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This work investigated the molecular epidemiology and antimicrobial resistance of methicillinresistant Staphylococcus aureus (MRSA) isolated from veterinarians in Australia in 2009. The collection (n = 44) was subjected to extensive molecular typing (MLST, spa, SCCmec, dru, PFGE, virulence and antimicrobial resistance genotyping) and antimicrobial resistance phenotyping by disk diffusion. MRSA was isolated from Australian veterinarians representing various occupational emphases. The isolate collection was dominated by MRSA strains belonging to clonal complex (CC) 8 and multilocus sequence type (ST) 22. CC8 MRSA (ST8-IV [2B], spa t064; and ST612-IV [2B], spa variable,) were strongly associated with equine practice veterinarians (OR = 17.5, 95% CI = 3.3-92.5, P < 0.001) and were often resistant to gentamicin and rifampicin. ST22-IV [2B], spa variable, were strongly associated with companion animal practice veterinarians (OR = 52.5, 95% CI = 5.2-532.7, P < 0.001) and were resistant to ciprofloxacin. A single pig practice veterinarian carried ST398-V [5C2], spa t1451. Equine practice and companion animal practice veterinarians frequently carried multiresistant-CC8 and ST22 MRSA, respectively, whereas only a single swine specialist carried MRSA ST398. The presence of these strains in veterinarians may be associated with specific antimicrobial administration practices in each animal species.

Objective To evaluate if methicillin-resistant Staphylococcus aureus (MRSA) is present in the horse population in Australia. Design A two-part retrospective study of laboratory submissions of microbial culture results from horses. Methods Part A: medical records of 216 horses that had MRSA screening performed on nasal swabs collected over a 30-day period at admission to the Scone Equine Hospital Clovelly Intensive Care Unit were retrieved. Part B: laboratory records from 2004 to 2009 of culture submissions to the Scone Veterinary Laboratory were reviewed and cultures that grew MRSA were identified. The MRSA isolates from Parts A and B were genotyped over an 18-month period. Results MRSA screening of 216 horses identified eight (3.7%) positive samples. MRSA was isolated from cultures of 80 (0.002%) clinical bacteriology samples over a 6-year period. Genotypic analysis was performed on 36 isolates. All MRSA characterised had the same pulse field gel electrophoresis pattern (type 1), with eight closely related subtypes identified (subtypes A-F and H) and 66% of isolates classified as subtype D, which multilocus sequence and staphylococcal cassette chromosome mec typing analysis identified as ST612-MRSA-IVa, a clonal complex (CC) 8 S. aureus strain. Antimicrobial resistance to more than two classes of antimicrobials was common. Conclusions MRSA was present in a population of horses in Australia. Genotypic analysis of the isolates identified the MRSA strain as CC8 S. aureus. Further research needs to be undertaken to evaluate MRSA infection and colonisation of horses and personnel in Australia.

