GEOCHEMICAL VARIATIONS IN THE SAMS CREEK GOLD PROSPECT, NW NELSON, NZ; U-PB DATING OF A GOLD BEARING HYDROTHERMAL EVENT
Multiple stages of hydrothermal activity have altered the dike including the precipitation of late arsenopyrite veins, base metal sulphides, and gold. Gold-silver alloy (~80-85% Au) occurs as small growths (up to 40 µm) cementing and in-filling brecciated and fractured arsenopyrite (the most abundant ore mineral). All samples from the Sams Creek Dike are highly enriched in LREEs, moderately enriched in HREEs, have a distinct negative Europium anomaly, and show no significant variation between stages of alteration. This suggests the source of mineralizing fluids shares a similar trace element chemistry to that of the dike.
Hydrothermal zircons occur as clusters and strings of <1-15µm crystals along grain boundaries of arsenopyrite and within the same micro fractures which gold grains occupy. We interpret these as hydrothermally remobilized magmatic zircons. Magmatic zircons also occur in un-mineralized samples as relatively large ellipsoidal individual grains. They exhibit a spongy dissolution texture and grain size of up to ~25µm. U-Pb analysis of the hydrothermal zircons by LA-ICP-MS assign a Cretaceous age for hydrothermal mineralization.