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首页> 外文期刊>Contributions to Mineralogy and Petrology >Ages and compositions of primary and secondary allanite from the Lala Fe-Cu deposit, SW China: implications for multiple episodes of hydrothermal events
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Ages and compositions of primary and secondary allanite from the Lala Fe-Cu deposit, SW China: implications for multiple episodes of hydrothermal events

机译：中国西南拉腊铁铜矿床初生和次生尿囊石的年龄和组成：对多次热液事件的影响

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Numerous Fe-Cu deposits in southwestern China form the Kangdian Iron-Oxide Copper-Gold (IOCG) metallogenic Province. These deposits have a close association of Fe-oxides and Cu-sulfides formed at different stages, which are possibly related to multiple hydrothermal events. In this paper, U-Pb dating and chemical analyses on allanite from different stages of the Lala deposit were used to constrain timing and origin of such events. Allanite occurs as disseminated grains or patches in Fe-Cu ores and is closely associated with chalcopyrite, molybdenite, calcite and minor titanite, postdating magnetite and apatite. High-resolution backscattered electronic (BSE) imaging, electron microprobe compositions and X-ray scanning profiles demonstrate that REE-rich primary allanite was replaced by later, relatively porous and REE-poor secondary allanite. Such a replacement was promoted by interaction between primary allanite and fluid fluxes infiltrating the minerals, following an exchange scheme of REE~(3+) + Fe~(2+)→ Ca~(2+) + Al~(3+). The secondary allanite has higher Fe~(3+)/(Fe~(3+)+Fe~(2+)) ratios and U contents, indicating involvement of relatively oxidized fluids during alteration. The alteration has also produced unidentified secondary REE minerals in fractures, indicating re-deposition of some of the removed REEs. The primary and secondaryallanites are dated by in situ LA-ICP-MS technique and have U-Pb ages of 1,067 ± 41 Ma and 880-850 Ma, respectively. The -1.07 Ga primary allanite was contemporaneous with the main Mo-Cu-LREE mineralization with a molybdenite Re-Os age of -1.08 Ga. The 880-850 Ma secondary allanite is comparable with the Ar-Ar ages (890-830 Ma) of biotite from hosting schists and undeformed sulfide veins occurring throughout the Kangdian Province, suggesting that such an event was possibly syn-deformational and represents a younger hydrothermal event. Occurrences of both primary and secondary allanites suggest that the mineralization may have involved multiple tectonothermal events including the -1.05-1.1 Ga intra-plate and subsequent 960-740 Ma arc magmatism in the Kangdian region.
机译：中国西南部的许多Fe-Cu矿床形成了康甸铁氧体铜金（IOCG）成矿省。这些沉积物在不同的阶段形成了Fe-氧化物和Cu-硫化物的紧密结合，这可能与多种水热事件有关。在本文中，对拉拉矿床不同阶段的尿囊石进行了U-Pb测年和化学分析，以限制此类事件的发生时间和成因。钙铝石在铁铜矿中以散布的晶粒或小片形式存在，并与黄铜矿，辉钼矿，方解石和次要钛铁矿，过时的磁铁矿和磷灰石密切相关。高分辨率背散射电子（BSE）成像，电子微探针组成和X射线扫描谱表明，富REE的原生铝矾石被后来的，相对多孔且REE贫乏的次级钙铝石替代。遵循REE〜（3+）+ Fe〜（2+）→Ca〜（2+）+ Al〜（3+）的交换方案，原生尿石和渗入矿物的流体通量之间的相互作用促进了这种置换。次生尿囊石具有较高的Fe〜（3 +）/（Fe〜（3 +）+ Fe〜（2+））比和U含量，表明蚀变过程中有相对氧化的流体参与其中。这种变化还使裂缝中产生了未确定的次生REE矿物，表明某些已去除的REE发生了重新沉积。初生和次生白长石通过原位LA-ICP-MS技术确定日期，U-Pb年龄分别为1,067±41 Ma和880-850 Ma。 -1.07 Ga的原生石与主要的Mo-Cu-LREE矿化同时存在，辉钼矿的Re-Os年龄为-1.08 Ga。880-850 Ma的次生石与Ar-Ar年龄（890-830 Ma）相当。整个康甸省发生的黑云母来自片岩和未变形的硫化物脉，表明这种事件可能是同形变，代表了较年轻的热液事件。初生和次生安拉石的发生都表明该矿化可能涉及多个构造热事件，包括康甸地区的板块内-1.05-1.1 Ga和随后的960-740 Ma弧岩浆活动。

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