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Preliminary results are reported from an ongoing isotopic study of the Bandelier Tuff and associated igneous rocks in the Jemez Mountains. The study aims to understand better the genesis of compositionally zoned magmatic systems and to improve knowledge of isotopic variations in an active hydrothermal system associated with sub-ore-grade Mo mineralisation as well as Cu, Pb, Zn, Mn, Bi, Te and Ag minerals., Preliminary results are reported from an ongoing isotopic study of the Bandelier Tuff and associated igneous rocks in the Jemez Mountains. The study aims to understand better the genesis of compositionally zoned magmatic systems and to improve knowledge of isotopic variations in an active hydrothermal system associated with sub-ore-grade Mo mineralisation as well as Cu, Pb, Zn, Mn, Bi, Te and Ag minerals.

The deposit is composed of hydrothermally altered equigranular granodiorite and porphyritic dykes which contain up to 4 wt% sulphides (pyrite, molybdenite, chalcopyrite, galena and sphalerite). Rb-Sr whole-rock isotopic analyses of nine samples from the equigranular granodiorite hosts and porphyritic dykes yield an apparent isochron age of 422+/-15 Ma and a strontium initial ratio (Sr(i)) of 0.70603+/-0.00019. The bulk of the geochemical data indicate that the Rb-Sr isotopic system was reset as a result of alteration, that the isochron age is not the crystallisation age of the stock nor of the mineralisation and that the Sr(i) value of the fluids involved during alteration modified the magmatic Sr(i) value. Fluid inclusion studies indicate that late mineralising fluids responsible for Cu mineralisation were pervasive throughout the system. They were of moderate temperature (less than 300 degrees C) and characterised by generally low salinities (up to 5 equiv wt% NaCl) and moderate CO2 contents (5-15 mole%). Widely varying CO2/H2O values of inclusions in quartz veins suggest that CO2 effervescence may have contributed to deposition of the second stage of mineralisation which produced chalcopyrite + sphalerite + galena + quartz +/- pyrite +/- calcite., The deposit is composed of hydrothermally altered equigranular granodiorite and porphyritic dykes which contain up to 4 wt% sulphides (pyrite, molybdenite, chalcopyrite, galena and sphalerite). Rb-Sr whole-rock isotopic analyses of nine samples from the equigranular granodiorite hosts and porphyritic dykes yield an apparent isochron age of 422+/-15 Ma and a strontium initial ratio (Sr(i)) of 0.70603+/-0.00019. The bulk of the geochemical data indicate that the Rb-Sr isotopic system was reset as a result of alteration, that the isochron age is not the crystallisation age of the stock nor of the mineralisation and that the Sr(i) value of the fluids involved during alteration modified the magmatic Sr(i) value. Fluid inclusion studies indicate that late mineralising fluids responsible for Cu mineralisation were pervasive throughout the system. They were of moderate temperature (less than 300 degrees C) and characterised by generally low salinities (up to 5 equiv wt% NaCl) and moderate CO2 contents (5-15 mole%). Widely varying CO2/H2O values of inclusions in quartz veins suggest that CO2 effervescence may have contributed to deposition of the second stage of mineralisation which produced chalcopyrite + sphalerite + galena + quartz +/- pyrite +/- calcite.

