challenges to global mineral resource security and options for future supply minerals are vital to support economic growth and the functioning of modern society demand for minerals is increasing as global population expands and minerals are used in a greater rangeof applications particularlyassociated with the deployment of new technologies while con cerns about future mineral scarcity have been expressed these are generally unfounded and based on over simplistic analysis this paper considers recent debate around security of mineral supply and technical geosciences based options to improve utilization of the resource base and contribute to replenishing reserves history suggests that increasing demand for minerals and higher prices will generally lead to technological and scientific innovation that results in new or alternative sources of supply recent assessments of global mineral endowment suggest that society should be optimistic about its ability to meet future demand for minerals provided that there is continued innovation and investment in science and technology reducing energy consumption and breaking the current link between metal production and greenhouse gas emissions are among the greatest challenges to secure a sustainable mineral supply however widespread adoption of low carbon mineral extraction technologies underpinned by multidisciplinary research and increased global utilization of low carbon energy sources will allow these challenges to be met gold open access this article is published under the terms of the cc by 3 0 license

geology of a major new porphyry copper center in the superior pioneer district arizona a new porphyry copper deposit has been discovered in the superior pioneer district of east central arizona lying under thick tertiary cover approximately 2 km south of the historic magma vein the porphyry center was encountered in the course of an exploration drilling campaign conducted from 1992 through 1997 comprising a series of subvertical surface core holes and subhorizontal underground core holes ranging in length from 1 000 to 1 955 m the system is large structurally intact and shows indications of a substantial hypogene mineralized zone that averages between 1 0 and 2 0 percent cu the deposit is hosted by a thick sequence of cretaceous volcaniclastic and siliciclastic sedimentary rocks the mesozoic strata rest disconformably on calcareous units of the uppermost paleozoic naco group and are intruded by an east northeast striking swarm of quartz porphyry dikes the dike swarm is truncated at the basal tertiary unconformity under which the mesozoic section is buried by 600 to 1 200 m of unmineralized overburden composed of the oligocene miocene whitetail conglomerate and the miocene 18 6 ma apache leap dacite tuff the attitude of the basal tertiary beds shows that the porphyry center has been tilted 30 to 35 to the east northeast a broad zone of hydrolytic alteration characterizes the high structural levels in mesozoic wall rocks peripheral propylitic alteration in the volcaniclastic rocks is marked by epidote and chlorite giving way inwardly to a narrow zone of chlorite dominant alteration in which epidote is destabilized in favor of smectite clays and carbonate this chlorite zone corresponds closely to the intermediate argillic alteration type of meyer and hemley 1967 the propylitic fringe of the system is erratically mineralized by vein controlled pyrite sphalerite and specularite with minor chalcopyrite and galena chloritic rocks in the intermediate argillic halo contain pyrite and chalcopyrite the intermediate argillic alteration mantles an inner zone of pervasive quartz sericite pyrite the sericitic zone is strongly pyritic with bornite and lesser chalcopyrite within sericitically altered rock pyrite chalcocite digenite bornite veins exhibit centimeters to meters wide halos of advanced argillic alteration in which sericite is replaced by kaolin group clays the quartz sericite pyrite zone is superimposed on earlier potassic alteration that remains preserved at deeper levels the base of the mesozoic sequence and shaly beds in the upper naco group section are pervaded with secondary biotite calcareous rocks in the naco group are altered to 1 pyroxene epidote hornfelses and minor garnet magnetite skarn overprinted by 2 actinolite and 3 chlorite carbonate clay alteration biotitically altered rocks are mineralized by quartz pyrite chalcopyrite anhydrite veins molybdenite is present in an early generation of quartz rich pyrite chalcopyrite veins hornfelses and skarn in the naco group are strongly mineralized by quartz poor chalcopyrite pyrite anhydrite veins with chloritic envelopes surface and underground drilling into the deposit has outlined a zone of 1 0 percent hypogene cu that is at least 750 m long by 250 m wide by 300 m high elongated to the east northeast the same volume of rock also averages 0 02 percent mo and 2 ppm ag this zone apexes approximately 300 m below sea level slightly more than 1 5 km below the ground surface and remains open in all directions laterally and at depth four of the last five drill holes penetrating this zone ended in rock assaying 2 0 percent hypogene cu

tectonic diffusion estimate of orogenic gold resources age frequency data are used to determine amounts of vertical tectonic displacement experienced by the global population of orogenic gold deposits following their emplacement at a crustal depth of 10 1 km knowledge of this tectonic dispersion allows for an estimate of the total crustal endowment of gold in orogenic gold deposits this estimate is based on a compilation of data on 365 orogenic gold deposits of which gold contents are available for 314 deposits and good age control is available for 126 deposits ages of well dated deposits form three clusters that range in age from 47 to 850 ma primarily phanerozoic 69 deposits 1730 to 2090 ma proterozoic 13 deposits and 2540 to 3107 ma archean 44 deposits gold endowments do not vary significantly among the three age groups and average 155 tonnes t per deposit for the entire population for which data on gold tonnages are available owing to the distinct tripartite nature of the age frequency distribution it is not possible that orogenic gold deposits represent largely invariant rates of ore formation and destruction uninterrupted tectonic dispersion would have resulted in the destruction of essentially all proterozoic and archean deposits separate tectonic diffusion calculations for each of the three deposit age populations were carried out while constraining biases to tectonic diffusion i e the most suitable ratios of uplift and erosion versus subsidence and burial with continental crustal thicknesses on the order of several tens of kilometers the results of these calculations indicated that a total of 25 236 orogenic gold deposits formed over the full span of geologic time that 23 664 of these 94 were destroyed during subsequent uplift and erosion and that 1 572 deposits remain at depth in earth s crust if all 365 known orogenic gold deposits have the same mean gold content as the deposits for which gold contents are available then 706 439 t of gold remain at depth in earth s crust gold in orogenic deposits constitutes about 0 0022 percent of the total gold content of the crust using estimates of gold released by prograde metamorphism of the otago schist gold in the deposits that remain in the crust could have been released from about 1 413 000 km3 of amphibolite facies rocks which constitute only about 12 percent of currently exposed metamorphic rocks if we assume a maximum depth of 3 km for future mining of these deposits the model results indicate that deposits containing almost 113 000 t of gold exist within crustal rocks above this depth discovered deposits make up about 8 percent of this endowment in the context of spatial density the areal concentration of orogenic gold deposits along phanerozoic metamorphic belts is about ten times that in proterozoic terranes and about three times higher than in archean belts this suggests that exploration for the next generation of orogenic gold deposits should be focused on phanerozoic terranes

ventifacts and wind abraded rock features in the taylor valley antarctica abstract an area north of lake fryxell in the taylor valley antarctica was surveyed to determine the frequency of occurrence of rocks that show strong evidence of wind abrasion and ventifaction which is defined here as rocks having well developed faceting to define their relative abundance in this area of the ice free mcmurdo dry valley system and to provide an indication of the role of wind as a geomorphic agent in this area the orientation of abrasion caused features facets keels and grooves with respect to the present day wind regime is also described rocks were examined on five linear transects ranging from 300 to 510 m in length a total of 1324 rocks were examined on average 60 of all rocks exhibited distinct wind abrasion features with polish being the most common feature and polished rocks were distributed equally between survey lines suggesting abrasion was ubiquitous in the study area approximately 4 of the rocks had distinct facets and or keels and fine grained ultramafic peridotite type rocks produced the most finely featured forms i e sharp facet edges and keels a larger percentage 12 5 had grooves grooves were typically associated with a tabular form of mafic diabase type igneous rock the distribution of faceted ventifacts and grooved rocks was not uniform for the five transects suggesting that the distribution mechanism for the surface rocks and the source areas determined to a large extent what form of ventifact could be produced at a location the orientation of the grooves and dip directions of the facets indicates the direction of the abrasive winds had a strong westerly component which coincides with the modern wind regime of winter katabatic flows that move down valley toward the ross sea the orientation of the facets and grooves suggests that the rate of formation of the ventifacts proceeds at a pace greater than other surficial processes e g down slope soil movement cryoturbation which should tend to remove trends in the facet and groove orientations or that the down slope movement of the surface is approximately perpendicular to the wind allowing preservation of the alignment

recent ventifact development on the central oregon coast western usa the unusual location of ventifacts on a boulder built jetty at the mouth of the siuslaw river oregon coast western usa allows ventifact age and wind abrasion rates to be estimated with some precision the jetty was built mainly between 1892 1901 and extended throughout the twentieth century consideration of historical shoreline position and the history of jetty construction and repair suggests the ventifacts have formed since about 1930 morphologically the ventifacts are aligned south to north reflecting winter winds and sediment transport from the adjacent beach wind parallel grooves and ridges with sharp sinuous crests are developed on inclined boulder surfaces on top of the jetty and reflect suspended sand transport in wind vortices deeply pitted surfaces on steep boulder surfaces nearest the beach reflect impact by saltating sand grains based on present wind regimes 1992 2000 from three regional weather stations southerly winds above the sand transport threshold occur for 21 9 29 6 per cent of the time based on estimated depth of loss from boulder surfaces wind abrasion rates are calculated to be on the order of 0 24 1 63 mm a 1 this is the first well constrained field estimate of ventifact age and ventifaction rate from a modern coastal environment copyright c 2003 john wiley sons ltd

