Enhancing Geological Understanding and Identifying Gold Anomalies in the Ailaoshan Orogen

The Ailaoshan Orogen in the southeastern Tibet Plateau,situated between the Yangtze and Simao blocks,underwent a complex structural,magmatic,and metamorphic evolution resulting in different tectonic subzones with varying structural lineaments and elemental concentrations.These elements can conceal or reduce anomalies due to the mutual effect between different anomaly areas.Dividing the whole zone into subzones based on tectonic settings,ore cluster areas,or sample catchment basins(Scb),geochemical and structural anomalies associated with gold(Au)mineralization have been identified utilizing mean plus twice standard deviations(Mean+2STD),factor analysis(FA),concentration-area(CA)modeling of stream sediment geochemical data,and lineament density in both the Ailaoshan Orogen and the individual subzones.The FA in the divided 98 Scbs with 6 Scbs containing Au deposits can roughly ascertain unknown rock types,identify specific element associations of known rocks and discern the porphyry or skarn-type Au mineralization.Compared with methods of Mean+2STD and C-A model of data in the whole orogen,which mistake the anomalies as background or act the background as anomalies,the combined methods of FA and C-A in the separate subzones or Scbs works well in regional metallogenic potential analysis.Mapping of lineament densities with a 10-km circle diameter is not suitable to locate Au deposits because of the delineated large areas of medium-high lineament density.In contrast,the use of circle diameters of 1.3 km or 1.7 km in the ore cluster scale delineates areas with a higher concentration of lineament density,consistent with the locations of known Au deposits.By analyzing the map of faults and Au anomalies,two potential prospecting targets,Scbs 1 and 63 with a sandstone as a potential host rock for Au,have been identified in the Ailaoshan Orogen.The use of combined methods in the divided subzones proved to be more effective in improving geological understanding and identifying mineralization anomalies associated with Au,rather than analyzing the entire large area.

Discovery of scheelite in the Zaozigou gold deposit of West Qinling Orogen,Northwest China and its implications for ore genesis

1.Objective The West Qinling Orogen extends east-west over 1500 km and is endowed with dozens of large-super large scale gold deposits.The Zaozigou gold deposit has a proven reserve of 134 t with an average grade of 3.08 g/t thus is one of the largest deposits in the West Qinling Orogen.However,whether the fluid type is metamorphic or magmatichydrothermal and ore-formation processes of the Zaozigou gold deposit are equivocal.Scheelite is a ubiquitous accessory mineral in geologically diverse ore-deposit types and attested to be a strong indicator of ore-forming conditions and oredeposit genesis.

Geology and mineralization of the Bayan Obo supergiant carbonatite-type REE-Nb-Fe deposit in Inner Mongolia, China: A review

The Bayan Obo supergiant carbonatite-related rare-earth-element-niobium-iron(REE-Nb-Fe) endogenetic deposit(thereafter as the Bayan Obo deposit), located at 150 km north of Baotou City in the Inner Mongolia Autonomous Region, is the largest rare-earth element(REE) resource in the world. Tectonically,this deposit is situated on the northern margin of the North China Craton and adjacent to the Xing’anMongolian orogenic belt to the south. The main strata within the mining area include the Neoarchean Se’ertengshan Group and the Mesoproterozoic Bayan Obo Group. Generally, the rare earth, niobium, and iron mineralization within the deposit are intrinsically related to the dolomite carbonatites and the extensive alteration of the country rocks caused by the carbonatite magma intrusion. The alteration of country rocks can be categorized into three types: contact metasomatism(anti-skarn and skarn alteration), fenitization,and hornfelsic alternation. As indicated by previous studies and summarized in this review, the multielement mineralization at Bayan Obo is closely associated with the metasomatic replacement of siliceous country rocks by carbonatite magmatic-hydrothermal fluids. The metasomatic process is comparable to the conventional skarnification that formed due to the intrusion of intermediate-acid magmatic rocks into limestone strata. However, the migration pattern of Si O2, Ca O, and Mg O in this novel metasomatic process is opposite to the skarn alteration. Accordingly, this review delineates, for the first time, an antiskarn metallogenic model for the Bayan Obo deposit, revealing the enigmatic relationship between the carbonatite magmatic-hydrothermal processes and the related iron and rare earth mineralization.Moreover, this study also contributes to a better understanding of the REE-Nd-Fe metallogenetic processes and the related fluorite mineralization at the Bayan Obo deposit.

