batopilas mining district chihuahua the batopilas mining district is one of the few mining districts where the major ore mineral is native silver the native silver occurs as fissure vein deposits in granodiorite fine grained diorite and dacite orebodies are irregularly shaped pods of massive native silver in calcite and may contain up to 75 wt percent silver the veins formed along north and northeast trending fractures and faults the geologic history of the district is summarized as follows intrusion of the pastrana dacite dolores microquartz diorite and tahonas granodiorite sequentially into preexisting mesozoic sediments and or igneous rocks some of these intrusive events may have vented to the surface after the intrusions were eroded the san jose arenal and casas coloradas flow breccias were deposited between each episode of flow breccia deposition there occurred periods of tectonism and erosion after a fourth major episode of tectonism and erosion the massive ignimbrites of the upper volcanic series represented by the yerbanis formation were deposited contemporaneous with yerbanis deposition was the intrusion of rhyolite dikes numerous andesitc dikes of uncertain age are also present the native silver orebodies are generally less than 30 m in length with the width varying from a few centimeters to 4 6 m and averaging 0 8 m the ore grade mineralization terminates abruptly in both vertical and horizontal directions the orebodies are connected vertically and along strike by up to 90 m of unmineralized fractures or vein stringers of calcite sometimes less than 3 mm wide flexures in vein orientation and or cross fractures are associated with some orebodies whereas other orebodies have no apparent structural control most orebodies are hosted by pastrana dacite and tahonas granodiorite three types of wall rock alteration are found with the silver mineralization 1 chlorite actinolite alteration 2 silicification and 3 pyritization chlorite actinolite alteration is often associated with gray and green argillization the host rocks of many but not all orebodies have experienced chlorite actinolite alteration and pyritization silicification occurs in dikelike masses within the dolores and pastrana units these silicified zones are generally less than 9 m wide pyritization is found in the intrusions minor quartz pyrite veins are found throughout gangue in the batopiias ores is calcite and is associated with small amounts of sphalerite galena and laumontite cobalt nickel arsenides and ruby silvers have been reported but their presence is not confirmed by this investigation pyrite is abundant in the host rocks but is absent from the ores two kilometers southwest of the village of batopilas is an area of approximately 5 km 2 devoid of vegetation the hillsides and tops have a thick gossan corralitos the underlying tahonas granodiorite exhibits widespread sericitic alteration and extensive to almost complete quartz veining and replacement are present chalcanthite stalagtites form on many overhangs along the arroyos this area is interpreted as the tahonas porphyry copper deposit a well developed pattern of mineralogic zonation exists in the district this zonation is concentric around the tahonas porphyry copper deposit preliminary fluid inclusion studies document homogenization temperatures t h between 217 degrees and 434 degrees c and salinities over 20 equiv wt percent nacl for quartz from the tahonas porphyry copper deposit studies on quartz from outlying regions give homogenization temperature ranges of 224 degrees to 351 degrees c and salinities of from 9 to 18 equiv wt percent nacl studies of the later generation of calcite silver and minor sulfides give t h values between 137 degrees and 257 degrees c for calcite and 170 degrees to 196 degrees c for sphalerite salinities in calcite are concentrated between 7 6 and 13 2 equiv wt percent nacl the estimated 300 million oz 9 3 million kg of silver produced to date probably was deposited from circulating connate waters adjacent to the tahonas porphyry copper mineralizing system

age and sources of gold mineralization in the marmato mining district nw colombia a miocene pliocene epizonal gold deposit abstract epigenetic gold mineralization occurs in the marmato mining district within the calima terrain of the setentrional andes colombia regional rocks associated with this mineralization include graphite and chlorite schists of the arquia complex metamorphosed during the cretaceous miocene sandstones shales and conglomerates of the amaga formation as well as pyroclastic rocks clasts of basalt andesites and mafic lavas and subvolcanic andesitic dacitic bodies of the combia formation 9 to 6 ma the subvolcanic marmato stock hosts mesothermal and epithermal low sulfidation au ag ores in the form of distensional veins stockwork and quartz veinlets within brecciated zones ore minerals are pyrite sphalerite and galena with subordinate chalcopyrite arsenopyrite pyrrhotite argentite and native gold electrum sericitized plagioclase from a porphyry dacite yielded a k ar age of 5 6 0 6 ma interpreted as the age of ore deposition this is in close agreement with the age of reactivation of the cauca romeral fault system 5 6 0 4 ma which bounds the calima terrain a porphyry andesite dacite 6 7 0 1 ma hosting the au ag veins shows a measured 87sr 86sr between 0 70440 and 0 70460 end between 2 2 and 3 2 and 206pb 204pb 207pb 204pb and 208pb 204pb ratios of 18 964 to 19 028 15 561 to 15 570 and 38 640 to 38 745 respectively the 87sr 86sr and end values of rocks from the arquia group range from 0 70431 to 0 73511 and 12 91 to 10 0 respectively whereas the corresponding pb isotopic ratios 206pb 204pb 207pb 204pb and 208pb 204pb range from 18 948 to 19 652 15 564 to 15 702 and 38 640 to 38 885 respectively 87sr 86sr and end values obtained on sulfides from the gold quartz veins which occur at shallow and intermediate levels range from 0 70500 to 0 71210 and from 1 11 to 2 40 in the deepest veins end values lie between 1 25 and 3 28 and the 87sr 86sr of calcite and pyrite fall between 0 70444 and 0 70930 the 206pb 204pb 207pb 204pb and 208pb 204pb ratios of all mineralization are in the ranges 18 970 to 19 258 15 605 to 15 726 and 38 813 to 39 208 respectively carbonates have an average 87sr 86sr ratio of 0 70445 which is within the range of values measured in the host dacite the sr isotopic data indicate that carbonic fluids have a restricted hydrothermal circulation within the host igneous body while the sr pb and nd isotopic compositions of the sulfides suggest that the fluids not only circulated within the marmato stock but also throughout the arquia complex inferring that these rocks offer a potential target for mineral exploration based on geological and geochronological evidence the epizonal marmato gold ores formed during the miocene to pliocene as a result of cooling of the marmato stock and reactivation along a crustal scale fault zone related to thermal processes in an accretionary oceanic continental plate orogen

epithermal au and polymetallic mineralization in the tulasu basin western tianshan nw china potential for the discovery of porphyry cuau deposits abstract the tulasu basin is an important epithermal au mineralization district in western tianshan in northwestern china geochemical and geochronological studies of the volcanic host rocks the dahalajunshan formation and associated intrusive rocks particularly the enrichment of large ion lithophile elements and depletion of high field strength elements suggest that the tulasu basin was located in a magmatic arc setting from late devonian to early carboniferous associated with the southward subduction of the north tianshan ocean beneath the kazakhstan yili plate geologic and geochemical characteristics of the au cu polymetallic deposits in the tulasu basin suggest that the mineralization is related to the late devonian to early carboniferous arc magmatism and is mainly of epithermal nature including both the adularia sericite type axi tawuerbieke and tabei and alunite kaolinite or acid sulfate type jingxi yelmend and tieliekesayi however some evidence of porphyry type mineralization has also been found including the presence of mineralized porphyry enclaves in volcanic rocks hosting the tawuerbieke au prospect and the development of porphyry style cu mineralization overprinted by vein type mineralization at kexiaxi considering the magmatic arc setting that is favorable for both epithermal and porphyry types of mineralization and the development of such mineralization systems in other parts of western tianshan and the altaid belt e g uzbekistan kazakhstan and kyrgyzstan we suggest that major porphyry cu au deposits may have been developed in the tulasu basin probably beneath or adjacent to known epithermal au mineralization

