Volcanic-hosted massive sulphide (VHMS) deposit.
Located 54 km south south east of Yalgoo.

The Gossan Hill deposit is 4 kilometres south-east of the Scuddles mine.

It has two separate ore zones; a lower Cu rich zone and an upper Zn rich zone. They are connected vertically by a stockwork of mineralisation. The upper part of the Cu zone contains massive magnetite. A steep west dipping horizon of thinly bedded chert and tuff within the Golden Grove Formation hosts the Zn mineralisation, underlain by coarse felsic pyroclastics and epiclastic rocks. At Gossan Hill multiple Zn lenses and Cu mineralisation are within an ore zone showing 400 metre strike and 20 metres wide.

Primary ore minerals are sphalerite, chalcopyrite and lesser galena. Gangue minerals are pyrite, magnetite and pyrrhotite.

The surface outcrop showed as a 500 x 600 metre crest of the Gossan Hill comprising ferruginous ironstone after massive magnetite.

Prolonged weathering has resulted in a 60-100 metre thick saprolite and oxidised sulphides. The top layer is a 1-3 metre thick lateritic gravel or lateritic duricrust. Next is a 0.5 metre mottled saprolite with vermicular ferruginous nodular concretions set in a clay matrix.

The upper Zn rich zone shows massive stratabound sulphides with bedded sandstone, siltstone, and pebble breccia. The sulphides comprise massive sphalerite, massive pyrite, and enveloping sulphide veins below and within the massive sulphides. This Zn rich zone is overlain by an oxidised near surface silver-gold resource.

The upper part of the underlying Cu rich zone, shows fine grained massive to disseminated magnetite in a matrix of ankerite-siderite-chlorite-talc. This is hosted by two tuffaceous sandstone sheets up to 40 metres thick. The upper part of this zone also shows oxidised copper sulphides over the copper sulphide lodes.

The mineralised horizon and footwall are enriched with Fe, Mn, Mg, base/precious metals, As, S, CO2 and H2O. Fractures are common and infilled with carbonate, chlorite and sulphides.

Locally intense hydrothermal zones surround the Gossan Hill deposit. These alteration zones are composed of chlorite, and ankerite-siderite grading stratigraphically upwards into intense silicification.

The lower Cu-Fe sulphide zone was formed below the sea floor in an extensive hot spring feeder system. The upper Zn-Fe sulphide zone was formed from precipitation out of hydrothermal plumes as they vented and mixed with seawater. The hanging wall and footwall were formed by large stratabound hydrothermal alteration. The upper hanging wall is little altered, but elsewhere there is moderate to intense feldspar destructive development of quartz, chlorite, sericite, and locally abundant carbonate, talc, and sulphides. Biotite is common in the Golden Grove Formation but not at Gossan Hill. Its absence and the presence of andalusite and chlorite represent an alkali depletion associated with intense hydrothermal alteration and mineralisation.

Other Regions, Features and Areas containing this locality

References