Pioneering U-Pb isotopic studies by a small group of workers in the mid-late 1980s demonstrated the feasibility of using rare accessory mineral chronometers in mafic(gabbroic)intrusive rocks.These examples showed that...Pioneering U-Pb isotopic studies by a small group of workers in the mid-late 1980s demonstrated the feasibility of using rare accessory mineral chronometers in mafic(gabbroic)intrusive rocks.These examples showed that mafic layered intrusions and diabase/dolerite dyke swarms alike crystallized high-temperature展开更多
The new GPS data can map crustal strain rates over large areas with a useful degree of precision. Stable strain measurement results open the door for improved estimates of earthquake occurrence. The Kostrov’s formula...The new GPS data can map crustal strain rates over large areas with a useful degree of precision. Stable strain measurement results open the door for improved estimates of earthquake occurrence. The Kostrov’s formula (1974) translates the smoothed strain rates in North China into geodetic moment rates. In North China, the ratio of seismic moment released to moment accumulated from GPS measurement is 60.6% in NS direction, 68.9% in EW direction, and 104.1% in NE shear direction. The near unit ratio points to the reliability of GPS measurements there. The combination of historical seismicity and GPS measurement offers a powerful attack on earthquake hazard.展开更多
With very few exceptions, orogenic gold deposits formed in subduction-related tectonic settings in accretionary to collisional orogenic belts from Archean to Tertiary times. Their genesis, including metal and fluid so...With very few exceptions, orogenic gold deposits formed in subduction-related tectonic settings in accretionary to collisional orogenic belts from Archean to Tertiary times. Their genesis, including metal and fluid source, fluid pathways, depositional mechanisms, and timing relative to regional structural and metamorphic events, continues to be controversial. However, there is now general agreement that these deposits formed from metamorphic fluids, either from metamorphism of intra-basinal rock sequences or de-volatilization of a subducted sediment wedge, during a change from a compressional to transpressional, less commonly transtensional, stress regime, prior to orogenic collapse. In the case of Archean and Paleoproterozoic deposits, the formation of orogenic gold deposits was one of the last events prior to cratonization. The late timing of orogenic gold deposits within the structural evolution of the host orogen implies that any earlier structures may be mineralized and that the current structural geometry of the gold deposits is equivalent to that at the time of their formation provided that there has been no significant post-gold orogenic overprint. Within the host volcano-sedimentary sequences at the province scale, world-class orogenic gold deposits are most commonly located in second-order structures adjacent to crustal scale faults and shear zones, representing the first-order ore-forming fluid pathways, and whose deep lithospheric connection is marked by lamprophyre intrusions which, however, have no direct genetic association with gold deposition. More specifically, the gold deposits are located adjacent to ~10°-25° district-scale jogs in these crustal-scale faults. These jogs are commonly the site of arrays of ~70° cross faults that accommodate the bending of the more rigid components, for example volcanic rocks and intrusive sills, of the host belts. Rotation of blocks between these accommodation faults causes failure of more competent units and/or reactivation and dilation of pre-existing structures, leading to deposit-scale focussing of ore-fluid and gold deposition.Anticlinal or antiformal fold hinges, particularly those of 'locked-up' folds with ~30° apical angles and overturned back limbs, represent sites of brittle-ductile rock failure and provide one of the more robust parameters for location of orogenic gold deposits.In orogenic belts with abundant pre-gold granitic intrusions, particularly Precambrian granitegreenstone terranes, the boundaries between the rigid granitic bodies and more ductile greenstone sequences are commonly sites of heterogeneous stress and inhomogeneous strain. Thus, contacts between granitic intrusions and volcano-sedimentary sequences are common sites of ore-fluid infiltration and gold deposition. For orogenic gold deposits at deeper crustal levels, ore-forming fluids are commonly focused along strain gradients between more compressional zones where volcano-sedimentary sequences are thinned and relatively more extensional zones where they are thickened. World-class orogenic gold deposits are commonly located in the deformed volcano-sedimentary sequences in such strain gradients adjacent to triple-point junctions defined by the granitic intrusions, or along the zones of assembly of micro-blocks on a regional scale. These repetitive province to district-scale geometrical patterns of structures within the orogenic belts are clearly critical parameters in geology-based exploration targeting for orogenic gold deposits.展开更多
It is quite evident that it is not anomalous metal transport,nor unique depositional conditions,nor any single factor at the deposit scale,that dictates whether a mineral deposit becomes a giant or not.A hierarchical ...It is quite evident that it is not anomalous metal transport,nor unique depositional conditions,nor any single factor at the deposit scale,that dictates whether a mineral deposit becomes a giant or not.A hierarchical approach thus is required to progressively examine controlling parameters at successively decreasing scales in the total mineral system to understand the location of giant gold deposits in non-arc environments.For giant orogenic,intrusion-related gold systems(IRGS) and Carlin-type gold deposits and iron oxide-copper-gold(IOCG) deposits,there are common factors among all of these at the lithospheric to crustal scale.All are sited in giant gold provinces controlled by complex fundamental fault or shear zones that follow craton margins or,in the case of most Phanerozoic orogenic giants,define the primary suture zones between tectonic terranes.Giant provinces of IRGS,IOCG,and Carlin-type deposits require melting of metasomatized lithosphere beneath craton margins with ascent of hybrid lamprophyric to granitic magmas and associated heat flux to generate the giant province.The IRGS and IOCG deposits require direct exsolution of volatile-rich magmatic-hydrothermal fluids,whereas the association of such melts with Carlin-type ores is more indirect and enigmatic.Giant orogenic gold provinces show no direct relationship to such magmatism.forming from metamorphic fluids,but show an indirect relationship to lamprophyres that reflect the mantle connectivity of controlling first-order structures.In contrast to their province scale similarities,the different giant gold deposit styles show contrasting critical controls at the district to deposit scale.For orogenic gold deposits,the giants appear to have formed by conjunction of a greater number of parameters to those that control smaller deposits,with resultant geometrical and lithostratigraphic complexity as a guide to their location.There are few giant IRGS due to their inferior fluid-flux systems relative to orogenic gold deposits,and those few giants are essentially preservational exceptions.Many Carlin-type deposits are giants due to the exceptional conjunction of both structural and lithological parameters that caused reactive and permeable rocks,enriched in syngenetic gold,to be located below an impermeable cap along antiformal "trends".Hydrocarbons probably played an important role in concentrating metal.The supergiant Post-Betze deposit has additional ore zones in strain heterogeneities surrounding the pre-gold Goldstrike stock.All unequivocal IOCG deposits are giant or near-giant deposits in terms of gold-equivalent resources,partly due to economic factors for this relatively poorly understood,low Cu-Au grade deposit type.The supergiant Olympic Dam deposit,the most shallowly formed deposit among the larger IOCGs,probably owes its origin to eruption of volatile-rich hybrid magma at surface,with formation of a large maar and intense and widespread brecciation,alteration and Cu-Au-U deposition in a huge rock volume.展开更多
