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The 2.95-2.8 Ga Yalgoo-Singleton greenstone belt is dissected by a number of structures including the unexposed c.60 km Mougooderra shear zone, host to most of the belt's current 1 000 000 oz Au resource, whose geometry and kinematics have been poorly understood although recent structural analysis has revealed that mineralisation along its length is structurally-controlled and conforms to a fault-valve model whereby high pore fluid pressures have facilitated reverse movement along a steeply-oriented structure. A paragenetic study reveals the sulphide assemblage at the 400 000 oz Au Silverstone deposit consists of pyrite, pyrrhotite and arsenopyrite, with minor chalcopyrite and Sb-sulphides, primarily ullmannite (NiSbS) and stibnite (Sb2S3). The ore zone has experienced intense carbonate alteration, with a chlorite-sericite-albite-calcite alteration assemblage in mafic protoliths and talc-magnesite-fuchsite assemblage in ultramafic protoliths. At least two discrete Au-bearing phases are identified, comprising an earlier phase of arsenopyrite and a later phase of Au-bearing antimony sulphides. Gold occurs both as inclusions and as free gold. These assemblages and textures are very consistent at deposits over a strike length of over 30 km. The uniformity of mineral assemblages, ore textures and sulphide S isotope data at deposits along the length of the shear zone supports structural analysis and demonstrate that mineralisation across the belt formed as part of the same episode of crustal shortening., 4 refs., The 2.95-2.8 Ga Yalgoo-Singleton greenstone belt is dissected by a number of structures including the unexposed c.60 km Mougooderra shear zone, host to most of the belt's current 1 000 000 oz Au resource, whose geometry and kinematics have been poorly understood although recent structural analysis has revealed that mineralisation along its length is structurally-controlled and conforms to a fault-valve model whereby high pore fluid pressures have facilitated reverse movement along a steeply-oriented structure. A paragenetic study reveals the sulphide assemblage at the 400 000 oz Au Silverstone deposit consists of pyrite, pyrrhotite and arsenopyrite, with minor chalcopyrite and Sb-sulphides, primarily ullmannite (NiSbS) and stibnite (Sb2S3). The ore zone has experienced intense carbonate alteration, with a chlorite-sericite-albite-calcite alteration assemblage in mafic protoliths and talc-magnesite-fuchsite assemblage in ultramafic protoliths. At least two discrete Au-bearing phases are identified, comprising an earlier phase of arsenopyrite and a later phase of Au-bearing antimony sulphides. Gold occurs both as inclusions and as free gold. These assemblages and textures are very consistent at deposits over a strike length of over 30 km. The uniformity of mineral assemblages, ore textures and sulphide S isotope data at deposits along the length of the shear zone supports structural analysis and demonstrate that mineralisation across the belt formed as part of the same episode of crustal shortening.

Scotland’s first ever commercial gold mine, with a current resource of 266 000 oz Au and 1 096 000 oz Ag, has ore consisting of a series of hydrothermal quartz+/-carbonate veins that occupy an anastomosing, transtensional fault zone striking NE-SW, sub-parallel to the nearby Tyndrum fault; mineralisation crosscuts multiply deformed stratigraphy of the Dalradian Supergroup, metamorphosed to epidote-amphibolite facies at c.470 Ma. Whilst Cononish displays broad commonalities with the orogenic group of ore deposits, K-feldspar alteration in an auriferous breccia yield Ar/Ar ages of c.408-407 Ma, linking mineralisation to the main episode of shear-modulated, post-Caledonian magmatism in the Grampian belt. S and Pb isotope analyses were conducted on a suite of early auriferous and later, non-auriferous vein sulphides in order to resolve the source(s) of S and Pb, and by inference the source(s) of gold. A comparison of the Pb isotopes with sedex, Dalradian and magmatic end-members supports the hypothesis that mixing between sedex and Dalradian strata was the main source of Pb to both auriferous and non-auriferous sulphides, implying that, given the homogeneity of Pb sources, these strata were not a major gold source and post-Caledonian magmatism was the most plausible genetic contributor., 9 refs., Scotland’s first ever commercial gold mine, with a current resource of 266 000 oz Au and 1 096 000 oz Ag, has ore consisting of a series of hydrothermal quartz+/-carbonate veins that occupy an anastomosing, transtensional fault zone striking NE-SW, sub-parallel to the nearby Tyndrum fault; mineralisation crosscuts multiply deformed stratigraphy of the Dalradian Supergroup, metamorphosed to epidote-amphibolite facies at c.470 Ma. Whilst Cononish displays broad commonalities with the orogenic group of ore deposits, K-feldspar alteration in an auriferous breccia yield Ar/Ar ages of c.408-407 Ma, linking mineralisation to the main episode of shear-modulated, post-Caledonian magmatism in the Grampian belt. S and Pb isotope analyses were conducted on a suite of early auriferous and later, non-auriferous vein sulphides in order to resolve the source(s) of S and Pb, and by inference the source(s) of gold. A comparison of the Pb isotopes with sedex, Dalradian and magmatic end-members supports the hypothesis that mixing between sedex and Dalradian strata was the main source of Pb to both auriferous and non-auriferous sulphides, implying that, given the homogeneity of Pb sources, these strata were not a major gold source and post-Caledonian magmatism was the most plausible genetic contributor.

s are included of the following presentations: Sedimentary copper mineralisation within the Yopzgat-Delice-Yerkoy basin, middle Anatolia, Turkey, by Nowecki J.P., Roberts S., Foster R.P. and Yildiz B., p.112-113; Alteration mineralogy, geochemistry and elemental mass balance through the hydrothermal alteration zones of Maher Abad Cu-Au porphyry deposit, Khusf, Iran, by Siahcheshm K and Abedini A., p.113-114; To make a mineral deposit - geothermal systems in ophiolites as examples of novel solutions for CO2 sequestration, by Stephen A.L., Jenkin G.R.T., Naden J., Styles M.T., Smith D.J. and Boyce A.J., p.115, 3 refs., on the part of the Semail ophiolite in the United Arab Emirates; Geology and geochemistry of the Jalal Abad IOCG deposit, central Iran, by Mehrabi B., Karimi B., Banks D.A. and Yardley B.W.D., p.117; and Hydrothermal alteration and Cu-Mo mineralisation in Kighal porphyry stock, north of Varzeghan, Easty-Azarbaidjan, Iran, by Simmonds V. and Calagari A.A., p. 118, 2 refs., s are included of the following presentations: Sedimentary copper mineralisation within the Yopzgat-Delice-Yerkoy basin, middle Anatolia, Turkey, by Nowecki J.P., Roberts S., Foster R.P. and Yildiz B., p.112-113; Alteration mineralogy, geochemistry and elemental mass balance through the hydrothermal alteration zones of Maher Abad Cu-Au porphyry deposit, Khusf, Iran, by Siahcheshm K and Abedini A., p.113-114; To make a mineral deposit - geothermal systems in ophiolites as examples of novel solutions for CO2 sequestration, by Stephen A.L., Jenkin G.R.T., Naden J., Styles M.T., Smith D.J. and Boyce A.J., p.115, 3 refs., on the part of the Semail ophiolite in the United Arab Emirates; Geology and geochemistry of the Jalal Abad IOCG deposit, central Iran, by Mehrabi B., Karimi B., Banks D.A. and Yardley B.W.D., p.117; and Hydrothermal alteration and Cu-Mo mineralisation in Kighal porphyry stock, north of Varzeghan, Easty-Azarbaidjan, Iran, by Simmonds V. and Calagari A.A., p. 118, 2 refs.

s are included of the following presentations: The nature and genesis of marginal Cu-PGE-Au sulphide mineralisation in Palaeogene macrodykes of the Kangerlussuaq region, East Greenland, by Holwell D.A., Abraham-James T., Keays R.R. and Boyce A.J., p.97-98; The origin and economic significance of dioritic sills within the Skaergaard intrusion, Kangerlussuaq region, East Greenland, by Bird P.J., Holwell D.A. and Abraham-James T., p.106-107, 1 ref.; Developing an exploration model for gold mineralisation associated with Archaean basement rocks Sortekap, East Greenland, by Butterworth K.G., Holwell D.A. and Abraham-James T., p. 107; The genesis of base and precious metal vein mineralisation in the Amdrup Fjord area, east Greenland - are lamprophyres the key? by Lawrence S.P., Holwell D.A. and Abraham-James T., p.110-111, 3 refs.; and Fault-valve action, fluid mixing and gold deposition - identification of grade-controlling mechanisms in Nalunaq gold mine, Greenland, by Smith M. and Bowers F., p.119., s are included of the following presentations: The nature and genesis of marginal Cu-PGE-Au sulphide mineralisation in Palaeogene macrodykes of the Kangerlussuaq region, East Greenland, by Holwell D.A., Abraham-James T., Keays R.R. and Boyce A.J., p.97-98; The origin and economic significance of dioritic sills within the Skaergaard intrusion, Kangerlussuaq region, East Greenland, by Bird P.J., Holwell D.A. and Abraham-James T., p.106-107, 1 ref.; Developing an exploration model for gold mineralisation associated with Archaean basement rocks Sortekap, East Greenland, by Butterworth K.G., Holwell D.A. and Abraham-James T., p. 107; The genesis of base and precious metal vein mineralisation in the Amdrup Fjord area, east Greenland - are lamprophyres the key? by Lawrence S.P., Holwell D.A. and Abraham-James T., p.110-111, 3 refs.; and Fault-valve action, fluid mixing and gold deposition - identification of grade-controlling mechanisms in Nalunaq gold mine, Greenland, by Smith M. and Bowers F., p.119.

Extended abstracts of papers from the following sessions are presented: Tectonic evolution and metallogenic potential throughout Earth history (14 abstracts); Evaluation and sustainable utilisation of mineral resources (9 abstracts); Catastrophism and the development of mineral resources (5 abstracts); Sediment-hosted mineral deposits - do they constrain the ancient atmosphere and hydrosphere? (10 abstracts); Origin and evolution of life - evidence from ancient mineral deposits (6 abstracts); New techniques for understanding mineral deposits (13 abstracts); and Earth processes and exploration for super-giant mineral deposits (13 abstracts)., Extended abstracts of papers from the following sessions are presented: Tectonic evolution and metallogenic potential throughout Earth history (14 abstracts); Evaluation and sustainable utilisation of mineral resources (9 abstracts); Catastrophism and the development of mineral resources (5 abstracts); Sediment-hosted mineral deposits - do they constrain the ancient atmosphere and hydrosphere? (10 abstracts); Origin and evolution of life - evidence from ancient mineral deposits (6 abstracts); New techniques for understanding mineral deposits (13 abstracts); and Earth processes and exploration for super-giant mineral deposits (13 abstracts).