The deposit consists of 55 000 000 t of Zn-Pb-Cu massive sulphide overlying a Cu-rich stockwork. The massive ore is overlain by up to 30 m of feldspar-phyric, rhyolitic volcaniclastic rock and locally by a jasper and/or chert layer up to 15 m thick. The orebody consists mainly of pyrite, sphalerite, galena, chalcopyrite, tetrahedrite-tennantite, arsenopyrite and bournonite, together with minor quartz, chlorite, sericite, carbonate, and barite. The orebody is up to 100 m thick and is underlain by a tabular alteration zone of chlorite-dominated, locally silicified, felsic volcanic rock, the upper 30 to 60 m of which contains chalcopyrite-quartz-chlorite-sericite-carbonate-bearing stockwork veins or veinlets that, prior to deformation, were at a shallow angle to the base of the massive orebody. The characteristics of the deposit suggest deposition of the massive sulphide on the sea floor. It shares most of the characteristics of Iberian Pyrite Belt deposits for which a brine-pool origin has been proposed from fluid inclusion data, suggesting a similar depositional origin despite equivocal evidence from fluid inclusions. The sulphate that underwent biogenic reduction may have been derived from mixing with seawater during early filling of the brine pool, diffusion across the brine-seawater interface and sulphate reduction in the footwall volcaniclastic rocks. Stable and radiogenic isotope compositions suggest involvement of modified seawater and crustal fluids convecting due to magmatic heating, but the calculated high fluid pressures in the stockwork may indicate the additional involvement of magmatic fluids., The deposit consists of 55 000 000 t of Zn-Pb-Cu massive sulphide overlying a Cu-rich stockwork. The massive ore is overlain by up to 30 m of feldspar-phyric, rhyolitic volcaniclastic rock and locally by a jasper and/or chert layer up to 15 m thick. The orebody consists mainly of pyrite, sphalerite, galena, chalcopyrite, tetrahedrite-tennantite, arsenopyrite and bournonite, together with minor quartz, chlorite, sericite, carbonate, and barite. The orebody is up to 100 m thick and is underlain by a tabular alteration zone of chlorite-dominated, locally silicified, felsic volcanic rock, the upper 30 to 60 m of which contains chalcopyrite-quartz-chlorite-sericite-carbonate-bearing stockwork veins or veinlets that, prior to deformation, were at a shallow angle to the base of the massive orebody. The characteristics of the deposit suggest deposition of the massive sulphide on the sea floor. It shares most of the characteristics of Iberian Pyrite Belt deposits for which a brine-pool origin has been proposed from fluid inclusion data, suggesting a similar depositional origin despite equivocal evidence from fluid inclusions. The sulphate that underwent biogenic reduction may have been derived from mixing with seawater during early filling of the brine pool, diffusion across the brine-seawater interface and sulphate reduction in the footwall volcaniclastic rocks. Stable and radiogenic isotope compositions suggest involvement of modified seawater and crustal fluids convecting due to magmatic heating, but the calculated high fluid pressures in the stockwork may indicate the additional involvement of magmatic fluids.

Objectives: Methicillin-resistant staphylococci (MRS) isolates from healthy and diseased cats and dogs were characterized by staphylococcal cassette chromosome mec (SCCmec), multilocus sequence typing (MLST) and cassette chromosome recombinase gene (ccrAB) sequencing. Methods: PCR-directed SCCmec typing was carried out for all MRS isolates and two Staphylococcus aureus and two Staphylococcus epidermidis strains were analysed by MLST. Strains belonging to SCC mec type III and IV were sequenced for their ccrAB gene of allotypes 3 and 2, respectively. Results: Five types of SCCmec, types I, III, IV, IV (paediatric) and V SCC mec, were found. The S. aureus strains belonged to sequence type (ST) 239 and the two S. epidermidis belonged to ST43 and ST60 respectively. High sequence conservation was observed for the ccrAB gene of allotypes 2 and 3. Conclusions: MRS isolates from cats and dogs demonstrate a similar diversity of SCC mec types to those found in human staphylococci and ST239-MRSA-III, a widely dispersed strain in human hospitals, was identified in diseased dogs.

Key features of iron oxide-rich hydrothermal systems that need to be included in any model are the abundance of magnetite and/or haematite, the chemically distinct suite of elements (REE-Cu-Co-Au-Ag-U), the variability of associated magmas, the distributions and volumes of associated hydrothermal alteration, and the broader geologic setting. Geological and geochemical evidence indicates that the ore-forming fluids are brines, but multiple sources, both magmatic and non-magmatic, are likely. Two end members (and several variants) are proposed for the Fe oxide-rich (Cu-Au) systems: one, distinctive of magmatic fluid sources, overlaps with porphyry copper-gold and related deposit types, while the other involves non-magmatic brines and economic ore grades are less common. Conceptual and quantitative models of magmatic and non-magmatic fluid sources are developed. Basalt-driven hydrothermal systems and young examples (Salton Sea) illustrate that non-magmatic fluids can generate Fe-oxide-rich sulphide-poor REE-Cu-Co-Au-Ag-bearing mineralisation., Key features of iron oxide-rich hydrothermal systems that need to be included in any model are the abundance of magnetite and/or haematite, the chemically distinct suite of elements (REE-Cu-Co-Au-Ag-U), the variability of associated magmas, the distributions and volumes of associated hydrothermal alteration, and the broader geologic setting. Geological and geochemical evidence indicates that the ore-forming fluids are brines, but multiple sources, both magmatic and non-magmatic, are likely. Two end members (and several variants) are proposed for the Fe oxide-rich (Cu-Au) systems: one, distinctive of magmatic fluid sources, overlaps with porphyry copper-gold and related deposit types, while the other involves non-magmatic brines and economic ore grades are less common. Conceptual and quantitative models of magmatic and non-magmatic fluid sources are developed. Basalt-driven hydrothermal systems and young examples (Salton Sea) illustrate that non-magmatic fluids can generate Fe-oxide-rich sulphide-poor REE-Cu-Co-Au-Ag-bearing mineralisation.