The static flux chamber method was applied to study natural emissions of methane to the atmosphere in the Luntai fault region of Yakela Condensed Oil/Gas Field in the Tarim Basin, Xinjiang Municipality, northwestern C...The static flux chamber method was applied to study natural emissions of methane to the atmosphere in the Luntai fault region of Yakela Condensed Oil/Gas Field in the Tarim Basin, Xinjiang Municipality, northwestern China. Using an online method, which couples together a gas chromatography/high-temperature conversion/isotope ratio mass spectrometry (GC/C/MS), 13^C/12^C ratios of methane in flux chambers were measured and showed that methane gases are liable to migrate from deep oil/gas reservoirs to the surface through fault regions and that a part of the migrated methane, which remains unoxidized can be emitted into the atmosphere. Methane emission rates were found to be highest in the mornings, lowest in the afternoons and then increase gradually in the evenings. Methane emission rates varied dramatically in different locations in the fault region. The highest methane emission rate was 10.96 mg/m^2·d, the lowest 4.38 mg/m^2, and the average 7.55 mg/ m^2·d. The 13^C/12^C ratios of the methane in the flux chambers became heavier as the enclosed methane concentrations increased gradually, which reveals that methane released from the fault region might come from thermogenic methane of the deep condensed oil/gas reservoir.展开更多
The current margins of the North China and Yangtze Cratons provide arguably the best examples globally of anomalously high mineral endowment within a 100 km buffer zone,hosting 66 diverse world-class to giant ore syst...The current margins of the North China and Yangtze Cratons provide arguably the best examples globally of anomalously high mineral endowment within a 100 km buffer zone,hosting 66 diverse world-class to giant ore systems that help explain China’s premier position as a producer of multiple metal and mineral commodities.After the cratonization of these crustal blocks during the Neoarchean-Paleoproterozoic,with incorporation of iron ores on assembled micro-block margins,the margins of the cratons experienced multiple convergence and rifting events leading to metasomatism and fertilization of their underlying sub-continental lithospheric mantle.The rifted margins with trans-lithosphere faults provided pathways for Cu-Au(Mo-W-Sn)-bearing felsic to Ni-Cu-bearing ultrabasic intrusions and REE-rich carbonatite magmas,and for the development of marginal sedimentary basins with both Cu-Pb-Zn-rich source units and reactive carbonate or carbonaceous host rocks.There was diachronous formation of hydrothermal orogenic gold,antimony,and bismuth systems in the narrow orogenic belts between the cratons.Complexity in the Mesozoic Paleo-Pacific subduction systems resulted in asthenosphere upwelling and lithosphere extension and thinning in the North China Craton,leading to anomalous heat flow and formation of orogenic gold deposits,including those of the giant Jiaodong gold province on its north-eastern margin.These gold deposits,many of which formed from fluids liberated by devolatilization of previously metasomatized sub-continental lithospheric mantle,helped propel China to be the premier gold producer globally.The thick sub-continental lithospheric mantle of the cold buoyant cratons helped the preservation of some of the world’s oldest porphyry-skarn and epithermal mineral systems.Although craton margins globally control the formation and preservation of a diverse range of mineral deposits,China represents the premier example in terms of metal endowment due to the anomalous length of its craton margins combined with their abnormally complex tectonic history.展开更多
We present a narrative of the eruptive events culminating in the cataclysmic January 15, 2022 eruption of Hunga Tonga-Hunga Ha’apai Volcano by synthesizing diverse preliminary seismic, volcanological, sound wave, and...We present a narrative of the eruptive events culminating in the cataclysmic January 15, 2022 eruption of Hunga Tonga-Hunga Ha’apai Volcano by synthesizing diverse preliminary seismic, volcanological, sound wave, and lightning data available within the first few weeks after the eruption occurred. The first hour of eruptive activity produced fast-propagating tsunami waves, long-period seismic waves, loud audible sound waves, infrasonic waves, exceptionally intense volcanic lightning and an unsteady volcanic plume that transiently reached-at 58km-the Earth’s mesosphere. Energetic seismic signals were recorded worldwide and the globally stacked seismogram showed episodic seismic events within the most intense periods of phreatoplinian activity, and they correlated well with the infrasound pressure waveform recorded in Fiji. Gravity wave signals were strong enough to be observed over the entire planet in just the first few hours, with some circling the Earth multiple times subsequently. These large-amplitude, long-wavelength atmospheric disturbances come from the Earth’s atmosphere being forced by the magmatic mixture of tephra, melt and gasses emitted by the unsteady but quasicontinuous eruption from 0402±1–1800 UTC on January 15, 2022. Atmospheric forcing lasted much longer than rupturing from large earthquakes recorded on modern instruments, producing a type of shock wave that originated from the interaction between compressed air and ambient(wavy) sea surface. This scenario differs from conventional ideas of earthquake slip, landslides, or caldera collapse-generated tsunami waves because of the enormous(~1000x) volumetric change due to the supercritical nature of volatiles associated with the hot,volatile-rich phreatoplinian plume. The time series of plume altitude can be translated to volumetric discharge and mass flow rate. For an eruption duration of ~12 h, the eruptive volume and mass are estimated at 1.9 km^(3) and~2 900 Tg, respectively, corresponding to a VEI of 5–6 for this event. The high frequency and intensity of lightning was enhanced by the production of fine ash due to magma-seawater interaction with concomitant high charge per unit mass and the high pre-eruptive concentration of dissolved volatiles. Analysis of lightning flash frequencies provides a rapid metric for plume activity and eruption magnitude. Many aspects of this eruption await further investigation by multidisciplinary teams. It represents a unique opportunity for fundamental research regarding the complex, non-linear behavior of high energetic volcanic eruptions and attendant phenomena, with critical implications for hazard mitigation, volcano forecasting, and first-response efforts in future disasters.展开更多
Discovery rates for all metals, including gold, are declining, the cost per significant discovery is increasing sharply, and the economic situation of the industry is one of low base rate. The current hierarchical str...Discovery rates for all metals, including gold, are declining, the cost per significant discovery is increasing sharply, and the economic situation of the industry is one of low base rate. The current hierarchical structure of the exploration and mining industry makes this situation difficult to redress. Economic geologists can do little to influence the required changes to the overall structure and philosophy of an industry driven by business rather than geological principles, However, it should be possible to follow the lead of the oil industry and improve the success rate of greenfield exploration, necessary for the next group of lower-exploration-spend significant mineral deposit discoveries. Here we promote the concept that mineral explorers need to carefully consider the scale at which their exploration targets are viewed. It is necessary to carefully assess the potential of drill targets in terms of terrane to province to district scale, rather than deposit scale, where most current economic geology research and conceptual thinking is concentrated. If orogenic, IRGD, Carlin-style and IOCG gold-rich systems are viewed at the deposit scale, they appear quite different in terms of conventionally adop- ted research parameters. However, recent models for these deposit styles show increasingly similar source-region parameters when viewed at the lithosphere scale, suggesting common tectonic settings. It is only by assessing individual targets in their tectonic context that they can be more reliably ranked in terms of potential to provide a significant drill discovery. Targets adjacent to craton margins, other lithosphere boundaries, and suture zones are clearly favoured for all of these gold deposit styles, and such exploration could lead to incidental discovery of major deposits of other metals sited along the same tectonic boundaries.展开更多
