Lithogeochemical exploration for polymetallic Sn-Cu-Ag-Au-Pb-Zn vein mineralization at north mammoth prospect, northeast victoria, australia

Abstract

A follow-up surface lithogeochemical survey was implemented at North Mammoth Prospect, northeast Victoria, to investigate possible extensions to polymetallic vein mineralization outcropping as a 20-m-wide by 200-m-long gossanous zone in rugged, scree-covered terrain. The en-echelon pyritic veins contain subeconomic Sn, Cu, Pb, Zn, Ag and Au mineralization and occur within locally folded, fractured, brecciated and bleached metasediments adjacent to high-level, altered, quartz feldspar porphyry dykes. The dykes form part of the 3.5-km-long Mammoth Porphyry Complex. An orientation traverse across the mineralized zone and adjacent wall rocks over a 1300 m × 200 m area involved the collection of 27 rock chip samples (0.5–1.0 kg) that were analyzed for 20 major and trace elements by XRF and AAS methods. Acid soluble Sn and cxF were also determined. The results showed that the less mobile elements including Sn (total), Au, As (as the arsenate), Pb and Ba were most effective in outlining the mineralized zone. Major elements (K, Na, Fe, Ca, Mg), more mobile trace elements (Cu, Zn, Rb, Sr, cxF), acid soluble Sn and element ratios (K/Na, Fe/Mg, Rb/Sr, Zr/Y, Ti/Zr) were either difficult to interpret or failed to increase the anomaly size. The expanded lithogeochemical programme (130 samples from a 2.4-km 2 area) showed that weakly to strongly anomalous Sn, Pb and As values outline a zone of mineralized and bleached metasediments east of the porphyry complex. A 750 m × 250 m halo of anomalous Sn values includes North Mammoth Prospect as well as possible strike extensions to the mineralized veins. Contrasting dispersions for Au and Ba may indicate a multiphase intrusive/mineralization history for the porphyry complex. Pervasive fracturing infilled by iron oxides in the host rocks has probably facilitated lithogeochemical trace element dispersion in the weathered zone.