origin of epithermal ag au cu pb zn mineralization in guanajuato mexico the guanajuato epithermal district is one of the largest silver producers in mexico mineralization occurs along three main vein systems trending dominantly northwest southeast the central veta madre the la luz system to the northwest and the sierra system to the east mineralization consists dominantly of silver sulfides and sulfosalts base metal sulfides mostly chalcopyrite galena sphalerite and pyrite and electrum there is a broad zonation of metal distribution with up to 10 cu pb zn in the deeper mines along the northern and central portions of the veta madre ore occurs in banded veins and breccias and as stockworks with gangue composed dominantly of quartz and calcite host rocks are mesozoic sedimentary and intrusive igneous rocks and tertiary volcanic rocks most fluid inclusion homogenization temperatures are between 200 and 300 c with salinities below 4 wt nacl equivalent fluid temperature and salinity decreased with time from 290 to 240 c and from 2 5 to 1 1 wt nacl equivalent relatively constant fluid inclusion liquid to vapor ratios and a trend of decreasing salinity with decreasing temperature and with increasing time suggest dilution of the hydrothermal solutions however evidence of boiling such as quartz and calcite textures and the presence of adularia is noted along the veta madre particularly at higher elevations fluid inclusion and mineralogical evidence for boiling of metal bearing solutions is found in gold rich portions of the eastern sierra system this part of the system is interpreted as the least eroded part of the district oxygen carbon and sulfur isotope analysis of host rocks ore and gangue minerals and fluid inclusion contents indicate a hydrothermal fluid with an initial magmatic component that mixed over time with infiltrating meteoric water and underwent exchange with host rocks mineral deposition was a result of decreasing activities of sulfur and oxygen decreasing temperature increasing ph and in places boiling

late cenozoic evolution of epithermal gold metallogenic provinces in kyushu japan kyushu island japan is located at the junction of the southwest japan arc and the ryukyu arc there are two major late cenozoic epithermal gold silver provinces in kyushu which are termed the northern and southern provinces the provinces are characterized by 1 pliocene volcanism dominated by calc alkaline andesite followed by quaternary volcanism including extrusion of both calc alkaline and tholeiitic magmas 2 formation of extensional grabens 3 pliocene to pleistocene mineralization which was dominated by abundant low sulfidation ls epithermal deposits with a few high sulfidation hs examples the two epithermal gold silver provinces have evolved differently since about 5 ma the northern province has exhibited diminished hydrothermal activity from the pliocene to pleistocene whereas the southern province has witnessed increased hydrothermal activity mainly in easterly and northerly directions changes of tectonic setting from the pliocene to pleistocene account for the variable trends in epithermal gold deposit formation westward oblique subduction of the philippine sea plate beneath the southwest japan arc caused development of the hohi graben and arc related volcanism at about 6 ma this was associated with widespread ls mineralization in and surrounding the hohi graben as is represented by the bajo and taio deposits the subduction of the relatively buoyant kyushu palau ridge during the early pliocene strengthened the coupling between the slab and overriding ryukyu arc leading to polygenetic andesite volcanism with associated hs kasuga iwato and akeshi and ls kushikino mineral deposits forming in the southern province a change of the subduction direction of the philippine sea plate from west to north northwest in the early pliocene increased the orthogonal convergence rate between the southwest japan arc and the philippine sea plate resulting in a decrease of volcanic and hydrothermal activity in the hohi graben of the northern province the more northerly subduction of the philippine sea plate shifted the locus of the kyushu palau ridge subduction northward resulting in underplating of the older 85 60 ma negatively buoyant amami basin oceanic slab in the southern province rather than continued subduction of the young 27 15 ma buoyant shikoku basin slab this replacement caused steepening of the slab angle and slab rollback in the southern province which was associated with regional extension an eastward shift of the ryukyu volcanic front and development of the kagoshima and shimabara grabens as well as the okinawa trough rhyolite and basalt volcanism in addition to andesite volcanism have occurred since 2 ma in the area of the ryukyu back arc coincident ls mineralization at hishikari and ohkuchi was affiliated with the rhyolite volcanism another change of the subduction direction of the philippine sea plate to the northwest occurred at 2 1 ma the forearc sliver of the southwest japan arc shifted westward in association with right lateral strike slip faulting along the median tectonic line due to the increase of the westward convergence rate this shift resulted in shortening and cessation of graben development in the hohi area restricting the subsequent volcanism and related hydrothermal activity to the central part of the graben

intermediate sulfidation epithermal gold base metal deposits in tertiary subaerial volcanic rocks sahinli tespih dere lapseki western turkey abstract gold in the sahinli and tespih dere intermediate sulfidation gold base metal deposits in western turkey occurs in relatively deep epithermal quartz veins along with base metal minerals which have epithermal textures including plumose quartz vug infills comb and cockade textures and matrix supported milled breccias the total sulfide content of the veins in the area is variable ranging from fluid inclusions in main stage quartz at sahinli are only liquid rich with homogenization temperatures ranging from 220 to 322 c and the majority of th values between 250 and 300 c salinity ranges from 4 3 to 6 9 wt nacl equiv first ice melting temperatures tmf between 24 5 and 19 0 c indicate that the fluids were dominated by nacl h2o during mineralization the relatively higher average th at the tespih dere deposit 295 c is attributed to a relatively deeper level of exposure calculated 18o values indicate that ore forming hydrothermal fluids in the study area had 18oh2o ranging from 1 1 to 9 7 average 3 8 strongly 18o enriched compared with present day hydrothermal meteoric water in the area 18o 8 5 d values of fluid inclusions in quartz range from 58 to 93 and d values of clay minerals and alunite from 40 to 119 d values from intermediate argillic alteration average 68 in the study area are very similar to d values of the present day local geothermal system average d 54 whereas d values from advanced argillic alteration average d 33 are very different from the present day local geothermal system the 34s values in samples from the sahinli and tespih dere deposits average 2 9 for pyrite 3 3 for chalcopyrite 5 4 for sphalerite and 7 6 for galena these data are consistent with derivation of the sulfur from either igneous rocks or possibly from local wallrock

a review of intermediate sulfidation epithermal deposits and subclassification abstract intermediate sulfidation is veins is one of the subtypes of epithermal deposits formed in subduction related arc settings or post collisional orogenic belts the economic and scientific significance of is deposits has been highlighting importance in ag au pb zn exploration and study of porphyry epithermal systems this epithermal clan of deposits typically have a close relationship with andesitic dacitic volcanic subvolcanic rocks and formed at a depth of 0 3 to as much as 1 km is deposits are typically related to oxidized calcic to calc alkaline magmatism fluid homogenization temperatures and salinities range between 150 and 350 c and 0 and 23 wt nacl equivalent respectively the o and h isotope compositions are consistent with a mixture of magmatic and meteoric water with an increase in meteoric diluent as the hydrothermal system wanes most of the is deposits in the world particularly those in circum pacific metallogenic belts formed during cenozoic time several mesozoic and paleozoic is deposits in the central asian orogenic belt imply great exploration potential for pre cenozoic is deposits in this area the presence of mn carbonate such as rhodochrosite and manganocalcite locally mn silicate e g rhodonite helvite typically in mid to late hydrothermal stages is a common diagnostic feature to discern is from low sulfidation ls deposits in addition the occurrence of intermediate sulfidation state sulfides such as pyrite chalcopyrite sphalerite galena and tetrahedrite tennantite associations are another indicator of the is type light colored fe poor sphalerite is typical of is deposits consistent with relatively oxidized fluids elevated fluid salinity is another characteristic with maximum salinity values of base metal rich is veins usually 5 wt nacl equiv the reported is deposits worldwide show that they develop in compressional volcanic arcs as well as in some extensional settings in this review is deposits are subdivided into nc neutral compressional type is with a low ag au ratio 60 formed in extensional settings such as extensional intra arc post collisional orogenic belts and back arc settings another notable feature of e type is deposits is their large ag endowment compared to nc type is nc type is au ag deposits can be associated with porphyry cu au and or high sulfidation hs au cu deposits and their economic metals are mainly gold and or silver by contrast some e type is deposits can occur on the flanks of porphyry molybdenum deposits e type is veins can also occur together with ls precious metal veins in back arcs or extensional continental margins the most representative examples occurring in mexico the occurrence of the two subtypes of is are largely controlled by the parent magma with parent magma of nc type is primarily derived from depleted mantle or juvenile crust while parent magma of e type is mainly from ancient continental crust the occurrence of is deposits is presumably controlled by tectono magmatic settings and fluid evolution paths neutral to compressive stress regime relatively great depth to an exsolving magma 4 km and low exsolution rate of magmatic fluids plus the presence of syn ore dikes in conjunction with the development of interconnected fracture networks above the porphyry stock could be conducive for the occurrence of is and also hs au veins upon porphyry copper deposits pcds confirmation of sub types and variations of is veins can aid in exploration for spatially and genetic related mineralization types such as porphyry and hs deposits

