The North China Craton(NCC) hosts numerous gold deposits and is known as the most gold-productive region of China. The gold deposits were mostly formed within a few million years in the Early Cretaceous(130–120 Ma), ...The North China Craton(NCC) hosts numerous gold deposits and is known as the most gold-productive region of China. The gold deposits were mostly formed within a few million years in the Early Cretaceous(130–120 Ma), coeval with widespread occurrences of bimodal magmatism, rift basins and metamorphic core complexes that marked the peak of lithospheric thinning and destruction of the NCC. Stable isotope data and geological evidence indicate that ore-forming fluids and other components were largely exsolved from cooling magma and/or derived from mantle degassing during the period of lithospheric extension. Gold mineralization in the NCC contrasts strikingly with that of other cratons where gold ore-forming fluids were sourced mostly from metamorphic devolatization in compressional or transpressional regimes. In this paper, we present a summary and discussion on time-space distribution and ore genesis of gold deposits in the NCC in the context of the timing, spatial variation, and decratonic processes. Compared with orogenic gold deposits in other cratonic blocks, the Early Cretaceous gold deposits in the NCC are quite distinct in that they were deposited from magma-derived fluids under extensional settings and associated closely with destruction of cratonic lithosphere. We argue that Early Cretaceous gold deposits in the NCC cannot be classified as orogenic gold deposits as previously suggested, rather, they are a new type of gold deposits, termed as "decratonic gold deposits" in this study. The westward subduction of the paleo-West Pacific plate(the Izanagi plate) beneath the eastern China continent gave rise to an optimal tectonic setting for large-scale gold mineralization in the Early Cretaceous. Dehydration of the subducted and stagnant slab in the mantle transition zone led to continuous hydration and considerable metasomatism of the mantle wedge beneath the NCC. As a consequence, the refractory mantle became oxidized and highly enriched in large ion lithophile elements and chalcophile elements(e.g., Cu, Au,展开更多
The West Qinling orogen in central China,formed from continental collision between the North China and Yangtze cratons in the Late Triassic,hosts numerous gold deposits with a total Au endowment of about 2000 t.Most d...The West Qinling orogen in central China,formed from continental collision between the North China and Yangtze cratons in the Late Triassic,hosts numerous gold deposits with a total Au endowment of about 2000 t.Most deposits were emplaced at ca.250-195 Ma and are genetically associated with the Triassic orogenesis.Here in situ U-Pb titanite dating with laser ablation inductively coupled plasma mass spectrometry indicates the Ma’anqiao gold deposit in the northern portion of this orogen has a distinctive age and under a contrasting tectonic regime.This structurally controlled gold deposit is hosted in Late Ordovician to Early Silurian sub-greenschist facies metasedimentary rocks.The gold mineralization is hosted in quartz-pyritepyrrhotite veins and pyrite-pyrrhotite disseminations in hydrothermally altered rocks,which are crosscut by K-feldspar-calcitechlorite±pyrite veins.Titanite,present both in the disseminated sulfide ores and later veins,was used for in situ U-Pb dating.Titanite from three disseminated sulfide ore samples with Th and U averaging 27.46 and 39.31 ppm(1 ppm=1μg g^(-1)),respectively,yielded lower-intercept ages of 121.1±3.1 to 120.7±3.5 Ma(2σ)in the Tera-Wasserburg diagram.Titanite from three later vein samples with much lower Th and U concentrations averaging 2.74 and 16.21 ppm,respectively,yielded overlapping ages of 120.8±3.2 to 120.3±5.8 Ma(2σ).These new titanite U-Pb ages tightly constrain the formation of the Ma’anqiao gold deposit at ca.121-120 Ma and,when combined with independent geological data,indicate it is not related to the Triassic Qinling orogeny.Rather,its formation is attributed to lithospheric thinning and destruction of the North China craton during the Late Jurassic to Early Cretaceous which has generated numerous gold deposits along the southern margin of this craton.This catastrophic event caused extensive magmatism in large areas of the North Qinling terrane and northern edge of the West Qinling orogen immediately to the south of the North China craton.The heat展开更多