Isotope data are reported for the shale-hosted Zn-Pb-Ag Red Dog deposits, other shale-hosted deposits near Red Dog and Zn-Pb-Ag sulphide and barite deposits in the western and central Brooks Range. The overall Pb isotope homogeneity is consistent with three types of control: a homogeneous regional source, mixing of Pb during leaching of a thick sedimentary section and fluid transport or mixing at the site of deposition. The isotopic variability of the hydrothermal fluids is consistent with a simple mixing system. Evidence indicates that galena was deposited from largely similar hydrothermal solutions throughout the district. Sr isotope data for barite, calcite, and witherite were compared with data from regional barite associated with sulphides and from barite in sulphide-poor occurrences. Early barite is similar to that typically formed in cold seeps along continental margins. This fine-grained barite formed before the main mineralisation event and suggests two possible sources of Sr, fluid-rock reactions involving radiogenic clastic minerals derived from ancient continental crust in strata underlying the Kuna Formation and/or mixing with radiogenic pore fluids in the Ikalukrok unit., Isotope data are reported for the shale-hosted Zn-Pb-Ag Red Dog deposits, other shale-hosted deposits near Red Dog and Zn-Pb-Ag sulphide and barite deposits in the western and central Brooks Range. The overall Pb isotope homogeneity is consistent with three types of control: a homogeneous regional source, mixing of Pb during leaching of a thick sedimentary section and fluid transport or mixing at the site of deposition. The isotopic variability of the hydrothermal fluids is consistent with a simple mixing system. Evidence indicates that galena was deposited from largely similar hydrothermal solutions throughout the district. Sr isotope data for barite, calcite, and witherite were compared with data from regional barite associated with sulphides and from barite in sulphide-poor occurrences. Early barite is similar to that typically formed in cold seeps along continental margins. This fine-grained barite formed before the main mineralisation event and suggests two possible sources of Sr, fluid-rock reactions involving radiogenic clastic minerals derived from ancient continental crust in strata underlying the Kuna Formation and/or mixing with radiogenic pore fluids in the Ikalukrok unit.

Textural, chemical, and isotopic data indicated a paragenesis involving: deposition of early brown sphalerite with abundant barite, minor pyrite, and trace galena immediately beneath the sea floor in unconsolidated mud; deposition of yellow-brown sphalerite during sub-seafloor hydrothermal recrystallisation and coarsening of pre-existing barite; open-space deposition of barite, red-brown sphalerite and other sulphides in veins and coeval replacement of barite; and postore sulphide deposition, including the formation of late tan-coloured sphalerite breccias. Hydrothermal activity ceased until Jurassic time when thrusting and large-scale fluid flow related to the Brookian orogeny remobilised and formed late tan-coloured sphalerite in tectonic breccias., Textural, chemical, and isotopic data indicated a paragenesis involving: deposition of early brown sphalerite with abundant barite, minor pyrite, and trace galena immediately beneath the sea floor in unconsolidated mud; deposition of yellow-brown sphalerite during sub-seafloor hydrothermal recrystallisation and coarsening of pre-existing barite; open-space deposition of barite, red-brown sphalerite and other sulphides in veins and coeval replacement of barite; and postore sulphide deposition, including the formation of late tan-coloured sphalerite breccias. Hydrothermal activity ceased until Jurassic time when thrusting and large-scale fluid flow related to the Brookian orogeny remobilised and formed late tan-coloured sphalerite in tectonic breccias.

The results are presented of geochemical analyses of samples from the Main, Aqqaluk, and Anarraaq deposits. Wall-rock alteration at Red Dog and Anarraaq removed calcite and minor dolomite during hydrothermal decarbonation reactions and introduced Si, Eu, and Ge during silicification. Sulphidation reactions deposited Fe, S, Co, Zn, Pb, Tl, As, and Sb while barite mineralisation introduced Ba, S, and Sr. Light REE and U were mobilised locally. Early hydrothermal silicification at Red Dog took place prior to or during massive sulphide mineralisation. Uniformly low Ca and Mg and uniformly negative Ce anomalies in highly siliceous wall rocks reflect hydrothermal decarbonation reactions and pervasive silicification owing to conductive cooling of oxidised metalliferous fluids. Chalcophile element anomalies in wall rocks at Red Dog and Anarraq are attributed to sulphidation reactions. Sedimentary wall rocks in the Red Dog district are characterised by a distinctive suite of geochemical anomalies. At Anarraaq, the Tl anomaly is most extensively developed. The magnitude of the enrichment and systematic behavior of Tl make it a promising geochemical exploration guide for Red Dog-type Zn-Pb-Ag deposits elsewhere., The results are presented of geochemical analyses of samples from the Main, Aqqaluk, and Anarraaq deposits. Wall-rock alteration at Red Dog and Anarraaq removed calcite and minor dolomite during hydrothermal decarbonation reactions and introduced Si, Eu, and Ge during silicification. Sulphidation reactions deposited Fe, S, Co, Zn, Pb, Tl, As, and Sb while barite mineralisation introduced Ba, S, and Sr. Light REE and U were mobilised locally. Early hydrothermal silicification at Red Dog took place prior to or during massive sulphide mineralisation. Uniformly low Ca and Mg and uniformly negative Ce anomalies in highly siliceous wall rocks reflect hydrothermal decarbonation reactions and pervasive silicification owing to conductive cooling of oxidised metalliferous fluids. Chalcophile element anomalies in wall rocks at Red Dog and Anarraq are attributed to sulphidation reactions. Sedimentary wall rocks in the Red Dog district are characterised by a distinctive suite of geochemical anomalies. At Anarraaq, the Tl anomaly is most extensively developed. The magnitude of the enrichment and systematic behavior of Tl make it a promising geochemical exploration guide for Red Dog-type Zn-Pb-Ag deposits elsewhere.

