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浙江省矾山明矾石矿床地球化学特征兼论中生代成矿体系
其他题名Geochemical Characteristics of the Fanshan Alunite Deposit and the Mesozoic Volcanic Mineralization System in Zhejiang Province
何玉良
2007-05-31
学位授予单位中国科学院地球化学研究所
学位授予地点地球化学研究所
学位名称博士
关键词浙江矾山 明矾石矿床 中生代火山岩 成矿体系 矿床地球化学
摘要矾山明矾石矿床位于江山-绍兴深断裂南东侧,海西印支褶皱带的南东侧,中国板块东南构造区与太平洋板块的交接处,属于中国板块东南构造区。该矿床产在矾山破火山口内,是一个超大型明矾石矿床,同时矿床中的钒、镓含量也达到了综合利用的品位。该矿床研究程度低,缺少地球化学特征研究。因此,本次工作系统研究了该矿床常量元素、微量元素、稀土元素、硫和铅同位素地球化学特征。本次对明矾石矿床的研究获得以下几点初步认识: 1:成矿物质来源于火山岩。矿区火山岩中的K、Al、Na等矿石元素含量明显比其他地区高,并且从围岩→矿化围岩→矿石呈明显的富集趋势。稀土资料和铅同位素资料也都表明成矿物质来源于中生代火山岩。 2:V、Ga含量达到了综合利用的品位。微量元素资料表明,矿石中V平均含量为211.6ppm,Ga平均含量为16.78ppm,都大于地壳丰度,尤其是V远大于地壳丰度;同时发现,成矿时V以V¬5+形式通过与Al3+发生类质同像进入明矾石晶格,而矿石中Ga含量除与Al3+外还与Fe3+含量有关。 3:明矾石的稀土元素地球化学特征比较复杂。根据δEu值不同可分为三类: Eu弱负异常型,Eu弱正异常型和Eu强正异常型。影响稀土元素分布的因素主要为成矿原岩中富含碱性长石和成矿时的氧逸度和温度,另外矿石结构(如孔隙度)对稀土元素分布也有影响。研究表明,矿石稀土配分模式为轻稀土富集型,与火山岩基本一致。 4:硫同位素研究发现,黄铁矿的δ34S值为1.9~3.2‰,明矾石的δ34S值为13.62~16.02‰,后者明显大于前者。本次研究认为黄铁矿的δ34S值代表当时的岩浆源硫,而明矾石较大的δ34S值为岩浆硫经过同位素分馏的结果。铅同位素研究发现,明矾石矿石的206Pb/204Pb=17.963~18.606,207Pb/204Pb=15.439~15.672,208Pb/204Pb=38.405~38.796。通过与中生代火山岩和基底变质岩的对比,本次研究认为明矾石的铅源为中生代火山岩来源,与基底变质岩并无直接的来源关系。 5:通过明矾石矿床的地球化学特征研究,结合实际地质特征和前人研究成果,本次研究提出了以下矿床成因:明矾石矿床形成环境为浅成低温氧化环境;成矿物质来源于围岩,成矿所需的硫源为分馏的岩浆硫;矿床形成时期为73~95Ma,比围岩晚10~20Ma;矿床成因为火山热液交代成因。 浙江省中生代火山岩成矿体系主要指受浙江省中生代火山构造、岩浆活动控制的一系列不同类型的矿床组合。成矿体系主要受江绍深断裂带和中生代陆相火山岩控制。前人对成矿体系中的单一矿床研究较多,但是缺少横向对比研究。本次工作主要通过对成矿体系中的两类矿床(金属矿床和非金属矿床)进行对比研究,结合中生代火山岩演化过程,初步探索成矿体系中各类矿床间的联系以及成矿体系与火山岩演变的关系。本次工作取得以下几点初步认识: 1:成矿体系中各类矿床的整体分布受江绍深断裂、温州-镇海大断裂等一些深大断裂控制。各矿床的具体控(容)矿构造都为次级压-压扭性断裂和破火山口构造,其中破火山口构造在成矿过程中占非常重要的作用。 2:成矿体系中各类矿床的成矿温度低,深度浅,为典型的浅成低温矿床。 3:铅同位素资料表明,矿床的铅源为中生代火山岩来源,与基底并无直接联系。氢氧同位素资料表明,各类矿床的成矿流体以中生代大气降水为主,岩浆水占很少部分或并无参与成矿。 4:成矿体系存在明显的成矿成岩时差,金属矿床在12.44~45.6Ma,萤石矿床为25~75Ma,其他非金属矿床为10~20Ma;铅锌(银)金等金属矿床为具有明显的两期成矿特征。
其他摘要The Fanshan alunite deposit is located in the southeast of the Jiangshan-Shaoxing deep fault zone and Hercynian-Indosinian fold belt, at the joint of the southeast tectonic zone of the China tectonic plate and the Pacific plate, belonging to the southeast tectonic zone of the China tectonic plate. This deposit is an ultra-large alunite deposit located in the Fanshan caldera. Vanadium and gallium in this deposit can be also used. But it had been poorly studied, even these is no geochemical study about it. Systematic geochemical studies have been carried out including major elements, trace elements, rare earth elements, sulfur isotope and lead isotpe. Base on these studies, the following achievements have been obtained: 1. The ore-forming materials of this deposit derived from the volcanic rocks. The contents of the ore-forming elements such as K, Al and Na in the volcanic rocks of mining area are higher than those in others areas. And the ore-forming elements represent obviously enrichment trend from country rocks to mineralization rocks and to alunite ores. The evidence that come from REE and lead isotope also indicate the ore-forming materials came from the volcanic rocks. 2. The contents of V and Ga of ores have arrived the comprehensive utilized grade, the average content of vanadium in ores is 211.6 ppm, and the average content of gallium is 16.7 ppm. And we suggested that vanadium entered into alunite crystal lattice by means of isomorphism as V5+ replaced the Al3+, while the content of gallium is correlated with the contents both Al3+ and Fe3+. 