seismic and geoelectric evidence for collisional and extensional events in the fennoscandian shield implications for precambrian crustal evolution extensive deep seismic and electromagnetic sounding programs have resulted in tens of deep refraction seismic profiles normal incidence reflection profiles several hundred magnetotelluric soundings and several magnetovariational array observations results are compiled into four maps 1 moho depth 2 thickness of the lower crustal high velocity layer vp 7 km s 3 depth to the upper interface of the high velocity layer and 4 distribution of upper and middle crustal electrical conductors the moho depth is approximately 40 km in the archaean domain and varies between 40 and 65 km in the svecofennian domain most of the thickness variation 0 24 km is concentrated in the lower crustal high velocity layer electrically the crust is formed of several rather homogeneous either resistive or conductive blocks that are bounded by upper and middle crustal conductive zones the cratonized archaean crust experienced an extensional phase during which a thin mafic lower crustal high velocity layer was produced in association with mafic dykes 2 2 2 1 ga and well conducting volcanogenic and metasedimentary belts 2 5 2 0 ga the moho of the archaean domain was consequently reformed in the early proterozoic major thickening of the crust 50 65 km occurred when a svecofennian island arc and the archaean craton collided the svecofennian orogeny 1 76 1 9 ga resulted in a collage of metasedimentary rocks squeezed between crustal blocks of the island arc the internal terrane boundaries are seen as good reflectors and or inclined or vertical conductors that extend at least to the middle crust the thick high velocity 7 km s lower crust is a combination of mafic lower crust of the island arc crustal blocks and mafic additions from either delamination of the lithosphere after the collision or from a period of late svecofennian subduction the collisional boundary is also preserved as a discontinuous conductive zone between the archaean and svecofennian domains the thickened crust was subsequently thinned to 42 km along e w striking zones during an extensional period characterized by the intrusion of anorogenic rapakivi granitoid batholiths coeval mafic dykes and gabbro anorthosite bodies 1 6 1 5 ga the crust of the central part of the shield has since remained virtually intact

suppression of eddy diffusivity across jets in the southern ocean abstract geostrophic eddies control the meridional mixing of heat carbon and other climatically important tracers in the southern ocean the rate of eddy mixing is typically quantified through an eddy diffusivity there is an ongoing debate as to whether eddy mixing in enhanced in the core of the antarctic circumpolar current or on its flanks a simple expression is derived that predicts the rate of eddy mixing that is the eddy diffusivity as a function of eddy and mean current statistics this novel expression predicts suppression of the cross jet eddy diffusivity in the core of the antarctic circumpolar current despite enhanced values of eddy kinetic energy the expression is qualitatively and quantitatively validated by independent estimates of eddy mixing from altimetry observations this work suggests that the meridional eddy diffusivity across the antarctic circumpolar current is weaker than presently assumed because of the suppression of eddy mixing by the strong zonal current

the rare earth element ree mineralisation potential of highly fractionated rhyolites a potential low grade bulk tonnage source of critical metals abstract the rare earth elements ree have become crucial for modern industry technology and medicine with the increase in demand for these elements over the past few years currently being met by relatively few well known mineral deposits this lack of a secure supply of the ree has led to increased research into potential alternative sources of these in demand elements the primary fractionation processes involved in the petrogenesis of highly fractionated high silica rhyolites can cause the magmas that form these units to become preferentially enriched in the ree especially in the more valuable heavy ree hree although this is dependent on the mineral assemblages fractionated by the system in question a factor that is in turn a function of the source and tectonic setting of a given magmatic event the mineralogy of the ree is also important with volatile exsolution and vapour phase activity within highly evolved rhyolite systems potentially having a key role in concentrating the ree and other elements into concentrations and more importantly potentially acid leachable and therefore processable minerals that may be economically viable to extract this combined with the fact these rhyolites are often enriched in other critical and or economically important metals e g y nb ta be li f sn rb th and u means that these volcanic units should be considered as potential sources of these critical metals in addition the large volume nature of these rhyolites combined with the fact they frequently crop out at the earth s surface makes them ideally suited for more economical bulk open pit extraction this suggests that these high silica ree enriched rhyolites should be considered potential ree analogues of bulk tonnage low grade porphyry cu deposits warranting further investigation to determine whether these rhyolites are a viable new source of the ree especially the hree and are potential targets for future mineral exploration

a tin mineralized topaz rhyolite dike with coeval topaz granite enclaves at qiguling in the qitianling tin district southern china abstract the qiguling topaz rhyolite is present as a dike within the qitianling biotite granite batholith of the nanling range of southern china here the rhyolitic dike 4 5 m wide and 500 m long contains enclaves of topaz granite these rhyolites contain up to 72 wt sio 2 have alumina saturation index asi 1 1 and have groundmasses with estimated fluorine contents of approximately 1 5 wt textural relationships provide evidence of a quenched silicate melt that contains quartz k feldspar albite and zinnwaldite phenocrysts in a groundmass containing abundant topaz the rhyolites in the study area are also strongly enriched in tin 90 2700 ppm and generally have a close association between cassiterite and zinnwaldite although cassiterite is also present as sponge textured fills between rock forming minerals granite enclaves and their hosted rhyolite have similar major geochemical compositions and mineralogies to each other zircon u pb dating indicates that the topaz rhyolite 147 150 ma and topaz granite enclaves 154 ma were formed contemporaneously with ages that overlap within analytical uncertainty in addition the major and trace element compositions of the rhyolite and their granite enclaves are dissimilar to those of the hosting qitianling biotite granite this discovery of granite enclaves within rhyolite dikes suggests the presence of a topaz bearing granite body at depth that may host tin mineralization the expected hidden tin granite may be of great interest in the further exploration

phase equilibria of a fluorine rich leucogranite from the st austell pluton cornwall highly evolved leucogranitic rocks in the st austell pluton cornwall of hercynian age contain accessory muscovite topaz and fluorite the authors have studied the h sub 2 o saturated melting behavior of one representative sample its solidus and liquidus pass through the points 663 and 725 sup 0 c respectively at 1 kbar 640 and 665 sup 0 c at 2 kbar 610 and 717 sup 0 c at 4 kbar and 608 and 700 sup 0 c at 8 kbar plagioclase is on the liquidus at low pressure and topaz is on the liquidus at 4 kbar the fluorite is consumed in the formation of the first formed liquid calcium can partition into an evolved granitic melt if complexed by fluorine the fluorite appears to be largely primary in fresh fluorite granite at st austell and not to reflect the albitization of oligoclase in the surrounding biotite granite such fluorine rich leucogranites can be expected to be of subsolvus character

