Discovery of the copper deposits with features of the Keweenawan type in the border area of Yunnan and Guizhou provinces

There existed intense Cu anomaly on the northeastern side of the geochemical boundary with NW strike in the border area between the Yunnan and Guizhou provinces. Through field observation, ore bodies of high-grade native coppers have been found. The copper mineralization was constrained by the ancient volcanic vents of Permian basalt eruption and the overlain strata of carbonaceous argillites. Native coppers with flaky, net veined and impregnated occurrences, fine-grained tenorites and massive chalcocites widely occur in volcanic breccias, tuffs, carbonaceous-siliceous argillites and siliceous bitumen rocks with bed thickness of about 15-80 m. Cu contents vary from 0.5% to 20%. The copper mineralization was tightly related to actinolite-tremolitization, zeolitization and bituminization and involved in extensive reduction environments. Continental flood basalts erupted in mantle plume environments usually have high Cu concentrations (～170 ×10-6 in the Emeishan basalts), which provided a copper source of mineralization. Thus, metallogenesis of the native copper deposits in the Yunnan-Guizhou border area is tightly associated with intensive crust-mantle and organic-inorganic interactions. The tremolitization and chalcocitization indicate that the metallogenic temperatures are in a range of 400-100℃. The geologic background and characteristics of ore and alteration for the native copper deposits in this area are somewhat similar to those of the Keweenawan native copper deposit in Michigan, USA.     

江西省万载县野猫冲铜矿控矿构造特征及找矿意义

江西省万载县野猫冲铜矿床为中低温热液（成矿流体）沿构造破碎带蚀变-蚀变岩型铜矿床。在地表地质调查、钻孔岩芯考察及岩矿鉴定的基础上,对野猫冲铜矿控矿构造进行详细研究,表明北东东向大型叠瓦状推（滑）覆构造控制矿区内各地质单元的延深与展布,北东向韧性剪切变形带控制矿区铜金矿体的展布,矿体呈似层状赋存于韧性剪切断裂之间的次级层间破碎带和小断裂带内,带内发育较强的动热变质,硅化、绢云母化和绿泥石化发育。矿石以黄铜矿为主,贫硫,成矿流体具有多期次的活动、叠加改造的特点。上栗-潭埠-宜丰断裂带自西至东已发现20余处铜多金属矿床（点）,显示该带具有巨大找矿潜力。     

Discovery of the copper deposits with features of the Keweenawan type in the border area of Yunnan and Guizhou provinces

There existed intense Cu anomaly on the northeastern side of the geochemical boundary with NW strike in the border area between the Yunnan and Guizhou provinces. Through field observation, ore bodies of high-grade native coppers have been found. The copper mineralization was constrained by the ancient volcanic vents of Permian basalt eruption and the overlain strata of carbonaceous argillites. Native coppers with flaky, net veined and impregnated occurrences, fine-grained tenorites and massive chalcocites widely occur in volcanic breccias, tuffs, carbonaceous-siliceous argillites and siliceous bitumen rocks with bed thickness of about 15–80 m. Cu contents vary from 0.5% to 20%. The copper mineralization was tightly related to actino-lite-tremolitization, zeolitization and bituminization and involved in extensive reduction environments. Continental flood basalts erupted in mantle plume environments usually have high Cu concentrations (～170 ×10^?6 in the Emeishan basalts), which provided a copper source of mineralization. Thus, metallogenesis of the native copper deposits in the Yunnan-Guizhou border area is tightly associated with intensive crust-mantle and organic-inorganic interactions. The tremolitization and chalcocitization indicate that the metallogenic temperatures are in a range of 400–100°C. The geologic background and characteristics of ore and alteration for the native copper deposits in this area are somewhat similar to those of the Keweenawan native copper deposit in Michigan, USA.     