predictive mapping of prospectivity and quantitative estimation of undiscovered vms deposits in skellefte district sweden mapping of mineral prospectivity and assessment of undiscovered mineral deposits both aim to delineate prospective ground for mineral exploration but the latter is usually carried out exclusive of the former we propose that the spatial distribution of known mineral deposits of the type sought is the key to link mapping of mineral prospectivity and assessment of undiscovered deposits we demonstrate this proposition in regional scale mapping of prospectivity for volcanogenic massive sulphides vms deposits and estimation of undiscovered vms endowment in the skellefte district sweden the results of analyses of the spatial distribution of known vms deposits and their spatial associations with geological features are consistent with existing knowledge of geological controls on vms mineralization in the district and we used them to define spatial recognition criteria of regional scale vms prospectivity integration of layers of evidence representing spatial recognition criteria of vms prospectivity via application of data driven evidential belief functions results in a regional scale map of prospective areas occupying 15 of the district and having fitting and prediction rates of 100 we used the map of prospective areas and proxy measures for degrees of exploration based on the spatial distribution of known vms deposits in one level prediction of undiscovered mineral endowment we obtained estimates of 709 kt undiscovered cu endowment 3190 kt undiscovered zn endowment 95 mt undiscovered ore tonnage and 48 undiscovered vms deposits these estimates are slightly ca 5 on average lower than and thus corroborated by estimates obtained via radial density fractal analysis of the spatial distribution of known vms deposits therefore mineral prospectivity mapping can be a part of mineral resource assessment if the spatial distribution of discovered deposits of the type sought is considered in both predictive modeling processes

the lasky cumulative tonnage grade relationship a reexamination the need for interdisciplinary research on resource appraisal techniques was recognized by samuel g lasky a u s geological survey geologist more than 30 years ago his efforts to devise an appraisal technique that incorporated many attributes of mineral resources resulted in a cumulative tonnage grade relationship that has been referred to as the arithmetic geometric a g ratio or lasky9s law by later writers a review of subsequent studies of the increases in available metal to be expected as grade decreases indicates that lasky9s work has at times been misinterpreted lasky9s relationship is shown to be consistent with studies of the correlation between average grades and tonnages of mineralized material in ore deposits the projection of lasky9s analysis to lower grades is limited because the mathematical formulation predicts physically impossible situations below some limiting grade

revisiting the cumulative grade tonnage relationship for major copper ore types in order to develop long term scenarios of copper supply and demand a grade tonnage density function model was developed for four major copper ore types the model was used to create cumulative grade tonnage curves representing 1 778 million metric tons mt of mineable copper these cumulative curves were then validated against 70 years of historical world average ore grade using production input by ore type from 1800 to 2000 additionally the curves were used in conjunction with estimates of the ultimate porphyry resource and copper concentration in common rocks to conduct a rough analysis of the validity of the bimodal log gaussian distribution hypothesis for the global copper resource base the resulting analysis did not confirm or refute the hypothesis but did provide guidance as to the way in which data from new resource exploration can be used to address the issue of the ultimate mineable copper resource as ore deposit grade tonnage data for other geochemically scarce metals becomes available the methods described in this paper can serve as a template for further investigations of resource quality

controls on the formation of coastal ventifacts abstract ventifacted boulders are present within the intertidal zone of a mixed sand and boulder beach in gweebarra bay northwest ireland the boulders show features typical of wind abrasion by sand including polished surfaces pits and grooves orientation of ventifact keels was measured and direction of prevailing winds responsible for ventifaction was inferred from a sample of 50 boulders in each of two adjoining locations on the beach 30 m apart the keel orientations and inferred wind direction are both strongly clustered but results from each location differ by 90 from one another and neither corresponds closely to the present day regional wind regime since wind flow patterns were not significantly different during the little ice age when the ventifacts were likely formed the orientation of ventifact keels cannot be used uncritically as in many studies as a proxy record of prevailing wind direction it is likely that ventifact development in gweebarra bay was controlled by sediment availability rather than by wind direction

assessment of undiscovered metal resources in finland this paper summarises the results of probabilistic estimates of the amounts of cu zn pb ni co pt pd au ag and mo in undiscovered orogenic au volcanogenic massive sulphide vms porphyry cu outokumpu type cu zn co synorogenic intrusion related ni cu komatiite related ni and layered intrusion hosted contact type and reef type pge deposits in finland the assessments were carried out down to the depth of one kilometre using the three part quantitative assessment method permissive areas tracts within which mineral deposits can exist based on their geological properties were delineated separately for each deposit type total number of tracts delineated was 188 and excluding overlap total area covered by the tracts is 190 700 km2 this means that 57 of the land area of finland holds potential for the discovery of new mineral deposits of the types included in the assessments orogenic au tracts cover the largest area 110 000 km2 and the contact type pge and talvivaara type tracts cover the smallest areas both 310 km2 the number of undiscovered deposits was estimated at several levels of confidence for each permissive tract the total expected number of undiscovered deposits across all permissive tracts is 309 deposits the largest expected numbers of deposits are associated with the orogenic au 90 synorogenic intrusion related ni cu 66 and vms 45 tracts statistical comparisons indicated differences in tonnage and grade values between fennoscandian and global data sets for several deposit types and between global precambrian and phanerozoic porphyry cu deposit data sets the reason for the differences is inconclusive but probably related to both global variations in exploration maturity and availability of grade and tonnage information due to the differences grade tonnage models were constructed using data from well known deposits within the fennoscandian shield for most of the assessed deposit types the orogenic au model was constructed using fennoscandian and north australian deposits and the porphyry cu model using global data on precambrian deposits the sum of median estimates of undiscovered resources across all the assessed deposit types is 9 7 mt cu 5 0 mt ni 1 8 mt zn 0 15 mt pb 0 10 mt mo 86 000 t co 12 000 t pd 5600 t pt 2100 t ag and 1400 t au layered intrusion hosted pge deposits and porphyry cu deposits are estimated to host the largest undiscovered resources containing the majority of the undiscovered cu ni pt pd and mo most of the undiscovered zn is in vms deposits and more than half of the undiscovered au is in orogenic au deposits comparison between discovered and estimated undiscovered resources indicates that practically all mo pt and pd resources and more than half of the au and cu resources in finland exist in undiscovered or poorly known deposits undiscovered resources of ni pb and ag are smaller than the discovered resources most of the total endowment of zn and co appears to be in discovered resources on a global scale the finnish resources are small the discovered resources and estimated total endowment for most of the metals assessed are 1 of the corresponding global identified resources platinum group elements ni co and possibly au might be exceptions to this at least on a european scale as a caveat to the results of this work we stress that a few potentially significant deposit types e g kevitsa and talvivaara types precambrian epithermal au were excluded from the assessments due to the lack of statistically reliable grade and tonnage data

elastic stress transmission and transformation estt by confined liquid a new mechanics for fracture in elastic lithosphere of the earth abstract we report on a new mechanical principle which suggests that a confined liquid in the elastic lithosphere has the potential to transmit a maximum applied compressive stress this stress can be transmitted to the internal contacts between rock and liquid and would then be transformed into a normal compressive stress with tangential tensile stress components during this process both effective compressive normal stress and tensile tangential stresses arise along the liquid rock contact the minimum effective tensile tangential stress causes the surrounding rock to rupture liquid driven fracture initiates at the point along the rock liquid boundary where the maximum compressive stress is applied and propagates along a plane that is perpendicular to the minimum effective tensile tangential stress and also is perpendicular to the minimum principal stress liquid driven fractures and dikes propagate along the axes of cylindrical zones that are perpendicular to the minimum compressive principal stress in rocks in non tectonic regions the minimum depth for liquid driven fracture which is induced by a spherical confined liquid and an isolated magma chamber in the elastic lithosphere ranges from 2 to 6 km whereas dikes with hemi cylinder shaped ends propagate upwards closer to the surface under gravity transmission of pumping pressure i e the pressure differences on the underside of a dike that is connected with a chamber from the source magma chamber to intermediate and shallow chambers increases liquid pressure and also the effective tensile tangential stress and therefore leads to new fractures and dike formation and to upwards transport of magmas that have stagnated in the intermediate chamber tectonic stress alters local stress fields in the surrounding country rocks and therefore synchronously varies the local effective tensile tangential stress and the nature and geometry of the liquid driven fractures

