concentration mechanisms of rare earth element nb zr be mineralization in the baerzhe deposit northeast china insights from textural and chemical features of amphibole and rare metal minerals

the solubility of nb ta zr hf w in granitic melts with li and li f constraints for mineralization in rare metal granites and pegmatites tantalum mineralization is associated with granites and pegmatites that invariably are rich in lithium this in part is due to the extreme fractionation that is necessary for melts to reach saturation in either a ta or an li phase however there may also be chemical interactions in melts that explain this association experiments therefore were conducted to determine the effect of lithium on the solubility of tantalite mnta 2 o 6 in water saturated granitic melts other important elements in rare metal granites include nb zr hf and w consequently the effect of li on the solubilities of columbite mnnb 2 o 6 zircon zrsio 4 hafnon hfsio 4 and hbnerite mnwo 4 in granitic melts was also investigated the haplogranitic melt compositions used in these experiments have constant mole percent si and al and the al li na k ratio was 1 0 for all experiments i e the lithium content was the only compositional variable columbite and tantalite solubilities in the granitic liquids increase by a factor of approximately 2 to 3 with the addition of 2 wt percent li 2 o to haplogranite at 750 degrees to 1 035 degrees c 2 kbars and water saturated conditions the solubility data were extrapolated to a lower temperature more reasonable for columbite tantalite crystallization then compared to compositions representative of evolved liquids from which rare metal granites and pegmatites crystallize it is estimated that at 600 degrees c these melt compositions could be saturated in columbite but not tantalite however tantalite saturation is predicted if the melts contained less li and f therefore the genesis of tantalum mineralization may be explained by ta being retained in the melt because of high li f concentrations tantalite crystallization is delayed until an li or f or p mineral crystallizes which lowers tantalite solubility and results in a general association of ta with li in mineralized granitic rocks in contrast to columbite and tantalite the solubility of wolframite is not affected by the lithium content of the melt with up to 3 8 wt li 2 o in starting glasses and the solubilities of zircon and hafnon decrease with increasing li content of the melt one possible interpretation of the hbnerite solubility data is that the melt contains dominantly w super 6 which behaves as a network former the decrease in zircon hafnon solubility with li may reflect the lower field strength of zr super 4 and hf super 4 compared to nb super 5 and ta super 5 i e zr and hf are less able to compete with li for nonbridging oxygens whereas nb and ta are more able to compete it is also significant that the solubility of hafnon is greater than that of zircon similar to the higher solubility of tantalite compared to columbite this can explain why zr hf and nb ta ratios both decrease with fractionation

the role of hydrothermal processes in concentrating high field strength elements in the strange lake peralkaline complex northeastern canada abstract the middle proterozoic peralkaline pluton at strange lake quebec labrador comprises hypersolvus to subsolvus phases which are unusually enriched in zr y rees nb be and f as exotic alkali and alkaline earth silicate minerals the highest concentrations of these elements are in subsolvus granite which underwent intense low temperature 200 c hydrothermal alteration involving hematization and the replacement of alkali high field strength element hfse minerals by calcic equivalents this alteration is interpreted to have been caused by meteoric or formational waters high temperature 350 c alteration attributed to orthomagmatic fluids is evident in other parts of the subsolvus granite by the replacement of arfvedsonite by aegirine comparisons of the chemical compositions of fresh and altered rocks indicate that rocks subjected to high temperature alteration were chemically unaffected except for depletion in zr y and hrees these elements were appreciably enriched in rocks that underwent low temperature alteration other elements affected by low temperature alteration include ca and mg which were added and na which was removed available data on hfse speciation in aqueous fluids and the chemistry of the pluton suggest that the hfses were transported as fluoride complexes if this was the case the low temperature fluid could not have been responsible for hfse transport because the high concentration of ca and low solubility of fluorite would have buffered f activity to levels too low to permit significant complexation we propose that hfse mineralization and accompanying alteration were the result of mixing in the apical parts of the pluton of a f rich essentially ca free orthomagmatic fluid containing significant concentrations of hfses with an externally derived meteoric dominated fluid enriched in ca as a result of interaction with calc silicate gneisses and gabbros according to this interpretation the latter fluid was responsible for the exchange of ca for alkalis mainly na in hfse rich minerals and by sharply reducing f activity in the mixed fluid through fluorite precipitation and or increasing ph destabilised the hfse fluoride complexes causing deposition of hfse bearing minerals an important implication of this study is that major hfse enrichment may be restricted to those rare cases where f rich ca free metal leaching environments and ca rich depositional environments are juxtaposed

uplift of quaternary shorelines in eastern patagonia darwin revisited during his journey on the beagle darwin observed the uniformity in the elevation of coastal eastern patagonia along more than 2000 km more than one century later the sequences of quaternary shorelines of eastern patagonia have been described and their deposits dated but not yet interpreted in terms of geodynamics consequently we i mapped the repartition of the quaternary coastal sequences in argentinean patagonia ii secured accurate altitudes of shoreline angles associated with erosional morphologies i e marine terraces and notches iii took into account previous chrono stratigraphical interpretations in order to calculate mean uplift rates since 440 ka mis 11 and proposed age ranges for the higher and older features up to 180 m and iv focused on the last interglacial maximum terrace mis 5e as the best constrained marine terrace in terms of age and altitude in order to use it as a tectonic benchmark to quantify uplift rates along the entire passive margin of eastern south america our results show that the eastern patagonia uplift is constant through time and twice the uplift of the rest of the south american margin we suggest that the enhanced uplift along the eastern patagonian coast that interested darwin during his journey around south america on the beagle could originate from the subduction of the chile ridge and the associated dynamic uplift

two dimensional modeling of the p t t paths of regional metamorphism in simple overthrust terrains quantitative modeling of metamorphic p t t paths in thrust belts has so far been limited to one dimensional simplification we have developed a two dimensional time dependent finite element procedure capable of tracing and updating fault and strata boundaries during faulting for modeling thermal evolution of overthrust terrains we show that the two dimensionality of an overthrust and the speed and duration of thrusting have significant effects on the p t t paths of rocks in orogenic belts the results suggest that petrological studies of p t paths of rocks from different lateral positions in an orogenic belt along with two dimensional modeling procedure can put strong constraints on models of regional tectonic processes

a model for low amplitude detachment folding and syntectonic stratigraphy based on the conservation of mass equation abstract this paper presents a model for the structural evolution of low strain detachment folds in which rock is treated as an incompressible deformable material and its kinematics is governed by the continuity equation the model also considers the following boundary conditions i the vertical flux across the core of the fold is described by a cosine function ii the horizontal flux due to transport along a basal detachment remains constant with depth and iii the depth of the detachment remains fixed upon finding analytical expressions for the velocity field of this deformation process a model for the accumulation of growth strata and the degradation of the topography created by folding is then derived these processes are approximated by means of the transport diffusion equation solutions of these two models are in excellent agreement with geometric and stratigraphic relations documented in fold and thrust belts and analog experiments moreover the model indicates that fold growth in this class of structures is a self affine process a compilation of detachment folds around the world indicates that these structures share a common profile moreover fold amplitude and wavelength of these folds are scaled by different amounts confirming this result the stratigraphy obtained with the growth strata model exhibits the typical thinning and truncation of timelines toward the core of the anticline cross cutting relations often observed in seismic cross sections and field data