Analysis of tectonic settings of global superlarge porphyry copper deposits

About three quarters of superlarge porphyry copper deposits throughout the world occur along the eastern Pacific basin rim, most of which were formed during the Mesozoic-Cenozoic. Porphyry copper deposits often occur in the upper parts of a subduction zone and in a within-plate orogenic belt. Some porphyry copper deposits are inconsistent with plate subduction with respect to their formation time, and most of them in the world are associated with tensional environment. Metallogenic porphyries originated from the mantle, and the involvement of the lower-crust or oceanic crust materials have played an important role. Based on the geochemical characteristics and tectonic settings of the ore-bearing porphyries in the Gandise and Yulong metallogenic zones, it is proposed that delamination may be the important mechanism of formation of porphyry copper deposits.     

Analysis of tectonic settings of global superlarge porphyry copper deposits

About three quarters of superlarge porphyry copper deposits throughout the world occur along the eastern Pacific basin rim, most of which were formed during the Mesozoic-Cenozoic. Porphyry copper deposits often occur in the upper parts of a subduction zone and in a within-plate orogenic belt. Some porphyry copper deposits are inconsistent with plate subduction with respect to their formation time, and most of them in the world are associated with tensional environment. Metallogenic porphyries originated from the mantle, and the involvement of the lower-crust or oceanic crust materials have played an important role. Based on the geochemical characteristics and tectonic settings of the ore-bearing porphyries in the Gandise and Yulong metallogenic zones, it is proposed that delamination may be the important mechanism of formation of porphyry copper deposits.     

The occurrences and geochemical characteristics of thorium in iron ore in the Bayan Obo deposit,Northern China

The Bayan Obo deposit in northern China is an ultra-large Fe–REE–Nb deposit.The occurrences,and geochemical characteristics of thorium in iron ores from the Bayan Obo Main Ore Body were examined using chemical analysis,field emission scanning electron microscopy,energy dispersive spectrometer,and automatic mineral analysis software.Results identified that 91.69%of ThO2 in the combined samples was mainly distributed in rare earth minerals(bastnaesite,huanghoite,monazite;56.43%abundance in the samples),iron minerals(magnetite,hematite,pyrite;20.97%),niobium minerals(aeschynite;14.29%),and gangue minerals(aegirine,riebeckite,mica,dolomite,apatite,fluorite;4.22%).An unidentified portion(4.09%)of ThO2 may occur in other niobium minerals(niobite,ilmenorutile,pyrochlore).Only a few independent minerals of thorium occur in the iron ore samples.Thorium mainly occurs in rare earth minerals in the form of isomorphic substitution.Analyses of the geochemical characteristics of the major elements indicate that thorium mineralization in the Main Ore Body was related to alkali metasomatism,which provided source material and favorable porosity for hydrothermal mineralization.Trace elements such as Sc,Nb,Zr,and Ta have higher correlation coefficients with thorium,which resulted from being related to the relevant minerals formed during thorium mineralization.In addition,correlation analysis of ThO2 and TFe,and REO and TFe in the six types of iron ore samples showed that ThO2 did not always account for the highest distribution rate in rare earth minerals,and the main occurrence minerals of ThO2 were closely related to iron ore types.     

The metallogenic mechanism of the sandstone-type copper deposits in the Chuxiong Basin,Yunnan Province

The sandstone-type Cu deposits in the Chuxiong Basin occur in the Cretaceous Gaofengsi Formation and the Maotoushan Formation and the orebodies are stratoid and lenticular in form, structurally controlled by their stratigraphical position. Ore structures are dominated by impregnated and striped ones. In addition, it has been observed that copper mineralization is controlled by water-discharge and deformation structures. Orebodies are commonly seen on the gently inclined limbs of the anticline, with the involution front. Copper mineralization shows a distinct zonation. S, Pb isotope and REE data suggest that the copper would stem from the country rocks and the sulfur largely from the lower strata. During diagenesis oxidized Cu-bearing brines derived from the upper parts and reduced brines from the lower parts are involved in metallogenetic reactions in the stress neutral plane, which is the key to the formation of copper deposits in the Chuxiong Basin.

