Fluorine in orthoamphibole dominated Zn–Cu–Pb deposits: examples from Finland and Australia
Leena Rajavuori, Leo M. Kriegsman, 2002. "Fluorine in orthoamphibole dominated Zn–Cu–Pb deposits: examples from Finland and Australia", The Timing and Location of Major Ore Deposits in an Evolving Orogen, D. J. Blundell, F. Neubauer, A. von Quadt
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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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As an outcome of the European Science Foundation scientific programme, GEODE, on geodynamics and ore deposit evolution, this book examines the underlying geodynamic processes that lead to the formation of ore deposits in order to discover what controls the timing and location of major ore deposits in an evolving orogen.
A collection of 19 research papers examines various aspects of ore genesis in the context of the geodynamic processes occurring within an evolving orogen. Although the majority of papers relate to Europe, their findings have a global significance for metallogenesis.
The book will be of interest to all those involved in research or mineral exploration concerned with metallogenesis. In addition, ore deposits provide new evidence about magmatism associated with transient, rapid changes in plate motions and subduction processes in unusual tectonic settings, and are therefore of interest to those involved in both the magmatic and tectonic processes of orogenesis.