| 根据矿物中包裹体的研究对玢岩铁矿的新认识 |
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| 引用本文：.1983.New understanding of porphyries type iron ore deposits acquired through inclusion studies[J].Mineral Deposits,2(2):25~32 |
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| New understanding of porphyries type iron ore deposits acquired through inclusion studies |
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| Abstract:A reinvestigation on inclusions in minerals of volcanic iron ore deposits from Nanjing-Wuhu region indicates convincingly the presence of ore-magma and deuteric mineralization during the formation of some of these deposits. The main minerals in the hypergene ore-magma deposits are determined to have crystallized in the sequence of pyroxene, garnet, apatite, magnetite, quartz and calcite. Of these minerals, different ones contain diverse inclusions: in pyroxene, there occur mainly melt inclusions, in garnet, apatite and magnetite, gas-liquid-solid polyphase and gas-liquid biphase inclusions are found together with melt ones, quartz in miarolitic cavity contains primarily gas inclusions; and calcite has in it chiefly liquid inclusions. All this demonstrates that ore-forming processes of ore-magma deposits started from "dry" ore magma and then gradually converted into ore fluids. Of numerous iron deposits spatially related to diorite or porphyrite, the deuteric pneumato-hydatogenic matasomatic iron deposits occurring within the intrusion have in their early pyroxene and apatite melt, polyphase and biphase inclusions,while the contact-metasomatic and hydrothermal deposits contain predominantly biphase inclusions, which suggests that: the ore-forming processes of these diverse deposits associated with diorite or porphyrite must have also started with the residual magma, then evolved into the hydrothermal stage. These facts bear out the claim that porphyrite iron deposits includes two genetic series, the iron ore magmatic deposits and residual magmatic deposits. The ore-forming temperatures of volcanic iron deposits have been measured and summarized thus: Ore-forming temperatures of the hypergene ore-magma iron deposits (Meishan) were in the range of 120℃ to 10750℃ with magnetite formed between 450℃ and 840℃, while hematite from the supergene ore-magma iron deposits (Gushan) has formation temperatures from 350℃ to 1040℃, higher than those of hypergene deposits. Such a phenomenon can well compare with the high formation temperatures of extrusive rocks relative to intrusive rocks. The widespread hematitization took place from 350℃ to 400℃ while siderate and pyrite occurred from 260℃ to 280℃. Melt inclrisions have been recognized in early apatite and diopside of deuteric pneumato-hydatogenic matasomatic deposits (Taochun). Impregnated magnetite has decrepitation temperature of about 800℃, indicating a deuteric genesis, whereas significant quantities of magnetite were deposited from 360℃ to 460℃, assigned to the pneumato-hydrothermal stage. Magnetite in contact metasomatic deposits (Baixiangshan and Xiangyang) was formed approximately from 500℃ to 630℃ during the hydrothermal stage, the main stage of its deposition. Inclusions in minerals from several iron deposits contain such gaseous components as H2O, CO-, CO, CH4 and H2, N2 and O2 have not yet been observed and sulphuric gases not analysed. It is suggested that CO2+CH4+H2 (Mol)/CO2 (Mol) be defined as reduction parameters, and a discussion is made concerning the relationship of these parameter to ore occurrence and mineral association. |
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