a special issue devoted to porphyry and epithermal deposits of the southwest pacific an introduction the southwest pacific is host to a number of mineralization styles including numerous world class porphyry cu au and epithermal au ag deposits cooke et al 2005 garwin et al 2005 the majority of the giant porphyry and epithermal au and cu deposits were formed within a series of middle to late cenozoic 25 1 ma arcs garwin et al 2005 maryono et al 2018 these arcs form a complex boundary between the eurasian pacific and indian australian tectonic plates stretching from japan in the northeast and myanmar in the northwest through the philippines indonesia new guinea and the volcanic island chains of the solomon islands new hebrides vanuatu and fiji fig 1

trace element composition of quartz from porphyry systems a tracer of the mineralizing fluid evolution trace element composition of hydrothermal quartz reflects the p t x conditions of the mineralizing fluids and can be a potential tracer of the fluid evolution to explore this potential quartz trace element data from 21 porphyry cu au mo and epithermal polymetallic deposits were compiled in addition quartz trace element data from six granite related systems granite pegmatite greisen sn w mo veins and from a subset of calc alkaline arc related volcanic rocks were also compiled for comparison for porphyry cu au mo deposits quartz compositions are from publications in which the sequence of quartz bearing veins and their potential reopening were documented as well as their precipitation temperatures and pressures the compiled dataset shows that trace element composition of quartz continuously evolved between the different porphyry veins and quartz generations a b c d and e the observed evolution reflects the cooling and or compositional variations of the hydrothermal fluids the quartz al ti sb ti ge ti and sb ge ti ratios allow for the discrimination of quartz from different vein generations of porphyry cu au mo deposits this study shows that quartz composition preferentially combined with cathodoluminescence images is an efficient proxy for tracing the evolution of the hydrothermal fluids in porphyry systems and can be used as a vectoring tool to target the centers of porphyry systems

sandstone petrology of the archean fig tree group barberton greenstone belt south africa tectonic implications it has become clear that simple vertical tectonics do not adequately describe the tectonic evolution of many greenstone belts and that horizontal shortening played an important role in the development of these unique terranes from earth9s early history the fig tree group of the barberton greenstone belt in south africa has recently been interpreted mainly by structural and stratigraphic analyses as having been deposited in a foredeep associated with thrusting sandstone modal mineralogy has been shown to primarily reflect tectonic setting and prove nance terrane fig tree sandstones have framework mineralogies that fall mainly in the recycled orogen field and show an evolution consistent with interpretations of the greenstone belt that utilize petrographic and other evidence

contemporaneous formation of adjacent porphyry and epithermal cu au deposits over 300 ka in northern luzon philippines there is commonly a close spatial relation between porphyry cu au and high sulfidation epithermal cu au deposits throughout the world although a genetic association has not been proven nowhere is this spatial association better seen than in northern luzon philippines where the lepanto epithermal cu au deposit overlies the far southeast fse porphyry cu au deposit both world class orebodies fresh rock and hydrothermal mineral separates yield k ar ages indicating that premineralization and postmineralization volcanism occurred at 2 2 1 8 ma and 1 2 0 9 ma respectively and that the hydrothermal system was active from 1 5 to 1 2 ma k ar ages of alunite from lepanto have the same range as those of hydrothermal biotite and illite from the fse deposit indicating that both epithermal and porphyry mineralization formed from an evolving magmatic hydrothermal system that was active for about 300 ka this temporal relation strengthens the argument for a genetic link between these two styles of ore deposit and has implications for exploration where one style of mineralization is found there is potential for the other nearby

geochemistry of metasedimentary rocks in the late archean hemlo heron bay greenstone belt superior province ontario implications for provenance and tectonic setting the late archean hemlo heron bay greenstone belt of the superior province near the hemlo gold deposit ontario consists mainly of fine grained clastic metasedimentary rocks with subordinate amounts of metavolcanic rocks cordierite anthophyllite rocks are also locally present but restricted to a single metasedimentary sequence and most likely represent metamorphosed mg and fe rich sedimentary rocks derived from predominantly mafic ultramafic sources the clastic metasedimentary rocks are geochemically highly immature some of their geochemical characteristics such as low al2o3 na2o ratio low cia k2o na2o 1 0 uniform th u ratio 3 6 and strong correlations of transition metals and mgo with fe2o3 are similar to those of typical archean sedimentary rocks however their ree compositions high contents of lree and steep chondrite normalized patterns are different from those of most archean sedimentary rocks and similar to those of more mature proterozoic sedimentary rocks the clastic metasedimentary rocks from the hemlo heron bay greenstone belt were derived mainly from felsic or intermediate volcanic sources admixed with variable amounts of mafic ultramafic volcanic components and possibly some continental weathering products and deposited rapidly as turbidites the geochemical uniformity of all clastic metasedimentary rocks indicates that the hemlo heron bay greenstone belt represents a single tectonic environment possibly equivalent to a modern island arc system rather than a juxtaposition of suspect terranes

ultra deep oxidation and exotic copper formation at the late pliocene boyongan and bayugo porphyry copper gold deposits surigao philippines geology mineralogy paleoaltimetry and their implications for geologic physiographic and tectonic controls the boyongan and bayugo porphyry copper gold deposits are part of an emerging belt of intrusion centered gold rich deposits in the surigao district of northeast mindanao philippines exhumation and weathering of these late pliocene age deposits has led to the development of the world s deepest known porphyry oxidation profile at boyongan 600 m and yet only a modest 30 70 m oxidation profile at adjacent bayugo debris flows volcanic rocks and fluviolacustrine sediments accumulating in the actively extending mainit graben subsequently covered the deposits and preserved the supergene profiles at boyongan and bayugo there is a vertical transition from shallower supergene copper oxide minerals malachite azurite cuprite to deeper sulfide stable assemblages chalcocite hypogene sulfides this transition provides a time integrated proxy for the position of the water table at the base of the saturated zone during supergene oxidation contours of the elevation of the paleopotentiometric surface based on this mineralogical transition show that the thickest portions of the unsaturated zone coincided with a silt sand matrix diatreme breccia complex at boyongan within the breccia complex the thickness of the unsaturated zone approached 600 m whereas outside the breccia complex e g at bayugo the thickness averaged 50 m contours of the paleopotentiometric surface suggest that during weathering groundwater flowed into the breccia complex from the north south and east and exited along a high permeability zone to the west the high relief 550 m on the elevation of the paleopotentiometric surface is consistent with an environment of high topographic relief and the outflow zone to the west of the breccia complex probably reflects proximity to a steep scarp intersecting the western breccia complex margin stable isotope paleoaltimetry has enabled estimation of the elevation of the land surface which further constrains the physiographic setting during supergene oxidation isotopic measurements of oxygen in supergene kaolinite from boyongan suggest that local paleometeoric water involved in weathering had a 18o composition of approximately 5 7 per mil at the latitude of the southern philippines this value corresponds to pleistocene rain water condensing at elevations between 750 and 1 050 m above contemporary sea level providing a maximum estimate for the surface elevation during weathering of the porphyry systems physiographic reconstructions suggest that the deep oxidation profile at boyongan formed in an environment of high topographic relief immediately east of a prominent 550 m escarpment the high permeability contrast between the breccia complex and the surrounding wall rocks coupled with the proximity of the breccia complex to the escarpment led to a depressed groundwater table and a vertically extensive unsaturated zone in the immediate vicinity of boyongan this thick vadose zone and the low hypogene pyrite copper sulfide ratios 0 6 at boyongan promoted in situ oxidation of copper sulfides with only modest 200 m supergene remobilization of copper in contrast higher hypogene pyrite chalcopyrite ratios 2 3 at bayugo led to greater acid production during weathering and more complete leaching of copper above the base of oxidation this process promoted significant 600 m lateral dispersion of copper down the paleohydraulic gradient into the diatreme breccia comple ultimately leading to the formation of an exotic copper deposit