Spatial-Temporal Distribution, Geological Characteristics and Ore-Formation Controlling Factors of Major Types of Rare Metal Mineral Deposits in China

Rare metals including Lithium(Li),Beryllium(Be),Rubidium(Rb),Cesium(Cs),Zirconium(Zr),Hafnium(Hf),Niobium(Nb),Tantalum(Ta),Tungsten(W)and Tin(Sn)are important critical mineral resources.In China,rare metal mineral deposits are spatially distributed mainly in the Altay and Southern Great Xingán Range regions in the Central Asian orogenic belt;in the Middle Qilian,South Qinling and East Qinling mountains regions in the Qilian-Qinling-Dabie orogenic belt;in the Western Sichuan and Bailongshan-Dahongliutan regions in the Kunlun-Songpan-Garze orogenic belt,and in the Northeastern Jiangxi,Northwestern Jiangxi,and Southern Hunan regions in South China.Major ore-forming epochs include Indosinian(mostly 200-240 Ma,in particular in western China)and the Yanshanian(mostly 120-160 Ma,in particular in South China).In addition,Bayan Obo,Inner Mongolia,northeastern China,with a complex formation history,hosts the largest REE and Nb deposits in China.There are six major rare metal mineral deposit types in China:Highly fractionated granite;Pegmatite;Alkaline granite;Carbonatite and alkaline rock;Volcanic;and Hydrothermal types.Two further types,namely the Leptynite type and Breccia pipe type,have recently been discovered in China,and are represented by the Yushishan Nb-Ta-(Zr-Hf-REE)and the Weilasituo Li-Rb-Sn-W-Zn-Pb deposits.Several most important controlling factors for rare metal mineral deposits are discussed,including geochemical behaviors and sources of the rare metals,highly evolved magmatic fractionation,and structural controls such as the metamorphic core complex setting,with a revised conceptual model for the latter.

Introduction of China's REE Deposits from Deposit Types and Geological Characteristics for Mineral Prospectivity Analysis

Thirty-six typical REE deposits extracted from literatures,mineral resource database or reports,which are served as a basis for classifying deposit type.And then the five principal deposit types were identified:(1)alkali-related type;(2)Ion-adsorbed type;(3)metamorphosed sedimentary type;(4)placer type;(5)sedimentary phosphate type.Data gathered for each deposit includes the deposit scale,geologic settings,main metallogenic ages,main and accessory minerals,and ore-bearing intrusions.

3D geological modeling for mineral resource assessment of the Tongshan Cu deposit,Heilongjiang Province,China

