Gold concentrations of magmatic brines and the metal budget of porphyry copper deposits

(Table1).In the Amazon lowlands the OSU simulation is substan-tially drier than the CLIMAP simulation(up to5mm d−1in DJF), and is consistent with evidence for Pleistocene aridity19.Both the CLIMAP and OSU simulations are in agreement with groundwater temperature estimates from Texas and Georgia4.Glacier data from the Andes20,Kilimanjaro21,New Guinea22,and Hawaii23indicate that equilibrium-line altitudes wereϳ900m lower than at present(ϳ780m reduction relative to lower sea level).But limiting dates for these advances range widely(20–15kyr ago for Huascara´n,30–10kyr for Kilimanjaro,Ͼ15kyr for New Guinea and22–9kyr for Hawaii),so the synchronicity of lowered equilibrium-line altitudes across the tropics remains uncer-tain.For Kilimanjaro and Huascara´n,the OSU simulation is3–5ЊC cooler than the control,yielding approximate temperature-related depressions of equilibrium-line altitudes of550–900m(based on a nominal tropical lapse rate of5.5ЊC km−1).In both areas net moisture at the LGM is greater than that of the control,which would further enhance glacier growth.The OSU simulation is thus consistent with regional glacier advances in the Andes and east Africa.We did not modify CLIMAP SSTs near New Guinea and Hawaii,and as a result temperatures in the OSU simulation are essentially the same as those of the CLIMAP simulation(3ЊC cooler and1ЊC warmer than the control,respectively)and perhaps inconsistent with local glaciation,indicating the need for further study of these regions24.The OSU simulation helps to resolve some,but not all,disagree-ments between land and ocean data.We did not consider climate feedbacks associated with LGM vegetation,and these may yield further modelled cooling over land25.Although the ice-age tropics in the OSU simulation are generally cooler and drier than the control,some regions such as the Andean highlands are cooler and wetter,suggesting substantial variation within the tropics both regionally and with altitude,consistent with recent data compilations26.The LGM cooling in the OSU simulation agrees well with recent ocean and atmosphere–ocean model simulations over the eastern Pacific,the equatorial Atlantic and regions of Africa and Asia9,27–29.To the extent that our AGCM results are model-independent,this agreement suggests convergence of data and models in these regions.In the western Pacific,the OSU reconstruction agrees with one ocean simulation29and one coupled atmosphere–ocean simulation28,but disagrees with a coupled atmosphere–ocean simulation that yields a cooling of4–6ЊC(ref.27).Nevertheless,our results highlight the potentially widespread influences of regional SST changes in circulation patterns and moisturefluxes associated with tropical–extratropical temperature gradients,and understore the need to reconstruct both the amplitude and the geographical distribution of LGM climate changes in much greater detail.ⅪReceived28January;accepted5May1999.1.CLIMAP Project Members.Seasonal reconstruction of the earth’s surface at the last glacial maximum.(Map&Chart Ser.MC-3,Geol.Soc.Am.,Boulder,Colorado,1981).2.Thompson,L.G.et te glacial stage and Holocene tropical ice core records from Huascaran,Peru.Science269,46–50(1995).3.Stute,M.et al.Cooling of tropical Brazil(5ЊC)during the last glacial maximum.Science269,379–383(1995).4.Stute,M.et al.Glacial paleotemperature records for the tropics derived from noble gases dissolved ingroundwater(abstr).Eos78,F44(1997).5.Guilderson,T.P.,Fairbanks,R.G.&Rubenstone,J.L.Tropical temperature variations since20,000years ago:modulating interhemispheric climate change.Science263,663–665(1994).6.Rind,D.&Peteet,D.T errestrial conditions at the last glacial maximum and CLIMAP sea-surfacetemperature estimates:are they consistent?Quat.Res.24,1–22(1985).7.Mix,A.C.,Morey,A.,Pisias,N.G.