melt inclusions in pegmatite quartz complete miscibility between silicate melts and hydrous fluids at low pressure fluorine boron and phosphorus rich pegmatites of the variscan ehrenfriedersdorf complex crystallized over a temperature range from about 700 to 500 c at a pressure of about 1 kbar pegmatite quartz crystals continuously trapped two different types of melt inclusions during cooling and growth a silicate rich h2o poor melt and a silicate poor h2o rich melt both melts were simultaneously trapped on the solvus boundaries of the silicate fluorine boron phosphorus water system the partially crystallized melt inclusions were rehomogenized at 1 kbar between 500 and 712 c in steps of 50 c by conventional rapid quench hydrothermal experiments glasses of completely rehomogenized inclusions were analyzed for h2o by raman spectroscopy and for major and some trace elements by emp electron microprobe both types of melt inclusions define a solvus boundary in an xh2o t pseudobinary system at 500 c the silicate rich melt contains about 2 5 wt h2o and the conjugate water rich melt about 47 wt h2o the solvus closes rapidly with increasing temperature at 650 c the water contents are about 10 and 32 wt respectively complete miscibility is attained at the critical point 712 c and 21 5 wt h2o many pegmatites show high concentrations of f b and p this is particularly true for those pegmatites associated with highly evolved peraluminous granites the presence of these elements dramatically reduces the critical pressure for fluid melt systems at shallow intrusion levels at t 720 c water is infinitely soluble in a f b and p rich melt simple cooling induces a separation into two coexisting melts accompanied with strong element fractionation on the water rich side of the solvus very volatile rich melts are produced that have vastly different physical properties as compared to normal silicate melts the density viscosity diffusivity and mobility of such hyper aqueous melts under these conditions are more comparable to an aqueous fluid

cretaceous ongonites topaz bearing albite rich microleucogranites from ongon khairkhan central mongolia products of extreme magmatic fractionation and pervasive metasomatic fluid rock interaction abstract ongonites were defined at their type locality at ongon khairkhan central mongolia as pristine magmatic topaz bearing albite quartz keratophyres with up to 4 wt f and containing phenocrysts of albite k feldspar quartz and rare mica and topaz hosted in a groundmass composed of the same minerals however detailed petrographic and sem eds studies indicate that these rocks underwent considerable subsolidus exchange with deuteric fluids as evidenced by the presence of albitic plagioclase ab 100 and end member orthoclase or 100 secondary li fe rich mica zinnwaldite enriched in rare metals sn w ta nb pitted feldspars containing fluid inclusions and disseminated fluorite the 120 ma old dyke rocks emplaced at a high structural level in the crust are strongly peraluminous leucogranites characterized by high al and alkalis that are also enriched in rb cs ga and ta depleted in mg ca zr ba sr and eu and have anomalous k rb rb sr zr hf and nb ta ratios compared to the average continental crust however the suite has nd isotopic ratios nd 120 1 similar to those of contemporaneous a type granites of the mongolian transbaikalian igneous province of the central asian orogenic belt the inferred primary 18 o 6 to 7 and pb isotopic values are consistent with a granitic parent magma and interaction with orthomagmatic fluids the ongonites and constituent minerals record 1 an extensive and protracted crystal fractionation history in part due to the presence of volatiles particularly f which depressed the solidus temperature of the felsic rocks and extended its duration of crystallization and 2 subsolidus exchange with fluids which includes late flux of heated meteoric water as indicated by modified whole rock 18 o values 0 5 to 2 7 the interaction of the ongonites with internally derived orthomagmatic fluids is considered to result in enrichment and or redistribution of several incompatible elements but not to have greatly modified their original major element chemistry which indicates that this suite represents the last stages of fractionation of a highly differentiated f rich granitic magma the escape of these evolved melts from the apical part of the underlying pluton is now represented by the ongonite dykes late stage magmatic water rich fluids enriched in incompatible elements including nb ta sn and w were responsible for the late to post magmatic alteration and associated w mineralization

the origin of skarn hosted rare metal mineralization in the ambohimirahavavy alkaline complex madagascar the cenozoic ambohimirahavavy alkaline complex in madagascar consists of several syenitic to granitic intrusions 24 2 0 6 ma the largest of which the ampasibitika intrusion is characterized by the presence in its outer flanks of late peralkaline granitic dikes intruding mudstone and limestone of the isalo group a network of dikelets and veinlets propagates from these dikes intruding along bedding or obliquely to bedding at the contact between the dikes and dikelets and a limestone a reaction zone enriched in rare metals dominated by calc silicate minerals such diopside and andradite grossular forms a rare example of skarn resulting from peralkaline igneous activity much of the rare metal mineralization ree zr nb th sn and ti occurs as secondary phases in the dikelets and skarn in the dikelets and endoskarn high field strength element hfse rich phases consist mainly of zircon bastnasite ce and ca ree and ca hfse rich phases in pseudomorphs after aegirine augite in the exoskarn the main hfse rich phases are bastnasite ce zircon pyrochlore nb rich titanite and an unidentified f rich ca zirconosilicate finely disseminated in a matrix composed of calcite diopside andradite phlogopite quartz fluorite and fluorapatite the secondary zircon is characterized by a low zr content and by the presence of ree ca al and fe three types of primary fluid inclusions were observed in dikelets and skarn in quartz calcite and diopside 1 liquid rich inclusions l v 20 to 40 vol vapor occur in all three minerals and homogenize to liquid 2 vapor rich inclusions v 90 vol vapor occur in diopside and quartz and homogenize to vapor and 3 halite bearing l v inclusions l v h occur in diopside and quartz and homogenize either by disappearance of the vapor bubble or by halite dissolution the l v inclusions have low to intermediate salinity and homogenize at temperatures ranging from 200 to 380 c the v inclusions have low salinity and homogenize at higher temperature 350 395 c the l v h inclusions mainly contain nacl 35 45 wt nacl equiv and homogenize by three modes namely bubble disappearance mode a halite dissolution mode b and simultaneous bubble and halite disappearance mode c the homogenization temperatures range from 260 to 380 c we propose a model in which rare metals were transported by a cl f and hfse rich orthomagmatic fluid exsolved at 400 to 450 c and about 20 mpa at these conditions the fluid was in the two phase region and vapor dominated the rare metals were deposited as a result of the interaction of this fluid with limestone and mixing with an external fluid this interaction mixing buffered the orthomagmatic fluid to higher ph and lower temperature resulting in the destabilization of ree chloride complexes and deposition of fluorocarbonate minerals in the limestone zr and nb which were likely transported as hydroxyl fluoride complexes precipitated as zircon and pyrochlore due to deposition of fluorite and a consequent decrease in fluoride activity

genesis and age of the toudaoliuhe breccia type gold deposit in the jiapigou mining district of jilin province china constraints from fluid inclusions h o s pb isotopes and sulfide rb sr dating abstract the jiapigou mining district jmd in the northeastern part of the north china block mainly contains quartz vein and altered rock type gold deposits that have been prospected and mined for over 200 years recently a breccia type gold deposit known as toudaoliuhe was discovered in the jmd that has attracted attention for prospecting and exploration in this paper we report the ore geology gold bearing sulfide i e pyrite galena and sphalerite rb sr age fluid inclusions fis and h o s pb sr isotope data of the toudaoliuhe gold deposit to determine its genesis and ore forming mechanisms gold orebodies mainly occur in the breccia cements as well as in several quartz veins controlled by nw trending brittle faults there were three hydrothermal stages the early quartz pyrite main quartz polymetallic sulfide and late quartz carbonate stages gold mineralization occurred in the main hydrothermal stage three types of fis were identified co2 h2o nacl c type h2o nacl w type and pure co2 pc type the fis in quartz from the early hydrothermal stage are predominantly of the c and w types with traces of pc type and have homogenization temperatures of 299 8 340 0 c and salinities of 6 5 14 8 wt nacl equivalent e the fis in the quartz and sphalerite forming the main hydrothermal stage are also predominantly of the c and w types with trace pc type and have homogenization temperatures of 169 1 298 7 c and salinities of 5 7 16 5 wt e the fis in the quartz and calcite from the late hydrothermal stage were solely of the w type and have homogenization temperatures of 126 0 210 2 c and salinities of 2 1 11 4 wt e the ore forming fluids are characterized by moderate temperature and low salinity suggesting a co2 h2o nacl system the h o s pb sr isotopic results suggest that the ore forming fluids were dominated by magmatic water and that the ore forming materials were mainly extracted from the middle jurassic magmatic reservoir 177 163 ma sourced mainly from the lower crust with trace mantle components fluid boiling was the dominant mechanism for gold and associated sulfide precipitation the rb sr isochron age of the gold bearing sulfides at 177 7 1 7 ma indicates that gold mineralization occurred in the early middle jurassic we therefore proposed that the toudaoliuhe is a mesothermal gold deposit that formed in an extensional setting related to the subduction of the paleo pacific plate beneath the eurasian continent