The Kern Mountains occurrence is unusual in that at least some, and possibly all, of the tungsten mineralisation is related to remobilisation by exchanged waters long (about 40 m.y.) after cooling of the two-mica granite., The Kern Mountains occurrence is unusual in that at least some, and possibly all, of the tungsten mineralisation is related to remobilisation by exchanged waters long (about 40 m.y.) after cooling of the two-mica granite.

An overview of ongoing field, petrological and geochemical studies of the Great Basin localities is presented., An overview of ongoing field, petrological and geochemical studies of the Great Basin localities is presented.

A study has been carried out of global patterns in molybdenite Re contents using a compilation of more than 3 000 measurements of Re in molybdenite from over 700 moderate- to high-temperature hydrothermal systems. The rhenium concentrations were found to have a lognormal distribution and varied systematically with type of geologic system, intrusive lithology, and Mo grade. The lowest-Re contents (up to 32 ppm) occurred in greisens, quartz vein-hosted W-Sn deposits, unmineralised granites and granodiorites, intrusion-related deposits, and porphyry W-Sn deposits. Rhenium was most enriched in molybdenites from volcanic sublimates (around 23 800 ppm), with Fe and Au skarns next (around 560and 540 ppm respectively) and porphyry Cu and Cu-Au deposits next (around 470 and 430 ppm respectively). In most systems, molybdenite Re content did not correlate with metal grade, but it may have an inverse correlation with Au grade in intrusion-related deposits and it also exhibits a strong inverse correlation with Mo grade. Most empirical correlations could be traced back to differences in redox state and sulphide concentration. It is concluded that the available molybdenite Re values largely depend on how the redox and sulphidation conditions varied during hydrothermal activity. Oxidised, high-sulphide conditions tend to concentrate Re in molybdenite, whereas reducing conditions tend to leave Re dispersed at low concentrations in the bulk rock., A study has been carried out of global patterns in molybdenite Re contents using a compilation of more than 3 000 measurements of Re in molybdenite from over 700 moderate- to high-temperature hydrothermal systems. The rhenium concentrations were found to have a lognormal distribution and varied systematically with type of geologic system, intrusive lithology, and Mo grade. The lowest-Re contents (up to 32 ppm) occurred in greisens, quartz vein-hosted W-Sn deposits, unmineralised granites and granodiorites, intrusion-related deposits, and porphyry W-Sn deposits. Rhenium was most enriched in molybdenites from volcanic sublimates (around 23 800 ppm), with Fe and Au skarns next (around 560and 540 ppm respectively) and porphyry Cu and Cu-Au deposits next (around 470 and 430 ppm respectively). In most systems, molybdenite Re content did not correlate with metal grade, but it may have an inverse correlation with Au grade in intrusion-related deposits and it also exhibits a strong inverse correlation with Mo grade. Most empirical correlations could be traced back to differences in redox state and sulphide concentration. It is concluded that the available molybdenite Re values largely depend on how the redox and sulphidation conditions varied during hydrothermal activity. Oxidised, high-sulphide conditions tend to concentrate Re in molybdenite, whereas reducing conditions tend to leave Re dispersed at low concentrations in the bulk rock.

