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Geology

The general geology of the Buena Vista area consists of basaltic volcanic rocks of Jurassic age that are intruded by a partially scapolitised gabbroic complex. Tertiary deposits are faulted against the Jurassic rocks in the eastern part of the area.


Away from the hills of volcanic rock, much of the older geology is obscured by surficial deposits.
Buena Vista Geology

 


Geology - Andesite Dyke

The principal magnetite deposits in the Mineral Basin District occur in a large body of rock made up of the assemblage scapolite-brown hornblende-clinopyroxene-calcite-magnetite, which can contain up to 90% scapolite. The contact of the scapolite rock with the overlying volcanic rock is poorly exposed and might indicate that the scapolite rock intrudes the volcanic rocks. 

Leucocratic dykes cut the scapolitic gabbro in the vicinity of the Buena Vista workings. The majority of these dykes trend northwest are steeply dipping and commonly occur in swarms. They tend to be narrow, only 1 metre or so in width, but can often be traced for distances of up to 300 metres.

Geology - Scapolitised DykeThe proposed mining area around the West ore body occurs in the contact zone between the intrusive diorite-gabbro and overlying basalt-andesite. The intrusive rocks and adjacent meta-volcanics have been highly scapolitised and, in the vicinity of the magnetite rich zones, chloritised. Post-mineralisation dykes cut both the diorite-gabbro and the meta-volcanic rocks.