continuity and discontinuity in the human use of the north coast of santa cruz patagonia argentina through its radiocarbon record in this paper the analysis of a radiocarbon database of the north coast of santa cruz central patagonia argentina is presented dated archaeological samples were obtained from 56 different types of archaeological sites open air residential sites and burials and also rock shelters the objective of this paper is assessing the continuities and discontinuities in the chronological signal of the area and identifying tendencies along the holocene the database currently contains 75 radiocarbon dates falling between ca 8000 and 300 bp the radiocarbon data base provides information on the chronological spatial and contextual variability of the archaeological record of north coast of santa cruz by means of different analysis of sum of probabilities we present three different chronological moments of human use of the coast and intermediate zone can be identified a first moment is represented by early evidence of settlement during middle holocene a second moment corresponds to a hiatus between ca 5800 and ca 3900 bp without archaeological evidence finally a third moment is where an increasing of chronological signal occurred related to greater artifactual variability and an increase in the intensity of human settlement in the patagonian region the causes that could have influenced in the discontinuity of the chronological signal of the study area and the characteristics of the different moments identified are discussed

structural analysis using thrust fault hanging wall sequence diagrams ogden duplex wasatch range utah detailed mapping and cross section traverses provide the control for structural analysis and geometric modeling of the ogden duplex a complex thrust system exposed in the wasatch mountains east of ogden utah the structures consist of east dipping folded thrust faults basement cored horses lateral ramps and folds and tear faults the sequence of thrusting determined by means of lateral overlap of horses thrust splay relationships and a top to bottom piggyback development is willard thrust ogden thrust weber thrust and taylor thrust major decollement zones occur in the cambrian shales and limestones the tintic quartzite is the marker for determining gross geometries of horses this exposed duplex serves as a good model to illustrate the method of constructing hanging wall sequence diagram a series of longitudinal cross sections that move forward in time and space and show how a thrust system formed as it moved updip over various footwall ramps a hanging wall sequence diagram also shows the complex lateral variations in a thrust system and helps to locate lateral ramps lateral folds tear faults and other features not shown on dip oriented cross sections

energy balance and deformation mechanisms of duplexes abstract a duplex consists of a series of imbricate faults that are asymptotic to a roof thrust and a floor thrust depending on the final orientations of the imbricate faults and the final position of the branch lines a duplex may be hinterland dipping foreland dipping or an antiformal stack the exact geometry depends on various factors such as the initial dimensions of the individual slices horses their lithology the amount of displacement normalized to size of horse on each fault and the mechanics of movement along each fault the energy required in duplex formation can be determined by calculating the total work involved in emplacing each horse this is given by where w t w p w b w g w i wp is the work involved in initiating and propagating a fracture wb is the work involved in basal sliding which may be frictional or some form of ductile flow wg is the work done against gravity during the emplacement of the horse and wi is the work involved in the internal deformation of the horse by calculating and comparing these work terms it is possible to predict the conditions under which the different types of duplexes will form normally the development of a hinterland dipping duplex is most likely however if deformation conditions are favorable displacements on individual imbricate faults may be very large compared to the size of the horses leading to the formation of either antiformal stacks or foreland dipping duplexes

hydrothermal transport and deposition of the rare earth elements by fluorine bearing aqueous liquids new technologies particularly those designed to address environmental concerns have created a great demand for the rare earth elements ree and focused considerable attention on the processes by which they are concentrated to economically exploitable levels in the earth s crust there is widespread agreement that hydrothermal fluids played an important role in the formation of the world s largest economic ree deposit i e bayan obo china until recently many researchers have assumed that hydrothermal transport of the ree in fluorine bearing ore forming systems occurs mainly due to the formation of ree fluoride complexes consequently hydrothermal models for ree concentration have commonly involved depositional mechanisms based on saturation of the fluid with ree minerals due to destabilization of ree fluoride complexes here we demonstrate that these complexes are insignificant in ree transport and that the above models are therefore flawed the strong association of h and f as hf and low solubility of ree f solids greatly limit transport of the ree as fluoride complexes however this limitation does not apply to ree chloride complexes because of this the high concentration of cl in the ore fluids and the relatively high stability of ree chloride complexes the latter can transport appreciable concentrations of ree at low ph the limitation also does not apply to sulphate complexes and in some fluids the concentration of sulphate may be sufficient to transport significant concentrations of ree as sulphate complexes particularly at weakly acidic ph this article proposes new models for hydrothermal ree deposition based on the transport of the ree as chloride and sulphate complexes

revisiting complete miscibility between silicate melts and hydrous fluids and the extreme enrichment of some elements in the supercritical state consequences for the formation of pegmatites and ore deposits abstract using water and major and trace element data obtained from melt inclusions primarily in pegmatite quartz we have shown in this and previous papers that melt melt fluid immiscibility is widespread and an important process during the generation of granitic pegmatites furthermore we have shown that the formation of pegmatites actually begins in the supercritical melt fluid stage in this study we extend previous work and in particular explore the behavior of 10 different elements be f p s cl as rb sn cs and ta in the supercritical range from preliminary studies we suggest that other elements such as b na k zn nb and sb will behave similarly near the solvus crest of a generalized pseudo binary melt water system this provides important evidence that pegmatite forming processes have already begun at high temperatures in the range of 850 750 c and that may require a re think on the partitioning behavior of metals in late stage residual melts exsolved from granitic magmas the existence of this parental supercritical silicate melt fluid although derived from granitic magmas imposes significant constraints of its own so drawing conclusions about pegmatite forming processes from data gained from slightly modified granite compositions becomes highly problematic we propose that the extremely high concentration of some elements over a small but well defined water concentration range symmetrically distributed around the critical point of the pseudo binary solvus must be derived from the unusual properties of the near critical or supercritical phases these unusual properties include extremely low density viscosity and surface tension and high diffusivity reactivity and mobility these are exactly the qualities that make such supercritical fluids an excellent medium for the formations of pegmatites by reactions with the existing matrix melt crystal mush and for the extreme enrichment of some ore forming elements highly soluble in alkali and water rich supercritical fluids a very important point in mineral crystallization is the non uniform local enrichment of rare and economically significant elements at specific locations in pegmatites granites and other rocks given the properties of the supercritical phase identified from melt inclusions the process of ostwald ripening can operate very effectively the driving force for ostwald ripening arises because the concentration of solute in the vicinity of small crystals or clusters is greater than and in the vicinity of larger crystals or clusters less than the average supersaturation the solute in the supercritical fluid therefore flows from the small crystals to the larger crystals and permits the growth of very large crystals at the expense of smaller ones this is favored by the extraordinary properties of supercritical fluids given the low surface tension the supercritical fluid can move also through grain boundaries and small channels or dislocation pipes aiding incompatible element transport additionally their consequences for the formation of some important granite related ore deposits are briefly outlined

dislocation formation and albitization in alkali feldspars from the shap granite orthoclase rich alkali feldspars in the lower devonian shap granite northwest england contain two generations of albite rich feldspar these have partially replaced earlier exsolution microtextures consisting of albite lamellae coarse semicoherent albite films and fine coherent albite platelets in tweed orthoclase the earlier generation of replacive albiterich feldspar ab90an9ori occurs together with orthoclase rich feldspar ab10or90 i n veins that crosscut exsolution microtextures throughout grain interiors this episode of recrystallization was mediated by magmatic fluids at 410 8c estimated from two feldspar geothermometry and was driven by stored elastic strain energy which was relatively homogeneously distributed throughout the microtextures the later generation of replacive albite rich feldspar which is restricted to grain margins and is compositionally pure ab 99 was produced by magmatic hydrothermal fluids at 370 8c this generation of albite rich feldspar does not crosscut exsolution microtextures and has selectively replaced volumes of highly elastically strained feldspar surrounding edge dislocations along semicoherent albite films marked differences in controls of the localization of the two generations of replacive albite rich feldspar by pre existing exsolution microtextures indicate that significant numbers of edge dislocations developed along albite films after the first phase of fluid feldspar interaction and associated albitization but before the second phase this relation indicates that edge dislocations formed between 410 and 370 8c these observations have important implications for understanding the factors that control the interaction of alkali feldspars with fluids both in cooling igneous rocks and in clastic sedimentary rocks during diagenesis

