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  • 1
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    Insights into the origin of the thermal springs of Bath and Bristol, England, from geophysical data (2013)
    Geological Society of London
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    Publication Date: 2013-09-21
    Description: The thermal springs of Bath, England, produce 1.25 Ml day –1 of water at 46.5 °C. The spring at Hotwells, Bristol, England, 15 km to the west, is estimated to produce between 0.17 and 0.39 Ml day –1 of water at a temperature between 22.8 and 24.4 °C. Published research suggests that the waters originate in the Mendip Hills, SW of Bath and Bristol, and are heated by geothermal energy within the Carboniferous Limestone basin (‘The Mendips Model’). The exact paths of the waters to the springs have not been established. We interpreted seismic reflection data for the urban district of Bath and for the Radstock Basin to the south of Bath. By combining the geophysical interpretations with published geological data we have established a potential route through the Carboniferous Limestone reaching sufficient depths for the waters to attain the required temperatures. We imaged a steeply dipping, fractured region of Carboniferous Limestone coincident with the valley of the River Avon and propose that this is the feature by which the thermal waters can rise rapidly to the surface, providing an explanation for the existence of these unique springs. We have incorporated these new aspects of the Mendip Model into the ‘Mendip–Avon Fracture Zone Model’.
    Print ISSN: 1470-9236
    Topics: Geosciences
    Published by Geological Society of London
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  • 2
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    Glacial dispersal of gahnite from the Izok Lake Zn-Cu-Pb-Ag VMS deposit, northern Canada (2015)
    Geological Society of London
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    Publication Date: 2015-10-27
    Description: The Izok Lake Zn–Cu–Pb–Ag volcanogenic massive sulphide (VMS) deposit in the Arctic region of Canada is one of the largest undeveloped Zn–Cu VMS resources in North America. In 2009, the Geological Survey of Canada initiated a detailed glacial dispersal study of the deposit focused on documenting its associated indicator mineral and till geochemical signatures. Glacial dispersal from the deposit is fan-shaped and was formed by an older SW ice flow and younger NW ice flow phases. Till samples contain chalcopyrite, sphalerite, galena, and pyrite up to 1.3 km down-ice and gahnite at least 40 km down-ice. Gahnite (ZnAl 2 O 4 ) is an ideal indicator mineral in till because of its visually distinctive bluish green colour combined with its high specific gravity (4–4.6) for recovery using density-based separation methods, moderate hardness (physical durability during glacial transport), chemical stability in oxidizing surficial environments (resistance to post-glacial weathering), and its occurrence in highly metamorphosed VMS deposits such as Izok Lake. Most gahnite grains in till down-ice are 0.25–0.5 mm in size. Coarser gahnite (0.5–2.0 mm) occurs only in till proximal to the deposit (〈3 km down-ice) and thus is an indicator of proximity to a gahnite-bearing bedrock source. Ore (Cu, Pb, Zn, Ag) and pathfinder element (As, Cd, Bi, Hg, In, Sb, Sb, Tl) contents in the 〈0.063 mm fraction of till reflect glacial dispersal up to a maximum of 6 km down-ice. A 15–20 km till indicator mineral sample spacing is sufficient to detect a gahnite glacial dispersal train such as that from the Izok Lake VMS deposit.
    Print ISSN: 1467-7873
    Electronic ISSN: 1467-7873
    Topics: Chemistry and Pharmacology , Geosciences
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  • 3
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    Till geochemical signatures of magmatic Ni-Cu deposits, Thompson Nickel Belt, Manitoba, Canada (2011)
    Geological Society of London
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    Publication Date: 2011-05-01
    Description: Sampling around the Ni-Cu deposits in the northern Thompson Nickel Belt (TNB), central Canada, was conducted to document Ni-Cu mineralization signatures in till. Samples used in this study include archived material collected in 1996 and new samples collected in 2005 and 2006. During the Late Wisconsinan, the Laurentide Ice Sheet flowed southwestward and subsequently westward across the TNB striating outcrops and transporting metal-rich till. Exploration along the belt and in the surrounding terranes should consider both the older SW and younger westward ice flow events when interpreting and following up till geochemical results. Till geochemistry of the 3 offer further discrimination of significant till geochemical anomalies. Using the deposit signatures in till as a guide, five anomalous till samples outside the belt represent new exploration targets because they contain significant elevated concentrations of, in various combinations, Pt, Pd, Cu, Cr, Mo, Sb, Bi and Fe.
