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The geology of the Rosebery ore deposit

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posted on 2023-05-26, 04:39 authored by Brathwaite, RL
The stratiform pyritic Zn-Pb-Cu and barite ore deposit at Rosebery is contained in a small shale lens within pyroclastic rocks (the Primrose Pyroclastics) which form part of the Mt. Read Volcanic Group -an extensive belt of silicic volcanic rocks of Cambrian age. The Primrose Pyroclastics consist of vitric, crystal and lithic tuffs, pyroclastic breccias, shale¬¨‚àëlenses and quartz-sericitechlorite schists derived from the pyroclastic rocks. The Primrose Pyroclastics contain probable ignimbrites and therefore may have been deposited on land. They are overlain to the east by massive lavas of the Mt, Black Volcanics. On the, west the Primrose Pyroclastics are flanked by and appear to intertongue with the Rosebery Group consisting of shale, quartz-wacke, greywacke conglomerate and dolomitic siltstone. The Cambrian rocks, particularly the volcanic formations, in the Rosebery area,have undergone low-grade regional metamorphism that has¬¨‚àëproduced mineral assemblages of the lower greenschist facies together with schistose fabrics. In the Rosebery Mine area the detailed stratigraphic sequence is: massive pyroclastics (vitric, crystal and lithic tuff), black slate, host rock ( siltstone with crystal tuff bands), Barite orebody, host rock, Z.n-Pb sulphide orebody with an Fe-Cu-rich basal zone, footwall schists, and footwall pyroclastics (crystal tuff). The contact between the massive pyroclastics and the underlying black slate or host rock appears, -ion part, to be a disconformity. The footwall schists below the¿í¬± Zn-Pb orebody possibly represent a zone of wallrock alteration.¿í¬± A post-ore basaltic dike is corelated with the Jurassic dole rite¿í¬± and is of interest because it contains probable rheomorphic galena-chalcopyrite veinlets.

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