In the Lower CretaceousMcMurray-Clearwater succession of the intracontinental Alberta Foreland Basin,Canada,detrital zircon U-Pb geochronology samples(referred to herein as DZ samples)have been used to interpret the s...In the Lower CretaceousMcMurray-Clearwater succession of the intracontinental Alberta Foreland Basin,Canada,detrital zircon U-Pb geochronology samples(referred to herein as DZ samples)have been used to interpret the strata as representing a paleo-continental-scale drainage system.However,the majority of DZ samples are relatively small(n≈90–100),and syndepositional DZ(i.e.,crystallization age<5 Ma older than depositional age)are rare.This has forced a reliance on dinocysts with long stratigraphic ranges to chronostratigraphically subdivide the McMurray-Clearwater succession rather than employing maximum depositional ages(MDAs)derived from DZ samples.Herein,43 DZ samples(taken from20 subsurface cores)are assigned to 1 of 5 stratigraphic intervals,and in each stratigraphic interval all associated DZ samples are combined to produce a grouped DZ sample.Analysis and comparison of individual and grouped DZ samples are used to(1)assess variability in provenance through time and space,and(2)assess the accuracy of chronostratigraphically subdividing the succession using MDAs.Along the main paleo-drainage axis,a comparison of dissimilarity between DZ samples from the same stratigraphic interval,as well as between stratigraphic intervals,reveals increasing average dissimilarity between individual DZ samples and their respective grouped DZ samplewith increasing spatial separation of samples.These data indicate that in the McMurray Depocenter some sediment is sourced from local tributaries,leading to geographical provenance variability.CalculatedMDAs for all 43 DZ samples and groupedMDAs(gMDAs)for the 5 grouped DZ samples are compared to an ash-derived absolute age and existing biostratigraphy.In theMcMurray Formation,comparison of MDAs to gMDAs shows that in basins with rare syndepositional DZ,the gMDA method improved depositional age estimates by transforming low-confidence MDAs(e.g.,youngest single grains)into high-confidence(multi-grain)gMDAs.In the Clearwater Formationwhere syndepositional DZ are plentiful(i.e.,>5%of the total DZ population),calculating maximumlikelihood ages fromgrouped DZ samples avoids negatively biased(i.e.,too young)MDAs.We suggest grouped DZ samples and the gMDA method be used in systems with multiple DZ samples from a well-defined stratigraphic interval as a means of assessing variability in provenancewithin a depositional system and for improving estimates of depositional ages using DZ.展开更多
Fig.8e in our paper(Groves et al.,2018)was incorrectly ascribed to Caddey et al.(1995).It is actually taken from Figure 3 in Morelli et al.(2010).In turn,this was derived from Bell(2013).The authors apologise for this...Fig.8e in our paper(Groves et al.,2018)was incorrectly ascribed to Caddey et al.(1995).It is actually taken from Figure 3 in Morelli et al.(2010).In turn,this was derived from Bell(2013).The authors apologise for this unintentional error.展开更多
A study has been reported on <sup>208</sup>Pb/<sup>206</sup>Pb and <sup>207</sup>Pb/<sup>206</sup>Pb ratio variations in ancient drums and Cu-., Pb- ores from Guangxi, C...A study has been reported on <sup>208</sup>Pb/<sup>206</sup>Pb and <sup>207</sup>Pb/<sup>206</sup>Pb ratio variations in ancient drums and Cu-., Pb- ores from Guangxi, China and can indicate that the Cu- and Pb- bearing ores for making the Beiliu and the Lingshan type drums were taken from Tongshiling of Beiliu County and its vicinity, that were not only ancient sites for smelting the copper ores, but possibly also for casting the bronze drums. Some of the Lengshuichong type drums have abnormal Pb isotopic ratios, which means that they were made of special ore sources, one of the possibilities is that the ore material or the drums were transported from South- East Asia to Guangxi Province, because they have been excavated there too.展开更多
IntroductionAncient bronze drums are representatives of the historical culture of the minori-ty people living in southern China,such as Yunnan,Guizhou and Guangxi.About 1400 drums ranging in age from the early Spring-...IntroductionAncient bronze drums are representatives of the historical culture of the minori-ty people living in southern China,such as Yunnan,Guizhou and Guangxi.About 1400 drums ranging in age from the early Spring-Autumn Dynas-ty(700-400 B.C.)to the Ming-Qing Dynasty(1368-1828 A.D.)havebeen found in China so far(Wang,K.R.,1982).A cemetory of 79 ancient tombs with 1002 Cu-bearing wares at Wanjiaba,Chuxiong County,Yunnan Province was excavated during 1975 to 1976.The4 bronze drums unearthed from Tomb No.23,were dated at 690±90 B.C.,while one from Tomb No.1 at 400±85 B.C.by the ^(14)C method(Tong,E.展开更多
Ophiolites consist predominantly of mafic-ultramafic rocks but also contain in subordinate amounts intermediate to silicic intrusive–extrusive rocks in them.These rocks,although not in large volumes in comparison to ...Ophiolites consist predominantly of mafic-ultramafic rocks but also contain in subordinate amounts intermediate to silicic intrusive–extrusive rocks in them.These rocks,although not in large volumes in comparison to mafic–ultramafic units,reveal significant clues about melt evolution,magmatic accretion processes,and partial melting of pre-existing oceanic crust during ophiolite evolution.They also yield ample accessory minerals,such as zircon and monazite,which are widely used to date the timing of oceanic crust generation.We present a global synthesis of the occurrence of such leucocratic,intrusive and volcanic rocks from 150 Phanerozoic to Archean ophiolites,and evaluate models for their genesis during the development of oceanic crust in different tectonic environments.In the ophiolite complexes we have investigated,intrusive and extrusive rocks show a wide range in composition.Intermediate rocks(with Si O2 between 52and 63 wt.%)include andesite and diorite,whereas the silicic rocks(with Si O2 more than 63 wt.%)include dacite,trondhjemite,tonalite and granite.For subduction-relatedandsubduction-unrelated MORB-type ophiolites in the Phanerozoic orogenic belts,the most commonly reported intermediate to silicic intrusive rocks,independent of their original tectonic setting,are trondhjemite,plagiogranite and tonalite,and less commonly quartz-diorite and diorite.These rock types have been documented from 80 percent of the 104ophiolites included in this study.Intermediate to silicic lavas and/or pyroclastic rocks(basaltic andesite,andesite,dacite and rhyolite)are less abundant,and have been reported from only 35 percent of the 104 ophiolites.Trachyte occurs in some of the Rift/Continental Margintype,subduction-unrelated ophiolitesEvolvedrocksinsubduction-unrelated,Rift/Continental Margin ophiolites are predominantly basaltic andesite and andesite,whereas MOR type(mid-ocean ridge)ophiolites exhibit nearly equal proportions of basaltic andesite/andesite and rhyodacite and Plume/MOR type ophiolites are characterized by rhyolites.Intermediate to silicic volcanic uints in the Backarc sub-group of subduction-related ophiolites are characterized by similar amounts of basaltic andesite/andesite and rhyodacite,whereas in the Backarc to Forearc,Forearc,and Volcanic Arc sub-groups they are mainly basaltic andesite/andesite.Intermediate to silicic rocks in Rift/Continental Margin and Plume/MOR type ophiolites are generally