Gravity, magnetic and radiometric evidence for the geological setting of the Lady Loretta Pb-Zn-Ag deposit - A qualitative appraisal

Semi-regional gravity, magnetic and radiometric data sets, augmented by a prospect-scale gravity survey, have been used to qualitatively assess the geological setting of the Lady Lady Loretta Pb-Zn-Ag deposit. Regional gravity and magnetic fields are influenced chiefly by the Eastern Creek Volcanics and are sensitive to the thicknesses of overlying clastic and dolomitic sedimentary sequences, including the McNamara Group which hosts the mineralization. These are primarily controlled by Isan orogeny deformation, but a number of earlier structures are discernible. The most important of these postulated syndepositional structures are a west-northwest-oriented bounding fault extending from Lady Loretta to the Mount Gordon fault along the Redie Creek fault, and a possible sub-basin or zone of alteration beneath the Lady Loretta orebody, which manifests as a magnetic low. Prospect-scale gravity data contain anomalies clearly associated with the mineralized strata at Lady Loretta. Contrasts between McNamara Group formations as well as older units are also apparent, reflecting differences in lithology or weathering characteristics. Higher Bouguer gravity signatures tend to be associated with the more dolomitic units. The radiometric data set allows for the mapping of surface geochemical signatures that are sensitive to a number of geological parameters. These include sedimentological factors such as provenance, maturity, and proportion of argillaceous material, as well as chemical alteration. This variation occurs within as well as between mapped stratigraphic units, and is itself variable across the region. Potassium-channel signatures are an example of this, implying a general westerly decrease in argillaceous of feldspathic content within some formations. Some radiometrically distinct layers visible within sedimentary units appear to be absent at the equivalent stratigraphic level elsewhere. These observations may have implications for attempts to erect a regional sequence stratigraphic framework based on gamma ray logs from relatively few locations.