Fe-bearing minerals and implications for gold mineralization for the Wangu deposit in Central Jiangnan Orogen

Hydrothermal alteration with bleaching of host rocks is the most important prospecting indicator for gold deposits in the Jiangnan Orogen Belt.The alteration has been identified as pre-ore carbonate(siderite)-sericitization and the Fe of siderite in the alteration zone is derived from the host rocks rather than fluids.In addition,such alteration decreases in intensity and width with depth and gold mineralization also occur in the non-bleached rocks,casting doubt on the reliability of the prospecting indicator.Detailed petrographic work and SEM analysis on the Wangu deposit indicate that there are two types of siderites,i.e.,Sd1 and Sd2.Among them,Sd1 grains are relatively small and distributed along the planes of unaltered host rocks,while Sd2 grains,only occurring in the altered slates,are commonly larger.Both types of siderites were altered by auriferous fluids,producing porous cores and minerals such as pyrite,quartz,and ankerite.Compared with unaltered parts,the altered parts have lower Fe,but higher U,Pb,and REE.In addition,Sd1 and Sd2 are similar in Mn,Na,V,and Sr concentrations but different in Fe and Mg.The occurrence and geochemical compositions of both siderites indicate that Sd1 could be transformed into Sd2 by pre-mineralization alteration through dissolution-reprecipitation.Chlorite is another important Fe-bearing mineral in the host rocks,and EPMA analysis suggests that it is ripidolite with relatively high Fe contents.Consequently,chlorite can also provide Fe to form the pre-ore carbonate(siderite)-sericitization.Geochemical modeling demonstrates that both ripidolite and siderite can result in sulfidation and therefore gold precipitation.As a result,this study demonstrates that pre-ore alteration with characterized bleaching is not a prerequisite for gold mineralization despite of its prominent features.Due to the presence of Fe-bearing Sd1 and chlorite,gold mineralization could still occur through sulfidation in the unaltered rocks.

A machine learning approach to tracking crustal thickness variations in the eastern North China Craton

The variation of crustal thickness is a critical index to reveal how the continental crust evolved over its four billion years.Generally,ratios of whole-rock trace elements,such as Sr/Y,(La/Yb)n and Ce/Y,are used to characterize crustal thicknesses.However,sometimes confusing results are obtained since there is no enough filtered data.Here,a state-of-the-art approach,based on a machine-learning algorithm,is proposed to predict crustal thickness using global major-and trace-element geochemical data of intermediate arc rocks and intraplate basalts,and their corresponding crustal thicknesses.After the validation processes,the root-mean-square error(RMSE)and the coefficient of determination(R2)score were used to evaluate the performance of the machine learning algorithm based on the learning dataset which has never been used during the training phase.The results demonstrate that the machine learning algorithm is more reliable in predicting crustal thickness than the conventional methods.The trained model predicts that the crustal thickness of the eastern North China Craton(ENCC)was-45 km from the Late Triassic to the Early Cretaceous,but-35 km from the Early Cretaceous,which corresponds to the paleo-elevation of 3.0±1.5 km at Early Mesozoic,and decease to the present-day elevation in the ENCC.The estimates are generally consistent with the previous studies on xenoliths from the lower crust and on the paleoenvironment of the coastal mountain of the ENCC,which indicates that the lower crust of the ENCC was delaminated abruptly at the Early Cretaceous.

Application of eDNA Metabarcoding for Detecting Anura in North China

eDNA metabarcoding is an advanced method formonitoring biodiversityproposed in recent years.By analyzing DNA in water,soil and sediment samples,the technology obtains species distribution and population quantity information.It was found that macrobarcode technology is more accurate than the traditional method in measuring the species richness of some groups.In Europe,America and South America,the relia bility of this technology in monitoring amphibian diversity in the wild was studied,and it was found to be better than traditional biodiversity monitoring methods in detecting species diversity.At present,amphibian monitoring mainly depends on various traditional methods,such as transects,drift fence traps,artificial shelters and mark-recapture.These monitoring techniques have many shortcomings,such as low accuracy and strong subjectivity of study results.These technologies have poor effects on rare,invasive and endangered species with strong concealment ability,low density and strong seasonality and are difficult to implement in sites inaccessible to people.Traditional monitoring technology also requires considerable investment of human and material resources,and the economic cost is relatively high,while eDNA metabarcoding ismore efficient and less costly,so it is important to use eDNA meta barcoding in amphibian monitoring in China.In this study,the eDNA meta barcoding and traditional line transect method(TLTM)were used to study the characteristics of the two methods in the Beijing-Tianjin-Hebeiregion.Repeated samplingwas conducted on 58 waterbodies in July 2019 and June 2020.After sequencing the samples using highthroughput sequencing technology,the differences between metabarcoding and commonly used TLTM surveys in detecting the diversity of four amphibians in North China were assessed.Our results showed that eDNA meta barcoding is more sensitive to the detection of the four amphibian species in the sampling area,and the combined use of eDNA metabarcoding and TLTM can improve the survey results of amphibians in the survey area to the greatest extent.In addition,in the process of species classification and identification of metabarcoding results,7 species of reptiles were detected,indicating that eDNA metabarcoding is also useful to detect reptiles.The results of this study indicate that metabarcoding in combination with TLTM can accurately estimate the diversityof amphibians in a short-term survey in North China and is also useful in reptile species detection.