&Hostetler,S.Foraminiferal faunal estimates of paleotemperature:Circumventing the no-analog problem yields cool ice age tropics.Paleoceanography14,350–359(1999).8.Slowey,N.&Curry,W.B.Glacial-interglacial differences in circulation and carbon cycling within theupper western North Atlantic.Paleoceanography10,715–732(1995).9.Ganopolski,A.,Rahmstorf,S.,Petoukhov,V.&Claussen,M.Simulation of modern and glacialclimates with a coupled global model of intermediate complexity.Nature391,351–356(1998). 10.Thompson,S.L.&Pollard,D.A global climate model(GENESIS)with a land-surface-transfer scheme(LSX),1,present-day climate.J.Clim.8,732–761(1995).11.Dorman,J.L.&Sellers,P.J.A global climatology of albedo,roughness length,and stomatal resistancefor atmospheric general circulation models as represented by the simple biosphere model(SiB).J.Appl.Meteorol.28,833–855(1989).12.Clark,P.U.,Licciardi,J.M.,MacAyeal,D.R.&Jenson,J.W.Numerical reconstruction of a soft-bedded Laurentide ice sheet during the last glacial maximum.Geology24,679–682(1996).13.Peltier,W.R.Ice age paleotopography.Science265,195–201(1994).14.Thunell,R.C.,Anderson,D.M.,Gellar,D.&Miao,Q.Sea-surface temperature estimates for thetropical western Pacific during the last glaciation and their implications for the Pacific warm pool.Quat.Res.41,255–264(1994).15.Prell,W.L.&Kutzbach,J.E.Monsoon variability over the past150,000years.J.Geophys.Res.92,8411–8425(1987).16.Markgraf,V.in Global Climates Since the Last Glacial Maximum(eds Wright,H.E.et al.)357–385(Univ.Minnesota Press,Minneapolis,1993).17.Zaucker,F.&Broecker,W.S.The influence of atmospheric moisture transport on the fresh waterbalance of the Atlantic drainage basin:General circulation model simulations and observations.J.Geophys.Res.97,2765–2773(1992).18.Zaucker,F.,Stocker,T.F.&Broecker,W.S.Atmospheric freshwaterfluxes and their effect on the globalthermohaline circulation.J.Geophys.Res.99,12443–12457(1994).19.Servant,M.et al.Tropical forest changes during the late Quaternary in African and South Americanlowlands.Glob.Planet.Change7,25–40(1993).20.Klein,A.G.,Seltzer,G.O.&Isacks,B.L.Modern and last local glacial maximum snowlines in theCentral Andes of Peru,Bolivia,and Northern Chile.Quat.Sci.Rev.18,63–84(1999).21.Downie,C.&Wilkinson,P.The Geology of Kilimanjaro(Univ.Sheffield Press,1972).22.Lo¨ffler,E.Pleistocene glaciation in Papua and New Guinea.Z.Geomorphol.13,32–58(1972).23.Porter,S.C.Chronology of Hawaiian glaciations.Science195,61–63(1977).24.Lee,K.E.&Slowey,N.C.Cool surface waters of the subtropical North Pacific Ocean during the lastglacial.Nature397,512–514(1999).25.Crowley,T.J.&Baum,S.K.Effect of vegetation on an ice-age climate model simulation.J.Geophys.Res.102,16463–16480(1997).26.Farrera,I.et al.Tropical climates at the last glacial maximum:A new synthesis of terrestrialpalaeoclimate data,I,Vegetation,lake levels,and geochemistry.Clim.Dyn.(in the press).27.Bush,A.B.G.&Philander,S.G.H.The role of ocean-atmosphere interactions in tropical coolingduring the last glacial maximum.Science279,1341–1344(1998).28.Weaver,A.J.,Eby,M.,Fanning,A.F.&Wiebe,E.C.Simulated influence of carbon dioxide,orbitalforcing,and ice sheets on the climate of the last glacial maximum.Nature394,847–853(1998). 29.Bigg,G.R.,Wadley,M.R.,Stevens,D.P.&Johnson,J.A.Simulation of two last glacial maximumocean states.Paleoceanography13,340–351(1998).30.Chervin,R.M.Interannual variability and seasonal predictability.J.Atmos.Sci.43,233–241(1986). Acknowledgements.We thank P.Bartlein for discussions and the design of Fig.2;P.Clark,N.Pisias, D.Pollard for discussions;P.Valdez for comments and suggestions;and A.Morey and D.Zahnle for assistance.Model simulations were conducted at the National Center for Atmospheric Research,the Environmental Protection Agency,and the College of Oceanic and Atmospheric Sciences at Oregon State University.The US Geological Survey(S.W.H.)and The National Science Foundation(A.C.M.) supported this research.Correspondence and requests for materials should be addressed to S.W.H.