    Print ISSN: 1467-7873
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    Topics: Chemistry and Pharmacology , Geosciences
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  • 4
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    Evolution of the west Greenland margin: offshore thermostratigraphic data and modelling (2012)
    Geological Society of London
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    Publication Date: 2012-09-01
    Description: The origin and age of topography along the west Greenland margin is a matter of continued debate. Evidence for tectonically driven Neogene uplift has been argued from interpretations of offshore seismic surveys, onshore fission-track data and inferred episodes of cooling. Here, analysis of seismic reflection profiles and 1D modelling of exploration wells along the Greenland margin of Davis Strait demonstrate that the data are consistent with a model of ancient continental topography affected by late Cretaceous–early Palaeocene rifting followed by thermal subsidence where offshore Neogene tectonic uplift is not required. This interpretation for the offshore evolution of the west Greenland margin has implications for the adjacent onshore evolution and for other continental margins developed throughout the Atlantic–Arctic rift system.
    Print ISSN: 0016-7649
    Topics: Geosciences
    Published by Geological Society of London
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  • 5
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    New single crystal 40Ar/39Ar ages improve time scale for deposition of the Omo Group, Omo-Turkana Basin, East Africa (2012)
    Geological Society of London
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    Publication Date: 2012-03-08
    Description: Six tuffaceous beds within the Omo Group of the Omo–Turkana Basin have been dated using the 40 Ar/ 39 Ar single crystal total fusion method on anorthoclase, yielding eruption ages. The Omo Group constitutes up to 800 m of subaerially exposed sediments surrounding Lake Turkana within the East African Rift system in northern Kenya and southern Ethiopia. Rhyolitic explosive eruptions produced tuffs and pumice clasts that are considered to have been deposited shortly after eruption. The new age data on feldspars from the pumice clasts range from 4.02 ± 0.04 Ma for the Naibar Tuff of the Koobi Fora Formation to 1.53 ± 0.02 Ma for Tuff K of the Shungura Formation. The Orange Tuff in the KBS Member of the Koobi Fora Formation was dated at 1.76 ± 0.03 Ma, providing good control in this part of the sequence where formerly there was a 〉200 ka gap. Data are consistent with earlier measurements and significantly improve age resolution within the Omo Group, which has yielded many vertebrate fossils, including hominin fossils comprising a number of species. We suggest new age estimates for a limited number of hominin specimens. Supplementary material: Eleven tables and nine figures are available at www.geolsoc.org.uk/SUP18506 .
    Print ISSN: 0016-7649
    Topics: Geosciences
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  • 6
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    Till sampling and geochemical analytical protocols used by the Geological Survey of Canada (2013)
    Geological Society of London
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    Publication Date: 2013-12-11
    Description: The Geological Survey of Canada (GSC) has developed field and lab methods protocols to guide till sample collection, processing, geochemical analysis of the till matrix, monitoring of quality assurance/quality control, and archiving procedures for reconnaissance- to local-scale geochemical surveys. The most significant concepts and procedures are described in this paper. Continued and long-term use of these protocols will ultimately allow GSC researchers to integrate and contrast multiple datasets and ensure minimum levels of quality assurance and control for all till geochemical data. This set of protocols is the first established for Canadian till sampling and analysis and represents a contribution to the GSC’s Geo-mapping for Energy and Minerals (GEM) Program. Sharing the GSC’s knowledge on till sampling and analysis with the international community will allow other researchers and explorationists to adopt similar procedures. This sharing of knowledge will ultimately allow comparison of till geochemical datasets from various parts of Canada and internationally as well as ensuring a minimum level of quality assurance and control for all till geochemical data.
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    Topics: Chemistry and Pharmacology , Geosciences
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  • 7
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    Review of gold and platinum group element (PGE) indicator minerals methods for surficial sediment sampling (2011)
    Geological Society of London
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    Publication Date: 2011-11-01
    Description: For gold deposits, varying combinations of gold grains, sulphides, platinum-group minerals (PGM), tellurides, scheelite and rutile, and some secondary minerals are useful indicator minerals depending on the deposit type, bedrock geology and weathering regime. Gold grain size, shape, and chemical composition for a variety of sediment types, including stream and glacial sediments, have been documented and the data used to determine potential source rocks and distance of transport. Useful indicator minerals for PGE deposits include those oxide and silicate minerals that indicate the host rocks and PGM, gold, sulphides, arsenides and antimonide minerals that indicate mineralization. Composition and morphology of PGM also have been well documented and this information is used to determine their genesis, potential source rocks and transport distance. Gold grains have been recovered from glacial and stream sediments for more than 100 years. PGM grains have a similar long history of recovery from streams, but only a few cases of recovery from glacial sediment have been reported. Research has focused on the development of microchemical characterization techniques for placer gold and PGM, while the focus for indicator minerals from glacial sediments has been the characterization of oxide and silicate suites.