LREE-enriched,whereas those in the MOR type vary from LREE-depleted to LREE-enriched.The Backarc and Backarc to Forearc types are similar to the MOR type;silicic rocks of the Forearc and Volcanic Arc types are generally LREE-enriched.The main process in the formation of the majority of the intermediate to silicic rocks in both subduction-unrelated and subduction-related ophiolites is partial melting of basaltic and/or gabbroic rocks beneath the spreading centers,whereas a minor volume in subduction-related ophiolites are adakites that were produced from partial melting of a subducting slab.Silcic to intermediate rocks in Plume/MOR type ophiolites are generated by fractional crystallization of basaltic melt.The incompatible,non-conservative elements,such as Ba and Th,are weakly to strongly enriched in subduction-related ophiolites as a result of shallow to deep enrichment associated with subduction zone processes.The field occurrence and the geochemical character of leucocratic rocks in ophiolites show considerable variations,providing additional constraints on the petrogenesis of ophiolites in different tectonic settings.Fractional crystallization appears to have been an important process in the formation of the intermediate to silicic rocks in Rift/CM and P/MOR ophiolites in the subduction-unrelated class,as well as VA ophiolites in the subduction-related class.In these types of ophiolites magma chambers might have operated as closed-systems for a sufficient amount of time for fractionation and compositional zoning of the magma to take place(Fig.1C1).Fractional crystallization was of subordinate importance during the igneous construction of the MOR,BA,FA,and BA-FA ophiolites.Instead,partial melting of hydrothermally altered crust was the most common process resulting in the majority of the intermediate to felsic rocks of the Rift/CM(estimated to 60%),MOR(estimated to 95%),and the BA,FA and BA-FA(estimated to 75%)ophiolites,as well as a high proportion of the VA ophiolites(;0%)(Fig.1C2).Slab-generated melts that result in the production of intermediate to silicic rocks of adakitic character represent a relatively small fraction(;5%in Phanerozoic ophiolites)of subduction-related ophiolites(Fig.1C3).Some adakites are very low in incompatible elements(e.g.,La),suggesting that these melts were generated from highly depleted MORB.Precambrian ophiolites contain a higher percentage of adakites(ca.35%),indicating that physical conditions were more favorable for slab melting during the Precambrian than in the Phanerozoic.This phenomenon may have resulted from higher geothermal gradient along relatively shallow-dippingsubductionzonesduringthe Precambrian.展开更多
There occur abundant cherts in the Mesozoic and Cenozoic strata in southern Tibet. Some of them possess characteristic hydrothermal structures such as layered, laminated, massive and breccia structures. Ratios of Al/...There occur abundant cherts in the Mesozoic and Cenozoic strata in southern Tibet. Some of them possess characteristic hydrothermal structures such as layered, laminated, massive and breccia structures. Ratios of Al/(Al+Fe+Mn), Co/Ni, Fe/Ti and TiO2-A1203 demonstrate that their origin is related to hydrothermal sedimentation. The chert formations have close relationship with Sb, Au and poly-metallic mineralization, and the ore-forming fluid show strong correlation with fossil hydrothermal water. There occur abundant cherts in the Mesozoic and Cenozoic strata in southern Tibet. Some of them possess characteristic hydrothermal structures such as layered, laminated, massive and breccia structures. Ratios of A1/(AI+Fe+Mn), Co/Ni, Fe/Ti and TiO2-A1203 demonstrate that their origin is related to hydrothermal sedimentation. The chert formations have close relationship with Sb, Au and poly-metallic mineralization, and the ore-forming fluid show strong correlation with fossil hvdrothermal water.展开更多
Orogenic garnet peridotites (metamorphic rocks containing the characteristic HP garnet-olivine mineral assemblage) exposed in ancient orogenic belts may contain quantitative data regarding formation of subcontinenta...Orogenic garnet peridotites (metamorphic rocks containing the characteristic HP garnet-olivine mineral assemblage) exposed in ancient orogenic belts may contain quantitative data regarding formation of subcontinental/ subcratonic lithosphere, evolution of a lithospheric mantle wedge, incorporation of garnet peridotite into subducted continental crust, subsequent (ultra-)high pressure metamorphism during ongoing continental subduction and final exhumation back to subcrustal levels.展开更多
Concept-based orogenic gold exploration requires a scale-integrated approach using a robust mineral system model.Most genetic hypotheses for orogenic gold deposits that involve near-surface or magmatic-hydrothermal fl...Concept-based orogenic gold exploration requires a scale-integrated approach using a robust mineral system model.Most genetic hypotheses for orogenic gold deposits that involve near-surface or magmatic-hydrothermal fluids are now negated in terms of a global mineral system model.Plausible models involve metamorphic fluids,but the fluid source has been equivocal.Crustal metamorphic-fluid models are most widely-accepted but there are serious problems for Archean deposits,and numerous Chinese provinces,including Jiaodong,where the only feasible fluid source is sub-crustal.If all orogenic gold deposits define a coherent mineral system,there are only two realistic sources of fluid and gold,based on their syn-mineralization geodynamic settings.These are from devolatilization of a subducted oceanic slab with its overlying gold-bearing sulfide-rich sedimentary package,or release from mantle lithosphere that was metasomatized and fertilized during a subduction event,particularly adjacent to craton margins.In this model,CO_2 is generated during decarbonation and S and ore-related elements released from transformation of pyrite to pyrrhotite at about 500 ℃.This orogenic gold mineral system can be applied to conceptual exploration by first identifying the required settings at geodynamic to deposit scales.Within these settings,it is then possible to define the critical gold mineralization processes in the system:fertility,architecture,and preservation.The geological parameters that define these processes,and the geological,geophysical and geochemical proxies and responses for these critical parameters can then be identified.At the geodynamic to province scales,critical processes include a tectonic thermal engine and deep,effective,fluid plumbing system driven by seismic swarms up lithosphere-scale faults in an oblique-slip regime during uplift late in the orogenic cycle of a convergent margin.At the district to deposit scale,the important processes are fluid focussing into regions of complex structural geometry adjacent to crustal-scale plumbing systems,with gold deposition in trap sites involving complex conjugations of competent and/or reactive rock sequences and structural or lithological fluid caps.Critical indirect responses to defined parameters change from those generated by geophysics to those generated by geochemistry with reduction in scale of the mineral system-driven conceptual exploration.展开更多
文摘Pioneering U-Pb isotopic studies by a small group of workers in the mid-late 1980s demonstrated the feasibility of using rare accessory mineral chronometers in mafic(gabbroic)intrusive rocks.These examples showed that mafic layered intrusions and diabase/dolerite dyke swarms alike crystallized high-temperature
文摘The new GPS data can map crustal strain rates over large areas with a useful degree of precision. Stable strain measurement results open the door for improved estimates of earthquake occurrence. The Kostrov’s formula (1974) translates the smoothed strain rates in North China into geodetic moment rates. In North China, the ratio of seismic moment released to moment accumulated from GPS measurement is 60.6% in NS direction, 68.9% in EW direction, and 104.1% in NE shear direction. The near unit ratio points to the reliability of GPS measurements there. The combination of historical seismicity and GPS measurement offers a powerful attack on earthquake hazard.