New occurrences of Na-Ca alteration at Charleston, Sycamore Canyon, Silver Bell, and the Ninetysix Hills in Arizona and the Central mining district in New Mexico (USA) are compared with sodic-calcic alteration at the Sierrita-Esperanza deposit, the Ajo mining district, the Tea Cup pluton, and the Eagle Pass dyke swarm in Arizona. Spatial positions, crosscutting relationships, and mineral assemblages and compositions are used to interpret the geochemical conditions of formation and implications for associated hydrothermal processes. Solid solution assemblages representative of calcic alteration typically occur in deep and/or distal positions whereas sodic-calcic and sodic alteration types occur more proximally to the porphyry. Sodic-calcic assemblages occur along granite cupolas near the base of ore-bodies, grading into shallower sodic assemblages. Mineral composition and fluid inclusion data suggest that Na-Ca plagioclase-bearing assemblages formed at higher temperatures than later albite-epidote assemblages. Na-Ca alteration assemblages are best developed at relatively deep levels of porphyry systems and probably originated from the incursion of saline external fluids. Several Laramide systems that are well exposed at comparably deep levels lack Na-Ca alteration, probably because sources of saline fluid were absent or hydrologic conditions were unfavourable for the incursion of saline external fluids. Na-Ca alteration in Laramide systems is volumetrically smaller than in Jurassic systems in the western USA, probably due to changes in the palaeoclimate from arid to humid conditions., New occurrences of Na-Ca alteration at Charleston, Sycamore Canyon, Silver Bell, and the Ninetysix Hills in Arizona and the Central mining district in New Mexico (USA) are compared with sodic-calcic alteration at the Sierrita-Esperanza deposit, the Ajo mining district, the Tea Cup pluton, and the Eagle Pass dyke swarm in Arizona. Spatial positions, crosscutting relationships, and mineral assemblages and compositions are used to interpret the geochemical conditions of formation and implications for associated hydrothermal processes. Solid solution assemblages representative of calcic alteration typically occur in deep and/or distal positions whereas sodic-calcic and sodic alteration types occur more proximally to the porphyry. Sodic-calcic assemblages occur along granite cupolas near the base of ore-bodies, grading into shallower sodic assemblages. Mineral composition and fluid inclusion data suggest that Na-Ca plagioclase-bearing assemblages formed at higher temperatures than later albite-epidote assemblages. Na-Ca alteration assemblages are best developed at relatively deep levels of porphyry systems and probably originated from the incursion of saline external fluids. Several Laramide systems that are well exposed at comparably deep levels lack Na-Ca alteration, probably because sources of saline fluid were absent or hydrologic conditions were unfavourable for the incursion of saline external fluids. Na-Ca alteration in Laramide systems is volumetrically smaller than in Jurassic systems in the western USA, probably due to changes in the palaeoclimate from arid to humid conditions.

Naica consists of at least 10 mantos and 40 chimneys that have produced over 15 million tons of ore with 10% Zn, 13% Pb and 13 oz/ton Ag. The ore occurs in thick-bedded, folded Cretaceous limestone. The mantos follow the dikes and have abundant early skarn with manganohedenbergite, calcic garnet, idocrase, quartz, calcite, wollastonite, schellite and later sulphides. The chimneys arise from the mantos and change from silicate-rich to silicate-free sulphide limestone replacements. Carbon, oxygen and sulpher isotope data on carbonates, silicates, sulphides and sulphates are compatible with a single evolving (magmatic ?) fluid., Naica consists of at least 10 mantos and 40 chimneys that have produced over 15 million tons of ore with 10% Zn, 13% Pb and 13 oz/ton Ag. The ore occurs in thick-bedded, folded Cretaceous limestone. The mantos follow the dikes and have abundant early skarn with manganohedenbergite, calcic garnet, idocrase, quartz, calcite, wollastonite, schellite and later sulphides. The chimneys arise from the mantos and change from silicate-rich to silicate-free sulphide limestone replacements. Carbon, oxygen and sulpher isotope data on carbonates, silicates, sulphides and sulphates are compatible with a single evolving (magmatic ?) fluid.

