A lithogeochemical study of the host rocks of the Strickland Showing

The Strickland showing consists of several zones of Zn-Pb-Cu-Ag mineralization hosted in a sequence of volcanic, volcaniclastic and sedimentary rocks which form a coherent belt stretching for 100 km along the south coast of Newfoundland. The sequence has been metamorphosed to upper greenschist facies and subjected to inhomogeneous cataclastic deformation. The mineralization identified in five principle zones (Main, Bog, Silver Hill, Copper and Carrot Brook) is interpreted to have been emplaced synvolcanically. This investigation is concerned with the identification of lithogeochemical signatures in the host rocks, produced by the mineralizing events. -- A total of 294 surface and 292 diamond drill core samples were collected in the Strickland area. They were analyzed for SiO₂, TiO₂, Al₂O₃, FeO, MnO, MgO, CaO, K₂O, Na₂O, P₂O₅ and LOI (loss on ignition). Most were also analysed for Cu, Pb, Zn and Ag and a selected number of surface samples for Zn, Sr, Rb, U, Th, Ga and Y. -- Two statistical approaches were taken in which regression techniques were used to generate residual values for elements in an effort to remove the effects of the rocks' primary composition, i.e. to define anomalies related to mineralization irrespective of lithology. In the first approach discriminant analysis showed that the elements TiO₂, Al₂O₃ and FeO contributed most to the discrimination between lithologies. These elements were then used as independent variables in curvilinear regression equations with which residual values were calculated. A second more refined approach was taken where the data were divided into three groups based on lithology, (igneous, sedimentary and mixed) and TiO₂ (an index of differentiation) was used as the independent variable in curvilinear regression equations to generate residuals for the igneous and mixed groups. Anomalous residual values combined with anomalous analyses from the sedimentary group are referred to as the second pass anomalies. These were found to be more effective in identifying anomalous samples irrespective of lithology than plots of the raw data or first approach residuals. -- The surface distribution of the anomalies from the second approach tend to be in sporadic, elongate, strike-parallel clusters except for a single cluster which stretches southeast across strike from the Copper Zone. It is marked by a lithogeochemical signature typical of hydrothermal conduits as observed beneath other massive sulphide deposits (positive SiO₂ and negative Na₂O, Al₂O₃ and CaO anomalies). Mineralization, typically silver rich, associated with carbonate-tremolite gangue (Main Zone and especially in the Silver Hill Zone) is marked by persistant positive MgO, CaO, FeO and negative Na₂O and SiO₂ anomalies. -- A horizon 25 m stratigraphically below the Silver Hill Zone characterized by negative Na₂O anomalies and positive K₂O anomalies is interpreted to be a stratiform hydrothermal conduit. -- The Strickland showing is analogous in some respects (age, host lithology, mineralization, Pb-isotopes) to the Bathurst camp of New Brunswick and it is therefore reasonable to speculate that, as in the Bathurst camp, other sulphide accumulations lay, as yet undiscovered, in the sequence of rocks which hosts the Strickland. -- When compared with regionally correlative rocks, those associated with the Strickland rocks (felsic flows in particular) are clearly anomalously low in sodium. The low sodium concentration of the Strickland volcanics, typical of the host rocks of many other volcanogenic massive sulphide deposits may prove to be a useful exploration tool in identifying such mineralized areas on a regional basis