Titanium mineralization in the ultrahigh-pressure metamorphic rocks from Chinese Continental Scientiflc Drilling 100 similar to 2000m main hole

The observation and documentation of both the rock- and ore-cores obtained by the Chinese Continental Scientific Drilling (CCSD) had revealed that the major titanium mineral phase of economic interest is rutile and then titano-magnetite. The most important ore-bearing rock types are bi-mineralic eclogite and quartz eclogite associated with phengite-rutile eclogite, kyanite-rutile eclogite,As a whole the eclogites occupy about 1000 m in the first 2000 m core. The principal ore-bearing layers are localized in various lithologic units (i.e. 100 similar to 608m) at the depths of 316 similar to 378m; 430 similar to 470m; and 530 similar to 600m respectively. The second ore-bearing layers are localized in the second lithologic unit (i.e. 608 similar to 737 m). The third ore-bearing layers are localized at the depths of 930 similar to 1011 m. The fourth ore-bearing layers are localized at 1595 similar to 1993 m. The cumulated thickness of the Ti-mineralization is 1017m. The modal content of rutile in eclogite is 2% similar to 5% (vol.) and is as high as 8% similar to 10% (vol.) The TiO2 content of rutile is above 95%wt which are mainly occurred in quartz eclogite and phengite eclogite. The TiO2 content in titano-magnetite is about 49 similar to 55% wt which are mainly present in pyrite-rutile-titanite-magnetile eclogite (546 similar to 608 m) in which the modal content of titano-magnetile is about 5% similar to 25% ( vol.). And part of them are in the gamet-clinopytoxene-peridotite (608 similar to 683 m, 5% similar to 10%) with a few in the biotiteepidote-amphibolite of the third ore-bearing layers (the modal content of titano-magnetite is above 6% (vol)). Some 30 eclogite and ultramafic rock samples with 8 kinds of minerals are probed altogether148 points which reveals that: the eclogites can be subdivided into 2 major groups: mantle-derived and crust-derived groups. The titano-magnetite are V, Ni, Cr bearing indicating that they were derived from mantle-sources while most of the rutile-bearing eclogites are metamorphic mafic igneous rocks having a long crustal resident history. During the deep subduction they had undergone ultrahigh-pressure (UHP) metamorphism and transformed to coesite-bearing eclogites. The coexistence of coesite and rutile in same hosting gamet or omphacite clearly indicates that rutile were equilibrated in UHP peak metamorphic stage. There are plenty of evidences suggesting that the titano-magnetite and rutile are retrograded to ilmenite and sphene. Therefore due to the uplift of the subducted plates the retrogressive metamorphism subsequent to the collision event had lead to the drop in grade of the titanium mineralization.