Carbonatites: related ore deposits, resources, footprint, and exploration methods

Abstract

Most carbonatites were emplaced in continental extensional settings and range in age from Archean to recent. They commonly coexist with alkaline silicate igneous rocks, forming alkaline-carbonatite complexes, but some occur as isolated pipes, sills, dikes, plugs, lava flows, and pyroclastic blankets. Incorporating cone sheets, ring dikes, radial dikes, and fenitisation-type halos into an exploration model and recognising associated alkaline silicate igneous rocks increases the footprint of the target. Undeformed complexes have circular, ring, or crescent-shaped aeromagnetic and radiometric signatures. Carbonatites can be effectively detected by soil, till, and stream-sediment geochemical surveys, as well as biogeochemical and indicator mineral surveys Carbonatites and alkaline-carbonatite complexes are the main sources of rare earth elements (REE) and Nb, and host significant deposits of apatite, vermiculite, Cu, Ti, fluorite, Th, U, natural zirconia, and Fe. Nine per cent of carbonatites and alkaline-carbonatite complexes contain active or historic mines, making them outstanding multi-commodity exploration targets.

Rare earth element mobility in and around carbonatites controlled by sodium, potassium, and silica

“…Our experiments mimic the most commonly observed intrusive sequence of rock-forming minerals in carbonatites. The igneous portions contain calcite and dolomite, followed by ankerite, consistent with known carbonatite petrology ( 13 , 18 – 21 ). Evolution of magnesite or ankerite to siderite is likewise described from natural rocks ( 18 , 22 , 23 ).…”

“…It has long been recognized that the key stage of REE enrichment takes place in transitional environments, after magma fractionation and as REE-bearing fluids exsolve from the carbonatitic melt due to cooling and decompression ( 6 , 61 ). Carbonatite-related REE deposits mostly form at shallow depths in the upper crust (<5 km), most probably in intrusions that did not erupt ( 13 , 16 , 19 ), allowing a carbonatite-derived hydrothermal fluid to circulate in and around the carbonatite ( 55 , 56 , 62 ). The greater solubility of alkali-dominated REE complexes allows their long-distance mobility.…”

3D Modeling of the Epembe (Namibia) Nb-Ta-P-(LREE) Carbonatite Deposit: New Insights into Geometry Related to Rare Metal Enrichment

“…Exploration for these deposit types, in a first stage of targeting, often includes stream sediment geochemistry, as well as airborne gamma-ray spectroscopy, magnetics, gravimetry [7], and rarely, ground-based seismic studies [10]. A comprehensive overview of deposit models and exploration strategies was published by Simandl and Paradis [11].…”

Mineralogy and Origin of Aerosol From an Arc Basaltic Eruption: Case Study of Tolbachik Volcano, Kamchatka

“…More felsic volcanic rocks typically contain 0.2–0.3% accessory apatite (e.g., Nakamaru et al, ; Piccoli & Candela, , and references therein). In intrusive bodies of calcium carbonatites, apatite is one of the main noncarbonate minerals (Simandl & Paradis, ). Pure phosphates have not been reported from fumarolic minerals but can form solid solutions with arsenates such as the rare mineral rhabdoborite, which is a complex borate‐phosphate‐arsenate found at Tolbachik (Pekov et al, ).…”