The ore deposits of the Mesozoic age in South China can be divided into three groups, each with different metal associations and spatial distributions and each related to major magmatic events. The first event occurred in the Late Triassic (230–210 Ma), the second in the Mid–Late Jurassic (170–150 Ma), and the third in the Early–Mid Cretaceous (120–80 Ma). The Late Triassic magmatic event and associated mineralization is characterized by peraluminous granite-related W–Sn–Nb–Ta mineral deposits. The Triassic ore deposits are considerably disturbed or overprinted by the later Jurassic and Cretaceous tectono-thermal episodes. The Mid–Late Jurassic magmatic and mineralization events consist of 170–160 Ma porphyry–skarn Cu and Pb–Zn–Ag vein deposits associated with I-type granites and 160–150 Ma metaluminous granite-related polymetallic W–Sn deposits. The Late Jurassic metaluminous granite-related W–Sn deposits occur in a NE-trending cluster in the interior of South China, such as in the Nanling area. In the Early–Mid Cretaceous, from about 120 to 80 Ma, but peaking at 100–90 Ma, subvolcanic-related Fe deposits developed and I-type calc-alkaline granitic intrusions formed porphyry Cu–Mo and porphyry-epithermal Cu–Au–Ag mineral systems, whereas S-type peraluminous and/or metaluminous granitic intrusions formed polymetallic Sn deposits. These Cretaceous mineral deposits cluster in distinct areas and are controlled by pull-apart basins along the South China continental margin. Based on mineral assemblage, age, and space–time distribution of these mineral systems, integrated with regional geological data and field observations, we suggest that the three magmatic–mineralization episodes are the result of distinct geodynamic regimes. The Triassic peraluminous granites and associated W–Sn–Nb–Ta mineralization formed during post-collisional processes involving the South China Block, the North China Craton, and the Indo-China Block, mostly along the Dabie-Sulu and Songma sutures. Jurassic events were initially related to the shallow oblique subduction of the Izanagi plate beneath the Eurasian continent at about 175 Ma, but I-type granitoids with porphyry Cu and vein-type Pb–Zn–Ag deposits only began to form as a result of the breakup of the subducted plate at 170–160 Ma, along the NNE-trending Qinzhou-Hangzhou belt (also referred to as Qin-Hang or Shi-Hang belt), which is the Neoproterozoic suture that amalgamates the Yangtze Craton and Cathaysia Block. A large subduction slab window is assumed to have formed in the Nanling and adjacent areas in the interior of South China, triggering the uprise of asthenospheric mantle into the upper crust and leading to the emplacement of metaluminous granitic magma and associated polymetallic W–Sn mineralization. A relatively tectonically quiet period followed between 150 and 135 Ma in South China. From 135 Ma onward, the angle of convergence of the Izanagi plate changed from oblique to parallel to the coastline, resulting in continental extensional tectonics and reactivation of regional-scale NE-trending faults, such as the Tan-Lu fault. This widespread extension also promoted the development of NE-trending pull-apart basins and metamorphic core complexes, accompanied by volcanism and the formation of epithermal Cu–Au deposits, granite-related polymetallic Sn–(W) deposits and hydrothermal U deposits between 120 and 80 Ma (with a peak activity at 100–90 Ma).

Major types and time–space distribution of Mesozoic ore deposits in South China and their geodynamic settings

http://or.nsfc.gov.cn/bitstream/00001903-5/261436/1/1000014253607.pdf

Tectonic architecture and multiple orogeny of the Qinling Orogenic Belt, Central China

Mesozoic molybdenum deposits in the east Qinling-Dabie orogenic belt: Characteristics and tectonic settings

Tectonic framework and crustal evolution of the Precambrian basement of the Tarim Block in NW China: New geochronological evidence from deep drilling samples

SIMS U–Pb zircon geochronology of porphyry Cu–Au–(Mo) deposits in the Yangtze River Metallogenic Belt, eastern China: Magmatic response to early Cretaceous lithospheric extension