magmatic and postmagmatic processes in tin mineralized granites topaz bearing leucogranite in the eurajoki rapakivi granite stock finland the 1 57 ga eurajoki stock in southwestern finland is composed been overemphasized at the expense of exsolution and reof biotite hornblende fayalite granite biotite granites and late stage crystallization topaz bearing granite as well as related topaz bearing rhyolite ongonite dykes miarolitic cavities indicate the presence of a separate fluid phase during late stages of crystallization of the topazbearing granite and greisen type sn be w zn mineralization is closely associated with it subsolidus reactions have modified the

late quaternary paleoclimate in the eastern mediterranean region from stable isotope analysis of speleothems at soreq cave israel abstract the eastern mediterranean continental paleoclimate during the past 25 000 years was determined by a high resolution petrographic stable isotopic and age study of speleothems from soreq cave israel 18o 13c trends indicate that all speleothems older than 7000 yr formed under conditions that differ from those of today the period from 25 000 to 17 000 yr b p was characterized by the highest 18o and 13c values which indicate deposition at temperatures of 12 16 c annual rainfall of 300 450 mm and vegetation typical of a mixed c3 c4type from 17 000 to 10 000 yr b p deglaciation in northern europe 18o values dropped progressively correlative with warming 2 3 c and a gradual increase in precipitation a simultaneous decrease in 13c gives a range expected for c3 type vegetation this period also shows significant 18o and 13c spikes which are correlatable with global events e g heinrich events and the younger dryas stade the speleothems that grew between 10 000 and 7000 yr b p have a unique petrography showing irregular thin laminae of various colors and much detritus they have the lowest 18o corresponding to 1000 mm rain coupled with the highest 13c caused by flooding events which stripped the soil cover from 7000 to 1000 yr b p conditions became closer to those of today this study demonstrates that global events which were recognized in northern europe and north africa are also evident in the eastern mediterranean and are reflected principally by large changes in the rainfall rate

tracking magmatic and hydrothermal nb ta w sn fractionation using mineral textures and composition a case study from the late cretaceous jiepailing ore district in the nanling range in south china abstract the jiepailing mining district in the nanling range in south china is well known for its granite related sn be f mineralization recently drill holes have exposed an nb ta w sn mineralized granitic porphyry and topaz bearing granite greisen at depth which we have studied here using mineral columbite rutile wolframite cassiterite zircon and mica major and trace element compositional data mineral textures and zircon and columbite u pb geochronology our age data shows that the porphyry and the granite and their mineralization formed at 91 89 1 ma in the late cretaceous and thus subsequent to the main ore forming events of the region continuous mineral compositional trends indicate that the studied granitoids are related by progressive fractionation we propose that 1 subhedral euhedral low ta columbite crystallized from melt 2 euhedral subhedral rutile and wolframite and subhedral and subhedral cassiterite up to 30 m in size formed at the magmatic hydrothermal transition of the system and 3 high ta columbite and subhedral cassiterite up to 10 m in size formed from subsolidus hydrothermal fluids in combination with the nb ta w and sn compositions of zircon and mica their textures and compositional variation allow us to track the magmatic to hydrothermal rare metal fractionation concentration mobilization and deposition of the system in detail despite our limited access to it through only two exploration drill cores using the nb ta w and sn concentrations in zircon refractory early crystallized and in micas late equilibrated respectively was particularly useful for tracing the partial loss of sn and w ore components from the intrusion and to constrain the information which is crucial for any rigorous ore exploration

rapakivi granites and related rocks an introduction abstract this article is an introductory chapter for the proceedings of the last seventh meeting of the international geological correlation programme igcp project 315 correlation of rapakivi granites and related rocks on a global scale 1991 1996 based on current knowledge progress made during the six years of the project and the seven papers published in this special issue a synthesis of the age distribution geotectonic environment petrogenesis geochemistry and metallogeny of the rapakivi granites and related rocks is presented

comparison of proterozoic and phanerozoic rift related basaltic granitic magmatism abstract this paper compares the 1 67 1 47 ga rapakivi granites of finland and vicinity to the 1 70 1 68 ga rapakivi granites of the beijing area in china the anorogenic 130 ma granites of western namibia and the 20 15 ma granites of the colorado river extensional corridor in the basin and range province of southern nevada in finland and china the tectonic setting was incipient aborted rifting of paleoproterozoic or archean continental crust in namibia it was continental rifting and mantle plume activity that led to the opening of southern atlantic at 130 ma the 20 15 ma granites of southern nevada were related to rifting that followed the triassic paleogene subduction of the farallon plate beneath the southwestern united states in all cases extension related magmatism was bimodal and accompanied by swarms of diabase and rhyolite quartz latite dikes rapakivi texture with plagioclase mantled alkali feldspar megacrysts occurs in varying amounts in the granites and the latest intrusive phases are commonly topaz bearing granites or rhyolites that may host tin tungsten and beryllium mineralization the granites are typically ferroan alkali calcic metaluminous to slightly peraluminous rocks with a type and within plate geochemical and mineralogical characteristics isotope studies nd sr suggest dominant crustal sources for the granites the preferred genetic model is magmatic underplating involving dehydration melting of intermediate felsic deep crust juvenile mafic magma was incorporated either via magma mingling and mixing or by remelting of newly hybridized lower crust in namibia partial melting of subcontinental lithospheric mantle was caused by the tristan mantle plume in the other cases the origin of the mantle magmatism is controversial for the fennoscandian suites extensive long time mantle upwelling associated with periodic migrating melting of the subcontinental lithospheric mantle governed by heat flow and deep crustal structures is suggested

upper paleozoic mafic and intermediate volcanic rocks of the mount pleasant caldera associated with the sn w deposit in southwestern new brunswick canada petrogenesis and metallogenic implications abstract upper paleozoic 365 ma mafic and intermediate volcanic rocks of the piskahegan group constitute a subordinate part of the mount pleasant caldera which is associated with a significant polymetallic deposit tungsten molybdenum bismuth zones 33 mt ore with 0 21 w 0 1 mo and 0 08 bi and tin indium zones 4 8 mt with 0 82 sn and 129 g t in in southwestern new brunswick canada the epicontinental caldera complex formed during the opening of the late paleozoic maritimes basin in the northern appalachians the mafic and intermediate rocks make up two compositionally distinct associations the first association includes evolved rift related continental tholeiitic basalts and the second association comprises calc alkaline andesites although both associations were emplaced penecontemporaneously the basalts have low mg 0 34 0 40 smooth chondrite normalized ree patterns with la yb n 5 6 primitive mantle normalized trace element patterns without noticeable negative nb ta anomalies and their nd t ranges from 2 5 to 2 2 the basalts were generated by partial melting of a transition zone between spinel and garnet mantle peridotite at a depth of 70 90 km the calc alkaline andesites of the second association have chondrite normalized ree patterns that are more fractionated with la yb n 7 8 5 but without significant negative eu anomalies compared to the basaltic rocks they have lower nd t values ranging from 0 5 to 1 9 and their mantle normalized trace element plots show negative nb ta anomalies the nd t values display negative correlations with indicators of crustal contamination such as th la th nb and sio2 the andesitic rocks are interpreted to have formed by assimilation fractional crystallization processes which resulted in the contamination of a precursor basaltic magma with crustal material the parent basaltic magma for both suites underwent a different evolution the tholeiitic basalts experienced shallow seated fractional crystallization and evolved along a tholeiitic trend of early iron enrichment non oxic conditions the contaminated magma of the second association followed a calc alkaline fractionation trend of no iron enrichment oxidizing conditions characterized by a high ph2o and po2 environment at the mid crust levels the piskahegan group which is associated with an important polymetallic mineral deposit differs from the numerous non mineralized rift related volcanic suites of the regional upper devonian to lower carboniferous successions in the maritimes basin by the presence of a significant amount of coeval calc alkaline andesite which may be an indicator of potential mineralization

