Strate—bound Anorthites in the Dachang Sn—Polymetallic Ore Field,Guangxi,China

From the petrological study of ore-hosting focks which contain large anorthits crystals and the occurrence and chemical composition of anorthites and related minerals,the authors consider that the large anorthite crystals are of authigenic origin. The distribution characteristics of anorthites,i.e.,they are distributed along the bedding and structurally weak zones but not restricted to synsedimentary slump structures,and the relationship for some elements between anorthites and other minerals indicate that anorthites have resulted from reaction of circulating alkaline solutions rich in Al and Si with carbonated during the Indosinian orogeny.The results of this work suggest that the association of authigenic anorthites with bedded orebodies in the Dachang ore field may be the evidence that the mineralization is related to circulating underground hot waters.     

Mineralization Zoning in Yindongzi—Daxigou Barite—Siderite,Silver—Polymetallic Deposits in the Qinling Orogen,China

The Yindongzi-Daxigou strata-bound barite-siderite,silver-polymetallic deposits discovered in the Qinling orogen are hosted within flysch facies in a deep-water fault-controlled basin on the passive northern margin of the Qinling microplate.The orebodies occur in a series of hydrothermal depositonal rocks.Mineralization zoning is characterized by Fe-Ba←Ba-Cu←Pb-Ab→Cu-Ag→Pb→Au.This is obviously a gradational transition mineralization from ventproximal mineralization to more distal mineralization.In this gradational transition between Chefanggou and Yindongzi,vent-proximal mineralization consists of silver-polymetallic orebodies(Pb-Ag),which is the center of hydrothermal mineralization.The Chefanggou Ba-Cu ore district in the west and the Yindongzi Cu-Ag ore district in the east represent vent lateral mineralization.Distal mineralization in the west is represented by the Daxigou Fe-Ba ore district while distal mineralization in te east is represented by the Pb ore district.Thick massive,laminated barren albite chert and jasperite,sometimes with minor silver-ploymetallic mineralization of commercial importance,and pyritization in rocks feature more distal mineralization.Geochemical anomalies of Au-As associations are found in ankerite phyllite and muddy sandstone.Actually,Au deposits are dominantly controlled by the late brittle-ductile shear zone.     

Application of Lead Isotopes to Geochemical Exploration of Gold Deposits in Baoban , Hainan Province, China

Lead isotopes have been widely applied in geochemical exploration and evaluation of ore deposits, as well as in ascertaining the age of mineralization and the source of ore fluids.Long-term practice showed that the method of lead isotope targeting is somewhat efficient for macroscopic evaluation of forecasting areas, but not powerful enough for for ecasting concealed orebodies. As the contents of U and the variation of U/Pb ratio sharply decrease with depth in the lithosphere, U-Th-Pb isotopic differentiation must have occurred during the crust-mantle e-volution. Lead isotopic ratios show a wide variation range, varying in the front of mineralizationand shallow-derived ores, but maintaining very stable in the major orebody and being usuallyclose to the average isotopic composition of the crust and mantle of the continent block fromwhich the ores were derived. Therefore, the lead isotopic composition can serve as a measure for identifying the position of mineralization. The lead isotope geochemistry was applied to the ex-ploration and evaluation of the Baoban gold deposits of Hainan Province, China. The an alyticalresults of ore veins and adjacent rocks showed that there is a correlation between the lead isotopedata and the position of orebody. Based on the experience from the Baoban gold deposits and other ore deposits in Yunnan Province, an exploration principle has been established, that is,positive anomalies of lead isotope eigenvectors for prospecting deep-seated orebodies and nega-tive anomalies of eigenvectors for enlarging lateral exploration surrounding the known deposit.The ore beds in the Erjia and Beiniu mining districts should be as signed to the deep part of the orebody and those in the Tuwaishan mining district should be the shallow part, so ore beds cor-responding to those in the Erjia and Beiniu mining districts may be found in the Tuwaishan min-ing district.     

