| 山西袁家村矿区前寒武纪铁矿的形成条件 |
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| 引用本文：.1987.The Formation Condition Of 'Rhe Precambrian Iron Ores In Yuanjiacun Ore Deposit, Shanxi Province[J].Mineral Deposits,6(1):11~21 |
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| The Formation Condition Of 'Rhe Precambrian Iron Ores In Yuanjiacun Ore Deposit, Shanxi Province |
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| Abstract:The Yuanjiancun deposit is characterized by low grade metamorphism, well exposed stratigraphic section, and simple tectonics. It therefore offers an ideal locality in studying formation environment and metamorphic processes of Precambrian banded iron ores. Developed in shallow water basin of eugeosyncline, the Yuanjiancun foimation some 1200 m thick comprises three sedimentation-ore formation cycles, each of which begins with coarse to medium-grained clastic rocks (quartz sandstone or arkose), passing through fine-grained siltstone and pelitic rocks, and grades into pure colloidal chemical deposits represented by thin-bedded ferruginous quartzites. The iron mineral facies present in the ore district are diverse. From the bottom of each cycle upwards, there generally occur in succession pyrite, siderite iron silicates (composed of Fe-chlorite, minnesotaite and stilpnomelane), magrtetite and hematite. These iron mineral facies are products of sedimentation, diagenesis and metamorphism of very low grade. The spatial distribution of iron mineral facies in stratigraphic section shows that the sedimentation-ore formation environment had an increasing oxygen fugacity in the course of each cycle. The main factors controlling the types of iron mineral facies and the valence state of iron are considered to be the proportion of pelitic-arenaceous components to colloidal chemical materials during deposition as well as the relative amount of organic substance they contain. The existence of abundant organic materials results in the formation of a reducing environment and the facies dominated by ferious minerals, whereas lack of organic materials leads to the development of oxidizing media and the formation of ferric or ferric-ferrous mineral facies. |
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