mueilha rare metals granite eastern desert of egypt an example of a magmatic hydrothermal system in the arabian nubian shield abstract the mueilha granite pluton is one of the rare metals bearing peraluminous granitic plutons in the arabian nubian shield it represents the apical part of a highly evolved magma chamber emplaced at a shallow level subsequent to the post pan african orogeny the pluton can be seen as a highly leucocratic medium grained albite oligoclase framework infilled with quartz k feldspar and muscovite that are variably overgrown by k feldspar muscovite quartz and topaz megacrysts the increasing number and size of the k feldspar megacrysts at the expense of the whitened albite oligoclase framework imparts variably red color to the mueilha granite contacts between the milky white and red granites are usually gradational but may be locally sharp or may form narrow transition zones resulting from abrupt variations in texture and lithology textural relations indicate an initial stage of hydrothermal albitization of magmatic plagioclase and crystallization of topaz megacrysts resulting from infiltration of na rich fluorine bearing fluids a subsequent stage of metasomatic enrichment is characterized by extensive growth of large k feldspar quartz and muscovite megacrysts at the expense of the albite oligoclase crystals as a result of infiltration of k si rich hydrous fluids post magmatic infiltration of hydrous fluids along the fault planes is shown by the intense replacement of alkali feldspar megacrysts by quartz development of myrmekitic intergrowth pockets along the k feldspar megacrysts and sealing of the micro fractures by cryptocrystalline mixtures of clay minerals iron oxides sericite and chlorite compositionally the red granitic rocks have higher sio 2 fe 2 o 3total k 2 o na 2 o ree y th u zr and zn and lower al 2 o 3 ga ta nb and mo compared to the milky white granites lile and sn do not show clear variation trends throughout the mueilha granite pluton suggesting their immobility during hydrothermal alteration microthermometric measurements indicate that the interactions with the hydrothermal fluids started at a minimum temperature 400 c most likely during the late stage crystallization of the mueilha granite and continued after their complete solidification i e subsolidus conditions at a temperature as low as 120 c the high fertility of mueilha granite is most plausibly the result of partial melting within the undepleted juvenile crust of the arabian nubian shield that has formed during the pan african orogeny

internal differentiation of rare element pegmatites effects of boron phosphorus and fluorine lithium rich rare element pegmatites are characterized by high concentrations of b p and f the interactions of these components with h2o and rare alkalis lower liquidas and solidus temperatures enhance silicate liquid h2o miscibility and control partitioning and concentration of group i elements and higher field strength cations boron f and perhaps p may form peralkaline na and li species that promote early saturation in mica quartz activities of f p and especially b are largely unbuffered throughout crystallization concentration of these components through fractional crystallization involving muscovite generates a peralkaline na aluminosilicate rich melt or vapor from which albitites rich in tourmaline phosphates f rich micas beryl zircon and nb ta sn oxides crystallize phase equilibrium experiments with peraluminous b p f rich rhyolite obsidian macusanite simulate many features of rare element pegmatites especially at h2o undersaturated conditions

the orestes melt zone mcmurdo dry valleys antarctica spatially distributed melting regimes in a contact melt zone with implications for the formation of rapakivi and albite granites

mineralogy and geochemistry of pegmatite hosted sn ta nb and zr hf bearing minerals from the southeastern part of the bastar malkangiri pegmatite belt central india abstract primary tin and rare metal mineralization in the bastar malkangiri pegmatite belt central india is associated with granitic pegmatites hosted by metabasic and metasedimentary rocks the rare metal minerals identified from six mineralized pegmatites at govindpal mundaguda mundval dhuramagurah haladikunda and bacheli include cassiterite columbite tantalite wodginite microlite fersmite and hf zircon ta nb poor cassiterite is ubiquitous and the most abundant ore mineral in all the mineralized pegmatites subtle differences are noted in the ore mineral assemblages and in the compositions of individual minerals in different pegmatites ta nb oxides are represented by microlite wodginite manganotantalite in li f p bearing lct pegmatites govindpal mundaguda and mundval in contrast least evolved members of the lct type pegmatites are characterized by the presence of ferrocolumbite dhuramgurah haladikunda and rare ferrotantalite bacheli the compositional variations of columbite tantalite in terms of ta ta nb and mn mn fe ratios and zircon in terms of hf contents from different pegmatites correlate with the degree of fractionation of the pegmatitic melt in the govindpal pegmatite ta nb poor cassiterite occurs as aggregates of grains small pockets and veinlets in the intermediate and core zone the ta nb oxides are restricted to the core margin texturally and compositionally distinct ta nb rich cassiterite along with ta nb oxides and hf zircon occur as irregular inclusions in ta nb poor cassiterite at the core margin the field evidence textural relations and compositions of the ore minerals suggest that the main mineralizing event was associated with hydrothermal precipitation of ta nb poor cassiterite which postdated precipitation of manganotantalite wodginite microlite hf zircon and ta nb rich cassiterite in the govindpal pegmatite the crystallization of ta nb oxides was facilitated possibly by the removal of li and f from the melt and that of ta nb rich cassiterite by increasing oxygen fugacity calculated higher fe 3 fe 2 in wodginite compared to manganotantalite suggests such a possible increase in oxygen fugacity anastomosing veins of microlite in ta nb poor cassiterite was the last mineralizing event in this pegmatite the consistently high ti contents of this subsolidus vein microlite compared to primary ta nb oxides manganotantalite wodginite and microlite might suggest contamination by ingress of metamorphic fluid during its formation

the miocene pliocene macusani volcanics se peru i mineralogy and magmatic evolution of a two mica aluminosilicate bearing ignimbrite suite