the bingham canyon porphyry cu mo au deposit i sequence of intrusions vein formation and sulfide deposition the bingham canyon porphyry copper gold molybdenum deposit is one of the largest and highest grade porphyry orebodies in the world this study focused on the northwest side of the deposit where quartz mon zonite porphyry qmp the first and largest porphyry intrusion hosts the bulk of the high grade copper gold ore 1 0 cu 1 0 ppm au the north northeast trending high grade zone had pre mining dimensions of 1 500 m strike 300 m vertical and 500 m width and contained more than 500 million tonnes mt of ore associated with potassic alteration and abundant quartz veins the lack of superimposed sericitic alteration yielded ideal exposures in which to study the early high temperature stages of ore formation a style of mineralization that in many porphyry deposits represents the major period of copper introduction we mapped multiple porphyry dikes in the sequence 1 qmp 2 latite porphyry lp 3 biotite porphyry bp 4 quartz latite porphyry breccia qlpbx and 5 quartz latite porphyry qlp porphyry dikes faults and quartz veins are steeply dipping and have two dominant orientations north northeast and northwest striking dikes have a north northeast strike but they thicken and develop northwest trending apophyses and host high grade copper gold zones at intersections with northwest faults indicating that magmatic hydrothermal fluids were focused by these structural intersections each porphyry intrusion was accompanied by a similar sequence of veins potassic alteration and sulfides biotite veinlets were followed by fractures with early dark micaceous edm halos of sericite k feldspar biotite andalusite and local corundum containing disseminated bornite chalcopyrite gold edm halos are cut by multiple generations of a quartz veins representing the main cu au ore forming event postdating all intrusions are quartz molybdenite veins followed by quartz sericite pyrite veins cathodoluminescence cl petrography identified distinct a quartz veinlets consisting of dark luminescing quartz filling fractures and dissolution vugs in earlier a quartz veins and adjacent porphyry wall rock these veinlets contain abundant bornite and chalcopyrite and minor k feldspar and are closely linked in time to the introduction of the bulk of the copper and gold although a similar sequence of veins was repeated on emplacement of all porphyry intrusions the vein density and intensity of potassic alteration declined with time the youngest porphyry qlp is mostly weakly mineralized and locally unaltered these observations indicate that magmatic hydrothermal fluids underwent a similar physiochemical evolution during and immediately following emplacement of each of several porphyry dikes the relationship between edm veins and a quartz veins requires that the flux of magmatic fluid from the magma chamber occurred in an episodic manner as opposed to a continuous discharge vein truncation relationships coupled with abrupt changes in copper gold grades sulfide ratios and potassic alteration intensity at porphyry intrusive contacts indicate that the mass of introduced copper and gold decreased significantly during successive porphyry intrusive hydrothermal cycles presumably due to depletion of metals and volatiles in the underlying magma chamber

geology and geochronology of the tiegelongnan porphyry epithermal cu au deposit tibet china formation exhumation and preservation history abstract the tiegelongnan rongna deposit is a giant porphyry epithermal cu au deposit within the duolong porphyry district in the south qiangtang terrane central western tibet china the deposit is centered on multiphase granodiorite porphyry gp intrusions intruded in jurassic sandstone phase 1 and 2 gp are associated with biotite and sericite alteration whereas gp3 and 4 occur in middle and shallow parts of the deposit affected by sericite and advanced argillic alteration alunite kaolinite dickite pyrophyllite sericite alteration is pervasive in the deep part of the deposit replacing biotite alteration and hosting porphyry stage chalcopyrite bornite pyrite molybdenite mineralization advanced argillic alterationis associated with epithermal stage high sulfidation tennantite enargite bornite and digenite mineralization overprints the sericite and biotite alteration from the shallow part of the deposit the top of the tiegelongnan hydrothermal system was weathered with a layer of supergene oxidation and enrichment zone exhumated and covered by andesite and gravel muscovite sampled from deep sericite alteration yields a 40ar 39ar age of 120 9 0 8 ma which is consistent with previously reported hydrothermal biotite 40ar 39ar age of 121 1 0 6 ma molybdenite re os ages of 121 2 0 6 and 119 0 1 4 ma and gp 1 and 2 zircon u pb ages of 121 5 1 5 120 2 1 0 ma la icp ms results and 118 7 0 9 ma sims result phase 3 gp 3 yields a ca id tims zircon u pb age of 119 9 0 2 ma which constrains the age of porphyry magmatic hydrothermal events the porphyry system was then unroofed weathered and superimposed by discrete stages of advanced argillic alteration and high sulfidation mineralization two pulses of alunite events yield 40ar 39ar ages of 116 3 0 8 ma and 111 7 1 0 ma which represent the principal epithermal alteration and mineralization ages at tiegelongnan the first alunite pulse age is consistent with younger porphyry gp4 age of 116 2 0 4 ma zircon la icp ms age weathering and exhumation of the porphyry epithermal deposit were continuing until the cover of andesite at 110 ma and by post andesite gravel the andesite was affected by a younger weak hydrothermal alteration at 108 7 0 7 ma constrained by a muscovite 40ar 39ar age another barren alunite yields a 40ar 39ar age of 100 6 2 0 ma which may represent the youngest hydrothermal event the long life span discrete hydrothermal activities from 120 to 100 ma in the tiegelongnan deposit is consistent with the long lasting tectonic magmatic events of the bangong nujiang suture zone the discrete epithermal mineralization events at tiegelongan are younger than the porphyry mineralization events which is analogous to several other epithermal deposits worldwide the 10 m y exhumation history at tiegelongan is slower than the typical and rapid erosion history of 1 2 m y porphyry deposits in low altitude tropical climates regions and during a specific abrupt uplift pulse in the andean region the slow exhumation at tiegelongnan is interpreted to be an integrated result of an arid climate environment relatively flat topography and a slow uplift condition during cretaceous in central western tibet

sims analyses of silicon and oxygen isotope ratios for quartz from archean and paleoproterozoic banded iron formations banded iron formations bifs are chemical marine sediments dominantly composed of alternating iron rich oxide carbonate sulfide and silicon rich chert jasper layers isotope ratios of iron carbon and sulfur in bif iron bearing minerals are biosignatures that reflect microbial cycling for these elements in bifs while much attention has focused on iron banded iron formations are equally banded silica formations thus silicon isotope ratios for quartz can provide insight on the sources and cycling of silicon in bifs bifs are banded by definition and microlaminae or sub mm banding are characteristic of many bifs in situ microanalysis including secondary ion mass spectrometry is well suited for analyzing such small features in this study we used a cameca ims 1280 ion microprobe to obtain highly accurate 0 3 and spatially resolved 10 lm spot size analyses of silicon and oxygen isotope ratios for quartz from several well known bifs isua southwest greenland 3 8 ga hamersley group western australia 2 5 ga transvaal group south africa 2 5 ga and biwabik iron formation minnesota usa 1 9 ga values of d 18 o range from 7 9 to 27 5 and include the highest reported d 18 o values for bif quartz values of d 30 si have a range of 5 from 3 7 to 1 2 and extend to the lowest d 30 si values for precambrian cherts isua bif samples are homogeneous in d 18 o to 0 3 at mm to cm scale but are heterogeneous in d 30 si up to 3 similar to the range in d 30 si found in bifs that have not experienced high temperature metamorphism up to 300 c values of d 30 si for quartz are homogeneous to 0 3 in individual sub mm laminae but vary by up to 3 between multiple laminae over mm to cm of vertical banding the scale of exchange for si in quartz in bifs is thus limited to the size of microlaminae or less than 1 mm we interpret differences in d 30 si between microlaminae as preserved from primary deposition silicon in bif quartz is mostly of marine hydrothermal origin d 30 si 0 5 but silicon from continental weathering d 30 si 1 was an important source as early as 3 8 ga

