Alkali metasomatism as a process for Ti–REE–Y–U–Th mineralization in the Saghand Anomaly 5, Central Iran: Insights from geochemical, mineralogical, and stable isotope data

Autor: Mehrdad Behzadi, Mohammad Reza Rezvanianzadeh, Saleh Deymar, Mohammad Yazdi
Rok vydání: 2018
Předmět:
Zdroj: Ore Geology Reviews. 93:308-336
ISSN: 0169-1368
DOI: 10.1016/j.oregeorev.2018.01.008
Popis: The Saghand Anomaly 5 is located in the Bafq-Saghand metallogenic province in the Central Iranian geostructural zone and contains Ti, REEs, Y, U, and Th mineralization. The mineralization is related to alkali-metasomatism and occurs in peripheral alteration zones around the iron ore deposits. Alkali-metasomatism and mineralization were controlled by tectonic activity along fault zones from ductile to brittle regimes of deformation. A metasomatic zoning is developed from outermost unaltered lithologies (subvolcanic diorite and quartz diorite host rocks) inwards to albite-actinolite metasomatite, phlogopite-actinolite metasomatite, and ultimately to magnetite orebodies. The last widespread hydrothermal event corresponds to an epidote2 ± chlorite ± calcite2 ± quartz paragenesis superimposed on all previous mineral associations. Microscopy studies reveal that ilmenite, davidite, allanite-(La), Ti–Y–U–Th-Oxide, REE-Oxide, rutile, and titanite and lesser amounts of thorite are ore minerals of Saghand Anomaly 5. The Ti–REE–Y–U–Th mineralization is related to Na–Ca-metasomatism and Ca-alteration and occurs as disseminated in albite-actinolite metasomatites and locally as veinlet-type in aplites and granites. The geochemical investigations indicate a calc-alkaline and continental-margin arc setting for granite and associated diorite-quartz diorite host rocks in the Saghand Anomaly 5. The REE patterns of the mineralized metasomatites show LREE enrichment and strong Eu negative anomalies. The presence of REE-rich hydrothermal phases suggests a significant mobilization and deposition of REEs, especially La, Ce and Y, by high temperature hydrothermal solutions within the Saghand Anomaly 5. The measured temperatures range from ∼748° to ∼766° C and ∼703° to ∼737° C for Na–Ca-metasomatic and K–Ca-metasomatic stages, respectively, using the magnetite1-actinolite and magnetite2-phlogopite oxygen isotope pairs, respectively. Both δD and δ18O values of actinolite and phlogopite indicate a magmatic source of actinolite and phlogopite forming fluids. In addition, C and O isotopic data of calcite2, from the late veinlets, indicate a magmatic origin of fluids in equilibrium with calcite2 and the formation temperature of 350 to 400° C.
Databáze: OpenAIRE
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