the partitioning behavior of silver in a vapor brine rhyolite melt assemblage abstract the partitioning of silver in a sulfur free rhyolite melt vapor brine assemblage has been quantified at 800 c pressures of 100 and 140 mpa and f o 2 nno nickel nickel oxide silver solubility 2 in rhyolite increases 5 fold from 105 21 to 675 98 g g as pressure increases from 100 to 140 mpa nernst type partition coefficients d ag i j 2 describing the mass transfer of silver at 100 mpa between vapor and melt brine and melt and vapor and brine are 32 30 1151 238 and 0 026 0 004 respectively at 140 mpa values for d ag i j 2 for vapor and melt brine and melt and vapor and brine are 32 10 413 172 and 0 06 0 03 respectively apparent equilibrium constant values 2 describing the exchange of silver and sodium between vapor and melt k ag na v m at 100 and 140 mpa are 105 68 and 14 6 the average values 2 for silver and sodium exchange between brine and melt k ag na b m at 100 and 140 mpa are 313 288 and 65 12 these data indicate that the mass transfer of silver from rhyolite melt to an exsolved volatile phase s is enhanced at 100 mpa relative to 140 mpa suggesting that decompression increases the silver ore generative potential of an evolving silicate magma model calculations using the new data suggest that the evolution of low density aqueous fluid i e vapor may be responsible for the the silver tonnage of many porphyry type and perhaps epithermal type ore deposits for example halter et al halter w e pettke t and heinrich c a 2002 the origin of cu au ratios in porphyry type ore deposits science 296 1842 1844 used detailed silicate and sulfide melt inclusion and vapor and brine fluid inclusions analyses to estimate a melt volume on the order of 15 km3 to satisfy the copper budget at the bajo de la alumbrera copper gold silver ore deposit using their melt volume estimate with the data presented here model calculations for a 15 km3 felsic melt saturated with pyrrhotite and magnetite suggest that a low salinity magmatic vapor may scavenge on the order of 7 1012 g of silver from the melt this quantity of silver exceeds the discovered 2 109 g of ag at alumbrera calculated tonnages for numerous other deposits yield similar results the excess silver in the vapor remaining after porphyry formation is then available to precipitate at lower ptconditions in the stratigraphically higher epithermal environment these data suggest that silver and perhaps other ore metals in the porphyry epithermal continuum may be derived solely from the time integrated flux of dominantly low salinity vapor exsolved from a series of sequential magma batches

stable isotope study of the mineralization and alteration in the madjarovo pb zn district south east bulgaria the madjarovo ore district is centred on the exposed section of a lower oligocene volcano and consists of radially disposed pb zn precious metal veins and attendant intermediate sulfidation wallrock alteration earlier high sulfidation and potassic porphyry style alterations are found in the centre of the district spatially associated with monzonitic intrusions the total duration of all mineralization and alteration was ca 300 ka stable isotope analyses s o h have been carried out on a suite of sulfides sulfates and silicates from the mineralization high and intermediate sulfidation alterations and a suite of basement rocks these data range between the following limits delta 34 s sulfides 1 2 operatorname to 6 8 text delta 34 s sulfates 21 4 text to 24 9 delta 18 o sulfates 5 8 operatorname to 11 6 delta d sulfates 35 1 operatorname to 67 1 delta 18 o silicates 5 2 text to 13 5 delta d operatorname silicates 36 3 to 77 0 we also analysed d of fluid inclusions in quartz and barite for which we obtained respectively the ranges of 43 6 to 78 6 and 58 4 to 67 1 the data show that high sulfidation alteration was dominated by magmatic fluids with minor meteoric water whereas the fluids responsible for the intermediate sulfidation alteration were essentially magmatic the fluids responsible for the intermediate sulfidation pb zn mineralization were mixed magmatic meteoric and certainly contained a significant meteoric component sulphur is likely derived from basement and or igneous sources the evolution of alteration and mineralization styles from potassic porphyry copper style to high sulfidation to intermediate sulfidation can be understood in terms of changing ore fluid composition resulting from an increasing permeability of the system and an increasingly remote source of magmatic fluid with time these changes link directly to the geological evolution of this volcanic centre

fluid density control on vapor liquid partitioning of metals in hydrothermal systems hot aqueous fluids both vapor and saline liquid are primary transporting media for metals in hydrothermal magmatic systems despite the growing geological evidence that the vapor phase formed through boiling of magmatic ore bearing fluids can selectively concentrate and transport metals the physical chemical mechanisms that control the metal vapor liquid fractionation remain poorly understood we performed systematic experiments to investigate the metal vapor liquid partitioning in model water salt gas systems h2o nacl kcl hcl at hydrothermal conditions measurements show that equilibrium vapor liquid fractionation patterns of many metals are directly related to the densities of the coexisting vapor and liquid phases despite differences in the vapor phase chemistry of various metals that form hydroxide chloride or sulfide gaseous molecules of contrasting volatile properties water solute interaction is a key factor that controls the metal transfer by vapor like fluids in earth s crust these findings allow quantitative prediction of the vapor liquid distribution patterns and vapor phase metal transport in a wide range of conditions our density model accounts well for the vapor brine distribution patterns of na si fe zn as sb and ag observed in fluid inclusions from magmatic hydrothermal deposits for au and cu the partitioning in favor of the liquid phase predicted in a sulfur free system contrasts with the copper and gold enrichment observed in natural vapor like inclusions the formation of stable complexes of cu and au with reduced sulfur may allow for their enhanced transport by sulfur enriched magmatic hydrothermal vapors