     

The metallogenic mechanism of the sandstone-type copper deposits in the Chuxiong Basin,Yunnan Province

The sandstone-type Cu deposits in the Chuxiong Basin occur in the Cretaceous Gaofengsi Formation and the Maotoushan Formation and the orebodies are stratoid and lenticular in form, structurally controlled by their stratigraphical position. Ore structures are dominated by impregnated and striped ones. In addition, it has been observed that copper mineralization is controlled by water-discharge and deformation structures. Orebodies are commonly seen on the gently inclined limbs of the anticline, with the involution front. Copper mineralization shows a distinct zonation. S, Pb isotope and REE data suggest that the copper would stem from the country rocks and the sulfur largely from the lower strata. During diagenesis oxidized Cu-bearing brines derived from the upper parts and reduced brines from the lower parts are involved in metallogenetic reactions in the stress neutral plane, which is the key to the formation of copper deposits in the Chuxiong Basin.     

Geology and isotopic composition of helium,neon, xenon and metallogenic age of the Jinding and Baiyangping ore deposits,northwest Yunnan,China

TheJindingoredeposit,locatedinthenorthwestYunnanProvince,isthelargestPb-Zndeposit(Pb Zn>15Mt1),averagingZn=6.08%andPb/Zn=1/4.7)inChinaatpresent.Toitsnorth,alargeCu-Co-AgdeposithasbeenfoundatBaiyangpingrecently1).TheJindingPb-Zndepositishostedinsandstonesa…     

Sulfur isotopic characteristics of late Cenozoic ore deposits at the arc junction of Hokkaido, Japan

Abstract Sulfide minerals of late Cenozoic vein-type deposits of southwest Hokkaido and Kuril Islands yielded δ³⁴_CDT S values of 2 to 8 permil, which are typical green-tuff values of magnetite-series igneous terrane. Sulfides of the Kitami district of northeast Hokkaido, on the other hand, are characterized by negative δ³⁴S_CDT values, ranging from 0 to - 7 permil. This unique value among ore deposits in the late Cenozoic back-arc terranes in the Japanese Islands is considered to have resulted from extraction of ³²S enriched sulfur from the basement rocks, because of well-developed N-S fracturing in the basement, which is characteristic of the axial belt and Kitami district of Hokkaido.     

The 2 Ga peraluminous magmatism of the Jacobina — Contendas Mirante Belt (Bahia) Brazil): Major and trace-element geochemistry and metallogenic potential

The Jacobina — Contendas Mirante belt represents a Transamazonian (2 Ga), N-S, 500-km long, elongated orogenic domain in the central part of the São Francisco craton, Bahia state. Numerous syntectonic to post-tectonic peraluminous leucogranites were emplaced along the major structures of the belt. Their mineralogical and geochemical and some of their metallogenetic characteristics are very similar to their Hercynian and Himalayan equivalents. However, their average peraluminous index varies from one granitic pluton to another and biotite is, on average, slightly more magnesian in the Transamazonian leucogranites. Higher oxygen fugacity is indicated by the general occurrence of magnetite, the stability of allanite and sometimes epidote in most of the plutons and by biotite chemistry. The peraluminous magmatism of the Jacobina-Contendas Mirante belt results from crustal partial melting during a continental collision event at 2 Ga.Trace-element geochemistry implies variable source composition and/or melting conditions for the different granitic plutons and some different facies within the same plutonic unit. The scarcity of ilmenite, the general occurrence of magnetite, and the relatively low peraluminous index of some of these granites suggest that graphite-beating sediments are not a significantly source material. From their mineralogical and geochemical characteristics, acid meta-igneous rocks such as the Sete Voltas TTG suite of presumed Archaean age, seem to represent a suitable source for these granites.Sn, W, Li, F and Be enrichment of most Transamazonian leucogranites is much weaker than in the mineralized Variscan equivalents. The Caetano-Aliança and Riacho das Pedras granites represent the most specialized granitic bodies. Beryl (emerald), molybdenite and scheelite mineralizations are related to some of these granites which intrude ultrabasic formations: the Campo Formoso and the Carnaiba granites. In many of these granites, uranium content is comparable to values measured in mineralized Hercynian leucogranites. The occurrence of hexavalent uranium minerals, mineralization and episyenitic alteration are favourable criteria for finding Variscan-type uranium ore deposits.     

