Barama Project

A detailed investigation of the Blue Mountain / Kauramembu area south of the central Barama River was done by the UN in the 1960's, to follow up an aeromagnetic anomaly. An area of nickel laterite was discovered overlying narrow bands of ultramafic rocks. Drilling of this area showed conclusively that though Ni grades were high, the area was too small for commercial exploitation. Investigation of the Ni-laterites also resulted in discovery of soapstone of a quality suitable for ornamental use, located at the margins of serpentinite zones.

Several workers had done extensive geological mapping along the Barama River, but other than mapping in the Blue Mountain area, the geology of the area to the south was poorly known. A field investigation was undertaken in November/December 1999, with the aim of exploring for other, hopefully larger Ni-laterite deposits in the area, and other elements of commercial value. Work done included regional geochemical sampling and geological mapping. In total 101 drainage samples were taken, and 57 rock samples. At most sites a pan-concentrate could be collected, and was inspected in the field for the presence of visible gold. Rock samples were examined petrologically, and 44 of the HM concentrates were examined using semi-quantitative XRD to establish the relationship between rock
mineralogy and geochemistry.

Prior to the start of fieldwork, a GIS database was set up, which included scanning of relevant geological maps. All outcrop data recorded by previous workers was compiled. Together with fieldwork information, and a detailed air photograph lineament analysis, this has resulted in production of a geological fact map, detailing outcrop lithology and structural information, and a new digital geological and structural map of the area.

UN soil sample geochemistry has also been digitised, and integrated with recent geochemistry. Recent geochemical results as well as previous UN data suggest that Cr values are much higher than Ni values, and that high Ni and Cr assays are derived from he small area previously identified by UN work (approximately 2km in strike length). No other areas with such high Ni and Cr values have been identified, though moderately high values derived from a number of other areas suggest that more small zones of ultrabasic rocks may occur.

Three separate gold enriched areas occur, two of which were not previously known. In the NE of the area examined a 6x 4 km anomalous zone has associated Au, As, Sb & W anomalies, probably related to known vein mineralisation in the Williams Mine-Waraikushuru area. Some gold anomalies occur at the north end of the Ni-Cr laterite area, where UN work suggests that quartz vein pods associated with structures in this area are gold-bearing.

In the south-central part of the area examined a 8x6km gold anomalous zone has no associated As, Sb or W, and appears to be geologically diverse, with both granite and greenstone / amphibolite outcrop, and possible ultramafic rocks. Local small scale underground mining is reported from the west of this area at a locality called Kalaloo. E-W trending quartz vein zones were seen in the field in the west-central part of this area, abandoned porknocker (artisan miner) workings in the east-central part of the area, while a distinctive circular air-photograph feature occurs in the NE of this area. No significant base metal mineralisation or other commercial mineralisation has been identified to date.

The geology of the area is complex, with numerous faults separating different lithologies. Main lithologies in the area are Mazaruni Group meta-sediments and meta-volcanics, old composite granite batholiths, ultramafic rocks as serpentinites in fault bounded slivers, as well as some areas with gneiss, and mineralogically unusual intrusions (e.g. monozites) and associated contact metamorphics.

The following diagrams summarise available information.

Geological Summary Map (150K)
Mineral Occurrence Map (115K)
Au Geochemistry Map (113K)
Auction Blocks Map (126K)

REFERENCE : Heesterman, L.J.L., Kemp, A.W. & Nestor, G. 2001. Barama-Kauramembu Project. A Summary of Geochemistry, Geology and Structure. Guyana Geology and Mines Commission, Geoservices Division Technical Report.