fan delta sequence in the archean fig tree group barberton greenstone belt south africa abstract the fig tree group of the barberton greenstone belt in south africa records the onset of tectonism and significant terrigenous and volcaniclastic sedimentation following a period of predominantly effusive volcanism in the southern part of the greenstone belt the lower fig tree conformably overlies the onverwacht group and can be grouped into either 1 volcaniclastic deposits consisting of pyroclastic and reworked volcanic detritus or 2 non volcanogenic terrigenous deposits of sandstone and conglomerate these petrologic groups are further divided into six lithofacies the lithofacies within the lower fig tree formation can be grouped into two facies associations 1 a subaqueous delta front association made up of fine grained airfall pyroclastic and slightly reworked pyroclastic debris along with resedimented land derived sandstone and conglomerate and 2 a subaerial association that is interpreted as forming from deposition of sandstone and conglomerate by flashy ephemeral stream processes on an alluvial fan surface the stratigraphic sequence coarsens upward from predominantly siltstone and fine grained sandstone at the base to pebble and cobble conglomerate at the top this sequence is interpreted as forming from the progradation of a fan delta into a body of relatively shallow quiet water composition of clasts in the conglomerates indicates that immediately underlying greenstone belt rocks or coeval volcanic rocks were the source for these coarse sedimentary accumulations erosion of uplifted greenstone belt terrain was apparently only to shallow levels both tectonic and volcanic activity played a role in producing several cycles of fan delta progradation

unidirectional solidification textures and their significance in determining relative ages of intrusions at the henderson mine colorado a variety of igneous textures displayed by stocks associated with the henderson molybdenite deposit are interpreted to result from unidirectional growth from the walls of magma chambers inward these igneous textures are present in layers and multilayered sequences consisting of crenulate quartz and feldspar pegmatites crenulate quartz dendritic alkali feldspar and quartz and dendritic and micrographic alkali feldspar quartz intergrowths minerals or intergrowths defining a layer within any one stock consistently terminate or branch inward away from the stock contacts the layers are separated by aplite or aplite porphyry and are most common in the apical and marginal parts of an individual stock layering generally parallels intrusive contacts differences in morphologies of phases among the various layers suggest changing conditions of growth from an undercooled melt and or aqueous solution changes in these physical and chemical conditions as the stock crystallized inward produced the observed textural and compositional layering unidirectional solidification textures can be used to determine the relative ages of individual stocks as well as the approximate orientation of stock contacts in the absence of other independent evidence unidirectional textures can also be used to indicate proximity to an intrusive contact these features are an invaluable aid in detailed mapping of multiple intrusion systems in which the units are compositionally identical or nearly identical

sedimentology of archean greenstone belts signatures of tectonic evolution abstract stratigraphic styles in archean greenstone belts are compared to those of modern and phanerozoic depositional basins in order to test the conformity of tectonic style through time six lithological associations in greenstone belts are recognized 1 mafic ultramafic volcanic 2 calc alkaline volcanic 3 bimodal volcanic 4 quartz arenite iron formation or carbonate 5 conglomerate wacke and 6 conglomerate arenite examples of the associations are described from the kaapvaal superior and zimbabwe provinces and the pilbara block each association differs only slightly between the four regions thereby emphasizing a common tectonostratigraphic theme sedimentary rocks are a minor component of the mafic ultramafic volcanic association they were deposited in two types of volcanic basin environments one similar to barred lagoons and bays around oceanic volcanic islands and the other similar to sediment starved platforms adjacent to coalesced volcanoes in inter arc intra arc and back are basins in contrast sedimentary rocks in the calc alkaline volcanic association comprise thick wedges of epiclastic and volcaniclastic detritus deposited in elongate sedimentary basins and thick wedges of pyroclastic and volcaniclastic detritus deposited adjacent to volcanic centers sedimentary facies were identical to those of forearc trench and marine volcanoplutonic arc settings chemogenic lithofacies in both volcanic associations were deposited in shallow to deep marine waters although shallow water profiles were selectively preserved in some terrains sedimentary rocks of the bimodal volcanic association are thick wedges of siliciclastic and volcaniclastic deposits interbedded with subaerial to submarine erupted flows of komatiite basalt and rhyolite depositional environments ranged from braid plain and braid delta to coastal marine and submarine fan starved basin deposits include banded iron formation and sulfidic black shale the association is identical to that of cratonic extensional basins in arc continent and intracontinental rifts sedimentary rocks of the quartz arenite iron formation or carbonate association onlap weathered basement or bimodal volcanic association rocks depositional environments were either transitional from fluvial to siliciclastic and carbonate marginal marine to offshore pelagic hemipelagic or from inshore intrabasinal clastic and volcaniclastic to offshore pelagic hemipelagic siliciclastic deposits are supermature two tectonic sites are represented those with siliciclastic facies represent continent adjacent syn to post rift stable shelves and those dominated by banded iron formation with volcaniclastic deposits represent arc adjacent post rift stable shelves sedimentary rocks of the conglomerate wacke association are represented by thick wedges of siliciclastic or volcaniclastic sandstone with minor volcanic components these were deposited in braid plain braid delta and submarine fan environments within elongate sedimentary basins coastal plain and pelagic basin facies are also present siliciclastic detritus was derived from syndepositional magmatic and metasedimentary thrust belts two stratigraphic styles are preserved one that records a flysch like stage of deep to marginal marine environments and the other that records a molasse like stage of marginal marine to fluvial environments the association is identical to that of compressional foreland basins of arc continent collisional and compressional arc tectonic affinities the conglomerate arenite association is preserved in elongate structural basins that transgress crustal components and all other supracrustal units it is dominated by thick wedges of siliciclastic sandstone although bimodal volcanic and volcaniclastic rocks can also be present depositional environments ranged from talus and alluvial fan and braid plain to either lacustrine or coastal marine local basin margins often show lateral offsets from source terrains and vertically skewed facies patterns longitudinal facies geometries are typical the association is similar to that of strike slip collisional graben in hinterland tectonic escape and terrane accretion orogens the examples show that despite all the ramifications of secular geophysical geothermal and geochemical global change the stratigraphic style of sedimentary rocks in archean greenstone belts can be matched with modern tectonic analogues thereby emphasizing the conformity of stratigraphic style through time the inseparable link between stratigraphic and tectonic styles implies that the tectonic style of greenstone belts was not temporally unique major differences exist with regards to the chemical composition of certain magmatic and sedimentary products but these are compensated for by their constant stratigraphic function in terms of depositional processes depositional environments and tectonic sites

