Northern Margin Of North China Craton Research Articles

Gold mineralization in the northern margin of the North China Craton: Influence of alkaline magmatism and regional tectonic during Middle Paleozoic-Mesozoic

The northern margin of North China Craton (NNCC) has undergone multiple tectonic and magmatic episodes associated with numerous gold mineralization during Devonian to Cretaceous. The origin of gold mineralization is a subject of debate in the NNCC, but there is a consensus on a metamorphic-hydrothermal origin and a magmatic-hydrothermal origin. For this study, we focused on four gold districts including the Daqingshan, Zhangjiakou, West Liaoning, and Changbaishan from west to east. We specifically constrain the link between the Hadamengou, Dongping, Jinchanggouliang, Erdaogou and Haigou gold deposits and their magmatic episodes. The Dahuabei and Haigou granites, and Dongping syenite rocks have an alkaline affinity. In contrast, the Xitaizi-Jinchanggouliang and Xiaoxigou granites as well as the Duimiangou quartz monzonites are calc-alkaline with high alkaline rocks. They are predominantly metaluminous and high fractionated I-type granites, except the Xiaoxigou granite which is A-type granites with peraluminous nature. This indicates a variable mixing between depleted mantle-derived mafic magma and ancient crust derived magma.The magmatic events overlap the gold mineralization episodes in the NNCC. We have identified four magmatic episodes during Middle Paleozoic to Mesozoic at 400–320 Ma, 245–221 Ma, 199–161 Ma, and 143–125 Ma. On the other hand, gold mineralization was emplaced from Carboniferous to Cretaceous (390–110 Ma) with a peak in the Middle Jurassic (170–160 Ma).The available sulfur, oxygen, and carbon isotopic data from the studied NNCC gold deposits suggest that the ore-forming fluids were derived from a mixture of magmatic fluids and meteoric waters that flow in the wall rocks, except for the Hadamengou and Jinchanggouliang gold deposits. Both late deposits present a multi-source involving organic matter and other regional crustal rocks as shown by their positive δ34S values (0.6–18.5‰). The intrusive rocks and sulfides in the NNCC display similar lead isotope data, suggesting that the lead isotopes might have similar origin. The gold-forming materials resulting from the mixing of these fluids are the product of several alkaline magmatism activities in this region. Hence, this study has proved that gold mineralization is spatially and temporally related to the alkaline magmatism in the NNCC.The dominant tectonic events in the NNCC are marked by post-collisional or anorogenic geodynamical setting which is characterized by high alkaline features and Andean-type arc related to subduction geodynamical setting and characterized by calc-alkaline features of the studied rocks. Both tectonic events are controlled by: (1) the collision between the NCC and the Bainaimiao arc, (2) the subduction of the Paleo-Asian-ocean plate beneath the NCC, (3) the collision between the Siberian Craton and the NCC, and (4) the subduction of the western Paleo-Pacific beneath the NCC. These tectonic regimes are expressed by a transitional regime changing from compression to extension at western and an extensional regime at western and eastern parts of the NNCC, respectively.

Late Mesozoic tectonostratigraphic division and correlation of the Bohai Bay basin: Implications for the Yanshanian Orogeny