U-Pb dating of volcanic rocks hosting the largest gold-pyrite-sericite deposits in the belt indicates the following ages: 550+/-3 Ma for high-sulphidation epithermal pyrite-enargite-gold at Brewer; 553+/-2 Ma for disseminated and semimassive pyrite gold in the Champion pit at Haile; and 556+/-2 Ma for disseminated syngenetic chert-hosted gold-pyrite at Ridgeway. Pb isotope compositions indicate multiple generations of pyrite, including early-crystallised pyrite closely associated with the original gold-mineralising event. Whole-rock Pb isotopes of volcanic rocks nearly match the range for sulphides in the gold deposits. Diversity of 206Pb/204Pb values and high 207Pb/204Pb values suggest that the deposits evolved adjacent to continental blocks, perhaps in a back-arc setting. Mantle-derived or oceanic-crust contributions were more important at the stratiform gold, base-metal and barite deposit of Barite Hill than at Brewer, Haile and Rdgeway, where thinned continental crust predominated., U-Pb dating of volcanic rocks hosting the largest gold-pyrite-sericite deposits in the belt indicates the following ages: 550+/-3 Ma for high-sulphidation epithermal pyrite-enargite-gold at Brewer; 553+/-2 Ma for disseminated and semimassive pyrite gold in the Champion pit at Haile; and 556+/-2 Ma for disseminated syngenetic chert-hosted gold-pyrite at Ridgeway. Pb isotope compositions indicate multiple generations of pyrite, including early-crystallised pyrite closely associated with the original gold-mineralising event. Whole-rock Pb isotopes of volcanic rocks nearly match the range for sulphides in the gold deposits. Diversity of 206Pb/204Pb values and high 207Pb/204Pb values suggest that the deposits evolved adjacent to continental blocks, perhaps in a back-arc setting. Mantle-derived or oceanic-crust contributions were more important at the stratiform gold, base-metal and barite deposit of Barite Hill than at Brewer, Haile and Rdgeway, where thinned continental crust predominated.

The identification of paragenetically early types of pyrite establishes that gold mineralisation was coeval with deposition of the host rocks and not solely related to Palaeozoic tectonic events. Replaced pumice and colloform structures containing both arsenic bands and electrum also point to coeval deposition of gold and the volcanic rocks, confirming the deposit's syngenetic origin. Early pyrite textures at other major deposits of the Carolina slate belt, such as Ridgeway and Barite Hill, provide strong evidence for sulphide ores having formed prior to tectonism. The role of Palaeozoic metamorphism was to remobilise and concentrate gold and other minerals in structurally prepared sites., The identification of paragenetically early types of pyrite establishes that gold mineralisation was coeval with deposition of the host rocks and not solely related to Palaeozoic tectonic events. Replaced pumice and colloform structures containing both arsenic bands and electrum also point to coeval deposition of gold and the volcanic rocks, confirming the deposit's syngenetic origin. Early pyrite textures at other major deposits of the Carolina slate belt, such as Ridgeway and Barite Hill, provide strong evidence for sulphide ores having formed prior to tectonism. The role of Palaeozoic metamorphism was to remobilise and concentrate gold and other minerals in structurally prepared sites.