from crucible to graben in 2 3 ma a high resolution geochronological study of porphyry life cycles boyongan bayugo copper gold deposits philippines the boyongan and bayugo porphyry copper gold deposits are part of a belt of gold rich copper deposits in the surigao district of northeast mindanao philippines the detailed age relationships described in this study provide insight into the geologically short life cycles that characterize porphyry formation in dynamic arc environments since their late pliocene emplacement 2 3 2 1 ma shrimp sensitive highresolution ion microprobe u pb zircon dating at depths of 1 2 2 0 km these deposits were exhumed deeply weathered and buried weathering of these deposits led to the development of the world s deepest known porphyry oxidation profile 600 m thick at boyongan and a modest 30 70 m oxidation profile at adjacent bayugo this earlymiddle pleistocene supergene event followed a period of rapid uplift and exhumation in northeast mindanao 2 5 km ma u th he apatite age elevation spectrum subsequent rapid subsidence 0 34 km ma radiocarbon age elevation spectrum and burial of these deposits are attributed to a mid pleistocene shift from transpressional tectonics to the present day transtensional setting in northeast mindanao during this period debris flows volcanic material and fluviolacustrine sediments accumulating in the actively extending mainit graben covered the weathered deposits preserving the supergene profiles beneath 50 500 m of cover this detailed geochronological study documents the geologically short 2 3 ma time scales over which these major intrusion centered mineral deposits evolved from emplacement exhumation deep oxidation and burial highlighting the dynamism of tectonic processes in environments such as the philippine mobile belt 2012 geological society of america

how long can a hydrothermal system be sustained by a single intrusive event published numerical calculations show that the convective systems which produce near surface geothermal systems or ore deposits are likely to cool their intrusion heat source in at most a few tens of thousands of years even if the intrusion is large generally hydrothermal circulation near surface geothermal activity and magmatic intrusion should be closely tied in time and space long lived approximately 1 m y hydrothermal activity normally suggests multiple pulses of intrusion with associated pulses of hydrothermal circulation however if the permeability of the intruded environment is just above that which allows convection and the volume of the intrusion is very large calculations presented here show that a single episode of intrusion can sustain hydrothermal circulation and near surface geothermal activity for approximately 800 000 yr for a deep sill heat source these unusually long lived hydrothermal systems can vent through a few very widely separated discharge sites and have the potential to produce isolated massive sulfide deposits of unusually large size

geology mineralization alteration and structural evolution of the el teniente porphyry cu mo deposit sir the el teniente cu mo deposit in central chile is an extraordinary accumulation of cu mo ore fig 1 and we welcome the opportunity provided by skewes and stern 2007 to discuss and clarify several important issues regarding its classification and interpretation and to address several incorrect assertions that they make regarding our manuscript cannell et al 2005 we have interpreted el teniente to be a typical porphyry deposit in terms of its alteration assemblages vein and breccia styles and spatial and temporal relationships between cu mo mineralization and felsic porphyries skewes and stern 2007 dispute our claims that mineralization occurred primarily in veins and was related to felsic intrusive activity they also take issue with our interpretations of the various geochronological datasets from el teniente and our classification of el teniente as a porphyry cu mo deposit we address each of these in turn below in order to facilitate the following discussion table 1 correlates the geologic nomenclature of skewes and stern 2007 with that of cannell et al 2005 figures 1 and 2 illustrate the location of the main geologic units on underground mine level 6 at el teniente also shown on figure 1 are the approximate locations of the hypogene sulfide mineral zones figure 2 shows the block model of mo grades in the mine for more details of geologic relationships at el teniente refer to figure 4 of cannell et al 2005 and figures 4 and 5 of skewes et al 2002 although the dacite porphyry dike is shown as a single unit on figure 1 note that rojas 2002 2003 mapped multiple phases within this composite intrusive body skewes and stern 2007 criticized our use of what they assert to be an outdated map of hypogene mineralization

mesozoic porphyry cu au mineralization and associated adakite like magmatism in the philippines insights from the giant atlas deposit the atlas porphyry cu au deposit is located in central cebu island in the philippines with a proven mineral reserve of 1420 mt at 0 45 cu 0 24 g t au 0 018 g t mo and 1 8 g t ag it is associated with the lutopan quartz diorite porphyry stock that was emplaced into the cretaceous volcano sedimentary sequences of the cansi formation two stages of hypogene alteration have been identified at atlas stage i quartz magnetite chalcopyrite pyrite veins associated with potassic and propylitic alteration and stage ii anhydrite pyrite chalcopyrite specularite veins associated with phyllic alteration supergene gypsum veins are also present mineralization is mainly associated with the stage i and stage ii veins the lutopan quartz diorite porphyry yielded a zircon u pb age of 108 5 1 6 ma and is characterized by high sr y 54 69 with the corresponding magma having high oxygen fugacity avg fmq 2 7 avg ce4 ce3 of zircon 439 and h2o concentrations presence of amphibole and biotite phenocrysts and low magmatic temperatures avg ti in zircon thermometry 706 c the relatively low la yb ratios 9 11 listric shaped normalized ree patterns with weak or absent eu anomalies together with zircon ehf t values of 3 4 to 10 0 whole rock isr values of 0 70373 0 70382 end t values of 2 4 3 4 and mg numbers of 49 53 suggest that the lutopan quartz diorite porphyry was likely derived from partial melting of young lower continental crust or interaction between asthenospheric melts and lower crust melts that evolved to adakite like trace element compositions through amphibole fractionation stage i veins yielded a pyrite re os isochron age of 110 2 5 6 ma making atlas the only mesozoic porphyry deposit discovered in the philippines

philippine porphyry and epithermal deposits an introduction the philippines is one of the most richly endowed parts of the southwest pacific with many porphyry copper gold and epithermal gold silver deposits scattered along the archipelago e g sillitoe and gappe 1984 mitchell and leach 1991 fig 1 chinese mining artifacts discovered in the baguio and masbate districts suggest that gold and silver mining dates back to at least the 14th century several placer gold mining regions were active during the spanish regime 1521 to 1898 bureau of mines and geosciences 1986 since world war ii gold and silver production has risen fairly steadily from 2 0 t au and 1 4 t ag in 1946 to 37 t au and 34 t ag in 2009 bureau of mines and geosciences 1986 fig 2 between 2005 and 2009 the philippines accounted for approximately 1 5 and 0 1 percent of global gold and silver production respectively when approximately 37 t au and between 14 and 34 t ag were produced each year george 2011 brooks 2011 fig 2 fig 1 a distribution of active copper gold silver zinc chromium and nickel mines in the philippines circa mid 2011 modified from philippines mines and geoscience bureau http www mgb gov ph b study site locations for this special issue fig 2 philippines gold and silver production in tonnes from 1910 to 2009 and copper production in millions of tonnes from 1947 to 2009 data sources wu 1984 bureau of mines and geosciences 1986 lyday 1989 edelstein 1994 1999 2004 2011 lucas 1994 reese 1994 amey 1999 hilliard 1999 brooks 2004 brooks 2011 and george 2011 the first large scale copper mining operations in the philippines commenced at