(e-mail:steve@). Gold concentrations of magmatic brines andthe metal budget ofporphyry copper depositsT.Ulrich*,D.Gu nther*†&C.A.Heinrich**Isotope Geology and Mineral Resources,Department of Earth Sciences,ETH Zentrum8092Zu¨rich,Switzerland ......................................................................................................................... Porphyry copper–molybdenum–gold deposits are the most important metal resources formed by hydrothermal processes associated with magmatism.It remains controversial,however, whether the metal content of porphyry-style and other mag-matic–hydrothermal deposits is dominantly controlled by metal partitioning between magma and an exsolving magmaticfluid phase1,2or by scavenging of metals from solid upper-crustal rocks by surface-derivedfluids3.It also remains unknown to what degree the metal content in such deposits is affected by selective mineral precipitation from the orefluid.Extremely salinefluids4, precipitating quartz and ore minerals in veins have been inferred to have a significant magma-derived component,on the basis of geological5,isotopic6,7and experimental evidence8,9.Here we report gold and copper concentrations of singlefluid inclusions in quartz,determined by laser-ablation inductively coupled plasma mass spectrometry.The results show that the Au/Cu ratio of primary high-temperature brines is identical to the bulk Au/Cu ratio in two of the world’s largest copper–gold ore bodies. This indicates that the bulk metal budget of such deposits is primarily controlled by the composition of the incomingfluid, which is,in turn,likely to be controlled by the crystallization †Present address:Laboratory of Inorganic Chemistry,ETH Zentrum8092Zu¨rich,Switzerland.process in an underlying magma chamber.Porphyry-type deposits occur along certain segments of the circumpacific and Alpine–Himalayan belts and are hosted in a dense network of quartz–sulphide veins cutting subvolcanic stocks of calcalkaline composition.Copper and gold are the most strongly enriched elements in these deposits,but to a highly variable degree.Copper concentrations in the ore bodies are up to about 1weight per cent (typical enrichment factor ϳ200compared to average crustal abundance),whereas gold concentrations vary from less than 0.05p.p.m.in gold-poor deposits to greater than 1p.p.m.in the economically most attractive porphyry copper–gold deposits (enrichment factors ϳ20–400)10.Gold and copper distributions within individual deposits are closely correlated at all scales,ranging from an intimate textural intergrowth at the mineral grain scale (Fig.1)to highly correlated element concentrations with charac-teristic Au/Cu ratios in ore samples across the deposit (Fig.2c).This close chemical and mineralogical association of Au and Cu in each deposit,with vastly different absolute concentrations and sig-nificant variations of Cu/Au ratios among different deposits,makes the two ore metals the obvious and most direct tracers for the hydrothermal enrichment process—provided that their concentration in the hydrothermal fluid can be determined independently.Here we report quantitative data on the concentration of gold in porphyry-mineralizing fluids.For this pilot study,we examined the highest-temperature,most saline brine inclusions from Grasberg (the world’s richest porphyry copper–gold deposit located in Irian Jaya 11,Indonesia),and from Bajo de la Alumbrera (another giant gold-rich copper deposit in Argentina 12,Fig.1).Quartz veins in pervasively altered porphyries containing hydrothermal quartz þK-feldspar þmagnetite þminor chalcopyrite (CuFeS 2)with asso-ciated gold were selected from the deepest part in the centre of the hydrothermal systems;we wanted to sample inclusions that represent