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).
Mineral deposits are typically tied to plate margin processes, such as accretion or rifting. However, some major deposits occur in plate interiors, e.g., deposits in the southern Great Xing'an Range, ...lacking a clear association with the supercontinent cycle. Intrusive activity in the southern Great Xing'an Range peaked in late Mesozoic (i.e., 155–120Ma), simultaneously with large-scale mineralization in this area. In addition, the late Mesozoic granitoids show initial Nd and Hf isotopic signatures of depleted mantle, possibly newly underplated basaltic materials, with variable contamination from older crust, and with model ages younger than 1.0Ga. Fluid inclusion waters extracted from ore minerals (pyrite, galena, sphalerite, and chalcopyrite) associated with the late Mesozoic mineralization have elevated 3He/4He ratios, indicating a contribution of mantle-derived helium. Stable isotopes of fluid inclusion waters (hydrogen and oxygen) and of sulfide minerals (sulfur) confirm a magmatic source for these components. Lead isotope data of ore minerals indicate a significant mantle lead contribution from the newly underplated material. Thus, the southern Great Xing'an Range is best described as a typical, late Mesozoic, intracontinental metallogenic belt related to magmatism with a significant mantle contribution. The magmatism and mineralization took place in a setting of lithospheric extension and resulted because of the break-off of the southerly-dipping Mongol–Okhotsk oceanic slab at depth during closure of the Mongol–Okhotsk Ocean, which also restricted the westward movement of the Paleo-Pacific oceanic plate. This interplay between plate-tectonic events and mantle dynamics provides a good example of the evolution of magmatism and hydrothermal activity in intracontinental settings.
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•Large-scale magmatism and mineralization occurred in the range of 155-120Ma.•It’s a unique intracontinental metallogenic belt with a significant mantle signature.•Mongol–Okhotsk oceanic slab break-off induces magmatism and mineralization.•The magmatism and hydrothermal activity are association with the supercontinent cycle.
Pyrite from the Dongping, Huangtuliang and Hougou gold deposits, Hebei Province, China, was investigated using a combination of ore microscopy, including back-scattered imaging, and in situ ...laser-ablation inductively-coupled plasma mass spectroscopy (LA-ICP-MS). A range of elements, including Au, Te, Ag, Pb, Bi, Cu, Co, Ni and As, was analyzed with the aim to constrain the textural controls and influence of superimposed deformation on the distribution of invisible gold in As-free pyrite.
The dataset shows excellent correspondence between measured high gold values and three key textural criteria: (i) areas of clustered telluride inclusions (especially in Dongping); (ii) microshearing and fracturing/brecciation (Dongping and Huangtuliang); and (iii) pyrite recrystallization (Huangtuliang). Invisible gold is only at trace levels in the Hougou and gold-bearing telluride minerals are not observed. This is considered to result from larger-scale remobilization of gold during advanced brecciation and recrystallization of pyrite.
Pyrite grains containing clustered inclusions have by far the highest gold concentrations (up to 1 wt.%) with consistent values of thousands of ppm Au. Interpretation of textures and LA-ICP-MS data infers that in these areas the distribution of telluride inclusions extends pervasively from micron- to nanoscale, i.e., as fields of nanoparticles. Local employment of coupled dissolution–reprecipitation reaction between pyrite and fluids driving the K-metasomatic alteration (dated at ~
150 Ma) is invoked to explain such patterns.
Syn-deformational grain-scale mobilization of gold and other elements took place leading to a portion of the gold being recrystallized within fractures and microshears. The deformational event leads to gold enrichment in the Huangtuliang pyrite, where brittle fracturing brecciation has been followed by a resorption and recrystallization. In the latter case, ‘foam’-textured pyrites, again without As, can contain up to hundreds of ppm gold.
The interpreted sequence of pyrite post-depositional events is in accordance with the protracted magmatic evolution of the area, starting with Variscan alkaline intrusions (~
390 Ma) and reactivated during the Yanshanian orogeny (~
150 Ma).
The study shows: (i) that As-free pyrite can readily contain significant amounts of invisible gold, both as nanoparticles and locked in the sulfide lattice; (ii) the critical importance of understanding ore textures in ‘mapping’ gold distributions and the capability of LA-ICP-MS methods in such studies; (iii) that gold is highly susceptible to small-scale mobilization under a range of conditions, creating unique distribution patterns within each grain dependent upon the local expression of overprinting (defined in turn by grain size, rheology, oriented stress/strain etc.); and (iv) the role played Te and other “low melting point chalcophile elements” (e.g., Bi in the case of Huangtuliang) in governing gold distribution patterns and leading to high concentrations.