source regions of granites and their links to tectonic environment examples from the western united states this review in honor of ilmari haapala s retirement reflects on lessons learned from studies of three granitic systems in western north america 1 mesoproterozoic samples from west texas and east new mexico 2 laramide granitic systems associated with porphyry copper deposits in arizona and 3 granites of the colorado mineral belt the studies elucidate relationships amongst tectonic setting source material and magma chemistry mesoproterozoic basement samples are from two different felsic suites with distinct elemental and isotopic compositions the first suite the plutonic province is dominantly magnesian calc alkalic to alkali calcic and metaluminous it has low k2o na2o and rb sr and nd model ages of 1 56 to 1 40 ga the second suite the panhandle igneous complex is magnesian metaluminous alkalic and is part of the mesoproterozoic belt of magmatism that extends from finland to southwestern united states samples from the panhandle igneous complex demonstrate three episodes of magmatism the first pulse was intrusion of quartz monzonite at 1380 to 1370 ma the second was comagmatic epizonal granite and rhyolite at 1360 to 1350 ma both of these rock types are high k to slightly ultra high k the third pulse at 1338 to 1330 ma was intrusion of ultra high k quartz syenite nd model ages 1 94 to 1 52 ga are distinct from those of the plutonic province and systematically older than crystallization ages implying a substantial crustal input to the magmas at the sierrita porphyry copper deposit in the mazatzal province of southeastern arizona trace element sr and nd isotopic compositions were determined for a suite of andesitic and rhyolitic rocks 67 ma intruded by granodiorite and granite isotopic composition and chemical evolution are well correlated throughout the suite andesite has the least negative initial end 4 3 and lowest 87sr 86sri 0 7069 it is also the oldest and chemically most primitive having low concentrations of rb sio2 and high concentrations of transition elements these parameters change through the system to the youngest unit granite which has the most negative end 8 5 the highest 87sr 86sri 0 7092 and is chemically most evolved correlation between chemical and nd isotopic evolution probably resulted from a continuous process of progressive assimilation in which mafic magmas invade and incorporate continental crust deposits in arizona with end values more negative than the 8 5 of sierrita lie in the older yavapai province in the northwestern part of the state the difference in the most negative epsilon nd implies that nd isotopic signature is sensitive to the age of the precambrian domain the granites from the colorado mineral belt were emplaced during the transition from laramide convergence to mid tertiary extension three different groups of granites are recognized the first is laramide and was formed during assimilation fractional crystallization involving lower crustal mafic source materials the second and third groups are mid tertiary and represent intracrustal melting of heterogeneous sources this change in source regions and melt regimes in transition from convergence to extension is fundamental to the mesozoic and cenozoic evolution of western north america

petrological and geochemical evolution of the kymi stock a topaz granite cupola within the wiborg rapakivi batholith finland abstract the 6 3 km kymi monzogranite stock represents the apical part of an epizonal late stage pluton that was emplaced within the 1 65 to 1 63 ga wiborg rapakivi batholith the stock has a well developed zonal structure from the rim to the center stockscheider pegmatite equigranular topaz granite porphyritic topaz granite the contact between the two granites is usually gradational within a few centimeters but local inclusions of the porphyritic granite in the equigranular granite indicate that the latter solidified later hydrothermal greisen and quartz veins some of which contain genthelvite beryl wolframite cassiterite and sulfides cut the granites of the stock and the surrounding country rocks the equigranular granite contains 1 to 4 vol topaz and its biotite is lithian siderophyllite the porphyritic granite has 0 to 3 vol topaz and the mica is siderophyllite the equigranular granite is geochemically highly evolved with elevated li rb ga ta and f and very low ba sr ti and zr the ree patterns show deep negative eu anomalies and tetrad effects indicating extreme magmatic fractionation and aqueous fluid rock interaction the zonal structure of the stock is interpreted as a result of differentiation within the magma chamber internal convection in the crystallizing magma chamber and upward flow of residual melt as a boundary layer along sloping contacts resulted in accumulation of a layer of highly evolved volatile rich magma in the apical part of the chamber crystallization of this apical magma produced the stockscheider pegmatite and the equigranular granite the underlying crystal mush solidified as the porphyritic granite much of the crystallization took place from volatile saturated melt and episodic voluminous degassing expelled fluids into opened fractures where they or their derivatives reacted with country rocks and caused alteration and mineralization

p t conditions of crystallization and origin of plagioclase mantled alkali feldspar megacrysts in the mesozoic granitoids in the qinling orogen china abstract the qinling orogen between the north china and south china cratons was intruded at 211 217 ma by calc alkaline quartz monzonitic to monzogranitic plutons characterized by i to a type geochemistry and in many places contain plagioclase mantled alkali feldspar megacrysts rapakivi texture sensu lato the felsic rocks contain mafic to intermediate magmatic enclaves suggestive of mingling and mixing of mafic and felsic magmas the p t conditions of crystallization have been determined for early mineral assemblages inner parts of alkali feldspar megacrysts and their plagioclase quartz amphibole and biotite inclusions and late assemblages matrix minerals of the rapakivi textured granitoids al contents in amphibole from the early and late mineral assemblages yield pressures of 1 2 3 0 and 0 7 3 0 kbar respectively and indicate only minor pressure change between the crystallization of the early and late assemblages amphibole plagioclase thermometry gives temperatures mainly of the order of 900 to 1000 c for both the early and late assemblages indicating nearly isothermal conditions feldspar thermometers yield lower temperatures relative abundances of minerals and their chemical compositions indicate that the late mineral assemblages tend to be richer in mgo na 2 o and cao than the early assemblages rapakivi texture is interpreted in this case mainly as a result of compositional changes related to the hybridization between granitic and more mafic magmas small release of pressure during crystallization of the magmas may have contributed to the origin of the mantled alkali feldspar megacrysts

the beauvoir topaz lepidolite albite granite massif central france the disseminated magmatic sn li ta nb be mineralization the beauvoir topaz lepidolite albite granite french massif central is the latest intrusion in a variscan peraluminous granitic complex composed of three units successively emplaced the concealed la bosse granite the colettes two mica granite and the beauvoir granite the 900 m deep drill hole of the geologie profonde de la france deep drilling program of the continental crust has provided a continuously cored section of the beauvoir granite the exposed section of the beauvoir granite is presently mined for kaolin in the upper 200 m it also represents a huge subeconomic disseminated li sn ta be deposit sharing many characteristics with rare metal bearing pegmatites compared to similar li f rich igneous bodies the beauvoir granite is strongly enriched in sn 200 1 400 ppm ta 20 400 ppm and be 20 300 ppm li is located in lepidolite and amblygonite ta and nb mainly in columbo tantalite and uranium rich microlite and sn in cassiterite be is located in lepidolite crystals and in unidentified mineral s the major element composition of the beauvoir granite is similar to that of macusani volcanic glasses of peru and ongonite subvolcanic rocks of mongolia the main structural textural mineralogical and geochemical characteristics of the beauvoir granite can be explained by extreme fractionation of f and li rich magmas and associated fluid phases most trace elements show a strong upward enrichment the high f sub o 2 low solidus temperature and high fluorine content of the beauvoir magma have considerably reduced sn and w fractionation in the expelled magmatic fluid despite its high chlorine content 25 30 wt nacl equiv however f and li enriched geochemical halos have developed in the enclosing mica schist in response to the boiling of the magmatic fluid the relatively deep emplacement of the granite 3 km has limited the development of hydraulic fracturing and subsequent hydrothermal circulation and mineralization thus despite the very high specialization of the beauvoir granite no significant vein type mineralization is directly related to it the la bosse quartz ferberite stockwork was developed before the emplacement of the colettes and beauvoir granites and is related to the earlier concealed la bosse granite