3. REE geochemical characteristics of alunite are complicated. According to the differences in δEu, they can be divided into three types: weak negative Eu anomaly, weak positive Eu anomaly and remarkable positive Eu anomaly. Main factors controlled the REE distribution patterns are the content of alkaline feldspar in source rocks, the fO2 and temperature during the mineralization period. And the ore texture such as the porosity could also effect it. The ores REE distribution patterns is LREE-enrichment pattern, as same as that of the volcanic rocks. 4. The δ34S of pyrite ranges from 1.9 to 3.2‰, while the alunite is 13.62-16.02‰. We considered that the values of δ34Spy represent the primary value of magmatic sulfur, while the values of δ34Saln represent the sulfur value after isotopic fractionation. The ores lead isotope compositions are 206Pb/204Pb=17.963-18.606, 207Pb/204Pb=15.439-15.672, 208Pb/204Pb=38.405-38.796. Compared with the lead isotope compositions of the Mesozoic volcanic rocks and basement metamorphic rocks, the ore lead came from the Mesozoic volcanic rocks and had nothing with the basement metamorphic rocks. 5. According to all the studies on geochemical characteristics of Fanshan alunite deposit, and combining with geological characters and references, the following ore genesis was proposed: the ore-forming environment is supergene, low temperature and oxidized; the mineralization materials came from the country rocks, and the source of sulfur came from magmatic sulfur that formed after isotopic fractionation; the mineralization age is 73-95 Ma, 10-20 Ma later than that of the wall rocks; the ore genesis is volcanic hydrothermal replacement deposit. The Zhejiang Mesozoic volcanic mineralization system mainly refers a series different types ore deposits assemblages that is controlled by the Mesozoic volcanic structures and magmatic activities in Zhejiang. Jiangshan-Shaoxing deep fault zone and continental volcanism of Mesozoic control this mineralization system. Many studies about single deposit in this system had been done, but the comparative research of the deposits was lacked. In this paper, we have elementarily studied the connection between metallic ore deposits and nonmetallic ore deposits base on the comparism of these two types of deposits. And we have also studied the correlation between the mineralization system and evolution of Mesozoic volcanic rock by connected with the evolution process of Mesozoic volcanism. Base on these, some points were achieved: 1. The distributions of all types of deposits of this system are controlled by deep or large faults such as Jiangshan-Shaoxing deep fault and Wenzhou-Zhenhai large fault. The ore-contol structures (or host structure) of deposits are 2nd ord compress-shear faults and caldera, especially the broken craters are very important in ore-forming processes. 2. All deposits of the mineralization system are typical epithermal deposits. 3. The lead isotope researches indicated the lead of all deposits derived from the Mesozoic volcanic rocks, and have not connection with the basement metamorphic rocks directly. According to the evidence of hydrogen-oxygen isotopes, mineralizing fluid of the deposits came from meteotric water of Mesozoic, while few magmatic water was involved in the ore-forming process. 4. Obvious time differences between mineralization and petrogenesis are existed, for metallic ore deposits is 12.44-45.6 Ma, for Wuyi fluorite ore deposits is 25-75 Ma and for other nonmetallic ore deposits is 10-20 Ma. And the Pb-Zn-Ag (Au) deposits represented obviously the character of two-period ore-forming process.
页数109
语种中文
文献类型学位论文
条目标识符http://ir.gyig.ac.cn/handle/352002/3286
专题研究生_研究生_学位论文
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何玉良. 浙江省矾山明矾石矿床地球化学特征兼论中生代成矿体系[D]. 地球化学研究所. 中国科学院地球化学研究所,2007.
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