Porphyry copper and tin-bearing porphyries a discussion of genetic models

The paper briefly describes the characteristics of the Chilean porphyry copper deposits, emphasizing the volcanic characteristics observed in the youngest ore bodies. Mention is made of the polymetallic ore bodies that are associated with rhyolitic porphyries intruding Jurassic sedimentary formations in the north of Chile, and the similarities and differences between the Chilean porphyry coppers and the Bolivian tin-bearing porphyries are pointed out.The models proposed by Sillitoe (1972), Brousse and Oyarzún (1971), and Mitchell and Garson (1972), are discussed and a new model is proposed agreeing with that of Mitchell and Garson for the genesis of the tin-bearing porphyries (the transportation of Sn as volatile halogenide by F liberated in the Benioff zone), but suggesting different generating mechanism for the porphyry coppers and polymetallic deposits related with porphyries. This mechanism, as a part of the global tectonic model, is based on the separation at depth of hydrogen sulphide from pyrite and water introduced with the upper layers of the lithospheric plate. The ascending migration of H₂S to high levels in the crust would be responsible for the porphyry copper mineralization by segregating sulphides of Fe, Cu, Mo and other sulphophile metals contained in the calc-alkaline magmas, brines, or sedimentary-volcanic formations intruded by the porphyries. The excess of H₂S would give rise to the formation of sulphur deposits normally present in the volcanic belt situated along the same line but at a higher level than those of the emplacement of porphyry coppers.The generation of copper and tin-bearing porphyries would be a consequence of the upward migration of volatile substances from different depths in the subduction zone, which explain its different emplacement with regards to the continental margins.     

Metallogenesis of the Ertix gold belt, Xinjiang and its relationship to Central Asia-type orogenesis

The Ertix gold belt is located on the boundary of the Kalatongke arc and the Kelan back-arc basin of D-C1. Most scholars used to interpret the formation and distribution of the gold deposits in the Ertix tectonic belt in terms of the petrogenic and metallogenic models for active continental margins. However, enormous data of isotopic dating and geologic research show that the mineralization was obviously later than the oceanic subduction, whereas exactly simultaneous with the collisional orogenesis during C₂-P, especially at the transition stage from collisional compression to extension. Based on study of metallogenic time, tectonic background, ore geology, ore fluid nature, ore material source, etc., we reveal that all the gold deposits possess the character of orogenic deposits formed in collisional orogenic system, and that their ore-forming materials mainly have derived from the stratigraphic terranes south to individual deposits. Accordingly, the theoretical tectonic model for collisional metallogenesis and petrogenesis is employed to explain the formation of the Ertix gold belt and to determine the gold exploration directions.     

Re-Os age for molybdenite from the Gangdese porphyry copper belt on Tibetan plateau: Implication for geody- namic setting and duration of the Cu mineralization

It is recognized that there are at least two sorts of significant environments for porphyry copper deposits, i.e. magmatic arcs and collisional orogens[14]. The deposits in the former environments are exampled by the circle-Pacific porphyry copper belt, such as An-dean-type deposits, which mainly formed in the period of the Andean tectonic cycle characterized by trans- pressional and transtensional movements along the arc-parallel strike-slip fault zone in the Late Eo-cene-Early Oligocene[5…     

On Electrical Conductivity at Depth in the Shanuch Copper–Nickel and the Aginskoe Gold-Ore Fields,Kamchatka

