Romaria mine, Romaria, Bagagem River valley, Coromandel district, Minas Gerais, Brazil
|Latitude & Longitude (WGS84):||18° 52' 40'' South , 47° 35' 3'' West|
|Latitude & Longitude (decimal):||-18.87778,-47.58444|
|Köppen climate type:||Aw : Tropical savanna, wet|
|Other/historical region names associated with this locality:||Romaria (former Água Suja)|
This diamond mine was opened around 1867 following discovery of diamonds in the nearby Água Suja stream, a tributary of the Bagagem river. The mine closed in 1984. While most diamonds in the Coromandel district were obtained from alluvial deposits, at Romaria diamonds were mined from a lithified conglomerate in the river bottomland. This conglomerate has been interpreted as a debris flow deposit consisting of materials reworked from surrounding metasedimentary bedrock including the Neoproterozoic Araxá Group and Cretaceous sedimentary rocks (Suguio et al., 1979; Andrade and Chaves, 2009). As the debris flow apparently followed modern topographic contours, it is most likely of Quaternary age. Fleischer (1998), however, presented evidence that normal block faulting led to erosion of the original diamondiferous conglomerate on the upthrown (west) side of the faults, with deposition occurring in alluvial fans on the down-dropped side. He correlated localized outcrops of this material for a little over 40 km in a NW-SE direction, and suggested existence of a faulted lineament along nearly the entire length of the Bagagem River valley. The diamonds were probably reworked from the Mata da Corda Group of Late Cretaceous age, a resistant unit that caps the mesas on either side of the Bagagem River valley.
Lithic clasts in the conglomerate are up to 0.8 meters in size, and include schist, phyllite, quartzite, basalt, reworked conglomerate, vein quartz, and siliceous concretions rich in opal. The matrix is arenaceous, and contains considerable kaolinite and illite. Framework grains include mm-scale grains of heavy minerals including pyrope, staurolite, "hornblende," epidote, kyanite, monazite, tourmaline, zircon, and anatase. The opaques include magnetite, hematite, goethite, and ilmenite. The pyrope is chromium-rich, with chromium/calcium oxide ratios plotting mostly in the G4, G5, and G9 fields, indicating poor likelihood of associated diamonds (Grütter et al., 2004). Nevertheless, diamonds from the area are large and clear, although commonly abraded and fractured, and suggest a proximal source, but that has yet to be identified.
Modified by NK, January 2017
18 valid minerals.
This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org
1000 - 1600 Ma
|Mesoproterozoic Tectonic assemblages, metamorphic schist belts, melanges|
Age: Mesoproterozoic (1000 - 1600 Ma)
Lithology: Tectonic assemblages, metamorphic schist belts, melanges
Reference: Geological Survey of Canada. Generalized geological map of the world and linked databases. doi:10.4095/195142. Open File 2915d.