fluid and melt inclusion evidence for the origin of idiomorphic quartz crystals in topaz bearing granite from the salmi batholith karelia russia abstract idiomorphic quartz crystals in topaz bearing granite from the salmi batholith contain primary inclusions of silicate melt and abundant mostly secondary aqueous fluid inclusions microthermometric measurements on melt inclusions give estimates for the granite solidus and liquidus of 640 680 c and 770 830 c respectively using published solubility models for h2o in granitic melts and the obtained solidus liquidus temperatures from melt inclusions the initial water concentration of the magma is deduced to have been approximately 3 wt and the minimum pressure about 2 kbar at this initial stage volatile undersaturation conditions of magma were assumed these results indicate that the idiomorphic quartz crystals are magmatic in origin and thus real phenocrysts during subsolidus cooling and fracturing of the granite several generations of aqueous fluid inclusions were trapped into the quartz phenocrysts the h2o inclusions have salinities and densities of 1 41 wt nacl eq and 0 53 1 18 g cm3 respectively

tin tantalum niobium mineralization in the penouta deposit nw spain textural features and mineral chemistry to unravel the genesis and evolution of cassiterite and columbite group minerals in a peraluminous system abstract the sn ta nb penouta granite is a highly evolved rare metal post kinematic leucogranite located in north western spain which was intermittently mined from roman times until 1985 when falling metal prices led to the closure of most mines in the country mineralization consists mainly of cassiterite cassiterite i and columbite group minerals cgm disseminated in the leucogranite that increase in abundance and crystal size towards the upper part of the granitic cupola especially in banded pegmatite like dikes upwards quartz veins and greisen zones associated with the wall rock mainly augen gneisses were developed containing coarse grained cassiterite cassiterite ii in contrast to nearly homogenous cassiterite chemistry cgm may show complex compositional zonation patterns in relation with compositional variations of the leucogranite taking into account the mineral chemistry and textural features of cgm two main groups were distinguished i the first one group i follows a general main trend from columbite fe to columbite mn and finally to tantalite mn which is in accordance with the evolution of the magma observed from the less to the more evolved zones of the leucogranite and from bottom to top of the body and responds to common fractionation patterns of decreasing nb ta ratios in the melt and ii a second group group ii with intermediate values of mn mn fe and ta ta nb due to local supersaturation effects of the melt during crystallization resulting in complex oscillatory zoned cgm crystals textural and chemical features of cassiterite and cgm support the magmatic origin for both minerals although cassiterite crystallized later in the sequence in both generations mineral chemistry evolution of cgm is in good agreement with a greater solubility of tantalite in the melt at the upper levels where besides the fluorine contents of apatite and muscovite were increased and the onset of fluorite crystallization occurred so the fluorine enrichment in the upper levels seems likely to be an important component to explain the mineral chemistry of the penouta granite although the same mineral chemistry scheme could also be explained in terms of white mica fractionation upwards furthermore the absence of typical textures originated by fluids in the cgm as well as the lack of these minerals in the quartz veins point to a low influence of the hydrothermal fluids in dissolution and recrystallization processes of the primary oxides

rare element enriched s type ash flow tuffs containing phenocrysts of muscovite andalusite and sillimanite southeastern peru ash flow tuffs of neogene age exposed over 2 500 km 2 in the macusani region of southeastern peru are the volcanic equivalent of s type granites the strongly peraluminous tuffs contain phenocrysts of andalusite sillimanite and muscovite and have high 87 sr 86 sr i 0 7258 and 0 7226 and 18 o 11 elevated concentrations of li cs be sn b and other minor elements compare with those in tin granites mineral phase relations and composition are indicative of low magmatic temperatures and oxygen fugacities and high a hf a h 2 o the chemical isotopic and mineralogical features and regional geologic relations are consistent with models of magma generation involving the incorporation of large amounts of pelitic rock

fluorite stability in silicic magmas recent experimental evidence is used to assess the conditions under which fluorite forms an early crystallising phase in silicic magmas fluorite solubility primarily depends on the na k al balance in the coexisting silicic melt reaching a minimum in metaluminous melts it can display reaction relationships with topaz and titanite depending on changes in melt composition during crystallisation an empirical model of fluorite stability in ca poor peralkaline rhyolite melts is derived and applied to selected rocks text f text melt left text wt right left left text na text k text al right left 2 1110 3 text t left circ c right 1 5778 right right 2 789

granitic systems a special issue in honor of ilmari haapala abstract this paper is an introduction to the special issue of lithos honoring ilmari haapala the 1982 2002 professor of geology and mineralogy of the department of geology university of helsinki the articles in the issue are based on invited presentations given at a january 12 14 2003 symposium granitic systems state of the art and future avenues that was held at the department of geology university of helsinki on the occasion of ilmari haapala s december 31 2002 retirement the scientific achievements of professor haapala are briefly reviewed and the main results of the papers that comprise the volume are discussed

non pegmatitic deposits of beryllium mineralogy geology phase equilibria and origin non pegmatitic occurrences of be minerals constitute a diverse set of geologic environments of considerable mineralogical and petrological interest they currently provide the majority of the world s be ore and emeralds and they contain the greatest resource of these commodities of the approximately 100 be minerals known see chapter 1 by grew appendix a most occur in hydrothermal deposits or non pegmatitic igneous rocks where their distribution varies systematically with the setting and origin table 1 fig 1 view this table table 1 beryllium minerals in non pegmatitic deposits formulas use and occurrence 1 figure 1 chemography of the principal solid phases in the beo al2o3 sio2 h2o f2o 1 bash system with the projected positions of helvite group and alkali be silicates also shown are generalized fields for some of the major types natural of occurrences cf table 1 fig 4 see text for discussion beryllium minerals are best known from geologic systems associated with felsic magmatism they also occur in a variety of settings that lack evident igneous associations environments range from the surface to the deep crust and host rocks range from feldspathic to carbonate to ultramafic in composition genetically related igneous rocks are felsic and share low calcium and high f contents but are diverse in composition setting and origin compositions range from strongly peraluminous to peralkaline and can be silica undersaturated beryllium minerals also occur in metamorphic and basinal environments and are redistributed by surface processes table 2 summarizes the types and significance of major groups of occurrences by their lithologic associations figure 2 shows the global distribution of some important examples and regional belts for most types at least one example has been described in some detail and can be used to help evaluate general patterns however