3d subduction dynamics a first order parameter of the transition from copper to gold rich deposits in the eastern mediterranean region the natural variability of geometry and dynamics of subduction zones leads to a variety of mantle and crustal processes that may influence the genesis of ore deposits in the overriding plate these complex interactions cannot be fully represented by two dimensional 2d models but require that the spatial and temporal evolution of ore deposits be examined in a detailed 3d tectonic framework we compare and discuss the geodynamic and metallogenic evolution of the eastern mediterranean subduction zone since the late cretaceous by integrating a newly compiled metallogenic database with a recent kinematic reconstruction model the resulting paleotec tonic maps identify 1 a late cretaceous cu rich metallogenic period with large deposits formed above a linear and stable subduction zone that produced large amounts of potentially fertile magmas in a narrow magmatic arc and 2 a late eocene miocene pb zn followed by au rich metallogenic period with generally smaller deposits spread over a wide back arc basin that was opened due to subduction retreat and lateral slab tearing supported by high resolution numerical modeling the proposed dynamic arc and back arc metallogenic models emphasize 1 the influence of 3d slab dynamics and associated asthenospheric flow on ore distribution in space and time and 2 the importance of exhuming metamorphic domes in extensional back arc setting to focus metal bearing fluid circulations these models differ from collision and post collision models and may be valid on the western and eastern terminations of the whole tethyan orogenic belt i e mediterranean and southeast asia where fast 3d subduction dynamics has influenced the geodynamic and metallogenic evolution of the overriding plate

a biogeochemical influence on the secular distribution of orogenic gold orogenic gold deposits are unevenly distributed in geologic time the richest period of orogenic gold deposit formation was the phanerozoic which followed a 1 b y period of relatively meager deposit generation during the proterozoic this proterozoic low gold period developed despite continent building episodes which should have been appropriate for orogenic gold genesis here a brief review of the changes in global geochemistry brought on by evolving interactions between plate tectonics and the biosphere is conducted before the consequences for gold uptake into sedimentary pyrite are discussed it is suggested that the extensive oxygenation of the deep oceans during the second great oxidation event over the period 635 to 510 ma produced conditions where gold was soluble in the deep oceans from that point on regions where bacterial sulfate reduction drove formation of sedimentary pyrite also destabilized this soluble gold promoting its uptake into pyrite and allowing formation of metallogenically enhanced sedimentary sequences these sediments would have become ideal source rocks for gold deposits during subsequent collisional tectonics and metamorphism this biogenic influence on source region enhancement may explain the association during the phanerozoic eon between some of the world s most gold productive regions and sedimentary sequences that contain pyritic carbonaceous rocks

surficial patterns of debris flow deposition on alluvial fans in death valley ca using airborne laser swath mapping data debris flows are a common event in mountainous environments they often possess the greatest potential for destruction of property and loss of lives in these regions delimiting the spatial extent of potential damage from debris flows relies on detailed studies of the location of depositional zones current research indicates debris flow fans have two distinct depositional zones however the two zones were derived from studies containing detailed analyses of only a few fans high resolution airborne laser swath mapping alsm data is used to calculate profile curvature and surface gradient on 19 debris flow fans on the eastern side of death valley the relationship between these parameters is assessed to 1 identify if debris flow fans are accurately represented by two depositional zones and 2 to assess how these terrain parameters relate to one another at the individual fan scale the results show at least three zones of deposition exist within the sampled fans these zones do not hold consistent when individual fan morphometry is analyzed in conjunction with localized fan surface gradients fans with consistently shallower gradients exhibit numerous depositional zones with more subtle changes in profile curvature steeper gradient fans exhibit significantly fewer zones with more pronounced local changes in profile curvature the surface complexity of debris flow fans is evident from these analyses and must be accounted for in any type of hazard studies related to these features

application of self organizing map and srtm data to characterize yardangs in the lut desert iran abstract yardangs an exclusive landform due to intensive wind erosion cover a large area in the hyper arid lut desert of iran this paper presents a new approach using self organizing map som as unsupervised algorithm of artificial neural networks for analysis and characterization of yardangs nowadays the shuttle radar topography mission srtm with 3 arc sec data approximately 90 m resolution and nearly world wide coverage provides uniform good quality data the srtm 3 arc sec data were re projected to a 90 m utm grid bivariate quadratic surfaces with moving window size of 5 5 were fitted to this dem the first derivative slope steepness and the second derivatives minimum maximum curvature and cross sectional curvatures were calculated as geomorphometric parameters used as input to the soms 42 soms with different learning parameter settings e g initial and final radius number of iterations and the effect of random initial weights on average quantization error were investigated a som with a low average quantization error 0 1040 was used for further analysis feature space analysis morphometric signatures three dimensional inspection auxiliary data like landsat etm and high resolution satellite imagery from quickbird facilitated the assignment of semantic meaning to the output classes in terms of geomorphometric features results are provided in a geographic information system as thematic maps of landform entities based on form and slope e g yardangs ridge corridors valley or planar areas the results showed that all yardangs and corridors were clearly recognized and classified by this method when their width was larger than the dem resolution but became unrecognizable if their width is much smaller than the grid resolution the identified yardangs and corridors are aligned nnw sse parallel to the prevailing direction of the strong local 120 days wind and cover about 31 and 42 of the study area respectively the results demonstrate that som is a very efficient tool for analyzing aeolian landforms in hyper arid environments that provides very useful information for terrain feature analysis in remote regions

road map to mineral supply access to metals and minerals is restricted mostly by geopolitical constraints and not by a shortage of mineable deposits in the face of rising demand a full inventory of these commodities in the earth s crust as well as in recyclable waste is urgently required

earth s copper resources estimated from tectonic diffusion of porphyry copper deposits improved estimates of global mineral endowments are relevant to issues ranging from strategic planning to global geochemical cycling we have used a time space model for the tectonic migration of porphyry copper deposits vertically through the crust to calculate earth s endowment of copper in mineral deposits the model relies only on knowledge of numbers and ages of porphyry copper deposits earth s most widespread and important source of copper in order to estimate numbers of eroded and preserved deposits in the crust model results indicate that 125 895 porphyry copper deposits were formed during phanerozoic time that only 47 789 of these remain at various crustal depths and that these contain 1 7 1011 tonnes t of copper assuming that other types of copper deposits behave similarly in the crust and have abundances proportional to their current global production yields an estimate of 3 1011 t for total global copper resources at all levels in earth s crust thus 0 25 of the copper in the crust has been concentrated into deposits through phanerozoic time and about two thirds of this has been recycled by uplift and erosion the amount of copper in deposits above 3 3 km a likely limit of future mining could supply current world mine production for 5500 yr thus quantifying the highly unusual and nonrenewable nature of mineral deposits

the role of exhumation in the temporal distribution of ore deposits we show here that the temporal age frequency distribution of ore deposits is controlled largely by exhumation the combination of burial uplift and erosion that exposes subsurface rocks and ore deposits exhumation rates calculated from modal ages and emplacement depths for epithermal porphyry copper and orogenic gold deposits of phanerozoic age are 167 158 and 63 m m y respectively these rates agree with rates estimated for continent scale terranes by numerous independent methods thus the scarcity of precambrian epithermal and porphyry copper deposits is probably due to their removal by exhumation archean and pale oproterozoic orogenic gold deposits are more abundant than indicated by the exhumation record of their phanerozoic counterparts suggesting that the precambrian deposits formed in greater numbers recognition of the pivotal role of exhumation requires that the temporal distribution of ore deposits be corrected for this effect before it can be used as an indicator of large scale changes in earth history

global rates of geologic cycling tectonic diffusion of upper crustal lithosomes abstractage frequency distributions of various rock types now exposed at earth s surface primarily reflect characteristic crustal depths at which they originate and the cumulative influence of vertical tectonic movements that displace them abundances of mid to upper crustal lithosomes increase rapidly to some modal age and then gradually decrease with increasing age paucity of exposures younger than the modal age reflects an intrinsic interval of geologic time needed for tectonic movements to exhume rock units while increasing rarity of exposures older than the modal age reflects the overall dispersion uplift and erosion subsidence and burial from initial lithosome positions relative to earth s surface we develop a random walk model that describes the geologic cycling of crustal rock as a tectonically driven diffusive system because at a globally averaged spatial and temporal scale tectonic subsidence burial and uplift erosion are essentially random processes from this we produce solutions to

geochemistry of late metamorphic hydrothermal alteration and graphitisation of host rock macraes gold mine otago schist new zealand abstract the macraes gold deposit in the otago schist new zealand formed during late metamorphic fluid flow through a lower greenschist facies shear zone mineralisation occurred near to the brittle ductile transition at about 300 c large volumes of host rock in a shear zone up to 120 m thick have been hydrothermally altered by this fluid activity most alteration is not structurally controlled apart from proximity to the shear zone ductile and brittle microshears traverse the most mineralised rocks and some structural control of fluid flow occurred as well fluid flow was slow similar to that in metamorphic rocks mm year and diffusion through interconnected fluid was a significant chemical process localised extensional hydrofractures m scale are filled with mineralised quartz most alteration of the host rocks was isochemical with respect to the lithophile elements and mineralised rocks have been variably enriched in as au sb w mo and bi but not co or cd addition of sulphur has occurred to both host rocks and mineralised rocks up to 1 wt above a background of 0 1 wt host rock sulphur is mainly pyritic and is not structurally controlled mineralised rocks have pyrite and arsenopyrite along microshears pyrite chalcopyrite sphalerite and galena have formed from sulphidation of silicates with no addition of metals graphite has been added to mineralised rocks along microshears up to 3 wt locally above a background of 0 1 wt noncarbonate carbon graphite deposition may have occurred as a result of mixing of two fluids water methane and water carbon dioxide graphitisation and sulphidation reactions released low d water which accumulated in the slow moving mineralising fluid distinction between this low d reaction water and meteoric water incursion is difficult

tectonism and exhumation in convergent margin orogens insights from ore deposits abstract three widespread and abundant types of ore deposits epithermal silver gold ag au porphyry copper cu and orogenic gold au form by hydrothermal activity during tectonic convergence along continental margins and their preservation provides new insights into rates of those processes that form and destroy ore deposits as well as overlying rock ages for each of the three deposit types define lognormal age frequency distributions that are nearly identical in form but differ in their modal ages epithermal ag au porphyry cu and orogenic au deposits exhibit age modes at 3 11 and 199 ma respectively these ore types form at depths of 0 5 1 9 and 10 km respectively such that modal age increases with depth of ore emplacement qualitatively the dearth of deposits younger than their modal age reflects the fact that ore deposits form at depth within the crust and time is required for exhumation to expose them continued erosion serves to destroy ore bodies giving rise to fewer deposits