This paper is concerned with the method of interpretation and with the results of magnetotelluric sounding (MTS) along the line connecting the Shanuch copper–nickel and the Aginskoe gold ore deposit. The interpretation revealed that the upper section divides into two blocks according to the electrical resistivity. The western block has a high resistivity, which is due to the metamorphic and igneous basement rocks that are exposed at the ground surface. The eastern block has a low resistivity, which is due to the presence of a conductive sedimentary–volcanogenic cover involving a wide network of discontinuities. A low resistivity layer was identified at depths of 30–60 km. The deep-seated faults that have been identified by interpretation in the eastern block penetrate through the lithosphere as far as the conductive layer; fluids can move along these faults upward into the upper crust where at lower temperatures they release minerals whose accumulations make up ore deposits of nonferrous and noble metals.     

淮北地区矽卡岩型铁铜矿床控矿条件分析与成矿模式

淮北地区位于安徽省北部,是重要金属成矿区之一。地质构造单元归属华北陆块,其矽卡岩型矿床的控矿条件和成矿模式既与华北地区邯邢式接触交代型铁矿床相似而又有区别。邯邢式铁矿主要围岩地层为奥陶系,矿石成分简单,以磁铁矿为主。淮北地区部分矿床具有这一特征,而另一部分矿床的特征与此有较大差异：围岩地层为寒武系,矿石成分复杂,以铁铜矿为主,并含有金、钼等其它有益元素,岩体分叉侵入,多层成矿,矿体产于燕山中期石英二长闪长玢岩与寒武系中上统内接触带及正接触带,镁质矽卡岩较发育,含铜矽卡岩可见于外接触带。为了与邯邢式铁矿区别,称其为前常式铁铜矿。本区矽卡岩型矿床的赋矿层位为中上寒武统一下奥陶统。其中,寒武系铁矿比例43．39％、铜矿比例92．67％、金矿比例100％,奥陶系铁矿比例56．61％、铜矿比例7．33％。本文在介绍地质背景的基础上、较系统地分析了控矿条件和成矿模式,提出了岩浆侵入活动中心（或活动带）与寒武系接触带为重点找矿方向的观点,并明确指出远离侵入中心（带）的岩床,其成矿性差。文中还介绍了覆盖区识别岩浆侵入活动中心（或活动带）的方法。     

西藏班戈日阿铜多金属矿床地质特征及找矿前景

西藏班戈日阿铜多金属矿床位于班戈-腾冲多金属成矿带,是近年来新发现的矽卡岩型铜多金属矿床,已探明资源量达中型规模。最新研究和找矿成果显示矿带呈北西向展布,受燕山晚期白垩纪花岗岩类岩体侵入作用控制,矿体分布于岩体与下白垩统灰岩地层接触带及附近部位。在空间上,矿床主要分为三个矿段：主矿体分布在矿区中西部,目前在西矿段已圈定5个（条）铜矿体,矿体呈似层状、透镜状,其中最大的Cu13号矿体长221 m,平均厚9 m,沿倾向已控制延深100 m以上,铜品位：0.45%~2.01%,平均0.9%。主要金属矿物为黄铜矿、磁铁矿。中矿段已经圈定3条矿体,成矿元素除铜外,铅、锌、银含量也较高,为铜多金属矿体。矿体呈似层状、透镜状。其中以Cu-23号矿体最大,长达300 m,矿体最宽处达110 m。矿体平均品位Cu1.48%,Pb 1.25%,Zn 2.52%,A g 32.52×1-0 6。本文在矿区地质特征研究的基础上,通过对1：5万水系沉积物测量成果分析,对比中、西矿段成矿条件,对矿区东段进行了预测评价,指出该矿区具有较好的铜多金属找矿前景。同时建议对已圈定的1：5万水系沉积物异常开展1：1万土壤地球化学测量工作,进而圈定该区铜多金属矿带或矿（化）体,为矿区深入勘查工作提供依据。     

