evaluation of recent tectonomagmatic discrimination diagrams and their application to the origin of basic magmas in southern mexico and central america discrimination diagrams to decipher tectonic settings have been in use for nearly 40 years although old diagrams have been extensively used the recent ones based on discriminant functions of ratio variables with or without log transformation proposed during 2004 2010 for the discrimination of four tectonic settings of island arc continental rift ocean island and mid ocean ridge were newly evaluated to show their high success rates of 57 3 100 and 58 5 100 for major element and immobile element based diagrams respectively for the continental arc of the andes evaluated for its similarity to island arc these four sets of diagrams showed success rates of 62 1 83 8 these four sets of five diagrams per set were therefore used to infer tectonic setting of the mexican volcanic belt mvb los tuxtlas volcanic field ltvf and central american volcanic arc cava using this approach the mvb especially its western central and eastern parts and the ltvf of southern mexico show a dominantly continental rift setting and the cava shows an arc setting the west central part of the mvb is consistent with dual tectonics of arc and rift these results confirm the application of an unusual mantle upwelling rift model for the mexican on land volcanism whereas the conventional plate tectonic subduction model seems to be applicable for the cava from guatemala to north western costa rica

fluid chemistry structural setting and emplacement history of the rosario cu mo porphyry and cu ag au epithermal veins collahuasi district northern chile the rosario cu mo ag deposit is located in the collahuasi district of northern chile it comprises high grade cu ag au epithermal veins superimposed on the core of a porphyry cu mo orebody rosario has mining reserves of 1 094 million metric tons mt at 1 03 percent copper an additional 1 022 mt at 0 93 percent copper occurs in the district at the nearby ujina and quebrada blanca porphyry deposits the rosario reserve contains over 95 percent hypogene ore whereas supergene sulfide ores dominate at ujina and quebrada blanca mineralized veins are hosted within lower permian volcanic and sedimentary rocks lower triassic granodiorite and late eocene porphyritic quartz monzonite the rosario fault system a series of moderate southwest dipping faults has localized high grade cu ag au veins at cerro la grande similar high grade cu ag au veins are hosted in north northeast trending sinistral wrench faults normal movement in the rosario fault system is interpreted to have been synchronous with sinistral strike slip deformation at la grande hydrothermal alteration at rosario is characterized by a k feldspar core focused in the rosario porphyry that grades out to a secondary biotite albite magnetite assemblage paragenetic relationships indicate that magnetite was the earliest formed alteration product but has been replaced by biotite albite vein crosscutting relationships indicate that k feldspar formed during and after biotite albite alteration chalcopyrite and bornite were deposited in quartz veins associated with both k feldspar and biotite albite assemblages the early hydrothermal fluid was a hypersaline brine 40 45 wt nacl that coexisted with vapor between 400 degrees and 600 degrees c weakly mineralized illite chlorite intermediate argillic alteration of the early k and na silicate assemblages was caused by moderate temperature 250 degrees 350 degrees c moderate salinity brines 10 15 wt nacl molybdenite was precipitated in quartz veins that formed between the potassic and intermediate argillic alteration events these fluids were 350 degrees to 400 degrees c with salinities between 10 and 15 wt percent nacl porphyry style ore and alteration minerals were overprinted by structurally controlled quartz alunite pyrite pyrophyllite dickite and muscovite quartz phyllic alteration assemblages the quartz alunite pyrite alteration formed at 300 degrees to 400 degrees c from fluids with a salinity of 10 wt percent nacl the pyrophyllite dickite assemblage formed between 250 degrees and 320 degrees c from dilute 5 wt nacl fluids an upward flared zone of muscovite quartz pyrite altered rocks surrounds the fault controlled domain of advanced argillic alteration thick veins 0 5 2 m wide of fault hosted massive pyrite chalcopyrite and bornite precipitated brines with a salinity of 30 wt percent nacl at temperatures of 250 degrees to 300 degrees c pressure depth estimates indicate that at least 1 km of rock was eroded at rosario between formation of the k na silicate and advanced argillic assemblages this erosion was rapid occurring over a period of 1 8 m y the rosario porphyry intruded immediately after the incaic tectonic phase implying that it was emplaced as the domeyko cordillera underwent gravitational collapse expressed as normal faults in the upper crust gravitational sliding potentially accelerated exhumation and helped to promote telescoping of the high sulfidation environment onto the rosario porphyry the hydrothermal system responsible for porphyry cu mineralization at rosario was partially exhumed prior to the formation of high sulfidation ore and alteration assemblages this implies that emplacement of a second blind intrusion occurred somewhere beneath the rosario and cerro la grande high sulfidation vein systems and is supported by the fault geometry and zoning of precious metals and sulfosalts at the district scale

