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

作者：Deymar Saleh; Yazdi Mohammad; Rezvanianzadeh Mohammad Reza; Behzadi Mehrdad

来源：Ore Geology Reviews, 2018, 93: 308-336.

DOI：10.1016/j.oregeorev.2018.01.008

• Alkali-metasomatism
• Ti-REE-Y-U-Th mineralization
• Saghand Anomaly 5
• Central Iran

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 epidote(2) +/- chlorite +/- calcite(2) +/- 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 hydro thermal 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 similar to 748 degrees to similar to 766 degrees C and similar to 703 degrees to similar to 737 degrees C for Na-Ca-metasomatic and K-Ca-metasomatic stages, respectively, using the magnetite(1)-actinolite and magnetite(2)-phlogopite oxygen isotope pairs, respectively. Both delta D and delta O-18 values of actinolite and phlogopite indicate a magmatic source of actinolite and phlogopite forming fluids. In addition, C and O isotopic data of calcite(2), from the late veinlets, indicate a magmatic origin of fluids in equilibrium with calcite(2) and the formation temperature of 350 to 400 degrees C.

• 出版日期2018-2