Geochemistry of meta-volcanic rocks from the Longbohe Cu deposit, Yunnan Province, China： Implications for the genesis and tectonic setting

The Longbohe Cu deposit, which is located in the southern part of the Honghe ore-forming zone, Yunnan Province, China, belongs to a typical ore field where volcanic rocks are of wide distribution and are associated with Cu mineralization in time and space. The volcanic rocks in the ore field, which have experienced varying degree of alteration or regional metamorphism, can be divided into three types, i.e., meta-andesite, meta-subvolcanic rock and meta-basic volcanic rock in accordance with their mineral assemblages. These three types of volcanic rocks in the ore field are relatively rich in Na and the main samples plot in the area of alkali basalts in the geochemical classification diagram. With the exception of very few elements, these three types of volcanic rocks are similar in the content of trace elements. In comparison to the basalts of different tectonic settings, the meta-volcanic rocks in the ore field are rich in high field strength elements (HFSE) such as Th, Nb, etc. and depleted in large ion lithophile elements (LILE) such as Sr, Ba, etc. and their primary mantle-normalized trace element patterns show remarkable negative Th and Nb anomalies and negative Sr and Ba anomalies. These three types of volcanic rocks are similar in REE content range and chondrite-normalized REE patterns with the exception of Eu anomaly. Various lines of evidence show that these three types of volcanic rocks in the ore field have the same source but are the products of different stages of magmatic evolution, their original magma is a product of partial melting of the metasomatically enriched mantle in the tensional tectonic setting within the continent plate, and the crystallization differentiation plays an important role in the process of magmatic evolution.     

Red Clay Type Gold Deposits in China

<正>Red clay type gold deposits,located in the south of China,are situated not only in orogenic belts,but also in inner cratons,where climate is tropical-subtropical with clear arid and humid.The lateritic weathering crust often can be divided into five zones,including topsoil,siliceous duricrust zone,multi-color zone(or red clay zone in some deposits),pallid zone and saprolite zone from surface to the base rock,several of which are absent in some deposits.The base rocks are composed mainly of carbonate rocks with minor clastic rocks,intermediate-basic volcanic rocks and intermediate-acid and alkalic intrusions.The orebodies are mainly located in the multi-color zone with part of them in the pallid and saprolite zones.The ore sources include orebodies of Carlin-type gold deposits and porphyry gold deposits,as well as gold-rich base rocks.The red clay type gold deposits experienced early-stage endogenic gold mineralization and laterization during the Tertiary and Quaternary.The areas with endogenic gold deposits,especially Carlin-type gold deposits and porphyry gold deposits in karst depressions on the plateau,structual erosional platforms in the middle-lower mountains,and intermountain basins in southern China are well worth studying to trace red clay type gold deposits.     

Geological characteristics and metallogenic significance of the Devonian intermediate-basic volcanic rocks in the Dachang deposit, Guangxi Zhuang Autonomous Region

Recently discovered intermediate-basic volcanic rocks in the Devonian strata at Dachang, Guangxi Zhuang Autonomous Region are dominated by basalts and andesites. Most of them belong to the calc-alkali and alkali series. Petrology and geochemistry data indicate that the volcanic rocks may be formed in a continental rift environment. The volcanic rocks are in conformable contact with the overlying and underlying wall rocks, with such typical sedimentary structures as laminated and striped ones, and the host rocks of the volcanic rocks contain lots of marine fossils such as tentaculite. Many pieces of evidence indicate that the eruption environment of the volcanic rocks is a sea-facies one. The volcanic rocks are of the LREE-enrichment type, with high ratios of light rare-earth elements to heavy rare-earth elements. In addition, they display moderately negative δEu anomalies and moderately negative δCe anomalies with a higher degree of LREE and HREE fractionation. Through the Q-cluster analysis of the REE samples, it is indicated that the ores have a closer relation with the layered volcanic rocks, and also possess a certain inheritance-consistency relationship with the layered volcanic rocks. The source of ore-forming materials may be related with volcanism. It is proposed that the ore deposit in the study area should be genetically explained as the result of marine volcano-sedimentary exhalation of hot water and late superposition-reworking.     