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

porphyry to epithermal transition in the altar cu au mo deposit argentina studied by cathodoluminescence la icp ms and fluid inclusion analysis the middle to late miocene altar porphyry cu au mo deposit located in the andean main cordillera of san juan province argentina is characterized by the superposition of multiple vein generations consisting of both porphyry type and high sulfidation epithermal style alteration and mineralization we constrain the physical and chemical evolution of the hydrothermal fluids that formed this deposit based on description and distribution of vein types scanning electron microscopy cathodoluminescence cl imaging trace elements in quartz veins and fluid inclusion microthermometry quartz cl textures and trace elements chiefly li al ti and ge differentiate among quartz generations precipitated during different mineralization and alteration events early quartz chalcopyrite pyrite veins and quartz molybdenite veins a and b veins show considerable complexity and were commonly reopened and some underwent quartz dissolution early quartz chalcopyrite pyrite veins a veins are dominated by equigranular bright cl quartz with homogeneous texture most of these veins contain higher ti concentrations than any other vein type average 100 ppm and have low to intermediate al concentrations 65 448 ppm quartz molybdenite b veins and chlorite rutile hematite c veins veins contain quartz of intermediate cl intensity that commonly shows growth zones with oscillatory cl intensity quartz from these veins has intermediate ti concentrations 20 ppm and al concentrations similar to those of a veins quartz from later quartz pyrite veins with quartz muscovite tourmaline halos d veins has significantly lower cl intensity low ti 15 ppm and elevated al concentrations up to 1 000 ppm and typically contains euhedral growth zones late veins rich in sulfides and sulfosalts show cl textures typical of epithermal deposits dark cl quartz crustiform banding and euhedral growth zones quartz from these veins typically contains less than 5 ppm ti and al li and ge concentrations are elevated relative to other vein types based on experimentally established relationships between ti concentration in quartz and temperature the decrease in ti content in successively later quartz generations indicates that the temperature of the hydrothermal fluids decreased through time during the evolution of the system vein formation at altar occurred at progressively lower pressure shallower paleodepth and lower temperature under lithostatic pressures the magma supplied low salinity aqueous fluids at depths of 6 to 6 8 km pressures of 1 6 1 8 kbar and temperatures of 670 to 730 c first quartz generation of early quartz chalcopyrite pyrite veins this parental fluid episodically depressurized and cooled at temperatures and pressures below the brine vapor solvus quartz molybdenite veins precipitated from fluids at temperatures of 510 to 540 c and pressures of 800 to 1 000 bars corresponding to depths of 3 to 3 7 km under lithostatic pressures further cooling of hydrothermal fluids to temperatures between 425 and 370 c under hydrostatic pressures of 200 to 350 bars produced pyrite quartz veins and pervasive quartz muscovite tourmaline and illite alteration that overprinted the early hydrothermal assemblages late veins rich in sulfides and sulfosalts that overlapped the deep and intermediate high temperature veins formed from fluids at temperatures of 250 to 280 c and pressures of 20 to 150 bars the epithermal siliceous ledges formed from low temperature fluids 230 c at hydrostatic pressures of 100 bars corresponding to depths of 1 km

la icp ms zircon u pb dating trace element and hf isotope geochemistry of the heyu granite batholith eastern qinling central china implications for mesozoic tectono magmatic evolution article i nfo mesozoic granitoids are widespread in the southern margin of the north china craton and of particular geo logical interests because of their indication for lithospheric evolution and close association with porphyry mo mineralization in this contribution in situ la icp ms u pb hf isotope and trace element analyses of zircon crystals have been combined to constrain the emplacement time and petrogenesis of the heyu granitic bath olith which hosts the yuchiling porphyry mo system henan province china as inferred from field investiga tions the concentrically zoned heyu batholith mainly consists of four texturally distinguishable phases and displays a pattern of monotonically decreasing u pb age from 143 0 1 6 ma for phase 1 through 138 4 1 5 ma for phase 2 through to ca 135 ma for phase 3 and to 133 6 1 3 ma for the mo mineralized yuchiling granite porphyry phase 4 the ehf t values 27 7 to 3 4 and the two stage hf model ages 1403 to 2924 ma of zircon grains together with the ages of local strata suggest that the magmas forming the heyu batholith were dominantly sourced from the crust with input of a mantle component the higher ce ce ratios of the zircon crystals in the mineralized yuchiling porphyry compared to those in the mo barren phases suggests that fluids exsolved from oxidic magmas might be more favorable for mo enrichment a regional synthesis suggests that intensive lithospheric thinning in the southern margin of the north china craton should not be earlier than 130 ma

geochemical evidence for a lithospheric source for magmas from los humeros caldera puebla mexico abstract this study reports new geochemical and sr nd pb radiogenic isotope data on hy normative quaternary basaltic to rhyolitic volcanic rocks as well as two samples of mesozoic to palaeozoic intrusive igneous rocks from los humeros caldera lhc located in the eastern part of the mexican volcanic belt mvb the isotopic ratios of mafic basaltic rocks range as follows 87 sr 86 sr 0 703350 0 703387 143 nd 144 nd 0 512867 0 512888 206 pb 204 pb 18 849 18 866 207 pb 204 pb 15 593 15 598 and 208 pb 204 pb 38 490 38 491 these values are similar to the rift related mafic rocks from the volcanic front of the central mvb for comparison the entire suite from basalt b to rhyolite r in the lhc shows the following ranges 87 sr 86 sr 0 703350 0 704678 143 nd 144 nd 0 512702 0 512888 206 pb 204 pb 18 710 18 866 207 pb 204 pb 15 593 15 631 and 208 pb 204 pb 38 444 38 594 the basaltic rocks from los humeros do not show the characteristic negative nb anomaly with respect to ba and ce as is typical of such magmas in volcanic arcs the available geochemical and isotopic evidence does not support the generation of the lhc mafic magmas by direct slab melting nor by indirect fluid transport to the mantle participation of the subducted cocos plate instead they could be generated in the upper mantle from a lithospheric source the evolved andesitic to rhyolitic magmas could have been originated from such mafic magmas through assimilation coupled with extensive fractional crystallisation two different compositions representing lower lc and upper crusts uc as well as a hypothetical crust ha were tested as plausible assimilants for the assimilation coupled with fractional crystallisation process