role of basement in epithermal deposits the kushikino and hishikari gold deposits southwestern japan abstract the magma ore deposit relationship of most low sulfidation epithermal ore deposits is still unclear partly because many stable isotopic studies of such deposits have indicated the predominance of meteoric waters within hydrothermal fluids however it is certainly true that hydrothermal systems are ultimately driven by magmatic intrusions and epithermal gold deposits might therefore be produced by magmatic activity even in deposits having has no obvious links to a magma we re examine the genesis of two typical low sulfidation epithermal gold deposits the kushikino and hishikari deposits using structural simulations and isotope data many epithermal gold deposits including the kushikino and hishikari deposits have been discovered in kyushu southwestern japan the kushikino deposit comprises fissure filling veins within neogene andesitic volcanics that overlie unconformably cretaceous sedimentary basement the veins consist of gold and silver bearing quartz and calcite with minor amounts of adularia sericite and sulfides although carbon and oxygen isotopic data for the veins indicate a meteoric origin of the ore fluid finite element simulations suggest that the vein system might have formed in direct response to magma intrusion in particular geophysical data suggest that intruding magma has uplifted the basement rocks thereby producing fractures and veins and a positive bouguer anomaly and providing the heat necessary to drive an ore forming hydrothermal system the second component of this study has been to investigate the nature and evolution of the kushikino and hishikari epithermal systems isotope data document the geochemical evolution of the hydrothermal fluids we conclude that the existence of sedimentary basement rocks at depth might have affected the strontium and carbon isotopic ratios of the kushikino and hishikari ore fluids the 87 sr 86 sr ratios and 13 c 18 o trend reveal that major ore veins in the hishikari deposit can be distinguished from shallow barren veins it was suggested isotopically that fluids responsible for the barren veins in nearby shallow and barren circulation systems were only controlled by the shallow host rocks such multi isotope systematics provide a powerful tool with which to determine the center of hydrothermal activity and thereby document the evolution of hydrothermal fluids

the zacatecas mining district a tertiary caldera complex associated with precious and base metal mineralization the zacatecas mining district is located in north central mexico at the transition of the sierra madre occidental and mesa central physiographic provinces the existence of a deeply eroded caldera is evidenced by concentric and radial fracture systems a ring fracture zone a thick pile of ash flow tuffs several subvolcanic plugs a lava flow dome two partially superimposed asymmetric collapse features and a resurgent dome the prevolcanic floor of the caldera is represented by a late cretaceous microdiorite laccolith which intruded metasediments of possible triassic age all overlain by a continental red conglomerate of paleocene age the volcanic center is spatially associated with economic mineralization and exerted strong structural control on the formation of the deposits three groups of veins are recognized varying in ore assemblage and structural position 1 the most important and extensive is the ag pb zn cu au system occurring in concentric and tangential faults and fractures that cut precaldera rocks 2 the au ag se system located in radial fractures that were emplaced in the caldera fill host rocks and 3 the f system subparallel to the other margin of the caldera and also located in caldera fill lithologies silver the dominant precious metal occurs mainly as acanthite silver sulfantimonides such as freibergite and native silver free gold and electrum were identified optically and aguilarite ag 2 ses was identified for the first time in the district pyrite sphalerite galena and chalcopyrite are also present gangue minerals are mainly quartz and calcite preliminary fluid inclusion data on samples from the cantera vein system which contains precious and base metals fall in the temperature range of 300 degrees to 160 degrees c the early tertiary mineralization in the district is epithermal and controlled by volcanotectonic features modified by erosion oxidation and supergene enrichment

geology of the escondida porphyry copper deposit antofagasta region chile the escondida porphyry copper deposit located in northern chile was one of the two largest copper producers of the world in the 1990s the hydrothermal evolution of this deposit is associated with the emplacement of a late eocene oligocene quartz monzonitic to granodioritic intrusive stock complex composed of at least three intrusive phases and hosted by paleocene andesite this paleocene andesite is underlain by mesozoic and paleozoic sedimentary and volcanic rocks which are characteristic of the basement of the precordillera de domeyko province in northern chile we propose that the intrusive stock associated with the mineralization at escondida was emplaced in a tensional gash formed between sinistral strike slip faults of the regional domeyko fault system the complete evolution of the porphyry system is characterized by overprinting of pervasive and vein associated alteration mineralization styles grouped in three main hydrothermal stages the early stage includes a zone of pervasive biotitization of andesite and development of a silicification shell around the intrusive complex propylitic alteration around the biotitic zone and a vein associated orthoclase quartz anhydrite biotite alteration that mark the end of stage one this early alteration contains magnetite chalcopyrite and bornite with less than 0 5 vol percent of sulfides and a hypogene copper grade of 0 2 wt percent the second hydrothermal stage is represented by vein and vein selvage associated chlorite sericite quartz and by quartz sericite with sulfides including chalcopyrite pyrite and molybdenite in the chlorite sericite and quartz sericite zones the content of sulfides ranges from less than 0 5 to 2 vol percent with a chalcopyrite to pyrite ratio of 3 to 1 and copper grades that range between 0 4 and 0 6 wt percent the intrusion of a rhyolite dike and a dome are at least 3 m y younger than the first and second hydrothermal stages and separate them in time from the late hydrothermal stage the late hydrothermal stage is represented by an acid sulfate mineral association that includes pyrophyllite alunite and quartz as alteration minerals and a variety of sulfides that include bornite chalcopyrite pyrite chalcocite covellite enargite sphalerite tennantite and galena this acid sulfate event occurred mainly in west northwest striking veins and also along the contact of the rhyolite and its host rock where sulfides from this event overprint previous sulfides the primary copper grades range from 0 6 to higher than 1 0 wt percent in the escondida deposit the highest hypogene and supergene copper grades occur in areas where all three hydrothermal stages are present

post caledonian tectonics along the billefjorden fault zone svalbard and implications for the arctic region the north south billefjorden fault zone of northern spitsbergen in the svalbard archipelago has been widely regarded as one of the classic areas for transpressional tectonics the fault zone coincides with a late caledonian shear zone and presently constitutes the eastern boundary of the main devonian basin of northern svalbard fold axial traces and thrust faults that developed in the devonian to permo carboniferous rocks parallel the strike of the fault zone there is no evidence for the rotation of fold hinges and nonaxial planar transecting cleavages are lacking folds and thrusts with similar geometries affect the whole 60 km wide devonian basin fill these observations together with analyses of fault and fold patterns indicate a pre devonian caledonian left lateral ductile shearing b late silurian early devonian extension c late devonian early carboniferous inversion accompanied by folding of devonian sedimentary rocks d early carboniferous extension followed by platform wide subsidence into late mesozoic time e late cretaceous paleocene east west contraction thrusting and folding and e post paleocene east west extension the late devonian deformation along the billefjorden fault zone is compared with the late devonian to early carboniferous ellesmerian orogeny of the canadian arctic the late devonian megashear model for the tectonic evolution of the north atlantic region is not supported by the evidence from svalbard

constraints on the ore fluids in the chah zard breccia hosted epithermal au ag deposit iran fluid inclusions and stable isotope studies the chah zard gold silver deposit in the central part of the urumieh dokhtar magmatic arc udma of iran is a breccia hosted low to intermediate sulfidation epithermal deposit with a resource of 2 5 mt averaging 1 7 g t au and 12 7 g t ag gold and silver mineralization occurs in breccia and veins associated with a 6 2 0 2 ma volcanic complex microthermometric measurements on quartz and sphalerite hosted two phase liquid rich fluid inclusions indicate that the mineralization may have taken place between 260 and 345 c from a moderately saline hydrothermal fluid 8 4 13 7 wt nacl equiv first ice melting temperatures between 37 and 53 c indicate that the aqueous fluids contained nacl cacl2 mgcl2 fecl2 coexisting liquid rich and vapor rich fluid inclusions in quartz and sphalerite provide evidence for boiling in ore stage breccia and veins additionally the occurrence of adularia and bladed calcite in high grade ore zones and the presence of hydrothermal breccias and chalcedonic quartz are consistent with boiling calculated 18o values of water in equilibrium with quartz 3 4 to 13 1 suggest that the fluid may have had a magmatic source but was 18o depleted by mixing with meteoric water the average calculated 34sh2s values are 0 2 for pyrite 0 2 for chalcopyrite 1 0 for sphalerite and 0 2 for galena the 34sh2s values are consistent with a magmatic source for sulfur gold deposition at chah zard is inferred to have been largely caused by boiling although fluid mixing and or wall rock reactions may also have occurred after rising to a depth of between 970 and 440 m the fluid boiled causing deposition of fine grained quartz and sealing of the hydrothermal conduit episodic boiling in response to alternating silica sealing and hydraulic brecciation was responsible for ore deposition gold and silver may have precipitated due to the destabilization of hs complexes caused by the boiling off of h2s to vapor whereas the dilution and or cooling of hydrothermal fluids led to the precipitation of base metals

