Abstract The source(s) of lode gold deposits formed in Precambrian cratons related to accretion/collision and cratonic reactivation, formerly attributed to either supercrustal volcano-sedimentary sequences or deep crustal/sub-crustal origin, remain controversial largely because gold deposits are spatially related to metamorphosed rocks, but geochemical data somewhat indicate a poorly understood deep source. Reconciling such conflicts is important to better understand the main factor controlling the formation of ore deposits and their genetic link with specific tectonic settings. Giant Late Mesozoic lode gold provinces in the North China Craton (NCC) were formed ca. 1.7 Ga later than cratonization metamorphism, and contemporaneous with intensively felsic to mafic magmatism related to cratonic reactivation. In this study, we conduct a comprehensive Pb isotope study on major gold deposits from the eastern Yanshan belt, northern margin of the NCC. In order to constrain the source(s) of gold, we attempt to map regional Pb isotope variations of lower continental crust (LCC), and develop a two stage quantitative model (punctuated by three prominent geological events at 2.80 Ga, 1.85 Ga and 0.16 Ga) to reproduce time-integrated Pb isotopic signatures of deep-seated lithospheric reservoirs to make a comparison with Pb isotopic signatures of the gold mineralization. Gold-bearing pyrites within different types of host rocks have relatively uniform Pb isotopic ratios, which are significantly different to high-grade metamorphosed host rocks, but similar to those of spatially associated Late Mesozoic granitic rocks. Our data show that the Pb isotopic signatures of gold deposits vary consistently with presumed regional Pb isotopes of the LCC during the Late Mesozoic. Lead isotopic heterogeneity of the LCC was likely caused by underplating of mafic magmas derived from mantle sources. During underplating, highly chalcophile elements (e.g. Au, Ag and Cu) were concentrated at the base of the LCC due to sulfide saturation from mafic magmas. Integrating petrological, geochemical, geochronological, and considering chalcophile element solubility, we propose a new genetic model to describe the formation of Late Mesozoic gold deposits in the NCC: (1) early formation of sulfide-bearing cumulates with high Au/Cu ratios during magma differentiation at the base of the LCC; (2) subsequent fluid-fluxed remelting of these cumulates at the onset of lithospheric extension and release and ascent of ore-forming fluids to the site of precipitation. Considering the metallogenic characteristics of other Au ore-forming systems, we suggest that metal fertilization in deep-seated reservoirs and subsequent tectonic decompression are important factors controlling the development of Au-rich ore deposits worldwide. This study demonstrates how Pb isotope can be employed to trace source(s) of gold deposits.

中文翻译：

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将华北克拉通中生代矿脉金矿床与金属肥沃的下陆壳联系起来：来自铅同位素系统学的证据

摘要 在前寒武纪克拉通形成的脉状金矿床的来源与吸积/碰撞和克拉通再活化有关，以前归因于超地壳火山沉积序列或深地壳/亚地壳起源，主要是因为金矿床在空间上相关到变质岩，但地球化学数据在某种程度上表明对深层源知之甚少。调和此类冲突对于更好地了解控制矿床形成的主要因素及其与特定构造环境的成因联系非常重要。大约在华北克拉通 (NCC) 中形成了巨大的晚中生代矿脉金矿区。1.7 Ga 晚于克拉通化变质作用，与强烈的长英质至镁铁质岩浆作用同时期与克拉通再活化有关。在这项研究中，我们对华北克拉通北缘燕山带东部的主要金矿床进行了全面的铅同位素研究。为了限制金的来源，我们尝试绘制下大陆地壳 (LCC) 的区域 Pb 同位素变化图，并开发了一个两阶段定量模型（以 2.80 Ga、1.85 Ga 和 0.16 Ga) 重现深部岩石圈储层的时间积分 Pb 同位素特征，以与金矿化的 Pb 同位素特征进行比较。不同类型围岩中含金黄铁矿的铅同位素比相对均匀，与高品位变质围岩有显着差异，但与空间伴生的晚中生代花岗岩相似。我们的数据显示，金矿床的 Pb 同位素特征与中生代晚期 LCC 的假定区域 Pb 同位素一致。LCC 的铅同位素异质性很可能是由地幔来源的基性岩浆的底镀引起的。在底镀过程中，由于基性岩浆的硫化物饱和，高度亲硫元素（例如金、银和铜）集中在 LCC 的底部。综合岩石学、地球化学、地质年代学，并考虑亲硫元素溶解度，我们提出了一种新的成因模型来描述 NCC 晚中生代金矿床的形成：（1）在岩浆过程中早期形成具有高 Au/Cu 比率的含硫化物堆积物LCC 基础上的差异化；(2) 在岩石圈扩张和释放开始时这些堆积物的流体流动重熔，以及成矿流体上升到降水地点。考虑到其他金成矿系统的成矿特征，我们认为深部储层中的金属肥化和随后的构造减压是控制全球富金矿床开发的重要因素。这项研究展示了如何使用铅同位素来追踪金矿床的来源。