Abstract:An investigation into metallogenic environments and ore-forming processes of hundreds of marine volcanic iron and/or copper deposits in China formed in different geologic periods reveals that ore magma and ore-bearing gases or fluids behaved differently in mineralization in two different environments-subterranean environment prior to their reaching sea floor and submarine environment after their effusing outside sea floor. In the former case, endogenic volcanic deposits were formed as a result of such actions as magmatic differentiation or pneumato-hydrothermal processes, while in the latter case volcanic eruptions, effusive accumulations and exhalative hot springs, in conjunction with submarine sedimentation, gave birth to exogenic volcanic deposit. As the volcanic magma had the characteristics of repeated activities and eruptions, complicated volcanic deposits might have been formed in the vicinity of the craters due to the superimposition of several times or multiple kinds of volcanic mineralizations or the transformation related to these activities. Located in age-old geosyncline regions all of these deposits underwent such geologic activities as regional metamorphism (medium to high grade), contact metamorphism, and migmatization, forming as a consequence transformed volcanic deposits. Based on these observations, the author has classified the marine volcanic iron and/or copper deposits into six types and still more subtypes: (1) iron and/or copper deposits related genetically to subvolcanic intrusions (porphyry, porphyrite, diabase, etc.); (2) volcanic pneumato-hydrothermal deposits (volcanic skarn deposits, volcanic hydrothermal deposits. etc.); (3) volcano-magmatic effusive deposits; (4) volcanic sedimentary deposits; (5) complex volcanic deposits (volcanic sedimentary pneumato-hydrothermal deposits, volcanic effusive sedimentary deposits, etc.); (6) volcanic deposits with an affinity to regional metamorphism, migmatization and contact metamorphism..In this paper, general features of these different types of deposits are also illustrated with examples. The occurrence of these deposits must have had much to do with lithology, alkalic metal contents and differentiation conditions of volcanic rock formations. The well differentiated alkaline volcanic complexes with calc-alkali indexes of 51-56 were favorable for the formation of endogenic and exogenic volcanic deposits. On the other hand, insufficiently differentiated, lithologically monotonous basic volcanic rocks (basalt, spilite, etc.) tended to form gigantic volcanic sedimentary deposits provided that adequate sedimentation played the role of compensation. In addition, the association of volcanic rocks of various petrofacies controlled directly the distribution of different types of ore deposits: endogenic volcanic deposits, volcano-magmatic effusive deposits and complex volcanic deposits constituted the predominant ore types in the petro-facies association of the central part of volcanic eruption; volcanic sedimentary deposits dominated the areas adjacent to or far away from the volcano sand containing mainly volcaniclastic rocks and volcaniclastic sedimentary rocks. The important role sedimentation played in the ore formation during submarine volcanic activities might be recognized in the fact that, of all the marine volcanic iron and copper deposits, volcanic sedimentary types, volcanic sedimentary pneumato-hydrothermal types to whose formation sedimentation made a contribution, and transformed volcanic sedimentary type possess a substantial proportion.
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姜福芝.1983.我国海相火山铁铜矿床的成因类型及其某些成矿特征的讨论[J].矿床地质,2(4):11~18.1983.A Discussion on Genetic Types and Metallogenic Characteristics of the Marine Volcanic Iron and/or Copper Deposits in China[J].Mineral Deposits2(4):11~18
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