Lithogeochemistry of wainaleka Cu-Zn volcanogenic deposit, Viti Levu, Fiji, and possible applications for exploration in tropical terrains

A small Kuroko-type Cu-Zn deposit exhibiting metal zoning and alteration assemblages comparable with documented proximal volcanogenic deposits, occurs at the top of a felsic fragmental pile, mantling a large sodic rhyolite domal complex. The domal complex occurs within predominantly mafic to intermediate lavas and volcaniclastic rocks with low-potash island-arc tholeiitic affinities, representing the basal section of the early Tertiary (Eocene to middle Miocene) Wainimala Group near the southern coast of Viti Levu, Fiji.Lithogeochemical trends identified in analyses of rock chip samples from traverses across the domal complex reflect alteration zoning. Sodium, Ca and Sr are strongly depleted within the quartz-sericite foot-wall alteration zone (Zone I) 200 m below mineralization. Potassium, Rb and weaker Mn, Zn and Co depletion and Cu, Pb and Mg enrichment define clay-sericite (Zone II) and clay carbonate (Zone III) footwall alteration 600 to 1200 m below mineralization. Hanging-wall albite-chlorite-calcite-zeolite alteration (Zone IV) is accompanied by enhanced Zn, Pb, Co, Mn, Sr and Na values.Significant mine-scale lithogeochemical trends obtained from systematic sampling of a mineralized borehole section include K and Rb enrichment in the zone of strongest quartz-sericite alteration associated with mineralization and broad depletion of Mn, Na, Ca and Sr within altered footwall fragmental rocks. Minor Cu, Pb, Zn and Ag enrichment has accompanied low-grade propylitic alteration of hanging-wall rocks up to 50 m above mineralization. Analysis of weathered bedrock samples from traverses above the mineralized borehole section indicates that primary geochemical trends occur in the weathered zone. Outcropping gossan has strongly anomalous Cu (535 ppm-21.5%), Zn (3300 ppm-6.15%), Pb (420–8200 ppm), As (200–7000 ppm) and Hg (33–670 ppm) values.Application of lithogeochemistry as a follow-up exploration method in a tropical area such as Wainaleka was investigated as a possible replacement for ridge, spur and base-of-slope soil sampling techniques. Ridge-top auger samples and creek outcrop samples were collected at approximately 100 m intervals and a density of 70/km². Elements (including Cu, Pb, Zn, Mn, Rb, Sr, Na, K, Ca and Mg) were selected for analysis because of specific associations with mineralization and alteration, and low analytical costs. Single- and multi-element dispersions effectively outline mineralization and attendant alteration.