nature and ore formation of the erdaohezi pb zn deposit in the great xing an range ne china abstract the erguna metallogenic belt is a large erdaohezi epithermal polymetallic sulfide pb zn deposit in the northern great xing an range that is associated with andesitic porphyry mineralization mainly occurs at the edges of andesitic porphyry and adjacent jurassic quartz porphyry and volcanic strata hydrothermal alteration minerals mainly include quartz sericite adularia chlorite and calcite while ore minerals include pyrite galena and sphalerite with minor argentite chalcopyrite and tetrahedrite three hydrothermal mineralization stages are recognized three categories of fluid inclusions fis are distinguished in quartz fluorite and sphalerite veins liquid rich gas rich and a few h2o co2 inclusions the stage i fis include all three inclusion types and present high homogenization temperatures 197 233 and salinities 0 7 6 8 wt nacl eq the stage ii fis mainly comprise liquid rich inclusions with a few h2o co2 types and present higher homogenization temperatures 167 190 and slightly higher salinities 0 9 7 6 wt nacl eq than those of stage i stage iii only contains liquid rich inclusions and presents the lowest homogenization temperatures 120 157 and salinities 0 5 4 8 wt nacl eq the ore forming fluids have low temperatures and salinities in an h2o nacl co2 ch4 system the o h isotope data 2 2 to 5 0 and 160 0 to 152 5 respectively suggest that ore forming fluids gradually evolved from mantle primary water to meteoric water sulfur strontium and lead isotopes imply a mixed crustal and mantle source for the ore forming materials sulfide rb sr dating yields a well defined isochron age of 130 5 3 6 ma from the main mineralization stage which is similar to the zircon age of 134 9 0 9 ma for the andesitic porphyry related to mineralization we therefore proposed that erdaohezi is a low sulfidation epithermal pb zn polymetallic deposit and fluid immiscibility was the dominant mechanism of ore deposition mineralization occurred in an early cretaceous back arc extensional setting that was related to the subduction of the paleo pacific plate

oxygen isotope trajectories of crystallizing melts insights from modeling and the plutonic record elevated oxygen isotope values in igneous rocks are often used to fingerprint supracrustal alteration or assimilation of material that once resided near the surface of the earth the 18 o value of a melt however can also increase through closed system fractional crystallization in order to quantify the change in melt 18 o due to crystallization we develop a detailed closed system fractional crystallization mass balance model and apply it to six experimentally and naturally determined liquid lines of descent llds which cover nearly complete crystallization intervals melt fractions of 1 to 0 1 the studied llds vary from anhydrous tholeiitic basalts to hydrous high k and calc alkaline basalts and are characterized by distinct melt temperature sio 2 trajectories as well as crystallizing phase relationships our model results demonstrate that melt fraction temperature sio 2 relationships of crystallizing melts which are strongly a function of magmatic water content will control the specific 18 o path of a crystallizing melt hydrous melts typical of subduction zones undergo larger increases in 18 o during early stages of crystallization due to their lower magmatic temperatures greater initial increases in sio 2 content and high temperature stability of low 18 o phases such as oxides amphibole and anorthitic plagioclase versus albite conversely relatively dry tholeiitic melts only experience significant increases in 18 o at degrees of crystallization greater than 80 total calculated increases in melt 18 o of 1 0 to 1 5 can be attributed to crystallization from 50 to 70 wt sio 2 for modeled closed system crystallizing melt compositions as an example application we compare our closed system model results to oxygen isotope mineral data from two natural plutonic sequences a relatively dry tholeiitic sequence from the upper and upper main zones uumz of the bushveld complex south africa and a high k hydrous sequence from the arc related dariv igneous complex mongolia these two sequences were chosen as their major and trace element compositions appear to have been predominantly controlled by closed system fractional crystallization and their llds have been modeled in detail we calculated equilibrium melt 18 o values using the measured mineral 18 o values and calculated mineral melt fractionation factors increases of 2 3 and 1 1 5 in the equilibrium melts are observed for the dariv igneous complex and the uumz of the bushveld complex respectively closed system fractional crystallization model results reproduce the 1 increase observed in the equilibrium melt 18 o for the bushveld uumz whereas for the dariv igneous complex assimilation of high 18 o material is necessary to account for the increase in melt 18 o values assimilation of evolved supracrustal material is also confirmed with sr and nd isotope analyses of clinopyroxene from the sequence beginning with a range of mantle derived basalt 18 o values of 5 7 pristine mantle to 7 0 heavily subduction influenced mantle our model results demonstrated that high silica melts i e granites with 18 o of up to 8 5 can be produced through fractional crystallization alone lastly we model the zircon melt 18 o fractionations of different llds emphasizing their dependence on the specific sio 2 t relationships of a given crystallizing melt wet relatively cool granitic melts will have larger zircon melt fractionations potentially by 1 5 compared to hot dry granites therefore it is critical to constrain zircon melt fractionations specific to a system of interest when using zircon 18 o values to calculate melt 18 o

the mobility of zirconium and other immobile elements during hydrothermal alteration abstract development of zircon and other zr phases in hydrothermal deposits indicates that zr can be highly mobile in these systems mobility is most common in but not restricted to f rich hydrothermal systems related to alkalic f rich igneous suites these suites can range from peralkaline through metaluminous to peraluminous a few examples are neither alkalic nor f rich three locations in the trans pecos magmatic province texas u s a demonstrate this hydrothermal zr mobility all three igneous systems are alkalic and f rich but vary in alkali al ratios peralkaline rhyolites and trachytes in the christmas mountains contain as much as 2100 ppm zr mostly in aegirine or arfvedsonite zircon is rare or absent fluorspar replacement deposits in limestone at contacts with the rhyolites contain as much as 38 000 ppm zr occurring as small disseminated zircons the deposits also are enriched in a variety of incompatible elements including be rare earth elements ree y nb mo hf pb th and u the sierra blanca intrusions a series of mildly peraluminous f rich rhyolite laccoliths contain as much as 1000 ppm zr mostly as zircon hydrothermal zircon occurs as overgrowths on magmatic grains as veinlets connected to overgrowths and in fluorspar replacement bodies in adjacent limestone the highest zr concentrations in fluorspar are 200 ppm metaluminous quartz monzonite from the infiernito caldera contains 400 600 ppm zr mostly as zircon euhedral zircon in quartz fluorite veins in the quartz monzonite indicates mobility of zr zirconium concentrations in the veins are unknown but the paucity of zircon suggests little zr enrichment relative to the host zircon and more rarely zirconolite occur in skarn in the ertsberg district of irian jaya indonesia unlike in texas related igneous rocks are metaluminous and the hydrothermal system was f poor worldwide hydrothermal zircon other zr phases and ti and al bearing phases occur in skarn epithermal precious metal veins volcanogenic massive sulfide deposits and mylonites we propose that differences in zr mineralogy of igneous source rocks is an important factor in determining the availability of zr to hydrothermal fluids although zr concentrations in the sierra blanca and christmas mountains rhyolites are similar zr enrichment in fluorspar was much greater in the christmas mountains we suggest that hydrothermal solutions could easily break down aegirine and arfvedsonite to release zr but that zircon was only moderately attacked therefore far more zr was available for transport and subsequent deposition in the christmas mountains than at sierra blanca availability of other trace elements probably is also governed by their mineral host although zr mobility is most common in f rich hydrothermal systems related to alkalic and f rich igneous systems mobility at ertsberg may have been promoted by sulfate complexing

