REE, Y, Nb, U, and Th contents and tetrad effect in zircon from a magmatic-hydrothermal F-rich system of Sn-rare metal–cryolite mineralized granites from the Pitinga Mine, Amazonia, Brazil
REE, Y, Nb, U, and Th contents and tetrad effect in zircon from a magmatic-hydrothermal F-rich system of Sn-rare metal–cryolite mineralized granites from the Pitinga Mine, Amazonia, Brazil
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DOI：
10.1016/j.jsames.2011.07.004
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发表时间：
2012-02
影响因子：
1.8
通讯作者：
L. Nardi;M. Formoso;K. Jarvis;L. Oliveira;A. C. B. Neto;E. Fontana
中科院分区：
文献类型：
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作者：
L. Nardi;M. Formoso;K. Jarvis;L. Oliveira;A. C. B. Neto;E. Fontana
利用LA-ICP-MS对巴西北部亚马逊地区Pitinga矿sn -稀有金属冰晶石矿床花岗岩中锆石的地球化学特征进行了探讨。该矿床是世界上最大的矿床之一，与1822±2 Ma的富f a型花岗岩侵入体有关。稀土元素Y、U Th, Nb,助教,Pb,高频内容确定的锆石颗粒albite-bearing相包含矿床和较少的进化相由amphibole-biotite和黑云母花岗岩。将锆石的微量元素含量与母岩进行比较，计算出的锆石/岩比值与天然花岗岩组成的锆石/熔体分配系数值相似。所有被分析的元素的浓度都是高度可变的，即使是在同一颗粒中进行的测定也是如此。然而，平均含量和模式与典型的岩浆锆石相似，可以指示它们结晶的熔体成分。锆石颗粒微量元素含量解释表明：(1)含钠长岩相中，锆石挥发相析出后结晶，呈现出典型的地球化学特征：Th/U比值为1 ~ 10，Y/Ho小于20，Sm/Nd比值普遍大于0.5，Nb/Y大于0.08，Hf大于2 wt%；（ii） f -配合物稳定化作用在多数分异熔体REE模式中产生m型四分异效应，并在部分锆石颗粒中保留；(3) Pitinga矿的矿床沉积始于岩浆结晶后期，主要是在岩浆沸腾后发生的。如果考虑矿物/熔体分配系数，锆石的微量元素含量对物源研究尤为重要，可以估计其火成岩源的大致微量元素格局。锆石中微量元素的地球化学特征，尽管其含量范围很广，但可以为成矿、成岩、勘探、年代学和物源研究提供一套非常重要的信息。
The geochemistry of zircon from the granites that host the Sn-Rare-Metal–cryolite deposit of Pitinga Mine in northern Brazil, Amazonia, is discussed based on data obtained by LA–ICP–MS. The ore deposit is one of the largest in the world and is related with F-rich A-type granite intrusions of 1822 ± 2 Ma. REE, Y, U, Th, Nb, Ta, Pb, and Hf contents were determined in zircon grains from the albite-bearing facies that contains the ore deposit and from less evolved facies composed of amphibole–biotite and biotite granites. The trace-element contents of zircon were compared to those of their host rocks and the calculated zircon/rock ratios are like the values of zircon/melt partition coefficients for natural granitic compositions. The concentrations found for all analysed elements are highly variable, even for determinations made in the same grain. However, the average contents and patterns are like those of typical magmatic zircon and can indicate the composition of the melts from which they were crystallized. The interpretation of trace element contents in the zircon grains suggests that: (i) in the albite-bearing facies, zircon crystallized after the volatile phase exsolution and shows typical geochemical features such as: Th/U ratios from 1 to 10, Y/Ho is lower than 20, Sm/Nd ratios are generally higher than 0.5, Nb/Y is higher than 0.08, and Hf is over 2 wt%; (ii) M-type tetrad effects were produced in the REE patterns of most differentiated melts by F-complex stabilization, and were preserved in some zircon grains; (iii) ore deposition in the Pitinga mine initiated in the late stages of magmatic crystallization mainly following resurgent boiling. The trace element contents of zircon are particularly relevant for provenance studies if mineral/melt partition coefficients are taken into account, so that the approximate trace element pattern of their igneous source can be estimated. The geochemistry of trace elements in zircon, in spite of the wide range of contents, can produce a very significant set of information useful for metallogenetic, petrogenetic, exploration, geochronological, and provenance studies.