Ni mineralization occurring in shears in Archean serpentinized peridotite near Nullagine. The bulk of the mineralization is attributed to the effects of hydrothermal and/or metasomatic activity along shears in the serpentine. The late veinlets of Ni minerals and the replacement of millerite and polydymite are attributed to supergene effects.

Located 23 km north of Nullagine. Discovered sometime around 1977 by prospector and miner, Charles Albert Otway, from Gosnells (Perth), Western Australia. He allowed the CSIRO access to study the mineral species it contained.

It is the type locality from nullaginite, otwayite, and paraotwayite.

Nullaginite is found at only three locations worldwide. It is crystallographically similar to rosasite and glaukosphaerite. Nullaginite at Otway occurs as ovoid to irregular nodules up to 2 mm, and cross-fibre veinlets, with a dull lustre in nodules and silky lustre in veinlets.

Otwayite is found at the location in narrow veinlets 0.5-1 mm, and represents a late stage fracture filling, and transects nickeloan serpentine, millerite, polydymite, and apatite. Also associated with otwayite in the veinlets are magnesite, gaspéite, and pecoraite. Otwayite has a fibrous habit, usually rosette-like aggregates. It is unique, with no close mineral group or other species with a similar chemical composition.

It is impossible to distinguish between otwayite and paraotwayite from the Otway Prospect, visually in hand specimens. Under SEM, paraotwayite shows a net-like pattern with a porous texture. Otwayite contains predominantly carbonate with some sulphate, and paraotwayite sulphate with some carbonate, suggesting a paragenetic relationship between the two in which carbonate is replaced by sulphate. Like otwayite, paraotwayite forms fibres to 0.5 mm in length, often intergrown forming net-like masses or rosettes. The species is found only at the Otway Prospect, and in a Chilean meteorite. All three type locality species are bright green.

The principal nickel minerals found at Otway are millerite, polydymite, and pecoraite, which occur as nodular grain concentrations 1-5 mm in diameter. Polydymite is replaced by millerite, which in turn is replaced by gaspéite. Other minerals in the shears include various types of serpentine and magnesite, coarse chlorite, and apatite. This assemblage is cut by late veinlets of gaspéite, pecoraite, otwayite, and nullaginite. There are also trace amounts of barite, cinnabar, parkerite, shandite, breithauptite, and nickeloan greenockite. The majority of mineralisation is attributed to the effects of hydrothermal and/or metasomatic activity along the shears in serpentine. However, concretionary magnesite in some of the shears is the result of Tertiary weathering. Late veinlets of nickel mineralisation, and the replacement of millerite with polydymite are from supergene effects.

The Mindat coordinates are where maps confirm the location to be, however, only possible very minor workings can be seen where mineral specimens have come from in the past (likely during the late 1970s). The deposit appears to be small, and/or never explored to any great extent after its initial discovery, beyond from a scientific standpoint.

Other Regions, Features and Areas containing this locality

References