metal fractionation between magmatic brine and vapor determined by microanalysis of fluid inclusions the major and trace element compositions of individual fluid inclusions from a range of magmatic hydrothermal ore deposits were analyzed by laser ablation inductively coupled plasma mass spectrometry to explore the behavior of ore forming components during fluid phase separation boiling in high temperature saline fluid systems data from 13 samples showing unambiguous evidence for coeval trapping of a liquid brine and a coexisting vapor phase identify two groups of elements with drastically different geochemical behavior na k fe mn zn rb cs ag sn pb and tl preferentially partition into the brine probably as cl complexes whereas cu as au probably as hs complexes and b selectively partition into the vapor fluid phase separation is probably a major previously underestimated process in the chemical differentiation that contributes to the extreme range of selective element enrichments in magmatic hydrothermal systems from deep plutons through porphyry style and greisen deposits to epithermal mineralization and volcanic fumaroles

giant ore deposits formed by optimal alignments and combinations of geological processes giant ore deposits are priority targets for mining companies a review of the characteristics of several giant porphyry and epithermal deposits worldwide suggests that they formed from ordinary processes that were fortuitously operating at maximum efficiency

fluid inclusions and isotopic characteristics of the jiawula pb zn ag deposit inner mongolia china abstract the large jiawula pb zn ag deposit is located in the derbugan metallogenic belt of the northern great xing an range the vein style orebodies of the deposit occur along nww to nnw trending fault zones the ore forming process at the deposit can be divided into three stages an early quartz pyrite pyrrhotite chalcopyrite stage a middle quartz carbonate pyrite galena sphalerite stage and a late quartz carbonate pyrite stage sulfide rb sr dating indicates that the jiawula deposit formed at ca 143 142 ma four types of fluid inclusions have been distinguished in quartz veins including liquid rich gas rich h2o co2 and daughter mineral bearing inclusions the fluid inclusions of the early stage are mainly liquid rich gas rich and h2o co2 types with a small number containing daughter minerals cumulatively the types have homogenization temperatures densities and salinities of 304 438 c 0 35 1 37 g cm3 and 0 8 44 6 wt nacl eqv respectively inclusions of the middle stage are mainly liquid rich and gas rich types with a small amount of h2o co2 and daughter mineral bearing types their homogenization temperatures densities and salinities vary from 242 c to 297 c 0 71 to 1 44 g cm3 and 0 4 wt to 36 8 wt nacl eqv respectively the late stage only comprises liquid rich inclusions with homogenization temperatures densities and salinities of 181 238 c 0 81 0 90 g cm3 and 0 2 1 9 wt nacl eqv respectively the ore forming fluids of the jiawula deposit are generally characterized by moderate temperature and low salinity and density and belong to an h2o nacl co2 ch4 system the 18owater values calculated for ore bearing quartz vary from 13 4 to 9 1 and the dv smow values from bulk extraction of fluid inclusion waters vary from 166 to 133 suggesting that the ore forming fluids mainly consist of meteoric water with a small amount of magmatic water the 34sv cdt values range from 1 2 to 8 4 the 206pb 204pb 207pb 204pb and 208pb 204pb values of the ore minerals are in the ranges of 18 319 18 377 15 499 15 596 and 38 094 38 314 respectively initial 87sr 86sr ratios of sulfides range from 0 712381 to 0 712770 the data for the s pb and sr isotopic systems indicate that the ore forming metals and sulfur came from mesozoic magma the jiawula deposit is a low sulfidation epithermal pb zn ag deposit and fluid boiling is the dominant mechanism for the deposition of ore forming materials

geologic and fluid inclusion studies of the tayoltita silver gold vein deposit durango mexico precious metal production from veins of the tayoltita mine totals more than 10 7 kg of silver and 2 x 10 5 kg of gold the deposit the largest in the san dimas mining district occurs in the central part of the sierra madre occidental volcanic pile which contains rocks reflecting two separate periods of magmatism k ar dating by mcdowell and keizer 1977 demonstrates that these were active between 100 and 45 m y and 32 and 23 m y ago encasing the veins are rhyolitic andesitic and granodioritic rocks of the older magmatic episode ignimbritic rocks of the younger period of magmatism postdate the mineralizing event which occurred about 40 m y ago with only one exception the n 15 degrees w arana fault vein economic mineralization is restricted to fractures striking east west to north northeast regional normal faults trending north northwest cut the rocks of both magmatic episodes and divide the district into tilted blocks dipping east supergene processes played an insignificant role in the formation of ore hypogene open space fillings can be divided into three paragenetic stages 1 quartz with or without abundant sphalerite and galena with or without minor silver gold values 2 quartz with or without three mutually exclusive gangue suites all occurring with ore grade 200 ppm ag and 2 ppm au precious metal values but each with or without dark green hydrothermal chlorite and copper lead zinc sulfides quartz rhodonite johannsenite albite quartz adularia and quartz calcite 3 white to amethystine vuggy quartz small amounts of pearceite native silver chalcopyrite calcite and zeolites were deposited in stage 3 vugs during the waning stage of the hydrothermal system silver and gold were deposited within a horizontal favorable zone minimally estimated to have been 600 m thick which essentially paralleled the untilted volcanic pile the distributions of both metals are zoned vein by vein with respect to two small granodiorite stocks with ag au varying from 44 to 105 with the lowest ag au closest to the intrusions filling temperatures for quartz of stage 2 250 degrees to 290 degrees c and stage 3 250 degrees to 310 degrees c show little time space variation of temperature during the mineralizing event indications of boiling in stage 3 quartz are found over a broad three dimensional range salinities of the inclusion fluids range from 4 1 to 9 7 equivalent weight percent nacl in stage 1 3 3 to 8 4 weight percent in stage 2 and 1 9 to 9 7 weight percent in stage 3 fluid inclusion data and field relationships indicate an approximate 400 m depth below the surface for the top of the favorable zone at the time of vein formation gas analyses of thermally decrepitated fluid inclusions indicate that water constituted over 99 5 mole percent of the liquid and gas phases with co 2 comprising most of the remainder the delta 18 o values of stages 2 and 3 vein quartz range from 3 9 to 4 8 per mil suggesting that meteoric water dominated the hydrothermal system