基金financial support provided by the National Natural Science Foundation of China (Grant No. 41702070)
文摘With very few exceptions, orogenic gold deposits formed in subduction-related tectonic settings in accretionary to collisional orogenic belts from Archean to Tertiary times. Their genesis, including metal and fluid source, fluid pathways, depositional mechanisms, and timing relative to regional structural and metamorphic events, continues to be controversial. However, there is now general agreement that these deposits formed from metamorphic fluids, either from metamorphism of intra-basinal rock sequences or de-volatilization of a subducted sediment wedge, during a change from a compressional to transpressional, less commonly transtensional, stress regime, prior to orogenic collapse. In the case of Archean and Paleoproterozoic deposits, the formation of orogenic gold deposits was one of the last events prior to cratonization. The late timing of orogenic gold deposits within the structural evolution of the host orogen implies that any earlier structures may be mineralized and that the current structural geometry of the gold deposits is equivalent to that at the time of their formation provided that there has been no significant post-gold orogenic overprint. Within the host volcano-sedimentary sequences at the province scale, world-class orogenic gold deposits are most commonly located in second-order structures adjacent to crustal scale faults and shear zones, representing the first-order ore-forming fluid pathways, and whose deep lithospheric connection is marked by lamprophyre intrusions which, however, have no direct genetic association with gold deposition. More specifically, the gold deposits are located adjacent to ~10°-25° district-scale jogs in these crustal-scale faults. These jogs are commonly the site of arrays of ~70° cross faults that accommodate the bending of the more rigid components, for example volcanic rocks and intrusive sills, of the host belts. Rotation of blocks between these accommodation faults causes failure of more competent units and/or reactivation and dilation of pre-existing structures, leading to deposit-scale focussing of ore-fluid and gold deposition.Anticlinal or antiformal fold hinges, particularly those of 'locked-up' folds with ~30° apical angles and overturned back limbs, represent sites of brittle-ductile rock failure and provide one of the more robust parameters for location of orogenic gold deposits.In orogenic belts with abundant pre-gold granitic intrusions, particularly Precambrian granitegreenstone terranes, the boundaries between the rigid granitic bodies and more ductile greenstone sequences are commonly sites of heterogeneous stress and inhomogeneous strain. Thus, contacts between granitic intrusions and volcano-sedimentary sequences are common sites of ore-fluid infiltration and gold deposition. For orogenic gold deposits at deeper crustal levels, ore-forming fluids are commonly focused along strain gradients between more compressional zones where volcano-sedimentary sequences are thinned and relatively more extensional zones where they are thickened. World-class orogenic gold deposits are commonly located in the deformed volcano-sedimentary sequences in such strain gradients adjacent to triple-point junctions defined by the granitic intrusions, or along the zones of assembly of micro-blocks on a regional scale. These repetitive province to district-scale geometrical patterns of structures within the orogenic belts are clearly critical parameters in geology-based exploration targeting for orogenic gold deposits.
基金funded by Talent Award under the 1000 Plan Project from the Chinese Government
文摘It is quite evident that it is not anomalous metal transport,nor unique depositional conditions,nor any single factor at the deposit scale,that dictates whether a mineral deposit becomes a giant or not.A hierarchical approach thus is required to progressively examine controlling parameters at successively decreasing scales in the total mineral system to understand the location of giant gold deposits in non-arc environments.For giant orogenic,intrusion-related gold systems(IRGS) and Carlin-type gold deposits and iron oxide-copper-gold(IOCG) deposits,there are common factors among all of these at the lithospheric to crustal scale.All are sited in giant gold provinces controlled by complex fundamental fault or shear zones that follow craton margins or,in the case of most Phanerozoic orogenic giants,define the primary suture zones between tectonic terranes.Giant provinces of IRGS,IOCG,and Carlin-type deposits require melting of metasomatized lithosphere beneath craton margins with ascent of hybrid lamprophyric to granitic magmas and associated heat flux to generate the giant province.The IRGS and IOCG deposits require direct exsolution of volatile-rich magmatic-hydrothermal fluids,whereas the association of such melts with Carlin-type ores is more indirect and enigmatic.Giant orogenic gold provinces show no direct relationship to such magmatism.forming from metamorphic fluids,but show an indirect relationship to lamprophyres that reflect the mantle connectivity of controlling first-order structures.In contrast to their province scale similarities,the different giant gold deposit styles show contrasting critical controls at the district to deposit scale.For orogenic gold deposits,the giants appear to have formed by conjunction of a greater number of parameters to those that control smaller deposits,with resultant geometrical and lithostratigraphic complexity as a guide to their location.There are few giant IRGS due to their inferior fluid-flux systems relative to orogenic gold deposits,and those few giants are essentially preservational exceptions.Many Carlin-type deposits are giants due to the exceptional conjunction of both structural and lithological parameters that caused reactive and permeable rocks,enriched in syngenetic gold,to be located below an impermeable cap along antiformal "trends".Hydrocarbons probably played an important role in concentrating metal.The supergiant Post-Betze deposit has additional ore zones in strain heterogeneities surrounding the pre-gold Goldstrike stock.All unequivocal IOCG deposits are giant or near-giant deposits in terms of gold-equivalent resources,partly due to economic factors for this relatively poorly understood,low Cu-Au grade deposit type.The supergiant Olympic Dam deposit,the most shallowly formed deposit among the larger IOCGs,probably owes its origin to eruption of volatile-rich hybrid magma at surface,with formation of a large maar and intense and widespread brecciation,alteration and Cu-Au-U deposition in a huge rock volume.