Three-dimensional geological modeling （3DGM） assists geologists to quantitatively study in three-dimensional （3D） space structures that define temporal and spatial relationships between geological objects. The 3D property model can also be used to infer or deduce causes of geological objects. 3DGM technology provides technical support for extraction of diverse geoscience information, 3D modeling, and quantitative calculation of mineral resources. Based on metallogenic concepts and an ore deposit model, 3DGM technology is applied to analyze geological characteristics of the Tongshan Cu deposit in order to define a metallogenic model and develop a virtual borehole technology; a BP neural network and a 3D interpolation technique were combined to integrate multiple geoscience information in a 3D environment. The results indicate： （1） on basis of the concept of magmatic-hydrothermal Cu polymetallic mineraliza- tion and a porphyry Cu deposit model, a spatial relational database of multiple geoscience information for mineralization in the study area （geology, geophysics, geochemistry, borehole, and cross-section data） was established, and 3D metallogenic geological objects including mineralization stratum, granodiorite, alteration rock, and magnetic anomaly were constructed; （2） on basis of the 3D ore deposit model, 23,800 effective surveys from 94 boreholes and 21 sections were applied to establish 3D orebody models with a kriging interpolation method; （3） combined 23,800 surveys involving 21 sections, using VC＋＋ and OpenGL platform, virtual borehole and virtual section with BP network, and an improved inverse distance interpolation （IDW） method were used to predict and delineate mineralization potential targets （Cu-grade of cell not less than 0.1%）; （4） comparison of 3D ore bodies, metallogenic geological objects of mineralization, and potential targets of mineralization models in the study area, delineated the 3D spatial and temporal relationship and causal processes among the ore bodies, alteration rock, metallo- genic stratum, intrusive rock, and the Tongshan Fault. This study provides important technical support and a scientific basis for assessment of the Tongshan Cu deposit and surrounding exploration and mineral resources.

A review of mineral systems and associated tectonic settings of northern Xinjiang,NW China

In this paper we present a review of mineral systems in northern Xinjiang, NW China, focussing on the Tianshan, West and East Junggar and Altay orogenic belts, all of which are part of the greater Central Asian Orogenic Belt （CAOB）. The CAOB is a complex collage of ancient microcontinents, island arcs, oceanic plateaux and oceanic plates, which were amalgamated and accreted in Early Palaeozoic to Early Permian times. The establishment of the CAOB collage was followed by strike-slip movements and affected by intraplate magmatism, linked to mantle plume activity, best exemplified by the 250 Ma Siberian Traps and the 280 Ma Tarim event. In northern Xinjiang, there ale numerous and economically important mineral systems. In this contribution we describe a selection of representative mineral deposits, including subduction-related porphyry and epithermal deposits, volcanogenic massive sulphides and skarn systems. Shear zone-hosted Au lodes may have first formed as intrusion-related and subsequently re-worked during strike-slip deformation. Intraplate magmatism led to the emplacement of concentrically zoned （Alaskan-style） mafic-ultramafic intrusions, many of which host orthomagmatic sulphide deposits. A huge belt of pegmatites in the Altay orogen, locally hosts world-class rare metal deposits. Roll-front,

Diagenetic and Mineralization Age of the Hehuaping Tin-polymetallic Orefield,Hunan Province

The Hehuaping tin deposit is a large deposit found in recent years during geological surveys. The discovered tin deposit includes not only rock-alteration type deposits in fault zones, but also deposits developed in interstratified rupture zones between Devonian carbonate rocks （Qiziqiao Formation） and sandstone （Tiaomajian Formation）. The finding of tin deposits of the latter type has greatly enriched tin-mineralization types in the famous Nanling polymetallic metallogenetic region and may provide us with a new potential orientation for prospecting of tin deposits in the region. It is commonly believed that the forming of the tin deposits in the Nanling region should be related to the Yanshanian instead of Indosinian granitic magmatism. Systematical zircon U-Pb SHRIMP dating in this paper shows that tin mineralizations have endured at least two stages. The early stage should be related to the intrusion of the main body of the Wangxianling granite, which was emplaced during the Indosinian period with a diagenetic and minerafized age of 224.0±1.9 Ma （MSWD=0.54）, and the late stage should be related to the intrusion of Yanshaulan granitic porphyry that took place after 142±3 Ma （MSWD=0.5）.