Many Ni-Cu-PGE sulphide breccia deposits are associated with an assortment of poorly sorted mafic-ultramafic rocks suggestive of dynamic emplacement and rapid crystallisation. The Munali deposit, a complex brecciated orebody in the Zambezi Belt, is located along a major structural lineament and consists of an unmineralised central gabbro surrounded by the heterogeneous mafic-ultramafic host breccia made up of poikilitic gabbro, olivine-gabbro, dolerite, magnetite-olivinite (Cr-poor dunite), wehrlite and phoscorite (apatite-magnetite-olivine cumulate). Mineralisation is characterised by an unusual carbonate-rich apatite-magnetite-sulphide assemblage predominately present as a semi-massive to massive sulphide ore. Carbonate within the ores shows intimate relationships with sulphide and micro-macro textures signifying the presence of carbonate melts, C and O isotope analyses of carbonate suggesting the interaction of carbonated mantle melts. Recently identified macrotextures have shown that sulphide mineralisation was not synchronous with ultramafic emplacement, the presence of fracture sets associated with coarse breccia clasts larger than 1 m indicate that the host rock was significantly deformed prior to sulphide melt infiltration. Both carbonate and sulphide melts appear to have independently utilised these pre-existing weaknesses to produce a pseudobreccia, resulting in the chaotic nature of the orebody. The textural relationships imply a major time interval from mafic-ultramafic crystallisation to sulphide liquid emplacement. Although the definitive timing and origin of both melts are unclear, the indication of sulphide representing a significantly later phase suggests that it may have been sourced and/or mobilised from a younger magmatic event and subsequently emplaced within the Munali system., Many Ni-Cu-PGE sulphide breccia deposits are associated with an assortment of poorly sorted mafic-ultramafic rocks suggestive of dynamic emplacement and rapid crystallisation. The Munali deposit, a complex brecciated orebody in the Zambezi Belt, is located along a major structural lineament and consists of an unmineralised central gabbro surrounded by the heterogeneous mafic-ultramafic host breccia made up of poikilitic gabbro, olivine-gabbro, dolerite, magnetite-olivinite (Cr-poor dunite), wehrlite and phoscorite (apatite-magnetite-olivine cumulate). Mineralisation is characterised by an unusual carbonate-rich apatite-magnetite-sulphide assemblage predominately present as a semi-massive to massive sulphide ore. Carbonate within the ores shows intimate relationships with sulphide and micro-macro textures signifying the presence of carbonate melts, C and O isotope analyses of carbonate suggesting the interaction of carbonated mantle melts. Recently identified macrotextures have shown that sulphide mineralisation was not synchronous with ultramafic emplacement, the presence of fracture sets associated with coarse breccia clasts larger than 1 m indicate that the host rock was significantly deformed prior to sulphide melt infiltration. Both carbonate and sulphide melts appear to have independently utilised these pre-existing weaknesses to produce a pseudobreccia, resulting in the chaotic nature of the orebody. The textural relationships imply a major time interval from mafic-ultramafic crystallisation to sulphide liquid emplacement. Although the definitive timing and origin of both melts are unclear, the indication of sulphide representing a significantly later phase suggests that it may have been sourced and/or mobilised from a younger magmatic event and subsequently emplaced within the Munali system.

Irish-type mineralisation is commonly attributed to fault-controlled mixing of a seawater-derived, sulphur-rich fluid and basement-derived, metal-rich fluid. However, maar-diatreme volcanoes discovered in close spatial and temporal association with Zn-Pb mineralisation at Stonepark in the Limerick basin (southwest Ireland) bring a new dimension to established geologic models and may increase the deposit-scale prospectivity in one of the world’s greatest Zn-Pb districts. Stonepark exhibits many incidences of dolomitic black matrix breccias with associated Zn-Pb mineralisation, the latter typically occurring within 150 m of the diatremes. Highly negative delta 34S pyrite values within country rock-dominated black matrix breccias (-12 to -34 per mille) are consistent with sulphide precipitation from bacteriogenic sulphur reduction in seawater-derived brines. Our delta 34S data suggest that diatremes provide more efficient fluid pathways for basement-derived fluids. The diatremes introduce another potential S source and facilitate a greater input of metal-rich basement-derived hydrothermal fluid into the system compared to other Irish-type deposits such as Navan and Lisheen. Irish-type deposits are traditionally thought to form in association with extensional basement faults and are considered unrelated to extensive Carboniferous magmatism. These results indicate that a direct link exists between diatreme volcanism and Zn-Pb mineralisation at Limerick, prompting a reevaluation of the traditional Irish-type ore formation model, in regions where mineralisation is spatially associated with volcanic pipes., Irish-type mineralisation is commonly attributed to fault-controlled mixing of a seawater-derived, sulphur-rich fluid and basement-derived, metal-rich fluid. However, maar-diatreme volcanoes discovered in close spatial and temporal association with Zn-Pb mineralisation at Stonepark in the Limerick basin (southwest Ireland) bring a new dimension to established geologic models and may increase the deposit-scale prospectivity in one of the world’s greatest Zn-Pb districts. Stonepark exhibits many incidences of dolomitic black matrix breccias with associated Zn-Pb mineralisation, the latter typically occurring within 150 m of the diatremes. Highly negative delta 34S pyrite values within country rock-dominated black matrix breccias (-12 to -34 per mille) are consistent with sulphide precipitation from bacteriogenic sulphur reduction in seawater-derived brines. Our delta 34S data suggest that diatremes provide more efficient fluid pathways for basement-derived fluids. The diatremes introduce another potential S source and facilitate a greater input of metal-rich basement-derived hydrothermal fluid into the system compared to other Irish-type deposits such as Navan and Lisheen. Irish-type deposits are traditionally thought to form in association with extensional basement faults and are considered unrelated to extensive Carboniferous magmatism. These results indicate that a direct link exists between diatreme volcanism and Zn-Pb mineralisation at Limerick, prompting a reevaluation of the traditional Irish-type ore formation model, in regions where mineralisation is spatially associated with volcanic pipes.

The Muratdere Cu-Mo (Au) porphyry deposit in western Turkey contains elevated levels of rhenium and is hosted within granodioritic intrusions into an ophiolitic mélange sequence in the Anatolian belt. The deposit contains several stages of mineralisation: early microfracture-hosted molybdenite and chalcopyrite, followed by a quartz-pyrite-chalcopyrite vein set associated with Cu-Au grade, a quartz-chalcopyrite-pyrite-molybdenite vein set associated with Cu-Mo-Re grade, and a later polymetallic quartz-barite-sphalerite-galena-pyrite vein set. The rhenium in Muratdere is hosted within two generations of molybdenite: early microfracture-hosted molybdenite and later vein-hosted molybdenite. In situ laser LA-ICP-MS analysis of sulphides shows that the later molybdenite has significantly higher concentrations of Re (av. 1 124 ppm, sigma = 730 ppm, n = 43) than the early microfracture-hosted molybdenite (av. 566 ppm, sigma = 423 ppm, n = 28). Pyrite crystals associated with the Re-rich molybdenite have higher Co and As concentrations than those in other vein sets, with Au associated with As. The microfracture-hosted sulphides have delta 34S values between -2.2 and +4.6 per mille, consistent with a magmatic source. The vein-hosted sulphides associated with the high-Re molybdenite have a delta 34S signature of 5.6 to 8.8 per mille, similar to values found in peridotite lenses in the Anatolian belt. The later enrichment in Re and delta 34S-enriched S may have been sourced from the surrounding ophiolitic country rock or may have been the result of changing redox conditions during deposit formation. (Authors.), The Muratdere Cu-Mo (Au) porphyry deposit in western Turkey contains elevated levels of rhenium and is hosted within granodioritic intrusions into an ophiolitic mélange sequence in the Anatolian belt. The deposit contains several stages of mineralisation: early microfracture-hosted molybdenite and chalcopyrite, followed by a quartz-pyrite-chalcopyrite vein set associated with Cu-Au grade, a quartz-chalcopyrite-pyrite-molybdenite vein set associated with Cu-Mo-Re grade, and a later polymetallic quartz-barite-sphalerite-galena-pyrite vein set. The rhenium in Muratdere is hosted within two generations of molybdenite: early microfracture-hosted molybdenite and later vein-hosted molybdenite. In situ laser LA-ICP-MS analysis of sulphides shows that the later molybdenite has significantly higher concentrations of Re (av. 1 124 ppm, sigma = 730 ppm, n = 43) than the early microfracture-hosted molybdenite (av. 566 ppm, sigma = 423 ppm, n = 28). Pyrite crystals associated with the Re-rich molybdenite have higher Co and As concentrations than those in other vein sets, with Au associated with As. The microfracture-hosted sulphides have delta 34S values between -2.2 and +4.6 per mille, consistent with a magmatic source. The vein-hosted sulphides associated with the high-Re molybdenite have a delta 34S signature of 5.6 to 8.8 per mille, similar to values found in peridotite lenses in the Anatolian belt. The later enrichment in Re and delta 34S-enriched S may have been sourced from the surrounding ophiolitic country rock or may have been the result of changing redox conditions during deposit formation. (Authors.)

Despite being distal to the main orebody, the 400 000 t 20% Zn, 1.6% Pb Island Pod is still very high-grade and hosts the best-quality ore at Lisheen while showing rapid lateral variation on a small scale, less than10 m, where adjacent boreholes can have zinc concentration differences of c.40%. It also displays a weaker structural control than elsewhere in the southern Irish orefield. The basic sulphide mineralogy for the Island Pod is pyrite, sphalerite and galena, with multiple generations of each observed along with several carbonate phases. Dendritic pyrite/galena, colloform sphalerite and sphalerite/dolomite intergrowth textures suggest an early, rapid mineralisation event, from a supersaturated fluid in a nonequilibrium depositional environment, marking the onset of fluid mixing. As the mineralising system came closer to equilibrium, sulphide textures changed, reflecting a slower precipitation environment. 34-S isotope data suggest a dominantly bacteriogenic source for S in the Island Pod, with minor positive 34 delta-S values recorded. This is consistent with the distal position of the orebody, away from the feeder ramp-relay fault system at Lisheen which is thought to have introduced metal-bearing hydrothermal fluids with 34 delta-S greater than 0. In addition, the orebody and its halo have very similar 34 delta-S values, signifying that a lack of hydrothermal sulphur is not what led to the halo being sub-economic; this may suggest that other factors were responsible for ore grade, such as the availability of bacteriogenic sulphur or stratigraphic controls such as the nature of host-rock permeability., Despite being distal to the main orebody, the 400 000 t 20% Zn, 1.6% Pb Island Pod is still very high-grade and hosts the best-quality ore at Lisheen while showing rapid lateral variation on a small scale, less than10 m, where adjacent boreholes can have zinc concentration differences of c.40%. It also displays a weaker structural control than elsewhere in the southern Irish orefield. The basic sulphide mineralogy for the Island Pod is pyrite, sphalerite and galena, with multiple generations of each observed along with several carbonate phases. Dendritic pyrite/galena, colloform sphalerite and sphalerite/dolomite intergrowth textures suggest an early, rapid mineralisation event, from a supersaturated fluid in a nonequilibrium depositional environment, marking the onset of fluid mixing. As the mineralising system came closer to equilibrium, sulphide textures changed, reflecting a slower precipitation environment. 34-S isotope data suggest a dominantly bacteriogenic source for S in the Island Pod, with minor positive 34 delta-S values recorded. This is consistent with the distal position of the orebody, away from the feeder ramp-relay fault system at Lisheen which is thought to have introduced metal-bearing hydrothermal fluids with 34 delta-S greater than 0. In addition, the orebody and its halo have very similar 34 delta-S values, signifying that a lack of hydrothermal sulphur is not what led to the halo being sub-economic; this may suggest that other factors were responsible for ore grade, such as the availability of bacteriogenic sulphur or stratigraphic controls such as the nature of host-rock permeability.

