|Latitude & Longitude (WGS84):||18° 33' 17'' South , 47° 1' 50'' West|
|Latitude & Longitude (decimal):||-18.55500,-47.03056|
|Köppen climate type:||Aw : Tropical savanna, wet|
The list of large diamonds found in alluvial deposits this area is impressive. Characters of the diamonds suggest they were not transported far from a primary kimberlite or lamproite source. The Vargem I kimberlite was analyzed as early as 1977, but the preliminary results indicated a poor chance that it contained diamonds. By virtue of several tons of alluvial matrix supplied by GAR Mining, another study of the chemistry of heavy minerals–primarily pyrope garnets–was undertaken,using the well-known evaluation system for kimberlites developed by Gütter et al. (2004), whereby certain ratios of calcium and chromium (as oxides) have been found to be associated with diamondiferous kimberlites more so than other ratios. Chaves (2012) reanalyzed garnets from Vargem-1, and not only found several samples showing favorable CaO/Cr2O3 ratios (plotting in the G10 field), but also found loose diamonds. Although less than 1 carat in size and of subeconomic potential, this discovery shows that other kimberlites in the area previously thought to be infertile for diamonds also should be examined more carefully and exhaustively. The Vargem I find helps solve the old puzzle of failing to find potential primary kimberlite sources near sites where alluvial diamonds have been recovered.
NK, January 2017
2 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 crystalline metamorphic rocks|
Age: Mesoproterozoic (1000 - 1600 Ma)
Lithology: Low grade unclassified metamorphic rock
Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529.