porphyry and epithermal deposits and 40ar 39ar geochronology of the baguio district philippines the baguio district is located in the central cordillera of northern luzon philippines it contains numerous mineralized porphyry copper gold epithermal gold silver and skarn gold lead zinc deposits the district is floored by cretaceous eocene metavolcanic and metasedimentary rocks which are overlain by marine to terrestrial sedimentary and volcanic rocks of early miocene to pliocene ages tertiary arc magmatism related to east directed subduction of the south china sea plate along the manila trench beneath northern luzon produced a major batholith the central cordillera intrusive complex which defines the eastern boundary of the baguio district the intrusive complex was emplaced in the early miocene based on 40ar 39ar age determinations for the lucbuban gabbro 22 6 0 5 ma and virac granodiorite 20 23 0 38 and 20 2 0 7 ma recent exploration has led to the discovery of several new porphyry copper gold and skarn prospects in the western baguio district mineralization was preceded by the intrusion of a suite of hornblende megacrystic andesite dikes in the central part of the district from 4 55 0 15 to 3 45 0 19 ma porphyry copper gold and skarn deposits at black mountain and mexico on the western side of the district formed between 3 09 0 15 and 2 81 0 24 ma the santo tomas ii cu au pd porphyry deposit was emplaced into the central southern part of the district at about 1 5 ma based on secondary biotite 40ar 39ar ages of 1 48 0 05 ma and 1 47 0 05 ma on the eastern side of the district porphyry style mineralization at the hartwell and ampucao porphyry cu au prospects returned 40ar 39ar ages of 1 09 0 10 and 0 51 0 26 ma respectively quartz carbonate base metal sulfide style epithermal gold silver veins are well developed on the eastern side of the baguio district and crosscut porphyry style mineralization at the acupan baguio gold and nugget hill deposits epithermal veining is inferred to have occurred in the past million years based on a reported k ar age determination of 0 65 0 07 ma from the acupan gold mine a large advanced argillic alteration zone the baguio lithocap crops out in the northwest part of the district and formed between 1 4 and 0 9 ma based on previous k ar dating pliocene pleistocene mineralization in the baguio district was triggered by the east directed subduction of the scarborough ridge ridge subduction caused the subduction angle along the manila trench beneath northern luzon to decrease which facilitated crustal thickening and exhumation ridge subduction also promoted the development of northwest trending faults in the upper plate that interacted with major arc parallel north and arc normal northeast trending fault sets associated with the philippine fault system fertile magmas were emplaced into transtensional strike slip relay basins resulting in the accumulation of more than 35 moz of gold and several million tonnes of copper over approximately 3 m y

tertiary and quaternary magmatism in mindanao andleyte philippines geochronology geochemistry and tectonic setting abstract a set of 230 igneous rock samples from leyte and mindanao philippines has beenstudied for their major and trace element chemistry mineralogy and geochronology 40k 40ar dating several volcanic sectors have been distinguished according to their geographic position tectonic framework and geologic history a in leyte the ophiolitic basement at 50 ma is morb type but characterized by negative nb 0 anomalies typical of back arc basalts miocene 20 and 11 ma and late pliocene to quaternary magmas 2 5 0 4 show typical island are talc alkaline characteristics in eastern mindanao eocene 47 46 ma magmatic rocks are arc tholeiitic while those of miocene 18 6 ma and early pliocene 4 5 ma age are generally talc alkaline dacites of 12 ma age have adakitic compositions the young 3 ma volcanics in surigao and north davao are mostly adakitic although talc alkaline basalts and basaltic andesites dated at 0 9 ma overlie adakites in surigao b in daguma oligocene 30 ma arc tholeiitic diorites intrude older arc sequences miocene0 17 0 7 7 ma dikes and flows in both daguma and sarangani peninsula are mostly talc alkaline andesites although minor adakites dated back to 18 ma have been found overlying undated breccias in daguma in southeast daguma the tale alkaline volcanic substratum of pliocene recent volcanoes is 8 6 ma old quaternary 1 83 ma to present andesitec and dacitic volcanics in mt parker and mt matutum southwest daguma are either talc alkaline or adakitic while mt blit northwest daguma is built up by 2 5 ma old hfse enriched basalts 1 ma old normal talc alkaline andesites and 0 8 ma old adakites c in central mindanao miocene andesites yield ages of 20 and 16 ma pliocene 2 5 ma 0 volcanism is dominated by talc alkaline and hfse enriched basalts and basaltic andesites quaternary lavas i ma to present range in character from tale alkaline to shoshonitic and exhibit wide variations in their trace element behavior d miocene lavas of 19 11 ma age in zamboanga are mostly talc alkaline though a lone 0 18 ma old adakite was also encountered pliocene quaternary basalts and basaltic andesites dated back to 2 2 1 ma are hfse enriched such that some display positive nb anomalies in spidergrams adakites of 3 8 0 7 ma age are located nearer the sulu trench the compositional variety of tertiary recent island arc magmatism in leyte and mindanao couldbe linked to the tectonic settings prevailing during each magmatic phase and is here utilized to refine paleokinematic reconstruction of the tectonic history of the philippine archipelago the identification of adakites at certain time periods is used to date timings of subduction initiations and arc polarity reversals major and abrupt changes in geochemical compositions are well exhibited by the pliocene pleistocene volcanism involving the collision related shift from talc alkaline to shoshonitic volcanism in central mindanao and adakite production in all the volcanic sectors defined the origin of the hfse enrichments among lavas younger than 3 ma could be attributed to the presence in their mantle source of an oib component or alternatively to the enrichment of this mantle source through percolation of slab derived melts

physicochemical processes in the magma chamber under the black mountain porphyry cu au deposit philippines insights from mineral chemistry and implications for mineralization the black mountain porphyry cu au deposit in the baguio district northern luzon philippines is associated with late miocene to pliocene intrusive rocks that retain primary crystallization signatures providing an excellent natural laboratory to study the details of magma chamber processes each igneous phase contains disequilibrium textures including resorptive textures in plagioclase and distinct core rim textures in amphibole high crystallization temperatures and pressures in felsic 880 c and 2 8 kbar and mafic 1 030 c and 7 7 kbar rocks recorded by amphibole phenocrysts reflect crystallization in the magma chamber amphibole in felsic rocks aged 6 39 0 49 to 2 83 0 23 ma have similar crystallization temperatures and pressures suggesting a long lived and hot felsic magma chamber under the black mountain deposit four independent oxybarometers including amphibole coexisting magnetite ilmenite magmatic anhydrite and zircon consistently show a high oxidation state of nno 1 for the felsic magma and nno 0 7 for the mafic magma element profiles across phenocrystic plagioclase display repeated oscillatory variations of ca fe and sr contents with large anorthite variations and a positive correlation between cao and feo the amphibole is classified as group 1 mg hornblende to tschermakite hornblende in felsic rocks and group 2 mg hastingsite in mafic rocks the group 1 amphiboles show a variety of major and trace element variations from core to rim in disequilibrated grains and transitional compositions to group 2 mg hastingsite both mineral textures and chemistry recorded by phenocrysts of plagioclase and amphibole indicate repeated mafic magma recharge in the felsic magma chamber the common occurrence of rounded or elongated sulfide inclusions in the megacrystic amphibole from the mafic rocks 2 81 0 15 ma suggests a greater enrichment of cu in mafic rocks relative to the ore forming porphyries 2 91 2 83 ma this is also consistent with higher cu contents 3 4 0 9 ppm in the megacrystic amphibole from the mafic rocks relative to amphibole in felsic rocks 1 0 0 2 ppm and may indicate up to 3 4 times higher cu in the mafic magma relative to felsic magma therefore large scale mafic magma recharge particularly at 2 8 ma likely introduced ore forming metals to the long lived felsic magma chamber further contributing to the fertility of the felsic rocks and ultimately to cu au mineralization at the black mountain deposit

