mo contents are distinctly lower than in the low-grade framboids. These results show that low-grade turbidites were a fertile source for Au and As for orogenic gold deposits such as Macraes. The pyrite to pyrrhotite transition, which occurred mainly under greenschist faciès conditions, was probably the most effective As and Au mobilisation reaction during Mesozoic metamorphism. © 2012 The Royal Society of New Zealand.

Item Type:	Refereed Article
Research Division:	Earth Sciences
Research Group:	Geochemistry
Research Field:	Exploration Geochemistry
Objective Division:	Mineral Resources (excl. Energy Resources)
Objective Group:	Mineral Exploration
Objective Field:	Precious (Noble) Metal Ore Exploration
Author:	Large, R (Professor Ross Large)
Author:	Thomas, H (Dr Helen Thomas)
ID Code:	81408
Year Published:	2012
Funding Support:	Australian Research Council (CE0561595)
Web of Science® Times Cited:	30
Deposited By:	Centre for Ore Deposit Research - CODES CoE
Deposited On:	2012-12-05
Last Modified:	2013-05-27
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