The Gejiu tin district in western Cathaysia block comprises a series of igneous rocks including equigranular and porphyritic granites, gabbro and nepheline syenite. Systematic SHRIMP or LA-ICP-MS ...zircon U–Pb analyses of 15 representative samples from various phases of the Gejiu complex yielded Late Cretaceous ages of 78–85Ma. Based on their mineralogical, geochemical and Sr–Nd–Hf isotope characteristics, these rocks are categorized into three groups: felsic rocks, alkaline rocks and mafic rocks. The felsic rock group includes the equigranular and porphyritic granites. Geochemical characteristics include high SiO2 contents, enrichment in Rb, Th, U, Nb, Ta, Nd and Hf and depletion in Ba, K, Sr, P, Eu and Ti compared to primitive mantle. REE patterns feature slight LREE enrichment with pronounced negative Eu anomalies. Geochemical data and Sr-, Nd- and Hf-isotopic compositions indicate that the felsic rocks were probably generated by partial melting of crustal source rocks with a minor input from mantle materials. The mafic rocks (gabbro and mafic microgranular enclaves) have distinct geochemical and isotopic features consistent with derivation from an enriched mantle source, with variable degrees of mixing with crustal-derived magmas. Strontium-, Nd- and Hf-isotopic compositions of the alkaline rocks are similar with those of the mafic rocks, suggesting that they have a similar source. Nevertheless, petrological and geochemical characteristics of these rocks indicate that they experienced extensive crystal fractionation and limited crustal contamination. Based on the emplacement of the gabbro–mafic microgranular enclaves–syenite–granites in the Gejiu district, together with contemporaneous geological events in other parts of the western Cathaysia block, we suggest that a widespread extension-related magmatic episode affected the entire region in the late Cretaceous, possibly as a result of lithospheric thinning, basaltic underplating and associated crustal melting.
•We present new ages, elemental and isotopic compositions of several igneous rocks.•New insights into the petrogenesis of these rocks were provided.•Combined mafic–felsic rocks to study mantle–crust interaction and setting•New understandings on magmatism in a world-class mining district were presented.
•The Eurasian continent hosts three huge metallogenic belts of porphyry deposits.•They include: Paleozoic Central Asian Ore Belt, Tethyan Eurasian Ore Belt, and East Margin Ore Belt.•In this issue ...the spatial–temporal distribution of porphyry systems and related geodynamic processes are described.•These ore systems and associated igneous rocks originated from partial melting of stagnant or residual oceanic slabs.•Mixing with crustal material during magma ascent to shallower levels is envisaged.
In the Eurasian continent there are three huge metallogenic belts of Cu and Mo porphyry deposits, comprising the Paleozoic Central Asian Ore Belt in the north, the Tethyan Eurasian Ore Belt of Jurassic to Cenozoic age in the southwest, and the East Margin Ore Belt of the Eurasian Continent of Jurassic to Cretaceous age in the east. The latter is considered to be part of the vast Circum-Pacific ore belt. Some of the main features of the spatial–temporal distribution of Cu and Mo porphyry systems and related geodynamic processes of the three metallogenic belts are described. In particular, the key role of post-subduction – related porphyry ore systems is emphasized, comprising collisional and post-collisional Cu–Mo porphyry deposits during the geological history of the Eurasian continent. The recurrent feature of these ore systems and related felsic rocks is their derivation from partial melting of stagnant or residual oceanic slabs, and mixing with a variable amount of crustal material during magma ascent to shallower levels.
Gejiu is one of the largest polymetallic tin ore districts in the world. Located at the westernmost end of the South China tungsten–tin province (or Nanling tungsten–tin province), it is a ...granite-related (Gejiu granite) magmatic-hydrothermal system. Nine samples from two phases of Gejiu granitic intrusions have been analyzed by SHRIMP and/or LA-ICPMS zircon U–Pb techniques, yielding ages ranging from 77.4
±
2.5
Ma to 85.0
±
0.85
Ma. Whole rock analysis shows that both phases are high-K and alkali-rich granites and their ACNK values fall mainly into a small range of 1.0–1.1. Moreover, Harker diagrams indicate that granites experienced strong fractional crystallization during magmatic evolution. Most granites display relative enrichment in LREE and strong Eu depletion. The whole rock average ε
Nd(
t) values of the Gejiu granites vary from −
9.3 to −
6.9, whereas a range of −
8.12
<
ε
Hf(
t)
<
1.21 is defined by magmatic zircons. Sr–Nd–Hf isotope data indicate that the granites have been mainly derived from crustal melts with minor input of mantle component. Two stage Nd and Hf model ages, together with isotopic characteristics, indicate that the Gejiu granite magmas were possibly derived from partial melting of Mesoproterozoic continental crust, with minor input of mantle-derived melts, followed by extensive fractional crystallization.
► SHRIMP and LA-ICP-MS U–Pb zircon dating indicate that the granites in the Gejiu area formed at around 80
Ma, which keeping consistent with magmatism and mineralization event in the western south China block. ► Geochemical and Sr–Nd–Hf isotopic data suggest that Gejiu granite magmas experienced a high degree of fractional crystallization after they have formed by partial melting of Mesoproterozoic crust with minor input from mantle-derived magmas. This will provide another example for understanding the intraplate magmatism, which is a hot topic in recent years. ► Granites in the Gejiu area are attributed to the “crust-mantle syntectic type” that display strong signs of mantle-crust interaction in an intraplate setting. This depart from the conventional I-, S-, M- and A-petrochemical types as treated in the literature.
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