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

giant porphyry deposits characteristics distribution and tectonic controls more than half of the 25 largest known porphyry copper deposits defined in terms of contained copper metal formed during three time periods the paleocene to eocene eocene to oligocene and middle miocene to pliocene these giant deposits are clustered within three provinces central chile northern chile and southwest arizona northern mexico other giant deposits occur in montana utah panama peru argentina irian jaya mongolia and iran compressive tectonic environments thickened continental crust and active uplift and erosion were associated with the formation of many of these deposits calc alkalic magmas are most favorable for the formation of giant porphyry copper deposits although several of the largest systems are associated with high k calc alkalic intrusions the 25 largest gold rich porphyry deposits are concentrated in the southwest pacific and south america with other occurrences in eurasia british columbia alaska and new south wales many of the deposits formed in the last 13 m y the largest of the deposits are associated with high k calc alkalic intrusions many calc alkalic porphyritic intrusions have also produced giant gold rich porphyries in the last 20 m y the formation of giant porphyry copper molybdenum and copper gold deposits in the circum pacific region has been closely associated with subduction of aseismic ridges seamount chains and oceanic plateaus beneath oceanic island and continental arcs in several examples these tectonic perturbations have promoted flat slab subduction crustal thickening uplift and erosion and adakitic magmatism coeval with the formation of well endowed porphyry and or epithermal mineral provinces similar tectonic features are inferred to be associated with the giant porphyry copper molybdenum provinces of northern chile eocene oligocene and southwest united states cretaceous paleocene topographic and thermal anomalies on the downgoing slab appear to act as tectonic triggers for porphyry ore formation other factors such as sutures in the overriding plate permeability architecture of the upper crust efficient processes of ore transport and deposition and in some cases formation and preservation of supergene enrichment blankets are also vital for the development of high grade giant ore deposits a low grade geochemical anomaly may be the final product of mineralization if ore forming processes do not operate efficiently even in the most favorable geodynamic settings

geology of the boyongan and bayugo porphyry cu au deposits an emerging porphyry district in northeast mindanao philippines the boyongan and bayugo porphyry cu au mineral deposits discovered under postmineralization cover during the previous decade are part of an emerging belt of intrusion centered au rich cu mineral deposits and prospects in the surigao district of northeast mindanao philippines since their formation in the early pleistocene exhumation and weathering of these deposits have led to the development of a 600 m thick oxidation profile at boyongan and a modest 30 70 m oxidation profile at bayugo debris flows volcanic material and fluviolacustrine sediments accumulating in the actively extending mainit graben subsequently covered the weathered deposits preserving their supergene profiles the mineral deposits formed in association with a composite diorite complex containing at least 12 discrete intrusive stages three premineralization diorite porphyry stocks and a silt sand matrix breccia complex represent early stages of magmatism and brecciation significant cu and au introduction followed these events and occurred in association with small early mineralization diorite porphyry stocks at boyongan and bayugo within the diorite complex the two mineral deposits are spatially distinct separated by approximately 1 km of premineralization diorites inter and late mineralization intrusions were emplaced as the magmatic hydrothermal system waned a characteristic progression of vein and k silicate alteration styles affected each of the synmineralization intrusions rare comb quartz unidirectional solidification textures stage 0 mark the transition from magmatic to hydrothermal conditions quartz poor wispy magnetite biotite k feldspar veinlets characterize stage 1 stage 2 veins consist of quartz with selvage and or disseminated magnetite or biotite and k feldspar halos stage 3 quartz veins have k feldspar halos but generally lack magnetite and biotite stage 4 veins consist of massive bornite chalcopyrite and chalcopyrite pyrite with k feldspar halos stage 3 quartz veins and stage 4 sulfide veins host cu au mineralization of the greatest volumetric significance reflecting the general paucity of sulfide in the earlier vein stages despite the simplicity of this sequence detailed paragenetic reconstructions reveal that this characteristic progression of veining and k silicate alteration was repeated with the emplacement of each synmineralization intrusive event revealing multiple magmatic hydrothermal cycles of alteration and mineralization at boyongan and bayugo intense and pervasive illite alteration in association with pyrite chalcopyrite and tetrahedrite tennantite developed in narrow structures crosscutting quartz k feldspar veins debris flows in the burial sequence above and adjacent to the boyongan bayugo complex also contain abundant clasts with intense pervasive illite and alunite pyrophyllite dickite kaolinite alteration assemblages that have overprinted k silicate style quartz veins in both mineral deposits cu and au are associated with intense quartz vein stockworks composed primarily of k silicate stage 3 veins despite this association not all of these quartz vein stockworks contain cu and au to the same tenor quartz vein stockworks in the eastern high grade of boyongan have been intersected over a vertical interval of 800 m having affected much of the early mineralization stock however hypogene cu grades exceed 0 5 by weight only in the upper 300 m of the stockwork in the cupola of the early mineralization stock superior grade development in high grade zones at boyongan locally exceeding 2 cu and 3 g t au developed where fertile vein stages from two or more magmatic hydrothermal cycles affected the same wall rock the documented paragenetic relationships demonstrate multiple discrete cycles of k silicate stage veining and alteration associated with each synmineralization intrusive event all such events predate formation of feldspar destructive illite smectite chlorite illite pyrite and quartz alunite clay assemblages existing geochronological constraints on the timing of magmatism and hydrothermal activity demonstrate that these repeated cycles supporting superior grade development transpired extremely rapidly in a period of less than 200 000 years 2 3 2 1 ma geologic and geochronological constraints on the life cycle of boyongan and bayugo describe an extremely dynamic history of emplacement exhumation weathering and burial over a period of 2 3 m y the study illustrates the spectrum of metallogenic processes operative over a geologically brief period and highlights some of the key elements responsible for formation of superior grades and for deposit preservation in an extensional setting

porphyry copper deposit density estimating numbers of undiscovered mineral deposits has been a source of unease among economic geologists yet is a fundamental task in considering future supplies of resources estimates can be based on frequencies of deposits per unit of permissive area in control areas around the world in the same way that grade and tonnage frequencies are models of sizes and qualities of undiscovered deposits to prevent biased estimates it is critical that for a particular deposit type these deposit density models be internally consistent with descriptive and grade and tonnage models of the same type in this analysis only deposits and prospects that are likely to be included in future grade and tonnage models are employed and deposits that have mineralization or alteration separated by less than an arbitrary but consistent distance 2 km for porphyry copper deposits are combined into one deposit only 286 deposits and prospects that have more than half of the deposit not covered by postmineral rocks sediments or ice were counted nineteen control areas were selected and outlined along borders of hosting magmatic arc terranes based on three main features 1 extensive exploration for porphyry copper deposits 2 definable geologic settings of the porphyry copper deposits in island and continental volcanic arc subduction boundary zones and 3 diversity of epochs of porphyry copper deposit formation porphyry copper deposit densities vary from 2 to 128 deposits per 100 000 km2 of exposed permissive rock and the density histogram is skewed to high values ninety percent of the control areas have densities of four or more deposits 50 percent have densities of 15 or more deposits and 10 percent have densities of 35 or more deposits per 100 000 km2 deposit density is not related to age or depth of emplacement porphyry copper deposit density is inversely related to the exposed area of permissive rock the linear regression line and confidence limits constructed with the 19 control areas can be used to estimate the number of undiscovered deposits given the size of a permissive area in an example of the use of the equations we estimate a 90 percent chance of at least four a 50 percent chance of at least 11 and a 10 percent chance of at least 34 undiscovered porphyry copper deposits in the exposed parts of the andean belt of antarctica which has no known deposits in a permissive area of about 76 000 km2 measures of densities of deposits presented here allow rather simple yet robust estimation of the number of undiscovered porphyry copper deposits in exposed or covered permissive terranes