The Dalradian Supergroup of Britain and Ireland is mineralised by gold-tellurium vein deposits. The host succession includes carbonaceous, pyritic shales (pelites) which were a source of trace elements, including gold and tellurium. LA-ICP-MS mapping of pyrite crystals shows that late stages are enriched in gold, tellurium and lead, representing concentration of these elements during metamorphism and related hydrothermal activity. The sulphur isotope composition of the pyrite varies with stratigraphic position, reflecting an origin for the pyrite in the depositional environment through microbial sulphate reduction. Where pyrite was converted to pyrrhotite, trace element contents are much lower, indicating element liberation during metamorphism. These observations are consistent with a model of black shale protoliths for orogenic gold deposits. (Authors.), The Dalradian Supergroup of Britain and Ireland is mineralised by gold-tellurium vein deposits. The host succession includes carbonaceous, pyritic shales (pelites) which were a source of trace elements, including gold and tellurium. LA-ICP-MS mapping of pyrite crystals shows that late stages are enriched in gold, tellurium and lead, representing concentration of these elements during metamorphism and related hydrothermal activity. The sulphur isotope composition of the pyrite varies with stratigraphic position, reflecting an origin for the pyrite in the depositional environment through microbial sulphate reduction. Where pyrite was converted to pyrrhotite, trace element contents are much lower, indicating element liberation during metamorphism. These observations are consistent with a model of black shale protoliths for orogenic gold deposits. (Authors.)

During the Tournaisian extensional stresses led to the rapid development of sedimentary basins in the British Isles, and debris flows formed as a result of slope failure at their faulted margins. Metalliferous sediments are closely associated with these flows. A study of the Silvermines deposit shows that mineralising fluids exhaled into fault-controlled brine-filled depressions on the Carboniferous sea floor shortly after subsidene began, though subsidence outlasted the mineralising episode. The Navan and Tynagh deposits have a broadly similar origin. The association of debris flows, variations in sediment thickness and in facies may aid in pinpointing zones of maximum syndepositional throw on faults and hence sites favourable for mineralisation of this type., During the Tournaisian extensional stresses led to the rapid development of sedimentary basins in the British Isles, and debris flows formed as a result of slope failure at their faulted margins. Metalliferous sediments are closely associated with these flows. A study of the Silvermines deposit shows that mineralising fluids exhaled into fault-controlled brine-filled depressions on the Carboniferous sea floor shortly after subsidene began, though subsidence outlasted the mineralising episode. The Navan and Tynagh deposits have a broadly similar origin. The association of debris flows, variations in sediment thickness and in facies may aid in pinpointing zones of maximum syndepositional throw on faults and hence sites favourable for mineralisation of this type.

Pyrite tubes 0.1 to 20 mm in diameter have been found in the Ballynoe sedimentary baryte deposit. They comprise concentric layers of pyrite with an outer rim of baryte where the tubes are not touching. The tubes have characteristics in common with the chimney spires found on the East Pacific Rise from which metal bearing solutions issue. The presence of the tubes implies that the baryte deposit was not a distal facies of the Silvermines sedimentary pyritic zinc and lead ore, but was produced from local hydrothermal exhalations., Pyrite tubes 0.1 to 20 mm in diameter have been found in the Ballynoe sedimentary baryte deposit. They comprise concentric layers of pyrite with an outer rim of baryte where the tubes are not touching. The tubes have characteristics in common with the chimney spires found on the East Pacific Rise from which metal bearing solutions issue. The presence of the tubes implies that the baryte deposit was not a distal facies of the Silvermines sedimentary pyritic zinc and lead ore, but was produced from local hydrothermal exhalations.

While it is clear that structure was the key to generation of the Tanzanian deposit, a number of atypical features may have been crucial genetic components. Early syngenetic pyrite associated with argillaceous shales was essentially barren, but may have later acted as a geochemical trap for the precipitation of gold mineralisation. Early saline fluids, recorded in quartz in the gold-bearing veins, suggest an early magmatic event that from lithogeochemical data probably involved pre-ore metal enrichment. The deposit is therefore interpreted as the result of a two-stage hydrothermal process, with the main lode-gold event having overprinted an early Cu-Au-enriched magmatic system to produce a large orebody containing 15 000 000 oz Au at an average grade of 12 g/t Au, enriched in copper to 0.7-2.0%., While it is clear that structure was the key to generation of the Tanzanian deposit, a number of atypical features may have been crucial genetic components. Early syngenetic pyrite associated with argillaceous shales was essentially barren, but may have later acted as a geochemical trap for the precipitation of gold mineralisation. Early saline fluids, recorded in quartz in the gold-bearing veins, suggest an early magmatic event that from lithogeochemical data probably involved pre-ore metal enrichment. The deposit is therefore interpreted as the result of a two-stage hydrothermal process, with the main lode-gold event having overprinted an early Cu-Au-enriched magmatic system to produce a large orebody containing 15 000 000 oz Au at an average grade of 12 g/t Au, enriched in copper to 0.7-2.0%.

The Silvermines base metal and barite deposits are thought to be of Sedex origin, and to be an end-member of Irish-type base metal deposits with clear syngenetic as well as epigenetic features. Despite the presence of fossil hydrothermal vent phenomena at the Ballynoe barite, recent work has highlighted the fact that stratabound, replacement mineralisation is dominant and the presence of any syngenetic features at Silvermines has been questioned. A pyritised tube worm has been found within a hydrothermal mound area at the deposit; it does not belong to any known Lower Carboniferous taxon, but is remarkably similar to the vent fossils recently reported from Phanerozoic volcanogenic massive sulphide deposits. The discovery indicates that seafloor hydrothermal exhalation did occur and that mineralisation had started by the late Courceyan (around 355 Ma)., The Silvermines base metal and barite deposits are thought to be of Sedex origin, and to be an end-member of Irish-type base metal deposits with clear syngenetic as well as epigenetic features. Despite the presence of fossil hydrothermal vent phenomena at the Ballynoe barite, recent work has highlighted the fact that stratabound, replacement mineralisation is dominant and the presence of any syngenetic features at Silvermines has been questioned. A pyritised tube worm has been found within a hydrothermal mound area at the deposit; it does not belong to any known Lower Carboniferous taxon, but is remarkably similar to the vent fossils recently reported from Phanerozoic volcanogenic massive sulphide deposits. The discovery indicates that seafloor hydrothermal exhalation did occur and that mineralisation had started by the late Courceyan (around 355 Ma).

A preliminary study of halogen compositions of fluid inclusions from the Tynagh and Silvermines lead-zinc deposits and veins hosted by the Lower Palaeozoic basement in Ireland has identified a complex range of fluid mixtures but suggests that seawater or evaporated seawater had a fundamental role in most of the fluid types recognised. The 10-15 wt% NaCl equiv. principal ore-fluid end-member observed in the basement and in the overlying deposits probably originated as partially evaporated seawater or seawater which had been dehydrated by fluid-rock interaction. The end-member saline fluid found at Tynagh has the halogen composition of a Cr-rich fluid. The involvement of evaporitic brines provided a potentially important constraint on the timing and genesis of Irish base metal deposits., A preliminary study of halogen compositions of fluid inclusions from the Tynagh and Silvermines lead-zinc deposits and veins hosted by the Lower Palaeozoic basement in Ireland has identified a complex range of fluid mixtures but suggests that seawater or evaporated seawater had a fundamental role in most of the fluid types recognised. The 10-15 wt% NaCl equiv. principal ore-fluid end-member observed in the basement and in the overlying deposits probably originated as partially evaporated seawater or seawater which had been dehydrated by fluid-rock interaction. The end-member saline fluid found at Tynagh has the halogen composition of a Cr-rich fluid. The involvement of evaporitic brines provided a potentially important constraint on the timing and genesis of Irish base metal deposits.

The Navan deposit, in Ireland, contains over 80 000 000 tonnes of ore and is hosted by a sequence of carbonate lithologies. Metal enrichment trends present within the deposit are associated with Lower Carboniferous faulting. In places, the faults are truncated and displaced by major extensional faults which control the current disposition of the orebody. These patterns indicate that either mineralisation took place after/during the development of the early faults, but prior to the evolution of the major faults, or that mineralisation was the product of metal-bearing fluids emanating from the major faults and using the minor, earlier and coeval fault sets to access areas of the host rocks enriched in bacteriogenic sulphide. It is thought that discrimination between these alternatives is possible by continued stable isotope and trace element geochemical investigations., The Navan deposit, in Ireland, contains over 80 000 000 tonnes of ore and is hosted by a sequence of carbonate lithologies. Metal enrichment trends present within the deposit are associated with Lower Carboniferous faulting. In places, the faults are truncated and displaced by major extensional faults which control the current disposition of the orebody. These patterns indicate that either mineralisation took place after/during the development of the early faults, but prior to the evolution of the major faults, or that mineralisation was the product of metal-bearing fluids emanating from the major faults and using the minor, earlier and coeval fault sets to access areas of the host rocks enriched in bacteriogenic sulphide. It is thought that discrimination between these alternatives is possible by continued stable isotope and trace element geochemical investigations.

The Las Cruces base and precious metal deposit, in Spain, is a hidden, secondarily enriched volcanic massive sulphide deposit, discovered in 1994 beyond the conventional limits of the Iberian Pyrite Belt. It is around 1 200 by 800 m in extent, lying below 100-150 m of Tertiary sediments. Mineralisation is hosted by, and sometimes interbedded with, Devonian to early Carboniferous volcanic and sedimentary rocks. The deposit has a well-preserved zone of major secondary mineralisation, which provides the main economic target. Mineralogy and geochemistry of the secondary mineralisation indicate two, and possibly three stages of secondary alteration/enrichment: seafloor hydrothermal oxidation, pre-Tertiary weathering, and post-Tertiary groundwater circulation., The Las Cruces base and precious metal deposit, in Spain, is a hidden, secondarily enriched volcanic massive sulphide deposit, discovered in 1994 beyond the conventional limits of the Iberian Pyrite Belt. It is around 1 200 by 800 m in extent, lying below 100-150 m of Tertiary sediments. Mineralisation is hosted by, and sometimes interbedded with, Devonian to early Carboniferous volcanic and sedimentary rocks. The deposit has a well-preserved zone of major secondary mineralisation, which provides the main economic target. Mineralogy and geochemistry of the secondary mineralisation indicate two, and possibly three stages of secondary alteration/enrichment: seafloor hydrothermal oxidation, pre-Tertiary weathering, and post-Tertiary groundwater circulation.

