| 鞍山、本溪地区鞍山群变质岩岩石化学研究及条带状铁矿的成矿条件 |
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| THE PETROCHEMICAL STUDY OF THE ARCHEAN BANDED IRON DEPOSIT IN ANSHAN-BENXI DISTRICT, LIAONING PROVINCE |
| The Archean Anshan group of the Anshan-Benxi district, Liaoning province, is composed of ortho-, para-metamorphic rocks and migmatite. Their original rocks are igneous (such as tholeiite, intermediateacidic volcanic rocks and tuffs), sedimentary rocks (such as . argillo-calcareous rocks) and banded iron deposits, etc. These rocks, which are of the Anshan group, constitute the Archean crust of this district. Among these rocks, the migmatites are the most widespread. Other metamorphic rocks appear like little boats floating in the "sea" of migmatites. But the other metamorphic rocks are mostly of basic and intermediate-acidic volcanic composition, rarely of seidmentary origin. This shows that igneous rocks instead of sedimenatry rocks are dominant in the oldest crust formed at the Archaeozoic age. Compared the metamorphosed sedimentary rocks with the Phanerozoic shale, the former are not argi-lloceous rocks, but argillocalcareous types, coarser clastic rocks being absent. The petrochemical characters of these rocks indicate that the surficial weathering-sedimentation of the Arch can was rather undeveloped.The chemical compostion of the banded iron deposit is quite unique, the sum of SiO2 and F2O3 + FeO reaching as high as 85-95%, much higherthan that of other types of iron deposits (40-80%).The magnetite in the bonded iron deposit is a very pure mineral, with the Fe2O3+FeO content averaging 98.12%. Accordingly its average Fe content is up to 70.20%, approaching the theoretical content of the magnetite. Such pure magnetite generally is considered as the product of complete sedimentation differentation.Based on the facts mentional above, the banded iron deposit should be a volcanic-sedimentary one.The model of the mineralizations the ore-forming Si-Fe material derived its source from the activity of the oceanic volcano. The source material existed in the strongly acidic sea water near the centre of volcanic activities. Far away from the centre the sea water under the influence of the terrestrial water became weakly acidic to intermediate, with a high Eh value. As the Si-Fe material migrated away from the centre of the marine-volcanic activities to the regions of strong terrestrial influence, it finally deposited in the weakly acidic to intermediate aquatic environment. In the long duration of mineralization, the change of the ore-forming conditions has led to the deposition of sporadic small iron lenses in the basic volcanic formation near the centre at the bottom of the sea, whereas in the areas remote from the centre were deposited thick banded iron deposits in the sedimentary-interme-diate-acidid volcanic formation. In between the two, multistratoid banded iron deposits were formed. |
| ZHOU Shi-tai.1987.THE PETROCHEMICAL STUDY OF THE ARCHEAN BANDED IRON DEPOSIT IN ANSHAN-BENXI DISTRICT, LIAONING PROVINCE[J].Acta Geoscientica Sinica,9(2):139-153. |
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