Geochronology and zircon geochemistry of auriferous intrusions in the Bumo deposit,Hainan Province,China

Intrusion-related gold deposits(IRGS)are a lowgrade,large-tonnage exploration target.Recently,auriferous magmatic rocks were found in the Bumo deposit of the Gezhen shear zone in Hainan Province,China.However,the geochronology and geochemical characteristics of the intrusions,as well as the mineralization potential,are still unclear.Field and petrographic work show that the sulfidebearing intrusions can be divided into diorite porphyrites,quartz monzodiorites and monzodiorites.Zircon LA–ICP–MS U–Pb dating demonstrates that diorite porphyrites,quartz monzodiorites and monzodiorites were formed at104±1,114±1,114±1 Ma,respectively.In addition,sulfides in Yanshanian intrusion-related gold mineralization haveδ;S values of 0.2–4.4%,lower than those in Hercynian-Indosinian(1.9–9.8%)orogenic deposits(ca.219–378 Ma)in the Gezhen shear zone.In addition,all these intrusions display close correlations between Eu/EuN*with Th/U,consistent with the differentiation of amphibole,apatite and titanite from a hydrous melt.Moreover,zircon Eu/EuN*in the intrusions are higher than0.4,demonstrating that the magmatic rocks have high water contents and oxygen fugacity values,favorable for gold mineralization.Consequently,the Yanshanian magmatic rocks can be a new potential gold exploration target in the Gezhen shear zone.

Role of Hematite-Rich Host Rocks in the Gold Mineralization of the Woxi Au(-Sb-W) Ore Deposit in Western Jiangnan Orogen of South China

The formation of many hydrothermal gold deposits is closely related to iron-rich rocks. The host rocks of the Madiyi Formation of the Mid-to Late Neoproterozoic Banxi Group for the Woxi Au(-Sb-W) deposit, which is located in western Hunan Province of the western Jiangnan Orogen, South China, is rich in hematite, which provides a good example for studying the relationship between the formation of gold deposit and iron-rich rocks. Field investigation and petrographic observation on the unaltered, weakly altered and strongly altered rocks demonstrate that the bleaching is caused by a combination of carbonatization, sulfidation and sericitization. Mass balance calculation suggests that, during decolourization there is no change in TFe_(2)O_(3), while FeO is gained and Fe_(2)O_(3)is lost. Geochemical modeling found that Au was mainly present as AuHS(aq) and Au(HS)-2, and that the water-rock interactions decreased the sulfur fugacity which destroyed the stability of such aqueous complexes. Combined with the locally occurred native gold in quartz veins, it is concluded that the major gold precipitation mechanisms are sulfidation and fluid boiling. Based on previous geochronological and geochemical research further gold mineralization is proposed to be generated by deep sourced magmatic or metamorphic fluid migrated upward along the Woxi fault, and the iron-rich Madiyi Formation is the idea chemical trap for gold deposition. The decrease of sulfur contents caused by fluid-rock interactions and fluid boiling are the major mechanisms for gold mineralization.