The mineralogically complex, epigenetic Pb-Mn-As-Sb-bearing Langban deposit is hosted by the Bergslagen Ore Province. It is characterised by syngenetic, felsic volcanic and carbonate-hosted Fe and Mn oxide ores; later stages of syn-orogenic plastic deformation, veining and subsequent post-metamorphic brittle tectonic fissure systems host epigenetic mineralisation with abundant rare minerals in the form of arsenates, arsenites, oxychlorides, native elements and minor silicates. Isotope data varies considerably in paragenetically well-controlled samples, broadly correlating with the time evolution of mineral paragenesis. In particular, sulphate delta S34 and carbonate delta O18 compositional trends suggest an evolution related to cooling and evolving mineral formation, starting with regional metamorphism at 500-600 degrees C and formation of silicates and arsenates, and subsequently ending with the formation of increasingly hydrated arsenates and arsenites at temperatures decreasing to less than 70 degrees C in a brittle tectonic environment., The mineralogically complex, epigenetic Pb-Mn-As-Sb-bearing Langban deposit is hosted by the Bergslagen Ore Province. It is characterised by syngenetic, felsic volcanic and carbonate-hosted Fe and Mn oxide ores; later stages of syn-orogenic plastic deformation, veining and subsequent post-metamorphic brittle tectonic fissure systems host epigenetic mineralisation with abundant rare minerals in the form of arsenates, arsenites, oxychlorides, native elements and minor silicates. Isotope data varies considerably in paragenetically well-controlled samples, broadly correlating with the time evolution of mineral paragenesis. In particular, sulphate delta S34 and carbonate delta O18 compositional trends suggest an evolution related to cooling and evolving mineral formation, starting with regional metamorphism at 500-600 degrees C and formation of silicates and arsenates, and subsequently ending with the formation of increasingly hydrated arsenates and arsenites at temperatures decreasing to less than 70 degrees C in a brittle tectonic environment.

Oxygen isotope analysis of iron oxide alteration from the Lower Carboniferous Zn-Pb deposits indicates that, whilst the silica and magnetite largely precipitated in equilibrium with formation waters at temperatures between 66 and 147 degrees C, haematite must have precipitated from a source containing oxygen with a much higher delta O18 than the formation water. The only realistic source of this isotopically heavy oxygen is currently considered to be dissolved atmospheric oxygen. Thus, despite being paragenetically later than most calcite cements, the haematite in these deposits is likely to have had access to dissolved atmospheric oxygen, implying a near surface genesis. Similar results are also seen in haematite from fluvial Old Red Sandstone lithologies. These results imply that major ironstones, associated with the stratabound base metal deposits, probably formed during early diagenesis when access to atmospheric oxygen was still available., Oxygen isotope analysis of iron oxide alteration from the Lower Carboniferous Zn-Pb deposits indicates that, whilst the silica and magnetite largely precipitated in equilibrium with formation waters at temperatures between 66 and 147 degrees C, haematite must have precipitated from a source containing oxygen with a much higher delta O18 than the formation water. The only realistic source of this isotopically heavy oxygen is currently considered to be dissolved atmospheric oxygen. Thus, despite being paragenetically later than most calcite cements, the haematite in these deposits is likely to have had access to dissolved atmospheric oxygen, implying a near surface genesis. Similar results are also seen in haematite from fluvial Old Red Sandstone lithologies. These results imply that major ironstones, associated with the stratabound base metal deposits, probably formed during early diagenesis when access to atmospheric oxygen was still available.

Fluid inclusion studies of gangue quartz from epigenetic base metal, fluorite and barite deposits in the Palaeozoic Massif Central have shown that, despite major variations in deposit mineralogy and host rock lithology, ore-forming fluids were brines with a salinity of 20-26 wt% NaCl equiv. Oxygen isotope analysis suggests that these brines were surface-derived but have shifted isotopic composition through exchange with country rocks in the hydrothermal system. Early fluids may have been buffered by country rocks at sites of deposition whereas fluids giving rise to ore-forming stages have retained oxygen signatures from further back in the hydrothermal flow path. The Br/Cl ratios indicate the expulsion of trapped bitterns or the incongruent dissolution of halite in evaporite horizons, leading to gradual depletion of Br as the mineralising fluids evolved., Fluid inclusion studies of gangue quartz from epigenetic base metal, fluorite and barite deposits in the Palaeozoic Massif Central have shown that, despite major variations in deposit mineralogy and host rock lithology, ore-forming fluids were brines with a salinity of 20-26 wt% NaCl equiv. Oxygen isotope analysis suggests that these brines were surface-derived but have shifted isotopic composition through exchange with country rocks in the hydrothermal system. Early fluids may have been buffered by country rocks at sites of deposition whereas fluids giving rise to ore-forming stages have retained oxygen signatures from further back in the hydrothermal flow path. The Br/Cl ratios indicate the expulsion of trapped bitterns or the incongruent dissolution of halite in evaporite horizons, leading to gradual depletion of Br as the mineralising fluids evolved.

Fluid inclusions and isotope data from fault-associated sulphide-bearing veins hosted by Lower Palaeozoic rocks in the SW Irish Midlands indicate that regional flow of mineralising fluid occurred in the fractured basement underlying the mineralised Carboniferous basins. Halogen and chemical data show that this fluid was ultimately derived from seawater that had circulated deeply within the basement and had equilibrated with the basement rocks. The observed data are best explained by density-driven convection within fault and fracture zones., Fluid inclusions and isotope data from fault-associated sulphide-bearing veins hosted by Lower Palaeozoic rocks in the SW Irish Midlands indicate that regional flow of mineralising fluid occurred in the fractured basement underlying the mineralised Carboniferous basins. Halogen and chemical data show that this fluid was ultimately derived from seawater that had circulated deeply within the basement and had equilibrated with the basement rocks. The observed data are best explained by density-driven convection within fault and fracture zones.

The Saint-Salvy Zn, Peyrebrune Zn+Fl, and Mont Roc Fl deposits represent a spectrum of vein mineralisation in the Palaeozoic basement of the SW Massif Central. Paragenetically these deposits are linked. In all deposits there is a history of multistage fluid incursion, but the fluids responsible for mainstage mineralisations were of high salinity (20-25 wt% NaCl equivalent) and low-moderate temperature; all were CaCl2-bearing. In addition, ore fluids have halogen contents indicative of fluids in equilibrium with evaporites. Isotope analysis indicates that the fluids were variably evolved meteoric waters, and in the case of the Saint Salvy and Peyrebrune deposits, an organic H contribution is suggested by very low isotope analysis. Ore fluids were probably meteoric waters which interacted with evaporite and hydrocarbon-bearing sequences in the adjacent Mesozoic Aquitaine Basin., The Saint-Salvy Zn, Peyrebrune Zn+Fl, and Mont Roc Fl deposits represent a spectrum of vein mineralisation in the Palaeozoic basement of the SW Massif Central. Paragenetically these deposits are linked. In all deposits there is a history of multistage fluid incursion, but the fluids responsible for mainstage mineralisations were of high salinity (20-25 wt% NaCl equivalent) and low-moderate temperature; all were CaCl2-bearing. In addition, ore fluids have halogen contents indicative of fluids in equilibrium with evaporites. Isotope analysis indicates that the fluids were variably evolved meteoric waters, and in the case of the Saint Salvy and Peyrebrune deposits, an organic H contribution is suggested by very low isotope analysis. Ore fluids were probably meteoric waters which interacted with evaporite and hydrocarbon-bearing sequences in the adjacent Mesozoic Aquitaine Basin.

The results are presented of a detailed S, C and O isotope study of the Harberton Bridge mineralisation together with new Pb and Sr isotope determinations. These do not support a basin brine expulsion origin for the deposit, as advocated for Mississippi Valley-type deposits, but place it within the existing genetic framework of Irish carbonate-hosted zinc-lead deposits while providing further insight into Carboniferous metallogenic processes., The results are presented of a detailed S, C and O isotope study of the Harberton Bridge mineralisation together with new Pb and Sr isotope determinations. These do not support a basin brine expulsion origin for the deposit, as advocated for Mississippi Valley-type deposits, but place it within the existing genetic framework of Irish carbonate-hosted zinc-lead deposits while providing further insight into Carboniferous metallogenic processes.

Tungsten mineralisation in Boulder County is mainly hosted by quartz-ferberite veins. Ore deposition was probably within an epithermal (meteoric water) system, genetically related to late Laramide intrusives. A geochemical/isotopic survey reveals that the most intensive zones of alteration are not coincident with the most productive areas, but rather, differential competency of host rocks determines the location of the most economic mineralisation., Tungsten mineralisation in Boulder County is mainly hosted by quartz-ferberite veins. Ore deposition was probably within an epithermal (meteoric water) system, genetically related to late Laramide intrusives. A geochemical/isotopic survey reveals that the most intensive zones of alteration are not coincident with the most productive areas, but rather, differential competency of host rocks determines the location of the most economic mineralisation.

Whilst it is clear that structure was the key to the Tanzanian deposit's generation, a number of atypical features may also have been crucial components. Early syngenetic pyrite associated with black shales was essentially barren of economically important elements but may have acted as a geochemical trap for later precipitation of gold. Early saline fluids, recorded in quartz in the gold-bearing vein mineralisation, suggest an early magmatic event that from lithogeochemical data is thought to have involved pre-ore enrichment in metal. The deposit's genesis is therefore interpreted as having been a two-stage hydrothermal process with the main lode-gold event overprinting and earlier Cu-Au-enriched magmatic system., Whilst it is clear that structure was the key to the Tanzanian deposit's generation, a number of atypical features may also have been crucial components. Early syngenetic pyrite associated with black shales was essentially barren of economically important elements but may have acted as a geochemical trap for later precipitation of gold. Early saline fluids, recorded in quartz in the gold-bearing vein mineralisation, suggest an early magmatic event that from lithogeochemical data is thought to have involved pre-ore enrichment in metal. The deposit's genesis is therefore interpreted as having been a two-stage hydrothermal process with the main lode-gold event overprinting and earlier Cu-Au-enriched magmatic system.

Total production from the orefield, whose last mine closed in 1998, is estimated at around 1 750 000 tonnes Sn, 1 000 000 t Cu and 130 000 t Zn. The integrated results of tectonic/structural geological and He/S isotope studies are briefly presented. It is concluded that, while Variscan convergence increased the geothermal gradient in the lower plate by causing modest thrust-related thickening, the Permian granite magmatism and associated magmatic-hydrothermal mineralisation was ultimately initiated and controlled by around 30 m.y. of post-collisional lithospheric extension., Total production from the orefield, whose last mine closed in 1998, is estimated at around 1 750 000 tonnes Sn, 1 000 000 t Cu and 130 000 t Zn. The integrated results of tectonic/structural geological and He/S isotope studies are briefly presented. It is concluded that, while Variscan convergence increased the geothermal gradient in the lower plate by causing modest thrust-related thickening, the Permian granite magmatism and associated magmatic-hydrothermal mineralisation was ultimately initiated and controlled by around 30 m.y. of post-collisional lithospheric extension.

