CALCITE U-Pb DATING UNRAVELS THE AGE AND HYDROTHERMAL HISTORY OF THE GIANT SHUIYINDONG CARLIN-TYPE GOLD DEPOSIT IN THE GOLDEN TRIANGLE, SOUTH CHINA
CALCITE U-Pb DATING UNRAVELS THE AGE AND HYDROTHERMAL HISTORY OF THE GIANT SHUIYINDONG CARLIN-TYPE GOLD DEPOSIT IN THE GOLDEN TRIANGLE, SOUTH CHINA
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方解石U-Pb定年揭示了华南金三角水银洞卡林型巨型金矿床的年龄和热液历史
DOI：
10.5382/econgeo.4870
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发表时间：
2021-09-01
期刊：
影响因子：
5.8
通讯作者：
Li, Jian-Wei
中科院分区：
文献类型：
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作者：
Jin, Xiao-Ye;Zhao, Jian-Xin;Li, Jian-Wei
中国南部金三角卡林型金矿床的时代一直受到质疑，因为普遍缺乏与金矿成矿有关的矿物，可以用常规的放射性同位素技术进行精确的定年。铀铅法的最新进展表明，方解石可以用来限制热液作用的年龄，但应用于矿床的研究很少。在这里，我们证明了这种方法可以用来约束在金三角产生和叠加水银洞卡林型巨型金矿床的热液活动的时间。根据横切关系、阴极发光颜色、化学成分(U、铅和稀土元素[REE])和同位素(C、O、Sr)，在该矿床中可识别出三个阶段的方解石(Cal-1、Cal-2和Cal-3)。CaL-1在结构上与热液蚀变碳酸盐岩中的矿期类碧玉和浸染型含金砷黄铁矿有关，表明它是同成矿化。CAL-2充满了空旷的空间，并有明显的橙色阴极发光，表明它是在第二次流体脉冲期间沉淀的。Cal-1和Cal-2具有相似的碳酸盐岩缓冲化学和同位素组成。Cal-3赋存于通常含有雄黄和/或雌黄的脉体中，其化学成分(低U、Pb和REE)和同位素特征(较高的C-13增量，较低的O-18和Sr-I值)与Cal-1和Cal-2不同，表明其形成于第三种流体。用激光烧蚀-电感耦合等离子体质谱(LA-ICP-MS)分析富U的CaL-1和CaL-2，以及用LA-多收集器(MC)-电感耦合等离子体质谱(MC)-ICPMS分析贫铀的CaL-3，得到了明确的年龄限制，分别为204.3~202.6 Ma、191.9 Ma和139.3~137.1 Ma。这些新的年龄表明，水银洞金矿床形成于晚三叠世，并在早侏罗世和早白垩世受到热液事件的叠加。根据CaL-3与雌黄、雄黄的共生关系，以及前人对金三角其他几个主要金矿床的年代学研究，我们推测方解石的最新阶段可能与早白垩世的一次区域性金矿成矿事件有关。结合区内已有的同位素年龄，提出金三角地区卡林型金矿床形成于晚三叠世印支造山运动和早白垩世古太平洋板块俯冲两期伸展背景下的成矿作用。研究表明，方解石U-Pb法可以用来约束卡林型金矿床的形成时间和后续的热液事件。
The ages of Carlin-type gold deposits in the Golden Triangle of South China have long been questioned due to the general lack of minerals unequivocally linked to gold deposition that can be precisely dated using conventional radiogenic isotope techniques. Recent advances in U-Pb methods show that calcite can be used to constrain the ages of hydrothermal processes, but few studies have been applied to ore deposits. Herein, we show that this approach can be used to constrain the timing of hydrothermal activity that generated and overprinted the giant Shuiyindong Carlin-type gold deposit in the Golden Triangle. Three stages of calcite (Cal-1, Cal-2, and Cal-3) have been recognized in this deposit based on crosscutting relationships, cathodoluminescence colors, and chemical (U, Pb, and rare earth element [REE]) and isotope (C, O, Sr) compositions. Cal-1 is texturally associated with ore-stage jasperoid and disseminated Au-bearing arsenian pyrite in hydrothermally altered carbonate rocks, which suggests it is synmineralization. Cal-2 fills open spaces and has a distinct orange cathodoluminescence, suggesting that it precipitated during a second fluid pulse. Cal-1 and Cal-2 have similar carbonate rock-buffered chemical and isotopic compositions. Cal-3 occurs in veins that often contain realgar and/or orpiment and are chemically (low U, Pb, and REE) and isotopically (higher delta C-13, lower delta O-18 and Sr-i values) distinct from Cal-1 and Cal-2, suggesting that it formed from a third fluid. U-Pb isotope analyses, by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) for U-rich Cal-1 and Cal-2 and by LA-multicollector (MC)-ICP-MS for U-poor Cal-3, yield well-defined age constraints of 204.3 to 202.6, 191.9, and 139.3 to 137.1 Ma for Cal-1, Cal-2, and Cal-3, respectively. These new ages suggest that the Shuiyindong gold deposit formed in the late Triassic and was overprinted by hydrothermal events in the early Jurassic and early Cretaceous. Given the association of Cal-3 with orpiment and realgar, and previous geochronologic studies of several other major gold deposits in the Golden Triangle, we infer that the latest stage of calcite may be associated with an early Cretaceous regional gold metallogenic event. Combined with existing isotopic ages in the region, these new ages lead us to propose that Carlin-type gold deposits in the Golden Triangle formed during two metallogenic episodes in extensional settings, associated with the late Triassic Indochina orogeny and early Cretaceous paleo-Pacific plate subduction. This study shows that the calcite U-Pb method can be used to constrain the timing of Carlin-type gold deposits and successive hydrothermal events.