Structural deformation, metallogenic epoch and genetic mechanism of the Woxi Au-Sb-W deposit, Western Hunan Province, South China

The remobilization,migration,precipitation,and enrichment of ore-forming elements are closely related to structures.Therefore,detailed regional and ore-field structural analyses are critical for determining the genesis of a mineral deposit.The Jiangnan Orogenic Belt(JOB)is an important gold polymetallic metallogenic belt in South China,which is characterized by multiple periods of gold mineralization in the Paleozoic and Mesozoic.However,the genesis of these gold polymetallic deposits is still not well understood due to a lack of systematic research on the regional geology,ore-controlling structures and metallogenic mechanism.In this study,a detailed structural survey at the surface and in the subsurface tunnels was conducted on the Woxi Au-Sb-W deposit,the genesis of which is relatively controversial among the gold polymetallic deposits in the JOB due to poor structural constraints.In addition,a wolframite U-Pb dating was carried out to further constrain the relationship between structures and mineralization.Based on the results of these studies,together with those from previous studies,it is proposed that the Woxi deposit and surrounding areas likely underwent six periods of regional deformation,which are constrained in time and geodynamic setting.Furthermore,we present a systematic discussion on the roles of ore-controlling structures in the transportation,distribution,and deposition of ore-forming elements and localization of orebodies.According to the wolframite dating results,structural analyses,and previous data,we propose that the Woxi Au-Sb-W deposit was formed in two stages during the Yanshanian:a W(wolframite)-Au mineralization stage at ca.140 Ma and an Au-Sb-W(scheelite)mineralization stage at<130 Ma.These mineralizing events are interpreted to have a tight relationship with tectonic reactivation,and the ore-forming fluids were derived from deep sources,including those of magmatic or metamorphic origins.The Woxi deposit can therefore be classified as an“intracontinental reactivation-type”,and the mineralization is related to lithospheric extension caused by plate retreat,retention,and delamination following the cessation of westward subduction of the Paleo-Pacific Plate beneath the East Asian continent.

Mass Transfer during Hematitization and Implications for Uranium Mineralization in the Zoujiashan Deposit,Xiangshan Volcanic Basin

The Zoujiashan uranium deposit in the Xiangshan ore field is the largest volcanic-related uranium deposit in China.Hematite-and fluorite-type ores are the predominant mineralization styles.Hematitization in the Xiangshan ore field is closely associated with uranium mineralization,mainly occurring as hematitized rocks enclosing fluorite-type vein ores developed in pre-ore illitized porphyritic lava.Detailed petrographic and mass balance calculation studies were conducted to evaluate the mechanisms for uranium precipitation and mass transfer during hematitization.Petrographic observations suggest that in the hematitized rocks,orthoclase is more altered than plagioclase,and quartz dissolution is common,whereas in the illitized rocks,pyrite commonly occurs within the altered biotite grains,and chlorite grains are locally found.Mass balance calculations indicate that Na2O and U were gained,K2O,Ca O and Si O2were lost,whereas Fe2O3-t remained more or less constant during hematitization.These observations suggest that the hydrothermal fluids were Na-and U-rich and Ca-K-poor,and the Fe2+used for hematitization was locally derived,most likely from biotite,pyrite and chlorite in the host rocks.The Fe2+is inferred to have played the role of reductant to precipitate uranium,and calculation indicates that oxidation of Fe2+provided by host rocks is sufficient to form ores of economic significance.Consequently,the hematite-type ore is interpreted to be generated by the reaction between oxidized ore fluids and reduced components in host rocks.The development of calcite and pyrite in the fluorite ores suggests that perhaps mixing between the U-rich fluid and another fluid carrying reduced sulfur and carbon may have also contributed to uranium mineralization,in addition to temperature and pressure drop associated with the veining.

Climate extremes,variability,and trade shape biogeographical patterns of alien species

Understanding how alien species assemble is crucial for predicting changes to community structure caused by biological invasions and for directing management strategies for alien species,but patterns and drivers of alien species assemblages remain poorly understood relative to native species.Climate has been suggested as a crucial filter of invasion-driven homogenization of biodiversity.However,it remains unclear which climatic factors drive the assemblage of alien species.Here,we compiled global data at both grid scale(2,653 native and 2,806 current grids with a resolution of 2°x 2°)and administrative scale(271 native and 297 current nations and sub-nations)on the distributions of 361 alien amphibians and reptiles(herpetofauna),the most threatened vertebrate group on the planet.We found that geographical distance,proxy for natural dispersal barriers,was the dominant variable contributing to alien herpetofaunal assemblage in native ranges.In contrast,climatic factors explained more unique variation in alien herpetofaunal assemblage after than before invasions.This pattern was driven by extremely high temperatures and precipitation seasonality,2 hallmarks of global climate change,and bilateral trade which can account for the alien assemblage after invasions.Our results indicated that human-assisted species introductions combined with climate change may accelerate the reorganization of global species distributions.