期刊
JOURNAL OF IBERIAN GEOLOGY
卷 47, 期 1-2, 页码 85-119出版社
SPRINGER INT PUBL AG
DOI: 10.1007/s41513-021-00162-3
关键词
IOCG; Magnetite; Geochronology; Radiogenic isotope geochemistry; Albitite
类别
资金
- Spanish Geological Survey (IGME)
- Society of Economic Geologists (SEG)
- Swiss funds (FNSNF)
- [RTI2018-099157-A-I00]
The Colmenar deposit formed by complex magmatic-hydrothermal processes related to the crystallization of water-rich albite-magnetite igneous rocks, possibly with iron-rich chemical sediments and amphibolite as protoliths. Hydrothermal breccias and widespread replacement of calc-silicate hornfels by magnetite-ferroactinolite-albite assemblage indicate exsolution of iron-rich fluids during crystallization, while geochronological data suggest a Variscan age and a potential relationship to IOCG systems worldwide.
A detailed geological and isotopic study of the Colmenar deposit (Ossa Morena Zone, SW Iberia) shows that the magnetite-rich mineralization formed by complex magmatic-hydrothermal processes related to the crystallization of water-rich albite-magnetite igneous rocks derived from the crystallization of unusual melts formed during anatexis in a high temperature-low pressure metamorphic regime. The most likely protolith includes a sequence of iron-rich chemical sediments, amphibolite and possible meta-evaporites of early Cambrian age. The albite-magnetite rock occurs as up to 20 cm-thick dyke and breccia bodies and show complex immiscibility relationships with an albite-K-feldspar-quartz leucogranite. Iron-rich fluids exsolved during the crystallization of these melts are responsible of the formation of hydrothermal breccias and the widespread replacement of the hosting calc-silicate hornfels by a magnetite-ferroactinolite-albite assemblage along syn-mineralization shear zones. Geochronological data obtained for mineralization and related hydrothermal alteration points to a Variscan age (ca. 340 Ma), interpreted also as the age of the high-grade metamorphism driving anatexis at the Valuengo Metamorphic Complex. Despite the low Cu and Au contents, this mineralization shares features with the IOCG systems, which in other districts show a spatial relationship with albite-rich rocks, evaporites and pre-existing iron mineralization. The observations presented from Colmenar support an alternative genetic model with prospective implications for the Ossa Morena Zone that can be extrapolated to other IOCG belts worldwide.
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