mineralogy and chemistry over a cycle of oil shale deposition in the brick kiln member rundle deposit queensland australia abstract chemical and semi quantitative mineralogical analyses have been made for ore type samples over a typical cycle of oil shale deposition within the brick kiln member rundle oil shale deposit the geochemistry and mineralogy were similar throughout with differences mainly following oil shale grade rather than ore type the main minerals included montmorillonite quartz feldspars calcite magnesian siderite and pyrite trace element abundances were similar to those for an average shale all samples were analyzed for a comprehensive range of major and trace elements correlation techniques selective leaching procedures x ray diffractometry and electron microprobe analyses were used to establish geochemical associations and specific mineralogical residences for elements important in processing and waste disposal s as and ni are mainly associated with pyrite and to a lesser extent with the kerogen mn occurs in the carbonate minerals calcite and magnesian siderite the chemical composition of magnesian siderite differed in some samples and warrants more study as a possible indicator of depositional or diagenetic environments

timing of the yuchiling giant porphyry mo system and implications for ore genesis the yuchiling mo deposit is a recently discovered giant porphyry system in the east qinling mo belt china its apparent causative intrusion i e the yuchiling granite porphyry is the youngest intrusion phase 4 of the heyu multiphase granite batholith which was emplaced between 143 and 135 ma new robust constraints on the formation of the yuchiling porphyry mo system are provided by combined zircon u pb biotite 40ar 39ar and molybdenite re os dating zircon grains from the mo mineralized granite porphyry yield weighted 206pb 238u age of 134 0 1 4 ma n 19 2 error mswd 0 30 magmatic biotite from the same sample yield a 40ar 39ar plateau age of 135 1 1 4 ma 2 error and an inverse isochron age of 135 6 2 0 ma n 7 2 error mswd 10 8 which are effectively coincident with the zircon u pb age within analytical error three pulses of mineralization can be deduced from the molybdenite re os ages namely 141 137 and 134 ma which agree well with the zircon u pb ages of granitic phases 1 2 and the yuchiling porphyry phase 4 respectively these well constrained temporal correlations indicate that mo mineralization was caused by pulses of granitic magmatism and that the ore forming magmatic hydrothermal activity responsible for the yuchiling porphyry mo system lasted about 8 ma the yuchiling mo deposit represents a unique style of porphyry mo system formed in a post collision setting and associated with f rich high k calc alkaline intrusions which differ from convergent margin associated porphyry mo deposits

timing and formation of porphyry cu mo mineralization in the chuquicamata district northern chile new constraints from the toki cluster the recently discovered toki cluster which includes the toki quetena genoveva miranda and opache porphyry cu mo prospects is located 15 km south southwest of the chuquicamata radomiro tomic mines in northern chile these prospects occur in an area of 5 6 km and are completely covered with neogene alluvial deposits inferred resources for the cluster are estimated at about 20 mt of fine copper with toki and quetena contributing 88 of these resources mineralization in these deposits is associated with tonalite porphyries that intruded andesites and dacites of the collahuasi group and intrusions of the fortuna los picos granodioritic complex hypogene mineralization in the toki cluster consists mainly of chalcopyrite bornite with minor molybdenite with mineralization grading outward to a chalcopyrite pyrite zone and ultimately to a pyrite halo alteration is dominantly of the potassic type with k feldspar and hydrothermal biotite sericitic alteration is relatively restricted to late quartz pyrite veins d type veins previous k ar geochronology for the cluster yielded ages within a range of 34 to 40 ma four new re os ages for toki indicate that molybdenite mineralization occurred in a single pulse at 38 ma re os ages for three different molybdenite samples from quetena are within error of the toki mineralization ages these ages are concordant with a new zircon u pb age of 38 6 0 7 ma from the tonalite porphyry in quetena two re os ages for genoveva 38 1 0 2 and 38 0 0 2 ma are also within error of the toki and quetena molybdenite ages four re os molybdenite ages for opache range between 36 4 and 37 6 ma the miranda prospect is the youngest with an age of 36 ma four new re os ages for the chuquicamata deposit range between 33 and 32 ma whereas nine new 40ar 39ar ages of biotite muscovite and k feldspar range between 32 and 31 ma analyzed molybdenites have re and os concentrations that vary between 21 3 099 ppm and 8 1 231 ppb respectively the highest re and os concentrations are found in the toki prospect three new 40ar 39ar ages for the toki cluster are younger than the re os mineralization ages the age spectra for these three samples show evidence of excess argon and have similar inverse isochron ages of 35 ma that probably reflect a late hydrothermal phyllic event the new geochronological data presented here for the toki cluster indicate that molybdenite mineralization occurred within a very short period probably within 2 ma and synchronously at 38 ma in three mineralization centers toki quetena and genoveva furthermore mineralization at the toki cluster preceded the emplacement of the chuquicamata deposit 35 31 ma and indicates that porphyry cu mo mineralization occurred episodically over a period of several million years in the chuquicamata district