We present the results of Mesozoic sequences of the Bohai Bay basin in North China, based mainly on geochronology and interpretations of seismic profiles and logging data. Five tectono-stratigraphic sequences are defined: Lower-Middle Triassic, Lower-Middle Jurassic, Upper Jurassic, Lower Cretaceous and Upper Cretaceous. Based on an analysis of detrital zircons, the clastic rocks recorded two intervals of Jurassic magmatic activity, during 180–175 and 160–152 Ma, which can be correlated to the Nandaling and Tiaojishan Formations in the Yanshan area, respectively. However, since Jurassic volcanic rocks have not yet been found in the Bohai Bay basin, we speculate that these two stages of activity were mainly concentrated around the periphery of the North China Craton (NCC) rather than within. Based on an analysis of zircons from volcanic rocks and pyroclastics, the early Cretaceous magmatism in the Bohai Bay basin can be divided into two stages, 125–120 and 110–100 Ma, which can be correlated to magmatism in the eastern part of the NCC. The zircon ages indicate an absence of volcanic activity during the late Tuchengzi and Zhangjiakou periods which may correlate to the uplift of the Bohai Bay basin in the late Late Jurassic. Comparison of the development of Mesozoic basins and sedimentary strata in the central-eastern part of Yanshan tectonic belt and the the Bohai Bay basin indicates that the two areas are generally comparable, but with substantial differences. The central-eastern part of the Yanshan structural belt lacks Early-Middle Triassic strata, and the Bohai Bay basin lacks late Jurassic-early Cretaceous strata. Based on research results from late Mesozoic sedimentary structures in the central and eastern parts of the Yanshan tectonic belt, we infer that episode A of the Yanshanian Orogeny was weak in the Bohai Bay basin and its periphery, while episode B of the Yanshanian Orogeny had a strong influence on the Bohai Bay basin and its periphery. The available data reveal differences in the expression of these episodes: the Bohai Bay basin is characterized by vertical uplift, and the northern margin of NCC is characterized by horizontal compression uplift.

Tectonic Transformation and Metallogenesis of the Yanshan Movement during the Late Jurassic Period: Evidence from Geochemistry and Zircon U-Pb Geochronology of the Adamellites in Xingcheng, Western Liaoning, China

The Yanshan Movement occurred mainly during the Middle-Late Jurassic, and gave rise to NE trending structures, magmatic events, volcanism and mineral resources. The transformation and evolution of the movement during the Middle-Late Jurassic were investigated from the rock assemblage, geochemistry, and chronology in adamellites which were exposed in the Xingcheng area, western Liaoning. Two types of adamellites were recognized—biotite adamellites with the formation age of 172–168 Ma and garnet-bearing adamellites of 158–152 Ma. All the samples of the two types of adamellites displayed enriched characteristics with high content of SiO2 (66.86–75.55 wt.%) and total alkali (Na2O + K2O = 7.56–8.71 wt.%), high large ion lithophile element (LILE: K, Rb, Sr), and low high field strength element (HFSE: Ce, Ta, P, Ti). The biotite adamellites belong to metaluminous-peraluminous I-type granites, and show volcanic arc granite characteristics, and were formed by partial melting of the ancient crust in the compressional setting that resulting from the subduction of the Paleo-Pacific plate beneath the north margin of the North China Craton (NCC). The garnet-bearing adamellites are also metaluminous-peraluminous I-type granites, with characteristics of both the compressional and extensional regimes, which were formed at the middle-late stages of the continuing subduction of the Paleo-Pacific plate, while simultaneously, the frontal side of the subduction slab began to roll back, leading to an extensional environment. Combining with regional geophysical studies and our petrological and geochemical studies, we propose that the eastern segment of the northern margin of NCC may have been controlled by the Paleo-Pacific tectonic domain at the latest in the Middle Jurassic, while the initiation of the tectonic regime from a compressional to an extensional environment was during the Late Jurassic (158–152 Ma) as a response of the Yanshan Movement. Simultaneously, geochronological statistics of the ore deposits in western Liaoning show that the Mesozoic endogenetic metalliferous deposits formed in a compressive environment influenced by the subduction of the Paleo-Pacific plate, similar to the magma events in ages, and the magmatism provided the thermodynamic condition and the source of metallogenic hydrothermal fluid for mineralization.