The vein system, hosted by 27 Ma and 26 Ma tuffs, has two mineral associations separated by brecciation and sedimentation in the veins. The early association consists of quartz, rhodonite, haematite, magnetite, electrum and Mn carbonate, Au-Ag sulphide, Ag sulphosalt and base metal sulphide minerals. The later mineral association cuts the Mn- and Au-bearing assemblages and consists of quartz, calcite, sericite, chlorite, haematite, adularia, fluorite, base metal sulphides and Ag-bearing tetrahedrite. Pb isotope data from galenas from the Alpha-Corsair vein shows that they are isotopically similar to galenas associated with North Amethyst Au-stage mineralisation, suggesting that unexplored segments of the Alpha-Corsair structure may have the potential for high Au contents. Isotope results indicate that early Au mineralisation of the North Amethyst area may represent the product of an older and relatively local hydrothermal system distinct from that of the younger base metal and Ag mineralisation found throughout the region., The vein system, hosted by 27 Ma and 26 Ma tuffs, has two mineral associations separated by brecciation and sedimentation in the veins. The early association consists of quartz, rhodonite, haematite, magnetite, electrum and Mn carbonate, Au-Ag sulphide, Ag sulphosalt and base metal sulphide minerals. The later mineral association cuts the Mn- and Au-bearing assemblages and consists of quartz, calcite, sericite, chlorite, haematite, adularia, fluorite, base metal sulphides and Ag-bearing tetrahedrite. Pb isotope data from galenas from the Alpha-Corsair vein shows that they are isotopically similar to galenas associated with North Amethyst Au-stage mineralisation, suggesting that unexplored segments of the Alpha-Corsair structure may have the potential for high Au contents. Isotope results indicate that early Au mineralisation of the North Amethyst area may represent the product of an older and relatively local hydrothermal system distinct from that of the younger base metal and Ag mineralisation found throughout the region.

Rhyolite-hosted Sn deposits occur in some multiple, overlapping Tertiary flow domes. They include cassiterite and can be divided into four types: sparse amounts of cassiterite in lithophysae, miarolitic cavities and tiny gash veins; in argillised zones and well-defined gash veins and anastomosing veinlets; in veins and stockwork-like areas of reticulate veinlets in the distal edges of rhyolite flow domes and in the underlying tuffs and ash-flow tuffs; and as placer accumulations. Placer mining of known deposits in the USA and Mexico is complete and environmental impact associated with mining activities is minimal. The solubility of Sn in surface water is very low, so has no impact on the environment. As-bearing minerals associated with lode, rhyolite-hosted Sn deposits are rare and minor., Rhyolite-hosted Sn deposits occur in some multiple, overlapping Tertiary flow domes. They include cassiterite and can be divided into four types: sparse amounts of cassiterite in lithophysae, miarolitic cavities and tiny gash veins; in argillised zones and well-defined gash veins and anastomosing veinlets; in veins and stockwork-like areas of reticulate veinlets in the distal edges of rhyolite flow domes and in the underlying tuffs and ash-flow tuffs; and as placer accumulations. Placer mining of known deposits in the USA and Mexico is complete and environmental impact associated with mining activities is minimal. The solubility of Sn in surface water is very low, so has no impact on the environment. As-bearing minerals associated with lode, rhyolite-hosted Sn deposits are rare and minor.