ta and sn concentration by muscovite fractionation and degassing in a lens like granite body the case study of the penouta rare metal albite granite nw spain abstract the penouta peraluminous low phosphorous granite is the most important low grade high tonnage sn ta nb bearing albite granite from the iberian massif a sheet or laccolith shape instead of a stock is inferred for the penouta granite maybe in relation with the low viscosity and high mobility of a fluorine bearing melt subhorizontal lateral extension of the magma is also inferred via vertical and horizontal geochemical variations the absence of compositional gaps in variation diagrams coupled with continuous evolutionary trends of compatible and incompatible elements with height discard a multi pulse intrusion and point to a single magma pulse mineral chemistry trace element and least squares mass balance modelling support a differentiation process from bottom to top in the emplacement place the absence of switch from incompatible to compatible behaviour bell shaped trends in sn nb and ta variation diagrams coupled to experimental constraints on tantalite and cassiterite saturation suggest that nb ta oxides and probably cassiterite were not fractionated mineral phases their crystallisation being related to concentration gradients within a trapped intercumulus melt major and trace element modelling support that the concentration upwards of ta and the ta nb ratio could be a consequence of mineral fractionation with a key role of muscovite mainly primary for the ta nb ratio as this mineral has a higher partition coefficient for nb than ta our results suggest that fluorine and peraluminosity had a limited effect in the ta nb ratio variations hence ta enrichment is mainly controlled by fractional crystallisation processes in most cases sn enrichment was also concomitant with ta indicating that crystal melt fractionation processes also played an important role in sn concentration nevertheless the strongest sn enrichment in the granite e g central part of the granite body does not correspond to a significant ta enrichment the high affinity of sn for fluids and the high partitioning of ta for melt could explain this decoupling nevertheless the magmatic signature of cassiterites in these strongly sn enriched zones central part of the granite body rules out a hydrothermal subsolidus origin for this fluid by analogy with models carried out in sill like bodies it seems likely that the sn enrichment in the central part of the granite body is related to fluid saturation degassing occurred in the lower margin as a consequence of cooling and crystallisation of mostly anhydrous minerals i e second boiling the vapour exsolved migrated into the hotter melt up to the central part where it probably was reabsorbed yielding cassiterite with a magmatic signature moreover we suggest that heat loss in the upper margin of the granite body might also contribute to the formation of a second fluid saturated zone as a result pegmo aplites and greisen were developed

proterozoic ferroan feldspathic magmatism abstract the proterozoic eon is characterized by an unusual abundance of ferroan feldspathic rocks that range in composition from granite to quartz syenites to feldspathoid bearing syenites three associations of ferroan rocks may be recognized on the basis of major element compositions 1 metaluminous alkalic to alkali calcic syenites and granites associated with anorthosites and iron rich basaltic rocks 2 alkaline intrusions in continental rifts and 3 calc alkalic metaluminous to peraluminous granitoid plutons that are less strongly ferroan than the other two groups the first two groups form by differentiation of tholeiitic to alkali basaltic parental magmas the third by partial melting of quartzo feldspathic crust although all three associations may form in intraplate settings only the alkaline intrusions which typically contain high incompatible trace element abundances plot entirely within the within plate granite fields on trace element discrimination diagrams processes of crustal melting and magma mixing have had a greater effect on the trace element compositions of ferroan granitoids from the other two associations causing some rocks to plot outside this field of these three associations the granitoids associated with anorthosites are the most voluminous and are essentially restricted to the proterozoic special conditions perhaps related to the presence of a long lived supercontinent under which widespread mantle upwelling took place appear required to explain the abundance of these rocks ferroan alkaline rocks although rarely preserved in archean crust are present in proterozoic and phanerozoic rifts the earliest alkaline intrusions thus may mark the establishment of rigid continents capable of rifting the formation of ferroan calc alkalic granites does not appear to be time dependent these granites have been generated throughout earth history in response to crustal melting

phase equilibria of a be u and f enriched vitrophyre from spor mountain utah abstract the equilibrium melting relations of a vitrophyre representative of topaz rhyolites have been experimentally determined in order to constrain the pre eruption temperature and h2o content of topaz rhyolite magmas the vitrophyre sample is strongly enriched in f and incompatible elements and consists of approximately 70 unaltered volcanic glass and 30 crystals of biotite quartz sanidine plagioclase magmatic fluorite and a variety of accessory phases biotite stability is strongly dependent on temperature pressure and ah2o in the melt and is apparently independent of the variations in o2 over the range investigated in this study the thermal stability of biotite increases relative to that of quartz sanidine and plagioclase in water saturated melts as pressure increases from 1 2 to 2 kbar fluorite is stable to temperatures below but within 50 to 75 c of the biotite stability curve and topaz is present in the products of runs at and near the solidus for all fluid conditions investigated the 1 2 wt f in the vitrophyre results in very low solidus temperatures of 525 c for all fluid conditions studied comparison of the experimentally determined crystallization sequence of the vitrophyre with the observed crystallization sequence of the vitrophyre and of the overlying topaz rhyolites indicates that the phenocrysts in the vitrophyre and in the topaz rhyolites crystallized at a pressure 1 kb that the magma contained at least 4 wt water during initial crystallization of biotite and that the magma contained a pre eruption water content of 5 wt