Recognising the signature of iron oxide(-copper-gold) or IOCG mineralisation depends on which view of its nature and origin is preferred, as no simple descriptive model can adequately capture the diversity of systems in this deposit class and there is no consensus on their origin. Nor does any set of geological features readily distinguish Cu-Au-rich from Cu-Au-poor iron oxide deposits with which they are often associated. Features common to most descriptions of iron oxide-copper-gold deposits and related systems are discussed. Hydrothermal features include extensive alkali-rich alteration. Economic mineralisation is dominated by late chalcopyrite and bornite within or near iron oxides, mainly distal and shallow haematite. Gravity and magnetic signatures reflect the distribution of bodies rich in iron oxides as well as imaging structural and igneous features. All genetic models require saline, sulphide-poor, relatively oxidised fluids to account for the abundant iron oxides and scarce sulphides, but they differ in their possible sources, paths and traps. The possibilities can be reduced to magmatic and non-magmatic fluid sources, the latter derived either by metamorphism or from surface or basin fluids. For each of these three categories, a table summarises the fundamental processes, igneous associations, hydrothermal alteration in feldspathic hosts, relationships of barren Fe oxides to Cu-Au, local depth/structural setting, global setting and key references., Recognising the signature of iron oxide(-copper-gold) or IOCG mineralisation depends on which view of its nature and origin is preferred, as no simple descriptive model can adequately capture the diversity of systems in this deposit class and there is no consensus on their origin. Nor does any set of geological features readily distinguish Cu-Au-rich from Cu-Au-poor iron oxide deposits with which they are often associated. Features common to most descriptions of iron oxide-copper-gold deposits and related systems are discussed. Hydrothermal features include extensive alkali-rich alteration. Economic mineralisation is dominated by late chalcopyrite and bornite within or near iron oxides, mainly distal and shallow haematite. Gravity and magnetic signatures reflect the distribution of bodies rich in iron oxides as well as imaging structural and igneous features. All genetic models require saline, sulphide-poor, relatively oxidised fluids to account for the abundant iron oxides and scarce sulphides, but they differ in their possible sources, paths and traps. The possibilities can be reduced to magmatic and non-magmatic fluid sources, the latter derived either by metamorphism or from surface or basin fluids. For each of these three categories, a table summarises the fundamental processes, igneous associations, hydrothermal alteration in feldspathic hosts, relationships of barren Fe oxides to Cu-Au, local depth/structural setting, global setting and key references.

