摘要
中国大陆科学钻探工程100-2000 m的岩心、矿心的观察、编录揭示主要有经济价值的含钛相是金红石,其次是钛磁铁矿。主要含矿岩石是普通金红石榴辉岩和石英金红石榴辉岩,其次有多硅白云母金红石榴辉岩,蓝晶石金红石榴辉岩,金红石黑云绿帘纤闪石岩(退变的石榴辉石岩)和金红石-含钒钛磁铁矿榴辉岩。划分了四个矿化层位。金红石在矿层中的含量一般为2%-5%(体积),多者高达8%-10%。金红石的TiO2含量在95%(重量)以上,多产于石英榴辉岩、多硅白云母榴辉岩中。钛磁铁矿的TiO2含量在49%-55%(重量),钛磁铁矿多见于黄铁矿-金红石-钛磁铁矿榴辉岩(546-608 m岩性段)中,含钛磁铁矿5%-25%,石榴单辉橄榄岩(608-683 m岩性段),含钛磁铁矿达5%-10%和第三含矿层中局部黑云绿帘角闪岩夹层内,含钛磁铁矿可达6%。30个榴辉岩和超铁镁质岩中8种主要造岩矿物148个点的电子探针分析结果揭示:榴辉岩可分为壳源和幔源两大类,钛磁铁矿富含V、Ni、Cr说明来自幔源,大部分金红石则来自壳源榴辉岩,它们的原岩是 曾经居留地表的基性火成岩,在深俯冲的过程中经超高压变质成为含柯石英的榴辉岩。岩石薄片中金红石和柯石英的假像共存于同一石榴石或绿辉石晶粒中,也见金红石粒内有”柯石英”假象,这清楚说明金红石结晶于超高压的峰期?
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-raineralic 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 -608m) at the depths of 316 -378m; 430 -470m; and 530 -600m respectively. The second ore-bearing layers are localized in the second lithologic unit (i. e. 608 ~ 737 m) . The third ore-bearing layers are localized at the depths of 930 -1011 m . The fourth ore-bearing layers are localized at 1595 - 1993 m. The cumulated thickness of the Ti-mineralization is 1017m. The modal content of rutile in eclogite is 2% - 5% (vol. ) and is as high as 8% - 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 - 55% wt which are mainly present in pyrite-rutile-titanite-magnetile eclogite (546 -608 m) in which the modal content of titano-magnetile is about 5% -25 % (vol. ). And part of them are in the gamet-clinopytoxene-peridotite (608 - 683 m, 5% - 10 %) with a few in the biotite-epidote-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.