special paper major gold deposits and belts of the north and south american cordillera distribution tectonomagmatic settings and metallogenic considerations a compilation of economically viable gold concentrations containing 10 moz in the north and south american cordillera reveals the existence of 22 discrete belts in addition to five major isolated deposits most formed over the last 150 m y the gold concentrations are attributed to eight widely recognized deposit types of which porphyry sediment hosted and high sulfidation epithermal are economically the most important individual gold belts are typically several tens to hundreds of kilometers long dominated by single deposit types and metallogenically active for relatively brief periods 5 20 m y many of the gold belts and major isolated deposits were generated under extensional or transtensional tectonic conditions in either arc or back arc settings nevertheless the two main high sulfidation epithermal gold belts were generated in thickening or already thickened crust during low angle subduction eight other gold belts or districts also accompanied compression or transpression with two of them the main orogenic gold belts occupying fore arc sites there is a strong suggestion that the preeminent cordilleran gold concentrations formed either during or immediately following prolonged contraction the major gold deposits and belts occur along the craton edge as well as in adjoining accreted terranes but almost all are of postaccretionary timing many of the gold belts and isolated deposits were localized by crustal scale faults or lineaments which may be either parallel or transverse to the cordilleran margin the gold concentrations accumulated during active subduction commonly in close spatial and temporal association with intermediate to felsic medium to high k calc alkaline igneous rocks by contrast the low sulfidation epithermal gold deposits accompany bimodal volcanic pulses of calc alkaline tholeiitic or alkaline affinity however a gold alkaline rock association is uncommon a genetic link between gold mineralization and coeval magmatism is widely accepted for most of the deposit types the exceptions being the sediment hosted and orogenic gold deposits notwithstanding the small cumulative extent of the gold concentrations relative to the entire cordilleran margin there is a marked tendency for two or more belts or isolated deposits of different ages and genetic types to occur in close proximity within relatively restricted arc including fore and back arc segments in the case of the western united states for example six belts and four isolated major deposits make up a particularly prominent cluster if fortuity is discounted this clustering or pairing of gold concentrations must imply a predisposition of certain arc segments to gold mineralization an analogous situation is evident for other metals particularly copper and tin the reason for the recurrent generation of major deposits and belts dominated by one or more metals remains uncertain although heterogeneously distributed metal preconcentrations favorable redox conditions or other parameters somewhere above the subducted slab between the mantle wedge and upper crust are widely contemplated possibilities elucidation of the reason s for this metallogenic inheritance at the scale of limited arc segments poses an important and challenging series of research questions as well as being critical to the planning of potentially successful greenfield exploration programs

zoned base metal mineralization in a porphyry system origin and evolution of mineralizing fluids in the morococha district peru porphyry related base metal vein and replacement mineralization i e cordilleran polymetallic mineralization in the morococha district central peru is part of a large magmatic hydrothermal system associated with the emplacement of several late miocene porphyry intrusions and formation of important cu mo mineralization zn pb ag cu veins overprint the giant toromocho porphyry cu mo deposit in the center of the district and display a typical concentric base metal zonation cu zn pb ag covering an area of approximately 50km2 a detailed fluid inclusion study supports the hypothesis that base metal mineralization precipitated from cooled and evolved metal rich intermediate density porphyry type fluids in early stages of cordilleran base metal vein formation fluid inclusions have low salinities of 2 to 5 wt nacl equiv co2 contents of 3 to 10mol and homogenization temperatures th of 380 to 340 c they are similar to intermediate density fluid inclusions trapped in a milky quartz vein predating cordilleran polymetallic mineralization with similar low salinities 3 0 3 8 wt nacl equiv and low co2 contents 6 5 8 mol but higher th of 420 to 410 c during cooling of the intermediate density fluids from 400 to 300 c the lithostatic pressure regime changed to a hydrostatic one the fluids underwent pressure drop as well as phase separation i e unmixing and lost most of their co2 they acquired moderate salinities in some cases intermediate up to 16 wt nacl to brine compositions however the bulk of the magmatic fluid retained low salinity while it continued to cool under open system conditions and precipitated tennantite tetrahedrite chalcopyrite enargite sphalerite and galena upon cooling below 270 c the fluids deposited abundant rhodochrosite and quartz while following the boiling curve toward lower p t conditions these data record an evolution of mineral precipitation from deep minimum depth of 2 1 5 km to shallow environments 300 800 m oxygen hydrogen and carbon stable isotope data indicate that the hydrothermal fluids have a dominantly magmatic signature and were diluted by meteoric waters during the carbonate stage copper 5 000 18 000 g g sulfur up to 12 000 g g and iron 2 100 6 000 g g concentrations in the intermediate density fluid inclusions in the milky quartz veins are approximately 5 to 10 times higher than in intermediate density inclusions of the early cordilleran base metal veins the base metals zn pb and mn have comparable concentrations between 100 and 1 000 g g for both types of fluid these findings suggest that the fluids identified in cordilleran polymetallic veins are compositionally similar to the porphyry type fluids and could have derived from the latter after precipitation of cu and fe bearing sulfides in a deeper porphyry environment the new data explain the commonly observed base and precious metal zonation patterns encountered in porphyry centered districts e g bingham butte and show that both porphyry and polymetallic mineralization can precipitate from similar magmatic hydrothermal fluid pulses

exploration tools for linked porphyry and epithermal deposits example from the mankayan intrusion centered cu au district luzon philippines the mankayan mineral district of northern luzon philippines hosts several significant ore deposits and prospects of various types within an area of similar to 25 km 2 including the far southeast porphyry cu au deposit the lepanto high sulfidation epithermal cu au deposit the victoria intermediate sulfidation epithermal au ag vein deposit the teresa epithermal au ag vein deposit the guinaoang porphyry cu au deposit and the buaki old palidan porphyry cu au prospects all having formed in a period of about 2 m y from similar to 3 ma the geologic units include 1 a basement composed of late cretaceous to middle miocene metavolcanic rocks volcaniclastic rocks 2 the miocene 12 to 13 ma tonalitic bagon intrusive complex 3 the pliocene similar to 2 2 to 1 8 ma imbanguila dacite porphyry and pyroclastic rocks and 4 postmineralization cover rocks including die similar to 1 2 to 1 0 ma bato dacite porphyry and pyroclastic rocks and the similar to 0 02 ma lapangan tuff extensive advanced argillic alteration crops out for similar to 7 kin along the inconformity between the basement rocks and the imbanguila dacite formation consists of quartz alunite pyrophyllite or diaspore with local zones of silicic alteration and a halo of dickite kaolinite the alteration and its subhorizontal geometry indicate that it is a lithocap or coalesced lithocaps the northwest striking portion is similar to 4 km long and hosts the lepanto enargite au ore deposit also controlled by the lepanto fault the lepanto epithermal deposit is related to the underlying far southeast porphyry the quartz alunite alteration halo of lepanto is contemporaneous with the similar to 1 4 ma potassic alteration of the porphyry there are also silicic advanced argillic alteration patches similar to 600 m above the far southeast orebody at the present surface these are interpreted to be perched alteration there is no systematic mineralogical or textural zoning in the lepanto lithocap that indicates direction to the intrusive source most surface samples of the lithocap contain less than 50 ppb au despite many being less than a few hundred meters from underground cu au ore this study found that several characteristics of the lepanto lithocap change systematically with distance from the causative intrusion the alunite absorption peak at similar to 1 480 nm in the short wavelength infrared swir spectrum shifts to higher wavelengths where the sample is closer to the intrusive center due to higher na and lower k content in the alunite published experimental studies indicate that high na na k is related to higher formation temperature high ca alunite including huangite also occurs at locations proximal to the intrusive center alunite mineral composition analyzed by laser ablation inductively coupled plasma mass spectrometry la icp ms indicates that the pb content decreases toward the intrusive center whereas sr la sr ph and la pb increase markedly whole rock compositions using only nonmineralized taken as cu similar to 350 m above the upper extent of the veins an airborne geophysics survey indicates that the far southeast orebody is associated with a wide zone of demagnetization due to extensive magnetite destructive phyllic alteration such low magnetic anomalies on the margin of a large lithocap elsewhere may deserve attention the directional indicators and mineralization signatures found in this study have the potential to indicate direction to the intrusive center during exploration of similar porphyry epithermal districts

