| 对41 4矿床成因的讨论 |
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| 引用本文：.1986.A Discussion On Genesis Of The 414 Deposit[J].Mineral Deposits,5(2):85~96 |
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| A Discussion On Genesis Of The 414 Deposit |
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| Abstract:The 414 granite type niobium-tantalum deposit is regarded as an important discovery in late 1960's ore prospecting. Up till now, it is almost unanimously considered that the formation of this deposit is related to the granitic magma; nevertheless, the author believes that, instead of being genetically connected with the granitic magma, this deposit seems to be a product of alkali-metasomatism in the process of granitization, i.e., being of nonmagmatic origin. Following is some convincing evidence: 1. The ore-bearing granite and its adjacent barren granite occur in bedded from; each bed has a thickness of 30-100cm with some even reaching l.2-2m. This character is with the attitude expressed by exfoliation, so the granite is called "bedded granite of its bedding consistent with that of the surrounding metamorphic rocks. 2. The ore-bearing granite varies considerably in lithology, and contains skialith of metamorphic rocks; the metamorphic rocks adjacent to the granite body have experienced granitization and migmatization. 3. Isotopic ages of the granite body vary from 157 Ma to 131 Ma within a distance of less than l.5 km where no phase or facies distinctions are observed, the ages inside the rock body are older than those along the margin of the rock body. 4. The triclinicity of potassium-feidspar from the granite is 0.82, and the order of plagioclase is 100, suggesting that these two minerals are of ordering type and thus the granite is of granitization origin. 5. Under the constant pressure of 2000 bar, the initial melting temperature of the granite is 576℃, much lower than that of magmatic granites in South China. 6. Rock type and chemical components of the ore-bearing granite as well as chemical composition of lithium muscovite all show bedded characteristics. 7. The formation temperatures of quartz from the ore-bearing granite fall into three groups, i. e., 483-53℃, 300-325℃; 80-187℃, which are all lower than crystallization temperature of magma and represent respectively temperatures of granitization, alkali metasoma+ism and late-stage silicification. 8. The development of multilayered pegmatites refutes the magmatic origin, each layer of pegmatoid stands for the peak plane of a alkali metasomatism. 9. Rather than being magmatic origin, the zonal texture of albite in quartz crystals from the ore is a combined product of early “self-cleaning process”of metacrystal and late alkali metasomatism. 10. The rare element abundances are relatively high in metamorphic rocks near the granite body with tantalum 10 times, niobium 7 times, lithium twice, rubidium twice aid cesium three times higher than their respective Clark values. This provides material basis for mineralization. |
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