The Nuri Cu-W-Mo deposit is a large newly explored deposit located at the southern margin of the Gangdese metallogenic belt. There are skarn and porphyry mineralizations in the deposit, but the formation age of the skarn and the relationship between the skarn and porphyry mineralizations are controversial. Constraints on the precise chronology are of fundamental importance for understanding the ore genesis of the Nuri deposit. To determine the formation age of the skarn, we chose garnets and whole rock skarn samples for Sm-Nd dating. We also selected biotite associated with potassic alteration for Ar-Ar dating to confirm the ore formation age of the porphyry mineralizations. The Sm-Nd ages of the skarn are 25.73 +/- 0.92 - 25.2 +/- 3.9Ma, and the age of the potassic alteration is 24.37 +/- 0.32Ma. The results indicate that the skarn and porphyry mineralization are coeval and belong to a unified magmatic hydrothermal system. Combined with a previous molybdenite Re-Os age, we think that the hydrothermal activity of the Nuri deposit lasted for 1.2 - 2.1 Myr, which indicates that the mineralization formed rapidly. The chronologic results indicate that the Nuri deposit formed in the period of transformation from compression to extension in the late collisional stage of the collision between the Indian and Eurasian continents.

Abundant magmatic rocks of various ages are exposed in Gangdese, southern Tibet. These rocks play an important role in understanding the tectonic transformation from the subduction of Neo-Tethyan oceanic crust to the collision of the Indian and Asian continents. Based on zircon U–Pb ages, geochemistry, and Sr–Nd–Pb–Hf isotopic data of the Late Cretaceous to early Oligocene (~96–30Ma) intrusive rocks in the Nuri Cu–W–Mo deposit, we discuss the Late Cretaceous to early Oligocene tectonic transformation of the region and the origin of Oligocene Cu–W–Mo mineralization in southern Gangdese. The Nuri intrusive rocks represent three magmatic episodes: 96–91, 56–52, and 33–30Ma. The 96–91 and 56–52Ma rocks have relatively low (87Sr/86Sr)i (0.7041 to 0.7060), and high εNd(t) (+3.1 to +3.5) and εHf(t) values (+3.7 to +15); the 33–30Ma rocks have relatively high (87Sr/86Sr)i (0.7061 to 0.7063) and Pb isotopes, and low εNd(t) (−3.8 to −1.8) and εHf(t) values (+0.6 to +10.1). The three stages of intrusive rocks have geochemical characteristics that are similar to those of coeval rocks in Gangdese. The 96–91 and 33–30Ma rocks are adakitic, whereas the 56–52Ma rocks have characteristics of arc calc-alkaline magmatic rocks. The 96–91Ma rocks were produced by the partial melting of Neo-Tethyan basaltic oceanic crust and minor sediments, whereas the 56–52Ma rocks were generated by the partial melting of juvenile crust and the 33–30Ma rocks were formed by the melting of Indian plate lower crust contaminated with overlying mantle materials. On the basis of the regional tectonic and magmatic characteristics, we suggest that Neo-Tethyan oceanic slab subduction and slab roll-back occurred from ~100 to 65Ma, collision between the Indian and Asian continents occurred at 65 to 40Ma, Neo-Tethyan oceanic slab break-off took place at ~50Ma, and the Indian continent subducted northwards beneath the Asian continent at ~30Ma. From the Late Cretaceous (96–91Ma) to Oligocene (~30Ma), the geodynamic setting of Gangdese was changed from Neo-Tethyan oceanic subduction to Indian continental subduction. In contrast to the Miocene metallogenic rocks, the magmatic source of Oligocene metallogenic rocks contains old Indian continental crust materials, which result in the formation of intense, unique Cu–W–Mo mineralization, especially W mineralization, in the southern Gangdese.