The root zones were characterised of four Laramide porphyry Cu systems in Arizona, USA: the Miami Inspiration system associated with the Schultze granite, the Sierrita-Esperanza system associated with the Ruby Star granodiorite, the Ray system associated with the Granite Mountain pluton, and the Kelvin-Riverside system associated with the Tea Cup pluton. Two root zones related to the Jurassic Yerington batholith in Nevada, associated with the Yerington mine and with the Ann-Mason deposit, were used as a basis for comparison. All six systems occur in areas with unusually large exposures in both lateral and vertical palaeodirections, as a result of post-ore extensional faulting and associated tilting. Many share hydrothermal characteristics including quartz veins and potassic alteration, sodic-calcic and sodic alteration, calcic alteration, and relatively coarse-grained muscovite-quartz. Some systems exhibit evidence of multiple cycles of release of magmatic fluid followed by incursion of saline ground waters. The characteristics of the root zones provide constraints on the exsolution and transport of the magmatic aqueous phase that leads to ore formation, the variable incursion of external fluids into the hydrothermal system and the degassing of magmatic volatiles that may not have been related directly to porphyry ore formation. The most robust conclusions are drawn from the localities that offer the greatest quality of exposure and degree of continuity between the roots and the ore deposit, from studies that identify timelines linking processes in the roots with those in the mineral deposit and from systems in which the deposit itself is well characterised., The root zones were characterised of four Laramide porphyry Cu systems in Arizona, USA: the Miami Inspiration system associated with the Schultze granite, the Sierrita-Esperanza system associated with the Ruby Star granodiorite, the Ray system associated with the Granite Mountain pluton, and the Kelvin-Riverside system associated with the Tea Cup pluton. Two root zones related to the Jurassic Yerington batholith in Nevada, associated with the Yerington mine and with the Ann-Mason deposit, were used as a basis for comparison. All six systems occur in areas with unusually large exposures in both lateral and vertical palaeodirections, as a result of post-ore extensional faulting and associated tilting. Many share hydrothermal characteristics including quartz veins and potassic alteration, sodic-calcic and sodic alteration, calcic alteration, and relatively coarse-grained muscovite-quartz. Some systems exhibit evidence of multiple cycles of release of magmatic fluid followed by incursion of saline ground waters. The characteristics of the root zones provide constraints on the exsolution and transport of the magmatic aqueous phase that leads to ore formation, the variable incursion of external fluids into the hydrothermal system and the degassing of magmatic volatiles that may not have been related directly to porphyry ore formation. The most robust conclusions are drawn from the localities that offer the greatest quality of exposure and degree of continuity between the roots and the ore deposit, from studies that identify timelines linking processes in the roots with those in the mineral deposit and from systems in which the deposit itself is well characterised.

Several lines of evidence, including mapping data and palaeomagnetic and geobarometric determinations, demonstrate that the rocks and large porphyry copper systems of the Sierrita Mountains in southern Arizona were dismembered and tilted 50 to 60 degrees to the south by Tertiary normal faulting. Repetition of geological and geobarometric features indicates that the area is segmented into at least three major structural blocks, with the present surface corresponding to oblique sections through the Laramide plutonic-hydrothermal complex, ranging in palaeodepth from about 1 to about 12 km. The results support an evolving picture of a north-south extensional domain with structures at a high angle to much of the extension in the southern Basin and Range province, contrasting with earlier interpretations of upright blocks dismembered by thrust faults, and highlight the necessity of restoring the Tertiary rotations before interpreting hydrothermal and structural features. They add to the broader understanding of the emplacement and evolution of porphyry copper systems., Several lines of evidence, including mapping data and palaeomagnetic and geobarometric determinations, demonstrate that the rocks and large porphyry copper systems of the Sierrita Mountains in southern Arizona were dismembered and tilted 50 to 60 degrees to the south by Tertiary normal faulting. Repetition of geological and geobarometric features indicates that the area is segmented into at least three major structural blocks, with the present surface corresponding to oblique sections through the Laramide plutonic-hydrothermal complex, ranging in palaeodepth from about 1 to about 12 km. The results support an evolving picture of a north-south extensional domain with structures at a high angle to much of the extension in the southern Basin and Range province, contrasting with earlier interpretations of upright blocks dismembered by thrust faults, and highlight the necessity of restoring the Tertiary rotations before interpreting hydrothermal and structural features. They add to the broader understanding of the emplacement and evolution of porphyry copper systems.