atacamite in the oxide zone of copper deposits in northern chile involvement of deep formation waters atacamite a copper hydroxychloride is an important constituent of supergene oxide zones of copper deposits in northern chile whereas in similar deposits elsewhere it is rare in chile it has generally been assumed to be a primary constituent of the supergene zones there are two difficulties with this supposition the first is that atacamite requires saline water for its formation whereas supergene oxidation was caused by percolating oxygenated meteoric water mainly rainwater the second is that atacamite dissolves rapidly or undergoes phase change when exposed to fresh water supergene enrichment of copper deposits in northern chile extended over a long period 44 to 9 ma being terminated by the onset of hyperaridity during this period there was at least intermittent rainfall exposing previously formed atacamite to dissolution or phase change furthermore atacamite bearing oxide zones in several deposits are directly overlain by thick miocene alluvial gravels the stream waters that transported these gravels would have permeated the oxide zones in some deposits atacamite bearing assemblages occur both in the oxide zones and in contiguous gravels we suggest that atacamite bearing oxide assemblages are more likely to have been a replacement of preexisting oxide phases after the onset of hyperaridity at about 9 ma a hyperarid climate made possible evaporation and concentration of chloride in meteoric waters in this paper we discuss another source of saline waters to modify oxide zones dewatering of the domeyko basin expelled brines along faults some of which had earlier guided the location of porphyry deposits at the spence porphyry copper deposit saline waters which d vs 18o isotope analyses identify as basinal brines are presently rising through the deposit then flowing away along the base of the covering gravels compositions of these waters lie within the stability fields of atacamite and brochantite the two minerals that comprise the oxide zone evidence is presented for other porphyry deposits radomiro tomic and gaby sur that basinal brines may have been involved in the late formation of atacamite

high precision 40ar 39ar dating of two consecutive hydrothermal events in the chuquicamata porphyry copper system chile 40ar 39ar data have been used to resolve the relatively high temperature 350 c potassic alteration event at chuquicamata from the lower temperature 350 c quartz sericite alteration phase four k feldspars from the potassic zone yielded plateau large domain ages in the range 32 9 33 8 ma mean 33 4 0 3 ma the fact that apparent ages of co existing biotites span a similar range suggests that there was very rapid cooling through feldspar and biotite closure temperatures especially if these minerals closed at substantially different temperatures multi domain diffusion modelling of the feldspar data suggests that at this time cooling was rapid ca 60 80 my through closure temperatures of 330 440 c as these closure temperatures are substantially higher than the ones normally assumed for biotite i e about 300 c they and or the calculated cooling rates may be unreliable four sericites from the quartz sericite zone yielded variably discordant age spectra the least discordant of these has a plateau at 31 1 0 3 ma and this is interpreted as the time of this alteration event some k feldspars in the quartz sericite zone were completely overprinted at this later time and most of the other ones studied show partial overprinting overprinting appears to decrease as distance from the central quartz sericite zone increases in the more remote areas effects of the later event appear constrained to narrow fault controlled alteration zones the data are consistent with a conceptual model proposed by zentilli et al zentilli m leiva g rojas j graves m c 1994a the chuquicamata system revisited extended abstract society of economic geologists symposium copper deposits of the andes new developments concepcion chile october 17 18 1994 proceedings 2 1647 1651 wherein potassic alteration by late magmatic fluids occurred at depth prior to rapid exhumation of the system quartz sericite alteration perhaps caused by a new pulse of porphyry intrusion at depth occurred some 2 3 my later principally in the core of the deposit although alteration did propagate outwards through the action of hydrothermal fluids passing through a brittle relatively shallow fracture system

duration of magmatic hydrothermal and supergene activity at cerro rico de potosi bolivia new high precision 40ar 39ar dating of sanidine and biotite from two rhyolitic domes and an ignimbrite combined with existing fission track data and a hydrothermal sericite age suggests that the world class ag deposit at cerro rico was emplaced during a protracted period of magma related hydrothermal activity beginning at 13 77 0 03 ma and continuing for at least 0 2 m y this may have been sustained by a large single injection or repeated injections of fractionated ag enriched magma into a high level magma chamber k ar dating of alunite indicates that supergene oxidation had begun by about 13 5 ma soon after dome emplacement and progressed semicontinuously for at least 7 5 m y this oxidation while not leading to significant enrichment has significantly enhanced the economic viability of the disseminated part of the orebody

physiographic and tectonic settings of high sulfidation epithermal gold silver deposits of the andes and their controls on mineralizing processes abstract gold and silver ores in the vast majority of andean high sulfidation epithermal au ag deposits occur at high present day elevations and typically 200 500 m below low relief landforms situated at 3500 to 5200 m a s l most deposits are middle miocene and younger and include el indio tambo pascua lama veladero el indio belt chile argentina cerro de pasco central peru pierina lagunas norte yanacocha northern peru quimsacocha ecuador and the california vetas mining district santander colombia jointly accounting for 130 moz au resources slightly older examples are only preserved in the atacama desert and include the middle eocene el guanaco and el hueso and the late oligocene early miocene la coipa deposits the absence of paleocene and older high sulfidation epithermal deposits can be explained by limited preservation potential imposed by transpressional tectonics within overall contractile episodes and surface uplift these conditions prevailed predominantly in segments of shallow angle subduction of the nazca or caribbean plate below the south american continent a tectonic setting also common for porphyry style cu au mo deposits stratovolcanoes are uncommon ore hosts and volcanic rocks coincident with mineralization are in most cases volumetrically restricted or absent recording the terminal stages of local arc magmatism however dacitic domes are important at e g yanacocha and la coipa at lagunas norte a small stratovolcano largely pre dating but temporally overlapping with mineralization occurs immediately east of the deposit and volcanic sector collapse may have occurred during hydrothermal activity mineralization is typically located near the backscarp of pediments or the heads of valleys incising now high elevation low relief surfaces in the california vetas mining district and el indio belt hydrothermal alunite ages become generally younger upstream along the incising valleys indicating that hydrothermal activity and by inference ore deposition were facilitated by erosion the lowering of the water table and reduction of hydrostatic and lithostatic pressure at these sites of high local relief are believed to have enhanced both boiling and mixing of magmatic with meteoric fluids ultimately enhancing ore deposition the host rock composition permeability and location of the water table control the distribution of alteration zones and ore intermediate volcanic rocks are the most common ore hosts but they typically pre date mineralization by several ma however high sulfidation epithermal mineralization can be hosted in any conceivable rock type including high grade metamorphic rocks california vetas mining district significantly older plutonic rocks pascua lama or quartzites lagunas norte large vuggy quartz alteration zones and commonly oxidized low grade large tonnage mineralization are best developed in relatively permeable volcaniclastic rocks or hydrothermal breccia bodies whereas coherent volcanic plutonic or metamorphic rocks may host fault and breccia controlled ores the near surface steam heated zone can attain a thickness of several hundred meters in dry climates e g veladero pascua lama tambo but is typically poorly developed and less than 20 m thick in humid climatic zones the physiographic and tectonic settings of high sulfidation epithermal deposits are distinct from low sulfidation epithermal districts such as those of patagonia el penon chile or fruta del norte ecuador the latter range to significantly older ages jurassic to early eocene occur at mainly lower elevations and were emplaced in extensional settings a temporal coincidence between uplift erosion and mineralizing processes as well as a spatial and temporal association with porphyry style mineralization is not evident for these low sulfidation districts

