Gold mobilization during prograde metamorphism of clastic sedimentary rocks: An example from the Liaohe Group in the Jiao–Liao–Ji Belt, North China Craton
Gold mobilization during prograde metamorphism of clastic sedimentary rocks: An example from the Liaohe Group in the Jiao–Liao–Ji Belt, North China Craton
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碎屑沉积岩顺变质作用过程中金的动员——以华北克拉通焦辽吉带辽河群为例
DOI：
10.1016/j.oregeorev.2021.104624
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发表时间：
2021-12
影响因子：
3.3
通讯作者：
Jinhui Yang
中科院分区：
文献类型：
--
作者：
Weilong Cui;Jinghui Guo;Guangyu Huang;Zaicong Wang;Yanhong Liu;Jinhui Yang
华北克拉通胶辽集带分布着丰富的金矿床。胶东半岛和辽东半岛的金矿床以石英矿脉或浸染型矿化为特征，围岩蚀变广泛，其下伏的岩石具有相似的地质背景，其特征是变质太古代和元古代的隆起块体被相对未变质的中元古代岩石和中生代花岗岩类岩体所包围。辽东金省（500 t）与胶东金省（5000 t）储量的巨大数量级差异引起了地质学家的关注。不同的C-H-O-S-Pb同位素和同位素定年引起了金矿床来源的争议。本文对华北克拉通胶辽集带辽河群古元古代变质碎屑沉积岩进行了锆石U-Pb测年、体岩组成、矿物学组成和高精度金分析等综合分析，其中金分析揭示了金在进变质过程中的活化作用。盖州巴罗维变质带各变质带样品的体岩金含量在上温呈单调下降趋势，绿泥石带为2.09 ppb，硅线石岩带为0.07 ppb。其他组在进变质作用中的Au含量演化与盖县组相同。不同变质带中黑云母的Au含量变化不大，变化范围在0.66 ~ 0.35 ppb之间，而不同变质带中白云母的Au含量主要由绿泥石带的2.60 ppb降至硅线石岩带的0.57 ppb，随变质品位的增加而降低。与此同时，在区域变质作用中，黑云母也发生脱氯作用。变质作用释放的氯可能在金的迁移过程中起了重要作用，金在变质过程中可以吸附到白云母和其他矿物上。绿泥石带的Au含量为4.67 t/km3，与原岩相当，在盖州巴罗维变质带中，上角闪岩级的变质作用将迫使岩石释放出52%的Au。综合前人对本研究结果的解释，我们认为前寒武纪岩石，如盖县组变质碎屑沉积岩，可能为辽东金省贡献了大量的金。辽河群在古元古代变质作用中释放出大量的金，可能为中生代金矿床提供了原生的金富集。
Abundant gold deposits are distributed in the Jiao-Liao-Ji Belt of the North China Craton. Gold deposits, characterized by quartz lode or disseminated styles of mineralization with extensive alteration of wall rock, of the Jiaodong Peninsula and Liaodong Peninsula are underlain by rocks of similar geological settings characterized by uplifted blocks of metamorphosed Archean and Proterozoic rocks surrounded by relatively unmetamorphosed Mesoproterozoic rocks and Mesozoic granitoid plutons. The huge order-of-magnitude difference in reserves between the Liaodong gold province (500 t) and the Jiaodong gold province (5000 t) attract the attention of geologists. Different C–H-O-S-Pb isotopes and isotopic dating have sparked controversy over the source of the gold deposits. In this study, we conducted integrated analyses of zircon U-Pb dating, bulk-rock compositions, mineralogical compositions and high-precision gold analyses on a series of meta-clastic sedimentary rocks from the Paleoproterozoic Liaohe Group in the Jiao-Liao-Ji Belt, North China Craton, of which the Au analyses reveal Au mobilization during prograde metamorphism. In the Gaizhou Barrovian-type metamorphic zone, the bulk-rock Au contents of samples within various metamorphic zones show a monotonic decrease up-temperature, from 2.09 ppb in the chlorite zone to 0.07 ppb in the sillimanite zone. The evolution in Au content during prograde metamorphism of other formations are identical to that of the Gaixian Formation. The Au concentrations of biotite in different metamorphic zones show little variation ranging from 0.66 to 0.35 ppb, whereas the Au concentrations of muscovite in different metamorphic zones mainly decrease from 2.60 ppb in the chlorite zone to 0.57 ppb in the sillimanite zone with increasing metamorphic grade in samples without metallic sulfides. Coincidently, there is a dechlorination process in biotites during regional metamorphism. Chlorine, released by metamorphism, may have played a vital role in the migration of Au, which could absorb onto muscovite and other minerals, during prograde metamorphism. Given an Au content of 4.67 t/km3 in the chlorite zone rock approximately equivalent to the protolith, metamorphism up to upper amphibolite grade would force the rocks to release 52% of the Au in the Gaizhou Barrovian-type metamorphic zone. Taking into account previous studies in the interpretation of our results, we propose that Precambrian rocks, such as the meta-clastic sedimentary rocks of the Gaixian Formation, may have contributed considerable amounts of Au to the Liaodong gold province. The Liaohe Group releasing large amounts of Au during Paleoproterozoic metamorphism, may thus provide the primary Au enrichment for the Mesozoic gold deposits.
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影响因子：
1.8
作者：
Yang Li
通讯作者：
Yang Li
影响因子：
2.2
作者：
R. Large;Helen Thomas;D. Craw;A. Henne;S. Henderson
通讯作者：
R. Large;Helen Thomas;D. Craw;A. Henne;S. Henderson
DOI：
10.1016/s0016-7878(12)80018-6
发表时间：
--
期刊：
--
影响因子：
--
作者：
G. Barrow
通讯作者：
G. Barrow
DOI：
--
发表时间：
1999
期刊：
--
影响因子：
--
作者：
Guo-Xi Hong
通讯作者：
Guo-Xi Hong
影响因子：
1.8
作者：
L. Fu
通讯作者：
L. Fu