Kui-Feng Yang

Geological and geochronological constraints on the genesis of the giant Tongkuangyu Cu deposit (Palaeoproterozoic), North China Craton

ABSTRACT The Zhongtiao Mountain region is endowed with some of the largest Cu deposits in northern China, among which the Tongkuangyu Cu deposit contains 70% of the total reserves of copper. The orebodies in this deposit are confined to metamorphosed volcanic tuff and monzogranitic porphyry which are enclosed within metasediments. Metamorphism and deformation resulted in intense modification of the deposit, leading to debates surrounding its genesis. In this study, we investigate the lithology, hydrothermal alteration, and mineralization in the deposit. Secondary ion mass spectrometer and laser ablation ICPMS zircon U–Pb dating show that the meta-monzogranitic porphyry was emplaced contemporaneous with the surrounding lithologies at 2180–2190 Ma as a sill, and that the basic volcanic rocks erupted slightly earlier at ~2220 Ma. The Re–Os geochronological data on molybdenite from the deposit constrain the timing of copper mineralization to 2122 ± 12 Ma. Together with published information from previous studies on this region, we infer that during ~2100–2200 Ma the Zhongtiao Mountain region experienced continental or back-arc rifting. We exclude a porphyry copper model for the deposit and favour sediment-hosted stratiform explanation for this deposit.

Origin of the Yinshan epithermal-porphyry Cu–Au–Pb–Zn–Ag deposit, southeastern China: insights from geochemistry, Sr–Nd and zircon U–Pb–Hf–O isotopes

The Yinshan deposit is a large epithermal-porphyry polymetallic deposit, and the timing and petrogenesis of ore-hosting porphyries have been hotly debated. We present new results from geochemical, whole-rock Sr–Nd and zircon U–Pb–Hf–O isotopic investigations. Zircon U–Pb data demonstrate that the quartz porphyry, dacitic porphyry, and quartz dioritic porphyry formed at ˜172.2 ± 0.4 Ma, ˜171.7 ± 0.5 Ma, and ˜170.9 ± 0.3 Ma, respectively. Inherited zircon cores show significant age spreads from ˜730 to ˜1390 Ma. Geochemically, they are high-K calc-alkaline or shoshonitic rocks with arc-like trace element patterns. They have similar whole-rock Nd and zircon Hf isotopic compositions, yet an increasing trend in ϵNd(t) and ϵHf(t) values typifies the suite. Older (inherited) zircons of the three porphyries display Hf compositions comparable to those of the Jiangnan Orogen basement rocks. In situ zircon oxygen isotopic analyses reveal that they have similar oxygen isotopic compositions, which are close to those of mantle zircons. Moreover, a decreasing trend of δ18O values is present. We propose that the ore-related porphyries of the Yinshan deposit were emplaced contemporaneously and derived from partial melting of Neoproterozoic arc-derived mafic (or ultra-mafic) rocks. Modelling suggests that the quartz porphyries, dacitic porphyries, and quartz dioritic porphyries experienced ˜25%, ˜10%, and ˜10% crustal contaminations by Shuangqiaoshan rocks. Our study provides important constraints on mantle–crust interaction in the genesis of polymetallic mineralization associated with Mesozoic magmatism in southeastern China.

Late Mesozoic Gold Mineralization in the North China Craton

The North China Craton (NCC) hosts numerous gold deposits and is known as the most gold-productive region in China. These deposits are generally sited in the cratonic margin. Main gold concentration districts include Jiaodong in the eastern margin, Xiaoqinling and Xiong’ershan in the southern margin, Jibei-Jidong, Chifeng-Chaoyang, Ji’nan, and Liaodong in the northern margin, and central Taihangshan in the central Craton. The gold deposits mostly formed within a few million years of the early Cretaceous (130–120 Ma), coeval with widespread occurrences of bimodal magmatism that marked the peak of lithospheric thinning or craton destruction of the NCC. Dehydration of the subducted and stagnant slab in the mantle transition zone has led to continuous hydration and considerable metasomatism of the mantle wedge beneath the NCC. The large-scale gold mineralization in the NCC in the early Cretaceous has genetic relation with craton destruction. The westward subduction of the west Pacific plate (Izanagi) beneath the eastern China continental margin during the Early Cretaceous has been an optimal setting for a large-scale gold mineralization throughout the NCC.