Coupling Effects on Gold Mineralization of Deep and Shallow Structures in the Northwestern Jiaodong Peninsula, Eastern China

For understanding the possible deep-seated processes and geodynamic constrains on gold mineralization, comprehensive physicochemical and geochemical studies of gold mineralization have been undertaken within the paleo-lithosphere framework during the metailogenic epoch from the northwestern part of the Jiaodong Peninsula in this paper. A general image of the paleo-crust has been remained although it has been superimposed and reformed by post-metailogenic tectonic movements. The gold ore deposits occur usually in local uplifts and gradient belts featuring a turn from steep to gentle in granite-metamorphic contact zones, relative uplifts of gradient zones of the Curier isothermal interfaces, depressions of the Moho discontinuity and areas where depth contours are cut by isotherms perpendicularly. Gold mineralization and lithogenesis are characterized by high temperature, low pressure and high strength of thermal flux. The depth of mineralization ranges from 0.8 to 4.5 km. The depth of the top interface of the granitic complex in the metallogenic epoch is about 3 km. There is a low-velocity layer （LVL） at the bottom of the upper crust with a depth close to 19.5 km, which may be a detachment belt in the crust. The appearance of the LVL indicates the existence of paleo-hyperthermal fluid or relics of molten magma chambers, which reflects partial melting within the crust during the diagenetic and metallogenic epochs and the superposition effects of strike-slip shearing of the Taulu fault zone. The subsidence of the Moho is probably attributed to the coupling process of the NW-SE continental collision between North China and the Yangtze Block and the strike-slip movement of the Tanlu fault accompanied with underplating of mantle magma in the northwestern part of the Jiaodong Peninsula. The underplating of mantle magma may result in partial melting and make granite magma transfer upwards. This is favorable for the migration of metallogenic materials from deep to shallow to be enriched to form deposits. Coupling interactions between the strike-slip of the Taulu fault, the underplating of mantle magma, partial melting within the crust, and hyperthermal fluid, etc. may be the important factors controlling the gold mineralization and spatial structures in the metailogenic system.

Effects of hydrocarbon generation on fluid flow in the Ordos Basin and its relationship to uranium mineralization

The Ordos Basin of North China is not only an important uranium mineralization province, but also a major producer of oil, gas and coal in China. The genetic relationship between uranium mineralization and hydrocarbons has been recognized by a number of previous studies, but it has not been well understood in terms of the hydrodynamics of basin fluid flow. We have demonstrated in a previous study that the preferential localization of Cretaceous uranium mineralization in the upper part of the Ordos Jurassic section may have been related to the interface between an upward flowing, reducing fluid and a downward flowing, oxidizing fluid. This interface may have been controlled by the interplay between fluid overpressure related to disequilibrium sediment compaction and which drove the upward flow, and topographic relief, which drove the downward flow. In this study, we carried out numerical modeling for the contribution of oil and gas generation to the development of fluid overpressure, in addition to sedi- ment compaction and heating. Our results indicate that when hydrocarbon generation is taken into account, fluid overpressure during the Cretaceous was more than doubled in comparison with the simu- lation when hydrocarbon generation was not considered. Furthermore, fluid overpressure dissipation at the end of sedimentation slowed down relative to the no-hydrocarbon generation case. These results suggest that hydrocarbon generation may have played an important role in uranium mineralization, not only in providing reducing agents required for the mineralization, but also in contributing to the driving force to maintain the upward flow.

Geochemical Characteristics and Geological Significance of Early Permian Baya'ertuhushuo Gabbro in South Great Xing'an Range

Field geological investigation and geochemical analysis are carried out on Baya＇ertuhushuo Gabbro in South Great Xing＇an Range. Field investigation reveals that the gabbro is a magmatic intrusion rather than a component of an ophiolite suite as previously thought. Zircon laser ablation inductively coupled plasma mass spectroscopy （LA-ICP-MS） U-Pb dating indicates the gabbro was formed in 274-275 Ma, just as the widespread volcanic rocks of Dashizhai Formation （P1d）, monzogranites and miarolitic alkali-feldspar granites in the study area. The gabbro has SiO2 content between 47.23 wt% and 50.17 wt%, high MgO and FeOT contents of 6.95-11.29 wt% and 7.32- 12.24wt%, respectively, and it belongs to low-K tholeiitic series in the SiO2-K2O diagram. The Chondrite-normalized rare earth element （REE） patterns and primitive mantle-normalized spider diagrams of the gabbro are similar to those of Normal Mid-Ocean Ridge Basalt （N-MORB） except for the enrichment of large ion lithophfle elements （LILE）, such as Rb, Ba and K. In trace element tectonic discriminative diagrams, the samples are mainly plotted in the N-MORB field, and Zircon in situ Lu-Hf isotopic analysis also indicates the gabbro originated from depleted mantle. Through synthetic studies of the geochemical characteristics and petrogenesis of Baya＇ertuhushuo gabbro, volcanic rocks of Dashizhai Formation and granitoids in the area, it is suggested that the early Permian magmatism in the Xilinhot-Xiwuqi area formed in the tectonic setting of asthenosphere upwelling, which was caused by breaking-off of the subducted Paleo-Asian Ocean slab.