The Nuri Cu-W-Mo deposit is located in the southern subzone of the Cenozoic Gangdese Cu-Mo metallogenic belt. The intrusive rocks exposed in the Nuri ore district consist of quartz diorite, granodiorite, monzogranite, granite porphyry, quartz diorite porphyrite and granodiorite porphyry, all of which intrude in the Cretaceous strata of the Bima Group. Owing to the intense metasomatism and hydrothermal alteration, carbonate rocks of the Bima Group form stratiform skarn and hornfels. The mineralization at the Nuri deposit is dominated by skarn, quartz vein and porphyry type. Ore minerals are chalcopyrite, pyrite, molybdenite, scheelite, bornite and tetrahedrite, etc. The oxidized orebodies contain malachite and covellite on the surface. The mineralization of the Nuri deposit is divided into skarn stage, retrograde stage, oxide stage, quartz-polymetallic sulfide stage and quartz-carbonate stage. Detailed petrographic observation on the fluid inclusions in garnet, scheelite and quartz from the different stages shows that there are four types of primary fluid inclusions: two-phase aqueous inclusions, daughter mineral-bearing multiphase inclusions, CO2-rich inclusions and single-phase inclusions. The homogenization temperature of the fluid inclusions are 280 degrees C386 degrees C (skarn stage), 200 degrees C340 degrees C (oxide stage), 140 degrees C375 degrees C (quartz-polymetallic sulfide stage) and 160 degrees C280 degrees C (quartz-carbonate stage), showing a temperature decreasing trend from the skarn stage to the quartz-carbonate stage. The salinity of the corresponding stages are 2.9%49.7 wt% (NaCl) equiv., 2.1%7.2 wt% (NaCl) equiv., 2.6%55.8 wt% (NaCl) equiv. and 1.2%15.3 wt% (NaCl) equiv., respectively. The analyses of CO2-rich inclusions suggest that the ore-forming pressures are 22.1 M Pa50.4 M Pa, corresponding to the depth of 0.9 km2.2 km. The Laser Raman spectrum of the inclusions shows the fluid compositions are dominated in H2O, with some CO2 and very little CH4, N2, etc. dD values of garnet are between -114.4% and -108.7% and d18OH2O between 5.9% and 6.7%; dD of scheelite range from -103.2% to -101.29% and d18OH2O values between 2.17% and 4.09%; dD of quartz between -110.2% and -92.5% and d18OH2O between -3.5% and 4.3%. The results indicate that the fluid came from a deep magmatic hydrothermal system, and the proportion of meteoric water increased during the migration of original fluid. The d34S values of sulfides, concentrated in a rage between -0.32% to 2.5%, show that the sulfur has a homogeneous source with characteristics of magmatic sulfur. The characters of fluid inclusions, combined with hydrogen-oxygen and sulfur isotopes data, show that the ore-forming fluids of the Nuri deposit formed by a relatively high temperature, high salinity fluid originated from magma, which mixed with low temperature, low salinity meteoric water during the evolution. The fluid flow through wall carbonate rocks resulted in the formation of layered skarn and generated CO2 or other gases. During the reaction, the ore-forming fluid boiled and produced fractures when the pressure exceeded the overburden pressure. Themeteoric water mixed with the ore-forming fluid along the fractures. The boiling changed the pressure and temperature, oxygen fugacity, physical and chemical conditions of the whole mineralization system. The escape of CO2 from the fluid by boiling resulted in scheelite precipitation. The fluid mixing and boiling reduced the solubility of metal sulfides and led the precipitation of chalcopyrite, molybdenite, pyrite and other sulfide.