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  • 8
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    Overview of common processing methods for recovery of indicator minerals from sediment and bedrock in mineral exploration (2011)
    Geological Society of London
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    Publication Date: 2011-11-01
    Description: Over the past two decades, the application of indicator mineral methods to mineral exploration has expanded significantly such that they are now used to explore globally for a broad spectrum of commodities. Indicator mineral suites have been identified for a variety of ore deposit types including diamond, Au, Ni-Cu, PGE, metamorphosed volcanogenic massive sulphide, porphyry Cu, U, Sn and W. Indicator minerals, which include ore, accessory and alteration minerals, are sparse in unconsolidated sediments, thus sediment samples must be concentrated in order to recover and examine them. Because most indicator minerals have a moderate to high specific gravity, processing techniques involving density separation, in combination with sizing and magnetic separation, are used to recover them from sediment samples. This paper reviews the commonly used processing methods including panning, hydroseparation, tabling, Knelson concentrators, spiral concentrators, dense media separators, jigs and various types of magnetic separators, as well as mineral selection and mineral chemistry determinations. Monitoring of quality control is essential at each stage in these processing, picking and analytical procedures. When reporting indicator mineral results, processing methods, fraction weights and size ranges, and laboratory name should all be recorded, in addition to indicator mineral abundance data.
    Print ISSN: 1467-7873
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    Topics: Chemistry and Pharmacology , Geosciences
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  • 9
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    An orientation study of the heavy mineral signature of the NICO Co-Au-Bi deposit, Great Bear magmatic zone, NW Territories, Canada (2011)
    Geological Society of London
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    Publication Date: 2011-11-01
    Description: An orientation study around the NICO Co-Au-Bi deposit in the Great Bear magmatic zone of NW Territories, Canada, was initiated in 2007 to establish a practical guide to geochemical and mineralogical exploration for iron oxide copper-gold deposits in glaciated terrain. Bedrock and till samples were collected up-ice, proximal and down-ice from mineralization and host rocks, to characterize their indicator mineral signatures. Results demonstrate that gold grain abundance, size and shape, as well as magnetite and hematite composition, have the best potential to fingerprint the mineralization at NICO. Pristine-shaped gold grains indicative of a local bedrock source and a short distance of glacial transport are relatively abundant in till samples collected immediately down-ice from several mineral occurrences at NICO and none were recovered up-ice. Iron oxide composition using preliminary discriminant diagrams shows some potential, using Ni/(Mn+Cr) versus Ti+V plots. In particular, magnetite and hematite from till samples collected over, or directly down-ice of, the NICO deposit have lower Ti+V compositions compared to magnetite and hematite from till collected up-ice from mineralization. Potential non-ferromagnetic indicator minerals are either not chemically stable in surface sediments (arsenopyrite, chalcopyrite, pyrite), not sufficiently coarse-grained or resistant to glacial transport (bismuthinite, tourmaline, ferroactinolite), not abundant enough in the mineralized bedrock (scheelite, molybdenite, cobaltite, allanite), or not sufficiently heavy (tourmaline) to be useful at NICO but may be at other deposits in the region or elsewhere in glaciated terrain. The development of indicator mineral methods, together with till geochemistry, will be tested with further sampling over the Great Bear magmatic zone.
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  • 10
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    Pyritiferous mudstone-siltstone: expansion rate measurement and prediction (2015)
    Geological Society of London
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    Publication Date: 2015-03-12
    Description: The expansion rates of a pyritiferous Irish mudstone–siltstone fill material have been measured over a period of 19 months in an apparatus devised to replicate underfloor conditions. The testing, performed in a temperature-controlled environment, has shown that both fill density and depth submerged in water have significant influences on the progress of the expansion. It appears that whereas thermal expansion or contraction has an effect on expansion rates immediately after a temperature change, there is no long-term temperature effect on the rate of expansion. In addition, an examination of chemical test results for 60 houses in a housing development in the Dublin area has confirmed that pyrite content is the dominant control over the degree of expansion. A molecular–molar analysis of the pyrite chemical process equations, in addition to a knowledge of the original pyrite content and rate of oxidation, has been used to give a lower-bound estimate of the amount of heave in the laboratory experiments.
    Print ISSN: 1470-9236
    Topics: Geosciences
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