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

interpretation of nisyros volcanic terrain using land surface parameters generated from the aster global digital elevation model abstract to model the morphotectonic evolution of nisyros stratovolcano in the aegean volcanic arc 36 35 n 27 10 e a 30 m resolution aster gdem was used nisyros is characterized by a relative pristine volcanic terrain elevation slope and aspect images the corresponding frequency distributions and rose diagrams enabled the geomorphometric analysis of nisyros revealing the major geomorphological structures that are associated to both endogenetic and exogenetic processes acting on the island either new or previously reported in the literature new elements include the number loci of issue relative age ogive structures of the voluminous precalderan nikia flows and their contact relationships with the avlaki flows the tectonic control fine feature morphology and flow paths of lavas and smaller domes associated with the main postcalderan domes become visually apparent particularities of the hydrographic network accentuate and bring forward non mapped radial faults intense landslide scarring and the volcanic stratigraphy of the intact units were revealed in the northeastern quadrant of nisyros major new volcano tectonic features include the division of the island into three northwesterly trending sectors and the dipping of nisyros towards the southeast as a result of segmentation by two major ring faults the kos ring fault krf and perigussa ring trapdoor fault prf which represent ring faults of the kos sagging caldera the aster gdem has provided suitable thematic information content in the geomorphometric analysis of nisyros and therefore it offers a reconnaissance tool in the geomorphological analysis of a volcanic landscape

round hill shear zone hosted gold deposit macraes flat otago new zealand evidence of a magmatic ore fluid the 0 8 moz round hill shear zone hosted gold deposit is one of several located on or near the hyde macraes shear zone macraes flat new zealand field relationships show stockwork veins are the oldest part of the hydrothermal system followed by flat and ramp veins hanging wall shear veins formed early but have been modified by late deformation fluid inclusion microthermometric results for dominant type i inclusions show that flat and ramp veins have the same average wt percent nacl equiv values 2 2 0 6 and were precipitated from the same fluid salinity data for these veins overlap with those from hanging wall veins average 1 3 0 3 and stockwork veins 1 6 0 6 for vein margins 0 9 0 3 for vein centers although both of the latter trend toward lower overall wt percent nacl equiv values suggesting mixing between relatively dilute and more saline end members all of the above veins have similar temperatures of homogenization t h ranging between 110 and 188 c fluid inclusion trapping temperatures are considered to be 300 c equating to a 10 km depth of formation carbon dioxide dissolved in the hydrothermal fluid is responsible for up to one third of fluid inclusion apparent salinities stockwork and hanging wall veins thus have true salinities of 1 wt percent nacl equiv 0 17 molal and flat and ramp veins have true salinities of fluid inclusion volatiles from round hill and other macraes deposits are dominated by h 2 o 99 02 99 69 mol with lesser co 2 0 14 0 76 mol n 2 0 03 0 32 mol and ch 4 0 06 0 17 mol noticeable concentrations of hydrocarbons occur in many of the samples fluid inclusion cation and anion data show few components of relatively low concentration are dissolved in the hydrothermal fluid consistent with co 2 corrected microthermometric measurements a range in fluid inclusion d h 2 o values obtained for the round hill deposit is coincident with the different vein types and also indicates mixing between two fluids one fluid is considered to be o isotope shifted meteoric water as trapped by the early stockwork veins and has the lowest d h 2 o values of 80 per mil the other fluid is represented by flat and or ramp and hanging wall veins that have d h 2 o values up to 40 per mil the macraes d h 2 o data show a trend toward the magmatic water end member for geothermal systems associated with convergent plate boundaries and are consistent with a 25 to 50 percent magmatic component in the macraes hydrothermal system

mapping lithology of the sarfartoq carbonatite complex southern west greenland using hymap imaging spectrometer data the sarfartoq carbonatite complex occurs in the southern west greenland in a transition zone between archaean gneiss complex to the south and a proterozoic mobile belt to the north the sarfartoq carbonatite complex consists of a core zone composed of dolomite carbonatite and minor sovite calcite carbonatite surrounded by a fenite zone and a marginal zone of gneisses frequently altered due to hydrothermal activity high spatial and spectral resolution imaging spectrometer data recorded by the hymap imaging system were used to map lithology of the sarfartoq carbonatite complex a careful analysis of the spectral reflectance properties of the carbonatite lithology preceded the hymap data analysis stage the spectral reflectance measurements showed that the various lithologic units including dolomite carbonatite sovite fenite and the marginal alteration zone have distinct spectral reflectance characteristics the analysis of the hymap data was based on an unsupervised clustering algorithm the self organizing maps som for the mapping of the main lithology and a hierarchical tree for the mapping of sparsely occurring sovite rocks spectral mixture analysis was applied to map fractional abundances and compare with the som results the resulting lithological map shows the spatial distribution of dolomite carbonatite sovite fenite with abundant carbonatite dykes representing the outer core of the carbonatite complex fenite and hematized gneiss marginal alteration zone the results compare well with the field data collected for the assessment of the mapping accuracy and due to the spatially contiguous nature of the hyperspectral data could be used to better map the outcropping carbonatite lithology the spectral reflectance measurements and the mapping results provide information of petrological importance for the carbonatite core zone

mineral precipitation in the quartz reefs of the bendigo gold deposit victoria australia gold precipitation at bendigo postdates cleavage development and was initiated during folding increased during a reverse faulting stage in bedding parallel quartz veins and culminated in quartz reefs associated with a strike slip faulting event some gold was remobilized along carbonate rich cataclasites associated with later brittle faults understanding the paragenesis of the sulfide and gangue minerals associated with the auriferous quartz reefs is critical to unraveling the cycle of ore genesis from source to sink in this study a petrographic approach closely tied to macroscopic structural observations along with stable isotope and fluid inclusion analyses places constraints on the relative timing of gold mineralization with respect to deformation early sulfide assemblages in bedding and cleavage parallel veins are dominated by pyrite pyrrhotite siderite and are free of visible gold later assemblages in reactivated bedding parallel veins and other fold related veins are characterized by the presence of arsenopyrite ankerite gold fault related veins and the massive quartz reefs are rich in sphalerite and galena with associated gold but lack pyrrhotite small amounts of late stage antimony bearing minerals occur in many vein types and postdate the precipitation of gold decreasing temperature and increasing sulfur activity controlled successively younger sulfide assemblages in the quartz veins stable oxygen isotope data show that quartz from all vein types 18 o 15 9 19 0 homogenized with the host rocks whereas carbon 13 c 14 0 to 4 1 and oxygen 18 o 4 5 24 0 in carbonate have a wider range in values that is interpreted to be a function of decreasing temperature this corresponds with early siderite pyrrhotite and anhedral pyrite and with later ankerite and ferroan dolomite associated with arsenopyrite galena and euhedral pyrite that are crosscut by calcite veins fluid inclusions in quartz veins are predominantly composed of water with carbon dioxide with smaller proportions of nitrogen and methane particularly in the later strike slip faults the sporadic occurrence of methane suggests that there was an open fluid system with incoming fluids from an external source mixing with those in the host rocks although several recent studies have argued that synsedimentary preenrichment may be a significant factor determining the size and distribution of gold in the bendigo orogenic gold deposits we believe there is little direct or deposit scale evidence for a relationship between original metal content in the host rock metasedimentary rocks and the distribution of the gold mineralization in specific structural sites it is suggested that deep seated faults act as conduits for fluid flow and the source for the gold at bendigo the gold is externally derived from deeply sourced auriferous metamorphic fluids that have been focused into discrete structural sites

ore deposits in an evolving earth an introduction ore deposits form by a variety of natural processes that concentrate elements into a small volume that can be economically mined their type character and abundance reflect the environment in which they formed and thus they preserve key evidence for the evolution of magmatic and tectonic processes the state of the atmosphere and hydrosphere and the evolution of life over geological time this volume presents 13 papers on topical subjects in ore deposit research viewed in the context of earth evolution these diverse yet interlinked papers cover topics including controls on the temporal and spatial distribution of ore deposits the sources of fluid gold and other components in orogenic gold deposits the degree of oxygenation in the neoproterozoic ocean bacterial immobilization of gold in the semi arid near surface environment and mineral resources for the future including issues of resource estimation sustainability of supply and the criticality of certain elements to society

