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A metamorphic mineral source for tungsten in the turbidite-hosted orogenic gold deposits of the Otago Schist, New Zealand

Citation

Cave, BJ and Pitcairn, IK and Craw, D and Large, RR and Thompson, JM and Johnson, SC, A metamorphic mineral source for tungsten in the turbidite-hosted orogenic gold deposits of the Otago Schist, New Zealand, Mineralium Deposita, 52, (4) pp. 515-537. ISSN 0026-4598 (2017) [Refereed Article]

Copyright Statement

Copyright 2016 Springer-Verlag Berlin Heidelberg

DOI: doi:10.1007/s00126-016-0677-5

Abstract

The orogenic gold deposits of the Otago Schist, New Zealand, are enriched in a variety of trace elements including Au, As, Ag, Hg, W and Sb. We combine laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) traverses and images to show that detrital rutile is the most important host mineral for W in the subgreenschist facies rocks. Furthermore, the prograde metamorphic recrystallisation of detrital rutile to titanite releases significant amounts of W (potentially 0.41 g/tonne of rock). Scheelite development closely follows the progression of this W-liberating reaction. Scheelite micrograins form early within the fabric of the rock evolving to locally and regionally sourced scheelite-bearing veins. Scheelite from syn-metamorphic veins at Fiddlers Flat and Lake Hāwea shows distinct differences in composition compared with scheelite from late-metamorphic veins at the Macraes Mine, the latter of which is enriched in REEs, Y and Sr. We suggest that the scheelite at Macraes became enriched due to the liberation of these elements during alteration of the Ca-silicate minerals epidote and titanite by the ore-forming fluid. These results are supportive of recent models for orogenic gold mineralisation in the Otago Schist, whereby prograde metamorphic recrystallisation of diagenetic or detrital metal-rich mineral phases (pyrite to pyrrhotite: Au, As, Ag, Hg and Sb; rutile to titanite: W) releases significant amounts of metals into the concurrently developing metamorphic fluids that can be subsequently focussed into regional structures and form significant tungsten-bearing orogenic gold deposits.

Item Details

Item Type:Refereed Article
Keywords:tungsten, scheelite, orogenic, Otago Schist
Research Division:Earth Sciences
Research Group:Geology
Research Field:Ore Deposit Petrology
Objective Division:Mineral Resources (excl. Energy Resources)
Objective Group:Other Mineral Resources (excl. Energy Resources)
Objective Field:Mineral Resources (excl. Energy Resources) not elsewhere classified
Author:Cave, BJ (Mr Ben Cave)
Author:Large, RR (Professor Ross Large)
Author:Thompson, JM (Mr Jay Thompson)
Author:Johnson, SC (Mr Sean Johnson)
ID Code:115497
Year Published:2017
Web of Science® Times Cited:1
Deposited By:CODES ARC
Deposited On:2017-03-28
Last Modified:2017-05-16
Downloads:0

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