the magmatic–hydrothermal fluids before substantial modification by fluid/rock reactions or mixing with upper-crustal waters.Coexisting low-density inclusions give evidence for the simultaneous entrapment of a high-temperature vapour phase of low salinity.Vapour and brine phases were trapped in the same quartz crystals as isolated inclusions,and have been studied indi-vidually by in situ trace-element analysis using laser ablation inductively coupled plasma mass spectrometry (ICP-MS)and microthermometry.The measurements were performed on regular-shaped fluid inclusions of 10–45␮m size in pre-ore vein quartz.Polyphase brine inclusions from Bajo de la Alumbrera (Fig.1b),from several inclusion assemblages within the same quartz vein,have similar salinities of 58–65wt%NaCl (equivalent)and homogenization temperatures of 550to 650ЊC.Brine inclusions along several trails in the Grasberg sample have apparent salinities of 68–76wt%NaCl (equivalent)and homogenization temperatures above 600ЊC.The salinity of vapour-rich inclusions from Grasberg (7:4Ϯ3wt%NaCl equivalent;high compared with experimental phase relations due to minor co-entrapment of brine)was determined from the tempera-ture of final ice melting.No microthermometry analyses could be performed on the low-density vapour-rich inclusions from Alumbrera owing to their small liquid content.For laser ablation ICP-MS analysis,selected individual inclusions were ‘drilled’out of the polished quartz samples with an ArF excimer laser 13,14.To detect Au we used a miniaturized helium transport system that carries the ablated inclusion content into a modified quadrupole ICP-MS for multi-element data acquisition 15.Helium increases the efficiency of aerosol transport from the ablation spot into the plasma,and enhances the signal-to-back-ground ratio for gold by an order of magnitude.Plasma and interface conditions of the ICP-MS were specifically adjusted to give maximum response on 197Au.A reduced set of elements (silicon,sodium,copper,gold and arsenic),and an increasedbgpycpaxchalcopyritehalite haematiteL50 µm30 µm yVFigure 1Photomicrographs of a polished section of ore and of a polyphase brine inclusion.a ,The intimate association of gold (g)and chalcopyrite (cp)Ϯpyrite (py)in prophyry-related ore deposits is shown by small gold grains occurring within chalcopyrite,possibly exsolved from a high-temperature solid solution.b ,A typical high-temperature,brine inclusion,which upon cooling and partial loss of H 2had exsolved into aqueous liquid (L),a vapour bubble (V),a salt crystal,small chalcopyrite and haematite grains and several unidentified crystals (x,y;sample from Bajo de la Alumbrera,Argentina).ab11010,0001,00010100C u (w t %)I n t e n s i t y (c .p .s .)Au (p.p.m.)Au (p.p.m.)Figure 2Cu plots from Grasberg and from early,high-temperature brine inclusions (filled circles surrounded by dashed line)and vapour-rich inclusions (open triangles);also shown for comparison are the metal concentration ratio of the bulk ore bodies (open square with diagonal line)and representative ore samples (small points).a ,Time-resolved ICP-MS signal showing the progress of laser ablation through host quartz,followed by the breaching of a brine inclusion and complete ablation,including an internally precipitated copper sulphide crystal to which gold is attached.Consistent element concentrations result from integration of these signals,as shown by results obtained from the giant porphyry Cu–Au deposits of Grasberg (b )and Alumbrera (c ).Both deposits contain high-temperature brine inclusions with Au and Cu in the same concentration ratio as the bulk ore.dwell time on197Au(50ms,compared to10ms for the otherelements)further improved the detection limit of gold.Limits of detection as low as0.1p.p.m.Au in25-␮m inclusions weredetermined,corresponding to a total mass ofϳ10−15g Au. Transient signals record the entire