relationship between copper tonnage of chilean base metal porphyry deposits and os isotope ratios re os isotopes in pyrite and chalcopyrite from early high temperature hypogene alteration assemblages in chilean porphyry copper deposits identify the source of os and by inference cu in these ore systems typical concentrations for os in both pyrite and chalcopyrite are between 7 and 30 ppt 10 12 g g and for re between 0 200 and 10 ppb 10 9 g g re os isochrons yield ages and initial 187 os 188 os ratios for the sulfides the isotopic data reflect the relative contributions of copper from the mantle and crust in chilean porphyry copper deposits seven ore deposits that reside in different tectonic terranes and represent distinct epochs of mineralization in chile were studied the initial osmium ratios of the first stage of mineralization at each of the deposits range from 0 15 to 5 these values are more radiogenic than the present chondritic mantle 0 13 and indicate significant crustal contributions of os to the magmatic and or hydrothermal systems there is a strong correspondence between the total copper content and initial os isotopic ratios in base metal porphyry deposits the larger deposits have lower initial os ratios than the smaller less significant deposits this relationship implies that larger deposits acquire a greater proportion of os from the mantle the initial os ratio of samples in the central segment of porphyry copper deposits of northern chile also decreases with decreasing age of the deposit a plausible interpretation of the re os data is that the later and larger deposits use regional tectonic and structural features that allow sampling of deeper more primitive magmatic sources

structural setting of fimiston and oroya style pyrite telluride gold lodes paringa south mine golden mile kalgoorlie 1 shear zone systems porphyry dykes and deposit scale alteration zones the golden mile in the 2 7 ga eastern goldfields province of the yilgarn craton western australia has produced 385 million tonnes of ore at a head grade of 5 23 g t gold 1893 2016 gold pyrite ore bodies fimiston lodes trace kilometre scale shear zone systems centred on the d2 golden mile fault one of three northwest striking sinistral strike slip faults segmenting upright d1 folds the fimiston shear zones formed as d2a riedel systems in greenschist facies actinolite albite tholeiitic rocks the 700 m thick golden mile dolerite gmd sill and the paringa basalt pb during left lateral displacement of up to 12 km on the d2 master faults pre mineralisation granodiorite dykes were emplaced into the d2 shear zones at 2674 6 ma and syn mineralisation diorite porphyries at 2663 11 ma the widespread infiltration of hydrothermal fluid generated chlorite calcite and muscovite ankerite alteration in the golden mile and paragonite ankerite chloritoid alteration southeast of the deposit fluid infiltration reactivated the d2 shear zones causing post porphyry displacement of up to 30 m at principal fimiston lodes moving the southwest block down and southeast along lines pitching 20 se d3 reverse faulting at the southwest dipping gmd pb contact of the d1 kalgoorlie anticline formed the 1 3 km long oroya shoot during late gold telluride mineralisation syn mineralisation d3a reverse faulting alternated with periods of sinistral strike slip d2c until ene wsw shortening prevailed and was accommodated by barren d3b thrusts north striking d4 strike slip faults of up to 2 km dextral displacement crosscut the fimiston lodes and the barren thrusts and control gold pyrite quartz vein ore at mt charlotte 2651 9 ma

age of supergene oxidation and enrichment in the chilean porphyry copper province twenty five samples of supergene alunite collected from deeply developed supergene profiles in porphyry copper deposits and prospects between latitudes 20 degrees and 27 degrees s in northern chile yield k ar ages ranging from about 34 to 14 ma therefore supergene oxidation and enrichment processes were active from the early oligocene to the middle miocene a minimum of 20 m y supergene activity at individual deposits lasted for at least 0 4 to 6 2 m y the early oligocene supergene activity affected deposits in the paleocene porphyry copper belt whereas early and middle miocene supergene processes are documented in the early cretaceous paleocene and late eocene to early oligocene porphyry copper belts middle miocene oxidation also affected the oldest epithermal gold silver deposits in the maricunga belt farther east supergene activity commenced no less than 11 m y after generation of each porphyry copper deposit because of the time required to unroof the copper bearing parts of the system supergene activity throughout northern chile ceased at approximately 14 ma the geologic features of deposits and prospects and their morphotectonic positions present latitudes and present elevations display no obvious correlations with the supergene chronology exploration for major cumulative enrichment blankets should not be carried out either beneath thick sequences of piedmont gravels or ignimbrites of oligocene through middle miocene age unless their accumulation is demonstrably late in the documented history of supergene activity or in porphyry copper provinces such as those of central chile and northwestern argentina which formed after approximately 14 ma the uplift responsible for efficient cumulative copper enrichment is difficult to correlate convincingly with the brief pulses of compressive tectonism postulated for northern chile and contiguous areas unless their effects were much more prolonged intensifying aridity is confirmed as the likely reason for the cessation of supergene activity in northern chile and tectonic uplift was its most probable cause however more fundamental global controls producing a period of chemical weathering followed by worldwide dessication also may have played a role

