Monitoring fluid chemistry in iron oxide–copper–gold‐related metasomatic processes,eastern Mt Isa Block,Australia

Most researchers in the Proterozoic eastern Mt Isa Block, NW Queensland, Australia, favour magmatic fluid and salt sources for sodic‐(calcic) alteration and iron oxide–copper–gold mineralization. Here we compare spatial, mineralogic and stable isotope data from regional alteration assemblages with magmatic and magmatic‐hydrothermal interface rocks in order to track chemical and isotopic variations in fluid composition away from inferred fluid sources. Tightly clustered δ¹⁸O values for magnetite, quartz, feldspar and actinolite for igneous‐hosted samples reflect high temperature equilibration in the magmatic‐hydrothermal environment. In contrast, these minerals record predominantly higher δ¹⁸O values in regional alteration and Cu–Au mineralization. This dichotomy reflects partial equilibration with isotopically heavier wallrocks and slightly lower temperatures. Increases in Si concentrations of metasomatic amphiboles relative to igneous amphiboles in part reflect cooling of metasomatic fluids away from igneous rocks. Variations in X_Mg for metasomatic amphiboles indicate local wallrock controls on amphibole chemistry, while variations in X_Cl/X_OH ratios for amphiboles (at constant X_Mg) indicate variable aH₂O/aHCl ratios for metasomatic fluids. Biotite geochemistry also reflects cooling and both increases and decreases in aH₂O/aHCl for fluids away from plutonic rocks. Decreased aH₂O/aHCl ratios for metasomatic fluids reflect in part scavenging of chlorine out of meta‐evaporite sequences, although this process requires already saline fluids. Local increases in aH₂O/aHCl ratios, as well as local decreases in δ¹⁸O values for some minerals (most notably haematite and epithermal‐textured quartz), may indicate ingress of low salinity, low δ¹⁸O fluids of possible meteoric origin late in the hydrothermal history of the region. Taken together, our observations are most consistent with predominantly magmatic sources for metasomatic fluids in the eastern Mt Isa Block, but record chemical and isotopic variations along fluid flow paths that may be important in explaining some of the diversity in alteration and mineralization styles in the district.     

Of Winds,Worms and Mana: the Traditional Calendar of the Torres Islands,Vanuatu

This paper explores how the expression of ‘capacity’ (mena, more commonly known as mana in other Oceanic settings) and the evocation of abundance are played out in relation to seasonal change and human‐environmental relations, as observed in the Torres Islands, Vanuatu. It considers the importance for communities of North and Central Vanuatu of the appearance of a ubiquitous sea worm known as the Palolo, in combination with the regular motions of the sun and the moon, the prevaling winds and various other ecological patterns. While human‐environmental relations are often mediated by the idea of mena, this also constitutes a basic social value that informs local senses of place and belonging. The study of temporality and environmental knowledge can help to de‐centre territorial notions of ‘place’ by situating this concept within the broader context in which people experience it. Finally, because these data bear on macro comparisons that span the Western Pacific, this article is aimed in part at putting the interpretation of time and calendrics within the Indo‐Pacific frame of reference that they should begin to take.     

UNOFFICIAL COINAGE IN THE THIRD CENTURY ad IN THE GALLO‐ROMAN WORLD: CHEMICAL AND PHYSICAL ANALYSES FOR DETERMINING THE LOCALIZATION OF THE WORKSHOP*

The third century ad was a complex period of crisis in the Roman world. In this paper, official and unofficial antoniniani, and double sestercii and sestercii, were analysed by fast neutron activation analysis (FNAA) to determine the alloys used by the craftsmen for producing forgeries. Moreover, at Châteaubleau, archaeologists discovered antoniniani and bronze forgeries from Postumus. Similar materials have been found in other hoards. They are believed to have been produced by a workshop called ‘atelier II’ by numismatists. The question was whether it is possible to differentiate the Châteaubleau production from the atelier II production.