Mars exploration——In situ K-Ar dating of jarosite

To accurately determine the chronological framework of climatic variations recorded by various Martian terrains, the absolute ages of Martian events and cratering rate need to be constrained by either in situ dating or returned samples. In situ K-Ar dating is currently a more plausible dating technique as compared with sample return. Jarosite(KFe_(3)[SO_(4)]_(2)[OH]_(6)) is the only confirmed K sulfate mineral that is widely present on Mars, as indicated by in situ detection, orbital remote sensing, and meteorite studies. Jarosite can be used for precise K-Ar and (40)Ar/(39)Ar dating. The preservation of jarosite on Mars provides information about the nature and duration of aqueous processes on the Martian surface. Different ages of Martian jarosite represent the key to constraining the transition from Martian surface water activity to arid climatic conditions. This paper summarizes recent advances in our knowledge of the spatial distribution of Martian jarosite, its mineralogical properties and stability on Mars, the Ar diffusion kinetics of jarosite, and the current status of in situ K-Ar dating. Moreover, we examine the key scientific issues to be addressed for in situ K-Ar dating of jarosite and Martian sample return missions, and discuss future research directions.

A Paleozoic mercury mineralisation event in South China:In situ U-Pb dating and chemical compositions of calcite from the Jianyan Hg deposit

The ages of hydrothermal Hg deposits are difficult to constrain because of the lack of suitable minerals for dating.The South China low-temperature metallogenic domain hosts numerous Hg deposits,including the Jianyan Hg deposit that is composed mainly of cinnabar and calcite.There are two stages of calcite in the deposit:syn-ore calcite(Cal-Ⅰ)and post-ore/barren calcite(Cal-Ⅱ).Cal-Ⅰis mainly euhedral-subhedral and fine-grained,has homogeneous grey luminescence,and is associated with cinnabar.Subhedral-anhedral Cal-Ⅱcrosscuts Cal-Ⅰand is relatively coarse-grained.The syn-ore Cal-Ⅰhas high U contents(0.1–1.3 ppm)and U/Pb ratios(up to 4.2),and is thus suitable for U-Pb dating.Using a laser ablation-inductively coupled plasma-mass spectrometer equipped with ion counters,we obtained a U-Pb age of 426.3±5.7 Ma(MSWD=1.5)for CalI.This age is interpreted to represent the timing of Hg mineralisation at Jianyan and is similar to ages of 440–400 Ma reported for many carbonate-hosted Pb-Zn and Ba-F deposits in South China.Based on the present results in combination with existing geochemical and geochronological data,we infer that these deposits belong to a Paleozoic Hg-Pb-Zn-Ba-F mineralisation system that was controlled by Caledonian tectonism.

Major Tectono-thermal Events in the Yangtze Craton: Insights from U-Pb-Lu-Hf Isotope Records in Zircons from End-Permian Volcanic Interlayers in Southwest China

The in situ zircon U-Pb-Lu-Hf isotope records from end-Permian volcanic interlayers in southwest China,integrated with previous studies,restructure the evolutionary history of the Yangtze Craton from Precambrian to Late Paleozoic.This includes early continental crust formation before 3.0 Ga and massive juvenile crustal growth at 2.6-2.4 Ga;large-scale crustal reworking at 2.1-1.7 Ga;Neoproterozoic crust addition at 1.1 to 0.7 Ga;collision and subduction along the craton margin between 700-541 Ma;Early Ordovician to Late Silurian magmatism;and large tectono-thermal events in the Middle Carboniferous to end-Permian.Some zircons with T(MD2)ages from 4.40 to 4.01 Ga and lower initial176Hf/177Hf values of 0.280592 to 0.280726 may imply the existence of Hadean crust relics beneath the Yangtze Craton and their provenances could be associated with Hadean crustal remelting.This study further clarifies that the Precambrian-age zircons between the end-Permian volcanic interlayers,the complexes in the western margin of the Yangtze Craton,and the sedimentary Kangdian Basin,may share an affinity based on similar U-Pb age spectra and Hf isotope features.It also shows that the Neoproterozoic tectono-thermal event may be associated with large-scale tectono-rifting activity,which is different from the Grenville-age continental collision between Yangtze and Cathaysia blocks in South China.The above findings support the inference of a widespread Archean basement extending to the western Yangtze Craton and a provenance in the Kangdian Basin that is derived from the weathering and erosion of Paleoproterozoic continental crust.