ablation process of eachinclusion,and demonstrate unambiguously that Au and Cu,and other trace,minor and major elements(including Na)originatedfrom within thefluid inclusion(Fig.2a).Consistently short andoverlapping peaks for Cu and Au show that gold is attached to a tiny chalcopyrite(CuFeS2)crystal,precipitated inside the inclusionsduring cooling of the host mineral to room temperature after trapping of a homogeneousfluid sample at high temperature andpressure(Fig.1b).Absolute trace-element concentrations are obtained by signal integration,calibration with an external stan-dard,and internal standardization of absolute concentrations using Na,which was determined previously for each inclusion bymicrothermometry14.Uncertainties of individual analyses are esti-mated to beϮ30%,increasing for small inclusions(Ͻ10␮m)orconcentrations near the detection limit.Table1gives average concentrations of Au,Cu,Na,and As in brine and vapour inclu-sions,together with additional elements analysed in the same inclusion assemblages.Au versus Cu concentrations of brine inclusions are shown in Fig.2b and c(filled circles),together with the bulk Au and Cucontents of the two giant ore bodies(open squares)and a spatially representative suite of ore-sample assays illustrating the variable buthighly correlated Cu and Au grades within the Bajo de la Alumbrera deposit(Fig.2c,small dots).The data from Grasberg(Fig.2b)showthat the average Au/Cu ratio in brine inclusions(0:9ϫ10Ϫ4by weight)is almost identical to that of the bulk deposit(1:1ϫ10Ϫ4;ref.16).Similarly,at Alumbrera(Fig.2c),one group of relatively Cu-rich brine inclusions overlaps the bulk metal ratio of the deposit(1:2ϫ10Ϫ4;refs17,18),although some petrographically identical inclusions have lower Cu concentrations at similar levels of Au of ϳ0.6p.p.m.Vapour inclusions coexisting with brine inclusions in the Grasberg sample(Fig.2b,triangles)have comparable Au/Curatios but contain,on average,about ten times higher concentra-tions of both metals19.Associated(but not necessarily coexisting)vapour inclusions in the Alumbrera sample have high copper concentrations but no detectable gold.We do not know whether the compositional variation among the brine inclusions at Alumbrera is due to preferential partitioning of Cu into the vapour phase,or to partial precipitation as a Cu–Fe sulphide. Aware of this uncertainty,we interpret the brines with the ore-matching metal ratio(filled circles marked by dashed lines in Fig.2b and c)as the best approximation to the initial composition of the main metal-introducingfluid in both hydrothermal systems.The correspondence of Au/Cu ratios in the primary orefluids and in the bulk deposits is remarkable,considering that individual concentrations of the two metals in common crustalfluids are likely to vary independently over many orders of magnitude.In conjunction with the variable but highly correlated ore grades,our observation leads to the conclusion that copper and gold must have been transported together in the samefluid,and were co-precipitated almost quantitatively within the volumes of the economic ore bodies.This strongly indicates that the composition of the incoming magmatic brine exerted the dominant chemical control on thefinal bulk composition of the two deposits.Co-transportation of Cu and Au is consistent with experimental data indicating that both metals in their+1valence state form stable chloride complexes in high-temperature saline solutions9,20.Their co-precipitation is probably driven byfluid cooling21,and is possibly aided by initial incorporation of Au into Cu-Fe sulphide solid solutions22.While co-precipitation of Cu and Au in both deposits was very efficient,metal precipitation was also highly selective,as shown by the high concentrations of other metals in the brine.Concentrations of lead and particularly zinc in the brines are comparable to,or even