The large, intrusion-related, sulphide-dominated Bolivian polymetallic vein deposits typically span the mesothermal and epithermal environments and are significant producers of Ag, Sn, Sn and Au. Cerro Rico, a classic example, has produced at least 1 000 000 000 oz Ag since 1544. This spectacular resource was largely a function of a highly efficient and focused silver precipitation mechanism that required the presence of a near-surface, acid-sulphate fluid of which the acid-sulphate lithocap, at least twice as thick as that at any other Bolivian deposit, is the expression. The physical and chemical properties of the vuggy silica zone impeded erosion so that both hypogene mineralisation and the supergene oxidation zone have been largely preserved in a distinctive conical hill., The large, intrusion-related, sulphide-dominated Bolivian polymetallic vein deposits typically span the mesothermal and epithermal environments and are significant producers of Ag, Sn, Sn and Au. Cerro Rico, a classic example, has produced at least 1 000 000 000 oz Ag since 1544. This spectacular resource was largely a function of a highly efficient and focused silver precipitation mechanism that required the presence of a near-surface, acid-sulphate fluid of which the acid-sulphate lithocap, at least twice as thick as that at any other Bolivian deposit, is the expression. The physical and chemical properties of the vuggy silica zone impeded erosion so that both hypogene mineralisation and the supergene oxidation zone have been largely preserved in a distinctive conical hill.

Textural, mineral, chemical and isotopic evidence suggests that the main-stage ore was precipitated as a consequence of rapid supersaturation caused by fluid mixing within the permeable dolomite breccias. The relatively high-temperature metal-bearing solutions were derived from a basement-equilibrated reservoir and the fluids rich in bacteriogenic H2S were shallow, saline formation waters. Minor metals are thought to have been stripped from the footwall during hydrothermal alteration. The availability of abundant sea-water sulphate, operation of open-system bacterial sulphate reduction and episodic availability of free oxygen imply that ore formed not far below the sea floor. Its cessation was due to the cutting off of the supply of S-rich brines, possibly by the deposition of impermeable hanging-wall sediments., Textural, mineral, chemical and isotopic evidence suggests that the main-stage ore was precipitated as a consequence of rapid supersaturation caused by fluid mixing within the permeable dolomite breccias. The relatively high-temperature metal-bearing solutions were derived from a basement-equilibrated reservoir and the fluids rich in bacteriogenic H2S were shallow, saline formation waters. Minor metals are thought to have been stripped from the footwall during hydrothermal alteration. The availability of abundant sea-water sulphate, operation of open-system bacterial sulphate reduction and episodic availability of free oxygen imply that ore formed not far below the sea floor. Its cessation was due to the cutting off of the supply of S-rich brines, possibly by the deposition of impermeable hanging-wall sediments.

The Alcudia Valley has a large number of Pb-Zn-Ag-Cu deposits hosted by neo-Proterozoic and Palaeozoic sedimentary rocks. Five distinct types of deposits are recognised. The most significant mineralising events were related to the two phases of deformation and granite emplacement during the Hercynian orogeny. Stable isotope and lithogeochemical data demonstrate that metals, as well as sulphur and carbon, were sourced from the local sedimentary rocks. Type A deposits are minor occurrences of stratabound mineralisation with Zn content greater than Pb, occurring as small disseminations and veins in Late Ordovician limestone. A syndiagenetic origin is proposed. Types B,C and D are syntectonic deposits with Zn content greater than Pb. Type E, the most abundant and economically significant, are post-tectonic vein deposits with Pb content greater than Zn occupying fractures of the second phase of deformation, widely distributed throughout the district and rock types. Mineral assemblages and Ag contents show a zonal relationship with monzogranites, indicating that late Hercynian magmatism was the source of heat driving the fluid migration., The Alcudia Valley has a large number of Pb-Zn-Ag-Cu deposits hosted by neo-Proterozoic and Palaeozoic sedimentary rocks. Five distinct types of deposits are recognised. The most significant mineralising events were related to the two phases of deformation and granite emplacement during the Hercynian orogeny. Stable isotope and lithogeochemical data demonstrate that metals, as well as sulphur and carbon, were sourced from the local sedimentary rocks. Type A deposits are minor occurrences of stratabound mineralisation with Zn content greater than Pb, occurring as small disseminations and veins in Late Ordovician limestone. A syndiagenetic origin is proposed. Types B,C and D are syntectonic deposits with Zn content greater than Pb. Type E, the most abundant and economically significant, are post-tectonic vein deposits with Pb content greater than Zn occupying fractures of the second phase of deformation, widely distributed throughout the district and rock types. Mineral assemblages and Ag contents show a zonal relationship with monzogranites, indicating that late Hercynian magmatism was the source of heat driving the fluid migration.

Fluid inclusion composition was measured using a crush-leach technique to provide data constraining the possible sources of fluids during and after mineralisation. Cl and Br concentrations indicated that the main ore fluid at Tynagh and Silvermines was sea water that had evaporated until the salinity was between 12 and 18 wt%. However, Na, K and Li data show that water-rock interactions depleted Na and enriched K and Li. The fluids that resulted in post-ore dolomitisation were also derived from evaporated sea water that had precipitated halite, but had not interacted with the same lithologies as the ore fluids; the major change to their composition was the exchange of Mg for Ca. It is proposed that the ore fluids could only have reached their high levels of salinity by evaporation of sea water on the extensive shallow-water shelf regions that existed over much of the Irish Midlands., Fluid inclusion composition was measured using a crush-leach technique to provide data constraining the possible sources of fluids during and after mineralisation. Cl and Br concentrations indicated that the main ore fluid at Tynagh and Silvermines was sea water that had evaporated until the salinity was between 12 and 18 wt%. However, Na, K and Li data show that water-rock interactions depleted Na and enriched K and Li. The fluids that resulted in post-ore dolomitisation were also derived from evaporated sea water that had precipitated halite, but had not interacted with the same lithologies as the ore fluids; the major change to their composition was the exchange of Mg for Ca. It is proposed that the ore fluids could only have reached their high levels of salinity by evaporation of sea water on the extensive shallow-water shelf regions that existed over much of the Irish Midlands.

The predictions of the Irish-type and Mississippi Valley-type models for ore genesis at Navan are tested with regard to their predicted metal distributions and S isotope patterns associated with various fault geometries, focusing on the basal 5 lens that contains 70% of the 90 000 000 t orebody. It is concluded that ore deposition took place when bacteriogenic sulphide, reduced from Mississippian seawater sulphate, reacted with rising, metal-bearing mesothermal fluids. Any model invoking an onset of mineralisation later than the mid-Lower Mississippian does not stand up to this scrutiny., The predictions of the Irish-type and Mississippi Valley-type models for ore genesis at Navan are tested with regard to their predicted metal distributions and S isotope patterns associated with various fault geometries, focusing on the basal 5 lens that contains 70% of the 90 000 000 t orebody. It is concluded that ore deposition took place when bacteriogenic sulphide, reduced from Mississippian seawater sulphate, reacted with rising, metal-bearing mesothermal fluids. Any model invoking an onset of mineralisation later than the mid-Lower Mississippian does not stand up to this scrutiny.

A programme of geological mapping and lithogeochemical and geochronological sampling has been carried out over 745 km2 around La Escondida, Zaldivar and Chimborazo. Andean-cycle arc magmatism began in the Triassic, moving eastward in the Palaeocene and producing widespread calc-alkaline intermediate to felsic volcanism throughout the Eocene. Stress relaxation at the end of the period coincided with the emplacement of voluminous diorites and also with porphyry development. Porphyry emplacement was localised within a broad zone of intersection between the West Fissure zone and a regionally extensive NW-trending structural corridor. The geometry of this junction may have been conducive to the formation of dilational structures, which focused the ascent and pooling of magma in the upper crust and maximised the potential for formation of magmatic-hydrothermal ore deposits., A programme of geological mapping and lithogeochemical and geochronological sampling has been carried out over 745 km2 around La Escondida, Zaldivar and Chimborazo. Andean-cycle arc magmatism began in the Triassic, moving eastward in the Palaeocene and producing widespread calc-alkaline intermediate to felsic volcanism throughout the Eocene. Stress relaxation at the end of the period coincided with the emplacement of voluminous diorites and also with porphyry development. Porphyry emplacement was localised within a broad zone of intersection between the West Fissure zone and a regionally extensive NW-trending structural corridor. The geometry of this junction may have been conducive to the formation of dilational structures, which focused the ascent and pooling of magma in the upper crust and maximised the potential for formation of magmatic-hydrothermal ore deposits.

Sulphur and lead isotope ratios in samples of sphalerite and galena concentrates from Navan, each representing up to a million tonnes of ore, show very limited variation. Calculations suggest that more than 90% of the sulphides were derived through bacteriogenic reduction of Mississippian seawater sulphate, whereas metals were acquired from a local, orogenic crustal source beneath the orebody. A palaeoenvironment strongly conducive to bacterial activity was evidently of central importance to the establishment of this giant deposit., Sulphur and lead isotope ratios in samples of sphalerite and galena concentrates from Navan, each representing up to a million tonnes of ore, show very limited variation. Calculations suggest that more than 90% of the sulphides were derived through bacteriogenic reduction of Mississippian seawater sulphate, whereas metals were acquired from a local, orogenic crustal source beneath the orebody. A palaeoenvironment strongly conducive to bacterial activity was evidently of central importance to the establishment of this giant deposit.

The development of large-scale delta-D, H2O+ and Rb/Sr lithochemical anomalies and wall-rock alteration to quartz ferberite veins in the tungsten district is attributed to the interaction of early Tertiary meteoric fluid with heated country rock. However, the fluid responsible for the ferberite veins may also have contained a magmatic component. The fact that the areas of most intense fluid-rock interaction do not correlate closely with the most productive ore zones or with W anomalies is most probably due to the involvement of separate pulses of hydrothermal fluid for alteration and mineralisation, as well as differences in competency between the two main host-rock types. The use of delta-D analysis to detect extensive exchange between hydrothermal fluids and country rocks has potential as an exploration guide., The development of large-scale delta-D, H2O+ and Rb/Sr lithochemical anomalies and wall-rock alteration to quartz ferberite veins in the tungsten district is attributed to the interaction of early Tertiary meteoric fluid with heated country rock. However, the fluid responsible for the ferberite veins may also have contained a magmatic component. The fact that the areas of most intense fluid-rock interaction do not correlate closely with the most productive ore zones or with W anomalies is most probably due to the involvement of separate pulses of hydrothermal fluid for alteration and mineralisation, as well as differences in competency between the two main host-rock types. The use of delta-D analysis to detect extensive exchange between hydrothermal fluids and country rocks has potential as an exploration guide.