fluid mineral relations in the comstock lode the comstock lode a world class precious metal vein deposit in the comstock district 15 mi 24 km southeast of reno nevada formed 13 7 ma in miocene eruptive rocks of the alta and kate peak formations and in pre tertiary metavolcanic and intrusive rocks production of 8 25 million oz 311 850 kg in gold and 192 million oz 7 26 million kg in silver came largely from bonanzas or vein segments containing hundreds of thousands to millions of tons and grading or 0 4 oz ton approximately 14 g ton gold and or 10 oz ton approximately 340 g ton silver within the 8 mi 12 9 km long comstock fault bonanza ores are distributed 3 mi 4 8 km along strike and persist from the present surface to 3 300 ft 1 007 m below the surface during the middle miocene andesitic to rhyodacitic alta and kate peak rocks formed a stratovolcano that exceeded 7 000 ft 2 134 m in elevation bonanza ores were deposited within this volcano from a 200 degrees c hydrothermal system that affected more than 37 mi 3 150 km 3 of rock at least one cretaceous and several miocene hydrothermal events were imposed on comstock district rocks the comstock lode vein assemblage which resulted from the youngest and only economically important event consists of quartz electrum silver minerals mainly acanthite pyrite base metal sulfides and minor amounts of calcite sericite chlorite k feldspar and albite andesite adjacent to veins is altered to quartz sericite and pyrite at vein contacts and quartz sericite montmorillonite chlorite and pyrite distally kaolinite is present in wall rocks adjacent to vein segments in which boiling occurred addition of the external components water co 2 and sulfur gases sufficed to produce all comstock vein alteration assemblages based on paragenetic and fluid inclusion studies multiple generations of hydrothermal fluid formed comstock district veins but the earliest and highest temperature fluid deposited ore minerals it ranged in temperature from 300 degrees c at the north end of the lode cedar hill to 6 wt percent nacl and was composed of both meteoric and magmatic water according to fluid isotopic analyses younger cospatial fluid s contained up to 2 1 wt percent co 2 the thermal center of the comstock lode hydrothermal system cedar hill is also the site of the highest measured ore fluid salinities ore fluid isotherms and to an extent salinity isopleths display reversals and convolutions that are spatially related to bonanzas these sharp temperature gradients coupled with mixing of ore fluid and at least one other high temperature fluid indicated by enthalpy salinity relationships and deuterium enrichment most likely caused precipitation of ore minerals sphalerite and electrum compositions indicate that bonanzas were deposited over a narrow range of f sub s 2 13 5 to 15 2 while sphalerites from low grade and barren vein segments indicate more widely variable f sub s 2 gold silver ratios both in electrum and bulk ore appear to be temperature controlled as higher temperatures generally correlate with high au ag ratios local boiling of 250 degrees to 285 degrees c fluid provides a paleosurface datum but vein temperatures 300 degrees c require up to 3 800 ft 1 152 m of cover over the tops of bonanzas during mineralization the distribution of both ore stage and late vein calcite partially reflects hydrothermal fluid circulation patterns in veins at district margins the abundance of late calcite marks the demise of hot water circulation and the influx of large amounts of cold miocene ground water into vein interstices kate peak intrusions between cedar hill and mount davidson share a common structural control with vein segments that comprise the comstock lode and their ages span vein ages the coeval kate peak magmas that provided heat for hydrothermal circulation formed the core of and uplifted the miocene stratovolcano which was centered over cedar hill partial symmetry of thermal compositional and kinetic gradients about cedar hill suggests that additional bonanzas await discovery along unexplored comstock fault segments within declining palcothermal gradients to the north

the relation between cu au ratio and formation depth of porphyry style cu au mo deposits constraints on gold and copper ore grades in porphyry style cu au mo deposits are re examined with particular emphasis on published fluid pressure and formation depth as indicated by fluid inclusion data and geological reconstruction defining an arbitrary subdivision at a molar cu au ratio of 4 0 104 copper gold deposits have a shallower average depth of formation 2 1 km compared with the average depth of copper molybdenum deposits 3 7 km based on assumed lithostatic fluid pressure from microthermometry the correlation of cu au ratio with depth is primarily influenced by the variations of total au grade despite local mineralogical controls within some ore deposits the overall cu au ratio of the deposits does not show a significant correlation with the predominant type of cu fe sulfide i e chalcopyrite or bornite primary magma source probably contributes to metal endowment on the province scale and in some individual deposits but does not explain the broad correlation of metal ratios with the pressure of ore formation by comparison with published experimental and fluid analytical data the observed correlation of the cu au ratio with fluid pressure can be explained by dominant transport of cu and au in a buoyant s rich vapor coexisting with minor brine in two phase magmatic hydrothermal systems at relatively shallow depth approximately 3 km and greater confining pressure is likely to precipitate copper molybdenum only while sulfur complexed gold remains dissolved in the relatively dense vapor upon cooling this vapor may ultimately contract to a low salinity epithermal liquid which can contribute to the formation of epithermal gold deposits several kilometers above the au poor porphyry cu mo deposit these findings and interpretations imply that petrographic inspection of fluid inclusion density may be used as an exploration indicator low pressure brine vapor systems are favorable for coprecipitation of both metals leading to au rich porphyry copper gold deposits epithermal gold deposits may be associated with such shallow systems but are likely to derive their ore forming components from a deeper source which may include a deeply hidden porphyry copper molybdenum deposit exposed high pressure brine vapor systems or stockwork veins containing a single type of intermediate density inclusions are more likely to be prospective for porphyry copper molybdenum deposits

the role of sulfur in the formation of magmatic hydrothermal copper gold deposits abstract essential resources of many rare metals including copper zinc molybdenum silver and gold occur in natural sulfide mineral deposits understanding the origin of these metal resources has been limited by a lack of data about the geochemistry of sulfur the most important and abundant element of ore deposits we report the first directly measured sulfur concentrations in high temperature fluids together with their ore metal contents using a new method for sulfur quantification in fluid inclusions by laser ablation inductively coupled plasma mass spectrometry la icp ms co genetic brine and vapor inclusions from magmatic hydrothermal ore deposits and granitic intrusions show an excess of sulfur over ore metals as required for efficient ore mineral precipitation the results demonstrate that s cu and au are highly enriched in vapor like magmatic fluids implying that such low salinity fluids are the key agent for the formation of porphyry copper and epithermal gold deposits

tectonic magmatic and metallogenic evolution of the tethyan orogen from subduction to collision abstract this paper reviews the tectonic magmatic and metallogenic history of the tethyan orogen from the carpathians to indochina focus is placed on the formation of porphyry cu mo au deposits as being the most characteristic mineral deposit type formed during both subduction and collisional processes in this region relatively little is known about the history of the paleotethys ocean which opened and closed between gondwana and eurasia in the paleozoic and few ore deposits are preserved from this period the neotethyan ocean opened in the permian early triassic as the cimmerian continental fragments the cores of turkey iran tibet and indochina rifted from the northern gondwana margin and drifted northwards these microcontinents docked with the eurasian margin at various points in the mesozoic and cenozoic and formed a complex archipelago involving several small back arc basins and remnants of the paleotethyan ocean the main neotethyan ocean and these smaller basins were largely eliminated by collision with india and africa arabia in the early eocene and early mid miocene respectively although neotethyan subduction continues beneath the hellenic arc and the makran the majority of porphyry type deposits are found in association with neotethyan subduction mainly in the mesozoic and paleogene and syn to post collisional events in the mid paleogene to neogene they are found throughout the orogen but some sections are particularly well endowed including the carpathians balkans rhodopes eastern turkey lesser caucasus nw iran se iran sw pakistan southern tibet and se tibet indochina other sections that appear barren may reflect deeper levels of erosion young sedimentary cover or lack of exploration although there may also be real reasons for low prospectivity in some areas such as minimal subduction e g the western mediterranean region or lithospheric underthrusting as proposed in western tibet over the last decade improved geochronological constraints on the timing of ore formation and key tectonic events have revealed that many porphyry deposits that were previously assumed to be subduction related are in fact broadly collision related some forming in back arc settings in advance of collision some during collision and others during post collisional processes such as orogenic collapse and or delamination of subcontinental mantle lithosphere while the formation of subduction related porphyries is quite well understood collisional metallogeny is more complex and may involve a number of different processes or sources these include melting of orogenically thickened crust previously subduction modified lithosphere including metasomatized mantle underplated mafic rocks or lower crustal arc plutons and cumulates or upwelling asthenosphere e g in response to delamination slab breakoff back arc extension or orogenic collapse the most fertile sources for syn and post collisional porphyry deposits appear to be subduction modified lithosphere because these hydrated lithologies melt at relatively low temperatures during later tectonomagmatic events and retain the oxidized and relatively metalliferous character of the original arc magmatism unusually metallically enriched lithospheric sources do not seem to be required but the amount of residual sulfide phases in these rocks may control metal ratios e g cu au in subsequent magmatic hydrothermal ore deposits relatively au rich deposits potentially form in these settings as observed in the carpathians e g rosia montan turkey kisladag copler and iran sari gunay dalli although the majority of syn and post collisional porphyries are cu mo rich and resemble normal subduction related deposits e g in the gangdese belt of southern tibet this similarity extends to the associated igneous rocks which being derived from subduction modified sources largely retain the geochemical and isotopic character of those original arc magmas while still retaining a broadly calc alkaline character these rocks may extend to mildly alkaline shoshonitic compositions and may display adakite like trace element signatures high sr y and la yb ratios reflecting melting of deep crustal garnet amphibolitic sources but they are otherwise hard to distinguish from normal subduction related magmas small post collisional mafic alkaline volcanic centers are common throughout the orogen but for the most part appear to be barren however similar rocks in other post subduction settings around the world are associated with important alkalic type porphyry and epithermal au cu deposits and the potential for discovery of such deposits in the tethyan orogen should not be overlooked