the interplay of evolved seawater and magmatic hydrothermal fluids in the 3 24 ga panorama volcanic hosted massive sulfide hydrothermal system north pilbara craton western australia the 3240 ma panorama volcanic hosted massive sulfide vhms district is unusual for its high degree of exposure and low degree of postdepositional modification in addition to typical seafloor vhms deposits this district contains greisen and vein hosted mo cu zn sn mineral occurrences that are contemporaneous with vhms orebodies and are hosted by the strelley granite complex which also drove vhms circulation hence the panorama district is a natural laboratory to investigate the role of magmatic hydrothermal fluids in vhms hydrothermal systems regional and proximal high temperature alteration zones in volcanic rocks underlying the vhms deposits are dominated by chlorite quartz albite assemblages with lesser low temperature sericite quartz k feldspar assemblages these assemblages are typical of vhms hydrothermal systems in contrast the alteration assemblages associated with granite hosted greisens and veins include quartz topaz muscovite fluorite and quartz muscovite sericite chlorite ankerite these vein systems generally do not extend into the overlying volcanic pile fluid inclusion and stable isotope studies suggest that the greisens were produced by high temperature 590 c high salinity 38 56 wt nacl equiv fluids with high densities 1 3 g cm3 and high 18o 9 3 0 6 these fluids are compatible with the measured characteristics of magmatic fluids evolved from the strelley granite complex in contrast fluids in the volcanic pile including the vhms ore forming fluids were of lower temperature 90 270 c lower salinity 5 0 11 2 wt nacl equiv with lower densities 0 88 1 01 g cm3 and lower 18o 0 8 2 6 these fluids are compatible with evolved paleoarchean seawater fluids that formed the quartz chalcopyrite sphalerite cassiterite veins which are present within the granite complex near the contact with the volcanic pile were intermediate in temperature and isotopic composition between the greisen and volcanic pile fluids t 240 315 c 18o 4 3 1 5 and are interpreted to indicate mixing between the two end member fluids evidence of mixing between evolved seawater and magmatic hydrothermal fluid within the granite complex together with the lack of evidence for a magmatic component in fluids from the volcanic pile suggest partitioning of magmatic hydrothermal from evolved seawater hydrothermal systems in the panorama vhms system this separation is interpreted to result from either the swamping of a relatively small magmatic hydro thermal system by evolved seawater or density contrasts precluding movement of magmatic hydrothermal fluids into the volcanic pile variability in the salinity of fluids in the volcanic pile combined with evidence for mixing of low and high salinity fluids in the massive sulfide lens is interpreted to indicate that phase separation occurred within the panorama hydrothermal system although we consider this phase separation to have most likely occurred at depth within the system as has been documented in modern vhms systems the data do not allow the location of the inferred phase separation to be determined

solubility of tin tungsten and molybdenum oxides in felsic magmas saturation versus undersaturation of granitic melts in tin tungsten and molybdenum oxides is discussed on the basis of experimental data results of dry and hydrothermal experiments are evaluated under the assumption of ideal solubility of sn w and mo oxides in granitic melts a conservative interpretation arrives at concentration levels of 1000 ppm sno2 wo3 and moo3 respectively considered as the maximum solubility of these components in granitic melts at 750 c 800 c such values are never reached in natural granites unaffected by hydrothermal alteration and therefore even highly evolved granites are expected to be undersaturated in these metals consequently cassiterite and scheelite are neither common liquidus minerals of ore bearing granites nor restite minerals from partial melting events

beryllium in silicic magmas and the origin of beryl bearing pegmatites this chapter addresses the portion of the geochemical cycle of beryllium that entails its transfer through the continental crust by the generation and migration of silicic magmas which will be referred to loosely as granitic but will include all of the textural variants of rocks derived from the granitic bulk compositions within the granite system we will examine the distribution of be between anatectic melts and residual crystals and we will track the accumulation of be in melt via crystal fractionation culminating in the saturation of pegmatite forming melts in the mineral beryl beryl is unquestionably the most common manifestation of be enrichment and the most abundant of the phases that contain essential beryllium see cern this volume to explain the presence of beryl in pegmatites we pose four questions 1 how much be does it take to saturate a granitic pegmatite forming melt in beryl 2 how much be is likely to be incorporated in silicic partial melts at their source 3 consequently how much fractionation of a typical granitic magma must occur to achieve beryl saturation in pegmatitic derivatives or is beryl saturation possible without extended magmatic fractionation 4 and should all granitic magmas be expected to achieve beryl saturation eventually or are there special attributes of the source material or crystalline phases in the magma that predetermine the likelihood of forming beryl in pegmatitic differentiates to address these questions we start with a review of beryl saturation in pegmatites we then examine the likely abundance of be derived by anatexis at the sources of granitic magmas with the two ends of the system bracketed we can then subject be fractionation to conventional modeling methods to ascertain how much fractionation must take place to bring granitic melts to beryl saturation as a review this chapter relies as much as possible on readily available publications

phase relations of a f enriched peraluminous granite an experimental study of the kymi topaz granite stock southern finland phase relations of f rich kymi equigranular topaz granite have been investigated experimentally at 100 500 mpa as a function of water activity and f content fluorite and topaz can crystallize as liquidus phases in f rich peraluminous systems but the f content of the melt should exceed 2 5 3 0 wt for the crystallization of topaz in peraluminous f bearing melts containing more than 1 wt f topaz and muscovite are expected to be the first f bearing phases to crystallize at high pressure whereas fluorite and topaz should crystallize first at low pressure following reaction models the saturation of fluorite and topaz caal2si2o8 plagioclase 2 alf3 melt caf2 fluorite 2al2sio4f2 topaz the obtained partition coefficient for f between biotite and glass d f bt glass ranges from 1 89 to 0 80 average value 1 29 and can be used as an empirical fluormeter to determine the f content of coexisting melts combined petrological and experimental studies of the kymi equigranular topaz granite indicate that plagioclase was the liquidus phase at nearly water saturated fluid saturated conditions and that the f content of the melt was at least 2 wt the mean f content of natural biotite 3 92 wt suggests that the late stage crystallization of biotite occurred in melts containing about 3 wt f the early crystallization of biotite and the presence of muscovite in our experiments at 200 mpa contrasts with the late stage crystallization of biotite and the absence of muscovite in the natural assemblage indicating that crystallization pressure may have been lower than 200 mpa for the granite

mineralogy and geochemistry of indium bearing polymetallic veins in the sarvlaxviken area lovisa finland abstract a number of polymetallic vein mineralizations of different styles and metal associations including base alloy noble and critical metals have been discovered around the sarvlaxviken bay in the westernmost parts of the mesoproterozoic wiborg batholith south eastern finland the veins occur in two rapakivi granite varieties coarse grained wiborgite and medium grained marviken granite the veins are divided into five groups based on the dominant metal associations the li as w zn mn pb zn and cu as in associations are hosted by wiborgite and are strongly controlled by a nnw trending tectonic pattern that evolved in two main stages the li as w zn mn association generation 1 formed in a typical greisen environment with li bearing mica in significant alteration halos around a narrow quartz vein this greisenization was accompanied by silicification followed by sericitization and chloritization the pb zn association occurs in a similar vein type but without typical high temperature minerals and is considered to have formed at a higher crustal level generations 2a and 2b formed under more brittle conditions leading to fracturing quartz veining and metal precipitation of ore minerals this metal association is characterized by very high contents of cu as and up to 1490 ppm in but with 0 4 zn which leads to very high in zn ratios up to 8400 enabling formation of abundant roquesite the as sn cu and mo bi be associations are hosted by alteration zones without hydrothermal quartz in the marviken granite mineralization with moderately high contents of as sn and cu is associated with greisenization while mineralization with spectacular contents of be as well as high contents of mo and bi is associated with sericitization chloritization and berylification the internal age relations between the wiborgite hosted nnw trending veins show a clear evolution from a typical greisen type environment the li as w zn mn and pb zn associations of generation 1 to cooler and more brittle conditions governing quartz veining and precipitation of ore minerals belonging to the cu as in association generations 2a and 2b the age relations between these wiborgite hosted veins and the veins in the marviken granite are more uncertain but the presence of a ns trending granitic dyke on the eastern side of the sarvlaxviken bay with similar ore fertile geochemical composition as the marviken granite indicates that the tectonically controlled veins formed simultaneously with the emplacement of the marviken granite and associated hydrothermal activity the polymetallic veins in the sarvlaxviken bay are unique for the fennoscandian shield not the least for the locally high indium grades and spectacular roquesite grains there is an obvious exploration potential for similar veins and hence a number of base alloy noble and critical metals also elsewhere in the entire wiborg batholith