Geological and geochemical character and genesis of the Jinlongshan-Qiuling gold deposits in Qinling orogen: Metallogenic mechanism of the Qinling-pattern Carlin-type gold deposits

The Qinling Carlin-type gold deposit belt is the second largest Carlin-type gold ore concentrated area in the world and occurs in Mesozoic intracontinental collisional orogen, contrasting to the Carlin-type gold deposits in the Basin and Range province in Cenozoic active continental margin of West America. With ore-forming ages focussed at the range of 197.45–129.45 Ma, its metallogenic geodynamic background was the decompression-pyrogenation regime at the transition stage from collisional compression to extension, indicating that gold mineralization synchronized with the Mesozoic continental collision. Geochemical studies discover that ore fluids and materials mainly came from the Hercynian-Indosinian tectonic layer. Mesozoic intracontinental subduction of Hercynian-Indosinian association along the Shuanghe-Gongguan fault led to the formation of Jinlongshan-Qiuling gold deposits. Accordingly, the tectonic metallogenic model is established for Qinling-pattern Carlin-type gold deposits.     

REE and (э)Nd of clay fractions in sediments from the eastern Pacific Ocean: Evidence for clay sources

Clay fractions in the non-calcareous surface sediments from the eastern Pacific were analyzed for clay minerals, REE and 143Nd/144Nd. Montmorillonite/illite ratio (M/I ratio), total REE contents ((REE), LREE/HREE ratio and cerium anomaly (бCe) may effectively indicate the genesis of clay minerals. Clay fractions with M/I ratio >1, бCe (0.85, (REE (400 μg/g, LREE/HREE ratio (4, and REE patterns similar to those of pelagic sediments are terrigenous and autogenetic mixed clay fractions and contain more autogenetic montmorillonite. Clay fractions with M/I ratio <1, бCe=0.86 to 1.5, ΣREE=200 to 350 μg/g, LREE/HREE ratio (6 and REE distribution patterns similar to that of China loess are identified as terrigenous clay fraction. The 143Nd/144Nd ratios or (э)Nd values of clay fractions inherit the features of terrigenous sources of clay minerals. Clay fractions are divided into 4 types according to (э)Nd values. Terrigenous clay minerals of type I with the (э)Nd values of -8 to -6 originate mainly from North American fluvial deposits. Those of type II with the (э)Nd values of -9 to -7 are mainly from the East Asia and North American fluvial deposits. Those of type III with (э)Nd values of -6 to -3 could come from the central and eastern Pacific volcanic islands. Those of type IV with (э)Nd values of -13 to -12 may be from East Asia eolian. The terrigenous and autogenetic mixed clay fractions show patchy distributions, indicating that there are volcanic or hot-spot activities in the eastern Pacific plate, while the terrigenous clay fractions cover a large part of the study area, proving that the terrigenous clay minerals are dominant in the eastern Pacific.     

Mineralization episode of porphyry copper deposits in the Jinshajiang-Red River mineralization belt: Re-Os dating

Re-Os isotopic dating for the molybdenites from the porphyry copper deposits of the Jinshajiang-Red River mineralization belt in Yunnan Province yields isochron ages of 33.9±1.1 Ma for the Machangqing deposit and 34.4±0.5 Ma for the Tongchang deposit. This result shows that both the Machangqing and the Tongchang porphyry Cu-Mo deposits from two different ore-fields formed simultaneously. This new data and the published Re-Os model ages of molybdenite (35.4 Ma, 35.9 Ma, 36.2 Ma) of the Yulong porphyry copper deposit in Tibet, which is located in the same Jinshajiang-Red River mineralization belt as the Machangqing deposit and the Tongchang deposit, suggest that these three Cenozoic porphyry copper deposits in the Jinshajiang-Red River mineralization belt were contemporary for their mineralization episode. That is to say, even their present locality is far away and nearly iso-distantly distributed, these three porphyry Cu(Mo) deposits belong to the same mineralization episode at the end of Eocene.