基金financially supported by the National Natural Science Foundation of China(Grant No.91414301)project of the State Key Laboratory of Lithospheric Evolution(Grant No.1303)
文摘The North China Craton(NCC) hosts numerous gold deposits and is known as the most gold-productive region of China. The gold deposits were mostly formed within a few million years in the Early Cretaceous(130–120 Ma), coeval with widespread occurrences of bimodal magmatism, rift basins and metamorphic core complexes that marked the peak of lithospheric thinning and destruction of the NCC. Stable isotope data and geological evidence indicate that ore-forming fluids and other components were largely exsolved from cooling magma and/or derived from mantle degassing during the period of lithospheric extension. Gold mineralization in the NCC contrasts strikingly with that of other cratons where gold ore-forming fluids were sourced mostly from metamorphic devolatization in compressional or transpressional regimes. In this paper, we present a summary and discussion on time-space distribution and ore genesis of gold deposits in the NCC in the context of the timing, spatial variation, and decratonic processes. Compared with orogenic gold deposits in other cratonic blocks, the Early Cretaceous gold deposits in the NCC are quite distinct in that they were deposited from magma-derived fluids under extensional settings and associated closely with destruction of cratonic lithosphere. We argue that Early Cretaceous gold deposits in the NCC cannot be classified as orogenic gold deposits as previously suggested, rather, they are a new type of gold deposits, termed as "decratonic gold deposits" in this study. The westward subduction of the paleo-West Pacific plate(the Izanagi plate) beneath the eastern China continent gave rise to an optimal tectonic setting for large-scale gold mineralization in the Early Cretaceous. Dehydration of the subducted and stagnant slab in the mantle transition zone led to continuous hydration and considerable metasomatism of the mantle wedge beneath the NCC. As a consequence, the refractory mantle became oxidized and highly enriched in large ion lithophile elements and chalcophile elements(e.g., Cu, Au,
基金financially supported by the National Natural Science Foundation of China(Grant No.42130814)。
文摘The West Qinling orogen in central China,formed from continental collision between the North China and Yangtze cratons in the Late Triassic,hosts numerous gold deposits with a total Au endowment of about 2000 t.Most deposits were emplaced at ca.250-195 Ma and are genetically associated with the Triassic orogenesis.Here in situ U-Pb titanite dating with laser ablation inductively coupled plasma mass spectrometry indicates the Ma’anqiao gold deposit in the northern portion of this orogen has a distinctive age and under a contrasting tectonic regime.This structurally controlled gold deposit is hosted in Late Ordovician to Early Silurian sub-greenschist facies metasedimentary rocks.The gold mineralization is hosted in quartz-pyritepyrrhotite veins and pyrite-pyrrhotite disseminations in hydrothermally altered rocks,which are crosscut by K-feldspar-calcitechlorite±pyrite veins.Titanite,present both in the disseminated sulfide ores and later veins,was used for in situ U-Pb dating.Titanite from three disseminated sulfide ore samples with Th and U averaging 27.46 and 39.31 ppm(1 ppm=1μg g^(-1)),respectively,yielded lower-intercept ages of 121.1±3.1 to 120.7±3.5 Ma(2σ)in the Tera-Wasserburg diagram.Titanite from three later vein samples with much lower Th and U concentrations averaging 2.74 and 16.21 ppm,respectively,yielded overlapping ages of 120.8±3.2 to 120.3±5.8 Ma(2σ).These new titanite U-Pb ages tightly constrain the formation of the Ma’anqiao gold deposit at ca.121-120 Ma and,when combined with independent geological data,indicate it is not related to the Triassic Qinling orogeny.Rather,its formation is attributed to lithospheric thinning and destruction of the North China craton during the Late Jurassic to Early Cretaceous which has generated numerous gold deposits along the southern margin of this craton.This catastrophic event caused extensive magmatism in large areas of the North Qinling terrane and northern edge of the West Qinling orogen immediately to the south of the North China craton.The heat