An integrated study has produced a model for the location and genesis of gold in the metamorphosed and deformed Upper Proterozoic cover of the Sperrin Mountains. Caledonian compressional deformation formed E-W-trending shears and probably reactivated the NNE-SSW Omagh lineament. The initial unmineralised veins post-dated the main metamorphic event. Reactivation at Curraghinalt and probably Cavanacaw resulted in brecciation and cementation of the primary quartz, synchronous with the first phase of sulphide and gold mineralisation as a result of fluid mixing. Mineralogical differences between the two deposits may reflect the relative influences of an initial magmatic fluid and a later basinal brine. Late quartz and associated remobilised gold were probably related to brittle deformation resulting from thrusting in the Upper Permian. Potential exploration targets would be Variscan structures, with the brine signatures used as a vector towards gold and base metals., An integrated study has produced a model for the location and genesis of gold in the metamorphosed and deformed Upper Proterozoic cover of the Sperrin Mountains. Caledonian compressional deformation formed E-W-trending shears and probably reactivated the NNE-SSW Omagh lineament. The initial unmineralised veins post-dated the main metamorphic event. Reactivation at Curraghinalt and probably Cavanacaw resulted in brecciation and cementation of the primary quartz, synchronous with the first phase of sulphide and gold mineralisation as a result of fluid mixing. Mineralogical differences between the two deposits may reflect the relative influences of an initial magmatic fluid and a later basinal brine. Late quartz and associated remobilised gold were probably related to brittle deformation resulting from thrusting in the Upper Permian. Potential exploration targets would be Variscan structures, with the brine signatures used as a vector towards gold and base metals.

Field and microscopic studies, K-Ar dating and stable isotope analysis demonstrate that some of the gold in the deposit's oxide cap is supergene, of two types: minute gold grains, 1-10 micrometres across, of high fineness and associated with jarosite and iron oxyhydroxides; and invisible gold, probably adsorbed on minerals such as jarosite and iron oxyhydroxides. S isotope values for pyrite are consistent with a magmatic origin, while those for sulphate are homogeneous and overlap closely with those of pyrite, supporting petrographic evidence that sulphate replaced pyrite. By contrast, O isotope values for sulphate are inhomogeneous within a large range, suggesting kinetically controlled reactions involving various proportions of atmospheric oxygen and local meteoric water in the seasonally dry Altiplano. Oxide-zone mineralogy indicates that groundwaters were acidic, oxidising and relatively saline, with halide complexes probably responsible for gold mobilisation. The alteration had begun by around 11 Ma and lasted until around 4 Ma., Field and microscopic studies, K-Ar dating and stable isotope analysis demonstrate that some of the gold in the deposit's oxide cap is supergene, of two types: minute gold grains, 1-10 micrometres across, of high fineness and associated with jarosite and iron oxyhydroxides; and invisible gold, probably adsorbed on minerals such as jarosite and iron oxyhydroxides. S isotope values for pyrite are consistent with a magmatic origin, while those for sulphate are homogeneous and overlap closely with those of pyrite, supporting petrographic evidence that sulphate replaced pyrite. By contrast, O isotope values for sulphate are inhomogeneous within a large range, suggesting kinetically controlled reactions involving various proportions of atmospheric oxygen and local meteoric water in the seasonally dry Altiplano. Oxide-zone mineralogy indicates that groundwaters were acidic, oxidising and relatively saline, with halide complexes probably responsible for gold mobilisation. The alteration had begun by around 11 Ma and lasted until around 4 Ma.

Massive fluorite in the area is hosted within large E-W striking fractures associated with large zones of hypersilicified tectonic breccia which form the wall of the mined deposits. Fluid inclusion data for pre-fluorite and fluorite stage fluids give salinities of 20-26 wt% NaCl equiv., with homogenisation temperature of 85-170 degrees C. Low first ice melting temperatures (around -50 degrees C) indicate the presence of significant CaCl2 and possibly MgCl2 together with NaCl. Calculated delta-O18 values for pre-fluorite quartz place the fluid on the present day meteoric water line and values for fluorite stage fluids indicate an interacted meteoric fluid origin. The main fluorite depositing fluid was typical of a basinal brine. A model is proposed which suggests that mineralisation was related to major Mesozoic extensional events coinciding with the gradual opening of the Atlantic and Tethys oceans., Massive fluorite in the area is hosted within large E-W striking fractures associated with large zones of hypersilicified tectonic breccia which form the wall of the mined deposits. Fluid inclusion data for pre-fluorite and fluorite stage fluids give salinities of 20-26 wt% NaCl equiv., with homogenisation temperature of 85-170 degrees C. Low first ice melting temperatures (around -50 degrees C) indicate the presence of significant CaCl2 and possibly MgCl2 together with NaCl. Calculated delta-O18 values for pre-fluorite quartz place the fluid on the present day meteoric water line and values for fluorite stage fluids indicate an interacted meteoric fluid origin. The main fluorite depositing fluid was typical of a basinal brine. A model is proposed which suggests that mineralisation was related to major Mesozoic extensional events coinciding with the gradual opening of the Atlantic and Tethys oceans.

The deposit, one of several gold prospects along the Highland Boundary fault zone and its extensions, is hosted by Dalradian metasediments thrust over an Ordovician arc terrane. Pyrite grains with Au-rich electrum are cross-cut by fractures containing later, Ag-rich electrum associated with Ag, Cu, Zn, Pb and Ba sulphides. Cathodoluminescence textural studies, combined with fluid inclusion and laser-fluorination oxygen isotope analysis, have provided good evidence of remobilisation of gold by low-temperature brines. Geological data are consisitent with these brines having been of basinal origin, derived from Carboniferous sediments and mobilised during Variscan tectonism. Although the gold transport mechanism is unclear, the results suggest that low-temperature brine transport of gold is possible and that this process could have been responsible for low-temperature gold mineralisation in hitherto unexpected environments., The deposit, one of several gold prospects along the Highland Boundary fault zone and its extensions, is hosted by Dalradian metasediments thrust over an Ordovician arc terrane. Pyrite grains with Au-rich electrum are cross-cut by fractures containing later, Ag-rich electrum associated with Ag, Cu, Zn, Pb and Ba sulphides. Cathodoluminescence textural studies, combined with fluid inclusion and laser-fluorination oxygen isotope analysis, have provided good evidence of remobilisation of gold by low-temperature brines. Geological data are consisitent with these brines having been of basinal origin, derived from Carboniferous sediments and mobilised during Variscan tectonism. Although the gold transport mechanism is unclear, the results suggest that low-temperature brine transport of gold is possible and that this process could have been responsible for low-temperature gold mineralisation in hitherto unexpected environments.

Analysis of 62 samples show that the sulphides throughout the igneous stratigraphy have a magmatic signature, with the exception of the uppermost gabbros and the lowermost basal thrust talc-carbonate lithologies. Mean delta-34S values for whole-rock samples from harzburgites, dunite pods in harzburgite, crustal dunites and wehrlites, the main and high-level pyroxenites and gabbros suggest that the primary sulphides derived their sulphur from a magmatic source enriched in 34S. This finding is compatible with the proposed origin of the ophiolite above a subduction zone. Values for pyrite mineralisation in the uppermost part of the gabbros are thought to result from precipitation from a seawater-derived fluid, while isotopically light sulphur in the basal thrust could have been introduced from underlying metasediments. The replacement of pentlandite by heazlewoodite has not led to sulphur fractionation., Analysis of 62 samples show that the sulphides throughout the igneous stratigraphy have a magmatic signature, with the exception of the uppermost gabbros and the lowermost basal thrust talc-carbonate lithologies. Mean delta-34S values for whole-rock samples from harzburgites, dunite pods in harzburgite, crustal dunites and wehrlites, the main and high-level pyroxenites and gabbros suggest that the primary sulphides derived their sulphur from a magmatic source enriched in 34S. This finding is compatible with the proposed origin of the ophiolite above a subduction zone. Values for pyrite mineralisation in the uppermost part of the gabbros are thought to result from precipitation from a seawater-derived fluid, while isotopically light sulphur in the basal thrust could have been introduced from underlying metasediments. The replacement of pentlandite by heazlewoodite has not led to sulphur fractionation.

Over 97% of the ore is hosted by a Lower Carboniferous succession of shallow-water, carbonate-dominated beds termed the Pale Beds. The ore occurs as complex, stratabound, tabular lenses often dislocated by faulting and truncated by a submarine erosional slide structure, above which lies the economically minor but genetically important Conglomerate Group. Sphalerite and galena predominate in a 5:1 ratio, with more pyrite and marcasite in Conglomerate Group ores and Pale Beds ore just below the erosion surface. The mineralisation ranges from high-grade massive sulphides to lower-grade sulphide layers between barren limestones, reflecting sub-seafloor emplacement. There is strong evidence for tectonic disruption during deposition. Sulphides were deposited by open-space growth and replacement; isotope analysis indicates two sources of sulphur, with contemporaneous sea water predominating., Over 97% of the ore is hosted by a Lower Carboniferous succession of shallow-water, carbonate-dominated beds termed the Pale Beds. The ore occurs as complex, stratabound, tabular lenses often dislocated by faulting and truncated by a submarine erosional slide structure, above which lies the economically minor but genetically important Conglomerate Group. Sphalerite and galena predominate in a 5:1 ratio, with more pyrite and marcasite in Conglomerate Group ores and Pale Beds ore just below the erosion surface. The mineralisation ranges from high-grade massive sulphides to lower-grade sulphide layers between barren limestones, reflecting sub-seafloor emplacement. There is strong evidence for tectonic disruption during deposition. Sulphides were deposited by open-space growth and replacement; isotope analysis indicates two sources of sulphur, with contemporaneous sea water predominating.

High-precision 40Ar/39Ar dating was carried out of sanidine and biotite from two rhyolitic domes and an ignimbrite. Combined with existing fission-track data and a hydrothermal selicite age, the results suggest that the world-class Ag deposit was emplaced during a protracted period of magma-related hydrothermal activity beginning at 13.11 +/- 0.03 Ma and continuing for at least 0.2 my. This may have been sustained by a large single injection or repeated injections of fractionated Ag-enriched magma into a high-level magma chamber. K-Ar dating of alunite indicates that supergene oxidation had begun by about 13.5 Ma, soon after dome emplacement, and progressed semi-continuously for at least 1.5 my. This oxidation has significantly enhanced the economic viability of the disseminated part of the orebody., High-precision 40Ar/39Ar dating was carried out of sanidine and biotite from two rhyolitic domes and an ignimbrite. Combined with existing fission-track data and a hydrothermal selicite age, the results suggest that the world-class Ag deposit was emplaced during a protracted period of magma-related hydrothermal activity beginning at 13.11 +/- 0.03 Ma and continuing for at least 0.2 my. This may have been sustained by a large single injection or repeated injections of fractionated Ag-enriched magma into a high-level magma chamber. K-Ar dating of alunite indicates that supergene oxidation had begun by about 13.5 Ma, soon after dome emplacement, and progressed semi-continuously for at least 1.5 my. This oxidation has significantly enhanced the economic viability of the disseminated part of the orebody.