a new kinematic evolutionary model for the growth of a duplex an example from the rangit duplex sikkim himalaya india abstract the lesser himalayan duplex lhd is a prominent structure through much of the lesser himalayan fold thrust belt in the darjeeling sikkim himalaya a component of the lhd is exposed in the rangit window as the rangit duplex rd the rd consists of ten horses of the upper lesser himalayan sequence gondwana buxa upper daling the duplex varies from hinterland dipping in the north through an antiformal stack in the middle to foreland dipping in the south the ramgarh thrust rt is the roof thrust and based on a balanced cross section the main himalayan sole thrust is the floor thrust at a depth of 10 km and with a dip of 3 5 n retrodeformation suggests that the rd initiated as a foreland dipping duplex with the early ramgarh thrust as the roof thrust and the rt as the floor thrust the rt became the roof thrust during continued duplexing by a combination of footwall imbrication and concurrent rt reactivation this kinematic history best explains the large translation of the overlying mct sheets the restoration suggests that rd shortening is 125 km and the original gondwana basin extended 142 km northward of its present northernmost exposures within the window

zircon of the no 782 deposit from the great xing an range in ne china implications for nb ree zr mineralization during magmatic hydrothermal evolution abstract niobium rare earth elements ree lanthanides y and zirconium are widely used in high tech applications the nb ree zr mineralization in the no 782 deposit of ne china developed in a fine grained porphyry porphyry that occurs as a ring shaped stock the ore forming porphyry is hosted in a coarse grained granite granite that dominates the study area zircon is the only zr bearing mineral in both the porphyry and the granite in contrast to the granite that hosts only magmatic zircon both magmatic type i and metasomatic type ii zircon crystals or aggregates are present in the porphyry most type i zircon occurs as individual crystals and are hosted mainly in interstitial quartz with evident oscillatory zoning most type ii zircon occurs as aggregates rather than individual crystals and exhibits vague zoning distribution of the type ii zircon in the porphyry is heterogeneous with great abundance in places where there are substantial albitization and snowball quartz crystals textural and chemical features of the type ii zircon and of the associated albite and snowball quartz crystals suggest that all these minerals are metasomatic nb is hosted mainly by fergusonite y and ree by fergusonite y and to a lesser extent by bastnasite ce and parisite ce where parisite ce occurs as a replacement of bastnasite ce the nb ree mineralization occurs either as a replacement of the type ii zircon or in chlorite quartz dominant veinlets that postdated both the type i and the type ii zircon most type i zircon crystals in the porphyry were intact from the replacement or alteration by the postdated nb ree minerals possibly because the type i crystals were encased earlier by other magmatic minerals the chronological and oxygen isotopic data of zircon suggest that the porphyry 453 8 3 1 ma is younger than the granite 487 0 4 0 ma and that the two granitic phases derived from different magma chambers the subtle age difference between magmatic type i and metasomatic type ii zircon cannot be shown by shrimp u pb data of zircon the mineral assemblages associated with type ii zircon and the chronological data suggest that the medium from which type ii zircon precipitated is likely an internally derived hydrosilicate liquid hsl that lies compositionally in between a silicate melt and a hydrothermal fluid during the magmatic hydrothermal transition textural features of the nb ree minerals combined with the fact that nb ree mineralization developed only inside the porphyry but not in surrounding country rocks i e the granite suggest that the nb ree mineralization originated from an aqueous fluid that was constrained to the porphyry

the origin of niobium and tantalum mineralization in the nechalacho ree deposit nwt canada the behavior of niobium and tantalum is poorly understood in rocks that have undergone significant hydrothermal alteration and niobium tantalum minerals of hydrothermal origin are rarely mentioned in the literature consequently the mobility of these critical metals although widely considered to be negligible has not been evaluated in this paper we present the results of a study of the genesis of niobium and tantalum mineralization in the nechalacho rare metal deposit northwest territories canada which contains one of the largest known resources of these metals in rocks that have undergone intense hydrothermal alteration analyses and examination of samples using the electron microprobe has led to the identification of a variety of niobium and tantalum bearing minerals in the nechalacho deposit niobium bearing zircon columbite fe fergusonite y and samarskite y were identified in the ore zones of the deposit uranopyrochlore and columbite fe were found outside the ore zones and magmatic fluornatropyrochlore was shown to be the sole niobium tantalum mineral in relatively unaltered syenites below the basal ore zone based on the paragenetic relationships among the above minerals variations in the composition of the columbite group minerals as a function of location in the nechalacho layered suite and the distribution of niobium tantalum zirconium and uranium in the bulk rocks we have developed a model to explain the occurrence of niobium and tantalum in the nechalacho deposit the first step in the concentration of these elements was the crystallization of niobium and tantalum bearing zircon and eudialyte in the subhorizontal upper and basal ore zones respectively this was accompanied by the crystallization of magmatic columbite fe in the upper ore zone fergusonite y crystallized in the basal ore zone and also formed due to the breakdown of eudialyte outside the ore zones there was crystallization of pyrochlore and to a lesser extent magmatic columbite fe this step led to the development of strong spatial associations among niobium zirconium and uranium that are evident as strong positive correlations in the bulk rock concentrations of these elements at the meter scale during the ensuing intense and widespread hydrothermal alteration niobium was locally remobilized hydrothermal columbite fe and fergusonite y formed at the cores of altered zircon grains wholesale replacement of magmatic columbite fe and fergusonite y by hydrothermal anhedral crystals occurred in the two ore zones the estimated relative proportions of the sources of these minerals in the ore zones although varying to some extent because of a dependence on the amount of niobium mobilized from zircon is 40 60 outside the ore zones columbite fe and uranopyrochlore are the present manifestations of the former pyrochlore with the exception of magmatic fluornatropyrochlore in the fresher syenites below the basal ore zone and a single example of magmatic columbite fe in an upper ore zone sample all niobium and tantalum minerals have a hydrothermal origin as a result of this pervasive alteration

distributional archaeology in central san jorge gulf sector santa cruz province patagonia argentina abstract in this paper results of archaeological studies conducted in the central san jorge gulf sector north coast of santa cruz province patagonia argentina are presented a distributional approach was employed and a systematic surface sampling in several landscape units were performed registering all lithic artifacts and other variables that could influence the archaeological visibility the landscape units identified in this sector were high plateau plateau flank canadon leon temporary lagoons and coast the artifactual assemblage recovered is presented analyzed and discussed in relation to several archaeological expectations derived from the resource availability of the different landscape units results are discussed in relation to ways in which these landscape units could have been used by hunter gatherer populations that inhabited this sector during late holocene considering the differential availability of resources of importance to patagonian human groups in this sense the archaeological expectations were contrasted with higher densities near the coast and lower densities on inland landscape units among the first the availability of alimentary resources mainly shellfish fish and pinniped would have produced longer residential settlement among inland landscape units some differences were observed which were related to variation in resources availability such as fresh water sources and lithic raw materials in this latter more variability than anticipated according to the archaeological expectations was detected

application of cathodoluminescence to magmatic quartz in a tin granite case study from the schellerhau granite complex eastern erzgebirge germany a model of the cooling history of tin bearing granitic magma forming the schellerhau granites eastern erzgebirge germany is shown on the basis of quartz textures similar grain size similar grain habit and correlatable growth textures of phenocrysts in different granite varieties give proof of a common crystallization history before the melts of the schellerhau granite varieties were intruded four nucleation events occurred during crystallization in different crustal levels between about 20 and 1 km depth the parental melt of the schellerhau granites is interpreted to have contained 2 5 wt h2o originally the water content of the melt during the subvolcanic intrusion stage amounted to more than 5 wt and characterizes highly evolved residual melts that enable the formation of tin deposits this study contributes to a better understanding of the development and behaviour of fractionated tin bearing granitic melts and links quartz cathodoluminescence cl with microanalytical studies

