| 西藏某铬矿床成因分析 |
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| 引用本文： | 池三川,师其政.西藏某铬矿床成因分析[J].地质科学,1981,0(4):343-350. |
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| 作者姓名： | 池三川 师其政 |
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| 作者单位： | 武汉地质学院北京研究生部 |
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| 摘 要： | 对于铬矿床,特别是对“非层状”超基性岩体内的铬矿床的成因和成矿规律,是一个尚未解决的地质问题。笔者在学习前人成果的基础上,根据1975—1977年的野外观察及室内鉴定分析,结合附生及造矿铬尖晶石类型、成矿与岩相及构造的关系,对西藏某铬矿床的成因进行了分析研究。
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| 关 键 词： | , |
| 收稿时间： | 1979-10-28 |
| 修稿时间： | 1979-10-28; |
GENESIS OF X CHROMITE DEPOSITS,XIZANG AUTONOMOUS REGION |
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| Chi Sanchuan,Shi Qizheng.GENESIS OF X CHROMITE DEPOSITS,XIZANG AUTONOMOUS REGION[J].Chinese Journal of Geology,1981,0(4):343-350. |
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| Authors: | Chi Sanchuan Shi Qizheng |
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| Institution: | Wuhan College of Geology |
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| Abstract: | The X ultrabasic igneous body is situated in the eastern segment of the southern Xizang ultrabasie igneous belt.It extends in a WNW-BSE direction and plunges due south.It is practically consistent with the orientation of the Yarlu Zangbo deep fault.It is a composite igneous body of multiple intrusions with marked intrusive contact relation to its country rocks T32.The magmatic differentiation is rather complete.The state whenever the magma was intruded into the deep-seated magma chamber is considered to be still molten or in the state of "crystal mush" and could hardly be in cold solid state.The chromite-bearing body,being high in m/f ratio and rich in chromium,is a sort of magnesian ultrabasic rock.Main ore bodies occurred chiefly in the middle and lower part of the dunite-harzburgite zone.The chromite deposits were formed under unstable tectonic environments.Structural deformations occurred in each mineralization stages,and fractures that were derived from the plastic deformation of the late magmatic stage,are the main ore-controlling factors.We classified the ore deposits into three genetical types.1.Deposits formed by crystallization segregation of late orthomagmatic stage.According to the manner of mineralization,they could be still subdivided into two subtypes,i.e.,segregation in situ,and segregation by pressure filtering.2.Primordial cumulative deposits of late orthomagmatic stage.The main feature of this kind of deposit is that the ore forming Cr-spinels are pissolitic,nodular and ellipsoidal in shape.They form nodular aggregates ores.The pissolites were oriented in a definite direction forming "sedimentary bedding" like structure by the graded granularity of the Cr-spinels.And this sort of nodular ore may at times give rise to massive ores.The contact between the ore bodies,and their neighbouring dunite ore gradational but rather sharp,they are considered to have been accumulated in the eddy currents of crystal mush by current differentiation and gravitational settlement,owing to the greater density of ehromite in the magma chamber.3.Late magmatic injection deposits.At the latest residual magmatic stage,rock body was plastically deformed by structural extruding pressure to form fractures and Cr-rich residual magma.The latter migrated along the fracture to form the injection deposits.The three types of mineralization mentioned above could occur separately or in combination.The genesis of the "Alpine-type" ultrabasic igneous rocka and the podiform ehromite in geosynclinal terrains,especially the genesis of pisolitic ores,have long beet argued.H.B.Pavloff suggested that the pisolitic ores had been formed by magmatic immissibility,and J.Dickey suggested that they had been formed as "snow balls trundling" in the magmatic segregation zones at the margin of the plates.It is because the separation of ehromite by magmatic immissibility in magnesian melt can hardly be possible as seen from the experimental data.Therefore,the present authors suggest that the pisolitic ores are formed as cumulative products of gravitational settlement by current differentiation. |
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