基金This study was supported by the Natural Science Foundation of China (grant No. 40273034)the Science Foundation of Hongzhou Danzi University.
文摘The static flux chamber method was applied to study natural emissions of methane to the atmosphere in the Luntai fault region of Yakela Condensed Oil/Gas Field in the Tarim Basin, Xinjiang Municipality, northwestern China. Using an online method, which couples together a gas chromatography/high-temperature conversion/isotope ratio mass spectrometry (GC/C/MS), 13^C/12^C ratios of methane in flux chambers were measured and showed that methane gases are liable to migrate from deep oil/gas reservoirs to the surface through fault regions and that a part of the migrated methane, which remains unoxidized can be emitted into the atmosphere. Methane emission rates were found to be highest in the mornings, lowest in the afternoons and then increase gradually in the evenings. Methane emission rates varied dramatically in different locations in the fault region. The highest methane emission rate was 10.96 mg/m^2·d, the lowest 4.38 mg/m^2, and the average 7.55 mg/ m^2·d. The 13^C/12^C ratios of the methane in the flux chambers became heavier as the enclosed methane concentrations increased gradually, which reveals that methane released from the fault region might come from thermogenic methane of the deep condensed oil/gas reservoir.
基金partly funded by the National Key Research Program of China(2019YFA0708603)the National Natural Science Foundation of China(42130801,41230311,41572069,41702070)+2 种基金the 111 Project of the Ministry of Science and Technology,China(BP0719021)the MOST Special Fund from the State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences(MSFGPMR201804)the Key Laboratory of Gold Mineralization Processes and Resource Utilization Subordinated to the Ministry of Natural Resources and Key Laboratory of Metallogenic Geological Process and Resources Utilization in Shandong Province,Shandong Institute of Geological Sciences(KFKT201801,KFKT201802)。
文摘The current margins of the North China and Yangtze Cratons provide arguably the best examples globally of anomalously high mineral endowment within a 100 km buffer zone,hosting 66 diverse world-class to giant ore systems that help explain China’s premier position as a producer of multiple metal and mineral commodities.After the cratonization of these crustal blocks during the Neoarchean-Paleoproterozoic,with incorporation of iron ores on assembled micro-block margins,the margins of the cratons experienced multiple convergence and rifting events leading to metasomatism and fertilization of their underlying sub-continental lithospheric mantle.The rifted margins with trans-lithosphere faults provided pathways for Cu-Au(Mo-W-Sn)-bearing felsic to Ni-Cu-bearing ultrabasic intrusions and REE-rich carbonatite magmas,and for the development of marginal sedimentary basins with both Cu-Pb-Zn-rich source units and reactive carbonate or carbonaceous host rocks.There was diachronous formation of hydrothermal orogenic gold,antimony,and bismuth systems in the narrow orogenic belts between the cratons.Complexity in the Mesozoic Paleo-Pacific subduction systems resulted in asthenosphere upwelling and lithosphere extension and thinning in the North China Craton,leading to anomalous heat flow and formation of orogenic gold deposits,including those of the giant Jiaodong gold province on its north-eastern margin.These gold deposits,many of which formed from fluids liberated by devolatilization of previously metasomatized sub-continental lithospheric mantle,helped propel China to be the premier gold producer globally.The thick sub-continental lithospheric mantle of the cold buoyant cratons helped the preservation of some of the world’s oldest porphyry-skarn and epithermal mineral systems.Although craton margins globally control the formation and preservation of a diverse range of mineral deposits,China represents the premier example in terms of metal endowment due to the anomalous length of its craton margins combined with their abnormally complex tectonic history.
基金partially supported by US Department of Energy Grant DE-SC0019759National Science Foundation (NSF) Grants EAR-1918126, EAR-2027150, EAR-1925965, and OCE-1842989。
文摘We present a narrative of the eruptive events culminating in the cataclysmic January 15, 2022 eruption of Hunga Tonga-Hunga Ha’apai Volcano by synthesizing diverse preliminary seismic, volcanological, sound wave, and lightning data available within the first few weeks after the eruption occurred. The first hour of eruptive activity produced fast-propagating tsunami waves, long-period seismic waves, loud audible sound waves, infrasonic waves, exceptionally intense volcanic lightning and an unsteady volcanic plume that transiently reached-at 58km-the Earth’s mesosphere. Energetic seismic signals were recorded worldwide and the globally stacked seismogram showed episodic seismic events within the most intense periods of phreatoplinian activity, and they correlated well with the infrasound pressure waveform recorded in Fiji. Gravity wave signals were strong enough to be observed over the entire planet in just the first few hours, with some circling the Earth multiple times subsequently. These large-amplitude, long-wavelength atmospheric disturbances come from the Earth’s atmosphere being forced by the magmatic mixture of tephra, melt and gasses emitted by the unsteady but quasicontinuous eruption from 0402±1–1800 UTC on January 15, 2022. Atmospheric forcing lasted much longer than rupturing from large earthquakes recorded on modern instruments, producing a type of shock wave that originated from the interaction between compressed air and ambient(wavy) sea surface. This scenario differs from conventional ideas of earthquake slip, landslides, or caldera collapse-generated tsunami waves because of the enormous(~1000x) volumetric change due to the supercritical nature of volatiles associated with the hot,volatile-rich phreatoplinian plume. The time series of plume altitude can be translated to volumetric discharge and mass flow rate. For an eruption duration of ~12 h, the eruptive volume and mass are estimated at 1.9 km^(3) and~2 900 Tg, respectively, corresponding to a VEI of 5–6 for this event. The high frequency and intensity of lightning was enhanced by the production of fine ash due to magma-seawater interaction with concomitant high charge per unit mass and the high pre-eruptive concentration of dissolved volatiles. Analysis of lightning flash frequencies provides a rapid metric for plume activity and eruption magnitude. Many aspects of this eruption await further investigation by multidisciplinary teams. It represents a unique opportunity for fundamental research regarding the complex, non-linear behavior of high energetic volcanic eruptions and attendant phenomena, with critical implications for hazard mitigation, volcano forecasting, and first-response efforts in future disasters.