This paper provides an overview on the genesis of Mesoproterozoic igneous rocks and associated iron oxide ± apatite (IOA) ± rare earth element, iron oxide-copper-gold (IOCG), and iron-rich sedimentary deposits in the St. Francois Mountains. The Missouri iron orebodies are magmatic-related hydrothermal deposits that, when considered in aggregate, display a vertical zonation from high-temperature, magmatic ± hydrothermal IOA deposits emplaced at moderate depths (ca. 1-2 km), to magnetite-dominant IOA veins and IOCG deposits emplaced at shallow subvolcanic depths. The shallowest parts of these systems include near-surface, iron oxide-only replacement deposits, surficial epithermal sediment-hosted replacement deposits, synsedimentary ironstone deposits, and Mn-rich exhalite deposits. Alteration associated with the IOA and IOCG mineralising systems of the host volcanic rocks dominantly produced potassic with lesser amounts of calcic- and sodic-rich mineral assemblages. No deposits are known to be hosted in granite, implying that the mineralising systems were operative during a relatively short, postvolcanic period yet prior to intrusion of the granitoids. Mineral chemical, fluid inclusion, and stable isotope data from new studies record the effects of metasomatic fluids that interacted with crustal reservoirs such as volcanic rocks or seawater., This paper provides an overview on the genesis of Mesoproterozoic igneous rocks and associated iron oxide ± apatite (IOA) ± rare earth element, iron oxide-copper-gold (IOCG), and iron-rich sedimentary deposits in the St. Francois Mountains. The Missouri iron orebodies are magmatic-related hydrothermal deposits that, when considered in aggregate, display a vertical zonation from high-temperature, magmatic ± hydrothermal IOA deposits emplaced at moderate depths (ca. 1-2 km), to magnetite-dominant IOA veins and IOCG deposits emplaced at shallow subvolcanic depths. The shallowest parts of these systems include near-surface, iron oxide-only replacement deposits, surficial epithermal sediment-hosted replacement deposits, synsedimentary ironstone deposits, and Mn-rich exhalite deposits. Alteration associated with the IOA and IOCG mineralising systems of the host volcanic rocks dominantly produced potassic with lesser amounts of calcic- and sodic-rich mineral assemblages. No deposits are known to be hosted in granite, implying that the mineralising systems were operative during a relatively short, postvolcanic period yet prior to intrusion of the granitoids. Mineral chemical, fluid inclusion, and stable isotope data from new studies record the effects of metasomatic fluids that interacted with crustal reservoirs such as volcanic rocks or seawater.

Determining whether the host rocks for uranium mineralisation at Coles Hill are part of the Martinsville Intrusive Complex or not is critical for developing a genetic model for the Coles Hill deposit and to identify future uranium exploration targets in the region, especially if it can be determined that the source of uranium is the meta-igneous host rocks. Even if these units are not the source of the uranium, they could provide a favourable environment for uranium deposition, owing to the abundance of reduced iron-bearing phases such as biotite, amphibole and pyroxene that can promote precipitation of uranium from oxygenated fluids. Here, new U-Pb zircon geochronology is presented that establishes the age of the mineralised and unmineralised Martinsville Intrusive Complex rocks (the felsic Leatherwood Granite and the mafic Rich Acres Formation) in the vicinity of the Coles Hill deposit., Determining whether the host rocks for uranium mineralisation at Coles Hill are part of the Martinsville Intrusive Complex or not is critical for developing a genetic model for the Coles Hill deposit and to identify future uranium exploration targets in the region, especially if it can be determined that the source of uranium is the meta-igneous host rocks. Even if these units are not the source of the uranium, they could provide a favourable environment for uranium deposition, owing to the abundance of reduced iron-bearing phases such as biotite, amphibole and pyroxene that can promote precipitation of uranium from oxygenated fluids. Here, new U-Pb zircon geochronology is presented that establishes the age of the mineralised and unmineralised Martinsville Intrusive Complex rocks (the felsic Leatherwood Granite and the mafic Rich Acres Formation) in the vicinity of the Coles Hill deposit.