The space-time progression of magmatism and hydrothermal activity in the Patagonia Mountains is based on field and paragenetic relationships and on geochronology of igneous and hydrothermal minerals. Laramide igneous rocks and adjacent Palaeozoic and Mesozoic rocks contain significant porphyry Cu-Mo deposits, Mo-Cu breccia pipes, Ag replacement deposits and numerous other Cu-Pb-Zn-Ag replacement and vein deposits. Ages of igneous and hydrothermal minerals from 20 U-Pb and 52 40Ar/39Ar determinations define four magmatic and magmatic-hydrothermal events that formed the batholith and altered parts of it and adjacent rocks; cumulatively the events span at least 16 m.y., from 74 to 58 Ma. The oldest event of this succession includes the 74 Ma Washington Camp stock and spatially associated Cu-Pb-Zn-Ag replacement deposits in Palaeozoic carbonate rocks of the Washington Camp-Duquesne district. The Red Mountain porphyry Cu-Mo system is hosted by 62 Ma granodiorite and Laramide volcanic rocks (73-68 Ma) at the northern end of the batholith. It includes a deep, chalcopyrite-bornite resource associated with potassic and sericitic alteration and a near-surface chalcocite-enargite resource (60 Ma) associated with advanced, supergene-enriched argillic alteration. The youngest event includes the Sunnyside porphyry Cu-Mo system and a Cu-Mo breccia deposit at Red Hill (Four Metals mine), both of which formed in large-volume quartz monzonite, granodiorite, quartz monzonite porphyry, and quartz feldspar porphyry (61-59 Ma). It is likely that the diversity of igneous and hydrothermal products reflects evolutionary processes occurring at multiple sites in the lithosphere and at different time scales., The space-time progression of magmatism and hydrothermal activity in the Patagonia Mountains is based on field and paragenetic relationships and on geochronology of igneous and hydrothermal minerals. Laramide igneous rocks and adjacent Palaeozoic and Mesozoic rocks contain significant porphyry Cu-Mo deposits, Mo-Cu breccia pipes, Ag replacement deposits and numerous other Cu-Pb-Zn-Ag replacement and vein deposits. Ages of igneous and hydrothermal minerals from 20 U-Pb and 52 40Ar/39Ar determinations define four magmatic and magmatic-hydrothermal events that formed the batholith and altered parts of it and adjacent rocks; cumulatively the events span at least 16 m.y., from 74 to 58 Ma. The oldest event of this succession includes the 74 Ma Washington Camp stock and spatially associated Cu-Pb-Zn-Ag replacement deposits in Palaeozoic carbonate rocks of the Washington Camp-Duquesne district. The Red Mountain porphyry Cu-Mo system is hosted by 62 Ma granodiorite and Laramide volcanic rocks (73-68 Ma) at the northern end of the batholith. It includes a deep, chalcopyrite-bornite resource associated with potassic and sericitic alteration and a near-surface chalcocite-enargite resource (60 Ma) associated with advanced, supergene-enriched argillic alteration. The youngest event includes the Sunnyside porphyry Cu-Mo system and a Cu-Mo breccia deposit at Red Hill (Four Metals mine), both of which formed in large-volume quartz monzonite, granodiorite, quartz monzonite porphyry, and quartz feldspar porphyry (61-59 Ma). It is likely that the diversity of igneous and hydrothermal products reflects evolutionary processes occurring at multiple sites in the lithosphere and at different time scales.

A genetic model is proposed in which meteoric fluids were circulated by heat released during crustal extension, scavenging gold from the sedimentary rock pile at depth before welling up and interacting with the various lithologies and/or other fluids to produce characteristic alteration and metal suites. Physical and chemical constraints implicit in the model were investigated to test its viability. Heat balance calculations indicated that ample surface waters could be heated to appropriate temperatures and circulated, while mass balance calculations showed that solution transport efficiencies of less than 10% could account for several times the known alteration and mineralisation. Geochemical modelling found near-neutral, low-chlorinity fluids the most effective at generating high Au and low base metal contents, with arkoses the best source rocks. The model rationalises the distribution of Carlin-type deposits in the central Great Basin, Nevada., A genetic model is proposed in which meteoric fluids were circulated by heat released during crustal extension, scavenging gold from the sedimentary rock pile at depth before welling up and interacting with the various lithologies and/or other fluids to produce characteristic alteration and metal suites. Physical and chemical constraints implicit in the model were investigated to test its viability. Heat balance calculations indicated that ample surface waters could be heated to appropriate temperatures and circulated, while mass balance calculations showed that solution transport efficiencies of less than 10% could account for several times the known alteration and mineralisation. Geochemical modelling found near-neutral, low-chlorinity fluids the most effective at generating high Au and low base metal contents, with arkoses the best source rocks. The model rationalises the distribution of Carlin-type deposits in the central Great Basin, Nevada.