Selenium Enrichment in Cambrian Stratabound Gold Deposits in the Western Qinling Mountains

Stratabound gold deposits in the western Qinling Mountains occur in Cambrian chert formation composed of carbonaceous chert and carbonaceous slate. The distinctive chert formation provides important grounds for the mineralization and controls on the formation of gold deposits. Study shows that Se is exceptionally higher in both host rocks and gold orebodies. It may be recovered as a valuable component in ores for total utilization, and in some localities even independent Se orebodies (which are mined exclusively for Se) may be delineated. In gold ore Se mainly occurs as independent minerals or in the isomorphous form in sulphides and there is a positive correlation between Se and Au.     

The Mechanism of Structural Control of Ore Formation and Geochemical Characteristics in the Massive Sulfide Deposits of the Wushan Copper Ore Field,Jiangxi

The ore-controlling mechanism of the bedding fault system in the massive sulfide deposits of the Wushancopper orefield may be generalized as the control of ore deposition by optimum surface in an ore-formingstructural trap. The mechanism has three major features: (1) timing of mineralization; (2) positioning of hostformation; and (3) dependence of ore-controlling structure on properties of rocks. The "optimum surface" is adivisional structural plane which marks obvious difference in physical, chemical and mechanical properties andis favorable for mineralization. It is also a unity of structures. lithofacies and orebodies. The structural and geochemical characteristics of the ore deposits indicate the migration trend of the ma-jor characteristic clements in the ore-controlling fault belt: elements with a small radius (Si, Fe, Mg and Al)moved towards and concentrated at the center of the belt while large-radius ones (Ca, K and Na) were remotefrom the center.     

Element Geochemistry and Petrogenesis of High—K Potassic Dike Rocks in Two Types of Gold Ore Fields in Northwest Jiaodong,Shandong,China

This paper deals with the high-K,potassic dike rocks in two types of gold ore fields at Linglong and Dayigezhuang,Northwest Jiaodong.The rocks can be divided into three types.i.e.,(1) lamprophyre,(2) andesite porphyrite,and (3) dacite porphyrite,based on their geological occurrence and space-time relationship with gold mineralization.These rocks were the products of early,synchronous and late mineralization.respectively,Element geochemistry shows that variations in chemical composition of major oxides follow the general rules of magmatic fractional crystallization.The fractional crystallization of mineral phases of augite in the early stage(namely in the lamprophyre stage)and hornblende and plagioclase in the late stge(namely from the andesite-porphyrite to dacite porphyrite stage)controlled the magma evolution.The rocks are enriched in alkili and have higher K2O and lower TiO2 contents,as well as strongly enriched in large ion lithophile elements such as Ba,Sr and Rb,and LREE but strongly depleted in transition elements such as Cr and Ni,Rb is depleted relative to Sr and Ba,and Rb/Sr ratios are low.Volatile constituents are abundant.These characteristics indicate that the initial magma originated from the metamorphic subduction ocean-crust that had been intensively contaminated by crustal materials,and retrogressive metamorphism is characterized by low-degree partial melting during back-arc spreading,Varying degrees of partial melting and different emplacement enviornments may be the main causes for the evolution of the rocks and mineralization in different degrees in the two gold ore fields at Linglong and Dayigezhuang,Shandong.     

Timing of formation of the Hongdonggou Pb-Zn polymetallic ore deposit,Henan Province,China: Evidence from Rb-Sr isotopic dating of sphalerites

