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Amba Donga |
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Gujarat, India |
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F
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Amba Donga carbonatite hosted fluorite deposits are located in the Baroda District of Gujarat State, India, some 400 km north-east of Bombay (Mumbai).
The Amba Donga complex comprises a series of sub-volcanic intrusions composed of carbonatite and associated syenites emplaced into tholeiitic and alkaline plateau flood basalts of the Deccan Trap volcanic province overlying Precambrian gneisses of the Dharwar Formation. On one side it also cuts late Cretaceous sandstones. It is emplaced adjacent to the major north-east trending Naramada rift.
The complex comprises a 2 km diameter calcite carbonatite ring dyke and a number of syenite intrusions randomly distributed around the ring. The interior of the dyke is lined by a ring of carbonatite breccia. Small, rounded, irregular shaped plugs of ankerite carbonatite are found on both sides of, and in one case cutting the carbonatite ring, locally containing up to 50% accessory minerals which include martite, minor apatite, bastnaesite, pyrochlore, monazite, thorite, pyrite, galena and chalcopyrite. Immediately adjacent to the ring is an up to 150 m wide discontinuous zone of potassic fennite in which quartz in the adjacent country rocks has been replaced by potassium feldspar.
Economic fluorite is contained only within the calcite carbonatite, although accessory amounts are found in the other carbonatite lithlogies. The economic deposits are found at the contact of the calcite carbonatite and the Cretaceous sandstones, near the ankerite carbonatite plugs. Veins of fluorite (1 to 20, locally up to 50 cm thick) fill concentric fractures within strongly silicified host rocks, which have also in part been replaced by fluorite.
The deposit contains approximately 11.6 Mt @ 30% CaF2.
The deposit also contains elevated levels of rare earth elements (REE) due to the enrichment in the groundmass/altered calcite grains of micron-sized REE phases. Sulphur-bearing, F-rich hydrothermal fluids that exsolved from late-stage carbonatitic magmas are interpreted to have caused dissolution of
the primary carbonates and simultaneous precipitation of REEs and other high field strength element (HFSE)-bearing minerals. This mineralisation includes REE fluorocarbonates, such as synchysite-(Ce), parisite-(Ce), bastnäsite-(Ce)] and florencite-(Ce) (Patel et al., 2022).
For detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 1996.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Palmer D A, Williams-Jones A E 1996 - Genesis of the Carbonatite-hosted fluorite deposit at Amba Dongar, India: Evidence from fluid inclusions, stable isotopes, and whole rock-mineral geochemistry: in Econ. Geol. v 91 pp 934-950
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Patel, A.K., Mishra, B., Upadhyay, D. and Pruseth, K.L., 2022 - Mineralogical and Geochemical Evidence of Dissolution-Reprecipitation Controlled Hydrothermal Rare Earth Element Mineralization in the Amba Dongar Carbonatite Complex, Gujarat, Western India: in Econ. Geol. v.117, pp. 683-702.
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