17:15 〜 18:45
[HRE13-P01] Petrochemistry of Tundulu Carbonatite, Chilwa Alkaline Province, Malawi: Implications to rare earth elements mineralization
キーワード：Chilwa alkaline province, Rare earth element, Magma differentiation, Tundulu Carbonatite
Carbonatites have become a target for mineral exploration due to their potential to host rare earth elements (REE). Mineralization and enrichment commonly of light rare earth elements (LREE) in carbonatite is primarily magmatic through differentiation. However, magmatic processes are commonly overprinted by hydrothermal processes, which, through remobilization, enrich REE in most carbonatites to an economic level. We intergrate petrography and whole-rock geochemistry to understand the magmatic evolution and its impact on mineralization in the Tundulu Carbonatite. The Tundulu Carbonatite is a sub-volcanic intrusion with three centers emplaced as a ring structure. The Tundulu carbonatite is comprised of calcio-carbonatite, magnesio-carbonatite, and ferruginous calcio-carbonatite. The mineral assemblages in each lithotype include; calcio-carbonatite - calcite, strontianite, apatite, and hematite; ferruginous calcio-carbonatite - ankerite, calcite, strontianite, barite, synchysite, fluorapatite, quartz, and pyrite; and magnesio-carbonatite - ankerite, siderite, dolomite, strontianite, synchysite, barite, pyrochlore and quartz.
Observed spatial association of the Tundulu Carbonatite and nepheline syenite suggests carbonatite formation from immiscibility of initial carbonate-silicate melt. The abundance of calcite shows the initial magma was Ca-rich. The Fe2O3 and MnO contents increase from calcio-carbonatite (0.6-12.3 wt. % and 0.3-2.2 wt. %), ferruginous calcio-carbonatite (5.2-15.4 wt. % and 0.1-2.3 wt. %) and magnesio-carbonatite (11.2-30.3 wt. % and 2.0-6.0 wt. %) respectively. The Sr and Ba contents increase from calcio-carbonatite (1050-20151 ppm and 58-22290 ppm), ferruginous calcio-carbonatite (1370-30821 ppm and 857-25468 ppm) and magnesio-carbonatite (1898-43507 ppm and 3129-95412 ppm). These trends suggest differentiation of magma. Both petrography and geochemical data suggest a trend from calcio-carbonatite that fractionated calcite and apatite to ferruginous calcio-carbonatite that fractionated calcite and ankerite, and magnesio-carbonatite that fractionated siderite and ankerite.
REE mineralization at the Tundulu Carbonatite occurred in interstitial spaces between quartz and apatite in association with strontianite and barite in calcio-carbonatite and ferruginous calcio-carbonatite. Mineralization in magnesio-carbonatite overprinted quartz or interstitial to quartz and dolomite. The chondrite normalized ratios of lanthanum and Ytterbium (La/Yb)N in calcio-carbonatite ranges from 33 to 289, ferruginous calcio-carbonatite from 30 to 56 and magnesio-carbonatite from 122 to 3035. These ranges suggest LREE are more enriched in magnesio-carbonatite. The main REE-bearing mineral is synchysite.
Observed spatial association of the Tundulu Carbonatite and nepheline syenite suggests carbonatite formation from immiscibility of initial carbonate-silicate melt. The abundance of calcite shows the initial magma was Ca-rich. The Fe2O3 and MnO contents increase from calcio-carbonatite (0.6-12.3 wt. % and 0.3-2.2 wt. %), ferruginous calcio-carbonatite (5.2-15.4 wt. % and 0.1-2.3 wt. %) and magnesio-carbonatite (11.2-30.3 wt. % and 2.0-6.0 wt. %) respectively. The Sr and Ba contents increase from calcio-carbonatite (1050-20151 ppm and 58-22290 ppm), ferruginous calcio-carbonatite (1370-30821 ppm and 857-25468 ppm) and magnesio-carbonatite (1898-43507 ppm and 3129-95412 ppm). These trends suggest differentiation of magma. Both petrography and geochemical data suggest a trend from calcio-carbonatite that fractionated calcite and apatite to ferruginous calcio-carbonatite that fractionated calcite and ankerite, and magnesio-carbonatite that fractionated siderite and ankerite.
REE mineralization at the Tundulu Carbonatite occurred in interstitial spaces between quartz and apatite in association with strontianite and barite in calcio-carbonatite and ferruginous calcio-carbonatite. Mineralization in magnesio-carbonatite overprinted quartz or interstitial to quartz and dolomite. The chondrite normalized ratios of lanthanum and Ytterbium (La/Yb)N in calcio-carbonatite ranges from 33 to 289, ferruginous calcio-carbonatite from 30 to 56 and magnesio-carbonatite from 122 to 3035. These ranges suggest LREE are more enriched in magnesio-carbonatite. The main REE-bearing mineral is synchysite.