The Nuri Cu-W-Mo deposit is a newly explored and proved large-size deposit,which lies on the southern margin of eastern Gangdese volcanic-magma arc and belongs to the southern subzone of the Gangdise metallogenic belt.There are some Late Cretaceous and Paleogene intrusive rocks exposed in the ore district.The strata in the ore district are mainly Cretaceous Bima Group and Danshiting Group.The skarn mainly occurs within the carbonate rocks and lithologic conversion boundaries,not in direct contact with the intrusions.The skarn minerals are mainly garnet,pyroxene,wollastonite,vesuvianite,epidote and actinolite.Metallic minerals mainly include chalcopyrite,pyrite,molybdenite,scheelite,bornite and tetrahedrite.Electron microprobe analyses show that the garnet comprises mainly grossular and andradite,with minor augite in skarn.The end member of pyroxene is dominated by diopside.The amphibole in the Nuri deposit is magnesiohornblende-actinolite belonging to ferroedenite.The end member of epidote group is dominated by epidote.In the horizontal and vertical direction,the skarn type shows significant zoning from garnet skarn through diopside skarn to diopside-wollite skarn from south to north in horizon profile and from shallow to deep in vertical profile.The zoning reflects the change of metasomation.Meanwhile,the mineralization also has zoning character.In the shallow part,the mineralization is mainly skarn type with tungsten mineralization.With the increasing depth,the mineralization type changes to vein mineralization with copper or copper-molybdenum mineralization.Some porphyry-type mineralization exposed in some drilling holes,characterized by copper mineralization with a small quantity of molybdenum.The components of garnet vary in the space,gradually changing from the dominance of andradite to that of grossular.The garnet records complex zoning patterns,the end member and chemical composition changing with the changing zonation.The type of zoning pattern demonstrates that the fluid which formed garnet was episodic,probably resulting from the geochemical self-organization and changes in fluid in association with garnet growth rates.The Kp shows that the deposit was formed in a weakly acid and fairly strong oxidation state.Combined with the distribution and composition variation,the authors infer that the skarn of the Nuri deposit was formed by metasomatism between carbonate and ore-forming fluid.The fluid might have originated from the deeper intrusion and migrated a long distance along the shatter zone or faults in the strata.Infiltration was probably the primary factor for the formation of skarn in the deposit.The changes of temperature and oxygen fugacity must have played an important role in the formation of skarn minerals.The skarn exposed in the Nuri deposit is the superficial skarn,with the probable existence of uniform skarn-porphyry ore-forming system.Therefore,there exsits great potential in finding porphyry Cu ore bodies in the deeper part of the existing skarn type mineralization,and this conclusion is of important significance for further exploration in the Nuri deposit and adjacent areas in south Tibet.

The Mingze porphyry Mo deposit is located in the southeastern margin of the Gandese metallogenic belt,north of the Yarlung Zangbo River suture zone.A variety of intrusions outcrop such as moyite,biotite monzogranite,granodiorite,porphyaceous adamellite and granite porphyry.The granite porphyry is the ore-froming related intrusion which is completely mineralized.Wall rocks suffered extensive alteration,mainly as potassic,silicification,chloritization,kaolinization and skarn alteration.Various types of alteration have the characteristics of vertical variations,and skarn formed where the intrusions interact with carbonate wall rocks.Potassic and silicification alteration occurred at deeper levels.Mineralization of the Mingze deposit also shows vertical variation.Cu and W mineralization in skarn formed in the relatively shallow subsurface,and Mo(Cu)mineralization in porphyry occurred at larger depths.Porphyry mineralization has vertical zoning characteristics.Texture of ores mainly includes massive,veinlet and disseminated form.Ore minerals mainly consist of molybdenite,chalcopyrite,pyrite and a little of bornites and scheelit.We selected pure biotite for the 40Ar-39Ar dating from the biotite-pyrite vein.The results show the plateau age is 28.2±0.33Ma,which coincides with the age of Re-Os.Combined with metallogenetic age previously reported,this age represents the metallogentic age of the southern belt of Gangdese between 30.26Ma-23.62Ma,which is obviously different from the northern or middle belt of the Gandese metallogenic belt.Dating of the metallogenic epoch of the Mingze deposit provides sound evidence for the multi-stage mineralization and the evolution of ore-forming related to the extensive tectono-magmatic activities.

The Nuri Cu-W-Mo deposit is a newly explored and proved large-scale deposit in southern Tibet.It lies in the southern margin of the eastern Gangdese volcanic-magma arc,and belongs to the southern subzone of the Gangdese Cu-Mo metallogenic belt.We chose the skarn,marble and limestone exposed in the ore district to conduct component analysis.The results show that the major elements(Ca,Ti,Al,Mg,Fe and Si)are transferring among marble,limestone and skarn rocks,and the content of the elements between these rocks exhibits a linear change.The skarn rocks are rich in LREE and deficit in HREE,and bear intense Eu negative anomalies.The marbles have the same REE distribution patterns as the skarn,so we conclude they may have some relation in petrogenesis.Based on the mineral assemblage and Eu negative anomalies in the REE distribution patterns,we infer the skarn rocks were formed in a weak oxidation,medium-high temperature environment,which is consistent with the conclusion from the study on fluid inclusions.Besides,the scarcely developed Ce anomalies in skarn rocks suggest that the fluids for skarn forming were mainly derived from magma,and mixed with a lot of meteoric water.Combined with the geochemical characteristics of different rocks,intense differentiation of LREE and HREE,Eu negative anomalies,and the fact that skarn rocks are different from the hydrothermal exhalative mineralization system,we infer that the Nuri deposit was formed by fluid metasomatism.