thrust tectonics in the south central pyrenees abstract surface structural data and published stratigraphies are combined to construct two balanced and restored sections through the nogueras zone of the south central pyrenees the allochthonous nogueras zone units are interpreted as the foreland dipping margin of a major antiformal stack in the palaeozoic rocks of the pyrenean axial zone their structural evolution is summarized in a hangingwall sequence diagram this reinterpretation of the nogueras zone is incorporated into a new n s balanced and restored section from the centre of the pyrenean axial zone to the ebro basin a classical rocky mountains piggy back thrust model is employed and the resulting section is a significant departure from those previously published it is argued that gravity gliding has never been an important mechanism in the alpine pyrenees section restoration casts doubt on the correlation of the surface expression of the north pyrenean fault and the seismically detected moho step beneath it

two ages of porphyry intrusion resolved for the super giant chuquicamata copper deposit of northern chile by ela icp ms and shrimp zircon u pb ages measured in situ by excimer laser ablation inductively coupled plasma mass spectrometry ela icp ms and verified by sensitive high resolution ion microprobe shrimp on ore bearing felsic porphyries from the chuquicamata porphyry copper molybdenum deposit northern chile identify two discrete igneous events the volumetrically dominant east porphyry has an age of 34 6 0 2 ma whereas the bench and west porphyries yield ages of 33 3 0 3 ma and 33 5 0 2 ma respectively the age of the east porphyry is indistinguishable from a re os age for early molybdenite mineralization 35 ma and the oldest reported 40 ar 39 ar ages for hydrothermal alteration confirming a genetic link with mineralization previous geological studies and 40 ar 39 ar and re os geochronology identify two main hydrothermal events high temperature potassic alteration with chalcopyrite at 33 4 0 3 ma followed by lower temperature quartz sericite alteration with pyrite at 31 1 0 3 ma the ages of the west and bench porphyries match the ages for potassic alteration younger quartz sericite alteration may reflect an additional fourth intrusion concealed at depth the anomalously large size of chuquicamata appears to be due to a protracted igneous history resulting in the superposition of at least two temporally distinct magmatic hydrothermal systems

textural features and chemical evolution in tantalum oxides magmatic versus hydrothermal origins for ta mineralization in the tanco lower pegmatite manitoba canada tantalum a key element in the electronics industry is produced mainly from rare element granitic pegmatites although their internal structure mineralogy and petrogenesis have been extensively investigated the processes that control tantalum mineralization remain poorly understood in particular the role of fluids in the crystallization of tantalum ore one of the major problems arises from the difficulty in distinguishing primary magmatic from secondary hydrothermal textures in such complex rocks in the tanco pegmatite manitoba canada tantalum mineralization shows a complexity that reflects the complex petrogenesis of its host pegmatite eight different families of tantalum oxides occur in various associations and compositions the tanco lower pegmatite is an isolated body beneath the main pegmatite body that contains abundant tantalum associated with mica alteration tantalum mineralization in the tanco lower pegmatite occurs as three different styles facies 1 is hosted by the wall zone and hosts primary magmatic ta oxides with simple textures progressive and oscillatory zoning facies 2 is hosted by the lower and upper intermediate zones where most mineralization occurs with dendritic amblygonite facies 3 is hosted by the central zone which is affected by mica alteration in this latter facies the oxides show particularly complex textures evident from x ray mapping by combining information obtained from textural observations and chemical analyses we are able to determine the paragenesis for each ta oxide bearing mineral assemblage and hence to evaluate the relative contributions of magmatic versus hydrothermal processes in complex associations we observe relics of primary ta phases that are replaced or overgrown by secondary ta phases we propose the paragenetic sequence columbite group minerals microlite early primary magmatic columbite wodginite group minerals microlite late primary magmatic wodginite group minerals microlite secondary magmatic ferrotapiolite secondary magmatic in addition chemical variations were identified in the columbite and wodginite group minerals both at the crystal scale and at the pegmatite scale columbite and wodginite group minerals show the typical ta ta ta nb and mn mn mn fe atomic ratios increase from earlier to later zones at the crystal scale the increase in ta and mn with fractionation in the columbite group is explained by the higher solubility of the ta end member relative to the nb end member and the crystallization of other minerals that shift the melt composition toward mn enrichment the fractionation trend in the wodginite group shows fe enrichment which is consistent with experimental results that show a higher solubility of the fe end member relative to the mn end member in columbite group minerals considering the available experimental data as well as the intimate association of ta oxides with zircon observed in this study we conclude that tantalum mineralization is a product of direct crystallization from the melt rather than hydrothermal in origin fluids are attributed an indirect role only as they could have brought minor elements fe mn or ca into the melt which resulted in the crystallization of secondary ta phases textural evidence shows that the late secondary phases were formed at the same time as mica alteration we suggest that mica alteration was due to a late melt rather than a hydrothermal fluid that reacted with the blocky k feldspar of the central zone during the alteration event tantalum was remobilized from primary phases and incorporated in new secondary ta oxide species

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

an early cretaceous ag pb zn mineralization at halasheng in the south erguna block ne china constraints from u pb and rb sr geochronology geochemistry and sr nd hf isotopes abstract the halasheng deposit located in the southern erguna block is a vein type ag pb zn deposit in the derbugan metallogenic belt the orebodies hosted in middle late jurassic volcanic rocks show a close spatial and temporal relationship with early cretaceous granites zircon u pb dating suggests that the granites were emplaced at 134 128 ma rb sr dating of ore related sphalerite gives an imprecise age of 122 18 ma indicating that the halasheng deposit formed in the early cretaceous whole rock major and trace element analyses show that the cretaceous granites belong to the metaluminous to peraluminous shoshonite to high k calc alkaline series and can be classified as a type granites they are enriched in large ion lithophile elements lile and light rare earth elements lree but depleted in high field strength elements hfse and heavy rare earth elements hree the quartz monzonite which has a spatial relationship with mineralization has low initial 87sr 86sr 0 7058 0 7069 and positive end t 0 42 0 61 and ehf t 3 47 6 45 with nd and hf two stage model ages of 0 81 0 85 ga and 0 69 0 86 ga respectively these geochemical features are similar to those of major mesozoic granite intrusions in the erguna block we propose that these graintes originated from partial melting of juvenile crust in an intraplate extensional setting taken together the halasheng ag pb zn deposit formed in the early cretaceous after the orogeny related to closure of the mongol okhotsk ocean the relatively low temperature of ag pb zn ore and alteration mineralogy suggest that there is only a distal relationship if any to nearby potentially causative granite intrusions

a kinematic model for the formation of duplex systems with a perfectly planar roof thrust we present a cross sectional kinematic forward model for the formation of duplexes with a perfectly planar roof thrust the major assumptions are a constant dip and constant spacing of the ramps in the undeformed state and sequential deformation in the direction of tectonic transport with equal displacement along each ramp the model is based on a coordinate transformation that simulates flexural slip parallel to the active fault surface this causes angular parallel folds and keeps the layer thickness constant except in the forelimbs of the horses attempts by previous workers to simulate the formation of duplexes with a perfectly planar roof thrust on the other hand were based on the assumptions of constant bed thickness and bed length or a different topology of the axial planes delimiting the forelimbs of the horses and resulted in corrugated roof thrusts we show that it is not possible to form a flat roof duplex type and preserve the forelimb thickness of the horses under flexural slip parallel to the active fault we describe duplexes by three parameters which are the separation s between ramps the ramp length l and the displacement u along the ramps in a us vs ls diagram duplexes with a perfectly planar roof thrust resulting from numerical experiments with our kinematic algorithm occupy specific families of straight lines our results are independent of the dip or internal geometry of the thrust ramps

textural features and chemical evolution in ta nb oxides implications for deuteric rare metal mineralization in the yichun granite marginal pegmatite southeastern china