Alteration and mineralization styles of the orogenic disseminated Zhenyuan gold deposit, southeastern Tibet: Contrast with carlin gold deposit

Orogenic disseminated and Carlin gold deposits share much similarity in alteration and mineralization.The disseminated orogenic Zhenyuan Au deposit along the Ailaoshan shear zone,southeastern Tibet,was selected to clarify their difference.The alteration and mineralization from the different lithologies,including meta-quartz sandstone,carbonaceous slate,meta-(ultra)mafic rock,quartz porphyry and lamprophyre were researched.According to the mineral assemblage and replacement relationship in all types of host rocks,two reactions show general control on gold deposition:(1) replacement of earlier magnetite by pyrite and carbonaceous material;(2) alteration of biotite and phlogopite phenocrysts in quartz porphyry and lamprophyre into dolomite/ankerite and sericite.Despite the lamprophyre is volumetrically minor and much less fractured than other host rocks,it contains a large portion of Au reserve,indicating that the chemically active lithology has played a more important role in gold precipitation compared to structure.LA-ICP-MS analysis shows that Au mainly occurs as invisible gold in fine-grained pyrite disseminated in the host rocks,with Au content reaching to 258.95 ppm.The diagenetic core of pyrite in meta-quartz sandstone enriched in Co,Ni,Mo,Ag and Hg is wrapped by hydrothermal pyrite enriched in Cu,As,Sb,Au,Tl,Pb and Bi.Different host rock lithology has much impact on the alteration and mineralization features.Carbonate and sericite in altered lamprophyre show they have higher Mg than those developed in other of host rocks denoting that the carbonate and sericite incorporated Mg from phlogopite phenocrysts in the primary lamprophyre during alteration.The ore fluid activated the diagenetic pyrite in meta-quartz sandstone leading the hydrothermal pyrite enriched in Cu,Mo,Ag,Sb,Te,Hg,Tl,Pb and Bi,but the hydrothermal pyrite in meta-(ultra)mafic rock is enriched in Co and Ni as the meta-(ultra)mafic rock host rock contain high content of Co and Ni.However,Au and As shear similar range in both types of host rocks indicating that these two elements most likely come from the deep source fluid rather than the host rocks.It was shown in the disseminated orogenic gold deposit that similar hydrothermal alteration with mineral assemblage of carbonate (mainly dolomite and ankerite),sericite,pyrite and arsenopyrite develops in all types of host rocks.This is different from the Nevada Carlin type,in which alteration is mainly dissolution and silicification of carbonate host rock.On the other hand,Au mainly occur as invisible gold in both disseminated orogenic and Carlin gold deposits.