mineralization parameters and exploration targeting for gold copper deposits in the baguio luzon and pacific cordillera mindanao mineral districts philippines a review abstract the baguio mineral district in luzon philippines is known to host several world class epithermal gold porphyry copper deposits the interplay of tectonic setting magma composition structural control and hydrothermal systems contributed to the generation of these deposits ridge subduction scarborough seamount resulting to flat subduction and a transpressional regime could also be related to the formation of epithermal gold porphyry copper deposits in baguio subduction processes leading to the formation of calc alkaline rocks associated with high water pressure oxygen fugacity and late sulfur saturation are almost always associated with the gold copper deposits in the district compared to the baguio mineral district less exploration work mine development and production were done in the pacific cordillera mineral district mindanao in southern philippines it is worth noting however that both mineral districts show similarities and overlapping features in terms of geological geophysical and geochemical characteristics this leads one to conclude that the pacific cordillera mineral district has ore deposits waiting to be discovered

exploration applications of copper isotopes in the supergene environment a case study of the bayugo porphyry copper gold deposit southern philippines copper isotope compositions of secondary phases from the supergene profile of the bayugo porphyry copper gold deposit philippines show significant isotopic fractionation relative to hypogene sulfide phases and reveal systematic patterns of isotopic enrichment in the leached cap iron oxides and supergene copper sulfides thirty nine iron oxide copper oxide and copper sulfide minerals yielded 65 cu values between 3 4 and 6 9 per mil samples of hypogene sulfides have a narrow range of values near zero per mil 0 6 to 1 0 in contrast samples of supergene sulfides chalcocite and djurleite collected from the exotic and enriched copper zones define a trend of decreasing 65 cu from the enriched source area and proximal exotic zone 3 downgradient to the distal portions these findings are significant because within exotic copper zones the copper isotope values of supergene sulfides can provide an indication both of proximity and direction to the source area the technique could be applied in the search for unrecognized porphyry centers upgradient from headless exotic copper occurrences by exploring for the supergene copper phases with the highest 65 cu values independently copper isotope ratios of iron oxides in surface samples or fossil leached caps might be used to rank prospects and to focus drilling in areas with the greatest potential for mature enrichment profiles by mapping the distribution of isotopically enriched leached cap iron oxides the leached cap screening and targeting tool could enhance the iron oxide mapping techniques traditionally applied in leached cap interpretation and exploration

provenance and tectonic implications of the 3 28 3 23 ga fig tree group central barberton greenstone belt south africa abstract sedimentary rocks provide a valuable record of non uniformitarian paleoarchean tectonic processes the rocks of the 3 28 3 23 ga mapepe formation mark the initiation of orogenesis in the barberton greenstone belt south africa however reconstruction of the mapepe basin s is challenging because the rocks occur in fault bounded structural belts that are characterized by lateral heterogeneity and whose correlation remains uncertain we have studied the petrography geochemistry and detrital zircon geochronology from outcrop and drill core samples from two adjacent structural belts the manzimnyama syncline and the eastern barite valley area to evaluate the timing of basin formation correlate between these two adjacent areas and provide constraints on the character of tectonic uplift in the eastern barite valley area sedimentation was initiated at about 3260 ma the section includes a lower deep water unit of mainly mudstone overlain by a shoaling upward sequence of fan delta sandstone and conglomerate the sandstone throughout the formation was derived by erosion of local uplifts of the underlying greenstone belt sequence except at the top of the section where sedimentation was dominated by dacitic volcaniclastic sediments dated at 3239 ma in contrast rocks of the mapepe formation in the manzimnyama syncline area 1 2 km south of the eastern barite valley area record the initiation of sedimentation at about 3277 ma with deposition of a rhyolitic tuffaceous unit followed by persistent deep water sedimentation of banded iron formation banded ferruginous chert and turbiditic sandstone siliciclastic sediments are immature and were derived by erosion of older supracrustal greenstone belt rocks no fig tree age volcanism younger than 3260 ma is recorded in this belt overall mapepe sedimentary rocks record the formation of numerous local uplifts of underlying supracrustal rocks with periodic volcanic activity and the dispersal of debris to form mainly small fan deltas flanked by deep water systems the contrasting ages lithologies depositional settings and provenance of the sedimentary rocks in the now adjacent eastern barite valley and manzimnyama syncline belts suggest that they were deposited in either different parts of a large complex fig tree basin or represent separate basins that have been juxtaposed during post fig tree tectonism and shortening

ore related breccias in volcanoplutonic arcs an overview of breccias related to a variety of base metal precious metal and lithophile element deposits in volcanoplutonic arcs permits definition of six possible mechanisms for subsurface brecciation 1 release of magmatic hydrothermal fluids from high level hydrous magma chambers during second boiling and subsequent decompression generates a spectrum of breccia types in which fragments may suffer collapse and or ascent single or multiple intrusion related breccia pipes and pre and intermineral breccias in porphyry copper deposits provide widespread examples 2 magmatic heating and expansion of meteoric pore fluids may lead to brecciation commonly of late or postmineral age and including pebble dikes in porphyry type and related deposits magmatic heating of rocks saturated with seawater may cause submarine hydrothermal eruptions late in the emplacement histories of kuroko type massive sulfide deposits many of the resultant breccias underwent limited sedimentary transport overpressuring of heated fluids beneath semipermeable partly self sealed cap rocks may lead to brecciation and subaerial hydrothermal eruptions in shallow epithermal precious metal settings magmatic heating or tectonic disturbance may have triggered brecciation 3 interaction of cool ground waters with subsurface magma can generate phreatomagmatic explosions postmineral phreatomagmatic diatremes associated with porphyry systems and premineral diatremes with epithermal precious or base metal deposits were generated in this manner these attained the palcosurface to produce pyroclastic base surge and fall deposits that accumulated as tuff rings around maar craters 4 magmatic hydrothermal brecciation may lead to disruption of rocks through to the paleosurface decompression and fragmentation and eruption of the top part of an underlying magma chamber pre and postmineral magmatic diatremes of this sort are inferred to accompany a few porphyry type and other base and precious metal systems they were manifested at the palcosurface by accumulations of pyroclastic fall and flow deposits 5 breccias may result from mechanical disruption of wall rocks during subsurface movement of magma any intrusion related deposit may include such intrusion breccias 6 tectonic breccias resulting from fault displacement may accompany any type of ore deposit a continuum exists between many of these breccia types and it is difficult to identify unique criteria for their unambiguous distinction