oxide mineralization at the radomiro tomic porphyry copper deposit northern chile the main copper oxide minerals in the radomiro tomic deposit are atacamite copper clays chrysocolla and copper wad their relative abundance provides the basis for dividing the oxide zone into two major geologic units the upper oxide unit and the lower oxide unit furthermore the study of mineral abundances in the oxide zones allowed the definition of an oxide mineral zonation that consists of five mineral assemblages based on the relative proportion of the three main copper oxide components atacamite copper clays and chrysocolla these classifications allow both an understanding of the distribution of copper minerals throughout the zone and an interpretation of the supergene processes that formed it the upper oxide unit is mineralogically heterogeneous the copper content is furnished on average by 40 vol percent atacamite 31 vol percent copper clays with minor chysocolla and copper wad the lower oxide unit is more homogeneous atacamite accounts for 70 vol percent of the copper ore minerals with minor amounts of copper clays and chrysocolla copper and chlorine concentrations and porosity are greater in the upper oxide unit whereas hematite chalcocite and molybdenite concentrations and specific gravity are greater in the lower oxide unit the vertical distribution of the cl cu ratio shows a chlorine deficient zone located between elevations of 2 780 and 2 870 m between these elevations the proportion of atacamite is lower and the proportion of copper clays chrysocolla and copper wad is higher than in other portions of either the upper oxide or lower oxide units the oxide zone at radomiro tomic was originated through the in situ oxidation of a preexisting secondary sulfide enrichment blanket oxidation produced an extensive zone of atacamite accompanied by weakly developed argillic alteration the upper part of the deposit was further enriched by lateral migration of copper rich solutions to the north and east where copper precipitated as chrysocolla copper wad and copper in clays in these areas strong argillic alteration characterized by the presence of montmorillonite was developed this second alteration phase impacted only the uppermost portion of the oxide zone and the base of overlying gravels

using iodine isotopes to constrain supergene fluid sources in arid regions insights from the chuquicamata oxide blanket although iodine is rare in crustal settings previous studies have documented its occurrence in the supergene zones of base and precious metal ore deposits in arid environments in this report we present a novel application of the iodine 129 129i isotope tracer to iodine rich samples from the world s largest supergene cu profile at the chuquicamata deposit in northern chile where anomalous concentrations of this element have been reported all supergene marshite cui samples from chuquicamata and iodine rich soil above the mansa mina deposit have 129i i isotope ratios 190 560 10 15 that are significantly lower than those of surface waters i e 1 500 10 15 indicating that iodine was most likely derived from a reservoir of marine origin rather than a meteoric and or atmospheric source geochemical modeling shows that the long term dilution of iodinerich deep formation waters by meteoric water during the main stage of supergene alteration 40 10 ma resulted in fluid 129i i ratios that are within the range of mineral soil 129i i ratios observed at chuquicamata strongly suggesting that iodine was remobilized from the lower jurassic to mid cretaceous marine basement results from this study show that iodine isotopes can be successfully applied to trace the origin and nature of supergene fluids in iodine rich oxide blankets leach caps and soils above buried cu deposits and also to constrain the timescales of fluid circulation during supergene enrichment

a special issue devoted to porphyry copper deposits of northern chile chile is known worldwide as the site of one of the largest copper concentrations on earth a total resource including production of about 400 million tons mt of fine copper has been identified in 50 porphyry copper deposits and numerous prospects fig 1 considering 10 mt of contained fine copper as a minimum tonnage to classify a porphyry copper deposit as a giant ore deposit the chilean cordillera contains nine of the 16 giant porphyries along the circum pacific belt among them are the three largest of all el teniente rio blanco los bronces and chuquicamata fig 1 all containing resources plus production of more than 50 mt of fine copper currently chile annually produces about 4 6 mt of fine copper that represents about 37 percent of the world production this enormous geologic potential has triggered numerous international mining companies to concentrate their exploration efforts in the central andes with emphasis in chile during the past 25 years exploration expenditures have surpassed a figure on the order of us 2 billion as a result a total of 76 copper and gold discoveries have been made 24 of which are already in production cabello 2000 among them the most relevant discoveries are the porphyries at la escondida escondida norte zaldivar rosario and ujina in the collahuasi mining district quebrada blanca lomas bayas and in the last 5 years spence and gaby sur the presence of such a significant number and large size of copper porphyries intrigued several generations of researchers during the twentieth century the ongoing exploration efforts have enhanced the interest in understanding the andean geological evolution and metallogenesis the geological processes that are common factors in controlling the emplacement of these orebodies have been the subject of research by numerous individuals in chile and elsewhere the support of mining companies has been