New Zircon U-Pb Geochronology of the Post-kinematic Granitic Plutons in the Diancang Shan Metamorphic Massif along the Ailao Shan-Red River Shear Zone and Its Geological Implications

The Ailao Shan-Red River fault zone is the boundary between the Yangtze block to the northeast and the Indochina block to the southwest.It is an important tectonic zone due to its role in the southeastward extrusion of the Indochina block during and subsequent to the Indian-Eurasian collision.Diancang Shan（DCS） high-grade metamorphic complex,located at the northwest extension along the Ailao Shan-Red River（ASRR） shear zone,is a representative metamorphic complex of the ASRR tectonic belt.Structural and microstructural analysis of sheared rocks in the high-grade metamorphic rocks reveals that they are coherent with solid-state high-temperature ductile deformation,which is attributed to left-lateral shearing along the ASRR shear zone.New LA-ICP-MS zircon U-Pb geochronological and microstructural studies of the post-kinematic granitic plutons provide a straightforward time constraint on the termination ductile left-lateral shearing and exhumation of the metamorphic massif in the ASRR shear zone.It is suggested that the left-lateral shearing along the ASRR shear zone ended at ca.21 Ma at relative lower-temperature or decreasing temperature conditions.During or after the emplacement of the young dikes at ca.21 Ma,rapid brittle deformation event occurred,which makes the DCS massif start fast uplift/exhumation and cooling to a shallow crustal level.

Singularity theories and methods for characterizing mineralization processes and mapping geo-anomalies for mineral deposit prediction

In this paper, we show that geo-anomalies can be delineated for mineral deposit prediction according to singularity theories developed to characterize nonlinear mineralization processes. Associ- ating singularity and geo-anomalies makes it possible to quantitatively study geo-anomalies with modern nonlinear theories and methods. This paper introduces a newly developed singularity analysis of nonlinear mineralization processes and nonlinear methods for characterizing and mapping geo-anomalies for mineral deposit prediction. Mineral deposits, as the products of singular mineralization processes caused by geo-anomalies, can be characterized by means of fractal or multifractal models. It has been shown that singularity can characterize the degree of geo-abnormality, and this has been demonstrated to be useful for mapping anomalies of undiscovered mineral deposits. The study of mineralization and mineral deposits from a nonlinear process point of view is a new but promising research direction. This study emphasizes the relationships between geo-anomalies and singularity, including singular processes resulting in singularity and geo-anomalies, the characterization of singularity and geo-anomalies and the identification of geo-anomalies for mineral deposit prediction. The concepts and methods are demon- strated using a case study of Sn mineral deposit prediction in the Gejiu mineral district in Yunnan, China.

Origin and Geological Significance of TTG Gneisses from the Maevatanana Greenstone Belt in North-Central Madagascar,and A Comparison with India

The Maevatanana greenstone belt in north-central Madagascar contains widespread exposures of tonalite-trondhjemite-granodiorite （TTG） gneisses, and is important for its concentrations of various metal deposits （e.g., chromium, niekle, iron, gold）. In this paper we report on the petrography, and major and trace element compositions of the TTG gneisses within the Berere Complex of the Maevatanana area, as well as LA-ICP-MS U-Pb ages and Lu-Hf isotopic compositions of zircons from the gneisses. The gneisses consist mainly of granitoid gneiss and biotite （± hornblende） plagiogneiss, and analysis of thin sections provides evidence of crushing, recrystallization, and metasomatism related to dynamic metamorphism. Samples have large variations in their major and trace element contents, with SiO2 = 55.87-68.06 wt%, Al2O3 = 13.9-17.8 wt%, and Na2O/K2O= 0.97-2.13. Geochemically, the granitoid gneisses and biotite plagiogneisses fall on a low-Al trondhjemite to granodiorite trend, while the biotite-hornblende plagiogneisses represent a high-Al tonalite TTG assemblage. Zircon U-Pb dating shows that the Berere Complex TTG gneisses formed at 2.5-2.4 Ga. Most εHf（t） values of zircons from the biotite （q- hornblende） plagiogneisses are positive, while most εHf（t） values from the granitoid gneisses are negative, suggesting a degree of crustal contamination. Two-stage Hf model ages suggest that the age of the protolith of the TTG gneisses was ca. 3.4-2.6 Ga, representing a period of paleocontinent formation in the Mesoarchean. Geothermometries indicate the temperature of metamorphism of the TTG gneisses was 522-612℃. Based on these data, the protolith of the TTG gneisses is inferred to have formed during the development of a Mesoarchean paleocontinent that is now widely exposed as a TTG gneiss belt （mostly lower amphibolite facies） in the Maevatanana area, and which records a geological evolution related to the subduction of an ancient oceanic crust and the collision of microcontinents during the formation of the Rodinia supercontinent. The lithological similarity of Precambrian basement, the close ages of metamorphism within greenstone belts and the comparable distribution of metamorphic grade all show a pronounced Precambrian geology similarity between Madagascar and India, which can provide significative clues in understanding the possible Precambrian Supercontinent tectonics, and also important constraints on the correlation of the two continental fragments.