deep ocean mineral deposits as a source of critical metals for high and green technology applications comparison with land based resources abstract ferromanganese fe mn crusts are strongly enriched relative to the earth s lithosphere in many rare and critical metals including co te mo bi pt w zr nb y and rare earth elements rees fe mn nodules are strongly enriched in ni cu co mo zr li y and rees compared to fe mn crusts nodules are more enriched in ni cu and li with subequal amounts of mo and crusts are more enriched in the other metals the metal ions and complexes in seawater are sorbed onto the two major host phases feo oh with a positively charged surface and mno 2 with a negatively charged surface metals are also derived from diagenetically modified sediment pore fluids and incorporated into most nodules seafloor massive sulfides sms especially those in arc and back arc settings can also be enriched in rare metals and metalloids such as cd ga ge in as sb and se metal grades for the elements of economic interest in sms cu zn au ag are much greater than those in land based volcanogenic massive sulfides however their tonnage throughout the global ocean is poorly known and grade tonnage comparisons with land based deposits would be premature the clarion clipperton fe mn nodule zone ccz in the ne pacific and the prime fe mn crust zone pcz in the central pacific are the areas of greatest economic interest for nodules and crusts and grades and tonnages for those areas are moderately well known we compare the grades and tonnages of nodules and crusts in those two areas with the global terrestrial reserves and resources nodules in the ccz have more tl 6000 times mn te ni co and y than the entire global terrestrial reserve base for those metals the ccz nodules also contain significant amounts of cu mo w li nb and rare earth oxides reo compared to the global land based reserves fe mn crusts in the pcz have significantly more tl 1700 times te 10 times more co and y than the entire terrestrial reserve base other metals of significance in the pcz crusts relative to the total global land based reserves are bi reo nb and w ccz nodules and pcz crusts are also compared with the two largest existing land based ree mines bayan obo in china and mountain pass in the usa the land based deposits are higher grade but lower tonnage deposits notably both land based deposits have

quantitative identification of metallogenic epochs and provinces application to phanerozoic porphyry copper deposits the terms metallogenic epoch and metallogenic province have been widely used for many years but are so poorly defined that most of earth s surface and geologic history has been designated a metallogenic feature of some sort we propose defining metallogenic epoch and metallogenic province as those time intervals of earth history and regions of earth respectively which contain a significantly greater number of deposits or larger tonnage of a specific deposit type than would have resulted from average rates of mineralization that have occurred over phanerozoic time here we evaluate the application of this definition to porphyry copper deposits metallogenic epochs for porphyry copper deposits can be identified by comparison between a real earth age frequency distribution based on ages of known deposits and a model age frequency distribution that simulates the formation of porphyry copper deposits and their subsequent vertical uplift and or subsidence relative to the earth s surface after they form the latter represents the age frequency distribution that would be expected if rates of mineralization did not deviate from the phanerozoic average and is determined by least squared minimization of differences between model and real earth age frequency values metallogenic epochs are defined as duration normalized time periods in which real earth numbers or sizes of deposits differ significantly from the model value of average numbers or sizes of deposits that have formed over the past 545 m y of earth history eight of the 80 phanerozoic stages constituting 5 5 percent of this time interval meet this definition these include the upper eocene paleocene all 3 stages lower triassic middle pennsylvanian upper silurian and upper ordovician metallogenically impoverished stages occurred during the upper cretaceous and the upper oligocene time intervals of deposit enrichment and scarcity exhibit little correlation with records of widely known global geologic features or processes at a more regional scale however mineralization along south and central america slightly postdated times of enhanced production of east pacific sea floor and many paleocene deposits underwent enhanced preservation beneath younger rocks metallogenic provinces appear to be recognizable through use of the power law relationship between the duration normalized spatial density of real earth deposits and the size of areas that host the deposits comparison of real earth spatial densities to a best fit line to data for all areas containing deposits allows recognition of areas that have greater spatial densities our analysis suggests that variation in the distribution of porphyry copper deposits in both time and space are largely unpredictable at even epoch and regional scales of consideration respectively and indicate that the presence or absence of deposits in one time interval or region does not effectively predict the abundance of other deposits in other time intervals or geographic localities this conclusion however does not preclude the importance of geologic controls on either deposits or metallogenic features rather it strongly affirms the widely accepted fact that the distribution of ore deposits and metallogenic features is due to a large number of geologic factors and processes that vary from place to place and time to time more rigorous definition of metallogenic epochs and provinces and more detailed geologic study at the local scale will lead to a better understanding of those processes that account for statistically anomalous concentrations of mineralization in both time and space

geomorphic controls on the origin and location of the tolman ranch ventifact site park county wyoming usa ventifaction on the tolman ranch terrace surface in northwest wyoming is controlled by factors other than intensity and direction of regional winds disintegration of granitic boulders in the terrace gravel causes large fine grained mafic boulders to be preferentially concentrated on the terrrace tread these boulders rise above a critical height needed for ventifaction quartz rich sand introduced into the system by weathering is used in the abrasive process while it is simultaneously removed from the system by topographically enhanced winds pronounced ventifaction in this area occurs only where granite disintegration and topography are properly combined to maximize abrasive work ventifaction in this setting may have been continuous or intermittent since deposition of the gravel thus features produced have no paleoclimatic implications

lithological mapping of the troodos ophiolite cyprus using airborne lidar topographic data traditional field based lithological mapping can be a time consuming costly and challenging endeavour when large areas need to be investigated where terrain is remote and difficult to access and where the geology is highly variable over short distances consequently rock units are often mapped at coarse scales resulting in lithological maps that have generalised contacts which in many cases are inaccurately located remote sensing data such as aerial photographs and satellite imagery are commonly incorporated into geological mapping programmes to obtain geological information that is best revealed by overhead perspectives however spatial and spectral limitations of the imagery and dense vegetation cover can limit the utility of traditional remote sensing products the advent of airborne light detection and ranging lidar as a remote sensing tool offers the potential to provide a novel solution to these problems because accurate and high resolution topographic data can be acquired in either forested or non forested terrain allowing discrimination of individual rock types that typically have distinct topographic characteristics this study assesses the efficacy of airborne lidar as a tool for detailed lithological mapping in the upper section of the troodos ophiolite cyprus morphometric variables including slope curvature and surface roughness were derived from a 4 m digital terrain model in order to quantify the topographic characteristics of four principal lithologies found in the area an artificial neural network the kohonen self organizing map was then employed to classify the lithological units based upon these variables the algorithm presented here was used to generate a detailed lithological map which defines lithological contacts much more accurately than the best existing geological map in addition a separate map of classification uncertainty highlights potential follow up targets for ground based verification the results of this study demonstrate the significant potential of airborne lidar for lithological discrimination and rapid generation of detailed lithological maps as a contribution to conventional geological mapping programmes

the environmental significance of ventifacts a critical review abstract ventifacts wind abraded clasts or rock surfaces are common features of many terrestrial hot and cold deserts coastal periglacial and mountain environments as well as on mars and have a long history of investigation this review paper discusses some of the main themes in terrestrial ventifact research including their formation and geomorphic controls the varied morphological forms of ventifacts in terrestrial environments and their environmental significance as indicators of past and present wind direction and sediment mobility are critically evaluated future research directions are identified

abundant sulphate in the neoproterozoic ocean implications of constant δ34s of barite in the aberfeldy sedex deposits scottish dalradian the timing and extent of ocean oxygenation is controversial proterozoic sulphur isotope datasets often show marked fluctuations over small stratigraphic intervals suggesting that oceanic sulphate concentrations were much lower than modern values a large accumulation of neoproterozoic sulphate 8 million tonnes preserved as stratiform barite rock is located in the grampian highlands near aberfeldy diagenetic metamorphic alteration has caused pronounced 34s variations near bed margins this aside barite throughout the deposits shows a narrow range in 34s mean 36 1 5 we infer that this is representative of contemporaneous seawater sulphate and that 34sseawater was constant during deposition of a stratigraphical thickness 250m of mostly fine grained clastic sediments uniformity of 34sseawater during barite precipitation even in thick 10m beds and with the co occurrence of abundant sulphides incorporating bacteriogenically reduced sulphur implies no limit to availability of seawater sulphate during hydrothermal exhalative events our data combined with previous 34s research on dalradian metasediments suggest a stability abundance and constancy of ocean sulphate in the neoproterozoic this contrasts with isotopic data using trace sulphate in limestones it appears that around the time of the marinoan glaciation c 635 ma the ocean although stratified at least locally comprised a substantial reservoir of sulphate bearing oxygenated seawater

does gold in orogenic deposits come from pyrite in deeply buried carbon rich sediments insight from volatiles in fluid inclusions the origin of volatiles in fluid inclusions was reviewed for testing the involvement at depth of carbonaceous pyritic sedimentary rocks as the source for orogenic gold mineralization fluid inclusions from selected deposits were analyzed by solid probe mass spectrometry fluids are mostly aqueous carbonic with variable amounts of n 2 ch 4 c 2 h 6 ar h 2 s h 2 and he for fluids with ch 4 and c 2 h 6 their ratios c 1 c 2 range from 2 6 to 25 5 indicating that c 2 h 6 is sourced from thermally degraded organic matter proportions of co 2 ch 4 c 2 h 6 and h 2 are highly variable and can be explained by hydrothermal reactions where c 2 h 6 is degraded to co 2 by water consumption such reactions may account for the problematic co 2 rich h 2 o poor fluids associated with some of the richest gold districts conditions needed for c 2 h 6 degradation are also fundamental for forming gold deposits such as hs enriched fluids for carrying gold and local weakly oxidizing conditions for promoting gold precipitation the c 2 h 6 content is recorded in fluids from mesoarchean to cretaceous gold deposits providing support for a general model where fluids and gold were sourced from deeply buried carbon rich and pyrite gold bearing sedimentary rocks