Age and fluid source constraints of the Haoyaoerhudong orogenic gold deposit,North China:Evidence from geochronology and noble gas isotopes

The Haoyaoerhudong gold deposit,located in the northwestern part of the North China craton(NCC),has produced over 120 metric tonnes(t)of gold since 2007.It has a total reserve of>240 t at average gold grade of 0.62 g/t,making it one of the largest open pit gold mines in China.The steeply dipping,large-tonnage,low-grade,vein-or veinlet-type gold orebodies are hosted in strongly-deformed Mesoproterozoic carbonaceous schist of the Bayan Obo Group.The laminated/boudinaged veins/veinlets in the sinistral ductile-brittle shear zones are dominated by quartz,biotite,gold-bearing löllingite,pyr-rhotite,(arseno)pyrite,with minor native gold,titanite and xenotime.In this paper,we present new in situ U-Pb geochronological data on magmatic zircon from the preore dikes,on metamorphic and hydrothermal xenotime,and on hydrothermal titanite from the hydrothermally altered carbonaceous schist and auriferous quartzsulfides veins/veinlets,as well as He-Ar isotopic analysis on gold-bearing(arseno)pyrite in the syn-ore stage.The metamorphic xenotime U-Pb age of 426±6.0 Ma(2σ)records a regional metamorphic event,possibly related to the accretion of the Bainaimiao arc onto the NCC.Two pre-ore andesitic dikes yielded similar emplacement ages at~278 Ma constrained by laser ablation-inductively coupled plasma-mass spectrometry(LA-ICP-MS)U-Pb zircon data.Hydrothermal xenotime grains from the altered carbonaceous schist and auriferous quartz-sulfides veins yielded U-Pb ages of 256.0±4.1 Ma(2σ)and 254.4±2.1 Ma(2σ),respectively,overlapping with that of the hydrothermal titanite at 255.4±0.8 Ma(2σ)from the laminated quartz-sulfides veinlets.This indicates that the gold mineralization occurred at ca.255 Ma.The~255 Ma gold mineralization age is much younger than the previously reported Early-Middle Permian regional magmatic activity(ca.291 Ma to 268 Ma),and may be associated with the regional sinistral strike-slip event in the late orogenic cycle related to the collision between the Siberian craton and the NCC.The 3He/4He(R/Ra)and 40Ar/36Ar values of the gold-bearing(arseno)pyrite are 0.04 to 0.09(average=0.07)and 375.8 to 2023(average=1045),which reveal the ore-forming fluids dominantly originated from the crustal rocks,with limited involve-ment from the mantle.Collectively,our new geochronological data,noble gas isotopic analyses,and geo-logical evidence support a typical orogenic gold deposit model at Haoyaoerhudong.

Geology and genesis of the Aqishan Pb-Zn deposit,NW China:Insights from mineralogy,geochemistry,and in situ U-Pb geochronology

The unique ore-forming processes and the key factors responsible for formation of skarn deposits are still obscure,and challenges exist in the determination of timing of Pb-Zn skarns owing to lacking suitable mineral chronometers.Here we present detailed paragenesis,bulk geochemistry,in situ U-Pb dating of zircon and garnet,and garnet oxygen isotopes together with in situ zircon Hf-O isotopes from the newly discovered Aqishan Pb-Zn deposit in the southern Central Asian Orogenic Belt(CAOB),northwest China.This comprehensive data set revealed a Late Carboniferous subduction-related distal Pb-Zn skarn system associated with the granitic magmatism.Pre-ore stage garnets are generally subhedral to euhedral with oscillatory zoning and show slightly fractionated rare earth element patterns with positive Eu anomalies that point to an infiltration metasomatism origin under high water/rock ratios.The syn-ore stage sphalerite is typically enriched in Mn and Cd and has moderate Zn/Cd ratios(337–482),with a formation temperature of 265℃to 383℃,which indicate magmatic-hydrothermal signatures.The isocons defined by P_(2)O_(5)decipher that the principal factors for skarn formation were elevated activities of Fe,Ca,and Si species,where remobilization of Pb metals,meanwhile,contributed to ore-forming budgets to mineralizing fluids.SIMS U-Pb dating of zircons from granite porphyry that occurs distal to the skarns and Pb-Zn orebodies shows that these intrusions emplaced at ca.311.3–310.6 Ma,recording the subduction of the Paleo-Tianshan oceanic plate.Hydrothermal garnets in close textural association with Pb-Zn sulfides yield indistinguishable in situ LA-ICP-MS U-Pb ages of 310.5±4.1 Ma.Whole-rock geochemistry and in situ zircon Hf-O isotopes(δ^(18)O=4.6‰–6.0‰)indicate that the granite porphyry was derived from partial melting of juvenile crust and influenced by subducted oceanic crust.Oxygen isotope compositions of garnets(δ^(18)O=8.0‰–9.0‰)demonstrate that the equilibrated ore fluids were inherited from fluid-rock interactions between a primary magmatic water and host tuff rocks.Our study highlights the application of garnets as a potential robust U-Pb geochronometer and isotopic tracer of ore fluids in skarn mineralizing systems in subduction-related arc environments.