Diversity of Mineralization and Spectrum of the Gejiu Superlarge Tin-Copper Polymetallic Deposit,Yunnan,China

The Gejiu （个旧） deposit is a superlarge tin-copper polymetallic ore-forming concentration area characterized by excellent metallogenic geological settings and advantageous ore-controlling factors. The deposit displays diverse mineralization properties due to different minerals and mineral deposit types. Based on the principal metallogenic factors, metallogenic mechanisms, mineralized components, and occurrence of mineral deposits or ore bodies, the Gejiu mineral district can be divided into 2 combinations of metallogenic series, 4 metallogenic series, 8 subseries, and 27 mineral deposit types. Spatial zonality is evident. The distribution regularity of the elements in both plane and section is Be-W, Sn （Cu, Mo, Bi, Be）-Sn, Pb, Ag-Pb, Zn around a granitic intrusion. The metallogenic epoch is mainly concentrated in the late Yanshanian. During this period, large-scale metallogenic processes related to movement caused by tectonics and magmatism occurred, and a series of magmatic hydrothermal deposits formed. The ore-forming processes can be divided into 4 stages： the silicate stage, the oxide stage, the sulphide stage, and the carbonate stage. Based on the orderliness and diversity （in terms of time, space, and genesis） of the mineralization, the authors have developed a comprehensive spectrum of ore deposits in the Gejiu area. This newly proposed diversity of mineralization and the spectrum developed in this work are useful not only for interpreting the genesis of the Gejiu deposit but also for improving mineral exploration in the area, and in particular, for finding large deposits.

Geochronology and geochemistry of the Donglufang porphyry-skarn Mo-Cu deposit in the southern Yidun Terrane and their geological significances

The newly-discovered Donglufang Moe Cu porphyry-skarn deposit is located in the southern Yidun Terrane, southeast Tibet, with more than 80 million tonnes(Mt) of reserves(grading 0.15 wt.% Mo and0.48 wt.% Cu) hosted in Triassic strata and Late Cretaceous granodiorite porphyry. Ree Os dating of molybdenum ore yielded a weighted mean age of 84.9 ± 1.0 Ma and an isochron age of 85.2 ± 0.6 Ma.LA-ICP-MS Ue Pb dating of zircons from the granodiorite porphyry yielded206 Pb/238 U ages ranging from 87.4 Ma to 84.2 Ma with a weighted mean206 Pb/238 U age of 85.1 ±0.5 Ma, indicating a temporal linkage between granitic magmatism and Moe Cu mineralization. Geochemical analyses show that the granodiorite porphyries are I-type granites with Si O_2 contents of 64.3 -66.7 wt.%. These rocks are typically metaluminous with high K_2 O/Na_2 O ratios, low Mg O(1.32 -1.56 wt.%), Cr(5.6 -12.9 ppm), Ni(3.79 -10.81 ppm), Mg#(43 -52) values, and high Sr(304 -844 ppm), Sr/Y(21.2 -50.8) and La/Yb ratios(37.0 -60.1). They are enriched in light rare-earth elements(LREE) relative to heavy rare-earth elements(HREE), with slightly negative Eu anomalies, and are enriched in Th, U and large ion lithophile elements(LILE, e.g., K and Rb), and depleted in high field strength elements(HFSE, e.g., Nb, Ta, P and Ti). They also show negative zircon εHf(t) values(-6.7 to -2.3) and negative whole rock εNd(t) values(à5.2 to-4.3), as well as old Hfe Nd model ages, indicating the magmas were derived from a thickened ancient lower crust within the garneteamphibolite facies. Considering the tectonic evolution of the Yidun Terrane, geochemical characteristics of granodiorite porphyry, and the ages of mineralization obtained in this study. We suggest that the Donglufang deposit was formed in a post-collisional setting, which has a genetic relationship with the emplacement of the granodiorite porphyry. The present study provide key information for the exploration of the Late Cretaceous metallogeny in the Yidun Terrane.

