Otwayite and theophrastite from the Lord Brassey Mine, Tasmania

RECENT investigation of samples labelled zaratite from the Lord Brassey Mine, near Heazlewood, Tasmania, in the mineral collection of the Museum of Victoria revealed the presence of the rare nickel carbonate, otwayite, and the rare nickel hydroxide, theophrastite. X-ray diffraction, electron microprobe and infrared analysis were utilised in the study, which failed to confirm the presence of zaratite. The Lord Brassey Mine is situated near the summit of Mt. Grey, 1.5 km northeast of the Waratah-Corinna Road bridge over the Heazlewood River, in western Tasmania. The mine is the type locality for two nickel-bearing minerals, heazlewoodite (Petterd, 1910; Peacock, 1947) and hellyerite (Williams et al . , 1959). The nickel ore occurs as narrow veins within a body of serpentinite 4 km long and 800 m wide, forming part of a large Cambrian ultrabasic complex consisting of pyroxenites and peridotites (Williams, 1958). The main ore consists of heazlewoodite with minor pentlandite and millerite generally intergrown with magnetite. In shear planes and fracture fillings a waxy, translucent, emerald-green amorphous mineral referred to as zaratite by Williams (1958) has been deposited along with thin coatings of pale blue hellyerite. Given that the secondary nickel carbonates and hydroxides from Lord Brassey Mine transect massive magnetite and serpentine minerals, and given their associations in other deposits, it is most likely that they precipitated from meteoric fluids which permeated the nickel sulphide orebody via shear planes and fractures.