An unusual manganese silicate occurrence at the Hoskins mine, Grenfell district, New South Wales
Titel:
An unusual manganese silicate occurrence at the Hoskins mine, Grenfell district, New South Wales
Auteur:
Ashley, P. M.
Verschenen in:
Australian journal of earth sciences
Paginering:
Jaargang 33 (1986) nr. 4 pagina's 443-456
Jaar:
1986-12
Inhoud:
Stratiform manganese silicate rocks overlie jasper and metabasah in the ?Middle Silurian Hoskins Formation at the Hoskins manganese mine near Grenfell, NSW. Two dominant mineral assemblages occur in the Mn silicate rocks: (1) a “reduced' assemblage, probably gradational into underlying jasper, containing abundant rhodonite and/or tephroite, plus subordinate carbonates, quartz, hausmannite, spessartine and Ba minerals, and (2) a well-laminated 'oxidized' assemblage rich in red Mn-rich alkali pyroxene and amphibole, braunite, manganoan pectolite and minor Mn-rich mica, alkali feldspars, carbonates, quartz and barite. Several Mn silicates implicitly contain trivalent Mn. The Mn silicate rocks are rich in Mn, Ba and Sr, and also contain anomalously high Co, Cu, As and W; oxidized assemblages are alkali-rich. Bulk compositions and geological setting suggest a submarine volcanic exhalative origin for the precursors of the Mn silicate rocks and jasper. Metamorphism has occurred at upper greenschist facies with original high oxygen fugacity conditions in the exhalative sediments being largely reflected in the resulting assemblages. Although analogues of the reduced Mn silicate rocks are widespread in metamorphosed Mn deposits, equivalents of the oxidized assemblages appear to be particularly uncommon.
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