False anomalies

Oehler, D.Z. and Sternberg, B.K., 1984. Seepage-induced anomalies, false anomalies and implications for electrical prospecting. Amer.Assoc. Pet. Geol. Bull., 68 1121-1145. 

Sample numbers have been randomised to minimise regional bias, help separate false from true anomalies and obtain meaningful estimates of the variance of duplicates. Field duplicates, analytical duplicates, in-house standards and certified reference materials are introduced at regular intervals in the analytical streams. 

Electrokinetic remediation is limited by the type of contaminant, heterogeneities or anomalies in the soil, extreme pHs, pore water chemistry, lack of pore water, contaminant and noncontaminant ion concentrations, metals precipitation, and reduction-oxidation changes induced by the process electrode reactions. It may be difficult to estimate the time that will be required to remediate a site using this technology. Laboratory treatability testing may provide a false indication of the applicability of electrokinetic remediation at a specific site. Further research is required to determine the technology s limitations and ramifications. 

Thin soils underlain by limestone can also be the source of false anomalies. On a traverse across a molybdenum deposit at Tongsban, Jiangsu province, which is covered by 0.3-1.0 m of eluvium, CO2 anomalies were found not only above the ore body but also on a nearby ridge. Here soils are particularly thin and poorly developed, and the underlying limestone creates an environment in which the pH can be as high as 8.5, allowing carbonate enrichment which in turn produces a false anomaly of CO2. 

Even if such false anomalies are present, the technique would be of value if it were certain that U mineralisation did yield He anomalies in overburden gases. Since this is not so, however carefully samples are collected and analysed, the technique must be considered to have very little application. This conclusion is supported by the mathematical modelling by Novikov and Kapkov (1965) and Jeter (1980), described above, which suggest that excess He contents in soil and overburden gas due to underlying, concealed U mineralisation would be far too low to be detected reliably. 

Mercury, by virtue of its coexistence with many types of base metal and precious metal deposits and its high vapour pressure, often forms secondary halos above ore deposits, including in soils. When soil is heated, Hg is released at different temperatures according to the form in which it occurs in the soil (Fig. 13-1). The choice of a particular temperature for thermal release of Hg in a certain form can produce geochemical data that are useful for locating deep blind ore deposits. Comparison of data obtained by thermal release at different temperatures allows the discrimination of significant anomalies related to such mineralisation from false anomalies related to various forms of pollution. 

False anomalies unrelated to mineralisation arise due to the use of fertilisers, pesticides and even simply proximity to villages. These false anomalies can be recognised by the departure of their Hg, Hg, ratios from the norm for the area, which is otherwise stable over both background and mineralised locations. Better still, false anomalies can be avoided by sampling below 50 cm, which has been found to be the lower limit of penetration of surface pollution in the areas studied. 

This result seems counterintuitive. After all, the test is 99% accurate. The reason for the apparent anomaly is that, although the chance of a false positive is only 1%, the number of people who could have that false positive is large (99.5% of the persons tested). Therefore, the false-positive result strongly affects the overall outcome. 

Here we use the classic HAZOP questions (see Rausand (2005)), as only the axis content anomalies now remain. Anomalies in content mean that false or ambiguous information is displayed. Ambiguous information can or cannot be interpreted correctly. Content is therefore divided into the two words information and interpretation (see Table 1). 

After Moseley published his work relating X-ray spectra to atomic number in 1912, it became known for the first time how many rare earth elements should exist, and it became possible to eliminate many of the elements which had been falsely reported in the literature. The anomaly that 14 elements with properties similar to lanthanum existed, intrigued the theorists, and the existence of these elements proved an important clue in developing our present theories of atomic structure. 

Another point to be aware of is that holographic grating monochromators have a polarization anomaly known as the Wood s anomaly. At certain wavelengths the light is polarized entirely in the horizontal plane. This can cause important spectral artefacts such as false maxima or false shoulders. The anomaly can be avoided by using an excitation depolarizer and emission polarizer as described above. 

This term is used to describe the principle that a detected anomaly must first be confirmed over one or more cycles before being processed, thereby limiting the impact of false alarms and temporary faults. This of course depends on the severity of the anomaly. 

The first one is the observation that in areas with persisting borderline iodine deficiency, transient hypothyroidism in the newborns and also some anomalies of thyroid func on in pre iant women can still be linked to such an easily preventable factor as iodine deficiency. In some of these areas it is now clear that in screening, for neonatal hypothyroidism, roughly 2 out of 3 newborns rec alled for abnormal thyroid hormone or TSH levels are false positive. Apart from the psycholomcal and economic al costs linked to the rectal proc ess per-se, this transient hypothyroidism might induce around birth, brain maturation retardation of unknown long term... 

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