The abandoned massive sulphide Callahan mine is unique because the open-pit operation was sited in a drained marine estuary. About 5 000 000 tons of sulphide-bearing waste and unprocessed ore remain on site, bordering ponds and tidal flats. The prominence and position of the waste relative to the tidal estuary constitute key features representing point sources of heavily contaminated debris. Pyrite, sphalerite, chalcopyrite and minor galena are hosted by bimodal volcanic rocks of the Cambrian Castine Volcanics. A total of 275 analyses of Pb isotopes were carried out to characterise fully barren volcanic, hydrothermally altered and mineralised rocks, massive and disseminated sulphides, waste rock and tailings, and pond sediments from drill cores, pit water, seeps, and aquatic biota (lobsters, crabs and bivalves). The tailings pile and Goose Pond sediments have high metal burdens. The mine signature decreases considerably in intensity away from the mine, within the estuary and towards the open waters of the Bagaduce river. Lead in the pond sediments is derived from mass wasting of Pb-bearing minerals in the waste and tailings piles and from metal-laden seeps that carry both dissolved and particulate Pb. The composition of bivalve shells and lobsters indicated that they are partially disturbed by mining activities., The abandoned massive sulphide Callahan mine is unique because the open-pit operation was sited in a drained marine estuary. About 5 000 000 tons of sulphide-bearing waste and unprocessed ore remain on site, bordering ponds and tidal flats. The prominence and position of the waste relative to the tidal estuary constitute key features representing point sources of heavily contaminated debris. Pyrite, sphalerite, chalcopyrite and minor galena are hosted by bimodal volcanic rocks of the Cambrian Castine Volcanics. A total of 275 analyses of Pb isotopes were carried out to characterise fully barren volcanic, hydrothermally altered and mineralised rocks, massive and disseminated sulphides, waste rock and tailings, and pond sediments from drill cores, pit water, seeps, and aquatic biota (lobsters, crabs and bivalves). The tailings pile and Goose Pond sediments have high metal burdens. The mine signature decreases considerably in intensity away from the mine, within the estuary and towards the open waters of the Bagaduce river. Lead in the pond sediments is derived from mass wasting of Pb-bearing minerals in the waste and tailings piles and from metal-laden seeps that carry both dissolved and particulate Pb. The composition of bivalve shells and lobsters indicated that they are partially disturbed by mining activities.

The report addresses the applicability of the three-step assessment methodology to improving the resource assessment programme as well as a broader array of issues. Written contributions to the committee are presented and there is a bibliography, a glossary and an index. A programme of research should seek ways to augment or replace the subjective probability method of estimating the number of deposits in a tract of land and a format for presentation of quantified results to clients should be designed. Premature release of information should be resisted, the number of simultaneous assessment studies reduced, guidelines prepared on standards and modelling, the library of deposit-type models improved, access to the Monte-Carlo-type resource simulator increased, Geographic Information Systems technology used more and Gross In-Place Value replaced by an economically determined in-place value for resources of near-term significance., The report addresses the applicability of the three-step assessment methodology to improving the resource assessment programme as well as a broader array of issues. Written contributions to the committee are presented and there is a bibliography, a glossary and an index. A programme of research should seek ways to augment or replace the subjective probability method of estimating the number of deposits in a tract of land and a format for presentation of quantified results to clients should be designed. Premature release of information should be resisted, the number of simultaneous assessment studies reduced, guidelines prepared on standards and modelling, the library of deposit-type models improved, access to the Monte-Carlo-type resource simulator increased, Geographic Information Systems technology used more and Gross In-Place Value replaced by an economically determined in-place value for resources of near-term significance.