Medium-sized and large-scale skarn Cu-Mo-W(Au)deposits,e.g.Nuri,Mingze,Kelu,Chongmuda and Chenba,are distributed in the Shannan area of the eastern section of the Gangdese belt.Intrusion-related skarn copper mineralization belongs to high K and calc-alkaline rock series,located in the late collision magmatic arc and formed between 20 to 30Ma.Copper mineralization occurs at the exocontact zone of the lower Cretaceous Bima Formation carbonate and other calcareous-bearing sedimentary rocks with intrusions.At present,three main mineralization types are identified,including skarn type,hydrothermal vein type and porphyry type.Mineralizing associations are Cu-W-Mo,Mo,Cu-Au and Cu.In ore districts,those mineralization types form an entire porphyry-skarn Cu-Mo-W(Au)ore-forming system.Alterations of the exocontanct are mainly skarnization and hornfelsization,while the alterations of the endocontact are sericitization,silicification,and chloritization of intrusions.The Cu-Mo-W(Au)deposits in the Shannan area are interpreted as the shallow level.Appearance of porphyry molybdenum mineralization in the Mingze deposit implies that skarn mineralization of the study area resemble to those in the central sub-metallogenic belt,having a uniform porphyry-skarn ore-forming system.Based on data above,a metallogenic model is built to indicate further ore-search direction towards the deep subsurface.

Giant porphyry Cu systems host the most widely distributed mineralization types at convergent plate boundaries,including porphyry deposits centered on intrusions,skarn and superjacent high-and intermediate-sulfidation epithermal deposits.While the giant Miocene Qulong porphyry Cu-Mo deposit,which formed in the Gangdese post-collision orogenic belt of southern Tibet,now,is thought to be the largest porphyry-type deposit in China,and with confirmed Cu ~ 10Mt and Mo ~0.5Mt,at least.Two contemporary skarn Cu deposits are located adjacently,the Zhibula and Langmujiaguo sharn deposits.The skarn deposits share exactly similar geological,mineralogical features:garnets with obvious oscillatory growth zoning are mainly andradite(Ca3Fe2Si3O12)and minor grossularite(Ca3Al2Si3O12);sulfides are chalcopyrite,pyrite,bornite,and chalcocite.These skarn deposits have obvious close temporal and spatial relations to the Qulong porphyry deposit,and the recent exploration work at the Langmujiaguo skarn deposit found that the same Miocene granodiorite and biotite monozogranite in the Qulong porphyry deposit were intruded under the skarks.So the porphyry deposit and the skarn deposits might result from the same ore-forming system.The features of porphyry Cu systems and the closely adjacent skarn deposits need to be taken into account during planning and exploration.

矽卡岩矿床一般认为是由岩浆侵入体与富碳酸盐地层通过接触交代作用而形成的一套硅酸盐矿物组合,通常都是产在富碳酸盐地层与岩浆侵入体的接触带附近,或是产在接触带附近地层的断裂或裂隙中（Meinert et al.,2005）。由于围岩的成分的不同,可以将矽卡岩分为钙质矽卡岩和镁质矽卡岩。通常根据矽卡岩中不同硅酸盐矿物出现的顺序,可将矽卡岩的成岩作

<正>矽卡岩矿床一般认为是由岩浆侵入体与富碳酸盐地层通过接触交代作用而形成的一套硅酸盐矿物组合,通常都是产在富碳酸盐地层与岩浆侵入体的接触带附近,或是产在接触带附近地层的断裂或裂隙中(Meinert et al.,2005)。由于围岩的成分的不同,可以将矽卡岩分为钙质矽卡岩和镁质矽卡岩。通常根据矽卡岩中不同硅酸盐矿物出现的顺序,可将矽卡岩的成岩作

Chemical behavior of chalcophile elements in the process of magma evolution and sulfide segregation is a window to demonstrate the formation of sulfide deposits.One direction of development of the study of sulfide deposit is to trace the behavior of chalcophile elements through laboratory results.The present paper summarizes the behavior of sulfur and chalcophile elements in magma evolution,and demonstrates their application in the study of magmatic sulfide deposits.They are discussed from five factors: ① by the study of sulfur solubility in basaltic magma,four factors control the sulfide segregation: magma mixing,rapid temperature decrease,crustal contamination,and rapid crystal fractionation;② according to the distribution of Ni between olivine and silicate magma,we simulate the correlated change of Ni in olivine to Fo;③ the D values of Ni—Cu and PGE between sulfide liquid and silicate melt is are summarized,and the controlling factors to D value and R-factor are discussed also;④ when olivine is surrounded by sulfide liquid,the interaction will happen,and Ni content in sulfide liquid can be estimated;⑤ by the distribution of chalcophile elements between MSS and sulfide liquid,the facts of ore-forming zonations are summarized.At the end,the present problems and direction of development are analyzed and suggested.