estimating usable resources from historical industry data historical production statistics are used to predict the quantity of remaining usable resources the commodities considered are mercury copper and its byproducts gold and silver and petroleum the production and discovery data are for the united states the results of the study indicate that the cumulative return per unit of effort herein measured as grade of metal ores and discovery rate of recoverable petroleum is proportional to a negative power of total effort expended herein measured as total ore mined and total exploratory wells or footage drilled this power relationship can be extended to some limiting point a lower ore grade or a maximum number of exploratory wells or footage and the apparent quantity of available remaining resource at that limit can be calculated for mercury ore of grades at and above 0 1 percent the remaining usable resource in the united states is calculated to be 54 million kg 1 567 000 flasks for copper ore of grades at and above 0 2 percent the remaining usable copper resource is calculated to be 270 million metric tons 298 million short tons remaining resources of its by products gold and silver are calculated to be 3 656 metric tons 118 million troy ounces and 64 676 metric tons 2 079 million troy ounces respectively the undiscovered recoverable crude oil resource in the conterminous united states at 3 billion feet of additional exploratory drilling is calculated to be nearly 37 6 billion barrels the undiscovered recoverable petroleum resource in the permian basin of western texas and southeastern new mexico at 300 million feet of additional exploratory drilling or 50 000 additional exploratory wells is calculated to be about 6 2 billion boe barrels of oil equivalent

gold in seawater abstract a suite of seawater samples has been analyzed for au by inductively coupled plasma quadrupole mass spectroscopy icpms the recently developed method involves preconcentration by anion exchange followed by flow injection sample introduction into a vg plasmaquad icpms profiles in the atlantic gulf stream northeast pacific and mediterranean are presented in addition the first measurements of au in hydrothermal fluids are reported the measured concentrations of au in the atlantic and northeast pacific 50 150 fmol l are within a factor of 2 3 of recently reported values for pacific waters 1 and nearly three orders of magnitude less than reported in the literature prior to 1988 indicating contamination problems with the earlier data in general au concentrations for atlantic and pacific samples reported here are the same 50 fmol l however differences of up to a factor of 2 between the oceans cannot be ruled out due to large uncertainties associated with the pacific data mediterranean deep waters contain higher concentrations of au 100 150 fmol l this is attributed to proximal aeolian dust and or riverine sources gold is enriched in hydrothermal fluids 10 100 s of pmol l with respect to ambient seawater although the fluxes remain poorly constrained preliminary budget considerations indicate that rivers and hydrothermal venting are the most significant sources of au to the oceans

tectonic evolution of the east junggar terrane evidence from the taheir tectonic window xinjiang china abstract the taheir tectonic window is located at the southern part of the yemaquan magmatic arc in east junggar this paper reports detailed petrology mineral chemistry whole rock and sr nd isotope geochemistry hornblende 40ar 39ar dating in situ zircon u pb dating and hf isotope analyses from igneous and meta igneous rocks from this region our new results show that the taheir tectonic window consists of metamorphic and deformed ordovician volcanic rocks and granitic porphyries ordovician silurian granites and undeformed silurian devonian granitic diorite diorites and rhyolitic porphyries the ordovician volcanic rocks and granitic porphyries and ordovician silurian granites in the taheir tectonic window exhibit distinct features of andean type continental arc such as enrichment in pb k and u depletion in nb p and ti negative eu anomalies high la yb th yb and ta yb values a high proportion of dacite rhyolite and andesite of the calc alkaline series massive contemporary granitic intrusions mixtures of the juvenile material and 2 5 ga crust and extensive crystallization differentiation these ordovician volcanic rocks witnessed a series of tectonic events including burial associated with the intrusion of 454 449 ma granitic porphyries underthrusting and subsidence to a depth in the middle crust associated with the intrusion of 443 432 ma granites the formation of albite hornblende schists hornblende albite quartz leptynites and amphibolites the transformation from continental to continental island arc at approximately 432 ma the exhumation associated with the intrusion of 416 406 ma diorites with geochemical signatures of continental island arc and exhumation and erosion between 398 ma and 390 ma are also identified the arc types that are associated with the taheir tectonic window and its host the yemaquan magmatic arc changed from andean type continental arc to continental island arc after the intra arc rifting that began at 432 ma on the basis of the new evidence the tectonic regime of the east junggar terrane is redefined and a new model is proposed it is suggested that the east junggar terrane is related to the southward subduction of the paleo asian ocean plate beneath the junggar continent in the early paleozoic and later shift to intra oceanic subduction

formation of bedrock cut ventifacts and late holocene coastal zone evolution county donegal ireland abstract wind etched rocks ventifacts at gweebarra bay county donegal northwestern ireland are located 2 m above mean high water springs mhws on a glacially eroded bedrock shore platform 10 m wide 200 m long at mhws prevailing southwesterly winds transport sand across the platform from the adjacent beach ventifacts found on the windward most 20 m of the platform decrease in frequency and degree of wind alteration with distance near the beach ventifacts have two to three wind etched faces facets both linear and serrated keels and are pitted grooved and polished farther from the beach ventifacts are less frequent have fewer facets pits and grooves and show curved keels facets nearest the beach lie perpendicular to prevailing winds but are wind parallel farther away this reflects structural control on the shape and orientation of bedrock blocks protruding into the wind stream nine possible ventifact morphologies are identified on the basis of wind approach angle and dip angl

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

global geologic maps are tectonic speedometers rates of rock cycling from area age frequencies relations among ages and present areas of exposure of volcanic sedimentary plutonic and metamorphic rock units lithosomes record a complex interplay between depths and rates of formation rates of subsequent tectonic subsidence and burial and or rates of uplift and erosion thus they potentially serve as efficient deep time geologic speedometers providing quantitative insight into rates of material transfer among the principal rock reservoirs processes central to the rock cycle areal extents of lithosomes exposed on all continents from two map sources geological survey of canada gsc and the food and agricultural organization fao of the united nations educational scientific and cultural organization unesco indicate that volcanic sedimentary plutonic and metamorphic rocks occupy 8 73 7 and 12 of global exposures respectively plots of area versus age of all mapped rock types display a power law relation where 6 5 of continental area is resurfaced with younger 10 volcanic 90 sedimentary units every million years and where areas of rock exposure decrease by 0 86 for each 1 increase in outcrop age r 2 0 90 area age relations for volcanic and sedimentary lithosomes are similar to the power law distribution defined by all rock units because 81 of mapped area consists of these two lithologies and reflect progressive decrease in amount of exposure with increasing age over the long term continental surfaces are blanketed by new volcanic rocks and sediments at rates of 1 5 and 12 1 10 6 km 2 ma respectively in contrast to power law distributed volcanic and sedimentary rocks that form at the earth9s surface age frequency distributions for plutonic and metamorphic rocks exhibit lognormal relations with modes at ca 154 and 697 ma respectively a dearth of younger exposures of plutonic and metamorphic rocks reflects the fact that these rock types form at depth and some duration of tectonism is therefore required for their exposure increasing modal ages from quaternary for volcanic and sedimentary successions to early mesozoic for intrusive rocks to neoproterozoic for metamorphic rocks demonstrate that greater amounts of geologic time are required for uplift to bring more deeply formed rocks to the earth9s surface the two different age frequency distributions observed for these major rock types a general power law age distribution for volcanic and sedimentary rocks and a lognormal distribution for plutonic and metamorphic rock ages reflect the interplay between depths of formation and mean rates of vertical tectonic displacement age frequency distributions for each of the major rock types are closely replicated by a model that presumes that individual crustal elements behave as a large population of random walks in geologic time and crustal depth and where the processes of surficial erosion associated with tectonic uplift serve to impose an absorbing boundary on this random walk space comparisons between model predicted age frequencies and those apparent in global map data suggest that mean rates of crustal subsidence and uplift are approximately equal in magnitude with mean rates of vertical tectonic diffusion of lithosomes from crustal depths of formation of about half a kilometer per million years rates of uplift and subsidence are strongly dependent on durations of tectonic dispersion lithosome ages however mean rates on the order of hundreds of meters per million years suggested by map age frequencies are the same as would be anticipated on the basis of hundreds of published rates of erosional uplift and exhumation determined by more conventional geochronometers this agreement suggests that geologic maps serve as effective deep time speedometers for the geologic rock cycle

variscan cycling of gold into a global coal reservoir this project is in support of the nerc sos security of supply of critical elements programme under grant ne m010953 1 j johnston and j bowie provided skilled technical help the manuscript benefitted from incisive reviews by n moles y wu carmine and an anonymous reviewer whose advice is much appreciated

application of airborne lidar to mapping seismogenic faults in forested mountainous terrain southeastern alps slovenia results are presented of the first airborne lidar survey ever flown in europe for the purpose of mapping the surface expression of earthquake prone faults detailed topographic images derived from lidar data of the idrija and ravne strike slip faults in nw slovenia reveal geomorphological and structural features that shed light on the overall architecture and kinematic history of both fault systems the 1998 mw 5 6 and 2004 mw 5 2 ravne fault earthquakes and the historically devastating 1511 m 6 8 idrija earthquake indicate that both systems pose a serious seismic hazard in the region because both fault systems occur within forested terrain a tree removal algorithm was applied to the data the resulting images reveal surface scarps and tectonic landforms in unprecedented detail importantly two sites were discovered to be potentially suitable for fault trenching and palaeo seismological analysis this study highlights the potential contribution of lidar surveying in both low relief valley terrain and high relief mountainous terrain to a regional seismic hazard assessment programme geoscientists working in other tectonically active regions of the world where earthquake prone faults are obscured by forest cover would also benefit from lidar maps that have been processed to remove the canopy return and reveal the forest floor topography