the specific case of the mid proterozoic rapakivi granites and associated suite within the context of the columbia supercontinent abstract rapakivi granites and the associated suite anorthosite mangerite and charnockite that developed during the mid proterozoic escape the global rules that control usual granitic magma formation about 40 points that characterise the proterozoic magmatism confirm the originality of the magmatism rapakivi granites developed without a global orogenic context within the supercontinent columbia the intrusions extend from the east european shield to the western us through fennoscandia greenland and labrador other occurrences in the amazonian shield australia or south china are less well documented they show no definite trend in age or chemistry that would explain large scale mantle plume effects a mantle upwelling of material is contradictory with the re assembly of a supercontinent because it occurred before this magmatic episode 1 9 1 8 ga at 1 7 ga the supercontinent columbia amalgamated with the collision of the yapavai and mazatzal provinces a model is suggested that takes into account the supercontinent re assembly defining a downwelling flow in the mantle that anchors the continent above it in contrast to a material flow heat is still delivered to the base of the continental lithosphere and is focused toward the juvenile suture zone the base of the crust must reach 1200 1300 c before producing anorthosite magmas under such a high temperature gradient lasting over a long time magmas are transferred toward the upper crust giving the thin 5 km and square shape 100 km that the intrusions presently have heat delivery is essentially conductive leading to long time spans for intrusions the presence of the supercontinent immobile over a descending cell poloidal mode of convection developed a tangential force toroidal mode of convection that partly split the continent through strike slip deformation due to plate rotation it developed progressively between 1 57 and 1 3 ga starting from fennoscandia and then passing to amazonia western us and labrador in a clockwise sense the associated rotation induced sinistral shear manifested by small scale shear zones and the orientation of late magmatic facies topaz bearing granites in each province the proterozoic magmatism appears to be unique because it requires a supercontinent with a zone of juvenile crust surrounded by older cratons the present moho still shows remnants of this process having bumpy undulations that may reach 22 km in amplitude over a distance of 200 km

sn polymetallic greisen type deposits associated with late stage rapakivi granites brazil fluid inclusion and stable isotope characteristics tin polymetallic greisen type deposits in the itu rapakivi province and rondonia tin province brazil are associated with late stage rapakivi fluorine rich peraluminous alkali feldspar granites these granites contain topaz and or muscovite or zinnwaldite and have geochemical characteristics comparable to the low p sub type topaz bearing granites stockworks and veins are common in oriente novo rondonia tin province and correas itu rapakivi province deposits but in the santa barbara deposit rondonia tin province a preserved cupola with associated bed like greisen is predominant the contrasting mineralization styles reflect different depths of formation spatial relationship to tin granites and different wall rock fluid proportions the deposits contain a similar rare metal suite that includes sn fw fta fnb and base metal suite zn cu pb is present only in correas deposit the early fluid inclusions of the correas and oriente novo deposits are 1 low to moderate salinity 0 19 wt nacl eq co2 bearing aqueous fluids homogenizing at 245 450 8c and 2 aqueous solutions with low co2 low to moderate salinity 0 14 wt nacl eq which homogenize between 100 and 340 8c in the santa barbara deposit the early inclusions are represented by 1 low salinity 5 12 wt nacl eq aqueous fluids with variable co2 contents homogenizing at 340 to 390 8c and 2 low salinity 0 3 wt nacl eq aqueous fluid inclusions which homogenize at 320 380 8c cassiterite wolframite columbite tantalite scheelite and sulfide assemblages accompany these fluids the late fluid in the oriente novo and correas deposit was a low salinity 0 6 wt nacl eq co2 free aqueous solution which homogenizes at 100 260 8c and characterizes the sulfide fluorite sericite association in the correas deposit the late fluid in the santa barbara deposit has lower salinity 0 3 wt nacl eq and characterizes the late barren quartz muscovite and kaolinite veins oxygen isotope thermometry coupled with fluid inclusion data suggest hydrothermal activity at 240 450 8c and 1 0 2 6 kbar fluid pressure at correas and oriente novo the hydrogen isotope composition of breccia greisen stockwork and vein fluids

vapor undersaturated experiments with macusani glass h 2 o at 200 mpa and the internal differentiation of granitic pegmatites vapor undersaturated fractional crystallization experiments with macusani glass macusanite a peraluminous rhyolite obsidian at 200 mpa yield mineralogical fabrics and zonation and melt fractionation trends that closely resemble those found in zoned granitic pegmatites and other granitoids of comparable composition typically peraluminous li be ta rich deposits the zonation from the edge of charges inward is characterized by 1 fine grained sodic feldspar quartz border zones 2 a fringe of very coarse grained graphic quartz feldspar intergrowths that flair radially toward melt and terminate with nearly monophase k feldspar 3 cores of very coarse grained nearly monominerallic quartz or virgilite lialsi5o12 mica and 4 late stage fine grained albite mica intergrowths that are deposited from alkaline na rich interstitial melt at vapor saturation similar experimental products have been observed in compositionally simpler less evolved systems liquid lines of descent from initially h2o undersaturated runs are marked by a decrease in sio2 and increases in na k b p f h2o and a variety of trace lithophile cations these trends are believed to be governed by three factors 1 disequilibrium growth of feldspars quartz via metastable supersaturation 2 fractionation of melt toward sio2 depleted na rich compositions due to increases in b p and f and 3 changes in nucleation and growth rates mostly as a function of the h2o content of melt x w m in contrast experiments that are cooled below the liquidus from the field of melt aqueous vapor london et al 1988 fail to replicate pegmatitic characteristics in most respects on the basis of these and other experiments we suggest that the formation of pegmatite fabrics stems primarily from fractional crystallization in volatile rich melts and that enrichments in normally trace lithophile elements result from melt differentiation trends toward increasingly alkaline silica depleted compositions although vapor saturation at near solidus and subsolidus conditions may promote extensive recrystallization an aqueous vapor phase does not appear to be necessary for the generation of most of the salient characteristics of pegmatites