RESUMEN
Kiruna-type iron oxide-apatite (IOA) deposits, an important source of iron, show close associations with andesitic subvolcanic intrusions. However, the processes of ore formation and the mechanism controlling iron concentration remain uncertain. Here, we report the widespread presence of high-temperature (>800°C) water-poor multisolid hydrosaline liquid inclusions in pre- and syn-ore minerals from IOA deposits of eastern China. These inclusions consistently homogenize to a liquid phase by vapor disappearance and mostly contain 3 to 10 wt % Fe, signifying a substantial capacity for iron transportation by such hydrosaline liquids. We propose that the hydrosaline liquids were likely immiscible from the dioritic magmas with high Cl/H2O in subvolcanic settings. Subsequent reaction with host rocks and/or decompression and cooling of the hydrosaline liquids is deemed responsible for the simultaneous formation of high-temperature alteration and magnetite ores, thereby providing important insights into the distinctive characteristics of IOA deposits in shallow magmatic-hydrothermal systems.
RESUMEN
Raman spectroscopy has been used for the identification of both common and uncommon minerals in melt inclusions in Group-I kimberlites from Siberia, Canada, SW Greenland and South Africa. The melt inclusions all contained high abundances of alkali-Ca carbonates, with varying proportions of cations, and Na-Ca-Ba sulphates. In accordance with its dry mineralogy, no hydrated carbonates or sulphates were detected in melt inclusions from the Udachnaya-East kimberlite. In contrast, the melt inclusions in kimberlites from Canada, South Africa and SW Greenland were found to contain bassanite, pirssonite, and hydromagnesite suggesting that greater amounts of water were present in their residual magmas. This suggests that enrichment in alkali carbonates and sulphates is widespread across a range of Group-I kimberlites and implies that they commonly have an alkali-, and sulphur-rich residual liquid.