higher than,the Cu concentration,and yet neither lead nor zinc is significantly enriched in the ore bodies.This demonstrates that very large quantities of ore metals areflushed through ore deposits,and ultimately become dispersed unless steep thermal and chemical gradients provide a driving force for efficient mineral precipitation. The source processes for Cu and Au can be constrained byfirst-order mass-balance considerations,based on the average concen-tration of the bulk-ore-matchingfluid(0.79p.p.m.Au and 0.76wt%Cu)and the total metal content of the Alumbrera deposit (460tonnes(t)of Au,and3:7ϫ106t of Cu)17,18.To advect this mass of metals to the deposit,at least5:8ϫ108t of brine are required. Calcalkaline melts are estimated to containϳ2p.p.b.Au or less23,24. To supply the gold content of the deposit would therefore require at least2:3ϫ1011t of magma.This is much larger than the quantity of porphyry that hosts and immediately underlies the ore body,and requires the presence of a deeper-seated magma chamber of100km3 volume or more,consistent with tentative aeromagnetic evidence and exposed remnants of a large stratovolcano25.To source the copper from the same magma chamber would only require extrac-tion of15p.p.m.,that is,one-quarter of the typical copper content of andesitic magmas(60p.p.m.;ref.26).Comparing the5:8ϫ108t of brine used for metal transport with2:3ϫ1011t of magma required to source the gold,we obtain a brine/magma ratio of 1=400¼0:2%;this is a small fraction of the water content(ϳ4wt%) estimated for typical porphyry copper source magmas based on petrological constraints27,28.Considering experimentalfluid/melt partitioning data27,29–32,we speculate that the highly Cl-,Cu-and Au-enriched ore brine could represent thefirst fraction offluid that exsolved from magma that contained initiallyϳ4wt%H2O and had a normal H2O/Cl ratio of about ten(ref.27).The magma was emplaced and started to crystallize at conditions nearfluid satura-tion,about3km below the current exposure level of the deposit. Alternatively,the highly metal-charged brine might indicate that an unusually gold-and/or chlorine-rich(H2O=Cl p10)magma was involved in the formation of the two porphyry copper–gold deposits that we studied.ⅪReceived30December1998;accepted13April1999.1.Candela,P.A.Rev.Econ.Geol.4,203–221(1989).2.Cline,J.S.&Bodnar,R.J.Can economic porphyry copper mineralization be generated by a typicalcalc-alkaline melt?J.Geophys.Res.96,8113–8126(1991).3.Sheets,R.W.,Nesbitt,B.E.&Muehlenbachs,K.Meteoric water component in magmaticfluids fromporphyry copper mineralization,Babine Lake area,British Columbia.Geology24,1091–1094(1996).4.Roedder,E.Fluid Inclusions(Mineralogical Soc.of America,1984).5.Hedenquist,J.W.&Lowenstern,J.B.The role of magmas in the formation of hydrothermal oredeposits.Nature370,519–527(1994).6.Sheppard,S.M.F.,Nielsen,R.L.&Taylor,H.P.J.Hydrogen and oxygen isotope ratios in mineralsfrom porphyry copper deposits.Econ.Geol.66,515–542(1971).7.Sheppard,S.M.F.,Nielson,R.L.&Taylor,H.P.J.Oxygen and hydrogen ratios of clay minerals fromporphyry copper deposits.Econ.Geol.64,755–777(1969).Table1Average concentrations offluid inclusionsAlumbrera GrasbergElement Brine Vapour*Brine Vapour ............................................................................................................................................................................. Au p.p.m.0:79Ϯ0:39Ͻ0.530:26Ϯ0:1810:17Ϯ6:20 Cu wt%0:76Ϯ0:493:30Ϯ1:200:30Ϯ1:001:20Ϯ1:30 Na wt%16:00Ϯ2:001:70Ϯ0:1416:00Ϯ1:003:00Ϯ1:00 K wt%12:50Ϯ2:700:72Ϯ0:2415:40Ϯ4:701:30Ϯ0:20 Mn wt%1:50Ϯ0:300:14Ϯ0:062:40Ϯ0:800:20Ϯ0:10 Fe wt%8:50Ϯ1:901:30Ϯ0:1513:00Ϯ3:501:00Ϯ0:50 Zn wt%1:40Ϯ0:300:12Ϯ0:031:30Ϯ0:400:15Ϯ0:07 Pb wt%0:45Ϯ0:130:02Ϯ0:010:50Ϯ0:250:04Ϯ0:01 Rb p.p.m.750Ϯ17525Ϯ6960Ϯ24080Ϯ30 Sr p.p.m.85Ϯ3010Ϯ7640Ϯ35030Ϯ20 Mo p.p.m.70Ϯ60Ͻ300600Ϯ12060Ϯ20 Ag p.p.m.45Ϯ70Ͻ401;200Ϯ300100Ϯ40 Cs p.p.m.60Ϯ1520Ϯ2070Ϯ355Ϯ1 