西藏冈底斯成矿带上的驱龙Cu-Mo矿床是一处典型斑岩Cu-Mo矿床。初步结果显示其铜矿资源量已超过藏东玉龙铜矿（650万吨）和江西铜厂铜矿（500万吨）,亦已成为我国第一大铜矿。矿区范围内多期次中酸性岩浆侵入到叶巴组地层中,从早到晚依次为:花岗闪长岩〔（19.5±0.4）Ma〕;黑云母二长花岗岩〔（16.35±0.40）Ma〕;二长花岗斑岩〔（17.58±0.74）Ma〕;花岗闪长斑岩(侵入黑云母二长花岗

东西长约800 km,南北宽100 km的冈底斯斑岩铜钼成矿带,由于近年来一系列大型-超大型斑岩铜钼矿床(驱龙、冲江、厅官等)和夕卡岩-斑岩复合型铜铅锌钼矿床(甲马等)的发现,已经成为国内外多地质学家研究的热点地区,是研究碰撞造山作用与成矿关系的很好的场所(侯增谦等,2001,2006a,b,c;莫宣学等,2003;李光明等,2004;Hou等,2003,2008;Qin等,2005;Li等,2006;Qu等,2007;侯增谦和王二七,2008;Tafti等,2009).

Recently, series of major breakthroughs for porphyry copper exploration have been made in the Gangdese Metallogenic belt in Tibet. Alteration and mineralization ages of the Gangdese porphyry-skarn Cu(Mo) deposits concentrate in the range of 30-12 Ma, formed in the extension environment of late stage of collision between India and the Asian continents or the transitional environment from the post-collisional compression setting to strike-slip extension. However, the independent porphyry molybdenum deposit associated with the collisional setting has not been reported so far. This paper studies the ore-bearing porphyries, the types and horizational and vertical zonation of hydrothermal alteration, the characteristics of hydrothermal vein system and mineralization, according to the systmatic fieldwork and the mapping work of the drilling holes. The granitic porphyry is the ore-forming intrusion with intensive alteration of 9 km2 in area. It concludes that, Sharang porphyry molybdenum is single porphyry molybdenum without any other important accompanying metal resources and it has been formed in the main collisional setting around 55 Ma. This study compares the scale of alteration and the intensity of mineralization with the same type of molybdenum deposits. Based on the comparisons and the results of TEM and induced electrical survey, the Sharang porphyry molybdenum deposit has rather large vertical extension to 800 m in the depth and showes excellent metallogenic conditions and great potential for further exploration. The establishment of the Sharang single porphyry molybdenum deposit will enrich the metallogenic pedigree of the giant Gangdese porphyry metallogenic belt. This discovery has a great significance for regional research and prospecting.

Ni-Cu sulfide mineralization occurred in series of mafic-ultramafic complexes in Eastern Tianshan. These deposits, however, failed to reach economic level for PGE, and some of the samples have lower PGE compositions even than primitive mantle. Low PGE contents can be caused in two ways: (1) sulfide segregation happens so early that a great deal PGE removed along with sulfide in the early stage of magma evolution; (2) because of low partial melting, large part of PGE remains in primitive mantle, so only little PGE goes into melt. In the case of Xiangshan and Tulargen, it is available to model the origin of primitive magma according to the geochemical behavior of PGE (luring partial melting and sulfide segregation. The results show that there is no sulfide segregation before the emplacement of the intrusions, and low degree of partial melting, about 10% to 20%, is responsible for the low PGE level in magma, for most of the PGE remains in the residual mantle after partial melting. Pd-Ni plot shows that no pre-segregation happened ever, and neither did sulfide fractionation happen. When R = 330, ( Pt + Pd) can reach 1. 27 x 10(-6) conduit system will be the most potential object to deposit PGE.