| 罗布莎铬铁矿区成矿构造条件的研究 |
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| 引用本文：.1983.A study fo the tectonic environment of the Lobusha chromite deposits[J].Mineral Deposits,2(1):48~57 |
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| A study fo the tectonic environment of the Lobusha chromite deposits |
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| Abstract:The chromite deposits in question are located at the vertex of the northward convex arc of the Lobusha ultrabasic body in the eastern sector of the southern Tibetan ultrabasic rock zone. This ultrabasic body is a composite one consisting of early magnesiam ultrabasic rock and late basic-ultrabasic rock formed by two intrusions during the Cretaceous period. Two types of rock can be recognized in the main: enstenite-peridotite and dunite, which exhibit distinct petrographic zonation. The ultrabasic body is controlled by Yaluzanbujiang deep-seated fracture zone, which possesses different features in different sectors of this intrusive body: compresso-torsion fault striking east-west is typical in eastern and western sectors; secondary tenso-torsion fault assuming a reversed NE trending S shape dominates the middle sector; the ultrabasic body itself is characterized by the development of various fracture planes and arc structures. Geologic features of tne ore deposit suggest that the commercial chromite bodies were formed by segregated chromite ore magma which, under the driving force of tectonic stress, migrated, concentrated and were injected into some fracture planes in certain directions. The occurrence of ore-bearing belts, ore swarms and ore bodies is a reflection of the fact that the migration and concentration of chromium during the evolution of magma were under the control of structural features of different generations and orders: the ore-bearing belt should be regarded as a tectonic-magmatic-metallogenic belt characterized by definite rock association and deformation, in it the ore swarms are generally restricted to the strongly sheared and compressed parts, and the ore bodies occur mostly inside the secondary tenso-shear and compresso-shear fractures. The distribution of the ore bodies agrees with the trajectories of the shear stresses, en echelon in plan and imbricated in profile. The main structural type controlling the ore bodies here is of Xi-type. The study of the tectonic environment of the deposit shows that the mechanical properties of structures and the manner of stress action during rock formation directly influenced the shape and occurrence of the ultrabasic body, the clistribution of the petrographic belts and the structural features inside this rock body as well as the magmatic differentiation, which, in turn, constituted the boundary conclitions that controlled the migration and concentration of chromium and the formation and clistribution of ore belts, ore swarms and ore bodies. |
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