the peralkaline granite related khaldzan buregtey rare metal zr nb ree deposit western mongolia the khaldzan buregtey rare metal nb zr ree etc deposit in peralkaline granitoids is located in western mongolia 45 km northeast of the town of kobdo the deposit which was discovered by the authors is composed of dome shaped stocks of rare metal peralkaline granite covering 0 85 km and represents the late plutonic phases of the devonian 380 390 ma multiphase khaldzan buregtey peralkaline granite massif the formation of the massif took place during tectonic extension as shown by the development of a major dike complex synchronous with granite emplacement the massif consists of peralkaline granitoids as well as gabbro and basalt and is characterized by a radial circular shape eight intrusive phases are recognized and consist of 1 nordmarkite 2 peralkaline granite 3 dikes of fine grained peralkaline granite 4 dikes of pantellerite 5 rare metal peralkaline granite 6 gabbroids 7 miarolitic peralkaline rare metal granite and 8 syenite and leucite basalt field relationships of the rare metal peralkaline granite bodies indicate an intrusive igneous origin the rare metal peralkaline granites consist of k na feldspar quartz albite arfvedsonite aegirine fluorite and diverse rare metal minerals ranging up to 25 vol percent ore minerals are represented by elpidite gittinsite and zircon pyrochlore nb rare metal flurocarbonate and monazite ree and polylithionite li the zirconium minerals often occur in the endocontact and apical parts of rare metal granite bodies and are reflected in the negative correlation of zr and nb contents in the seventh phase granites the rare metal peralkaline granites of the deposit differ from those of other massifs by their high and variable ca and f contents the granites are rich in zr up to 5 3 wt nb up to 0 8 wt ree up to 0 4 wt y up to 0 3 wt be sn rb and sometimes li pb zn hf and ta they are depleted in sr and ba and have an almost flat ree distribution pattern with a small negative eu anomaly the initial 87 sr 86 sr ratio of fluorite from rare metal peralkaline granite is 0 70433 or 7 the end value for these rocks at 386 ma ranges from 4 3 to 5 7

early cretaceous bimodal magmatism related epithermal mineralization a case study of the gaosongshan gold deposit in the northern lesser xing an range ne china abstract low sulfidation ls gold mineralization is partially associated with bimodal volcanism in origin sources of ore mineralized fluids and relevant dynamic processes remain poorly understood to better understand these issues a study including deposit geology petrology zircon u pb dating and element and sr nd hf isotope geochemistry of bimodal volcanic rocks at gaosongshan was conducted the bimodal volcanic rocks are composed of andesitic rocks basalt andesite andesite trachyandesite andesitic pyroclastic of the meifeng formation and overlying rhyolite lava of the fuminhe formation cut by equivalent porphyry stocks which contain pyrite bearing granular textured quartz cavity with a sugary appearance with trapped single phase magmatic fluids the andesitic suite formed at approximately 106 108 ma prior to eruption of the younger rhyolitic magmas 105 6 1 7 ma n 13 mswd 1 2 the andesites show calc alkaline affinities which is a subduction related characteristic and show moderate la ybn 7 91 11 36 and weakly negative europium anomalies 0 80 1 02 indicating a source in the asthenospheric mantle with varying contamination by both subduction and continental materials a type rhyolitic rocks are geochemically comparable to the andesitic suite and their higher la ybn 13 01 30 05 and lower eu eu 0 66 0 73 indicate evolved products of andesitic magmas the estimated oxygen fugacity of dry 1 2 water rhyolite lava is fmq 1 87 whereas rhyolite porphyry is more oxidized fmq 0 12 and water rich 2 5 2 8 with probably being water saturated at 2 0 2 4 km depths therefore it is assumed that the essential constraints of bimodal magmatism on epithermal gold mineralization are sequential processes from ascending and gradual differentiation of crustal level mantle derived basaltic magmas to releases of hydrothermal solutions from the silica rich magma reservoir at shallower levels most importantly the oxygen fugacity of and the fluid fluxes from dry rhyolitic melts are critical restricting parameters for the limited reserves at gaosongshan thus this research contributes objective evidence for investigations of deposit genesis and prospecting targets

hydrothermal transport deposition and fractionation of the ree experimental data and thermodynamic calculations abstract for many years our understanding of the behavior of the ree in hydrothermal systems was based on semi empirical estimates involving extrapolation of thermodynamic data obtained at 25 c haas et al 1995 wood 1990a since then a substantial body of experimental data has accumulated on the stability of aqueous complexes of the ree these data have shown that some of the predictions of haas et al 1995 are accurate but others may be in error by several orders of magnitude however application of the data in modeling hydrothermal transport and deposition of the ree has been severely hampered by the lack of data on the thermodynamic properties of even the most common ree minerals the discrepancies between the predictions of haas et al 1995 and experimental determinations of the thermodynamic properties of aqueous ree species together with the paucity of data on the stability of ree minerals raise serious questions about the reliability of some models that have been proposed for the hydrothermal mobility of these critical metals in this contribution we review a body of high temperature experimental data collected over the past 15 years on the stability of ree aqueous species and minerals using this new thermodynamic dataset we re evaluate the mechanisms responsible for hydrothermal transport and deposition of the ree we also discuss the mechanisms that can result in ree fractionation during their hydrothermal transport and deposition our calculations suggest that in hydrothermal solutions the main ree transporting ligands are chloride and sulfate whereas fluoride carbonate and phosphate likely play an important role as depositional ligands in addition to crystallographic fractionation which is based on the differing affinity of mineral structures for the ree our models suggest that the ree can be fractionated hydrothermally due to the differences in the stability of the lree and hree as aqueous chloride complexes

incorporation mechanisms of ta and nb in zircon and implications for pegmatitic systems to investigate the processes that control ta incorporation in zircon two types of synthesis experiments were performed 1 crystallization of zircon from an li mo flux at 1 atm and 2 crystallization of zircon with or without coexisting tantalite from a highly fluxed pegmatitic melt at 200 mpa and nearly water saturated conditions the first type of experiment is used to identify the influence of various doping elements hf p al and mn on ta incorporation in zircon these experiments reveal that p hinders the incorporation of ta whereas al enhances ta incorporation via charge balancing and that ta can be incorporated in the absence of any other doping element via the creation of vacancies in the zircon structure hafnium does not affect significantly ta incorporation manganese and lithium do not enter the structure of zircon except in the presence of p experiments with nb show that the concentration of this element in zircon is nearly one order of magnitude lower than ta for similar ta and nb concentrations in the flux the second type of experiments show how ta is incorporated in zircon in natural granite and pegmatite systems in those systems p and al have elevated concentrations and p is preferentially incorporated in zircon via al substitution to maintain charge balance below a p ta atomic ratio of 10 in the melt ta competes with p for al and p is involved in a coupled substitution with mn for charge balancing concentrations up to 3 7 wt ta 2 o 5 0 03 apfu calculated to four atoms of oxygen were measured in these zircon samples the partition coefficients of ta between melt and zircon are around 1 at 800 900 c at conditions close to tantalite saturation these results show that zircon incorporates significant amounts of ta from the melt in p poor peraluminous granites with a p ta atomic ratio lower than 10 which may ultimately affect the precipitation of ta minerals such interactions between cations both in melts and in mineral structures are important to constrain in order to understand rare metal enrichment in granitic systems

kinematic modeling of cross sectional deformation sequences by computer simulation we derive a kinematic algorithm which permits simulation of postulated cross sectional deformation sequences in sedimentary rocks affected by faulting fault related folding and simple shear the transformations are to a more deformed state and are formulated analytically in terms of the less deformed configuration forward modeling lagrangian description the medium is subdivided into domains of constant dip and homogeneous displacement vector fields which are delimited by the axial planes of the fault inflections the displacement trajectory is of constant length for all the displaced particles throughout the medium and parallel to the underlying active fault segment as a consequence the deformation path is continuous but not smooth and causes an angular style of parallel folding except at the deformation front where the layer thickness is not conserved the inhomogeneity of the displacement vector field across axial planes introduces longitudinal and angular shear strains whereas the area of the medium remains constant these strains which are superposed on the externally applied simple shear make the mapping transformation unconformal we define the stratigraphic layering of the undeformed medium by an approximating body of finite quadrilateral elements evaluate the defined displacement functions for the grid nodes and graph the deformed mesh eventually we create with the algorithm synthetic deformation sequences for simple boundary conditions and try in a specific case study to match the resulting synthetics with the available observational and experimental data