As p.p.m.20Ϯ20n.a.20Ϯ10190Ϯ220 Ba p.p.m.95Ϯ2540Ϯ20380Ϯ17010Ϯ10 ............................................................................................................................................................................. *Estimated from experimental phase relations and microthermometric data of brine inclu-sions;absolute element concentrations of these vapour inclusions are less certain than concentration ratios.n.a.,not 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transport.Geochim.Cosmochim.Acta58,5215–5221(1994).Acknowledgements.We thank MIM Exploration forfinancial and logistic support at Bajo de la Alumbrera,and Freeport Ltd for guidance at Grasberg.We thank H.Barnes,J.Hedenquist,S.Kesler and S.Matthai for critically reading the manuscript.Project and equipment funding by ETH Zu¨rich and Schweizerischer Nationalfond is acknowledged.Correspondence and requests for materials should be addressed to C.H.(e-mail:heinrich@erdw.ethz.ch).A diapsid skull in anew species of theprimitive bird Confuciusornis Lianhai Hou*,Larry D.Martin†,Zhonghe Zhou*†,Alan Feduccia‡&Fucheng Zhang**Institute of Vertebrate Paleontology and Paleoanthropology,Chinese Academy of Sciences,P.O.Box643,Beijing100044,China†Natural History Museum and the Department of Ecology and Evolutionary Biology,University of Kansas,Lawrence,Kansas66045,USA‡Department of Biology,University of North Carolina at Chapel Hill, Chapel Hill,North Carolina27599-3280,USA .........................................................................................................................Since the description of Confuciusornis(the oldest beaked bird) in1995,based on three partial specimens,large numbers of complete skeletons have been recovered1,2.Most new material of Confuciusornis3,4can be assigned to a single sexually dimorphic species,C.sanctus.Here we report a new species based on a remarkably well preserved skeleton with feathers and,for thefirst time in the Mesozoic record,direct evidence of the shape of a horny beak.It has a complete and large preserved postorbital that has a broad contact with the jugal bone.This character is presently only known in Confuciusornis,and may confirm pre-vious suggestions of a postorbital in Archaeopteryx5.The squamosal is in tight contact with the postorbital.These two bones form an arch dividing the upper and lower temporal fenestrae,as in other diapsid reptiles6.The presence of a typical diapsid cheek region with two openings in Confuciusornis may preclude the presence of prokinesis(upper jaw mobility against the braincase and orbital area),a feeding adaptation found in most modern birds.The presence of a horny beak,characteristic of modern birds,coupled with a primitive temporal region provides new evidence for a mosaic pattern in the early evolution of birds.Aves Linnaeus1758Sauriurae Haeckel1866Confuciusornithiformes Hou et al.1995Confuciusornithidae Hou et al.1995Confuciusornis Hou et al.1995Confuciusornis dui sp.nov.Etymology.The species name is dedicated to Mr.Wenya Du,who collected and donated the specimen to the Institute of Vertebrate Paleontology and Paleoanthropology(IVPP)for scientific research. Holotype.A nearly complete skeleton.IVPP Collection Number V 11553.Paratype.IVPP11521,a partial skeleton consisting of a sternum, ribs,vertebrae,pelvis,femora and tail.Horizon and locality.A two-metre thick interval within the Yixian Formation(Late Jurassic-Early Cretaceous);Libalanggou,Zhang-jiying,Beipiao,Liaoning,northeast China.Diagnosis.The holotype,a presumed male,is about15%smaller than the holotype of C.sanctus(a small individual and presumed female).Large male individuals of C.sanctus are about30%larger than the new species.The mandible is more slenderanteriorly,Figure1Cast of the elongate tail feathers of C.dui(IVPP Collection V11553) whitened with ammonium chloride,showing that it was probably male.。