The Hongdonggou Pb-Zn polymetallic ore deposit,located in the southwestern part of the Luanchuan Mo-W-Pb-Zn-Ag polymetallic ore mineralization in Henan Province,China,is an important part of the East Qinling metallogenic belt.The orebodies in the deposit,which are vein,bedded and lenticular,are mainly hosted in the syenite porphyry,and formed within the carbonate and clastic rocks of the Yuku and Qiumugou formations partially.The genesis of the deposit has previously been argued to be of hydrothermal-vein type or of skarn-hydrothermal type.In this study,we report the results of Rb-Sr isotopic dating based on sphalerites from the main orebody of the Hongdonggou Pb-Zn polymetallic ore deposit,which yield an isochron age of 135.7 ± 3.2 Ma,constraining the timing of mineralization as early Cretaceous.The age is close to those reported for the Pb-Zn deposits in the Luanchuan ore belt.The(~(87)Sr/~(86)Sr),values of the sphalerites(0.71127 + 0.00010) are lower than that of terrigenous silicates(0.720) and higher than the mantle(0.707),suggesting that the metallogenic components were mainly derived through crust-mantle mixing.Combining the results from this study with those from previous work,we propose that the Hongdonggou Pb-Zn polymetallic ore deposit is a hydrothermal-vein deposit associated with the early Cretaceous tectonothermal event,and the mineralization is controlled by NWand near EW-trending faults in the Luanchuan Mo-W-Pb-Zn-Ag polymetallic ore concentration belt.     

广西大厂锡多金属矿区钙长石产出的地质环境及成因机制

本文对广西大厂锡多金属矿区容矿岩石内含有钙长石大晶体岩石的岩石学，钙长石的产状，钙长石及有关矿物的成分特征等作了较为细致的研究，对其自生成因的机理进行了探讨，阐明了成岩作用对矿床的形成有关重要的地质意义。     

Oxygen and carbon isotope zonations of wall rocks around the Kamioka Pb---Zn skarn deposits, central Japan: application to prospecting

Mapping of the oxygen and carbon isotopic composition of hydrothermally altered wall rocks was conducted during blind ore prospecting for Pb---Zn skarn deposits in the Kamioka mining district, central Japan. The wall rocks consist of heterogeneous rock units. Oxygen and carbon isotope ratios were determined for 35 limestones and 33 silicate rocks from the area around the Mozumi deposit (3 km × 3 km) in the Kamioka mining district. The results (δ¹⁸O_spsmow of − 1.1 to + 17.3% and δ¹³C_sppdb of − 5.0 to +4.8% for limestones, and δ¹⁸O_spsmow of −0.8 to + 12.5% for silicate rocks) show isotope zonations of the wall rocks, with lighter isotopic compositions toward the center of mineralization. The isotope zonations likely formed by interaction of thermal waters with the wall rocks during skarn mineralization. The isotopically light zone indicates a higher paleotemperature or higher water-to-rock ratios, and occurs in the footwall of the 7Gohi fault. This structure is spatially related to the distribution of orebodies, indicating that the fault was the main conduit of the ore-forming fluids. The oxygen and carbon isotopic compositions of limestones vary regularly across limestone bodies hosted by the silicate wall rocks, suggesting that the thermal waters were pervasive throughout the wall rocks at the time of mineralization.An isotopically light zone was also found in the southeastern corner of the study area, where significant mineralization had yet to be identified. This suggested an extension of the extinct hydrothermal system to this area, and the possibility of hidden orebodies underneath. Recent drilling in this area has intercepted a zone 45 m thick with a grade of 13.4% Zn, 0.03% Pb and 8 g per metric ton at about 380 m depth.     

河南水洞岭—桑树坪铜锌矿区找矿前景分析

根据大地构造环境、区域北景值、矿区构造、海相火岩及含矿物、矿体及成矿元素分布规律的综合分析，认为水洞岭－桑树坪地区细碧角斑岩系火山岩发育，分异演化较好，含矿岩性为无长石带的石英角斑凝灰岩及热水沉积的硅质岩，重晶石岩、铜矿化显示向深部有变富的趋势。因此具有铜成矿前景。     

A preliminary discussion on the geochemical role of country-rock media in cassiterite-polymetallic sulphide mineralization,Dachang ore field,Guangxi, China

Our metallogenic studies of the Dachang ore field show that the country-rock media have great influence on the process of mineralization. They can not only contribute part of the ore-forming material, but also have influence on the geochemical evolution of granitic magma and ore fluids. The Dachang ore field can be taken as a typical example to show the influence of country-rock media on mineralization. Geological field investigations indicate that where granites intruded weakly alkalic country rocks (e.g. middle Devonian limestones and silicorites of platform facies in the Dachang), instead of carbonaceous shales of reducing basin facies, Sn would be able to enter rock-forming minerals in large quantities to form cassiterite-sulfide ore deposits of commercial value. So, it may be concluded that the process of magmatic differentiation-evolution, mineralization and tectonic settings of ore deposits are, more or less, controlled by their country-rock media.     