resources of gold in phanerozoic epithermal deposits we have estimated earth s endowment of gold in phanerozoic epithermal deposits using a tectonic diffusion model which simulates the emplacement of deposits at a shallow crustal depth and their subsequent vertical tectonic migration in the crust the calculation was calibrated by least squares comparison of a calculated age frequency distribution to the age frequency distribution for 448 epithermal deposits of phanerozoic age results indicate that 17 percent of the epithermal deposits that formed through phanerozoic time remain in the crust today whereas 83 percent have been removed by erosion assuming a similar age distribution for all 1 181 epithermal deposits in our compilation indicates that 307 000 deposits formed throughout phanerozoic time that 63 000 of these remain in the crust and that 244 000 have been eroded grade and tonnage data of gold in 757 epithermal deposits in the compilation have an arithmetic average of 34 7 t and yield an estimate of 2 2 106 t of gold for epithermal deposits remaining in the crust using the model based vertical distribution of deposits remaining in the crust we estimate that epithermal deposits in the upper kilometer of the united states contain 2 9 104 t of gold adjusting for areas of outcropping volcanic rocks in each continent increases our estimate to 4 0 104 t these estimates are similar to the 1 7 104 t gold resource estimated by the u s geological survey using completely different methods several comparisons based on these results provide insights into the efficiency of processes that form epithermal deposits and the outlook for sustainability for instance all of the epithermal deposits that formed through phanerozoic time represent only about 0 03 percent of the gold in the crust only about 0 007 percent of crustal gold remains in epithermal deposits the rest has been eroded and recycled this is consistent with comparisons based on the flux of gold in the taupo volcanic zone which indicate that epithermal deposits trap only 0 1 to 0 2 percent of the gold that moves through convergent margin hydrothermal systems epithermal gold deposits that remain in the crust can supply current production from them for 1 400 to 5 000 years depending on success of exploration and depth of mining finally we are consuming gold from epithermal deposits about 17 000 times faster than earth is replenishing the supply

origin and geochemistry of the chapada cu au deposit goias brazil a metamorphosed wall rock porphyry copper deposit chapada is a large 134 x 10 6 metric tons low grade 0 44 cu 0 35 g metric tons au disseminated chalcopyrite pyrite deposit within a geologically complex pan african mobile belt in central goias state brazil mineralization is hosted largely by subhorizontal biotite schist with lesser amphibolite muscovite schist and feldspathic quartzite a foliated diorite is separated from the deposit by a shallow diping 40 m thick mylonite zone discontinuous lenses of mica amphibole schists within the deposit are considered hydrothermally altered equivalents of this diorite which have intruded geochemically related wall rocks such as the locally porphyritic amphibolite seen in the deposit previous assignment of a mid proterozoic age to chapada must be revised in view of our rb sr whole rock isochron which yields a pan african age of 561 or 9 m y for the host schists rare earth element patterns of chapada rocks have steep negative slopes with no eu anomalies petrochemical data and an 87 sr 86 sr initial i value of 0 70414 or 0 00005 indicate chapada host schists and diorite are similar to peraluminous calc alkaline andesites of magmatic arc affiliation mineralization occurred prior to upper amphibolite grade regional metamorphism at 532 or 1 m y as indicated by an rb sr mineral isochron as well as by sulfides paralleling foliation sulfide inclusions in metamorphic minerals and the presence of gahnite and zincian staurolite estimated conditions of peak metamorphism were 650 degrees or 20 degrees c 7 5 or 1 kb log f sub o 2 13 to 14 log f sub s 2 0 5 to 0 5 and a sub h 2 o 0 85 mineral zonations in and around chapada include a central magnetite rich zone a pyritic shell and peripheral pyrrhotite and sphene these mineral zonations and x fe of biotites reflect a gross zonation in oxygen and sulfur fugacities from high within the deposit to relatively low in peripheral rocks pyrite and chalcopyrite have delta 34 s values of 0 4 to 0 6 per mil k 2 o is enriched and cao and na 2 o are depleted in the host schists relative to the unaltered diorite within the deposit several major element abundances describe a symmetrical pattern about the center of the deposit the tonnage grade and ore mineralogy of the chapada deposit are comparable to those reported from porphyry copper deposits of island arc settings much of the gangue mineralogy at chapada is also typical of porphyry deposits and has survived metamorphism whereas the more aluminous original gangue minerals are now represented by such metamorphic minerals as kyanite and staurolite these similarities combined with the textural zoning and geochemical characteristics of the host rocks suggest that chapada is a metamorphosed porphyry copper deposit which hosts mineralization in both wall rocks and intrusive rocks

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

the massawa gold deposit eastern senegal west africa an orogenic gold deposit sourced from magmatically derived fluids the massawa gold project is situated on the senegalese side of the highly prospective productive palaeo proterozoic birimian kedougou kenieba inlier which hosts several world class orogenic gold deposits districts in western mali e g loulo and sadiola the massawa ore body has a strike length of at least 4 km and a current resource of 3 61 moz at a grade of 2 8 g t 1 the ore body is structurally controlled and located within a package of low grade regionally metamorphosed volcaniclastic sediments agglomerates tuffs and ash tuffs quartz feldspar and lithic wackes carbonaceous shales hydrothermal breccias and gabbro and porphyry sills these rocks have undergone pervasive silica alteration followed by a sericite ankerite chlorite alteration event related to mineralization two major styles of mineralization are recognized at massawa from field and laboratory studies the first stage of sulphide au mineralization is associated with disseminated arsenopyrite pyrite which follows shear zones in the sedimentary and volcano sedimentary host rocks the second stage consists of quartz stibnite tetrahedrite veining distinguished by coarse visible gold and represents a late stage overprint on the primary mineralization the two stages of gold mineralization are separated by a phase of quartz molybdenite veining a distinctive base metal trace assemblage is linked to stibnite formation including multiple sb phases such as chalcostibite zinkenite roshchinite aurostibite jamesonite and robinsonite secondary ion mass spectroscopy based gold deportment data indicate that up to 90 of stage 1 gold is held as a solid solution within either arsenopyrite or arsenian pyrite stable isotope data yield 34ssulphide values of between 0 and 4 1 and 18oh2o values of 5 5 10 9 for all stages of mineralization suggesting a magmatic fluid influence this is consistent with field data that suggest that mineralization is synchronous with emplacement of a sequence of concordant felsic sheets that mineralization occurred at shallow 6 km depths is suggested both by the presence of stibnite and by fluid inclusion studies low temperature homogenization temperatures between 150 c and 230 c h2o nacl fluids 6 wt nacl equiv and coeval co2 ch4 inclusions observed in both phases of mineralization indicate trapping conditions of 220 315 c at 1 1 65 kbar a combination of phase petrology fluid inclusion and stable isotope data suggests deposition of gold from low salinity magmatic fluids most probably released from felsic rocks similar to those emplaced into the massawa sequence during mineralization

tectonic environments of south american porphyry copper magmatism through time revealed by spatiotemporal data mining porphyry ore deposits are known to be associated with arc magmatism on the overriding plate at subduction zones while general mechanisms for driving magmatism are well established specific subduction related parameters linking episodes of ore deposit formation to specific tectonic environments have only been qualitatively inferred and have not been formally tested we develop a four dimensional approach to reconstruct age dated ore deposits with the aim of isolating the tectono magmatic parameters leading to the formation of copper deposits during subduction we use a plate tectonic model with continuously closing plate boundaries combined with reconstructions of the spatio temporal distribution of the ocean floor including subducted portions of the nazca farallon plates the models compute convergence rates and directions as well as the age of the downgoing plate through time to identify and quantify tectonic parameters that are robust predictors of andean porphyry copper magmatism and ore deposit formation we test two alternative supervised machine learning methods the random forest rf ensemble and support vector machines svm we find that a combination of rapid convergence rates 100 km myr subduction obliquity of 15 a subducting plate age between 25 70 myr old and a location far from the subducting trench boundary 2000 km represent favorable conditions for porphyry magmatism and related ore deposits to occur these parameters are linked to the availability of oceanic sediments the changing small scale convection around the subduction zone and the availability of the partial melt in the mantle wedge when coupled these parameters could influence the genesis and exhumation of porphyry copper deposits