Laser Ablation ICP-MS U-Pb Zircon Geochronology of Granitoids and Quartz Veins in the Shihu Gold Mine, Taihang Orogen, North China: Timing of Gold-mineralization and Tectonic Implications

The Shihu gold deposit, situated in the Taihang Mesozoic orogen of the North China Craton （NCC）, is hosted by ductile-brittle faults within Archean metamorphic core complex. The deposit is characterized by gold-bearing quartz-polymetallic sulfides veins. The Mapeng granitoids stock and intermediate-basic dikes intruded the metamorphic basement rocks, and are spatially related to gold mineralization. Detailed laser ablation inductively coupled plasma mass spectrometry （LA ICP-MS） U-Pb zircon ages of the granitic rocks, dykes and mineralized quartz veins in the studied area reveal its magmatic and mineralized history. The mineralized quartz veins contain inherited zircons with ages of about 2.55 Ga and 1.84 Ga, probably coming from the basement. These two Precambrian events are coeval with those in other parts of the NCC. The Mapeng granitoid stock, the largest intrusion in the area, was emplaced at ca. 130 Ma, and is coeval with magmatic zircon populations from diorites and quartz diorite pophyrites in the same region. The ca. 130 Ma magmatism and gold mineralization were most likely related to an underplating event that took place in the Taihang orogen at Late Mesozoic. The timing of gold mineralization with respect to felsic magmatism in the area is similar to those observed in other major gold-producing provinces in the NCC. This episode is simultaneous with those in the eastern margin of NCC, indicative of a widespread late Yanshanian metallogenic event that was a response to the Early Cretaceous lithosphere in the eastern NCC, in which the mesothermal gold deposits were formed from similar tectono-magmatic environments.

Metallogenic‘factories’and resultant highly anomalous mineral endowment on the craton margins of China

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.

GIS-Based (W^+-W^-) Weight of Evidence Model and Its Application to Gold Resources Assessment in Abitibi ,Canada

The weight of evidence （WofE） model has been widely used for mineral potential mapping. During the conversion of a multiclass map into a binary map a lot of mineralization information is artificially added or lost because the generalization of the class within the cumulative distance interval to a linear feature is based on a maximum contrast, which matches a cumulative distance interval. Additionally, some categorical data evidence cannot be generated by this method because a maximum contrast does not exist. In this article, an alternative （W^＋ -W^- ）-based WofE model is proposed. In this model, the ＂（W^＋ -W^- ） greater than zero or not＂ is used as a criterion to reclassify the corresponding categorical class into a presence or absence class to convert a multielass map into a binary map. This model can be applied to both categorical data and successive data. The latter can be operated as categorical data. The Wt and W^- of the generated binary maps can be recalculated, and several binary maps can be integrated on the condition that the reclassified binary evidences are conditionally independent of each other. This method effectively reduces artificial data and both nominal and categorical data can be operated. A ease study of gold potential mapping in the Abitibi area, Ontario, Canada, shows that the gold potential map by the （W^＋ -W^- ） model displays a smaller potential area but a higher posterior probability （POP）, whereas the potential map by the traditional （W^＋ - W^- ） model exhibits a larger potential area but a lower POP.