Exhumation history of the Sanshandao Au deposit, Jiaodong: constraints from structural analysis and (U-Th)/He thermochronology

The Sanshandao gold deposit contains an estimated Au resource of >1500 tons, however little is known about the history of exhumation, and the magnitude of displacement on the ore-hosting fault. Structural measurement revealed two phases of normal and one phase of sinistral movement on the fault. Despite of intra-sample dispersions, (U-Th)/He ages from two sub-vertical profiles show decreasing trends from the surface down to −3560 m (zircon: 123 Ma to 55 Ma; apatite 103 Ma to 0.3 Ma). Over-dispersion of AHe ages likely reflects the presence of undetected inclusions. According to the age-depth pattern, we infer that the deposit underwent an early phase of rapid cooling in the late Early Cretaceous, which was followed by a short period of thermal stagnation and a revived rapid cooling between 75 Ma and 55 Ma in response to a combined effects of late normal movement and erosion. Since the Eocene, the deposit has experienced a slow monotonic cooling. Exhumation magnitude estimates suggest that the deposit have been denudated > 5.1 km. The two phases of normal displacement along the fault occurred in the late Early Cretaceous and Late Cretaceous to Paleocene, leading to a total offset magnitude of 0.5–2.3 km.

Fluid Evolution in the Sanshandao Gold deposit, Jiaodong Peninsula, China

The Jiaodong gold province located in the Jiaodong Peninsula of eastern China is the most important goldproducing district and is the host for several world-class gold deposits (>100 t gold) in the country (Zhou and Lü, 2000; Qiu et al., 2002; Fan et al., 2003; Hu et al., 2013). Gold deposits here were divided into two types according to ore occurrence, referred to as “Linglong-type” and “Jiaojia-type” (Qiu et al., 1988; Goldfarb and Santosh, 2014). The Linglong-type lode gold mineralization is characterized by massive auriferous quartz veins with narrow alteration halos and usually occurs in subsidiary secondor third-order faults. The Jiaojia-type disseminated and stockwork gold mineralization is usually surrounded by broad alteration zones and generally develops along major first-order regional faults. The Jiaodong gold province hosts dozens of gold deposits. Although most of them have been extensively described, evolution of the ore-forming fluids within the scope of 4000 meters deep from the surface has not been investigated. This study attempts to evaluate the nature and evolution of the ore-forming fluid in the Sanshandao gold deposit from fluid inclusion and stable isotope analysis.

Insights into the Ore Genesis of the Giant Bayan Obo REE-Nb-Fe Deposit and the Mesoproterozoic Rifting Events in the Northern North China Craton

Bayan Obo ore deposit is the largest rare earth element (REE) resource and the second largest niobium (Nb) resource in the world. The REE enrichment mechanism and genesis of this giant deposit still remains intense debated. The deposit is hosted in the massive dolomite, and nearly one hundred carbonatite dykes occur in the vicinity of the deposit. The carbonatite dykes can be divided into three types from early to late: dolomite, coexisting dolomite–calcite, and calcite type, corresponding to different evolutionary stages of carbonatitic magmatism, and the latter always has higher LREE content. The origin of the ore-hosting dolomite at Bayan Obo has been addressed in various models, ranging from a normal sedimentary carbonate rocks to volcano-sedimentary sequence, and a large carbonatitic intrusion. More geochemical evidences and field interspersed relationship show that the coarse-grained dolomite represents a Mesoproterozoic carbonatite pluton and the fine-grained dolomite resulted from the extensive REE mineralization and modification of the former one. The ore bodies, distributed along an E-W striking belt, occur as large lenses and underwent more intense fluoritization and fenitization with wall rocks. The first episode mineralization is characterized by disseminated mineralization in the dolomite. The second or main-episode is banded or massive mineralization, cut by the third episode consisting of aegirine-rich veins. Various dating methods gave different mineralization ages at Bayan Obo, resulting in long and hot debates. Compilation of available data suggests that the mineralization is rather variable with two peaks at ~1400 and 440 Ma. The early mineralization peak closes in time to the intrusion of the carbonatite dykes. A significant thermal event at ca. 440 Ma resulted in the formation of late-stage veins with coarse crystals of REE minerals. Fluids involving in the REE-Nb-Fe mineralization at Bayan Obo might be REE-F-CO2-NaCl-H2O system. The presence of REE-carbonates as an abundant solid in the ores shows that the original ore-forming fluids are very rich in REE, and therefore, have the potential to produce economic REE ores at Bayan Obo. The Bayan Obo deposit is a product of mantle-derived carbonatitic magmatism at ca. 1400 Ma, which was likely related to the breakup of the supercontinent Columbia. Some remobilization of REE occurred due to subduction of the Palaeo-Asian oceanic plate in the Early Paleozoic, forming weak vein-like mineralization.