文摘Discovery rates for all metals, including gold, are declining, the cost per significant discovery is increasing sharply, and the economic situation of the industry is one of low base rate. The current hierarchical structure of the exploration and mining industry makes this situation difficult to redress. Economic geologists can do little to influence the required changes to the overall structure and philosophy of an industry driven by business rather than geological principles, However, it should be possible to follow the lead of the oil industry and improve the success rate of greenfield exploration, necessary for the next group of lower-exploration-spend significant mineral deposit discoveries. Here we promote the concept that mineral explorers need to carefully consider the scale at which their exploration targets are viewed. It is necessary to carefully assess the potential of drill targets in terms of terrane to province to district scale, rather than deposit scale, where most current economic geology research and conceptual thinking is concentrated. If orogenic, IRGD, Carlin-style and IOCG gold-rich systems are viewed at the deposit scale, they appear quite different in terms of conventionally adop- ted research parameters. However, recent models for these deposit styles show increasingly similar source-region parameters when viewed at the lithosphere scale, suggesting common tectonic settings. It is only by assessing individual targets in their tectonic context that they can be more reliably ranked in terms of potential to provide a significant drill discovery. Targets adjacent to craton margins, other lithosphere boundaries, and suture zones are clearly favoured for all of these gold deposit styles, and such exploration could lead to incidental discovery of major deposits of other metals sited along the same tectonic boundaries.
基金We acknowledge BP plc,Cenovus Energy,Husky Energy,Nexen CNOOC Ltd.,and Woodside Energy Ltd.for funding the McMurray Research Consortium,and GeoLOGIC for providing the GeoScout software used in this study.
文摘In the Lower CretaceousMcMurray-Clearwater succession of the intracontinental Alberta Foreland Basin,Canada,detrital zircon U-Pb geochronology samples(referred to herein as DZ samples)have been used to interpret the strata as representing a paleo-continental-scale drainage system.However,the majority of DZ samples are relatively small(n≈90–100),and syndepositional DZ(i.e.,crystallization age<5 Ma older than depositional age)are rare.This has forced a reliance on dinocysts with long stratigraphic ranges to chronostratigraphically subdivide the McMurray-Clearwater succession rather than employing maximum depositional ages(MDAs)derived from DZ samples.Herein,43 DZ samples(taken from20 subsurface cores)are assigned to 1 of 5 stratigraphic intervals,and in each stratigraphic interval all associated DZ samples are combined to produce a grouped DZ sample.Analysis and comparison of individual and grouped DZ samples are used to(1)assess variability in provenance through time and space,and(2)assess the accuracy of chronostratigraphically subdividing the succession using MDAs.Along the main paleo-drainage axis,a comparison of dissimilarity between DZ samples from the same stratigraphic interval,as well as between stratigraphic intervals,reveals increasing average dissimilarity between individual DZ samples and their respective grouped DZ samplewith increasing spatial separation of samples.These data indicate that in the McMurray Depocenter some sediment is sourced from local tributaries,leading to geographical provenance variability.CalculatedMDAs for all 43 DZ samples and groupedMDAs(gMDAs)for the 5 grouped DZ samples are compared to an ash-derived absolute age and existing biostratigraphy.In theMcMurray Formation,comparison of MDAs to gMDAs shows that in basins with rare syndepositional DZ,the gMDA method improved depositional age estimates by transforming low-confidence MDAs(e.g.,youngest single grains)into high-confidence(multi-grain)gMDAs.In the Clearwater Formationwhere syndepositional DZ are plentiful(i.e.,>5%of the total DZ population),calculating maximumlikelihood ages fromgrouped DZ samples avoids negatively biased(i.e.,too young)MDAs.We suggest grouped DZ samples and the gMDA method be used in systems with multiple DZ samples from a well-defined stratigraphic interval as a means of assessing variability in provenancewithin a depositional system and for improving estimates of depositional ages using DZ.
文摘Fig.8e in our paper(Groves et al.,2018)was incorrectly ascribed to Caddey et al.(1995).It is actually taken from Figure 3 in Morelli et al.(2010).In turn,this was derived from Bell(2013).The authors apologise for this unintentional error.
文摘A study has been reported on <sup>208</sup>Pb/<sup>206</sup>Pb and <sup>207</sup>Pb/<sup>206</sup>Pb ratio variations in ancient drums and Cu-., Pb- ores from Guangxi, China and can indicate that the Cu- and Pb- bearing ores for making the Beiliu and the Lingshan type drums were taken from Tongshiling of Beiliu County and its vicinity, that were not only ancient sites for smelting the copper ores, but possibly also for casting the bronze drums. Some of the Lengshuichong type drums have abnormal Pb isotopic ratios, which means that they were made of special ore sources, one of the possibilities is that the ore material or the drums were transported from South- East Asia to Guangxi Province, because they have been excavated there too.
文摘IntroductionAncient bronze drums are representatives of the historical culture of the minori-ty people living in southern China,such as Yunnan,Guizhou and Guangxi.About 1400 drums ranging in age from the early Spring-Autumn Dynas-ty(700-400 B.C.)to the Ming-Qing Dynasty(1368-1828 A.D.)havebeen found in China so far(Wang,K.R.,1982).A cemetory of 79 ancient tombs with 1002 Cu-bearing wares at Wanjiaba,Chuxiong County,Yunnan Province was excavated during 1975 to 1976.The4 bronze drums unearthed from Tomb No.23,were dated at 690±90 B.C.,while one from Tomb No.1 at 400±85 B.C.by the ^(14)C method(Tong,E.
