Geochemistry and fluid inclusions of scheelite-mineralized granodiorite porphyries from southern Anhui Province, China.
Geochemistry and fluid inclusions of scheelite-mineralized granodiorite porphyries from southern Anhui Province, China.
复制标题
中国皖南白钨矿化花岗闪长斑岩的地球化学和流体包裹体。
DOI：
10.1016/j.oregeorev.2017.08.004
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发表时间：
2017
影响因子：
3.3
通讯作者：
Wang YG
中科院分区：
文献类型：
--
作者：
Wang YY;von den Kerkhof AM;Xiao YL;Sun H;Yang XY;Lai JQ;Wang YG
本文报道了皖南东源和竹溪岭白钨矿化花岗闪长斑岩的岩石学、阴极发光、常量和微量元素分析以及流体包裹体研究结果。东源花岗闪长斑岩体大部分矿化，钨含量高达1140 g/t（总储量> 140000 t），而竹溪岭矿化在空间上较为有限。矿化岩石蚀变强烈，含大量方解石，无新鲜斜长石。与未矿化岩石相比，矿化岩石中K、Pb含量高，Na、Sr、Ti含量低。移动的元素（K、Na、Pb、Sr、Rb等）之间的协变和W，结合岩石学观察，证明流体蚀变一定控制了矿化。在两个矿床的石英中，均识别出4种类型的流体包裹体，水-碳包裹体（WC型）、水包裹体（W型，又分为含微量CO2的Wm型和不含CO2的Wn型）、碳包裹体（纯CO2，C型）和晚期次生水包裹体（LW型）。WC型和LW型包裹体分别代表原始岩浆流体和大气沃茨。其他包裹体代表与蚀变、矿化密切相关的岩浆流体。WC型、Wm型和Wn型包裹体具有较高的盐度和较低的均一温度，表明流体不渗透，具CO2富集性。此外，在斜长石蚀变和钾长石和绢云母沉淀过程中，K/Na比值降低，Ca释放。白钨矿的沉淀必须通过增加流体中的Ca含量以及由于CO2损失而增加pH来促进。研究结果表明，对于无钙质围岩的花岗质岩石，斜长石破碎是白钨矿成矿的关键因素。富CO2流体的存在表明，这两个矿床形成于与南岭地区相同的陆内伸展环境。因此，皖南燕山期花岗岩具有很大的钨成矿潜力，特别是深部隐伏花岗岩。
We report petrological, cathodoluminescence (CL), major and trace element analyses and fluid inclusion studies on scheelite (W)-mineralized granodiorite porphyries from Dongyuan and Zhuxiling, southern Anhui Province (China). In Dongyuan, the larger part of the granodiorite porphyry body is mineralized with W concentrations up to 1140 g/t (total WO3reserves >140 000 tonnes), whereas in Zhuxiling mineralization is spatially more limited. All mineralized rocks are strongly altered, containing abundant calcite and no fresh plagioclase. W-mineralized rocks show higher K, Pb and lower Na, Sr, Ti contents compared to the non-mineralized ones. Co-variations between mobile elements (K, Na, Pb, Sr, Rb, etc.) and W, combined with petrological observations, demonstrate that fluid alteration must have controlled the mineralization. In quartz from both deposits 4 types of fluid inclusions have been recognized, i.e., aqueous-carbonic (WC-type), aqueous (W-type, subdivided into Wm-type containing minor detected CO2and Wn containing no CO2), carbonic (pure CO2, C-type) and late secondary aqueous inclusions (LW-type). WC- and LW-type inclusions represent the original magmatic fluids and meteoric waters, respectively. The other inclusions represent evolved magmatic fluids which are closely related to alteration and mineralization. WC-, Wm- and Wn-type inclusions show higher salinity and lower homogenization temperatures, indicating fluid immiscibility with CO2effervescence. Additionally, during plagioclase alteration and precipitation of K-feldspar and sericite the K/Na ratio is lowered and Ca released. The precipitation of scheelite must have been promoted by increasing Ca contents in the fluid and also by increasing pH due to CO2loss. The present study demonstrates that for granitic rocks without calcareous wall rock, plagioclase breakdown must have been the key factor for scheelite mineralization. The presence of CO2-rich fluid indicates that both deposits formed in the same intracontinental extension setting as those in the Nanling region. Thus, the Yanshanian granites from southern Anhui Province may have a great potential for W mineralization, especially the blind ones in deep levels.