Age, igneous petrogenesis, and tectonic setting of the Bilihe gold deposit, China, and implications for regional metallogeny

The Bilihe gold deposit, along the northern margin of the North China Craton (NCC), is hosted in Permian intrusions that were emplaced into Bainaimiao Group greenschist- to amphibolite-facies Mesoproterozoic basement rocks, the early Paleozoic Bainaimiao Arc, and late Paleozoic sedimentary and volcanic cover rock sequences. The Middle Ordovician to Early Silurian calc-alkaline arc comprises volcanic sequences of basalt, andesite, and felsic lavas, and an intrusive complex ranging from gabbro through granite. The deposit is genetically related to ilmenite-series and highly fractionated quartz diorite porphyry host rocks. The most fractionated variety of the quartz diorite porphyry is granitic, which contains dendritic quartz phenocrysts and occurs at the top part of the intrusions. Gold mostly occurs as Au grains (>990 fineness) in trails in dendritic quartz, and the gold trails typically occur along certain crystallographic elements of dendritic quartz. The gold is believed to have crystallized directly from magma at temperatures of at least 750–800°C. The Fe2O3/(Fe2O3+FeO) ratio of the quartz diorite ranges from 0.21 to 0.29, and there is significantly more ilmenite than magnetite, suggesting that the magma was moderately reduced. There are also post-ore syenogranite porphyries in the deposit area. Zircon U-Pb LA-ICP-MS dating in this study shows that two samples of the volcanic wallrock have ages of 274±3Ma and 270±4Ma, two samples of gold-forming quartz diorite porphyries have ages of 261±2Ma and 259±3Ma, with 440–400Ma and 1344–1316Ma cores, and one syenogranite porphyry sample is dated at 253±3Ma.The mineralized quartz diorite porphyries exhibit a high-K calc-alkaline composition, high Mg# (46–51), and a high content of compatible elements (V: 114–164ppm; Cr: 80–93ppm; Ni: 37–42ppm) and Rb, Th, and U, as well as depletions in Ba, Sr, and HFSE (e.g., Ti, Nb, and Ta), suggesting melt from a slab fluid-metasomatized enriched mantle. The LREE enrichment, the intermediate oxidation state, and the presence of the Silurian and Mesoproterozoic zircon cores indicate that crustal materials also played a significant role in porphyry formation. In addition, the rocks have slightly negative εNd(t) (−2.5–0.1), but variable (87Sr/86Sr)i (0.70328–0.70573). Based on the above features, we propose that quartz diorite porphyries were produced by partial melting of the metasomatized mantle coupled with the assimilation of crustal materials of the Bainaimiao Group, Late Ordovician-Silurian subduction-related plutons, and Late Carboniferous-Early Permian marine sedimentary rocks. The assimilation of rocks of the Bainaimiao Group, which have an elevated gold content of 26.3ppb, is speculated to have played important roles in the formation of a rarely documented magmatic gold deposit. In contrast, syenogranite porphyries are characterized by high contents of K2O+Na2O (10.3–10.6wt%), Al2O3 (16.3–16.5wt%), K, Hf, and Zr; low CaO (0.6–1.2wt%), Mg# values (17–21), compatible elements (V: 16–21ppm; Cr: 4.9–7.9ppm; Ni: 2.8–4.5ppm), and Eu, Sr, and HFSE; and positive εNd(t) (1.4–1.5) with low (87Sr/86Sr)i (<0.70431), indicating that the porphyries were formed by partial melting of the subduction-modified lower crust with a minor input of asthenospheric materials.It is concluded that the quartz diorite porphyries formed during the southward subduction of the Paleo-Asian ocean underneath the northern margin of the NCC. This confirms that the northern margin was not a passive continental margin, but an active margin with subduction and development of a continental arc. In addition to Bilihe, there are at least four more gold deposits (Hadamiao, Changshanhao, Saiyinwusu, and Chaihulanzi) that formed at the northern margin of the NCC from Middle Permian to Early Triassic. Such a timing indicates that they may also be ultimately related to the tectonic regime imposed by southward subduction of the Paleo-Asian ocean. Based on the new understanding of the tectonic setting, with significant known mineral occurrences along the length of the margin, it is inferred that the >1000-km-long northern margin of NCC may have a large potential for subduction-related mineralization.