TRIAL HARBOUR
Location: 18km west of Zeehan, following the signs to Trial Harbour (C248) | Google Maps Reference
Key facts about this geosite:
• Contact metamorphism can be observed between granite and serpentine.
• The metamorphism has led to the occurrences of striking diopside to tremolite and nephritejade.
Geosite Description: 18 kilometres west of Zeehan along a winding gravel road the rugged granite hills of Mount Heemskirk meet the ocean and create a wave beaten shoreline. Immediately to the south are some serpentine rich rocks which have been baked by the granite. The most remarkable and well preserved rock exposures can be observed along the coast to the south and north of the main car park in the village.
This area between Zeehan and Trial Harbour has a very complex geological setting, with the oldest rocks comprising a sheared sequence of Precambrian, Cambrian, Ordovician and Siluriansedimentary rocks, interleaved with early Cambrian mafic and ultramafic igneous rocks. These sequences were intruded by Devonian granites, accompanied by considerable metamorphism, metasomatism and some mineralisation (Green, 1966a). In the contact zone between the altered ultramafics and Cambrian hornfels, Green (1966b) described a diopside rich reaction zone containing some tremolite-rich rocks, which he ascribed to retrograde alteration of the diopside rocks. The granite is to the north of the township as depicted in the far distance in the photograph.
