Temporal association of arc–continent collision, progressive magma contamination in arc volcanism and formation of gold-rich massive sulphide deposits on Wetar Island (Banda arc)

Whole-rock 87Sr/86Sr and δ18O analyses of volcanic rocks and 3He/4He analyses of sulphides and sulphates from mineralized rocks on Wetar, Indonesia indicate a variable contribution of assimilated crustal material or sediment sourced from the subducted Australian craton to the south. These new data support the idea of progressive source contamination with precisely dated events showing that Wetar Island hosts the most extreme examples of crustal assimilation in the region. The increased continental contamination occurs during the Pliocene (Zanclian to Piacenzian) during distinct magmatic events between 5 and 4 Ma, and at 2.4 Ma when 87Sr/86Sr ratios in unaltered lavas, with whole-rock δ18O values between 5.7 and 9.6‰, increase from 0.707484 to extreme radiogenic values of 0.711656.The earlier of these magmatic events is important in the generation of the hydrothermal systems responsible for the mineralization recorded on Wetar. Samples from this yield radiogenic 3He/4He ratios between 0.5 and 1.4 R/RA, similar to the data from volcanic rocks on nearby Romang. The later magmatic event coincides with the arrival of the Australian Continental Margin at the subduction zone along the Banda arc. Progressive incorporation of continental-sourced components into the source region below the Wetar Island edifice coincides with the formation of gold-rich volcanogenic massive sulphide deposits hosted within the contaminated volcanic pile.

Graphical AbstractSchematic 3-D figure of the arc–continent collision along the Banda arc showing the generation of contaminated magmas in response to progressive subduction of continental material and transfer of components from the slab to melts generated in the sub-arc mantle wedge.Figure optionsDownload as PowerPoint slideResearch Highlights
► New Sr, O and He isotope data for lavas from the Banda arc.
► Progressive contamination of magmas from subducted continental material.
► Formation of gold-rich VMS deposits coincident with extrusion of contaminated lavas.