High resolution in situ U-Pb zircon geochronology on zoned grains can obtain isotope signatures from multiple growth or thermal events.We present a method using laser ablation-multicollector-inductively coupled plasma-mass spectrometry(LA-MC-ICP-MS) to overcome complications associated with intricately zoned zircon crystals through in situ sampling of zircon volumes as small as 12 μm,25 μm and 40 μm in diameter by about 10 μm in depth.High precision U-Pb age of a series of zircon standard covering a wide age range of 30 to 1 065 Ma was acquired using LA-MC-ICP-MS.The precision of measured Pb/U ratios in homogeneous zircon is about 2%(2σ),resulting in routinely achieved precision of U-Pb ages obtained by external calibration of～1%(2σ) or better.All masses of interest can be simultaneously recorded with a multi-ion counting system(MIC) operating in static mode,and the short ablation required to achieve such precision results in spatial resolution that is superior to comparable U-Pb zircon analyses by single collector ICP-MS.The resulting present U-Pb age for five zircon reference samples and two geological samples show an excellent agreement with the previously reported ID-TIMS or SHRIMP data.

In situ U-Pb zircon dating using laser ablation-multi ion counting-ICP-MS

The Yuchiling Mo deposit located in Songxian County of Henan Province is a newly discovered superlarge porphyry Mo deposit in the East Qinling molybdenum belt. The deposit is hosted in the porphyritic monzogranite and breccia unit of Heyu composite granitic pluton. The host rock is characterized by rich silica and aluminum,poor calcium and abundant alkali with high K2O/Na2O ratios and F content. The main ore-forming types in the deposit include disseminated,veinlet,stockwork,and laminated molybdenite mineralizations,and the major alteration types of wall rocks comprise potassic alteration,silicification,sericitization,pyritization,phyllic alteration,epidotization,chloritization,argillic alteration etc.,which constitute typical ore-forming and alteration characteristics of porphyry Mo deposits. Six molybdenite-bearing samples of different mineralizing types were selected for precise Re-Os dating,which yielded model ages ranging from (130.3±2.0)Ma to (131.7±1.9) Ma and an isochron age of (131.2±1.4) Ma. The deposit was formed in the Early Cretaceous,which is consistent with the emplacing age of the host rock Heyu granitic pluton. The authors thus believe that they are products of the same magma-structure-fluid activity. The Re contents of molybdenite are (12.48~53.39)×10-6,indicating that they were derived from mixed crust and mantle sources. The Yuchiling Mo deposit was formed at the same time with the Donggou and the Tangjiaping Mo deposits,and hence should be the response to Late Mesozoic large-scale regional lithospheric extension in East Qinling-Dabie area.

Geological characteristics and molybdenite Re-Os isotopic dating of Yuchiling porphyry Mo deposit in western Henan Province

The (porphyry-)skarn Cu-Fe-Au polymetallic deposits in southeastern Hubei constitute an important component part of the Middle-Lower Yangtze River metallogenic belt. The Tonglushan ore district is characterized by various types of mineralizations and large-sized ore bodies and represents the most important economic mineral district in southeastern Hubei Province. Nevertheless, little research work has been done on the timing of various skarn deposits and the genetic association of igneous rocks with mineralization as well as the tectonic framework of these deposit. Molybdenites from the Tonglushan skarn Cu-(Fe-Au) deposit and the Jiguanzui skarn Cu(Au) deposits yielded Re-Os model ages ranging from(136.8±1.9) to (138.1±1.8)Ma and from (137.1±1.9) to (138.8±1.9) Ma, respectively, with isochronal ages being (137.1±1.9) Ma and (138.2±2.2) Ma, which are considered to be reliable estimates for the timing of the Tonglushan and the Jiguanzui deposit. These data indicate that ages of various skarn deposits are almost identical to the zircon SHRIMP U-Pb age of (140.3±1.8)Ma for the related granodiorite, almost the same as ages of other (porphyry-)skarn Cu-Mo deposits and skarn Fe deposits in southeastern Hubei Province and even those of the Jiurui Cu-Au (Mo), the Anqing Cu-Fe-Mo (Au) and the Tongling Cu-Au ore districts in the Middle-Lower Yangtze River metallogenic belt. Combined with geological, geochemical and geophysical evidence, it is proposed that the skarn Cu-Fe-Au deposits in Tonglushan constitute a part of extensive igneous rocks and corresponding skarn Cu-Fe-Au mineralization that resulted from lithospheric thinning and basaltic magma underplating, which, in turn, were triggered by the rollback and /or window of the downgoing slab related to the subduction of Pacific plate in East China.

