Study On Spatio-temporal Distribution Of Chromite Deposits In The Yaluzangbu Suture Zone, Tibet, China

This thesis divided the ophiolite-related chromite deposits along the Yaluzangbu suture zone into two classes, upon comprehensive analysis of typical deposits and related lithological assemblages, via applying regional ore-forming theory. By synthesizing spatial distribution features of ophiolites and related geochemical and geophysical anomalies, this thesis delineated six potential areas for future prospecting of chromite deposits.Based on age data of ophiolites along the Yarluzangbu suture are collected from published data and their spatial distribution features, the author suggests that a northeastern trending transform fault was possibly developed to the south of Renbu.The Yaluzangbu suture is located in the central-south region of the Tibet autonomous region. It is sandwiched between the Yangluzangbu back-thrust belt and southern Gandese magmatic arc to the north and the North Himalaya fold-and-thrust belt to the south. According to the emplacement time and lithology assemblages, the ophiolite suites along the Yaluzangbu suture are classified into three groups, i.e., Saga-Bailang group, Zedang-Jiacha-Langxian group and Jiadang-Yumai group. The Saga-Bailiang gourp locates from Angren to Rikaze area, which is characterized by Cretaceous ophiolite formation. The Zedang-Jiacha-Langxian and Jiadang-Yumai groups located from Renbu to Qusong area, and the ophiolite complexes were formed in Jurassic The ore-bearing ophiolites were formed in Jurassic, and emplaced in Paleocene to Neocene.The ophiolite complexes, which were oceanic relicts, were further classified as the Angren ophiolite massif, the Rikaze ophiolite massif, the Bailang-Lianxiang ophiolite massif, the Renbu ophiolite massif, the Zedang ophiolite massif, and the Luobusha ophiolite massif. Chromite deposits are known from all of the six massifs.The ophiolite in Renbu was formed in early Cretaceous, which was later than the age of ophiolites in Angren to the west, and Zedang and Luobusha to the east. The rational interpretation is that a northeastern-trending transform fault had developed in Cretaceous, and its irregularity generated pull-apart depression and the younger oceanic crust therein, which was finally emplaced to the south of Renbu.The chromite deposits are all podiform deposits according to traditional classification scheme. The podiform chromite deposits are further subdivided into mantle podiform deposits and crustal cumulate deposits according to host rock lithology and formation depth. The mantle podiform deposits are mainly hosted by harzburgite, with nodulous ore texture; and the crustal cumulate deposits are hosted by dunites in crustal gabbroic cumulates, with disseminated or massive ore texture.Based on analysis of lihthology assemblages, this thesis concluded that all the six ophiolite massifs (Luobusha, Zedang, Rikaze, Renbu, Bailang-Lianxiang and Angren) can be potential hosts of mantle podiform chromite deposits, and the potential areas for crustal cumulate chromite deposits are limited within the Luobusha and Renbu ophiolite massifs.Fourty-six ophiolite-related chromite deposits (or occurrences) have been discovered along the Yaluzangbu suture. According to spatial distribution, lithologic assemblages of known deposits and their spatial correlation with geochemical and geophysical anomalies, six potential areas for future prospecting of chromite deposits are delineated, including two class-A potential areas, three class-B potential area and one class-C potential area: (1) Aangren-Saga potential area for chromite deposit hosted by mantile peridotite (ⅠB); (2) Rikaze-Bailang potential area for chromite deposit hosted by mantile peridotite (ⅡB); (3) Renbu potential area for chromite deposit hosted by both mantile peridotite and cumulates (ⅢA); (4) Langkazi potential area (ⅣC); (5) Zhalang-Sangri potential area for chromite deposit hosted by mantile peridotite (ⅤB); (6) Qusong-Jiacha potential area for chromite deposit hosted by both mantile peridotite (ⅥA).