Authigenic Sanidine as a Mineral Indicator of Gravitation-Brine Catagenesis in Carboniferous Rocks in the Southern Limb of the Moscow Syneclise

The article presents data on numerous findings of authigenic K-feldspars in the Lower–Upper Carboniferous carbonate and terrigenous rocks in the southern limb of the Moscow syneclise, including the Oka–Tsna bar. In terms of the composition and crystalline structure, all feldspar morphotypes (idiomorphic monocrystalline fringes on the surface of sandy clastic grains, fine-crystalline aggregates, pseudomorphously replacing organogenic carbonate detritus, and pseudoskeletal crystals) are composed of K-sanidine with the overwhelming predominance of K over Na and extremely low concentrations of Ca, Ba, and Sr. As can be seen from 40Ar/39Ar dating, the authigenic sanidine mineralization took place during the Permian, i.e., 20–55 Ma later than the accumulation of host Carboniferous rocks. Mineralogical observations, as well as paleofacies and paleogeographic reconstructions, suggest that the formation of authigenic K-feldspars is associated with the gravitation-brine catagenesis in the southern limb of the Moscow syneclise as a result of the seepage of high-mineralization brines from Permian evaporate marine basins into the underlying older rocks.     

西藏错那洞穹隆祥林铍锡多金属矿地质特征及找矿方向

错那洞穹隆是北喜马拉雅片麻岩穹隆带(NHGD)中发现的新成员,穹隆由核-幔-边3部分组成。核部由寒武纪花岗质片麻岩组成,幔部由早古生代云母片岩和夕卡岩化大理岩组成,边部由变质沉积岩组成。在穹隆核部后期侵入有淡色花岗岩和伟晶岩脉。祥林铍锡多金属矿位于错那洞穹隆北部,矿区内发育多条南北向、北东向张性断裂。通过系统的地表工程控制,在穹隆幔部和断层破碎带内新发现了铍锡多金属工业矿体。通过错那洞穹隆北部祥林矿区的解剖,矿化类型可初步划分为夕卡岩型、锡石-石英脉型、锡石-硫化物型和花岗伟晶岩型。夕卡岩型矿体赋存在穹隆幔部的夕卡岩化大理岩内,矿化以铍、锡、钨为主,锡品位变化较大。锡石-石英脉型矿体受北东向张性断裂控制,矿化以锡、铍、钨为主,矿石品位相对较富。锡石-硫化物型矿体受大理岩内的层间滑脱构造控制,富锡,而铍、钨相对较贫。伟晶岩型矿体矿化为铍为主,伴生铷等。钻孔深部验证发现夕卡岩型矿体、锡石-硫化物型矿体、锡石-石英脉型矿体深部延伸较稳定。通过岩浆与铍锡多金属成矿作用的关系的研究,提出了祥林矿区两期次铍锡钨多金属矿成矿作用,分别与弱定向二云母花岗岩及白云母花岗岩两期次淡色花岗岩浆活动密切相关。在矿体特征研究和矿床类型总结的基础上,明确了下一步的找矿标志和方向。锡石-硫化物型铍锡多金属矿和锡石-石英脉型铍锡多金属矿铍、锡、钨品位相对较富,为今后主攻的矿床类型。     

A Preliminary Study on Exhalative Mineralization in Permian Basins, the Southern Segment of the Da Hinggan Mountains, China – Case Studies of the Huanggang and Dajing Deposits–