Re-Os dating of molybdenite from Tonglüshan ore district in southeastern Hubei Province,Middle-Lower Yangtze River belt and its geological significance

The Weishancheng area in Tongbai County of Henan Province is an important Au-Ag ore concentration area in the Qinling-Dabie orogenic belt between the North China Plate and the Yangtze Plate. Three large-size gold and silver deposits,i.e.,the Poshan Ag deposit,the Yindongpo Au deposit and the Yindongling Ag deposit,are hosted by the Neoproterozoic Waitoushan Formation within the Heqianzhuang anticline in Weishancheng area. In order to obtain the ore-forming ages,the authors studied the altered minerals separated from the major gold and silver deposits by the 40Ar/39Ar incremental heating method. The 40Ar/39Ar age dating of biotite from the altered kersantite dyke in the Poshan Ag deposit gives a plateau age of (129.0±1.1)Ma,an isochron age of (128.4±3.5) Ma (2σ) with the MSWD being 0.12,and an initial 40Ar/36Ar value of (304 ± 84) (2σ),while the sericite from the auriferous quartz vein in the Yindongpo Au deposit gives a plateau age of (373.8±3.2)Ma,an isochron age of (373±13)Ma (2σ) with the MSWD being 0.073,and an initial 40Ar/36Ar value of (301±320) (2σ). In comparison,the 40Ar/39Ar age dating of sericite from the altered rocks in the Yindongling Ag deposit gives a plateau age of (377.4±2.6) Ma,an isochron age of (377.8±5.7) Ma (2σ) with the MSWD being 0.70,and an initial 40Ar/36Ar value of (312±55) (2σ). These 40Ar/39Ar ages can represent the ore-forming time of these gold and silver deposits in Weishancheng area. It is thus held that the formation of these major gold and silver deposits in Weishancheng area,namely the Poshan Ag deposit,the Yindongpo Au deposit and the Yindongling deposit,are related to the collision and compressional metamorphism resulting from the closure of the Erlangping back-arc basin. Therefore,these gold and silver deposits are orogenic deposits. The Poshan Ag deposit might have been transformed during the intrusion of the Liangwan stock in Yanshanian period,as evidenced by the fact that the biotite from the altered Caledonian kersantite dyke in the Poshan Ag deposit has a 40Ar/39Ar plateau age of (129.0±1.1) Ma,a bit younger than the emplacement age of the Liangwan stock.

Geochronology of major gold and silver deposits in Weishancheng area,Tongbai County,Henan Province

The Yechangping Mo deposit is a porphyry-skarn Mo deposit in the East QinlingDabie orogenic beltIts ore-hosting wall rock is chert banded dolomite belonging to Longjiayuan Formation of Middle Proterozoic Guandaokou Group,its main ore types are veinlets,stockworks,disseminations and banding,and its major wall rock alterations include diopsidization,phlogopitization,talcization,chloritization,serpentinization,silicification,potassic alteration and carbonationFive molybdenum-bearing samples were selected for precise Re-Os dating,which yielded model ages ranging from(1454±21) Ma to(1436 ± 24) Ma and an isochron age of(1453 ± 44) Ma(2σ,MSWD=080),indicating that the molybdenum deposit was formed in the Late Jurassic-Early Cretaceous periodBased on a study of geodynamic settings of molybdenum deposits of different ages in the East Qinling-Dabie molybdenum belt,the authors hold that the geodynamic setting of the Yechangping Mo deposit is widespread magmatism and back-arc extension caused by subduction of the paleo-Pacific plate beneath the Eurasian continent

Mrl Key

Papers

In situ U-Pb zircon dating using laser ablation-multi ion counting-ICP-MS

Geological characteristics and molybdenite Re-Os isotopic dating of Yuchiling porphyry Mo deposit in western Henan Province

Re-Os dating of molybdenite from Tonglüshan ore district in southeastern Hubei Province,Middle-Lower Yangtze River belt and its geological significance

Geochronology of major gold and silver deposits in Weishancheng area,Tongbai County,Henan Province

Molybdenite Re-Os isochron age of Yechangping Mo deposit in western Henan Province and its geological implications