Knowledge of propylitic assemblages and how they form in porphyry ore systems is crucial to effective exploration, as they may be the only visible sign of hydrothermal activity. Quantification of metal and ore-related element fluxes through the principal alteration zones at Northparkes by bulk rock geochemistry and chemical mass transfer analysis was combined with mapping of the elements' mineralogy through the propylitic zone. The results show that the alteration is not isochemical, elements such as Cu, Fe and Co, lost from the potassic zone, typically being gained in the propylitic zone and extensive outward dispersion of other elements being reflected in a halo of higher values such as Zn and Mn with an outward decrease in concentration of Cu, Si, Ti and S. Similar trends exist, often with a greater magnitude of variation, in the chemistry of epidote and chlorite from the innermost to outermost propylitic zone. Such patterns, supported by stable isotope values, indicate a close link in space and time between intense propylitic alteration and ore formation; it is argued that the alteration was generated mainly by lateral and upward infiltration of magmatic fluids into the host rocks. Exploration requires detailed recording of mineral chemistry assemblages, alteration intensity and texture., Knowledge of propylitic assemblages and how they form in porphyry ore systems is crucial to effective exploration, as they may be the only visible sign of hydrothermal activity. Quantification of metal and ore-related element fluxes through the principal alteration zones at Northparkes by bulk rock geochemistry and chemical mass transfer analysis was combined with mapping of the elements' mineralogy through the propylitic zone. The results show that the alteration is not isochemical, elements such as Cu, Fe and Co, lost from the potassic zone, typically being gained in the propylitic zone and extensive outward dispersion of other elements being reflected in a halo of higher values such as Zn and Mn with an outward decrease in concentration of Cu, Si, Ti and S. Similar trends exist, often with a greater magnitude of variation, in the chemistry of epidote and chlorite from the innermost to outermost propylitic zone. Such patterns, supported by stable isotope values, indicate a close link in space and time between intense propylitic alteration and ore formation; it is argued that the alteration was generated mainly by lateral and upward infiltration of magmatic fluids into the host rocks. Exploration requires detailed recording of mineral chemistry assemblages, alteration intensity and texture.

The Navan deposit's outer epigenetic (E2) halo, 500-3 000 m from the main orebody and best developed close to large fractures/faults, was found by S-isotope analysis to have some sulphide textures formed from hydrothermal sulphide and others from mixing of hydrothermal sulphide with cool bacteriogenic seawater brines, as at the main orebody. Simple textures, usually galena-dominated, have the hydrothermal signature of positive 34S values whereas more complex sphalerite-rich textures are dominated by bacteriogenic sulphide with negative 34S, distributed in patches up to 2 700 m from the main deposit and correlated with high 66Zn values including some much higher than in the main deposit. It is concluded that for exploration purposes proximity to a large Irish-type deposit may be indicated by recognisably different sulphide textures, identification of bacteriogenic sulphide textures, pockets of sulphide with bacteriogenic 34S signature and correlation of 66Zn sulphide values with 34S, showing halo 66Zn fractionation separate from that of the main deposit., The Navan deposit's outer epigenetic (E2) halo, 500-3 000 m from the main orebody and best developed close to large fractures/faults, was found by S-isotope analysis to have some sulphide textures formed from hydrothermal sulphide and others from mixing of hydrothermal sulphide with cool bacteriogenic seawater brines, as at the main orebody. Simple textures, usually galena-dominated, have the hydrothermal signature of positive 34S values whereas more complex sphalerite-rich textures are dominated by bacteriogenic sulphide with negative 34S, distributed in patches up to 2 700 m from the main deposit and correlated with high 66Zn values including some much higher than in the main deposit. It is concluded that for exploration purposes proximity to a large Irish-type deposit may be indicated by recognisably different sulphide textures, identification of bacteriogenic sulphide textures, pockets of sulphide with bacteriogenic 34S signature and correlation of 66Zn sulphide values with 34S, showing halo 66Zn fractionation separate from that of the main deposit.

The recently highlighted apparent strong correlation of orthomagmatic Ni-Cu-PGE sulphide deposits with plume magmatism intruding through Archaean cratonic margins makes the British Palaeocene igneous province (BPIP) potentially the most prospective PGE province in western Europe, given its intrusion into the Lewisian segment of the North Atlantic craton, its evidence of an enriched lithospheric keel in the form of Cu-Au-PGE-enriched spinel lherzolite mantle xenoliths and this keel's magmatic contributions to widespread melting events in the form of the Palaeoproterozoic Scourie dyke swarm. Powdered whole-rock grab samples were analysed for major and trace elements and PGE and Au abundances as well as a selection undergoing S-isotope analysis. Comparison with similar volcanic rocks in Greenland suggests that S-saturation had been variably achieved prior to eruption and may hint at possible mineralisation deeper in the magmatic system. Ultramafic volcanic plugs on Rum contain abundant late-magmatic sulphides pentlandite, chalcopyrite and pyrrhotite, for which S-isotope signature and abundances are directly correlated to PGE abundance and grade. By correlating Jurassic mudrocks, the most likely S-rich crustal contaminants, across the Hebridean basin, a mechanism can be envisaged by which late-magmatic PGE-bearing sulphides accumulated and slumped during volcanic plug cessation., The recently highlighted apparent strong correlation of orthomagmatic Ni-Cu-PGE sulphide deposits with plume magmatism intruding through Archaean cratonic margins makes the British Palaeocene igneous province (BPIP) potentially the most prospective PGE province in western Europe, given its intrusion into the Lewisian segment of the North Atlantic craton, its evidence of an enriched lithospheric keel in the form of Cu-Au-PGE-enriched spinel lherzolite mantle xenoliths and this keel's magmatic contributions to widespread melting events in the form of the Palaeoproterozoic Scourie dyke swarm. Powdered whole-rock grab samples were analysed for major and trace elements and PGE and Au abundances as well as a selection undergoing S-isotope analysis. Comparison with similar volcanic rocks in Greenland suggests that S-saturation had been variably achieved prior to eruption and may hint at possible mineralisation deeper in the magmatic system. Ultramafic volcanic plugs on Rum contain abundant late-magmatic sulphides pentlandite, chalcopyrite and pyrrhotite, for which S-isotope signature and abundances are directly correlated to PGE abundance and grade. By correlating Jurassic mudrocks, the most likely S-rich crustal contaminants, across the Hebridean basin, a mechanism can be envisaged by which late-magmatic PGE-bearing sulphides accumulated and slumped during volcanic plug cessation.

This study tests the utility of the minor to trace element composition of sphalerite to discriminate between possible sources of ore-forming fluids, and to constrain processes involved in ore genesis of the world-class Irish-type Navan Zn-Pb orebody, Ireland. Detailed petrography and electron microprobe microanalysis were performed on layered sphalerite previously analysed for Zn, Fe, and S isotope compositions. Layered sphalerite displays a wide range of chemical composition at both sample and crystal scales. The colour, style and scale of layering show variations with chemical composition, but none of these correlations are consistent between samples. However, there are strong intersample correlations between chemical and S-Fe-Zn isotope compositions at the millimeter scale. Sphalerite precipitated from deep, hydrothermal fluids with 34S-enriched sulphide is enriched in Cd, Sb, Cu and Ag, whereas Fe and As are enriched in sphalerite precipitated from shallow, bacteriogenic brines with isotopically light S. Significant chemical variations also occur at the micrometer scale in sphalerite regardless of its genetic affinity. These variations are interpreted as being due to variations in temperature, pH and sulphur activity following the arrival at the site of deposition of pulses of hydrothermal fluids at specific stages of sphalerite growth. Therefore the chemistry of sphalerite, coupled with its texture, appears to be a powerful tool to elucidate fluid typing and ore genesis., This study tests the utility of the minor to trace element composition of sphalerite to discriminate between possible sources of ore-forming fluids, and to constrain processes involved in ore genesis of the world-class Irish-type Navan Zn-Pb orebody, Ireland. Detailed petrography and electron microprobe microanalysis were performed on layered sphalerite previously analysed for Zn, Fe, and S isotope compositions. Layered sphalerite displays a wide range of chemical composition at both sample and crystal scales. The colour, style and scale of layering show variations with chemical composition, but none of these correlations are consistent between samples. However, there are strong intersample correlations between chemical and S-Fe-Zn isotope compositions at the millimeter scale. Sphalerite precipitated from deep, hydrothermal fluids with 34S-enriched sulphide is enriched in Cd, Sb, Cu and Ag, whereas Fe and As are enriched in sphalerite precipitated from shallow, bacteriogenic brines with isotopically light S. Significant chemical variations also occur at the micrometer scale in sphalerite regardless of its genetic affinity. These variations are interpreted as being due to variations in temperature, pH and sulphur activity following the arrival at the site of deposition of pulses of hydrothermal fluids at specific stages of sphalerite growth. Therefore the chemistry of sphalerite, coupled with its texture, appears to be a powerful tool to elucidate fluid typing and ore genesis.

Kimbali's principal deposit, the KCD, had an inferred resource of 13 900 000 oz Au at the end of 2012 in three stacked NE-dipping tabular lodes hosted by heavily altered volcano-sedimentary agglomerate and laterally confined by large vertical shears that bisect the host greenstone belts. Satellite deposits within the adjacent mineralised corridors have a total inferred resource of 18 900 000 oz Au and include three under development: Mengu, Pakak and Pamao. The KCD deposit has multiple generations of disseminated pyrite, arsenopyrite, chalcopyrite and pyrrhotite hosted in quartz vein structures, Mengu is dominated by pyrite while Pakaka and Pamao have zones significantly enriched in arsenopyrite, but in all cases pyrite 2 is the most abundant phase and shows the strongest correlation with Au mineralisation. The wider Kibali study area straddles three geological terranes: the Kibali granite-greenstone belt in the north, the West Nile gneiss and the Upper Zaire granitoid massif in the south, the latter two considered barren of gold deposits. It is hypothesised that the gold resource formed in a convergent tectonic environment as part of a thickening thrust stack along the edge of the forming Upper Zaire granitic massif, where devolatilised fluids from the lower stack scavenged sulphur and metals as they ascended along faults., Kimbali's principal deposit, the KCD, had an inferred resource of 13 900 000 oz Au at the end of 2012 in three stacked NE-dipping tabular lodes hosted by heavily altered volcano-sedimentary agglomerate and laterally confined by large vertical shears that bisect the host greenstone belts. Satellite deposits within the adjacent mineralised corridors have a total inferred resource of 18 900 000 oz Au and include three under development: Mengu, Pakak and Pamao. The KCD deposit has multiple generations of disseminated pyrite, arsenopyrite, chalcopyrite and pyrrhotite hosted in quartz vein structures, Mengu is dominated by pyrite while Pakaka and Pamao have zones significantly enriched in arsenopyrite, but in all cases pyrite 2 is the most abundant phase and shows the strongest correlation with Au mineralisation. The wider Kibali study area straddles three geological terranes: the Kibali granite-greenstone belt in the north, the West Nile gneiss and the Upper Zaire granitoid massif in the south, the latter two considered barren of gold deposits. It is hypothesised that the gold resource formed in a convergent tectonic environment as part of a thickening thrust stack along the edge of the forming Upper Zaire granitic massif, where devolatilised fluids from the lower stack scavenged sulphur and metals as they ascended along faults.