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

dating the giant zhuxi w cu deposit taqian fuchun ore belt in south china using molybdenite re os and muscovite ar ar system abstract the recently discovered zhuxi w cu ore deposit is located within the taqian fuchun ore belt in the southeastern edge of the yangtze block south china its inferred tungsten resources based on new exploration data are more than 280 mt by 2016 at least three paragenetic stages of skarn formation and ore deposition have been recognized prograde skarn stage retrograde stage and hydrothermal sulfide stage secondly greisenization marmorization and hornfels formation are also observed scheelite and chalcopyrite are the dominant metal minerals in the zhuxi deposit and their formation was associated with the emplacement of granite stocks and porphyry dykes intruded into the surrounding carboniferous carbonate sediments huanglong and chuanshan formations and the neoproterozoic slate and phyllites the scheelite was mostly precipitated during the retrograde stage whereas the chalcopyrite was widely precipitated during the hydrothermal sulfide stage a muscovite 40ar 39ar plateau age of about 150 ma is interpreted as the time of tungsten mineralization and molybdenite re os model ages ranging from 145 9 2 0 ma to 148 7 2 2 ma for the subsequent hydrothermal sulfide stage of activity as the time of the copper mineralization our new molybdenite re os and muscovite 40ar 39ar dating results along with previous zircon u pb age data indicate that the hydrothermal activity from the retrograde stage to the last hydrothermal sulfide stage lasted up to 5 myr from 150 6 1 5 to 145 9 1 ma and is approximately coeval or slightly later than the emplacement of the associated granite porphyry and biotite granite the new ages reported here confirm that the zhuxi tungsten deposit represents one of the mesozoic magmatic hydrothermal mineralization events that took place in south china in a setting of lithospheric extension during the late jurassic 160 150 ma it is suggested that mantle material played a role in producing the zhuxi w cu mineralization and associated magmatism

origin and ore forming consequences of the advanced argillic alteration process in hypogene environments by magmatic gas contamination of meteoric fluids metasomatic effects have been thermodynamically computed for magma derived sulfur gases which may contaminate convecting meteoric fluids in the monzonite k silicate protore and are compared with natural assemblages in the butte district of montana the advanced argillic assemblage with covellite is produced in hypogene environments at 300 degrees c by sulfur metasomatism of protore only for a limited range of net sulfur valences essentially 1 to 2 placing limiting constraints on the possible ratios of so 2 and h 2 s gases a second important factor is the relative reaction rates of protore and contaminating sulfur gases contamination by sulfur gases is a third factor of importance a final factor is that a minimum negative net volume of reaction causes by wall rock dissolution and fracture enlargement the high permeability necessary for circulation of enormous quantities of hydrothermal fluids and vein growth characteristic of this extreme alteration facies modified journal abstract

a re os study of sulfide minerals from the bagdad porphyry cu mo deposit northern arizona usa rhenium and osmium isotopes in sulfide minerals from the bagdad porphyry cu mo deposit have been used to determine timing of mineralization and the source of osmium and by inference ore metals molybdenite chalcopyrite and pyrite were analyzed mainly from the quartz monzonite and porphyritic quartz monzonite units which are characterized by moderate to strong potassic alteration secondary biotite and k feldspar rhenium concentrations in molybdenite are between 330 and 642 ppm four re os analyses of two molybdenite samples from the quartz monzonite and porphyritic quartz monzonite yield a weighted average age of 71 8 0 2 ma 2 analyses of a third sample from a molybdenite vein in precambrian rocks outside of the main ore zone yield a weighted average age of 75 9 0 2 ma 2 and provide evidence of two separate mineralization episodes chalcopyrite samples contain 6 to 12 ppt os and 1 7 to 4 1 ppb re 187os 188os initial ratios are between 0 1 and 0 8 pyrite samples have osmium and rhenium concentrations varying in the range 8 17 ppt and 3 9 6 8 ppb respectively analyses from these pyrite samples yield an eight point isochron with an age of 77 15 ma 2 and an initial 187os 188os ratio of 2 1 0 8 mswd 0 90 the results presented here add to the growing body of work indicating that porphyry type mineralization is produced by long term multiple episodes of magmatism and associated mineralization the data also support the hypothesis that a significant part of the metals and magmas may have a crustal source as has been suggested for other copper deposits and districts in arizona

linking mineral deposit models to quantitative risk analysis and decision making in exploration this paper describes a methodology of translating mineral deposit models into flexible probabilistic structures based on 1 extraction of ore components fluids metals and ligands from crustal or mantle sources or both 2 fluid or melt assisted transport of ore components from source to trap zones 3 formation of trap zones i e effective melt or fluid channels that can focus melt or fluid migration and accommodate large amounts of metal and 4 operation of the physicochemical processes that promote and sustain the deposition of metal from fluids or melts passing through a particular trap site our approach integrates these critical mineralization processes and conditions with concepts of probability theory decision analysis and financial modeling the principal objective is to make mineral deposit models amenable to financial risk and value analysis and suitable for communication of value creating geologic concepts to financial stakeholders in economic terms a case study based on an actual porphyry copper project illustrates how the resulting probabilistic mineral systems model can generate a measure of the probability of ore occurrence as an input for exploration decision trees and simulations to calculate the expected value of an exploration project and the probability distribution of all possible surrounding net present values npvs within a minimum and maximum range formulation of the probabilistic model closely follows and combines principles of the well established petroleum and mineral systems approaches and makes use of excel based model templates with decision tree and simulation add in software packages

