| 华南一蚀变火山岩型绿柱石矿床的成因探讨 |
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| 引用本文：.1985.A preliminary study on genesis of an altered volcanic type beryl deposit in south china[J].Mineral Deposits,4(3):19~30 |
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| A preliminary study on genesis of an altered volcanic type beryl deposit in south china |
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| Abstract:The beryllium-molybenum deposit in the study area occurs in Jurassic acidic volcaniclastic rocks with distinctive alteration zoning from the active center of the hydrothermal fluids outwards, in the order of secondary quartzitization→sericite quartzitization→sericitization. There are five secondary quartzite bodies in the study area; they can be mineralogically divided into monoquartz and sericite facies. Beryllium-molybdenum ore bodies occur mainly in secondary quartzite of sericite facies and sericite quartzite. No such mineralizations are observed in the secondary quartzite of monoquartz facies. The distribution of secondary quartzite bodies and mineralizations are structurally controlled by fractures. Beryllium mineralization is genetically related to the late stage superimposed hydrothermal silicification. The beryllium ore mineral--beryl--is veinlet-disseminated and veinlike in altered volcanic rocks and is closely associated with silicified quartz. Of all inclusions in the deposit, 1iquid inclusions are best developed and a certain quantity of gaseous inclusions have also been recognized. This implies that ores were formed mostly in an environment dominated by hydrothermal solutions and party in the boiling state. Fluid inclulusion studies indicate beryl homogenization temperatures of 166—268℃, suggesting that beryl was formed in mesothermal stage. In addition to beryl, there also exist a small quantity of bertrandite and euclase in the ore bodies. The intimate association of beryl and silicified quartz and the depletion in fluorine-bearing minerals suggest that beryllium was transported in the form of beryllium-silicon complex such as K2(Be2Si3O9) and K2(BeSi3O8)in acidic solution. During the silicification process, the alkali metal(K)and Al were brought into the solution, which decreased th e acidity of solution, decomposed Be-bearing complex, and resulted in the deposition of beryl. According to the modes of occurrence of beryllium and molybdenum minerals, their close association in the deposit and their similar form of element transportation, the author holds the opinion that beryllium and molybdenum complexes might have coexisted in the same mineralizing fluids and migrated together along the same conduit from greater to shallow depths, which probably accounts for the coexistence of beryllium and molybdenum at very small depth. The deposit should genetically belong to post-volcanic hydrothermal type. |
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