Abstract: The southern segment of the Da Hinggan Mountains is a well‐known tin–polymetallic metallogenic belt of North China with Jurassic‐Cretaceous volcanic–plutonic rocks widespread. Principally because of this, most of the deposits are regarded as epigenetic hydrothermal deposits in genetic connection with the Mesozoic magmatism. But nearly 90 % of the deposits occur in Permian strata, and show concordant stratiform mineralization with a spatial distribution constrained by sedimentary facies of the Permian strata. A close association between mineralization and Permian strata is recognizable. The Huanggang Fe‐Sn deposit was regarded as a standard skarn‐type deposit formed by magmatic hydrothermal solutions in connection with Mesozoic granites. But there are abundant fabrics indicating submarine hydrothermal exhalation both in magnetite ores and in skarns, including bedding/lamination, soft–deformation, synsedimentary brecciation, and collo‐form fabrics. The magnetite orebodies and skarn‐bodies are predominantly concordant stratiform, and extend nearly 20 km along certain stratigraphic horizon, that is, the upper section of the Lower‐Permian submarine volcanic rocks. The Mesozoic granitic rocks crosscut the magnetite and skarn zone. Instead of skarnization, they show strong greisenization associated with cassiterite‐quartz veins, distinct from the magnetite skarn‐ore with disseminated tin in the Permian rocks. The Dajing Sn‐polymetallic deposit is generally regarded as subvolcanic‐hydrothermal origin, principally because of the close spatial association between ores and some of the Mesozoic subvolcanic dikes (called rhyolitic porphyry). Detailed geological, fabric, petrographical and mineralogical study demonstrates that this very kind of subvolcanic rocks is actually a new type of exhalites (called ‘siderite‐sericite chert’ according to its mineral assemblage), formed by hydrothermal sedimentation during the evolution of the Later‐Permian lacustrine basin. There are, however, indeed some rhyolitic porphyry dikes that crosscut orebod–ies. The orebodies and their associated exhalite predate, and thus have no genetic relation, to the Mesozoic magmatic process. We thus conclude that subaqueous exhalative mineralization did occur during the basin evolution at the Permian time in the southern segment of the Da Hinggan Mountains, which is ignored and poorly understood, but might be as important as the hydrothermal mineralization connected with the Mesozoic magmatism.     

Fluid inclusion and stable isotope characteristics of the Karalar (Gazipaşa,Antalya) barite-galena deposits,Southern Turkey

The Karalar galena-barite deposits are typical examples of the carbonate-hosted barite-galena deposits widely occurring in the Central Tauride Belt. These deposits are located in Permian limestones as ore veins along fault zones that are discordant to the bedding planes and as thin veinlets within hardly brecciated bottom zones of Permian limestones. The ore deposits contain mainly barite and galena and small amounts of sphalerite, pyrite, fahlore, limonite, quartz, and calcite. Barites occur during the earlier episode of mineralization and were mylonitized before the formation of galena. Galena and other minerals occur epigenetically with barite along porous zones between brecciated barite crystals and are especially abundant in the hardly mylonitized zones. Fluid inclusion studies indicate that the ore deposits of the area were developed by hydrothermal fluids with following characteristics: they contained NaCl, CaCl₂, and MgCl₂; the salinity of the fluids was relatively high and their temperature was low during the crystallization of barites in the earlier episode of mineralization; and the salinity of the fluids decreased and their temperature increased during the crystallization of sulfide minerals through the later episode of mineralization. δ₁₈O and the δD results indicate that the water in the mineralizing fluid was of meteoric origin. The deposits were formed by deep meteoric water circulating through marine sediments. Shallow circulating and slightly warmed fluids dissolved Ba and sulfate from marine sediments of the basement and transported them to the mineralization environment during the early episode, while deep circulating and more heated fluids dissolved Pb, Zn, and other elements from the basement and reached the environment during the later episode of mineralization. The text was submitted by the authors in English.     

湖南省金和有色金属矿床成矿系列初论

湖南省内生金属矿产资源颇为丰富。钨、锡、铅、锌、锑为省内优势矿种；稀土、稀有、金、银、铜、汞也占有十分重要的地位。按照成矿过程中的主导地质作用，省内金和有色金属矿床可以划分为五个矿订成矿系列。本文对各矿床成矿系列的形成地质背景、产出构造条件、赋矿围岩、矿床类型进行了总结；并对其时空展布规律进行了讨论。