Carbonates of the magnesite–siderite series from four carbonatite complexes

Abstract

Carbonates of the magnesite-siderite series have been found and analysed in carbonatites from the Lueshe, Newania, Kangankunde, and Chipman Lake complexes. This series has been represented until now only by a few X-ray identifications of magnesite and three published analyses of siderite and breunnerite (magnesian siderite). Most of the siderite identified in carbonatites in the past has proved to be ankerite, but the new data define the complete solid-solution series from magnesite to siderite. They occur together with dolomite and ankerite and in one rock with calcite. The magnesites, ferroan magnesites and some magnesian siderites may be metasomatic/hydrothermal in origin but magnesian siderite from Chipman Lake appears to have crystallized in the two-phase calcite + siderite field in the subsolidus CaCO3-MgCO3-FeCO3 system. Textural evidence in Newania carbonatites indicates that ferroan magnesite, which co-exists with ankerite, is a primary liquidus phase and it is proposed that the Newania carbonatite evolved directly from a Ca-poor, Mg-rich carbonatitic liquid generated by partial melting of phlogopite-carbonate peridotite in the mantle at pressures >32 kbar.K EYWO R D S: carbonate, carbonatite complexes, magnesite, siderite, breunnerite.

Hydrothermal alteration in metasedimentary rock-hosted orogenic gold deposits, Reefton goldfield, South Island, New Zealand

“…8). Following Buckley and Woolley (1990), the boundary between dolomite and ankerite is taken at an Fe:Mg ratio of 1:4, and the magnesite-siderite series is subdivided at Mg:Fe ratios Dolomite-ankerite and ferroan magnesite-magnesian siderite are also characteristic of many of the orogenic gold deposits in Victoria, Australia (cf. Fig.…”

Calcite and dolomite in intrusive carbonatites. I. Textural variations

“…Although this mineral can potentially develop at the expense of igneous calcite in collision zones, its preservation will require exhumation rates and fluid regime that are rarely attained in the natural environment (Ghent et al 1996;Huang 2003). Other carbonate minerals that may locally gain the rock-forming status include the magnesitesiderite-rhodochrosite series, (Mg,Fe,Mn)CO 3 (Buckley and Wooley 1990;Zaitsev 1996;Thompson et al 2002;Zaitsev et al 2004); kutnohorite, Ca(Mn, Fe)(CO 3 ) 2 (Zaitsev 1996); fluorocarbonates of light rare-earth elements (REE) and burbankite, (Na,Ca) 3 (Sr, Ca,Ba,REE) 3 (CO 3 ) 5 (Zaitsev et al 1998;Castor 2008;Kynicky et al 2013); strontianite, SrCO 3 , and barytocalcite, CaBa(CO 3 ) 2 (Konev et al 1996). The present work focuses on calcite and dolomite because these minerals account for the bulk of terrestrial igneous carbonate material.…”

Origin of REE-rich ferrocarbonatites in southern Siberia (Russia): implications based on melt and fluid inclusions

“…It also can serve as a cement for explosive carbonatite breccias in diatremes. There are some examples of such relationships in the alkaline massifs: Sallanlatvi carbonatites of the Kola Peninsula, Russia (Sitnikova et al 2001); Cargill Township Carbonatite Complex, Canada (Sage 1988); complexes Lueshe, DR Congo, Newania, India, Kangankunde, Malawi, and Chipman Lake, Canada (Buckley and Woolley 1990); Gifford Creek ferrocarbonatite complex in Western Australia (Pirajno et al 2014), and other (Guilbert and Park 1985;Pirajno 2015). Siderite is traditionally considered as a late-stage mineralization in the Bayan Obo, China (Zhang et al 1996); Mountain Pass, USA (Laznicka 2010), and Tomtor, Russia (Kravchenko and Pokrovsky 1995) massifs.…”

“…Small crystals of magmatic siderite occur in carbonatite deposits from Canada, where they are replaced by ankerite and calcite or magnesite (Buckley and Woolley 1990). Calcite and dolomite carbonatite formation by liquid immiscibility during the crystallization of alkaline silicate melt has been studied experimentally (Brooker and Hamilton 1990;Wyllie 1997, 1998;Safonov et al 2009).…”