magmatic vs hydrothermal origins for zircon associated with tantalum mineralization in the tanco pegmatite manitoba canada complex textures in zircon associated with ta oxides have been used to assess the processes at the origin of zircon crystallization and associated ta mineralization in pegmatites in particular the role of magmatic vs hydrothermal processes the tanco pegmatite is used as an example because its zircon is devoid of post magmatic alteration and its petrogenesis is well constrained zircon in primary units is metamict with high u pb th contents by contrast in secondary assemblages affected by late magmatic micaceous alteration zircon is devoid of radiogenic elements but it may contain abundant ta2o5 up to 4 7 wt the incorporation of ta into zircon may occur through coupled substitution mechanisms involving other minor elements such as p al mn or li the presence of ta accounts for the distorted structures in the ta rich zircon as revealed in high resolution tem images four zircon types occur sequentially in single zircon crystals which permits a new model for zircon growth and evolution in rare element pegmatites to be advanced 1 zircon z1 is ta rich and crystallized possibly before discrete ta phases 2 z1 was overgrown by regularly zoned zircon z2 and z3 which show lower ta and extreme zr hf fractionation hfo2 up to 38 9 wt suggesting crystallization from a highly fractionated melt possibly at the onset of ta mineralization and 3 close to the solidus the aqueous fluid at the origin of micaceous alteration corroded the distorted structure of z1 and a low ta zircon z4 replaced z1 by dissolution reprecipitation whereas z2 and z3 resisted this alteration tantalum was no longer stable in the zircon structure and crystallized as ta oxide inclusions in the reequilibrated zircon z4

geochronology and geochemistry of the dasuji mo deposit in the northern margin of the north china block implications for ore genesis and tectonic setting abstract the dasuji mo deposit is located in the northern margin of the north china block ncb in this paper we present the whole rock major and trace elements and the sr nd isotopic data zircon u pb and hf isotopic data and molybdenite re os data for the units associated with the deposit laser ablation inductively coupled plasma mass spectrometry la icp ms dating of zircons from the granite porphyry yielded an age of 220 3 0 7 ma which was interpreted to be the emplacement age of this intrusion the molybdenite re os dating yielded model ages of 219 9 217 4 ma an isochron age of 222 1 4 7 ma and a weighted mean model age of 218 9 1 6 ma representing the timing of the formation of the mo mineralization the dasuji granite porphyry contains high k calc alkaline and peraluminous rocks and is characterized by relatively high lrees and low hrees depleted ba sr p and ti and negative eu anomalies and are of highly fractionated i type granitoids the whole rock end t and zircon ehf t values for the granite porphyry range from 13 9 to 12 8 and 16 4 to 7 3 respectively indicating that the magma was generated by the partial melting of ancient lower crust materials the dasuji mo deposit may have formed in a post collisional extensional setting

textural and chemical constraints on the formation of disseminated granite hosted w ta nb mineralization at the dajishan deposit nanling range southeastern china the dajishan deposit located in the nanling range of southeastern china is the largest wolframite deposit in the world approximately two thirds of the tungsten resource is contained in large quartz wolframite k feldspar muscovite scheelite sulfide beryl veins but the remainder occurs as wolframite and lesser scheelite disseminated through the nb ta mineralized no 69 granite which is characterized by abundant snowball quartz crystals disseminated granite hosted wolframite mostly occurs as a replacement after lath shaped muscovite although an interstitial variety is present in some samples the major element chemistry of the disseminated and vein hosted wolframite is similar however the former has one to two orders of magnitude higher concentrations of high field strength elements hfse including nb and ta disseminated muscovite in the no 69 granite is fe and mg rich replacement rims on these muscovite crystals are enriched in ta sn and cs but more depleted in nb related to the original phase vein hosted muscovite is characterized by lower nb ta rb and cs contents than the granite hosted muscovite although sn and w concentrations are comparable columbite mn is the principal nb ta ore mineral and occurs disseminated through the no 69 granite where it is hosted by snowball quartz crystals some of the columbite has been altered and overgrown by wodginite the restriction of these altered columbite crystals to within snowball quartz along with the ta and sn enrichment of the alteration rims on muscovite tie the formation of snowball quartz to a ta sn metasomatic event high ge ti and al ti ratios in the snowball quartz relative to interstitial quartz are also consistent with a late stage of formation for the former variety the disseminated granite hosted w mineralization formed through fluid rock interaction the fluids that precipitated the disseminated wolframite were most likely those that formed the veins but were modified through reaction with the hfse enriched no 69 granite nb ta mineralization however is represented by magmatic columbite and by a later metasomatic stage of wodginite the low solubility of ta in aqueous fluids combined with the evidence for ta sn metasomatism suggests that the ta sn metasomatic event was caused by hydrosilicate liquids a transitional fluid that lies compositionally between silicate magmas and hydrothermal fluids whole rock and mineral chemistry both suggest that deep level fractional crystallization of the no 69 granite was required to elevate ta and nb concentrations to allow saturation of columbite

duplex structures and imbricate thrust systems geometry structural position and hydrocarbon potential duplexes and imbricate thrust systems form some of the most complex hydrocarbon traps in overthrust belts the geometry of a duplex is controlled by the ramp angle thgr and height hr the final spacing between adjacent thrusts a prime and the relative displacements on them d1 d2 for constant thgr and hr three different classes are recognized 1 independent ramp anticlines and hinterland sloping duplexes 2 true duplexes and 3 overlapping ramp anticlines imbricate thrust systems consist of several thrust faults each of which loses displacement upsection and eventually dies out by progressively transferring its displacement to a fold at its tip or by distributing it among several splays hybrid duplexes are ormed from systems of fault propagation folds that are subsequently carried over ramps so they have a more complex geometry and a greater structural relief these different types of thrust systems occur as outcrops and prospect scale structures and they define the regional structural styles of most fold and thrust belts second and third order duplexes and imbricate thrust systems occur in specific structural positions such as footwalls hanging walls and frontal zones of major thrust ramps and in cores of major anticlines several types of duplexes and imbricate thrust systems form important hydrocarbon traps examples include the system of independent anticlines of the turner valley and highwood oil and gas fields the hinterland sloping duplex consisting of the chestnut ridge sandy ridge system of the ben hur oil field the partly overlapping anticlines of the waterton and savanna creek gas fields and the completely overlapping anticlines of the rose hill oil field

magmatic to hydrothermal crystallization in the w sn mineralized mole granite nsw australia part i crystallization of zircon and ree phosphates over three million years a geochemical and u pb geochronological study abstract zircon monazite and xenotime crystallized over a temperature interval of several hundred degrees at the magmatic to hydrothermal transition of the sn and w mineralized mole granite magmatic zircon and monazite thought to have crystallized from hydrous silicate melt were dated by conventional u pb techniques at an age of 247 6 0 4 and 247 7 0 5 ma respectively xenotime occurring in hydrothermal quartz is found to be significantly younger at 246 2 0 5 ma and is interpreted to represent hydrothermal growth from associated fluid inclusions it is concluded that it precipitated from a hydrothermal brine 600 c which is below the accepted closure temperature for u pb in this mineral these data are compatible with a two stage crystallization process precipitation of zircon and monazite as magmatic liquidus phases in deep crustal magma followed by complete crystallization and intimately associated sn w mineralization after intrusion of the shallow sill like body of the mole granite later hydrothermal formation of monazite in a biotite fluorite topaz reaction rim around a mineralized vein was dated at 244 4 1 4 ma which distinctly postdates the mole granite and is possibly related to a younger hidden intrusion and its hydrothermal fluid system obtaining precise age data for magmatic and hydrothermal minerals of the mole granite is hampered by uncertainties introduced by different corrections required for multiple highly radiogenic minerals crystallising from evolved hydrous granites including 230 th disequilibrium due to th u fractionation during monazite and possibly xenotime crystallization variable th u ratios of the fluids from which xenotime was precipitating elevated contents of common lead and post crystallization lead loss in zircon enhanced by the fluid saturated environment the data imply that monazite can also survive as a liquidus phase in protracted magmatic systems over periods of 10 6 years the outlined model is in agreement with prominent chemical core rim variation of the zircon