constraints on the origin of alkaline and calc alkaline magmas from the tuxtla volcanic field veracruz mexico lavas erupted in the tuxtla volcanic field tvf over the last 7 ma include primitive basanites and alkali basalts mildly alkaline hy normative mugearites and benmoreites and calc alkaline basalts and basaltic andesites the primitive lavas are silica undersaturated with high concentrations of both incompatible and compatible trace elements variable la yb with constant yb at 6 to 8 times chondritic and low sr and o and variable pb and nd isotopic ratios the primitive magmas originated by increasing degrees of melting with pressure decreasing from greater than 30 kbar to 20 kbar in the garnet stability field another group of alkali basalts and hawaiites has lower ni and cr concentrations and higher fe mg ratios and was derived from the primitive group by crystal fractionation at pressures of several kbar incompatible trace elements in these silica undersaturated lavas show depletion in high field strength elements hfse relative to large ion lithophile elements similar to subduction related basalts ba nb ratios are nearly constant and thus the hfse depletion cannot be the result of a residual hfse bearing phase in the source but could be the result of generation from a source contaminated by fluids or melts from the subducted lithosphere the silica saturated mugearites and benmoreites and the calc alkaline basalts and basaltic andesites were erupted only between 3 3 and 1 0 ma these have incompatible element concentrations generally lower than in the silica undersaturated lavas and thus could not have been derived by crystal fractionation from the silica undersaturated alkaline magmas magmas parental to the silica saturated magmas originated by higher degrees of melting at lower pressures than the primitive magmas melting may have been promoted by an influx of fluid from the subducted lithosphere trace element and sr nd pb and o isotopic data suggest that three components are involved in the generation of tvf magmas the mantle a fluid from the subducted lithosphere and continental crust tvf alkaline lavas are similar to those erupted in the back arc region of the mvb and japan and show characteristics similar to alkaline magmas erupted in the southern andean volcanic arc these low degree melts reach the surface along with calc alkaline lavas in the tvf due to an extensional stress field that allows their passage to the surface

correction to isotopic and trace element constraints on the origin and evolution of alkaline and calc alkaline magmas in the northwestern mexican volcanic belt by surendra p verma and stephen a nelson

controls on supergene enrichment of porphyry copper deposits in the central andes a review and discussion the central andes host some of the world s largest porphyry copper deposits the economic viability of these deposits is dependent on the size and quality of their supergene enrichment blanket published models that have strongly influenced exploration policy suggest that supergene enrichment ceased at 14 ma due to an increase in aridity here we discuss these models using published geochronological geomorphological and geological data geochronological data indicate that supergene oxidation and enrichment has been active between 17 and 27 s across the forearc of northern chile and southern peru from 44 to 6 ma and on the bolivian altiplano and eastern cordillera of argentina from 11 ma to present there is evidence for cessation at 20 14 and 6 ma however a major problem is that as more geochronological data become available the age ranges and periods of enrichment increase this suggests that the full spectrum of enrichment ages may not have been sampled the relationship between supergene enrichment and the age of regional pediplain surface development is not well constrained only in two areas have surfaces related to enrichment been directly dated southern peru and south of 26 s in chile and suggest formation post 14 ma sedimentological data indicate that a fluctuating arid semi arid climate prevailed across the atacama desert until between 4 and 3 ma climatic conditions that are thought to be favourable for supergene enrichment the balance between uplift erosion burial and sufficient water supply to promote enrichment is complex this suggests that a simple model for controlling supergene enrichment is unlikely to be widely applicable in northern chile general models that involve climatic desiccation at 14 ma related to rainshadow development and or the presence of an ancestral cold upwelling humboldt current are not supported by the available geological evidence the integration of disparate sedimentological geomorphological and supergene age data will be required to fully understand the controls on and distribution of supergene oxidation and enrichment in the central andes

a combined fluid inclusion and isotopic geochemistry study of the zhilingtou mo deposit south china implications for ore genesis and metallogenic setting abstract the zhilingtou mo deposit is recently discovered and occurs in the qin hang metallogenic belt south china vein stockworks are hosted in the granite porphyry and the surrounding paleoproterozoic badu group basement three stages of mineralization and wallrock alteration were developed the early stage quartz k feldspar veins with potassic alteration the ore stage quartz molybdenite veins with strong phyllic alteration overprinting early potassic alteration and the late stage quartz pyrite calcite veins with propylitization two phase liquid rich aqueous type i inclusions in the early stage veins show homogenization temperatures th of 366 442 c with salinities of 5 3 14 1 wt nacl equivalent two phase gas rich aqueous type ii and coexisting halite bearing type iii inclusions in the ore stage veins display th of 335 433 c and 329 396 c and salinities of 0 5 6 2 and 38 6 44 8 wt nacl equivalent respectively type i inclusions in the late stage veins yield th of 187 282 c with salinities 3 5 7 7 wt nacl equivalent fluid boiling occurred during the ore stage and probably promoted a rapid precipitation of molybdenite laser raman analysis implies that ore fluids are co 2 poor hydrogen and oxygen isotopes indicate that mineralizing fluids are primarily magmatic in origin with apparently involvement of external meteoric water in the late stage lead isotopes suggest that the metals are sourced from the ore bearing granite porphyry trace elements of the ore bearing granite porphyry display obvious nb and ta depletion indicating arc magma geochemical affinities vein stockworks intensive phyllic alteration co 2 poor ore fluids and continental arc setting suggest that the zhilingtou mo deposit is likely to be an endako type porphyry mo deposit it is distinctly different from porphyry mo deposits in the east qinling dabie metallogenic belt in china which were formed in a post collisional setting and characterized by intensive potassic alteration and co 2 rich ore fluids