cycling phosphorus on the archean earth part i continental weathering and riverine transport of phosphorus abstract phosphorus p is the key nutrient thought to limit primary productivity on geological timescales phosphate levels in archean marine sediments are low but quantification of the p cycle and how it changed through a billion years of recorded archean history remain a challenge hindering our understanding of the role played by p in biosphere geosphere co evolution on the early earth here we design kinetic and thermodynamic models to quantitatively assess one key component of the early p cycle continental weathering by considering the emergence and elevation of continents as well as the evolution of climate the atmosphere and the absence of macroscopic vegetation during the archean eon our results suggest that the weathering rate of apatite the major p hosting mineral in the rocks was at least five times higher in the archean eon than today attributable to high levels of pco2 g despite this the weathering flux of p to the oceans was negligible in the early archean eon increasing to a level comparable to or greater than the modern by the end of eon a consequence of accelerating continental emergence furthermore our thermodynamic calculations indicate high solubilities of primary and secondary p hosting minerals in the acidic weathering fluids on land linking to high archean pco2 g thus weathering of p was both kinetically and thermodynamically favorable on the archean earth and river water could transport high levels of dissolved p to the oceans as also supported by the observed p depletion in our new compilation of archean paleosols lastly we evaluated the relative rates of physical erosion and chemical weathering of silicates during the archean eon the results suggest that continental weathering on the early and middle archean earth might have been transport limited due to low erosion rates associated with limited subaerial emergence and low plateau elevations by the late archean however continental weathering would have transited to kinetically limited state because of continental emergence increased plateau elevation and weakening weathering rates overall our weathering calculations together with paleosol evidence indicate an increasing flux of bioavailable p to the oceans through time associated with late archean continental emergence reaching levels comparable to or higher than modern values by the end of the eon increased p fluxes could have fueled increasing rates of primary production including oxygenic photosynthesis through time facilitating the irreversible oxidation of the earth s atmosphere early in the proterozoic eon

erosion of archean continents the sm nd and lu hf isotopic record of barberton sedimentary rocks abstract knowing the composition nature and amount of crust at the surface of the early earth is crucial to understanding the early geodynamics of our planet yet our knowledge of the hadean archean crust is far from complete limited by the poor preservation of archean terranes and the fact that less attention has been paid to the sedimentary record that tracks erosion of these ancient remnants to address this problem and get a more comprehensive view of what an archean continent may have looked like we investigated the trace element and sm nd lu hf isotopic records of archean metasedimentary rocks from south africa we focused our study on sandstone and mudstone from drill core in the fig tree group 3 23 3 26 ga of the barberton granite greenstone belt but also analyzed the 3 4 ga buck reef cherts and still older 3 5 3 6 ga meta igneous rocks from the ancient gneiss complex swaziland based on principal component analysis of major and trace element data the fig tree metasedimentary rocks can be classified into three groups crustal detritus rich sediments si rich sediments and ca fe rich sediments the detritus rich sediments have preserved the sm nd and lu hf isotopic signatures of their continental sources and hence can be used to constrain the composition of crust eroded in the barberton area in the paleoarchean period based on sm nd ratios we estimate that this crust was more mafic than today with an average sio 2 content of 60 5 2 wt this composition is further supported by isotopic mixing calculations suggesting that the sedimentary source area contained equal proportions of mafic ultramafic and felsic rocks this implies that the archean crust exposed to weathering was more mafic than today but does not exclude a more felsic composition at depth neodymium and hf crustal residence ages show that the eroded crust was on average 300 400 ma older than the deposition age of the sediments which highlights the importance of intracrustal reworking of older crust at 3 2 ga in the barberton area the si rich sediments have slightly positive e nd t 3 23ga but extremely radiogenic e hf t 3 23ga up to 11 based on analyses of 3 4 ga buck reef cherts we suggest that the radiogenic hf isotopic signature of the si rich sediments can be accounted for by the old chert clasts or detrital silicified rock fragments present in the rocks the latter have extremely high lu hf ratios such that their e hf values would increase dramatically by about 100 epsilon units every 100 ma in the ca fe rich sediments one sample contains carbonate that preserves the typical rare earth element features of seawater precipitates the initial nd isotopic composition of this sample e nd t 3 23ga 1 7 is within the range of previous estimates for archean anoxic seawater

early magnetite amphibole plagioclase alteration mineralization in the island copper porphyry copper gold molybdenum deposit british columbia the initial hydrothermal event in the evolution of the ca 377 mt 0 41 percent cu island copper porphyry cu au mo deposit northern vancouver island was the formation of an extensive alteration mineralization facies dominated by magnetite calcic amphibole and intermediate to sodic plagioclase early stage quasipervasive magnetite rich alteration and associated magnetite rich veinlets in this middle jurassic island arc hosted hydrothermal system developed in both an axial dacitic porphyry dike and contiguous basaltic flows and pyroclastic strata the magnetite rich alteration zone 500 to 700 m wide and originally extending over at least 450 m vertically exhibits an outward zonation from quartz magnetite albite an sub or 6 amphibole trace apatite trace through quartz magnetite amphibole albite an sub 6 10 or oligoclase andesine an sub 15 36 apatite trace or scapolite trace to amphibole magnetite oligoclase or sodic andesinc an sub 15 39 or quartz or apatite trace assemblages definition of early stage mineral assemblages impeded by unusually intense later intermediate argillic alteration and more local phyllic and advanced argillic alteration was facilitated by the use of novel petrographic techniques including incident light nomarski differential interference contrast microscopy early stage mineralization comprises several well defined vein veinlet types which were demonstrably emplaced prior to the main stage chalcopyrite pyrite stockwork and associated k silicate alteration minor chalco pyrite and pyrite occur in some early stage veins and magnetite is a constituent of many later main stage sulfide rich veins but the distinction between these two major vein systems is clear mass exchange calculations demonstrate that early alteration involved intense iron metasomatism of both felsic and mafic country rocks with an fe enrichment approaching 450 percent 20 g 100 cc in the dacite dike and lesser and more variable na enrichment with both ti and al behaving as mobile constituents paragenetically early fluid inclusions in the quartz phenocrysts of the dike are tentatively correlated with the magnetite rich alteration mineralization and imply that this event was initiated above 650 degrees c and at pressures of at least 1 kbar and was generated by fecl 2 rich brines at first single phase and moderately saline avg 15 wt nacl equiv but latterly boiling at ca 560 degrees to 645 degrees c and or ca 0 55 kbars the main stage potassic alteration zone has the configuration of an annulus ca 100 to 150 m in width which was entirely superimposed on the more extensive early alteration mineralization zone at ca 430 degrees to 575 degrees c and below 450 bars gold although correlated overall with cu and potassic alteration was probably extensively introduced in the early stage it is inferred that the scarcity of sulfides in the early alteration assemblages reflects the highly oxidized nature of the initial fluids in which so super 2 exceeded both h 2 s and so super 2 4 the deposition of abundant magnetite and the widespread and intense fe metasomatism which define the early stage record the high solubility of fe as fecl 2 in high temperature brines in equilibrium with magnetite bearing quartzofeldspathic rocks as well as the retrograde solubility of magnetite between ca 550 degrees and 750 degrees c whereas the high so 2 h 2 o so 4 ratios of the initial hydrothermal fluids at island copper and in other similar deposits may have resulted from the high inherent oxygen fugacity of the parental dacitic magmas they may have directly reflected the composition of supercritical fluids expelled on quenching of underplating s rich mafic melts the mineral assemblages of the early stage veins and associated quasi pervasive alteration cannot be assigned to the accepted alteration mineralization facies of porphyry systems such as a veins and potassic alteration and record specific and distinct conditions of fluid rock interaction