文摘Ophiolites consist predominantly of mafic-ultramafic rocks but also contain in subordinate amounts intermediate to silicic intrusive–extrusive rocks in them.These rocks,although not in large volumes in comparison to mafic–ultramafic units,reveal significant clues about melt evolution,magmatic accretion processes,and partial melting of pre-existing oceanic crust during ophiolite evolution.They also yield ample accessory minerals,such as zircon and monazite,which are widely used to date the timing of oceanic crust generation.We present a global synthesis of the occurrence of such leucocratic,intrusive and volcanic rocks from 150 Phanerozoic to Archean ophiolites,and evaluate models for their genesis during the development of oceanic crust in different tectonic environments.In the ophiolite complexes we have investigated,intrusive and extrusive rocks show a wide range in composition.Intermediate rocks(with Si O2 between 52and 63 wt.%)include andesite and diorite,whereas the silicic rocks(with Si O2 more than 63 wt.%)include dacite,trondhjemite,tonalite and granite.For subduction-relatedandsubduction-unrelated MORB-type ophiolites in the Phanerozoic orogenic belts,the most commonly reported intermediate to silicic intrusive rocks,independent of their original tectonic setting,are trondhjemite,plagiogranite and tonalite,and less commonly quartz-diorite and diorite.These rock types have been documented from 80 percent of the 104ophiolites included in this study.Intermediate to silicic lavas and/or pyroclastic rocks(basaltic andesite,andesite,dacite and rhyolite)are less abundant,and have been reported from only 35 percent of the 104 ophiolites.Trachyte occurs in some of the Rift/Continental Margintype,subduction-unrelated ophiolitesEvolvedrocksinsubduction-unrelated,Rift/Continental Margin ophiolites are predominantly basaltic andesite and andesite,whereas MOR type(mid-ocean ridge)ophiolites exhibit nearly equal proportions of basaltic andesite/andesite and rhyodacite and Plume/MOR type ophiolites are characterized by rhyolites.Intermediate to silicic volcanic uints in the Backarc sub-group of subduction-related ophiolites are characterized by similar amounts of basaltic andesite/andesite and rhyodacite,whereas in the Backarc to Forearc,Forearc,and Volcanic Arc sub-groups they are mainly basaltic andesite/andesite.Intermediate to silicic rocks in Rift/Continental Margin and Plume/MOR type ophiolites are generally LREE-enriched,whereas those in the MOR type vary from LREE-depleted to LREE-enriched.The Backarc and Backarc to Forearc types are similar to the MOR type;silicic rocks of the Forearc and Volcanic Arc types are generally LREE-enriched.The main process in the formation of the majority of the intermediate to silicic rocks in both subduction-unrelated and subduction-related ophiolites is partial melting of basaltic and/or gabbroic rocks beneath the spreading centers,whereas a minor volume in subduction-related ophiolites are adakites that were produced from partial melting of a subducting slab.Silcic to intermediate rocks in Plume/MOR type ophiolites are generated by fractional crystallization of basaltic melt.The incompatible,non-conservative elements,such as Ba and Th,are weakly to strongly enriched in subduction-related ophiolites as a result of shallow to deep enrichment associated with subduction zone processes.The field occurrence and the geochemical character of leucocratic rocks in ophiolites show considerable variations,providing additional constraints on the petrogenesis of ophiolites in different tectonic settings.Fractional crystallization appears to have been an important process in the formation of the intermediate to silicic rocks in Rift/CM and P/MOR ophiolites in the subduction-unrelated class,as well as VA ophiolites in the subduction-related class.In these types of ophiolites magma chambers might have operated as closed-systems for a sufficient amount of time for fractionation and compositional zoning of the magma to take place(Fig.1C1).Fractional crystallization was of subordinate importance during the igneous construction of the MOR,BA,FA,and BA-FA ophiolites.Instead,partial melting of hydrothermally altered crust was the most common process resulting in the majority of the intermediate to felsic rocks of the Rift/CM(estimated to 60%),MOR(estimated to 95%),and the BA,FA and BA-FA(estimated to 75%)ophiolites,as well as a high proportion of the VA ophiolites(;0%)(Fig.1C2).Slab-generated melts that result in the production of intermediate to silicic rocks of adakitic character represent a relatively small fraction(;5%in Phanerozoic ophiolites)of subduction-related ophiolites(Fig.1C3).Some adakites are very low in incompatible elements(e.g.,La),suggesting that these melts were generated from highly depleted MORB.Precambrian ophiolites contain a higher percentage of adakites(ca.35%),indicating that physical conditions were more favorable for slab melting during the Precambrian than in the Phanerozoic.This phenomenon may have resulted from higher geothermal gradient along relatively shallow-dippingsubductionzonesduringthe Precambrian.
基金Ministry of Science and Technology 973 Program(Grant No.2002CB412600-VI)NSFC(Grant No.40073010)the Ph.D.Training Base Fund the National Education Ministry of China(Grant Nos.20040558050,20000099815)
文摘There occur abundant cherts in the Mesozoic and Cenozoic strata in southern Tibet. Some of them possess characteristic hydrothermal structures such as layered, laminated, massive and breccia structures. Ratios of Al/(Al+Fe+Mn), Co/Ni, Fe/Ti and TiO2-A1203 demonstrate that their origin is related to hydrothermal sedimentation. The chert formations have close relationship with Sb, Au and poly-metallic mineralization, and the ore-forming fluid show strong correlation with fossil hydrothermal water. There occur abundant cherts in the Mesozoic and Cenozoic strata in southern Tibet. Some of them possess characteristic hydrothermal structures such as layered, laminated, massive and breccia structures. Ratios of A1/(AI+Fe+Mn), Co/Ni, Fe/Ti and TiO2-A1203 demonstrate that their origin is related to hydrothermal sedimentation. The chert formations have close relationship with Sb, Au and poly-metallic mineralization, and the ore-forming fluid show strong correlation with fossil hvdrothermal water.
文摘Orogenic garnet peridotites (metamorphic rocks containing the characteristic HP garnet-olivine mineral assemblage) exposed in ancient orogenic belts may contain quantitative data regarding formation of subcontinental/ subcratonic lithosphere, evolution of a lithospheric mantle wedge, incorporation of garnet peridotite into subducted continental crust, subsequent (ultra-)high pressure metamorphism during ongoing continental subduction and final exhumation back to subcrustal levels.
基金partly funded by the National Natural Science Foundation of China(Grant Nos.41230311,41572069,41702070)the National Key Research and Development Project of China(2016YFC0600307)+2 种基金the National Key Research Program of China(Grant Nos.2016YFC0600107-4 and 2016YFC0600307)the MOST Special Fund from the State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences(Grant No.MSFGPMR201804)the 111 Project of the Ministry of Science and Technology,China(Grant No.BP0719021)。
文摘Concept-based orogenic gold exploration requires a scale-integrated approach using a robust mineral system model.Most genetic hypotheses for orogenic gold deposits that involve near-surface or magmatic-hydrothermal fluids are now negated in terms of a global mineral system model.Plausible models involve metamorphic fluids,but the fluid source has been equivocal.Crustal metamorphic-fluid models are most widely-accepted but there are serious problems for Archean deposits,and numerous Chinese provinces,including Jiaodong,where the only feasible fluid source is sub-crustal.If all orogenic gold deposits define a coherent mineral system,there are only two realistic sources of fluid and gold,based on their syn-mineralization geodynamic settings.These are from devolatilization of a subducted oceanic slab with its overlying gold-bearing sulfide-rich sedimentary package,or release from mantle lithosphere that was metasomatized and fertilized during a subduction event,particularly adjacent to craton margins.In this model,CO_2 is generated during decarbonation and S and ore-related elements released from transformation of pyrite to pyrrhotite at about 500 ℃.This orogenic gold mineral system can be applied to conceptual exploration by first identifying the required settings at geodynamic to deposit scales.Within these settings,it is then possible to define the critical gold mineralization processes in the system:fertility,architecture,and preservation.The geological parameters that define these processes,and the geological,geophysical and geochemical proxies and responses for these critical parameters can then be identified.At the geodynamic to province scales,critical processes include a tectonic thermal engine and deep,effective,fluid plumbing system driven by seismic swarms up lithosphere-scale faults in an oblique-slip regime during uplift late in the orogenic cycle of a convergent margin.At the district to deposit scale,the important processes are fluid focussing into regions of complex structural geometry adjacent to crustal-scale plumbing systems,with gold deposition in trap sites involving complex conjugations of competent and/or reactive rock sequences and structural or lithological fluid caps.Critical indirect responses to defined parameters change from those generated by geophysics to those generated by geochemistry with reduction in scale of the mineral system-driven conceptual exploration.