| 鞍本太古代绿岩盆地铁矿的成矿特征 |
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| 引用本文：.1984.Metallogenic Characteristics Of Iron Deposits In Archean Greenstone Basin Of Anshan-Benxi Area,Northeast China[J].Mineral Deposits,3(2):1~10 |
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| Metallogenic Characteristics Of Iron Deposits In Archean Greenstone Basin Of Anshan-Benxi Area,Northeast China |
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| Abstract:Lots of research work has been conducted by previous geologists on ore-bearing metamorphic rock series and related iron deposits in the Anshan-Benxi area, On such a basis, the authors have further looked into this world-famous iron-occurring base area during the past several years and come to some new conclusions as follows: The Anshan-Benxi area is a fairly typical Archean greenstone basin and the iron deposits occurring within it are of Algoma type whereas the western Anshan-Yanqianshan is an early Proterozoic miogeosyncline, and the iron deposits it holds are assigned to Superior type. It is therefore presumed that all of the over 120 iron ore deposits or occurrences in this area do not simply belong to a single genetic type-the commonly known Anshan type, and that more than 110 iron deposits (occurrences) hosted by the Anshan-Benxi greenstone basin make up a specific successive metallogenic series which, in accordance with the stratigraphic position and geologic setting of the ore, could be further divided into five subtypes, i.e., Xiaolingzi, Shanchengzi, Gongchangling, Jiajiabaozi and Hongshanling sybtypes. Any iron deposit in this metallogenic series, whichever sybtype it pertains to, is confined to greenstone basin. Some apparent regularity governing this metallogenic series has been recognized: (1) Time and space factors: Ore-forming processes bear time-bound and stratabound characteristics; size and shape of ore deposits as well as ore tenor and ore type are obviously controlled by geological age and stratigraphic position. The Anshan Group has five iron-bearing strata, of which the Yanlongshan Formation of middle Yanshan Group possesses the majority of large and gigantic iron deposits and the Hongshanling Formation is most: favorable for mineral exploration. (2) Structural elements: Iron deposits are strictly controlled by geotectonic environments; iron-bearing rock series occur along the margin of the Anshan-Benxi greenstone basin and large and gigantic iron deposits are distributed circularly, dipping towards the center of this basin; secondary synclines are major ore-containing passages for large and gigantic iron deposits while fractures, as ore channelways for late stage migmatic fluids, have played important role in the formation of rich ore bodies. (3) Volcanic eruptive sedimentary cycle and magmatic components: The Anshan Group was a huge volcanic eruptive-sedimentary cycle, and iron deposits were formed during the transition stage when basic volcanic rocks evolved progressively into acid volcanic rocks. These deposits are closely associated with basic volcanic rocks, especially with those enriched in CaO and Na2O+K2O. (4) Metamorphism: High-grade metamorphism and abundant ferriferous silicate minerals seem unfavorable for the iron mineralization; iron deposits in granulite facies, high-grade amphibolite facies are hence of low tenor and small size; on the contrary, low-grade greenschist facies and low-grade amphibolite facies probably favored the formation of large iron deposits due to their insufficient ferriferous silicate minerals. (5) Migmatization: Previous work indicates that iron ore bed might lie within vast migmatic granite masses and that under suitable structural conditions, pay ore was likely to form through the replacement of lean iron ore body by migmatic fluids at depth. The Gongchangling large pay iron ore deposit serves well as an example. The original rock sequence had an intimate bearing on the formation of iron deposits. Large Algoma type iron deposits occur in calc-alkaline volcanic rocks of middle Anshan Group within the Archean greenstone basin, iron sources being associated with the basic volcanic activity; the Superior type iron deposits are present in Proterozoic sedimentary sequence of Guanmenshan Formation, Liaohe Group, iron material derived from the transformation of ferriferous volcanic rocks of Anshan Group by exogenic ore-forming processes. The iron deposits in this area might be genetically classified into three types, i. e., volcanic type, volcanic-sedimentary type and sedimentary type, consisting of a closely related genetic series. |
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