A xenon gas purity monitor for EXO

We discuss the design, operation, and calibration of two versions of a xenon gas purity monitor (GPM) developed for the EXO double beta decay program. The devices are sensitive to concentrations of oxygen well below 1 ppb at an ambient gas pressure of one atmosphere or more. The theory of operation of the GPM is discussed along with the interactions of oxygen and other impurities with the GPM's tungsten filament. Lab tests and experiences in commissioning the EXO-200 double beta decay experiment are described. These devices can also be used on other noble gases.Comment: 41 pages, 26 figure

Investigations at Polyphant, near Launceston, Cornwall

A geophysical survey was conducted in the vicinity of the Carrock tungsten mine, Cumbria. The object of the survey was to establish an optimum geophysical exploration procedure for the location of the style of mineralisation known at Carrock. The VLF-EM method recorded only weak or indistinct anomalies over much of the known mineralisation but a weak anomaly coincident with the Emerson vein was traced northwards for one km. Several similar linear features were recorded in the area on trends favourable for mineralisation and two, at Poddy Gill in the east and Arm o’ Grain in the west, are coincident for part of their strike with exposed mineralisation. Resistivity measurements indicated that most fault structures have coincident low resistivity zones; a detailed traverse across the Emerson vein showed a minor high resistivity peak within the low zone. Induced polarisation, magnetic and self potential anomalies were recorded only within the gabbro on the extrapolated positions of the Smith and Wilson lodes. It is concluded that these anomalies are caused by discontinuous near-surface lenses of pyrrhotite which have little VLF response. The VLF method is identified as the best tool for the location of structures which may carry mineralisation in this environment. Incidentally to the main objectives of the work, three VLF anomalies are identified which appear to warrant investigation by drilling; the Arm o’ Grain anomaly, the Emerson vein extension and the Poddy Gill feature

Mineral investigations near Bodmin, Cornwall. Part 3, the Mulberry and Wheal Prosper area

Investigations in the area between the former opencast tin workings of Mulberry and Wheal Prosper suggest that the most promising ground for future mineral exploration lies to the south of the latter workings. The north-south Mulberry mineralisation trend, although recognisable south of the calcsilicate belt, gives rise to only sporadic and lowamplitude tin anomalies in the soils. Near to the surface there is no evidence of an analogue of the Mulberry deposit; its existence or absence at depth could only be proved by speculative drilling. Traced westwards, the Prosper mineralisation becomes more tenuous and, at shallow depth, uneconomic. Strong geochemical evidence, supported by less f’lrm geophysical indications, points to the presence of a previously unrecognised mineralised zone subparallel to the Prosper vein sheets and some 200 m south of them. The presence of tin, copper, zinc and a little tungsten is indicated

Stratabound arsenic and vein antimony mineralisation in Silurian greywackes at Glendinning, south Scotland

Stratiform and disseminated pyrite-arsenopyrite concentrations are overprinted by fracturecontrolled polymetallic mineralisation including stibnite through at least tens of metres of Silurian sediments at Glendinning, near Langholm. Three shallow boreholes were drilled on an anomaly defined by VLF-EM and II? surveys and by antimony values X0 ppm in thin B-C horizon soils. A parallel conductive zone with an accompanying soil anomaly but lacking an IP response was investigated by a fourth hole. The stratabound sulphides form disseminations and bands parallel to the bedding and are particularly concentrated in intraformational breccia units regarded as debris flows, which, together with the presence of smaIl scale slump folds in the greywackes, testify to the existence of an unstable slope during sedimentation. The thickest such unit has a true thickness of 4 m and together with 8 m of adjoining greywackes grades 0.7% As. Phases of fracture-controlled Fe-As-Sb-Pb- Zn-Cu-(?)Hg mineralisation associated with widespread dolomite and quartz veinlets and narrow breccia veins are superimposed on the stratabound mineralisation. Their spatial association with the stratabound mineralisation, the presence of up to 0.33% Sb in the stratiform arsenopyrite and as much as 5% As in the stratiform pyrite, favour a common source for the arsenic and antimony. This source was probably a synsedimentary metal accumulation in a mid or lower fan environment where euxinic conditions periodically developed

Volcanogenic and exhalative mineralisation within Devonian rocks of the South Hams district of Devon

Soil samples were collected from 77 reconnaissance traverses across the outcrop of the Devonian volcanic rocks in the South Barns district of Devon, between the River Yealm in the west and Totnes in the east, and were analysed for at least 15 elements including Cu, Pb, Zn, As, Sb and Ba. Several geochemical anomalies were found, the most extensive and highest amplitude of which comprise a) Ba with smaller amounts of other elements in the Burraton area, b) Ba and other elements in the Higher Ludbrook area and further north-east, c) Sb in the Ladywell area, d) As in the extreme west of the area, e) Cu in association with a diabase near Weeke and f) Zn and Pb around Willing Cross, near Rattery. Several of these anomalies appeared to follow the strike of the volcanic and associated rocks and the first three were investigated further by means of geophysical techniques and drilling. In the Burraton and Higher Ludbrook areas d. c. resistivity, IP, VLF-EM, VLF-R and some detailed gravity surveys were carried out. Around Burraton resistivity anomalies were generally coincident with soil Ba anomalies but there Has no coincident gravity anomaly. In the Higher Ludbrook area a massive carbonate horizon found by drilling is responsible for a zone of high apparent resistivity, detected with the dipole-dipole array, and a residual Bouguer anomaly high; dipole-dipole IP anomalies indicate that disseminated mineralisation may be extensive, although the results of EH and resistivity surveys suggest that the massive pyrite intersected in one of the boreholes is of limited lateral extent. Limited geophysical surveys were also carried out in the vicinity of Ba anomalies around Whetcombe Cross and near Fursdon in an area of diffuse geochemical anomalies. A small amplitude IP anomaly in the Fursdon area indicates a possible zone of disseminated mineralisation