world class base and precious metal deposits a quantitative analysis over 62 percent of the 193 000 metric tons of gold discovered to date is located in four countries and more than 68 percent occurs in four types of mineral deposits about 55 percent of the 1 740 000 metric tons of silver found is in four countries and 45 percent is in four types of deposits fifty six percent of the 1 52 billion metric tons of discovered copper is from four countries and four types of deposits contain 88 percent of the total over 50 percent of both the 713 000 000 metric tons of zinc and 349 000 000 metric tons of lead discovered to date come from four countries and 70 percent of both metals occur in four types of deposits all discovered gold would fit in a cube with a height of 22 m silver in a 55 m cube copper in a 550 m cube zinc in a 460 m cube and lead in a 310 m cube at least 74 percent of gold silver zinc and lead is in deposits having average grades above the respective median grades and 44 percent of copper is in deposits with average grades above the median grade of all deposits lower grade deposits contain less total metal than higher grade deposits tonnage of mineralized rock is an even better predictor of contained metal with over 96 percent of each metal s total residing in deposits having greater than median size and between 47 and 79 percent of metal contained in the largest 10 percent of deposits world class deposits defined as the upper 10 percent of deposits in terms of contained metal account for over 86 percent of all gold 79 percent of silver 84 percent of copper 71 percent of zinc and 73 percent of lead these giant deposits contain at least 100 metric tons 3 2 moz gold 2 400 metric tons 77 moz silver 2 million metric tons copper 1 7 million metric tons zinc or 1 million metric tons lead mineral deposits occur rarely in the earth s crust and large ones are especially uncommon this analysis shows that only the unusually large deposits can significantly affect supply

fluid evolution in the w cu zn pb san cristobal vein peru fluid inclusion and stable isotope evidence abstract the zn pb ag cu san cristobal district is located 100 km east of lima in the western cordillera of peru it is centred around the chumpe intrusion and is composed of vein and carbonate replacement ore types the main san cristobal vein presents a paragenesis that can be divided into three stages a an early wolframite quartz pyrite stage b a quartz base metal stage and c a late quartz carbonate barite stage fluid inclusions in quartz from the tungsten stage are biphase lv at room temperature and homogenise to the liquid phase between 146 and 257 c their salinities range between 2 1 and 5 1 wt nacl equiv rare inclusions contain an additional crystal of halite and have salinities of 46 54 wt nacl equiv data of the first two stages show a decrease in homogenisation temperatures concomitant with a salinity decline fluid inclusions in quartz from the late stage homogenise at higher temperatures between 252 and 323 c with salinities ranging between 4 6 and 6 7 wt nacl equiv hydrogen and oxygen isotope data indicate a two stage evolution isotopic compositions of the fluid associated with the first two stages define a trend with constant 18 o values and decreasing d values 18 o 3 2 to 5 0 v smow and d 60 to 112 v smow which is interpreted as mixing of a dominantly magmatic component with minor meteoric water that had equilibrated with the host rocks this interpretation is supported by sulphur and lead isotopic data from previous studies by contrast the quartz carbonate barite stage bears isotopic characteristics defining a trend with a coupled decrease of 18 o and d 18 o 8 1 to 2 5 v smow and d 57 to 91 v smow and is explained by addition of meteoric water to the system and subsequent mixing with a less important magmatic component different fluid origins are confirmed by laser ablation icp ms analyses of the triphase lvh and biphase lv primary inclusions the concentrations of the major ore elements i e w cu zn and pb decrease throughout the paragenesis w and to a lesser extent cu show significant variations associated with a steep decrease in their concentration the decreasing concentrations can be explained by mineral deposition and dilution by the meteoric fluid differences in the rate of decrease indicate selective precipitation of w fluid inclusions of the quartz carbonate stages show an abrupt increase in ba and sr concentrations this is interpreted to reflect a higher volume of host rock silicate alteration probably due to the increasing size of the fluid flow cell and is explained by the input of a third fluid of unknown origin la icp ms analyses show that the fluids were already depleted in w and cu before reaching the emplacement of carbonate replacement ore type whereas zn and pb were still present in considerable amounts this is again due to selective precipitation and is consistent with the interpretation that the economically interesting metals were dominantly introduced by magmatic fluids

porphyry cu au mo epithermal ag pb zn distal hydrothermal au deposits in the dexing area jiangxi province east china a linked ore system abstract based on previous studies and detailed field investigations of the dexing porphyry copper deposit the yinshan ag pb zn deposit and the jinshan shear zone hosted gold deposit in the dele jurassic volcanic basin in the northeastern jiangxi province east china we propose that the three deposits share spatial temporal and genetic relationships and belong to the same metallogenic system dexing is a typical porphyry cu au mo deposit in which both ore forming fluid and metals are derived from the granite porphyry the yinshan deposit consists of a porphyry copper ore located in the cupola of a quartz porphyry stock in the lower part and ag pb zn ore veins in the upper part the hydrothermal fluids were mainly derived from the magma in the early stages of the mineralizing event and became mixed with meteoric waters in the late stages its ore metals are magma derived both the jinshan base metal veins and the hamashi dongjie and naikeng quartz vein type gold deposit are hosted by brittle ductile structures which are distal in relation to the porphyry intrusions and were formed by mixed magmatic fluids and meteoric water whereas the gold was mainly leached from the country rocks mesoproterozoic shuangqiaoshan group phyllite and schist the deposits show a distinct spatial arrangement from porphyry cu to epithermal ag pb zn and distal au we suggest a porphyry epithermal distal vein ore system model for this group of genetically related mineral deposits they were formed in a back arc setting in a middle jurassic active continental margin with magmas derived from the subducted slab

triggers for the formation of porphyry ore deposits in magmatic arcs porphyry ore deposits supply much of the copper molybdenum gold and silver used by humans a review of the main processes that trigger porphyry ore formation suggests that sulphide saturation of the magmas that supply the metals could be the overriding mechanism that helps control the temporal and spatial distribution of the ore deposits