Precious-metal mineralisation occurs both within the Tertiary layered gabbroic intrusion and in some, but not all, of its surrounding gabbroic, 100-500 m wide metadykes. Within the Skaergaard intrusion, low-volume precious metal-bearing sulphide deposits with mostly magmatic S isotope ratios support theories that the PGE-Au Platinova reefs resulted from prolonged magma fractionation. Similar metal profiles suggest that a common magma also formed the spatially related macrodykes but significant crustal S isotope content in their precious metal mineralisation indicates localised crustal contamination, interaction with local basin sediments appearing to have determined their prospectivity., Precious-metal mineralisation occurs both within the Tertiary layered gabbroic intrusion and in some, but not all, of its surrounding gabbroic, 100-500 m wide metadykes. Within the Skaergaard intrusion, low-volume precious metal-bearing sulphide deposits with mostly magmatic S isotope ratios support theories that the PGE-Au Platinova reefs resulted from prolonged magma fractionation. Similar metal profiles suggest that a common magma also formed the spatially related macrodykes but significant crustal S isotope content in their precious metal mineralisation indicates localised crustal contamination, interaction with local basin sediments appearing to have determined their prospectivity.

Four presentations at the meeting considered the Caledonian gold deposits at Curraghinalt in Northern Ireland and Cononish, near Tyndrum, in Scotland. New light is thrown by Rice et al. on the uncertain relation between gold mineralisation and regional tectonics, magmatism and metamorphism by high-precision Ar-Ar and Re-Os ages showing that gold mineralisation at Curraghinalt dates from 462-449 Ma, following peak metamorphism in the Grampian orogeny, whereas that at Cononish and Rhynie was empaced at 408-407 Ma, the very end of the Caledonian orogogeny, and was linked to the Inner Starav granite as well as being close to the late Silurian-early Devonian movement on the Tyndrum fault. The Curraghinalt mesothermal deposit, described by Lawther and Moloney, is hosted by late Precambrian Dalradian rocks thrust over the Ordovician Tyrone volcanic group and has measured resources of 20 000 tonnes grading 21.51 g/t Au with a further 1 110 000 t at 12.84 g/t indicated and 5 450 000 t at 12.74 g/t inferred. At least ten primary gold-bearing composite veins developed by four distinct periods of quartz and sulphide-rich fluid injection are controlled by a series of high-angled shears. Cononish, a study of whose mineralising system is reported by Hill et al., is a structurally controlled quartz vein hosting a total of 169 200 oz Au and 631 300 oz Ag in measured, indicated and inferred resources. Electrum is related to sulphides across all mineralisation types in the study area, the assemblage being dominated by pyrite and galena with sporadic chalcopyrite, sphalerite and arsenopyrite; a first Au phase is closely associated with galena, as inclusions in pyrite, and a second is accompanied by late void-filling galena and sphalerite. Increasingly heavy delta-34S values over time support the evolution of the system from a magmatic-dominated to a sedimentary-dominated source of sulphur. Work at the University of Leicester, reported by Spence-Jones et al., to develop new hydrometallu, Four presentations at the meeting considered the Caledonian gold deposits at Curraghinalt in Northern Ireland and Cononish, near Tyndrum, in Scotland. New light is thrown by Rice et al. on the uncertain relation between gold mineralisation and regional tectonics, magmatism and metamorphism by high-precision Ar-Ar and Re-Os ages showing that gold mineralisation at Curraghinalt dates from 462-449 Ma, following peak metamorphism in the Grampian orogeny, whereas that at Cononish and Rhynie was empaced at 408-407 Ma, the very end of the Caledonian orogogeny, and was linked to the Inner Starav granite as well as being close to the late Silurian-early Devonian movement on the Tyndrum fault. The Curraghinalt mesothermal deposit, described by Lawther and Moloney, is hosted by late Precambrian Dalradian rocks thrust over the Ordovician Tyrone volcanic group and has measured resources of 20 000 tonnes grading 21.51 g/t Au with a further 1 110 000 t at 12.84 g/t indicated and 5 450 000 t at 12.74 g/t inferred. At least ten primary gold-bearing composite veins developed by four distinct periods of quartz and sulphide-rich fluid injection are controlled by a series of high-angled shears. Cononish, a study of whose mineralising system is reported by Hill et al., is a structurally controlled quartz vein hosting a total of 169 200 oz Au and 631 300 oz Ag in measured, indicated and inferred resources. Electrum is related to sulphides across all mineralisation types in the study area, the assemblage being dominated by pyrite and galena with sporadic chalcopyrite, sphalerite and arsenopyrite; a first Au phase is closely associated with galena, as inclusions in pyrite, and a second is accompanied by late void-filling galena and sphalerite. Increasingly heavy delta-34S values over time support the evolution of the system from a magmatic-dominated to a sedimentary-dominated source of sulphur. Work at the University of Leicester, reported by Spence-Jones et al., to develop new hydrometallu

The complex hosts a number of base and precious metal mineralisation occurrences including the Flammefjeld porphyry Mo deposit and a suite of epithermal-style base and precious veins in an area around the Sonde Syenitgletscher. Re-Os dating was used for a previously unknown occurrence of molybdenite-pyrite-scheelite-bearing quartz veins associated with alkali basalt dykes which intrude the main syenites of the complex. The veins appear to be cogenetic with the dykes, which crosscut and brecciate granodiorites of the Cirque 1320 complex. S isotope signatures of molybdenite and pyrite in the veins are consistent with a magmatic source related to the intrusion of the dykes. Molybdenite from the veins gave an Re-Os age some 13 m.a older that the molybdenite at the Flammefjeld porphyry Mo deposit, distinguishing this metallogenic episode as a distinct, temporally unrelated event. The data suggest that the complex may be slightly older than the 50 Ma currently accepted and closer to 53 to 52 Ma., The complex hosts a number of base and precious metal mineralisation occurrences including the Flammefjeld porphyry Mo deposit and a suite of epithermal-style base and precious veins in an area around the Sonde Syenitgletscher. Re-Os dating was used for a previously unknown occurrence of molybdenite-pyrite-scheelite-bearing quartz veins associated with alkali basalt dykes which intrude the main syenites of the complex. The veins appear to be cogenetic with the dykes, which crosscut and brecciate granodiorites of the Cirque 1320 complex. S isotope signatures of molybdenite and pyrite in the veins are consistent with a magmatic source related to the intrusion of the dykes. Molybdenite from the veins gave an Re-Os age some 13 m.a older that the molybdenite at the Flammefjeld porphyry Mo deposit, distinguishing this metallogenic episode as a distinct, temporally unrelated event. The data suggest that the complex may be slightly older than the 50 Ma currently accepted and closer to 53 to 52 Ma.

The deposit is the world’s largest hydrothermal tin lode, with a total resource of about 1 000 000 tonnes metal at an average grade of 4.7 wt% Sn. The mineralisation is of the cassiterite-sulphide type and occurs in a vertically extensive vein-breccia system centered on a shallow-level, late Oligocene granitoid stock. The tin ores form cassiterite-quartz-chlorite-bearing veins and breccias hosted by several large fault-jogs at depth in the lode. By contrast, the copper ores, which contain disseminated acicular cassiterite, are localized in the upper part of the system. Both ore types are associated with a very distinctive, strong chloritic alteration, which was preceded by intense sericitisation, tourmalinisation, and tourmaline veining. The delta 34S values of the sulphides range between 2 and 6 per mil, and vary very little with location in the deposit. This indicates that the hydrothermal system was large, with a relatively homogeneous source of sulphur, probably of magmatic origin. This is confirmed by stability relationships of ore minerals, which indicate that the ore fluids were initially reducing. Microthermometric studies of fluid inclusions in cassiterite, quartz, tourmaline, and fluorite show that the fluids responsible for the early, barren stage were hot, hypersaline brines (380-540 degrees C, 34-62% NaCl equiv), whereas the ore-stage fluids had moderate to low salinity (0-21 wt % NaCl equiv) and were of moderate temperature (290-380 degrees C). In addition to the marked dilution of the ore fluids with evolution of the hydrothermal system, they became progressively more oxidising, as inferred by the local association of minor haematite with cassiterite and the ubiquitous replacement of pyrrhotite by pyrite and marcasite. The delta18-O values of the fluid decreased systematically with time, as indicated by the delta18-O values of different generations of tourmaline, cassiterite, and quartz. This evolution was paralleled by an increase in the delta D valu, The deposit is the world’s largest hydrothermal tin lode, with a total resource of about 1 000 000 tonnes metal at an average grade of 4.7 wt% Sn. The mineralisation is of the cassiterite-sulphide type and occurs in a vertically extensive vein-breccia system centered on a shallow-level, late Oligocene granitoid stock. The tin ores form cassiterite-quartz-chlorite-bearing veins and breccias hosted by several large fault-jogs at depth in the lode. By contrast, the copper ores, which contain disseminated acicular cassiterite, are localized in the upper part of the system. Both ore types are associated with a very distinctive, strong chloritic alteration, which was preceded by intense sericitisation, tourmalinisation, and tourmaline veining. The delta 34S values of the sulphides range between 2 and 6 per mil, and vary very little with location in the deposit. This indicates that the hydrothermal system was large, with a relatively homogeneous source of sulphur, probably of magmatic origin. This is confirmed by stability relationships of ore minerals, which indicate that the ore fluids were initially reducing. Microthermometric studies of fluid inclusions in cassiterite, quartz, tourmaline, and fluorite show that the fluids responsible for the early, barren stage were hot, hypersaline brines (380-540 degrees C, 34-62% NaCl equiv), whereas the ore-stage fluids had moderate to low salinity (0-21 wt % NaCl equiv) and were of moderate temperature (290-380 degrees C). In addition to the marked dilution of the ore fluids with evolution of the hydrothermal system, they became progressively more oxidising, as inferred by the local association of minor haematite with cassiterite and the ubiquitous replacement of pyrrhotite by pyrite and marcasite. The delta18-O values of the fluid decreased systematically with time, as indicated by the delta18-O values of different generations of tourmaline, cassiterite, and quartz. This evolution was paralleled by an increase in the delta D valu