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Fluorine in orthoamphibole dominated Zn–Cu–Pb deposits: examples from Finland and Australia

By
Leena Rajavuori
Leena Rajavuori
Department of Geology, University of Turku 20014 Turku, Finland
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Leo M. Kriegsman
Leo M. Kriegsman
Department of Geology, University of Turku 20014 Turku, FinlandNational Museum of Natural History PO Box 9517, 2300 RA Leiden, the Netherlandskriegsman@naturalis.nnm.nl
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Published:
January 01, 2002

Abstract

Volcanogenic massive sulphide (VMS) deposits commonly occur within much larger fluorine (F)-bearing hydrothermal systems, where cordierite–orthoamphibole rocks are characteristic pathfinder assemblages. Here we report whole-rock and mineral F contents for orthoamphibole bearing rocks and associated rock types from Zn–Cu–Pb deposits in Finland (Orijärvi, Iilijärvi, Pyhäsalmi, Mullikkoräme) and central Australia (Oonagalabi). Textural and mineralogical data suggest that F influx predates peak metamorphism in these deposits.

The Mullikkoräme whole-rock data show positive correlations between F and XMg = molar Mg/(Mg + Fe) and between F and elements of relatively low mobility (Ti, Al, Mg) and negative correlations between Fe and these elements. This suggests that iron was leached from silicate rocks by F-bearing fluids and was transferred to the Fe-rich sulphide ore. When normalized to immobile elements, F correlates positively with total metal content (Cu + Pb + Zn + Fe), consistent with the commonly observed increase of F content towards ore bodies.

Combining all microprobe data, hydrous minerals show the following order of decreasing F/(F + OH) ratio when coexisting: apatite > chondrodite > biotite > gedrite > (hornblende, muscovite, anthophyllite) > chlorite. The low- to medium-grade Finnish samples (Mullikkoräme: 500–560 °C at 1–3 kbar; Orijärvi: 550–650 °C at 3–5 kbar; Pyhäsalmi: 600–700 °C at 5–7 kbar) contain mainly F-poor anthophyllite, whereas F-rich gedrite is dominant in the higher grade Oonagalabi deposit (750–800 °C, 8–9 kbar). Temperature seems to have a significant, but XMg a negligible influence on F partitioning between biotite and orthoamphiboles.

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Contents

Geological Society, London, Special Publications

The Timing and Location of Major Ore Deposits in an Evolving Orogen

D. J. Blundell
D. J. Blundell
Royal Holloway, University of London, UK
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F. Neubauer
F. Neubauer
University of Salzburg, Austria
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A. von Quadt
A. von Quadt
ETH-Z, Zurich, Switzerland
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Geological Society of London
Volume
204
ISBN electronic:
9781862394520
Publication date:
January 01, 2002

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