Tin exploration at Mount Isa — A case history

Abstract

Abstract Minor tin, tungsten, tantalum and beryllium mineralization occurs near Mount Isa in pegmatites along the eastern rim of the Queen Elizabeth pluton, a multi-phase pluton in the Proterozoic Sybella Granite batholith of northwest Queensland. The Queen Elizabeth pluton and adjacent metamorphic rocks were explored by Mount Isa Mines Limited during 1980–1983 to assess the tin potential of the area. An orientation study was carried out over an existing tin deposit, using stream-sediment, soil and rock-chip sampling, magnetometer and scintillometer surveys and percussion drilling. This defined the geophysical and geochemical features of the deposit, and indicated that monazite and cassiterite had related distributions and could be used as heavy-mineral tracers. Broader exploration used stream-sediment and rock-chip sampling, and airborne magnetic and gamma-ray spectrometry surveys. The eastern rim of the Queen Elizabeth pluton was found to be enriched in thorium and tin, and an area of approximately 2000 × 400 m with anomalously high tin values in bedrock was delineated in a part of the pluton not previously known to be mineralized. An economic assessment led to relinquishment of the area at that stage. Although no new areas of economic mineralization were found, the study indicated that in this region the thorium gamma-ray response can be used in regional airborne surveys to define areas of prime interest for tin exploration, and that monazite in stream sediments can be used as a heavy-mineral tracer for pegmatitic tin mineralization.