Rutile in Amphibolite Facies Metamorphic Rocks: A Rare Example from the East Qinling Orogen, China

Rutile is an important ore mineral to meet the increasing demand of critical metal Ti in various sectors. Here we report a rare example of rutile deposits hosted within the Baishugang-Wujianfang amphibolite-facies metamorphic rocks in the East Qinling Orogen, central China. The rutiles are mostly located within or along the margins of biotite and show 94.6 to 99 wt% TiO2. Rutiles occur as chains, thin layers along the foliation, and dense clusters. The grains are coexisted with magnetite. Based on Zr-in-rutile thermometer the estimated crystallisation temperature is at 630 degrees C at 7.0 kba. Based on Cr/Nb ratio, the source of the rutile is correlated with Ti-bearing silicate minerals such as biotite from aluminous sedimentary protoliths. The rutile deposit formed during lower amphibolite-facies metamorphism, and is distinct from the eclogite- and granulite-related types elsewhere in the orogen. The LA-ICP-MS U-Pb analyses of rutiles from the deposit yield lower intercept U-238/Pb-206 ages of 386 +/- 16 Ma at the Baishugang-Wujianfang district. These ages correspond to a Devonian arc-continent collisional event between the South and North Qinling domains in the East Qinling Orogen.

Automated summary

This study reports a rare example of rutile deposits hosted within amphibolite-facies metamorphic rocks in the East Qinling Orogen, central China. The rutile deposit formed during lower amphibolite-facies metamorphism, and is distinct from other types of deposits elsewhere in the orogen. The source and formation temperature of the rutile were determined through Zr-in-rutile thermometer and Cr/Nb ratio analysis.