The Sila batholith is the focus of an extensive petrogenetic research programme, which includes an assessment of its potential to host granite-related ore deposits. Univariate and multivariate statistical techniques were applied to major- and minor-element rock geochemical data. The analysis indicates that the highest potential for mineralisation occurs in corundum-normative, peraluminous, unfoliated, relatively late-stage plutons. The plutons are enriched in Rb, Nb, Ta and U, but depleted in Fe, Mg and Sr. The K/Rb, Ba/Rb, Rb/Sr and Rb3/Ba.Sr.K indices and high R-factor scores of Si-K-Rb are typical of mineralised granitic rocks. A reconnaissance fluid inclusion study indicates that the sub-solidus rock was infiltrated by solutions of widely different temperatures (50-416 degrees C) and variable salinities (0 to 26 wt.% NaCl equivalent). The higher-temperature solutions probably represent granite or magmatic-related Hercynian fluids, whereas the lower-temperature fluids may be either Hercynian or Alpine in age. Fluids with characteristics typical of mineralised "porphyry" systems have not been recognised., The Sila batholith is the focus of an extensive petrogenetic research programme, which includes an assessment of its potential to host granite-related ore deposits. Univariate and multivariate statistical techniques were applied to major- and minor-element rock geochemical data. The analysis indicates that the highest potential for mineralisation occurs in corundum-normative, peraluminous, unfoliated, relatively late-stage plutons. The plutons are enriched in Rb, Nb, Ta and U, but depleted in Fe, Mg and Sr. The K/Rb, Ba/Rb, Rb/Sr and Rb3/Ba.Sr.K indices and high R-factor scores of Si-K-Rb are typical of mineralised granitic rocks. A reconnaissance fluid inclusion study indicates that the sub-solidus rock was infiltrated by solutions of widely different temperatures (50-416 degrees C) and variable salinities (0 to 26 wt.% NaCl equivalent). The higher-temperature solutions probably represent granite or magmatic-related Hercynian fluids, whereas the lower-temperature fluids may be either Hercynian or Alpine in age. Fluids with characteristics typical of mineralised "porphyry" systems have not been recognised.

White micas from intensely fractured and hydrothermally altered rocks containing abundant disseminated sulphides show a broad positive correlation between their aluminium content and the Cu content of the whole rock. The compositional gradients in the white micas are not clearly related to their position in the regional hydrothermal zonation. Compositional variability of the white micas is best explained by superposition and overprinting of fluids during mineralisation and during the last stages of hydrothermal alteration. The general correlation between white mica composition and base metal content in the mineralised rocks at Catheart Mountain suggests that white mica composition could be a useful indicator of the mineralisation gradient., White micas from intensely fractured and hydrothermally altered rocks containing abundant disseminated sulphides show a broad positive correlation between their aluminium content and the Cu content of the whole rock. The compositional gradients in the white micas are not clearly related to their position in the regional hydrothermal zonation. Compositional variability of the white micas is best explained by superposition and overprinting of fluids during mineralisation and during the last stages of hydrothermal alteration. The general correlation between white mica composition and base metal content in the mineralised rocks at Catheart Mountain suggests that white mica composition could be a useful indicator of the mineralisation gradient.

The composition of tourmalines in the metasedimentary and metaigneous lithologies in the Grenville lowlands was studied, and compared with those from mineralised districts for which chemical data are available. The range in the composition of tourmaline found in rocks of different bulk compositions in a possible evaporitic setting is documented, but because of the absence of published analyses of tourmaline in stratabound deposits within evaporitic terranes, the comparisons rely for the most part on tourmaline compositions from the Sullivan Mine, British Columbia. These comparisons and the geologic setting of the study area allow speculation on the genesis of tourmaline-rich rocks and their possible economic implications., The composition of tourmalines in the metasedimentary and metaigneous lithologies in the Grenville lowlands was studied, and compared with those from mineralised districts for which chemical data are available. The range in the composition of tourmaline found in rocks of different bulk compositions in a possible evaporitic setting is documented, but because of the absence of published analyses of tourmaline in stratabound deposits within evaporitic terranes, the comparisons rely for the most part on tourmaline compositions from the Sullivan Mine, British Columbia. These comparisons and the geologic setting of the study area allow speculation on the genesis of tourmaline-rich rocks and their possible economic implications.