Ore-forming Fluids and Ore Genesis in the World-class Mesozoic Gold Province, Jiaodong Peninsula, Eastern China

The Jiaodong Peninsula is currently the most important gold province in China, with a total gold ore reserve of >1300 tons (Li et al. 2007). Seven world-class gold deposits (> 100 t gold), eight large gold deposits (20 to 100 t gold) and more than one hundred middle to small gold deposits (< 20 t gold) have been discovered in the peninsula (Fig. 1) during the past three decades, accounting for about 25% of China’s gold reserves (Fan et al. 2003). It is located along the southeastern margin of the North China Craton, which is the largest and oldest (3.8– 2.5 Ga) craton in China. Mesozoic granitoids, occupying >50 percent of the northwestern part of the Jiaodong Peninsula, intrude Precambrian basement rocks that have undergone amphibolite to granulite facies metamorphism. The majority of gold resources (>95%) are hosted by these granitoids, making the Jiaodong gold province one of the largest granitoid-hosted gold provinces recognized in the world. The Jiaodong Peninsula occupies the easternmost edge of the Eastern Block of the North China Craton (Zhai and Santosh) and is geologically divided into the southeastern Ludong terrane and the northwestern Jiaobei terrane by the Mishan fault. The Ludong terrane petrotectonically belongs to the northern margin of the South China Block, which records a subduction history associated with a Triassic collisional event. The Jiaobei terrane petrotectonically belongs to the North China Craton. Almost all gold deposits are hosted in the Jiaobei terrane, and more than 80% of the gold reserves are concentrated in the Zhaoyuan-Laizhou gold belt (Fig. 1). The Precambrian basement in the Jiaobei terrane is principally defined by the Archean Jiaodong Group and the Paleoproterozoic Fenzishan and Jingshan Groups. Mesozoic magmatic rocks are widely exposed in the Jiaobei terrane and two main periods of magmatism are recognized, Jurassic and Early Cretaceous. The Jurassic magmatic activity is represented by the crustallyderived Linglong, Luanjiahe, and Kunyushan granitoids, emplaced at 160–150 Ma (Yang et al. 2012). In the Early Cretaceous, extensive magmatism took place through strong crust-mantle interaction, including formation of widespread granitoids (130–126Ma, and 113–110 Ma), mafic to felsic volcanic rocks in the Jiaolai Basin (130– 110 Ma), and numerous mafic dikes (124–122 Ma) with less commonly at 110 to 102 Ma (Yang et al. 2012; Cai et al., 2013). The Mesozoic granitoids are hosts for most gold deposits. Gold deposits in the peninsula can be divided into three mineralized belts from west to east, which include Zhaoyuan-Laizhou, Penglai-Qixia, and Muping-Rushan (Fig. 1). Each belt is separated by Jurassic to Cretaceous volcanic-sedimentary basin. Gold deposits have been classified as the Linglong-type and the Jiaojia-type, both of which are essentially fault controlled. The Linglongtype mineralization is characterized by massive auriferous quartz veins hosted in subsidiary secondor third-order faults cutting Mesozoic granitoids, whereas the Jiaojiatype mineralization consists of disseminatedand stockwork-style ores located in regional faults, which are enveloped by broad alteration halos.