experimental silicate mineral melt partition coefficients for beryllium and the crustal be cycle from migmatite to pegmatite partition coefficients dbemineral melt for beryllium between hydrous granitic melt and alkali feldspars plagioclase feldspars quartz dark mica and white mica were determined by experiment at 200 mpa h2o as a function of temperature 650 900 c activity of be in melt trace levels to beryl saturation bulk composition and thermal run direction at trace levels be is compatible in plagioclase of an31 1 84 at 700 c and muscovite 1 35 at 700 c but incompatible in biotite 0 39 0 54 from 650 800 c alkali feldspar 0 38 0 19 from 680 850 c quartz 0 24 at 800 c and albite 0 10 at 750 c the partition coefficients are different at saturation of the melt in beryl lower in the case of plagioclase of an31 0 89 at 700 c muscovite 0 87 at 700 c biotite 0 18 0 08 from 675 800 c alkali feldspar 0 18 0 14 from 680 700 c and quartz 0 17 0 08 from 750 800 c but higher in the case of albite 0 37 at 750 c with other data sources these new partition coefficients were utilized to track first the distribution of be between aluminous quartzofeldspathic source rocks and their anatectic melts and second the dispersion or concentration of be in melt through igneous crystal fractionation of different magma types e g s type i type up to beryl saturated granitic pegmatites and finally into their hydrothermal aureoles among the rock forming minerals cordierite calcic oligoclase and muscovite in this order control the fate of be because of the compatibility of be in these phases in general beryl bearing pegmatites can arise only after extended crystal fractionation of large magma batches to f fraction of melt remaining 0 05 granitic magmas that originate from cordierite bearing protoliths or that contain large modal quantities of calcic oligoclase will not achieve beryl saturation at any point in their evolution

a climate signal in exhumation patterns revealed by porphyry copper deposits porphyry copper deposits are emplaced at a fixed crustal depth in convergent tectonic settings the age and distribution of deposits exposed at the surface suggest that mountain exhumation is influenced by precipitation rates

identifying structural trend with fractal dimension and topography a digital elevation model dem derived from light imaging detection and ranging lidar altimetry data is used to investigate the fractal characteristics and structural trends of a topographic surface the study area is located on the southeastern rim of the sudbury basin a meteorite impact feature in ontario canada visual interpretation and statistical analysis of fractal dimension d indicate that the geological units in the study area are characterized by statistically different distributions of d in addition the landscape exhibits two predominant aspect directions 127 and 290 or se and nw high values of d correspond to these predominant aspect directions topographic ridgelines exhibit a ne sw trend which is perpendicular to that of the highest fractal dimensions and the predominant aspect directions it is suggested that these ridgelines are topographic expressions of tectonic fabrics present in the various geological units genesis of the tectonic fabric is related to the nw se directed shortening of the sudbury basin impact crater

metal source and tectonic setting of iron oxide copper gold iocg deposits evidence from an in situ nd isotope study of titanite from norrbotten sweden titanite occurs as a widespread accessory phase in mineralized zones and alteration associated with iron oxide copper gold iocg and iron oxide apatite ioa deposits of norrbotten county sweden and is a major host of the ree in these deposits in situ analyses of sm nd isotope ratios in titanites previously analysed for u pb geochronology and trace element composition confirms previous interpretations of grain scale isotopic heterogeneity initial nd isotope ratios expressed relative to chur range from 3 to 8 in ioa deposits from 1 to 9 in iocg deposits and from 2 to 4 in the most cu rich deformed iocg deposits of the nautanen deformation zone within individual ioa deposits at valkommen malmberget from 1 4 to 5 7 in grain cores and 7 2 to 8 2 in grain rims rim at gruvberget and from 3 0 to 6 0 in grain cores and from 5 8 to 7 1 in grain rims at luossavaara in iocg deposits at rakkurijarvi iocg dpeosits at nautanen from 1 3 to 2 3 these values are consistent with the derivation of the ree and potentially economically enriched metals from the local volcanic sequence either via granitic melts or directly by leaching by metasomatic fluids the most cu rich deposits reflect the involvement of more basic protoliths the age distribution of these deposits suggest ioa deposit formation during the collisional phase of the svecofennian orogeny 1 9 1 8 ga and iocg mineralization during this phase and during post orogenic collapse 1 8 1 7 ga whilst model ages indicate the ultimate enrichment of the continental crust in these metals during pre collisional extensional and subduction related basic magmatism these processes underscore the importance of continental cycles both in producing the preserved geological record of orogenic ore deposition and in the generation of fertile continental crust from which metals can be mobilised by subsequent events nd varies relative to chur from 3 1 to 4 0 nd varies from 6 1 to 7 1 and in deformed iocg dpeosits at nautanen from 1 3 to 2 3 these values are consistent with the derivation of the ree and potentially economically enriched metals from the local volcanic sequence either via granitic melts or directly by leaching by metasomatic fluids the most cu rich deposits reflect the involvement of more basic protoliths the age distribution of these deposits suggest ioa deposit formation during the collisional phase of the svecofennian orogeny 1 9 1 8 ga and iocg mineralization during this phase and during post orogenic collapse 1 8 1 7 ga whilst model ages indicate the ultimate enrichment of the continental crust in these metals during pre collisional extensional and subduction related basic magmatism these processes underscore the importance of continental cycles both in producing the preserved geological record of orogenic ore deposition and in the generation of fertile continental crust from which metals can be mobilised by subsequent events

formation of gold deposits a metamorphic devolatilization model a metamorphic devolatilization model can explain the enrichment segregation timing distribution and character of many goldfields such as those found in archean greenstone belts slate belts and other gold only provinces in this genetic model hydrated and carbonated greenschist facies rocks particularly metabasic rocks are devolatilized primarily across the greenschist amphibolite facies boundary in an orogenic setting devolatilization operates on the scale of individual mineral grains extracting not just h2o and co2 but also s and in turn au elevated gold in solution is achieved by complexing with reduced s and by h2co3 weak acid buffering near the optimal fluid ph for gold solubility the buffering is more important than being at the point of maximum gold solubility low salinity ensures low base metal concentrations in the auriferous metamorphic fluid migration of this fluid upwards is via shear zones and or into hydraulic fracture zones in rocks of low tensile strength the geometry of the shear zones dictates the kilometre scale fluid migration paths and the degree of fluid focusing into small enough volumes to form economic accumulations of gold deposition of gold from solution necessitates breakdown of the gold thiosulphide complex and is especially facilitated by fluid reduction in contact with reduced carbon bearing host rocks and or by sulphidation of wallrocks to generate iron bearing sulphide and precipitated gold as such black slate carbon seams banded iron formation tholeiitic basalt magnetite bearing diorite and differentiated tholeiitic dolerite sills are some of the important hosts to major goldfields gold deposition is accompanied by carbonation sulphidation and muscovite biotite alteration where the host rock is of suitable bulk composition the correlation of major gold deposits with rock type even when the gold is primarily in veins argues for rock dominated depositional systems not fluid dominated ones as a consequence a general role in gold deposition for fluid mixing temperature decrease and or fluid pressure decrease and boiling is unlikely although such effects may be involved locally several geological features that are recorded at gold only deposits today reflect subsequent modifications superimposed upon the products of this generic metamorphic devolatilization process overprinting by higher grade metamorphism and deformation and or palaeo weathering may provide many of the most obvious features of goldfields including their mineralogy geochemistry geometry small scale timing features geophysical response and even mesoscopic gold distribution

geodynamic settings of mineral deposit systems mineral deposits represent extraordinary metal concentrations that form by magmatic magmatic hydrothermal or hydrothermal processes in geodynamic environments typified by anomalously high thermal and or mechanical energy near plate boundaries as they require the conjunction of specific environmental conditions to form particular mineral deposit types tend to occupy specific geodynamic niches the temporal distributions of mineral deposit types reflect both formational and preservational processes in the archaean and palaeoproterozoic these were linked because of preservation in continental crust connected to thick buoyant subcontinental lithospheric mantle sclm but were decoupled by the neoproterozoic and phanerozoic as a result of evolution to thinner increasingly dense sclm the transition marks a change from mantle plume influenced plate tectonics to modern style plate tectonics with broadly coincident environmental changes and a major impact on the nature and abundance of preserved mineral deposit types as mineral deposits represent an integral part of tectonic process they are essential indicators of that process and geodynamic settings and should be incorporated into any holistic tectonic terrane analysis their distribution also provides a particularly critical test on ancient continental reconstructions derived from palaeomagnetic data conversely such reconstructions provide a first order targeting tool for the conceptual exploration required to discover new mineral provinces and deposits under cover

the immobilization of gold from gold iii chloride by a halophilic sulphate reducing bacterial consortium a consortium containing halophilic dissimilatory sulphate reducing bacteria was enriched from basque lake 1 located near ashcroft british columbia canada to evaluate the role these bacteria have on the immobilization of soluble gold the consortium immobilized increasing amounts of gold from gold iii chloride solutions under saline to hypersaline conditions over time gold iii chloride was reduced to elemental gold in all experimental systems salinity did not affect gold immobilization scanning electron microscopy and transmission electron microscopy demonstrated that reduced gold iii chloride was immobilized as c 3 10 nm gold colloids and c 100 nm colloidal aggregates at the fluid biofilm interface the precipitation of gold at this organic interface protected cells within the biofilm from the toxic effect of ionic gold analysis of these experimental systems using x ray absorption near edge spectroscopy confirmed that elemental gold with varying colloidal sizes formed within minutes the immobilization of gold by halophilic sulphate reducing bacteria highlights a possible role for the biosphere in intercepting mobile gold complexes within natural hydraulic flow paths based on the limited toxicity demonstrated in this experimental model significant concentrations of elemental gold could accumulate over geological time in natural systems where soluble gold concentrations are more dilute and presumably non toxic to the biosphere